Warpage of FDM parts: Experimental tests and analytic model

Abstract

Analysis of thermal distortions on parts built by extrusion-based additive manufacturing.Measurement of geometric deviations on block-shaped specimens in ABS thermoplastic.Main original finding: maximum warpage occurs at intermediate values of part thickness.Suggested explanations: shrinkage on multiple layers, occurrence of plastic deformation. Similarly to most additive manufacturing processes, Fused Deposition Modeling involves the processing of material by thermal cycles which can create distortions (warpage) in the built parts. The paper aims to characterize this defect on block-shaped parts in ABS thermoplastic resin as a function of some geometric variables related to the process: the size of the part in the three directions, and the thickness of deposited layers. For this purpose, the geometric deviations on parts manufactured with different combinations of the above variables have been measured and statistically analyzed in order to identify the influence factors and to estimate their individual and interaction effects on warpage. The results have given one main further insight compared to previous studies, namely the occurrence of a maximum distortion at intermediate values of part height. The attempt to explain it has suggested two additional hypotheses for the physical explanation of distortions: the extension of thermal stresses to multiple layers due to heat conduction from the last deposited layer, and the occurrence of bending stresses beyond the yield point of the material. These effects have been modeled by analytic equations in order to verify whether they can help improve the accuracy of warpage estimation.