Search

The amount of aluminium sheets in future body-in-white concepts is still on the rise. There is a need for optimizing the joining techniques, caused by the different characteristics compared to the established steel components. Especially the electrode life for resistance spot welding as a reliable and established process needs to be improved. One reason for the short electrode life when welding aluminium is the insulating effect of the aluminium oxide layer. One possibility to reduce the electrode wear is the mechanical destruction of the oxide layer before the welding. This paper describes the influence of a translational and rotational electrode movement on the electrode wear. The oxide layer destruction is detected by resistance measurement. It could be shown that the destruction of the oxide layer already occurs at low movements. However, a homogeneous, large-area destruction is necessary for a wear reduction.

Laser fusion cutting commonly applies a high-pressurized nitrogen gas jet to blow the molten material out of the cut kerf. However, theoretical considerations suggest that the use of a plasma jet may offer some advantages over this conventional approach. In this preliminary investigation, the characteristics of a non-transferred plasma jet for the application as auxiliary gas in laser beam cutting are analyzed using numerical CFD simulation. Based on this study, a first prototype of a plasma jet generator was manufactured and used in initial cutting experiments on 6 mm thick AISI 304 stainless steel. Two different cooling concepts for the plasma torch were considered and investigated in practice. Suitable values for the nozzle exit diameter, the distance between the electrodes of the plasma torch, the auxiliary gas flow rate and the electric current were identified both model-based and experimentally. The achieved cutting performance is considered a proof-of-principle of the suggested approach of a plasma-assisted laser beam cutting process.

The work carried out is based on the thesis properties of clinched joints are determined by the proportions of binding mechanisms form-closure, force-closure and material-closure. To describe the acting binding mechanisms and thus to derive the joint properties, detailed knowledge of the local effect of the individual binding mechanisms is necessary to ensure their targeted adjustment by the joining process. The targeted setting of different proportions of the binding mechanisms is achieved firstly via tool geometry and secondly via surface condition of the joined parts. An introduced form-closure component can be quantified by metallographic cross section with subsequent measurement of the quality-determining parameters such as undercut, penetration depth and neck thickness. To qualify the force-closure component, a torsional load can be applied mechanically at rotationally symmetrical clinch joints. This also allows the influence of different surface conditions on the tribological system to be quantified. Measurement of electrical resistance can reveal the binding mechanisms of force- and material-closure. These investigations are carried out on an aluminum joining part combination of the same type. As a result of these investigations, the clinched joints can be designed according to the load occurring in the later life cycle in the form of an optimum and compromise variant with regard to minimum loads to be transmitted mechanically, electrically with regard to low resistance or manufacturing with minimum energy input.

Capacitor discharge welding is an efficient, cost-effective and stable process. It is mostly used for projection welding. Real-time monitoring is desired to ensure quality. Until this point, measured process quantities were evaluated through expert systems. This method is strongly restricted to specific welding tasks and needs deep understanding of the process. Another possibility is quality prediction based on process data with machine learning. This requires classified welding experiments to achieve a high prediction probability. In industrial manufacturing, it is rarely possible to generate big sets classified data. Therefore, semi-supervised learning is investigated to enable model development on small data sets. Supervised learning models on large amounts of data are used as a comparison to the semi-supervised models. A total of 389 classified weld tests were performed. With semi-supervised learning methods, the amount of training data necessary was reduced to 31 classified data sets.

The use of clinch joints, e.g. vehicle structures, is determined by the reliability of the joint and its strength properties - in particular the fatigue strength. Clinch connections offer the advantage over form-closure and force-closure processes that they can also be used for hybrid material combinations. In order to be able to evaluate the influence of the geometry parameters such as e.g. undercut, neck thickness or also base thickness on the fatigue behavior, three clinch connections (in optimum and compromise design) with different tool parameters were designed and examined using the example of a joining task with aluminum sheet material. For this purpose, fatigue curves (F-N curves) in the range of high to very high numbers of load cycles (N = 105 to 107) were determined. In this load cycle range, a so-called "neck fracture" is mainly to be expected as the type of failure, whereas for quasi-static tests, a “buckling” is more likely to occur. The tests were carried out on single-cut overlapping shear tensile specimens. Metallographic and scanning electron microscopic examinations of the joints and the fracture surfaces served to identify the crack initiation site and to clarify the respective type of failure. Significant differences in the damage behaviour of the three clinching variants could be shown. This observation enables one step into the direction of fully understanding the relationship along the causal chain "joint requirements - joining process - fatigue strength". Thus the adaptability of the clinching process can be improved.

