Perfection in every tooth
In addition to the wide diversity, there is another characteristic that is typical for Liebherr-Verzahntechnik in Kempten’s range of customers: the high standards of quality. The Allgau-based company therefore relies on circular grinding machines from Kellenberger for finishing.
Liebherr-Verzahntechnik GmbH’s, incorporated in Kempten, has an impressively broad range of products. It covers gear technologies like gear shaping, swarf cutting, hob peeling, continuous gear grinding and profile grinding, chamfering and deburring to finish any kind of gears. The high-precision machines work in sectors like aerospace, automotive construction with suppliers, wind power, the coal and steel industry as well as robotics and medical technology. The same
applies to all of those sectors: The customers have enormously high quality requirements. Grinding work on machine components is therefore executed on, among other thing, circular grinding machines manufactured by the Swiss manufacturer Kellenberger.
Grinding technology is the nucleus of precision manufacturing
The Liebherr modular system contains thousands of different workpieces from which the base machine series are equipped with components for customer-specific finishing, which makes every machine a quasi customized machine. On occasion, Liebherr engineers develop customers for customer finishing jobs that aren’t even on the market yet. Grinding is the supreme discipline in machining and Liebherr’s grinding shop is like the nucleus of the highest precision for core components. This production department has been housed in a new, air-conditioned hall since 2013 – a crucial factor for high precision in finishing.
As in all areas of production at Liebherr, only specialized experts work at the machines in the grinding shop. Gerd Eising, the grinding shop master, his colleague and
deputy, Jürgen Rimac, and the sixteen staff members, working in two shifts, ensure the high quality assurance standards are met. “Precision very clearly dominates over everything at Liebherr,” confirms Gerd Eising. “At 3 micrometers, the quality assurance starts getting nervous; irregularities and dimensional deviations of more than 3 micrometers basically mean exclusion.”
So it is no wonder a close look is taken when procuring the machine For circular parts finishing, universal circular grinding machines from Kellenberger were selected years ago. The first KEL Varia circular grinding machine Kellenberger was put into operation at Liebherr Verzahntechnik in 1995. A second machine with a Kelco 120 controller was procured in 2010 and specially used for non-circular grinding. Two additional KEL Varia machines were procured, one of them to replace the first, now discontinued model. The parts ground on the machines are between 5 and 1500mm long.
The KEL Varia universal circular grinding machine is the predecessor model to the current Kellenberger 1000 premium series and, like it, stands for the highest finishing and surface quality. More than 1500 machines from this series are in now in use worldwide. The machine owes its success to its high static and dynamic stiffness and stability; both crucial factors for high precision and high productivity. The Varia’s scope of performance is based on the quality requirements for the
precision manufacturing of prototypes, small and mediumsized series.
Good accessibility and simple programming as plus points
The KEL Varia machines are designed with peak widths of 1000/600 mm and a peak height of 200 mm for workpiece weights of up to 150 kg. The machines are equipped with hydrostatic guides on all main axes for the highest form precision when performing grinding work with interpolating axes. The B axes has a direct drive. With it, the revolver grinding head pivots three times faster than without and positions with a prevision of less than one arc second. Particularly when the finishing process requires various grinding discs to swivel in, this reduces the auxiliary times which increases productivity. The trained application grinder and programmer Jürgen Rimac can name exact the reasons for choosing Kellenberger: “Of course the competition also had good machines. But it wasn’t just the finishing quality of the machines at Kellenberger that convinced us, but also the accessibility to a well-structured, orderly working area, in particular, the more simplified programming that is normally handled directly on the machine by the grinders.” The easy programmability of the Kellenberger machines also offers clear benefits to trained grinder, Jörg Bachmayer: “Things never get boring with respect to tolerances here in the grinding shop. Good programs make the work immensely easier.” The newer KEL Varia machines have the programming features KEL-Soft and KEL-Assist with which existing programs can be easily adapted to modified requirements. Various finished software solutions – BLUE solution for simple workpieces, RED Solution with visualized workpiece programming for complex workpieces in the shortest finishing time and the BLACK solution for creating complex contours and profiles are always included with the standard version or can be added as options.
Automated Kellenberger 100 for relatively small parts
The most recent acquisition in the grinding shop, the Kellenberger 100 universal circular grinding machine is equipped with a simple user guidance function executed via an intuitive touchscreen interface. The machines are equipped with the newest CNC Fanuc 21i with a 19” touchscreen, with a choice of the newly designed cycle programming or workpiece-based graphic programming. The platform design of the Kellenberger 100, as a modular solution, has been combining tried-and-tested tooling machine concepts from the Hardinger group with those from the Kellenberger brand for decades. A very broad range of configuration options is available for a very broad range of grinding options. To keep auxiliary times as low as possible, the Kellenberger 100 is largely programmed externally by Jörg Bachmayer. Jürgen Rimac programs non-circular contours and all contours that have to be created in grinding discs; also at an external work station.
The Kellenberger 100 is also designed with peak widths of 1000/600 mm, a peak height of 200 mm and for workpiece weights of up to 150 kg. The high drive power of the grinding disc ensures a high level of productivity and the newly developed Z guide ensures high profile precision. The C axis with a direct drive allows for higher precision in non-circular grinding than usual. The technological highlights of the Kellenberger 100 include an innovative compact grinding head (ten variants, 11.5 kW drive power, 500 mm disc up to 63 m/s, HF spindles for interior grinding, including diagonal and tandem arrangement), a collision-free universal head with three tool positions and one measurement position and a new measuring probe arrangement without a swivel arm mechanism for increased measuring accuracy. A synchronous tailstock allows for the entire shaft to be finished without carriers which means the entire length of the workpiece can be fully finished.
Customized pallet automation
Automation is a major topic in the grinding workshop since, in addition to the two regular shifts, a half shift runs without staff.. The flexibility of the Kellenberger 100, supplemented by a modern automation solution, WeFlex, manufactured by the Swiss automation specialist Wenger, specially adapted to this tooling machine, meets the specified requirement and played a major role in the purchasing decision. The loader for chuck parts and shaft parts with it own programming includes 40 to several hundred parts. The batch sizes span from 1 to 100 in the grinding shop and, in rare cases, even up to 200. “From more than 5 parts, it is worth using the loader,” says Jörg Bachmayer. “We also load eccentric bolts via the loader.” In response to the question as to why Kellenberger is awarded the contract again and again, Gerd Eising answers: “It isn’t automatic. When procuring a machine, all potential machine manufacturers are considered. The machine with the most suitable technology and best price-to performance ratio is awarded the contract. Kellenberger is a competent point of contact regarding all technical and service inquiries. The after sales service for the Kellenberger grinding machines is located in Switzerland and the production site in St. Gallen is practically around the corner.” So, it is very likely that the next grinding machine in Kempten will be from Kellenberger
Andrea Jäger is a freelance journalist in