Different types of welding processes
In this series, we look at the different types of welding processes used by A&G Engineering in its fabrication processes.
Metal Inert Gas (MIG) Welding
Metal Inert Gas (MIG) welding is a process that uses an electric arc to heat metals. An electric arc is a strong electric current that flows between two electrodes – in this case, the surface to be welded and a continuously-fed wire filler electrode. The filler is the product that is added during the welding process to join the metals together.
When the control trigger on the welding gun is activated by the operator, the wire feed is initiated together with electric power and the shielding gas flow, causing an electric arc to be struck.
Choosing the Correct Electrode
The electrode is a metallic wire, called a MIG wire, whose selection, alloy, and size, is based primarily on the composition of the metal being welded, joint design, and the material surface conditions. In general, the finished weld metal should have mechanical properties similar to those of the base material with no defects such as discontinuities, entrained contaminants or porosity within the weld. A wide variety of electrodes are available and electrode selection greatly influences the mechanical properties of the weld and is a key factor of weld quality.
Along with the wire electrode, a shielding gas feeds through the welding gun, and protects the molten weld from reacting with atmospheric gases such as nitrogen and oxygen. In addition, the shielding gas has a significant impact on the transfer of metal and the stability of the arc. The choice of a shielding gas depends on several factors, most importantly the type of material being welded. Pure inert gases such as argon and helium are only used for nonferrous (non-steel) welding, while a carbon dioxide-argon-oxygen mixture is commonly used for steel.
Voltage Impacts Arc Length
Most MIG applications use a constant voltage power supply. As a result, any change in arc length (which is directly related to voltage) results in a large change in heat input and current. A shorter arc length causes a much greater heat input, which makes the wire electrode melt more quickly and thereby restores the original arc length. This helps operators keep the arc length consistent even when manually welding with hand-held welding guns.
Why is MIG Welding Better?
MIG is a very popular method of welding because it can be used to weld most metals including stainless steel, carbon steel and aluminium. It is used extensively in the sheet metal industry and is a very fast and cost-effective welding process.
MIG welding is often used for spot welding as a replacement for riveting. It is also popular for automated welding where robotic units handle the workpieces and welding gun to accelerate manufacturing. MIG can be difficult to perform well outdoors since drafts can dissipate the shielding gas and allow contaminants into the weld.
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