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Thunderbike invested in a 5-axis Hermle C 42 U MT machining centre to create a 40 kg monoblock wheel out of 290 kg of high-strength aluminium alloy

Image: Schunk Intec India
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Workholding & Fixtures Customised perfection

Sep 22, 2016

An application story on how a manufacturer of custom bikes uses quick-change clamping modules to utilise the capabilities of small 5-axis machining centres in the exacting manufacture of single components and small series

Anyone who enters the Thunderbike showroom in Hamminkeln, a town in the district of Wesel, in North Rhine-Westphalia, Germany, will think he is in a biker’s dream: shiny chrome exhaust pipes complete with flat black steel wheels and tanks with an exquisite matte finish. Customers who come here do not just buy a motorcycle – they are looking for something exceptional. It is not about mass-produced products, but rather about philosophy. Nearly all of the machines from the well-known custom bike specialist and authorised Harley Davidson and Buell dealer of the Lower Rhine region are delivered with a personal touch. The Thunderbike catalogue is also quite extensive, with some 3,000 special parts. Those who want something even more exquisite can purchase one of the custom bikes for which Thunderbike is world famous and which are manufactured entirely in Hamminkeln with the exception of only a few components.

Efficient small-series production

The realm of Herbert Niehues begins two doors behind the showroom. Herbert and his team turn about 25 to 30 tonnes of aluminium per year into premium quality bike components. It takes 40 hours of precision machining, for example, to create a 40 kg monoblock wheel out of 290 kg of high-strength aluminium alloy. Just for such applications, Thunderbike invested in a 5-axis Hermle C 42 U MT machining centre. What, in the past, required six clamping setups on two machines can now be accomplished with only three clamping setups on this one machine. To ensure the strength of the wheels all the way to the centre, the raw material consists only of blocks made from rolled plates. The machines used in the past regularly reached their limits with respect to both the weight and the length of travel, especially in the production of exclusive front wheels with a size of up to 30 inches.

“With the solid alloys, it really gets tough,” Niehues emphasises. It is even more challenging to find a clamping system with a low height and sufficient clamping forces as well as high repeat accuracy and maximum flexibility for the different components and sizes. “Despite the many different clamping systems in existence, very few fulfill the requirements of such demanding machining processes,” Niehues relates.

Reliable locking

The pneumatically controlled VERO-S NSE mini quick-change modules from SCHUNK have a height of only 20 mm and offer ideal conditions for retrofitting of existing machines, full utilisation of the machining area and direct clamping of even small workpieces. A patented dual stroke actuation concept ensures extremely high power density of the compact modules from the innovative family owned company. With a module diameter of 90 mm and a clamping pin diameter of only 20 mm, the standard integrated turbo function achieves enormous pull-in forces of up to 1,500 N. The clamping pin is positioned via short tapers and fastened with three slide assemblies. Locking is achieved mechanically by means of a self-locking and form-fit spring assembly. Large contact areas between the slide assemblies and the pins minimise the surface compression in clamped state, therefore reducing wear on the modules. Since the minimum distance between two clamping pins is only 100 mm, NSE mini can be used to achieve very small and variable borehole gauges for workpiece or pallet clamping. Even small workpieces can be clamped directly for complete machining from five sides, with no hindrance by the chuck or clamping jaws. The clamping pins of the quick-change pallet system are screwed directly into the workpiece. Parts can then be changed into the machine in a matter of seconds and positioned, fastened and clamped into the quick-change modules with repeat accuracy of < 0.005 mm. To maximise the life span and process reliability, NSE mini – like all VERO-S modules – is fully equipped even in the standard version: all functional components such as the base body, clamping pins and slide assembly are made of stainless steel. In addition, the low-maintenance modules are protected against chips, dust and cooling lubricant. As part of the world’s largest modular system for high-efficiency workpiece clamping, they can be combined with numerous SCHUNK clamping pallets, devices and multiple clamping stations. As with the Thunderbike, it is possible to purchase the modules separately in lieu of a complete system and to combine the components with the necessary hoses, grid plates or attachments.

Module height extensions

A major advantage at SCHUNK, according to Herbert Niehues, is the ‘double pot’. That is his name for the module height extensions of the SCHUNK quick-change pallet system designed for applications in tool and mould making, which can be positioned flexibly so that four modular assemblies are sufficient for all required machining tasks. To ensure optimal accessibility, Niehues ordered the height extensions in a special height of 80 mm, to allow access by the machine spindle to all five sides of the workpiece without special tools. Special mounting plates that Niehues custom-manufactured for the different applications make it possible to re-equip the entire machine within only 15 minutes. The actual workpiece changing by means of the quick-change pallet system then takes only a few seconds.

The experienced professional has no doubt that the investment in the machine and the clamping system was worthwhile. The machining time of the monoblock wheels alone, which are generally manufactured as one-off items, has been reduced from about 60 hours to 40 hours. Due to the flexibility of the SCHUNK clamping system, Niehues can meanwhile also use the machine for manufacturing multi-piece wheels in batch sizes of 50 to 60, wheel spiders, and also for the production of air cylinders with diameters up to 60 mm, which are used in the Thunderbike air-ride suspension systems. The high process stability even makes fork arms possible.

Convinced, Niehues said, “Compared with clamping by means of claws or blank holders, clamping with the SCHUNK quick-change pallet system is not only much faster and more reliable, but also more precise.” In addition, the surface quality has improved significantly. That pays off in the form of enormous time savings during downstream grinding, high-gloss densification and polishing processes. ☐

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