MEM05026C Apply Welding Principles - Learner Guide

7/26/2019 MEM05026C Apply Welding Principles - Learner Guide

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MEM05 Metal and Engineering

Training Package

Learner guide

Version 2

Training and Education Support

Industry Skills Unit

Meadowbank

Product Code: 5807

MEM05026CApply welding principles


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MEM05026C Apply welding principles

TAFE NSW (Training & Education Support Industry Skills Unit, Meadowbank) 2014

AcknowledgmentsThe TAFE NSW Training and Education Support Industry Skills Unit, Meadowbankwould like to acknowledge the support and assistance of the following organisationsand people in the production of this learner guide.

BOC Gases AustraliaCIGWELD/Thermadyne AustraliaFronius AustraliaLincoln Electric Company AustraliaSilverwater Welding SuppliesStandards AustraliaWelding Industries of Australia

Writers:Ed Harkness (From existing TAFE publications)Stephen Davies (TES Industry Skills Unit)

Reviewers:John Anderson (Hunter Institute)Vince Aranda (Illawarra Institute)Peter Stauffer (Hunter Institute)

Project Manager:Stephen DaviesEducation Programs ManagerTAFE NSW

Enquiries

Enquiries about this and other publications can be made to:

Training and Education Support Industry Skills Unit, Meadowbank Meadowbank TAFE

Level 3, Building J, See Street,

MEADOWBANK NSW 2114

Tel: 02-9942 3200 Fax: 02-9942 3257

TAFE NSW (Training and Education Support, Industry Skills Unit

Meadowbank) 2014

Copyright of this material is reserved to TAFE NSW Training and EducationSupport, Industry Skills Unit Meadowbank. Reproduction or transmittal in wholeor in part, other than for the purposes of private study or research, and subject tothe provisions of the Copyright Act, is prohibited without the written authority ofTAFE NSW Training and Education Support, Industry Skills Unit Meadowbank.

ISBN: 978-1-74236-515-2


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Table of Contents

Introduction ................................................................................. 11

1. General introduction ........................................................................... 11

2. Using this learner guide ....................................................................... 11

3. Prior knowledge and experience ........................................................... 13

4. Unit of competency overview ............................................................... 13

Topic 1: Welding regulations ........................................................ 21

Introduction .......................................................................................... 21

Workplace health and safety (WHS) ......................................................... 23

Review questions ................................................................................... 24

Topic 2: Welding safety ................................................................ 27

Introduction .......................................................................................... 27

Hazards ................................................................................................ 27

Hazardous locations ............................................................................... 28

Industrial gas cylinders ........................................................................... 34

Scaffolding ........................................................................................... 37

Skin and eye damage prevention ............................................................. 38

Protective clothing and equipment (PPE) .................................................. 39

X-ray and gamma-ray radiation ................................................................ 40

Industrial injuries ................................................................................... 40


Topic 3: Electrical terms ............................................................... 45

Introduction .......................................................................................... 45

Types of welding current ......................................................................... 46

Alternating current ................................................................................ 47

High frequency machines (HF) ................................................................. 49

Constant current (drooping voltage) welding machine ................................. 50

Constant potential welding machine .......................................................... 51

Motor generators ................................................................................... 51

Other equipment .................................................................................... 54


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Topic 4: Arc welding conditions .................................................... 63

Introduction .......................................................................................... 63

Current/amperage .................................................................................. 63

Polarity ................................................................................................. 65


Topic 5: Manual metal arc welding electrodes .............................. 71

Introduction .......................................................................................... 71

Covered electrodes ................................................................................. 71

Electrode classication............................................................................ 72

Type of ux coatings ............................................................................... 75

Storage, handling and conditioning electrodes ............................................ 78


Topic 6: Elements in carbon steel ................................................. 83

Introduction .......................................................................................... 83

Weldability of carbon steels ..................................................................... 83

Inuence of elements on weldability of carbon steels.................................. 86


Topic 7: Heat treatment ............................................................... 93

Introduction .......................................................................................... 93

Effects of welding heat on carbon steels ................................................... 94

Effects of heat on mechanical properties.................................................... 95

Heat treatments method ......................................................................... 95

Heating methods ................................................................................... 98

Temperature measuring devices ..............................................................101

Review questions ..................................................................................104

