Numerical Model and Experimental Validation for Laser Sinterable Semi-Crystalline Polymer: Shrinkage and Warping

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.

Multidisciplinary topology optimization incorporating process-structure-property-performance relationship of additive manufacturing

“…A combination of low LS, high SS, and HS causes weak mechanical performance. On the contrary, within the process window, to increase LS and decrease SS/HS can enhance the stiffness of sintered parts since it improves the input energy (Li et al 2020a). As shown in Fig.…”

Laser-based additively manufactured polymers: a review on processes and mechanical models

“…Through ray-tracing algorithms, the trajectories of the light rays, or photons, emitted by the laser source can be simulated probabilistically when travelling into the considered medium, until they hit a pre-defined area. According to the model proposed by Xin et al [93], the initial position of a photon in the laser beam section is defined in spherical coordinates by the radius and the azimuthal angle u, where the angle is distributed uniformly in the interval 0; 2p ½ , while the radius [93,94] Particle-based Semi-crystalline (PA12) Thermal [87] Analytical Semi-crystalline (PVA) Thermal [88,96] Finite elements Semi-crystalline (PA6) Thermal [89,90] Finite elements Semi-crystalline (PA12) Thermal, sintering [80,82,83,86] Finite elements Amorphous (PC) Thermal, sintering [79,81] Finite differences Amorphous (PC) Thermal, sintering [84] Finite volumes Amorphous (PC) Thermal, sintering [85,90] Finite elements Semi-crystalline (PA12) Optical, thermal, sintering [93] Particle-based Semi-crystalline (PA12) Thermal, mechanical [91,128] Finite elements Semi-crystalline (PA12) Thermal, mechanical [92] Finite elements Semi-crystalline (PP)…”

“…being a ref the reference degree of crystallisation and A C a; T ð Þ the shift function [91]. Recently, Li et al [128] proposed a thermo-mechanical model to accurately predict residual stresses, shrinkage and warping of polymeric parts (polyamide PA-12). With respect to the previous models, they included both the heating and cooling steps in a numerical finite element model, and accounted for the recrystallisation-induced strains in the material.…”

Ultra‐Strong and Proton Conductive Aqua‐Based Adhesives from Facile Blending of Polyvinyl Alcohol and Tungsten Oxide Clusters

“…[ 21–23 ] This is extremely true for semi‐crystalline PVA, which shows significant shrinkage upon curing. [ 24 ] Therefore, although PVA is expected to bind strongly to smooth polar surfaces, for example, glass, for its abundant hydroxyl groups, this case is yet rarely reported for pure PVA. To reduce its crystallinity and minimize the effect of shrinkage, polyvinyl butyral with soft side chains has been chemically derived from PVA as glass binder, which, however, sacrifices the hydroxyl side groups and reduces affinities to polar surfaces.…”