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The potential of paper and paperboard as fiber-based materials capable of replacing conventional polymer-based materials has been widely investigated and evaluated. Due to paper’s limited extensibility and inherent heterogeneity, local structural variations lead to unpredictable local mechanical behavior and instability during processing, such as mechanical forming. To gain a deeper understanding of the impact of mechanical behavior and heterogeneity on the paper forming process, the Finite Element Method (FEM) coupled with continuum modeling is being explored as a potential approach to enhance comprehension. To achieve this goal, utilizing experimentally derived material parameters alongside stochastic finite element methods allows for more precise modeling of material behavior, considering the local material properties. This work first introduces the approach of modeling heterogeneity or local material structure within continuum models, such as the Stochastic Finite Element Method (SFEM). A fundamental challenge lies in accurately measuring these local material properties. Experimental investigations are being conducted to numerically simulate mechanical behavior. An overview is provided of experimental methods for material characterization, as found in literature, with a specific focus on measuring local mechanical material structure. By doing so, it enables the characterization of the global material structure and mechanical behavior of paper and paperboard.

The potential of paper and paperboard as fiber-based materials capable of replacing conventional polymer-based materials has been widely investigated and evaluated. Due to paper’s limited extensibility and inherent heterogeneity, local structural variations lead to unpredictable local mechanical behavior and instability during processing, such as mechanical forming. To gain a deeper understanding of the impact of mechanical behavior and heterogeneity on the paper forming process, the Finite Element Method (FEM) coupled with continuum modeling is being explored as a potential approach to enhance comprehension. To achieve this goal, utilizing experimentally derived material parameters alongside stochastic finite element methods allows for more precise modeling of material behavior, considering the local material properties. This work first introduces the approach of modeling heterogeneity or local material structure within continuum models, such as the Stochastic Finite Element Method (SFEM). A fundamental challenge lies in accurately measuring these local material properties. Experimental investigations are being conducted to numerically simulate mechanical behavior. An overview is provided of experimental methods for material characterization, as found in literature, with a specific focus on measuring local mechanical material structure. By doing so, it enables the characterization of the global material structure and mechanical behavior of paper and paperboard.

Abstract The process design of flat die rolling operations can be a tedious and costly process due to the challenges posed by small process windows. Within this work, an effort is made to closely investigate and understand the process limits caused by excessive slippage of the workpiece. Optical measurements are carried out to capture the characteristics of excessive slippage and the influence of the stroke rate and the tribological system on this process limit. Large differences in slippage were observed, depending on the tribological system. While systems with polymer based lubricants showed excessive slippage at low stroke rates, systems using oil or no lubricant endured higher stroke rates before process limits were reached. The optical measurements revealed three major forms of slippage: successful rolling without slippage, failure due to excessive slippage at process start, and failure due to excessive slippage at around one workpiece rotation.

In dentistry, the most commonly used implant materials are CP-Titanium Grade 4 and Ti-6Al-4V ELI, possessing comparably high Young’s modulus (>100 GPa). In the present study, the second-generation titanium alloy Ti-13Nb-13Zr is investigated with respect to the production of advanced dental implant systems. This should be achieved by the fabrication of long semi-finished bars with high strength and sufficient ductility to allow the automated production of small implants at low Young’s modulus (

A novel process design for the damage-free and highly accurate positional integration of an optical multi-axial force sensor into a hollow tube by means of rotary swaging is introduced. Numerical simulations reveal the relevant process phenomena of thin disc joining inside a pre-toothed hollow tube and help us to find an optimal process design. Experimental trials show the significant effect of the axial material flow and the number of tools on the rotary swaging process. By taking these effects into account, successful form- and force-fit joining of the sensor carrying discs into the tube can be achieved. Successful joining of an optical sensor for bending force and torque measurement shows hysteresis-free sensory behavior and thus backlash-free joining of the sensor carrier discs. The paper concludes with a presentation of the results of a numerical study on a potential closed-loop approach to the joining process.

