A compliant first article inspection verifies mold tooling before mass production. This guide covers prerequisites, measurement steps, and common mistakes to ensure dimensional stability and surface quality in early production runs.
- A first article inspection must verify dimensions, surface quality, and material flow before releasing the tool for mass production.
- The FAI process requires a defined sample set, calibrated gauges, and a documented approval workflow.
- Common mistakes include measuring only critical features and ignoring mold release or ejector pin marks.
- Final verification requires a signed approval and a clear handover to the production schedule.
Why You Need a First Article Inspection
A first article inspection checks the first batch of parts from a new or reworked mold. It confirms the tooling meets the drawing before mass production starts. The process stops costly rework and protects the supplier relationship. Without it, defects appear later in the run when the cost to fix them is much higher.
The inspection covers three areas. Dimensional accuracy, surface finish, and material properties. It also includes a visual check for flash, sink marks, and ejector pin impressions. The goal is to verify the mold produces parts that fit the design and function as intended.
Consider a housing for an automotive sensor. If the mounting boss is 0.5mm too large, the sensor will not align with the chassis. If the surface is too rough, the paint may peel. The first article inspection catches these issues before the mold runs for thousands of cycles. It also creates a baseline. If a problem appears in week three of production, you can compare the current parts to the approved first article. If the data matches, the problem is likely in the machine or material. If it does not match, the mold has changed.
What You Need Before Starting
Before the first shot, gather the documents and equipment. The customer drawing with all critical dimensions is required. The mold number and cavity count must match the purchase order. A first article inspection form or report template should be ready.
Bring calibrated measuring tools. Calipers, micrometers, and height gauges are standard. For complex parts, a Coordinate Measuring Machine or optical comparator may be needed. The tools must have current calibration certificates. If the part has optical or electrical tests, prepare the relevant fixtures.
The drawing must be the current revision. Old revisions cause errors. If the customer changes a radius or a hole size, the inspector needs the updated version. The report template should have fields for every critical dimension. It should also have a space for notes on defects and photos. The mold tag is a physical label attached to the mold. It usually has the mold number, cavity count, and last maintenance date. Keep it visible during the inspection.
Step 1: Confirm the Mold and Material Setup
Start by verifying the mold number and the material used. Match the mold tag to the work order. Check the resin lot number against the purchase order. A wrong material can cause dimensional shifts that no amount of measurement will fix.
Confirm the machine settings. Record the barrel temperatures, injection pressure, and cycle time. These settings are the baseline for the first article inspection. If the supplier changes settings later, the parts may not match the approved sample.
Check the mold release agent. Some release agents leave a residue that affects surface finish. If the customer requires a specific release agent, verify it. The material lot number is critical. Resins vary between lots. A lot with higher moisture content will produce more shrinkage. The resin supplier usually provides a certificate of analysis. Keep it with the report. If the part is made from a recycled material, the variability is higher. You may need to check the material properties more frequently.
Step 2: Select the Correct Sample Set
The first article inspection requires a specific sample set. The standard practice is to take five to ten parts per cavity. The sample size depends on the part complexity and the number of cavities. For a four-cavity mold, take five parts from each cavity.
Take the samples after the machine reaches stable temperature. Do not inspect parts from the first few shots. The mold needs time to reach thermal equilibrium. The parts should be from a consecutive batch to show consistency. If any part looks wrong, note it and take another set.
Mark each sample with its cavity number. Use a marker or a label. If you measure part A from cavity 1 and part B from cavity 2, you cannot tell which is which later. The sample set should represent the steady state of the production run. If the machine is new, it may take longer to stabilize. If the mold is old, the hot spots may be established. The inspector should watch the first ten or twenty shots and discard them. The parts from shot 25 onward are more representative.
Step 3: Perform Visual Inspection
Check each part for visible defects. Look for flash, which is thin material extruded at the mold parting line. Check for sink marks, which are depressions where the material contracted. Inspect for ejector pin marks, which are small indentations from the ejection system.
Examine the surface finish. Compare the gloss and texture to the customer sample. Check for weld lines, which are the seams where the material flows and meets. A weld line can be a stress point. Note its location and severity on the report.
