Abstract
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.
Highlights
Ceramic Injection Moulding (CIM) is a widely used mass production process consisting of three main steps: injection moulding, debinding and sintering
The feedstock material is presented alongside a description of the experimental setup, control system and the process parameters employed on the CIM trials
The performance of the novel thermal control system will be evaluated by analysing its effect on the macro- and micro-structural properties of injection moul ded green parts
Summary
Ceramic Injection Moulding (CIM) is a widely used mass production process consisting of three main steps: injection moulding, debinding and sintering. The employment of these process parameters brings about challenges in feature replication capability for thin-walled and micro components [2]. To cope with these issues, mould tempera ture has been proven to be the most significant parameter to ensure replication capability and dimensional accuracy for features having aspect ratios [3]. A technique known as “Rapid heat cycle moulding” (RHCM) is often used and implemented through steam [4,5,6], consisting of a first increase of cavity temperature during filling to keep the feedstock viscosity low ( enhancing feature replication capability and weld line formation), and a fast cool down of the dietool [7]. High investments in cooling technologies are required for complex thermal control systems which need to guarantee fast and uniform cooling of the injected components to ensure that both the mould and subsequently the part are cooled down to a suitable ejection temperature quickly enough to achieve industry-standard cycle times
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