When evaluating an OEM manufacturer's quality system, understanding the three-stage QC model — IQC, IPQC, and OQC — gives you a framework for asking the right questions and interpreting the documentation you receive.
IQC — Incoming Quality Control
IQC is the quality inspection performed when raw materials, purchased components, and sub-contracted parts arrive at the factory. Its purpose is to verify that the incoming materials meet specifications before they enter production.
What IQC covers for precision metal manufacturing: - Material certs review (chemical composition, heat treatment lot traceability, tensile strength) - Dimensional sampling of purchased components (thread gauging, OD/ID measurement) - Visual inspection for defects, contamination, or damage in transit - Supplier qualification status verification (is this an approved supplier?)
What good IQC documentation looks like: - An IQC record for each material/component lot received, with: lot number, quantity received, inspection results, accept/reject decision, and inspector signature - AQL sampling plan documented (e.g., AQL 1.0 at inspection level II) - Material certs filed and cross-referenced to the lot number
Red flags in IQC: - No material certs on file, or certs that don't trace to the production lot - IQC records that are identical across multiple lots (copy-paste documentation) - No defined AQL or sampling plan
IPQC — In-Process Quality Control
IPQC is performed during production, at defined checkpoints within the process flow. Its purpose is to detect process drift before it affects a large quantity of parts, and to prevent defects from propagating through subsequent operations.
Key IPQC checkpoints for safety hardware: - After forging/casting: visual inspection for defects, dimensional check of critical features - After CNC machining: dimensional measurement against drawing tolerances - During assembly: functional verification (gate function for carabiners, buckle engagement for PPE hardware) - After surface treatment: coating thickness, adhesion, appearance inspection
Statistical process control (SPC) is the formal framework for IPQC in high-volume manufacturing. Control charts monitor key process parameters in real time. When a measurement trend toward a control limit, the process is corrected before the limit is breached — this is process control, not defect sorting.
What good IPQC documentation looks like: - Control plan identifying which parameters are monitored, at what frequency, with what measurement method, and what the control limits are - IPQC records (patrol inspection logs) showing actual measurements over the production run - Corrective action records when process drift was detected and corrected
OQC — Outgoing Quality Control (Pre-Shipment Inspection)
OQC is performed on finished goods before they leave the factory. It is the final gate before product reaches the customer.
For safety-critical hardware, OQC includes: - Dimensional sampling (AQL 1.0 or 0.65 for critical dimensions) - Functional testing (gate opening force, locking mechanism engagement, buckle release) - Load testing where applicable (proof load per Z359.12, or batch load testing per customer spec) - Appearance inspection (surface finish, anodising quality, marking legibility) - Packaging verification (correct labelling, quantity count, accessory inclusion)
What good OQC documentation looks like: - Pre-shipment inspection report (often called PSI or Certificate of Conformance) with measurement results, accept/reject decision, inspector signature, and lot identification - Tensile test report if load testing is performed (showing machine ID, calibration date, results) - Final packaging list cross-referenced to the order
How QC documentation links to certification
For CE-certified products, IQC, IPQC, and OQC records are not just internal quality tools — they are part of the technical file and may be reviewed by the notified body during a factory audit. A manufacturer that can produce complete QC records for a production run demonstrates process control to the level that CE Category III requires.
Questions to ask your supplier about their QC system
- Can you show me an IQC record for a recent material lot?
- What is your AQL sampling level for incoming components?
- Do you have a control plan for this product? What parameters does it monitor?
- Can you show me an IPQC log from a recent production run?
- What does your pre-shipment inspection include, and who performs it?
- If an OQC failure is found, what is your disposition process?
A factory that can answer these questions with documentation — not just verbal assurances — has a quality system that works.