
Stefan BöhmUniversity of Kassel · Institute of Production Technology and Logistics (IPL)
Stefan Böhm
Univ.-Prof. Dr.-Ing.
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272
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1,357
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Introduction
Additional affiliations
September 1994 - December 1999
October 2002 - March 2010
April 2010 - present
Publications
Publications (272)
State of the art in tooling for cutting granites are sintered grinding tools having synthetic diamond grains bound together in metal matrix usually a cobalt copper alloy. Routers for CNC machining of stone surfaces come in various forms such as face milling tools, end milling cutters, edge profiling tools etc. and have either segmented or continuou...
Bisphenol A is the most important chemical for producing epoxy resins, but as of today is not bio-based accessible. Furthermore, it is rated as a substance of very high concern and possesses reproductive toxic and endocrine-disrupting properties. Phlorotannins, a class of polyphenols, are structurally highly suited for serving as sustainable bisphe...
Nickel-titanium shape memory alloys (NiTi) as well as titanium alloys (Ti) are essential materials in various modern medical technology applications. Combining them in functionally-graded components would allow the fabrication of highly innovative products with major economic and technical advantages. While dissimilar fusion welding of these materi...
In this publication, an in-process quality assurance method for electron beam welding based on a structure-borne sound emission test for the detection of weld irregularities arising in the process is presented. For this purpose, different sheet materials, i.e., AISI 304, AZ31 and AlMg3, were welded in a butt-joint and the resulting process noises w...
Climate change exacerbates the need for resource-efficient and cost-effective production processes across manifold industries, including the field of electrical connections. This specific field is characterized by a conflict of objectives, i.e., weight reductions while maintaining joint strength and electrical conductivity. From a material point of...
Joining of NiTi shape memory alloys with commercially pure titanium (Ti) is of great interest for manifold industrial applications. However, dissimilar fusion welding of these materials is associated with the formation of extremely brittle intermetallic compounds, e.g. , Ti 2 Ni and TiNi 3 , which drastically limit the mechanical properties of NiTi...
Climate change exacerbates the need for resource-efficient and cost-effective production processes across manifold industries, including the field of electrical connections. This specific field is characterized by a conflict of objectives, i.e., weight reductions while maintaining joint strength and electrical conductivity. From a materials point o...
In the present investigation, commercially pure titanium is welded to AISI 316L stainless steel by intermixing niobium as filler material in a lap joint configuration. For this purpose, a pulsed Nd:YAG laser with various pulse durations and pulse peak powers is employed to obtain different mixing conditions for the materials. It will be demonstrate...
In present work, the monotonic and cyclic properties of a novel Al‐Mg‐Zn‐Cu‐Si compositionally complex alloy (CCA) are investigated. Microstructural studies reveal that a eutectic phase and fishbone‐type structures are embedded in the Al‐matrix. The mechanical properties of this CCA obtained under compressive loading are found to be promising. Howe...
Wood composites are a sustainable alternative to lightweight materials, but most often only possess low to medium mechanical properties. The stiffness and strength of wood-based panels can however greatly be enhanced by a densification process. In this context the question arises as to whether the increase in density and the associated compaction o...
Especially in the building industry the demand for in situ monitoring concepts of adhesive joints persists. In a new approach, microcapsules filled with special dyes, are added into a rubbery adhesive. Certain stress levels within the adhesive lead to a breakage of the capsules, which release their liquid cores. This results in a detectable colour...
Friction stir welding enables joining of high‐strength, lightweight aluminum alloys, e.g., EN‐AW‐7075, below the melting point by induced plastic deformation. Therefore, heat transfer into the adjacent regions beneath the weld seam is significantly reduced as compared to fusion welding processes such as laser beam welding. However, specific zones a...
The present study focuses on the weldability of hot-rolled Fe-Mn-Al-Ni shape memory alloy sheets by vacuum electron beam welding. Tailored process-specific welding parameters, such as preheating with electron beam or beam oscillation during welding, allowed defect-free joining with very thin weld seams and heat-affected zones. By applying a post-we...
The use of 7000 aluminum alloys has an important role in future lightweight structures in the field of mobility due to the low density and high strength. However, these alloys can only be fusion welded to a limited extent because welding defects can rarely be prevented. For this reason, investigations are carried out to identify the most suitable w...
