Finite element modelling of high air pressure forming processes for polymer sheets

 In this paper we describe the mathematical modelling and computational simulation of the high air pressure (HAP) thermoforming process which is used in the creation of thin walled polymeric structures. This involves, using data from material tests, an elastic-plastic constitutive equation valid for large deformations and a constrained deformation in which there is frictional contact between the polymeric sheet and a constraining surface (the mould surface). Despite a number of simplifying assumptions and some uncertainities in the mathematical model the finite element computations presented predict quite well the actual shape and thickness distribution which are found on sample products. RID="*" ID="*" The work for this paper was supported in part by the EPSRC under grant GR/M38070 for the Materials Processing for Engineering Applications (MaPEA) programme. Dedicated to the memory of Prof. Mike Crisfield, for his cheerfulness and cooperation as a colleague and friend over many years. The authors would like to acknowledge the help of the Department of Mechanical Engineering at the University of Leeds in allowing testing equipment to be used and also for the contribution of A. M. Wiese to this testing. Further testing was undertaken at the IRC in Polymer Science and Technology, University of Bradford. The contribution of Drs. P. Caton-Rose and J. Sweeney to this testing is also gratefully acknowledged.