APQP plans quality before series production begins; industrial CT delivers the measurement data that makes this planning reliable. To turn requirements, FMEA and control plans into sound decisions, you need measurements on the real part. CT complements classical metrology wherever internal structures, concealed geometries or defects have to be evaluated non-destructively and in three dimensions.
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Planning quality also means planning measurability
Advanced Product Quality Planning (APQP) is a structured approach to quality planning from product idea to stable series production. It is meant to ensure that the required steps in each phase are completed on time and that the product satisfies the customer. The underlying idea: quality assurance starts in the design and planning stage, not later in series production. The method connects customer requirements, product development, process development, validation and continuous improvement. A binding framework is provided by established methods:
- QFD (Quality Function Deployment) to translate customer requirements,
- DFMEA and PFMEA to assess design and process risks,
- the control plan for process control [6],
- measurement system analysis (MSA) and SPC for capable measurements and stable processes.
These methods, however, depend on reliable information. Only measurements on the real part show whether a design feature can actually be manufactured, how process parameters affect product quality, and whether the series process meets the requirements reproducibly. Metrology is therefore not a downstream inspection step but a central source of information for the entire APQP process.
Key point: APQP defines what has to be achieved and controlled. Metrology delivers the objective evidence. Industrial CT extends that evidence to the complete part volume.
The role of metrology in APQP
A consistent measurement strategy answers four questions right at the start of the project:
- Which product and process characteristics are critical to quality or function?
- Which measurement method can capture these characteristics with the required accuracy?
- Is the measurement system suitable for development trials, capability studies and later series inspection?
- How are measurement data documented, compared and fed back into FMEA, control plan and process control?
Not every characteristic calls for the same method. Tactile coordinate metrology is often highly accurate for accessible single dimensions; optical systems capture surfaces quickly and across large areas; 2D X-ray, ultrasonic testing and other non-destructive methods each answer specific questions.
Industrial CT becomes particularly interesting when several external and internal characteristics are to be examined in one shared 3D data set.
What industrial CT adds
In CT, the part is X-rayed from many directions and reconstructed as a three-dimensional volume. External and internal structures can thus be examined non-destructively. Depending on part size, material, inspection task and required resolution, the following evaluations are possible in particular:
- dimensional inspection and actual/nominal comparison against CAD data,
- measurement of wall thicknesses, internal dimensions and hard-to-reach geometries,
- analysis of pores, shrinkage cavities, cracks and inclusions by size and position,
- verification of assembly, joining and connection states, including at assembly level,
- comparison of prototypes, variants, tools, cavities and process states,
- archiving of a digital 3D record for later evaluations.
CT therefore does not simply replace other measurement methods. It closes an information gap: while conventional methods usually deliver selected accessible characteristics or projections, CT can capture many relevant characteristics spatially, non-destructively and in their mutual context.
Metrology and CT across the five APQP phases
Planning and definition
Customer requirements, quality targets, critical characteristics. Measurability is settled now, not in phase 4.
Product development
DFMEA, building and measuring prototypes: does the real part match the design, including internal features?
Process development
PFMEA, control plan, inspection planning. Measurement data from trial parts secure the process window.
Validation
Production run under series conditions, MSA, first article inspection, capability evidence: the basis for PPAP approval.
Series
SPC, trend monitoring, root cause analysis. In-process inspection detects drift before scrap occurs.
Between the phases sit quality gates where the transition to the next phase is decided.
Phase 1: Planning and definition
At the start, it is defined what the product has to deliver and how that will later be measured.
Goal of the phase. First, the needs and expectations of the customer are understood, for example from the design specification; then the project frame is defined, along with quality and reliability targets and the fundamental product and process risks.
Role of metrology. Critical characteristics must not only be specified but also be measurable. Already at this stage it should be clarified which accuracy is required, how inspections will later be performed and which data will be needed for approvals.
Contribution of industrial CT. Based on CAD data, material, part size and required detail detectability, it can be assessed early whether CT is technically suitable. This avoids untestable specifications, unrealistic resolution requirements or later capacity bottlenecks.
Possible deliverables: preliminary measurement and inspection concept, feasibility analysis of CT suitability, documented manufacturing feasibility review with the supplier, definition of critical characteristics and data requirements.
Phase 2: Product design and development
In this phase, prototypes show whether the design delivers what the engineering promises.
Goal of the phase. The product design is detailed, risks are assessed in the DFMEA and prototypes are built.
Role of metrology. Measurement data verify whether the real part meets the design assumptions. They support design reviews, tolerance decisions and the assessment of special characteristics. What matters is not only the deviation from nominal but also its possible functional impact.
Contribution of industrial CT. CT accelerates development loops because prototypes can be examined completely without disassembly or sectioning; the comparison against CAD data makes local deviations immediately visible.
Possible deliverables: prototype findings, actual/nominal comparisons, verified DFMEA assumptions and pointers for design optimization.
Phase 3: Process design and development
Phase 3 still deals with the product design, but the focus shifts to the process: this is where product measurement turns into process knowledge.
