Machinery's Handbook, 31st Edition
1580 Gas Metal Arc Welding width, and reducing porosity potential. A gas mixture that has worked well in practice and can be used on the majority of aluminum applications is argon + 25 to 35 percent helium. Mixtures with higher helium content, of 50 to 90 percent, require voltages and flow rates that may be excessive for many established aluminum applications. Welding Controls.— The two primary controls for welding with GMAW are the electrode wire feed control on the wire feeder and the voltage control on the power source. As shown in Fig. 1, these controls typically consist of switches and knobs but do not have the scales, seen enlarged at the upper left, that indicate combinations of wire feed rate, wire gage, volts, and amps. These scales have been added here to allow clearer explanation of the functioning of the wire feed control. The typical wire feed unit provides maximum feed rates of 600 to 800 in/min(15.2– 20.3 m/min). The scale surrounding the setting knob on a wire feed control unit usually has only 10 unnumbered graduations, somewhat like the hour markers on a clock face. On most machines, each of these graduations represents an adjustment of the feed rate of approximately 70 in/min (1.8 m/min). For each increase in the wire feed rate of 70 in/min (1.8 m/min), depending on the voltage, the welding current increases by approximately 20 to 40 amps, depending on the wire diameter and wire feed positions. In Fig. 1, a black sector has been drawn in on the wire feed rate adjustment knob to indi cate the range of wire feed rates usable with the gas mixture and the electrode diameter (gage) specified. The wire feed and voltage settings shown are for welding thin-gage car bon, low-alloy, or stainless steels with a 0.030 or 0.035 inch (0.76 or 0.89 mm) diameter electrode. The left edge of the sector on the wire feed knob is set to the eight o’clock posi tion, corresponding to 70 in/min (1.8 m/min). The optimum voltage for this wire feed rate is 15. If a setting is too low, the knob is turned to the second (nine o’clock) or third (ten o’clock) position to increase the current. The voltage typically increases or decreases by 1 volt for each graduation of the wire feed quadrant. The short-circuit transfer current range of 50 to 200 amps corresponds to a wire feed rate of 70 to 420 in/min(1.8–10.7 m/min), and is typically found between the eight and one o’clock positions on the scale, as indicated by the black sector on the knob in Fig. 1.
180 19 12
Optimum Settings
200
170
21
18
10
14
Ar 15–25 CO 2
140
350 150 420 180
17
280 120
16
350 150 420 180
210 90
280 120
210 90
Wire Feed Control Unit
100 16 18
140 60
140 60
70 30
ON OFF
0
70 30
23
15
0
60
17
14
21
0.035-in. (0.9-mm) electrode
Voltage Control
VOLTS
Fig. 1. Wire Feed Settings for Short-Circuit Welding of Carbon, Low-Alloy, and Stainless Steel Sheet
Diagrammatic quadrants have been added at the left in Fig. 1, to show the material thick ness, voltage, and current that correspond to the setting of the wire feed rate adjustment knob. Optimum settings are easily made for short-circuit welding of sheet metals. When
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