Dual.Material CT

The Industrial Metrology Business Unit of Nikon Corporation (https://industry.nikon.com) has introduced a new reconstruction algorithm allowing scanning times to be reduced by typically 10-fold. Dual.Material CT, as its name implies, achieves this dramatic increase in efficiency on assemblies comprising two materials of different densities. It significantly improves the ability to distinguish between the two materials in the voxel (3D pixel) image reconstructed from 2D X-rays taken as the component rotates in the chamber of a Nikon X-ray CT machine.

The benefits of X-ray CT for non-destructive inspection and measurement of both the interior and exterior of components are well known. Traditionally however, CT scanning of assemblies made from two materials such as metal and plastic, which is common in industry, is unsuited to quality control (QC) in a production environment.

This is because a long scan time is required to generate datasets that are sufficiently clear to be processed, which is contrary to the requirements for real-time inspection. Alternatively, if scanning speed is raised, manual post-processing by highly skilled operators is needed to remove artefacts that appear in the images to achieve accurate results. Again, this slows the procedure and introduces variability due to human intervention.

Dependent on the size and complexity of the component, pre-launch trials demonstrated that Dual.Material CT performed an order of magnitude faster on a typical metal and plastic connector, making production line integration on the shop floor a possibility alongside sample inspection. Core applications will be found in factories producing over-molded connectors, for example, or medical assemblies such as inhalers or adrenaline pens. Dual.Material CT is also likely to find uses in non-industrial environments, such as research.

During each image reconstruction, the software engine reduces the degree to which streak artefacts, caused by the higher-density material, obscure the lower-density areas. Typical systems on the market use reconstruction engines that assume the X-rays are monochromatic, when in fact they are polychromatic. This means they must use X-ray filtration, which lengthens exposures and slows image capture. Nikon’s reconstruction engine overcomes the effects of a polychromatic X-ray beam by adjusting the attenuation for the different material combinations in dual-material assemblies, greatly improving the contrast-to-noise ratio. Consequently, the X-ray source with a Dual.Material CT scan does not require filtration, so the detector can be used at much shorter exposures, resulting in faster frame rates and scan times.

As it is automated, reconstruction by Dual.Material CT is highly repeatable from component to component and does not require advanced knowledge of scanning techniques when inspecting assemblies comprising two materials of different densities. QC productivity is raised by enabling better visualization and more accurate definition of defects (on the surface or inside a component) in a fraction of the time taken by traditional CT image reconstruction. The high-speed scanning, and the fact that no manual data editing is required thanks to the new software and automated part handling, enables fast and automated quality control of dual material assemblies in a production environment, consistent with the requirements of Quality 4.0.

Written by Nikon engineers, the Dual.Material CT algorithm is specifically designed to operate seamlessly with the company's range of X-ray CT machines built in-house. The option is available for all new installations or may be retrofitted to existing equipment in the field, irrespective of the machine configuration and its power.