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Introduction
Selective laser sintering (SLS) and selective laser melting (SLM) are two production technologies offering great advantages and opportunities compared to traditional material removal techniques ([3], [4] Kruth et al. , 2003, 2004). However, the residual stresses that arise in the parts being produced impose some serious limitations to the practical use, since they introduce part deformations and/or micro cracks. Moreover, large residual stresses can limit the load resistance of the parts compared to a stress free state.
In the field of Laser Engineered Net Shaping, a lot of effort has been done to measure, predict and control residual stresses ([9] Vasinonta et al. , 2000; [1] Aggarangsi and Beuth, 2003). Whereas researchers mainly focussed on the stresses in the growth-direction at the substrate-part connection, the current research will focus on the stresses perpendicular to the build direction, and their variation along the build direction.
In order to investigate the residual stresses, the origin of the stresses is firstly explained. Next, a simple theoretical model is presented to predict the basic residual stress distribution. Using an experimental procedure, residual stress profiles are then measured in a set of test samples having different kinds of process parameters. Thus, the effect of the process parameters on the residual stress can be concluded. Finally, some guidelines are presented to reduce the residual stress in SLS and SLM.
The difference between SLS and SLM concerns the binding mechanism that occurs between the powder particles ([4] Kruth et al. , 2004). In SLS, either a combination of a low melting binder and high melting structural material is used -called liquid phase sintering (LPS) or the powder particles are just partially molten. In case of LPS, a post treatment is generally necessary to enhance the mechanical properties and to increase the part's density. In SLM, the powder particles are fully molten. Since the border between SLS and SLM is rather vague, the stress inducing mechanisms are explained generally for the case of SLM. In the case of partial melting without infiltration, the same stress inducing mechanisms will occur. On the other hand, in the case of the LPS mechanism, the furnace cycle that is used to infiltrate the parts, will result in stress relaxation, so the resulting parts can be...