70 GMAW/FCAW Handbook Copyright Goodheart-Willcox Co., Inc. 4. Multiply wire length by six (10 seconds = 1/6 of a minute). The resulting number is the wire speed in inches per minute. Keep the end of the wire away from the work or disconnect the work clamp and make sure it is safely out of the way. If contact is made, an arc will occur. Welding Voltage The welding voltage determines the arc gap established between the end of the electrode and the workpiece. This parameter is set on the welding machine. The machine automatically changes the amperage output to maintain this preset arc length. Charts listing the initial welding parameters for steel, stainless steel, and aluminum are located in the Refer- ence Section. Electrode Extension Electrode extension is the distance from the contact tip to the end of the electrode. It is important to measure the actual distance from the contact tip to the end of the electrode and not just the amount of electrode extending from the end of the gas nozzle. The term stickout refers to the length of unmelted t electrode extending past the end of the gas nozzle. The dimensions used for these terms are shown in Figure 7-2. The welder controls electrode extension through the handling of the gun while welding. Changing the extension from the originally established dimen- sion has a marked effect on the melting of the elec- trode. Increasing the extension causes more resistance heating of the wire and a lower welding amperage, which is useful when welding on gapped joints to prevent burn-through. Burn-through is caused by excessive amperage for the thickness of the material to be welded. Conversely, decreasing the extension makes less wire available for resistance heating. This increases amperage for greater penetration, Figure 7-3 Travel Speed The travel speed of the welding gun must be regu- lated to produce a good weld. In machine welding, the speed is set in inches per minute (ipm). In manual Goodheart-Willcox Publisher Figure 7-1. To establish wire speed, carefully measure the length of wire fed in 10 seconds. Multiply the length by 6 for wire speed inches per minute. Wire speed directly affects the welding current. Gas nozzle Contact tube Gas shield Consumable electrode Stickout Workpiece Electrode extension Goodheart-Willcox Publisher Figure 7-2. The actual electrode extension is from the end of the contact tip to the end of the electrode. The term stickout describes the distance from the nozzle to the end t of the electrode wire. Short Electrode Extension Long Electrode Extension Goodheart-Willcox Publisher Figure 7-3. Electrode extension variations. Use these variations from the welding procedure dimensions to increase or decrease welding heat into the molten weld pool.