Abstract:
The objectives of this thesis are to study the factors causing defects and to find means to improve the manufacturing process
and product quality in order to help reducing defects caused by scratches in the General Assembly process. This study is based
on problem solving and applying by Six Sigma Approach, as a guild line to solving problems and to develop the manufacturing
process. For this study, the researcher had good cooperation from General Motors (Thailand) Company Limited, which was used
as a case study for the research. The production line under study is a truck line in the General Assemble department which has
chronic problems of defects caused by scratches on the trucks. These problems must be taken care of in the end process.
This problem send effect to production line in first time quality index, which is called Non Value Added to products.
The goal of this research is 60 percent reduction of defects from 0.25 DPV to 0.12 DPV. The problem solving operation started
with the study of the manufacturing process in order to find key factors of the problems as well as carrying out measurement
system analysis until it was reasonably acceptable. After that, all factors expecting to cause the problem had been analyzed
using the statistical testing hypothesis. It was discovered that the major cause of the problem is the lack of personal protection
equipment, dust of metal collected in the protectors and length of the power bit. So after the improvement process found DPV
reduced to 0.12 that can save labor cost of about 3,259,370 baht per year. That can achieve to target.