Comparing geometric tolerance capabilities of additive manufacturing systems for polymers

In all manufacturing processes, there are several factors for which the final product exhibits dimensional and shape deviations from its ideal nominal geometry. In additive manufacturing (AM) and 3D printing, a part is built layerwise in a single manufacturing step and is often net-shaped. In most cases, no finishing operation is applied to change the dimensions of the product, apart from a reduction of the superficial roughness through sandblasting or polishing. Therefore, knowing the dimensional tolerance of AM processes in advance is of fundamental importance, but little information is currently available in the literature. A benchmarking analysis of three different AM systems for polymers is presented in this paper. The compared machines are based on different AM techniques which are fused filament fabrication (FFF), selective laser sintering (SLS) and Arburg plastic freeforming (APF). The dimensional accuracy of the machines has been defined using the ISO IT grades of a reference artifact. In the analysis of the benchmarking results, a specific focus is made on the importance of the thermal household in SLS and a parameter named SLS modulus is proposed to identify critical heat concentrations in the powder bed that may influence the dimensional accuracy of the manufactured part.