Towards Improving the Properties of Plaster Moulds and Castings

Abstract

The plaster moulding process is commonly used for casting prototypes of aluminium components designed for subsequent production by die casting. Plaster moulded prototype castings possess dimensional tolerances and surface quality comparable to die castings, but without the high tooling costs and lead times. Unfortunately, the mechanical properties of plaster castings are significantly inferior to their die cast counterparts. This is due primarily to the low thermal conductivity of plaster which extends casting solidification time significantly compared to die or even sand casting processes. Long solidification times result in large grained castings demonstrating low strength and hardness. This work is an experimental investigation into the effects of various levels of silica sand and carbon fibre additions on the properties of foaming plaster moulds and associated aluminium castings. Data and statistical analyses are presented and conclusions drawn regarding the wet and dry strength of plaster moulds as a function of sand and carbon fibre content. Likewise, conclusions regarding the associated casting characteristics such as surface finish, solidification time, hardness and tensile strength are presented. The effectiveness of silica sand and carbon fibre additions with respect to improving the properties of plaster moulded prototype castings is also discussed.

Evaluation and Modification of the Block Mould Casting Process Enabling the Flexible Production of Small Batches of Complex Castings

“…In conjunction with rapid-prototyped patterns the block mould casting process enables realtime production of metallic prototypes or small batches of castings. Using the ideal moulding material, nearly all casting materials can be processed using this casting method, whereby the process time is much shorter compared to the more time-consuming investment casting process [6,8,22,23].…”

“…The GBIs or PBIs have not until now been in continuous use. This raises the price of the moulding material and limits the economic batch size at around 1,500 castings, depending on the size and geometry of the components [23]. Prior to their mixing with water, the moulding material exists as a powder, which promotes exposureto health problems in the workplace.…”

“…This limits the casting weight to approximately 10 kg. In addition to this, their low strength can lead to cracks in the moulds, decreasing the quality of the castings [23]. Regarding the economy of the block mould casting process, it can be concluded that this casting process is the more economical the more complex the geometry is and the smaller the dimensions of the potential cast components are.…”

“…Owing to the low heat conductivity of the moulding materials used, the cast metal solidifies relatively slowly producing a coarse microstructure and a high dendrite arm spacing (DAS). These microstructural parameters lead to decreased mechanical properties of the metallic components [23,38]. Besides the mechanical properties, the low cooling rate impairs the casting properties.…”

Defect Minimisation in Vacuum-Assisted Plaster Mould Investment Casting Through Simulation of High-Value Aluminium Alloy Components

“…A yield strength of 140 MPa and 210 MPa (respectively) is predicted after heat treatment. Brevick et al [14] investigated the effect of different levels of silica sand and carbon fibre additions on the properties of plaster moulds and related aluminium alloy castings. Analysis of statistical data showed the relationship between wet and dry strength of plaster moulds with sand and carbon fibre content.…”