Dip Degreasing Stage Improvement in Car Body Pretreatment Process by Six Sigma

Abstract

An automobile company in this research faced the consistency problem from the chemical concentration in degreasing bath which was one of the stages in the pretreatment process. The problem came from the proportion of total alkaline (T.Al) lower than the lower control limit (LCL) which was set at 18.2 points during February – May 2020. This resulted in the low values of Cp and Cpk, i.e. 0.83 and 0.51, respectively. To remedy the problem, Six Sigma (DMAIC) was applied to improve the process stability. The cause and effect matrix was used to analyse the potential causes of problems and prioritise the causes to solve. It was found that four (causes) factors were solved by auto titration and feeding controller installation to reduce variance and increase stability. Another one factor, quality of water, was improved by adding a check item to monitor and collect data during the initial implementation stage. The result after improvement showed that Cp and Cpk were increased to 1.82 and 1.52 in August 2020, respectively.