Reduction of Cost of Quality by Using Robust Design: A Case Study in Automobile Industry

Keywords: robust design, cost of quality, parameter design, control factors, noise factors, signal to noise ratio, taguchi quality loss function and tolerance limit.The aim of a parameter design experiment is to identify and design the settings of the process parameters that optimize the chosen quality characteristic and are least sensitive to noise (uncontrollable) factors. Cost of Quality is evaluated in terms of dimensional tolerances. Robust design is implemented in a gear hobbing process. The optimum setting of parameter is to be obtained in presence of uncontrollable noise factors. The target value for Root Diameter of a spur gear used in shaft in an automobile is 28.00 mm. The dimensional tolerance for of a spur gear 27.90-28.10 mm. It was found that these were arbitrarily accepted as the tolerance limit and any component within this tolerance limit would be accepted as good quality. This concept is a traditional design concept where every part within a range is accepted as of good quality. Taguchi parameter design tries to find an optimum value so that component meets the desired specification or in other words meets the target value. Experimental analysis is performed at different levels of control factors and noise factors. Optimum value of control factors is found by studying Signal to Noise ratio (nominal the best). Again the tolerance ranges for Root Diameter were calculated and it was effectively found that the tolerance range was found as 29. 95-28.05 mm. The tolerance was reduced from 0.2 mm to 0.1 mm which led to overall reduction in cost of quality of a spur gear