Quality assurance & certification in 3D printing
Non-destructive testing, in-situ monitoring and regulatory requirements for series use.
1. Introduction: The trust problem in 3D printing
In traditional manufacturing processes (such as casting or machining from forged blocks), the material structure already exists before the part is shaped. The semi-finished product can be certified. In additive manufacturing, however, the material is only created during the construction process through millions of small melting processes.
Especially in safety-critical industries (aviation, medical technology, energy), the central question is: How do I know that there are no pores, no cracks and no bonding errors inside my component? This white paper is dedicated to quality assurance (QA) and certification.
Why quality assurance in 3D printing is so expensive
Inspecting an additively manufactured titanium aircraft part can often be more expensive than the printing process itself. Since each part is potentially unique, random sampling is often not enough - a 100 percent inspection of all safety-relevant components is required.
2. In-situ monitoring: monitoring every second
The supreme discipline of additive quality assurance is monitoring during (in-situ) the process.
- Melt Pool Monitoring: High-speed cameras (usually in the infrared range) coaxially in the laser beam path observe the shape, size and temperature of the melt pool. If this deviates from the norm (e.g. because it gets too hot locally and evaporates, which causes pores), this is recorded precisely in the 3D coordinates.
- Optical tomography: With each layer of powder applied, a camera takes an image of the entire construction platform. This creates a three-dimensional "X-ray view" of the construction process, layer by layer, long before the part is finished.
3. Non-Destructive Testing (NDT)
After printing, the component must be checked for internal errors without damaging it.
- Industrial computed tomography (CT scans): CT is the most reliable but also the most expensive procedure. X-rays shine through the component and reveal even pores in the micrometer range. However, when it comes to massive components (e.g. thick steel or Inconel), the radiation output of conventional CT scanners reaches its physical limits.
- Ultrasonic testing: A proven process that, however, has its limits when it comes to additively manufactured, rough surfaces and complex lattice structures.
- Dye penetrant testing (PT): An extremely cost-effective method for finding microcracks that extend to the surface. Ideal after heat treatment.
4. Destructive Testing
In order to demonstrate the mechanical properties (tensile strength, yield strength, notched impact strength), statistical destruction is used.
- Tensile bars: With every printing job, standardized tension bars are printed on the edge of the build platform. After the process, these sticks are torn apart in a testing laboratory. The premise: If the tensile test passes the stress test, the components on the same platform also have the required mechanical characteristics.
5. Certification and qualification of the supply chain
In order to be certified in aviation, for example, not only the component but the entire supply chain must be “frozen”.
- Powder traceability: Every gram of powder must be completely traceable from the powder manufacturer through the sieving station to the construction platform. Contamination (e.g. cross-contamination of titanium with steel powder) is absolutely fatal.
- Fixed Process Certification: The manufacturer is not allowed to make any changes to the parameters (laser power, scanning speed, powder batch) after approval. Every printer software update theoretically requires a new, expensive validation.
6. Conclusion: The path to digital certification
The manual inspection and CT scanning of each individual component does not scale to mass production. The future of certification lies in machine learning: If AI algorithms can evaluate the in-situ monitoring so perfectly that they guarantee: “This print was error-free,” then the component will be certified directly from the machine (Born Certified). Until then, QA remains a cost-intensive but essential part of additive value creation.