Goal of the phase. The manufacturing sequence is designed, process risks are assessed in the PFMEA (process FMEA), and a robust process and a suitable control plan are developed.
Role of metrology. Parts from trial runs and pre-series are linked to process parameters. This reveals which settings, tools or cavities influence relevant quality characteristics and where a reliable process window lies.
Contribution of industrial CT. CT delivers quantitative target values for trial planning and root cause analysis, for example pore volume, defect sizes, positional deviations, distortion or wall thicknesses. Because the part remains undamaged, CT findings can also be correlated with functional or load tests on the same part. A practical example: with hairpin stators, the pore assessment of the weld serves as the target value that is correlated with the welding parameters; on this basis Microvista has evaluated more than 200,000 stators.
Possible deliverables: data basis for PFMEA and control plan, cause-and-effect relationships, comparison of process variants, tools or cavities, and definition of a robust process window.
Phase 4: Product and process validation
This phase decides on approval: this is where FAIR, PPA/PPF and PPAP evidence is produced.
Goal of the phase. Under near-series conditions, it is demonstrated that product and manufacturing process meet the requirements of the customer reproducibly.
Role of metrology. The measurement systems used must be suitable and deliver traceable results. Measurement system analysis, first article inspection and capability studies create the data basis for PPA/PPF [5] and PPAP [2]. A distinction must be made between product conformity and process capability: one good part does not yet prove a stable process.
Contribution of industrial CT. CT provides complete 3D data sets for first articles. Decisive in this phase: for capability values, the characteristic, evaluation method, sample and suitability of the measurement process must be clearly defined. Not every CT evaluation automatically qualifies as a measurement process suitable for capability studies.
Possible deliverables: FAIR and PPA/PPF or PPAP evidence, documented measurement results, inspection reports, MSA results and capability data for defined characteristics.
Phase 5: Feedback, assessment and corrective action
After the start of series production, it becomes clear whether the process remains under control.
Goal of the phase. After SOP, process performance, product quality and customer feedback are monitored; deviations lead to corrective and improvement actions. The aim is the long-term fulfilment of customer requirements and the reduction of variation within production; the target result is minimized variation in the manufacturing processes.
Role of metrology. Series measurements reveal trends, process drift and changes in variation. Good measurement data enable SPC, targeted reaction plans and a fact-based root cause analysis for complaints or blocked lots.
Contribution of industrial CT. In-process CT makes internal quality characteristics statistically evaluable as well. Automated evaluation workflows and defined inspection decisions enable reproducible inspections. In case of deviations, CT also delivers detailed information for root cause analysis and effectiveness checks.
Possible deliverables: trend and SPC data, evidence of stable series quality, root cause analyses, effectiveness checks, and updated FMEAs and control plans.
Overview: from APQP question to CT contribution
The table summarizes the 5 phases: which measurement question is at the centre of each, what CT contributes and what value that has for APQP.
| Phase | Key measurement question | CT contribution | Value for APQP |
|---|---|---|---|
| 1 Planning | Can the critical characteristics be measured reliably at all? | Feasibility assessment of penetrability, resolution and inspection concept | Secure measurability early |
| 2 Product | Does the real part match the design, including internal features? | 3D actual/nominal comparison, internal dimensions, wall thicknesses, defect and assembly analysis | Objectify design decisions |
| 3 Process | How do parameters and tooling affect part quality? | Quantitative CT characteristics from trial and pre-series parts | Secure the process window and PFMEA |
| 4 Validation | Are requirements met reproducibly? | Defined measurement and inspection reports for FAIR, PPA/PPF and PPAP, and capability evidence | Base approval on reliable data |
| 5 Series | Does the process remain stable and under control? | Series inspection, trend analysis, automated evaluation and root cause analysis | Detect drift early and improve |
From measurement data to process understanding and predicted quality
CT data become particularly valuable when they are not viewed in isolation but connected with process and functional data. For every examined part, for example, machine parameters, material batch, tool or cavity, CT characteristics and the results of a functional test can be brought together.
Step by step, this builds a reliable cause-and-effect model: which process variables change which internal quality characteristics, and which of these characteristics influence function?
CT initially serves as a high-resolution quality reference. On this basis, statistical or AI-based models can later estimate part quality directly from process data (predicted quality). CT samples remain important to validate these predictions and to detect changes in the process.
Process data
- Machine parameters
- Material batch
- Tool and cavity
CT characteristics
- Pore volume and defect sizes
- Wall thicknesses and dimensions
- Distortion
Functional testing
- Load tests
- Leak testing
- on the same, undamaged part
Regular CT samples verify whether the predictions hold and whether the process has changed.
Prerequisites for reliable CT results
Even a powerful inspection method does not automatically produce reliable quality evidence. For use in APQP, the following points should be clearly defined:
- inspection task and the characteristic to be assessed, including tolerance or acceptance criterion,
- suitable scan parameters, resolution, part orientation and reconstruction conditions,
- consistent evaluation and segmentation rules,
- validation of the measurement or detection capability for the specific task,
- traceability, documentation and versioning of the evaluation software,
- representative samples and a clear approach to measurement uncertainty and borderline cases.
