# Control charts for WPC profile dimensions

Canonical: https://woodplasticcomposite.net/guides/control-charts-for-wpc-profile-dimensions/
Language: en
Updated: 2026-10-15
Version: 1
Review: AI-assisted English editorial draft. Human technical review has not been recorded.

## Summary

A control chart can help distinguish expected process variation from signals requiring investigation. It is not the same thing as a product tolerance band.

## Technical context

Control limits describe behaviour estimated from a suitable process baseline; specification limits describe acceptance requirements. Confusing them can hide an unstable process or cause unnecessary adjustments to normal variation.

https://woodplasticcomposite.net/guides/control-charts-for-wpc-profile-dimensions/#technical-context

## What to measure and document

Choose the chart and sampling arrangement with competent statistical input. Record changes in tooling, material and operating conditions. Investigate signals using the production history rather than changing machine settings reflexively after every high or low reading.

https://woodplasticcomposite.net/guides/control-charts-for-wpc-profile-dimensions/#verification-plan

## Implications for development and specification

Use the chart as part of a response plan that includes product identification and disposition. A stable process can still fail the specification, while an apparently acceptable sample can come from an unstable process. Both process behaviour and product conformity matter.

https://woodplasticcomposite.net/guides/control-charts-for-wpc-profile-dimensions/#practical-decision

## Related reading and evidence limits

General engineering-statistics guidance; not a WPC product standard. Use the linked work as related reading. The practical checks above are editorial recommendations, not reported test results or a substitute for product qualification.

https://woodplasticcomposite.net/guides/control-charts-for-wpc-profile-dimensions/#reading-scope

## Key points

Control limits describe behaviour estimated from a suitable process baseline; specification limits describe acceptance requirements.
Choose the chart and sampling arrangement with competent statistical input.
Use the chart as part of a response plan that includes product identification and disposition.

## Comparison

Review step | Evidence to retain
Material and geometry | Exact specimen or product identity
Verification | Method, conditions and individual observations
Decision | Approved scope and documented limitations

## What evidence is needed for control charts for WPC profile dimensions?

Choose the chart and sampling arrangement with competent statistical input. Record changes in tooling, material and operating conditions. Investigate signals using the production history rather than changing machine settings reflexively after every high or low reading.

## Sources

1. NIST engineering statistics handbook — https://www.itl.nist.gov/div898/handbook/