In this publication, the different metal transfer modes of a hot-wire GTAW process with indirect resistive preheating of the wire are presented. The hot-wire GTAW process is characterized by an additional preheating unit that is used to heat the wire before it reaches the melt pool. Thus, to preheat the wire, the contact between the melt pool and the wire is not necessary. In order to examine the metal transfer of the wire, deposition welds are analysed using a high-speed camera with a laser light source as well as a data acquisition unit. The presented results comprise the impact analysis of the GTAW current, the hot-wire current, the wire feeding rate, the wire feeding angle as well as the wire feeding direction. The observed metal transfer modes can be characterized as either a constant melting bridge (cmb) between the wire and the melt pool or a recurring melting bridge (rmb). The analysis also reveals that the influence of the process parameters and thus the metal transfer mode on the bead properties is only marginal.

Mixed joints made of aluminium and copper are increasingly important in industrial applications. This type of mixed joint is of interest, e.g. when good electrical and thermal properties, as in power electronics cooling, are required. The joining requirements consist of the formation a metallurgical bond and planar joint between aluminium alloys and copper. The fluxfree vacuum brazing process is considered one appropriate joining technology. When using standard filler metals, formation of brittle phases and erosion of the aluminium base metal occur due to increased copper diffusion at high brazing temperatures. Based on these findings and an energetic consideration of the brazing process, an AlCuSi filler metal with a reduced liquidus temperature has been developed. In fundamental studies the wetting and brazing behaviour of this newly developed filler metal has been investigated. The filler metal is used as a foil and preapplied as a thermally sprayed coating on an EN AW-3003 aluminium base sheet. The formation and the structure of the braze metal as well as observations focused on the interaction between the components involved are discussed.

Gas metal arc welding (GMAW) processes are used in a wide range of applications due to their high productivity and flexibility. Nevertheless, the supplied melting wire electrode leads to a coupling of material and heat input. Therefore, an increase of the melting rate correlates with an increase of the heat input by the arc at the same time. A possibility to separate material and heat input is to use an additional wire, which reduces penetration and worsens the wetting behaviour. Consequently, bead irregularities such as bonding defects or insufficient root weldings can occur. In the context of this article, a controlling system for a two-dimensional magnetic arc deflection is presented, which allows to influence arc position as well as material transfer. The analysed GMAW hot wire process is characterised by high melting rates while also realising a sufficient penetration depth and wetting behaviour.

The presented work deals with the development of a novel TIG hot-wire process for the additive manufacturing of metallic components, which, in contrast to previous arc processes, enables a significant increase in melting performance with simultaneously reduced heat input. This is achieved by means of an upstream resistance heating of the wire between two contact points within the hot wire feeding system. The torch, hot wire feeder and gas nozzle are designed in such a way that a constant bead geometry can be guaranteed regardless of the machining direction. On the one hand, this can improve the dimensional accuracy; on the other hand, an increase in productivity is achieved through a significant reduction of process times. Essential parts of the work include the simulation-supported development of the processing system, the design and implementation of an innovative process control system and the testing of the new technology.

The multi-material design and the adaptability of a modern process chain require joining connections with specifically adjustable mechanical, thermal, chemical or electrical properties, whereby previous considerations have focused primarily on the mechanical properties. With clinching, the multitude of possible combinations of requirements, materials and component or joint geometry makes it impossible to determine these joint properties empirically. As a result of the established and empirically based procedure, no model exists to date that considers all questions of joinability, i.e. the materials (suitability for joining), the design (joining safety) and the production (joining possibility) and allows a calculation of the achievable properties. It is therefore necessary to describe the physical properties of the joint as a function of the three bonding mechanisms force closure, form closure and material closure in relation to the application. This approach enables the illustration of the relationships along the causal chain "joint requirement - binding mechanism - joining parameters". In this way the adaptability of the mechanical joining technology can be improved. A geometric comparison is made using metallographic cross sections, of clinched joints of the combination of aluminum and steel. The torsional testing of the rotationally symmetric clinching points for detection of the mechanical stress state are qualified as examination method and technological test. By measuring the electrical resistance in the base material, in the clinch joint and during the production cycle (after clinching, before precipitation hardening and after precipitation hardening), this change in the stress state can also be detected.

