ABSTRACT
Squeeze casting is a method of casting which blends the benefit of casting and forging processes which result in excellent quality of components compared to the convectional casting techniques. Existing literature has revealed that squeeze casting enhances the mechanical properties of cast products and has the advantage of producing products almost without porosity. However, improper combination of squeeze casting parameters can result in defects such as oxide inclusion, porosity, extrusion segregations, cold laps, extrusion debonding, blistering, under fill, sticking, hot tearing, case debonding, centerline segregation and shrinkages. These defects can ultimately have detrimental effect on the quality of squeeze cast parts. Consequently, the need for numerical models and optimum conditions to further improve the production of squeeze cast parts has therefore remained an undertaken for researchers. Hence, the aim of this study was to create optimum models that holistically predicted and optimized the following responses: yield strength, ultimate tensile strength, impact strength, hardness and surface roughness based on the interactions between the process parameters of squeeze pressure, pressure duration, pouring temperature and initial die temperature. Using the range and levels of the independent variables, the design of experiment based on the Box-Behnken and Taguchi method that had a total of 27 experimental runs was developed. Three pairs of mild steel moulds were fabricated. The mould were used to cast 186 specimen measuring 180๐๐ ร 25๐๐ ร 10๐๐. Thereafter, the samples were subjected to destructive tests such as yield strength, ultimate tensile test, hardness, impact and surface roughness tests. Experimental results were obtained via a series of measurements and laboratory tests. To analyze the input and output data, two intelligent methods, namely Response surface Methodology (RSM) and Taguchi approach were employed. From the analysis of results, the second order polynomial model was adopted. Also, the larger the better and smaller the better multi- objectives of the Taguchi method for the squeeze casting process were used to establish the optimal combination of process parameters and to reduce the variation in quality. To test for the model significance, adequacy and validity, the analysis of variance (ANOVA) was done and goodness of fit was determined. The results showed that in the case of yield strength, RSM yielded value of 345.71MPa and 302.86MPa for Taguchi approach. RSM gave higher value for yield strength. Same goes with ultimate tensile strength as RSM yielded 387.65MPa while Taguchi yielded 347.72MPa. In vii the case of hardness, the value of Taguchi (166) was lower than the value of RSM (178). Surface roughness for RSM was 7.09 ยตm lower than that of Taguchi (7.92 ยตm). Impact strength value for RSM was 23.11J, higher than the value of Taguchi 26.59J. As observed from the values, RSM performed better than Taguchi as regards yield strength, ultimate tensile strength and hardness. Taguchi method performed better than RSM with regards to impact strength and surface roughness. The difference between the property values obtained under the two approaches was less than 5 %, which showed that the two approaches were fit for optimization of the casting parameters, however, RSM performed better.
