Raising (and Folding) the Roof
The Mercedes plant in Bremen, Germany, employs more than 16,000 people. It is the third-biggest Mercedes-Benz passenger car plant in Germany. It produces the C-class, the CLK coupe, the SL, and the SLK roadster. All that said, there is one interesting thing about one of the vehicles built at the Bremen plant. The vehicle in question is the SLK.
That roadster is fitted with what is called the “vario folding roof.” This is a hardtop. It has two-sheet steel construction. But with a push of a button on the console, the hardtop is folded into the trunk—in 25 seconds. What happens is that the roof is actually two pieces with the seam running width-wise across the top of the vehicle. The two pieces that compose the front half are joined and reinforced with a roof frame that surrounds them. The rear half of the roof comprises the C-pillars and the rear window; there is additional reinforcement that takes the form of a multiple-piece inner shell. When the roof is closed, the two pieces are tightly joined by a kinematic mechanism that’s locked in place. But when the button is pushed, a hydraulic pump in the trunk kicks into play; it activates five different hydraulic cylinders. Two of the cylinders actuate cables that unlatch the two halves of the roof and activate various sliders and kinematic mechanisms. Two cylinders are used to handle the trunk. Its lid hinges at its trailing edge—but only when the top mechanism is actuated—so that the roof can be folded in two and stored within it. (The final cylinder is used to assure that the roof locks in place on the windshield when the roof is being closed.)
All of which is to say that the vario roof is (1) a complicated engineering task and (2) something that, because of all of the various kinematic elements involved, is a complicated manufacturing task.
You may be surprised to learn that Mercedes doesn’t make the SLK top. Nor does Porsche produce the similar hardtop that graces the 911 Carrera Cabriolet. Well, that’s not precisely right. You see, there is a company, Car Top Systems (CTS), that is a 50/50 joint venture between DaimlerChrysler AG and Dr. Ing. H.c. F. Porsche AG that was established in 1996. And this is the company that actually manufactures the roof systems for not only those cars, but for various others, be they retractable hardtops (e.g., the forthcoming Cadillac XLS) or soft tops (Ferrari F 360 Spider).
In the case of the SLK, the production was initially performed in a CTS facility in Hamburg, where the Saab 9-3 soft top also is assembled, but then it was moved to a 24,000-ft2 CTS facility that’s on the grounds of the Mercedes Bremen plant. The so-called “panoramic vario top” for the SL-R230 is built there, too. The 911 tops, as well as the Boxster hard- and soft-tops, the Mercedes G-class soft top, and the Ferrari 360 are handled in a plant in Korntal-München, near Stuttgart. The XLS retractable hardtop will be produced in a new 27,000-ft2 plant in Bowling Green, Kentucky, near to the Corvette plant where the Cadillac will be built. (Models of the next-generation Corvette will also be roofed by CTS.)
Reiner Steinleitner, whose card indicates that he’s Leiter Planung und Qualitätssicherung is essentially the man who is in charge of production for CTS. He explains that the CTS engineers tend to bring increasingly complex assemblies for the manufacturing people to figure out how to build. “They show me these things, and I think ‘impossible,’” he says with a smile, then adds, “But we figure out how to do it.” In order to manufacture these tops, there is an array of competencies required. Among the operations performed are stamping, forging, casting, welding, riveting, and assembling. Because the roofs must perform with not only reliability (up and down and up and down) but also leak-tight accuracy, there is precision machining performed by CTS personnel of kinematic components. They cut and sew textiles (think headliners). They also have glass adhesive bonding expertise.
Because CTS is involved in a variety of functions, the firm has established centers of competency. For example, people in Hamburg specialize in kinematics and latches while in Stuttgart it’s retractable hard- and soft tops and sliding roof systems. The information developed in these centers is then shared throughout the organization. Steinleitner explains that lessons learned in producing the tops for various customers has lead to faster launches and process improvements (e.g., when they moved the SLK line from Hamburg to Bremen, they got it back up and running within four weeks).
For 2002, CTS should produce 50,500 textile folding tops; 65,600 retractable hardtops; and 8,000 removable hardtops and panels. Based on estimates and awarded programs, those numbers in 2005 should grow to 65,400 soft tops; 130,100 retractable hardtops; and 25,500 removable hardtops and panels. Steinleitner certainly has his hands full.
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