Ni-Mn-based Heusler alloys like Ni-Mn-Sn show an elastocaloric as well as magnetocaloric effect during the magneto-structural phase transition, making this material interesting for solid-state cooling application. Material processing by additive manufacturing can overcome difficulties related to machinability of the alloys, caused by their intrinsi...
In laser‐based direct energy deposition (DED‐LB) additive manufacturing (AM), wire or powder materials are melted by a high‐power laser beam. Process‐specific characteristics enable robust in situ fabrication of compositionally graded materials, e.g., through an adaption of powder mass flow from independent hoppers. Based on the high flexibility of...
In many technological areas, especially in the medical sector, stainless steel parts are being used due to their longevity, good biocompatibility, and high resistance against hygrothermal conditions related to sterilization procedures. Numerous medical products include an adhesive bond that have to reliably withstand these harsh conditions encounte...
Overthelastdecades,growingdemandforutilizinglightweightmaterialsalongwiththenecessityofmanufacturingpartsbeingabletomeetthestrengthrequirementsofrecentstandardsmotivatedresearcherstofocusonaluminumalloys.Amongaluminumalloys,aluminum7075hasbeenextensivelyutilizedinaerospace,automobile,andtransportationapplicationsduetoitsoutstandingspecificstrength,...
Despite the formation of a passive layer, corrosion also occurs in austenitic stainless steels. One of the most common and most dangerous types is pitting corrosion, in which the material beneath the surface is completely dissolved. Since this type of corrosion only produces small holes on the surface, it is difficult to detect without nondestructi...
In the present investigation, thin sheet geometries of commercially pure titanium (cp, grade 4) are butt-welded to AISI 316L stainless steel as well as Nitinol by means of micro electron beam welding using filler materials. In order to avoid mixing of the base materials, the refractory metals tantalum, niobium and hafnium are applied as intermediat...
Ferritic stainless steels are prone to grain coarsening and precipitation of chromium-rich grain boundary phases during fusion welding, which increase intergranular corrosion susceptibility. State-of-the-art techniques to overcome these challenges mainly feature heterogeneous nucleating agents with regard to grain coarsening or alternating alloy co...
In this paper, the potential of directional ultrasonic wave superposition by moving sound gen-erators for laser beam welding of high-strength steel alloys 1.5528 (22MnB5) is studied. Steel sheets of identical thickness and in form of tailored blanks were joined in butt joint configuration. The influences of the various excitation parameters of the...
Over the past 10-15 years, significant progress has been made in the application development of active thermography for the inspection of welded joints of semi-finished metal products. Various research projects have demonstrated the potential for detecting the quality-relevant flaws in these joints. With the simultaneous steady improvement of the s...
Im Rahmen dieser Veröffentlichung wird das Potential der körperschallbasierten Schallemissionsprüfung während des Elektronenstrahlschweißens zur Detektion von Schweißnahtunregelmäßigkeiten vorgestellt. Dazu wurden die Fügepartner aus unterschiedlichen Werkstoffen im Stumpfstoß miteinander verschweißt und die Prozessgeräusche mittels Körperschallsen...
Microstructure design allows to prevent intergranular cracking and premature failure in Co–Ni–Ga shape memory alloys. Favorable grain boundary configurations are established using additive manufacturing techniques, namely, direct energy deposition (DED) and laser powder bed fusion (L‐PBF). L‐PBF allows to establish a columnar grain structure. In th...
The present study provides an overview of previous studies on the welding of the AA7075-T6 aluminum alloy, followed by an investigation of the influence of short-time solution annealing on the mechanical properties of the weld. Conventional laser welding of Al-Zn-alloys leads to a low weld strength, which makes a post weld heat treatment (PWHT) fav...
The intergranular corrosion susceptibility of ferritic stainless-steel weldments is strongly dependent on chromium carbide precipitation phenomena. Hence, stabilization is widely used to mitigate the aforementioned precipitation. In contrast, stabilization has proved ineffective to fully prevent intergranular corrosion due to segregation of unreact...
