By Jürgen Warmbold

After hitting upon the idea of industrialising the building trade with the aid of prefabricated steel box panels, Wolfgang Langer began to search for an integrated automation solution for their production. The difficulty until now was the question of how to bend the starting material: metal plates up to six metres long and weighing up to 480 kilograms. Langer's firm, BSC Bau-System-Center, was finally able to implement the system with a team of two cooperating KUKA KR 500 robots, which carry out the handling tasks at the press brake. 

BSC Bau-System-Center Entwicklungs- und Vertriebsgesellschaft GmbH & Co. KG, based in Eisenhüttenstadt, Germany, is the world's only industrial manufacturer of customised building structures made from specially bent, large-area steel box panels. The company currently employs about 20 people. It supplies ready-made, precision-fit elements in a wide variety of shapes and sizes, currently available in lengths of up to six metres. 

"Steel box panel technology can be used to industrialise the building trade. I had the idea back in 1989," explains BSC Managing Director Wolfgang Langer. "This system concept allows a great degree of planning flexibility and thus customer-specific solutions." 

This requires careful, detailed preparation, but the advantages, once building work is in progress, include time savings, improved quality and safety, and reduced environmental impact. Furthermore, significant savings in materials increase cost-effectiveness. 

Accurate to within a tenth of a millimetre Wolfgang Langer had to wait 16 years, however, from the idea's conception to a production system for the steel box panels. The reason is that it was simply not possible to bend such large, heavy panels either manually or automatically. "The robots, with their payload capacity of 500 kg combined with their teamwork skills, provided the breakthrough," Langer emphasises. "KUKA has supported us immensely. Without cooperating robots, this production line would not exist. Another important factor was the ability to integrate the robot controllers into the overall system program." 

The use of cooperating robots is based on the RoboTeam technology from Augsburg-based KUKA Roboter GmbH. The process ensures exact synchronisation and geometrical coordination of all path motions and operations within the team. The high process accuracy results from the high-precision synchronisation and the real-time exchange of all the data required for the cooperation. 

Each robot in the RoboTeam has its own standard controller. The KR 500 robots communicate with one another via a high-speed local Ethernet network and coordinate their actions. One robot is the team leader. Parallel to the RoboTeam, KUKA developed a new programming philosophy. Here, it is not the motion of the individual robots that is programmed, but that of the workpiece. 

Unique worldwide 

The resulting production line is unique worldwide. It processes metal plates with maximum dimensions of 6,570 x 2,000 mm and a thickness of 5 mm. The system was put into operation in May 2005. BSC expects a payback period for the entire system of one and a half years. 

The production line is in operation around the clock, six days a week. Only 20 days a year are planned for maintenance and servicing. High availability is thus essential. Regarding the robots, which are in continuous operation, the value is close to 100 percent. The offline programming of the KR 500 robots also makes a major contribution, as the process is uncoupled from the manufacturing process, meaning that the robots can continue bending while programming is being carried out. 

"Our requirements on the robots go way beyond this, however," says Wolfgang Langer. "One precondition for the production of the box panels is an angular and dimensional accuracy of up to one tenth of a millimetre relative to the entire workpiece. Furthermore, we require a cycle time of 8.5 minutes in order to be able to process the planned annual quantity of approximately 400,000 square meters of metal plate. The robots must also be very flexible, due to the varying lengths and widths of the finished steel box panels, which can measure from 2,800 to 6,000 mm and from 1,080 to 1,500 mm respectively." The flexibility of the KR 500s is also demonstrated by the fact that they can be operated independently of the other machines in the overall system. This fact can be exploited for contract work, for example. 

Versatile grippers 

Once a gantry crane has loaded a coil onto the coil lift truck of the line, the automatic process begins. This truck, which runs on a track, transfers the hot steel strip, weighing up to 30 tonnes and five millimetres thick, to the uncoiler. The strip is then processed by a straightening unit, before a laser system cuts holes, corner indentations for the folds, apertures for supply lines and other order-specific apertures into the plate. 

The plate is then carried by a roller conveyor to the two six-axis KR 500s. It is first positioned against a stop and then pushed into a defined position by pneumatic cylinders. The process is monitored by sensors. If the dimensions of the plates change, BSC enters the new values into the computer. 

The robots generally grip all plates centrally. In the case of very wide workpieces, however, the operators can also program an eccentric pickup position. Employees trained at KUKA College benefit here from the familiar Windows interface of the KUKA Control Panel. 

Traversing along a common linear unit, the two KR 500s pick up the plate with their suction cup grippers, which are 2,600 millimetres long and 1,000 millimetres wide. The end effectors developed for this application are each fitted with six different suction cup modules. Depending on the specific task, the system operator specifies via the controller, which gripper modules are to be activated. 

Complex, counter-directional motions 

It takes two robots to handle the plates, which can be up to six meters long and weigh up to 480 kg. Otherwise, the plates would sag. Apart from that, they would be too heavy for a single robot. Wolfgang Langer points to the KR 500s as they rotate a plate in order to hold it in a defined position against the back gauges of the press brake. "Just take a look at these complex, counter-directional motions. They clearly show that cooperating robots were the only possible solution for this application." 

The plates are bent on all four sides, with each side being bent twice at an angle of 90 degrees. They are guided by the KR 500s during these process steps. Their motions correspond to the downward motion of the beam in the press brake. In other words, when the beam reaches its lowest position, the robots are also at the end point of their motion paths. 

The KR 500s bend first the long sides and then the short sides of the plate. After each bend, they set the plate down on a turntable, which rotates it through 90 or 180 degrees. 

The setdown and pickup position on the turntable is programmed. Once the bending process has been completed, the KUKA robots set the steel box panel down on a support. From here, the workpieces are carried away on a roller conveyor to be welded.

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