QMT Features: July 2007
Measurement revolution
Industrial computer tomography techniques are driving a measurement revolution at automotive parts supplier, Delphi. Non destructive 3D measurement inside workpieces shrink processes from weeks to hours.

The new year had an auspicious beginning for the automotive parts supplier Delphi of Wuppertal, Germany  which has been pilot-testing an all-new measuring machine for nearly a year. The machine in question is a customised computer tomograph (CT), soon to be officially approved and certificated as measuring equipment. What is new is that the CT system also measures inside the workpiece, something that is unknown territory to conventional 3D coordinate metrology systems.

At the outset of every "health reform" there is often an illness. This was the case for the quality assurance department at Delphi Deutschland GmbH. In 2000, following an accident,  quality manager Peter Knauff underwent a medical examination which utilised a computer tomograph to scan him in very precise detail.

After recuperating Knauff, fascinated by the technology, wondered whether CT technology could be used in quality assurance as well.  Based in Wuppertal, the automotive parts supplier Delphi develops automotive electronics and  connectors. Filigree parts of complex geometry are manufactured in injection moulds built by the company. The resultant injection mouldings must be compared with the digital design at a very early stage of development. Depending on complexity, which can involve a component with hundreds of quality characteristics to be measured, this procedure can often take weeks.

Yet time is a scarce commodity in the development of automotive parts that must be fully validated in time for the start of production at the customer's site. Quality manager Peter Knauff put forward his concept as follows, "Computer tomography renders a high-precision 3D digital image of all kinds of bodies. There's no reason that we can't utilise this property for digital length measurements as well."  With the support of YXLON International CT Development GmbH of Hattingen*, a CT was developed that, in the first instance, provides high precision measurement of components.

Hours instead of weeks

The system works by generating a point diagram which the user can zoom down to pixel size (0.007 mm) to measure any point in the 3D map. Delphi overlays these records in several steps with the corresponding CAD values. At the same time, each measured detail of the component is compared as a numerical value with the CAD model. The greater this difference, the more intense the colour the software applies to mark these deviations. Knauff explained: "In this manner, CT cuts the time needed to validate a complex component by up to 70 per cent. And that is equivalent to hard cash for us employers." A full set of measurements that the automotive industry demands once a year for each part keeps a metrologist busy for three to four weeks. According to Delphi the CT, system now manages to provide this set of measurements in three to four hours.

The maximum thickness of a component is a function of the material's strength. For example, CT can be used to examine deep-drawing steel with walls 3.0-4.0 mm thick. High-strength steels beyond the 1 000 MPa threshold, on the other hand, can be examined only on very small components. One interesting application involves diesel injection nozzles of high-strength steel whose efficiency is determined directly by the contour of the 0.08 mm holes.

Official certification of the measuring equipment, is now imminent as Knauff explains: "I expect our CT system to be approved soon as measuring equipment for the products we manufacture in Wuppertal-Ronsdorf." l

Contact: Delphi Deutschland GmbH

Thomas Aurich email:  thomas.aurich@delphi.com


(*This company is a subsidiary of YXLON International X-Ray GmbH of Hamburg,  manufacturers of X-ray-based systems for non-destructive material testing.)

The "revolution in metrology",  featuring CT technology, will be a central theme at EMO Hannover 2007, 17 to 22 September.

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