Mechanical optimization of the injection system in a compression molding machine

Minardi Andrea - SACMI (Italy)



SACMI is an international group manufacturing machines and complete plants for the Ceramics, Beverage & Packaging, Processing and Plastics industries. This group consist about 70 companies all around the world.
The case study under investigation is about the optimization of pneumatic actuator. In the injection system of our machine we have particular pneumatic pistons that work with high frequency. These pistons are subjected to high acceleration and impact, in both axial direction. To move the piston with a lower pressure as possible, avoiding the broken of the piston and of the surrounding parts as well, we need to design a lightweight piston, but able to resist to the stress which it is subjected. For all this reason a multi-objective optimization has been carried out to find a right compromise between weight and stress, executing a lot of iteration, by means of modeFRONTIER.
A parametric model of the piston has been built, with particular attention on robust and consistent generation of the geometry model. The CAD model and the related FE model have been integrated into modeFRONTIER which is able to manage an high number of iteration in automatic way, changing all geometry parameters and avoiding invalid geometry. This tridimensional model was really time-consuming but in this case we have been able to exploit the axial symmetric property to develop a new 2D FE model simulation with e lower runtime. In this simulation is been considered that the piston in its working cycle undergoes many collision.
A new optimal geometry has been found, with the same weight as the original one but with an increase safety factor of 45%. The whole process of optimization takes less than 300 simulation, it means about 10 h in terms of computational time.