Tag Archives: carbon Fiber Reinforced Plastic (CFRP)

Approaching Photonic Serial Production: Laser-remote-processing of Automotive CFRP Components

Posted on by
Reply

By: Dr.-Ing. Peter Jaeschke, Laser Zentrum Hannover e.V.

The efficient use of limited resources is one of the greatest challenges of our times. To address this, lightweight solutions and concepts are already being adapted for the transportation industry, in particular within the automotive and aerospace sectors. However, in order to broaden the use of lightweight materials, there needs to be suitable processing, testing and measuring techniques in place for a variety of materials, constituting a prerequisite for economic, flexible and automated high volume production. In this context, photonic technologies can provide solutions. Since the operating mode of the laser is both highly flexible as well as no-contact, and thus wear-free, it offers numerous benefits for the machining materials, especially as an alternative to conventional processing methods encumbered by high tool wear. Furthermore, the energy input, tailored to the respective manufacturing requirements, offers new possibilities for the processing of temperature-sensitive materials.

In the supporting measures “Photonic Processes and Tools for Resource-Efficient Lightweight Construction” within the framework of the program “Photonics Research Germany“, the German Federal Ministry of Education and Research (BMBF) is aiming at overcoming existing constraints regarding the wide use of lightweight materials in serial production. For the corresponding R&D activities, the BMBF is providing a total amount of approx. 30 Mio. €. The initiative “Photonic Processes and Tools for Resource-Efficient Lightweight Construction“ is coordinated by Laser Zentrum Hannover e.V., Hannover, Germany (Figure 1).

Figure 1. The German initiative “Photonic Processes and Tools for Resource-Efficient Lightweight Construction“ is supported by the Federal Ministry of Education and Research and co-ordinated by Laser Zentrum Hannover e.V. (Source: LZH)

Within this research initiative, nine co-operative projects under industrial leadership are working on the development of laser sources and optical components as well as system technology and applications. In addition to welding and the surface preparation for both metallic parts and hybrid materials, the laser based processing of composites, particularly continuous carbon and glass fiber reinforced plastics forms the core issues of the BMBF initiative.

In this context, the main R&D activities focus on composite processing. This is comprised of cutting and drilling RTM parts, robotically-guided 3-D scanning optics and CFRP reparation preparation using short pulsed laser radiation. Other examples include composite surface preparation for adhesive applications, direct bonding, and joining of metal-metal interfaces as well as composite-metal hybrids. In the field of laser material processing, continuous carbon fiber reinforced plastic (CFRP) based parts and components represent a relatively new material class, exhibiting outstanding mechanical properties at a low density. As a result, such composites have been identified to have significant potential in lightweight construction for a wide variety of industrial applications.

During the manufacturing process of CFRP parts, trimming, drilling and ablation steps are of particular importance. Another point is the layer-by-layer removal to prepare the repair or rework of defects. In this context, conventional machining techniques, such as milling, drilling, grinding or abrasive waterjet cutting, which are well developed for a wide variety of industrially established materials, suffer from high tool wear, insufficient quality or their complex setup and limited flexibility when it comes to the requirements of CFRP machining.

The main reason for this is the heterogeneous composition of CFRP. Combining both carbon fibers, either arranged as fabrics or non-crimped fabrics, with a polymer matrix, either thermoset or thermoplastic, produces a unified material with very different individual material properties, and as results presenting a very unique challenge from a material processing perspective. Furthermore, for cutting applications both components have to be processed simultaneously which causes enormous difficulties. In this regard, the processing of CFRP components brings many challenges.

Photonic processes, however, offer solutions for many of these: Including the high flexibility and, in particular, the contactless, wear-free mechanism of the laser that offers advantages for the processing of CFRP materials. For the processing of complex components or temperature-sensitive materials, the locally limited and to the given manufacturing requirements adjusted energy input offers new opportunities. An implementation of laser-based processes in serial production in industry, however, requires a thorough understanding of the process, a high degree of automation as well as the consideration of environmental and occupational safety aspects.

If CFRP is processed with NIR lasers, carbon fibers show excellent optical absorption and heat dissipation, contrary to the plastics matrix. Therefore heat dissipation away from the laser focus into the material is driven by heat conduction of the fibers. The matrix is heated indirectly by heat transfer from the fibers. To cut CFRP, it is required to reach the melting temperature for thermoplastic matrix materials or the disintegration temperature for thermoset systems as well as the sublimation temperature of the reinforcing fibers simultaneously. One solution for this problem is to use short pulse nanosecond lasers, as has been demonstrated in one of the joint research projects, HolQueSt3D.

Figure 2. Towards serial production: Laser-Remote-Processing of automotive CFRP components (Source: LZH).

