Optimization of the injection molding process of passive vibration isolators

This paper discusses a case study on the variability of the mechanical properties (static and dynamic stiffnesses, loss factor) observed in engine mounts used to isolate vibration in all-terrain vehicles. In order to avoid passenger's discomfort during engine operation, uniformity of the damping provided by each passive vibration isolators is capital. Transmitted forces should also be minimized in order to prevent excessive structural stress in the vehicle. Isolators are produced through manual cycles of an injection molding process. Quantifying how human and machine parameters affect the performance of the final product is fundamental. The purpose of this work is to provide better understanding of the discrepancies on mechanical properties occurring during the industrial process. Design of experiments is a well-established method to optimize a process. Screening experiments were performed to identify the most significant variables (vulcanization temperature, curing time and injection pressure) as well as the parameters that are detrimental to the manufacturing process. Important variables were used as input parameters of a D-optimal split-plot design in accordance with the response surface methodology. Quadratic prediction models were obtained to represent product properties as functions of the process variables identified. The numerical results helped improving the production yield, but also replaced the costly trial and error method used during prototype development. Increased life expectancy of the products is expected from this case study.