Abstract
Amorphous thermoplastics, as a type of engineering plastic material, are used in various industrial sectors. In order to manufacture high-performance products, it is important to optimize their forming process to mitigate residual stresses. However, stress in a plate is difficult to measure, therefore, modeling provides a powerful way to investigate and understand the evolution of stress. In this study, the forming process of a polyetherimide (PEI) plate was modelled using finite element analysis, and then validated through a comparison with a warpage experiment. This study reveals that the whole forming process can be divided into three stages by the glass transition temperature Tg of the PEI. The second stage, corresponding to the plate cooling from above Tg to below Tg, contributes a large portion of the residual stress in a short time. The final residual stress, the magnitude of which is affected by the cooling rate and plate thickness, shows a parabolic distribution through the thickness of the plate. These important conclusions are beneficial for improving the quality of an amorphous thermoplastic plate, while allowing highly efficient production.
Highlights
IntroductionThermoplastics have attracted increasing attention from both academia and industry owing to their unique advantages of highly efficient production and recyclability compared to thermosetting plastics
Thermoplastics have attracted increasing attention from both academia and industry owing to their unique advantages of highly efficient production and recyclability compared to thermosetting plastics.Thermoplastics can be classified as semi-crystalline and amorphous
Residual stress inside a plate is difficult to monitor in situ, modelling, especially finite element analysis (FEA), provides a powerful and feasible method for researchers to understand the stress evolution process and its mechanism
Summary
Thermoplastics have attracted increasing attention from both academia and industry owing to their unique advantages of highly efficient production and recyclability compared to thermosetting plastics. Reducing the molding time saves costs and enhances productivity, but typically leads to poorer quality, including both visible distortion, such as warpage and spring-in, and invisible internal damage [2] These defects could affect product performance, shorten their lifetime, and could even induce catastrophic failure of the material structure. Liu conducted a two-dimensional FEA of thermally-induced stress and warpage of, an amorphous plastic, based on a viscoelastic phase transform model [3]. Compression molding and tape fiber placement have been used to manufacture continuous fiber-reinforced thermoplastics In these processes, the flow induced stresses can be neglected, but thermal stresses play a dominant role [7]. We establish a three-dimensional FEA program comprising thermal-viscoelastic models to accurately examine the stress evolution process of, an amorphous plate during its cooling phase in a mold.
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