RESEARCH ARTICLE Simulation of crystallization evolution of polyoxymethylene during microinjection molding cycle Benayad Anass 1,2,3 | Boutaous M'hamed 2 | El Otmani Rabie 3 | El Hakimi Abdelhadi 1 | Touache Abdelhamid 1 | Kamal R. Musa 4 | Derdouri Salim 5 | Refaa Zakariaa 6 | Siginer Dennis 7 1 Mechanical Engineering Laboratory, Sidi Mohamed Ben Abdellah University, Faculty of Sciences and Technologies of Fez, Fez, Morocco 2 University of Lyon, CNRS, National Institute of Applied Sciences of Lyon, CETHIL, Lyon, France 3 Chouaib Doukkali University, National School of Applied Sciences El Jadida, Science Engineer Laboratory for Energy (LabSIPE), El Jadida, Morocco 4 Department of Chemical Engineering, McGill University, Québec, Canada 5 National Research Council Canada, AST Boucherville, Québec, Canada 6 Department of Architecture and Civil Engineering, Chalmers University of Technology, Gothenburg, Sweden 7 Botswana International University of Science and Technology & Universidad de Santiago de Chile, Santiago, Botswana Correspondence El Otmani Rabie, Chouaib Doukkali University of El Jadida, National School of Applied Sciences (ENSAJ), Science Engineer Laboratory For Energy (LabSIPE), Route nationale No. 1 (route d'Azemmour), km 6 Azemmour EL HAOUZIA, BP: 1166 El Jadida Plateau 2400, Morocco. Email: rabieelotmani@gmail.com A mathematical model coupled with a numerical investigation of the evolving material properties due to thermal and flow effects and in particular the evolution of the crystallinity during the full microinjection molding cycle of poly (oxymethylene) POM is presented using a multi-scale approach. A parametric analysis is performed, including all the steps of the process using an asymmetrical stepped contracting part. The velocity and temperature fields are discussed. A parabolic distribution of the velocity across the part thickness, and a temperature rise in the thin zone toward the wall have been obtained. It is attributed to the viscous energy dissipation during the filling phase, but also to the involved characteristic times for the thermal behavior of the material. Depending on the molding conditions and the locations within the micro-part, different evolution of crystallization rates are obtained leading to at least three to five morphological layers, obtained in the same part configuration of a previ- ously work, allowing a clear understanding of the process-material interaction. KEYWORDS microinjection molding, computer modeling, crystallization kinetics, viscous dissipation, morphology 1 | INTRODUCTION Microinjection molding products are of growing interest in various fields; communication, health, aerospace, and automotive sectors among many others. The processing steps of the microinjection mold- ing process are similar to those in conventional injection molding. However, the small size of the parts and flow geometries lead to new complex physical phenomena, which must be investigated to enable the analysis and the understanding of the process-material interac- tions in complex configurations. Microinjection molding of polymers is increasingly attractive for its various technical advantages such as a high production rate and the possibility of obtaining complex small parts with high surface quality at low costs. Indeed, several micro- devices such as micro-pumps, optical, biomedical, biochemical, and communications industries, 1 fiber optic waveguides, 2 surgical devices, 3 and micro-gears 4 were successfully manufactured via this process. Microinjection molding parts are significantly different from those obtained by the conventional injection molding process, espe- cially given their characteristic micro-structural features and layered induced morphology. 5 An in-depth investigation on the induced Received: 17 September 2019 Revised: 11 November 2019 Accepted: 11 November 2019 DOI: 10.1002/pat.4819 Polym Adv Technol. 2019;1–15. wileyonlinelibrary.com/journal/pat © 2019 John Wiley & Sons, Ltd. 1