The decisive question is therefore not only: “Can we scan the part?” But: “Can we measure or detect the relevant characteristic with sufficient confidence and derive a reliable APQP decision from it?”
When CT adds particular value
The use of industrial CT offers particularly high value when at least one of the following conditions applies:
- quality-critical characteristics are internal or geometrically hard to access,
- destruction or disassembly would alter the finding or prevent further tests,
- several dimensional, defect and assembly characteristics are to be assessed from the same data set,
- process variants or trial parts have to be compared quickly and comprehensively,
- a spatial correlation of defects to functional surfaces is required,
- in case of complaints or scrap, the cause has to be narrowed down without guesswork.
If one of these points applies to a critical characteristic, CT inspection belongs in the APQP measurement strategy from the very beginning.
How Microvista supports the APQP process
Microvista supports companies not only with individual CT inspections but with an end-to-end data and inspection strategy along the product life cycle:
- feasibility assessment and design of the CT inspection task,
- prototype and variant inspection for short development loops,
- CT measurement series for process development and securing process windows,
- dimensional and non-destructive inspections for FAIR, PPA/PPF and PPAP,
- temporary additional inspection capacity for pre-series and ramp-up,
- in-process inspection, automated evaluation and support with quality problems.
Industrial CT thus evolves from a mere defect detector into a development and process tool: it makes quality measurable, explains relationships and delivers the objective data basis for decisions in APQP.
Frequently asked questions
APQP stands for Advanced Product Quality Planning. The APQP method is a structured approach to quality planning across the entire product development process, from the definition and development of a product to stable series production [1]. The method connects quality planning with project management; the structured process is divided into five phases connected by quality gates. Core goals are the long-term fulfilment of customer requirements, defect prevention instead of defect detection, and the reduction of variation in the manufacturing processes. APQP is thus a central process in quality management. The methodology is taught by the AIAG reference manual and corresponding training courses.
APQP was developed in 1982 by the three American car manufacturers Chrysler, General Motors and Ford. Their joint task force for supplier quality requirements drove the harmonization of the manuals, from which the QS-9000 guidelines published in 1994 emerged. Today APQP is based on the reference manual of the Automotive Industry Action Group (AIAG), in its 3rd edition since 2024 [1].
APQP is the overarching planning process across all five phases. PPAP (Production Part Approval Process) is the approval procedure at the end of phase 4: sampling according to PPAP demonstrates to the customer that product and process are ready for series production [2]. PPAP is thus a component and result of APQP, not a competing method.
The central tools are the FMEA (as DFMEA for the product, as PFMEA for the process), the control plan as the instrument of process control [6], measurement system analysis (MSA) to qualify the measurement systems, SPC to monitor series production, and QFD to translate customer requirements. The result forms the basis for creating control plans; the formal conclusion of validation is the PPAP [2].
A central one. Suppliers are ideally involved as early as phase 1, because quality planning has to extend across the entire supply chain. One of the early deliverables is therefore the documented manufacturing feasibility review with the supplier.
Defects detected early cost a fraction of what rework in series production costs: APQP shifts defect prevention to the start of the project. Add clear responsibilities via quality gates, reliable evidence for approval, and a predictable ramp-up with fewer complaints.
In principle in all five phases: from the feasibility assessment of the inspection task through prototype and process development to validation, series monitoring and root cause analysis. Intensity and evaluation scope change from phase to phase.
No. CT is part of a coordinated measurement strategy. For easily accessible single dimensions, tactile or optical methods can be more economical or more accurate. CT is particularly strong for internal, concealed and combined characteristics.
Yes, provided the specific inspection task, the evaluation method and the suitability of the measurement process are defined traceably. CT reports can deliver dimensional results, wall thicknesses, and defect or assembly assessments for the approval, among other things.
Yes, for clearly defined quantitative characteristics and given a suitable measurement process and a representative sample. A single CT inspection or a purely visual assessment is not sufficient for capability evidence.
Ideally as early as the definition of special characteristics, and not shortly before sampling. This allows technical feasibility, measurement capability, inspection time, cost and required capacity to be taken into account in good time.
Sources and normative context
The statements in this article are based on the following standards and manuals:
- [1] AIAG (2024): Advanced Product Quality Planning (APQP), 3rd edition.
- [2] AIAG (2006): Production Part Approval Process (PPAP), 4th edition.
- [3] IATF (2016): IATF 16949:2016. Quality management system requirements for automotive production and relevant service parts organizations.
- [4] SAE International (2016): AS9145. Aerospace Series: Requirements for Advanced Product Quality Planning and Production Part Approval Process.
- [5] VDA QMC (2020): VDA Volume 2. Quality Assurance for Supplies: Production Process and Product Approval (PPA/PPF), 6th edition.
- [6] AIAG (2024): Control Plan Reference Manual, 1st edition.