Three years of CMT welding
Three years of the CMT welding process – review and prospects
Since it was launched on the market in 2005, the CMT (cold metal transfer) process has revolutionised thermal joining practice. This third birthday is a good time to take stock, and the conclusion is positive.
Many users in the metalworking industry use the "cold" process because of the significant advantages it offers: considerably wider gaps can be bridged, less thermal distortion and there is virtually no spatter; these factors combine to make CMT welding the preferred solution ahead of conventional processes.
Far more than a mere extension of the earlier MIG/MAG welding process, CMT offers new opportunities for solving technical welding and brazing problems.
The results of the improvements implemented since 2005 are impressive: even finer control with reversing wire movements up to 90 Hz improves material transfer and gap bridging still further. These result in increased working speed and even more precise control of material and heat input. Workpieces that are virtually spatter-free require no costly mechanical finishing. This saves any interim handling that would otherwise be required, not to mention a second quality inspection.
Welding correctly in the first place enables the workflow to be optimised, thus assisting with efforts to move towards reliable production.
The user can also take even greater advantage of the two other important characteristics of CMT, namely the reduction in heat input and the bridging of wide gaps. Depending on the particular application, these characteristics can be precisely combined and tailored to meet the requirements.
This innovative process is particularly suitable in situations where precision is important. As the arc interruption is electronically controlled, the workpiece remains cooler and thermal distortion is largely avoided.
The ability to bridge wide gaps will be useful in situations where the gap in a workpiece is of uneven width. In individual cases, uneven gaps varying in width from 0 to 3 mm can be bridged. Another advantage is that the CMT process can also be used for thick/thin joins and for joining "problematical", high-alloy materials.
These significant advantages can be attributed to the fact that the developers at Fronius have broken new ground with this idea and are totally committed to digitisation.
Significant differences between the CMT process and conventional digital short-arc processes include the way the wire movement is integrated into the process control, how the arc is precisely established and extinguished, and the way the droplets are detached accurately and without any spatter.
The extremely complex interplay between the arc control and the movement of the welding wire is a result of the electronic control system.
