Porosity Control in Copper Rotor Die Castings

This paper reports on the results of an investigation to minimize and control the distribution of porosity in edge-gated copper rotor die castings. A Flow 3-D computer modeling exercise was used to simulate shot profiles that result in formation of large pores in the end rings, as well as to predict improved profiles that will reduce or eliminate the residual porosity. These model results were then tested by die casting a series of copper rotors using an existing edge-gated rotor die set on a Buhler 750-ton real time shot controlled die casting machine. Shot profiles are shown to be very instrumental in controlling porosity. Profiles designed to pre-fill a portion of the gate end ring at the slow shot speed prior to accelerating to the fast velocity to fill the conductor bars and ejector end ring are shown to be very effective in minimizing and controlling porosity and to achieve a fairly uniform distribution of small pores present largely in the end rings. Thermal management of the entire system is also important to casting quality including metal superheat, and shot sleeve and die temperatures.