Completed projects

Title:
Development of a manufacturing solution for novel coated welding consumables and integration into an existing welding process
Funding: ZIM
Duration: 07/17 – 09/19
Abstract:
As part of the project, PVD coatings on welding wire electrodes and their influence on weld bead properties and processing characteristics during the welding process were investigated. Through a systematic analysis of the influence of single-element coatings with varying film thicknesses, multi-component and multilayer coatings were also developed as the project progressed. As a result, the weld metal achieved an average yield strength of up to 1100 MPa with a notched impact energy of 37 J. Effects on the arc length were documented using a high-speed camera. To achieve scientifically reproducible results, the welding wire electrodes used in the welding tests were coated using a PVD system that meets industrial standards. In addition to developing a wide variety of coating systems, a prototype system for the continuous coating of wire electrodes was developed and built. The speed of the industrial wire drawing process cannot be matched by the coating system; therefore, the idea was pursued to coat the wire as an intermediate product with a larger diameter and then use it to manufacture the final product. Serving niche markets with exceptional requirements for the metallurgy of a welded material is conceivable thanks to the developed continuous wire coating process and the flexibility it offers.

Title:
Hybrid composite forging as a joining process for solid aluminum parts and steel sheets
Funding: DFG
Duration: 04/17 – 08/19

Abstract:
The objective of the proposed research project was to develop a hybrid composite forging process for the steel/aluminum material combination. In an initial process step, a solid aluminum part was to be formed onto a steel sheet, and a material-bonded joint between the two elements was to be created through the forming process. The material-bonded joint was to be achieved using zinc as a brazing material, which is melted during the process and subsequently solidifies again. In a subsequent step, the hybrid component was further formed to analyze the joint’s suitability for further processing. The process was modeled to illustrate the joint quality of the components as a function of the forming process parameters.

At ISAF, the optimal joining parameters for the combination of sheet steel and a solid aluminum part using zinc solder were determined. To this end, a test setup was developed using compression tests in a furnace. During these tests, various process parameters were varied to characterize their influence on the joint. These included temperature, pressure, time, and the surface condition of the materials used. Based on these test results, the adhesion mechanisms and the behavior of the materials were analyzed in order to incorporate the findings into the design of the combined forming and joining process. A joint was produced that exhibited only isolated brittle Fe-Al phases. Strengths of 2.1 kN were achieved.

The second step was the implementation of the determined process range into the forging process, which was carried out by the IPH. This was followed by the determination of a potential parameter range supported by FEM simulations. In particular, the adjustment of the desired process parameters from the model experiments in the joining zone was to be achieved through targeted variation of the forming parameters in the FEM simulations. Following the FEM simulations, test forgings were performed using the forming parameters determined by simulation. To investigate the possibility of further processing the produced hybrid components, they were subjected to a sheet metal forming process while the joint was under load. The results demonstrated, on the one hand, a defined process window within which the production of composite-hybrid components appears feasible, as well as the existence of composite-hybrid forged and sheet-metal-formed workpieces.

In addition to the experiments, the relationships between joint quality and forming parameters were determined. To this end, the manufactured components were examined for their mechanical and metallographic properties both after joining and after sheet metal forming. Based on these results, as well as the analysis of the measurement and simulation data, a comprehensive model was subsequently developed that correlates the input parameters with the quality of the joint.

Title:
Load-resistant arc-welded joints of high-strength thin steel sheets: metallurgical and geometric aspects
Funding: DFG (joint proposal)
Duration: 12/13 – 11/16

Abstract:
According to the current state of research, there is a significant discrepancy between the potential applications and the actual use of arc-brazed joints. This is due to the fact that, at present, our understanding of the failure of arc-brazed thin-sheet joints under static and cyclic loading is not yet sufficient to enable the load-optimized design of the joined components.

This fundamental understanding of the relationships between the geometric design of the brazed joint—particularly at the lap joint—and its local metallurgical composition, as they affect joint properties, is to be developed within the scope of this research project. The locations where an arc-brazed lap joint typically fails are known for both static and cyclic loading. However, the exact local processes and failure mechanisms have so far been inadequately described. The goal of the planned research project is therefore to investigate in detail the key factors influencing static and cyclic joint strength in order to infer the underlying failure mechanisms. This will enable a more reliable assessment of the causes of failure.

The objective of the research project is thus divided into two sub-objectives. Sub-objective 1 is to create a brazed joint characterized by high static strength at the base material level while still maintaining good cyclic strength. Sub-goal 2 is to create a joint that exhibits very good strength under cyclic loading—significantly exceeding the previously achievable 25% of the base material’s allowable load—while still maintaining good static strength. High reliability and reproducibility of the results with low variability are integral requirements for both of the aforementioned sub-goals. This will result in a more reliable and stronger joint with respect to the predominant load.

Title:
VentiWear: customized wear protection systems for lightweight structural design of industrial fans
Funding: ZIM
Duration: 03/13–03/15


Abstract:
Industrial fans are subjected to massive wear and tear during operation, making it necessary to perform regular technical inspections as well as maintenance and repair measures. One way to reduce this wear is to use prefabricated wear plates supplied by specialized subcontractors. However, this conventional solution allows for only a limited number of material variants in high-speed large fans, meaning that certain required properties of the armor are not available. Furthermore, the hard-phase morphology required for erosion wear caused by fine particles cannot be achieved using the coating processes employed to date. Further disadvantages include the fact that the structural materials in the primary lining are often not coated directly, as they are subjected to such severe thermal stress by available conventional coating methods—such as plasma powder deposition welding, open-arc processes, and metal-inert-gas processes—to such an extent that their original mechanical and technological properties are irreversibly lost, and they therefore cannot be included as load-bearing cross-sections in the structural analysis.

As part of the research project, wear-protection systems tailored to the stress conditions and coating processes were therefore developed for the build-up welding of heavily loaded structural components made of high-and ultra-high-strength fine-grained structural steels through modern, controlled (low-energy) welding-based coating processes for lightweight fan assemblies. In addition to a massive increase in service life (> 340%) of the coatings compared to the uncoated base materials, a significant reduction in fan weight—i.e., the weight of the coated individual parts—of > 20% was achieved.

Title:
Development and characterization of an SOFC stack with individually connected cells in parallel “El PaSO”
Funding: AiF/DECHEMA
Duration: 12/2012 – 02/2015

Abstract:
Due to their high efficiency and fuel flexibility, SOFC fuel cells are considered a promising technology for future energy supply in stationary and mobile applications. In addition to high costs, issues related to service life and degradation currently represent a major obstacle to rapid market entry.

Some of the parameters influencing stack degradation are directly related to the standard series connection of the individual cells. This necessitates the use of electrically insulating seals, for which glass solders are typically employed. However, these are usually unable to withstand the demanding operational conditions (temperature range, thermal cycling) over the required service life. Furthermore, the series connection means that a safe operating point is defined by the weakest individual cell. Monitoring all individual cell voltages is not provided for in practical systems due to the high effort involved. As a result, the stack operating point is controlled solely by the total voltage. The operator is thus effectively “blind” to the condition of the individual cells. This creates the risk that the weakest cells will be operated below their threshold voltage and thus continue to degrade. This self-reinforcing mechanism is inherent in series connection as long as no individual cell monitoring is performed.