During the manufacturing process of adhesive bonds different faults can occur, leading to a loss of structural integrity of the entire structure. This requires a thorough study of the connection behaviour in the presence of faults and localisation of such faults. For this purpose, double cantilever beam specimens were manufactured with and without...
Ferritic stainless steels are prone to localized corrosion phenomena such as pitting corrosion or intergranular corrosion, in particular when jointed by fusion welding processes. State-of-the-art techniques to avoid intergranular corrosion mainly consist of alternating alloy concepts or post-weld heat-treatments—all of which are associated with inc...
In the present investigation, laser-induction welding using oscillating beam guidance is employed to joint sheets of nodular grey cast iron, which typically exhibit poor weldability properties. Through non-destructive dye-penetrant testing, a reduction of more than 50 % in crack density as a result of manipulted thermal cycles is identified. The mi...
Development of an online quality assurance method based on acoustic emissions using magnetic pulse welding
Reliable magnetic pulse welding and easy-to-implement process monitoring is essential for the implementation of modern joining processes in the industrial environment. Ideally, the quality of the joint is already predicted during the joining...
Adhesive bonding is considered a special process, for which very high quality standards exist with regard to manufacturing. These include, amongst other, controlled environmental conditions and avoidance of any contamination of adherend’s surfaces, for which reasons it is performed in dedicated shops by staff specially trained for these tasks. Addi...
In the present study, compositionally-graded structures of AISI 316L and CoCrMo alloy are manufactured by powder-based laser-beam directed energy deposition (DED-LB). Through a process-integrated adjustment of powder flow, in situ alloying of the two materials becomes feasible. Thus, a sharp and a smooth transition with a mixture of both alloys can...
This paper presents a computational design strategy and manufacturing technique for a curved steel beam using interlocking connections. Although there have been developments in industrial robotic setups to automate steel beam bending, these processes rely on an iterative approach and are time-consuming and costly when there is a need for high accur...
Additive manufacturing (AM), as resource-efficient fabrication processes, could also be used in the dimensions of the construction industry, as a variety of experimental projects using concrete and steel demonstrate. In timber construction, currently few additive technologies have been developed having the potential to be used in large scale. Curre...
Laser-based Directed Energy Deposition (DED-LB) represents a production method of growing importance for cladding and additive manufacturing through the use of metal powders. Yet, most studies utilize substrate materials with thicknesses of multiple millimeters, for which laser cladding of thin-sheet substrates with thicknesses less than 1 mm have...
Additive manufacturing (AM) enables the cost‐effective production of complex components, many of which are traditionally manufactured using costly subtractive processes. During laser‐based powder bed fusion of metals (PBF‐LB/M), internal pores and rough surfaces are typically inevitable, reducing fatigue and corrosion resistance compared to traditi...
Friction stir welding has become important in many areas of production and is increasingly used for joining aluminum components. For long welding seams, conventional tools with only one welding pin reach their technical limitations due to low gap bridgeability. When welding aluminum, the stirred in surface layers, such as oxides, lead to a decrease...
Laser welding experiments have been carried out using stainless steel specimens (1.4003/1.4005) with different sulphur contents (S1:10ppm, S2:210ppm, S3:2770ppm). A parameter for spatter control, the capillary widening ratio mainly affected by the side-gas jet is considered. This value can be controlled by welding speed, laser power and side-gas pr...
Additive manufacturing (AM) enables the cost-effective production of complex components, many of which are traditionally manufactured using costly production steps among other processes. One widely applied AM process is Laser-based Powder Bed Fusion of Metals (PBF-LB/M); however, internal pores and rough surfaces are typically inevitable with PBF-L...
Welding and joining of components processed by additive manufacturing (AM) to other AM as well as conventionally produced components is of high importance for industry as this allows to combine advantages of either technique and to produce large-scale structures, respectively. One of the key influencing factors with respect to weldability and mecha...
In the present study, Iron-based FeMnAlNi and Cobalt-based CoNiGa shape-memory alloys (SMA) were processed by laser metal deposition for the first time. The materials show susceptibility to cracking upon processing when unheated substrates are employed. Pre-heating of the substrate materials eliminated cracking completely and enabled robust deposit...
