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  • 1.
    Dewi, Handika Sandra
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Fischer, Andreas
    University of Kassel, Institute of Materials Engineering – Metallic Materials.
    Volpp, Joerg
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Niendorf, Thomas
    University of Kassel, Institute of Materials Engineering – Metallic Materials.
    Kaplan, Alexander F.H.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Microstructure and mechanical properties of laser surface treated 44MnSiVS6 microalloyed steel2020In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 127, article id 106139Article in journal (Refereed)
    Abstract [en]

    Fatigue property improvement for automotive components such as crankshafts can be achieved through material selection and tailored surface design. Microalloyed steels are of high interest for automotive applications due to their balanced properties, excellent hardenability and good machinability. Lasers facilitate efficient and precise surface processing and understanding the laser-material-property interrelationships is the key to process optimisation. This work examines microstructural development during laser surface treatment of 44MnSiVS6 microalloyed steel and the resulting mechanical properties. Laser beam shaping techniques are employed to evaluate the impact of beam shaping on the process. It revealed that ferrite structures remain in the treated area surrounded by martensite due to insufficient heating and dwell time of carbon diffusion.

  • 2.
    Frostevarg, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Volpp, Jöerg
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Thompson, Cassidy
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Prasad, Himani Siva
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Fedina, Tatiana
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Brückner, Frank
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development. Fraunhofer Institute for Material and Beam Technology, Dresden, Germany.
    Influence of the vapour channel on processing in laser powder bed fusion2019In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 36, p. 80-87Article in journal (Refereed)
    Abstract [en]

    Additive Manufacturing provides many opportunities to design and manufacture parts that are difficult or not possible to produce with conventional methods. In Selective Laser Melting (SLM) in powder bed fusion (PBF), melt pool dynamics and stability is dependent on a large number of factors, e.g. laser power output, power density, travel speed, reflectivity of powder bed, rapid heating and vaporization. Since travel speeds are often very fast and the laser interaction zone is small, the physical events become difficult to predict but also to observe. This work aims to describe the formation and geometrical characteristics of the vaporization zone during processing. Using a combination of theoretical descriptions, resulting material structures and a comprehensive analysis of high-speed images of the processing zone for different heat inputs and travel speeds, explanations for the dynamic melt pool behaviour are derived. The melting and pressures from processing involved moves powder particles next to it, changing the conditions for neighbouring tracks due to lack of material. These findings can provide a basis for creating more efficient and stable SLM processing, with fewer imperfections.

  • 3.
    Kaplan, Alexander F.H
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Robertson, Stephanie M.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Frostevarg, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Volpp, Joerg
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Ramasamy, Anandkumar
    Lincoln Electric Europe, Nijmegen, Netherlands.
    Kalfsbeek, Bert
    Lincoln Electric Europe, Nijmegen, Netherlands.
    Microstructure morphology characterization of welding consumables studied by pulse-shaped laser heating2019In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 36, p. 184-191Article in journal (Refereed)
    Abstract [en]

    During welding, wire consumables can essentially contribute to the resulting microstructures and mechanical properties. In order to maintain high toughness even for high strength steel, certain microstructures are desirable, particularly acicular ferrite. An efficient, controllable test method was developed during which the wire is molten and experiences a thermal cycle by a shaped laser pulse, or a sequence of pulses, which shall resemble continuous laser-arc hybrid welding or narrow gap multi-layer laser welding. Different thermal cycles and wire chemistries have led to manifold microstructures. The morphology of the microstructures can become complex. Therefore, more detailed characterization of essential morphology aspects was carried out, to distinguish different results. The thermal cycles from quenching have led to shorter, thicker laths with more random orientation. The latter can be favourable for high toughness. Short reheating cycles by about 200 K/s caused finer, longer and more parallel laths, as for bainite, in varying size of blocks. Other aspects considered were grain boundary ferrite and non-metallic inclusions. Systematic variation of the thermal cycle by the testing method along with systematic description of microstructure morphology in more detail is a promising method to identify and optimize favoured routes for wire chemistry and welding techniques.

