ORIGINAL ARTICLE Optimal gating system design for investment casting of sterling silver by computer-assisted simulation N. Thammachot & P. Dulyapraphant & E. L. J. Bohez Received: 14 November 2009 / Accepted: 18 September 2012 / Published online: 29 September 2012 # Springer-Verlag London 2012 Abstract The first requirement of all casting processes is complete filling without any defects after solidification. However, casting defects often occur in casting process- es, especially incomplete filling. The causes of incom- plete filling are related to poor gating system, incorrect pouring, and molding temperature. A suitable shape and dimension of gating system will increase the melt flow while it is feeding into mold cavity by eliminating excessive pouring and molding temperature. The objec- tive of this study is to develop a new design of gating system for eliminating incomplete filling. The new shape and dimension of pouring cup, main sprue, and sprue base are proposed and investigated. The compu- tational flow model is solved with the aid of computer simulation. The targets of an optimum solution are increasing the efficiency of metal flow and reducing turbulence. The experiments are conducted to validate the simulation data. The results of this study will aid in the elimination of casting defects and increase the productivity. Keywords Computer simulation . Gating system . Investment casting . Jewelry casting . Sterling silver Abreviations and symbols A 1 Area of the sprue entrance A 2 Area at any other location in the sprue Z 1 Level of the pouring basin above the sprue entrance Z 2 Distance from top of the pouring basin to the loca- tion of A 2 Q Volume flow rate A Cross-sectional area of the stream V Velocity of fluid flow ϕ T Dissipation function L Latent heat f s Fraction solid ρ Density λ Thermal conductivity c p Specific heat capacity μ Dynamics viscosity f VOF function VOF Volume of fluid 1 Introduction Incomplete filling is one of the most important problems in the casting of jewelry products using the investment casting process. The percentage of casting defect in casting process of a typical jewelry company is shown in Fig. 1 (case study conduced by the first author). The highest percentage of casting defects is incomplete filling (cold shut and misrun) which is 53.36 % from the grand total of 100 %. The total number of products in year 2006 – 2008 was about 11,275,000 pieces. The causes of incomplete filling include pouring and molding temperature, velocity of melt flow into N. Thammachot (*) : E. L. J. Bohez School of Engineering and Technology, Design and Manufacturing Engineering, Asian Institute of Technology, GPO Box 4, Klong Luang, Pathumthani 12120, Thailand e-mail: st102869@ait.ac.th E. L. J. Bohez e-mail: bohez@ait.ac.th URL: www.ait.ac.th P. Dulyapraphant National Metal and Materials Technology Center (MTEC), 114, Paholyothin Rd., Klong 1, Klong Luang, Pathumthani 12120, Thailand e-mail: pongsakd@mtec.or.th URL: www.mtec.or.th Int J Adv Manuf Technol (2013) 67:797–810 DOI 10.1007/s00170-012-4523-3