Multiphysics modeling and experiments of grayscale photopolymerization with application to microlens fabrication

M. M. Emami, M. Jamshidian, D. W. Rosen

Research output: Contribution to journalArticlepeer-review

Abstract

A phenomenological model of a single-shot grayscale photopolymerization process is developed and used within a virtual process planning framework for microlens fabrication. Along with previous research, the kinetic relations describing the solidification of UV-curable resin are derived based on the underlying chemical reactions involved in free radical photopolymerization. As enhancements to the state-of-the-art, our multiphysics model includes a recently proposed super-Gaussian description of the light field, as well as the photobleaching effect due to the live reduction in photoinitiator concentration during UV illumination. In addition, heat generation and thermal strains due to the exothermic chemical reactions, and chemical shrinkage due to polymerization and cross-linking of monomers are considered. The model is numerically implemented via finite element method in COMSOL MULTIPHYSICS software. Using a simulation-based virtual process planning framework, customized microlenses are fabricated with an in-house grayscale lithography experimental setup for digital micromirror device (DMD)-based volumetric additive manufacturing. Simulation and experimental results show that after the end of exposure, the temperature quickly rises by the advancement of exothermic chemical reactions and reaches a maximum rise of 100 K in a few seconds, followed by a slow cooling and recovery of thermal strains. It is observed that chemical and thermal shrinkages can compromise the dimensional accuracy of the final part near the resin-substrate interface due to the strong adhesion of the solidified part to the rigid substrate that prevents material shrinkage in the vicinity of the rigid substrate.

Original languageEnglish
Article number091005
JournalJournal of Manufacturing Science and Engineering, Transactions of the ASME
Volume143
Issue number9
Early online date31 Mar 2021
DOIs
Publication statusE-pub ahead of print - 31 Mar 2021

Keywords

  • Additive manufacturing
  • Grayscale lithography
  • Microlens fabrication
  • Modeling and simulation
  • Multiphysics modeling
  • Photopolymerization
  • Rapid prototyping
  • Solid freeform fabrication

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Mechanical Engineering
  • Computer Science Applications
  • Industrial and Manufacturing Engineering

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