MIG Welding – Equipment

MIG WELDING Heat source:electric arc Shielding media:a gas or gas mixture which cannot react with the metal being welded Current range:60–500 A Range of electrode sizes: 0.6 to 1.6 mm diameter A number of terms have been used to refer to this welding process: MIGMetal Inert Gas (now the most common term) MAGMetal Active Gas MIG/MAGA combination of the two above terms MAGSMetal Arc Gas Shielded (a term once used in education) GMAWGas Metal Arc Welding (American terminology) CO 2 Carbon Dioxide (named after the first shielding gas to be used for the process, these days the term is not used much)

MIG Welding

Equipment Image: T Coles

Equipment The basic requirements of a metal-arc gas-shielded welding system are: dc power source (normally with inductance control) contactor wire feed unit welding lead and gun (connected to dc +ve) welding return (connected to dc -ve) welding earth shielding gas supply water cooling where necessary Image: EITB Training Manual - General Welding and Cutting

Welding Guns Images: EITB Training Manual - General Welding and Cutting

Secondary supply leads Welding leads for MIG welding are noticeably different from a lead that would be used for MMA welding. The construction of the lead needs to embody supplies of: electric current shielding gases electrode wire contactor wires coolant water supply and return where applicable.

Guide tube - ‘liner’ Cross-section of MIG lead

Wire feed unit Images: EITB Training Manual - General Welding and Cutting

In addition the wire feed unit could contain several of the following: an electrode feed jogging switch to feed the electrode through the unit when not welding a shielding gas purging switch for manual control of shielding gas flow wire feed speed or arc voltage adjustment a breaking system to prevent the wire stubbing into the molten weld pool when welding has stopped timers for pre-weld and post-weld gas flow a water pressure switch to ensure coolant flow. Wire feed unit

The following precautions for the selection and use of the nozzle and contact tip should be observed: correct size contact tips should be used the nozzle and tip should be cleaned regularly during use to remove spatter and dirt a silicone spray should be used on nozzles and contact tips before use and at intervals thereafter. Welding nozzle and contact tip

'Burn back’ Image: EITB Training Manual - General Welding and Cutting

Earthing Images: McDonagh, et al - Physical science for technicians

Electrode wire Electrode wire for steels is copper coated to: improve conductivity between wire and contact tip reduce friction at high speeds minimise corrosion whilst in stock.

It is very important to ensure the careful storage of electrode wire in order to: facilitate correct selection avoid contamination and damage avoid weld faults or operational faults arising from defective electrode wire. The following storage and handling conditions should be used. Always use electrode wire designed specifically for MIG welding. Store under clean, dry conditions to prevent deterioration. Do not mix different types of wire — ensure that the packaging labels make for easy and correct selection. When preparing the reel of wire for use ensure that the wire is free from contamination, such as: rust, scale, oil, grease and moisture. Storage and handling