Topic 8: Welding terms and symbols .......................................... 107

Introduction .........................................................................................107

Types of welds .....................................................................................107

Parts of a weld and general terms ...........................................................108

Parts of a preparation ............................................................................111


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Weld positions ......................................................................................113

Welding symbols ...................................................................................115


Topic 9: Preparing weld joints .................................................... 125

Introduction .........................................................................................125

Types of edge preparations .....................................................................126

Fusible inserts ......................................................................................129

Methods of preparing joints ....................................................................130

Jigs and xtures ....................................................................................131


Topic 10: Metal cutting and gouging ........................................... 135

Introduction .........................................................................................135

Preparing metal parts for welding ............................................................135

Guided cutting ......................................................................................140

Oxygen-fuel gas gouging ........................................................................142

Applications ..........................................................................................142

Automated thermal cutting ....................................................................145

Electrode holder ....................................................................................153

Operating techniques .............................................................................154

Plasma arc cutting .................................................................................155

Hazards ...............................................................................................161

Maintenance of equipment ......................................................................162

Mechanical cutting .................................................................................162


Topic 11: Welding procedures .................................................... 167

Introduction .........................................................................................167

Proving a welding procedure ...................................................................167

Types of procedures...............................................................................168


Topic 12: Weld testing ................................................................ 177

Introduction .........................................................................................177


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Types of weld testing .............................................................................177

Destructive testing ................................................................................177

Non-destructive testing methods .............................................................184

Weld faults ...........................................................................................188

Topic 13: Welding alloy steels .................................................... 199

Introduction .........................................................................................199

Physical and Mechanical properties ..........................................................199

Alloy steels ...........................................................................................199

Effects of alloying elements on steel ........................................................203

Welding processes for joining low alloy steels ............................................208

Welding processes for HSLS ....................................................................209


Topic 14: Non-ferrous metals ..................................................... 219

Introduction .........................................................................................219

Aluminium and aluminium alloys .............................................................219

Copper and copper alloys .......................................................................225

Nickel and nickel alloys ..........................................................................228

Cutting non-ferrous metals .....................................................................230

Safety precautions ................................................................................231


Topic 15: Gas tungsten arc welding (GTAW) .............................. 237

The process ..........................................................................................237

Equipment ...........................................................................................239

Polarity/current .....................................................................................249

Weld defects .........................................................................................253

GTAW safety .........................................................................................255


Topic 16: Gas metal arc welding (GMAW) and

Flux cored arc welding (FCAW) ................................... 261

Introduction .........................................................................................261

The GMAW process ................................................................................261


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Welding guns ........................................................................................264

Welding variables ..................................................................................267

Correcting weld and machine faults .........................................................278

Safety .................................................................................................280

Flux cored arc welding (FCAW) ................................................................281

Flux cored wires ....................................................................................282

Shielding gases .....................................................................................286


How the process works ..........................................................................291

Equipment ..........................................................................................291

Consumables ........................................................................................296

SAW variables .......................................................................................297

Edge preparations .................................................................................300

Typical SAW faults .................................................................................303

Safety ................................................................................................304

Electro-slag welding (consumable guide) ..................................................306

Topic 18: Oxyacetylene welding (OAW)...................................... 311

The OAW process ..................................................................................311

Equipment for OAW ...............................................................................312

Welding torches ....................................................................................318

OAW weld faults ....................................................................................324

Low temperature welding processes .........................................................324

Consumables ........................................................................................326

Uses ....................................................................................................327

Resource Evaluation Form .......................................................... 333


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Page 15 of 336 TAFE NSW (TES, Industry Skills Unit Meadowbank) 2014


Re co g n i t i o n o f p r i o r l e a r n i n g ( R PL )

RPL is not applicable for this competency unit. MEM05026C Apply welding principlesis a welder certication unit and therefore will require candidates to formally

undertake an externally set examination as previously indicated.

This unit, along with all other AS 1796 Certications require a formal examination/ assessment process as outlined in section 2 of the Standard. Students who havesuccessfully achieved a TAFE NSW AS 1796 Certication are eligible to receivefull recognition for certicates 1-9 from external industry associations such as theAustralian Welding Institute (AWI) and Welding Technology Institute of Australia(WTIA). For detailed information on recognition procedures, students will need tocontact either or both of the two industry associations on their respective websites:

http://www.austwelding.com.au/ and

http://www.wtia.com.au/

U n i t p a r t h w a y

MEM05026C Apply welding principlesis a unit in the MEM05, Metal EngineeringIndustry Training Package. It is a unit of study in Certicate III and IV inEngineering and Diploma in Engineering-Advanced Trade. It may also be selectedas a unit of study in other Engineering courses, packaged to include a group offabrication and specialist units.

