Numerical and experimental investigation of the isothermal assumption in selective laser sintering of PA12

Selective Laser Sintering (SLS) of polymers represents a powder-bed based additive manufacturing technique which can produce parts with a large geometrical freedom as well as adequate mechanical properties. The standard process model of the SLS process consists of three stages. (i) The preheating stage, where the building chamber is heated up, (ii) the layer-wise building stage during which cross sections of the part are molten using a laser beam and remain as melt, captured by the surrounding powder, and (iii) the cooling stage where crystallization of the part is assumed to be induced. In the present work we investigate this process model by means of experiments and a verified and validated finite element simulation tool. It will be shown that crystallization may already be induced during the building stage after the deposition and melting of a few layers. To account for typical temperature fields as they arise in SLS, i.e. with negative and positive cooling rates, the standard Nakamura crystallization model is adapted to allow for negative crystallization rates of partially crystallized material, once the melting temperature is reached. Further, a dependency of the average temperature and crystallization fields on the geometry will be shown.

Automated summary

Selective Laser Sintering (SLS) is a powder-bed based additive manufacturing technique that can produce parts with large geometrical freedom and adequate mechanical properties. The standard process model of SLS consists of three stages: preheating, layer-wise building, and cooling. Research shows that crystallization rates of partially crystallized material may be induced during the building stage.