Dr.-Ing.

Janssen, Henning

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  • Publication
    Adaptive tape placement process control at geometrically changing substrates
    ( 2019)
    Brecher, Christian
    ;
    Emonts, Michael
    ;
    Striet, Philipp
    ;
    Voell, Annika
    ;
    Stollenwerk, Jochen
    ;
    Janssen, Henning
    The laser-assisted tape placement process faces thermal challenges at geometrically changing substrates. Due to changing optical conditions and thereby varying local energy absorption, local differences of the process temperature occur. These temperature inhomogeneities become even more pronounced due to restrictions with regard to machine dynamics. In particular, strong directional changes, which are necessary e.g. for small machining radii, result in the relative speed between workpiece and laser beam not being constant. The use of vertical-cavity surface-emitting lasers (short: VCSEL) as adaptive heat sources could improve the temperature control especially by use of application adapted intensity distributions that can be calculated through inverse simulations. In this work, the optical and thermal effects during tape placement on geometrically changing substrates are described and analyzed. A possible solution to the described challenges is shown by using application adapted intensity distributions, which aim at a suitable, constant process temperature. The simulations will consider the three-dimensional part geometry, specific intensity distributions of the VCSEL as well as machine dynamics. By the use of tape placement equipment of the Fraunhofer IPT the occurring local temperature changes and the resulting degree of process optimization are experimentally validated.
  • Publication
    Transient thermal analysis of laser-assisted thermoplastic tape placement at high process speeds by use of analytical solutions
    ( 2018)
    Weiler, Thomas
    ;
    Emonts, Michael
    ;
    Wollenburg, Lukas
    ;
    Janssen, Henning
    This article presents a transient thermal analysis of laser-assisted thermoplastic tape placement at high process speeds. The article revises modeling simplifications made in the literature and introduces novel ones. Analytical solutions to the thermal problem are proposed, for the heating and the cooling period. The process analysis of high speeds assumes a high-power laser in combination with a well-functioning temperature control. Due to this assumption, the final (surface) temperature is kept equal in all analyzed cases. The process analysis will show that the through-thickness temperature distribution changes significantly at higher speeds and becomes the determining factor for the bond interface temperature. General conclusions about process design and limits of tape placement are drawn. Finally, novel control methods are presented, which promote a dual control of surface temperature and temperature distribution. It will be shown how this is achieved by appropriate setting of the laser power and heating length.
  • Patent
    Induktiv beheizbares Formwerkzeug
    ( 2017)
    Emonts, Michael
    ;
    Werner, Daniel
    ;
    Janssen, Henning
    ;
    Steinmayer, Marc
    ;
    Michelis, Benedict
    Ein induktiv beheizbares Formwerkzeug, umfassend eine Induktor-Aufnahme (12) sowie einen als Empfänger des von einem Induktor (8, 11) erzeugten elektromagnetischen Wechselfeldes dienenden Suszeptor, kennzeichnet sich dadurch, dass die Induktor-Aufnahme (12) unterschiedliche Verlegemuster des Induktors (8, 11) erlaubt. Insbesondere kann die Induktor-Aufnahme (12) mindestens einen sich verzweigenden Kanal (15) aufweisen. Ein für ein solches Formwerkzeug Teilwerkzeug-System umfasst mindestens zwei Stützkörper 6, 9) und mindestens einen Formkörper (7, 10), wobei jeder Formkörper (7, 10) an jedem Stützkörper (6, 9) lösbar fixierbar oder verspannbar ist.
  • Publication
    Optical modelling of VCSEL-assisted thermoplastic tape placement
    ( 2016)
    Weiler, Thomas
    ;
    Emonts, Michael
    ;
    Striet, Philipp
    ;
    Gronenborn, S.
    ;
    Janssen, Henning
    Due to high intensities and low response time, laser-assisted tape placement offers high processing speeds and precise temperature control. Therefore, the process and its systems gain more and more interest in several industries, which want to utilize continuously-reinforced thermoplastics. Especially high-volume production of structural and semi-structural components, like pressure vessels, pipes or automobile parts, is of interest. Further combinatorial potentials, like the combination with injection molding promise complex, yet cost-effective, product designs. Current laser-based tape placement systems are able to control the laser intensity distribution between tape and substrate by electro-mechanically tilting the laser optics or the whole laser beam source [1], [2]. The use of novel Vertical-Cavity Surface-Emitting Lasers (VCSEL) offers new possibilities to control the laser intensity distribution by use of discrete electrically-controllable emitter lines [3]. Tap e and substrate can be heated independently with adjustable intensity profiles in the width or in feed direction. The basis for a purposeful laser intensity distribution is knowledge of the intrinsic process intensity distributions in the process zone, which depends on the process geometry, the VCSEL angular intensity distribution and the effect of laser reflection. This paper proposes a method to calculate the process intensity distribution for VCSEL-assisted tape placement.