In conjunction with further units of study, welder certication provides students withthe knowledge and skills to carry out rst class welding operations in an engineeringworkshop or site. A pathway of training in the use of applying welding principlescould include the following competency units:

MEM05043BPerform

welds to codestandards

using GMAW

MEM05026CApply Welding

Principles

MEM05042BPerform

weld to codestnadards

using FCAW

MEM05044BPerformweldingto code

standardsusing GTAW

MEM05045BPerform pipewelds to code

standardsusing MMAW

MEM05046BPerform

weld to codestandards

using MMAW


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El em e n t s a n d p e r f o r m a n c e cr i t e r i a :

Element Performance criteria

1. Apply all statutory andregulatory requirementsto welding procedures.

1.1. Statutory and safety requirements are appliedto welding

2. Interpret all weldingterms, codes andsymbols.

2.1. Welding terms and symbols are correctlyinterpreted.

3. Determine the effects ofheat treatment on metalin relation to welding.

3.1. Reasons for performing heat treatment areidentied.

3.2. Processes such as pre-heat/post-heattreatment, stress relieving, normalising andannealing are appropriately applied.

Required knowledge and skillsThe following describes the knowledge and skills required for this unit. Theseinclude:

R eq u i r e d k n o w l e d g e :

Any applicable industry standards, national/Australian standards, NOHSC guide-lines, state/territory regulatory codes of practice/standards for the applicablewelding processes

Safe work practices and procedures

Hazards related to welding

Safety equipment and procedures related to welding activities

Welding terminology

Welding codes and symbols

Logical sequence of welding processes

Tools, equipment, techniques used in welding

Effect of heat treatment on metal.

Re q u i r e d s k i l ls

Interpreting welding specications including terms, codes and symbols Planning the sequence of welding operations

A c c es s a n d e q u i t y c o n s i d e r a t i o n s

All workers in Metal and Engineering industries should be aware of access,equity and human rights issues in relation to their own area of work

All workers should develop their ability to work in a culturally diverseenvironment

In recognition of particular issues facing Aboriginal and Torres Strait Islandercommunities, workers should be aware of cultural, historical and current issues

impacting on Aboriginal and Torres Strait Islander people


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Assessors and trainers must take into account relevant access and equity issues,in particular relating to factors impacting on Aboriginal and/or Torres StraitIslander clients and communities.

W o r k h e a l t h a n d s af e t y ( W H S)

Your teacher will encourage you to assist in identifying/eliminating hazards and todevise control measures for potential risks to yourself and others that may ariseduring practical sessions. The Work, Health and Safety Act 2011 (WHS Act) andWHS Regulations are enforced throughout all Australian States and Territories.

This legislation is aimed at providing consistency, certainty and clarity acrossAustralia making it easy to understand workplace health and safety responsibilities.The WHS Act and its regulations will require both teachers and learners to takereasonable steps to control and monitor potential risks in the classroom, practicalworkshops and in the workplace. Detailed information relating to the WHS Act andregulations can be found on the following websites:

WorkCover Authority of NSW www.workcover.nsw.gov.au

Safe Work Australia www.safeworkaustralia.gov.au

What you will need

Students will require the following:

Pens, pencils and calculator

Learner resource MEM05026C Apply welding principles

Wallet card

Upon successful completion of this knowledge based unit and at least one (1) of thefollowing practical competency units (see list below) you will be eligible to receive aTAFE NSW issued wallet card which recognises your certication to AS 1796.

MEM05042B Perform welds to code standards using ux core arc weldingprocess

MEM05043B Perform welds to code standards using gas metal arc weldingprocess

MEM05044B Perform welds to code standards using gas tungsten arc weldingprocess.

MEM05045B Perform pipe welds to code standards using manual metal arcwelding process

MEM05046B Perform welds to code standards using manual metal arc weldingprocess.


