Design for Reliability

Chapter 8

Six Sigma Approach to Requirements Development

Samuel Keene

Early Experiences with Design OF Experiments

The present author was fortunate to have a positive defining reliability experience in the 1970s related to design of experiments (DOE) as the foundation for six sigma and design for six sigma (DFSS) processes and tools. I was involved with a team designing one of the first laser scanners. The active element was a HeNe laser, the type with a red beam that we see regularly in foodstore checkout lanes. Early HeNe lasers were chaotic in their parametric performance and their demonstrated lifetimes. Up to that time, these lasers had been used only under laboratory conditions and at construction sites; there had been no emphasis on high-reliability lasers. The industrial application of a photoscanner demanded higher reliability.

High reliability could only be achieved with testing and design changes, which would prove to be a great burden to the program. The test samples had a long delivery time and were expensive, about $5000 apiece. Their performance, sample to sample, varied widely. There were differences in their starting voltage, run current, and important from a reliability standpoint, in their lifetimes. These qualities are labeled key process output variables (KPOVs) in the six sigma vernacular. The life goal was 5000 hours before replacement. The laser test samples that were exercised in initial tests were exhibiting 50 hours on average, with maximum lifetimes ...