Quality planning is the work that happens before the first part is cut: agreeing on which dimensions are critical, how they will be measured, what evidence the buyer needs to approve the part, and what statistical proof shows the process will hold tolerance across a full run. On a fabricated sheet-metal part that means tying every called-out dimension on the print to an inspection method, a measurement system, and a capability target, then packaging that proof in a form the customer’s quality engineer can sign. Get the plan right and the first article passes, the purchase order releases, and reorders run without re-inspection. Skip it and parts get rejected at incoming inspection after they are already built and shipped.
This guide covers the frameworks that govern that proof for fabricated parts: APQP and PPAP as defined by the AIAG, First Article Inspection per AS9102, the quality management system requirements of ISO 9001:2015, dimensioning under GD&T per ASME Y14.5-2018, and the process-capability indices (Cpk and Ppk) that quantify whether a process can actually hold a tolerance. Every framework, form family, submission level, and capability threshold below is tied to its governing source. Atlas Manufacturing runs an in-plant quality suite, and its Minneapolis facility operates an ISO 9001:2015 certified quality management system, so the requirements described here are the ones a part actually moves through on the floor.
APQP: Planning Quality Before the First Part
Advanced Product Quality Planning (APQP) is the structured, up-front planning framework published by the Automotive Industry Action Group (AIAG). It exists to move quality decisions forward in time, so that risks are designed out during development rather than discovered during production. The same discipline applies directly to a fabricated part: deciding which features are critical, how the process will hold them, and what evidence will prove it, all before tooling and the first run.
APQP is organized into five phases (AIAG APQP framework). Each phase produces deliverables that feed the next, and the framework draws on the companion AIAG core-tool manuals for FMEA, MSA, and SPC.
| APQP phase | Focus | Key outputs for a fabricated part |
|---|---|---|
| 1. Plan and define program | Capture customer requirements and design goals | Critical-to-quality feature list, preliminary process flow, reliability and quality goals |
| 2. Product design and development verification | Make the design robust and producible | DFMEA, design reviews, DFM feedback on bends, holes, and tolerances |
| 3. Process design and development verification | Design the process that will make the part | Process flow diagram, PFMEA, control plan, measurement plan |
| 4. Product and process validation | Prove the process makes good parts | Production trial run, First Article Inspection, MSA, initial capability study, PPAP package |
| 5. Launch, assessment, corrective action | Stabilize and improve in production | Reduced variation, lessons learned, ongoing SPC |
The aerospace sector uses the same logic under AS9145, Requirements for Advanced Product Quality Planning and Production Part Approval Process, which formalizes APQP and PPAP for aviation and makes First Article Inspection a required Phase 4 deliverable (First Article Inspection, AS9145 reference).
PPAP: The Evidence Package That Approves the Part
The Production Part Approval Process (PPAP) is the standardized package of documents a supplier submits to prove that a part meets the print and that the process producing it is capable and controlled. It is published by the AIAG, and the document that summarizes and certifies the package is the Part Submission Warrant (PSW): the supplier’s quality lead signs it, and the customer’s quality engineer signs to approve (AIAG PPAP, Wikipedia summary). Until the PSW is approved, production parts cannot be shipped against the order.
The 18 PPAP elements
A full PPAP package is built from 18 standard elements defined in the AIAG PPAP manual. Not every element applies to every part, but the customer’s chosen submission level dictates how many are sent versus retained on file.
| # | PPAP element | # | PPAP element |
|---|---|---|---|
| 1 | Design records (ballooned drawing) | 10 | Records of material and performance tests |
| 2 | Authorized engineering change documents | 11 | Initial process studies (Cpk / Ppk) |
| 3 | Customer engineering approval | 12 | Measurement System Analysis (MSA) studies |
| 4 | Design FMEA (DFMEA) | 13 | Qualified laboratory documentation |
| 5 | Process flow diagram | 14 | Appearance Approval Report (AAR) |
| 6 | Process FMEA (PFMEA) | 15 | Sample production parts |
| 7 | Control plan | 16 | Master sample |
| 8 | Measurement system analysis plan | 17 | Checking aids |
| 9 | Dimensional results (FAI) | 18 | Customer-specific requirements and PSW |
PPAP submission levels
The customer specifies which of five submission levels applies. The level controls what is physically submitted versus what the supplier retains and makes available on request (AIAG PPAP submission levels). Level 3 is the most common default for a new part.