  • 4.
    Laskin, Alexander
    et al.
    AdlOptica GmbH.
    Volpp, Joerg
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Laskin, Vadim A.
    AdlOptica GmbH.
    Ostrun, Aleksei B.
    St. Petersburg National Research University of Information Technologies, Mechanics and Optics.
    Beam shaping of focused radiation of multimode lasers2018In: High-Power Laser Materials Processing: Applications, Diagnostics, and Systems VII 2018 / [ed] Kaierle S.,Heinemann S.W., SPIE - International Society for Optical Engineering, 2018, Vol. 10525, article id 1052507Conference paper (Refereed)
    Abstract [en]

    Performance of various laser technologies like welding, metal sheet cutting based on the use of powerful multimode fiber lasers, fiber-coupled solid-state and diode lasers can be improved by manipulation of energy distribution perpendicular and along optical axis. Welding, cladding with 0.5-2 mm size working spots benefit from "inverse-Gauss" intensity profiles, and doubled or tripled spots perpendicular to axis are good solutions to provide more uniform temperature profiles on a workpiece. Thick metal sheet cutting, some types of welding get benefits from distributing the laser energy along the optical axis resulting in more efficient usage of laser energy, higher and more stable cutting edge quality, faster processing. Since the radiation of multimode lasers is of low spatial coherence, characterized by big Beam Parameter Products (BPP) or M2 values, it is difficult to control the intensity distribution by methods other than imaging of a fiber end using a collimator and focusing objective. A promising suggested solution is combining of imaging the fiber end and geometrical separation of focused spots either perpendicular to or along the optical axis using dedicated optical components. Thus, energy of high power lasers is distributed among multiple foci. To provide reliable operation with multi-kW lasers and avoid damages the multi-focus optical devices are designed as refractive elements with smooth optical surfaces. The paper presents descriptions of multi-focus optics as well as examples of intensity profile measurements of beam caustics and application results

  • 5.
    Laskin, Alexander
    et al.
    AdlOptica Optical Systems GmbH, Berlin, Germany.
    Volpp, Joerg
    BIAS - Bremer Institut für angewandte Strahltechnik GmbH, Bremen, Germany.
    Laskin, Vadim
    AdlOptica Optical Systems GmbH, Berlin, Germany.
    Ostrun, Aleksei
    St. Petersburg National Research University of Information Technologies, Mechanics and Optics, St. Petersburg, Russia.
    Elongation depth of field by focusing radiation of multimode lasers using multi-focus beam shaping optics2017In: 2017 ICALEO Conference Proceedings (Electronic Access), Laser Institute of America , 2017, article id 603Conference paper (Refereed)
  • 6.
    Laskin, Alexander
    et al.
    AdlOptica GmbH (Germany) .
    Volpp, Joerg
    Bremer Institut für angewandte Strahltechnik GmbH (Germany) .
    Laskin, Vadim
    AdlOptica GmbH (Germany) .
    Ostrun, Aleksei
    St. Petersburg National Research Univ. of Information Technologies (Russian Federation).
    Multi-focus beam shaping of high power multimode lasers2017Conference paper (Refereed)
  • 7.
    Laskin, Alexander
    et al.
    AdlOptica GmbH.
    Volpp, Joerg
    Laskin, Vadim
    AdlOptica GmbH.
    Ostrun, Aleksei
    St Petersburg National Research Univ of Information Technologies.
    Refractive multi-focus optics for material processing2016Conference paper (Refereed)
  • 8.
    Moradi, M.
    et al.
    Malayer Univ, Dept Mech Engn, Fac Engn, Malayer, Iran. Malayer Univ, Laser Mat Proc Res Ctr, Malayer, Iran.
    Khorram, A.
    KNToosi Univ Technol, Dept Mech Engn, Tehran, Iran.
    Fallah, M.M.
    Shahid Rajaee Teacher Training Univ, Tehran, Iran .
    Volpp, Joerg
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Nd:YAG Laser Welding of Ti6-Al-4V: Mechanical and Metallurgical Properties2019In: Lasers in engineering (Print), ISSN 0898-1507, E-ISSN 1029-029X, Vol. 43, no 1-2, p. 21-33Article in journal (Refereed)
    Abstract [en]

