Statistical analysis on accuracy of wax patterns used in investment casting process

The primary objective of this research work is to determine the accuracy of wax patterns produced by hard and soft tooling and optimise the injection parameters used in low pressure injection moulding. Wax patterns are produced using both the hard (polyurethane mould) and soft (RTV mould) tools. It is essential to use the optimal injection parameters during moulding in order to obtain good dimensional accuracy of wax patterns. From the current study it is noticed that the polyurethane mould produce accurate patterns than the silicone mould. Based on the study on optimisation of the injection parameters, it is found that using a lower pressure with higher temperature for the polyurethane mould will produce an accurate patterns provided that appropriate care is taken while choosing the holding time. A short holding time will yield a more accurate pattern, but too short a holding time will cause distortion when removing it from the mould, as it is too soft. Too long a holding time will cause more shrinkage. For the silicone mould, only the injection temperature has an effect on the dimensions of the wax patterns. The dimensional errors incurred during dipping are also measured and found that generally, there is a reduction of 0.2-0.4% in dimension. These studies will help the investment caster to estimate the allowance required in the initial CAD drawings to produce a final casting with minimal dimensional inaccuracy. (C) 2003 Elsevier Science B.V. All rights reserved.