The stack concept proposed here, with a parallel connection of the individual cells, offers advantages. Since all cells are operated at the same voltage, the operating state of all cells can be determined and monitored through a simple and cost-effective measurement of a single voltage. This allows critical operating conditions to be reliably detected and appropriate countermeasures (e.g., reducing the load current) to be taken at an early stage. At the same time, the individual layers no longer need to be electrically isolated and sealed, so soldering and welding processes using metallic sealing materials can be employed for sealing. The parallel configuration also offers advantages in terms of reliability: while in a series connection the failure of a single cell leads to total failure of the stack (“domino effect”), in a parallel connection only the available power is reduced.

In this project, two different design variants for SOFC high-temperature fuel cells were developed: An all-ceramic design with a cell housing made of 3YSZ, joined using reactive air brazing (RAB), and a metallic housing made of Crofer 22 APU, which was laser-welded.

By taking into account the respective component tolerances, their differing coefficients of thermal expansion, and the chemical aspects of the material pairings used, it was demonstrated that the concept of a parallel-connected double cell—comprising two electrically connected single cells as a repeat unit—is viable and promising. By joining ceramic-ceramic and ceramic-metal pairings using RAB, the glass solders—which are prone to embrittlement—could be replaced. This would also increase the service life of such stacks.

The performance and robustness of the ceramic stack design were confirmed in several test setups and a 1,200-hour long-term test. Analyses conducted after the tests concluded showed that the RAB joint is suitable as a gas-tight connection between metal and ceramic components, but also revealed further potential for improvement in this new stack concept.
 

Title:
Development of welding elements for rotating-arc stud welding to replace welding nuts
Funding: ZIM
Duration: 03/13–02/15

Abstract:
The goal of the collaborative project was the systematic further development of the MARC (Magnetic-Rotating-Arc) welding process—developed by project partner HBS—toward an application for processing weld nuts, comparable to DIN 929 and DIN 934, which are used by the millions in small- and medium-sized industries, for example in control cabinet and enclosure manufacturing. In its previous form, the MARC process already offered numerous advantages and unique selling points in the field of stud welding, but it always had to be tailored to the specific welding element. However, this approach—which relied largely on empirical data—was not sufficient to adapt the process to the range (M6–M12) of non-rotationally symmetric parts for sheet thicknesses of 1–5 mm, as required for successful market positioning, since fundamental knowledge regarding the exact process sequence and the influence of the welding element geometry in the weld zone was lacking. The project aimed to develop this knowledge with the goal of

1. developing welding electrodes with suitable geometries
; 2. further developing the equipment technology and qualifying the welding process

In a program supported by statistical experimental design, electrode geometries and parameter ranges were developed to ensure reliable welding of the nuts in accordance with the requirements; these are made available to users by the consortium partner.

Title:
Development of an NT-PEM-FC with a rotated membrane-plate plane (ProPa-FC)
Funding: ERDF
Duration: 01/13–08/14

Abstract:
The goal is to develop a parallel low-temperature PEM fuel cell (NT-PEM-FC) with vertically arranged membranes and horizontally arranged gas distributor plates in the temperature range of 60°C – 80°C based on a novel multicomponent polymer plate. Using a small stack, the feasibility of the concept and the manufacturing technology will be verified, the operational behavior of the fuel cell will be investigated, and it will be compared with fuel cells that can be considered state-of-the-art. These multicomponent plastics are characterized by their composition of an electrically conductive core and an insulating frame, which enables new designs and improved fuel cells. For this reason, an NT-PEM fuel cell with a conventional design is being developed for comparison, which also utilizes this new multicomponent plastic.

Title:
Investigation of liquid metal embrittlement caused by zinc during the welding of novel high-manganese steels
Funding: DFG
Duration: 01/12 - 12/14

Abstract:
Steel manufacturers are consistently driving the development of innovative materials to meet the metalworking industry’s demands for diverse properties. In this context, high-manganese steels have been developed that are characterized by very high strength and ductility. During the joining of these materials in their surface-treated state, the phenomenon of brazing cracks has been observed, particularly when creating mixed joints in combination with ferritic steels. As part of this project, the factors influencing the formation of brazing cracks during the welding of high-manganese steels will be thoroughly analyzed. Based on these findings, a joining concept for resistance spot welding will be developed to enable the production of joints with reduced brazing cracks.

Title:
Development of coatings for aluminum bipolar plates for high-temperature PEM fuel cells with flow-optimized channel structures
(AlBB)
Funding: ZIM
Duration: 02/12–01/14

Abstract:
The goal of this collaborative project is to make aluminum bipolar plates—which have not been usable to date in the high-temperature PEM sector—suitable for use through the application of appropriate coatings. While the previously used expensive and very brittle graphite composite materials are capable of withstanding the demanding conditions—including high temperatures, phosphoric acid, and high current density—the plan is now to replace them with the more cost-effective aluminum in order to also take advantage of its superior material properties, such as electrical conductivity. The resulting higher efficiency, combined with the use of more cost-effective manufacturing processes, justifies this novel approach.
The goal is to develop a coating material that is, on the one hand, extremely corrosion-resistant and, on the other hand, exhibits low electrical contact resistance. The greatest challenge here is the high coefficient of thermal expansion of aluminum relative to the coatings, which must nevertheless remain completely undamaged. Among other things, the adhesion of the coatings can be improved through design measures, which is why the bipolar plates are being optimized via simulation to address this issue.

Title:
Grain refinement of aluminum casting alloys using powder metallurgy-produced master alloys
Funding: ZIM, Berlin
Duration: 12/2009 – 10/2011

Abstract:
The goal of this joint project is to make AlCu alloys suitable for use in complex components subjected to high thermomechanical stresses by improving their castability through the use of new grain refiners.
As part of the project, a systematic approach will be developed to tailor grain refiners specifically to the respective aluminum alloy systems in order to achieve improved effectiveness. These particles are to be introduced via powder metallurgically produced master alloys, which are manufactured by mechanically alloying the particles with a carrier material and subsequently consolidating the mixture. Upon addition of the master alloy to the aluminum melt, it dissolves, causing the higher-melting particles it contains to disperse in the melt and serve as heterogeneous nuclei for solidifying phases. The effectiveness of the master alloys is expected to be reflected not only in improved castability but also in the mechanical properties.
Alternative manufacturing processes for the grain refiners that have the potential for mass production will also be investigated. Ultimately, a production process chain will be defined that enables efficient and cost-effective manufacturing.
In addition to Clausthal University of Technology, an industrial company is also participating in this research project.

Title:
Nano- and quasi-nanostructured coatings for abrasive and erosive stresses—technology comprising filler material, energy delivery, and the SUNA torch system; coating technology, conduct of tribological tests, and evaluation; determination
of process parameters Funding: ZIM, Berlin
Duration: 12/2009 – 11/2011

Abstract:
According to estimates by the Society for Tribology, wear causes annual damage totaling approximately 35 billion euros in the German economy alone.
If signs of wear are unavoidable due to the nature of the process, appropriate wear-resistant coatings must be designed or applied to the wear-exposed functional surfaces of the relevant plants, machines, and equipment in order to increase economic efficiency.
Nickel- and cobalt-based hard alloys, for example, are available for this purpose; however, they are not competitive with iron-based alloys in terms of the ratio of service life to cost, so the use of iron-based alloys in particular is considered especially promising for cost-effective wear protection.
The main factors influencing the wear behavior of materials—aside from the tribological system causing the wear—include not only the type and arrangement but also the size and distribution of the wear-resistant hard phases within the metal matrix. These properties depend, on the one hand, on the alloy composition and, on the other hand, on coating-process-specific characteristics—such as energy input, solidification cross-section, cooling rate, and mixing of the base material—and can be specifically manipulated using modern alloying and process engineering techniques. Particularly under abrasive-erosive stress caused by fine and ultrafine particles, microstructures with fine grain sizes are crucial for providing wear protection; thus, especially in this application area, nanostructures in iron-based alloys meet the requirements for cost-effective and effective wear protection. Alloy costs can be further reduced through the use of alternative hard-phase formers, while ensuring that the resulting material exhibits a property profile at least equivalent to that of conventional hard phases.
The provision of ready-to-use and tribologically evaluated, innovative, highly wear-resistant (quasi-)nanostructured iron-based hard alloys for thermal spraying and selected cladding welding processes—combined with a novel torch system for PTA processes and an adapted energy delivery system—are the primary objectives of this research project.
This highly practice-oriented research task is of a fundamental nature, as the theoretical foundations currently known regarding microstructure formation in the range of the targeted alloy compositions are still insufficient; consequently, the path to the finished component necessarily involves an extensive experimental phase.
In addition to Clausthal University of Technology, one other university and two industry partners are participating in this research project.
 

