EQUIPMENT - ZEDTEC ENGINEERING
CMT Fronius Welding
This modern joining method satisfies increasingly stringent demands, some of the most important of which are process stability, reproducibility and cost-effectiveness.
The bundling together of specific material properties opens up a number of interesting possibilities. Material compounds impart to a component or product the desirable properties of the constituent materials.
Previously, such results could only be achieved by mechanical means or by bonding. Of much greater interest, however, is the ability to use heat to join materials with differing properties. The main focus in this respect is on the joining of steel and aluminium, as this will be of particular interest to the automotive sector, where it could spawn a whole range of previously undreamt innovations.
Basic System Principle
The joining of dissimilar materials requires precise knowledge of the properties of each material. Aluminium is highly regarded due to its low specific weight and its excellent usability and processing characteristics. On the other hand, its strength and low cost make steel indispensable in many areas of industry.
Other requirements primarily address anti-corrosion features, thermal expansion coefficient, and atomic properties. When joining steel and aluminium under the influence of heat, what is known as an intermetallic phase is created at the interface between the two materials. The more heat that is applied, the more extensive the intermetallic phase and the poorer the mechanical properties of the join will be.
However, the chemical and physical properties also require appropriate measures to be taken. The different thermal expansion coefficients of the two materials create a stress field around the join. There is also a marked tendency for corrosion to form as a result of the large electrochemical potential difference between steel compared with aluminium.
All the technologies that have been used to join steel and aluminium in the past have only been able to deal with certain geometries or have required extensive control inputs. Although the perceived wisdom among many metallurgists was that steel and aluminium could not be welded together, extensive research in the field of MIG/MAG welding indicated that arc welding was indeed a potential way of joining the two materials.
The CMT process evolved from the continuous adaptation of the MIG/MAG process to resolve the problems posed by the joining of steel and aluminium. CMT is a controlled process and allows the material transfer to take place with barely any flow of current. The aluminium base material melts together with the aluminium filler material, with the melt wetting the galvanised steel. The filler wire is constantly retracted at very short intervals.
The precisely defined retraction of the wire facilitates controlled droplet detachment to give a clean, spatter-free material transfer. The wire movement takes place at a very high frequency and requires a quick-response, gearless wire drive directly on the torch. Obviously, the main wire feeder will not be able to keep up with these movements. The wire feeding hose is therefore provided with a wire buffer that compensates for the additional forward and backward movement of the wire.
