Spending too much (time or money) on part disposition? Start with an analysis of your measurement system. Even a marginal measurement system could contribute up to 30% of the variation seen in your control chart. Reducing the measurement error to 10% could improve your capability index from a rather poor 1.0 to a more respectable 1.2 (for example). When processes have marginal capability, and measurement error is significant, you will scrap good parts and ship bad parts, even with 100% inspection.
In daily operations, we regularly use our measurement system to detect and isolate output unacceptable to our customers. If we are serious about quality, we recognize Deming’s argument that only processes in statistical control are predictable; otherwise, we are often forced into 100% inspection of the process to ensure output meets requirements. The statistical control of the process forms the basis of process capability analysis. (See also: Is your Process Performing, Quality Magazine; June 27, 2011).