A new method for the measurement of two-dimensional heat flux profiles for GTAW processes is presented. The method is based on a least squares reconstruction algorithm for the inverse heat transfer problem for a steady-state temperature distribution in a specimen body. The temperature is measured with an experimental setup suited for the heat input of a welding process. The temperature distribution is then used to reconstruct the heat flux distribution on the specimen surface using a heat flux approach function. To calculate the temperature distribution ratio for the current approach heat flux profile, a numerical simulation model of the specimen is embedded in the reconstruction procedure. The residuum between the actual temperature distribution and the test function temperature is reduced using a least squares optimization step until convergence. The method is verified using a numerically calculated temperature distribution which is compared with a predefined heat flux profile. Moreover, the method is compared with a split-anode measurement for one-dimensional and two-dimensional reconstruction approaches. Measurements of a process with an inclined torch as well as a process with a magnetically deflected arc demonstrate the capability of the new method for the measurement of two-dimensionally resolved heat flux distributions of GTAW processes.

Capacitor discharge welding primarily applies to projection welding. Components with ring projections up to 200 mm diameter can be welded with peak currents up to 1000 kA and welding times less than 10 ms. Weld nuggets are expected to occur, as the CD-Welding belongs to resistance welding. Although the required strength is given, welding nuggets in cross-sections cannot invariably be verified. According to recent researches, joining occurs without a welding nugget, but with metal vaporisation and linked activation of the surfaces. This process is called short-time welding with high thermal current density. The type of the welded joint depends on the heating properties in the weld zone. Different welding energies, electrode forces and welding times result in different welded joints. The process-specific advantages can be taken, and new application areas for CD welding can be developed by knowing the cause-and-effect relationships.

Resistance spot welding is used as a high-productivity joining process for the increasing use of lightweight materials in industrial applications. The main challenge for the welding of aluminum alloys is the wear of the electrodes. Due to the natural oxide layers on the metal surface, high contact resistances exist between the sheet metal and the electrode. This results in increased heat generation at this interface, which leads to increased alloyage on the electrode. Breaking the insulating natural oxide layers can be achieved by a friction-free or friction-assisted motion overlay and leads to a reduced electrode wear. The complex physical correlations involved are currently being investigated in a basic research project at TU Dresden. In addition to welding tests on a test rig, simulation-based analyses are also carried out. These allow a physic-based modeling of the effects and can be used later on for an extrapolation of any resistance welding process with motion overlay. In this paper, first experimental and analytical considerations for the mechanical destruction of the oxide layer of aluminum are discussed. Subsequently, the developed extended simulation model is presented and compared according to the quality of simulation of the welding process with motion overlay. The simulation method used is a multiphysics FEM simulation with ANSYS.

With the tightened emission limits the amount of aluminum sheets in future body-in-white concepts is on the rise. Thus, there is a need for optimizing the joining techniques to fulfill the upcoming challenges linked to high volume production. Especially the electrode life for resistance spot welding as a reliable and established process needs to improve. In order to do so the effect of electrode geometries on the electrode life is investigated. It is shown that the radius of curvature, the size of the face diameter, and the cone angle influences the electrode life. The reason for this behavior is explained by a numerical simulation developed by the TU Dresden. Based on these findings, an analysis with the purpose of investigating an improved electrode geometry is conducted. It is shown that a domed electrode with a radius of curvature of 150 mm should be used. This electrode combines the ability to crack the oxide layer effectively while ensuring a sufficient area of contact between electrode and sheet.

Electrodes for resistance spot welding inevitably wear out. In order to extend their service life, the tip-dressing process restores their original geometry. So far, however, the point in time for tip-dressing is mainly based on experience and not on process data. Therefore, this study aims to evaluate the in-situ or inline wear during the welding process without using additional sensors, and to base the timing for tip-dressing on continuous process monitoring, extending electrode life even further. Under laboratory conditions, electrode wear is analyzed by topographical measurements deepening the knowledge of the known main wear modes of resistance-spot-welding electrodes, mushrooming and plateau forming, and characterizing an electrode length delta over the number of spot welds. In general, electrode wear results in deformation of the electrode contact area, which influences process parameters and thereby weld quality. The conducted tests show correlation between this deformed contact area and the electrode length delta. The study shows that this electrode length delta is visible in actual process data, and can therefore be used as a criterion to characterize the wear of electrodes. Furthermore, this study gives reason to question commonly used spot-welding quality criteria and suggests different approaches, such as basing spot-welding quality on the possibility of nondestructive testing.

