The bridge workshop of Deutsche Bahn in Dresden has upgraded its cutting technology to the latest state of the art. Since the beginning of the year, the sheet metal cutting has been carried out with an erlcut e540 gantry cutting system. The BIBER cutting robot system is used for weld seam preparation. With the two systems from ERL Automation, the company not only registers improved cutting results, but also a significant time saving.
The bridge workshop was founded in 1927, at that time still with a railway siding, in the immediate vicinity of the place where Germany's first long-distance train arrived in the 19th century. Formerly a company of the Deutsche Reichsbahn, the bridge workshop has been part of the DB Bahnbau Gruppe GmbH, a subsidiary of Deutsche Bahn AG, since 2010. Steel railway bridges in particular are manufactured and repaired in Dresden to a high standard of quality and with the necessary know-how. " The bridge workshop deals with steel construction repairs of mainly railway bridges, but also station roofs and suchlike. In new construction, we manufacture bridge structures weighing up to 70 tonnes, but also auxiliary bridge systems and signal booms - everything Deutsche Bahn requests made of steel," explains Andreas Naumann, head of the bridge workshop. Two production halls are available for this purpose: While steel is cut, drilled and mechanically processed in the first, full or partial production is on the agenda in the second. To ensure that the whole thing lasts a long time, the parts are blasted and coated in the company's own corrosion protection plant.
Up to now, a cutting machine for vertical cutting was used to cut the required components. For reasons of age, it could no longer fully meet the requirements. Problems with the guiding accuracy and the process, but also the increasing lack of availability of spare parts, prompted those responsible to think about how the system could be brought back up to the state of the art. This also included considerations regarding a beveling unit, because weld seam preparation was previously carried out at manual workstations (grinding, milling, nibbling) in a time-consuming manner or was carried out externally.
ERL has developed a concept that has proved its worth: A new gantry machine with the latest technical features for vertical cutting with plasma and oxy-fuel technology is integrated into the existing periphery, consisting of a cutting table and extraction system. For weld seam preparation, the BIBER robotic cutting system is used, which offers a wide range of applications and can also produce very flat angles. "After we saw the components, it was clear relatively quickly that this could not be mapped with a chamfering unit," says Sebastian Biermeier, authorized signatory and sales manager at ERL Automation GmbH. "Material thickness leaps often have to be made, which sometimes require very flat bevels. A bevelling unit very quickly reaches its limits here," he explains further.
New gantry machine reduces production times
Like its predecessor, the new gantry machine, an erlcut e540 with a track width of 4 m, is designed for sheet metal formats up to 2.5 x 13 m. The gantry is equipped with three oxy-fuel torches with integrated ignition and internal height control and a plasma torch. The existing HiFocus 280i power source could continue to be used after it had been overhauled at the manufacturer. Cutting lengths of up to 30 mm can be achieved with the plasma process and cutting lengths of up to 200 mm with the oxy-fuel process.
The cutting system provides very precise cutting results. The components installed in the erlcut are decisive for this, such as double-sided toothed rack drives with brushless AC servo motors, which offer excellent dynamic properties with high contour accuracy. In addition, the rigidity of the gantry and the fully automatic and precise Z-axis are decisive for the accuracy of the cutting results.
Furthermore, the erlcut is equipped with an automatic pneumatic belt clamping system. This ensures that the towed torch carriages are automatically clamped to the steel belt at the correct distance, depending on the programme. On the one hand, this is very convenient for the operator, on the other hand, measurement inaccuracies can be excluded and non-productive times minimized.
While standard gantry cutting systems operate with only one proportional valve even in multi-torch mode and thus require operator intervention when switching torches on and off to ensure a consistent flame pattern, the erlcut has one proportional valve per torch. This means that in multi-torch operation, the amount of gas and oxygen is automatically adjusted to the number of torches in use. Correction of the flame pattern by the operator is not necessary and the resulting savings are not insignificant.
Naumann also confirms this: "He names speed as one of the biggest advantages compared to the previous system. But the possibility of making adjustments to the programme directly on the control system is also a significant relief, he says. "We had adjustment options before, but everything had to be done via a computer workstation. Now, small details can also be solved on site," says Naumann.
