How to Audit a Die Casting Supplier: A Practical Guide

A die casting supplier audit is more than a checklist exercise. It is a structured way to see whether a facility can hold your tolerances, meet your deadlines, and maintain the quality controls you require. Most audits fail because the buyer stays in the conference room or relies entirely on the supplier’s sales team. You need to walk the floor, inspect the machines, and ask questions that force a clear answer.

What to prepare before you arrive

Before you step onto the production floor, define the scope of your die casting supplier audit. Do not arrive with an open-ended plan. List the parts you plan to order, the materials involved, and the critical dimensions that define a good or bad casting. Know your acceptance criteria. If you are casting aluminum, understand the difference between a semi-solid and a true die cast part. If you are casting zinc, know the impact of porosity and flash on your assembly.

Prepare a copy of your quality requirements. Bring your PPAP, FMEA, and any specific test methods you require. Ask the supplier for their control plan in advance. If they cannot produce it, that is a red flag. A supplier that cannot show you their process control plan is not ready to hold your tolerance.

Consider the specific part features that will test their capability. A small automotive bracket with a tight bore and a threaded insert requires different verification than a large housing with deep internal cavities. Bring your drawing and mark the critical dimensions. Mark the dimensions that have caused scrap in past production. This focuses your inspection on what actually matters for your line.

Prepare a list of questions that target process stability. Ask about the shot time for similar parts. Ask about the hold time. Ask about the eject force. Ask about the mold temperature control system. Do not ask if they follow standard operating procedures. Ask them to show you the procedure and explain how they verify it is being followed. The answer is in the records, not the verbal explanation.

Bring a notebook or a digital device for notes. You will walk the floor for hours. You will see many details. You will forget most of them if you do not write them down immediately. You will need these notes to build your final report and to compare what you saw with what they claim.

How to inspect the production floor

The production floor inspection is the core of the audit. Walk the line. Do not let the supplier stand behind you. Watch the machines. Look at the die casting machines. Check the mold temperature. Look at the shot pressure. Observe the discharge cycle. A well-run facility will have clean dies, consistent mold temperatures, and a clear discharge area.

Check the die maintenance area. This is where many suppliers hide their problems. Look at the die condition. Check for pitting, cracking, or excessive wear. Ask how often they inspect the dies. A supplier that only inspects dies when a problem occurs is not managing the process. They are reacting to it. You want to see a schedule. You want to see records.

Look at the casting area. Check for flash, porosity, and dimensional variation. Pick up a few castings. Measure them. Do not just look at the first five pieces. Look at the last five from the batch. This tells you about process stability. If the variation is high at the end of a run, the facility is not controlling its process.

Inspect the melt handling area. Check the crucible or the melt pot. Look for dross accumulation. Ask if they skim the melt regularly. Ask if they monitor the melt temperature. A high melt temperature can cause gas absorption in the casting. It can also increase the risk of die wear. A low melt temperature can cause incomplete fill. Look at the temperature gauge. Verify that it is not just a sticker on the wall.

Check the discharge area. Look at the area where the casting comes out of the die. Look for the ejector pins. Look for the ejector plates. Look for the ejector rods. Check for wear. Check for burrs. Check for corrosion. A well-maintained discharge area prevents the casting from sticking in the die. It also prevents damage to the casting surface.

Watch the operator work. Watch how they load the shot. Watch how they check the mold. Watch how they remove the casting. Watch how they dispose of scrap. Watch how they handle a defective part. The operator is the first line of defense for quality. If they are careless, the quality control team will have to catch every mistake.

How to verify vendor compliance

Vendor compliance is often treated as a paperwork exercise. It is not. It is a way to confirm that the facility follows the rules it claims to follow. Check their quality management system. Look for the control plan. Look for the inspection records. Look for the calibration records.

Do not just ask if they are certified. Ask them to show you the certificate. Ask them to show you the scope of the certification. Ask them to show you the last audit report. If they cannot produce it, that is a problem. A supplier that claims to be certified but cannot show the documentation is not compliant.

Check their supplier management. Ask who their raw material suppliers are. Ask how they verify the material. Ask if they test the ingot. Ask if they keep certificates of conformance. If they cannot show you the material traceability, you cannot trust the material.

Request a sample of the material traceability records. Ask for the batch number of the ingot used for your part. Ask for the heat number. Ask for the chemical analysis. Ask for the certificate of conformance. Trace the batch back to the mill. If they cannot show you the link between the ingot and the casting, you have a gap in their control.

Check their handling of nonconforming material. Ask how they segregate bad parts. Ask how they store scrap. Ask how they prevent scrap from re-entering the melt. Ask how they prevent a bad casting from being sent to the customer. A supplier that cannot show you their nonconformance control process is not managing quality. They are just hoping for the best.

Look at their document control. Ask how they manage their procedures. Ask how they control their drawings. Ask how they verify that operators have the right version of the procedure. Ask how they verify that the drawing on the floor matches the drawing you provided. If they use outdated drawings, they will produce the wrong part. If they do not control their documents, they will make mistakes.

How to review the quality control process

The quality control process is where the supplier earns your trust. Look at their inspection equipment. Check the CMM. Check the gauge blocks. Check the micrometers. Verify that they are calibrated. Look at the calibration stickers. Verify the dates.

