Combining CERAM's modelling expertise with novel pressure casting techniques has enabled extremely rapid product development compared to empirical mould design which can be expensive and time consuming. The following shows that simulation can help prevent unnecessary iterations in the design of a working mould.

Traditional casting methods use capillary action from plaster moulds to remove water from a suspension of ceramic powder (called slip). However the process is slow and labour intensive. Pressure casting speeds up the process by using pressure to extract the water.

An innovative machine has been developed as part of the FLEXIFORM Project led by CERAM. FLEXIFORM provides a new technology for pressure casting of ceramic tableware and sanitaryware shapes requiring multi-part moulds. The mould assembly is produced from a novel mould material which has a high compressive strength and dimension stability.

This advanced technique provides excellent results especially in terms of process time and product performance. By combining this new moulding technique with CERAM's modelling expertise has enabled extremely rapid product development and fault diagnosis. For example during the early development of the method, cracks occurring in the mould despite the pressures ostensibly being well below the moulds design strength, were rapidly explained and eliminated.

Issues Addressed

The project considered the effect of casting pressure on the mould. To achieve this, a 3D solid model of the die assembly was produced. The solid model was imported into a Finite Element modelling package and set of virtual tests were performed on the model to determine its behavior under different moulding conditions.

Figure 1: Solid Model (shown in cross section) of Mould Assembly

Simulation

The tests included conditions designed to simulate the actual pressure casting operation and de-moulding using a back pressure.

Figure 2: Loads and Constraints Applied to Simulate Casting or De-Moulding

Conclusions

By combining CERAM's modelling expertise with its understanding of engineering and processes, a simulation of the de-moulding operation was able to show that under normal conditions the pressures present would not be great enough to damage the mould.

Figure 3: Safety Factor During Normal De-Moulding

However, de-moulding was achieved using water applied from a mains system through a simple gate valve. By considering the instantaneous pressure seen by the mould when this valve is rapidly turned on, it was shown that the stress in the mould material easily exceeded its design limit. Thus the simple inclusion of a soft start valve successfully prevents any mould damage.

Figure 4: Safety Factor During De-Moulding with Water Hammer Effect