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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.

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.

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.

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.

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.

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.

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.

The plasma–metal inert gas (MIG) process is characterized by a variety of process parameters. Numerical simulation can be used to investigate the influence of these process parameters and thus helps to improve the properties of the weld. In this paper we discuss a procedure to describe the plasma–MIG process by coupling numerical models of the arc and the droplet detachment with a three-dimensional model for the plasma–MIG weld pool. Using the magnetohydrodynamic (MHD) arc model, the effects of process parameters on the arc pressure profile and the energy input profile on the workpiece can be analyzed. The volume-of-fluid (VoF)–MHD model of the droplet detachment describes the properties of the resulting droplet in terms of its size, temperature and speed. In the three-dimensional VoF model of the weld pool, the influences of the arc and the droplet are simplified by source terms in the mass, momentum and energy equations. Due to these simplifications in the physical complexity, the process and the seam shape can be described with reasonable computational effort.

In this paper, the results for keyhole welding of stainless steel 1.4301 and mild steel 1.0117 with a cathode focussed gas tungsten arc process are presented. These tests were carried out in preparation for welding the root faces of Y- or double V-groove weld preparations of thick metal plates. Welded plate thicknesses range from 6 to 10 mm for stainless steels and 6 to 12 mm for mild steels. Welding speeds are in the range of 20 to 115 cm/min at currents from 400 to 800 A. Especially for stainless steel, a big range of applicable and stable process parameters could be found. The process also works fine for mild steel even though the achievable parameter range is smaller.

Aluminium is a widely used material in industrial processes due to its good material properties, e.g. minor density in combination with a high strength, good corrosion resistance as well as good thermal and electrical conductivity. For its application, a material joining is often necessary. In contrast to other well-brazeable materials, e.g. copper, aluminium has a significant disadvantage: its natural oxide layer at the surface. Due to this layer, there is always an additional surface activation necessary for welding and brazing, e.g. the effect of an arc, flux or vacuum. These methods are efficient, if the natural oxide layer corresponds to the standard thickness and composition. However, the properties of the natural oxide layer can vary due to a raised humidity in the ambient atmosphere or increased temperatures. This paper describes the constitution of the natural oxide layer and gives an overview about methods for analysing these only nanometer-thick layers. Additionally, a method is introduced for aluminium brazing in a shielding gas furnace without using flux. The mechanisms for this surface activation method are characterised. This method is used afterwards to analyse the correlation between the aluminium surface composition and the brazeability.

Plasma arc welding (PAW) is a modern welding technique for challenging joining tasks in a wide range of materials and plate thicknesses, A further improvement of the welding characteristics involving achievable welding speed, process stability and penetration depth is expected by an additional low energy laser beam with a maximum output power of 600 W, The paper presents an experimental and numerical analysis of the interaction between a plasma arc and a superimposed laser beam, The experiments are carried out with a non-concentric set-up of the plasma arc column and the laser beam, As results of bead-on-plate welding trials the cross-sectional weld areas were presented in order to demonstrate benefits of the combined process in comparison to separately conducted arc and laser welding, Fur thermore, high speed video images (1 kHz frame rate) with synchronized current and voltage recording (1 MHz frame rate) were used, The experimental results demonstrate a different behaviour for welding steel and aluminium, In case of welding aluminium, an arc guidance was observed whereas destabilization effects occur for welding ferrous alloys, A numerical magneto hydro dynamical (MHD) arc model with a concentric set-up of arc column and laser beam set-up was aimed to improve our understanding of relevant interaction phenomena between the plasma arc and the laser beam.

This paper presents extensive investigations about the influence of He-additions to argon TIG-arc properties. Results of diagnostic methods, numerical simulations and welding trials are combined to improve the comprehension about the mode of action of gas mixtures. Additionally, selected results of the investigation with H2- and N2-additions are summarized. The investigations show that all gas additions cause an increase of the heat input into the workpiece. However, the stagnation pressure depends on the gas composition: He-additions result in a decrease of the stagnation pressure which depends on the arc length, whereas H2-and N2-additions increase the pressure. By a systematic choice of the gas mixture the weld depth and also the maximum feed speed can be influenced.

GMA welding is one of the most frequently applied welding techniques in industry. Particularly the joining of aluminium, high alloyed steels or titanium requires a cover of shielding gas in order to provide a low PPM concentration of oxygen. The result of the welding process depends essentially on the chemical and thermophysical properties of the process gas used. Consequently, it is necessary to be able to describe and to analyse its flow with respect to various influencing variables. However, it is very difficult to realize this during arc welding processes; a poor access is predominant due to the covered areas inside the welding torch and temperatures of up to 20 000 K cause the strong radiation of the arc and electromagnetic fields. This paper deals with experimental and numerical methods for visualization and quantification of process gas flows in arc welding and gives examples for their technical applications. Unlike previous work, the described methods consider the arc as a dynamic element which determinates the gas flow. Advanced Particle Image Velocimetry (PIV) and Schlieren measurement were used for characterization of the flow field in the direct vicinity of the arc in GTA and GMA welding. Furthermore, a numerical model including magneto-hydrodynamics and turbulence models was used for a detailed visualization of the flow in the free jet and in the hidden interior of the torch. It is based on a commercial CFD code which allows to model complex 3-D geometries of torch and workpiece design. Mixing effects and turbulence model were validated by oxygen measurements in the gas shield.