Title:
Investigations into the production of partial cladding from Ni-based alloys using the cold metal transfer process (CMT)
Funding: AiF/DECHEMA
Duration: 01/2010 – 12/2011

Abstract:
The objective of this project is to investigate cladding layers produced using the CMT process from the material group of corrosion-resistant nickel-based alloys. The goal is to develop process parameters that enable the reliable and reproducible build-up welding of various nickel-based materials, such as Alloy 59 (2.4607) and Alloy 686 (2.4606) and Alloy 625 (2.4831) as a reference material. Initially, the influence of various process parameters dependent on the filler metal—including variations in shielding gas, layer thickness, and heat input—on bead shape, penetration, mixing, and microstructure will be investigated. By determining mechanical and technical properties, such as bending strength and hardness distribution, the resulting material composites will be thoroughly characterized. Based on the results obtained, the process control will then be optimized for the different materials within defined parameter ranges to produce single-layer coatings with minimal mixing. The influence of these welding process parameters on the corrosion properties of the produced cladding will be investigated.
In addition to established testing methods, which typically involve immersion tests, this research project will modify and further develop electrochemical testing methods for use with welded cladding of nickel-based alloys onto high-alloy steels.
 

Title:
Fabrication, property analysis, and wear behavior of technical surfaces made of microstructured metallic materials and coatings
Funding: DFG/Bonn
Duration: 01/2010 – 12/2011

Abstract:
Wear represents a significant economic burden. For engineering surfaces subjected to severe material removal due to unlubricated abrasive, adhesive, or erosive wear stresses, the adjustment of specific material properties is the only way to minimize wear-induced material removal. The combination of hard and soft microstructural components with a fine-grained microstructure and finely dispersed precipitates, together with defined manufacturing processes and conditions, results in materials and layered structures that are adapted to the wear stresses. This allows material removal to be kept to a minimum.

The proposal encompasses the modification of modern coating technologies for the targeted microstructuring of materials, the qualification of materials and applied layers with regard to their wear resistance, as well as the investigation of light metals to improve the wear resistance of this material group. In addition, the alloys and coating composites are subjected to an analysis of their metallurgical and mechanical-technical properties.

Powder-based thermal coating processes, such as PTA welding and plasma spraying, are used; these processes are particularly notable for their high flexibility regarding powder composition and thermal management. In addition, the process-related advantages of hot isostatic pressing are utilized to develop wear-resistant coatings for extreme loads.

WP 3: welding-based production of wear-resistant coatings with finely dispersed, oriented hard-phase inclusions
The statistical distribution of the hard-phase particles in terms of size, shape, and arrangement has a significant influence on the wear resistance of a wear-resistant coating made of hard alloys. When exposed to granular materials, the distance between hard phases must be smaller than the average diameter of the abrasive particles. In addition to row spacing, an oriented arrangement of elongated hard phases can also improve wear resistance. The creation of these defined microstructural morphologies through targeted manipulation of the temperature-time cycles during the production of the cladding layers via PTA welding is being investigated.

WP 4: model wear studies on different coating systems as a function of manufacturing-related characteristics
Wear is a system parameter that depends on the overall mechanical and physical behavior of all components involved and their mutual interaction, as well as on the prevailing wear mechanism. Using selected model tests, the correlation between microstructure and wear behavior will be investigated both qualitatively and quantitatively. Of particular interest are the expected differences in wear-off behavior between the various model tests, which simulate different wear mechanisms.

Participating partners:

WP 1: Fabrication and properties of novel Fe-based pseudoalloy coatings via hot isostatic pressing
(LWT), RUB Bochum

WP 2: analysis of the fatigue behavior of coated materials with high wear resistance
(IWW, TU Clausthal

) WP 5: Thermal spraying of PTA material systems
, IWW, TU Chemnitz

; WP 6: Plasma anodizing of thermally sprayed aluminum layers to produce wear-resistant surface layers
, IWW, TU Chemnitz

 

Title:
Fabrication and joining of SLM-fabricated components made of cemented carbide
Funding: AiF/DVS
Duration: May 1, 2010 – April 30, 2012

Abstract:
In tool and mold making and mechanical engineering, wear occurs on tools and molds, leading to significant financial losses due to repairs and component downtime. Currently, two main methods are used to counteract this wear. The first option is to apply a wear-resistant coating to the relevant components. Depending on the process used, this can have a negative impact on the base material and result in significant rework. A second option is to manufacture the components entirely from wear-resistant materials. However, this is very costly, as the hard machining required for this is very labor-intensive. A third option, which was examined in greater detail as part of the project, involves manufacturing wear-resistant components from cemented carbide using a generative SLM (Selective Laser Melting) process and then bonding them to cost-effective metallic base bodies. The advantage of SLM technology is the ability to create a functional component via an additive manufacturing process. During the production of SLM components, even slight variations in process parameters can lead to very different properties. For joining laser-fabricated cemented carbide products to one another or to substrates, brazing and high-temperature soldering (e.g., furnace brazing, plasma brazing (Plasmatron)) of these material combinations are considered suitable joining methods. At the conclusion of the research project, a demonstrator component—designed based on the findings and optimized for PbA—will be joined and tested under real-world conditions. The approach pursued by BIAS and ISAF—involving the material-bonded joining of wear-resistant components and easily machinable base bodies—offers not only a technologically innovative approach but also economic potential, particularly for small and medium-sized enterprises (SMEs) that are strongly represented in the tool and mold making sector.

Title:
Investigations into the production of partial cladding from Ni-based alloys using the cold-metal-transfer process (CMT)
Funding: AiF/DECHEMA
Duration: 01/2010 – 03/2012

Abstract:
The objective of this project is to investigate cladding layers produced using the CMT process from the material group of corrosion-resistant nickel-based alloys. The goal is to develop process parameters that enable reliable and reproducible cladding of various nickel-based materials, such as Alloy 59 (2.4607) and Alloy 686 (2.4606), as well as Alloy 625 (2.4831) as a reference material. Initially, the influence of various process parameters dependent on the filler metal—including variations in shielding gas, layer thickness, and heat input—on bead shape, penetration, mixing, and microstructure will be investigated. By determining mechanical and technical properties, such as bending strength and hardness distribution, the resulting material composites will be thoroughly characterized. Based on the results obtained, the process control will then be optimized for the different materials within defined parameter ranges to produce single-layer coatings with minimal mixing. The influence of these welding process parameters on the corrosion properties of the produced cladding will be investigated. In addition to established testing methods, which typically involve immersion tests, this research project will modify and further develop electrochemical testing methods for use with welded cladding of nickel-based alloys onto high-alloy steels.

