Fabian Fischer

Laser Surface Pre-Treatment of CFRP for Adhesive Bonding in Consideration of the Absorption Behaviour

The use of carbon fibre-reinforced plastics (CFRP) is growing significantly in all areas of lightweight construction. Thermosets like epoxy still build a major part of deployed matrix material. A suitable joining technology for CFRP is adhesive bonding. However, the bonding performance is well reduced because of contaminations. To achieve full bond-strength, adhesion of the adhesive to the components is essential. One innovative method for surface pre-treatment is laser radiation. Former investigations show that an important parameter is the absorption. As a result of that, a UV laser (wavelength of 355 nm) and a CO2 laser (wavelength of 10600 nm) were used to pre-treat specimens manufactured from 120°C curing epoxy. The focus is to achieve a selective removal of resin without impairing the fibres. Lap-shear specimens have been pre-treated, bonded with an one component epoxy film adhesive and tested. The laser pre-treated specimens achieve the same bond strength as references prepared by manual abrading. Furthermore, the mechanisms of interaction between laser radiation and matrix material as well as fibres are discussed considering the different heat deposit and absorption behaviour of the emitted radiations.

Using excimer lasers to clean CFRP prior to adhesive bonding

Dr. Fabian Fischer and Stefan Kreling of the Technical University of Braunschweig, and Frank Gabler and Dr. Ralph Delmdahl of Coherent compare the various laser technologies that have been considered for cleaning carbon fibre reinforced plastic (CFRP) and discuss the implementation of the excimer laser technique in particular.

Carbon black nanoparticle alignment using magnetic particles creating local percolation spots for electrical conductivity in structural adhesives

Due to the rise of structural multi-material concepts in automotive and aerospace industries the role of adhesive bonding is becoming more important in the joining process. In contrast to joining technologies like welding or riveting, an electrical separation of the material by an insulating adhesive layer is given. This might be a problem if humans or electronic devices need to be protected against static discharge. This study investigates the effect of the alignment of non-magnetic spherical carbon black particles by magnetic forces enabled by adding secondary magnetic-sensitive fillers. To achieve this, an epoxy resin filled with carbon black and a small concentration of metal-based particles is used. The metal-based particles are aligned by magnetic forces provided by an external source. During the migration of the metal particles through the viscous epoxy adhesive, the carbon black particles are attached by adhesive forces. It is shown that this effect provides the alignment of non-magnetic carbon black particles, which results in an increased conductivity in carbon black filled epoxy resins.

Novel form-flexible handling and joining tool for automated preforming

Abstract The production rates of carbon fiber reinforced plastic (CFRP) parts are rising constantly which in turn drives research to bring a higher level of automation to the manufacturing processes of CFRP. Resin transfer molding (RTM), which is seen as a production method for high volumes, has been accelerated to a high degree. However, complex net-shape preforms are necessary for this process, which are widely manually manufactured. To face these challenges a new concept for the manufacturing of carbon fiber preforms with a form-flexible gripping, draping and joining end-effector is presented and discussed. Furthermore, this paper investigates the application of this concept, describes the initial build-up of a demonstrator, focusing on material selection and heating technology, and discusses test results with the prototype. This prototype already validates the feasibility of the proposed concept on the basis of a generic preform geometry. After a summary, this paper discusses future in-depth research concerning the concept and its application in more complex geometries.

Sauber und prozesssicher

Der Einsatz von Faserverbundkunststoffen (FVK) im Automobil ist spätestens seit der Bekanntmachung, dass der BMW i3 ein Life-Modul aus kohlenstofffaserverstärktem Kunststoff (CFK) besitzen wird [1], nicht mehr nur auf die Kleinstserie im Sektor hochpreisiger Sportwagen beschränkt. Es bestehen jedoch noch erhebliche Herausforderungen, diese Materialien zu fügen, da gebräuchliche Verfahren — wie etwa das Punktschweißen — nicht eingesetzt werden können und Techniken, bei denen mechanische Verbindungselemente verwendet werden, zu einer lokalen Zerstörung der Fasern und erheblichen Spannungsspitzen führen. Es empfiehlt sich der Einsatz der Klebtechnik, die allerdings eine Vorbehandlung voraussetzt, um Trennmittelrückstände und andere Kontaminationen von den Oberflächen zu entfernen [2]. Mit dem Einsatz von FVK in größeren Stückzahlen entsteht dabei auch die Notwendigkeit, Verfahren zu entwickeln, mit denen automatisiert und mit hoher Prozesssicherheit und -geschwindigkeit die Klebvorbehandlung erfolgen kann.

