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What Questions Should Manufacturers Be Asking About 3D Computed Tomography?

By Shana Telesz at GE Measurement & Control. This article appears in the September/October 2015 issue of Inspectioneering Journal

Introduction

While computed tomography (CT) scans are common and well-known as a critical evaluation tool in the medical field, they are becoming increasingly important in industrial settings. Three dimensional (3D) industrial CT for non-destructive testing (NDT) has long been confined to the research and development (R&D) environment and its application restricted to structure and defect analysis of high value, complex components and new materials. But imagine an automotive manufacturer being able to fully examine and measure a cylinder head, or an aerospace component manufacturer being able to inspect and measure highly complex turbine blades or parts made by additive manufacturing technologies.

Recent automation, speed, and accuracy developments are driving the migration of CT technology onto the production floor. There, it can be used as a powerful quality control and process optimization tool, providing fast inspection and accurate 3D measurement of components which are difficult to examine by conventional two dimensional (2D) radiography or coordinate measuring machines (CMMs). Because of technological advancements and speed enhancements, the same internal structure visibility provided to medical professionals by CT technology can now be invaluable for manufacturers and inspectors.

Understanding CT Technology

CT imaging begins with the acquisition of a large number of 2D X-ray images. The acquisition can be through a fan beam, where discrete slices are radiographed as the component is rotated in small angular steps and moved linearly through the fan beam. As a result, the data collected is a series of slices through the component. Alternatively, it can be done by means of a cone beam, where a cone of radiation captures the target piece and takes discrete 2D images as the component is rotated 360 degrees in small steps. Fan beam CT traditionally provides much better results due to minimized scatter radiation artifacts, but can take up to 100 times longer than cone beam CT. For extremely fast scanning of large parts such as cylinder heads, the sample can be moved in the scanner on the inspection table while x-ray tube and multiline detectors rotate around. This inspection method is particularly useful for parts that are cast molded in a foundry, including automotive and engine parts and cylinder blocks. It also can easily inspect compressor blades and valve bodies. In all cases, the accumulated raw data from inspection is then used in reconstruction algorithms to calculate and visualize the volume data.

The basic data-acquisition hardware components of a CT system are a high power source of radiation, a component manipulation table with rotation unit, and an X -ray detector. The quality of the raw data and the accuracy of all subsequent evaluations are significantly influenced by the sharpness of the X-ray images. The sharpness of the X-ray images ultimately depends on the quality of the source and detector and the stability and precision of the manipulation mechanism.

CT developments are not just in the hardware, but also in the speed of volumetric reconstruction, in the ease of operation, in image quality, and in the storage, retrieval, and management of data.

So how do these advancements apply to the production floor and what do manufacturers need to know?

From shortening the prototype process, to reducing processing costs, to getting faster feedback during the production process, the benefits of CT technology are endless. In order to determine whether CT technology is right for their facility, manufacturers must ask the right questions.

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