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X-ray and gamma-ray radiation

Some non-destructive weld testing methods involves radiography. Radiographictesting is done by trained personnel who are responsible for ensuring the area

is safety-signposted. All other persons must remain outside the designated areaduring testing. Exposure to radiographic rays can cause long term damage and mustbe avoided at all times.

Canaryyellow

Black

R ad i a t i o n w a r n in g s y m b o l

Industrial injuries

While good housekeeping and safe work practices prevent most industrial accidents,injuries sometimes happen. Typical industrial injuries include:

burns (minor and major)

cuts abrasions

bone fractures

neck and spinal damage.

Many cuts burns and abrasions are minor and are treated with little loss of worktime. However all injuries, no matter how small, should be reported to the rst aidofcer to help plan future safety procedures.

More serious injuries should be treated by qualied personnel. On-the-spot rst aidshould not be a substitute for qualied assistance. The following steps, in the eventof an accident are a guide only:

act quickly

switch off any electrical circuits involved

do not touch burns or remove clothing from burnt areas

send for medical assistance

stay with the victim at all times

never move the victim if a back or neck injury is suspected.


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Review questions

These questions have been included to help you revise what you have learnt inTopic 2:Welding safety.

S h o r t - a n s w e r q u e st i o n s

1. Listfour (4) sources of fumes generated from thermal cutting or weldingoperations.

______________________________________________________________

______________________________________________________________

______________________________________________________________

2. List three (3) precautions that must be taken when welding in a conned space.

______________________________________________________________

______________________________________________________________

______________________________________________________________

3.Explain how gas cylinders should be supported when they are lifted by a crane.

______________________________________________________________

______________________________________________________________

______________________________________________________________

4. Briey explain why MMAW electrodes must be removed from holders when hungon scaffold staging where there are wire ropes.

______________________________________________________________

______________________________________________________________

5. Name three (3) harmful rays emitted from an electric arc.

______________________________________________________________

______________________________________________________________

______________________________________________________________


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Mu l t i p l e c h o i c e q u e s t i o n s (tick the correct answer)

6. The rst precaution against re or explosion in a hazardous location is:

no welding or cutting is permitted high frequency equipment must not be used there must be an inspection of the area the tradesperson must hold a current pressure welding certicate

7. The background colour of the identifying shoulder label on an oxygen cylinder is:

red white yellow green

8. Conned spaces require:

degreasing before welding adequate ventilation workers to take salt tablets regularly to avoid dehydration small diameter electrodes to be used

9. Welding lter lens must be:

shade 13 minimum approved and identied by Australian Standards made in Australia green

10. The primary circuit, high frequency units and welding leads:

are serviced by welding tradespersons are safe to use in wet conditions can be assumed free of all hazards can all be hazardous

True or False questions(circle the correct response)

11. A container that has held ammable or toxic materials must be examined by aresponsible person before welding.

True False

12. All lead lighting in conned spaces must be 32 volts maximum.

True False


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13. Acetylene cylinders are colour coded peacock blue.

True False

14. Radiographic weld tests present no danger to the operator.True False

15. LPG is a fuel gas.

True False

16. Argon cylinders are tted with right hand threaded connections.

True False


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Topic 3: Electrical terms

Introduction

Welding operators must have a basic knowledge of electricity and understand theelectrical requirements of various arc welding processes. This topic is intended toassist you understand the basic terminology and application of electricity associatedwith arc welding processes. The electrical terms in common use are brieyexplained below:

Cu r r e n t ( Sy m b o l I o r A )

Also referred to as amperage, current is the measurement of electron ow througha given circuit. The term current measures the amount of electricity that owsthrough a circuit in a second. The level of current supplies the heat energy requiredfor welding. An amp is a unit of electric current.

V o l t a g e ( Sym b o l V o r E)

Voltage or electric potential is the driving force (force or pressure) that enables acurrent to ow within an electrical circuit. A volt is a unit of electric pressure.

Resistance (Symbol O or )

Resistance is the restriction to current ow in an electrical circuit. Every componentin the circuit, including the conductor, has some degree of resistance to currentow. The unit of resistance is the ohm. The welding arc has its heat energy releasedand resulting high temperature from the resistance in the arc column.

