Case Study 4: Are you really working on the right problem?

A client was developing a new product for its customer, which was a large company.  The product contained a subassembly that was required to cycle at least 50,000,000 times.  The mechanism included a shaft that slid in and out of a bearing.  Several test units failed to meet the requirement.  The engineers focused on the lubrication between the shaft and bearing as the root cause of the problem.  Also, the subassembly supplier made recommendations about the materials to use for the shaft and bearing to solve the problem. They spent several months pursuing both approaches, without any success.

How did the materials engineering perspective help solve the problem?

The materials engineering perspective requires an examination of the materials comprising the shaft and bearing to understand how the materials degraded to the point that the shaft would not slide in the bearing.  Without this examination, any assigned root cause was just a guess.

Analysis of the shaft and bearings revealed several important pieces of information.  First, the bearings did not always meet the requirements for composition, microstructure, and the amount of oil that they were supposed to contain.  Second, the shaft materials did not always meet the requirements for hardness.  Third, the bearing surface texture varied from sample to sample.  Finally, foreign material was found on the shaft and bearings of failed samples.

The information about the bearing and shaft materials indicated that the supplier had poor control over the manufacturing of these components.  The information about the foreign material indicated that the cycling tests needed to be designed so that foreign material could not get into the space between the shaft and bearing

Busted Myths

The engineers found that intuition was not enough when trying to solve a problem with materials.  Once the focus was on understanding the materials involved the root cause of the problem quickly became clear.  The engineers also learned that suppliers cannot always be counted on for materials engineering support.  In this case the supplier was part of the problem.