Checklist: Sheet Metal Supplier Quality Audit

Why a supplier quality audit before the first order

A supplier quality audit is a structured review of a fabricator’s quality control processes and inspection methods. It is not a formality. It is the difference between a part that arrives in spec and a part that requires rework, re-fitting, or re-ordering.

When you place a sheet metal order, you are transferring risk to the fabricator. The metal may look right, but the hole position may be off. The bend angle may be close, but the flat pattern may not be. The weld may pass a visual check, but the part may not fit the assembly.

An audit before the first order helps you verify that the supplier has the systems to catch these problems before they reach you. It also tells you how the supplier handles failure. Do they quarantine bad parts? Do they communicate quickly? Do they have the capability to fix the process, or do they only fix the part?

This checklist is written for buyers and engineers who need a practical, copyable audit tool. It is not a certification standard. Use it as a working document for supplier selection, onboarding, and periodic re-audits.

Audit the documentation and traceability

Start with records. If the supplier cannot show you where a part came from, what material it was made from, and how it was inspected, you do not have a verifiable quality system.

1. Request the last three material certificates for a recent order. Check that the certificate matches the material grade, thickness, and lot number on the purchase order.
2. Ask for the inspection report from the last completed order. It should show the part number, revision, date, inspector name, and pass/fail results for each critical dimension.
3. Verify that the supplier keeps a nonconformance report for every rejected part. The report should state the defect, the quantity, and the disposition.
4. Confirm that the supplier can trace a finished part back to the raw material lot and the tooling or program version used to produce it.
5. Ask how the supplier controls engineering changes. A revision change that is not reflected in the tooling or CNC file is a common source of scrap.

Red flags:

• The supplier provides a generic material certificate that does not match the specific order.
• Inspection reports are handwritten or missing inspector names.
• There is no record of how rejected parts were handled.
• The supplier cannot show the revision history for a drawing.
• The supplier says “we always check it” but cannot show the check.

A supplier with a working quality system will not be defensive about documentation. They will hand over the records.

Verify inspection methods and capability

Inspection methods determine whether the supplier can detect defects. A visual check is not the same as a CMM measurement. A single caliper check is not the same as a full dimensional audit.

1. Ask which dimensions are critical on your part. The supplier should be able to identify them from the drawing, not ask you to list them.
2. Confirm that the supplier uses the right tool for each check. A CMM is appropriate for complex geometry. A caliper and square are appropriate for simple flat parts. A gauge or fixture is appropriate for repeated features.
3. Ask how the supplier checks bend angle and flat pattern. A bend angle check without a flat pattern check can miss errors that appear after assembly.
4. Verify that the supplier checks hole position, not just hole size. A hole that is the correct diameter but the wrong location will fail in the field.
5. Ask about first article inspection. The supplier should inspect the first part after tooling or program changes, not after a full batch.

A practical way to test this is to ask the supplier to show you a recent first article inspection package. It should include the drawing, the inspection report, and the measured values. If the package is missing or incomplete, the supplier is likely relying on experience rather than measurement.

Red flags:

• The supplier measures only the dimensions you point out, not all critical dimensions.
• The supplier uses the same tool for every check, regardless of complexity.
• There is no record of first article inspection.
• The supplier says “our machinists know what they are doing” and refuses to show measurement records.

Review tooling, fixtures, and process control

Tooling and fixtures are where sheet metal parts are made. A good process control system keeps those tools in a state that produces parts in spec.

1. Ask how the supplier maintains bending tools. A press brake die that is worn will produce a bend angle that drifts over the run.
2. Confirm that the supplier uses a setup sheet or program check for each job. The setup sheet should list the part number, material, thickness, and bend sequence.
3. Ask how the supplier verifies the CNC file before cutting. A file check catches coordinate errors before the laser or plasma torch burns the metal.
4. Verify that the supplier inspects tooling at the start of a shift or at the start of a run. A tool that was fine yesterday may not be fine today.
5. Ask how the supplier handles tooling changes. If the part design changes, the tooling should change too. A tool that is used for multiple part numbers without verification is a risk.

Red flags:

• The supplier has no setup sheet or uses the same sheet for multiple jobs.
• Tooling is stored in the production area with no identification.
• The supplier cannot explain how they verify a CNC file before cutting.
• The supplier does not inspect tooling at the start of a run.

