The Direct Metal deposition (DMD) with laser is a free-form metal deposition process for dense pieces, which allows generating a prototype or small series of near net-shape structures. One of the most critical issues is that produced pieces have a deleterious surface finish which requires post machining steps. This problem has never been fully addressed before
The present work describes investigations on the DMD process, using a Nd-YAG laser, and a widely used aeronautical alloy : (TA6V) to understand the influence of the main process parameters on the surface finish quality.The focus of our work was: (1) to understand the physical mechanisms responsible for deleterious surface finishes, (2) to propose different experimental solutions for improving surface finish.
For this purpose, we manufactured a large number of multi-layers walls using different process parameters (P(W), V(m /min) and Dm (g/min)) and simultaneously we recorded the dimensions of the melt Pool and the dynamics of the melt-pool – powder stream coupling using a fast camera. Last, we investigated wall morphologies and surface finish and their variations with process parameters, using 2D and 3D profilometry.
The results confirm that surface degradation depends on two distinct aspects: the sticking of non-melted or partially melted particles on the free surfaces, and the formation of menisci with more or less pronounced curvature radii. Among other aspects, a reduction of layer thickness and an increase of melt-pool volumes to favor re-melting processes are shown to have a beneficial effect on surface finish.