Title:
Prototype development of a novel high-temperature fuel cell
(H2-HTFC)
Funding: N-Bank
Duration: 01/2008 – 12/2010

Abstract:
The goal of this project is to produce a functional fuel cell stack based on simple and cost-effective components that has the potential for mass production. The novel membranes used in these fuel cells are intended to be composites with polymer electrolyte membranes that can be operated at high efficiency in the temperature range of 100 to 160 °C without complex humidification regimes.
The fuel cell is structurally based on a graphite-polymer, symmetrical base plate. The flow channels are being developed and optimized at ISAF using flow simulation. The goal here is to realistically model the electrochemical processes in a HT-PEM. The assembly of stacks, due to their geometries, will ensure both reliable gas flow and gas tightness of the system, while simultaneously maintaining high power density.
Furthermore, the use of thermally stable membranes with sufficient to good conductivity and high thermal resistance leads to increased efficiency through higher operating temperatures and reduced effort required for fuel gas humidification. The polymer membrane may also serve as a gas seal, which would yield further cost-saving potential.

Title:
Process and material investigations for the welding fabrication and qualification of components made of multiphase steels
Funding: DFG / SFB 362 T6
Duration: 10/2007 – 09/2010

Abstract:
Considering the entire process chain in thin-sheet metal processing is an essential prerequisite for improving the strength assessment of thin-sheet metal components. Particularly when using multiphase steels, strength control plays a significant role, including with regard to utilizing the bake hardening potential. Within the scope of the proposed subproject, welding process simulation based on the thermal effects of the process will be verified and made assessable—both experimentally and numerically using commercially available software—for thin-sheet structures made of multiphase steels.
 

Title:
Design methodology for the development of high-strength, locally adapted structures using finite element design (FED)
Funding: DFG / SFB 675 TP C7
Duration: 07/2008 – 06/2010

Abstract:
The potential of structures with locally modified properties can be most effectively harnessed in practice if this knowledge is available to the designer as early as the conceptual phase of the product development process. The goal of subproject C7 is therefore to develop a design methodology based on the finite component element as the smallest design unit (FED—Finite Element Design). This approach takes into account the potential for local property optimization and highlights the interactions between material, manufacturing, and design. This methodology represents a novel approach to solving complex design problems, one that has not yet been applied. In the first phase of the project, the development of the new design methodology (FED) will be initiated and validated using multi-material design components produced by joining processes.
 

Title:
Material-adapted process control in the welding of locally hardened materials for the production of nodes and structures
Funding: DFG / SFB 675 TP B5
Duration: 07/2008 – 06/2010

Abstract:
The importance of welding technology for product manufacturing has, in the past, led to the continuous development and refinement of welding and joining processes. This trend has continued with increasing intensity in recent decades. This is due to the challenges associated with processing modern steels (e.g., dual-phase steels, TRIP steels, martensitic steels) and light metal alloys. The plans within Collaborative Research Center 675 to unlock new material potential through the targeted adjustment of local properties in modern lightweight materials present new challenges for welding-based manufacturing. In the simplest case, the goal is to preserve the thermally unstable local properties of the starting semi-finished products. At the same time, there is the possibility of using the joining process itself to improve the structural and component properties.
High-frequency welding offers excellent potential for achieving the desired transfer of local property adjustments into the finished component by initiating suitable material reactions. On the one hand, the HF welding process strongly limits the thermal stress on the base material due to the skin and proximity effects. On the other hand, the process-specific coupling of heating and forming (compression process) offers the possibility of significantly improving the properties of the weld seam. Possible applications include grain refinement of the weld microstructure to increase strength and improve ductility—comparable to a thermomechanical treatment during final forming in the rolling of steel strips—or the deliberate introduction of plastic deformation. A systematic investigation of the qualitative and quantitative possibilities for generating defined material reactions in HF welds is therefore the goal of the process- and equipment-related subproject B5.
 

Title:
Low-heat joining – fabrication and fatigue strength of brazed, locally strengthened structures
Funding: DFG / SFB 675 TP C3
Duration: 07/2006 – 06/2010

Abstract:
In order to utilize materials with locally tailored properties for a wide range of applications, even under cyclic loading, a service life calculation concept is required for design, and material-specific processing is necessary for reliable manufacturing. To this end, the interaction of brazing parameters, brazing systems, and pre- and post-treatments is being investigated for arc brazing, and a manufacturing concept is being developed. In addition, a service life calculation concept for brazed joints subjected to cyclic loading on materials with locally tailored properties is developed and adapted to brazed component-like structures.
 

Title:
Investigations into MSG flat-wire welding of aluminum materials
Funding: AIF 13.141 B
Duration: 03/02 – 02/04

Abstract:
The goal of the research project was to establish the process-engineering prerequisites for the welding of aluminum materials using flat-wire electrodes. Detailed investigations were conducted into process stability and material transfer in pulsed and spray arcs as a function of the geometry and orientation of the joint. Furthermore, by varying the process parameters, the weldability of various alloys, the potential applications of specific shielding gas compositions, and the corrosion resistance of the joints were determined. The properties of the welded joints were also examined using metallographic methods and mechanical-technological tests, taking into account the base materials, filler metals, and welding process conditions used.
The results of the investigations were integrated into an industrially viable manufacturing technology and were thus intended to facilitate rapid implementation in industrial operations.

Title:
Metallurgical investigations for the development of cu- and ni-based filler materials for the plasma-powder brazing process
Funding: AiF
Duration: 02/02–01/04

Abstract:
In addition to new materials, lightweight construction requires innovative joining techniques, as improved material properties can only be effectively utilized if the joining method allows these properties to be transferred to the entire structure. At the same time, the importance of corrosion protection is growing due to decreasing sheet thicknesses. Consequently, there is a need for techniques that enable the production of joints with low heat input, minimal distortion, and low residual stress—while ensuring sufficient strength—in a reliable and cost-effective manner. For this very purpose, brazing processes offer enormous potential for many design tasks. However, due to the mechanical properties achievable with existing filler materials, the areas of application are currently limited to the joining of deep-drawing steels in low-strength ranges.
The goal of this research project is to establish the metallurgical prerequisites for plasma-powder brazing of surface-treated thin sheets made of medium- and high-strength steel materials.
Another focus of this proposal is the investigation of how process energy, the powder used, and the coating properties of the sheet metal interact to influence diffusion and alloying processes, as well as microstructural changes in the weld and the base material, and the resulting weld properties.

