WLD 132 Gas Metal Arc Welding Pulse Transfer on Mild Steel ...€¦ · As defined by the American Welding Society (AWS), Gas Metal Arc Welding (GMAW) is an electric arc welding process

WLD 132 Gas Metal Arc Welding

Pulse Transfer on Mild Steel and Aluminum

WLD 132 2017 NSF-Ate Project - Advanced Materials Joining for Tomorrow’s Manufacturing Workforce

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INDEX

Syllabus 3-11

Information Sheets • Introduction to GMAW• GMAW Equipment• Shielding Gases• Filler Metal Classification• Classification of Aluminum• GMAW Variables• Pulse Welding

1213-27

2829-3031-3536-3839-41

Work Sheets 42-49

Math on Metal 50-57

Science on Steel and Aluminum 58-65

Craftsmanship Expectation for Welding Projects

66

Welding Projects 67-98

Final Exam Information 99-103

Grading Rubric for the Practical Exam 104

GMAW-P Final Exam 105-107

Assessment Breakdown for the Course 108

This project was supported, in part, By the

National Science Foundation Opinions expressed are those of the authors And not necessarily those of the Foundation

PCC/ CCOG / WLD Course Number:

WLD 132

Course Title: Gas Metal Arc Welding-Pulse

Credit Hours: 4

Lecture Hours: 0

Lecture/Lab Hours: 80

Lab Hours: 0

Special Fee: $24.00

Course Description Develops knowledge and skills using the gas metal arc welding - pulse transfer process on

common mild steel and aluminum joints in all positions. Prerequisites: Department permission

required. Audit available.

Addendum to Course Description This is an outcome based course utilizing a lecture/lab format. This course includes classroom discussion, videos, theoretical concepts, lab demonstrations and technical skills. Course outcomes include; theoretical concepts, lay out, fabrication, oxy-fuel cutting, and safety.

Intended Outcomes for the course Upon completion of the course students should be able to: • Function safely in the PCC Welding Lab. • Interpret blueprints to accurately lay out, prepare, and assemble weld joints. • Understand and apply fundamentals of GMAW-pulse operations. • Weld common joint assemblies with the GMAW-pulse to AWS D1.1 Structural Steel Welding Code

visual acceptance criteria in the following joints and positions. • Apply visual examination principles and practices in accordance with AWS D1.1.

Course Activities and Design

Welding lec/lab courses are Open Entry and Open Exit (OE/OE) and are offered concurrently. Courses are designed to meet the needs of the students with flexible scheduling options. Students may attend full time or part time. This is an OE/OE course which does not align with the normal academic calendar.

Outcome Assessment Strategies The student will be assessed on his/her ability to demonstrate the development of course outcomes. The methods of assessment may include one or more of the following: oral or written examinations, quizzes, written assignments, visual inspection and welding task performance.

Course Content (Themes, Concepts, Issues and Skills) Function safely in the PCC Welding Lab. • Understand and practice personal safety by using proper protective gear • Understand and practice power tool safety • Understand and maintain a safe work area

o Recognize and report dangerous electrical and air/gas hose connections o Understand and practice fire prevention

Interpret blueprints to accurately lay out, prepare, and assemble weld joints. • Interpret lines, symbols, views and notes • Lay out material per specifications • Assemble project per specifications

Understand and apply fundamentals of GMAW-P Operations. • Describe and demonstrate equipment setup, shut down, and operation • Identify pulse transfer characteristics • Demonstrate proper stick out and travel speed • Demonstrate correct starting, stopping and restarting techniques • Demonstrate proper bead placement

Weld common joint assemblies with the GMAW-P to AWS D1.1 Structural Steel Welding Code visual acceptance criteria in the following joints and positions: Flat Position: (mild steel) • Bead plate

Horizontal Position: (mild steel and Aluminum) • T-Joint • Lap Joint

Vertical Position: (mild steel and Aluminum) • T-Joint • Lap Joint

Overhead Position: • T-Joint • Lap Joint

Apply visual and destructive examination principles and practices in accordance with AWS D1.1. • Evaluate welds using appropriate welding inspection tools • Assess weld discontinuities causes and corrections


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Course Assignments

Reading Welding Principles and Applications, By Larry Jeffus

Chapter 10, Gas Metal Arc Welding Equipment, Set-up, and Operation Chapter 11, Gas Metal Arc Welding

Information sheets Introduction to GMAW-P

Power Source Welding Gun

Wire specification and identification Shielding Gas Welding procedures Workmanship Standards Visual Inspection

Video training Miller GMAW 1 Process description, safety and equipment set up Miller GMAW 2 Equipment and process variables Miller GMAW 7 Spray transfer on steel Miller GMAW 10A Aluminum Miller GMAW 10B Aluminum Miller GMAW-P 1 What is Pulse Mig? Miller GMAW-P 2 Welding variables Miller GMAW-P 3 Equipment and set up Miller GMAW-P Operator techniques

Work sheets Video review work sheet

GMAW fundamentals worksheet Welding projects Mild Steel Horizontal position (Spray transfer)

T - Joint Groove Joint Horizontal position (Pulse transfer)

T – Joint Lap Joint Vertical position (Pulse transfer)

T - Joint Lap Joint Overhead position (Pulse transfer)

T - Joint Lap Joint

Aluminum Horizontal position

T – Joint Lap Joint Vertical position

T - Joint Lap Joint

Overhead position T – Joint

Lap Joint


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Final Exam Part one (Closed book exam) Part Two (Practical Exam)

Required Texts Welding Principles and Applications, By Larry Jeffus

Chapter 10 Gas Metal Arc Welding Equipment, Setup, and Operation Chapter 11, Gas Metal Arc Welding

Timeline Open-entry, open-exit instructional format allows the students to work at their own pace. It is the student’s responsibility to complete all assignments in a timely manner. See your instructor for assistance.

Outcome Assessment Policy The student will be assessed on his/her ability to demonstrate the achievement of course outcomes. The methods of assessment may include one or more of the following: oral or written examinations, quizzes, written assignments, visual inspection techniques, welding tests, safe work habits, task performance and work relations.

Grading criteria The student's assessment will be based on the following criteria: 20% of grade is based on Safe work habits and shop practices 20% of grade is based on Completion of written and reading assignments 20% of grade is based on demonstrating professional work ethics (Habits) 40% of grade is based on completion of welding exercises


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Grading Scale 90 - 100% A – Superior

Honor grade indicating excellence. Earned as a result of a combination of some or all of the following as outlined in the course-training packet. Superior examination scores, consistently accurate and prompt completion of assignments, ability of to deal resourcefully with abstract ideas, superior mastery of pertinent skills, and excellence attendance. Probable success in a field relating to the subject or probable continued success in sequential courses.

80 - 89% B - Above average Honor grade indicating competence. Earned as a result of a combination of some or all of the following as outlined in the course training packet. High examination scores, accurate and prompt completion of assignments, ability to deal with abstract ideas, commendable mastery of pertinent skills and excellent attendance. Probable continued success in sequential courses.

70 - 79% C – Average Standard college grade indicating successful performance earned as a result of a combination of some or all of the following as outlined in the course training packet. Satisfactory examination scores, generally accurate and prompt completion of assignments, ability to deal with abstract ideas, fair mastery of pertinent skills and regular attendance. Sufficient evidence of ability to warrant entering sequential courses.

60 - 69% D – Substandard Substandard but receiving college credit. Substandard grade indicating that the student has met only minimum requirements as outlined in the course training packet. Earned as a result of some or all of the following: low examination scores, generally inaccurate, incomplete or late assignments, inadequate grasp of abstract ideas, barely acceptable mastery of pertinent skills, irregular attendance, insufficient evidence of ability to make advisable the enrollment in sequential courses. Does not satisfy requirements for entry into course where prerequisite are specified.

0 - 59% F – Failure Non-passing grade indicating failure to meet minimum requirements as outlined in the course training packet. Earned as a result of some or all of the following: non-passing examination scores, inaccurate, incomplete or late assignments, failure to cope with abstract ideas, inadequate mastery of pertinent skills, repeated absences from class. Does not satisfy requirements for entry into course where prerequisites are specified.


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Pass Acceptable performance. A grade of “P” represents satisfactory achievement that would have been graded “C” or better on the grading scale, but is given instead of a letter grade. By the end of the eighth (8th) week of class (or equivalent) students shall choose the graded or pass option. By the end of the eighth (8th) week of class or equivalent), students may rescind an earlier request of the pass option.

No Pass No Pass: Unacceptable performance or does not satisfy requirements for entry into courses where prerequisites are specified. This grade may be used in situations where an instructor considers the “F” grade to be inappropriate. The NP mark is disregarded in the computation of the grade point average.

CIPR Course In Progress Re-register A mark used to only for designated classes. To receive credit, a student must reregister because of equipment usage is required. This may include course in modular or self-paced programs. This mark may also be used in skill-based course to indicate that the student has not attained the skills required to advance to the next level. If the course is not completed within a year, the “CIPR” changes to an “AUD” (Audit) on the transcript unless the course was repeated and a grade earned.

AUD AuditSome courses may allow the students to attend a course without receiving a grade or credit for the course. Tuition must be paid, and instructor permission must be obtained during the first three weeks of class (or equivalent). Instructors are expected to state on their course handouts any specific audit requirements. Does not satisfy requirements for entry into courses where prerequisites are specified.

Repeated Courses Courses with grades of “D,” “F,” “NP,” or “CIP,” and “CIPR,” may be repeated for a higher grade. All grades earned will appear on the transcript. The first earned grade of “C” or “P” or better will count in the accumulated credit total. The first grade of “C” or better will be used for the GPA calculation.


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SPECIAL If you have a special limitation or disability, which requires special NOTE: assistance please notifies your instructor.

IMPORTANT: Grades will no longer be mailed to you automatically. You may request a copy by calling: T.R.A.I.L. at 977-5000 and select Option 4. Or you can access your grades on the World Wide Web at https://banweb.pcc.edu/.

Notice: All projects must be completed in the PCC Welding Lab within your course time.


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INTRODUCTION TO GMAW SPRAY AND PULSE SPRAY TRANSFERS

Process Description As defined by the American Welding Society (AWS), Gas Metal Arc Welding (GMAW) is an electric arc welding process that joins metallic parts by heating them with an arc between a continuous fed filler electrode and the work. A shielding gas protects the electrode and the molten weld metal from contamination. The American Welding Society has modified the GMAW classification system to include information to identify the process by the mode of metal transfer. An example GMAW-S is used to identify the short-circuiting mode of metal transfer and GMAW-P is used to identify the pulse spray arc mode. These examples are formal AWS process designations.

GMAW may also be known as Metal Inert Gas (MIG) and Metal Active Gas (MAG). There are also a variety of “trade names” used to describe the process such as “spray arc”, “short arc”, ”hard wire”, and ”pulse arc”. The process was developed in and made commercially available in 1948.

The purpose of this course our focus will be on GMAW (spray transfer) and GMAW-P. Please refer to course WLD 131 for information on GMAW-S (Short Circuiting transfer and Surface Tension Transfer).

GMAW Advantages • Used on a variety of metals including: carbon and low alloy steels, stainless steels,

aluminum, magnesium, copper, bronze and titanium.• Capable of producing x-ray quality welds.• The pulse mode can be used in all positions.• Produces no slag during welding so there is little post weld clean up and less chance

for inclusions.• High metal deposition rates are available.

GMAW Disadvantages • Equipment is more advanced and expensive.• It is not as portable as other welding processes.• Material must be clean prior to welding.• Subject to wind drafts that reduce shielding and cause contamination of the weld.• Shielding gases can be expensive• Axial Spray transfer is limited to flat and horizontal positions only.

