A review of rapid prototyping integrated investment casting processes

Investment casting has been used to manufacture weapons, jewellery and investment casting during the ancient civilization. Today, its applications include jewellery/art castings, turbine blades and many more industrial/scientific components. The present paper reviews various investigations made by researchers in different stages of investment casting and highlights their importance. The paper initially highlights the investigations made on pattern wax properties, effects of blending, additives and fillers. Different ways through which pattern properties (like surface finish, dimensional accuracy, etc.) could be enhanced by properly controlling the injection processing parameters are thoroughly discussed. The paper also looks into the investigations made to enhance the strength, surface finish, etc. of ceramic shell for ferrous alloys/non-ferrous alloys as well as superalloys in investment casting. Investigations made on incorporation of nylon fibers and polymer additions confirm that a ceramic shell reinforced with nylon fibers attains additional permeability compared to the one with polymer additions.

Different investigations carried out on autoclave dewaxing and microwave dewaxing conclude that the wax properties are less altered with microwave dewaxing when compared to an autoclave dewaxing. Some recent investigations carried out on pouring and post-treatment operations are also discussed in the paper. The advent and emergence of rapid prototyping in shell mold casting are broadly exposed in the subsequent sections of the paper. Various aspects of rapid prototyping like rapid investment casting, rapid freeze prototyping, etc., along with their advantages are projected. The emerging areas of applications of rapid prototyping like dentistry, etc., are duly discussed.

The casting of titanium based alloys presents considerable problems, including the extensive interactions that occur between the metal and refractory. In this work, CaO stabilised zirconia was used as a primary coat material on the investment casting mould. The reaction between the zirconia face-coat and a Ti-46Al-8Nb-1B alloy was evaluated at three mould pre-heating temperatures: 500°C, 1000°C and 1200 °C. The effect of casting dimensions on interaction was also included in this work and the computer simulation of metal cooling profiles was carried out to assist the analysis. Higher mould pre-heat temperature and larger casting dimensions enhanced the interaction between the shell and the TiAl alloy associated with longer metal solidification time. During the high temperature casting process, not only were O and Zr observed penetrating into the metal from the decomposition of the face-coat materials, but also Si which had penetrated from the backup coat was found to have interacted with the metal.

Investment casting is competitive with all other casting processes where the size of the product is within a mutually castable range. Though investment casting is used to produce metal parts of any intricate shapes with excellent surface finish, it suffers from long lead time and high tooling costs, which makes it uneconomical for the production of either single casting, or small and medium production units. These problems could be overcome by the applications of rapid prototyping and rapid tooling technologies for low-volume investment casting production runs. The present article analyzes different classifications of rapid prototyping techniques and it reviews various investigations made on the usability of rapid prototyping- and rapid tooling-integrated investment casting process, with their advantages and limitations. The emerging areas of applications of rapid prototyping like dentistry, jewelry, surgical implants, turbine blades, etc., are accordingly discussed. Further, an elaborate discussion is made on the application of newer technologies for directly developing ceramic shells. This article also emphasizes on various future scopes possible in rapid prototyping-integrated investment casting process.