8
The remaining factors have comparatively
little effect on pene- tration and do not provide a good means of
control. Figure 7-8 illustrates the
effect of welding voltage. In this example, penetration is greatest at 24 volts
and decreases as the voltage is either
increased or decreased. Twenty-four volts is the optimum voltage for
the amperage used and yields the most
stable arc. Arc instability decreases penetration. Effects
of arc travel speed are similar to that of welding voltage – penetration
is a maximum at a certain value and
decreases as the arc travel speed is varied. Figure
7-9 shows that at 12 inches per minute (30.5 cm/min)
travel speed, penetration is at a maximum.
At either 7 ipm (17.8 cm/min) or 17 ipm (43.2 cm/min) it is
decreased. With the lower speeds, too
much metal is deposited in an area and the molten weld tends to roll
in front of the arc and ”cushions”
the base plate. This prevents further penetration. At high speeds, the heat
generated by the arc hasn’t sufficient
time to substantially melt the area of base material. Torch
position has a slightly greater effect than does welding voltage or arc travel
speed. The effect of changing
the longitudinal torch angle, or switching from a forehand to backhand welding
technique is shown in
Figure 7-10. It can be seen that generally the forehand welding
technique yields shallower penetration than does
the backhand technique. Maximum weld penetration is achieved with a torch angle
of 25 deg. and the backhand
welding technique. However, beyond this degree of torch angle, arc instability
and spatter will increase.
For very thin materials or where low penetration is required, a forehand technique
is generally used. Figure
7-8 – Effect of Welding Voltage on Weld Penetration
Aluminum-Spray Arc-Argon Shielding
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