GMAW Uses • Structural steel assemblies • Pressure vessels• Pipelines • Water tanks• Automobiles and trucks • Rockets and missiles• Motorcycles & off road vehicles • Lawn and garden equipment• Campers and recreational equipment • Ships, barges, boats and submarines


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GMAW EQUIPMENT

Identification The GMAW process can be used either semiautomatic or automatic. The basic equipment required for GMAW consists of the following:

• A welding power source• A wire feeder• A welding gun assembly• A regulated supply of shielding gas• A supply of electrode• Interconnecting cables and hoses

The Welding Power Source For the purpose of this course you will use a Lincoln INVERTEC V350-Pro CC/CV Inverter Welding Power Source.

LN7 and Cobramatic wire feeders mated to the Invertec V350 Pro Power source.

The Invertec V350-PRO is the most powerful inverter power source in its class. Extremely lightweight, the smart design allows it to handle any constant current Stick (SMAW), TIG (GTAW), carbon arc gouging and constant voltage MIG (GMAW) and Flux-Cored welding applications.


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Advanced inverter technology gives you a very portable power source that can be carried to just about any DC welding job needing between 5 and 425 amps. Built tough. The V350-PRO can endure the rigors of virtually any work environment. The Invertec V350-PRO is also versatile and well suited for applications that require an extremely smooth arc, process versatility and portability. Examples include: construction sites, shop and maintenance welding applications, welder training schools, technical training centers and pressure and process piping.

The Invertec V350-Pro offers multi-process CV, CC, DC welding and is rated 350 amps, 34 volts at a 60% duty cycle. It is also rated at 275 amps, 100% duty cycle.

Operational Features and Controls for the Invertec V350-Pro.

1. Amps Meter 7. Weld Mode Select2. Volt Meter 8. Hot Start and Arc Control3. Output Control (Volts /Amps) 9. Twist Lock Welding lead connections4. Weld Terminals – Remote / On 10. On / Off Switch5. Thermal Indicator Light 11. Brain Cable Connection6. Control – Remote / Local 12. Brain Cable Connection


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Upper Control Panel 1. AMPS meter• Prior to STICK or TIG operation (current flow), the meter displays preset current value

(either 2 amps or +/- 3% (e.g. 3 amps on 100), whichever is greater).• Prior to CV operation, the meter displays four dashes indicating non-preset table AMPS.• During welding, this meter displays actual average amps.• After welding, the meter holds the actual current value for 5 seconds. Output adjustmentwhile in the "hold" period results in the "prior to operation" characteristics stated above.The displays blink indicating that the machine is in the "Hold" period.

2. Volt meter• Prior to CV operation the meter displays desired preset voltage value.• Prior to STICK or TIG operation, the meter displays the Open Circuit Voltage of thePower Source or four dashes if the output has not been turned on.• During welding, this meter displays actual average volts.• After welding, the meter holds the actual voltage value for 5 seconds. The displays blinkindicating that the machine is in the "Hold" period.• Output adjustment while in the "hold" period results in the "prior to operation"characteristics stated above.

3. Output control• Output control is conducted via a single turn potentiometer.• Adjustment is indicated by the meters as stated above.

4. Weld terminals- remote / on• Two status lights indicate the location of trigger control as determined by the "WELDTERMINALS" push button.

• If trigger control is local "weld terminals on", the ON display will be lit.• If trigger control is remote "weld terminals remotely controlled", the REMOTE displaywill be lit.

• The unit will power up in "pre-determined preferred" trigger modes.

For all versions, these trigger modes can be over-ridden (switched) with the WELD TERMINALS push button. When changed, the unit will power up in the configuration it was in when it was last powered down.

5. ThermalThis status light indicates when the power source has been driven into thermal overload. Ifthe output terminals were "ON", the "ON" light will blink indicating that the out-putwill be turned back on once the unit cools down to an acceptable temperature level. If theunit was operating in the "REMOTE" mode, the trigger will need to be opened before orafter the thermal has cleared and closed after the machine has cooled down to an acceptabletemperature to establish output.


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6. Control - remote / local• Two status lights indicate the location of output control as pre-determined by the powersources auto-configure sys-tem.

• The LOCAL display will be lit when control is at the power source.• The REMOTE display will be lit when a remote pot/control is detected.

These Output Control configurations can be overridden (switched) with the CONTROL push button. When changed, the unit will power up in the configuration it was in when it was last powered down.

7. Weld mode selectThe Mode Control button selects from the following welding modes:

CC- stick soft:The Stick Soft process features continuous control ranging from 5 to 425 amps.This mode was intended for most SMAW applications, and Arc Gouging.

• The Hot Start control regulates the starting current at arc initiation. Hot Start canbe adjusted from minimum (0), with no additional current added at arc start, tomaximum (10), with double the preset current added for the first second after arcinitiation.

• The Arc Control regulates the Arc Force to adjust the short circuit current. Theminimum setting (-10) will produce a "soft" arc and will produce minimal spatter.The maximum setting (+10) will produce a "crisp" arc and will minimize electrodesticking.

CC- stick crisp:The Stick Crisp mode features continuous control from 5 to 425 amps. This modewas intended primarily for pipe welding applications. • The Hot Start controlregulates the starting current at arc initiation. Hot Start can adjust starting current upor down by 25% of the preset value.

• The Arc Control regulates the relative Slope of the process. Slope dynamicallycontrols the force the arc has to penetrate an open root. At the minimum setting, ArcControl is very soft and is similar to the Stick Soft mode. At the maximum setting,the slope is reduced, the OCV is reduced, and the operator has full control off thearc force required to penetrate an open root joint. For vertical down, open root pipewelding applications, the recommended setting is between 8 and 10.

TIG GTAW: The TIG mode features continuous control from 5 to 425 amps. The TIG mode can be run in either the TIG touch start or high frequency (optional equipment required) assisted start mode. The Arc Control is not used in the TIG mode.


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CV-Wire: The CV-WIRE mode features continuous control from 10 to 40 volts.The mode was intended for most GMAW and FCAW applications. The Hot Startcontrol is not used in the CV-WIRE mode.• The Arc Control regulates pinch effect. At the minimum setting (-10), minimizespinch and results in a soft arc. Low pinch settings are preferable for welding withgas mixes containing mostly inert gases. At the maximum setting (+10), maximizespinch effectand results in a crisp arc. High pinch settings are preferable for welding FCAW andGMAW with CO2.

CV-Flux cored: The CV-FLUX CORED mode features continuous control from 10to 45 volts. This mode was designed for self-shielded flux cored wires that requiretight voltage control. The Hot Start control is not used in the CV-FLUX COREDmode.• The Arc Control regulates pinch effect. At the minimum setting (-10), minimizespinch and results in a soft arc. At the maximum setting (+10), maximizes pincheffect and results in a crisp arc. Most self-shielded wires work well at an ArcControl setting of 5.

V 350 Pro Advanced Process Panel


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To program Welding modes use the Select knob is used to scroll through all Welding modes. The Memory button is used to store and access Welding modes into locations M1 thru M8.

Modes In addition to the 5 welding modes described above the Advance Process Panel allows you to select the following additional modes.

Constant Power mode In the Power Mode, the work point will be in the Volts window. The Amp window will have CP displayed indicating Constant Power. Once current starts flowing and during the 5 second “Hold” feature the displays will show Volts and Amps respectively. The Constant Power mode is the mode selected for GMAW axial spray transfer. This will be the mode you will use for the first two welding exercises in this course.

Gouge Air Carbon Arc Cutting (CAC-A) is a physical means of removing base metal or weld metal by using a carbon electrode, an electric arc and compressed air. Although the equipment is capable of this option you will not be using the power source for this application.

Pulsed Modes In Pulse Modes, the work point will be in the Amps window and should be set close to the wire feed speed of the wire feeder in inches per minute. The Volts window will have SPd displayed indicating Wire Feed Speed. Once current starts flowing and during the 5 second “Hold” feature the displays will show amps and volts. Pulse Mode features that are displayed while selecting a Welding pulse mode are listed below;

Steel - .030, .035, .045, .052 – Argon Blends. This is the mode you will choose for the pulse steel exercises in this course.

Stainless Steel - .030, .035, .045 – Argon Blends & Helium/Argon Blends

Aluminum - .035, 3/64, 1/16 – 4043 & 5356. This is the mode you will choose for the pulse aluminum exercises in this course. Metal Core - .045, .052 – Argon Blends Nickel - .035, .045 – Argon/Helium blends

The Memory button and Select knob are used together to select a welding process and store it in (M1thru M8). The SELECT knob scrolls through the, welding process modes and memory modes M1 thru M8. The MEMORY button stores the welding process in memory.


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Select button" (The right button) selects between the "Hot Start" or "Arc Control". The will indicate the active feature shown below. Right Digital Window "Hot Start" (-10 to 0 +10) "Arc Control" (0 to 10) .

The Adjust knob adjusts the desired settings for the Hot Start or Arc Control feature that is active.

Examples of saving welding modes to memory The following example is how to select Pulse MIG using .035 steel and store it into memory. 1. Turn the Select knob until welding process is displayed. Pulse MIG Argon BlendsSteel .035

2. Wait two seconds and the right window will display Arc Control on the second line onthe right side. Pulse MIG Argon Blends Steel .035 Arc Control ### <

3. SPd is displayed in the upper right Volts window. The left Amps window matches the desired wire feed speed that is set on the wire feeder. Adjust the Output knob until desired number is displayed.

4. Start welding. If the arc length is too short turn the Output knob up. If the arc length istoo long turn the Output knob down. The Arc Control which is displayed in the rightdigital window can be used to fine-tune the arc length and characteristics.

5. After all adjustments have been made press and hold the Memory button until thedisplay changes. The right and the left window will display what memory to save in, letssay M1. To store in M1 push the Memory button again to save the Pulse Mig mode tomemory M1.

6. The display in the digital windows read as follows: M1 Pulse MIG Argon BlendsSteel .035 Arc Control 1.2

7. Saving or entering a second welding mode to a memory, M2. Turn the Select knob untilthe desired welding process mode is displayed in right digital window. Then follow steps 1thru 6. Press the Memory button till the digital window reads, Save to MEMM2Press the Memory button again and the New Welding process is saved in M2.

8. Adjust the output control to the correct wire feed setting and the V350-PRO is ready toweld again. (Note: The wire feed speed setting is not stored in memory and will need to bereset.)

9. Adjust the Arc Control and note that the M1 goes away indicating that the V350-PROsettings no longer match what is stored in memory. Going back to the original settings willnot bring the M1 back. You will need to push the Memory button to recall


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the original settings in M1. Note: After all memory’s M1 thru M8 are used and the welder needs to store another welding process, a new welding process will overwrite what was originally in the memory and will read, Save to MEM M1 Overwrite M1 which stored Pulse Mig is Overwritten with the new welding process.

Weld Mode details V350-PRO Mode Range Comments Stick Soft 5 - 425 amps The stick soft mode is the best selection for general stick applications.

GTAW (Tig mode) 5 - 425 amps The tig mode produces a soft, steady constant current waveform for either touch start or high frequency assisted start DC GTAW applications.

GMAW - CV 10 - 45 volts. The GMAW - CV mode is the best selection for general MIG welding, Metal core, and gas shielded applications. Arc Control = Pinch (Min = min pinch, softest arc), (Max = max pinch, crispest arc)

GMAW - Power 1 - 18 volts. The GMAW Power mode features good stable short arc performance when welding small diameter (.025 and .030 steel & stainless) wires at low procedures. This mode also performs well welding aluminum in the spray mode.

