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SPC for Welding: X‑bar/R Charts, Cp/Cpk, and Thermal Limits

A practical guide to SPC for welding: pick characteristics, set control limits, read X‑bar/R charts, and compute Cp/Cpk from live measurements and thermal proxies.

Published: November 12, 2025

Choosing characteristics that matter

Focus on features that move rejects and rework: bead width, penetration proxies, toe cooldown slope (t8/5), and travel speed. QMS Copilot reads these from inline sensors and updates charts automatically.

Reading X‑bar/R for weld stability

Operators need fast signals. The chart below shows subgroup means and ranges across time with centerlines and control limits.

X‑bar and R ChartsX‑bar / RX‑barR

Capability made simple

Compute Cp/Cpk on the same stream. Use rolling windows so the values reflect current reality, not last quarter’s data.

Cp/Cpk TrendCp/Cpk TrendCpk=1.0Cpk=1.33

Alerts and actions

When limits break, the system alerts operators and opens a nonconformity. With QMS Copilot, CAPA is ready with evidence attached.

Last updated: 2025-11-12