Process Control in Die Filling and Die Design

Abstract

Until recently, much of the SSM technology was highly proprietary and unknown to the general casting world. In the last several years, however, sufficient information has become available to make it possible to identify a number of alternative technical solutions that have been implemented around the world for the commercial production of high quality parts. Of particular note, it is now clear that real-time controlled machines are not an absolute pre-requisite for the production of safety critical or other high quality parts. Many parts are being produced in high volume and with excellent results on standard three-phase injection machines ((a) pre-set injection velocity, (b) pre-set ramp and (c) pre-set consolidation time under pressure before final ejection), as indeed were the very first semisolid die castings produced in the MIT laboratories. Rather, the key ingredients of a successful SSM system approach are: A reliable source of consistent quality raw material An appropriate delivery system for semisolid material to the casting machine A diaphragm or alternative approach to strip oxides from the slug’s surface or delivery system and eliminate or minimise the entrapment of oxides within the formed parts (see Figure 11.1) A powerful, repeatable, injection system capable of generating sufficient static pressure to feed solidification shrinkage throughout the freezing cycle Appropriate processes and controls to optimise the heat-treatability of the formed parts Coupled with intelligent die design to facilitate both turbulent-free filling and adequate feeding of shrinkage, these features have a proven record of producing high quality parts over long time periods.