FCAW-SS 10 - 45 volts The FCAW-SS mode is designed for Self Shielded Innershield products that require tight voltage control. For example; the NR 203 series or NR 207 Arc Control = Pinch (Min = min pinch, softest arc), (Max = max pinch, crispest arc,)

Pulse Programs V350-PRO The V350 non synergic pulse programs allow independent control of the wire feed speed and the arc length. The V350 Output Control Knob adjusts the arc length similar to other processes. When operating in a pulse mode, the V350 displays a reference number as the relative arc length. Setting this reference number to the actual wire feed speed of the feeder will produce close to the right arc length. The V350's output knob can then be adjusted to dial in the correct arc length. The Arc Control knob will fine tune the arc length to obtain the desired results.

Lower Case Panel The output studs, line switch and remote connector are located on the lower case front. Both STUDS contain "Twist-Mate" connector inserts. The Negative stud is configured to accept the pass through gas system.

The ON-OFF switch is a 3-phase circuit breaker rated at 100 amps per leg.

The METER POLARITY switch is located above the output connectors. The switch provides a work connection for wire feeder voltmeters. Place the switch in the position of the electrode polarity indicated by the decal. The switch does not change the welding polarity.


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Remote control of the Output Control and Weld Terminals The Invertec V350-Pro has auto sensing of remote output controls. If after connecting or removing a remote, the Invertec V350-Pro did not configured the way you would like the local or remote control settings can be changed by pushing the OUTPUT CONTROL or WELD TERMINAL button.

Summary This completes the review of adjustments and controls as presented in the Operators Manual produced by Lincoln Electric for the INVERTEC V350-PRO. It is helpful to understand the capabilities and limitations of the equipment you are using. For the purpose of this course the power source settings required for your welding exercises will be specified in your set up procedures.

Wire Feeders The wire feeder houses all the electrical controls and a variable constant feed motor to move the wire from the supply spool through the gun to the contact tip where it is energized. The feeder also contains solenoids for operating shielding gas flow valve and water coolant flow valve when used. You will be using two wire feed systems in this course. You will use the Lincoln LN7 feeder for all steel welding exercises. You will use the Lincoln Cobramatic feeder equipped with Lincolns’ Prince XL gun system for all aluminum welding exercises.

Cobramatic Wire feeder –A Push Pull wire feeder system

LN-7 Wire Feeder – A Push type feeder

There are a wide variety of wire feeders available today. The basic types of wire feeders include:

Push-type. This method is used to push the wire from the spool to the welding gun. The LN-7 feeder is an example of a push type system.

Pull type. This method is used to pull the wire from the supply spool to the drive rollers in the welding gun.


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Push–pull type. This method is used to push the wire from the wire feeder to a set of drive rollers in the welding gun. This type of system is used for welding with soft wires, since these wires may buckle in the cable if pushed for long distances. The Cobramatic feeder with the Prince XL gun is a push-pull system.

Spool gun type. This type of unit has a small spool of wire located on the welding gun and is often a choice for soft wire applications such as aluminum.

Wire feeder controls The number and types of controls will vary depending on the model of the feeder. The major controls include the power switch (off/on control), The wire feed potentiometer (wire feed speed control) and the spool brake control (stops the wire spool at the end of welding).

Auxiliary wire feeder controls may include: Trigger lock-in control. This control allows the welder to weld without the need to depress the gun trigger during the entire operation.

Burn back (anti-stick) control. This control prevents the wire from sticking in the weld pool. It sets the time that the arc power is on after the trigger is released to burn the wire back from the weld pool.

Purge control. This control allows the welder to open the gas solenoid. The amount of gas can be set on the flow meter without activating the welding circuit.

Wire inching (jog) control. Moves the wire through the system with out activating the welding circuit. It may be used in setting up the equipment or to determining wire feed speed.

Wire reel brake control. The reel brake control should be adjusted so that the spool will stop rotating at the same time the wire stops feeding. If the wire is allowed to over spool and touch the feeder housing it may cause a short circuit or the wire may “bird nest” (tangle).

Other auxiliary controls may be available on some units. Consult the owners manual for specific functions of special controls.

Wire Feeder Drive Roll System The system for driving the electrode from the spool to the gun may be either a two-roll or a four–roll system. The LN7 Feeder uses a standard two- roll system. The drive rollers are grooved for specific types and sizes of wire. The drive roller used must be designed to fit the diameter of wire you are using Wire drive rollers have different groove designs for hard and soft wires. A knurled U groove is the best choice for soft wires such as Aluminum. Smooth V grooved rollers are used for hard wires such as steel or Stainless Steel. A knurled type is often the choice for flux-cored wires.


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To insure smooth consistent movement of the wire “wire guides” are installed to guide the wire from the spool into the drive rollers and out of the rollers into the gun. The amount of pressure applied to the drive rollers can be adjusted. The pressure should be set so the wire feeds smooth and consistently. Too little pressure will result in slippage of the wire and may cause a burn back. Too much pressure will deform the wire and cause it to become stuck in the contact tip.

Get in the habit of checking the operation of all the components of a system before using it.


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Welding guns Welding guns are available in a wide variety of types and sizes. In this course you will be using a Goose- neck style Tweco gun for the steel exercises and the Prince model push pull for the Aluminum exercises.


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The Goose-Neck Tweco Mig Gun The components of the gun are: the power cable, the cable liner or conduit, the trigger switch, gas diffuser, insulator, contact tip and gas nozzle.

Power Cable The power cable carries the welding current to the contact tip. It must be large enough for the amperage being used and like all welding power cables it is well insulated.

Cable Liner (conduit) The liner provides movement of the wire through the cable and gun. The liner is secured in place with a set screw at the head of the gun and at the end of the gun. The liner must be of appropriate size to allow smooth movement of the diameter of wire being used.

Trigger Switch The trigger activates the solenoids to close the welding circuit, initiate gas and wire feed. Some guns are available with a locking devise so the welder does not have to squeeze the trigger continuously. This adds to the welder’s comfort when making long welds.

Gas Diffuser The gas diffuser is a brass fixture that screws into the head of the gun. It contains a set screw that holds the liner in place. The female end of the fixture is threaded to receive the contact tip. The diffuser has a series of ports (holes) around it that disperse the shielding gas.

Insulator The insulator is made of a nonconductive material. Its’ purpose is to insulate the gas nozzle from the contact tip. The insulator fits over the gas diffuser and threads onto the head of the gun. Note that the insulator has a blank end and a threaded end. Install the insulator with the blank end toward the gun. Make certain when threaded in place the insulator is below the gas ports on the diffuser. If you put it on upside down the insulator will cover the gas ports and you will not get proper shielding.

Contact Tip The contact tip is a copper alloy tube. The purpose of the contact tip is to complete the electrical contact with the wire. The contact tip is the point in the system that the wire picks up the welding current. The hole in the contact tip must match the diameter of the wire being used to insure good electrical contact.

Gas Nozzle (Cup) The gas nozzle or cup is also made of a copper alloy. Copper is the choice because of its ability to resist spatter. The purpose of the gas nozzle is to direct the shielding gas over the weld pool. Although copper resist spatter an anti-spatter dip or spray should be used to assist in ease of cleaning of the gas cup. A build up of spatter on the cup can interfere with your shielding gas.


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The wire feed speed adjustor knob will rotate 3 3/4 revolutions. Due to this, you will need to calculate a six second wire length into inches per minute (IPM) by multiplying the 6 second length by 10 seconds to determine the IPM.

WFS Adjustor Prince XL Welding Gun

The PRINCE XL torch was specifically designed to operate as both a push-pull gun and a spool gun. You will be using the push-pull system configuration. The model of the PRINCE gun you will be using is a 200 Amp/25 Volt air cooled gun. The drive motor on the gun is controlled by a 3¾ turn potentiometer recessed in the end of the pistol grip. The motor can provide a maximum of 750 inches per minute of wire feed speed. The PRINCE is designed with a Built-in pre and post gas flow. The trigger is designed so that when it is partially depressed, gas flow starts prior to ignition of the arc. When the trigger is partially released after welding gas flow, continues until the trigger is fully released.

The PRINCE comes with standard knurled drive rollers that will handle from .023 – 1/16 inch diameter wires. Optional grooved drive rollers are available and are preferred for Aluminum wires. Drive roll tension is accomplished by means of a pressure adjusting screw located on the left hand side of the torch. Proper tension is achieved when the wire does not slip if a small amount of pressure is added to the wire as it exits the tip. All equipment performs better when properly maintained. Maintenance of the gun will normally consist of general cleaning of the wire guide system, including tubes, drive rollers, and conduit at regular intervals.


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Straight Barrel Assembly Guide for the Prince Gun


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Shielding Gases

Shielding gas may be a pure gas or a mixture of several gases. In GMAW gases are used to: • Shield the electrode and molten metal from the atmosphere.• Transfer heat from the electrode to the metal.• Stabilize the arc pattern.• Aid in controlling bead contour and penetration• Assist in metal transfer from the electrode.• Assist in the cleaning action of the joint and provide a wetting action.

The common shielding gases include argon, helium, carbon dioxide, and oxygen. Argon and helium are inert gases (those that are chemically inactive and will not combine with any product of the weld area). They may be used as a single gas or as part of a mixed gas. Carbon dioxide in an active gas. It may be used alone or as part of a mixed gas. Oxygen is always combined with other gases.

For the purpose of this course you will be using the following gas mixtures: • 98% Argon 2% Oxygen for Axial Spray transfer• 90% Argon 10% Carbon Dioxide for Pulse Spray transfer• Pure Argon for Pulse transfer on Aluminum

Gas Supply Your gas will be supplied by individual cylinders (pressurized bottles) using a combination regulator and flow meter system. The combination regulator/flow meter reduces the pressure from the cylinder and regulates the flow of gas to the gun. The amount of flow is indicated by reading from the top of the float ball. The flow rate should be set at 35-45 cfh (cubic feet per hour). Remember to open the cylinder valve all the way, and close the cylinder valve fully when you shut down the system.

Cylinder with flow meter


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GUIDE TO AWS CLASSIFICATION OF CARBON STEEL FILLER METALS FOR GAS SHIELDED

ARC WELDING

AWS Electrode Wire Classification System

The classification system follows AWS filler metal specifications. The inherent nature of the products being classified has; however, necessitate specific changes that more ably classify the product.

Example = ER70S-6 • "E" designates an electrode as in other specifications.• "ER" designates a classification indicating that the bare filler metal may be used as

an electrode or welding rod.• "70" designates the required minimum tensile strength in multiples of 1000 psi of

the weld metal in a test weld made using the electrode in accordance with specifiedwelding conditions.

• "S" designates a bare, solid electrode or rod.• A suffix relates to the specific chemical composition. NOTE: Welding position is

determined by mode of transfer, not filler composition.

ER70S-2 Classification

This classification covers multiple deoxidized steel filler metals that contain a nominal combined total of 0.20 percent zirconium, titanium, and aluminum in addition to the silicon and manganese contents. These filler metals are capable of producing sound welds in semi-killed and rimmed steels as well as in killed steels of various carbon levels. Because of the added deoxidants these filler metals can be used for welding steels that have a rusty or dirty surface. There is a possible sacrifice of weld quality depending on the degree of surface contamination. Fillers can be used with a shielding gas of argon-oxygen mixtures, C02, or argon-C02 mixtures. These mixtures are preferred for out-of-position welding with the short circuiting type of transfer because of their ease of operation.


These filler metals will meet the requirement of this specification with either C02 or argon-oxygen as a shielding gas. They are used primarily on single-pass welds, but can be used on multiple-pass welds, especially when welding killed or semi-killed steel. Small diameter electrodes can be used for out-of-position welding with argon-C02 mixtures or C02 shielding gases. However, it should be noted that the use of C02 shielding gas in connection with excessively high heat inputs may result in failure to meet the minimum specified tensile and yield strength.


