EFFECT OF PROCESS VARIABLES ON THE QUALITY OF CASTING IN INVESTMENT CASTING

Abstract

Investment casting is known for its ability to produce components of excellent surface finish, dimensional accuracy and complex shapes. The ceramic shell investment casting process has gained an important position in the family of precision casting techniques owing to the scientific advances in many of its aspects, such as binder solutions, refractory materials, pattern materials,. and in the manufacturing process. Yet, the process parameters behind the preparation of wax blends and ceramic slurry make the investment casting process laborious and troublesome. The dimensional changes between the pattern and its corresponding cast part occur as a result of thermal expansion, shrinkage of the pattern material (wax), mould material (shell), and solidifying alloy during processing. The wax blend composition plays an important role to minimize the expansion and shrinkage of pattern and the ceramic slurry composition plays an important role to improve and stabilize the ceramic slurry. In the proposed work, experiments were conducted with different types of waxes namely Paraffin wax, Bees wax, Montan wax and Carnauba wax, varying their proportion. Experiments were also conducted on the ceramic shell by varying the proportions of zircon flour, fused silica; colloidal silica as a binder and catalyst to form the stabilized slurry. The performances of different waxes were studied w.r.t. the shell formation. Using the data obtained from the experiments an attempt was made to find out the set of input parameters, which could offer a set of ideal properties of the wax blend and ceramic slurry. Taguchi method was used to optimize the process parameters. The orthogonal array which represents the matrix of number of parameters that were varied gives the number of tests to be conducted. Taguchi method has successfully suggested the set of input parameters which could offer the desired properties.