Thesis (M.Eng.)--Chulalongkorn University, 2007

The objectives of this research is to reduce the number of defects in the tire mould production and calculating the return on quality investment of the process improvement. Initially, the team study the production process, statistics and the cost calculation method. FMEA is used to investigate the failure modes. The failure modes with RPN above 150 are selected for further analysis. They are from 4 processes, machining M2 & M3 and turning T1& T2. Fishbone analysis revealed that most of the problem come from inadequate control system and unskill operator. Training are given and controll doccuments are introduced. The team also found that the drill and reamer used for maching M3 process is inappropriate, creating oversized hole with rough surface. The carbide drill and inserted reamer will be tested via DOE. From screening experiment (2k factorial), cutting speed (Vc) and feed rate per tooth (fz) is found significant. 3k factorial technique is then used to find the optimal cutting parameters to obtain diameter between 19.85-19.86mm. The calculated Vc and fz are 95mm/min and 0.1404mm/tooth respectively. 3k factorial technique is employed to find optimal reamer condition. The optimal cutting parameters are 110mm/min for Vc and 0.0611mm/tooth for fz respectively with target diameter of 20.01mm. The calculated composite desirability of the new drill and reamer parameters are 1. The ROQI is divided into 2 parts, the ROQI from the entire tire mould production process and ROQI from the change of the new drill and reamer. The over all ROQI on monthly basis is 12.54 times and the ROQI from new setting is 42.65 times.