Chapter Chapter Gas Metal Arc Welding Procedures and Techniques Copyright Goodheart-Willcox Co., Inc. 69 Objectives After studying this chapter, you will be able to: ❑ Adjust welding current and voltage parameters to produce desired weld qualities. ❑ Vary electrode extension, travel speed and direction, and gun angle to produce desired weld qualities. ❑ Distinguish between bead patterns. ❑ Determine values for a weld schedule based on results from test welds. Technical Terms backhand welding burn-through downhill welding electrode extension forehand welding pull welding push welding stickout stringer bead pattern travel angle uphill welding weave bead pattern welding voltage weld schedule wire feed speed work angle Welding Variables and Parameters The GMAW process can be either a semiautomatic or a fully automatic operation. In fully automatic oper- ation, the machine controls all of the parameters and variables. In the semiautomatic operation, the hands- on skill of the welder signifi affects the final ficantly fi quality of the weld. The welder must be able to set up the machine properly and skillfully operate the gun in order to create a weld that meets the quality require- ments of the fabrication specifi Welding vari- fication. ables that are determined after the material type and thickness and mode of welding have been selected are described in the following sections. Welding Current/Amperage (Wire Feed Speed) With a constant voltage machine, the welding current is established by the wire feed speed. The wire feed speed is the rate at which the welding wire is fed through the welding gun. Increasing the wire feed speed increases welding current, while decreasing wire feed speed decreases welding current. Wire feed speed is measured in inches per minute (ipm). Determine wire feed speed as follows: 1. Turn the machine on and run the wire to the end of the gas nozzle or the contact tip. 2. Depress the arc start switch (this starts wire feed) and run for 10 seconds. 3. Measure wire length from the end of the contact tip or the gas nozzle, Figure 7-1.