Processing Composite Materials Using Laser
LASYS 2012: Laser offers huge potential in cutting, drilling and welding fibre-reinforced plastics
The processing of composite materials, in particular carbon fibre-reinforced plastics (CRP) presents a special challenge. It is often one of the biggest hurdles when substituting metallic materials in large-scale production. Laser can help solve these problems and can be seen in action at LASYS, the international trade fair for laser material processing, which is taking place in Stuttgart from 12 to 14 June 2012.
Composite materials are, unlike metals, physically inhomogeneous. But it is precisely these different properties which are brought together in a new material and used advantageously. This, however, makes processing difficult, as Prof. Dr. Thomas Graf, Director of the IFSW Institut für Strahlwerkzeuge at the University of Stuttgart, explains: "On the one hand, this inhomogeneity influences the distribution of the laser beam; on the other hand, the heat conduction is very anisotropic and the parameters that are decisive for the ablation of the materials are very different." The result: In the event of incorrect process control the high heat conductivity of the carbon fibres in carbon fibre-reinforced materials and the very different properties of carbon and plastic may cause serious damage to the plastic matrix. These fundamental aspects are being examined at the IFSW in an effort to develop guidelines for optimised process control. Prof. Graf: "They present a big challenge for the development of suitable laser systems. In particular, very high infeed speeds, high precision with high dynamics and a precise focus position control are some of the challenges presented."
"The challenge for laser processing is to achieve the highest possible surface effectiveness at a homogeneous energy input, for example for large components from the aerospace industry or infinite pipes in the offshore and onshore area", adds Michael Nagel, Technical Sales Manager at Laserline GmbH in Mülheim-Kärlich. He goes on to say that the main advantage of laser is the efficient processing of thermoplastic fibre-reinforced composites whilst protecting the materials. The processing is generally in the form of a tape, performed in one single process step and without any additives. In contrast, thermosetting plastics require special epoxy resins, which are pressed into special hot air autoclaves and hardened at approx. 400° C and 20 bar. Laserline primarily focuses on very efficient diode lasers when processing composite materials, which are currently manufactured up to 15,000 W, and corresponding optics. "They are also sufficient for large focus dimensions for wide tapes and make available energy for the welding process, also homogeneously."
The different properties in composite materials demand "very different optical and thermal properties of the composite partners, which lead to very irregular processing results when processing using continuously emitting lasers", states Dr. Wolfram Rath, Product Manager for Laser Beam Sources at Rofin-Sinar Laser GmbH in Hamburg, knowingly. Procedures with a shorter interaction time may help in this situation: "This can be achieved either by a correspondingly short pulse duration of the laser beam or by correspondingly quicker processing speeds."
Composite materials such as carbon fibre-reinforced materials are becoming more and more important mainly on account of their light weight - primarily in mobility industries such as the automotive industry or the aerospace industry. The manufacturers of laser beam sources of course do not want to shy away from this billion-dollar market. Rath: "We are very interested in being able to provide solutions for processing these materials." He added that close contact has been established with many laser institutes. "We are observing very precisely the processing opportunities of these materials". Test applications are also being performed in in-house applications labs, he continued. "We are using all types of laser technology and wavelengths, solidstate lasers or fibre lasers, as well as CO2 lasers." Currently the CO2 laser is ahead of the pack. Initial results revealed that its wavelength is particularly well-suited for processing composite materials in operation with a continuous beam. On the other hand, "ultra-short pulse lasers could be interesting for these applications, which due to their extremely short pulse duration practically cause no heat input into the material being processed".
The control of the physical basics in the interaction between laser beam and composite material is a prerequisite for productive and high-quality processes and suitable system concepts. The IFSW is working on this in cooperation with companies and other research institutes in order to be able to provide new processes for processing composite materials using laser. Dr. Rudolf Weber, Manager of Process Development at the IFSW: "We are currently focussing on cutting carbon fibre-reinforced materials, but also other composite materials, as well as their manufacture, are being examined." There are already cooperation ventures in this area with the automotive manufacturers Daimler, Audi and Porsche, he stated. The aim is to "significantly increase productivity and quality in the manufacture of body parts compared to traditional mechanical processing", he added.
Michael Nagel from Laserline sees huge potential primarily in the aerospace industry. Because particularly for large aircraft areas and structures it comes down to high rigidity and lightweight designs when saving energy. "New applications are also being developed parallel to this such as pressure-resistant pipelines with an almost infinite length for pipeline construction, or the reinforcement of pressure tanks and structural enhancements in the car body area or for wind power stations." Nevertheless, most applications are still in the research and development stage, confesses Nagel, who is confident, however, that "laser material processing will continue to play a key role in this technology area, also requiring high process efficiency in comparison to alternative energy types such as infrared or hot air".
Also at Rofin-Sinar the focus is currently still on research. Dr. Wolfram Rath: "To what extent the huge market potential of composite materials can be made accessible for optical technologies depends on the research results." Rath sees the most interesting laser applications in cutting and trimming, as well as surface processing. For instance the surfaces can be cleaned and activated for further work steps using laser, he added. In conclusion, Rath stated: "The laser industry is currently still in the development stage of these processes, however. Thus a well-founded market assessment is still too early at present."
Approximately 200 exhibitors are expected at LASYS 2012, which is taking place from 12 and 14 June in Stuttgart. They will showcase their innovations and further developments in laser technology in Hall 4. The exhibition programme will focus on laser applications and product solutions, laser production systems for micro and macro material processing, as well as for precision technology. LASYS is aimed specifically at users and providers of laser material processing. With its cross-industry design covering all types of materials it is unique in the trade fair portfolio.
SOURCE: LASYS 2012