Alloy Shrinkage Factors for the Investment Casting of 17-4PH Stainless Steel Parts
- PDF / 1,193,758 Bytes
- 14 Pages / 593.972 x 792 pts Page_size
- 99 Downloads / 257 Views
ODUCTION
FOR the investment casting process, the tooling depends on dimensional changes associated with the wax pattern, ceramic molds, and cast alloys. The nominal casting dimensions can be achieved, provided that the die tools were dimensioned with an appropriate degree of accuracy. As a step toward predicting tooling dimensions, it was showed that, for the investment casting of aluminum alloys, alloy shrinkage factors were predicted with a high degree of accuracy when the deformation of the mold is considered.[1] Wax patterns are made by injecting wax into metal dies; ceramic shells are made by the successive application of ceramic coatings over the wax patterns; and the alloys are cast into the dewaxed shell molds. The dimensional changes associated with wax, shell mold, or alloy are referred to as wax, shell mold, or alloy shrinkage factors (or tooling allowances), respectively. The usual practice for estimating the dimensions of the die tools is to adjust the nominal casting dimensions with the shrinkage factors. Critical properties of the alloy materials, which have to be considered for calculating casting dimensions, were reviewed in Reference 2, in which it was concluded that solidification, heat transfer, stress state, and the ensuing deformation behavior of the metal in the ADRIAN S. SABAU and WALLACE D. PORTER, Research Staff Members, are with the Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 378316083. Contact e-mail: [email protected] Manuscript submitted October 24, 2007. Article published online February 8, 2008. METALLURGICAL AND MATERIALS TRANSACTIONS B
semisolid and solid state must be considered in order to predict the final dimensions in the investment casting process. For permanent mold castings, Bellet et al.[3] found that the combined effect of thermoelastic, plastic, and creep-induced strain-stress fields must be considered in order to predict the final shape. The evolution of the state of stress during casting solidification has been a topic of many studies.[4–6] Sabau[1] showed that, for the investment casting of aluminum alloys, the deformation of the mold must be considered in order to predict the final dimensions of investment casting parts. The main focus of this study is to predict the alloy tooling allowances based on a combined analysis of heat transfer and deformation phenomena for 17-4PH stainless steel parts. The numerical simulations need to include the solidification and subsequent cooling to temperatures close to room temperature. Although 17-4PH is a common material, the material properties for this alloy were not readily available, since the demand for the dimensional predictions of complex parts has only recently risen. First, the experimental data on material properties were reviewed. The CompuTherm database (CompuTherm, LLC, Madison, WI)[7] and methodologies described in Reference 8 were used to obtain material properties, especially at high temperatures. Material properties that were computed using ProCAST* were *ProCAST is a trademark of
Data Loading...
