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See Inside with CT Scanning

CT scanning—the same imaging technique used in the medical field—makes it possible to nondestructively inspect and measure manufactured parts. However, special considerations must be made for workpieces made of dense materials.

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In the same way that a computed tomography (CT) scanner at a hospital enables healthcare providers to “see” inside a patient, industrial CT scanning technology makes it possible to nondestructively measure and inspect the inside of a workpiece. The method works by passing an object (patient or part) between an X-ray-emitting tube and a sensor, generating a point cloud that is then interpreted with software to create 2D images or 3D models. A medical CT scanner rotates the X-ray emitter around the patient, whereas in industrial applications it’s typically the workpiece that moves, rotating slowly on a manipulator table while the sensor records data at set intervals. (For a brief overview of how the technology works, see this video on how a moldmaking firm uses CT scans.)

But apart from the different configurations of the CT scanner itself, scanning a metal part and obtaining precise measurements requires different capabilities than scanning a human patient. Metal parts have a greater tendency to absorb the X-rays, a characteristic which can introduce artifacts and affect the resolution of the generated image, especially when scanning denser workpieces. To maintain resolution on dense parts, industrial CT scanning systems must operate at higher kV power than medical scanners. GE’s Phoenix VTomeX M scanner, for example, is equipped with a 300-kV microfocus X-ray tube and a temperature-stabilized detector array. (A medical CT scan is typically conducted in the neighborhood of 70 to 140 kV.) The company says that these features enable the system to scan faster and achieve scanning accuracy down to 2 microns on parts ranging to 500 mm in diameter, 600 mm in height and weighing as much as 50 kg (110 lbs).

This ability to scan dense parts more quickly was a key draw for Exact Metrology, which recently installed a Phoenix VTomeX M CT scanner at its main facility in Cincinnati, Ohio. Using the Phoenix scanner, the company says it is able to generate a first article inspection report—including internal dimensions—in less than an hour, faster than using a tactile or optical CMM. Exact, which provides 3D scanning services in addition to metrology equipment, plans to use the CT scanner to offer process control as well as customer R&D services. Possible applications may include light metal castings, electronic assemblies, thermoplastic molded and composite parts, in addition to various machined metals.

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