Defect reduction in alloy casting industry

Abstract

The objective of this research is to reduce the defect rate in aluminum alloy casting process. The selected product is chair's leg of a garden set, which has the most production volume in the case study company. There are three defect types that mostly occur in the casting process, which are Metallic Projection, Cavities, and Defective Surface. These defect types cause rework costs for the case study company. The research was started from defining potential factors that might be the causes of three defect types by using brainstorming and research. There are six potential factors that found. The six potential factors are pouring height, number of gates, snow powder quantity, solidification time, aluminum combination, and gate size. These six potential factors were tested using DOE techniques, where the three types of defects were used as three responses. Then, ANOVA was used to test for significant factors. The result shows that the effects of some factors are not consistent between some responses. Thus, the total cost of rework was then used as the decision criteria for factor level selection. The chosen levels are pouring height at 10 centimeters, 1 number of gate, 10 grams of snow powder, 10 minutes for solidification time, aluminum combination of 18 bars of solid type and 2 bars of resilient type, and gate at size 2x7 centimeters. The findings are confirmed by follow-up runs. After improving the process, the production time for a garden set has reduced from 6 hours and 1 minute to 5 hours and 40 minutes, or it reduces by 6% as a result of the reduction of rework time. If calculate it in term of products that the company can gain after implementing this new setting. The company can actually produce the products 26.43 extra garden sets from the original setting and gain the income by about 330,313 baht. However, the new setting only applies to the chair's legs. If this experiment expands to the rest of the chair parts, the income will likely increase.