Curl Distortion Analysis During Photopolymerisation of Stereolithography Using Dynamic Finite Element Method

Abstract

Stereolithography is one of the rapid prototyping processes which uses a photopolymer as the raw material to build prototypes. The photopolymer absorbs energy by selective laser exposure. The curing effect starts when the absorbing energy exceeds a critical value, and the process is called photopolymerisation. The photopolymerisation changes the phase from liquid to solid. The cured volume can expand and then shrink on cooling. The process parameters such as the scanning speed, scanning path, scanning pitch, and the slicing thickness, lead to different shrinkage and curl distortion, so, the photopolymerisation process is a dynamic material behaviour. In this study, a dynamic finite element simulation code has been developed to simulate the photopolymerisation process. The simulated result for a suspended beam which corresponds to the process parameters shows that a short raster causes less curl distortion than a long raster. The experimental result agrees very well with the simulated result.

Fundamental study and theoretical analysis in a constrained-surface stereolithography system

“…The material is solidified point by point. Photo polymerisation is the key Moreover, the behaviour of the cure resin is a function of absorption laser exposure E and elapsed time t. As a result, the deformation of the resin consists of elements as follows [11]:…”

“…In addition, the absorption energy is determined by exposure time. This polynomial curve of the utilised resin NAF202 was proposed by Huang et al [11]. The constants a a and b had been obtained, respectively, to be 0.31 and 0.44.…”

“…The cure shrinkage curve can also be expressed as a function of absorption laser energy and elapsed time like the approximation formulas for the elastic modulus. A completely dynamic model has been established [10,11] and is written as follows:…”

“…a 2 and a 3 are used to express the continuing shrinkage and to illustrate the initial part of the cure shrinkage curve respectively. Hence, the constants of a 1 , a 2 and a 3 are 0.32, 0.0037 and 0.421 [11]. The Poisson ratio and thermal expansion rate are already known as 0.3 and 0.0063.…”

Organic and Hybrid interpenetrated Polymer Networks for Advanced Materials

“…Beyond the fact that the free radical photopolymerization of these compounds is really sensitive to the atmospheric oxygen, a significant shrinkage appears, the increase in density yielding to stress, distortions and even cracks 1,2 . Through ring opening polymerization, epoxide monomers exhibit less significant shrinkage 3 .…”