Clean and reliable

The use of fiber-reinforced plastics (FRP) in the automotive industry is no longer limited to the smallest-batch series of expensive sports cars, at least not since the announcement that the BMW i3 will have a Life-module made of carbon fiber-reinforced plastics (CFRP) [1]. But there are still considerable challenges as regards the bonding of these materials, as conventional procedures (for instance spot welding) cannot be applied and technologies using mechanical fasteners lead to a local destruction of the fibers and considerable stress peaks. The use of adhesive bonding is recommended which, however, requires a pretreatment to remove release agent residues and other contaminations from the surfaces [2]. With the use of FRP in larger quantities it also becomes necessary to develop procedures which allow automated bonding pretreatment with a high reliability and low process times.

Gluing instead of stapling or nailing

A new kind of rapid bonding technology offers specific economical and technical advantages over commonly used bonding techniques in load-bearing timber construction for prefabricated house building. It could even prove to be an effective supplement to the widely used nailing or stapling techniques for connecting wooden frames for laying planks and, especially, the planking boards and allow a more stable construction.

Reliable bonding using mobile laser technology

In the course of ever increasing efforts to reduce the CO2 emission of airplanes and vehicles, the material lightweight construction plays a more and more important part. In the past few years, it is mainly fiber-reinforced plastics that have become the focus of interest. In order to make the best use possible of the potential of these lightweight materials, a lot depends on the bonding techniques and the corresponding design of the bonding areas. The so far most frequently used bonding technique, the riveting, has the essential disadvantage of the fibers carrying the main load being disrupted by the needed bores, and in addition, stress peaks occur at the margins of the joint elements. Apart from that, due to the net weight of the rivet, a weight increase not to be neglected occurs in lightweight constructions with several rows of rivets. A great potential, however, lies in adhesive bonding. Due to the achievable flat force input, which is done without damaging the fibers, stress peaks can be avoided, thus enabling a clearly improved utilization of the material. It is the pre-treatment of the adhesive surfaces that is essential for a structural and ageing-resistant adhesive joint. Because of the release agent residues frequently remaining on the surfaces from the manufacturing process, this point requires a high level of attention, especially with fiber-reinforced materials.

Improved performance of binder-free zeolite Y for low-temperature sorption heat storage

The sustainable generation of energy and low-energy consuming technologies are two main approaches to combat climate change and reduce carbon dioxide emissions. Sorption heat storage is part of the second approach. Therefore, adsorbents that achieve high energy storage density under the working conditions of the storage application are required. In this study, the hydrophilic properties of a granulated binder-free zeolite NaY were tailored with the aim of increasing its performance at a desorption temperature of 140 °C for mobile sorption heat storage. Top-down approaches, such as chemical treatment with the chelating agent H4EDTA, treatment with the inorganic acid HCl and sequential ion exchange with acid treatment, were used in order to decrease the desorption temperature and optimize the low-temperature heat storage density. All the modified samples showed a decrease in the desorption temperature from 10 to 30 °C compared to the parent sample; only the desorption temperature of the acid-treated Mg-exchanged NaY sample increased. The effect of different treatments on the structural properties of the materials, including the generation of framework defects and mesoporosity was determined. The energy storage densities of the NaY and all the modified samples are considerably higher in comparison to the currently used adsorbent (NaMSX) in mobile sorption heat storage for low-temperature industrial waste heat recovery.

Klebvorbehandlung von FVK durch Unterdruckstrahlen – Sauber und prozesssicher

Das Kleben als flachige Verbindungstechnik erlaubt eine hohe Ausnutzung des Leichtbaupotentials von Faserverbundkunststoffen (FVK). Voraussetzung ist allerdings eine geeignete Vorbehandlung der Fugeteile. Fur den Einsatz in der Serienproduktion empfiehlt sich das Unterdruckstrahlen, das die Klebvorbehandlung von FVK mit hoher Prozesssicherheit und -geschwindigkeit ermoglicht.