© 2010 Quality Digest Magazine. All Rights Reserved.
By: Alex Lucas
Top-100 automotive supplier, Kautex, relies on Metris XC50-LS Cross Scanner on LK CMM to verify the production quality of composite fuel tanks. Kautex engineers set up and execute automatic measurement routines that speed up the serial inspection process for fuel tank by 30 percent. Incorporating three lasers in a cross pattern, the scanners capture the finest details of freeform surfaces and critical geometric features in one go. The insight gained by automatically digitizing fuel tanks and generating graphic Focus reports enables Kautex to tackle problems that were hard to solve in the past.
Tier-one supplier, Kautex, a Textron company, headquartered in Bonn, Germany, manufactures fuel tanks that meet tight environmental standards for Chrysler, Ford, GM, Honda, Toyota, and other major car brands. To guarantee smooth assembly, the shape of fuel tanks must fall within strict geometric tolerances to match the allocated space envelop within the vehicle. To monitor the quality of all its fuel tank production lines in the United States, Kautex installed the same metrology equipment in Avilla, Indiana, and San Antonio, Texas. In multiple shifts, metrology professionals at both production plants run inspection on LK horizontal-arm CMMs equipped with XC laser scanners and tactile sensors.
“Serial production of fuel tanks is a swift but complex process that cranks out a new specimen every two minutes or so. The advanced blow molding and cooling technology that is applied requires optimum dynamic pressure and temperature conditions,” says Don Morse, quality manager for Kautex in Avilla, Indiana. “These boundary conditions are of capital importance as well as the blow molding fixtures that shape multilayer base material that is being air inflated. To meet the desired dimensions at the end of the cooling stage, we systematically verify the geometric quality of serial produced tanks.”
To prepare an inspection routine for a new fuel tank type, Kautex’s quality team sets up an inspection macro in Focus Scan software. Defining the dynamic motion and orientation of the XC50-LS scanner is quite straightforward. “Significant tolerance on scanner-to-part distance drastically reduces head indexing as well as the number of CMM movements,” says Michael Boltz, CMM specialist for Kautex. “It is much easier to define scanner motion and orientation than to program the hundreds of touch sensor points for a tactile inspection job. Most of the time, we prepare inspection macros off-line, allocating CMMs exclusive for digitizing fuel tanks.”
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Color-coded reports illustrate geometry deviation and highlight where geometry tends to go are out of range. |
Laser scanning also reduces or eliminates the effort that is required to align fuel tanks on the CMM. As fuel tanks have sufficient weight and rigidity, there is no need to invest in complex clamping and fixation tools. Boltz explains that a fuel tank is presented for inspection by positioning it on vertical stands that support the tank in free-state condition.
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Laser scanning yields graphic part-to-CAD reports from which the underlying metrology data can be retrieved easily. |
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Critical fuel tank features that require detailed verification are datum reference points as well as metal or plastic tube/hose connection pieces that are molded in into the tank surface. Three lasers incorporated in a cross pattern enable the XC50-LS scanner to capture all 3-D details of geometric features and freeform surfaces in a single scan. This compares favorably to line scanners that digitize features multiple times under different angles to capture all details.
“The scanning routine for an entire fuel tank, covering freeform surfaces and geometric features, is completed in the order of 30-40 minutes,” says Boltz. “Laser scanning outperforms tactile point-by-point acquisition technology, both in speed and number of inspection points. A point cloud of a fuel tank consists of several millions of measurement points, which is further reduced by an innovative filtering algorithm. Currently, we run quality control with sampling rates of one in every 50 to 100 fuel tanks.”
Boltz explains that the inspection process at Kautex is embedded into the digital CAD-centric manufacturing process. An advantage of digitizing fuel tanks up front is the flexibility to run analysis at any later time. After aligning the acquired point cloud with the nominal shape, Focus highlights geometry deviation between fuel tank and CAD or between two tanks. Automatic geometry comparison is performed either using global best fit or alignment on the basis of datum reference points. “At a single glance, we see where geometry tends to go out of range. We apply different fitting methods to easily distinguish between inaccurate fuel tank geometry and incorrect datum point levels. Quickly gaining relevant insight is critical for us in efficiently tuning the mechanical blow molding fixtures used in production. We share graphic reports with colleagues and customers, who interactively analyze them using the license-free Focus Viewer,” continues Boltz.Â
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Kautex runs laser scanning to effciently capture the freeform surfaces and geometric features of fuel tanks |
Cross section of fuel tank uses color indication to mark geometry deviation of any point of interest. |
“Metris laser scanning is a success story,” concludes Morse. “The scanners help us save time in every step of the metrology process, including measurement preparation, execution and analysis. Overall, the digital inspection process that we have implemented speeds up metrology operations on average with 30 percent. Instead of entering discussions with Excel tables, we now share graphic Focus reports to drive technical consultation and efficient decision making. The insight that we gain from these reports enables us to tackle problems that could not be solved in the past, and increase our technical credibility toward customers.”