With the increasing usage of high-strength steel, tool wear becomes a major challenge in sheet metal forming. As tribological properties are in consequence of the system characteristics, wear prediction is extremely difficult. The wear resistance characteristic curve is introduced in a former publication of the authors to predict wear in sheet metal forming. With the help of this curve, the evaluation of the tool life spans in strip drawing tests under different contact pressures is possible. However, other influencing factors on tool wear should also be taken into account. In this paper, two types of tools made from cold working steel and cast iron are used to investigate the influence of the tool characteristics hardness and surface roughness on the wear behavior and the life span in strip drawing tests with high strength steels. Moreover, the dominating wear mechanisms with respect to different tool properties are also discussed. As a consequence, the wear resistance characteristic curves are derived and new values to characterize the wear resistance in terms of hardness and surface roughness are presented. With the results, more knowledge about the influencing factors on wear is given and the life spans of different tribological systems can be quantitatively predicted. Finally, the wear behavior of the tools after rework is also discussed.

The relevance of the magnetic Barkhausen noise (MBN) and the non-destructive characterization of material properties in near surface layers, has increased in recent years.With the development of new signal processing techniques, the method was further developed into a powerful evaluation technique and is used in various areas of online and offline measurement. In addition to the established use in the detection of grinding burn, the method is increasingly used in the context of soft sensors for property controlled processes, due to its short analysis times. By a detailed description of a soft sensor concept for the novel forming process punch-hole-rolling this work focuses on the offline characterization of the process specific cause-effect relationships. This is done by analyzing the process interactions as well as the surface layer state by a metallographic investigation. Additionally a non-destructive characterization by means of MBN was done and correlated with the surface layer state. This provides important findings for the use of a MBN-sensor in a soft sensor concept and the potential integration into the forming process.

Higher levels of automation necessitate active spacer and adjusting elements generating high stroke forces. For these, the multitude of applications inside a manufacturing system requires a space- and cost-effective design. Conventional actuator concepts struggle with these demands. A new and efficient actuator concept for establishing closed-loop control circuits is needed. This article presents a new actuator concept, based on the phase change material paraffin wax. Although paraffin wax actuators are a convenient solution for microactuators, high force macroscopic actuators are not established yet. On a macroscopic scale the design of the actuator housing and the manufacturing process are challenging. The presented concept consists of a closed housing, which surrounds the phase change material. A compact actuator design without sealed moveable parts is realized. Thus, the actuators provide high axial forces. Compared to existing solutions an increase in performance by a factor of 7 could be achieved. The essential actuator structure is introduced, characterized and the challenges in manufacturing are discussed. A possible application is demonstrated by a thermal compensation element activated by energy from the surroundings. Keywords: Paraffin wax, Actuator, Phase change material, Machinery property adjustment, Automation

The Middle East will face tremendous water scarcity by 2050, which can only be mitigated by large-scale reverse osmosis seawater desalination. However, the coastal land in the region is rare and costly, so outsourcing the desalination facility to artificial islands could become a realistic scenario. This study investigated the ecological and economic challenges and possible advantages of that water supply option by analysing conceptual alternatives for offshore membrane-based desalination plants of up to 600 MCM/y capacity. Key environmental impacts and mitigation strategies were identified, and a detailed economic analysis was conducted to compare the new approach to state-of-the-art. The economic analysis included calculating the cost of water production (WPC) and discussing the differences between offshore alternatives and a conventional onshore desalination plant. In addition, the study investigated the impact of a changing energy mix and potential carbon tax levels on the WPC until 2050. The results indicate that offshore desalination plants have ecological advantages compared to onshore desalination plants. Furthermore, the construction cost for the artificial islands has a much lower effect on the WPC than energy cost. In contrast, the impact of potential carbon tax levels on the WPC is significant. The specific construction cost ranges between 287 $/m2 and 1507 $/m2 depending on the artificial island type and distance to the shoreline, resulting in a WPC between 0.51 $/m3 and 0.59 $/m3. This work is the first to discuss the environmental and economic effects of locating large-scale seawater desalination plants on artificial islands.

