About 10% of the time, an aircraft part would fail to meet the quality specifications agreed upon with the customer over the weight of the product. This created 15-30 minutes of paperwork for the support engineer to write a waiver to the customer, stating that it still performs adequately. This problem had been going on for many years with no issues expressed by the customer for any of the waived products. However, in the past 2 years, there were 100 waivers written, creating 25-50 hours of labor to the company, along with time wasted for the customer to review and approve the waiver.
A Six Sigma project was launched to understand why the waivers were needed. A capability analysis was performed (Cpk = 0.31), showing the weight was excessively low and below the optimum target weight. This confirmed why a certain % of product would fail to meet specifications.
To understand the sources of the variation, and why the process was offset on the low end of the specification, a series of designed experiments were performed. The DOE selected factors that the team thought were impacting the weight, but no significant factors could be identified during the analysis. Additional analysis was proposed, but because the product was older, there was no interest in investing more time and effort into experiments.
Therfore, the team proposed a permanent change to the specifications that reflected the last few years of actual performance, which was working well for the customer.
As a result of the approval from the customer on the new specifications, the weight was now centered between the specifications (Cpk = 1.1).
Since the change, there were no additional waivers written on this product, saving approximately $5000 per year in internal labor costs.
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