Based on an existing lightweight part used in the automotive industry, LZH has developed remote cutting processes for three-dimensional composite structures (Figure 2). A newly developed high-power disc laser of the TRUMPF Laser GmbH serves as the basic process technology. This fiber-guided laser source emits at 1030 nm and is providing a maximum average output power of 1.5 kW. With a constant pulse length of 30 ns, the maximum pulse energy of 80 mJ is realized for a repetition rate of 18.8 kHz. For remote processing of the automotive part, the KMS Automation GmbH has designed a clamping system, custom designed to address the specific requirements of laser processing of CFRP components. One of these requirements is an integrated exhaust system for the process emissions. The impact of laser processing on the characteristics of the components as well as on possible subsequent processes, e.g. primer and painting steps, has been investigated by the partners Volkswagen AG and INVENT GmbH.

Another priority was the development of repair concepts for 2D and 3D components. For this purpose, the LZH developed process strategies for the scarfing of defective areas. Due to the flexible system technology, it is possible to remove large areas on complex free-form surfaces. After the laser based repair preparation, the TU Clausthal developed repair concepts that work without hardening in autoclaves, making a more flexible and cost-efficient repair possible.

Furthermore the detection and analysis of the process emissions as well as the development of a catalytic exhaust air treatment system matching the requirements of laser-based CFRP processing played an important role. Based on the emission measurement during the processing, the Jenoptik Automatisierungstechnik GmbH has developed a fully regenerative, continuously working exhaust air cleaning system. As the involved end user, the Volkswagen AG supported the development of the process during the whole duration of the project, and evaluated its suitability for serial production. By processing an existing component used in automotive industry, the suitability of the developed processes was proven at the end of the project.

The supporting measures “Photonic Processes and Tools for Resource-Efficient Lightweight Construction“ within the framework of the program ”Photonics Research Germany“ is funded by the German Federal Ministry of Education and Research (BMBF). The author would like to express his gratitude to the corresponding overall project management VDI Technologiezentrum GmbH for their support. Furthermore the author would like to thank all coordinators of the involved co-operative research projects for their engagement and their support of the co-ordination work as well as all partners of the HolQueSt3D-project for their excellent work in a constructive manner.

Laser Technology Enables Car Efficiency

Posted on by
Reply

By Ralf Kimmel

Laser technology is an important key to letting CO2 emissions be reduced in passenger cars. A multitude of laser-based innovations in automobile production contributes to achieving this goal. The following article provides an overview.

Coming generations of vehicles will be far lighter than their predecessors. Laser-based manufacturing processes play an important part in this progress. Examples include parts without flanges, the increasing use of aluminum, CFRP and other high-performance plastics, thermoforming and joining plastics to metals. All these innovations help to reduce vehicle weight, in turn extending the cruising range and shaving CO2 emissions.

Lightweight Vehicle Construction Thanks to Lasers
When joining sheets with conventional spot welding it is necessary to overlap the edges. By comparison, welding with a laser beam makes possible flangeless designs. Here the individual sheets are first assembled by way of tongue-and-groove joints and then welded by the laser. This offers several advantages: processing time drops when compared with spot welding; the elements thus joined can be of differing materials and thicknesses; the resulting structures have no redundant material and thus save weight. In addition, the prepositioning of the parts one with another reduces the – otherwise enormous – effort for clamping technology, permitting simple and cost-favorable clamping aids.

Non-flanged structures, when compared with conventional spot welding, offer many benefits in regard to processing time, material use and the weight.

Where greater loads demand additional stability, reinforcing structures can be attached as needed. The corresponding structures – such as the underbody of a vehicle – can be made up with less tooling. Neither are any special tools required for this purpose, which have to be manufactured in an elaborate process when preparing for production. Instead, all the required steps in processing can be carried out by a standard laser welding robot.

One outstanding example of this process is the “StreetScooter” deployed by the German Post Office. It was engineered by an academic spin-off of the Rhenish-Westphalian Technical University at Aachen, Germany, and is built on an underbody made up without flanges. At present about 40 of these microvans are in trial use, which has been thoroughly successful to date.

Using Lasers Permits Innovative Mixes of Materials
CFRP – carbon fiber reinforced plastic – is also being used more frequently in lightweight vehicle engineering, especially in vehicles powered solely by electricity.  Laser technology also offers clear advantages when cutting and processing materials like this. In this way the incisions are made without touching the material or exerting any force whatsoever, ensuring that the shape and structure of the material remain unchanged. This eliminates all risk of warping, even in non-reinforced materials. Depending on the production process being used, cutting and processing can take place either before or after the CFRP parts have been shaped. When cutting blanks from carbon fiber materials, TRUMPF offers the laser systems in its TruFiber series; spatially shaped, 3D parts can be cut with the TruDisk beam sources made by TRUMPF. If CFRP – or a glass or carbon fiber mat already embedded in the binder – is to be cut, then the TRUMPF TruFlow series is an excellent choice. Here the laser melts away the fibers cleanly.

Carbon fiber reinforced plastics can be cut with the laser either before or after shaping. If desired, the pure carbon fiber mats can be cut prior to or after filling with the binding polymer.

 

Cutting a hardened CFRP part: for materials less than four millimeters thick, the laser works two to three times faster than a water jet or milling tool and produces a higher-quality cut.

