The decisive criterion for the competitiveness of special machinery manufacturers is the ability to implement sophisticated developments in less time with minimal cost and high quality. This increases the demands on the suppliers have to offer customized solutions quickly and reliably, so that customer requirements can be implemented individually. For feed belts to press lines, Schuler Automation relies on the Torque ball bushings by Dr. Tretter.
These elements ensure optimum and low-wear operation. "Our press lines are used by many well-known car manufacturers in Germany, Europe-wide, overseas and Far East," says Andreas Herb. The graduate engineer is head of mechanical design at the Schuler Automation GmbH & Co. KG in the Baden-Württemberg Gemmingen near Heilbronn. "Here at the factory, we take care of devices that automatically feed sheet metal to press plants, and that very efficiently." In addition, there are washer and spray units for the sheets, which are also called blanks, as well as integrated, customer-tailored solutions for loading and finished stacking systems ,
Press shop equipment and logistics conceptThe company is one of the specialists when it comes to automation issues in press shop equipment and logistics concepts. "Our services include project planning and consulting, planning and construction, delivery of turnkey systems, commissioning and training, as well as service and maintenance," notes Andreas Herb. "We offer tailor-made system solutions for new plants, conversions and re-engineering." Schuler Automation has an export quota of 45% and supplies about 300 to 400 customers, primarily from the automotive industry. These include well-known companies such as BMW, Audi, Mercedes, Ford, Volkswagen, Volvo and their suppliers. "Here in Gemmingen we employ about 300 employees," says Andreas Herb.
At the site, the systems are assembled and put into operation. With the press themselves, they are married to the customer on site. "In addition to our own production, various assemblies and components are procured from selected suppliers," says Herb. Schuler Automation places high demands on its suppliers. Reliability, price, on-time delivery, but especially fast delivery play an important role. The company tries to limit the number of partners to a few. One of the selected providers is Dr. Ing. Tretter GmbH & Co from the Swabian Rechberghausen. "For us, the high quality of the components is crucial," explains Herb. "Because our systems should not only fulfill their task. With our solutions we want to provide users with significant increases in efficiency, precision, and productivity. "
Forming the boards to KarossrieteilenIn the assembly hall, construction manager Andreas Herb points to conveyor belts that are currently under construction and that later in the automotive industry feed the presses large-area sheets with widths of up to 4,30 and depths down to 2,20 m. These so-called boards are transformed into body parts such as doors, hoods, trunk lids, side walls or fenders. At the customer, the conveyor belt is usually loaded by two destacking robots. Alternately, they take the boards one by one from a stack and place them on the conveyor belt. Spreading magnets prevent the simultaneous lifting of two sheets.
"Depending on customer requirements, we equip these conveyor lines, for example with a part tracking. At the same time, sensors permanently recognize where the component is located, "says Andreas Herb. There are also controls that prevent sheets from sliding over each other. A camera system checks the position of the sheet on the belt. If this is not correct, a centering robot moves it into the correct position. At the end of the conveyor line, an inserter removes the component and places it in the press. "We can also equip the line with a washer that cleans the sheets before forming," says Herb.
Schuler Automation adapts the systems individually to the conditions of the user. The length can be up to 20 m - it can be a stretch of up to three conveyor belts assembled. Each conveyor belt consists of six to ten conveyor belts. Each belt strand consists essentially of a toothed belt with two pulleys, which run in a profile. To transmit the drive torque to the individual strip strands torque ball bushings are used, which are located in the pulleys.
Backlash-free torque ball bushings replace worn splinesThese drive units depend on the speed. Because this decides on the number of components that are produced in a certain time unit. And because the boards on the way to the press at different stations hold, the tape must be stopped and accelerated again. "The torque ball bushings are almost free of play. This is important because with this dynamic movement they do not fail when stopping and accelerating again. This significantly reduces wear, "explains Herb.
Until about ten years ago, the engineers still used splines. These units took off faster due to their play in constantly changing accelerations and brakes. In addition, there may be a lack of lubrication at the pressure points, as a board change and thus an adjustment of the pulleys do not have to be done every day. This can lead to tribo corrosion in the episode.
Keep even distanceDepending on how large the sheets to be processed, they can lie with their sharp edges directly on one of the strip strands. If the belt accelerates or decelerates, the edges will stick to the strand due to the inertia of the boards and damage it. The sheets must therefore lie on the conveyor belt so that they touch the strands with their sharp edges as little as possible. Therefore, the side edges of the boards must protrude over the strip strands. "When changing the blank, when sheets of other dimensions are being transported, we have to change the distances of the strip strands accordingly," explains Andreas Herb.
The minimum distance from the center of the strip to the center of the strip is, for example, 200 mm. "With six belt strands, three are shifted in blocks from the center to the left and to the right," explains Herb. Now, a threaded spindle ensures even spacing in the blocks. For this purpose, it has different thread pitches: With a drive all strip strands of a block are fanned out stepless to always equal distances. To combine this adjustment movement with the output of the conveyor belt, initially splined shafts were used, which were soon replaced by torque ball bushings.
High-precision longitudinal guides prevent tiltingTorque ball bushings are high-precision longitudinal guidance systems for torque transmission. They allow a smooth, parallel adjustment of the belts in every position - without tilting them. This is ensured by the rolling element ball. Thus, the torque ball bushing experiences only a lateral force. During transmission, they perform the function of a splined shaft. The special feature is that due to the rolling element no stick-slip effect occurs. The translation movement is almost jerk-free. In the case of the torque ball bushings, the ball runs in ground grooves.
Thus, these machine elements are much more wear-free than the splines. That's because of the geometry of the touching body. Because the convex circular arc groove snuggles against the also convex ball closely. The Schuler engineers also have the advantage of being able to realize very compact designs with the torque ball bushings. "Even if the machine elements are a bit more expensive, in the end we get the cheaper solution," says Herb. The torque ball bushings are currently paired with rippled shafts. These are designed so performance-oriented and high-quality that ready-to-use standard elements are used.
Torque ball bushing beats ground torque shaft"In the meantime, Schuler still had a competitor with ground torque shafts in use," recalls Manuel Lauppe of Dr. med. Tretter, who works as a calculation engineer at the Swabian supplier and was in charge of Schuler at that time. "However, we were able to convince the automation engineers of our torque ball bushings because we recommended torque waves drawn for this application." The company thus scored with very short delivery times and a lower price, without sacrificing functionality.
A drawn torque shaft is not so accurate and the game can not tolerate as tight as a ground shaft. But this can certainly be an advantage in a case like Schuler. "Real components usually have errors," says Lauppe. "Now, when these components are assembled, and there are four or six other components on one element, which in turn are coupled by an element, the resulting play is reduced." The same is true of accuracy. "These effects have been proven by the use of profile rail guides in machine tools," emphasizes the engineer.
Know-how, trust and proximityAnother, not insignificant, reason for Schuler Automation, for Dr. med. Deciding to rely on suppliers as a supplier is also the closeness and trust that has built up during the long-standing business relationship between the two companies. "We can supply our customers with press lines that are characterized by high output and quality combined with short tool change times," emphasizes Andreas Herb. With this combination, Schuler makes a decisive contribution, with which users can reduce their parts costs and thus increase the profitability of their press shops. Every year, up to 15 feeders for these efficient press lines leave the plant in Gemmingen.
Picture above: The conveyor belts feed the sheets to the presses. The torque ball bushings not only drive the belt strands, they also ensure the optimum distance to each other.