    Titanium and their alloys have high strength to weight ratio, good corrosion resistance and high melting point temperature lead to their application in engineering. Ti-6Al-4V alloy has been widely used in medical, chemistry and aerospace industries. In this research, laser welding of Ti-6Al-4V sheet with the thickness of 1.7 mm performed using a 400 W pulsed Nd:YAG laser. The effects of laser peak power, pulse duration and laser pulse energy on the weld bead profile, weld microhardness, tensile strength and microstructure were studied. Results showed that by increasing laser peak power, decreasing pulse duration and increasing laser pulse energy, the weld penetration increases. Metallurgical observations revealed that welded zone comprises of acicular αˊ phase within prior coarse β grains. Microhardness distribution is more uniform in welded zone. The microhardness value in the welded zone is the highest which is attributed to high martensitic phase content in the welded zone. The ultimate tensile strength (UTS) values show the variation from 649 to 998 MPa in the Nd:YAG laser welded samples.

  • 9. Volpp, Joerg
    Analytisches Modell zur Vorhersage der Keyhole-Geometrie beim Laserstrahltiefschweißen2013In: Schweißen und Schneiden, ISSN 0720-9223, Vol. 65, no 3, p. 136-137Article in journal (Other academic)
  • 10.
    Volpp, Joerg
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Behavior of powder particles on melt pool surfaces2019In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 102, no 5-8, p. 2201-2210Article in journal (Refereed)
    Abstract [en]

    Additive Manufacturing is in progress to change the production and manufacturing environments and possibilities; however, thecomplex processes taking place are not completely understood yet. A better understanding of the incorporation mechanism of theparticles into the melt pool during blown powder processes could lead to methods to increase the powder and energy efficiency.Therefore, the incorporation mechanism was investigated in experiments and simulation. High-speed images made it possible toobserve the behavior of single particles on the melt pool. A model based on the temperature-dependent surface tension/energydifference between the particle and the melt pool calculated the time until particle incorporation. It was shown that the surfacetension characteristics during particle heating can even lift the particle from the melt pool. The calculated wetting behavior incombination with high kinetic energies should lead to an immediate immersion of the particle into the melt pool. Since observationsdo not show this behavior, it is concluded that the surface tension plays a role in the incorporation mechanism, but othereffects like the occurrence of oxide layers or additional particle heating by the laser beam seem to lead to different mechanismsand heat conductions to support an earlier incorporation.

  • 11.
    Volpp, Joerg
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Einfluss der Strahlformung mittels Bifokaloptik auf die Spritzerbildung beim LaserstrahltiefschweißenIn: Article in journal (Other academic)
  • 12. Volpp, Joerg
    Einfluss des Strahlprofils auf die Porenbildung2015In: Schweissen und schneiden, Vol. 2015, no 4, p. 198-Article in journal (Other academic)
  • 13. Volpp, Joerg
    Impact of process parameters on particle distribution and wear resistance during laser deep alloying processes2015Conference paper (Refereed)
  • 14. Volpp, Joerg
    Impacts on keyhole oscillations and process pores during laser deep penetration welding2015Conference paper (Refereed)
  • 15.
    Volpp, Joerg
    BIAS - Bremer Institut für angewandte Strahltechnik GmbH.
    Investigation on the influence of different laser beam intensity distributions on keyhole geometry during laser welding2012In: Laser Assisted Net Shape Engineering (LANE 2012), Physics Procedia, ISSN 1875-3892, Vol. 39, p. 17-26Article in journal (Refereed)
    Abstract [en]

    An analytical quasi-static model of the keyhole during laser deep penetration welding is introduced. This model is used to calculate the keyhole geometry depending on spatial laser beam intensity. Keyhole shapes can be found solving the energy and pressure equations. All necessary physical effects like Fresnel and plasma absorption, heat conduction and vaporization are implemented in the model. For evaluation a Gaussian and a top hat beam profile were used. Experimental measurements of the keyhole shape using copper inlays in aluminum base material show good agreement with the results of the modeling.