Look at their inspection records. Ask them to show you a sample report. Ask them to show you the dimensions they measure. Ask them to show you the acceptance criteria. Ask them to show you the disposition of any nonconforming parts. A supplier that cannot show you how they handle bad parts is not managing quality.

Check their lab. Look at their lab equipment. Look at their test records. Look at their failure analysis process. A supplier that only does visual inspection is not doing enough. They need to understand the material. They need to understand the process.

Ask about their in-process inspection. Ask when they check the mold. Ask when they check the shot parameters. Ask when they take the first piece of the batch. Ask when they check the last piece of the batch. Ask how often they check the critical dimensions during the run. A supplier that only inspects at the start and end of the batch is not monitoring the process. They are not detecting drift.

Look at their statistical process control. Ask if they use control charts. Ask how they interpret the charts. Ask how they respond when a point goes outside the control limits. Ask how they respond when there is a shift in the mean. A supplier that uses SPC is not just reacting to bad parts. They are predicting problems before they happen.

Check their measurement uncertainty analysis. Ask if they have calculated the uncertainty of their measurements. Ask if the uncertainty is small compared to their tolerance. If their measurement uncertainty is close to their tolerance, their measurements are not reliable. They may be accepting bad parts. They may be rejecting good parts.

How to evaluate the people on the floor

The people on the floor are the final check. Talk to the operators. Ask them about their job. Ask them about the process. Ask them about the quality requirements. A good operator will know the process. They will know the tolerances. They will know what to do when a part fails.

Watch their body language. Are they engaged? Are they proud of their work? Do they look like they understand the process? A supplier with disengaged operators is not going to hold your quality. They are not going to hold your deadline. They are not going to hold your tolerance.

Ask the operator to explain the process. Ask them to explain the shot parameters. Ask them to explain the mold temperature. Ask them to explain the eject cycle. Ask them to explain what happens if the mold temperature drops too low. Ask them to explain what happens if the melt temperature is too high. A good operator will answer these questions without hesitation. A poor operator will look at the supervisor or say they do not know.

Check their training records. Ask how they trained the operator. Ask how long they trained them. Ask how they verified their competency. Ask if they have a training matrix. A supplier that does not train their operators is not managing their people. They are not managing their quality.

Ask about their communication. Ask how they communicate problems to the supervisor. Ask how they communicate problems to the quality engineer. Ask how they communicate problems to the production planner. A supplier with good communication will catch problems early. A supplier with poor communication will let problems grow until they become costly.

Common mistakes to avoid

The biggest mistake in a die casting supplier audit is relying on the sales team. The sales team will tell you what you want to hear. They will not tell you what you need to know. Walk the floor. Look at the machines. Look at the parts. Look at the records.

Another mistake is not measuring the parts. Do not just look at them. Measure them. Pick up a part. Measure it. Compare it to your drawing. If the variation is high, the facility is not controlling its process.

The third mistake is not checking the die maintenance area. This is where the problems hide. Look at the dies. Look at the records. Look at the schedule. If they are not maintaining the dies, they are not maintaining the quality.

Do not skip the scrap area. Look at the scrap. Look at the reason codes. Look at the quantity of scrap. Look at the trend. A supplier with high scrap rates is not efficient. A supplier with high scrap rates is not profitable. A supplier with high scrap rates is likely to pass the cost on to you.

Do not skip the storage area. Look at the finished goods. Look at the packaging. Look at the labeling. Look at the segregation. A supplier that cannot store their parts properly will damage them. They will mix them up. They will ship the wrong part.

Final verification step

The final step is to verify that what you saw matches what they told you. Go back to the conference room. Ask for the control plan. Ask for the inspection records. Ask for the calibration records. Ask for the material certificates. Compare what you saw on the floor with what they show you on paper. If they match, you have a compliant supplier. If they do not match, you have a problem.

You should also verify that the facility can scale. Ask them about their capacity. Ask them about their lead time. Ask them about their contingency plan. If they cannot show you a plan for when something goes wrong, they are not ready to hold your production.

Ask about their capacity for growth. Ask how they plan to add capacity. Ask how they will train new operators. Ask how they will maintain quality as they scale. A supplier that cannot show you a plan for growth is not ready to be your long-term partner. They will become a bottleneck. They will become a risk.

Ask about their contingency plan. Ask what happens if a machine breaks down. Ask what happens if a die breaks. Ask what happens if the melt supply is delayed. Ask what happens if a key operator is sick. A supplier with a good contingency plan will keep your production running. A supplier without a plan will stop your production.

How to document your findings

Document everything. Write down what you saw. Write down what you measured. Write down what you asked. Write down what they answered. Do not rely on memory. Memory is unreliable. Write it down.

Create a scorecard. Rate each area. Rate the production floor. Rate the quality control. Rate the vendor compliance. Rate the people. This gives you a clear picture of where the supplier stands. It also gives you a way to track them over time.

Share the findings with your team. Do not keep the audit to yourself. Your team needs to know what you found. They need to know what the supplier can do. They need to know what the risks are. This is a team decision.

Include photos in your report. Include photos of the machines. Include photos of the dies. Include photos of the parts. Include photos of the records. Photos are objective. They cannot be argued with. They provide evidence.

Include your measurements in your report. Include the dimensions you measured. Include the tolerance you compared them to. Include the result. Include the date and the time. This provides a clear record of the condition of the parts at the time of the audit.

Include your questions and their answers in your report. This provides a record of their knowledge. It provides a record of their honesty. It provides a record of their commitment.