Finite element analysis of thickness distribution in vacuum forming of PMMA/PVC sheets with varying draw ratios

Abstract

Vacuum forming is a widely used process in plastic sheet manufacturing, particularly for fabricating airplane cabin interior components. However, improper mould design can result in defects like non-uniform thickness distribution, webbing, bridging, or even breakage. Therefore, an effective numerical method to simulate the vacuum forming process and evaluate the effect of mould geometry is essential to replace trial-and-error approaches. This study employs finite element analysis (FEA) using AniForm software to simulate the forming process and predict the thickness distribution of a polymethyl methacrylate (PMMA) and polyvinyl chloride (PVC) blended amorphous thermoplastic sheet. Two constitutive models were implemented to describe material behaviour: the Mooney-Rivlin model, which captures the elastic response and large deformations during forming, and the Cross model, which characterises the material’s shear-thinning rheological behaviour at elevated temperatures. Model parameters were obtained from elevated temperature tensile tests and oscillatory rheometer tests at the sheet’s forming temperature. Male moulds with different draw ratios were considered in FEA to investigate their influence on thickness distribution. The draw ratio in this study is defined as the ratio of the surface area of the formed part to its footprint area. Results show that increasing the draw ratio beyond 2:1 compromises the uniformity of sheet thickness distribution.