  • 16.
    Volpp, Joerg
    Bremen University.
    Keyhole oscillations during laser deep penetration welding at different spatial laser intensity distributions2014Conference paper (Refereed)
  • 17.
    Volpp, Joerg
    Bremer Institut für angewandte Strahltechnik GmbH, Bremen, Germany.
    Keyhole stability during laser welding – Part II: Process pores and spatters2017In: Production Engineering, ISSN 0944-6524, E-ISSN 1863-7353, Vol. 11, no 1, p. 9-18Article in journal (Refereed)
  • 18. Volpp, Joerg
    Multifokusoptik zum Laserstahltiefschweißen2017In: Schweissen und schneiden, ISSN 0036-7184, no 4, p. 212-213Article in journal (Other (popular science, discussion, etc.))
  • 19. Volpp, Joerg
    Potentials of beam shaping in laser deep penetration welding2017Conference paper (Refereed)
  • 20.
    Volpp, Joerg
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Powder particle movement during Powder Bed Fusion2019In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 36, p. 26-32Article in journal (Refereed)
    Abstract [en]

    Powder Bed Fusion is a widely used technique to produce complex parts with different materials. In principle, a pre-placed powder layer is locally melted by a laser beam and thereby fused to the previous tracks and layers. This technique offers high flexibility at fast processing speeds. High-speed laser scanning enables, on the one hand, the fast processing but induces heat, forces and pressure in and around the processing zone on the other hand. The behavior of the single particles on the powder bed around the processing zone is hard to observe and therefore not sufficiently investigated. High-speed-imaging was used in this work to track the movement of the powder particles of the powder bed during Powder Bed Fusion in order to observe and explain their behaviour. It could be observed that powder particles move towards the melt pool affecting a large area around the melt pool, which changes the powder distribution of the powder bed. This indicates that a strong gas flow is constantly present during processing, which is thought to be due to the metal vapour induced by laser evaporation but can be also induced when no vapour is present due to the temperature and pressure increase around the processing zone.

  • 21. Volpp, Joerg
    Verschleißfeste Randschichtbereiche mittels Tieflegieren2014In: Schweissen und schneiden, ISSN 0720-9223, no 7, p. 383-384Article in journal (Other (popular science, discussion, etc.))
  • 22.
    Volpp, Joerg
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Brueckner, Frank
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development. Fraunhofer-Institute for Material and Beam Technology IWS, Dresden, German.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Track geometry variations in selective laser melting processes2019In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 31, no 2, article id 022310Article in journal (Refereed)
    Abstract [en]

    Selective laser melting processes are widely used for many industrial applications using a laser beam to melt preplaced powder materiallayer by layer to create technical parts. The building process of those structures requires remelting of adjacent tracks and layers in order toavoid cavities and achieve the joining of the new track to the previous track and layer. In order to achieve a sufficient overlap and minimizecavities, usually conservative processing parameters are chosen. A higher energy and powder usage efficiency would be achieved if knowingabout the formation process of the single tracks and their geometrical dimensions depending on the available powder. In this work, it isshown that the cross-sectional track geometry significantly varies within one layer. A simple model is developed describing the influence ofthe available powder for each track within one layer. Depending on the hatch distance, different variation patterns are observed andmodeled showing that the track variations are inherent phenomena of the process. It can be concluded that the variations of powder avail-ability can cause the geometric variations of the tracks.