Use a light source. A bright light helps you see small defects. Check the part from different angles. Some defects are only visible at a specific angle. Look for color variation. If the resin is tinted, check for streaks or discoloration. Check for burn marks. Burn marks occur when the material is too hot or the speed is too high. They usually appear as dark spots. Record the location and size of any burn marks.
Step 4: Measure Critical Dimensions
Measure the critical dimensions first. These are the features that affect assembly and function. Use the drawing to identify the tolerance for each feature. Measure each part in the sample set. Record the actual value, not just pass or fail.
For a bracket with a 10mm hole, measure the diameter at multiple points. Check the hole depth if specified. Measure the overall length, width, and height. If the part has a threaded boss, verify the thread pitch and depth. Record all values in the report.
Measure the part in a controlled environment. Temperature affects dimensions. If the room is hot, the part may expand. If it is cold, it may contract. Use the temperature on the drawing as the reference. If the drawing says 20 degrees Celsius, measure at that temperature. If you measure at 25 degrees, the part will be larger. Record the room temperature. If the part has a flat surface, check for warp. Use a straight edge and a feeler gauge. If the gap is greater than the tolerance, the part may not seat flat.
Step 5: Check Surface Finish and Texture
Surface finish is often judged by the customer’s standard. If the drawing specifies a gloss value, use a gloss meter. If it specifies a texture class, compare it to a physical sample. Record the method used. A gloss of 50 on a matte part is different from a gloss of 50 on a shiny part.
Check the texture for uniformity. Look for areas where the mold steel texture may have worn or changed. A worn texture can cause parts to look different from the approved sample. Note any variation in the report.
Use the gloss meter at a specific angle. Usually, 20 degrees or 60 degrees is standard. Record the angle used. If the part has a textured surface, the gloss meter reading may be inconsistent. In that case, use visual comparison. Hold the part next to the approved sample under the same light. Look for differences in the pattern. If the texture is too deep, it may affect the paint. If it is too smooth, it may show fingerprints. The customer usually has a standard for this. If they do not, use the approved sample as the reference.
Step 6: Verify Material Properties
If the part requires specific material properties, test them. For engineering plastics, a tensile test may be needed. Take coupons from the same material lot. Measure the tensile strength, elongation, and heat deflection temperature.
For consumer products, a drop test or impact test may be required. The test method should match the customer’s specification. Record the results. If the material fails, the parts are not approved. The mold is not the problem, but the material is not fit for purpose.
The tensile test uses a standardized specimen. The specimen is pulled until it breaks. The machine records the force and the distance. From this, you calculate the tensile strength and the elongation. If the part is for a medical device, the material may need to be certified. The certificate should list the lot number and the test results. If the part is made from a material with additives, the properties may vary. The resin supplier should provide a datasheet. Compare the datasheet values to the test results. If the test results are lower than the datasheet, the material may be degraded or contaminated.
Step 7: Review the Report and Get Approval
Compile the data into the first article inspection report. Include the date, mold number, material lot, and machine settings. List each measurement and its result. Mark each item as pass or fail. If a dimension is out of tolerance, state the action taken.
The report needs a signature. The inspector signs after the measurements are done. The quality engineer or customer representative signs after reviewing the data. Without the signature, the parts are not approved. The production schedule cannot start until the report is signed.
The report should be clear and objective. Do not write “looks good.” Write “gloss is 45 at 60 degrees, matching the sample.” Do not write “no defects.” Write “no flash, sink, or ejector marks visible.” The report is a legal document. It defines what was accepted. If there is a dispute later, the report is the reference. If a dimension is out of tolerance, the report should state the value, the tolerance, and the action. For example, “Hole 1 is 10.05mm. Tolerance is 10.00 to 10.04mm. Action: Rejected. Mold adjusted.” The report should be kept with the mold records. If the mold is used again, the previous report helps the inspector know what to watch for.
Step 8: Final Verification and Handover
The final verification step is a simple check. Confirm that the approved parts are stored correctly. Label them with the lot number and the approval date. Store them in a clean area to prevent scratches or contamination.