The present study provides an overview of previous studies on the welding of the AA7075-T6 aluminum alloy, followed by an investigation of the influence of short-time solution annealing on the mechanical properties of the weld. Conventional laser welding of Al-Zn-alloys leads to a low weld strength, which makes a post weld heat treatment (PWHT) favorable. The PWHT includes solution annealing, quenching and subsequent aging. For solution annealing, different holding times and cooling rates are investigated in this study. The focus of the investigation is on a short solution annealing time, which on the one hand is ecological and economically favorable and on the other hand offers great potential for inline heat treatments. The shortest solution annealing time of 10 s shows a significant increase in weld strength (joint efficiency of 72%), compared to the non-heat treated weld (joint efficiency of 52%). The microstructural analysis reveals that the cooling rate after solution heat treatment affects the formation of precipitates in the microstructure of the welded AA7075 alloy. Moreover, the enhancement of mechanical properties is related to the formation of Mg-Al-Cu and Mg-Zn rich precipitates.

Collision welding is a joining technology that is based on the high-speed collision and the resulting plastic deformation of at least one joining partner. The ability to form a high-strength substance-to-substance bond between joining partners of dissimilar metals allows us to design a new generation of joints. However, the occurrence of process-specific phenomena during the high-speed collision, such as a so-called jet or wave formation in the interface, complicates the prediction of bond formation and the resulting bond properties. In this paper, the collision welding of aluminum and copper was investigated at the lower limits of the process. The experiments were performed on a model test rig and observed by high-speed imaging to determine the welding window, which was compared to the ones of similar material parings from former investigation. This allowed to deepen the understanding of the decisive mechanisms at the welding window boundaries. Furthermore, an optical and a scanning electron microscope with energy dispersive X-ray analysis were used to analyze the weld interface. The results showed the important and to date neglected role of the jet and/or the cloud of particles to extract energy from the collision zone, allowing bond formation without melting and intermetallic phases.

In this paper we present a novel, cost-effective camera-based multi-axis force/torque sensor concept for integration into metallic load-bearing structures. A two-part pattern consisting of a directly incident and mirrored light beam is projected onto the imaging sensor surface. This allows the capturing of 3D displacements, occurring due to structure deformation under load in a single image. The displacement of defined features in size and position can be accurately analyzed and determined through digital image correlation (DIC). Validation on a prototype shows good accuracy of the measurement and a unique identification of all in- and out-of-plane displacement components under multiaxial load. Measurements show a maximum deviation related to the maximum measured values between 2.5% and 4.8% for uniaxial loads (Fx, Fy,Fz,Mz) and between 2.5% and 10.43% for combined bending, torsion and axial load. In the course of the investigations, the measurement inaccuracy was partly attributed to the joint used between the sensor parts and the structure as well as to eccentric load.

In sheet metal forming, free deformation of the sheet takes place frequently without contact with forming tools. The pre-straining resulting from the free deformation leads to a surface roughening of the sheet metal. It is assumed that the roughening has an influence on friction and wear behavior of the following forming process as well as the painting quality after the manufacturing. In this paper, a numerical prediction based on a polycrystalline model is first proposed to predict the effect of surface roughing based on the material data of the as-received state of the sheet metal. Different states of strain are analyzed and the numerical result is validated through experimental evaluation. Besides the numerical prediction, the friction behavior after pre-straining is evaluated in strip drawing tests and the coefficient of friction (COF) is calculated. For interpretation of the measured COF, the surface roughness after the friction test and the surface image are evaluated by a transparent toolset. It is shown that the surface transformation as a result of pre-straining has a negative influence on the lubricating effect of the sheet metal and degrades the friction behavior. Finally, the influence of the strain-induced surface roughening on wear is discussed based on wear testing in strip drawing test with draw bead geometry.

Growing demand for sustainable products has led to increased interest in the use of paperboard as a structural material. Paperboard products are almost exclusively manufactured by embossing, pulp molding, and bending processes. Other well-known forming methods, such as deep or stretch drawing, are only rarely applied to paperboard. This is primarily ascribed to the lack of knowledge concerning the process design and limits when paperboard is employed. In the present work, the applicability of well-established design strategies and characterization methods for metals to paperboard is investigated. Therefore, forming limit diagrams for paperboard are determined in a first step. Additionally, significant material parameters are identified in order to describe the material influence upon the forming limit. Furthermore, the influence of a hydrostatic counter pressure onto the forming limit is investigated. To predict the forming behaviour of a complex formed paperboard demonstration part, a numerical model of a hydroforming process is set up, executed, and validated.

