How In-Process Metrology Works in Metal Additive Manufacturing
In the additive manufacturing sector, monitoring is not enough: only by measuring precisely during the process can repeatable and scalable quality be guaranteed.
Metal additive manufacturing (AM) is no longer judged solely on its ability to print, but on the reliability, repeatability, and scalability of the process. As technology transitions from prototyping to production, manufacturers face a crucial industrial challenge: how to guarantee constant quality without relying on costly and lengthy post-process inspections? The answer lies in the integration of metrology systems calibrated directly into the production cycle, capable of providing traceable quantitative data instead of subjective signals.
Limitations of Traditional Monitoring Solutions
Current monitoring techniques provide qualitative information but lack the metrological accuracy required for critical processes.
Most metal powder bed fusion (PBF) systems today rely on combinations of optical imaging, infrared cameras, photodiodes, or AI-assisted anomaly detection. These tools offer useful visibility, but are fundamentally subjective and uncalibrated, relying on “black box” AI systems that produce relative signals rather than absolute measurements.
In traditional production, quality decisions are never based on subjective monitoring alone. Machined parts are verified with calipers, coordinate measuring machines (CMMs), and measuring instruments: all devices that produce traceable data based on standard units of measurement. AM, by contrast, has spent years attempting to infer quality from relative signals that vary from machine to machine and from build to build.
As AM programs scale, this gap becomes a business risk. Post-process inspection can represent more than half the cost of a qualified AM metal part and, in some cases, becomes physically impossible, such as for large aerospace components. The industry does not need more monitoring: it requires in-process inspection that enables early decisions and fewer downstream surprises.
In-Process Metrology: Fundamentals and Requirements
To effectively integrate quality control into the production cycle, systems must provide quantitatively valid and traceable measurements.
The fundamental difference between monitoring and in-process metrology lies in the nature of the data collected. While monitoring detects qualitative variations, metrology provides calibrated dimensional measurements, comparable to recognized standards and repeatable across different machines and facilities.
To be effective in an industrial setting, an in-process metrology system must meet precise requirements: certified accuracy according to international standards (such as VDI/VDE 2634), resolution adequate to detect critical defects, traceability of measurements, and the capability to generate data usable for immediate production decisions. These requirements align AM with IQ, OQ, and PQ qualification frameworks and support emerging standards such as SAE 7032 and NASA-STD-6033/6035.
In-process metrology transforms AM from a monitored process to a controlled process: when the anomalies that matter are measured and controlled, qualification becomes a continuous process rather than a costly final obstacle.
Fringe Optical Techniques: Principle and Industrial Application
Fringe technology enables precise and reproducible measurements, directly applicable in the additive production environment.
Structured light technology, and specifically fringe optical techniques, represents an advanced metrology solution for in-process inspection. These systems project structured light patterns onto the surface of the component being built, observed by calibrated cameras that reconstruct the three-dimensional geometry via triangulation.
Instead of indirectly estimating the process state, these systems directly measure the three-dimensional surface profile of each layer (fused surface and distributed powder) during the build. For laser powder bed fusion, this translates to quantitative measurements of powder layer uniformity, fused surface topology, and actual layer thickness.
Since these measurements are calibrated and based on standard units, they can be compared across different machines, materials, and facilities, providing an essential requirement for industrial qualification and process control. The capability to acquire millions of points in seconds, without physical contact and in a non-destructive manner, makes this technology ideal for integration into high-throughput production cycles.
Case Study: Implementation on Phase3D Platform
A practical example shows how the integration of in-process metrology improves efficiency and reliability compared to traditional final controls.
Phase3D has developed Fringe Inspection, a system that applies structured light metrology to metal AM. In collaboration with the Additive Manufacturing Institute of Science and Technology (AMIST) at the University of Louisville, the system was used to quantify spatter – molten or partially molten material ejected during laser melting – recognized as a primary cause of surface roughness and porosity.
Using 17-4PH stainless steel samples printed on an EOS M 290, the system captured metrology-grade height maps of every layer, objectively quantifying spatter particles, surface roughness, and their spatial distribution in the build area. Data showed that regions with higher surface roughness and spatter counts consistently exhibited greater porosity, while smoother regions produced denser parts.
This result demonstrates a direct, quantitative link between in-process surface measurements and final component quality. Economically, the implications are significant: manufacturers gain the ability to identify poor-quality regions immediately, instead of discovering defects after post-print inspection. Conservative estimates indicate the US and EU qualification market was approximately $3.3 billion in 2025, growing toward $7.8 billion by 2030.
A recent joint EASA-FAA workshop on Additive Manufacturing highlighted the need for high-fidelity, real-time in-situ inspection methods for qualification, confirming the strategic direction toward integrated metrology systems.
Conclusion
The adoption of in-process metrology systems represents a breakthrough for the reliability and scalability of industrial additive manufacturing.
With calibrated surface data available layer by layer, manufacturers can implement closed-loop strategies, automatically adjusting powder distribution, modifying laser behavior, or flagging localized risk zones. Objective inspection enables the creation of clear go/no-go criteria based on quantified thresholds linked to known defect risks, replacing intuition with data-driven decisions.
This approach naturally aligns with IQ, OQ, and PQ frameworks and supports emerging standards, transforming AM from a craft process to a mature industrial process. When quality becomes predictable through in-process metrology, additive manufacturing becomes truly industrial, enabling scaled production with confidence and without quality compromises.
Evaluate the integration of certified metrology solutions into your production processes to anticipate defects and reduce scrap.
article written with the help of artificial intelligence systems
Q&A
- What is the main difference between monitoring and in-process metrology in metal additive manufacturing?
- Monitoring provides qualitative and subjective information, while in-process metrology offers quantitative, calibrated, and traceable measurements relative to recognized standards. This enables immediate and reliable production decisions.
- Why does post-process inspection represent a challenge in metal additive manufacturing?
- Post-process inspection can represent more than half the cost of a qualified metal part and is sometimes impossible to perform physically, especially for large components like aerospace ones.
- What requirements must an in-process metrology system meet to be effective in an industrial setting?
- It must guarantee certified accuracy according to international standards, sufficient resolution to detect critical defects, traceability of measurements, and the ability to generate data usable for immediate production decisions.
- How does fringe technology work in in-process metrology?
- It projects structured light patterns onto the component's surface and, through calibrated cameras, reconstructs the 3D geometry via triangulation. It directly measures parameters like powder layer uniformity and surface roughness.
- What benefits did the implementation of Phase3D's Fringe Inspection bring in a case study?
- It allowed for quantifying spatter and directly correlating it to the final porosity of the component. It made it possible to identify low-quality areas in real-time, avoiding costly post-print inspections and improving process reliability.
