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Abstract
Shrinkage and warping of additive manufacturing (AM) parts are two critical issues that adversely influence the dimensional accuracy especially in powder bed fusion processes such as selective laser sintering (SLS). Powder fusion, material solidification, and recrystallization are the key stages causing volumetric changes of polymeric materials during the abrupt heating–cooling process. In this work, the mechanisms of shrinkage and warping of semi-crystalline polyamide (PA) 12 in SLS are well investigated. Heat-transfer and thermo-mechanical models are established to predict the process-dependent shrinkage and warping. The influence of raw material- and laser-related parameters are considered in the heat-transfer and thermo-mechanical models. Such models are established considering the natural thermal gradient and dynamic recrystallization, which induce internal strain and volumetric change. Moreover, an experimental design via orthogonal approach is introduced to validate the feasibility and accuracy of the proposed models. Finally, the quantitative relationships of process parameters with product shrinkage and warping are established; the dimensional accuracy in part-scale can be well predicted and validated with printed parts in a real experiment.
Highlights
Powder bed fusion including selective laser sintering (SLS) is an essential category of multiple additive manufacturing (AM) technologies that is used to fabricate three-dimensional objects with arbitrary geometry via a digitally controlled layer-by-layer fusion-solidification process
This section introduces the capabilities of the thermo-mechanical model in predicting the temperature distribution, residual stress profile, and shrinkage/warping of laser-sintered specimens
It is worth noting that the powders are considered to be continuum this with the thermo-mechanical model, the stress distribution, the part-scale shrinkage, and warping media with homogenized thermal and mechanical properties in the macro-scale thermo-mechanical can be predicted systematically
Summary
Powder bed fusion including selective laser sintering (SLS) is an essential category of multiple additive manufacturing (AM) technologies that is used to fabricate three-dimensional objects with arbitrary geometry via a digitally controlled layer-by-layer fusion-solidification process. Zeng et al [11] reviewed the heat-transfer analysis via SLS, including analytical solutions, numerical solutions, and thermal measurements They conducted a case study to predict the temperature profile of laser scanning. It is still challenging to search the optimal combination of parameters to minimize the corresponding shrinkage/warping and the specific quantitative relationship from material characterization to the part-scale shrinkage and warping, systematically coupling experimental works with modeling prediction. This eventually connects the virtual and physical model of DTT in practical terms. A theoretical model combined with heat-transfer, thermo-mechanical, and material crystallization kinetics is developed to anticipate temperature distribution, residual stress, and entire shrinkage/warping at part-scale. A representative structure is employed for macro-scale shrinkage and warping prediction based on the proposed thermo-mechanical model to manifest its applicability
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