Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Unit 27 Arc Welding Mild Steel and...

Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.

Unit 27

Arc Welding Mild Steel and GMAW/GTAW Welding


Safety Procedures

• Welding area should consist of– metal benches

– booths made of fireproof or fire-resistant materials

– fire extinguishers for class a, b, and c fires

– safety equipment, first-aid kit, and wool fire blanket

– buckets of water

– no oil, grease, paper, sawdust, rags, or other flammable materials


Safety Procedures (continued)

• Personal protection– #10 shade lens with safety glasses or a flip-up lens

– Fire-resistant coveralls

– High leather shoes

– Leather gloves

– Cover all exposed skin


Setting Up• Pick appropriate electrode• Eliminate fire hazards• Gather all necessary materials• Make sure the welding machine has suitable

welding cables• Put on safety clothing including helmet• Select your amperage• Be sure the metal is clean and free of any oil,

grease, or rust• Strike the arc


Beads

• A bead is produced by handling the electrode so that there is a proper mix of base and filler metal

• Stringer bead: made without weaving

• Weaving: moving the electrode back and forth (side to side) to create a wider bead


Running a Bead

• Electrode angle– Lean slightly in the direction of travel; usually a 75° to 80° angle

(or 10° to 15° from vertical)

• Obtain correct arc length• Move across metal at a uniform travel speed• Check for correct amperage setting (semicircles

should be wider than they are long)• If weaving for the first time, start using a circular

pattern


Butt Welds

• Butt joint: pieces placed end to end or edge to edge

• Leave a gap between the two pieces that is about the thickness of the electrode core

• Be sure all slag is removed between beads to ensure a solid weld without voids


Fillet Welds

• Fillet joint: two parts come together to form a 90-degree angle

• Be sure to prepare the vertical piece so the weld metal will fuse both pieces completely

• Follow a procedure similar to butt welds

• Remember that heat rises, so watch the top piece for overheating


Welding Positions

• Horizontal: moving horizontally across a vertical piece of metal

• Vertical: moving up or down across vertical piece of metal (weaving is not recommended)

• Overhead: the metal is positioned above the welder


Pipe

• When welding pipe– Use E6013

– Generally welded without grinding

– Maintain same arc length used for straight areas

– Flatten ends first


GMAW Welding

• GMAW: Gas Metal Arc Welding • Uses short-circuit arc method to transfer weld

material • Uses thin welding rods, low current, and low voltage• Welding wire is fed automatically at a constant speed• Produces a short arc between base metal and wire• Ideal for

– exhaust system work – installing trailer hitches and truck bumpers – repairing mechanical supports


GMAW Safety• Follow manufacturer’s recommendations• Check all cables and be sure equipment is properly

grounded• Wear protective clothing• Use approved helmet• Never touch electrical connections or wires while

switch is on• Never weld in wet locations


GMAW Safety (continued)

• No flammable materials in clothing pockets

• Handle hot metal with pliers or tongs

• Weld only in well-ventilated areas

• Do not do your own repair work on welding equipment

• When finished, be sure equipment is turned off and safely stored


GMAW Equipment

• Most equipment is semiautomatic• Components

– shielding gas supplied by a regulator– wire speed/feed control– spool of electrode wire– welder connected to electrical power supply– work cable and clamp assembly– welding gun and cable assembly


GTAW Welding

• GTAW: Gas Tungsten Arc Welding

• Used to weld very light, thin metals

• Originally used DC current, today most use AC current (which provides a better weld)

• Slower than GMAW welding

• Similar in some ways to oxyacetylene welding


GTAW Safety

• Use the same safety procedures as GMAW welding

• Wear hearing protection when utilizing pulsed-power and high-current settings

• Never touch the tungsten electrode with body parts or the filler rod

• Keep the settings within the limits set by the manufacturer


GTAW Equipment

• Three major components– power supply– welding gun– gas cylinder with flow meter

• AC welding is primarily used for nonferrous metals

• Cups available in variety of sizes and flow rates• Foot control also available• Electrodes available in 1/16-, 3/32-, and

1/8-inch diameters


Plasma Arc Welding • Creates an ionized gas called plasma• Plasma conducts electricity and produces very intense

heat in a small, concentrated area• Metal melts and fuses together quickly• Provides a very stable arc• Makes use of low amperage currents, which allow the

welding of very small instruments


Automated and Robotic Welding

• Newest process in welding

• Uses computer control and robots

• Used on assembly lines

• Very efficient and produces high-quality welds

• Very expensive and reserved for high-output productions


Important Terms

• Pad: practice metal• Crater: a low spot in the metal where the

force of the arc has pushed out molten metal• Pass: one bead or layer of filler metal• Root pass: the first and most important

welding pass

Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED. Unit 27 Arc Welding Mild Steel and...

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