Sand castings are used in order to manufacture complex shapes. The castings are bound to have one or more defect. The presence of defects may subject casting to rejection. The defect causes stress concentration. More time and money would be saved if it ever becomes possible to produce to hundred percent good casting. It may cause casting to fail in fatigue, impact etc. Defects can be minimized by taking precautionary measures in the casting processes. This thing can be achieved by predicting these defects prior to metal pouring. This research work will identify the cause of occurrence of blowhole and provide the solution to remove these defects by developing a model for blowhole optimization & for the same purpose chlorine will use as a catalyst for reducing blowhole defects.