PERFORMANCE IMPROVEMENT OF CONTINUOUS HOT-DIP GALVANIZING LINE (CGL) WORK ROLL SURFACE HARD CHROME

Abstract

Continuous Hot-Dip Galvanizing Line (CGL) is a supporting facility in automotive industry. This facility produces the steel sheets with mechanical specifications, surface flatness, surface roughness and other parameters which needed by the automotive industry. The company under study focused on defect reduction in CGL work roll surface hard chrome. The company received order for 1,386 unit between January 2019 and November 2021. During this term there were some defects of products as many as 196 units, or 14.14 % of total or in Defect per Million Opportunity (DPMO) is 28,283 unit. This is above the expectation which is 3.25% based on best practice in the industry. This study applied Six Sigma methodology. The method is well-known as DMAIC flow to identify faults in the work roll repair process, assess and establish their causes, and make recommendations for process changes to eliminate defects. Define phase covered the project charter creation for this process improvement project, starts with VOC (Voice of Customer), define CTQ (Critical to Quality), and process mapping. A control chart and a Pareto chart were applied to find the highest number faults which were the errors in chrome plating thickness. Defect rate and Capability Index were also computed to assess the status and the goals for improvement. To discover the most impacting factors, the Analyze phase examines the cause-and-effect diagram. The application of multi linear regression to analyze defect causes and generate improvement methods to reduce defect rates. The regression equation was identified significant factors to be utilized to adjust the repair thickness. The results showed that a reduction in DMPO to 9,756 units or an improvement of 65.51% in DPMO, 12.61% in Sigma level and 12.28% in capability index were found during validation. This has impacted to positive performance of company quality.