Warpage in Material Extrusion Additive Manufacturing of Amorphous and Semicrystalline Polymers

Material Extrusion Additive Manufacturing (MEAM) offers the ability to manufacture complex geometries through layer-by-layer deposition. MEAM involves fast heating and cooling of polymers, processes that involve thermal expansion and contraction of materials that may undergo phase transitions. These phenomena may lead to warpage: distortion of the printed parts or deviation from the intended geometry, which significantly compromises the dimensional accuracy and functionality of parts. Mitigation or even cancelling warpage has become one of the roadblocks toward further widespread application of MEAM technology, a target that requires a thorough understanding of the phenomenon. To contribute to this goal, this review presents and discusses the current knowledge of warpage in MEAM, starting with a general presentation of the technology and its intrinsic features, followed by details of the fundamental mechanisms of warpage, highlighting the crucial interaction between processing parameters, material characteristics, and part geometry. A thorough analysis of the experimental methodologies used to quantify warpage is presented, alongside a comparative exploration of warpage behavior in amorphous and semicrystalline polymers. The state-of-the-art of current modeling approaches aimed at predicting the warpage phenomenon is also presented and discussed, with a focus on the capability to effectively consider the complex thermo–mechanical history specific to MEAM.