Özet:

The purpose of this study is to apply six sigma in a firm producing valve within the framework of Total Quality Management (TQM) approach. Fiat, an important client of the firm, made some modifications on the valves produced for it and therefore, the machines on which the valves are produced became incompetent. To overcome this deficiency, a six sigma project was conducted. First, the problems about the valves were defined. These were circularity and deflection problems. The root causes of these problems were discovered with the help of fishbone diagrams. The values having optimum results were determined by making some modifications on the parameters entered in the machines during the production phase. These parameters are the amount of cutting depth (the amount of swarf that the machine puts away at once while processing the valve) and the process period. The circularity of valves produced as a result of low and normal cutting depth tests were measured. T-test was applied for the data and it was seen that the two data sets were different from each other. Furthermore, it was realized that better results were obtained with low amount of cutting depth by making the process capability analysis for the optimum amount of cutting depth. Then, three trials were conducted for the process period. The T-Tests were applied to these data and it was seen that they were different. The process capability analysis revealed that the optimum duration was 10 seconds for the solution of circularity problem. A regression analysis was done by developing a model for the deflection problem and it was shown that deflection problem was not sourced from bonnet, body and shank deflection. It was understood that the deflection problem was due to the pens mechanism that holds the valve while processing it and the grinding wheel that performs the process. The grinding wheel was changed after discussing with the supplier and process became capable by preferring pens that holds the valve from one point instead of two. At the end, a successful six sigma project was applied via raising the sigma levels from 1,68 and 1,69 for the problematic processes to the levels 4,64 and 4,89. Via interviews with the black belt, the viewpoints of the firm on six sigma were presented. The firm defined six sigma as a quality tool with very powerful statistical aspect under the umbrella of TQM. Finally, the following formulation was proposed in the firm: “Six Sigma + Other Quality Management Tools = TQM”.

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