Question

In Statistical Process Control (SPC), what does a detected process drift signify regarding product quality?

Accepted Answer

In Statistical Process Control, a detected process drift signifies that the manufacturing process is shifting away from its established target or mean over a period of time. This drift indicates that the process is no longer operating under stable conditions, meaning it is losing its state of statistical control. When a process drifts, the likelihood of producing defective items increases because the output is gradually moving toward the specification limits, which are the boundaries defining acceptable product quality. If the drift continues, the product will eventually fall outside these limits, resulting in non-conforming items that fail to meet quality requirements. For example, if a machine cutting metal parts gradually wears down, the thickness of the parts will slowly increase; detecting this drift allows an operator to recalibrate the machine before any parts are produced that exceed the maximum allowed thickness. Consequently, a detected drift serves as a critical early warning sign that allows for corrective action to be taken to restore the process to its intended state before actual product failures occur.

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In Statistical Process Control (SPC), what does a detected process drift signify regarding product quality?