MINIMIZATION OF THERMAL CYCLING

6.6 THERMAL CYCLING EFFECTS WITH POWDER LUBRICANTS 107 Vacuum Line Vacuum Valve AirPowder Feed Line Nozzle Figure 6.4 Shot sleeve and tool design for use with closed die powder lubricant application. powder feed nozzle, as shown in Figure 6.4. The same system used in vacuum die casting can be utilized with powder lubricant application, although vacuum valve placement may not be com- mon. Figure 6.5 is an illustration of the powder lubricant casting cycle. Initially, the plunger is positioned in the shot sleeve a such that the pour hole is closed. A vacuum is applied to the closed die cavity while a controlled quantity of powder lubricant is metered b into the shot sleeve. The vacuum pulls the lubricant into the die cavity c, creating a thin layer of lubricant on the surface. The plunger is retracted d opening the pour hole. Liquid metal is metered into the shot sleeve e and then injected f through a runner system into a die cavity g under high pressure. High pressures are maintained on the alloy during solidification. After complete solidification, the die opens h and the component is ejected. Although powder die lubricants are commercially available, their use is not widespread. Some companies have reported ex- tended die life, shorter cycle times, and improved plant cleanli- ness. The increase in productivity is attributed to the elimination of spray automation. 108 THERMAL BALANCING AND POWDER DIE LUBRICANT PROCESSES a b c d e f g h Figure 6.5 Processing cycle for closed die powder lubricant application.

6.7 APPLYING THERMAL MANAGEMENT METHODS

IN REAL WORLD APPLICATIONS As with all high integrity die casting processes, thermal balancing of dies and powder lubricant processes require the commitment of additional resources in comparison to conventional die casting. As such, strict thermal management and balancing of dies are not required for all applications. For cases in which component sur- face finish and extended die life are a necessity, thermal balancing and powder lubricant processing offer opportunities for improve- ment. REFERENCES 109 REFERENCES 1. Vinarcik, E., ‘‘Finite Element Analysis of Process Data Curves for Statistical Process Control,’’ SAE Paper Number 970081, Society of Automotive En- gineers, Warrendale, PA, 1997. 2. Roshan, H., V. Sastri, and R. Agarwal, ‘‘Die Temperature Control in Pressure Die Casting,’’ AFS Transactions, American Foundrymen’s Society, Des Plaines, IL, 1991, p. 493.