A calibration method to predict shape change during sintering: Application to 316L parts made by Metal Binder Jetting

Abstract

Metal Binder Jetting (MBJ) is a promising sinter-based additive manufacturing technology allowing to produce parts with complex geometries in small to medium series. However, the required sintering step leads to a drastic shrinkage because of the initially low green density of the part ($\approx 50\text{–}60\text{\%}$) but also to large shape distortions due to gravity sagging. The prediction of those deformations is therefore paramount to reach near-net shape parts. A step-by-step method, relying on both experimental and numerical procedures, is proposed to predict shape changes during the sintering of 316L stainless steel made by MBJ. The anisotropic linear shrinkage is determined thanks to dilatometry while the viscous deformations are numerically fitted thanks to a calibration part. The numerical implementation is performed in the proprietary HP 3D Digital Sintering software and is tested for various sintering cycles. Optimization loops are proposed to fit correctly all the constitutive parameters leading to deviations of the simulated results with experimental parts below 1%. Then, angular sectors exhibiting various angles of overhangs are sintered to assess the performance of the model. It turns out that most predictions exhibit maximum deviations below 5%, with filleted parts exhibiting the better predictions. Beyond the model ability to predict shape, the parts proposed in this work show interesting features that allow to capture complex thermophysical mechanisms though they are of simple design. In this way, those could become standard calibration parts for any model for initial printing stages.