Optimization of bonded magnet injection moulding

Recently the use of injection moulded bonded magnets has become very widespread. This is mainly due to their good value and low cost. There are several bonded-magnet compounds commercially available, even with rare hearth alloys that yield magnetic performances comparable to those ones offered by sintered magnets. However the magnetic properties of injection moulded bonded magnets are negatively affected by the thick solidification layer which develops during the filling of a mould cavity. This is due to the lack of orientation that filler particles have during magnetization in a solid matrix and it is stressed by high cooling rates, due to the high diffusivity which is proper of the metallic filler. This paper presents an approach to improve the magnetic performance by applying a fast mould heating and cooling system and by varying some influent process parameters. A fast mould heating and cooling system based on cartridge heaters has been implemented in a CFD code, in order to simulate the mould thermal behavior. A process simulation based on FEM has been used for cost and final part quality prediction. The numerical predictions about skin thickness distribution were compared to experimental SEM micrographs results in order to validate them. Furthermore, a multi-objective optimization algorithm, based on numerical simulations, has been implemented with the aim of minimizing the overall moulding cost, by determining the optimal value of skin thickness that balances material cost against process cost.