Robust and durable, with an unmistakable look: the exterior appearance of the Mercedes G-Class has changed very little since its market launch. Following the latest update, the off-road icon is 53 mm longer and 121 mm wider, giving it an even greater presence both on and off the road. Otherwise, however, the focus has been more on technology than on looks. The ladder frame, the core element between the body and chassis that gives the vehicle the necessary stability, was also revised as part of the new edition. At the same time, the new G-Class also ushered in a new era in production: Where previously much of the welding was done by hand, Magna Presstec now uses an automatic production line from Kuka for this work.

"This was the first time we had worked with Kuka," says Armin Kleemaier, Project Manager at Magna Presstec. The decisive factor for establishing contact was a reference with a similar task that Kuka had already implemented a few years ago. The starting point for the joint project was a workshop. "It was very positive to visualize the goals and requirements of both sides together and to start implementing them," explains Armin Kleemaier. The initial rough concept of what the facility could look like was increasingly refined and fleshed out over the course of the project.

Cramped conditions

One particular challenge: the hall geometry. "The total production and logistics area is around 2,000 m². However, not the entire area can be used for the production facility. In addition, the production hall is very long and narrow," says Dominik Pfeiffer, Project Manager at Kuka. This meant that space was at a premium and individual solutions had to be found. For example, by creating a supply aisle for wire drums or robot equipment on the left-hand side of the hall. Component racks are used to store the individual parts during the production process.

Then there were the dimensions and weight of the component: With a length of 4.30 m and a width of 1.20 m, the ladder frame weighs over 230 kg. Approximately 145 individual parts are processed. The total length of the weld seams is almost 80 m, and over 200 spot welds are also used.

Specially developed shell construction system

The ladder frame is made up of two main groups and other individual parts. The production lines for the front and rear frames have the same system, but the arrangement is mirror-inverted. Essential components are the two squeezing stations, which have proven to be necessary in several lessons-learned units carried out worldwide. Using a sophisticated welding process, the parts are then welded with as little distortion and stress as possible. The subsequent geometry-forming station (geo-station) connects the side members with the cross members and the spring domes; from this point onwards, we speak of the front or rear structure. The special feature: tacking and welding is not carried out in separate welding stations, but directly in the respective stations of the line. After further small parts have been attached, each sub-assembly is subjected to a quality check by a worker at the end of the line. Only then does a robot place the component in a rack and it is fed to the next work step.

Welding of small parts for the front and rear end. Welding takes place directly in the line, separate welding stations are not required. © Kuka

In a further geo-station, the front and rear sections are joined together with other individual parts to form the substructure or ladder frame. The attached parts are welded out in subsequent stations. A buffer is installed upstream of the punching machine, in which the components cool down to a uniform temperature. After the final inspection by an inline measuring system and quality inspector, the finished ladder frame is automatically transferred for surface finishing.

Control with miKuka

Kuka's own miKuka standard was used for control. Information on the machine status is displayed transparently and standardized functions facilitate operation. With miControl and miView as integral components of the software solution, end customers receive proven and tested program modules. They enable the user to create and expand operating and display functions very quickly and without much effort. "This control system enables our customers to produce in line with Industry 4.0. With our control technology, we provide the necessary networking, self-configuration and self-diagnosis," says Dominik Pfeiffer.

20,000 ladder frames per year

Transfer to the inline measuring station for final inspection. After the final inspection, the ladder frame is automatically transferred for surface finishing. © Kuka

The system has been interlinked and in operation since May 2017. "Welding is now extremely process-stable and we achieve optimum quality and high output with minimal manpower," summarizes Dominik Pfeiffer. There are 45 robots in use, in particular KR 30 L16 welding robots and KR240 handlers. At a final inline measuring station, a robot with a camera and line laser measures the components and ensures that the frames are 100% checked for dimensional features such as holes, bolts, edges and surfaces. This guarantees consistent component quality.

Magna Presstec achieves an output of 20,000 ladder frames per year in two shifts. Armin Kleemaier is satisfied with the process and the result. His conclusion: "The cooperation with Kuka was good and improved even further over time. When disruptive factors arose, we were always able to work through them well. This is how we made the project a success together."

Sebastian Schuster, Global PR & Content Manager at Kuka / ag