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From a Different Angle: A Perspective - Defects, P-F and the Rest of the Story

From a Different Angle: A Perspective - Defects, P-F and the Rest of the Story by Joel Levitt

From a Different Angle: A Perspective - Defects, P-F and the Rest of the Story

Joel Levitt

Think about all the initiator causes of failure that are not really related to maintenance. Initiator causes are those events, possibly microscopic, that initiate decay shown by the P-F curve. Examples of initiator causes might include heat, dirt, or overloading.

Figure 1 shows a P-F curve, with the arrow pointing to a potential failure that is precipitated by some initiator. This initiator can be microscopic, such as a piece of dirt, or macro, like a steel slab hitting the rollers off-center. Once the potential failure is realized or initiated, the march to destruction is inevitable. The only unknown is how long it will take. At this point, the only thing of interest is how soon the march to destruction can be detected.

Figure 1: Potential failure shown on a P-F curve. Copyright 2016-2018. NetexpressUSA Inc. d/b/a Reliabilityweb.com.

Most often, the cause of the initiator is one of the five big sources of defects that lead to breakdowns. According to Winston P. Ledet, a consultant and workshop instructor on proactive manufacturing and maintenance and coauthor of the book, Don’t Just Fix It, Improve It!, these defects are:

As you can see, 29 percent of the defects are due to maintenance causes and the rest are due to a small group of outside causes.

Because the sources are both inside of maintenance and, more commonly, outside of maintenance, it is correct to say:

The reason is simple: Since the source is outside of maintenance, then it is likely that the solution must also be outside of maintenance. No pure maintenance solution will address even a simple majority of the causes of reliability problems. While this is true, it is not the whole story.

While the cause of the defect is outside of maintenance, mitigation of the defect is certainly inside of maintenance. For example, if a hidden rock comes into a sawmill inside a log, the defect’s source is outside of maintenance, but the detection, mitigation and resolution is certainly within the scope of maintenance.

A multilayered defense is necessary. This approach is called defense in depth. If defects that are bad enough to disrupt reliability can come in from five sources, you must:

This ability can be a competitive advantage. For example, an East Coast manufacturer makes small stampings. The company is very good at doing this, but even with skill, it is difficult to make much money since the material cost is 70 percent of the cost of goods sold (COGS). The manufacturer also had problems when the steel coils purchased were not pristine. Defects in the raw material were the biggest problem. Gradually, the manufacturer adapted the stamping tooling to accommodate the most common defects (i.e., variance in thickness, flatness, slight rust, etc.). To add insult to injury, sources in China and Asia were opening up, so there was already pricing pressure.

The manufacturer realized those common defects could be turned into a competitive advantage. Since its tooling could work with a wide range of defects in the coils, the company started to intentionally buy defective coils. The tooling could make good parts from coils that were slightly rusty, warped, too narrow for others, or designated scrap by larger manufacturers. Since the manufacturer could work with secondary coils, it dropped its COGS by 50 percent. This allowed the company to both compete and make an excellent profit. Today, the manufacturer is selling a selection of its products in China to be incorporated into their products.