Nondestructive testing (NDT) of spot welds still poses a great challenge for industrial mass production like automotive body manufacturing or rail vehicle constructions. In these productio...

Numerical investigations on the thermal efficiency in laser-assisted plasma arc welding (LAPAW) have been carried out by the combination of a magneto-hydrodynamic (MHD) arc model and a smoothed-particle-hydrodynamics (SPH) model of the weld pool. The comparison of the calculated weld seam cross-sections gained from numerical simulation as well as experimental examinations shows a good agreement. By the use of the weld pool model, the sensitivity of different influencing variables was investigated. The analysis clearly reveals the major influence of the central heat flux density on the penetration profile and on the thermal efficiency of the process. The higher the heat flux of the laser beam and the higher the constriction of the heat flux profile of the arc, the higher the thermal efficiency of the process.

In this paper, we present a numerical model for the calculation of weld pool dynamics and the resulting weld seam structure with regard to the arc forces. The model uses an incompressible smoothed particle hydrodynamics method and is suitable for three-dimensional calculations with a high spatial resolution at low computational costs. The model is applied to a GTAW process, where the arc forces as well as the arc heat input is modelled on the basis of known values from measurement and literature. The validity of the model is shown for different arc currents by comparison of the calculated penetration profile with measurements. Finally, the model is used to perform parameter studies on the influence of the arc pressure and the arc shear on the penetration profile. The parameter studies show the strong influences of the arc forces on the penetration depth.

The shortage of resources takes their toll in product development. This means for the drive engineering that the power density has to increase and the manufacturing costs have to decrease. So, the parts and assemblies have to become smaller, while the performance should rise. Following this trend, the joining technologies cannot stand still. At the drive engineering, the elementary press fit (PF) for shaft-hub joints (SHJ) is well known. Its manufacturing is easy and cheap. As a disadvantage, the joint strength is limited due to the coefficient of friction and the maximum possible allowance for interference. Through the combination of an elementary PF with local firmly bonded pressure-soldered joints (PSJ), it is possible to increase the joint strength up to three times of elementary PF by keeping his advantages. For the so-called press fit/pressure-soldered joint (PF/PSJ), it is essential to coat one or both joint areas with a low-melting metal (solder). The main connection is the press fit based on a joint pressure at the joint area. This pressure can be used to generate PSJs (secondary connection). On one hand, the joining area is activated by cracking the oxide layers and on the other hand the inner and outer parts being approached at the distance of influence of atomic forces. The attributes of PF/PSJ are explained with the development of local PSJ at the micro contacts. If the connection will be overloaded (mechanical training), the relative movement causes deformations at the roughness peaks and effects frictional heat. This enhances the size and number of PSJs and increases the joint strength significantly. Another way to increase the transmittable torque is thermal training. With increasing temperature and time, while heating up the shaft-hub joint, the total area of PSJs grows up and a higher torque can be transmitted. The value of contact pressure is just as crucial for the development of PSJs as the temperature, the joining procedure, and the training process.

To date, several numerical models predicting the properties of TIG-arcs are available. Recently, effort has been put into testing the reliability of these models for varying process parameters by means of comparing plasma temperatures and arc voltages against measured data. However, from an engineering point of view, the goal of these models is to predict the properties of weld beads. Therefore, the heat input into and the pressure applied onto the workpiece have to be predicted. This paper deals with the comparison of measured arc pressure data and the results of an approach which couples a simplified cathode sheath model with an LTE arc model.

Laser-based joining is a potential key manufacturing process for realizing metal plastic hybrids. Therefore, surface preparation is essential to achieve a mechanical form fit. A new approach for surface preparation is based on a tungsten inert gas (TIG) arc process with anodic polarity. This TIG structure was characterized compared to fiber laser manufactured structures in cw and pw mode. The comparison of different preparations was based on pure ultimate tensile strength tests on spot joints. Finally, a transfer to overlap joints was successfully carried out and characterized by tensile shear tests using fiber reinforced plastics.