Op e n c i r c u i t v o l t a g e ( OCV )

Open circuit voltage is the potential available when the welding machine is turnedon but before the arc is struck. The OCV can be measured with a voltmeter at theoutput terminals of the welding machine before welding takes place. The level ofOCV is carefully controlled by manufacturers of welding machines to avoid electricshock to the operator. Modern machines are tted with a voltage reduction device(VRD) to provide added safety to the operator.

Examples of open circuit voltages:

a.c. manual arc welding machines 50-80 OCV (80 volts maximum)

d.c. manual arc welding machines 60-115 OCV (115 volts maximum).

Some types of a.c. manual metal arc welding machines have dual OCV ranges.These machines allow the operator to deal with a wider range of situations, such as:

the use of small diameter electrodes which require a high OCV and lowcurrent

special electrode types such as hydrogen controlled, have basic uxes. Theycan be difcult to strike and require a high OCV between 70-80 volts toestablish the arc

large electrodes with larger cross sectional area require less OCV.


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A r c v o l t a g e

Arc voltage is the measure of voltage across a welding machines terminals while themachine is working and welding is taking place. The arc voltage for most machines

is in the range of 20-35 volts.

Vo l t a g e r e d u c t i o n d e v i c e ( VRD )

VRD stands for voltage reduction device and is safety device tted to a weldingmachine. The purpose of a VRD is to reduce the maximum unloaded open circuitvoltage (OCV) across the machines terminals to a safe voltage. When a weldingcircuit resistance is greater than 200 ohms (for example when touching the humanbody) the machine's VRD will sense this and limit the OCV to around 12 volts.

When a load less than 200 ohms resistance is applied to the machines output, theVRD will sense this and allow the machines maximum OCV to ow to enable weldingto take place.Australian Standards 1674.2 2003states the voltage across the

machines terminals must be less than 35 volts for d.c. and 25 volts for a.c.

Types of welding current

Direct current

When the electrons move in the same direction at all times, this is called directcurrent(d.c.).

In a direct current machine, the electrons ow constantly from the terminal markednegative (-) to the terminal marked positive (+).

The way these terminals are connected to the welding circuit determines thepolarityof the connection.

+

Time

D i r e ct c u r r e n t

The diagram above shows the current and voltage delivered over a period of time.The level stays constant because the current ows in only one direction.

Australian Standard 1101.3-2005 denes this as either electrode positiveorelectrode negative. The word polesimply means the end of the arc polaritymeans which terminal is connected to the electrode end of the arc.


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The normal connection is electrode negative (-) because of the direction of electronow, the job is at the positive (+) receiving end of the electron ow in the arc andmore heat is released at that point.

Heat distribution in a direct current arc is approximately 2/3rds at the positive poleand 1/3rd at the negative pole. For this reason, consumable wire electrodes suchas those used with the GMAW process are connected to the positive (+) terminal toallow the wire to rapidly melt-off to form the weld.

When using the GTAW process the opposite is in place, the non-consumabletungsten electrode is connected to the negative (-) terminal. This arrangementallows 2/3rds of the heat energy to ow from the electrode tip into the workpiecewhere it is required.

Alternating current

When the electron ow reverses its direction at regular intervals, it is called an

alternating current (a.c.). Australian standard cycle time for alternating current is50 cycles per second, or 50Hz (hertz).

1 cycle = 1/50 of a second or 20 ms

Time

T y p i c a l a .c . si n e w a v e

The current acts for the same length of time for both the positive (+) and negative(-) parts of the cycle (10ms) ie. the time distribution between positive and negativeis 50/50. This gives a 50/50 heat distribution as well.

a.c. phases

The single wave graph shown below illustrates a single alternating current phase.This is the type of current available from a 240v power point. Power generationplants that supply mains power, deliver three phase current to make better use ofthe distribution system.

S i n g l e p h a s e a . c.


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The main industrial supply is 415v 3-phase. Some of the transformer type weldingmachines will only use 415v single phase input. This is clearly marked on powersource compliance plates, which also gives the rating and duty cycle of the machine.

T h r e e p h a s e a . c.

Rectifed a.c.

a.c. can be changed to d.c. by passing the current through a heavy-dutysemi-conducting diode. This will allow the current to pass in one direction but not inthe reverse. The result is a single-directional current ow.

