The essential guide
The principle of the CMT process lies in the fact that the wire is withdrawn from the weld pool whist the arc voltage and current are reduced at high frequency levels. The result is that thermal input is reduced and virtually spatter free welding is achieved.
This MIG welding process has been developed by Fronius. It was specifically designed for robotic automation and offers many interesting possibilities for critical welding applications. The key feature is that heat input is limited and therefore allows successful welding of very thin materials. Due to the nature of this cold weld the risk of burn through is practically eliminated. For some applications it may be possible to replace TIG or plasma welding with CMT. These processes are quite difficult to manage with a welding robot as they rely on extremely accurate component fit up. However, CMT can not compete with the superior weld finish of these TIG and plasma welding.
The process also lends itself very well for Aluminium welding, where push pull torches are often required when feeding the soft aluminium wire. Aluminium has a low melting point and the cold welding process ensures that the material can welded much easier.
The CMT process has a higher tolerance to bridge gaps, so if fit up exceeds the limits of what is normally acceptable for robot welding (about the wire diameter that is being used), it would be advantageous to use this process.
The cost of the equipment tends to be about twice that of a good quality synergic welding package. In practice this means that many companies will only invest in this process if it is absolutely required for the application. Other manufacturers claim to be able to deliver similar results through electronic means. It appears, however, that Fronius has a lead in the market with this process.