To specify sheet metal inspection, define the acceptance criteria, test methods, and reporting requirements clearly. Break down checks by part feature and process. A structured RFQ reduces ambiguity, prevents costly disputes, and ensures the supplier understands exactly how the finished part will be evaluated.
- Define inspection criteria for each critical feature, not just the whole part.
- Distinguish between visual checks, dimensional measurements, and non-destructive testing methods.
- State the sampling plan and acceptance limits to avoid ambiguous supplier interpretations.
- Specify the format of the final inspection report and traceability requirements.
- Review the RFQ inspection section with the supplier to confirm mutual understanding before issuing the quote.
What to include before writing the inspection section
Before drafting specific inspection requirements, review the engineering drawings and process flow. Identify every feature that determines function, safety, or fit. A bracket with a bent flange, a welded joint, and a hole pattern are three distinct inspection challenges. Each requires a different method and a different level of documentation.
Gather the material specifications, process requirements, and surface finish standards as well. The inspection criteria must align with these inputs. If the drawing calls for a galvanized finish, the inspection section must address coating thickness and adhesion, not just dimensional accuracy. If the part involves welding, the inspection section must cover joint integrity and welder qualification.
Confirm the supplier’s capabilities early. If you require X-ray inspection but the selected fabrication shop only performs visual checks, the RFQ will fail. Request a list of approved inspection methods and instruments. This prevents the situation where a supplier quotes a low price, then flags the inspection requirements as outside their standard scope.
Step 1: Define the scope of inspection
Start the inspection section by stating what is being inspected. Specify whether inspection applies to incoming materials, in-process steps, and final assembly. Do not assume the supplier will inspect every step.
A typical RFQ will say “inspect parts before shipment.” This is too vague. It does not say if the inspection happens after bending, after welding, or after finishing. Write it explicitly: “Final dimensional inspection after all processes and surface treatment.” If you need in-process checks, list them separately.
This step sets the boundary of the supplier’s quality responsibility. It also defines what evidence they must provide. If you only want final inspection, you save on cost. If you want full traceability, you must pay for more documentation and hold points.
Step 2: Establish inspection criteria for each critical feature
Do not write a single sentence like “parts must meet drawing tolerances.” Instead, break the inspection down by feature. A flat plate, a bent bracket, and a welded assembly all need different checks.
For flat sheets, check thickness, flatness, and edge quality. For bent parts, check bend angles and flange dimensions. For welded parts, check weld size, penetration, and joint alignment. For machined features, check hole position and surface finish.
Use the drawing references to anchor each criterion. For example: “Inspect bend angle on Feature A per drawing detail 4.” This removes guesswork. The inspector does not have to decide which dimension is critical. They just check the list.
Step 3: Select the inspection method
For each feature, name the method. Do not leave it to the supplier to choose. “Measure with calipers” is acceptable for simple dimensions. “Verify weld integrity” is not. It does not say how.
For visual checks, specify the lighting conditions and inspection distance. For dimensional checks, name the instruments. Calipers, micrometers, gauges, and coordinate measuring machines all have different accuracy levels. If a part has a tolerance of +/- 0.1 mm, a standard caliper may not be sufficient. A coordinate measuring machine or a high-precision gauge may be required.
For non-destructive testing, name the method. Visual inspection, magnetic particle testing, or dye penetrant inspection are different methods with different capabilities. If you require X-ray, state it. Do not assume “weld inspection” means the same thing to everyone.
Step 4: Define acceptance limits and sampling plans
State the acceptance limits clearly. If the drawing tolerance is +/- 0.5 mm, the acceptance limit is the same. If you are tighter, say so. Do not rely on implied tolerances.
Decide the sampling plan. For small batches, 100 percent inspection is common. For large production runs, use a statistical sampling plan. State the sample size and the acceptance number. For example: “Inspect 10 parts per lot. Accept if zero defects are found. Reject if one or more defects are found.”
