Computed tomography (CT) in 3D printing
The high-resolution X-ray view into the heart of titanium and Inconel components.
1. Introduction: A look inside
When engineers invest hundreds of hours and thousands of dollars into 3D printing a rocket engine or a spinal implant, they need to be sure that the component is completely flawless. A look from the outside is not enough here, and cutting it open (destructive testing) is of course not an option.
Industrial computer tomography (CT) is the premier class of non-destructive testing (NDT). It enables a high-resolution 3D X-ray view into the heart of solid metal components and has established itself as an absolute standard in AM quality assurance.
How does industrial CT differ from medical CT?
A hospital CT scan penetrates soft tissue and bone with relatively weak radiation. Industrial CT scanners use massive X-ray tubes (often 450 kV or even linear accelerators for extreme penetration) to force radiation through thick blocks of titanium or Inconel. In addition, in industry the component is rotated on a turntable while the tube is stationary - with humans it is the other way around.
2. Detect porosity and varnish of fusion
The main task of CT is the search for the invisible.
- Porosity analysis: The CT scan virtually breaks down the component into millions of small cubes (voxels). Special analysis software searches for voxels whose density corresponds to that of air. In this way, microscopic pores inside can be localized with millimeter precision.
- Lack of Fusion: If the laser in the PBF process has not properly fused two layers (bonding error), a shallow but dangerous crack will occur. These are often invisible on conventional 2D X-ray images (if you look through them from the wrong side), but are immediately recognized in the 3D CT model.
3. Metrology: measuring what you can't touch
The CT scan not only provides images, but also exact geometric data. The resulting point cloud of the component is overlaid with the original CAD model (target-actual comparison).
- Measuring Internal Dimensions: How do you measure the diameter of a 3D printed, convoluted cooling duct deep inside an engine block? This is impossible with a caliper. The CT software measures the internal geometry with micrometer precision.
- Wall thickness analysis: The software colors areas in which the printed wall thickness has become too thin due to warping.
4. The Challenges: Artifacts and Density
Physics sets limits to computer tomography.
- Material density: Aluminum (light) can be easily irradiated. Tungsten, tantalum or molybdenum (extremely dense) absorb the X-rays almost completely. Even the strongest commercial scanners often fail because of solid tungsten components.
- Scattered radiation (artifacts): When hard X-rays hit edges made of thick metal, they scatter wildly. The resulting image often has beam hardening or scattering artifacts that can appear to have pores where none exist. Experienced CT experts and good software filters are crucial here.
5. Conclusion: An expensive but essential x-ray vision
Industrial CT systems usually cost between 500,000 and over 1 million euros. Scanning a large Inconel component can take many hours. This is oversized for non-critical tools. However, for additive series manufacturing in regulated industries (aviation, space travel, medicine), computer tomography is not a luxury, but the only way to guarantee the ultimate trust in additively manufactured structures.