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August 2009 Volume 60

www.plastverarbeiter.de

RepRint

First article inspection "just in time"

Application Report Julius Blum GmbH

Werth Messtechnik GmbHSiemensstr. 1935394 GiessenPhone: +49-(0)641-7938-0Fax: +49-(0)641-7938-719E-Mail: mail@werth.deInternet: www.werth.de

First article inspection “just in time”

Computer tomography for mea-suring components The first arti-cle inspection report determines whether the corresponding tool can be released for production. For a hardware manufacturer, this ex-tensive part evaluation used to ta-ke several days using conventional 3D measurement technology. Using computer tomography, the company was able to reduce the ti-me required to a few hours.

S ince 1952, Blum in Vorarlberg in Höchst has produced high quality hardware for high end furniture.

With about 5,000 employees worldwide, the company is a reliable partner for fur-niture manufacturers and aftermarket hardware dealers. In order to meet their customers’ high quality standards, this hardware manufacturer has used Werth multisensor coordinate measuring tech-nology for many years. The measuring machines, which are used in great num-bers, include models from the Video-Check, Inspector, and TomoScope series. All measuring machine are equipped with the WinWerth software package for machine control and measurement data evaluation. The company previously used conventio-nal 3D measurement technology for first article inspection in order to release the final tool for production. This process of-ten took several days. In order to signifi-cantly reduce the time required, they changed to coordinate measuring machi-nes with tomography sensors for some ti-

Author Detlef Ferger, Executive Vice President Sales, Werth Messtechnik, Gießen, detlef.ferger@werth.de

Plastic part from the Blumo-tion series (top to bottom: 3D point cloud, triangulated surface representation, and color-coded deviation plot relative to the CAD model)

Special offprint out of 08/2009 � Huethig GmbH, Heidelberg, by order of the customer Werth, Gießen

NEW TECHNOLOGY At a glance The tomography process detects and measures all internal and ex-ternal geometries of a part. The color-coded presentation of the de-viations allows rapid evaluation of dimensional accuracy. Both the deviations from a CAD model, and the deviations between the cur-rent part and a master part (actual to actual comparison) can be vi-sualized.

Definition of cross sections in the 3D point cloud for de-termining dimensions in a 2D sectionMeasurement using the 3D point cloud (top: patch selection using the CAD model, bottom: dimensional check of a cylinder)

3D point cloud are automatically assig-ned to the corresponding surfaces of the desired feature. This makes it very easy to determine dimensions, such as a dia-meter of a cylinder within the 3D point cloud. In addition, cross sections can be freely defined within the measured CT point cloud. The sections are evaluated using 2D contour evaluation. This eliminates the need to cut and destroy components, saving time and money. Measurement ti-mes of many hours to a few days can thus be reduced to a few hours or even minu-tes. The increase in efficiency that can be achieved due to the particularly fast ge-neration of first article inspection reports enabled Blum to amortize its first measu-ring machine in about one year. Another machine was purchased just after the ROI of the first one. Although, classical optical and tactile measurement techniques will remain in-dispensable for rapid sample inspection during production, modern computer to-mography provides new solutions. It will continue to develop in the future.

maximum permissible error (MPE) are on the order of 4.5 μm or better. The ap-plication of these specifications to real measured objects, however, is possible only for “cooperative” parts. Variation in wall thicknesses of actual components, complex geometries, and different mate-rial properties influence the measure-ment results. This is caused by physical measurement deviations, known as arti-facts, which arise due to X-rays penetrati-on of the measured object. Artifact devia-tions depend heavily on the object geo-metry and the object material itself, and therefore cannot be corrected analytical-ly with sufficient precision. However, be-cause the errors are systematic, Werth AutoCorrection (patent pending) pro-vides the ability to capture corresponding measurement points with high-precision optical or tactile sensors and correct er-rors in the tomography using these mea-surement points. In practice, the deviati-ons between the tomography scan and a reference sensor are simply determined – only for dimensions with appropriately precise tolerances, of course – and any systematic errors are then fully automati-cally compensated by the software for all subsequent parts.

Simple standard measurements In order to evaluate regular geometries with classical dimensioning, areas of the

The TomoScope 200 combines computer tomography and multisensor coordinate measurement in one machine

me now. The measurement results are available in a few hours in the form of meaningful color-coded 3D presentations of deviations. In order to guarantee the measuring process capability of this mea-surement equipment, high quality tech-nology is needed.

Integration in a coordinate measuring machine The high requirements for mechanical and thermal stability for reliable compu-ter tomography measurements can only be met by complete integration of this sensor into a coordinate measuring ma-chine. In addition to the stable granite ba-se, proven components and methods from coordinate measuring technology are used. These include, for example, the guides and drives of standard measuring machi-nes. High accuracy is achieved by intelli-gent reconstruction processes and a ras-ter principle in imaging. This method al-lows measurements with increased reso-lution for determining the smallest featu-res, even on large parts, and expands the measurement range of computer tomo-graphy. Traceable measurement results can be obtained by a calibration compara-ble to VDI/VDE 2617 part 13 using stan-dards, such as spheres, gage blocks, or ballbar standards. The precisions that are achieved thereby, in the form of specified