Arc Welding: Introduction and Fundamentals

Arc Welding:Introduction and Fundamentals

IMS Curriculum 8609-B

Objectives

• Students will know the following after the presentation:

1. Students will be familiar with vocabulary2. Students will know pieces of ARC welders3. Students will know accessories of ARC

welding

Vocabulary

1. Arc Welding2. Electrode3. Welders4. Rectifier5. Alternating Current6. Direct Current

7. Duty Cycle8. Flux9. Polarity10. Slag11. Welder12. Base Metal

History

• Dates back to the 19th century

• Arc Welding is the process of fusing two or more pieces of metal together through the use of an electric arc.

The Process of Welding

The process uses an arc struck between and electrode and metal. The arc heats the metal to a melting point. The electrode is removed to break the arc, allowing metal to freeze or solidify. This flame (arc) of intense heat is generated as the electric current passes through a highly resistant air gap.

Challenge to Strengthen Welds

• Molten metal would get O2 and N2 in it and it would destroy the strength of the weld.

• Some form of cover was needed to “shield” the molten pool of the metal.

Shielded Metal Arc Welding

Shielded Metal Arc Welding Process

SMAW Process Again

SMAW

SMAW

• http://www.me.gatech.edu/jonathan.colton/me4210/arcwelding.mpeg

Types of ARC Welding Machines

• AC ( alternating current ) • DC ( direct current )• AC/DC ( alternating and direct current )• TIG ( tungsten inert gas )• MIG ( metallic inert gas )

AC/DC

MIG

MIG Again

TIG

TIG Again

Duty Cycle

• All machines have a duty cycle• Duty cycle is the percentage of a ten-minute

period that a welding machine can be safely operated at a given output.

• A 225-ampere AC welding machine typically will have a duty cycle of 20%.

• As amperage increases, duty cycle decreases and vice versa.

Electrodes

• Three types:• 1. Coated

– Most common used• 2. Bare

– Smoke free– Weld is visible

• 3. Carbon– Melts slowly

Electrode

• An Electrode is a core wire that can be left bare or covered with a flux.

• Flux is the fusible material that covers the electrode that is meant to produce a shielding gas during the welding process.

Flux

• Prevents the formation of oxides, nitrides, and other undesirable inclusions during welding.

• As a person welds the flux floats out he impurities in the air and then settles on top of the weld as slag.

Slag

• Is beneficial in most welding processes because it holds heat and keeps the weld from cooling too quickly,

Selecting Electrodes

• Depends on three factors:1. Metal Type2. Metal thickness3. Welding Postion

Electrode Classification

• The American Welding Society (AWS) provides a standardized way for classifying rods.

• First set-up in 1942.• Uses a number system with 4 digits that

represents four factors.

The Digits

• 1st and 2nd digit represents the minimum tensile strength of the weld metal.

• 3rd digit refers the welding position the rod should be used in.

• 1 = All positions• 2 = Flat and Horizontal• 3 = Flat only

• 4th digit indicates the weld current that is to be used and the type of flux covering.

E6010

• E = electrode• 60 = 60,000 psi tensile strength• 1 = welds in all positions• 0 = indicates DC and electrode positive

current

Size of the Electrode

• The diameter of the “bare” end of the rod determines the size of the electrode.

• Ex. 1/16, 3/32, 1/8, 5/32, 3/16, 7/32, ¼, 5/16, 3/8

• As a general rule, the diameter of the electrode should never exceed the thickness of the metal being welded.

Arc Welding Fundamentals

• 1. Body position• 2. Correct electrode size• 3. Correct electrode type• 4. Correct amperage setting• 5. Correct arc length• 6. Correct travel speed• 7. Correct electrode angle

Striking an Arc

• People who have never welded struggle most with this.

Arc length

• Maintain a constant arc length and move in a circular pattern.

Arc Angle

Factors Shown

The End

• Now time for some hands on experience!

Picture Sources

• http://www.twi.co.uk/j32k/twiimages/spgvmar98f1.jpg

• http://www.tollgas.com/products/images/arc_access.jpg

• http://images.encarta.msn.com/xrefmedia/sharemed/targets/images/pho/t048/T048805A.jpg

Picture Sources

• http://images.google.com/imgres?imgurl=http://class.et.byu.edu/mfg130/processes/descriptions/thermaljoining/smawwelding1.jpg&imgrefurl=http://class.et.byu.edu/mfg130/processes/descriptions/thermaljoining/smawwelding.htm&h=278&w=459&sz=37&tbnid=RuzWWCIuL3oJ:&tbnh=75&tbnw=123&start=4&prev=/images%3Fq%3Dshielded%2Bmetal%2Barc%26hl%3Den%26lr%3D

Pictures

• http://www.murexwelding.co.uk/mrxcont/images/sixofbest.jpg