An experimental investigation on dimensional stability of injected wax patterns of gas turbine blades

An experimental study on dimensional stability of simplified waxed models of gas turbine blade is presented. Gas turbine blades, made of a super alloy, have narrow dimensional and geometrical tolerances. Blades are manufactured by investment casting process consisting of wax injection, ceramic coating, wax removal, metal casting, and finishing. The dimensional accuracy of wax injection step introduces a great influence on the final blade dimension and thus on finishing process. The focus of this experimental work was on the injection stage, investigating the effects of processing parameters and blade geometrical features on the shrinkage of critical dimensions. To reduce the complexity of the analysis and mold manufacture, two designed models were extracted from the blade geometry. A mold was manufactured with two cavities (for two models). Injection temperature and holding time were chosen as variable processing parameters. The results indicated that the effect of blade curvature and non-uniform thickness are noticeably different. The effect of the holding time was found to be more dominant than that of the injection temperature.