Hand over the report to the production manager. The manager uses the report to start the mass production run. The mold is now in service. The settings are locked. The first article inspection is complete.
The approved samples should be kept. If the mold is stored for a long time, the mold may change. The approved samples serve as a reference. If the mold is reworked, the new first article inspection should compare to the old samples. If the mold is sent to a different location, the samples should travel with the mold or be kept in a secure archive. The production manager needs the report to start the run. The report confirms that the mold is ready. It also confirms that the material is correct. The settings are locked to prevent changes. If a machine operator changes a setting, the parts may not match the first article. The report should state that the settings are locked.
Common Mistakes to Avoid
The most common mistake is measuring only the critical dimensions. A part may fit the assembly but have a bad surface finish. The customer will reject it. Measure all specified features.
Another mistake is using uncalibrated tools. A caliper that is off by 0.1mm can make a part look good when it is not. Always use calibrated gauges.
A third mistake is taking samples too early. The first few shots can be inconsistent as the mold heats up. Wait for stable production.
Another mistake is not checking the material. If the resin is contaminated with moisture, the part may have voids. The voids may not be visible at first, but they cause weak points. Always check the material lot and the drying process. If the material is from a different lot than the approved sample, the properties may change. The first article inspection should verify the material properties if the lot is different.
A Simple Checklist for the Inspector
| Check Item | Method | Acceptance Criteria |
|---|---|---|
| Dimensional accuracy | Calipers, micrometers | Within drawing tolerance |
| Surface finish | Gloss meter, visual | Matches customer sample |
| Flash and sink | Visual inspection | None visible under standard light |
| Material properties | Tensile test, impact test | Meets material specification |
| Mold release | Visual inspection | No residue or sticking |
When to Escalate a Failed Inspection
If a dimension is out of tolerance, do not guess. Record the value and the tolerance. If the part fails a material test, stop the run. The mold may be fine, but the material is wrong. Contact the supplier and the customer.
A failed first article inspection is not a failure. It is a data point. It tells you what to fix. The mold can be adjusted, the settings changed, or the material replaced. The goal is to get the parts right before mass production.
If a dimension is consistently out of tolerance, the mold may need repair. If a dimension is in tolerance for some cavities and not for others, the mold may be unbalanced. If the surface finish is wrong, the mold steel may need polishing. If the material fails, the resin supplier may need to provide a better lot. The inspector should not decide the fix. The inspector records the problem. The quality engineer or the mold maker decides the fix. After the fix, a new first article inspection is needed. The new inspection should compare to the old report. If the new parts match the drawing, the mold is approved again.
Final Thoughts
A first article inspection is a practical process. It verifies the mold before mass production. It protects the customer and the supplier. It follows a clear path: prepare, sample, inspect, measure, and approve. Do it every time. It saves money and prevents problems.
The first article inspection is not a formality. It is a check. If you skip it, you are betting on the mold. If you do it, you have proof. The proof protects you. If a problem appears in production, you can trace it. If the parts match the first article, the problem is in the process. If they do not match, the mold changed. The first article inspection is the anchor. It keeps the process honest. It keeps the customer informed. It keeps the supplier accountable. Do it. Keep the records. Use the data. The mold is a tool. The first article inspection makes sure the tool works as intended.
Frequently asked questions
How many parts do I need for a first article inspection?
Take five to ten parts per cavity. The exact number depends on the part complexity and the number of cavities.
Can I use the same mold for a different material without a new first article inspection?
Yes, a new first article inspection is required when the material changes. The dimensional behavior and material properties will be different.
What if a dimension is out of tolerance by a small amount?
Record the value. Contact the customer for a waiver if the part still meets the functional requirement. Do not assume it is acceptable.
Who signs the first article inspection report?
The inspector signs after measuring. The quality engineer or customer representative signs after reviewing. Both signatures are needed for approval.
Is a first article inspection required for every production run?
No, only for new molds, reworked molds, or when the material or process changes. A new first article inspection is not needed for a standard production run.