Title:
investigations into the welding of silicon-based hard materials to increase wear
resistance Funding: AiF
Duration: 03/02–02/04

Abstract:
Silicon is of great importance in materials engineering. It is used for deoxidation, alloying, and the formation of hard phases.
The use of silicon carbide as a hard material has so far taken place primarily outside of fusion metallurgical processes. For example, silicon carbide is used as an abrasive for high-strength materials. It is also used in high-temperature ceramics in combination with various matrix materials.
Initial approaches to the metallurgical processing of silicon carbide have been explored in particle-reinforced aluminum. In some cases, silicon carbide is also used in thermal spray coatings.
In welding metallurgy, silicon carbide has not yet been processable due to its covalent bond and its specific high-temperature properties (decomposition above 2500°C). The reactivity of silicon in metal melts is also problematic, as the carbide often dissolves in favor of other phases. However, due to its high hardness and low density compared to the carbides typically used in welding technology, silicon carbide is particularly well-suited for wear-resistant coatings on light metals.
From a business perspective, the low production costs of silicon carbide compared to other carbides support its use in heavy-metal coatings as well.
If silicon carbide can be successfully and flawlessly incorporated into weld metallurgical coatings, there is significant potential for improving the properties of wear-resistant coatings and reducing costs.
The objective of the project is to investigate the metallurgical behavior of silicon carbide during welding and brazing processes in various matrix materials and to develop suitable coating materials and material systems that are appropriate for different substrate materials.
Due to the specific properties of silicon carbide—high hardness, low density—light metals are particularly well-suited as substrate materials, although it is advisable to match the melting points between the substrate and the coating material. Aluminum-matrix materials with varying alloy contents are therefore used.
However, the low manufacturing costs of SiC also make its use in other matrix materials and for other substrate materials an attractive option. To largely rule out decomposition of the carbide above 2500 °C, the investigations therefore include self-flowing (low-melting-point) NiCrBSi or NiBSi matrix materials, which are widely used for coatings on steel substrates.
The welding processes to be investigated are the plasma-powder process, which, due to the high energy density in the plasma jet, ensures concentrated heat input with minimal mixing, and the MSG flux-cored wire process, which, as a cost-effective and straightforward coating method, can be advantageously used especially under construction site conditions.
The use of silicon carbide as a hard phase in wear-resistant coatings is expected to result in coatings with a lower specific weight, which, due to the low production costs of silicon carbide, are more cost-effective than the tungsten carbide-reinforced coatings used to date.

Title:
Seam design and material reactions in electron beam welding of aluminum materials in air
Funding: AiF
Duration: 03/01–02/03

Abstract:
The objective of the research project was to gain new insights into weld design and the material reactions that occur during high-power electron beam welding of aluminum materials in air (NV-EBW) through structural and metallurgical investigations. The study aimed to investigate the extent to which the quality of aluminum welded joints can be improved through weld design and process-related measures. In particular, the study focused on the influence of high welding speeds on the microstructure, precipitation behavior, and mechanical and technological properties of the welded joints, as industrial users in particular must capitalize on potential for streamlining welding cycle times due to international cost pressures.
In addition to determining realistic ranges for the high welding speeds to be used, the metallurgical and materials-science processes involved in the joining process were to be investigated, and based on this, specific guidelines and instructions for the design, specification, and execution of high-quality joints in these materials were to be derived. The primary focus was on determining a joining technology adapted to the heat-treated condition of the base material through targeted thermal influence. Tolerance ranges and process limits were to be established.
Temperature, dwell time, and cooling rate significantly determine the nature of metallurgical processes. A key focus of the investigations was therefore to elucidate the thermal processes in the weld zone and the heat-affected zone (HAZ) as a function of the material condition and process parameters, as well as their effect on the mechanical and technological properties of the weld (static strength, hardness, deep-drawing ability). The aim here was to gain insight into the microstructure and precipitation behavior by correlating the variables that influence the process. The causes leading to the deterioration of the material’s properties after welding were to be identified, and measures to improve the quality of the welded joints were to be developed.
In addition, the requirements for the components to be welded in terms of design and preparation were to be determined. The aim here was to understand the relationships between joint configuration, component thickness, and outgassing processes in the melt—and thus pore formation.
 

Title:
Metallurgical and corrosion-chemical investigations into the production of plasma-powder overcladding from Ni-based alloys
Funding: AiF
Duration: 03/01–02/03

Abstract:
The objective of this research project is to produce corrosion-resistant cladding layers of Ni-based materials with low layer thickness using the high-power plasma-powder welding process on joint-welded, plated sheets, to investigate them, and to optimize them in terms of quality and deposition rate. The required coating properties are to be achieved using a single-pass technique with a coating thickness of 2 to 4 mm. Due to the required coating quality (high corrosion resistance), minimal mixing is necessary. For economic reasons, a minimum welding deposition rate of 12 to 15 kg/h is required.
As part of the research project, reliable findings regarding the performance and potential applications of re-cladding using high-performance plasma powder cladding are to be developed. Compared to previously used methods, this process is expected to offer significant advantages in the area of highly stressed, thin, and high-alloy corrosion-resistant coatings, resulting in a substantial increase in efficiency. Furthermore, the high coating quality, material savings, and the modification of the existing high-performance torch to process pipe nominal diameters of 200 mm could open up new areas for the production of components made from cladding sheets.
Replacing conventional processes (RES / TIG) is particularly suitable in industrial sectors where high-alloy coating materials, such as nickel-based alloys, are used to meet very high corrosion resistance requirements and for components with relatively small diameters.

 

Title:
Investigations into the qualification of plasma-powder fusion welding of aluminum for industrial use
Funding: AiF
Duration: 03/01–02/03

Abstract:
The favorable properties of aluminum and its alloys—such as low specific gravity, low susceptibility to corrosion, relatively good formability and machinability, as well as good to very good mechanical and technological properties—are opening up an ever-increasing number of application areas for aluminum materials.
As with steels, processability is one of the essential properties of aluminum materials, serving as a prerequisite for the broad range of applications of this material group. In this context, joinability—particularly weldability—plays a decisive role. Gas-shielded welding has become the standard method for welding aluminum materials. Depending on the welding task, both processes using a non-consumable electrode (TIG) and those using a consumable electrode (MIG) are employed.
Even in TIG/plasma processes, a welding filler material in wire form is used in the majority of cases. Furthermore, certain aluminum alloys cannot be welded without a filler material due to their susceptibility to hot cracking.
Welding with wire-form filler material leads to well-known disadvantages due to the external wire feed, such as wire slippage, limited accessibility, and restricted freedom of movement—particularly with tight and small-scale component contours as well as complex workpieces.
Plasma-powder fusion welding is a new process variant that prevents the aforementioned problems from arising in the first place. The powdered filler material is fed into the weld pool centrally and without an electric current via the torch. This allows the weld bead geometry to be controlled independently of the set energy per unit length. Furthermore, the process offers an additional degree of freedom due to the directional independence of the filler material feed.
The objective of the project was to qualify plasma-powder welding for joining aluminum materials.
The goal was to determine the parameters for reliable and reproducible joint welding of various materials from the group of non-hardenable aluminum alloys.
To reliably destroy the thermally stable oxide skin, it is necessary to include newly developed plasma process variants in the investigations.

 

Title:
investigations into the development of precipitation-hardening coatings from nickel-based superalloys
Funding: AiF
Duration: 12/00 – 11/02

Abstract:
The objective of the research project was the application-oriented alloy development of precipitation-hardening nickel-based superalloys. The alloys to be developed were intended to form precipitates already during welding, so that optimal mechanical properties for high-temperature applications could be achieved through a relatively simple heat treatment—i.e., one that is short and carried out at relatively low temperatures.
A particular focus of the investigations was on determining the precipitation mechanisms in order to provide users with concrete guidance for specific solutions that enable the successful use of the alloys in high-temperature applications, both in repair work and in the manufacture of new parts.
 