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These filler metals contain slightly higher manganese and silicon contents than those of the ER70S-3 classification and produce a weld deposit of higher tensile strength. The primary use of these filler metals is for C02 shielded welding applications where a slightly longer arc or other conditions require more de-oxidation than provided by the ER70S-3 filler metals. These filler metals are not required to demonstrate impact properties.


This classification covers filler metals that contain aluminum in addition to manganese and silicon as de-oxidizers. These filler metals can be used when welding rimmed, killed, or semi-killed steels with C02 shielding gas and high welding currents. The relatively large amount of aluminum assures the deposition of well-deoxidized and sound weld metal. Because of the aluminum, they are not used for the short circuiting type transfer, but can be used for welding steels which have a rusty or dirty surface, with a possible sacrifice of weld quality, depending on the degree of surface contamination. These filler metals are not required to demonstrate impact properties.


Filler metals of this classification have the highest combination of manganese and silicon, permitting high current welding with C02 gas shielding even in rimmed steels. These filler metals may also be used to weld sheet metal where smooth weld beads are desired and steels which have moderate amounts of rust and mill scale. The quality of the weld will depend on the degree-of surface impurities. This filler metal is also usable out of position with short circuiting transfer.


These filler metals have substantially greater manganese content (essentially equal to that of ER70S 6) than those of the ER70-S-3 classification. This provides slightly better wetting and weld appearance with slightly higher tensile and yield strengths and may permit increased speeds compared with ER70S-3 filler metals. These filler metals are generally recommended for use with argon-oxygen shielding gas mixtures, but they are usable with argon-C02 mixtures and C02 under the same general conditions as for the ER70S-3 classification. Under equivalent welding conditions, weld hardness will be lower than ER70S-6 weld metal but higher than ER70S-3 deposits.

ER70S-G Classification

This classification includes those solid filler metals which are not included in the preceding classes. The filler metal supplier should be consulted for the characteristics and intended use. This specification does not list specific chemical composition or impact requirements. These are subject to agreement between supplier and purchaser. However, any filler metal classified ER70S-6 must meet all other requirements of this specification.


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CLASSIFICATION OF ALUMINUM

Aluminum alloys are broadly classified as 1) casting and 2) wrought. Our focus will be on the wrought alloys. This group includes those alloys that are designed for mill products whose final physical forms are obtained by working the metal mechanically, rolling, forging, extruding, and drawing. These products include: sheet, plate, wire, rod, bar, tube, pipe, forgings, angles, structural channels, and rolled and extruded shapes.

The Aluminum association has designed a four digit index system for designing wrought aluminum and its alloys.

The first digit identifies the alloy group: Aluminum Alloy Designation Aluminum - 99.0% 1xxx Copper 2xxxManganese 3xxxSilicon 4xxxMagnesium 5xxxMagnesium and Silicon 6xxx Zinc 7xxxOther elements 8xxx Unused series 9xxx

Second digit indicates modification or impurities, last two digits indicate minimum aluminum percentage, i.e. 1075 is 99.75% pure aluminum.

Example: 6061 Aluminum

6 = Magnesium and Silicon is the major alloy group 0 = no modifications or significant impurities 61 = percent aluminum


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MAJOR ALUMINUM ALLOYS AND THEIR APPLICATIONS

Alloy Series

Description of Major Alloying Element

Typical Alloys

Typical Additions

1xxx 99.00% Minimum 1350 Electrical conductor Aluminum 1060 Chemical equipment, tank cars

1100 Sheet metal work, cooking utensils, decorative

2XXX Copper (Al-Cu) 2011 Screw Machine parts 2219 Structural, high temperature (Al-Cu-g)2014 Aircraft structures and engines,

truck frames and wheels 20242618

3XXX Manganese 3003 Sheet metal work, chemical 3004 Equipment, storage tanks

4XXX Silicon 4032 Pistons 4043 Welding electrode4343 Brazing Alloy

5XXX Magnesium 5005 Decorative, architectural 5050 Anodized automotive-trim5052 Sheet metal work, appliances 5657(>3%Mg)5083 Marine, welded structures 5086 Storage tanks, pressure5454 Vessels, armor plate 5456 Cryogenics

6XXX Magnesium and Silicon 6061 Marine, truck frames 6063 Bodies, structures, architectural,

furniture 7XXX Zinc (Al-Zn-

Mg) 7004 Structural, cryogenics, missiles 7005 (Al-An-Mg-Cu)7001 High strength structural 7075 Aircraft7178


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ALUMINUM ALLOYS

A temper designation system is used to indicate the condition of a product. It is based on the sequence of basic treatments used to produce the desired mechanical properties. This designation follows the alloy designation. Subsequent divisions of the basic letter tempers are indicated by one or more digits following the letter. These digits designate a specific sequence of basic treatments.

BASIC TEMPER DESIGNATIONS FOR ALUMINUM ALLOYS F As-Fabricated O Annealed H1 Strain hardened only H2 Strain hardened and partially annealed H3 Strain hardened and thermally stabilized W Solution heat-treated T1 Cooled from an elevated temperature shaping process and naturally aged T2 Cooled from an elevated temperature shaping process, cold worked and naturally

aged T3 *Solution heat-treated, cold worked, and naturally agedT4 Solution heat-treated and naturally aged T5 Cooled from an elevated temperature shaping process and then artificially aged T6 Solution heat-treated and then artificially aged T7 Solution heat-treated and stabilized T8 Solution heat-treated, cold worked, and then artificially aged T9 Solution heat-treated, artificially aged, and then cold worked T10 Cooled from an elevated temperature shaping process, cold worked, and then

artificially aged

*Achieved by heating to and holding at a suitable temperature long enough to allowconstituents to enter into solid solution and then cooling rapidly to hold the constituents insolution.


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Nonheat-Treatable Alloys

The initial strengths of the nonheat-treatable alloys depend primarily upon the hardening effect of alloying elements such as silicon, iron, manganese, and magnesium. These elements increase the strength of aluminum by formation of dispersed phases in the metal matrix or by solid solution. The nonheat-treatable alloys are mainly found in the 1XXX, 3XXX, 4XXX and 5XXX series depending upon their major elements. Iron and silicon are the major impurities in commercially pure aluminum, but they do contribute to its strength. Magnesium is the most effective solution-strengthening addition. Aluminum magnesium alloys of the 5XXX series have relatively high strength in the annealed condition. All of the nonheat-treatable alloys are work harden able.

The nonheat-treatable alloys may be annealed by heating to an elevated temperature to remove the efforts of cold working and improve ductility. The proper annealing schedule to use will depend upon the alloy and its temper. When welding the nonheat-treatable alloys, the heat affected zone may lose the strengthening effects of cold working. Thus, the strength in this zone may decrease to near that of annealed metal.

Heat-Treatable Alloys

The heat-treatable alloys are found in the 4XXX, 6XXX and 7XXX series. The strength of any of these alloys depend only upon the alloy composition, in the annealed condition as do the nonheat-treatable alloys. However, copper, magnesium, zinc, and silicon, either singly or in various combinations, show a marked increase in solid solubility in aluminum with increasing temperature. Therefore, these alloys can be strengthened by appropriate thermal treatments.

Heat-treatable aluminum alloys develop their improved strength by solution heat treating followed by either natural or artificial aging. Cold working before or after aging may provide additional strength. Heat-treated alloys may be annealed to provide maximum ductility with a sacrifice in strength properties. Annealing is achieved by heating the component at an elevated temperature for a specified time, and then cooling it at a controlled rate.

During welding, the heat-affected zone will be exposed to sufficiently high temperatures to overage heat-treated metal. As a result this zone will be softened to some extent.

Reprinted from American Welding Society Welding Handbook, Seventh Edition, Volume 4, Metals and Their Weldability.


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Aluminum Filler Metal

Selection of a compatible filler wire is an important step in successful Aluminum welding. The filler metal composition must be compatible with the composition of the base material or cracking will result. Filler for aluminum is classified in the same way as wrought aluminum alloys.

A relatively small number of filler alloys can be used to weld a wide range of aluminum alloys. Certain filler alloys, 5356 or 5183 for example, can be used for practically all aluminum welding.

The chart below lists filler selection based on base material. Those listed under the "strength" group produced stronger and harder weld composite. The group "elongation" produce softer, more ductile welds.

Recommended filler for various Aluminum Alloys Recommended Filler Metal

Base Metal For Maximum As-Welded Strength

For Maximum Elongation

EC 1100

1100 1100,4043

EC, 1260 1100, 4043

2219 2319 (2)3003 5183, 5356 1100, 4043 3004 5554, 5356 5183, 4043 5005 5183, 4043, 5356 5183, 4043 5050 5356 5183, 40435052 5356, 5183 5183, 4043, 5356 5083 5183, 5356 5183, 5356 5086 5183, 5356 5183, 5356 5154 5356, 5183 5183, 5356, 5654 5357 5554, 5356 53565454 5356, 5554 5554, 5356 5456 5556 5183, 53566061 4043, 5183 535636063 4043, 5183 535637005 5039 5183, 53567039 5039 5183, 5356

Notes: 1. Recommendations are for plate of "0" temper.2. Ductility of weldments of these base metals is not appreciably affected by filler metal.

Elongation of these base metals is generally lower than that of other alloys listed.3. For welded joints in 6061 and 6063 requiring maximum electrical conductivity, use

4043 filler metal. However, if both strength and conductivity are required, use 5356filler metal and increase the weld reinforcement to compensate for the loverconductivity of 5356.


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GMAW Welding Variables “Essential Variables” is a term used in the welding codes to identify the critical components of a welding application that if changed would require re-qualification. The essential variables for GMAW are:

• Current (DCRP vs. DCSP)• Wire type and size• Voltage setting• Amperage (Wire feed speed)• Shielding gas selection

A change in any of these variables is going to effect a change in the resulting weld. Note that some of the essentials variables are decisions made when setting up to weld. In trouble shooting weld problems most can be traced back to one or more of these essential variables. It is imperative that the welder understands the effect of each of these variables on the weld.

Current Type The type of current used in GMAW is Direct Current Reverse Polarity. This means the electrode is connected to the positive poll and the work or “ground” is negative. Using the wrong polarity can result is such defects as under bead cracking, porosity and excessive spatter.

Wire Type and Size The type of wire is usually determined by matching the properties and composition of the base material. The choice of diameter of wire is based on mode of metal transfer desired, thickness of base material and position the welding is to be done in.

Voltage Think of voltage as the source of heat in GMAW. Voltage wets the base metal. High voltage will give a long arc length. Low voltage will give a tight arc length and the weld bead is narrow. Voltage is also one of the factors that determine the mode of metal transfer. Trial runs are necessary to adjust the arc voltage if it is to produce the most favorable filler metal transfer and weld bead appearance. These trial runs are essential because arc voltage is dependent upon a variety of factors, including metal thickness, the type of joint, the position of welding, electrode size, shielding gas composition, and the type of weld. From any specific value of arc voltage, a voltage increase tends to flatten the weld bead and increase the fusion zone width. Reduction in voltage results in a narrower weld bead with a high crown. Excessively high voltage may cause porosity, spatter and undercutting; excessively low voltage may cause porosity, cold lap and lack of fusion.

Amperage (Wire Feed Speed – WFS) The wire feed speed is measured in inches per minute and controls the welding amperage in GMAW. In adjusting the GMAW equipment there must be a balance between the wire feed speed and the arc voltage. Think of wire feed speed as the amount of filler metal you are feeding to a given amount of heat (voltage) to consume the filler. If the wire feed speed is


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to slow the result will be a longer arc in extreme cases the wire may melt to the contact tip (burn back). If the wire speed is to fast for the amount of voltage the result will be a high crowned bead with a lot of spatter and little fusion.

