Workholding
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Applications - Grob Werke
Constructive cooperation
a reference for technically feasible solutions concerning effective set-up

If a manufacturer of workholding technology buys several 5-axes machining centres, these should certainly be equipped with their clamping elements and should be a reference for technically feasible solutions concerning effective set-up. The acquisition of three new Grob-Universal machines Series G350 and G550 by the Römheld GmbH required several changes – an effort that was worthwhile for both companies.

Hans-Walter Parr, head of preliminary planning at Römheld GmbH in Laubach, suggested a Grob G350 with a modular shuttle table and zero point clamping systems to his management out of a dozen single-spindle 5-axis machining centres he had compared. The company was looking for a replacement for a Stama 530 and a CSK 300, which had run for almost 100,000 hours since the mid-1990s. The state-certified master mechanical engineer had very specific ideas about the desired machine: it should be modular in design, compact in construction and efficient in production. For the frequently changing and complex components produced at ROEMHELD, the machine should be equipped quickly and easily with different workpiece fixtures via zero point clamping systems. For this purpose, the company wanted to use products from their company, Stark Spannsysteme GmbH, a subsidiary of the ROEMHELD Group.

Insisted on zero point clamping systems

The G350 of the machine tool manufacturer Grob in Mindelheim turned out to be the first choice in the eyes of all participants at ROEMHELD. However, Grob's engineering department initially turned down the equipment requests: technically too much deviating from the standard. Clamping on T-slot plates was too uneconomical and not flexible enough for the large number of different workpieces with batch sizes between five and ten pieces in a single clamping, said Parr, whose technical ambition was aroused. The first person he convinced was Christian Ried from Universal Machine Sales and Project Manager at Grob: “Persistently and very meticulously, Mr. Parr showed us the advantages of the desired zero point clamping systems for production and explained that they could be realised on our machines.”

Not that Grob did not have a good experience with the ROEMHELD Group's workholding technology - on the contrary: On many of the machining centres, clamping elements of the brands HILMA and ROEMHELD have proven themselves for decades and they are also successfully used in their production in Mindelheim. Parr now had the unusual idea of combining two zero point clamping systems in one machine table.

Smooth integration

Once convinced, all participants got down to work with commitment and solved the task to everyone's satisfaction. In the end, the G350 was equipped with a specially designed shuttle table in which five ROEMHELD zero point clamping elements are integrated: in the centre there is a Speedy Classic 2, four Speedy Classic 1 are grouped around it. “The four outer clamping pots are for clamping pallets with diameters of 550 mm, the middle one can additionally be used to clamp individual workpieces”, explains Parr the principle. Three of the outer clamping pots are floating, the fourth, together with the central clamping system, centres the applied fixtures. They are supplied with pressure by a ROEMHELD hydraulic power unit with proportional technology, which is integrated in the machine control, so that the clamping elements can be operated centrally from there.

The co-operation and the integration of the ROEMHELD clamping technology ran smoothly. The adaptation of the rotary table and the machine control which required additional functions to control the clamping elements and fixtures has only required “some hours of work”, says Ried.

High flexibility with short machine downtimes

Thanks to its special design, the modified G350 can be fitted with a wide variety of fixtures with different workpiece clamping systems during short machine downtimes, and set-up can take place during machining. The media feed-throughs and quick-coupling systems for compressed air, water and hydraulic oil are already integrated in the zero point clamping systems used. There are no exposed lines, so the risk of contamination is minimised.

For the fast machining of complex components, the G350 ordered by ROEMHELD can access 139 tools, 40 in a disc magazine and 99 in a further additional magazine. The rotary distributor is suitable for the different clamping systems, so single as well as double-acting hydraulic clamping elements can be used. The machining centre also has an internal coolant supply of 80 bar through the main spindle and a cleaning device for tools so that swarf is quickly removed. The hydraulic pressures can be completely regulated by the machine's NC control, which, thanks to the use of proportional valves, can also be used to release and close machine vices mounted on the zero point clamping system. To check the precision of the machining process already on the machine, the G350 is also equipped with a radio measurement probe on special request from ROEMHELD. The additional option of remote diagnosis makes it easier to quickly correct any errors that may occur.

The co-operation and the integration of the clamping technology ran smoothly.“
Christian Ried, project manager at GROB - Werke
Field test passed

“We were able to implement the numerous special requests so quickly because we have a high vertical range of manufacture and were therefore able to find and implement the solutions in-house”, says project manager Ried confidently. Since August 2011, the G350 is working trouble-free in two shifts at ROEMHELD and is a great success, assures Hans-Walter Parr: “At first, we were not aware of the performance of the Grob machine. In the meantime, we have moved on to manufacture more demanding and complex flange parts with up to forty tools.” The precision is very high, confirms the trained machine fitter, as shown by the measurements on the machine, which is confirmed by the quality assurance department.

Time saving: Set-up in 30 minutes instead of 70

Parr is enthusiastic about the variety of possible applications and the time saved. Previously, on the 3-axis machines, it took 24 minutes to machine a lid, an now it is ready in 14 minutes. The savings in set-up are even more significant: “Instead of 70 minutes, we now only need 30 minutes, less than half.”

Convinced by the machine and the cooperation, ROEMHELD has already ordered another G350 from Grob in addition to the 5-axis universal machining centre supplied, as well as a G550, the larger model. All of them of course with ROEMHELD zero point clamping systems integrated in the rotary table, the G550 will even have nine instead of five pots. With the new machines, which will be delivered in summer 2012, the number of machining centres in Laubach will then increase to 15.

The additional effort for the special equipment has also paid off for Grob, emphasizes Christian Ried: “We can now recommend the STARK elements supplied to ROEMHELD to a customer who is looking for a suitable zero point clamping system for his G350 or G550.” Since the plans for this are now available, this equipment variant can also be delivered quickly.

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