Title:
Investigations into resistance spot welding of thin sheets made of newly developed high- and ultra-high-strength steels
Funding: AiF
Duration: 10/00 – 12/02

Abstract:
Multiphase steels (DP, TRIP, CP) represent an innovative material that is expected to have a broad range of applications in the future. Due to their combined structural properties, these alloys can be used in a variety of ways across many industrial sectors. While their use offers advantages, a wide range of factors must be considered for lightweight steel construction. In addition to the choice of material, aspects such as material-appropriate design and reliable manufacturing technology play an important role here.
To date, there has been insufficient knowledge regarding the welding process and the associated weldability of high-strength steels. Inquiries from industry have shown that there are some reservations regarding the use of these materials in mass production, particularly in conjunction with resistance spot welding. While there are numerous recommendations for parameter settings for conventional steel materials, such recommendations are, naturally, still largely lacking for the newly developed materials.
As part of the research project AiF-FV No. 12.618N, “Investigations into the resistance spot welding of thin sheets made of newly developed high- and ultra-high-strength steel materials,” high-strength steel materials of the types DP, RA, CP, and MS in various strength grades and coating variants. To characterize their welding behavior, weld zones were examined in both homogeneous and mixed combinations. Adjusting the welding parameters to increase electrode forces generally results in wider current ranges and the formation of macroscopically defect-free weld beads. A post-weld heat treatment phase has a positive effect on the hardness profiles of the welded joint. Cold working prior to the welding process results in higher forces in the shear tensile test due to increased work hardening of the base material. No material-related influence on the fatigue strength properties could be

demonstrated in the investigations conducted. 

Title:
Comparative studies on the influence of high-power beam welding on the metallurgical properties of Al and MG alloys
Funding: AiF
Duration: 10/00 – 9/02

Abstract:
The objective of the project was to develop welding and design specifications for welding aluminum and magnesium alloys using high-energy beam processes (high-power Nd:YAG laser and electron beam in air). In particular, the study focused on investigating the influence of high welding speeds of 10 m/min and above on the microstructure, precipitation behavior, and mechanical and technological properties of the welded joints, as industrial users in particular must exploit potential for rationalization in terms of welding cycle times due to international cost pressures. The base materials were commercially available die-cast and wrought alloys with thin walls.
The investigations were intended to identify the metallurgical and material-related processes occurring during joining and, based on these findings, to derive specific guidelines and instructions for the design, specification, and fabrication of high-quality joints in these materials.
A key focus of the investigations was to elucidate the thermal processes in the heat-affected zone as a function of the material’s condition and process parameters, as well as their effect on the weld properties with regard to corrosion resistance and mechanical-technological properties (static and dynamic strength, hardness). The primary objective was to develop a joining technology tailored to the heat-treated condition of the base material through targeted thermal control. The aim was to determine tolerance ranges and process limits.

 

Title:
Investigations into the weldability of precipitation-hardening stainless steel alloys
Funding: AiF
Duration: 5/99 – 4/01

Abstract:
The objective of this project is to develop welding and design specifications for gas metal arc welding (GMAW) and laser beam welding of precipitation-hardening stainless steels, including those in the heat-treated condition. To this end, the metallurgical and materials science processes involved in the joining process will be investigated, and based on these findings, design principles and criteria for the design, specification, and execution of high-quality welded joints in these materials will be derived. The primary focus is on developing a welding technology tailored to the heat-treated condition of the base material through targeted thermal control.
A key focus of the planned investigations is to elucidate the thermal processes in the weld zone, i.e., in the heat-affected zone (HAZ), as a function of the material’s condition and process parameters, as well as their effect on the weld properties with regard to corrosion resistance and mechanical-technological properties (toughness, strength, hardness). The aim here is to gain insight into the microstructural development in the HAZ and the precipitation behavior by correlating the variables that influence the process. The causes leading to the deterioration of the material’s properties after welding must be identified, and measures to improve the quality of the welded joints must be developed.
Temperature, dwell time, and cooling rate are decisive factors in determining the nature of the metallurgical processes. Establishing criteria for evaluating critical cooling conditions as a function of the material’s state is therefore another sub-goal of the project.
Based on these findings, a model will ultimately be developed to quantitatively describe the interaction between heat transfer during the process, the base material, and the desired properties of the welded components.

 

Title:
Process control and design concepts for the joining of complex components
Funding: DFG / SFB 390 TP B3
Duration: 98/01

Title:
Superplastic properties and diffusion welding of magnesium-based alloys
Funding: DFG / SFB 390 TP C1
Duration: 98/01

Abstract:
Very little fundamental knowledge is available regarding the superplastic behavior of magnesium alloys, which—due to their density being approximately 40% lower than that of aluminum materials—can make a further decisive contribution to weight reduction in lightweight construction. As experience with aluminum and titanium alloys shows, exploiting superplastic properties is particularly advantageous for magnesium alloys due to their limited cold formability. Superplasticity refers to a material’s ability to withstand deformation levels—exceeding the typical limits of “normally plastic” materials—typically around 10 to 40%—by several hundred to over 1,000%.
Over the past 5 years of the ongoing SFB390 project, extensive investigations have been conducted into ways to improve the superplastic properties of magnesium-based alloys. A primary goal was to reduce the grain size in the microstructure to d < 10 µm. To this end, two simple methods were developed in subproject C1; these methods enable the superplastic properties of ZRE1 and AM20 magnesium casting alloys to be significantly improved through pre-deformation by extrusion. The results confirm the assumption that grain size is the primary factor influencing superplastic deformation properties. For example, for a conventional ZRE1 magnesium alloy at a constant strain rate of 1.6×10^{× 10⁻⁴ s⁻¹} and for a conventional AM20 magnesium alloy at a constant strain rate of 10⁻³ ^s⁻¹ an elongation at break of 550%. The significantly reduced grain size also resulted in the modified alloys showing substantial improvements not only in their superplastic properties but also in their general properties, such as hardness and tensile strength.

Title:
Welding under extreme conditions
Funding: DFG / SFB 264 TP B3
Duration: 98/01

Abstract:
As part of this research project, extensive fundamental investigations are being conducted to develop a concept for an underwater welding system designed for automated manufacturing, as well as to improve the quality of underwater welds. In particular, the aim is to identify correlations between the boundary conditions for welding under pressure and in the presence of moisture and the resulting process and material behavior.

Title:
Alternative materials for wire bonding at the closest pitch
Funding: AiF
Duration: 12/98 – 11/00

Title:
Metallurgical investigations into the coating of thin substrates with sheets >2 mm
Funding: AiF
Duration: 12/98 – 11/00

Abstract:
The objective of this project is to use the plasma-powder process to produce single-layer coatings of Fe- and Ni-based alloys on thin substrates with wall thicknesses of 2–6 mm. Furthermore, the properties and economic viability of these coatings are to be determined. Optimal coating properties can be achieved through a targeted combination of alloy composition and powder feed. These process-influencing variables were successfully determined during the project. To classify the results obtained, investigations are also being conducted on commercially available open-arc (OA) welds. The investigations carried out will provide insights into the achievable properties of the composite material, enabling the industrial application of this coating process and thus leading to weight savings in component manufacturing.

 

Title:
Development of a consulting system for surface protection via thermal spraying
Funding: AiF
Duration: 11/98 – 10/00

Abstract:
The planned system (working title “SPRIWARE”) is intended to demonstrate, using plasma spraying as an example, that a suitable selection or specification of spray materials is possible based on tribological systems (wear parts with mating surfaces, environmental and friction conditions) as well as spraying process and equipment parameters.

Title:
investigations into the determination of process interactions and the influence on weld properties in combined plasma-arc-laser welding
Funding: AiF
Duration: 11/98 – 10/00

Abstract:
The goal of the planned research project is to develop, through practical investigations, a joining technique based on combined plasma-arclaser welding—using workpieces sensitive to hardening and the joining of aluminum alloys as examples—that enables high productivity even at low beam power. Another key focus of the process investigations is improving gap bridging, for which the use of filler wire is also planned. To achieve the research objective, a hybrid welding system—developed based on the results of the applicant’s preliminary investigations—must first be adapted to address the aforementioned challenges.