Within the framework of the bilateral CORNET projects MeTexCom and MeTexCom2, new approaches were developed and tested to improve the adhesion strength of metal textile composites, with a focus on the targeted roughening of aluminum surfaces and the development of new acoustically insulating nonwovens. The metal textile composites were produced by melting thermoplastic components of the textile composites without a separately applied adhesive.For improved adhesion strength between metal and textile, roughness was generated on the metal surface by means of a novel arc treatment by an anodic polarized TIG process or a cw (continuous wave) fiber laser process. On the one hand, the goal was to produce uniformly rough, untercut surface structures in micro-and nanodimension by means of a highly dynamic arcing process. On the other hand, a similar approach was pursued with the cw laser method by using a single-mode as well as a multi-mode laser.

Gas metal arc welding (GMAW) processes are characterized by a high number of simultaneously running physical processes. The process capability is mainly determined by the properties of a metal vapour influenced arc and the material transfer. In recent years, experimental as well as numerical methods are being used increasingly in order to understand the complex interactions between the arc and material transfer. In this paper, we discuss the influence of metal vapour on GMAW processes in spray as well as pulsed material transfer mode. With respect to the high complexity of the process, experimental and numerical methods are combined in a targeted manner in order to obtain a high level of expressive capability with moderate numerical and experimental effort. The results illustrate the high influence of the changing vaporization rate not only on the arc properties but on the arc attachment at the filler wire. It could be shown, that in many cases the metal vapour concentration in the arc region has a greater influence on the arc properties and the material transfer than different shielding gas components like oxygen, hydrogen or helium.

Resistance spot welding is the dominant process in the present mass production of steel constructions without sealing requirements with single sheet thicknesses up to 3 mm. Two of the main applications of resistance spot welding are the automobile and the railway vehicle manufacturing industry. The majority of these connections has safety-related character and therefore they must not fall below a certain weld diameter. Since resistance spot welding has been established, this weld diameter has been usually used as the gold standard. Despite intensive efforts, there has not been found yet a reliable method to detect this connection quality non-destructively. Considerable amounts of money and steel sheets are wasted on making sure that the process does not result in faulty joints. The indication of the weld diameter by in-process monitoring in a reliable way would allow the quality documentation of joints during the welding process and additionally lead through demand-actuated milling cycles to a substantial decrease of electrode consumption. An annual, estimated reduction in the seven- to nine-figure range could be achieved. It has an important impact, because the economics of the process is essentially characterized by the electrode caps (Klages 24). We propose a simple and straightforward approach using data mining techniques to accurately predict the weld diameter from recorded data during the welding process. In this paper, we describe the methods used during data preprocessing and segmentation, feature extraction and selection, and model creation and validation. We achieve promising results during an analysis of more than 3000 classified welds using a model tree as a predictor with a success rate of 93 %. In the future, we hope to validate our model with unseen welding data and implement it in a real world application.

In this paper, the suitability of different constructional concepts of gas trailing shields concerning the reduction of heat-tints is discussed. The evaluation of these concepts as well as the description of the main contamination mechanisms of gas trailing shields with atmospheric gases are performed for tungsten inert gas welding of stainless steel by a purposeful coupling of experimental as well as numerical methods. Furthermore, advantages and disadvantages of these design concepts are investigated regarding their constructional complexity, robustness against varying process parameters, and its feasible working distances. Finally, a modular concept is presented which allows the usage of the same constructional concept for a variety of different welding tasks.

The process capability of gas metal arc welding (GMAW) processes is mainly determined by the arc properties and the material transfer. In recent years, numerical methods are being used increasingly in order to understand the complex interactions between the arc and material transfer in gas metal arc welding. In this paper, we summarize a procedure to describe the interaction between an arc and a melting and vaporizing electrode. Thereafter, the presented numerical model is used to investigate the arc properties and the metal transfer for a pulsed GMAW process of mild steel in argon. The results of the numerical simulation are compared with OES measurements as well as high-speed images at different times in the pulse cycle and show excellent agreement. The results illustrate the high influence of the changing vaporization rate on the arc attachment at the wire electrode in the high current phase. It could be shown that a substantial part of the current does not participate in the constriction of the wire electrode via the resulting lorentz force which explains the nearly spatter-free droplet detachment in pulsed GMAW processes of mild steel in argon shielding gas.