Single diode rectifer

The graph shown above is for a single diode rectier. It only uses one half-cycleand the full power of the input is not used. This is called half-waverectication.If diodes are used in pairs the whole of the ac input is put to use. This called fullwaverectication.

a . c. f u l l - w a v e s i n g l e p h a s e

( a l l a v a i l a b l e c u r r e n t i s u s e d i n t h e n e g a t i v e c y c le )

More advanced welding power sources used for MMAW, GMAW and GTAW will usethe full three phases and full wave rectication. Output level is much more steadyand similar to the direct current generator. These machines use a bridge rectier

which is made up of three diodes to cope with the three phases.


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0

T y p i c a l t h r e e p h a s e c u r r e n t

High frequency machines (HF)

Alternating current (ac) welding machines work well when using ux coatedelectrodes requiring a current of about 80 amps or more, but when current values

are lowered for smaller electrodes, striking the arc becomes difcult.

A high frequency(HF) unit generates a high voltage (3000v) but minimal currentat 2 million Hz (2 MHz). This secondary superimposed voltage allows the weldingarc to ignite (strike) without the electrode physically touching the surface of the

job. It will also maintain an arc when the voltage and current values are low. Highfrequency current does not add to the heat input of the main welding arc.

Welding leads are covered with a special type of insulation to avoid the highfrequency arc through and to prevent being degraded by the ozone generated in thecorona discharge surrounding them while the current is owing.

High frequency is used for:

welding with small diameter electrodes

gas tungsten arc welding with a.c.

initiating an arc when using gas tungsten arc welding with d.c.

High frequency safety

When using high frequency with welding equipment, the operator must take care toavoid accidental, unintentional arcing causing eye injury. As indicated above, thearc can start without the electrode physically striking the work surface.

Care should be taken to protect the high frequency unit from wet weather or

moisture conditions as this greatly increases the risk of fatal electric shock. Whilehigh frequency current does not have high amperage it will assist in directing themain welding current through a persons body.

Electrode leads should be kept clear of metal surfaces as the high frequency pilotarc will discharge through the insulation causing rubber-covered leads to breakdown. Securely fasten the work clamp to the work and ensure that both the workand work table are isolated from building frames or support structures.

Failure to do this may result in the welding current damaging both the machine andthe primary wiring potentially creating an electrical hazard for workshop personnel.


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Constant current (drooping voltage) welding machine

All manual metal arc welding machines which maintain constant current have adroopingvolt/amp characteristic curve. The open circuit voltage(OCV) is higher

than the voltage needed for welding, but is needed at that value to enable easystriking of the electrode.

Once the arc is established, the voltage will drop to a pre-set level for welding.This is called the arc voltage. This characteristic holds the current constant evenduring small variations in arc length, which naturally occur because the electrode ismanually fed into the arc.

When the electrode makes contact with the job it results in a short-circuit whichallows maximum current to ow. As the contact is broken the arc establishes andthe pre-set current and voltage come into action for welding.

The graph below shows the volt-amp conditions during welding. It can be seen from

the graph that a comparatively large change in voltage will only have a small effecton the current setting. This effectively maintains a near-constant current to the arc.

Current (amps)

Voltage

V o l t - a m p c u r v e i n a d r o o p i n g v o l t a g e m a c h i n e

Some modern electronically controlled power sources deliver true constant currentwhereby a change in arc length results in no change in welding current. A typicalvolt-amp characteristic of a true constant current power source is shown in thediagram below.

U (V)

I (A)no change inwelding currentwith change

Co n s t a n t c u r r e n t p o w e r s o u r ce


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It can be seen that there is no change in welding current despite a change in arclength.

Constant potential welding machine

Gas metal arc welding (GMAW) machines have a relatively atvolt-amp outputcurve. These machines have a lower open circuit voltage than those used formanual metal arc welding and are not suitable for this process.

To produce consistently uniform welds, GMAW power sources must be able toproduce and maintain a constant voltage and arc length throughout the weldingoperation. This consistency is achieved by using a constant voltage (CV), also calledconstant potential power source in conjunction with a wire feed mechanism.

Constant voltage machines are designed to produce a relatively at voltage/currentcharacteristic. For example, as the wire stick out length increases with this type ofmachine the welding current will automatically decrease. Conversely, as wire stick

out length decreases, welding current will increase but voltage remains constant.An example of the at voltage/current type relationship is illustrated below.

