Computed tomography (CT) delivers three-dimensional images visualizing the inner structures of a scanned object, including the exact spatial position of defects or other regions of interest.
The benefits of industrial CT for quality assurance and R&D
Computed tomography is one of the most important and powerful non-destructive testing methods in quality assurance and quality control. Comet Yxlon CT inspection systems support manufacturers and scientists, e.g., in the electronics, automotive, and aerospace industries, in their pursuit of maximum product quality, and efficient production processes – with fewer rejects and recalls, less waste, and less downtime.
How does industrial CT create 3D data?
To generate the 3D representation of an object under inspection, an industrial CT scanner system first creates a series of 2D X-ray images at different rotational angles, so-called projections. As the 2D images are captured, the reconstruction can begin, e.g., by a back-projection algorithm. For each row of pixels, the system creates tomograms – virtual slices through the three-dimensional object. These tomograms are then joined together by software to produce the final 3D data of the object.
Different shades of gray correspond to different density values of the material, so flaws or irregularities can be spatially localized with the greatest accuracy. When describing image sizes, industrial CT speaks of voxels (volume pixels), which are the 3D equivalents of pixels.
Industrial CT: a wide range of applications
Identification of porosity and inclusions
Casting flaws, welding defects, porosity, cracks, inclusions, or voids – during 3D inspection, computed tomography reliably visualizes irregularities with their exact position and shape. Comet Yxlon offers a wide variety of CT inspection systems for almost all sizes of objects – from the smallest microchips to complete aircraft or car engine blocks.
Structural analysis, e. g. in AM
CT allows insights into the interior of a variety of objects – from geological specimens like core samples to construction materials used in roads and bridges to additively manufactured products. In additive manufacturing (AM), CT scanning helps detect typical flaws that can occur during powder bed fusion, such as porosity, balling, excessive surface roughness or micro-structural issues.
Analysis of composite materials
Fiber orientation (e. g. of carbon fibers) is an essential part of the composite analysis because it is critical to a product’s properties. With CT, operators can visualize the orientation of a part’s fibers using software that assigns specific colors to every angle in space. Major misalignments can be highlighted with an easy-to-identify color.
In metrology, 3D scanning is widely used for comparing external and internal surfaces, e.g., for nominal-actual-comparisons, where a CT scan can be matched against a CAD model, or two CT scans can be compared to each other. Industrial CT also allows the dimensional survey of internal structures, e. g., for creating compliance reports on each cavity of multi-cavity dies for injection-molded plastic parts.
Industrial CT can be used to check the mechanical form and fit of assemblies or to visualize components within a product, like gaskets or heating elements. In defect analysis of electronic components and printed circuit boards (PCB), CT offers details about the volume of blowholes, or the pad surface structure of a defective solder ball. It also helps analyze structures of only a few microns in size within housings, like in inspections of semiconductor packaging.
The components of a CT inspection system
The most important parts of an industrial CT system are the X-ray source, the X-ray detector, the manipulator, and the imaging software.
The X-ray source or X-ray tube
According to their focal spot size, the different X-ray sources are called mini-, meso-, micro-, and nano-focus. Today, mainly two basic types of X-ray sources are used in CT systems: Mini-focus tubes have higher power than micro-focus tubes, with potential energies from ca. 20 keV to ca. 600 keV. Micro-focus tubes for microCT applications are available with potential energies between ca. 20 keV to ca. 300 keV. The focal spot size determines how sharply the internal details of the object can be visualized. The higher the energy of the tube, the denser or larger objects the X-rays can penetrate.
Modern CT systems are typically equipped with either a flat-panel digital detector array (DDA) for cone-beam CT or a line-detector array (LDA) for fan-beam CT, see more details about techniques below. All these detectors offer very high sensitivity, resolution, and bit depth, and produce very clear images with excellent contrast. LDAs are particularly suitable for high-quality fan-beam CT scans of thick-walled components inspected at high X-ray energies.
Innovation through co-creation: the CTScan 3
The close exchange with customers and a sharp eye for market developments are the drivers behind innovation at Comet Yxlon. Just one example: inspired by the need for scan results that are not affected by scattered X-rays, as they occur in high-energy applications when examining dense materials, Comet Yxlon developed the CTScan 3, a line-detector array (LDA) that is unbeaten in terms of image quality, e.g., resolution, contrast, and stability.
The manipulator positions and rotates the inspection object to allow the X-ray source and detector to take multiple images at many different viewing angles. Depending on the application, some CT systems have steel frame-based manipulators, while others are based on granite for simpler mechanical alignment due to increased temperature stability compared to steel.
The software: Geminy
Geminy is Comet Yxlon’s single user interface for all workflows. Using wizards and presets, it guides users through the inspection process and optimizes image quality and speed with powerful CT techniques.
What are the basic CT scanning techniques?
There are two basic CT scanning techniques, namely fan-beam CT and cone-beam CT which uses a broad variety of scanning trajectories for image acquisition, e.g. helical scan CT or computed laminography.
During a cone-beam CT, the emitted cone-shaped X-ray beam is detected by a flat-panel digital detector array (DDA). Cone-beam CT systems are well-suited for low to mid-density or mid-sized (< approx. 600 mm diameter) parts to achieve optimal CT data quality. They deliver a typical data set in 15 minutes or less. Techniques like half-beam scans, detector shifts, or vertical and horizontal scan extensions enlarge the field of view (FOV).
During a helical CT, the sample describes a helical (or spiral) trajectory relative to the source, while a flat-panel detector acquires the transmitted radiation of the cone beam. Helical CT scans can be a faster way to achieve a high-quality data set of tall samples with fewer artifacts.
Computed laminography (CL) eliminates the need to rotate the object fully around its axis, which is useful when inspecting very flat components like microchips at the highest magnification close to the X-ray tube or big flat parts like aircraft doors. Instead, in CL both tube and detector carry out the movement on both sides of the inspection object and thus penetrate it from different angles. The image is processed into single or multiple slices.
Traditional fan-beam CT uses a fan-shaped X-ray beam that is detected by a line-detector array (LDA). Fan-beam CT systems rotate the scanned object to produce a single cross-sectional slice, while vertical stitching or stacking of slices produces a 3D volume. Fan-beam CT systems are ideal for very large and dense parts, and for high-energy applications (≥320 kV).