Journal
JOURNAL OF MATERIALS PROCESSING TECHNOLOGY
Volume 213, Issue 5, Pages 791-800Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.jmatprotec.2012.11.015
Keywords
Laser; Manufacturing; Deposition; Surface; Titanium
Funding
- French National Agency for Research (ANR) under the frame of the ASPECT Project [ANR- 09-BLAN-0014]
- Agence Nationale de la Recherche (ANR) [ANR-09-BLAN-0014] Funding Source: Agence Nationale de la Recherche (ANR)
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The direct metal deposition (DMD) with laser is a free-form metal deposition process for manufacturing 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 systematically requires post machining steps. This problem has never been fully addressed before. The present work describes investigations on the DMD process, using an Yb-YAG disk laser, and a widely used titanium alloy (Ti-6Al-4V) 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 have carried out: (1) a precise characterization of the laser beam and the powder stream; (2) a large number of multi-layered walls using different process parameters (P(W), V(m/min),D-m (g/min), Gaussian or uniform beam distribution); (3) a real time fast camera analysis of melt pool dynamics and melt-pool - powder stream coupling; (4) a characterization of wall morphologies versus process parameters using 20 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 roughness parameters. Last, a simple analytical model was proposed to correlate melt-pool geometries to resulting surface finishes. (C) 2012 Elsevier B.V. All rights reserved.
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