During the development cycle, the task that often takes longest time is production of prototype, which may itself be costly and also delay testing. If the prototype performance is not adequate, the design may have to be changed and the prototypes have to be reproduced until they meet the design specification and execute the task for which they are intended. In the present work, 3D printing technique was used for cost-effective, rapid shell casting of aluminium alloys. Efforts were made through experiments to study the feasibility of decreasing the shell wall thickness from the recommended one (12 mm) to 2 mm, in order to reduce the cost and time of production. Some important mechanical properties are also compared to verify the suitability of the castings. The results of study suggested that with decrease in shell wall thickness, there is hardly any effect on mechanical properties and microstructure of casting obtained; however, cost of production and production time are appreciably reduced.

Recent advances in the field of Computer-Aided Design (CAD) and Rapid Prototyping (RP) have given designers the tools to rapidly generate an initial prototype from a concept. There are currently several different RP technologies available, each with their own set of competencies and limitations. Three-Dimensional Printing (3DP) based on Massachusetts Institute of Technology (MIT) ink-jet technology under US patent No. 005340656 (Sachs et al., 1994) is an example of Solid Freeform Fabrication (SFF) or Layered Manufacturing (LM) of RP technology. Powdered materials are deposited in layers and selectively joined with binder from an ink-jet print head. Figure 1 shows the schematic of 3DP processes.

This 3DP technique based on layer-by-layer manufacturing is extending their fields of application far beyond the original idea of generating design iterations. These parts are used in the various stages of a product development cycle. Wohlers (1995) conducted a survey and found that around 23.4% of RP parts are used as visual aids, whereas 27.5% of them are used as master patterns for secondary manufacturing process and for direct tooling. In particular, layer-by-layer construction applied to the tool and die making, directly from virtual designs (from CAD or from animation modeling software), is defined as Rapid Tooling (RT). Manufacturers are increasingly looking towards RT, especially for short production runs which do not justify the investment required for conventional hard tooling (Ashley, 1997). Variety of manufacturing applications such as rapid pattern making and Rapid Tooling (RT) using the 3DP process directly or as core technology were presented (Dimitrov et al., 2006). For the purpose of classification, tooling is divided into direct or indirect tooling (Chua et al., 1999). In direct tooling, the tool or the die is created directly by the RP process. In the second method, which is used in the present research work, i.e., indirect tooling, only the master is created using the RP technology. From this master, a mold is made out of a material such as silicone rubber, epoxy resin, soft metal or ceramic. Most rapid tooling today is indirect: RP parts are used as patterns for making molds and dies. Patterns, cores and cavities for metal castings can be obtained through these Rapid Casting (RC) techniques (Song et al., 2001; Rooks, 2002; and Bernard et al., 2003). By using 3D printing, to produce the ceramic shells with integral cores directly from the CAD model, a number of disadvantages of the traditional process are avoided. Most significant is that the metal dies are typically expensive and time-consuming to produce, with lead times ranging from two to six months. For relatively small and complex parts, the benefits of additive manufacturing can be significant (Bak, 2003; and Ramos et al., 2003).

Mechanical Engineering Journal, Rapid Prototyping (RP), 3DP, Shell casting, Aluminium alloys, Microstructure, Mechanical properties.