Ck, which some people now refer to as Ca (Accuracy), represents how close a process output is to the target value. Using a target-shooting example: if someone fires six bullets and all land near the bullseye, the Ck value is good (meaning low), because the average result is close to the center of the specification — a direct hit.
Cp (short for Precision) is a measure of how tightly a process is centered and how consistently it produces results. Using a target-shooting analogy, if someone fires six bullets and they all hit the same tight spot, that means the process has high Cp. The tighter the grouping, the higher the Cp value.
Cpk is commonly used as an overall indicator of a factory’s manufacturing process capability. However, it can also be applied across different industries to measure the ability to meet a target. A popular analogy is how well you can hit the bullseye when shooting arrows at a target.
Of course, the higher the Cpk value, the better. But Cpk is actually made up of two components: Cp and Ck.
Many of you might already know what a fishbone diagram is. But do you know how to actually draw one? And what should you watch out for when creating one?
As the name suggests, the diagram looks like the skeleton of a fish—that’s where it gets its nickname. Its formal name is Cause-and-Effect Analysis Diagram, because it’s used to trace a problem (effect) back to its possible causes.
In the previous article, Workingbear mentioned a serious DOA (Dead on Arrival) customer complaint involving one of the company’s products. Most of the defective units had unresponsive keypads—specifically the 3, 6, and 9 buttons—and it was eventually traced back to oil contamination. At the time, the company formed a special task force to investigate the issue, and even sent engineers to the contract manufacturer’s factory to track down the root cause.
To be fair, the factory was quite cooperative and had already done some internal troubleshooting to rule out several possibilities.
