Product Code: ICA11_1705

Influence of Process Conditions on Surface Finishes Obtained with the Direct Metal Deposition Laser Technique
Authors:
Myriam Gharbi, PIMM; Paris France
Cyril Gorny, PIMM; Paris France
Patrice Peyre, PIMM; Paris France
Remy Fabbro, PIMM; Paris France
Simon Morville, LIMATB, Université De Bretagne-Sud; 56321 Lorient Cedex France
Muriel Carin, LIMATB, Université De Bretagne-Sud; 56321 Lorient Cedex France
Thierry Mallot, STAMP; -
Presented at ICALEO 2011

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 an Nd-YAG laser, and two widely used alloys (TA6V and 316L) 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
In order to understand the physical mechanisms responsible for deleterious surface finishes, we carried out the following procedure : (1) a precise characterization of the laser beam and the powder stream, (2) we carried out a large number of multi-layers walls using different process parameters (P(W), V(m/min) et Dm (g/min)) (3) we analyzed the dynamics behavior of the Melt Pool and the melt-pool powder stream coupling with a fast camera (4) we measured wall morphologies 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 Ra, and the formation of menisci with more or less pronounced curvature radius Wa. Among other aspects, a reduction of layer thickness, an increase of melt-pool volumes to favor re-melting processes and the use of an impultional laser are shown to have a beneficial effect on roughness parameters.