Checklist: Verifying Die Casting Supplier Process Controls

Why Process Controls Matter for Die Cast Parts

Aluminum die casting is a process where small variations in temperature, pressure, or alloy chemistry can show up as dimensional drift, porosity, or surface defects. When you source from multiple suppliers or manage a long production run, you need more than a final inspection report. You need to see how the supplier manages the process from melt to final trim.

This checklist is a practical tool for verifying supplier process controls. It is organized by theme, with a short explanation and red flags to watch for. Use it during a site visit, a document review, or a remote audit. The goal is to confirm that the supplier has systems in place to keep the process stable and to catch problems before they reach your incoming inspection.

1. Verify Die Maintenance and Machine Calibration

The die is the most expensive asset in the facility, and it is the primary driver of part geometry. A well-maintained die produces consistent parts; a worn or poorly maintained one produces out-of-tolerance parts, flash, or surface defects.

Checklist Items:

1. Review die maintenance logs. Confirm that the supplier tracks die cycles, heat treatment, and repair work. Look for records of die face grinding, core insert replacements, and lubricant changes.
   • Red Flag: No logbook or records are only kept verbally. No scheduled maintenance intervals are defined.
2. Check machine calibration certificates. The die casting machine (hot shot, squeeze, or gravity) must have calibration records for stroke, pressure, and timing.
   • Red Flag: Calibration certificates are expired or missing. The supplier cannot show how machine parameters are verified regularly.
3. Inspect die storage and handling. Dies are sensitive to thermal shock and physical damage. Check how dies are stored, moved, and protected.
   • Red Flag: Dies are stored in uncontrolled environments, moved without care, or show visible cracks or pitting.

What to look for in practice:
Ask the supplier to show you the die maintenance schedule for the specific die casting your part uses. If they have a 1,000-cycle die, do they have a log showing it was inspected at cycle 500? If they do, ask what the inspection found. A good supplier will show you the repair work order, the die face photo, and the requalification results.

Control Area	Typical Check	Red Flag
Die Maintenance	Log of cycles, repairs, heat treatment	No log or verbal-only records
Machine Calibration	Certificate for stroke, pressure, timing	Expired or missing certificates
Die Handling	Storage conditions, physical condition	Cracks, pitting, uncontrolled storage

2. Confirm Metallurgical Controls and Alloy Chemistry

Aluminum die casting alloys (like A380, A356, A383) have specific chemistry ranges. Out-of-spec chemistry leads to poor casting quality, low strength, or corrosion issues. The supplier must control the melt chemistry and verify it consistently.

Checklist Items:

1. Review melt chemistry records. Confirm that the supplier tests melt chemistry per batch or per melt. Look for records of alloying additions, furnace temperature, and final chemistry results.
   • Red Flag: Chemistry is only tested once per week, not per melt. No records of alloying additions.
2. Check melt filtration and degassing records. Filtration removes inclusions; degassing removes dissolved gases. Confirm the supplier uses filtration and degassing and records the results.
   • Red Flag: No filtration or degassing process, or no records of when filters were changed or degasers were calibrated.
3. Verify alloy traceability. The supplier should be able to trace the raw ingot or billet to the final die cast part.
   • Red Flag: No lot traceability from raw material to part. Mixing of different alloy lots without documentation.

What to look for in practice:
Ask to see the chemistry report for a recent melt of the alloy you are using. If you are using A356, the chemistry should show silicon and magnesium within the specified range. Ask how they handle out-of-spec chemistry. A good supplier will reject the melt or add alloying elements to bring it in spec. They will not cast the part and hope it passes.

3. Inspect In-Process Monitoring and Statistical Process Control

In-process monitoring means the supplier checks the process during production, not just at the end. Statistical Process Control (SPC) uses data to track process stability and predict future performance. This is how you catch small drifts before they become scrap.

Checklist Items:

1. Review SPC charts. Confirm that the supplier monitors key parameters (temperature, pressure, cycle time) using control charts. Look for X-bar and R charts, or I-MR charts.
   • Red Flag: No SPC charts, or charts are only created for final dimensions, not process parameters.
2. Check capability studies (Cpk/Ppk). Confirm that the supplier performs capability studies for critical dimensions. Look for Cpk values of 1.33 or better for critical features.
   • Red Flag: No capability studies, or Cpk values below 1.0 for critical dimensions.
3. Review control plan. The control plan should list critical characteristics, control method, frequency, and response plan.
   • Red Flag: No control plan, or the plan is generic and not specific to the part.

What to look for in practice:
Ask to see the SPC chart for a critical dimension, such as a bore or a mounting hole. Look at the last 30 points. Are they in control? Are there any out-of-control signals? Ask what the response plan is if a signal is detected. A good supplier will stop the process, investigate the cause, and document the corrective action.

4. Verify Quality Assurance Systems and Documentation

Quality assurance is the system that ensures the quality of the product and process. It includes documentation, traceability, and corrective action. This is what you audit when you ask for the supplier’s quality system.

