A methodology to reduce the counter gear subassembly reworks

The counter gear subassembly is an integral part of an actuator. The actuators are used to regulate the functions of the control valves. A company manufacturing actuators is facing the severe problem of counter gear subassembly reworks. The past data showed that around 58% of the counter gear assemblies are reworked monthly. Hence this study is undertaken to solve to the counter gear subassembly rework problem. The discussions with technical and design experts revealed that four critical dimensions are majorly causing the rework,namely gear 8 teeth thickness (x inf 1 /inf ),sleeve with chamfered gear length (x inf 2 /inf ),gear with chamfer (x inf 3 /inf ) and gear 8 teeth and drive milling depth (x inf 4 /inf ). Hence it is decided to study the effect of the aforementioned factors using design of experiments. Two levels are chosen for each of the four factors. Two interactions namely x inf 1 /inf x inf 2 /inf and x inf 3 /inf x inf 4 /inf are also included in the study. For each treatment combination,twenty counter gears are assembled and the number of assemblies reworked is counted. Since the response variable is binary,a model is developed for proportion of reworks using generalized linear model approach with response variable distribution as binomial and link function as logit function. The optimum combination of factor levels which would reduce the percentage of the reworks below 10% is identified. The results are validated by assembling another 50 counter gears with optimum factor level combination. The study resulted in reducing the rework from 58 % to 8%. The study also demonstrated a methodology to develop designs with minimum number experiments by augmenting the traditional fractional factorial designs with additional runs. This will help in separating out the effects of confounded interactions in traditional fractional factorial designs. The study also demonstrated an approach for analysing the design of experiments with binary response variable. © School of Engineering,Taylor’s University.