  • 23.
    Volpp, Joerg
    et al.
    BIAS – Bremer Institut fuer angewandte Strahltechnik GmbH, Bremen, Germany.
    Dietz, T.
    BIAS – Bremer Institut fuer angewandte Strahltechnik GmbH, Bremen, Germany.
    Vollertsen, F.
    BIAS – Bremer Institut fuer angewandte Strahltechnik GmbH, Bremen, Germany.
    Particle property impact on its distribution during laser deep alloying processes2014Conference paper (Refereed)
  • 24.
    Volpp, Joerg
    et al.
    Bremer Institut Für Angewandte Strahltechnik GmbH.
    Freimann, D
    Bremer Institut Für Angewandte Strahltechnik GmbH.
    Indirect measurement of keyhole pressure oscillations during laser deep penetration welding2013In: ICALEO 2013 - 32nd International Congress on Applications of Lasers and Electro-Optics, 2013Conference paper (Refereed)
  • 25.
    Volpp, Joerg
    et al.
    BIAS GmbH.
    Gatzen, Marius
    BIAS GmbH.
    Unterschiedliche Strategien zur Strömungssimulation des Laserstrahltiefschweißens2013Conference paper (Refereed)
  • 26.
    Volpp, Joerg
    et al.
    BIAS – Bremer Institut fuer angewandte Strahltechnik GmbH, Bremen, Germany b.
    Hohenäcker, V.
    BIAS – Bremer Institut fuer angewandte Strahltechnik GmbH, Bremen, Germany b.
    Tyralla, D.
    BIAS – Bremer Institut fuer angewandte Strahltechnik GmbH, Bremen, Germany.
    Freiße, H.
    BIAS – Bremer Institut fuer angewandte Strahltechnik GmbH, Bremen, Germany.
    Brocke, N.
    OSCAR PLT GmbH, Klipphausen, Germany.
    Silze, F.
    OSCAR PLT GmbH, Klipphausen, Germany.
    Schnick, M.
    OSCAR PLT GmbH, Klipphausen, Germany.
    Thomy, C.
    BIAS – Bremer Institut fuer angewandte Strahltechnik GmbH, Bremen, Germany.
    Observing melt pool temperature fields for process characterization2017Conference paper (Refereed)
  • 27.
    Volpp, Joerg
    et al.
    BIAS – Bremer Institut fuer angewandte Strahltechnik GmbH, Bremen, Germany.
    Srowig, Jennifer
    BIAS – Bremer Institut fuer angewandte Strahltechnik GmbH, Bremen, Germany.
    Vollertsen, Frank
    BIAS – Bremer Institut fuer angewandte Strahltechnik GmbH, Bremen, Germany. University of Bremen, Bremen, Germany.
    Spatters during laser deep penetration welding with a bifocal optic2016In: Advanced Materials Research / [ed] Jens P. Wulfsberg, Marc Fette, Tobias Montag, 2016, Vol. 1140, p. 123-129Conference paper (Refereed)
  • 28.
    Volpp, Joerg
    et al.
    aBIAS – Bremer Institut für angewandte Strahltechnik GmbH, Bremen, Germany.
    Vollertsen, F.
    aBIAS – Bremer Institut für angewandte Strahltechnik GmbH, Bremen, Germany;University of Bremen, Germany.
    Correlation of keyhole dynamics and pore formation2015In: WLT: LIM 2015, German Scientific Laser Society (WLT) , 2015Conference paper (Refereed)
    Abstract [en]

    Imperfections like pores occurring due to high process dynamics during laser deep penetration welding reduce the weld quality and the strength of welded joints. It is assumed that keyhole instabilities are responsible for the high process dynamics. In order to better understand the correlation between pore formation and keyhole dynamics an analytical process model has been developed describing keyhole radius fluctuations in different depths depending on the process parameters. Modelled radius oscillation frequencies have been compared to experimentally measured process emissions. Frequency spectrums of acoustic process emission observations show similar tendencies of keyhole dynamics compared to the calculations. For pore detection x-ray photography has been used while pore percentage and pore number in the weld seams have been evaluated. The pore formation in the solidified weld seam is compared to the observed dynamic characteristics during the process. Higher keyhole frequencies tend to correlate with increased pore numbers at reduced pore sizes.

  • 29.
    Volpp, Joerg
    et al.
    Bremer Institut für angewandte Strahltechnik GmbH, Bremen, Germany.
    Vollertsen, F.
    Bremer Institut für angewandte Strahltechnik GmbH, Bremen, Germany. University of Bremen, Bremen, Germany.
    Modeling keyhole oscillations during laser deep penetration welding at different spatial laser intensity distributions2015In: Production Engineering, ISSN 0944-6524, E-ISSN 1863-7353, Vol. 9, no 2, p. 167-178Article in journal (Refereed)
  • 30.
    Volpp, Joerg
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development. Bremer Institut fuer angewandte Strahltechnik GmbH, Bremen, Germany.
    Vollertsen, Frank
    Bremer Institut fuer angewandte Strahltechnik GmbH, Bremen, Germany; University of Bremen, Bremen, Germany.
    Impact of multi-focus beam shaping on the process stability2019In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 112, p. 278-283Article in journal (Refereed)
    Abstract [en]

