Underbodies in BMW's X5 Body Shop are precisely attached to a "geometry skid" that helps to maintain weld precision as the bodies move from station to station.
"Definitely the geometry skid we use for the X5," answers Manfred Moser, who is the manager of the Body Shop at BMW Manufacturing Corp. Given that he has been with BMW for 17 years and was deeply involved in the set ups for both the Z3 line (1992) and X5 line (1998), it is evident that he knows where the fundamental differences can be found.
"We use this skid system to locate and position the underbody," he says. The underbody consists of three main elements: the motor compartment, floorpan, and rear compartment. Importantly, Moser notes, "This is more than just a transportation device. The advantage of this system is that it means we could easily introduce a second product into our main line." Given that BMW is (comparatively) a producer of niche vehicles, the inherent flexibility of this approach is valuable.
Moser also points out that in addition to flexibility, the geometry skid system provides accuracy and repeatability to the build. "Our plants in Germany use a transportation system that is either floor- or ceiling-based. They use a special jig to locate the part in every station. Our underbody remains on the skid throughout all the stations." The importance of this is that the tolerance stack that can occur when repositioning parts in fixtures is eliminated. He adds, "That's why we think we are a little bit more accurate than other systems." (They are, after all, building what is described as "The Ultimate Driving Machine.")
The X5 framing line also uses what's called the "Geo-Box," made by Nothelfer (Lockweiler, Germany). It's a solid frame that holds the body parts in place while they are being welded by robots. The framing line is made up of three stages: the first adds the body side inner and the roof rails, the second adds the body side outer and the third welds the roof in place. The geo box moves through all of the stations and provides a solid surface that locates all of the disparate parts. Moser comments, "The main advantage is accuracy because you locate to a very precise frame. And it's very repeatable." But flexibility is also a key design criterion behind the geo box. The main body line for the X5 can handle up to four different underbodies and can potentially build eight different body sides. In other words, the South Carolina plant's body shop can build just about anything that is currently being built in Germany.
This is not the case with the Z3 line. While it is flexible, it is not as flexible. From the beginning, the Z3 line was engineered to make just three models: the 3-series sedan, the roadster, and the coupe. Automation is limited compared with the X5 line: 25% rather than 75%.
When asked whether there was a change in manufacturing philosophy between 1992 and 1998, Moser answers that the Z3 line was built on a different premise and has met its design parameters. Next time, however, things will be different: "We are currently in the process of preparing for the successor to the roadster and are building a new line for that. There will be more automation than we have on the current Z3 line. The new roadster design is quite different than the current one."
If the new $300 million Z3 Body Shop follows in the footsteps of the X5 facility, it will not only be more flexible, but will have been rigorously tested in computer simulations and brought into production quickly. The X5 project took only 33 months from clay freeze to mass production, which is world class for a luxury maker. In fact, it cut BMW's standard 65-month development period in half.
BMW Manufacturing Hosts
This year's Southern Automotive Manufacturing Conference (SAMC) is being hosted by BMW Manufacturing Corp. at the Palmetto Expo Center in Greenville, South Carolina from October 8 to10. Carl W. Flesher Jr., vice president Community/ Corporate Relations for BMW is the executive chairperson of this year's event, which will cover the best of both domestic and international manufacturing practices. Programs will focus on:
- Workforce Development
- Supply Chain
- Innovative Technology
Plant tours of BMW Manufacturing and a special session of the BMW Driving Experience will also be available. To find out more contact SAE: phone: 724-772-7131; fax: 724-776-0002; email:firstname.lastname@example.org.