Abstract:
This research aims to find the optimal mixing ratio of resin coated sand, which yields product properties that meet customer requirements and also has the minimal total cost of sand and resin. Previously, each formulae was mixed by trial and error since there was no clear mixing standard to find the proper mixing ratio. This leads to excessive time and cost of raw material. This research applied the Central Composite design (CCD) for finding the optimal mixing ratio. The independent factors were the proportions of Sand A, Sand B, Resin A, Resin B, and %Resin. The responses of interest were Bending Strength, Loss of Ignition, Thermal Expansion, Bend, Melting Point, Gas and total cost of sand and resin materials. After obtaining all experimental results, Stepwise Regression analysis with backward elimination technique was used to determine the relationship equation of independent factors and responses. Next, the optimization technique was applied to determine the optimal mixing ratio given the required property levels. After testing the new mixing ratio of 25 product formula. It was found that the six properties of these product formula were within the acceptable ranges. In addition, the total cost of sand and resin materials was reduced by 28.36% comparing with previous mixing ratio. The total cost of sand and resin materials of these 25 formula was reduced by 42,293,318 baht per year.