Tandem gas metal arc welding (GMAW) has been developed in order to increase the productivity of the GMAW process and enables rapid joint completion. However, the very small distance between the two arcs and the superposed magnetic fields causes arc interactions and weld pool instabilities, which reduces the process capability. In this article, an advanced tandem GMA welding process is presented, in which a separation of the two arcs is achieved by a centrally fed filler wire. In high-speed recordings and numerical calculations, the arc stabilizing effect by the filler wire is investigated. The geometric boundary of the filler wire separates the arc streams in the flow area and forms a barrier in the weld pool to reduce unfavorable weld pool oscillation. Furthermore, the arc deflection can be influenced via a hot-wire technique and a positive effect is obtained when the hot-wire polarity is opposed to the arc wires. In addition, the deposition rate can also be increased by the resistive preheating of the filler wire. As a result, the process capability and the productivity of the tandem GMAW process are increased significantly. However, it was shown that even with the more stable advanced tandem GMAW process, sufficient shielding gas coverage can only be achieved within a common shielding gas nozzle used in conventional tandem GMAW processes.

Applications of structural concrete require use of reinforcement in one form or another. The known reinforcement concepts in additive concrete construction typically rely on conventional reinforcement approaches, which provide a solid basis for structural design, since existing guidelines and codes can be used. However, the use of conventional steel reinforcement poses serious limitations to the digitalization and automation of fabrication techniques. The article at hand presents two alternative approaches of reinforcing 3D-printed concrete structures: (1) additive manufacturing of steel reinforcement elements, (2) use of high-performance microfiber to achieve strain-hardening behavior of printed concrete. For both approaches materials and manufacturing techniques are briefly described followed by the results of mechanical testing and complimentary microscopic investigations. The printed steel bars showed similar mechanical performance in comparison to ordinary steel bars of the same cross-section area and comparable bond behavior to concrete too, as observed in pull-out experiments. The addition of 1% to 1.5% high-density polyethylene microfiber to fine-grained matrix enabled for printable strain-hardening cement-based composites (SHCC) with a tensile strain capacity of up to 3.2%.

To date, several numerical models representing the tungsten inert gas (TIG) arc are available. However, little has been done on testing the reliability of these models for parameter values differing from the ones used in the respective papers. This paper deals with the comparison of measured arc welding data provided by E. Siewert from Linde AG and the results of the two most common arc and cathode sheath models. These models make different degrees of simplification of the actual processes in the arc, especially the cathode sheath. Different shapes of the electrodes, different welding currents and shielding gases are taken into account as well as the resolution of the numerical grid on which the calculations are carried out. The findings of this paper are used to show when a simplified approach still leads to valid results and when more sophisticated models have to be used.

The high potential of Friction Stir Welding (FSW) is already widely used in industrial applications. In combination with a suitable machine concept, this technology is appropriate for small components and can be extended to applications on structures of several meters in length. Using a 3D-capable system that is stiff enough to handle the high process forces, machining and friction stir welding of complex geometries can be carried out directly in one set-up. In order to ensure reproducible, high quality welds, appropriate control strategies are needed. Furthermore the use of various tool types such as standard or bobbin tools can extend the range of weldable geometries tremendously. The aforementioned aspects have been part of process development work for FSW at Fraunhofer IWS Dresden in the last few years. Within the current paper interesting findings are discussed in detail. This includes the realization of a fully 3D-capable FSW machine based on a so-called Pentapod concept. This parallel-kinematic system is suitable for large and complex three-dimensional structures up to 7 meters in length. The FSW research is focused on the welding of aircraft structures and mixed-material joints; examples of research projects and their results are given. Selected welding examples of wrought and cast aluminum, high strength alloys and copper will be presented as well as experiences, which have been made in terms of process development and process control.

Slip-resistant connections are preferred for steel constructions if subjected to fatigue loads and/or load reversals, no slip in the connection is permitted and joining on construction site is necessary. These connections are pre-pared with a high manufacturing effort due to the intensive preparation of the faying surfaces, or the contact area between the steel plies and it must receive special consideration in design and coating application. The typical corrosion protection for steel structures is still the hot-dip galvanizing. The follow-up work of the faying surfaces for a use in slip-resistant connections is related to a high effort and guarantees no high slip factors. Furthermore the slip factor may deviate more or less high with the properties of the zinc layer. Against this background, investigations have been carried out in a recently concluded research project which show an increase in the load bearing capacity of slip-resistant connections by the combined use of adhesive. In the case of the process combination, which is also referred and named as a preloaded hybrid connection, the applied preload of the highstrength bolts is responsible for the considerable increase in load bearing capacity compared to the elementary joining processes adhesive bonding or just slip-resistant connections. If the two methods are carefully combined, the individual load bearing -capacities can approximately add up.