Check material handling and storage

Material handling affects finish, flatness, and corrosion. A supplier that stores rolled steel in a damp area will produce parts that rust. A supplier that stacks parts too high will produce bent or dented workpieces.

1. Ask where raw material is stored. It should be dry, protected from the elements, and off the floor.
2. Confirm that the supplier checks material flatness before cutting. A warped sheet will produce a part that does not lie flat.
3. Ask how the supplier handles different alloys. Stainless, aluminum, and mild steel have different handling requirements.
4. Verify that the supplier marks the material with the part number or lot number as it moves through the shop.
5. Ask about surface protection. Parts that sit for days before shipping should be protected from handling damage.

Red flags:

• Raw material is stored outdoors or on the floor.
• The supplier does not check material flatness.
• Material is moved without identification marks.
• Finished parts are stacked on top of each other without separation.

Evaluate nonconformance and corrective action

Every fabricator makes bad parts. The difference is how they handle them.

1. Ask how the supplier identifies a nonconforming part. Is there a quarantine area? A red tag? A separate bin?
2. Confirm that the supplier does not ship rejected parts. A rejected part that leaves the factory is a quality failure, not a scrap issue.
3. Ask how the supplier communicates nonconformance to the customer. The communication should state the defect, the quantity, and the proposed action.
4. Verify that the supplier performs root cause analysis. A root cause analysis should explain why the defect happened, not just how the part was fixed.
5. Ask for a corrective action plan. It should include the change made, the date, and the verification that the change worked.

Red flags:

• The supplier ships rejected parts with a note saying “please accept as is.”
• The supplier does not have a quarantine area.
• The supplier cannot explain the root cause of a defect.
• The same defect appears on multiple orders without a corrective action plan.

Audit the supplier with a sample part

The most useful part of the audit is a sample. Do not rely on documents alone. Ask the supplier to produce one part from a drawing that you control.

1. Provide a drawing with clear critical dimensions and tolerances. Include a note that the part must pass a full inspection before release.
2. Ask the supplier to produce the first article and send the inspection report.
3. Inspect the part yourself if you can. Use the same methods the supplier used.
4. Compare the part to the drawing. Check dimensions, surface finish, and edge quality.
5. Ask the supplier to explain the process. How did they cut it? How did they bend it? How did they inspect it?

This sample audit tells you more than any document. It shows you how the supplier works when they are not being watched. It also gives you a reference part for future comparisons.

Red flags:

• The supplier refuses to produce a sample part.
• The inspection report does not match the part.
• The part has visible defects that the report does not mention.
• The supplier cannot explain how they made the part.

Keep an audit scorecard

Use a simple scorecard to track your audit results. It helps you compare suppliers and identify recurring issues.

Audit Area	Pass/Fail	Notes
Documentation and traceability
Inspection methods and capability
Tooling and process control
Material handling and storage
Nonconformance and corrective action
Sample part verification

Mark each area as pass, fail, or conditional. A conditional pass means the supplier has a process but needs improvement. Write down the specific issue. For example, “Inspection report missing inspector name” or “Tooling not identified.”

Review the scorecard after each order. If the same area fails twice, escalate the issue. If the supplier fixes the issue, update the scorecard.

A supplier quality audit is not a one-time event. It is a relationship tool. Use it to build trust with good suppliers and to weed out bad ones.

When to re-audit

Re-audit a supplier after major changes. A new plant, a new press brake, a new CNC operator, or a change in material source can affect quality.

1. Re-audit after a major equipment change.
2. Re-audit after a significant defect report.
3. Re-audit after a change in supplier management or ownership.
4. Re-audit annually, even if the supplier has no issues.

A supplier that resists re-audits is a risk. A supplier that welcomes them is a partner.

Final checklist

Use this list as your working audit tool.

1. Request material certificates and inspection reports for recent orders.
2. Verify traceability from finished part to raw material lot.
3. Confirm inspection methods for critical dimensions.
4. Check tooling maintenance and setup control.
5. Review material handling and storage.
6. Ask about nonconformance handling and corrective action.
7. Produce a sample part and inspect it yourself.
8. Record results on a scorecard.
9. Re-audit after major changes.
10. Use the scorecard to make the final supplier decision.