During clinical implant replacement procedure, recurring of damaged bone with artificial parts is done. The damaged joints will be replaced with metal implants which are manufactured by investment casting process. These complex shapes can be easily produced using investment casting process. The patterns required for investment casting process will be made up of metal, wood, wax, and plastic. The thermoplastic material is now used widely as a pattern for investment casting process. Such a pattern is developed using rapid prototyping (RP) method. The rapid prototyping method comprises of layer-by-layer preparation of component in a closed or open platform. The individual components of implant patterns will be prepared using rapid prototyping method and these parts then assembled as a tree for investment casting process. This chapter presents the experimental procedure of rapid manufacturing process for custom knee casting. For implant, casting material used is 316L stainless steel. Development of customized knee implant using investment casting has done in this study. To avoid defect in casting, casting simulations has performed virtually to have sound, quality castings. The modern uses of best in class added Additive manufacturing (AM) methods in metal casting innovation are also discussed. The casting method framework for multifaceted shapes has been illustrated. The RP design-based investment casting process is opted than the customary wax design process. By utilization of simulation program, the mold filling also solidification is guaranteed the nature of castings with more significant level of certainty and lessens expense of rejects. For this work, the CT scan data of knee implant is used to develop the customized implants in 316L stainless steel which can be used for knee replacement.