In the present study, polyurethane replicas (to be used as pattern) were prepared by Silicon Molding (SM) process. The prototype with three different types of materials (polyurethane) was prepared under three different conditions of de-mold time, de-mold temperature and mixing ratio (hardener:softener). Relationship between these input and output parameters (dimensional accuracy, surface roughness and micro hardness) was deduced by using Taguchi L9 Orthogonal Array (OA) for industrial applications. The results of study suggest that polyurethane replicas produced by SM are acceptable as per ISO UNI EN 20286-i (1995) and DIN 16901 standards. Further, the type of material is a significant factor contributing dimensional accuracy and micro hardness to SM process. For surface roughness, mixing ratio is the most significant factor.

Silicon Molding (SM) is widely used in industry to obtain plastic functional parts (Singh and Singh, 2010). It is one of the simplest and oldest techniques, where a Rapid Prototyping (RP) positive pattern is suspended in a vat of liquid silicon or rubber (Levy et al., 2007). Rubber molds, partially due to their inherent low stiffness characteristics, only allow the production of limited number of functional parts with expectable quality control (Hopkinson and Phill, 2001). Depending on the geometry and dimensions of the part, the resulting rubber mold can be used to cast up to 20-30 polyurethane replicas of the original RP part. If a large number of parts are to be obtained, the choice is normally based on the RP technique by manufacturing stiffer material molds (Kruf et al., 2006). It is a soft tooling process, because of the flexibility of the rubber. SM is a copying technique characterized by the use of a vacuum during the processes of mold fabrication and the casting of parts (Lan, 2009). Typical silicon rubber is usually used for making the mold which can only support castings in small batches before breaking down (Dunne et al., 2004; and Denoual et al., 2006). Silicon rubber molds can be fabricated directly from the master pattern, unlike most existing molding methods that require multiple steps of producing the mold. Fine geometrical details of the master pattern can be faithfully reproduced in the mold cavities. This is critical where the production of small parts is concerned. There are no restrictions pertaining to the design, material and fabrication of the master patterns (used to make the molds for SM process). The master patterns can thus be fabricated using the most cost-effective method and further used for generating polyurethane replicas. Silicon rubber possesses high chemical resistance and low interfacial energy (Cheng and Jia-Hung, 2008). This means that a wide range of resins, including wax, plastic and metals can be cast without any worry of possible reaction with the surface of the silicon rubber mold. SM allows the possibility of harnessing the potential of silicon rubber molds in the batch production of functional prototypes, uses cheaper tools and materials, and is simpler than conventional process (Singh, 2011).

Mechanical Engineering Journal, Silicon molding, Surface roughness, Micro hardness, Dimensional accuracy.