Zero-point clamping system application at FIBRO RT

Supplementary zero-point clamping systems from AMF virtually pulverise clamping processes and set-up times for the production of rotary tables, which are often customer-specific. And the running times of the machine are optimally utilised through competent programming. Even space exploration benefits from such solutions.

"Our old vertical lathe has been around for over 100 years, so it was clear that a new solution was needed," says Harald Werner. Nevertheless, the Production Manager at FIBRO RT did not want to take the obvious route and simply replace the 34-year-old machine, which was running in three-shift operation. The seven clamping operations on three machines, which were necessary for the production of the rotary table housings, were also a thorn in his side. These are an important part of the rotary tables for which the Weinsberg-based company is known as an all-rounder. Werner immediately sees the potential that lies in turn-milling and that a new turning/milling centre to be procured could exploit.

Better surfaces thanks to lower vibrations

No other manufacturer covers this range of different drive and locking concepts for rotary tables like FIBRO RT. The repertoire includes worm drives or Hirth serrations as well as triple Hirth serrations or torque drives. The diameters range from category zero to twelve, i.e. from 100 to 2500 millimetres. They are used for assembly tasks, as swivelling or positioning axes and as workpiece carriers in machine tools. In doing so, FIBRO RT has established itself as an original equipment manufacturer for numerous well-known machine tool manufacturers. The Weinsberg-based company also offers a heavy-duty positioning table for the dynamic and precise positioning of large and heavy parts. Tanks for the ESA Ariane 5 launching rockets are welded on the largest rotary table built by FIBRO RT with a diameter of 4400 mm and a load capacity of 400 tonnes.

The demanding production of the mostly customised rotary tables mainly includes the processes of turning, cutting and grinding. Up to 100 tools are used alone for machining the underside of such a housing. A new software version for the NC programming system was procured for this purpose. This was a challenging task for programmer Valeri Hochweiß, but the existing version could not cope with the complex new tasks, especially the milling-turning operations with 5-axis application.

In terms of hardware, a zero-point clamping system was to become the most important component. In doing so, this was based on previous experience, when five systems had been tested for another project, three pneumatic and two hydraulic. After the basic decision was quickly made in favour of hydraulics, the AMF zero-point clamping system won the comparison with competitors. Werner describes a decisive advantage: "We achieved better surfaces and significantly longer tool life with the AMF solution." For AMF Sales Manager Erik Laubengeiger, this is not much of a surprise. “With our extremely powerful hydraulic modules, we are repeatedly able to keep vibrations to a minimum during rough machining and finishing, which not only produces great called but also serves Precision.” This is just as important for Werner, after all, ‘we need an accuracy of 1/100 mm in three planes, namely the top as well as bottom of the housing and coaxially for the bores for the worm gears.

Zero-point clamping modules pulverise set-up times

With pull-in forces of 25 kN and holding forces of 55 kN, hydraulically actuated AMF zero-point clamping modules of the type KH20 clamp heavy workpieces. “The hydraulic actuation with 50-60 bar opening pressure makes it possible to install very strong springs inside that constantly re-tension without the medium being prevented", explains Erik Laubengeiger. This high clamping force that is permanently active counteracts the entire system in which the workpiece could loosen due to the vibrations that occur during machining if, for example, weaker clamping modules with less holding force are used. This awareness has been present at FIBRO RT since the decision was made to use AMF zero-point clamping modules for the best surfaces. The covers and pistons of the modules are hardened. The repetition accuracy in clamping is better than 0.005 mm (5 µ).

Eight modules are embedded in a spacer plate, which in turn is anchored to the rotary table of the machining centre. The base plate for workpiece clamping is placed on this. Four clamping consoles, each 200 mm long, are clamped on top of this, which AMF manufactures to customer specifications. AMF zero-point clamping modules are also integrated into the top and bottom sides, with which they are anchored directly to the pull-studs on the base plate on the one hand, and into which the workpiece, the blank of a rotary table, is clamped on the other. This is also done by means of pull-studs that are directly integrated into the workpiece. This makes five-sided machining possible and the underside can be machined in the same clamping operation as the other surfaces. “In three to four minutes, a workpiece is now clamped ready for machining. In the past, with clamping arms, spacers and screw connections, this took 30 to 90 minutes," emphasises FIBRO RT veteran Werner, whose career began in 1980 with an apprenticeship as a fitter at the Weinsberg-based company.

Realising existing potential for greater productivity

Machine operator Daniel Karsch now has less responsibility for ensuring that the workpiece is correctly clamped. "Everything is much easier, faster and safer. Now I can concentrate much more on the quality of the machining process." For a workpiece like this, the process can sometimes take longer than its shift duration and last ten hours. "It's all the more important that we know right from the start that the component is correctly clamped," summarises master craftsman Thomas Scholl.

Werner swears by the potential of turning-milling machining on a single machine. "There is still a lot of productivity to be implemented, which we will gradually exploit." And the experienced expert is not just referring to the number of clamping operations and the time savings. But most importantly, it's also about precision, emphasising that "the accuracy is greater if clamping is only carried out once. This also means that we have less tension in the part, which later requires greater tolerances." In doing so, Werner also looks beyond the boundaries of machining. "With production in Germany, we always have to think about how we can utilise all potential for increasing productivity in order to remain competitive." The acceptance test at machine manufacturer Reiden was like an exhibition run with lots of praise for the "very well-prepared FIBRO RT team".

Powerful clamping significantly extends tool life

What else the built-in clamping modules can contribute is demonstrated when machining the cam track of a base body for a cam gear. The cam tracks are milled into the vertically clamped workpieces, which are up to 400 mm long and up to 350 mm in diameter, and then ground after heat treatment. "Extremely difficult work," explains Scholl. The higher surface quality, which is due to the lower vibrations, is particularly evident here. And the service life of the tool has improved significantly. "A special milling process takes around 90 minutes. "We now do this with a single tool, where we used to have to use two or three," says Scholl.

AMF specialist consultant Laubengeiger is happy to contribute to this with know-how, experience and the right products. "We not only support our customers in the use of our products, but also advise them from our huge pool of applications on how production processes can be fundamentally optimised." Laubengeiger has no objections when this is achieved in such close cooperation and with the right AMF zero-point clamping systems, as is the case with FIBRO RT. And if this also serves the exploration of space by Ariane, then it lifts everyone's work to even higher spheres.