Abstract: Defects like warpage and volume shrinkage occurring in injection molding process of a casing were investigated by means of robust design, mean analysis and variable analysis methods.Based on the results obtained in this work, optimum combination of processing parameters as well as various influencing factors was obtained for minimizing warpage and volume shrinkage.To obtain a qualified product in both surface and size, such a combination included a melt temperature of 250 ℃, mold temperature of 250 ℃, a mold temperature of 250 ℃, injection time of 1.3 s, holding time of 25 s, cooling time of 19 s, and a holding pressure of 100 %.