TIG narrow gap welding is one of the most important methods for joining thick components. Using narrow gap welding, steel plates with a gap, being only a few millimeters wide but several centimeters deep can be joined. Today’s developments are aimed at increasing the process reliability as well as the filling speed. Basic requirements are a sophisticated process understanding — especially concerning the arc attachment and the resulting energy input in the workpiece. Furthermore, the quality of the shielding gas coverage is one of the main important aspects for arc stabilization and the final welding result. In this article, new experimental and numerical methods for the determination of the energy input into the workpiece and the shielding gas coverage are presented. Measurements of electrical current and heat flow distribution as well as oxygen concentration at the workpiece surface are used to validate the numerical model. With the help of the validated model, physical effects can be considered separately, which allows a better investigation of narrow gap welding. The numerical model is also capable of visualizing high-speed processes, such as the transient gas flow and shielding gas coverage.

This paper focuses on the description of damage propagation around rivets in multiple joined single lap carbon fiber reinforced plastics (CFRP)-steel structures due to loads as a consequence of different coefficients of thermal expansion. Materials and rivets were chosen according to automotive body shop applications. Specimens were evaluated non-destructively in ultrasonic C-scans to characterize damage behavior of blind and self-piercing rivets in CFRP-steel-connections before and after the application of thermal loads. An algorithm for an automated detection of damage size on ultrasonic C-scan images was developed as the basis for further damage classification. The results show that blind riveting (BR) causes crack-like initial damage that broadens to roundish plane defects due to heating. Initial extensive damage due to self-piercing riveting (SPR) propagates in elliptic shape. Additionally, tension tests revealed a loss in ultimate load by 10–15 % induced by thermal loads and associated with damage propagation. A correlation between initial damage, relative displacement, and thermal loads was observed.

The conventional clinching of steels is currently limited to tensile strength less than 800 N/mm2 and to elongation at fracture more than 14 %. To realise the clinching of high-strength steels, the sheet can be heated locally at the joint, to improve ductility. Thereby the material characteristics outside the joint should be maintained. This could be achieved by means of short-time laser heating. The short-time tempering behaviour of press hardened steel 22MnB5 has been analysed. The mechanical properties during a short-time heat treatment were investigated by thermo-mechanical analysis in a deformation dilatometer. Thereby laser-assisted clinching shall be established and an efficient form-closed and force-closed connection shall be produced. As a result, the press hardened steel 22MnB5 could be clinched by laser assistance for the very first time.

In order to industrialize friction stir welding (FSW) processes, not only the machine concept itself needs to be evaluated, but also the robustness of the process application being carried out on the machine. Especially for FSW of medium-sized and larger parts, a small degree of misalignment can have an increasing influence on the weld quality. Therefore an exemplary tolerance study for friction stir welded butt joints was conducted. The intentional introduction of gaps between the sheets to be welded can limit the welding process and thus the weld quality. However, for the considered experimental set-up it can be shown that the introduction of a well-defined gap can support the welding process and weld quality. The experimental procedure was carried out on a parallel kinematic machine - a so-called Pentapod. This machine is suitable for large and complex three-dimensional structures. Although the machine is able to record the process forces (Fx, Fy and Fz) acting on the tool–work piece interface, the forces acting perpendicular to the clamping system are still unknown. Therefore additional load cells were integrated into the clamping system to measure the in-process reaction forces. The combined results of the force measurements give a nearly complete overview of the internal loads during the process. In conjunction with knowledge about gaps and misalignment, the data gained in this study can help to understand and predict the clamping behaviour, and thus design rules for future clamping systems can be derived.

Clinching of high strength steels is currently difficult due to their relative low ductility. Hence a new method has been developed to clinch these steel grades. This could be achieved by heating the sheets locally at the joint by a laser during the clinching process. The short-time tempering behaviour of the press hardened steel 22MnB5 has been investigated by dilatometry respectively calorimetry experiments. Different stages of the tempering process have been identified depending on heating rates up to 1000 K s−1. Characteristic tempering reactions were shifted to higher temperatures with increasing heating rate. Based on these results, suitable short-time heat treatment parameters have been selected and transferred to the clinching process. Thereby the press hardened steel 22MnB5 has been successfully clinched with laser assistance for the very first time. The laser assisted clinched joint has been characterised by metallographic analysis and hardness testing. It could be shown, that in the cli...