    Unwanted process defects occur during laser deep penetration welding. The formation mechanisms of the main process defects like spatters and pores are not completely identified yet. Several methods like beam oscillation or laser power modulation are known to help reducing the occurrence of defects. These methods change the temporal energy input. It can be assumed that also beam shaping influences the energy input into the keyhole and has the potential to influence process defects as well. Due to the adapted energy input keyhole instabilities, that are assumed to influence the formation of the defects, can be avoided. A newly developed multi-focus beam shaping optic that creates multiple beam waists in axial direction is used in this work. The additional areas with increased intensities are used to modify the energy input in the keyhole in order to explain the mechanism of spatter formation and evaluate the potential of the axial beam shaping for defect suppression during laser deep penetration welding. It is found that the number of spatters can be reduced when the middle sections of the keyhole are illuminated with a high intensity. It can be concluded that spatters can be reduced when a keyhole collapse is avoided and a high enough energy input is guaranteed in the upper keyhole sections.

  • 31.
    Volpp, Joerg
    et al.
    Bremer Institut für angewandte Strahltechnik GmbHBremenGermany.
    Vollertsen, Frank
    Bremer Institut für angewandte Strahltechnik GmbH, Bremen, Germany. University of Bremen, Bremen, Germany.
    Keyhole stability during laser welding – Part I: Modeling and Evaluation2016In: Production Engineering, ISSN 0944-6524, E-ISSN 1863-7353, Vol. 10, no 4-5, p. 443-457Article in journal (Refereed)
    Abstract [en]

    The keyhole is a requirement in order to establish the energy efficient process of laser deep penetration welding. However, the process is highly unstable which results in unwanted pore and spatter formation. In order to avoid process defects, the physical effects in the keyhole have to be better understood to find ways for compensation. This work aims to describe the keyhole properties at different welding parameters for welding of aluminum (EN AW 1050) with the help of a semi-analytical model based on energy and pressure equations and differential equations. The resulting dynamic characteristics of different keyholes are evaluated with frequency analysis of optical observations during the welding process. The spring coefficient, that describes the radial pressure change at radius deviation, is a good indicator for the resulting keyhole dynamics. Dynamic behavior is influenced by the spatial laser intensity distribution, while higher frequencies at lower amplitudes are found at a Top Hat distribution compared to a Gaussian intensity profile.

  • 32.
    Volpp, Joerg
    et al.
    BIAS – Bremer Institut für angewandte Strahltechnik GmbH.
    Vollertsen, Frank
    BIAS – Bremer Institut für angewandte Strahltechnik GmbH.
    Verschleißeigenschaften von Lasertiefdispergierten Aluminiumrandschichten2016In: Dialog, ISSN 2193-3383, p. 109-109Article in journal (Other (popular science, discussion, etc.))
  • 33. Volpp, Joerg
    et al.
    Vollertsen, Frank
    Gatzen, M
    Simplified analytical modeling of dynamic behavior of the keyhole for different spatial laser intensity distributions during laser deep penetration welding2013In: The Paton Welding Journal, ISSN 0957-798X, no 3, p. 14-17Article in journal (Refereed)
  • 34.
    Volpp, Joerg
    et al.
    BIAS – Bremer Institut für angewandte Strahltechnik GmbH, Bremen, Germany.
    Vollertsen, V
    BIAS – Bremer Institut für angewandte Strahltechnik GmbH, Bremen, Germany.
    Analytical modeling of the keyhole including multiple reflections for analysis of the influence of different laser intensity distributions on keyhole geometry2013In: Lasers in Manufacturing (LIM 2013). Physics Procedia, ISSN 18753884, Vol. 41, p. 460-468Article in journal (Refereed)
    Abstract [en]

    An analytical model of the keyhole for deep penetration welding is presented. Based on a pressure and energy equilibrium the initial keyhole radii in different depths are calculated depending on different incident beam intensity distributions. Multiple reflections are included by using a ray tracing method in a second step to improve calculation of the keyhole shape. A Gaussian and a top hat beam profile are used for evaluation and show similar resulting keyhole geometries and different pressure gradients.

