Checklist: Verifying Secondary Processing Supplier Capabilities

Why Secondary Capabilities Fail

Secondary processes determine the final cost and performance of a die casting. A well-cast part with a poor secondary process fails in the field. A lower cost part with the correct finishing, plating, or machining may pass every requirement. The failure usually comes from a mismatch between what the buyer expects and what the supplier can actually prove.

This checklist is for buyers and engineers who need to verify a secondary processing supplier’s ability to execute specific post casting operations. It is not a general supplier qualification form. It is a working tool for a specific part, a specific process, and a specific set of requirements.

Use it when you are evaluating a new supplier, when you are moving a part to a second source, or when you are expanding an existing supplier’s scope. It works best when you have the part drawing, the secondary operation specification, and the supplier’s capability statement in front of you.

Equipment and Process Setup

Start with the physical setup. A supplier who owns the equipment is not automatically capable of using it correctly. The question is whether the equipment, the operator, and the process control are aligned for your specific part.

1. Confirm the equipment type and condition for the specific process.
2. Ask for the process parameters that apply to your part.
3. Verify that the parameters match the material and part geometry.
4. Check that the supplier has a documented setup procedure for your part.

For example, if the part requires a specific coating thickness, the supplier needs equipment that can hold that thickness across the part surface. If the part has thin walls or complex geometry, the equipment may not be able to reach all areas uniformly. This is a common gap. A supplier can process a standard housing without issue. The same supplier may not be able to process a thin-walled connector with the same coating.

The setup procedure matters as much as the equipment. A documented setup tells you that the supplier has a repeatable method. It also gives you a reference point when you audit. If the setup changes, you can trace the change and its impact.

Process Controls and Documentation

A supplier’s capability is only as good as its process control. You need to see that the process is not just run, but controlled. This means parameters are set, recorded, and reviewed.

1. Request the process control plan for the specific operation.
2. Verify that critical parameters are defined.
3. Ask for the inspection frequency and method.
4. Confirm that out-of-specification results are documented and reviewed.

The process control plan should list what is measured, how it is measured, and what the acceptable range is. If the plan is generic, it is not useful. It needs to be tied to your part. If the supplier gives you a standard template with no part-specific details, that is a red flag. It means the supplier may not have run your part before, or it may not have a method for your specific requirements.

For plating, the process control plan should cover bath chemistry, current density, and rinse quality. For machining, it should cover tooling, coolant, and hold-down. For painting, it should cover primer thickness, cure temperature, and adhesion. The more specific the control plan is to your part, the more confident you can be.

Inspection and Verification Methods

Finishing verification is not just a visual check. You need functional and dimensional verification. A part can look correct and still fail in service.

1. Confirm the inspection method for each critical requirement.
2. Ask for the acceptance criteria.
3. Verify that the supplier has the equipment to perform the inspection.
4. Request a sample of inspection records.

For a plating requirement, a visual check is not enough. You need a thickness measurement. For a coating, you need a cure verification. For a machined feature, you need a dimensional report. The inspection method must match the requirement. If the requirement is a surface finish of a specific microinch value, a visual inspection will not verify it. You need a roughness tester.

The acceptance criteria must be clear. “Acceptable” is not a criterion. “0.2 to 0.4 mils” is a criterion. If the supplier cannot state the acceptance criteria in numbers, you do not have a verification method. You have an opinion.

Supplier Audit and Traceability

A supplier audit is not a one-time event. It is a way to confirm that the capability you verified in the factory will hold in production. You need traceability. You need to be able to follow a lot from raw material to finished part.

1. Verify lot traceability from raw material to final operation.
2. Ask for the method of identifying each lot.
3. Confirm that inspection records are kept for the required period.
4. Check that the supplier can provide a quality report for a specific lot.

Traceability is the backbone of a supplier audit. If the supplier cannot trace a lot, it cannot prove that the process was controlled for that lot. If the supplier cannot provide a quality report, it cannot prove that the part met the requirement. These are not nice-to-have items. They are the minimum for a secondary process that affects function.

When you audit, do not just look at the equipment. Look at the records. Look at the operator’s log. Look at the inspection report. The records tell you what actually happened. The equipment tells you what could happen. The records are the proof.

Red Flags in Secondary Operations

Not every supplier will pass the checklist. Some red flags are obvious. Others are subtle. Here is a table of common red flags and what they mean.

Red Flag	What It Means	Action
Generic capability statement	No part-specific method	Request a process control plan for your part
No documented setup	Method may vary between runs	Require a written setup procedure
Visual only inspection	Functional failure risk	Add functional inspection to the spec
No lot traceability	Cannot prove compliance	Require a traceability system
Vague acceptance criteria	No objective pass/fail	Define numeric limits in the spec
Out-of-spec not documented	Quality issue is hidden	Require a nonconformance report

If you see multiple red flags, stop. Do not push forward. The risk is too high. A secondary process failure can lead to field returns, recalls, and lost trust. The cost of verifying capability now is far lower than the cost of fixing a failure later.

Final Verification Before Production

Before you release a part to production, run the checklist one last time. Confirm that every item is closed. Confirm that the supplier has the capability for the specific part, not just in general. Confirm that the inspection method matches the requirement. Confirm that the supplier can provide a quality report.

The final step is a first article inspection. This is not optional. It is the last check before you commit to volume. The first article inspection should include every requirement in the specification. It should be inspected by the supplier and reviewed by you. It should be signed off before production starts.

If the first article inspection fails, do not release the part. Do not ask the supplier to “fix it.” Ask why it failed. The first article inspection is the last chance to catch a capability gap. If you skip it, you are taking a risk that can be very expensive.

The checklist is a tool. It is not a guarantee. A supplier can pass the checklist and still have a problem. But it gives you a standard way to evaluate capability. It gives you a reference point when you audit. It gives you a way to catch gaps before they become failures. Use it for every secondary process. Use it for every part. Use it every time.