Versatile clamping devices

Lightweight construction is a particularly topical issue for tool manufacturers. It’s only when he looks at the automotive industry that Lothar Horn, Managing Director of the tool manufacturer Hartmetall-Werkzeugfabrik Paul Horn GmbH from Tübingen, realises the entire diversity of materials entailed by lightweight construction.

“With the increase in materials like CFRP or aluminium, the requirements for tools are changing,” says Lothar Horn. “We are accordingly upsizing the role of CVD diamond cutting tools, which ensure process reliability.” Besides the trend towards more expensive, streamlined and more durable tools, says Lothar Horn, dry-machining is becoming progressively more widely used. In this context, minimal-quantity lubrication is increasingly popular as a compromise between an abundant supply of cooling lubricants and thoroughbred dry machining.

Cryogenic cooling: interesting, elaborate and cost-intensive

In order to stabilise the metal-cutting process, internal coolant feed has meanwhile proved an effective option. “We have further refined the entire system, so as to bring the coolant to the blade even more directly than hitherto,” reports Lothar Horn. Cryogenic cooling with liquid nitrogen or carbon dioxide, by contrast, he describes as an interesting, but elaborate and cost-intensive solution, in which the firm has already done intensive work. “I regard it as a “nice-to-have”, a sort of contingency solution for subcategories,” comments Lothar Horn.

With conspicuous frequency, the useful lifetime was mentioned in the past in addition to process reliability. In order to increase productivity when machining sophisticated materials like high-strength steels as well, tool manufacturers are opting for significantly more thermally stable coatings. “The proportion of aluminium in the layers has increased, and thus completely altered the thermal conductivity,” explains Lothar Horn.

Lightweight construction is also an important issue for Mapal Dr. Kress KG from Aalen: the company’s product portfolio accordingly features tools for drilling, milling and reaming an enormous spectrum of disparate lightweight materials. To quote Dr. Jochen Kress, a member of the company’s board: “Specifically for the category of fibre-reinforced plastics like CFRP and GFRP, for multi-layered composites, for aluminium, various plastics and difficult-to-machine materials like Inconel and titanium, we have developed tool solutions that meet the specialised requirements involved. With individualised tool concepts, we work closely together with our customers to optimise the machining jobs concerned. Depending on the application in question, our tools feature special geometries and high-performance coatings.”

Matched to the machine tool

For machining lightweight materials, which are widely used in the aviation sector, it is important to match the tool not only to the material involved, but also to the machinery concept involved. “If the part is being produced on a machining centre, the tool has to exhibit different characteristics from manually controlled machines, for example, which are widely used in final assembly operations for aircraft,” says Jochen Kress. “It’s important here to make sure that the tool guides itself into the borehole, and compensates for the lack of a stable machine tool.”

Kress has created the OptiMill-Honeycomb milling tool specifically for milling lightweight materials. The light, and at the same time very bending-resistant honeycomb composite constructions with a honeycomb-shaped support are often used for supporting and reinforcing aircraft constructions or wind power systems. The difficulty during machining, however, is the looseness of the compound. To quote Jochen Kress: “The OptiMill-Honeycomb eight-bladed solid-carbide end-milling cutter has extremely sharp blades, a spiral angle of 15 degrees and fine toothing. The milling tool also provides reliable machining of honeycomb materials with an enormous range of different top layers or inserted core fillers.”

The performative capabilities of tools stand and fall with clamping tools, of the kind produced by the Römheld Group at the company’s facilities in Laubach, Hilchenbach, and Götzis in Austria. To quote Managing Director Hans-Joachim Molka: “As a leading manufacturer of clamping devices, we offer not only major specific customer benefits in the fields of hydraulics, electro-mechanics and pneumatics, but also a combination of these. This is precisely the precondition needed for mastering the trend towards lightweight construction.” Stringent requirements are posed here for the lightweight workpieces, which by reason of sophisticated stiffness/weight-optimised design are becoming ever more filigree. The need is for sensitive and at the same time securely gripping clamping devices, since excessive clamping forces will warp or deform the workpiece concerned. The contact forces of support elements have to be very small, too. To quote Hans-Joachim Molka: “More and more frequently, workpieces are now being clamped in a floating configuration, meaning that the component is firmly clamped at defined points, and several holding points are added so as to securely absorb the machining forces introduced.”

Floating clamping elements much in demand

Römheld had identified this trend early on, and some time ago had already developed a range of what it calls “position-flexible or floating clamp elements”, with which thin-walled workpieces can be clamped with minimised distortion. The clamping elements in this range provide initial clamping of the workpiece with a slight force, and then hold it in place securely with an additional clamping function, so as to introduce machining forces from several different directions. “A position-flexible clamping element is thus also ideally suited for multi-sided machining,” explains the expert from Römheld. For sizeable components, electro-mechanical adjusting cylinders with integrated vacuum clamping technology are used.

There are three observable trends, says Markus Kleiner, Managing Director of Heinz-Dieter Schunk GmbH & Co. Spanntechnik KG from Mengen, when it comes to metal-cutting companies: “The principal focus is on falling batch sizes, a steadily rising diversity of variants, and last but not least, progressively more stringent requirements for precision. Metal-cutting production operations are faced with the increasingly frequent challenge of having to cover a maximally wide spectrum of parts in as few operations as possible and with minimised make-ready times.” This, he says, is why versatile clamping devices are needed, which enable different applications to be alternated, while at the same time assuring high levels of accuracy and process stability.