Computed Tomography in Additive Manufacturing Applications

Introduction to Industrial CT: 3D Inspection and Metrology for Additive Manufacturing 

Computed Tomography (CT) provides an essential tool for inspecting and measuring complex components in additive manufacturing (AM). By comparing the final product with its original 3D design, CT ensures that all critical internal dimensions are accurately replicated. This technology is particularly vital in industries where performance and safety are non-negotiable. 

The Significance of Additive Manufacturing 

Additive manufacturing represents a transformative shift in engineering, on par with the advent of casting and machine tools. It has revolutionized parts design, rapid prototyping, and the production of intricate components. These developments, which were previously impossible to achieve in a single piece, now require precise quality control. Here, 3D inspection and metrology through industrial computed tomography (CT) become indispensable. 

Understanding Industrial Computed Tomography 

Industrial CT operates by acquiring numerous 2D X-ray images, which are then reconstructed into a 3D volume. The object under inspection is placed on a precision turntable within a secure cabinet and exposed to high-energy radiation. As the object rotates incrementally, radiation is absorbed, and 2D images are captured by a detector. These images are mathematically reconstructed to produce a detailed 3D representation. 

Fan Beam vs. Cone Beam CT Techniques 

Industrial CT employs two main techniques: fan beam and cone beam. Both rely on the same fundamental principles but differ in radiation direction and data detection methods. 

Fan beam CT slices the workpiece into thin sections as it rotates and moves linearly through the X-ray beam. A collimated line detector captures the slices, which are then reconstructed to form the 3D volume. Although effective for high-density metal parts, this method is slower due to scattered radiation artifacts. 

Conversely, cone beam CT uses a flat panel detector that captures the entire workpiece in a single rotation. While this technique is faster, it is more susceptible to scatter radiation, resulting in less precise images compared to fan beam CT. 

Challenges in Additive Manufacturing Metrology 

Additive manufacturing creates three-dimensional parts by layering material, a process distinct from subtractive manufacturing. Various AM techniques include sintering, melting metal powders with lasers or electron beams, and stereolithography. 

Computed tomography can be applied across these techniques, from raw material quality control to final part metrology. High-resolution nanofocus CT, for example, ensures powder consistency by analyzing particle size, shape, and porosity. These factors influence the final build's density and potential defects. 

Ensuring Process Accuracy 

CT scans are also critical in detecting flaws during the AM process. Imperfections in powder quality or layering can introduce voids or impurities. These defects, while within tolerance initially, can cause significant distortions after heat treatment. CT technology identifies the size, location, and distribution of such flaws, allowing for process optimization. 

Precision in Final Part Inspection 

CT inspection of finished parts verifies that the manufactured product matches its initial 3D design. This includes dimensional analysis of internal features, wall thicknesses, and other aspects challenging to measure with traditional methods. Advanced CT scanners can achieve measurement accuracy within a few micrometers, enabling precise quality control. 

Enhancements in CT Technology for Additive Manufacturing 

Manufacturing industries are continually pushing for faster production without sacrificing quality. Recent advancements in CT technology have made this possible, supporting design optimization, production ramp-up, and component validation. 

Innovations in CT Hardware and Software 

Recent years have seen significant improvements in CT systems, including high-resolution nanofocus scanning and scatter correction technologies. Scatter correction, for instance, reduces artifacts caused by scatter radiation in cone beam CT, enhancing image quality to rival that of fan beam CT while significantly reducing scan times. 

Additionally, new detectors provide high-resolution images, enabling the detection of subtle defects. Advanced software now integrates all necessary functions for system control, data acquisition, volume reconstruction, and accurate surface data generation. Higher X-ray power focused on smaller spots allows for either improved resolution or faster scanning. 

The Future of Additive Manufacturing and CT 

Additive manufacturing, though still evolving, has moved from rapid prototyping to production, particularly in the aerospace sector. Its potential for creating parts with unparalleled internal complexity is now being realized across various industries. As AM technology advances, so too does CT, which now offers in-line machines for automated, 100% inspection on production floors. 

Conclusion 

As additive manufacturing expands across industrial sectors like aerospace and automotive, the role of industrial computed tomography will become increasingly critical. CT will continue to meet the evolving challenges of inspection and quality control, ensuring the integrity and performance of tomorrow's products.