Evaluation of some process parameters for production of investment bar castings

Abstract

This investigation aims at evaluating some process parameters for the production of aluminium alloy investment castings using polystyrene as pattern material and Plaster of Paris as investment slurry. The process parameters considered are the shell thickness, casting thickness and pouring temperature and the effect of varying these parameters on the mechanical properties of aluminium silicon magnesium alloy (A356) produced through the investment casting method is being investigated in this work. The effects of these variables were studied using design of experiments (D.O.E) via Taguchi’s L9 orthogonal array method. The castings produced were subjected to mechanical tests such as tensile strength, impact strength and hardness test using Monsanto tensometer and Avery impact and Avery hardness testing machines respectively. The results obtained were analysed using Minitab software 17. The results showed that the tensile strength, impact strength and hardness were optimum when the shell thickness was 5 mm, pouring temperature was 665^oC and the bar cross section was 64 mm² respectively. The investigation concludes that investment shell of thin thickness, casting thickness of smaller bar sections and lower pouring temperatures in the range of 665^oC - 690^oC were the most suitable parameters that produced optimum results with better mechanical properties in this study.

Keywords: Investment casting, Polystyrene pattern, Plaster of Paris slurry