Michael Frauenhofer

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.

Fast Curing of Adhesives in the Field of CFRP

The interest in carbon fiber reinforced plastic (CFRP) structures does not only increase in the area of aircraft construction, but also in the automotive industry. Due to the two-dimensional load transfer adhesive technology offers a particularly high potential of joining structures in lightweight construction. The adhesive systems applied for joining relevant CFRP structures show an insufficient initial strength thus necessitating additional fixing of the components or an accelerated curing of the adhesive. Induction technology has proved to be the most adequate heating technique for fast curing of metal bonds since it achieves high heating rates and enables a drastic reduction of the curing times. Due to their electrical conductivity, CFRP can also be heated by induction. Well-founded studies have been published explaining the physical mechanism behind the generation of heat within CFRP by electromagnetic induction. However, the relation between material and process parameters and the resulting heat generation and temperature distribution in CFRP parts still need to be investigated since, contradictory statements can be found in the literature. A profound knowledge of these relations, though, is elementary in order to predict the heat generation which is necessary to design a safe, fast curing process and to avoid damages to the material. Thus, the fundamental relations existing between the material/process parameters, the heat generation, and the resulting joining characteristics will be verified and discussed.

Wirtschaftliches Fügen in Serie und im Reparaturfall

Um dem Nachteil des langsamen Festigkeitsaufbaus struktureller Klebstoffe zu begegnen, werden heute vielfach Hybridfugeverfahren wie das Clinch-Kleben eingesetzt. Uberall dort, wo hybride Verfahren nicht anwendbar sind, bedarf es anderer Wege, die zu einem schnellen Festigkeitsaufbau fuhren. In Rahmen eines dreiteiligen Beitrags werden diese umfassend dargestellt. Der folgende erste Teil beleuchtet den Stand der Technik auf diesem Gebiet und beschreibt ein interessantes Untersuchungskonzept.

Wirtschaftliches Fügen in Serie und Reparatur

Um beim strukturellen Kleben die Vorteile der elektromagnetischen Direkterwarmung im industriellen Prozess nutzen zu konnen, bedarf es einer Abstimmung der jeweils eingesetzten Klebstoffe auf den Ausharteprozess. Nachdem der erste Teil dieser Folge (s. adhasion 12/08, S. 39) einen Uberblick uber den derzeitigen Stand der Technik und das experimentelle Vorgehen vermittelte, wird im Folgenden beantwortet, auf welche Weise sich verschiedene strukturelle Klebstoffe in ihrer Schnellhartbarkeit unterscheiden.

Green Production of CFRP Parts by Application of Inductive Heating

Long process times, high energy consumption, low automation level and high costs for textiles, resin and production tools are the main reasons for the low acceptance of fiber-reinforced plastics (frp) in high-volume production, especially in automotive applications. This paper presents the potential of the application of inductive heating techniques for the reduction of process time and energy consumption in different CFRP manufacturing processes based on different studies that have been performed at the institute of joining and welding. The described processes are the preforming and curing steps in the RTM process and the tape warming in the ATL process for thermoplastic composites.