Browse Publications Technical Papers 2010-32-0071
2010-09-28

The CMT Process - News and Its Advantages in Industry 2010-32-0071

The cold metal transfer process (CMT) was introduced into industry more than 4 years ago. This process was developed to reduce heat transfer to the substrate during the welding of metals. The CMT process has distinct advantages over the conventional gas metal arc welding process (GMAW), in which the heat input is much greater. CMT was developed specifically for the dip transfer method, which until now has been notoriously difficult to work with. An example of a process which has been made easier through the use of CMT is the butt welding of thin sheet aluminium (0.3mm) using 1.2mm filler material. Unlike conventional processes, this can be achieved without the use of backing protection or heat sinks. Another example is the welding of mild steel using CO₂ as a shielding gas. With CMT, this can be done with a significant reduction in spatter. The reduced heat input which distinguishes CMT from previous GMAW processes is achieved by a new method for droplet detachment, whereby the welding consumable is fed into and retracted away from the weld pool in a controlled manner. The welding consumable oscillates at a frequency of up to 100Hz. By reducing heat input, the CMT process improves weld quality by reducing distortion and spatter. Improved weld quality reduces post-production rework, leading to an increase in manufacturing and efficiency. Although the application possibilities for CMT throughout the various industries are endless, this paper concentrates on the automotive industry. This is not to say that CMT can not be used in other industries. It is purely because of the young age of the CMT process that it has not been possible to explore these possibilities until now.
It should be noted that the automotive and the small engines industries have very similar application possibilities; it is believed that the CMT process would lend itself very well to the manufacture of frames for example on motorcycles or the welding of fuel tanks, other possibilities like exhaust systems will be discussed later in the paper, although the exhaust systems mentioned are automotive it should be noted that there is a distinct size difference, the CMT process because of its very low heat input would be ideal for exhaust systems in the small engine industry, a further possibility which is not to be overlooked is in the small to mid size boat building industry whereby the hull can and are sometimes built using aluminium, the necessity to reduce distortion is high and it is felt that the CMT process would lend itself to this application very well.

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