Checklist Items:

1. Review quality manual and procedures. Confirm that the supplier has a documented quality management system. Look for procedures for first article inspection, in-process inspection, and final inspection.
   • Red Flag: No written procedures, or procedures are not followed.
2. Check first article inspection (FAI) records. Confirm that the supplier performs FAI for new dies or significant changes. Look for FAI reports showing all critical dimensions and features.
   • Red Flag: No FAI, or FAI is only done once and not updated after changes.
3. Review corrective action records. Confirm that the supplier has a process for handling nonconforming material and customer complaints. Look for corrective action reports (CAR/CAR) with root cause analysis.
   • Red Flag: No corrective action process, or actions are not verified for effectiveness.

What to look for in practice:
Ask for the corrective action report for a recent nonconformance. Look for the root cause, not just the symptom. If a part was out of tolerance, was the die repaired? Was the machine recalibrated? Was the process changed? A good supplier will document the root cause and the corrective action, and verify that it worked.

5. Confirm Traceability and Batch Control

Traceability is the ability to track a part from raw material to final product. It is essential for recalls, investigations, and continuous improvement.

Checklist Items:

1. Review lot and batch numbering. Confirm that the supplier uses a lot or batch number for each production run. Look for how the lot number is applied to the part (stamped, marked, or recorded).
   • Red Flag: No lot numbering, or lot numbers are not applied to the part.
2. Check raw material traceability. Confirm that the supplier can trace the raw ingot or billet to the final part. Look for mill test reports (MTR) or heat numbers.
   • Red Flag: No MTRs, or heat numbers are not recorded.
3. Verify heat treatment records. If the part requires heat treatment, confirm that the supplier records the heat treatment parameters (temperature, time, quench).
   • Red Flag: No heat treatment records, or parameters are not recorded.

What to look for in practice:
Ask to see the traceability record for a specific part number. Start with the part lot number, and ask to see the corresponding melt chemistry report, die maintenance log, and heat treatment record. If the supplier cannot link them, that is a red flag.

6. Assess Corrective Action and Continuous Improvement

A supplier that only reacts to problems is a risk. A supplier that learns from problems and improves the process is a partner. Corrective action and continuous improvement are how you ensure the process gets better over time.

Checklist Items:

1. Review 8D or corrective action reports. Confirm that the supplier uses a structured process for corrective action. Look for reports that include root cause, corrective action, and preventive action.
   • Red Flag: No structured process, or reports are not closed out.
2. Check continuous improvement projects. Confirm that the supplier has projects to improve process stability, reduce scrap, or improve efficiency.
   • Red Flag: No improvement projects, or projects are not tracked.
3. Review supplier scorecards or internal audits. Confirm that the supplier audits its own process and tracks performance.
   • Red Flag: No internal audits, or audits are not documented.

What to look for in practice:
Ask for the last three corrective action reports. Look at the trends. Are the same problems recurring? If so, what is the root cause? Is the supplier taking action to prevent recurrence? A good supplier will show you the trend and the action taken.

7. Final Documentation and Sign-Off

Before you sign off on the supplier, confirm that all documentation is complete and accessible. You need a single source of truth for the process controls.

Checklist Items:

1. Compile the audit package. Gather all the documents you reviewed: die maintenance logs, chemistry reports, SPC charts, control plan, FAI reports, corrective action reports, traceability records.
   • Red Flag: Documents are missing, incomplete, or not accessible.
2. Confirm document control. Confirm that the supplier has a document control process. Look for version control, approval dates, and distribution lists.
   • Red Flag: No document control, or documents are not versioned.
3. Sign off on the audit. Document the findings, any nonconformances, and the agreed actions.
   • Red Flag: No sign-off, or nonconformances are not tracked.

What to look for in practice:
Create a single folder with all the documents. If you cannot find a document, that is a gap. If a document is outdated, that is a gap. The audit package should be a snapshot of the supplier’s process controls at the time of audit.

Red Flags to Watch For (Summary)

• No die maintenance logs or machine calibration certificates.
• Melt chemistry is not tested per batch or per melt.
• No SPC charts or capability studies for critical dimensions.
• No documented corrective action process.
• No lot or batch traceability from raw material to part.
• Corrective actions are not verified for effectiveness.
• Documents are missing, incomplete, or not versioned.

How to Use This Checklist

This checklist is a starting point. Adapt it to your specific part, alloy, and quality requirements. If your part is a structural die casting, you may need to add checks for heat treatment and mechanical testing. If your part is a consumer product, you may need to add checks for surface finish and cosmetic quality.

The goal is not to pass or fail the supplier. The goal is to understand the supplier’s process controls and identify gaps. A supplier with a few gaps is not a bad supplier. A supplier who will not show you the process controls is a risk.

Use this checklist during a site visit, a document review, or a remote audit. Ask the questions. See the documents. Watch the process. If you see a red flag, ask for more information. If you cannot get the information, document it as a nonconformance and agree on a corrective action.

That is how you verify die casting process controls.