Towards in-process x-ray CT for dimensional metrology

Abstract

X-ray computed tomography (CT) offers significant potential as a metrological tool, given the wealth of internal and external data that can be captured, much of which is inaccessible to conventional optical and tactile coordinate measurement machines (CMM). Typical lab-based CT can take upwards of 30 min to produce a 3D model of an object, making it unsuitable for volume production inspection applications. Recently a new generation of real time tomography (RTT) x-ray CT has been developed for airport baggage inspections, utilising novel electronically switched x-ray sources instead of a rotating gantry. This enables bags to be scanned in a few seconds and 3D volume images produced in almost real time for qualitative assessment to identify potential threats. Such systems are able to scan objects as large as 600 mm in diameter at 500 mm s −1 . The current voxel size of such a system is approximately 1 mm-much larger than lab-based CT, but with significantly faster scan times is an attractive prospect to explore. This paper will examine the potential of such systems for real time metrological inspection of additively manufactured parts. The measurement accuracy of the Rapiscan RTT110, an RTT airport baggage scanner, is evaluated by comparison to measurements from a metrologically confirmed CMM and those achieved by conventional lab-CT. It was found to produce an average absolute error of 0.18 mm that may already have some applications in the manufacturing line. While this is expectedly a greater error than labbased CT, a number of adjustments are suggested that could improve resolution, making the technology viable for a broader range of in-line quality inspection applications, including cast and additively manufactured parts.

Computed tomography metrological examination of additive manufactured acetabular hip prosthesis cups

“…Therefore, CT is the only holistic examination available to provide qualitatively and quantitatively the required information without destroying any components. The application of this technology is considerably new as an NDT and in dimensional metrology, nevertheless recent studies on Real Time Tomography (RTT) X-ray CT demonstrate its potential in production examinations [34]. As a result, international standard organisations have not yet provided any standards that can be followed to ensure the quality of the examinations, although they are currently being developed such as ISO/NP 10360-11 [35].…”

Neural network Hilbert transform based filtered backprojection for fast inline x-ray inspection

“…Ideally, it should allow individual inspection of every single sample, while preserving a sufficiently high throughput. Inline inspection techniques are already used in different industries, such as agriculture [1,2], powder metallurgy [3], log scanning [4], dynamic processes [5], metrology [6], and baggage inspection [7].…”

SparseBeads data: benchmarking sparsity-regularized computed tomography

“…A collection of 48 x-ray CT datasets called SparseBeads was designed for benchmarking SR reconstruction algorithms. Beadpacks comprising glass beads of five different sizes as well as mixtures were scanned in a micro-CT scanner to provide structured datasets with variable image sparsity levels, number of projections and noise levels to allow the systematic assessment of parameters affecting performance of SR reconstruction algorithms 6 . Using the SparseBeads data, TV-regularized reconstruction quality was assessed as a function of numbers of projections and gradient sparsity.…”

“…However, laboratory-based micro-CT remains slow with scan times on the order of hours, which presents a barrier to studying processes which occur on a faster time scale and to higher throughput in industrial imaging applications. An alternative for fast scans (seconds) is provided by real-time tomography (RTT) x-ray CT systems developed for airport baggage scanning [5] which have been explored for production inspection [6], however with resolution only on the millimeter scale. Naturally, accelerating high-resolution micro-CT is an active research venue with better sources and detectors coming to the market.…”