Operating mig welding equipment

Operating MIG Welding Equipment : Starting to Weld

Press the inch button and allow enough wire electrode to emerge from the nozzle until 1/2 in. (13 mm) protrudes beyond the end of the nozzle. With the main line switch “ON” and the argon gas and power sources adjusted properly, the operator may begin to weld. When welding in the open air, a protective shield must be installed to prevent the argon gas from being blown away from the weld zone and allowing the weld to become contaminate. Press the torch trigger. This sends current down the torch switch cable and through the contactor cable, closing the contactor. When the contactor closes, the welding circuit from the generator to the welding torch is completed.

At the same time the contactor closes, the argon gas solenoid valve opens, allowing a flow of argon gas to pass out of the nozzle to shield the weld zone.

Lower the welding helmet and touch the end of the wire electrode to the workpiece. The gun is held at a 90 degree angle to the work but pointed at a 10 degree angle toward the line of travel.


To prevent overloading the torch motor when stopping the arc, release the trigger; never snap the arc out by raising the torch without first releasing the trigger.

Welding will continue as long as the arc is maintained and the trigger is depressed.

Setting the Wire Electrode Feed.

A dial on the front of the voltage control box, labeled WELDING CONTROL, is used to regulate the speed of the wire electrode feed. To increase the speed of the wire electrode being fed from the spool, turn the dial counterclockwise. This decreases the amount of resistance across the arc and allows the motor to turn faster. Turning the dial clockwise will increase the amount of resistance, thereby decreasing the speed of wire electrode being fed from the spool. At the instant that the wire electrode touches the work, between 50 and volts dc is generated. This voltage is picked up by the voltage pickup cable shunted back through the voltage control box into a resistor. There it is reduced to the correct voltage (24 V dc) and sent to the torch motor.


Two 10-ampere fuses, located at the front of the voltage control box, protect and control the electrical circuit within the voltage control box. A 1-ampere fuse, located on the front of the voltage control box, protects and controls the torch motor.

Installing the Wire Electrode.

Open the spool enclosure cover assembly, brake, and pressure roll assembly. Unroll the straighten 6 in. (152 mm) of wire electrode from the top of the spool. Feed this straightened end of the wire electrode into the inlet and outlet bushings; then place spool onto the mounting shaft. Close the pressure roller and secure it in place. Press the inch button, feeding the wire electrode until there is 1/2 in. (13 mm) protruding beyond the end of the nozzle.

Setting the Argon Gas Pressure.

 Flip the argon switch on the front of the voltage control panel to the MANUAL position. Turn on the argon gas cylinder valve and set the pressure on the regulator. When the proper pressure is set on the regulator, flip the argon switch to the AUTOMATIC POSITION. When in the MANUAL position, the argon gas continues to flow. When in the AUTOMATIC position, the argon gas flows only when the torch trigger is depressed, and stops flowing when the torch trigger is released.

Generator Polarity. The generator is set on reverse polarity. When set on straight polarity, the torch motor will run in reverse, withdrawing the wire electrode and causing a severe burn-back.

Reclaiming Burned-Back Contact Tubes. When the contact tubes are new, they are 5-3/8 in. (137 mm) long. When burn-backs occur, a maximum of 3/8 in. (9.5 mm) may be filed off. File a flat spot on top of the guide tube, place a drill pilot on the contact tube, then drill out the contact tube. For a 3/64 in. (1.2 mm) contact tube, use a No. 46 or 47 drill bit.

Preventive Maintenance.

Keep all weld spatter cleaned out of the inside of the torch. Welding in the vertical or overhead positions will cause spatter to fall down inside the torch nozzle holder and restrict the passage of the argon gas. Keep all hose connections tight. To replace the feed roll, remove the nameplate on top of the torch, the flathead screw and retainer from the feed roll mounting shaft, and the contact ring and feed roll. Place a new feed roll on the feed roll mounting shaft, making certain that the pins protruding from the shaft engage the slots in the feed roll. Reassemble the contact ring and nameplate.