Shielding Gas When molten, most metals combine with the basic elements in air, oxygen, and nitrogen to form metal oxides and nitrides contamination of the weld metal can result in low strength, low ductility and excessive weld defects such as porosity and lack of fusion.

The primary purpose of the shielding gas in GMAW is to protect the molten weld metal from contamination and damage by the surrounding atmosphere. However, several other factors affect the choice of a shielding gas some of these factors are as follows:

• Arc and metal transfer characteristics during welding• Penetration, width of fusion, and shape of reinforcement• Speed-of welding• Undercutting tendency

All of the above factors influence the finished weld and the overall result. Cost must also be considered.

Argon and helium, (used most frequently for GMAW of nonferrous metals) are completely inert. The selection of one or the other, or mixtures of the two in various combinations, can be made so that the desirable metal transfer, penetration bead geometry, and other weld characteristics can be obtained.

Although the pure inert gases protect the weld metal from reaction with air, they are not suitable for all welding applications. By mixing controlled quantities of reactive gases with them, a stable arc and substantially spatter-free metal transfer are obtained simultaneously. Reactive gases and mixtures of such gases provide other types of arcs and metal transfer. Only a few reactive gases have been successfully used either alone or in combination with inert gases for welding. These reactive gases include oxygen, nitrogen and carbon dioxide. Although hydrogen and nitrogen have been considered as additives to control the amount of the joint penetration they are recommended only for a limited number of highly specialized applications where their presence will not cause porosity or embrittlement of the weld metal. As a rule, it is not practical to use the reactive gases alone for arc shielding. Carbon dioxide is the outstanding exception. It is suitable alone or mixed with inert gas, or mixed with oxygen for welding a variety of carbon and low alloy steels. Carbon dioxide shielding is inexpensive. All the other gases except nitrogen are used chiefly as small additions to one of the inert gases (usually argon). Nitrogen has been used alone, or mixed with argon, for welding copper. The most extensive use of nitrogen however, is in Europe where little or no helium is available.

Shielding Gas Selection The choice of a shielding gas depends on the metal to be welded, section thickness process variation, quality requirements metallurgical factors, and cost. Argon, helium and argon-helium mixtures are generally used with nonferrous metals. Argon-oxygen,


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argon-carbon dioxide, argon-helium mixtures, and also pure carbon dioxide are employed for ferrous metals. The application needs, therefore, determine shielding gas selection.

Non-Essential Variables These are variables that can be change at the discretion of the welder and do not require re-qualification. Examples of these variables are:

• Travel Speed• Electrode extension (Stick Out)• Electrode angle (Work and Travel)

Travel Speed Travel speed is the linear rate at which the arc is moved along the weld joint. Travel speed effects bead width and level of penetration. The penetration will decrease when the travel speed is increased, and the weld bead will become narrower. To slow of travel may result in excessive penetration and melt through. To large of a bead in the horizontal position can result in roll over and cold lap. To fast of travel speed can result in under cutting and lack of fusion.

Electrode Extension (Stick Out) The electrode extension is the distance between the last point of electrical contact, usually the end of the contact tube, and the end of the electrode. Resistance heating causes the electrode temperature to rise. There is a need to control electrode extension, because too long an extension results in excess weld metal being deposited with low arc heat. This will cause poor weld bead shape and shallow penetration also, as the contact tube-to-work distance increases the arc becomes less stable. Good electrode extension is ¾” for spray and pulse welding.

Electrode Angle (Work and Travel) As with all arc welding processes, the position of the welding electrode with respect to the weld joint affects the weld bead shape and penetration. The effects are greater than those of arc travel angle. Electrode position is described by the relationships of the electrode axis with respect to (1) the direction of travel, (2) the travel angle, and (3) the angle between the axis and the adjacent work surface (work angle). When the electrode points opposite from the direction of travel. It is called the backhand welding technique. When the electrode points in the direction of travel, is called the forehand welding technique. When the electrode is changed from the perpendicular to the forehand technique with all other conditions unchanged, the penetration decreases and the weld bead becomes wider and flatter. When producing fillet welds in the horizontal position, the electrode should be positioned about 45 degrees to the vertical member (work angle). For all positions, the electrode travel angle normally used is in the range of 5 to 15 degrees for good control of the molten weld pool.


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GMAW Pulse Welding

Pulsed current transfer is a GMAW process variation capable of all-position welding at a higher energy level than with the short-circuiting transfer. In this variation, the power source provides two current levels: a steady “background” level, too low in magnitude to produce any transfer; and a “pulsed peak current, superimposed upon the background current at a regulated interval. The combination of the two currents produces a steady arc (background current) with a controlled transfer of weld metal in the spray mode (pulsed peak current)

Terms and Definitions for Pulse Welding Waveform Control Waveform Control Technology is a term that is used in conjunction with Lincoln Electric high-tech welding equipment, indicating total control of the arc. The term refers to infinite variability with respect to adjusting amperage and voltage over the output range of the machine. It is most commonly used for the pulse welding application. Most materials that are weldable have different types of reactions to changes in amperage and voltage. For example, some materials that are exposed to rapid or drastic increases in amperage take longer to respond (liquefy), than other materials exposed to the same types of amperage increases (steel vs. aluminum). Waveform control technology allows a custom wave, specifically designed for a particular material with a given wire diameter and type of cover gas, to be used in order to achieve optimal welding performance for each given material. Each of the waves is separate and distinct, even if there are only slight changes due to differences in gas type and wire diameter. Waveform Control technology was designed so the best performing weld parameters are easy for the operator to find, and require minimal interaction with the machine to maintain optimal performance throughout the course of a working day. In a pulsing application, a wave is set through adjusting peak amperage, peak time, tailout time, tailout speed, background amperage, background time, frequency, and ramp up rate. These variables are all separate and distinct, and they will all change as wire feed speed is adjusted. The design of a wave is relatively complicated, but this approach is simple because Lincoln does the design for you. In practice, the pulsing package is now simpler and easier to control and much more versatile than any other machine. (See Appendix A-2 and A-3 for waveform examples and diagrams).

Trim Trim is a control of total heat input. In the past, for a pulsing application, heat input was controlled through a series of adjustments. Due to the development of waveform control technology, trim is a one-knob adjustment that gives you the same control of the same variables that required three to four knobs to adjust in the past. In a constant voltage application, the operator will choose a wire feed speed and adjust the voltage until the wire is transferring smoothly, slightly above the molten pool of weld material. (See appendix A-3). This will establish a distance between the wire and the molten puddle so the wire isup above the puddle, but not so high that the filler material is spraying to the outside of theintended weld area. This is commonly referred to as arc length (see appendix A-4). Agood arc length is smooth and relatively focused. In the pulse-welding mode, trim controlsthe exact same thing as voltage does in the constant voltage mode. Trim can be set from a


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minimum of 0.50 to a maximum of 1.50. As the factory develops different waves for different materials, the trim setting is automatically calibrated to 1.00 as the optimal setting across the wire feed speed range, according to the most desirable transfer that is achieved in the lab. This is a good setting to start with each time the machine is changed into a different mode. This is not as complicated as it sounds. As the operator adjusts the trim value, he or she will see the arc length get shorter or longer. To set the machine, this is all an operator needs to know.

Arc Control This is the secondary adjustment for heat input. In constant voltage welding mode this is an inductance control and can adjust arc transfer characteristics to the operator’s preference. This setting ranges from +10 to –10 with the average setting being “off” or 0. For pulse welding, arc control adjusts frequency and background current. As the arc control is increased, the frequency increases while the background decreases, and vice versa as the arc control is decreased. The controls have similar effects on the metal transfer, and resulting weld bead, whether you are in constant voltage or pulsing mode. Increasing this setting leads to a slightly colder or harsher arc, while decreasing softens up the transfer.

Synergic Welding This is a term that refers to the communication that takes place between the power source and the wire feeder. A synergic system has a direct communication channel between the wire feeder and the power source. In other words, the welding power is set directly proportional to the amount of filler material that is being fed into the weld pool. In a non-synergic system, the wire feed speed controls the tachometer for the wire drive motor. On the power source, the output controls the voltage. The operator must set both controls correctly in order to get a smooth arc transfer. In a synergic system, an increase in wire feed speed automatically increases the welding power output. Since the two settings are now working together, or synergic, the power source is aware of changes in the wire feed speed. In order to gauge this correctly, the machine must also have a very accurate voltage sensing feed back circuit. With this addition, the output characteristics of the machine also improve. Not only does the output of the machine respond to changes in wire feed speed, but since the feedback loop is so quick, the machine maintains a much more consistent power output having the ability to compensate for even small changes in the electrical stick out or operator movement. The resulting benefits to the operator are; decreases in the smoke and spatter levels, one knob wire feed speed adjustment, and a more consistent arc length and metal transfer. Due to the need for a voltage feed back loop in the power source and the wire feeder, older machines are not capable of this type of communication and can not be converted.

V 350 vs. Power Wave 455 The Power Wave system is a synergic system, and the V350 is not. However, both machines have the same capabilities in terms of utilizing waveform control technology. Although the memory storage of the power wave is much greater than the V350, new waves can be downloaded from any computer into either machine. Since the power wave is synergic, in the pulsing mode as described previously, adjusting trim controls the arc


40

length. The V350 is not synergic, so the machine uses a different number system to control the same thing. When it is set in the pulsing mode, the LED reads SPD in the left window and a number in the right window (e.g. 250). This number is an approximate heat setting that relates to the wire feed speed that the feeder is set at. Since this is a non-synergic system, you must tell the power source approximately how quickly you will be feeding material into the weld pool. Matching the SPD setting to the wire feed speed setting will give the operator a good starting point that will need to be fine tuned in order to obtain the most desirable arc transfer. As the operator needs more or less filler material, both settings will have to be adjusted as needed to fine-tune the arc. Given the same set of circumstances the advantage of a synergic system is, only the wire feed speed would have to be adjusted to increase or decrease the amount or filler material in a weld.


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Miller Pulse MIG Video Review Work Sheet

Name: _______________________________ Date: __________________

1. What are the four main components of a GMAW system?

2. What welding current is used for GMAW?

3. How do you confirm that the system is set up for the type of current you need.

4. List the modes of metal transfer available in GMAW.

5. List two primary factors that determine your choice of shielding gas.


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6. What is the required travel angle for welding Aluminum with GMAW?

7. Describe the effect of travel angle on penetration in GMAW of steel.

8. What type of shielding gas is required for GMAW Spray transfer?

9. What determines the type and size of Drive Rollers needed?

10. What is a “burn back”? List three things that may cause a “burn back.


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GMAW WORK SHEET

Name: ______________________________ Date: ______________________

1. Please define the following abbreviations; GMAW, GMAW-S, GMAW-P, MIG,MAG.

2. List three advantages of the GMAW process.

3. List three disadvantages of the GMAW process.

4. What is the basic equipment required for GMAW?

5. Using the select knob what “mode” do you select for GMAW axial spraytransfer?


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6. Using the select knob what “mode” do you choose for the pulse steel exercises?

7. Using the select knob what “mode” do you choose for the pulse aluminumexercises?

8. What control on the Invertec 350 Pro adjusts the arc length?

9. List the four basic types of wire feeders.

10. What determines the size of drive rollers used in a wire feeder?

11. Give two examples of problems that may result from improper tension settingon the drive rollers.


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12. List seven components of a welding gun.

13. Describe the purpose of the insulator.

14. Describe the purpose of the contact tip.

15. Why is a copper alloy the choice for gas cups?

16. How do you know when proper tension is achieved on a drive roll system?

17. List six purposes that shielding gas serves in GMAW.


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18. List the three gases / gas mixtures you will be using in this course and identify theapplication of each.