  • Publication
    Mass customization of high performance composites with low investment costs
    ( 2015)
    Brecher, Christian
    ;
    Buschhoff, Clemens
    ;
    Janssen, Henning
    ;
    Emonts, Michael
    One of the most important factors for the industry today is the energy-efficient production of lightweight components. An affordable process that enables the mass customization of high performance composites with low investment costs is the goal. An automated manufacturing approach is developed that allows affordable high performance products made by fiber-reinforced thermoplastic composites. This concept caters to a wide variety of industries with the help of one production technology. On a technological level it is demonstrated that with the new approach (a mutual consideration of tape placement and thermoforming), superior parts can be produced with less effort than today. On economical level it will demonstrated that this can be achieved with equipment that allows a short return on invest and that improves the competiveness on a long term. The technology is an automated manufacturing solution that allows flexible volume production of recyclable high performance composite parts with nearly any shape. This is achieved by exploiting the synergy of efficient primary shaping technologies (laser-assisted tape placement) and reshaping (thermoforming).
  • Publication
    Economic production of load-optimized thermoplastic composites
    ( 2013)
    Brecher, Christian
    ;
    Kermer-Meyer, Alexander
    ;
    Janssen, Henning
    ;
    Werner, Daniel
    ;
    Emonts, Michael
    Sustainable production methods for fibre-reinforced plastics (FRP) are one of the key challenges of modern production technology, especially in comparison to established process chains such as metal working. In plastic processing, thermoforming and injection moulding are used in high-volume series production by integrating short or long fibres. The use of continuous fibre-reinforced thermoplastic (FRTP) composite blanks is growing. Load-optimized hybrid- or multi-material structures with a combination of different fibres, such as glass or carbon fibres, are promising with regard to economic efficiency and reduced consumption of material and energy.
  • Publication
    Herstellung von belastungsoptimierten thermoplastischen Faserverbundbauteilen
    ( 2013)
    Brecher, Christian
    ;
    Emonts, Michael
    ;
    Kermer-Meyer, Alexander
    ;
    Janssen, Henning
    ;
    Werner, Daniel
    Das Fraunhofer IPT hat Produktionspfade zur Herstellung, lokalen Verstärkung und Funktionalisierung von thermoplastischen Organoblechen mittels laserunterstütztem Thermoplast-Tapelegen entwickelt und umgesetzt. Durch die Verarbeitung von Tapes mit thermoplastischem Matrixsystem entfällt im Vergleich zu Duroplast-Prozessen eine energie- und zeitintensive Aushärtung im Autoklaven. So lassen sich vollständig konsolidierte Bauteile mit hoher Schlagzähigkeit in kurzer Taktzeit flexibel und ohne Kontamination der Produktionsanlage großserientauglich herstellen. Durch Wandstärkenminimierung im Bereich geringerer Belastung und lokales Verstärken der lastkritischen Bereiche wird das Leichtbaupotenzial faserverstärkter Kunststoffe optimal genutzt. Durch eine geschickte Kombination verschiedener Verstärkungsfasern, wie Kohlenstofffasern und Glasfasern wurden am Fraunhofer IPT erstmals belastungsoptimierte Hybrid oder Multimaterialsysteme großserientauglich hergestellt. Mit dem Fokus aufeine großserientaugliche Produktion mit kurzen Zykluszeiten und vollständiger Automatisierbarkeit ermöglicht die Kombination der vorgestellten Produktionsprozesse, laserunterstütztes Tapelegen und Thermoformen mit hauptzeitparalleler Insert-Integration, einen wirtschaftlichen Ansatz zur Herstellung funktionsintegrierter Leichtbauteile.
  • Publication
    Customized solutions for laser-assisted tape placement
    ( 2012)
    Brecher, Christian
    ;
    Kermer-Meyer, Alexander
    ;
    Werner, Daniel
    ;
    Stimpfl, Joffrey
    ;
    Janssen, Henning
    ;
    Emonts, Michael
    In this paper, Fraunhofer IPT's specialists in the field of laser-assisted tape placement describe the key points of this specific composite manufacturing method. They also show that this technique is suitable for many industries, and not only for aerospace, and explain how to develop the most cost-effective solution.