MIG WELDING MACHINE
Functioning a satisfactory MIG Welding process requires more than just semi operative skill. The setup, voltage, current, electrode extension, and welding angle, as well as other factors, can dramatically affect the weld produced. The very best welding conditions are those that will allow a welder to produce the largest quantity of successful welds in the shortest period of the time with the highest productivity. Because these are semiautomatic or automatic processes, increase productivity may require only that the welder increase the travel speed and current.
MIG WELDING MACHINE SETUP
In complete MIG welding machine setup, we require GMAW or MIG power source, welding torch, wire feeder unit, shielding gas supply, gas regulator, flow meter & heater, shielding gas hoses and MIG wire.
If the shielding gas supply is a cylinder, it must be chained securely in place before the valve protection cap is removed. Standing to one side of the cylinder, quickly cracked the valve to blow out any dirt in the valve before the flowmeter regulator is attached.
Install the reel of electrode (welding wire) on the holder and secure it. B sure the power is off before attaching the welding cables. The electrode and work leads should be attached to the proper terminals. The electrode lead should be attached to electrode or positive (+). If necessary, it is also attached to the power cable part of the gun lead. The work lead should be attached to work negative (-).
CHECK WIRE FEEDER UNIT
Using the MIG Welding Machine that was properly assembled, we need to turn the machine on and thread the electrode wire through the system. Switch on the power and check the gun switch circuit by depressing the switch. The power source relay, feeder relays, gas solenoid and wire feeder motor should all active.
Cut the end of the electrode wire free. Hold it tightly so that it does not unwind. The wire has a natural curve that is known as its cast. The cast is measured by the diameter of the circle that the wire would make if it were loosely laid on a flat surface.
Note: With the wire feeder running, adjust the feed roller compression so that the wire reel can be stopped easily by a slightly pressure. Too light a roller pressure will cause the wire to feed electrically. Too high a pressure can turn a minor problem into a major disaster.
GAS DENSITY AND FLOW RATES
Density is the chief determinant of how effective a gas is for arc shielding. The lower the density of a gas the higher will be the flow rate required for equal arc protection. Flow rates, however, are not in proportion to the densities. Helium, with about one-tenth the density of argon, requires only twice the flow for equal protection.
ARC VOLTAGE AND AMPERE CHARACTERISTICS
The arc-voltage and amperage characteristics of MIG Welding are different form most other welding processes. The voltage is set on the welder, and the amperage is set by changing the wire feed speed. At any one voltage setting the amperage required to melt the wire must change as it is fed into the weld. It requires more amperage to melt the wire the faster it is fed, and less the slower it is fed.
Because of the constant-potential (CP) power supply, the welding current will change as the distance between the contact tube and the work changes. Although this change is slight, it is enough to affect the weld being produced. The longer the electrode extension the greater the resistance to the welding current flowing through the small welding wire.
With a standard MIG Welding CC power supply this would also reduce the arc voltage, but with a CP power supply the voltage remains constant and the amperage increases. If the electrode extension is shortened, the welding current decreases.
WELDING GUN ANGLE
The term welding gun angle refers to the angle between the MIG Welding gun and the work as it relates to the direction of travel. Slight changes in the welding gun angle can be used to control the weld as the groove spacing changes. A narrow gap may require more penetration, but as the gap spacing increases a weld with less penetration may be required. Changing the electrode extension and welding gun angle at the same time can result in a quality weld being made less than ideal conditions.