Direct Laser Sintering of metal parts: Characterisation and evaluation of joining mechanisms
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Direct Laser Sintering of metal parts: characterisation and evaluation of joining mechanisms. E. Bassoli1, A. Gatto1, L. Iuliano2, E. Atzeni2 1 Dept. of Mechanical and Civil Engineering, Univ. of Modena and Reggio Emilia, via Vignolese 905/B, 41100 Modena, Italy. 2 Dept. of Manufacturing Systems and Economics, Polytechnic of Turin, C.so Duca Abruzzi 24, 10129 Turin, Italy. ABSTRACT Rapid Prototyping and Tooling are playing a more and more important role in the achievement of compressed time-to-market solutions, where prototype parts and tools are produced directly from the CAD model. In particular, Selective Laser Sintering (SLS) of metal powders with liquid phase is frequently applied for the production of inserts for injection moulding of plastic parts. An experimental campaign has been planned to investigate the surface finish and mechanical performances of Direct Laser Sintering technique, with particular regard to the effect of the laser sintering strategy on the anisotropy of the final part. Tensile specimens of DirectMetal 20 and DirectSteel 20 materials have been produced, with different orientations in regard to laser path. Rupture surfaces after the tensile tests were observed at the SEM, in order to understand failure mechanisms, whereas the observation of polished sections helped investigating joining phenomena between the particles. The proposed experimental methodology allowed correlating the macroscopic performances to the micro-mechanisms ruling the process, proving that no considerable differences can be noticed between samples produced in the X and Y direction within the plane of powder deposition.
INTRODUCTION SLS is well recognized as one of the most diffused techniques for layer-by-layer construction, thanks to the wide variety of available materials. In particular, the processes using metal powders are largely applied for Rapid Tooling [1-6]. A commonly-accepted standardization of terms could be helpful in indicating the different versions of the process [7,8]: • Solid state SLS, or Indirect Metal Sintering, using metal powders mixed with a polymeric binder. After laser forming the part is furnace treated and infiltrated, to obtain a higher density. • Direct LS (DLS), providing the formation of a liquid phase that ensures a sufficient degree of densification, without any post-treatment. In further detail, this process is defined Direct Metal Sintering when applied to singlecomponent metal powders, with high melting point, densified by a high-energy laser leaving high residual porosity. Lasers with lower power are used to sinter powder mixtures containing two or more metal components, the process being sometimes referred to as Binary Phase Sintering [8]. In this
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case the liquid phase is originated from the low-melting component, which acts as a matrix and ensures the part consolidation. The present research regards the last-mentioned process, developed and marketed by EOS GmbH, for which two kinds of materials are available: a bronze-based powder named DirectMetal and a stai
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