Collision welding is a high-speed joining technology based on the plastic deformation of at least one of the joining partners. During the process, several phenomena like the formation of a so-called jet and a cloud of particles occur and enable bond formation. However, the interaction of these phenomena and how they are influenced by the amount of kinetic energy is still unclear. In this paper, the results of three series of experiments with two different setups to determine the influence of the process parameters on the fundamental phenomena and relevant mechanisms of bond formation are presented. The welding processes are monitored by different methods, like high-speed imaging, photonic Doppler velocimetry and light emission measurements. The weld interfaces are analyzed by ultrasonic investigations, metallographic analyses by optical and scanning electron microscopy, and characterized by tensile shear tests. The results provide detailed information on the influence of the different process parameters on the classical welding window and allow a prediction of the different bond mechanisms. They show that during a single magnetic pulse welding process aluminum both fusion-like and solid-state welding can occur. Furthermore, the findings allow predicting the formation of the weld interface with respect to location and shape as well as its mechanical strength.

Collision welding processes are accompanied by the ejection of a metal jet, a cloud of particles (CoP), or both phenomena, respectively. The purpose of this study is to investigate the formation, the characteristics as well as the influence of the CoP on weld formation. Impact welding experiments on three different setups in normal ambient atmosphere and under vacuum-like conditions are performed and monitored using a high-speed camera, accompanied by long-term exposures, recordings of the emission spectrum, and an evaluation of the CoP interaction with witness pins made of different materials. It was found that the CoP formed during the collision of the joining partners is compressed by the closing joining gap and particularly at small collision angles it can reach temperatures sufficient to melt the surfaces to be joined. This effect was proved using a tracer material that is detectable on the witness pins after welding. The formation of the CoP is reduced with increasing yield strength of the material and the escape of the CoP is hindered with increasing surface roughness. Both effects make welding with low-impact velocities difficult, whereas weld formation is facilitated using smooth surfaces and a reduced ambient pressure under vacuum-like conditions. Furthermore, the absence of surrounding air eases the process observation since exothermic oxidation reactions and shock compression of the gas are avoided. This also enables an estimation of the temperature in the joining gap, which was found to be more than 5600 K under normal ambient pressure.

In the spirit of flexible manufacturing, the novel forming process “flexible roller beading„ was developed, which allows the incremental production of height-variable sheet metal profiles. After designing the process and realizing a test facility for flexible roller beading, the feasibility was experimentally shown. The following step addresses the expansion of the process limits. With this aim, the mechanical behavior of the sheet metal during the process was investigated by means of FEA. Due to the variable cross-section development of the sheet metal profile, a multidimensional stress distribution was identified. Based on the present state of stress and strain, conclusions about the origin of appearing defect formations were drawn. Observed defects were sheet wrinkles as a result of compressive stresses in the profile flange and material thinning in the profile legs and bottom due to unintendedly exceeding tensile stresses. The influences of the forming strategy as well as tool- and workpiece-side variations on the quality of the manufacturing result were investigated. From the results of the analyses, measures to avoid component failure were derived. Given all the findings, guidelines were concluded that are to be considered in designing the forming sequence. With the insights into the occurring processes and the mastery of this novel forming process, important contributions are made to its industrial suitability. The approach of lightweight and load-oriented component design can be extended by realizing new families of sheet metal profiles. With respect to Industry 4.0, on-demand manufacturing is increasingly required, which is why flexible roller beading is of substantial relevance for the industrial sheet metal production.

The tribological system plays a critical part in designing robust and efficient cold forging operations. The appropriate selection of lubrication allows to forge defect-free workpieces with high dimensional precision and desired surface finish while ensuring that no defects, such as cracks or seams, occur. Additionally, friction and wear are highly affected by the choice of tribological system, which in turn influence the cost-effectiveness of the forging operation by preventing premature tool failure. Next to the employed tool coating and work piece material, the lubrication system and work piece surface topography are the main factors influencing the aforementioned constraints when designing efficient forging operations. In order to choose the appropriate tribological system before implementing it within an industrial forging operation, tribometers are used to characterize the performance of the tribological system. In this paper, the necessity to account for not only the tribological loads when designing these tribometer tests as is typical for existing methodologies, but also for process and lubricant specific properties will be highlighted. With the help of the tribometer sliding compression test, it will be shown that using liquid lubricants necessitates the need to account for the escape of lubricant, while this is not true for solid lubricants. The escape of lubricant from the contact zone is governed by lubricant properties as well as the contact kinematics and may lead to significantly different results regarding friction and wear. In order to account for this escape, the tribometer test must be specifically designed to reproduce the contact kinematics of the investigated industrial forging operation.