In the investigation at hand, sheets of ferritic and pearlitic grey cast iron with spheroidal graphite are welded using a fiber-laser. The influence of varying laser power and welding speed on the macroscopic characteristics of the weld seam and crack formation are analyzed and discussed. Substantial crack formation with crack densities of up to 2....
Additive Fertigung wie z.B. selektives Laserschmelzen (SLM) ermöglicht die kostengünstige Produktion komplexer Bauteile, die mit anderen Verfahren oftmals mehrere aufwendige Fertigungsschritte umfassen. Allerdings können beim SLM Verfahren prozessbedingt Poren und raue Oberflächen entstehen, welche zu einer geringeren Schwingfestigkeit dieser Struk...
Additive manufacturing has gained increasing attention in recent years in numerous industrial sectors due to its inherent characteristics, e.g. tool-free production and unprecedented freedom of design. However, in some applications such as heat exchangers the design has to follow certain restrictions, e.g. to allow for the removal of unfused powder...
The relevance of sustainable structural materials is increasing in automotive components for sustainable construction. The sustainable material wood in particular can be used due to the very good specific mechanical material properties and has a high potential to be used as a structural material in hybrid constructions for the automotive components...
Adhesive bonding is a joining technique that enjoys increasing popularity in industry, including timber engineering. However, two major shortcomings still delay their widespread use, in particular on-site: long process times, and temperature requirements for curing. Accelerated curing is seen as one way to overcome both. In this paper, resistive he...
Nitinol is a shape memory and superelastic alloy, respectively, and stainless steels are widely used materials in medical engineering, e.g., for implants and medical instruments. However, due to its high price and poor machinability, there is a high demand for dissimilar welding of nitinol components to stainless steel. During welding of titanium-c...
Glued-in rods (GiR) are a successful class of structura bonded joints
for timber engineering applications. However, they suffer from two
limitations: relatively slow curing processes, and requirements
related to minimum temperatures for the bonding process. Both,
to some extent, limit their wider application, in particular on site.
Inductive heatin...
In recent years surface texturing of the cutting tools has proved to improve tribological characteristics at tool/chip and tool/ workpiece interface and help to reduce cutting and feed forces as well as tool wear. Most, if not all, of the studies have focused on subtractively made textures whereby the material is removed from the surface. This stud...
Collision welding is a high-speed joining technology based on the plastic deformation of at least one of the joining partners. During the process, several phenomena like the formation of a so-called jet and a cloud of particles occur and enable bond formation. However, the interaction of these phenomena and how they are influenced by the amount of...
Spattering is a quality issue within deep penetration laser welding processes resulting in time-consuming and cost-intensive post-processing. In this study, the formation of unconventional weld shapes, e.g. with bulge formation was observed in a lap-joint, while using a side-gas jet to enlargen the capillary opening. During quasi-stationary conditi...
Collision welding processes are accompanied by the ejection of a metal jet, a cloud of particles (CoP), or both phenomena, respectively. The purpose of this study is to investigate the formation, the characteristics as well as the influence of the CoP on weld formation. Impact welding experiments on three different setups in normal ambient atmosphe...
Eingeklebte Gewindestangen sind ein aus dem Holzbau nicht mehr wegzudenkender Anschlusstyp. Aktuell werden hierzu 2K‐Epoxide (EPX) und Polyurethane (PUR) verwendet. Diese haben jedoch zwei wesentliche Nachteile: Der Prozess der Aushärtung erstreckt sich, je nach Klebstoffsystem, über mehrere h bis hin zu 10 d. Zum anderen benötigen die zugelassenen...
In the present investigation, thin sheets of stabilized and unstabilized ferritic stainless steel were welded in butt joint configuration using irradiation of a 1070 nm fiber-laser. Using optical microscopy, the microstructural evolution upon alternating heat input was characterized. In addition to that, hardness and tensile tests were carried out...
Interesting effects on the microstructural evolution and dynamic tensile deformation behavior of aluminum alloys AA6082 and AA7075 are revealed by investigating the influence of cooling rates within a novel thermo‐mechanical process. Dynamic tensile tests at strain rates of 40 to 400 s−1 coupled with digital image correlation show an increase in yi...