19. What two types of aluminum fillers can be used for practically all aluminumwelding.

20. List four essential variables of GMAW.

21. Identify the type of current required for GMAW and explain the electrode and workconnections.

22. What determines the type and size of wire to be used in a welding application?

23. Describe the effect of voltage on arc length.


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24. What is the affect of slow and fast wire feed speed?

25. Describe the effects of travel speed.

26. Why is there a need to control electrode extension and what affect does it have onthe weld?

27. Define the terms “backhand” and “forehand” welding technique and describe theaffect on penetration.

28. Define the term “work angle.


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29. List four problems that may occur when the molten metal combines with the basicelements in air.

30. List ten factors that affect the choice of a shielding gas.

31. In pulse welding what does the adjustment “Trim” control?

32. In pulse welding what does the adjustment “arc control” do?


49

Math

on

Metal

The Welding Fabrication Industry needs qualified welder fabricators who can deal with a variety of situations on the job. This portion of the training packet explores mathematics as it relates to industry requirements.


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Solving Formulas

Solving the formulas that are typically used by welders is easy to do. There are several rules that you need to follow in order to successfully use a formula.

Step #1 Read the formula and understand what it says a. What do the letters (variables) stand for?b. What math operations does the formula tell you to perform?

Step #2 Substitute the numbers for the letters Step #3 Follow the rules for ‘order of operation’ to solve the

problem

Step #1 Read the formula and understand what it says

Example: V = IR

This formula says: Voltage equals current times resistance

Each letter in a formula is called a variable. A letter stands for a word(s). Make sure you know what the letters in your formula stand for

In this example of Ohm’s law V =Voltage I = Amperage (current flow) R = resistance

Be careful when reading formulas because in different formulas the same letters can stand for something different. In the following formula

V = L x W x H

V stands for volume (not volts). This formula says volume equals length times width times height.

After you determine what the letters or variables stand for in the formula you must figure out what the formula says to do with them. (Do you add them together, subtract, multiply or divide?)

Let’s go back to our original example

V = IR

What this formula says is ‘voltage equals current times resistance.”

This means you multiply current times resistance.

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Anytime you see variables next to each other with no separation between them you multiply them together.

So IR is the same as I x R.

In fact there are several ways to indicate multiplication in a formula. They are:

V = IR V= I x R V= I * R V= I • R V = I (R) Each different example above tells you to multiply current times resistance

There are also different ways to indicate division in a formula.

Example: R = V/ I You would read this formula: Resistance equals voltage divided by current. The slanted line (/) tells you to divide. It is the same as writing R = V ÷ I Other ways to indicate division are: R = V/I

R = V÷I

R = V A fraction is just another way of telling you to divide the top I number by the bottom number.

Step #2 Substitute numbers for variables. Going back to our original formula:

V = IR

If: Current (I) equals 5 amps and Resistance equals 4 ohms (Ω)

We replace the letter I with 5 amps and we replace the letter R with 4 ohms

V = 5 amps x 4 ohms Always include the units when you substitute numbers for variables.

We can now solve our equation: 5amps x 4 ohms = 20 volts

Step #3 Follow the rules for order of operation How do we handle a formula that has more than one mathematical operation in it? You must follow the correct order of operation. (Do anything within parenthesis first, next do



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exponents, then multiplication and division and finally addition and subtraction.) For details please see the following page on order of operations.

Example: Let’s says we wanted to know the Fahrenheit temperature when we know that it is 28 Celsius outside?

The formula to convert Celsius temperatures to Fahrenheit temperature is:

3259

+= CF Read the formula and understand what it says;

Fahrenheit degrees equals 9 times Celsius degrees .

Next divided by 5 plus 32.

322859

+=F Substitute numbers for variables. In this case 28

Degrees is substituted for C

284.50 +=F Follow the correct order of operation: first multiply 9/5 x 28. Hint: use your fraction key to multiply the fraction and the whole number together.

4.82=F º Finally do the addition


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Order of Operation Rules


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Manipulating simple formulas

As we work on various calculations in welding applications, we will run into quite a few mathematical formulas which follow a certain pattern and therefore can benefit from being taught together. We will not introduce all of them now, but the few shown here will give you an idea of how useful it is to understand their pattern and how to work them.

All of the formulas we present here are of one of these two patterns:

answer = number x number these two are basically

or the same, just makeovers of each other

answer = number ÷ number

Here are some examples:

Arearectangle = length x width Areacircle = π x r2

Distance = Rate x Time Voltage(V) = Current(I in amps) x Resistance(R) Power (P in watts)= Current(I) x Voltage(V) or (E)

These shop math circles are a good visual aid. Here’s how they work . . . The numbers in the bottom two quarter spaces multiply together to get the number in the top space. The number in the top half divided by either of the numbers on the bottom gets you the other number on the bottom. So you can think of the horizontal line as a division sign and the vertical line as a multiplication sign.

Putting your thumb over the information you want is a good way to determine which action to take. If the numbers you have uncovered are separated by a vertical line, you multiply. If they are separated by a horizontal line, then you divide to get your answer.

Suppose you have an area of 25 sq in and a width of 8”. Input your numbers as in the following example. If you put your thumb over the information section you want, area, you see that you have the ‘25’ and the ‘8’ both showing and separated by the vertical line indicating multiplication. You multiply them together and get 200 in3. Now, to check, put your 200 in3 into the areasection and 8 into the width section; this time you want to calculate the area

Area of circle

π r2

Area

Width Length


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Cover that length with your thumb and see that what is showing is the 200 over and the 8, separated by the horizontal line (like a fraction) indicating you should divide. 200 ÷ 8 = 25 area ÷ width = Length

Later we will be introducing the following formulas:

Voltage = Curretn x Resistance Power = Voltage x Current

Can you see that they also follow the same pattern?

Try putting them into these shop math circles and check them to make sure they will work correctly.

Complete the following worksheet on calculating power to practice this circle method of manipulating a formula

(area)

8 25

200 sq in

8 length

Voltage

? ?


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REVIEW OF ELECTRIC POWER PROBLEMS AND MANIPULATING EQUATIONS

P = I2R I = _____ R = ______

1. How many kilowatts (groups of 1000 watts) are in a system with 12amps current and 140 ohms resistance?

2. How many kilowatts are in a system with 10 amps and 120 ohmsresistance?

3. How much current do you have in a system with 120 ohms resistanceand 8 kilowatts (8000 watts) power?

4. How much current do you have in a system with 130 ohms resistanceand 11 kw power?

5. How much resistance is in a system with 9 kw (= 9000 watts) powerand 10 amps current?


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Math Lingo ( . . . or when “divided by” doesn’t mean “divided into” . . .)

The language of math can be totally confusing at times; there sometimes seems to be a hidden cipher or code needed to magically turn word problems into calculations involving the four operations of multiplication, division, addition and subtraction. It helps to have a small glossary of conversion codes to make sense of it all:

First of all, let’s look at some words that mean addition:

and, add, plus, more (than), in addition

Examples: 2 and 4 make/equal 6 add 4 to 2 and you get 6 2 plus (+) 4 = 6 4 more than 2 is 6 4 (more) in addition to the 2

. . . and some more words signaling addition:

totaling, total, all, altogether, sum, . . .

Examples: 2 eggs and 4 eggs, totaling . . . the total of 2 chickens and 4 chickens $2 for this, $4 for that, how much in all? $2 today, $4 tomorrow, how much altogether? the sum of 2 and 4

For subtraction, we have:

subtract, less, minus, take away . . .

Examples: 10 subtract 7 is/equals 3 10 eggs less 7 eggs is 3 eggs 10 minus 7 is/equals 3 10 take away 7 is/equals 3

Note: In subtraction, order is important. 10 less 7 is not the same as 7 less 10 (THINK OF YOUR CHECKBOOK, when you’re operating in the negative!! UGH!) The same goes for “10 subtract 7” ≠ “7 subtract 10 ( = -3)”, “10 - 7 ≠ 7 - 10,” “10 take away 7” ≠ “7 take away 10,” etc.

Here are some more words signaling subtraction:

the difference between, take out, take from, remainder, left over . . .


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Examples: The difference between 10 and 7 is/equals 3 What’s your remainder when you take 7 out of 10? What’s left over after you take 7 from 10?

Language gets a little more tricky with multiplication and division.

Words signaling multiplication:

times, multiplied by, each, of, altogether, for every, . . .

Examples: 3 times 5, 3 multiplied by 5 3 x 5 3 • 5 2 of those tickets at $45 each, how much altogether? $45 for every ticket, how much for 10 tickets?

Words signaling division:

out of, each . . . Examples:

3 out of 4 becomes ¾ = 3 ÷ 4 = .75 or 75%

$50 total buys how many tickets at $10 each? ⇒ 50 ÷ 10 = 5

AND . . . divided by, divided into, into, goes into

6 divided into 18 is 3 Notice these two require the exact

18 divided by 6 is 3 opposite order of numbers 6 & 18

6 into 18 is/equals 3 Order counts here as well

6 goes into 18 three times

Through it all, notice that the word “is” means “EQUALS” (“=”) always.


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Heat Input Lab

In this exercise you will perform two welds in order to measure the heat input as expressed in Joules per inch.

Remember heat input is a fancy way of stating the amount of heat you’re putting into a metal while welding. Knowing the heat input is important because heat may affect the manufacturing properties of the metal.

In this lab you will compare the heat input in Joules/ inch in the: 1. Pulse process2. Spray process

In order to calculate heat input we need to know three different variables. Current measured in Amps (I) Voltage measured in volts (V) Travel speed expressed in inches per minute (S)

In this lab you will be assigned different current and voltage settings, you will measure the travel speed and then calculate the heat input for the various processes.

The formula for heat input is:

Heat Input = V x I x 60 S

Note: the 60 in the formula allows you to express the speed in inches per minute rather than inches per second.

How to solve a heat input problem: For detailed instructions on solving heat input problems see welding packet #253 or the math reference packet; for a refresher see the example below.

Example: I have two welds that are the same size. I need to know which settings generate the least heat input.

The first weld was made with settings of 175 Amps, 25 volts. The travel speed was 3 inches per minute.

The second weld was performed at 310 amps, 35 volts and 8 inches per minute Which weld required less heat input?

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Solution: 175amps x 25 volts x 60 seconds/minute = 87,000 joules/in. 3 inches/ minute

310 amps x 35 volts x 60 seconds/minute = 81, 395 joules/in. 8 inches/minute

The second weld process generated less heat as measured in joules/inch.

Please complete the following lab in order to compare heat input in two different welding processes. Note: your weld lengths must be the same.

Record your settings and times in the table below, then calculate the heat input.

Spray Process

Spray process for a ________ inch weld.

My current setting is ____________________Amps (I)

My voltage setting is_____________________Volts (V)

It took me_____________minutes to complete my weld.

The heat input for this weld is__________________Joules/inch

Pulse Process

Pulse process for a ___________ inch weld.

My current setting is ____________________Amps (I)

My voltage setting is_____________________Volts (V)

It took me_____________ minutes to complete my weld.

The heat input for this weld is ________________Joules/inch

Which process generated less heat?



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Something to Think About

Technical Note on “ Dimensional Analysis”

A good way to do a ‘sanity check’ on a formula is to look at the units for each variable and make sure that the units you end up with match the units you expect to see in your answer.