 

Laser light enables woven parts to be smoothly cut to near net shape. No finishing work is required for the cut edges.

A further way to improve the production processes using laser technology is thermal joining of plastics to metallic materials – without the use of adhesives. Since metals and plastics have widely differing melting points, this would not be possible with traditional welding technology.  Using a short-pulse laser makes it possible, however, to create a defined pattern of undercuts in the metal, into which the heated partner, made of plastic, is pressed. Once the plastic has cooled and hardened, the two materials are joined by a form-fit connection. Examinations of the tensile strengths in such connections show that the union once again attains the strength of the basic material. Connections made this way are pressure-proof and waterproof and remain stable even under dynamic loading. 

Securely joining metal and fiber composites: an ultra-short pulse laser creates an undercut in the metal part, ensuring that the polymer and hot metal fuse together properly.

The Use of Lasers in Hotforming
Hot stamping processes allow for considerable reductions in the weight of body parts. However, the hardened steels are too strong to be cut in a press. Laser technology presents an elegant solution for this problem, too. The parts are cut out by 3D laser cutting, without wear and without applying force. This tremendously productive technology can also be used for 2D cutting of the feedstock material prior to its being shaped in the press. Here optimized cutting patterns can save material. If model facelifts or derivatives require subsequent modifications, these can be effected simply by reprogramming the laser robot. No new punching tools need to be engineered and manufactured.

Conversely, laser light can also be used to induce partial softening to improve the formability in a closely defined area or to reduce the hazard of the material becoming brittle or breaking. The RF generators in the TruHeat series offered by TRUMPF are ideal for this purpose.

The beam of a laser can also be utilized to remove coatings from areas in the steel sheet in preparation for later welding. In other words, ablating an aluminum-silicon coating 10 to 25 microns thick. The process can be regulated so finely that the amount of aluminum remaining is adjusted exactly, enabling precise control of the material properties. The laser systems used here, such as the TRUMPF TruMicro series, can undertake the ablation described here with a velocity greater than 30 meters per minute.

3D laser cutting makes it possible to cut parts without wear and without applying force – and at high productivity.

In the following phases in the work, lasers can also apply lettering, marks, QR codes and the like. And lasers also serve to subsequently weld parts prepared by thermoforming.

Laser Technology Opens the Way for New Production Processes
Even other approaches are offered by the techniques known as laser metal fusion (LMF) and laser metal deposition (LMD). Both processes are based on concepts such as those made familiar by 3D printing and additive manufacturing. They make it possible to produce parts that could not be manufactured at all with conventional processes. Complexity is free. This is true both in regard to their shape and in regard to the properties of the materials, especially since these innovative processes even permit combining differing materials within a single workpiece.

In laser metal fusion (LMF) an extremely fine metallic powder is applied uniformly to a metallic substrate and then melted or fused selectively with laser energy and allowed to harden. When using this process to create a workpiece, the 3D engineering data are “sliced” into individual layers 20 to 100 microns thick. The 2D image of each layer is the basis for the additive build-up of the workpiece. Exact control of the laser makes it possible to fuse each new layer of powder to the layers below – at the desired places and at the required material thickness.

In the case of laser metal deposition (LMD), the laser beam generates a weld pool on a metallic substrate, into which another material such as titanium, nickel, cobalt, tungsten-carbide or steel alloys is introduced as a powder. The powder melts and forms a layer which then coalesces with the substrate. LMD even makes it possible to create multi-layer workpieces which, if desired, can comprise several different bonded alloys.

Laser metal deposition (LMD) makes it possible to create multi-layer workpieces which, if need be, may comprise differing alloys which are bonded one with another.

The additive processes described here are already available today and in the coming years may be on par with conventional processes from an economic point of view. They can, by the way, also be used to apply structural reinforcements or additional structures to workpieces manufactured with other techniques. This adds flexibility to production processes in regard to the placement, geometry and size of the supplementary structure. And since additional material is attached only wherever it is really necessary, this technique once against saves weight in the finished part.

Perspectives for Novel Concepts
But even the processes introduced up to this point by no means exhaust the options for using laser technology in vehicle engineering. Rather, they form the basis for numerous novel concepts. Only a single example is described at this juncture.

Remote fillet welding makes it possible to weld two workpieces at an overlapped seam. When compared with the laser welding normally used today, the amount of material can be further reduced by shortening the flanges in the overlapping zone. The seam is then welded by the laser beam direct in the fillet created here, requiring no additional filler material. One example of an application is welding seams in the frames for vehicle doors.

This process does, however, require the highest positioning accuracy for the laser beam. This can be achieved by using appropriate sensors to register the orientation of the workpiece and continuously re-regulate the position of the laser beam.

To summarize, laser-based processes make it possible to produce vehicle bodies with lower weights and to do so in different ways. This makes laser processing an important advance along the way to reducing emission levels, increasing cruising ranges and beyond this, to speed up, reduce the costs for, and add flexibility to automotive production.

Ralf Kimmel is with TRUMPF Laser- und Systemtechnik GmbH.