  • 35.
    Volpp, Jörg
    Universität Bremen, Germany.
    Dynamik und Stabilität der Dampfkapillare beim Laserstrahltiefschweißen2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The keyhole which is typical for laser deep penetration welding is responsible for the highly dynamic process behavior, which results in unwanted pore and spatter formation. This work aims to better understand the dynamic keyhole properties and occurrence of process defects. Therefore, a semi-analytical model is developed and validated by optical emission analysis. Spatter characteristics are evaluated in high speed videos and porosity in x-ray analysis. Correlations between keyhole behavior and spatter and pore characteristics could show that pores can form due to a keyhole collapse and spatter detachment requires more than the momentum from keyhole wall fluctuations. Dynamic behavior and process defects are influenced by the spatial laser intensity distribution.

  • 36.
    Volpp, Jörg
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development. Bremer Institut fuer angewandte Strahltechnik GmbH.
    Formation mechanisms of pores and spatters during laser deep penetration welding2018In: Journal of laser applications, ISSN 1042-346X, E-ISSN 1938-1387, Vol. 30, article id 012002Article in journal (Refereed)
    Abstract [en]

    During laser deep penetration welding process, defects cannot be completely avoided yet. Due to the dynamic process, especially process pores and spatters occur. Keyhole dynamics are assumed to be responsible for the initiation of both pores and spatters. However, it is not completely clear yet how spatters and pores are formed. A semianalytical model of a keyhole is used to simulate dynamic keyhole properties of laser beam welding of aluminum. These are related to characteristics of spatters and pores occurring during laser deep penetration welding recorded using high-speed-imaging technique and x-ray analysis, respectively. Correlations of keyhole shapes and pore formation show that the volume underneath a keyhole collapse can be sufficient to capture the gas that is necessary for the formation of a pore and a keyhole expansion is not necessarily needed to produce the pores found in the weld seam. Calculated keyhole wall fluctuations are found to be not sufficient to detach spatters from the keyhole wall without additional forces from the melt pool.

  • 37.
    Volpp, Jörg
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Impact of fume particles in the keyhole vapour2019In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 125, no 1, article id 70Article in journal (Refereed)
    Abstract [en]

    During laser material processing, the energy of the laser beam needs to be efficiently and constantly transported to theprocessing zone to guarantee constant processing. However, spatters or ejected particles from the keyhole can absorb andscatter the laser energy leading to inhomogeneous heat input and can initiate defect occurrence like pore formation. Theimpact of ejected particles from the keyhole on the energy transport of the laser beam is not completely understood sincethey are difficult to observe due to the small size and high speeds of the ejections. In this work, the particle characteristicswere derived from a simulation of the keyhole wall movement. The behavior of the calculated particles in a side shielding gasjet was calculated to derive the height, at which the particles leave the laser beam and are not interrupting the laser energytransfer to the processing zone. Low impulse values of the particles were calculated e.g., at defocusing positions slightlyunderneath the material surface, where also highest melt pool sizes were found. These observations indicate that the fumeparticles can be one reason to limit the energy delivery. An efficiency increase can be achieved by adjusting the keyholeparameters to a more stable keyhole.

  • 38.
    Volpp, Jörg
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Prasad, Himani Siva
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Behavior of heated powder particles on solid surfaces2018In: Procedia Manufacturing, E-ISSN 2351-9789, Vol. 25, p. 365-374Article in journal (Refereed)
    Abstract [en]

    Powder particles applied through a powder nozzle as used e.g. in laser additive manufacturing or cladding processes are heated during their flight through the laser beam. The heating process and the interaction of the particle with the solid substrate were modeled in this work. In addition, the particle interaction with the solid substrate was observed using high speed imaging. At a high temperature and a high speed of the particles, the heat conduction into the base material is not fast enough to solidify the particles due to the short interaction time with the substrate.

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