Quantum leap in accuracy

At the Röhm GmbH plant in Sontheim Germany, 750 employees manufacture technology-oriented solutions for the automotive industry, mechanical engineering and aerospace sectors in a 41,000sq/m facility. The parts in question are finished on Kellenberger Premium grinding machines.

The company’s portfolio fits perfectly with the existing business areas of Rothenberger Holding, which generates a sales volume of €1.3billion with over 100 operating companies, many of them in the machine tool sector. Applying an extensive restructuring project, an investment sum of several million Euros was made available, which flowed into new machinery and systems. The aim for the future was to produce Röhm‘s high-tech products with even better quality and at the same time more cost-effectively.

For division manager Alexander Scheitenberger and his 35 staff members, the investment came exactly at the right time. Scheitenberger‘s department manufactures tool clamping systems, 40% of which are customised special designs. A trained industrial mechanic, Scheitenberger has been with Röhm since 1990 and is very familiar with all machining processes and the Röhm portfolio, which includes drill chucks, centre punches, lathe chucks and vices, robot gripping technology, power chucks, clamping cylinders, mandrels and tool clamping systems. 

The parts were machined on a KEL-VARIA universal grinding machine with a centre width of 1m, which had been in use for 18 years. With spare parts for key components no longer available, making a replacement investment became unavoidable. Scheitenberger and head of production Erhard Bader agreed, that the new machine should again be a KELLENBERGER. “We have had a very good experience with the KEL-VARIA. The reliability, accuracy and process safety of the machine over the runtime were outstanding. In addition, the cooperation with KELLENBERGER has always been characterised by a high level of professionalism. Erich Ziegler, the KELLENBERGER area manager who is responsible for us, gave us excellent advice on the new procurement.” Since 2018, the KELLENBERGER product portfolio has offered two machine designs, which can meet the machining tasks at Röhm. The new KELLENBERGER 100 platform concept proved to be the best solution, especially as Swiss manufacturer Wenger had specially adapted automation to the machine.

The task assigned to the engineers in St. Gallen, Switzerland, regarding the KELLENBERGER 100 was to develop a platform on which different machine concepts could be realised with a strong customer orientation. The segment of high-performance, low-cost grinding machines within the group was integrated into the concept. The modular solution on a common platform and a new assembly concept to reduce throughput time enable cost-efficient production of the machine and thus a very good price/performance ratio. 

The KELLENBERGER 100 offers the widest range of standard configurations for a variety of grinding operations. The machine is available in centre widths of 1,000/600mm and a centre height of 200mm and is designed for part weights of up to 150kg. A higher drive power for the grinding wheel (11,5kW) ensures increased productivity, while the newly designed guide in the Z-axis brings greater profile accuracy. For higher accuracy in non-circular grinding, the C-axis is equipped with a direct drive. Röhm opted for a machine with a centre width of 1m.

The K100 has a compact, collision-free tandem grinding head with motor spindles. Ten grinding head variants are available for the optimised design of the machine concerning the machined parts. The reinforced casing allows the largest grinding wheel diameters for internal grinding up to 125mm. 

The user-friendly, ergonomic design of the KELLENBERGER 100 machine is complemented by intuitive operator guidance via touch screen interface. The machines are equipped with a state-of-the-art FANUC 31i CNC control with a 19” touch screen. Various ready-made software packages are included as standard or can be added as an option. They cover simple workpieces, complex workpieces in the shortest machining time, and complex contours and profiles.

Swiss automation specialist Wenger has custom-designed the loading solution WeFlex for chucks and shaft parts, especially for the K100. The WeFlex loader enables automated processing of shaft parts from Ø6 to 100mm with a length from 20 to 600mm with a maximum gripper diameter of 80mm with workpiece weights up to 5kg in alternating mode and 15kg in single part mode. Interchangeable gripper heads facilitate quick changeover between the shaft and chuck parts. In the stacking module, 8 pallet spaces of size 400 by 600mm are available. Inserts for shaft or chuck parts can be inserted in the pallet frames.

The machine is loaded via telescopic line gantry and an automatic hatch closes off the machine room during machining to ensure the thermal stability of the machine. Directly at the infeed, electricity and compressed air are recorded, which allows the energy consumption of the WeFlex to be recorded and visualised. To reduce energy consumption, the speed of the WeFlex is automatically adjusted to the cycle time of the processing machine. An image-guided setup wizard assists the operator when changing over to a new workpiece. Wenger Managing Director Michael Wenger supervised the initial commissioning, which was followed by training for the Röhm employees at KELLENBERGER. One week after machine commissioning, the 3-shift operation was resumed. “The reliability of the loader works is very high and we haven’t had any downtime so far,“ reports Alexander Scheitenberger. 

The service package also includes remote maintenance of the machine and minor service work is handled internally at Röhm. “A couple of our employees have undergone service training with a focus on the new machine, so they can carry out minor repairs themselves,“ says Scheitenberger. “There is no need to call the KELLENBERGER service team for a minor issue. But if you do need the service, it’s fast and reliable.”

The conclusions of Alexander Scheitenberger and his colleagues are very positive: “In terms of accuracy, the new machine has brought us a quantum leap. Today, we grind with an accuracy of 2 microns with process reliability. The surface quality of the machined tool clamp is so good that, with the same polishing times, the results are many times better, from Ra 0.3-0.4 microns to below Ra 0.1. Due to the larger grinding wheel and because the new machine is simply faster than the old one, we have a 25% increase in productivity. In addition, personnel costs are 30% lower as the automation ensures that one operator is sufficient for two machines.”