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High-precision internal grinding of even the smallest diameters - BURO GmbH

October 31, 2023 - Hardinge Blog, Press Releases
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Contract manufacturers must be able to adjust permanently to changing parts and batch sizes. A large machine park is indispensable for this required high flexibility. BURO GmbH, based in Winden im Elztal, has more than 70 machines covering the entire range of manufacturing processes. In the field of cylindrical grinding, the company has relied fully on Kellenberger for decades.

Company boss Jürgen Burger’s motto is to offer his customers everything from a single source. In doing so, he accepts every challenge, even that of integrating a new type of machining into production or machining even more complex parts. BURO GmbH is a family business. From the beginning in 1969, company founder Ludwig Burger ensured steady growth with high-quality precision parts in contract manufacturing. The industries he supplied with well-known companies in the region were initially mechanical and apparatus engineering, electrical engineering, fastening technology and the phonographic and paper industries.

Today, with Jürgen Burger, the second generation is responsible for the workforce, which has now grown to more than 116 employees, all of whom are experts and highly qualified. “Here, everyone knows what they are doing,” says Jürgen Burger. “And we cover every type of machining across the entire process chain.”

In the beginning, the company concentrated on turned parts with ø 3 to 42 mm and milled parts. Grinding parts were outsourced for a long time, although the know-how was certainly available. In the mid-1980s, the machinery was expanded with the first grinding machines, and in 2006, as a capacity expansion, the company invested in the first Kellenberger grinding machines from the KEL-Varia (now KELLENBERGER 1000) and KEL-Vista (now KELLENBERGER 100) series.  “Right from the start, I was completely convinced by the Kellenberger machines, both technically and in terms of price” remembers Jürgen Burger. “Above all, the procurement of the KEL-Varia with its high precision and functionality was a huge step forward for us. Due to the large grinding length, we can even grind 1.5 m long shafts between centres with steady rests with high precision. And we have also been using the machine for a long time for out-of-round and thread grinding.”

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Even very small internal diameters can be ground on the VOUMARD 1000 can be ground without any problems

In 2019, the need for another Kellenberger grinding machine arose. “We wanted to broaden our grinding range once again in order to expand the variety of parts and, in particular, to be able to manufacture very small components with complex geometries and small bores in a highly precise and economical manner. Above all, the internal grinding area was to be strengthened,” says Jürgen Burger. One of the triggers was an enquiry for a complex workpiece to be ground in large series, a bushing with an outer diameter of 10 mm and an inner diameter of 7 mm, with two bevels and a sealing edge. The required cylindricity was less than 1 µm. On the machine side, dynamics and speed were required here. In addition to another Kellenberger 1000, Jürgen Burger also considered a Kellenberger 100 as an alternative.

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Sales Manager Erich Ziegler, Project Manager Patrick Zünd (both Kellenberger) and BURO boss Jürgen Burger

Kellenberger Sales Manager Erich Ziegler and Project Manager Patrick Zünd analysed the upcoming machining tasks together with Jürgen Burger. To Burger’s surprise, the two grinding specialists from Kellenberger offered not only the favoured Kellenberger machines, but also the universal internal + external cylindrical grinding machine VOUMARD 1000, newly launched in 2020, which focuses on internal grinding and is optimised for flexible, universal internal and external cylindrical machining of complex workpieces up to a length of 300 mm. The variety of workpieces ranges from the smallest individual parts for injection systems in car engines, ball bearing rings and gears to hydraulic components and complex components in machine tool construction – for example spindles. The traditional Swiss brand Voumard has been part of Kellenberger since 2015.


The machine

The special feature of the VOUMARD 1000 are the two high-precision hydrostatic B axes: B1 axis with spindle turret, B2 axis with table turret. The two B axes also carry out all the necessary movements of the dressing and measuring devices. This flexibility makes a large number of machining variants possible and shortens set-up times. The spindle turret on the hydrostatic B1 axis is equipped with a uniquely compact grinding spindle head with flexible internal grinding spindle arrangement.

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Available spindles for the required speed spectrum and measuring sensors can thus be optimally positioned and allow the machining of almost any workpiece shape as well as the execution of several internal and external grinding processes in a single clamping.The machine at BURO has one external grinding spindle and three high-frequency internal grinding spindles with 45,000/90,000 and 120,000 rpm.

The table turret on the hydrostatic B2 axis can be optionally equipped with a work headstock and a high-precision rotary axis (C axis) including direct path measuring system and torque motor. This setup enables the highest roundness as well as precision in the fine adjustment of the cylindricity of the inner diameter during cylindrical grinding and also brings high precision during non-circular grinding.


Whether internal or external grinding – the VOUMARD 1000 grinds with the highest precision

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Whether internal or external grinding – the VOUMARD 1000 grinds with the highest precision

Like the Kellenberger machines, the VOUMARD 1000 has hydrostatic guides with linear motors. The highly dynamic linear axes are backlash-free for positioning accuracies in the nano range. This allows workpieces to be ground extremely precisely with the highest repeat accuracy and machine availability over the entire service life of the machine. Minimal maintenance costs, better machine availability and higher contour accuracy and process reliability are the advantages.

The machine is equipped with a Fanuc31i CNC control and the innovative BLUE Solution software, which is used as standard on all Kellenberger and Voumard machines and is characterised by its user-friendliness.

Erich Ziegler emphasises the extraordinary performance of the VOUMARD 1000 precisely because of the two B axes. “Even the highest technical requirements, such as the oscillating grinding of cones for injection technology, the grinding of carbide tools or of complex parts with special geometries, are completely unproblematic on the VOUMARD 1000.”

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BURO designer Olaf Behler was present at the first grinding tests at Kellenberger: “I found the innovative machine concept of the VOUMARD 1000 very convincing. The patented dressing concept with three dressing tool stations ensures collision-free dressing, thus enabling a wider range of workpieces and is also ideally suited for parts with larger internal diameters, such as flanges. What was particularly interesting for us, however, was that the machine was ideally suited for grinding even the smallest internal diameters.” Jürgen Burger saw it the same way. “As with our Kellenberger machines, one of the things that convinced us about the VOUMARD was the wear-free hydrostatic guides.” The decision was made in favour of the VOUMARD 1000, which was commissioned in September 2021.

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Sergej Bachmann confidently grinds the most complex workpieces on the VOUMARD 1000

The experience has been extremely positive. Machine operator Sergej Bachmann is a grinding specialist and has been with BURO for 15 years. He knows the Kellenberger machines inside out and gets the last µ out of the machines. He is also very impressed with the performance of the VOUMARD 1000. Has BURO ever considered another grinding machine manufacturer? Jürgen Burger denies it: “In general, we are very loyal to the supplier if everything fits. And with Kellenberger, everything really does fit. The technology as well as the people. We also appreciate the very good support and the good service.

The question of machine automation, which is very important in today’s world, does not arise for the VOUMARD 1000 at the moment. “At our company, it is mainly lathes and milling machines that are automated due to the higher batch sizes,” says Jürgen Burger. “For the VOUMARD 1000, the topic will probably only become relevant when batch sizes increase.” This is also not a problem for the specialists at Kellenberger: “The VOUMARD®1000 can be automated with an integrated handling system if required” says Patrick Zünd. And he adds: “We have the right automation solution for each of our machines.”