Gustav Schöneweiss opened his business in 1866 with four workers and a few hammers, thus laying the foundation for what would later become a leading forge shop and a force to be reckoned with on the world market. The company was first registered officially by the royal district court in Hagen. After three years as a wholesaler, Schöneweiss built his own factory for the production of fence bar finials and rosettes. Wrenches and other products were added later.
Today, Schöneweiss & Co GmbH is a supplier of components to the automotive industry; other customers include manufacturers of railroad rolling stock. The main emphasis is on the production of front axles and other chassis parts, steering elements and engine parts for commercial vehicles, and drive train components for passenger cars. The company, which employs more than 600 people, offers all types of heat treatment and sells its products worldwide. Most of its customers are based in Germany, the UK, France, Sweden, Turkey, or the US.
In the year 2000 Schöneweiss had total sales of DM 124.8 million, of which exports accounted for DM 37.2 million. The company is certified in accordance with VDA 6, Part 1, and has a forging capacity of about 40,000 tonnes per year. The weight of the forgings ranges from 1 kg to 140 kg, with a maximum length of 2000 mm.
Greater productivity and process reliability
Since the beginning of January 2001 Schöneweiss has used a KUKA KR 350 heavy-duty robot to handle red-hot truck and bus front axles weighing from 80 to 180 kg. The six-axis robot replaced a so-called “andromat”. This was a manipulator equipped with a gripper and a cab for the operator. Two persons were assigned to the manipulator in each shift. While one person operated the manipulator, the other rested from this very strenuous work, or carried out less demanding tasks.
“This conversion was essential because the Andromat was old and subject to frequent malfunctions. Moreover, it was much slower than a jointed-arm robot”, says engineer Rainer Liebermann, assistant to the division manager, forge shop 1, with regard to the decision. “The advantages of the new concept were obvious: we were able to permanently boost our productivity and process reliability, while at the same time saving two operators per shift. The automatic handling also reduces absenteeism due to health problems. Furthermore, the employees could be reassigned to other areas of the company, easing our severe shortage of personnel.”
Playing with fire
The heavy-duty robot is used in the forging line for axle production. The sequence begins there in an induction system, where the steel is heated to 1,250 °C. The material is then pre-formed on a forging roll. From there it is transferred by a manipulator on a rail to the bending press, which pre-bends the steel. As soon as the robot controller receives the signal from the controller that the material can be removed, it sends the corresponding command to the KR 350. The robot has to be able to handle 42 different axles using its gripper. The corresponding programs for this are stored in the robot’s controller. The robot is largely shielded from the harsh environmental conditions by a protective suit. Once it has gripped the red-hot steel, it moves with it on a linear unit to the forge hammer and places it in the recess of the bottom die. The motion of the linear unit as a seventh axis is also coordinated by the robot controller.
At the forge hammer, the number of strokes depends on the form and weight of the axle. Once the machine operations are completed, another manipulator installed on a rail running under the ceiling takes the axle to a trimming press. From here the axle drops automatically into the calibrating press. There it is picked up by a second robot and placed on a traversing carriage, from which it is removed by a crane gripper and placed in a rack for cooling. The final process steps in the forging line include hardening, tempering and shot blasting.
High load-carrying capacity
During handling, the six-axis robot has to reach about two meters into the machine. In addition to the payload, which is already quite heavy, the gripper itself weighs about 100 kg. What this means are particularly large force moments on the lever arm. Rainer Liebermann explains: “As for the robot, load-carrying capacity was our top priority. The KR 350 was the only robot which could handle such heavy loads in combination with the required long reach.” Since then, KUKA Roboter GmbH, Augsburg, Germany has introduced the KR 500, which has even more power, but whose load capacity of 500 kg would have been excessive for this particular task.
Among Schöneweiss’ other requirements were high repeatability with tolerances under a millimeter, nearly 100 percent availability, and high flexibility. And flexibility does not involve merely the many different types of axle, important though that may be; it also means simple programming of new axle types via the KUKA Control Panel’s familiar Windows interface. The user also wanted a fast robot which could achieve short cycle times. The cycle time is determined by the size of the particular axle and therefore its dwell time in the induction furnace and at the forge hammer; for the KR 350 this is generally about 60 seconds per axle, including the motions to and from the bending press and the forge hammer.
Secondary benefit
Schöneweiss purchased the robot directly from KUKA. The integration was carried out by Lasco Umformtechnik GmbH, Coburg. Lasco also supplied the gripper, which was developed specially for this application, and the about 4.5 meter long linear unit. Because of the variety of axles to be handled, both wide and narrow jaws were provided for use on the gripper.
Since the robot is faster than the Andromat that was used before, Schöneweiss now has handling capacity reserves in this area. The company would consequently have no problems adapting the handling system if some day larger quantities of smaller axes are produced, requiring shorter cycle times. The potential for increasing throughput is only a secondary benefit, however; for the user the most important goals were high process reliability and making operations as efficient as possible.
Author: Jürgen Warmbold, freelance technical journalist, 27327 Martfeld, Germany