Basics of Six Sigma- Statistical Process Control

A: Charting with a noisy gage hides real shifts and triggers false alarms, wasting hours and confidence. Proving the measurement system works keeps the signals tied to the process, not the tool.

A: Letting a trend run ends with parts drifting out of tolerance mid-shift and a scramble to contain product. Trend rules exist to catch predictable physical changes early, before the limits are crossed.

A: Poor subgrouping smears signals until a real shift looks like background noise, delaying action. Rational subgroups mirror how the process actually changes, so assignable causes show up fast.

A: Chasing frequency or limits wastes days while bad parts keep shipping. Mismatched definitions between SPC and inspection are common and fixing that alignment often resolves the conflict immediately.

A: Each unnecessary tweak pushes the process around until scrap piles up and tools wear early. Recognizing tampering keeps hands off a stable process and preserves the capability you already paid for.

A: Running the wrong chart breaks the agreed reaction plan and can invalidate audits, costing schedule later. Aligning to the approved control plan keeps decisions defensible and traceable.

A: Skipping monitoring invites silent drift until failures hit the customer and trigger recalls. Continuous checks catch physical changes early, when correction is cheap and contained.

A: Chasing false alarms burns labor and trust in SPC. Matching chart type and sample size to the defect level avoids mathematical noise being mistaken for real process trouble.

A: Recalculating too early bakes instability into the chart and masks problems during ramp-up. Waiting for stability after an approved change keeps SPC sensitive to real issues again.