Ensuring the reliability and reduction of quality control costs by minimizing process variability

This paper presents a method for planning the range of quality control while ensuring its reliability and minimizing costs. The method is dedicated to destructive inspection, in which the cost of performing the measurement is significant in relation to the cost of manufacturing a part or product. The methodology was divided into four main stages: (1) selection of the measurement system and definition of the inspection scope and sample size, (2) process control, (3) redefining the scope of control and (4) verification of control cost and reliability after sample size change. The article presents the results of applying the author's procedure to the process of evaluating seat belts in automotive industry. Belts are used in the process of controlling the final product, which is a seat belt anchor plate. This approach allowed to reduce the number of destroyed parts during control while maintaining the credibility of the decision based on the assessment. As a result of double-decreasing the sample size, the costs of seat belt quality control were reduced. Assuming an average of 40 seat belt deliveries per year, the material cost was reduced by 50%. Limiting the sample size to 15 pieces per delivery would reduce the cost of testing from by 45%. It was achieved maintaining the appropriate level of credibility of decisions made greater than 0.8.