For programming, the universal programming system act/cut is used, which the bridge workshop had already had implemented by ERL a few years earlier. The modern software offers the advantage that metal sheets can be nested automatically, which had to be done manually with the programme used before. The system also allows several processes to be combined in one cutting programme. Plasma cutting and marking, for example of centre punch points, can thus be carried out in one programme sequence.
The standard software package can be extended with numerous additional functions. The bridge workshop has chosen the act/sign module, which makes it possible to prepare logos, graphics and fonts quickly and easily and to create a dxf file from them. Numerous graphic formats can be converted. An optimization function makes it possible to improve the quality of the contours to be cut. With the extension act/manager, the bridge workshop has also received an interface for creating and managing production orders and stocks. The module allows the assignment of parts to the individual order items as well as the use of the material stock for nesting (whole and cut sheet metal panels). Since the software is manufacturer-independent, the erlcut could be connected without any problems.
Automated weld seam preparation
Chamfering work that was previously carried out by grinding, milling or nibbling is now done by the BIBER robot cutting system. The system is suitable for automatically creating bevels of almost any type. Whether simple bevels, double bevels, bevels with or without a bridge - the BIBER can be used to apply a wide variety of bevels to already shape-cut parts. For cuts from above, chamfer angles of 30° to 90° are possible, for cuts from the front between 15° and 89°, provided that the torch is accessible. Normally, all this is considered to be very time-consuming to prepare and programme. This is not the case with this robot system. The BIBER system from ERL Automation is characterized by simple offline programming and handling. No matter whether series parts, different components or only individual parts are to be cut - the BIBER generates bevels with high precision and speed with a short preparation time. The new system at the bridge workshop is designed for sheet metal formats up to 2,000 x 9,000 mm. This large working area is made possible by the fact that a cutting robot is mounted on an upstream console and can be moved on a linear unit that is about 10 m long. The company can use the cutting table with integrated suction system in its entire size, for example for very large dimensioned components. "In addition, the user can divide the table by means of a partition wall system. This then results in two cutting areas that can be used for machining smaller workpieces in 2-station operation," says Biermeier. The robot and the system operator then work simultaneously - while the robot is chamfering components on one side of the partition wall, the operator can unload the finished components and reload the table on the other side at the same time.
For the plasma technology, ERL relies on a HiFocus 360i power source for cutting lengths up to 50 mm. It is equipped with an automatic gas console that mixes the plasma gases optimally for each cutting task - a separate database ensures the exact regulation of the required gases. A torch with automatic integrated ignition is used for oxy-fuel cutting. This makes cuts of up to 200 mm possible. For both processes, the employees of the bridge workshop have an integrated cutting database at their disposal, which is based on ERL's many years of experience. By calling up the stored data records, the process parameters are set automatically - so even inexperienced operators can start producing parts in just a few steps. Tool change is also very simple and can be carried out in just a few steps. This is made possible by a special tool holder with which plasma and oxy-fuel torches can be exchanged within a few minutes. The torches can be detached from their respective positions by means of a screw connection, exchanged and reattached at the new position. Automatic torch calibration via measured stop systems in the torch holder ensures the correct Tool Centre Point (TCP).
The systems have been in operation in Dresden since the beginning of the year. The employees were able to familiarize themselves with the machines during a training course parallel to production. After only a few weeks, the results were positive throughout. With the BIBER, for example, the user was able to increase productivity in weld seam preparation enormously. "We cut bulkheads for signal booms with the BIBER just yesterday. With manual processing, it would certainly have taken us a little more than an hour. The BIBER cut the bevels in 3 minutes," reports Naumann.
However, it is not only the process that ensures short machining times, but also the simple handling of the system. The components only have to be placed on the cutting table. This is designed in such a way that both top and bottom bevels can be cut without having to turn the components. No fixtures are required for this. The camera system intelliplace attached to the robot automatically determines the respective component position on the table. The associated component programs are also automatically called up from the directory, assigned and nested. The only prerequisite is that the operating personnel first record the component data (data matrix code on the component or barcode on the accompanying documents) with a handscanner. This system is particularly advantageous with a large variety of components because it saves time and, not least, reduces operator errors, since calling up similar or mirror-image component programmes is ruled out. "The employees have quickly familiarized themselves with the system - it is very well received, also because the noise emissions are lower. Although the BIBER can also be noisy during plasma cutting, it makes a difference whether the BIBER runs for 3 minutes or the nibbling machine for over an hour," says Naumann.