MIG WELDING MACHINE DIFFERENT VARIABLES
In MIG Welding Machine semi-automatic versions requires the holding of the welding gun in hand so that the operator may switch on or off the system as desired. Before initiating the welding arc it is usual to set the open circuit voltage on the panel of the power source with the regulator provided on the unit itself.
Apart from setting the open circuit voltage it is also required to decide about the other welding machine variable so as to control the welding processes to obtain the desired results. These variables may include the wire feed rate, electrode stickout, nozzle-to-plate distance, electrode-to-work angle, and gas flow rate.
With a flat characteristics power source the arc voltage is controlled mainly by setting the open circuit voltage (O.C.V). A small difference in the actual value of the arc voltage and the set value of the O.C.V. is on account of the voltage drop in the cable and the slight drop in the V-I characteristic of the power source itself.
The change in arc voltage leads to change in arc length and that affects the bead width directly. The change in arc voltage not only affects the outer dimensions of the bead but also influences the micro structure and even the success and failure of the operation by affecting the mode of metal transfer.
Wire Feed Rate
For a flat characteristic power source the welding current varies with the change in wire feed rate and a generalized relationship between the two. The relationship is linear at lower feeding rate however as the wire speed is increased, particularly for small diameter wires, the melting rate curve becomes non-linear. This is normally attributed to increased resistance heating which itself is increased with the increase in wire feed rate.
Weld penetration is maximum at a particular welding speed and it decreases as the speed is varied either way. However, the decrease in speed is accompanied by increase in width while increase in speed results in narrower beads. The decrease in penetration with reduction in speed is caused due to excessive molten metal sliding into the weld pool resulting in shallower weld pool.
The distance from the lower tip of the contact tube to the tip of the protuding electrode wire. It is an important mig welding machine or welding machine parameter for controlling the deposition rate and the bead geometry.With the increase in stickout its electrical resistance increases and that results in preheating of wire which leads to lower requirement of current at any given wire feeder rate in mig welding machine.
Weld bead geometry is also affected by the position in which the work piece is held with respect to the welding gun. Down hand or flat welding position gives the most satisfactory bead shape and all modes of metal transfer can be effectively utilised. However, overhead and vertical welding position demand that metal transfer be either by sprays or short-circuit mode.
Each electrode wire size has a workable limit within which it can be effectively used. Welding current lower than the optimal range results in lack of fusion and higher current results in increased spatter, porosity and poor bead appearance.
Electrode size also affects the penetration and weld width in that for the same current lower diameter wire gives deeper penetration while welder beads with shallow penetration are obtained with bigger diameter wires.
Overall, however, there is a tendency to use smaller diameter wires because of the following reasons.
a) Rapid arc length adjustment,
b) Spray mode of metal transfer,
c) Easy to spool,
d) Higher deposition efficiency.
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