Cold metal transfer process – A review

Abstract

The welded joints of dissimilar metals find numerous applications in the field of automobiles, marine, nuclear energy, construction, aerospace. The dissimilar metal welding has lower weld efficiency until the emergence of the Cold Metal Transfer (CMT) process. The process is termed as cold since the heat input is low when compared to the conventional MIG process. This process uses a principle called ‘short-circuiting,’ where the feed wire is retracted when the liquid droplet falls from the welding wire to the substrate. The retraction is done by the electronic regulators of the robot arm of the process, and the arc is reignited when the liquid droplet is fully transferred to the substrate. This paper is based on the different characteristics, microstructure and mechanical properties exhibited by the dissimilar metal welded joints joined by using the CMT process. Discussions were limited to titanium, stainless steel, aluminium, copper and magnesium joints. Welding was performed with optimum parameters of CMT and the results were analysed. Due to the super low heat input of the CMT welding process, rapid heating and cooling was realized. Titanium and stainless steel joint fetched a maximum tensile strength of 318 MPa with the ductility of 8.5%. Magnesium with Aluminium joints produced a max strength of 230 MPa and was high towards the magnesium side and lowered towards the aluminium side. Minimum diffusion layer and changes in the diffusion zones of Al-HAZ and Mg interfaces are observed. The diffusion of the Al matrix was found to be high.