What do tooling product designers and manufacturers understand about the economic needs of shops and fabricators working with carbon fiber-reinforced plastics (CFRPs), composites, etc.? What new tool concepts are available? And, what does the future hold? Kennametal specialists have been working on issues relating to CFRPs for many years, building up considerable expertise.
Kennametal reports its new KCN05 Beyond milling cutters, specially developed for milling CFRP, deliver long service lives and achieve high-quality surface finishes, thanks to the combination of a special substrate and a grown diamond layer.
The trend toward lightweight construction materials will accelerate, and not just in the aerospace environment. As far as lightweight construction is concerned, alongside titanium, aluminum and magnesium, fiber-reinforced plastics and their composite materials in particular will dominate the field in the future. For the moment, at least as Oliver Sax sees things, the technological impetus still lies with the aircraft industry: "Here, we can see a clear customer trend toward tool-specific inquiries regarding working methods for CFRP and composites."
However, the senior manager for solid-carbide milling equipment at Kennametal, in Frth, Germany also sees considerable interest in CFRPs, etc., developing in another quarter: "The internal technology departments of major motor vehicle manufacturers report strong interest in the material." Thus, he is confident that "the automotive industry will be the next technological driving force for fiber-reinforced plastics."
His assessment is no accident. According to a Roland Berger e-mobility survey, by 2025 about 40% of new motor vehicles registered will feature hybrid or fully electric drive systems. From an economic standpoint, this is only logical if new lightweight construction concepts are implemented. For tool manufacturers, this could be both a blessing and a curse: the resulting work in the engine/motor and drive fields will be reduced, but on the other hand, the new lightweight construction materials constitute an attractive field of activity.
For machining work on pure CFRP, the burr-style router is a universal tool that is being optimized continually. The Kennametal down-cut style router has been specially designed for milling recesses and surfacing work.
Werner Penkert, manager for the European aerospace market at Kennametal, foresees a certain reversal in trends over the next ten years: "The switch from aluminum and steel to composite materials is bound to lead to a certain reduction in levels of metal-removal work,” he said. “Nonetheless, there will still be a certain amount of mechanical work on CFRP materials, such as that for the connecting and mating surfaces."
Automakers accelerate
For the moment, tool manufacturers are benefiting, though unintentionally, from the ‘tool-eating’, (i.e., service-life-reducing) properties of CFRP materials. Although the aerospace industry has come to terms with this to a certain extent, in part because new developments involve long trial periods and lead times due to safety considerations, the motor vehicle industry will take a different approach. If series production of vehicles with significant levels of CFRP parts gets the go-ahead, a highly dynamic development and conversion phase can be expected.
"If a series production vehicle is available,” said Sax, "the next steps will be very different from those in the aircraft industry. High-volume activities will kick in immediately, for the manufacturers and their suppliers alike."
At Kennametal, they are well prepared. Their years of experience working with the aircraft industry have led them to look hard at the composite processing theme. In the meantime, the numerous projects have enabled them to build up considerable know-how and find solutions.
As well as the usual cause, such as de-lamination (tearing away or destruction of the fiber matrix) and shorter service lives, the specialists at Kennametal are also looking closely at other more fundamental themes. One very important field is classification of CFRP materials. "That's why it's important, to think along the same lines as our customers in our discussions with them, at least to start with,” added Oliver Sax.
It is true that up to now CFRP materials were shown in materials lists under ‘C’ for (carbon fiber-reinforced plastic); but all the CFRP materials were lumped together, with the pure carbon-fiber matrix, rubbing shoulders with the tricky-to-work stacks, a composite of aluminum, CFRP and titanium.
As this nomenclature is not very useful for purposeful technological discussions with users, Kennametal’s developers established five sub-groups, which should result in clearer material profiles and a consistent basis for discussions. The following classes were defined:
- C1, for pure CFRP;
- C2, for CFRP in combination with nonferrous metals;
- C3, for CFRP in combination with high-temperature resistant steels;
- C4, for CFRP in combination with stainless steels;
- C5, for CFRP in combination with nonferrous metals and high-temperature resistant steels.
Oliver Sax acknowledged the system does not cover the full spectrum of the theme, but he noted it is important to make a start on the problem. “We are one of the first companies anywhere to try to approach this highly complex theme in a structured way,” he said. “We also set out to show users that each material has its own highly specific requirements, and put forward the solutions we can provide."
Seen from the tooling standpoint, the requirement profiles have hardly changed at all in recent years. The main themes are still those of de-lamination and service life, which have already been much discussed.
The challenge is drilling
The particular problem of drilling work, which is the main area for de-lamination effects, led Kennametal to develop a wide range of tools with some impressive results. For Thilo Mller, Kennametal’s manager for boring and fine-surfacing products Kennametal, there are two main avenues of development: diamond-coated carbide tools to machine CFRP and PKD tools to machine stacks, i.e. composite metal and CFRP materials.
"To machine pure CFRP,” Mller said, "it is certainly our diamond-tipped SPF drill that provides the best value for money in terms of service life and the best results as to de-lamination."
Several hundred drilling sequences can be executed, he noted.
PKD tools provide service lives that are up to 30-50% longer, but users also have to accept certain restrictions in tool diameter and geometry, and solid PKD tools can provide a solution.
For these tools, the diamond crystals grow directly on the carbide-supporting shaft. The advantage here is that a different ground section can be provided from what is possible with brazed PKD cutting edges, with positive front rake angles. Contoured cutting edges also can be provided. "In short,” according to Penkert, "we can make contours that are similar to those for carbide cores."
There is also a relatively recent area of process development — orbital drilling. Here, in a way similar to circular milling, the drilling is done with a milling tool. The tool axis is slightly tilted along the Z-axis to enable free cutting. This R&D is being carried out in cooperation with the Swedish machine manufacturer Novator.
Contrary to normal manual drill feed units, which are commonplace in aircraft manufacturing, the Novator machines feature a CNC-controlled machining unit. Werner Penkert sees this as a very interesting alternative. "A measurement procedure can be used to compensate for tool wear by modifying the circular movement," he explained.
As well as drilling systems, the Kennametal researchers are working on milling systems for CFRP, etc.
Above all, according to Sax, what are known as compression style routers, with their V-shaped geometry, spiraled to the right at the tip and to the left on the shaft, provide the optimal set-up for cutting grooves and trimming work. "The V-shaped inverted spirals press the matrix layers together,” Sax said. “That enables us to execute very fine surfacing work."
The burr-style router
For machining work on pure CFRP, Kennametal offers a universal tool — the burr-style router. It is constantly being optimized through further development, and service lives of 25 m can be achieved currently.
The down-cut style router has been specially designed for milling recesses and for surfacing work. The main advantage of the left-spiraled tool lies in the higher cutting speeds that can be reached. For this tool, the developers have resorted to a substrate with a low cobalt content, to enhance the adhesion of the diamond layer, and therefore to create a very easy-cutting tool.
The returns on Kennametal’s R&D work are not limited to customer acceptance; rival technologies like water-jet cutting can be countered, or so Werner Penkert maintained.
"With our routers, we already provide highly attractive machining times and service lives,” Penkert stated. “Water is no longer the only investment solution, now that these routers can be used."
