X-bar R Control Chart
Upload or paste process data to automatically generate control charts with out-of-control points highlighted
Requires ≥10 data points
Enter process data and click "Generate Chart"
X-bar R control chart will appear here
In mass production, 5 parts are sampled from a CNC machine every hour for outer-diameter measurement. The X̄-R chart simultaneously monitors process mean stability (X̄ chart) and process variation (R chart); any out-of-control signal immediately triggers a line-stop investigation. Unlike simple specification inspection, control charts detect drift trends before the process starts producing out-of-spec parts — a core preventive quality control tool and a requirement of ISO 9001 and IATF 16949.
25 subgroups (5 pieces each), outer diameter (mm): X̄_bar = 50.02, R_bar = 0.18 A2 (n=5) = 0.577, D3 = 0, D4 = 2.114 X̄ chart control limits: UCL_X̄ = 50.02 + 0.577 × 0.18 = 50.12 LCL_X̄ = 50.02 - 0.577 × 0.18 = 49.92 R chart control limits: UCL_R = 2.114 × 0.18 = 0.38 LCL_R = 0 → Subgroup 18: X̄ = 50.14 exceeds UCL, triggering a line-stop investigation
FAQ
Related Tools
I-MR Control Chart
When only one measurement is available per time point (destructive testing or slow production), use the I-MR chart instead of X̄-R to monitor process stability.
Open toolProcess Capability Index
Once the control chart confirms process stability, calculate CPK to quantify whether process capability meets customer specs (typically CPK ≥ 1.33).
Open toolCUSUM Control Chart
Shewhart charts are sensitive to large shifts; CUSUM detects small shifts (0.5σ–1.5σ) more effectively. The two complement each other for different detection needs.
Open tool