In the heat input example your answer needs to come out in Joules/inch :

Our original formula was:

Heat input= V x I x 60 S Substituting units for symbols this translates into:

Joules/inch = Volts x Amps x seconds/minutes inch/minute

We already know that Volts x Amps = Watts and that Watts are Joules/second

Substituting Joules/seconds for Volts x Amps we get:

Joules/inch = Joules/second x second/minutes inch/minute

Note: inches/ minute in the denominator become minutes/inch in the numerator,so:

Joules/inch = Joules/second x second/minute x minutes/inch


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Science On

Steel &

Aluminum The Welding Fabrication Industry needs qualified welder fabricators who can deal with a variety of situations on the job. This portion of the training packet explores science as it relates to industry requirements.


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Contents of this Packet are: - Purpose of Pulsing with GMAW- Gas Shielding for Pulsed GMAW- Plasma Formation in the Arc- Use of Diatomic and Tri-atomic Gases with Argon or Helium- Stabilizing the Arc for GMAW of Steel- Fundamentals of Axial Spray- “Fingerlike” Penetration with Pure Argon Spray GMAW- When to Use Arg0n-Helium vs. Ar-CO2 vs. Ar-O2 Pulsed Spray Arc GMAW- Oxidation Potential of Argon-Rich Gas Mixtures- Optimum Gas Flow Rate- Pulsed GMAW of Steel vs. Aluminum- Synergic GMAW with Waveform Control

Purpose of Pulsing with GMAW There are many advantages of pulsing current during GMAW. Perhaps the most important advantage is that out-of-position welding can be performed as a direct result of pulsed GMAW with a spray transfer. Pulsing provides high energy density spray arc during a pulse while maintaining a low overall heat input. Because of this high energy density arc at low heat input, out-of-position welding and thick-to-thin sections welding can be performed much more successfully than with conventional GMAW.

Historically, out-of-position welding using either globular transfer or spray transfer was not practical with conventional GMAW. So, GMAW had to be used in the short circuit arc welding mode to provide a low heat input arc to weld out-of-position. The problem with short arc was that the arc action, such as frequency of short circuit transfer, was too inconsistent and too dependent on welder preferences for most applications. Furthermore, the re-ignition of the arc during the short circuit cycle produced substantial spatter, since the mode of metal transfer was globular. In fact, many modern welding codes such as MIL-STD-278 completely prohibit short circuit arc welding for ships and military structures. Short arc has been completely replaced in the military and many civilian codes with electronically controlled pulsed GMAW. Pulsing provides spatter-free spray transfer for out-of-position welding.

Gas Shielding for Pulsed GMAW Although gas metal arc welding of steel is performed routinely, it is a very complicated process involving gas-metal reactions affecting the resulting mode of metal transfer and weld quality. The gases commonly used for GMAW include:

- argon (Ar) - Inert - helium (He) - Inert - Oxygen (O) - Chemically Active - carbon dioxide (CO2)- Chemically Active

As shown above, Ar and He are totally inert because their outer shell of electrons is “full”. Chemical reactions between gases and weld metal can only take place if the gas is active like O2 because these gases have partially filled outer shells containing “valence electrons” that can bond with other materials. For example, oxygen has an unfilled outer electron

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shell containing valence electrons, which combine with the valence electrons of the molten iron to form iron oxide. Similarly, CO2 is an active gas because it dissociates under the arc to CO and O. Such reactions can not happen with Ar or He. Thus, Ar and He provide excellent protection of the molten weld pool because no chemical reaction can occur between Ar, He and molten metal. The shielding gas composition greatly affects the burn-off rate, type of metal transfer (short circuit, globular, or spray), and penetration.

Plasma Formation in the Arc This is because electricity is conducted through the arc (from the cathode to the anode) by means of plasma. The plasma consists of ionized gas and ionized metal generated by the hot arc. A plasma can form in any gas or metal vapor if the temperature is high enough. The ionization potential of a substance is the energy required to remove an electron from the outer shell of a gas or metal vapor atom. Large atoms with many shells containing electrons usually have low ionization potentials because the outer electrons (negatively charged) are very far away from the positively charged nucleus. Since argon has three major shells of electrons and helium has only 1 outer electron shell, the ionization potential of helium is much higher than that for argon. So, the heat input for helium gas shielded weld deposits is always higher than similar welds deposited with argon shielding. For example, the heat input (H) for a arc weld by GMAW is:

H = E I / v Where E is the voltage, I is the amperage and v is the travel speed For welding aluminum with an argon shielding gas, the voltage is 15V, the current is 250amps and the travel speed is 636 mm/s. The heat input is:

H = E I / v = (15 volts) (250 amps) / 7mm/s H = 536 J/mm If the same weld were made with helium shielding gas and 250amps and 7mm/s travel speed, the voltage would be higher (to achieve ionization) at 20 volts. So the heat input would increase to:

H = E I / v = (20 volts) (250 amps) / 7mm/s H = 714 J/mm

Once the gas is ionized, electricity can pass through the arc just as electricity passes through a wire by obeying Ohm’s law. For example, argon in GMAW forms a plasma to conduct electricity through the arc in accordance with ohm’s law, where: E = I R

Where: E is the welding voltage, I is the welding amperage, and R is the resistance across the arc. Once a plasma if formed, it has an average electrical resistance which is a combination of the resistances of the ionized shielding gas and metal vapors. Some ionization potentials for shielding gases and metal vapors are given in Table 1.



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Table 1 Ionization potentials for common shielding gases and metal vapors Gas or Metal Vapor Ionization Potential

(electron-volts) Density (g/cm3)

Atomic Number

Argon Helium CO2 O

Fe Al

15.7 24.5 14.4 13.2

3.5 – 4.0 3.8 – 4.3

0.00180 0.00012 0.00130 0.00095

7.87 2.7

18 2 - 8

26 13

Use of Diatomic and Tri-atomic Gases with Argon or Helium When a diatomic gas like O2 is used with Ar or He, the effect is to produce a hotter arc similar to an increase in the welding voltage. Diatomic gas will increase the heat transferred to the molten pool. For example, when H2 dissociates into 2H atoms in the arc heat is extracted from the very hot arc for this dissociation to take place. When the 2H atoms reach the cooler molten pool, H2 forms (exothermically) and a great of heat pumped into the weld. This exothermic reaction is helpful when welding thick plates of highly conductive metals like copper. Here again, the use of pure N2 or Ar + N2 provide an intensely hot arc for welding copper.

This same principle is true for tri-atomic shielding gas like CO2. CO2 is an active gas because it decomposes into CO + O in the arc just under the extremely hot electrode. When the CO+O reaches the cooler weld pool it recombines to CO2 in an exothermic reaction causing substantial heating of the weld area.

Stabilizing the Arc for GMAW of Steel Although Oxygen (O) forms oxide inclusions in the weld metal, O must be added to Ar in order to stabilize the arc when welding steel. CO2 can also be added to Ar for arc stability because during welding CO2 breaks down to carbon monoxide (CO) plus oxygen as shown below:

CO2 → CO + O2 .

If oxygen comes into contact with the molten metal, a metal oxide will form instantly. For example, Ar-2%O is commonly used to weld steel. The 2% O combines with iron to form iron oxide in the molten weld pool as well as on the hot wire entering the weld zone. When GMAW steel, DCEP is used, so the weld pool is the cathode and the filler wire is the anode. In order for an arc to be stabile, it must be rooted to cathode spot on the weld pool closest to the electrode. Similarly, the anode spot must be stable and located at the end of the electrode. If the anode and cathode spots are not stable, the arc will wander all over the weld pool as well as up and down the wire electrode. The presence of 1-5% oxygen in Ar shielding provides enough oxide layer to stabilize the arc by stabilizing the cathode and anode spots. The oxide substantially reduces the “work function” of the cathode, that is the energy required to emit an electron from the cathode and pass through the arc to the stable


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anode spot. The oxide has this property of stabilizing the anode and cathode spots. As a result, welding gases used for GMAW steel can never be composed of pure Ar, otherwise arc instability will occur. The welding gases must be Ar-1% to 5%O, or various mixtures of Ar and at least 5%CO2 . Even pure CO2 can be used. However, the greater the Ar content the less spatter and greater the mechanical properties of the weld metal.

Fundamentals of Axial Spray GMAW For reasons that are not well understood, argon is the only shielding gas that is capable of producing an axially-propelled spray arc that is quiet, stable, spatter-free, and highly directed. Spray arc produces over 100 droplets/s, and these droplets are smaller than the filler metal diameter. For any diameter of filler metal, there is a threshold value of current, above which a directed axial spray mode of metal transfer occurs. The transition current to spray is proportional to the wire diameter. Despite the fact that helium and CO2 have much higher ionization potentials than Ar, neither helium nor CO2 are capable of producing a spray transfer. Although helium and CO2 can generate a greater heat input than Ar, the mode of droplet transfer is a non-directed globular transfer through the arc.

Fortunately, however, we can take advantage of the high-heat-input characteristics of helium, CO2, and other gases by mixing these gases with Ar. As long as there is more than a critical amount of Ar present in the gas mixture, a true spray arc can be achieved while the heat-producing effects of helium, CO2 , O, N, and H are obtained. For example, true spray can be obtained with the following Ar gas mixtures :

- Ar-He mixtures containing at least 80%Ar- Ar-CO2 mixtures containing at least 85%Ar- Ar-O2 mixtures containing at least 95%Ar

The size of droplets in spray transfer are characteristically smaller than the diameter of the wire. As current increases, drop size decreases but frequency of droplets and deposition rate increase. With increasing current, wire diameter must increase to maintain a smooth and stable arc. Because the heat input for spray arc is high, only flat and horizontal fillets positions are used. Using DCEP with a spray arc, the maximum penetration is obtained for GMAW.

“Fingerlike” Penetration with Pure Ar Spray GMAW The directed axial flow of over 100 droplets/s produces a visible depression of the molten weld pool under the spray arc. The momentum of the rapid stream of axially directed droplets provides the mechanism for deep penetration directly beneath the arc with very little penetration along the side walls of the weld pool. The kinematic viscosity (defined as the viscosity multiplied by the density) of the shielding gas has a substantial effect of penetration. Since Ar has a greater kinematic viscosity than He, the axially directed penetration of Ar is far greater than that for He even though He has a higher ionization potential than Ar. This is why Ar produces fingerlike penetration and He produces more uniform penetration. Since penetration is affected by viscosity and density of the shielding gas, increasing the ambient pressure during welding can also decrease penetration. Increasing pressure of Ar atoms produces a drag or friction force resisting the speed of


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droplets streaming into the weld pool. As a result, increasing ambient pressure decreases weld penetration.

Fingerlike penetration of Ar spray GMAW is not desirable in welds. The most effective way to eliminate fingerlike penetration and promote a more uniform penetration pattern is by the addition of small amounts of a second gas. For example, Ar with 2 to 5% O or Ar with 5 to 25% CO2 greatly reduces and even eliminates fingerlike penetration. As discussed earlier, the primary purpose of adding O2 or CO2 to Ar is to establish arc stability. However, a secondary benefit of adding O2 or CO2 to Ar is to eliminate fingerlike penetration.

When to Use Ar-He vs. Ar-CO2 vs. Ar-O2 Pulsed Spray Arc GMAW The only gases that can be used to weld reactive metals (like aluminum, magnesium, and others) are either pure Ar or Ar-He mixtures. Since both Ar and He are inert, the reactive metals will not be contaminated during welding. Also, aluminum and magnesium have such thick refractory oxide layers that neither Ar-CO2 nor Ar-O2 mixtures are needed to achieve arc stability when welding these metals. In fact, the presence of CO2 or O2 would substantially oxidize and deteriorate the weld metal by impairing its mechanical properties. Thus, only pure Ar or Ar-He mixtures can be used to weld aluminum and magnesium. For thin sections, pure Ar is adequate. When high heat input welds are deposited on thick-section aluminum or aluminum alloys, a mixture of Ar and He is needed.

