Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    High-power laser beam welding for thick section steels - new perspectives using electromagnetic systems
    ( 2022)
    Rethmeier, M.
    ;
    Gumenyuk, A.
    ;
    Bachmann, M.
    In recent years, it was shown that the introduction of additional oscillating and permanent magnetic fields to laser beam and laser-arc hybrid welding can bring several beneficial effects. Examples are a contactless weld pool support for metals of high thickness suffering from severe drop-out when being welded conventionally or an enhanced stirring to improve the mixing of added filler material in the depth of the weld pool to guarantee homogeneous resulting mechanical properties of the weld. The latest research results show the applicability to various metal types over a wide range of thicknesses and welding conditions. The observations made were demonstrated in numerous experimental studies and a deep understanding of the interaction of the underlying physical mechanisms was extracted from numerical calculations.
  • Publication
    The Effects of HLAW Parameters for One Side T-Joints in 15 mm Thickness Naval Steel
    ( 2021)
    Churiaque, C.
    ;
    Sánchez-Amaya, J.M.
    ;
    Porrúa-Lara, M.
    ;
    Gumenyuk, A.
    ;
    Rethmeier, M.
    The present contribution is the first research reporting full penetration HLAW joints in 15 mm thick EH36 steel butt T-welds with square grooves on 2F welding position by single-sided welding. The effects of welding parameters were investigated to increase the quality of the joints. Conditions leading to defect-free full penetration welds fulfilling naval regulations includes a laser power of 12.5 kW, a welding speed of 1.6 m/min and the vertical laser offset distance from the flange of 1 mm. Advanced characterization of selected welds included a microstructural identification by optical microscopy, SEM, and XRD, revealing the presence of acicular, polygonal and Widmanstätten ferrite, lath martensite, and some retained austenite at FZ. Hardness and microhardness mapping tests showed values of 155 HV at base metal and 200 to 380 HV at the fusion zone connecting the web to the flange.
  • Publication
    Investigation of the gap bridgeability at high-power laser hybrid welding of plasma-cut thick mild steels with AC magnetic support
    ( 2021)
    Üstündag, Ö.
    ;
    Bakir, N.
    ;
    Gumenyuk, A.
    ;
    Rethmeier, M.
    One of the challenges of the high-power hybrid laser welding of thick steels is the sensitivity of the process of the process to manufacturing tolerances. This usually leads to a time-consuming preparation of the welding edges, such as milling. The study deals with the influence of the edge quality of milled and plasma-cut steel made of S355J2 with a wall thickness of 20 mm on the laser hybrid welded seam quality. Furthermore, the gap bridgeability and the tolerances towards edge misalignment was investigated. An AC magnet was used as backing support to prevent sagging and positioned under the workpiece, to generate an upwards directed electromagnetic pressure. The profiles of the edges and the gap on the top and root side were measured using a digital camera. Single-pass laser hybrid welds of plasma-cut edges could be welded using a laser beam power of just 13.7 kW. A gap bridgeability up to 2 mm and misalignment of edges up to 2 mm could be achieved successful. Additionally, the independence of the cutting side and the welding side was shown, so that samples were welded to the opposite side to their cutting. For evaluation of internal defects or irregularities, X-ray images were carried out. Charpy impact strength tests were performed to determine the toughness of the welds.
  • Publication
    Influence of oscillating magnetic field on the keyhole stability in deep penetration laser beam welding
    ( 2021)
    Üstündag, Ö.
    ;
    Bakir, N.
    ;
    Gumenyuk, A.
    ;
    Rethmeier, M.
    The stability of the keyhole decreases for deep penetrated high-power laser beam welding. The keyhole tends to collapse with increasing laser power and e.g. keyhole induced porosity can occur. This study deals with the observation of the keyhole during high-power laser beam welding in partial penetration mode by means of a high-speed camera. A butt configuration of 25 mm thick structural steel and transparent quartz glass was used for the experiments. An oscillating magnetic field was applied perpendicular to the welding direction on the root side of the steel plate. The keyhole was highlighted with a coaxial diode laser. It was ascertained that the stability of the keyhole and the weld penetration depth were increased by applying an oscillating magnetic field with an oscillating frequency of 1.2 kHz and a magnetic flux density of 50 mT.
  • Publication
    Shielded metal arc welding of 9%Ni steel using matching ferritic filler metal
    ( 2021)
    El-Batahgy, A.
    ;
    Saiyah, A.
    ;
    Khafagi, S.
    ;
    Gumenyuk, A.
    ;
    Gook, S.
    ;
    Rethmeier, M.
    Motivated by the tensile strength loss of 9%Ni steel arc welded joints made using Ni-based austenitic filler metals, the feasibility of maintaining the tensile strength using matching ferritic filler metal has been demonstrated. In comparison with shielded metal arc welded joint made using Ni-based austenitic electrode ENiCrMo-6, higher tensile strength comparable to that of the base metal was obtained using matching ferritic electrode. Besides, sufficient impact toughness energies with much lower mismatch were obtained for weld metal and heat-affected zone. Welded joint with a lower mechanical mismatching is of considerable importance for achieving acceptable combination of tensile strength and impact toughness. A better combination of these mechanical properties is ensured by applying a post weld heat treatment.
