Coupled thermo-mechanical analysis for plastic thermoforming

An FEM software ARVIP-3D was developed to simulate the process of 3-D plast ic thermoforming. The coupled thermo-mechanical analysis, thermal stress an d warpage analysis for plastic thermoforming was carried out by means of th is software. Rigid visco-plastic formula was adopted to simulate the deform ing process. During this process, the method of comparing velocity, time an d area was adopted as the contact algorithm at different nodes and triangul ar elements. Sticking contact was assumed when the nodes become in contact with tool surface. The Arrhenius equation and the Williams equation were em ployed to ascertain the temperature dependence of material properties. In o rder to analyze the temperature field of plastic thermoforming, the Galerki n FEM code and the dynamic heat conduction boundary condition were adopted; latent heat and deformation heat were treated as dynamic internal heat sou rces. Based on the above, the model of coupled thermomechanical analysis wa s established. Assuming that the thermal deformation occurs under elastic c onditions, the thermal stress and the warpage following the cooling stage w ere estimated. Experiments of plastic thermoforming were made for high-dens ity polyethylene (HDPE). An infrared thermometer was used to record the tem perature field and a spiral micrometer was used to measure the thickness of the part, Results of numerical calculation for thickness distribution, tem perature field and warpage were in good agreement with experimental results .