Thermo-mechanical finite element simulation and validation of rubber curing process

Vulcanization, or curing, is a very important process in producing useful rubber products. The curing process takes place when heat is transferred to the rubber compounds inside a heated mold. The temperature distribution in the rubber significantly affects cure level distribution throughout the part. The problem of non-uniformity of cure level of the final product often occurs in a large rubber component, such as a tire or a rubber track, leading to poor quality and performance. The expansion of the rubber due to temperature increase and the rise of elastic modulus during the curing process lead to an increase in stress inside the mold, which can cause excessive mold deformation and the appropriate mold press force should be determined. This work’s aim was to develop a methodology for the analysis of the vulcanization process using a coupled thermo-mechanical finite element method to simulate a nonlinear heat transfer process coupled with curing kinetics and the evolution of thermal and mechanical properties. User subroutines UMATHT and UMAT were developed and implemented into the finite element package ABAQUS to evaluate the cure level distribution and stress developed inside the mold during curing. Experimental tests were carried out to study and evaluate the thermal, curing, and mechanical properties as dependent functions of temperature and cure level. A simple compression molding test was performed and the results were used to validate the simulated predictions. It is shown that the predictions of the temperature, cure level distribution in the rubber part and press force during curing process obtained from the developed finite element analysis are in the good agreement with the experimental data. Furthermore, the simulations with thermal and mechanical properties varying with temperature and cure level are closer to the measured data than one with constant properties.