  • Publication
    In situ determination of the critical straining condition for solidification cracking during laser beam welding
    ( 2020)
    Bakir, N.
    ;
    Gumenyuk, A.
    ;
    Pavlov, V.
    ;
    Volvenko, S.
    ;
    Rethmeier, M.
    In recent years, laser beam welding has found wide applications in many industrial fields. Solidification cracks are one of the most frequently encountered welding defects that hinder obtaining a safe weld joint. Decades of research have shown that one of the main causes of such cracks is the strain and the strain rate. Obtaining meaningful measurements of these strains has always been a major challenge for scientists, because of the specific environment of the measurement range and the many obstacles, as well as the high temperature and the plasma plume. By applying novel metrology based on optical flow (OF) algorithm, the critical strain conditions for solidification crack formation for the stainless steel 1.4828 in the immediate vicinity of the solidification front was identified. The developed two-dimensional technique allows for obtaining full strain distribution in the hot cracking critical zone.
  • Publication
    Experimental and numerical study on the influence of the laser hybrid parameters in partial penetration welding on the solidification cracking in the weld root
    ( 2020)
    Bakir, N.
    ;
    Üstündag, Ö.
    ;
    Gumenyuk, A.
    ;
    Rethmeier, M.
    The aim of the present study is to investigate the influence of the laser hybrid welding parameters on the solidification cracks in the weld root for partial penetration welding. Welding trials were performed on thick-walled high-strength steels of grade S690QL under the same critical restraint intensity, with a variation of the welding velocity, wire feeding rate, and the focal position of the laser beam. It was ascertained that the welding velocity has a high impact on the solidification cracking phenomenon. A decrease in the welding speed leads to a reduction of the number of cracks in the weld root. The arc power has also a slight influence on the solidification cracking, while the change of the focal position of the laser beam shows also a remarkable effect. Besides, numerical simulation was performed to understand the thermomechanical behavior of the welds for different welding parameters to assist the interpretation of the experimental results.
  • Publication
    LMD coatings as filler material for laser beam welded 30 mm thick plates
    ( 2020)
    Straße, A.
    ;
    Üstündag, Ö.
    ;
    Gumenyuk, A.
    ;
    Rethmeier, M.
    The development of high energy laser sources enables single-pass welds of thick plates up to 30 mm, but often additional materials are needed to influence the properties of the weld seams. However, the homogenous distribution of filler materials in form of e.g. electrodes is only possible up to 7 mm while the elements are only traceable up to a depth of 14 mm. To overcome this problem a two-step process is used where first the edges of the weld partners are coated with the filler material by laser metal deposition (LMD) and afterwards are welded by laser beam. Single-pass welds with electromagnetic weld pool support of 30 mm thick S355 J2+N-plates with austenitic AISI 316L-coatings were investigated as well as the influence of the coatings to the penetration depth of the laser beam without electromagnetic weld pool support in double-sided joints. The weld seams were tested by X-ray inspection and cross sections.
  • Publication
    Notch impact toughness of laser beam welded thick sheets of cryogenic nickel alloyed steel X8Ni9
    ( 2020)
    Gook, S.
    ;
    Krieger, S.
    ;
    Gumenyuk, A.
    ;
    El-Batahgy, A.M.
    ;
    Rethmeier, M.
    The paper deals with the investigations of the impact toughness of laser beam welded 14.5 mm thick sheets made of cryogenic steel X8Ni9 as a function of preheating. This 9% nickel alloyed steel is widely used in the liquefied natural gas (LNG) industry. An application of highly efficient welding processes such as high-power laser beam welding (LBW) in LNG sector requires an understanding of the interactions between the LBW process parameters and weld properties, in particular the impact toughness. The results show that the original fine-grained martensitic microstructure of the base metal (BM) is significantly changed by melting and crystallization during the LBW, what can lead to a decrease in the impact toughness of the weld metal (WM) below the required level. An optimal preheating temperature range leads to the favorable thermal welding cycle and is of remarkable importance for maintaining the notch impact toughness of laser beam welded joints of these thick steel sheets. A parameter window was identified in which V-notch impact toughness comparable to that of the BM at -196 °C was achieved.
  • Publication
    Development of a novel optical measurement technique to investigate the hot cracking susceptibility during laser beam welding
    ( 2019)
    Bakir, N.
    ;
    Pavlov, V.
    ;
    Zavjalov, S.
    ;
    Volvenko, S.
    ;
    Gumenyuk, A.
    ;
    Rethmeier, M.
    The weldability of materials is still for many years a highly contentious issue, particularly regarding the causes of the hot crack formation. Because of the process-related temperature and emissions, direct measurement for the arising strain in the close vicinity of the welding process is challenged. Therefore, the externally loaded hot cracking tests remain for decades the only way to determine the critical straining conditions for solidification cracking. In this study, a novel 2D in situ observation technique has been developed to analyze the strain evaluation during the welding process in the moment of crack formation. For the first time, the employed technique enabled the in situ measurement of the transient strain field at the surface of the workpiece directed to the laser beam in the critical range, where the solidification cracking normally occurs. Thus, the critical threshold strain values at high temperatures characterizing transition from crack-free to crack-concomitant welding process could be deduced. The influence of the global straining conditions on the direct local measured strain and strain rate for the stainless steel 316 L has been analyzed and discussed.