 

Title:
Investigation and optimization of the mechanical and corrosion properties of welded joints made of wrought aluminum alloys in combination with cast aluminum alloys
Funding: AiF
Duration: 9/98 – 12/00

Abstract:
The planned work aims to establish the fundamental principles of welding technology and materials science in order to improve the load-bearing capacity and, in particular, the corrosion properties of welded components combining wrought aluminum alloys with cast aluminum alloys, as well as to determine their structural properties. Materials relevant to apparatus and vessel construction will be joined using plasma welding with variable polarity in various positions. The goal is to reduce the number of pores and, above all, to improve or harmonize the corrosion properties of the base materials and the weld metal. Electrochemical investigations are intended to provide insight into the pitting corrosion behavior and potential differences in the weld zones. In addition, stress corrosion cracking tests and aging tests in various media are planned. Concurrently, metallographic, analytical, and X-ray examinations will be conducted to characterize the microstructural and weld properties.

 

Title:
Use of nitrogen-containing high-temperature plasmas for reactive coating via plasma cladding
Funding: AiF
Duration: 8/98 – 7/00

Abstract:
The targeted addition of nitrogen to the plasma and powder carrier gas during plasma cladding is intended to achieve nitriding of iron-based hard alloys during the cladding process and mixed-crystal strengthening through nitrogen precipitated into the matrix. The reactive formation of hard phases in the molten state is expected to result in fine-grained precipitation of the hard phases, and the intense turbulence of the melt—a characteristic of the process—is expected to ensure homogeneous distribution across the cross-section of the coating.
Building on the high base wear resistance of Fe-Cr-V alloys, the goal is to increase abrasive wear resistance by raising the hard-phase content without coarsening the hard phases.
Fine-grained precipitates are a prerequisite for the use of highly wear-resistant coatings on the cutting edges of machine knives or similar tools and wear parts.
As part of the research project, various process variants of plasma powder surfacing (plasma arc process, plasma jet-plasma arc process) will be investigated. By varying the addition of nitrogen to the plasma and carrier gas, as well as using different shielding gases, the influence of the nitrogen content in the working gases on the hard-phase content and the proportion of dissolved nitrogen in the matrix material will be investigated. Optimal process conditions will be determined through parameter studies.
Metallographic, GDOS, and TEM analyses will be used to detect the resulting nitrides and the dissolved nitrogen content. Through wear tests (sandpaper test, friction wheel tribometer) and field trials of prototype tools, the increased wear resistance and the suitability of the coatings for machine blades will be demonstrated.

Title:
Investigations into the underwater
welding of high-alloy Cr-Ni steels with self-shielding flux-cored wires Funding: AiF
Duration: 8/98 – 12/00

Abstract:
The objective of the proposed research project is to conduct investigations into the design and use of self-shielding flux-cored wire electrodes for mechanized underwater welding of high-alloy Cr-ni steels, and thereby to gain insights into the influence of the filler wire composition and design on the metallurgy and, consequently, the properties of the joint. From this, requirements for appropriate electrodes are to be derived, and a concept for a suitable filler wire is to be developed.

 

Title:
Metal inert gas welding of light metal materials using magnesium alloys
as an example Funding: AiF
Duration: 8/98 – 12/00

Abstract:
The objective of this research project is to conduct fundamental investigations into the influence of power source characteristics and welding parameters on process reliability during gas-shielded welding of magnesium alloys. Furthermore, the suitability of various alloys made from wrought and die-cast materials for gas-shielded metal arc welding is to be investigated. The focus of this investigation is on hot cracking susceptibility and the formation of the weld, including the heat-affected zone (HAZ), such as precipitates occurring therein. A third objective is to determine the static strength and fatigue strength to the extent that reliable numerical values can be provided for the design of structures. Finally, it is planned to develop reliable findings on corrosion using the salt spray test in accordance with DIN 50 021.

Title:
Investigations into the corrosion and wear behavior of hard-substance-reinforced magnesium alloys
Funding: AiF
Duration: 7/98 – 6/00

Abstract:
The objective of this research project is to use the plasma welding process—by melting the surface while selectively adding hard-material particles (SiC, TiC, TiB₂, ZrB₂)—to create surfaces on magnesium alloys that are both corrosion- and wear-resistant. The study will examine how the wear resistance—and possibly also the corrosion resistance—of magnesium surfaces can be improved by incorporating hard materials while adjusting the process parameters. In addition, the study will investigate the influence of hard-substance incorporation on microstructure development and on precipitation behavior as a function of temperature and composition.

Title:
Diffusion welding of metals with ultrafine-grained ceramics
Funding: VW-Vorab
Duration: 4/98 – 12/99

Title:
Investigations into arc welding with sintered strip electrodes
containing hard materials Funding: AiF
Duration: 1/98 – 12/99

Abstract:
The objective of the planned research project is to produce and subsequently investigate hard-metal-reinforced cladding layers using the UP, RES, and MSG arc welding processes. This is to be achieved through the use of sintered ribbon electrodes containing hard metals. By utilizing sintering technology, hardmetal particles—tungsten fused carbides (WSC)—are to be incorporated into ferritic and austenitic matrix materials and processed as strip electrodes using the aforementioned processes.

Title:
Influence of solidification and transformation conditions on the ferrite content and ferrite morphology of metastable austenitic weld metal
Funding: DFG
Duration: 98/99

Title:
SPP “Mechanism-oriented service life prediction for cyclically loaded metallic tools” Improvement of service life prediction under multi-axial oscillatory loading by considering microcrack initiation and microcrack propagation
Funding: DFG
Duration: 98/99

Title:
Determination of quality-relevant material and process parameters for the combined forming and joining of thin
sheet metal Funding: DFG / SFB 362 TP A3
Duration: 98/99

Abstract:
In the effort to shorten process chains and thereby further reduce manufacturing costs, the use of materials tailored to the local stresses in the component—via tailored blanks with linear seams—has already achieved great success. This has made it possible to specifically avoid oversizing and to eliminate forming and assembly steps. However, the use of tailored blanks also has disadvantages, which lie primarily in the cost-intensive adaptation of forming tools—for example, through segmentation or the incorporation of recesses to accommodate seam displacement occurring during the forming process. Furthermore, the design of the forming tools must be adapted to the varying sheet thicknesses of the processed blanks to prevent wrinkling when the surface pressure is too low or tearing when it is too high. Furthermore, for manufacturing reasons, it is rarely possible to position the seam along a constant contour (trajectory). The use of tailored components with non-linear seams and contour welding offers a solution here. The term “tailored components” encompasses not only parts manufactured using the welding-forming sequence but also the reverse process, whereby, for example, blanks are formed using existing, conventional machines and tools and then joined by contour welding. This approach offers the following advantages: By using non-linear seams and contours, cost-optimized components can be produced that were previously unmanufacturable using conventional methods; the costly modification of forming tools—including a time-consuming try-out phase—required by the use of tailored blanks is eliminated in contour welding, and it also accommodates the strong industry trend toward modular design.
High-frequency welding is particularly well-suited for the production of non-linear seams and contour welds due to its simple seam preparation, minimal equipment requirements, and very high welding speed of up to 1 m per second. Thus, the process can be integrated into the running cycle of modern press lines.

