Defects Reduction in the process of automotive injection plastic part by using Design of Experiment (DOE)

Abstract

The objective of this research is to reduce the amount of Injection Molding defects. Statistical principles are applied to analyze causal factors that affect product’s quality. In addition, before beginning the research, the problems about large, non-standard shape defects which affected production costs are the main problem for the factory. The research is conducted by using Cause and Effect Diagram to analyze the causes to determine the most 3 critical factors for further analysis. The FMEA is consequently used to identify the first three importance factors; holding pressure, mold temperature, and cycle time. Those factors are used in designing the experiment with 2^k Factorial Design to test them if affect this problem significantly. Finally, the factors considered are adjusted to decrease the defects. The result from the research reveals that those factors affect to the problem by both main effect and interaction among the factors. After adjusting the factors, the amount of defects has reduced from 39.05 percent to 2.78 percent follow objective target 50% refer company policy. It can be explained when mold temperature is higher, it allows the product to generate more crystal structure opportunity to reducing size. In terms of Cycle Time, the shorter cycle time is forced the product to cool down outside the mold and promote more shrinkage. Lastly, low Holding Pressure would lower the product’s mass. The experiment showed that Mold temperature is 45 degree Celsius, Cycle time is 32 second and holding pressure is 10 Mpa would be the most appropriate for this case.