Sparks are flying – precisely and decentrally positioned

It's the surface that counts: the surfaces of automotive body parts have to be perfect. This is achieved using high-precision textured rolls that prepare the sheet metal parts for processing.

The texturing machines from Maschinenfabrik Herkules use electric arcs to process the rolls with the utmost accuracy. Now, the drive specialist Baumüller has assisted in optimizing the machines by converting them to decentralized drive technology.

Together with its customer, Maschinenfabrik Herkules, drive technology specialist Baumüller has converted an EDT machine (EDT = Electrical Discharge Texturing) to decentralized drive technology. The conversion has boosted the machine's efficiency, cut the amount of cabling required, improved serviceability, reduced the machine footprint, and simplified installation.

Die TexturiermaschineThe texturing machine / image: Herkules

The texturing machine

The Herkules EDT machine uses spark extrusion to process the surface of steel rolls, which in turn are used to process sheet metal. The texture on the roll is transferred to the sheet metal, improving its properties for painting and deep drawing. In addition, the texturing of the surface extends the life of the rolls. The texturing machines offered by Herkules feature a high level of performance, productivity and availability and meet the highest demands for accuracy. Herkules machines cover a wide range of roll sizes and diameters.

For machining, the roll lies in a dielectric bath, usually a non-conductive oil. The roll is inserted into a headstock and driven in rotary motion around the longitudinal axis by a DA1 main drive with b maXX 5100 mains inverter and b maXX 5300 axis units from Baumüller. The electrodes are advanced to the roll by servo motors. Generators produce a voltage at the electrodes, generating an electric field between the negative pole at the roll and the positive pole at the electrode. If the distance is correct, then a defined discharge occurs. The resulting arc burns a microscopic crater into the surface. The structure can be programmed very precisely to ensure a homogeneous surface quality. The permissible machining tolerances are very narrow. For a perfect surface, the distance between the roll and the individual electrodes is crucial and must be constantly readjusted. This is where the decentralized b maXX 2500 drives from Baumüller are used in the latest generation of EDT machines. By minimally readjusting the electrode position, the drives can compensate for concentricity tolerances of the roll caused by clamping.

The specifications of the Herkules texturing machines:

  • Surface accuracies obtained: 0.5 to over 15 µm
  • Roll weight up to 10 t
  • Roll diameter up to 800 mm
  • Processing capacity of over 1,200 rolls/month

The decentralized drives

Vorderansicht der Maschine mit den Elektroden
On the left, the front view of the machine with the electrodes, which have to be positioned at the exact distance from the roll. On the right, the rear view with the decentralized drives with hybrid connection technology.

Decentralized drive concepts move the control and power electronics from the control cabinet to the drive. Optimized cooling concepts and innovations in power units have paved the way for decentralized drive technology. This falls directly in line with the trend toward machine modularization. It also enhances efficiency in plant engineering, reduces cabling costs and increases compactness.

The decentralized drives that Baumüller has integrated into the Herkules texturing machine move the individual electrodes up to the roll so that the arc strikes the surface for texturing. The most important requirement for the drives was positioning accuracy. Depending on the expansion stage, between 27 and 50 decentralized drives of the b maXX 2500 series are installed in the Herkules EDT machine for positioning the electrodes. The decentralized drives of the 2500 series are highly dynamic servo motors with directly mounted controllers. For this application, Baumüller has combined its b maXX 3300 servo drives with the DSD2 servo motors to create a compact positioning drive with a degree of protection of up to IP65 and various connection options, such as connectors for individual cables, hybrid cables, and connection cables for customer assembly.

The advantages

The idea of converting the texturing machine from centralized to decentralized drive technology was suggested by Baumüller. One key advantage, considering the large number of up to 50 drives, is the reduced wiring complexity. The changeover has eliminated a number of cumbersome cable ducts, and the amount of wiring required has been significantly reduced, especially through the use of the hybrid connector, which combines a DC link connection, electronics supply, and fieldbus. The use of the hybrid connector has also improved serviceability, allowing drive units to be replaced quickly and easily. Moving the converters from the control cabinet directly to the motor eliminates the need for any external main motor connection and encoder cables. This means that EMC measures can be implemented with a significantly smaller extent of work. Combining the decentralized drive technology with a power supply unit with integrated safe DC link disconnection makes it extremely easy to implement the STO (safe torque off) safety function. Another important advantage gained is the improved efficiency in the planning and setup of the Herkules machine. One reason for this is the climate control in the control cabinet, which is now smaller because the drives have been moved away from the control cabinet to the machine. The smaller control cabinet also made it possible to reduce the overall footprint of the machine.

Conversion from centralized to decentralized drive technology – The advantages at a glance

  • Less wiring effort
  • Greater serviceability
  • Improved efficiency in planning and setup
  • Avoidance of disturbing influences
  • Reduced machine footprint
  • Fewer interfering cables

The system could be converted from centralized to decentralized drive technology without any mechanical redesign. The flange and shaft dimensions of the drives remained the same, and no adjustments were needed regarding fieldbus communication and the connection to the machine control system. The operating software for the drives continues to be the proven ProDrive; no familiarization with new software was necessary. “Thanks to the compatibility of the decentralized drives with the other Baumüller servo drives, the changeover was straightforward and quick to implement,” says Harald Kraft, Senior Director Electrics at Herkules, in praise of the new system.

The partnership

The partnership between drive and automation specialist Baumüller and Maschinenfabrik Herkules spans many years.

Herkules is the world's leading specialist for roll machining equipment. Wherever powerful machine tools are required to machine workpieces with a high degree of precision, Herkules roll grinding and turning machines are in their element. With a history of over 100 years, the family-owned company stands for tradition paired with innovation and the continuous optimization of its machine tools.

Herkules particularly values the fact that Baumüller is committed to customized standards for its products. This gives products a certain degree of flexibility in design and offers a wide range of options. This is of great benefit when it comes to the individual machines produced by the Herkules machine factory. “Baumüller is also a medium-sized, family-run company, which is a good match for Maschinenfabrik Herkules, which is also family-run,” says Harald Kraft. Even as a medium-sized company, Baumüller has service centers worldwide to provide support for end customers.

Conclusion

The idea is sound. The move to decentralized drive technology has paid off for Herkules and its customers. The changeover was easy and the advantages are clear: Smaller footprint, higher efficiency, less wiring effort, better serviceability, etc. In future, Herkules EDT machines will be equipped with the decentralized drives as standard.


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