Key facts
- Purpose: confirm product meets drawings, specifications and customer requirements, and stop defects leaving the plant.
- Where it happens: incoming materials, in the process and at final inspection.
- Typical inputs: a control plan, inspection criteria, gauges and test equipment.
- Typical outputs: accept, reject or rework decisions, plus data on defects and trends.
What are the main quality control methods in manufacturing?
| Method | What it does | Example |
|---|---|---|
| Incoming inspection | Checks materials and components when they arrive | Measuring a sample from each supplier batch |
| In-process inspection | Checks product while it is being made | Operator checks a dimension every hour |
| First article inspection | Verifies the first part after setup or changeover | Full check before a run is released |
| Final inspection and testing | Verifies the finished product | Functional test and visual check before dispatch |
| Statistical process control | Tracks measurements on a control chart to spot drift | Plotting bore diameter and reacting to a trend |
| Sampling | Inspects a defined sample instead of every unit | Checking 5 units from each batch of 200 |
How does a quality control process work?
- Define the requirement. Turn the specification into clear pass and fail criteria for each characteristic.
- Set the check points. Decide where, how often and by whom each check is done, usually in a control plan.
- Inspect or test. Measure against the criteria with calibrated gauges and record the result at the time.
- Contain. Segregate and tag anything that fails, and check what else could be affected.
- Raise a non-conformance. Record the defect, quantity, location and who found it.
- Fix the cause. Use root cause analysis and corrective action so the defect does not return, then verify the fix worked.
How is quality control different from quality assurance?
Quality control checks the product and detects defects. Quality assurance manages the process and aims to prevent them. A plant that only inspects pays for the same scrap and rework again and again, so QC results should drive improvements to the process itself, for example through error-proofing or layered process audits.
How do you know quality control is working?
Look at first pass yield, scrap and rework rates, customer complaints and how long non-conformances stay open. If the same defect keeps appearing, the checks are finding it but the cause is not being fixed.