Key takeaways
- An FAI proves the first part against the drawing. A PPAP proves the process can repeat it.
- A moulded housing needs conditioned dimensions, material evidence and the flame rating at the actual wall.
- The control plan and the PFMEA are the part of the pack that shows how the process is held, not just what it made once.
- Approve the pack, not the sample. A good sample with a weak control plan is a risk.
Two documents, two different jobs
A first article inspection report proves that the first part made from a tool matches the drawing. It records every dimension, the material, the finish and any functional result. A production part approval process pack proves that the process can repeat that part at the quoted rate, with the controls, the capability and the records to support it.
The two are often requested together, and they are sometimes treated as one document. They are not. An FAI can pass on a sample that was hand-finished, measured after a long cooling time or taken from a single cavity. A PPAP has to show that the same result comes from the production process, across the cavities, over the run.
For a moulded housing, the distinction matters because the process is the product. The shrink, the warp, the colour and the insert retention all depend on the tool, the material and the cycle. A pack that lists dimensions without the process evidence is only half the story.
What the FAI report should contain
The FAI report starts with the drawing revision, the part number, the material batch, the tool number and the date. Every dimension on the drawing should be ballooned and recorded with the nominal, the tolerance and the result. A report that samples a few dimensions is not an FAI, unless the drawing or the customer defines a reduced scope.
The report should also record the measurement condition. For a plastic part, that means the conditioning time, the temperature, the humidity and the fixture. A dimension measured dry and a dimension measured after conditioning are different results, and the report has to say which one it is.
Add the material certificate, the colour and the flame rating evidence, and any functional test. If the housing has inserts, add the insert position, the pull-out and the torque results. If it has a sealing face, add the leak or pressure result. The FAI is the place to show that the part works, not just that it measures.
Dimensions, datums and the plastic condition
The datum scheme on the drawing decides how the part is measured. A housing that locates on two mounting holes and a face should be measured from those features, not from a convenient edge. The fixture should support the part at the datums and avoid clamping out a warp that the drawing is trying to control.
Critical dimensions are the ones that locate the cover, the terminals, the breaker or the mounting. A general tolerance can cover the rest. If the drawing has a profile control on a sealing face, the FAI should report the profile result, not a set of linear dimensions that happen to cross the face.
Wall thickness deserves its own check. A calliper at the edge can miss a thin section in the middle of the part. An ultrasonic gauge or a section cut gives a more useful result. For a glass-filled part, the wall and the flow direction both affect the strength, so the section should note the location and the direction.
The PPAP elements that matter for a moulding
A PPAP pack usually includes the design records, the engineering change status, the process flow, the PFMEA, the control plan, the measurement system analysis, the dimensional results, the material and performance results, the initial process study, the sample parts and the part submission warrant.
The PFMEA and the control plan are the heart of the pack for a moulded part. The PFMEA should cover the moulding, the insert loading, the assembly and the inspection. The control plan should name the process parameter, the specification, the monitoring method and the reaction plan. A control plan that lists only the final dimensions does not control the process that makes them.
The measurement system analysis should cover the gauges and the fixtures used for the critical features. A gauge that is repeatable on a steel part may not be repeatable on a flexible plastic part. The initial process study should show capability on the critical characteristics, with the sample size and the acceptance criterion agreed with the customer.
The plastic-specific evidence
A moulded housing has evidence that a generic metal checklist does not cover. Shrinkage and warp should be measured after a defined cooling time, and the result should be compared with the tool design. Colour and gloss should be checked against the approved standard under a defined light. The flame rating should be confirmed at the actual wall thickness and colour.
If the housing contains inserts, the pack should include the insert position, the pull-out and torque results, and a section through the boss. If the housing is overmoulded, add the bond and seal results. If the material is moisture sensitive, add the conditioned dimensions and the drying record.
The material certificate should identify the grade, the batch and the supplier. If the grade is flame retardant, add the yellow card reference and the rating at the wall thickness. If the part is coloured, add the colour batch and the approval record. These are the details that turn a dimensional report into a material record.
| Element | Evidence | Plastic-specific check |
|---|---|---|
| Design record | Drawing and model at the current revision | Datum scheme suits a flexible part |
| Material | Certificate, grade and batch | Flame rating at the actual wall and colour |
| Dimensions | Ballooned FAI results | Conditioned state and fixture recorded |
| Process flow | Moulding, insert, assembly, inspection | Drying, cycle and insert loading included |
| PFMEA | Failure modes and controls | Sink, warp, short shot and insert retention |
| Control plan | Parameters, methods and reaction plan | Moulding window, not just final dimensions |
| MSA | Gauge and fixture studies | Repeatability on a flexible plastic part |
| Initial study | Capability on critical characteristics | Sample size and acceptance agreed |
| Sample and warrant | Production sample and signed PSW | Sample from the production tool and process |
The exact pack depends on the customer and the industry scheme. Confirm the required elements before the run, not after the samples are made.
Review the pack before approval
A review should ask three questions. Does the part meet the drawing? Does the process control the features that matter? Is the evidence from the production process, not from a special sample? If any answer is no, the pack is not ready.
Check the dates and the revisions. A drawing revision that changed after the FAI was measured invalidates the report. A material batch that is not the production batch weakens the evidence. A sample that was hand-finished after ejection is not a production sample.
Check the open issues. A deviation, a concession or a temporary change should be listed with an owner and a close-out date. An approval with an open issue is a decision, not an oversight, and it should be recorded as one.
Requalification after a change
A PPAP is not permanent. A change of tool, material, colour, insert supplier, moulding site or process can change the part. The customer's change notification procedure should define when a new FAI or a partial PPAP is required. A change that is not notified can invalidate the approval.
For a long programme, agree a requalification interval and a change trigger list. A tool that has been repaired, a cavity that has been replaced or a material batch that behaves differently are all triggers. The record should show what changed, what was tested and who approved it.
Keep the master sample and the checking aids in a controlled location. A master sample that has been handled, faded or damaged is not a reference. A checking aid that has worn is not a gauge. The pack is only as good as the records that support it after the approval.
Frequently asked questions
What is the difference between FAI and PPAP?
An FAI proves the first part matches the drawing. A PPAP proves the production process can repeat it, with the PFMEA, control plan, MSA, capability and sample records. A PPAP usually includes the FAI results, but it covers more than dimensions.
Do plastic parts need conditioned dimensions in the FAI?
Yes, if the material is moisture sensitive or the drawing specifies a conditioned state. PA66 can grow after moulding, so a dry dimension and a conditioned dimension are different. Record the conditioning time, temperature and humidity with the result.
What capability should a moulded housing show?
The requirement depends on the customer and the industry scheme. Initial process studies often use a Ppk target such as 1.67 unless the customer specifies otherwise. Agree the characteristic, the sample size and the acceptance criterion before the study.
When does a moulded part need a new PPAP?
When a change affects the part or the process: a tool repair or replacement, a material or colour change, a new insert supplier, a different moulding site or a process change. Follow the customer's change notification procedure and record what was tested.
Sources and further reading
- AIAG Production Part Approval Process, 4th edition
- AS9102, Aerospace first article inspection requirement
- ISO 20457:2018, Plastics moulded parts, tolerances and acceptance conditions
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