Statistical Process Control (SPC)

Statistical Process Control (SPC) is the logical capability of monitoring a manufacturing process by sampling key characteristics, plotting them on control charts, and reacting to statistically significant signals (out-of-control points, runs, trends) before the process produces nonconforming parts. SPC is the “voice of the process” complement to specification limits — distinguishing common-cause variation (in-control, leave alone) from special-cause variation (intervene).

What it covers

• Control charts — X-bar/R, X-bar/S, individuals/moving range, p, np, c, u charts.
• Process capability — Cp, Cpk, Pp, Ppk indices versus specification limits.
• Measurement Systems Analysis (MSA) — gauge R&R, bias, linearity, stability.
• Sampling plans and rational subgrouping.
• Linkage to FMEA control plans and CAPAs when out-of-control conditions trigger investigation.

Relationships (see sidebar)

• Supports Quality Management, Manufacturing Execution, and Supplier Quality Management.
• Pairs with FMEA (the control plan column linking each special characteristic to an SPC chart).
• Standardized via AIAG SPC and ISO 22514; common in MES and quality-management platforms.