Apr 27 2005
Components that deviate from their specified dimensions by only a few hundredths of a millimeter often have to be scrapped. Manufacturers regularly inspect all measurements. Industrial computer tomography can accelerate this process, also revealing material defects.
Survival sometimes doesn’t depend on a silken thread, but on a tiny cogwheel. In safety belts, for example, these small parts ensure that the belt tightens at the right moment – but only if the size and shape of the cogwheels are exactly as they should be. Manufacturers therefore regularly check whether all components produced by their machines have the correct measurements. Traditionally, they use optical methods or surface scanning. Either process can take several hours. However, it is difficult or impossible to inspect complex contours that have undercut sections, like a screw thread, by using such methods. X-rays make it possible. Scientists from the Fraunhofer Network Vision have developed an advanced version of the CT-MINI X-ray computed tomography scanner and equipped it with software for such material tests.
In this new application, the device registers the transition from solid body to air, determining the contours of the component and thus its actual measurements. In order to compare these with the specified measurements, the CAD design dataset, the software converts the tomography data into a three-dimensional cloud of measuring points. Another algorithm automatically identifies geometrical forms such as planes and cylinders, and thus describes the X-rayed components in 3D – to an accuracy of within ten micrometers. In this way, drill hole diameters, clearances and angles can be determined and reworked if necessary. Alternatively, to provide fast initial visualization, the voxel cloud can be converted into STL surface data. Processes such as rapid prototyping can use these to build up models layer by layer (see article no. 4). “This test device has enabled us for the first time to complete the process chain from a CAD model to the production of a sample and back to the CAD model,” sums up Randolf Hanke, head of the Fraunhofer Development Center for X-Ray Technology in Fürth near Nuremberg.
ITW Deltar, a supplier of parts to the automotive industry, plans to start using the CT-MINI in May for initial sampling of injection-molded parts. “We produce safety belt components that must not deviate from their specified dimensions by more than 50 micrometers,” says the company’s quality manager Ralf Wulf. “We expect the new X-ray technology to cut our measuring time by half.” Interested parties can find out more about the uses of CT-MINI in three-dimensional metrology at the Control trade fair in Sinsheim near Heidelberg from April 26 to 29 (Hall 6, Stand 6306).
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