Arc welding with gas

Gas metal arc welding

This process is widely used in industrial applications due to its numerous benefits. It can weld almost all metallic materials, in a large range of thicknesses (above 1 mm up to 30 mm or more) and is effective in all positions. The process is sensitive to the effects of wind, which can disperse the shielding gas, and it is difficult to use in narrow spaces due to the torch size.
A schematic representation of the process of GMAW:

  • GMAW is a very economic process because it has higher speeds and higher deposition rates than for example the manual metal arc process, and does not require frequent stops to change electrodes, as is the case of this former process.
  • In addition, minimal post weld cleaning is needed because slag is almost absent.
  • Less operator skill is required than for other conventional processes because electrode wire is fed automatically (semi-automatic process) and a self-adjustment mechanism maintains the arc length approximately constant even when the distance weld torch to work-piece varies within certain limits.
  • These advantages make the process very well adapted to be automated and particularly to robotic welding applications.
  • The process is sensitive to the effects of wind, which can disperse the shielding.

Welding Equipment: Basic equipment for conventional GMAW is consists of the power source; the electrode feed unit, the welding torch and the shielding gas regulator.

Voltage: Arc voltage is directly related to current, as indicated above, and with arc length, increasing with it. Voltage also depends on the shielding gas and electrode extension. The increase of arc voltage widens and flattens the weld bead. Low voltages increase the weld reinforcement and excessively high voltages can cause arc instability, spatter, and porosity and even undercut.

Welding Speed: Increase in the welding speed gives a decrease in the linear heat input to the workpiece and the filler metal deposition rate per unit of length. The initial increase in welding speed can cause some increase in penetration depth, because the arc acts more directly in the parent material, but further increase in speed decreases penetration and can cause undercut, due to insufficient material to fill the cavity produced by the arc.

Electrode Extension: The electrode extension is the electrode length that is out of the contact tube. The increase of electrode extension, produced by the increase of the torch distance to the work-piece for a specific parameters set, increases electrode melting rate because of the Joule effect. Electrode extension ranges from 5 to 15 mm for dip transfer, being higher (up to 25 mm) for the other transfer modes.

Shielding Gas: Shielding gases have an effect on arc stability, metal transfer mode, weld bead shape and melting rate. Gases used in GMAW can be pure gases, binary, ternary and exceptionally quaternary mixtures. Common pure gases are argon, helium and carbon dioxide. The first two are inert gases and are used principally in welding of light alloys, nickel, copper and reactive materials. Helium has a higher ionization potential than argon, providing larger weld pools, but is more expensive. Carbon dioxide is an active gas and is used in welding of carbon steels. It produces high levels of spatter but provides high penetration depth.

(Source: arc welding machine price in india)