OCV

Vo

ltage

Operating point

CV at volt /current characteristic

Note: Modern inverter power sources can produce drooping and constant potentialpower supply depending on the welding process selected.

Motor generators

There are two types of motor generators, these include:

1. 415v mains supply connected to an electric motor which drives a generatorproducing a suitable range of welding currents. This type machine features avariable voltage for ner control over arc conditions.

2. Petrol or diesel engine driven generators produce welding current. Most of thecurrently produced by this type of machine is based on heavy-duty alternators.Current output can be rectied to d.c. as needed.

Both a.c. and d.c. welding supplies are available as welding output current. Many ofthem provide auxiliary outlets for power tools and wire feeder units.


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Review questions

These questions have been included to help you revise what you have learnt in

Topic 3: elementary electricity.

S h o r t a n sw e r q u e s t io n s

1. Dene the following electrical terms:

Voltage.

________________________________________________________________

________________________________________________________________

Amperage.

________________________________________________________________

________________________________________________________________

Open circuit voltage (OCV).

________________________________________________________________

________________________________________________________________

2. Explain why all welding machine terminals must have tight, metal to metalconnections.

________________________________________________________________

________________________________________________________________

3. Name three(3) types of power sources capable of delivering direct current(d.c.) for welding.

________________________________________________________________

________________________________________________________________

________________________________________________________________


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Mu l t i p l e c h o i c e q u e s t i o n s (tick the correct answer).

4. Which of the following power sources does not have a choice of polarity?

rectier inverter transformer generator

5. Which of the following power sources can be used on locations without on-sitepower?

rectier inverter

transformer generator

6. Welding work clamps are rated by:

size of clamp opening voltage range size of welding cable current carrying capacity

7. A high frequency unit is attached to a welding machine to

increase weld metal deposition enable the arc to be struck without touching the work prevent undercut change a.c. to d.c.

8. An alternating current (a.c.) sine wave has a:

positive half cycle and a negative half cycle

positive cycle only negative cycle only at characteristic

T r u e / f a ls e q u e s t i o n s (circle the correct response).

9. All welding power sources have the same open circuit voltage.

True False


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10. The maximum open circuit voltage for a.c. welding machines is 80v.

True False

11. Voltage is the unit of pressure in an electrical circuit.

True False

12. d.c. inverters can be used for MMAW, GTAW and GMAW.

True False


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Topic 4: Arc welding conditions

Introduction

With electric arc welding the variables depend on the process selected. In this topicwe compare the effects of changes to weld conditions on weld quality and stabilityof the arc using the manual metal arc welding process.

Current/amperage

The current/amperage setting controls the heat energy available to the weldingarc. Electrode manufacturers will always label the electrode packet with the type ofelectrode and current range settings recommended for that type and size.

Using recommended current settings will give the deposited metal its full strengthand other important properties. Most general purpose (GP) electrodes are used at

currents near the top of their recommended range. Lower settings make electrodesdifcult to run consistently. Using too low a current/amperage setting for a giventype and size electrode can:

reduce arc stability making it difcult to strike and maintain the arc reduce penetration produce poor weld appearance cause problems removing slag from the toes of the weld reduce welding speeds increase the risk of slag inclusions produce excessively convex bead shapes.

When operating within the recommended current range, penetration and beadshape improve as current settings increase. However, using too high a current/amperage setting for a given type and size electrode can cause:

porosity due to overheating of the electrode and deterioration of the uxcoating

increased spatter levels poor weld appearances undercut a reduction in alloying elements from the deposited metal increased consumption rate of the electrode.

Attempts to gain increased penetration by increasing current settings beyond the

recommended maximum can be counter-productive. If deep penetration is requiredthen a deep-penetration electrode should be used.

Voltage

A minimum arc voltage is needed to maintain the welding arc. MMAW electrodes willoperate successfully within a fairly narrow voltage range. Within this range there isa noticeable effect upon weld penetration, bead width and blending at the toes ofthe weld run.

The general effect of increasing arc voltage is to spread and atten the weld bead,which can be said for all arc processes. Basic types of a.c. transformer and a.c./d.c.transformer-rectier machines have no means of varying the arc voltage. Sometransformer machines have dual-voltage terminals however this only gives a choice

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MEM05026C Apply Welding Principles - Learner Guide