Test structures were performed using the CMT process, as this possesses certain characteristics that make it excellent for controlled deposition. The mechanical wire control leads to low spatter, which is important for minimising the amount of post process machining and the low heat input nature of the process results in minimal melting of the substrate material or prior runs.
The relatively high deposition rate allows the production of high volume structures in a relatively short period of time. For example, generating a 5183 grade aluminium structure using a 1mm diameter wire resulted in a deposition rate of 0.94kg/hour. It is predicted that it is possible to deposit similar volumes of steel and nickel-based alloys.
The CMT process is designed for use only on a robotic system and therefore suited for additive manufacture, where a pre-determined path will be used to generate complex structures repeatedly in a production line process.
The CMT process was able to construct “walls” and “pads” by performing multipass welds with either a vertical or horizontal offset. While the production of vertical walls and pads was easily achieved with a standard vertical torch alignment, the experimental trials showed that structures could be produced with a range of orientations by varying the torch angle in line with the desired orientation. Figure 1 shows an example of the range of orientations achieved, by building up on a horizontal substrate. All of these different orientations were produced with similar deposition rates.
It is reasonable to extrapolate from these initial trials that it is possible to produce multi-angled structures for use in either repair of pre-existing components, or to generate complex geometries without significant machining.