Title:
Crimp seam welding of thin sheet metal—material- and process-related simulation and interactions with the forming process
Funding: DFG / SFB 362 TP B6
Duration: 98/99

Abstract:
The concept of process-integrated post-treatment of squeeze welds, developed in Subproject B6, has proven to be highly effective. Utilizing the welding heat during post-smoothing results in significantly better formability than with cold post-smoothing.
Post-weld heat treatment of the weld seam is only beneficial if the squeeze weld has been re-rolled. Without leveling the weld ridge, the strength and deformation properties of the squeeze welds are so good that heat treatment is not necessary. The inductive heat treatment method has proven to be very effective. By appropriately adjusting the inductor geometry, distance from the workpiece, and operating frequency, it is possible to selectively heat the weld zone without thermally affecting the base material. Despite the extremely short holding times of only up to three seconds, a significant improvement in hardness values, tensile strengths, and formability was demonstrated. Using three different steels as examples, it was demonstrated that rolled, post-heated squeeze welds exhibit formability at least equivalent to that of the base material. Post-treatment of the welds does not impair, and may even improve, the fatigue strength.

Title:
Fundamentals of reaction engineering, the design, and construction of ultrasonic reactors
Funding: DFG / SFB 180 TP B14
Duration: 98/99

Abstract:
As part of this project, the Institute for Welding Technology and Separative Manufacturing Processes is analyzing the wear mechanisms prevalent during cavitation with the aim of selecting and optimizing materials for use as sonotrode and reactor materials in ultrasonic reactors. Through testing in accordance with ASTM G32-85, various materials for the reactor core are being evaluated, as well as the influence of different surface treatments —PVD and CVD thin films, laser treatments—on the cavitation resistance of the titanium alloy TiAl6V4, which is frequently used as a sonotrode material in ultrasonic technology, against direct and indirect cavitation. Another focus is on investigations of the local cavitation behavior of weld seams on the reactor materials, as well as the influence of manufacturing parameters on wear behavior. Distilled water and the liquids used in phase-transfer catalysis in an ultrasonic reactor serve as test media. The goal is to significantly increase the service life of ultrasonic reactors by minimizing wear caused by cavitation through targeted surface modification and process control during the welding fabrication process.

Title:
Atmospheric electron beam welding of thin sheet metal materials—fundamental investigations into material and process behavior
Funding: DFG / SFB 362 TP B9
Duration: 98/99

Abstract:
Electron beam welding in open air (NV-EBW) is a key technology that is beginning to establish itself in high-volume production for certain applications. This process not only replaces conventional fabrication techniques but also offers excellent approaches for producing cost-effective, high-quality welded joints in thin-gauge sheet metal materials. Due to the high power density, heat transfer can be precisely controlled. The lower thermal load keeps the molten pool small and the heat-affected zone narrow, which promises good weld properties. The process is also characterized by high processing speed, good integrability into production lines, and simpler handling than vacuum electron beam welding, since the downtime required to generate a vacuum is eliminated. Furthermore, the use of filler materials to prevent edge notches and weld depression in thin components or for joining dissimilar metals is practically easier to implement. From an economic standpoint, the decisive advantage of NV-EBW over current high-power lasers stems primarily from its lower operating costs and higher efficiency in beam generation.

Title:
Investigations into the influence of process behavior and weld bead properties through the use of meted-out welding filler materials in high-power metal-active-gas (MAG) welding
Funding: DFG
Duration: 98/99

Abstract:
The proposed research project aims to conduct fundamental investigations into the influence of the wire electrode—taking into account the shielding gas composition—on weld bead formation and porosity, specifically in high-power MAG welding at higher wire feed rates. The focus is on fundamental research into the targeted influence on processes in the weld pool through the use of basic-doped welding consumables. To this end, the effects of basic elements in the welding filler metal on weld pool formation will be examined in greater detail, with particular emphasis placed on the processes occurring at the surface. These will be documented, among other methods, through high-speed photography. For welding and metallurgical reasons, it makes sense to optimize the efficiency of the doping so that the desired phenomena can be achieved with minimal proportions of basic additives.
Building on these fundamental investigations, the extent to which the use of special flux-cored electrodes with a low basic content is possible and advisable will be examined. Furthermore, based on the preliminary investigations, the possibility of incorporating basic slag formers into a solid wire will be investigated in greater detail.
In addition to the fundamental investigations into the material-specific properties of the doped wire electrode and the effects on welding parameters, other quality-determining issues must be considered. These relate to process- and filler material-specific aspects such as wire composition, stiffness, and the influence of deformation; wire feeding behavior; and requirements for current transfer and contact tube spacing in order to achieve reproducible penetration profiles and corresponding weld quality. Systematic, scientific investigations are intended to clarify the key parameter dependencies, while addressing remaining knowledge gaps in the field of basic-doped welding consumables.
In addition to scientific insights, the investigations are also expected to provide impetus for broad areas of welding technology. This involves, on the one hand, a better understanding of the processes occurring in the weld pool and the resulting developments. Specifically, implementing the results at a later stage could lead to an expansion of the application range of high-performance MAG welding processes and thus to an improvement in the market opportunities for German companies.
The results of these investigations are intended to make it possible to increase the efficiency and quality of high-performance MAG-welded joints, thereby enhancing the cost-effectiveness of high-performance MAG processes and strengthening competitiveness. The goal is to enable the production of pore-free, high-quality welds at deposition rates exceeding 23 m/min using 1.2 mm wires—comparable to SG2 quality—in order to increase, even in areas where X-ray-inspection-compliant welded joints are required, to increase the performance of the welding process while ensuring consistent weld quality, and thereby enhance overall manufacturing efficiency.

Title:
Surface modification via vacuum coating of ultra-fine gold wires to improve ultrasonic weldability at low process temperatures
Funding: DFG
Duration: 98

Title:
Material-specific numerical simulation of thermal processes in production engineering
Funding: DFG
Duration: 1/97 – 12/99

Abstract:
The goal of this subproject is to implement the numerical simulation of material and process behavior during fusion welding, with a focus on a methodological, holistic approach to the joining process as a whole. This means that a holistic approach and solution methodology for the material/welding process system is sought in order to establish a basis for predicting suitable process parameters as well as weld properties.

Title:
Mechanism-oriented life prediction of surface-nitridized titanium alloys taking into account fracture mechanics modeling of short-crack behavior
Funding: DFG
Duration: 7/97 – 7/99

Abstract:
The objective of mechanism-oriented life prediction is to model the microstructural fatigue processes occurring in the material during cyclic loading and to directly link them to life predictions. Surface-nitrided titanium alloys are suitable model materials for this task. Such materials possess high innovation potential for use under combined dynamic and tribological loads. At the same time, surface treatments influence fatigue behavior, although there is a significant knowledge gap regarding both the fatigue mechanisms and the prediction of service life.
The goal of the project is to establish the fundamentals for a mechanism-based service life prediction of surface-nitrided titanium alloys. To this end, surface layer conditions with distinctly different surface and core properties are to be established using plasma nitriding and laser nitriding, so that divergent microstructural fatigue processes occur under cyclic loading. The respective prevailing mechanisms are to be analyzed using analytical and experimental methods under single-stage alternating tensile-compressive loading with variable stress ratios and modeled in a short-crack progression model. Based on these investigations, a concept is to be developed that enables the application of fracture mechanics approaches to the prediction of service life under single-stage, medium-stress loading. It is expected that, within the scope of the proposed project, fundamental insights into the fatigue behavior of surface-treated composites, the application potential of surface-nitrided titanium alloys, and the qualification of the surface treatment processes used can be obtained.