| Level | What is submitted to the customer |
|---|---|
| Level 1 | Part Submission Warrant (PSW) only |
| Level 2 | PSW with product samples and limited supporting data |
| Level 3 | PSW with product samples and complete supporting data (common default) |
| Level 4 | PSW and other requirements as defined by the customer |
| Level 5 | PSW with product samples and complete supporting data reviewed at the supplier’s manufacturing location |
First Article Inspection: Proving the First Part Matches the Print
First Article Inspection (FAI) is the documented verification that a representative production part meets every requirement on the drawing. It is the dimensional-results element of a PPAP package and the validation gate of APQP Phase 4. In aerospace, FAI is governed by AS9102, the North American standard for First Article Inspection requirements (with EN9102 in Europe and SJAC9102 in Japan). AS9102 documents the inspection on three standard forms (AS9102 First Article Inspection).
| AS9102 form | Name | What it captures |
|---|---|---|
| Form 1 | Part Number Accountability | Part identity, drawing revision, sub-assembly accountability |
| Form 2 | Product Accountability | Materials, special processes, and functional testing called out by the print |
| Form 3 | Characteristic Accountability, Verification and Compatibility | Every drawing characteristic, ballooned and matched to its measured result |
The mechanics are the same whether or not the part is aerospace: every dimension and note on the print is uniquely numbered (“ballooned”), and each balloon gets a measured value and a pass or fail verdict. A typical PPAP dimensional study reports a minimum of about six parts per product and process combination so that variation, not just a single lucky part, is visible.
GD&T: Making the Print Unambiguous
A quality plan is only as good as the print it inspects against. Geometric Dimensioning and Tolerancing (GD&T), defined in ASME Y14.5-2018, is the symbolic language that states design intent precisely: how features relate, which datums establish the coordinate system, and how much each feature may vary in form, orientation, and location (ASME Y14.5-2018, Dimensioning and Tolerancing). On a fabricated part, GD&T is what tells the inspector whether a hole pattern is held to true position relative to a folded edge or merely to a coordinate.
GD&T matters to the quality plan in three concrete ways. First, datum references decide how the part is fixtured for measurement, which changes the result. Second, position and profile tolerances usually carry tolerance zones that are checked on a coordinate measuring machine (CMM) rather than with hand tools. Third, the balloon-to-result mapping in FAI and PPAP only works if every callout is unambiguous, which is exactly what Y14.5 enforces.
Measurement: The In-Plant Quality Suite and CMM Inspection
Inspection results are only trustworthy if the measurement itself is trustworthy. Atlas runs a dedicated in-plant quality suite: a purpose-built area within the facility where calibrated measurement equipment is used to verify parts from raw material through final product. Centralizing inspection in a controlled space is what makes a measurement system analysis (MSA, PPAP element 12) meaningful, because gage repeatability and reproducibility depend on consistent equipment and method.
For dimensioned and toleranced features, a coordinate measuring machine (CMM) is the workhorse. A CMM probes discrete points on a part and computes feature geometry (diameters, positions, profiles, flatness) against the CAD model or ballooned print. It is how GD&T position and profile callouts get verified, how Form 3 of an AS9102 report gets populated, and how the dimensional-results element of a PPAP is generated. Hand tools (calipers, micrometers, height gages, pin gages) remain the right choice for simple in-process checks, but the formal inspection record for tight or geometric tolerances comes off the CMM.
Process Capability: Cpk and Ppk
A single good first article proves one part was made right. Process capability proves the process will keep making parts right. The capability indices compare the spread and centering of the process to the tolerance band. Cp measures potential capability (tolerance width versus process spread); Cpk accounts for how far off-center the process is; Pp and Ppk are the long-term performance equivalents (Process capability index).
Cpk is computed as the smaller of (USL minus mean) and (mean minus LSL), each divided by three standard deviations:
Cpk = min[ (USL – mean) / (3σ), (mean – LSL) / (3σ) ], where USL and LSL are the upper and lower specification limits and σ is the process standard deviation. Ppk uses the same formula with the long-term standard deviation.