Steel is readily welded by the GMAW process, but pure Ar can not be used due to the arc instability problem (discussed above). For high toughness applications, steels used in shipbuilding and bridges are usually welded with Ar-2%O or Ar-5%CO2 . In this way, only the minimum amount of O or CO2 is used for arc stability. If more than 2%O or 5%CO2 are used, excessive oxidation and carburization would severely impair mechanical properties particularly Charpy impact toughness. To ensure good Charpy impact toughness, steel filler metals contain Si, Mn, and/or Al deoxidizers. Oxides of Si, Mn, and Al (such as SiO2, MnO, and Al2O3) are formed in the weld metal. Since the densities of these oxides are much lower than the molten steel weld metal, most of the oxides float to the top of the pool forming very thin islands of glassy slag.

Oxidation Potential of Ar-Rich Gas Mixtures The addition of CO2 or O2 to argon to increase arc stability, which is required for GMAW of steel, also oxidizes the molten steel but to different degrees. The oxidation potential of Ar containing 1 to 3% O2 is equivalent to about Ar containing 2 to 4% CO2 . The oxidation potential of Ar containing up to 30% CO2 is roughly similar to Ar-O2 mixtures containing O2 about half the level of CO2.

Optimum Gas Flow Rate It is sometimes believed that increasing Ar gas flow rate to higher and higher levels provides increased protection for the weld pool. This is only true up to a certain critical value of flow rate, and then detrimental turbulence occurs. Once turbulence occurs, the air contamination is entrained into the gas column across the arc. The formation of turbulence is dependent upon the Reynolds Number (R) for the flowing gas. R is calculated from:


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R = Dvρ / µ

Where, D is the diameter of the tube or nozzle diameter, v is the average gas velocity, ρ is the density of the gas, and µ is the viscosity of the gas. If the Reynolds Number exceeds 2300, the flow becomes turbulent. Unfortunately, the larger the diameter nozzle, the lower the critical gas flow velocity is for turbulent flow. So, there is only a limited improvement in Ar gas shielding by using larger diameter nozzles. Since gun design also affects Reynolds Number, the manufacturer’s recommendations for gas flow settings are important for best protection of the weld pool.

Pulsed GMAW of Steel vs. Aluminum Because has much higher thermal, electrical conductivity, low melting point, greater chemical reactivity, less solid solubility of hydrogen than steel, conventional GMAW of aluminum is much more difficult-to-control than welding steel. When similar welds are deposited on aluminum and steel, the aluminum weld metal is more susceptible to porosity and more sensitive to changes in welding parameters. For example, in comparing similar welds of aluminum and steel, the aluminum weld is over 10 times more sensitive to changes in wire feed rate than is steel. Unlike steel, small changes in wire feed rate causes a substantial change in arc length. In addition, because aluminum is so much more electrically conductive than steel, the use of “stick out” to control arc characteristics such as deposition rate are not as effective as that for steel.

Pulsed GMAW provides many advantages for both steel and aluminum welding. Although pulsing provides out-of-position capability with spray transfer for both aluminum and steel welding, pulsing is particularly beneficial for aluminum welding. The high energy density during a pulse helps to overcome the heat-draining effect cause by the high thermal diffusivity of the aluminum. The thermal diffusivity is defined as:

Thermal diffusivity = thermal conductivity / (density x specific heat)

The thermal diffusivity of aluminum alloys is about 10 times higher than aluminum, because aluminum alloys have both high thermal conductivity and low density. The thermal diffusivity of aluminum is 0.85 cm2/s while that for steel is only 0.09 cm2/s. Combined with aluminum’s low melting point of only 660º C (melting temperature of iron is 1539º C. This property of aluminum limits the conventional welding. Because molten aluminum readily dissolves hydrogen during welding and then rejects all of it during solidification, aluminum welds are extremely sensitive to porosity. Workmanship for welding aluminum must include extreme cleanliness in both the wire and work piece. Any source of hydrogen (moisture, oil, grease, paint, etc) is immediately converted to porosity. Steel welds are much less sensitive to porosity.

Synergic Pulsed GMAW with Waveform Control Since the pulsing unit on a GMAW machine is an electronic control, the waveform can be controlled for optimum performance. Synergic-pulsed GMAW ensures that each pulse will produce one droplet of molten metal. Non-synergic pulsed GMAW produces many


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droplets per pulse. Although pulsed GMAW are both excellent for out-of-position welding, the synergic pulsed GMAW system allows further control of the metal droplet transfer. Today, pulsed synergic GMAW software is available for the welding engineer and welder to manipulate welding waveforms on their personal computers in order to produce the excellent welds. This is especially needed for welding of aluminum because of aluminum’s high thermal diffusivity and low melting point. A modified constant current output is used in very high speed synergic pulsed GMAW. The pulsed current provides consistent penetration profile, reduced spatter, improved fluidity, increased in travel speed, reduced heat input and lower distortion. Manipulation of synergic pulse waveforms have a strong influence over the weld bead shape, spatter, fumes, and welding speed. For example, welding 0.035 inch aluminum is extremely difficult for conventional GMAW. The problem of burn-through is always difficult to overcome. By using synergic pulsed GMAW, the pulsed waveform can be optimized to produce low heat input while maintaining full penetration without spatter, burn-through, or cold laps and with minimum distortion.


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Craftsmanship Expectations for Welding Projects The student should complete the following tasks prior to welding.

1. Thoroughly read each drawing.2. Make a cutting list for each project. Cut at least two project assemblies of

metal at a time. This will save a great amount of time.3. Assemble the welding projects per drawing specifications.4. Review the Welding Procedure portion of the prints to review welding

parameter information.5. See the instructor for the evaluation.

Factors for grading welding projects are based on the following criteria:

Metal Preparation Project Layout Post Weld Clean-up Oxyacetylene cut quality Accurate (+/- 1/16”) Remove Slag/Spatter Grind all cut surfaces clean Limit waste Remove sharp edges

Example of a High Quality Weld

Weld Quality per AWS D1.1 VT Criteria Cover Pass

Reinforcement (groove welds) Flush to 1/8” Fillet Weld Size See specification on drawing

Undercut 1/32” maximum depth Weld Contour Smooth Transition Penetration N/A

Cracks None Allowed Arc Strikes None Allowed

Fusion Complete Fusion Required Porosity None Allowed Overlap None Allowed


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Information Sheet Mild Steel Pulse Spray Arc Welding

With the V350 Pro Welder

The Pulse spray arc on mild steel section of this packet will require the “welder” to follow the welding procedure on the Blue Print. The following terms will be defined to clarify the procedure.

Program mode Pulse Mig Steel .035” Arc Control Knob next to program mode. This controls the fluidity

of the puddle. Read off machine when the machine is on but there is no welding. This is referred to as Open Circuit Voltage (OCV). Volts read off power source meter - SPd Amps read off power source amp meter WFS read directly off the LN7 wire feeder Shielding Gas 90% Argon and 10% Oxygen Special Note All the knobs on this equipment are ultra sensitive. Any

slight movement of the knobs will result in a large adjustment on the equipment.


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GMAW Pulse Transfer T Joint (2F) Project #3

Technique Use a stringer technique and push gun progression

Welding Sequence

VT Criteria Student Assessment Instructor Assessment Reinforcement (0” –1/8”)

Undercut (1/32”) Weld Bead Contour

Penetration Cracks (none)

Arc Strikes (none) Fusion (complete)

Porosity (none) Grade Date


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GMAW Pulse Transfer Lap Joint (2F) Project #4


Welding Sequence







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GMAW Pulse Transfer T Joint (3F) Project #5 Technique Use a Z pattern weave with vertical up progression.

Welding Sequence Root Pass = Z pattern with an oscillation width of approximately ½”. Cover Pass = Z pattern with an oscillation width of 3/4 “ to 1”







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Technique Use a Z pattern weave and vertical up progression. Use a slant loop circular technique emphasizing the top toe to prevent undercutting.

Welding Sequence







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GMAW Pulse Transfer T Joint (4F) Project #7


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Aluminum Welding Projects

Welding Technology Equipment Supported by

The Lincoln Electric Company


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Information Sheet Aluminum Pulse Spray Arc Welding

with the V350 Pro Welder

The Pulse spray arc on mild steel section of this packet will require the “welder” to follow the welding procedure on the Blue Print. The following terms will be defined to clarify the procedure.

Program mode Pulse Mig Al. .035” 4043 Arc Control Knob next to program mode. This controls the fluidity

of the puddle. (+7.2) Read off machine when the machine is on but there is no welding. This is referred to as Open Circuit Voltage (OCV). Volts read off power source meter - SPd Amps read off power source amp meter WFS WFS – The wire feed speed adjustor knob will rotate 3

3/4 revolutions. Due to this, you will need to calculate a six second wire length into inches per minute (IPM) by multiplying the 6 second length by 10 seconds to determine the IPM. This is what (actual) on the print means.

Shielding Gas 100% Argon Special Note All the knobs on this equipment are ultra sensitive. Any

slight movement of the knobs will result in a large adjustment on the equipment.


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GMAW Pulse Aluminum Transfer T Joint (2F) Project #9


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GMAW Pulse Aluminum Transfer Lap Joint (2F) Project #10


Welding Sequence







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Final Exam

Part One This portion of the final exam is a closed book test. Consult with your instructor to determine items that you may need to review. Once you determine that you are ready for the exam, request it from your instructor. Complete the exam and write all answers on the answer sheet provided. Once completed, return the exam to your instructor for grading.

Part Two This portion of the exam is a practical test where you will fabricate and weld a weldment from a “blue print.” The evaluation of this portion of the exam will be based on the rubric.


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Final Grading Rubric for practical exam Class Name: WLD 132

Name:________________________________ Date:_______________________Hold Points are mandatory points in the fabrication process, which require the inspector to check your work. You are required to follow the hold points. PointsPossible

HoldPoints Instructor’s Evaluation

5points BlueprintInterpretationandMaterialCutList

5 points = 0 errors, all parts labeled and sized correctly 3points=1errorinpartsizingand/oridentification2points=2errors1point=3errors0points=4ormoreerrors

10points MaterialLayoutandCutting(Tolerances+/-1/16”)10points Layoutandcuttingto+/-1/16” Smoothnessofcutedgeto1/32”7pointsLayoutandcuttingto+/-1/8”Smoothnessofcutedgeto1/16REWORKREQUIREDIFOUTOFTOLERANCEBYMORETHAN1/8INCH

10points Fit-upandTackweld(Tolerances+/-1/16”)10pointsTolerances+/-1/16” Straightandsquareto+/-1/16”7Points Tolerances+/-1/8” Straightandsquareto+/-1/8”REWORKREQUIREDIFOUTOFTOLERANCEBYMORETHAN1/8INCH

15points WeldQualitySubtract1pointforeachwelddiscontinuity,incorrectweldsizeandincorrectspacingsequence.

28points Minimumpointsacceptable.ThisequatestotheminimumAWSD1.1Coderequirements.

TotalPoints /40

WLD132GMAWPulse:ProjectAssessmentFormStudentName:________________Date_________MildSteelPulse FlatPosition Assessment

BeadPlate HorizontalPosition Assessment InstructorSignature/DateT-Joint LapJoint VerticalPosition Assessment InstructorSignature/DateT-Joint LapJoint OverheadPosition Assessment InstructorSignature/DateT-Joint LapJoint AluminumPulse Assessment InstructorSignature/Date

Horizontal T-Joint LapJoint Vertical T-Joint Lapjoint Overhead T-Joint LapJoint

Documents

WLD 132 Gas Metal Arc Welding Pulse Transfer on Mild Steel ...€¦ · As defined by the American Welding Society (AWS), Gas Metal Arc Welding (GMAW) is an electric arc welding process