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The Mercedes A-class. This vehicle combines a small exterior package with a roomy interior.

Building the Hatchback for the Mercedes A-Class

Here's a step-by-step walk through of an automated line in Brazil that uses 12 robots to assemble hatchbacks. It's an innovative line for an innovative vehicle.

Without a doubt, one of the most innovative cars to come down the pike (well, not in the U.S., but maybe someday it will) is the Mercedes A-class. It is perhaps—unfortunately enough for Daimler-Benz—best known for its flipping over during a test by a couple of journalists during which time they were simulating dodging a moose that might wander onto a motorway. That problem has been resolved through both mechanical and electronic improvements.

Although the A-class is a compact vehicle—just 3.57 meters long and just 1,040 kg on the scale—it not only provides the safety standard of the much larger E-class, but with an interior length of 1.83 meters, it offers the interior room of a C-class, which has a 90-centimeter longer body.

There is also plenty of room for cargo. That is, depending on where the seats are located (e.g., there are 72 different seat variations being offered, so that the vehicle can seat from five people to just the driver), the cargo capacity ranges from 390 to 1,740 liters (the larger figure being the driver and his or her gear).

This vehicle is not some sort of pared-down unit, either. It features not only dual front airbags, but side airbags in the front doors, as well. It is also equipped with an electronic driver authorization system (ELCODE, or Electronic Code System) to help assure that the driver is actually the person who is authorized to do so.

The technological sophistication of the A-class is also reflected in the manufacturing operations that are used to produce it. One example can be found in a plant in Minas Gerais, Brazil, operated by Peguform, a tier-one supplier based in Barcelona, Spain. There, the A-class hatchback is produced in support of the Mercedes plant that is scheduled to go on-line in December 1998. The system, which was supplied on a turnkey basis to Peguform, was designed and built by Reis Robotics (Obernburg, Germany; domestic operations: Elgin, IL).

There are 12 robots in the system. There are seven RV6L models which have a maximum payload capacity of 6 kg, straight-out reach (with a 300-mm gripper) of 1,935 mm and a repeatability of ±0.05 mm. Six of these are mounted on C-frames, which means that they are inverted. The seventh is floor mounted. There are five RV130s. These are bigger units, with a maximum payload of 130 kg, a straight out reach (with a 500-mm gripper length) of 2,850 mm, and a repeatability of ±0.2 mm. All of the RV130s are floor mounted.

With regard to the pieces that are processed by the robots to produce the hatchbacks there are:

•Interior frame 
•Exterior lower body panel 
•License plate light cover 
•Rear spoiler 
•Backlight (or rear window).

All of these components, with the exception of the window, are injection molded plastic. This means, of course, that adhesive bonding, not welding, is the assembly method of choice.

The processing system is organized into a main line and an adjacent subassembly carousel. Although each of the robots performs dedicated tasks, all of the robots are networked to a main controller that checks and tracks equipment performance.

The sequence begins with the loading of the interior frame onto a part carrier. At the first robotic station an RV6L is used to preheat an area on the frame where the adhesive—a two-part polyurethane—is to be applied. At the next station, another RV6L applies a primer. The adhesive is applied by a RV130; the two parts of the adhesive are mixed in a nozzle on the robot's end-of-arm tooling.

Meanwhile, over on the carousel, three RV6Ls (one floor-mounted) are used to attach the license plate light cover to the lower exterior body panel. Here, the sequences involved—preheating, priming, gluing—are similar to those just described. The spoiler and exterior body panel are pretreated and primed to get them ready for attachment to the interior frame.

The lower exterior panel assembly and the spoiler are picked up with an RV130 that's fitted with a gripper that can handle both pieces. They are positioned on the interior hatchback frame.

The part carrier is indexed to a calibration station. Here, all of the gap dimensions are set; positioned pieces are pressed into final position; and the clamps on the part carrier are set and tightened. Once this is completed, the carrier is moved into a vertical stacking curing station that is sized so that the parts exiting the station are fully cured.

After curing, the frame is prepped—preheated, primed, and glued—for the insertion of the rear window. This sequence uses, as in the first part of the line, two C-frame mounted RV6Ls and a floor-mounted RV130. The glass is put into place by an RV130. Then clamping fixtures for the window are engaged.

This fully assembled unit is moved into a second curing station. Once it exits, the final RV130 removes the hatchback from the line.

Throughout the operation, the robot controller is monitoring all aspects of the assembly—preheating temperature, primer and glue flow rates, clamping pressures, speed of parts flow. If any anomalies are detected, the assembly is rejected at the end of the line.

Overall, when the line is full, there are 40 hatchbacks-in-becoming in the system. It takes 13 minutes from the initial load to the completed unload. One hatchback is produced every 72 seconds.

 

1-Interior Frame is loaded  1. At the lower left, the interior frame is loaded. The first robot (the orange one), an RV6L, will perform pretreating; the adjacent black-colored RV6L does the priming. (The robots doing priming are painted black.) Next to it is an RV130 that will apply adhesive. On the far right there is an RV6L on the subassembly carousel. The difficult-to-discern RV130 (to the right of the other RV130) picks up the exterior panel and the spoiler from the carousel.

2-Interior shell is visible  2. Here, the interior shell is visible in its fixture. The processing proceeds as is indicated in the series of steps described in (1).

3-RV130  3. This RV 130 has the lower exterior body panel in its gripper. 

.4-spoiler gets gripped  4. In (3) the exterior body panel was put in place on the tool. Here, the spoiler gets gripped.

.5-exterior fitted to interior  5. The lower exterior body panel is fitted to the interior frame.

.6-spoiler attached to interior frame  6. The spoiler is attached to the interior frame with the RV130.

7-end of the line  7. End of the line: the finished hatch-back is removed from the parts carrier with an RV130.