The widely used minimum thresholds come from accepted process-capability guidance (Process capability index, recommended values). The common contractual floor for an established process is Cpk ≥ 1.33; safety-critical or new processes are held higher.
| Situation | Recommended minimum (two-sided spec) | Recommended minimum (one-sided spec) |
|---|---|---|
| Existing process | 1.33 | 1.25 |
| New process | 1.50 | 1.45 |
| Safety or critical, existing process | 1.50 | 1.45 |
| Safety or critical, new process | 1.67 | 1.60 |
| Six Sigma quality process | 2.00 | 2.00 |
These indices map directly to how many bad parts a process produces. For a centered, normally distributed process, capability translates to a sigma level and a defect rate measured in parts per million (PPM):
| Cp | Sigma level | Process yield | Process fallout (PPM) |
|---|---|---|---|
| 1.00 | 3σ | 99.73% | 2,700 |
| 1.33 | 4σ | 99.9937% | 63 |
| 1.67 | 5σ | 99.99994% | 1 |
| 2.00 | 6σ | 99.9999998% | 0.002 |
One caution: these figures assume a normal distribution and a stable, centered process. A high Cpk on an unstable process is misleading, which is why the capability study sits alongside SPC and a control plan, not in place of them. Where a characteristic runs well above Cpk 2.5, the extra precision is usually just added cost.
ISO 9001:2015: The System Behind the Documents
All of the above sits inside a quality management system. ISO 9001:2015 is the internationally recognized QMS standard; certification means an organization operates a documented, audited system built on risk-based thinking, process control, and continual improvement (ISO 9001:2015). Atlas Manufacturing’s Minneapolis facility is ISO 9001:2015 certified, which is why its inspection records, calibration, and corrective-action processes are systematized rather than ad hoc.
Automotive and aerospace buyers layer sector-specific requirements on top of an ISO 9001 baseline through their contracts and customer-specific requirements. Those contracts are what make APQP, PPAP, and FAI deliverables expected rather than optional, so the practical question for a buyer is not just which certificate a supplier holds but whether the supplier already runs the balloon-to-result, capability-study, and control-plan discipline these frameworks demand.
A Worked Example: Quality Planning on a Regulated Part
Atlas applied this exact discipline on a complex medical-device fabrication project that required FDA clearance. The path through the frameworks looked like this: the critical-to-quality features were identified up front (APQP Phase 1 to 3), a PFMEA and control plan defined how each would be held, a First Article Inspection proved the first parts matched the ballooned print (APQP Phase 4), initial Cpk studies showed the process held the critical dimensions, and the whole package was assembled as the evidence the customer and regulator needed. The result was high-quality production and FDA clearance, which is what a quality plan is supposed to deliver: approval the first time, not rework after rejection.
Frequently Asked Questions
What is the difference between APQP and PPAP?
APQP is the up-front planning framework that runs through the whole development of a part, across five phases from defining the program to launch. PPAP is the evidence package produced near the end (APQP Phase 4) that proves the part meets the print and the process is capable. APQP is the process; PPAP is the deliverable that gets the part approved.
How many PPAP submission levels are there?
There are five PPAP submission levels defined by the AIAG. Level 1 sends only the Part Submission Warrant; Level 2 adds samples and limited data; Level 3 (the common default) adds samples and complete supporting data; Level 4 is customer-defined; and Level 5 keeps the complete package available for review at the supplier’s site. The supplier generates the full evidence at every level; the level just sets how much is physically submitted.
What Cpk value is acceptable?
The common contractual floor for an established process is Cpk of at least 1.33, which corresponds to a 4-sigma process and about 63 defective parts per million. New processes are typically held to 1.50, and safety-critical new processes to 1.67 (a 5-sigma, roughly 1-PPM process). These thresholds assume a stable, normally distributed, centered process.
What is First Article Inspection?
First Article Inspection (FAI) is the documented verification that a representative production part meets every requirement on the drawing. In aerospace it follows AS9102 and is recorded on three forms: Form 1 (part number accountability), Form 2 (product accountability), and Form 3 (characteristic accountability, where each ballooned drawing feature is matched to a measured result). FAI is the dimensional-results element of a PPAP and a required deliverable of APQP Phase 4.
Does a sheet-metal supplier need ISO 9001 certification?
ISO 9001:2015 is the general quality management system standard and the baseline for a precision fabricator: certification means inspection records, calibration, and corrective action run inside a documented, audited system. Atlas Manufacturing’s Minneapolis facility is ISO 9001:2015 certified. Automotive and aerospace buyers add sector requirements through their contracts, which is what makes APQP, PPAP, and FAI deliverables mandatory on those programs.
