Effect of cavity pre-fill and geometry on flow patterns and air entrapment in the die cavity in cold chamber die casting

In die casting, location, size and total volume of gas porosity are influenced by the method chosen to fill the cavity with molten alloy. In industry, one common approach in transition regime of injection is the cavity pre-fill approach. Cavity pre-fill means that the cavity is partially filled with molten alloy using slow shot velocity before fast shot starts.; However, the effects of cavity geometry and injection parameters for machine set points associated with cavity pre-fill to obtain maximum quality castings are not known.; In this research, using computer modeling, flow patterns in the die cavity were visualized when cavity pre-fill was employed. The computer flow models were evaluated by water analog test results. Also, a method to measure the amount of air entrapment in die cavities using computer flow model was developed.; Using the computer flow models and the developed method to estimate the amount of air entrapment, a designed computer experiment was conducted to evaluate the significance of the selected parameters associated with cavity pre-fill influencing the amount of entrapped air in die cavities. The parameters were cavity pre-fill percentage, transition time from slow to fast shot, cavity pre-fill velocity, the ratio of gate thickness and width to total casting thickness and width, gate angle, and complexity of cavity geometry. As a result, important parameters were identified. A quadratic polynomial regression model to predict the amount of air entrapment was also developed. Using regression model, optimum injection parameters were assessed.; The lateral expansion was a major beneficial effect of cavity pre-fill, which helps reduce air entrapment in the die cavity. Inappropriate combinations of parameters employing cavity pre-fill caused more amount of air entrapment in the die cavity. Thus, both injection and geometry factors should be considered concurrently when optimum values of injection parameters for the cavity pre-fill approach are determined to minimize the amount of air entrapment in the die cavity.