ASSESSMENT OF SURFACE FINISH AND DIMENSIONAL ACCURACY OF TOOLS MANUFACTURED BY METAL CASTING IN RAPID PROTOTYPING SAND MOULDS

In this paper, an initial assessment of the quality parameters of the surface finish and dimensional,accuracy of tools made by metal casting in rapid prototyping (RP) sand moulds is undertaken. A case study from a local tool room, dealing with the manufacturing of an aluminium die for the lost wax process, is employed. Modern techniques, including surface roughness analysis and three dimensional scanning, are used to determine and understand how each manufacturing step influences the final quality of the cast tool. The best surface finish obtained for the cast die had arithmetic average roughness (Ra) and mean average roughness (Rz) respectively equal to 3.23 mu m and 11.38 mu m. In terms of dimensional accuracy, 82% of cast-die points coincided with the Computer Aided Design (CAD) data, which is within the typical tolerances of sand cast products. The investigation shows that mould coating contributes slightly to the improvement of the cast tool surface finish. The study also found that the additive manufacturing of the sand mould was the chief factor responsible for the loss of dimensional accuracy. These findings indicate that machining will always be required to improve the surface finish and the dimensional accuracy of cast tools in RP sand moulds.