1. Arc Welding Mild Steel and GMAW/GTAW Welding
Unit 27
Arc Welding Mild Steel and GMAW/GTAW Welding

2. 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

3. 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

4. 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

5. 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

6. Running a Bead Electrode angle Obtain correct arc length
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

7. 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

8. 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

9. 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

10. Pipe When welding pipe Use E6013 Generally welded without grinding
Maintain same arc length used for straight areas
Flatten ends first

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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