Current numerical models of gas metal arc welding (GMAW) attempt to combine a magnetohydrodynamic (MHD) model of the arc and a volume-of-fluid (VoF) model of metal transfer. But in these models vaporization of metal is neglected and the arc region is assumed to be composed of pure argon, as it is common practice for models of gas tungsten arc welding (GTAW). These models predict temperatures over 20 000 K and a temperature distribution similar to GTAW arcs. However, recent spectroscopic temperature measurements in GMAW arcs have demonstrated much lower arc temperatures. In contrast to GTAW arcs, they found a central local minimum of the radial temperature distribution. The paper presents a GMAW arc model that considers metal vapour and which is in very good agreement with experimentally observed temperatures. Furthermore, the model is able to predict the local central minimum in the radial temperature and the radial electric current density distributions for the first time. The axially symmetric model of the welding torch, the workpiece, the wire and the arc (fluid domain) implements MHD as well as turbulent mixing and thermal demixing of metal vapour in argon. The mass fraction of iron vapour obtained from the simulation shows an accumulation in the arc core and another accumulation on the fringes of the arc at 2 000 to 5 000 K. The demixing effects lead to very low concentrations of iron between these two regions. Sensitive analyses demonstrate the influence of the transport and radiation properties of metal vapour, the welding current and the evaporation rate.

In modem AC power sources, both balance and current of EP (tungsten electrode positive) and EN (tungsten electrode negative) can be readily adjusted. According to conventional assumptions the surface of aluminium workpieces is cleaned during EP but the tungsten electrode is more heated due to electron work function. During EN the tungsten electrode cools down and the workpiece is melted. Therefore, optimal settings of the power source mostly aim for maximal penetration and minimal electrode wear. This paper presents a study of arc attachments in TIG welding on aluminium. Two different arc attachments to the cathodic workpiece could be attested with only one of them actually cleaning the surface. The first one is a spot mode (highly dynamic) that attaches to the edges of oxide layers and cracks them. The second one is also a spot mode, but it attaches to weld pools. It does not clean the surface but heats the base material intensively. Both arc attachment modes compete against each other. As a result, the cleaning area narrows with wider weld pools due to an increasing attachment to the weld pool during EP. The influences on the arc attachment to the aluminium cathode as well as the contradictions in present literature are discussed. Possible adjustments of the AC balance for optimized processes are proposed.

Plasma Tungsten Arc Welding (PTAW) compared with TIG Welding enables an increased welding speed, a reduced energy input per unit length and butt joint welding of plates without preparation of the welded seam due to keyhole effect. However, because of missed profound understanding of effects in plasma arcs, the indisputable advantages of this process increase demands on education and especially on the experience of developers and operators. In this paper, process parameters, properties of the plasma jet and the molten pool are derived from the numerical modelling of arc and sheath layer under consideration of the process gas properties and the effects of demixing. Basics of the model and the testing site are introduced in this paper. Additionally, influences of current intensity, plasma gas quantity, process gases and their specific properties, torch geometry on plasma jet and energy input into work piece is shown by an exemplary torch. Model and numerical results have been validated by impact pressure measurements at the surface of the work piece and penetration profiles (cross section).

Gas metal arc welding (GMAW) of aluminium, high alloyed steel or titanium requires a shielding gas cover in order to provide preferably low parts per million concentration of oxygen at the joint. Consequently, it is necessary to be able to describe and to analyse the flow of shielding gas. The paper presents numerical and diagnostic investigations concerning the shielding gas flow in gas metal arc welding. Therefore, a numerical model and several diagnostic methods have been developed. The model used is based on ANSYS CFX and includes the effects of magneto hydrodynamic, turbulence and diffusion depending on temperature. The model is verified by Particle Image Velocimetry, Schlieren-technique, and gauging the oxygen concentration. Advantages and disadvantages of these particular methods and the potential of their combined application to analyse welding processes and torch design are shown. The methods introduced were used for the precise analysis of the shielding gas flow and the construction of torches in GMAW. The formation of turbulence by actual concepts of gas distributors and the advantages of optimised and innovative torch constructions are demonstrated. Furthermore the interaction between the process and the shielding gas flow is described and the explicit dependency of the gas cover based on the current profile employed (pulse welding) is visualised. Based on these results, the way in which different gas nozzles influence the shielding gas flow and what happens if the position of the torch or the type of joint changes is explained. In summary, the paper details the profound physical correlations between the construction of the torch and the shielding gas cover as well giving concrete advice for users of the GMAW processes.