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.