This prevents disputes. If a supplier inspects only one part and you expected ten, you have a communication failure. If a supplier finds one defect in a batch of five and you expected acceptance at two defects, you have a specification failure. The sampling plan removes both.
Step 5: Specify reporting and documentation
State what the supplier must deliver with the part. A simple “inspection certificate” is not enough. Specify the format. A PDF report, a stamped paper document, or an electronic file with photos.
Include what must appear in the report. Part number, serial number, date, inspector name, and the results for each checked feature. If you require non-destructive testing, the report must include the test method, the test level, and the pass or fail status.
For traceability, require a unique serial number on each part and in the report. This links the physical part to its inspection record. If a part fails in the field, you can trace it back to the batch and the inspection data. This is standard practice for safety-critical parts and is increasingly common in industrial applications.
Step 6: Assign hold points and first article inspection
Decide where the supplier must stop and wait for your approval. A hold point is a stage where work cannot proceed until you sign off.
First article inspection is a hold point at the beginning of production. The supplier makes the first part or a small batch and sends it for your review. You approve the process, and they proceed to full production. This is cheaper than catching defects in the finished batch.
State where the hold points are. “First article inspection before full production” is a clear hold point. “Inspect after bending” is another. Do not assume the supplier knows where to stop. If you do not want a hold point, state that the supplier may proceed without approval.
Step 7: Define nonconformance and rework procedures
State what happens if a part fails inspection. Do not leave this to negotiation. Write it into the RFQ.
If a part fails, the supplier must identify the root cause. They must propose a rework method. They must get your approval before reworking. This prevents the supplier from hiding a defect or reworking a part without your knowledge.
State who bears the cost. If the failure is due to the supplier’s process, the supplier pays for rework. If the failure is due to your specification change, you pay. This is standard, but it must be written down. It avoids disputes later.
Common mistakes that weaken RFQ inspection requirements
The most common mistake is using vague language. “Inspect quality” is not an instruction. “Check dimensions” is not specific enough. Use feature names, method names, and acceptance limits.
Another mistake is missing the sampling plan. If you do not state how many parts to inspect, the supplier will inspect the minimum. This leaves you exposed.
A third mistake is not defining the report format. If you want a digital report with photos and the supplier sends a stamped paper document, you have a mismatch. State what you need.
A fourth mistake is assuming the supplier knows your standards. If you require a specific welding procedure or a specific coating standard, name it. Do not rely on the supplier knowing your internal requirements.
Final verification step
Before issuing the RFQ, send the inspection section to the supplier for a clarification meeting. Ask them to read it back. Ask them to identify any ambiguity. Ask them to confirm their ability to meet each requirement.
This step is not optional. It is the difference between a specification and a negotiation. If the supplier cannot explain a requirement, it is not clear enough. Revise it before quoting.
After the quote is returned, check the pricing against the inspection requirements. If the price is low, check if the supplier excluded some inspection steps. If the price is high, check if the supplier included more inspection than you asked. The price should reflect the inspection scope you wrote.
Review the final PO to ensure it matches the RFQ. A small change in the RFQ can create a large gap in the PO. Keep the inspection section identical in both documents.
Frequently asked questions
Can I rely on the supplier’s standard inspection procedures?
Only if your requirements are basic and non-critical. For safety, fit, or function features, you must specify the inspection method and acceptance limits in the RFQ.
Do I need to inspect every part?
Not always. For small batches, 100 percent inspection is common. For large runs, use a sampling plan. State the sample size and acceptance number in the RFQ.
What if the supplier does not have the equipment for a required inspection method?
State the method in the RFQ. If the supplier cannot perform it, they must state this during clarification. Do not assume they have the equipment.
Should I require a first article inspection?
Yes, for new parts or after process changes. It catches process errors before full production. It is cheaper than rework after the batch is complete.
How do I handle defects found after shipment?
State the rework and cost responsibility in the RFQ. If a part fails after shipment, the supplier must identify the cause and propose a fix. You must approve the rework method.
