A computerized approach to calculate the nonconforming rate for product interference problems

It is very common that most product assemblies in industry require two mating parts where one must fit into the other. However, we may observe interference if the shaft does not fit within or over the shaft, or we may experience excessive clearance. In calculating the percentage of interference or excessive clearance, most industries usually assume normal distribution for quality characteristics of mating parts and use a distribution of their difference to analyze the interference or clearance. However, it has not been proved that the collected data matches the assumption of normality. Therefore, it is doubtful that the calculated nonconforming rate truly reflects the performance of the assembly process. This research focuses on the clearance and interference analysis for the non‐normal data of product assembly. Comparisons have also been made between actual nonconforming rate and the assumed normal percentage of nonconformance by overlooking their theoretical distributions of two mating parts. Finally, a computer program has been proposed to simplify tedious calculation process for estimating the nonconforming rate under non‐normal distribution.