Quality Exclusives

Case Studies: Challenges of Modern Body-in-White Inspection

January 2, 2008
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A metrology technician inspects the dimensional accuracy of the left fender on a body-in-white. The comparison between the actual and CAD data is displayed in real time on an application PC running the PolyWorks Inspector software. Source: Leica Geosystems


The almost complete absence of people is the first thing noticed while walking the endless corridors of DaimlerChrysler's ultra-modern plant in Bremen, Germany. Hundreds of robots go about their work with surgical precision. They move different sheet metal parts into place, weld them together, transport completed parts to the next station and transfer finished products overhead to maximize space utilization. Viewed from afar, the ubiquitous robots seem to be dancing. The few factory workers seen use bicycles to jet between different parts of the factory.

Many more daring body shapes can leap from the automotive designers' drawing board to the assembly line due to significant technological progress in manufacturing processes. In the not-so-distant past, cars had relatively simple, square shapes, with individual parts fitting to one another along straight-forward lines. Modern cars boast far more complex shapes than the cars of yore.

The task of inspecting how automotive parts fit together has also gotten increasingly more complex. The Body-In-White (BIW) Rollout and Process Optimization Department is entrusted with the job of verifying how well the various body parts fit to one another. More importantly, based on their measurements, feedback is given to the production facilities so targeted adjustments can be made on the tooling.

Deviations from CAD data are visually displayed using the PolyWorks Inspector software, with deviations shown either using a color palette or vectors. Source: Leica Geosystems

Looking for a Perfect Fit

Operational Engineer Henning Siemers is involved in BIW measurement and inspection tasks. He explains, "Our job is to ensure dimensional accuracy of the entire body-in-white. Of course, every BIW consists of many individual parts, and they must all fit perfectly. Our primary duty is to inspect the entire BIW, both individual parts and the whole vehicle, including the panel gaps, and then analyze the data we get. Based on the analysis we perform, we then go back to the production facilities and make adjustments to the tools and make sure that what comes out is an automobile whose parts fit together flawlessly."

In the past, Siemers' department has relied on hand-operated measurement instruments. However, the shape complexity of today’s cars coupled with ever-increasing tolerances has pushed such instruments to their limits. Siemers continues, "Viewed in retrospect, cars used to be made of almost square-like segments which used to fit nicely together without much hassle. Nowadays, cars are much more curvaceous, with round areas suddenly changing shapes and meeting other panels at all kinds of angles and lines. Plus, the much higher requirements for the nearly seamless fit between individual panels mandate that we work with very tight tolerances."

Leica T-Scan Delivers

"With the shapes of our vehicles getting more complex, we have been on the lookout for new technologies that deliver," continues Siemers. "Our Quality Engineer, Karl-Heinz Boecker, has been attending the Control trade show in Sinsheim, Germany, each year, and he had his first encounter with the Leica T-Scan system a couple years ago, when it was still just a prototype. Based on the announced specs, we knew this could be something for us, but we wanted to wait until we were positive that the product was truly ready for the market. The primary issue that we saw with many of the other scanning solutions out there was that the software could not keep up with the hardware. Collecting all those points is relatively simple, but what do you do afterwards? We were under the impression that many manufacturers did not award the same attention to the software as they did to the hardware."

Boecker's team arranged a Leica Geosystems product demonstration at their facilities. A Leica LTD840 Laser Tracker coupled to a Leica T-Probe and Leica T-Scan was chosen. And the Leica system delivered. "It was immediately clear to us that the Leica T-Scan and the PolyWorks software were a mighty combination. We already knew that the Leica T-Scan was a great sensor, and we were also shown that the PolyWorks suite is a worthy match for it. The software is very capable, and we knew we would be on the right track."

A technician inspects the gap between the left fender and the engine hood. Source: Leica Geosystems.

Change is Good

Since the system delivery, the Leica T-Probe/T-Scan system has been used, among other things, to measure panel gaps, examine part curvatures and inspect reference holes. Siemers also has been busy testing different applications for the Leica T-Scan system. "One of the new applications we have found is inline calibration. In the past, BIWs were inspected by being placed inside a grid station and measured using conventional CMM (coordinate measuring machine) equipment. When you have 150 pallets and want to measure with high tolerances, you're quickly reaching the limits with traditional methods. That's why we wanted to be able to measure linearly both the pallets and the tools, and this is where the Leica T-Scan system will come into play. Another application of interest to us is the inspection of the entire robot path, and this is something we plan on doing in the near future."

A Leica Laser Tracker follows the position of the Leica T-Probe, accounting not only for the 3-D coordinates of the walk-around probe, but also keeping track of its pitch, yaw and roll. The position of the reference holes in the A-pillar is being checked. Outer sheathing will later attach to the holes located in the A-pillar. Source: Leica Geosystems.

Quality Information = Good Analysis

When asked about what has changed since the implementation of the Leica T-Scan system, Siemers is specific: "By relying on scanning, I am in the possession of much more useful information. The quality of part analysis has improved. We are able to get to the root of a problem much more quickly, therefore coming up with targeted solutions for what needs to be changed, intervening at the tools at such and such point and changing the parameters based on the results seen in PolyWorks."

And benefits of using the Leica T-Scan are manifold. "We really appreciate the portability. With the Leica Geosystems equipment, I can gather all the information I need in just two to three hours and perform the analysis later. This way, I am not blocking production for too long, because the system lets us work in parallel: While one operator is taking the measurements, another one can already be working on sorting out the results."

The fact that the Leica T-Scan is part of a modular system is important to Siemers’ team. "We purchased a Leica T-Probe at the same time we got the rest of the system. Tactile wireless measurement is of great value to us when we measure easily twistable parts like the hood. We perform a quick measurement with the Leica T-Probe to get a rough idea about the condition of the part. If we were to start scanning immediately, it would take longer to realize that the hood is twisted. With the Leica T-Probe, collecting just a few points will let us know fairly immediately how we are doing. And we are performing this within the same software, merely switching between the Leica T-Probe and the Leica T-Scan."

The Leica T-Probe/T-Scan combination measures within a range of 15 meters, thus giving the technicians a measurement volume of 30 meters. If measurement requirements should change in the future, Siemers and his team are well equipped for operating in a measurement volume large enough to accommodate several BIWs at once.
    Leica Geosystems
    +41 62 737 67 88
    www.leica-geosystems.com


Benefits

  • The Leica T-Scan System allows DaimlerChrysler to effectively measure the complex designs and tight tolerances of today’s automotive parts.

  • The system’s portability facilitates efficient production.

  • The system measures within a range of 15 meters, thus giving the technicians a measurement volume of 30 meters.
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