Regional temperature control in ceramic injection moulding: An approach based on cooling rate optimisation

The injection moulding of ceramic components with uneven wall thickness presents challenges due to differential cooling rates developing in the injected parts, which cause premature solidification of the feedstock at thin features and lead to detrimental defects, worsening in components from green to sintered states. To cope with this, suitable mould thermal control approaches have to be selected and validated, as current control methods are based on the achievement of a uniform cavity surface temperature, which is not tailored to such complex geometries. In this work, a novel thermal control system is proposed, based on regional mould temperatures, implemented with the use of Peltier modules, which locally and independently heat and cool different cavity features according to their thickness. The regional temperature profiles are optimised over time with the use of a coupled Finite Element - Particle Swarm Optimisation (FE-PSO), to achieve uniform cooling rates throughout the moulded components. The performance of this approach is compared to both constant ambient mould temperature and Rapid Heat Cycle Moulding (RHCM) techniques, which instead aim at achieving uniform temperatures throughout the mould cavity surface. Results show that the novel proposed method, based on regional temperature control and uniform cooling rates, promotes the simultaneous solidification of features with a 10-times difference in surface-to-volume ratio. Due to this, in terms of components quality, the novel method brings the advantages of higher dimensional control and reduction of differential shrinkage compared to the other analysed approaches, thus increasing the capability to use injection moulding to manufacture ceramic components characterised by non-uniform wall thickness.