Experimental and numerical study on residual stress and geometric distortion in powder bed fusion process

The objective of the present work is to experimentally and numerically study the effect of the part size on the distortion of a part printed by a powder bed fusion process. A simplified thermo-mechanical finite element model was developed using a so-called superlayer concept (i.e., numerous layers deposited at once) to predict the geometric distortion induced by the thermal stress. A set of seven cylinders with different dimensions were modeled with this method. The same geometries were printed using a commercial selective laser melting machine and cut from the build plate using wire electrical discharge machining. The distortion of different cylinders was measured before and after the removal from the build plate using a coordinate measuring machine and compared with the simulation results. The experimental results showed the final distortion is largely contributed by the build plate removal process because it relaxes the thermal stress accumulated during the printing process. The modeling results show a high consistency with the experimental results, especially for the thicker parts. As the part thickness decreases, the prediction accuracy of the model decreases. When a superlayer thickness of 1 mm is used, the model can accurately predict the distortion for a cylinder with a diameter of 45 mm and a thickness of greater than 6 mm. This model provides an effective approach for geometric control of printed parts.