In production processes, many adjustment tasks have to be carried out manually. In order to automate these activities, there is a need for cost and space efficient actuators that can provide comparatively high forces. This paper presents a novel actuator concept based on the phase change material paraffin wax. Furthermore, a numerical modelling strategy is introduced enabling the prediction of actuator properties. The model considers paraffin wax as a deformable body. The temperature-dependent volume expansion data of the paraffin wax is obtained experimentally to allow for a realistic description of the thermal-mechanical properties. The simulation is verified, using experimental data from actuators with varying paraffin wax volumes. With a maximum deviation of 6%, the simulations show a good agreement with the experiments.

The precise knowledge of frictional behavior is highly relevant for accurate modelling in sheet metal forming simulations. This allows e.g., the precise prediction of restraining forces which, in turn, determines an optimal draw bead strategy and blank-texture-development for automotive components. As a result, tryout loops can be avoided and thus production costs can be reduced. Nevertheless, the benefit of this detailed friction description is often ignored by the use of a constant friction coefficient. Finding a practical solution has motivated numerous research projects in recent decades. In this context, many efforts have been made to develop test stands to gain a better understanding of friction and to determine load-dependent friction coefficients for simulations. However, different test stands for friction investigation show a big quantitative difference in friction value which makes the direct use of the values in finite element simulation questionable. Therefore, the focus of this paper is to compare two different common strip drawing tests and detect the sources of deviation. In particular, the influence of the contact area between tool and blank is investigated. The results indicate that while the effect of the different test stands is negligible, a high dependency of the friction coefficient on the contact area was shown. This phenomenon is caused by macroscopic lubricant distribution over the contact area, which varies according to the size of the tools. The results show a potential field of research in categorizing different friction test stands and resolving the issue of quantitative non-comparable coefficients of friction.

Amorphous hydrogenated carbon coatings (a-C:H) are well known for their exceptional tribological properties and are established as tool coatings for numerous forming applications. However, utilized in dry forming processes of aluminium a premature failure of an a-C:H coated tool often occurs due to strong adhesive wear. In this paper the run-in behaviour of a-C:H is investigated and as a possible reason for the premature tool failure evaluated. Therefore, oscillating ball-on-disc tribometer tests and strip drawing tests, for a more realistic emulation of real forming processes, will be conducted. According to these tests, the run-in period of a-C:H coatings is characterized by a high friction value and adhesion tendency and thus is decisive for the tool performance. Based on a subsequent analysis of the coating wear, the predominating wear mechanisms during the run-in period are discussed. The intrinsic nanomater-scale a-C:H roughness is identified as a crucial factor determining the tribological properties of the run-in behaviour. By reducing the coating roughness prior to the forming process, the adhesion tendency and friction value can be reduced significantly. The results demonstrate the tribological performance of pre-treated a-C:H coatings for dry sheet metal forming of aluminium EN AW-5083.

Products of forming processes are subject to quality fluctuations due to uncertainty in semi-finished part properties as well as process conditions and environment. An approach to cope with these uncertainties is the implementation of a closed-loop control taking into account the actual product properties measured by sensors or estimated by a mathematical process model. Both methods of uncertainty control trade off with a financial effort. In case of sensor integration the effort is the cost of the sensor including signal processing as well as the design and manufacturing effort for integration. In case of an estimation model the effort is mainly determined by the time and knowledge needed to derive the model, identify the parameters and implement the model into the PLC. The risk of mismatch between model and reality as well as the risk of wrong parameter identification can be assumed as additional uncertainty (model uncertainty). This paper evaluates controlled and additional uncertainty by taking into account process boundary conditions like the degree of fluctuations in semi-finished part properties. The proposed evaluation is demonstrated by the analysis of exemplary processes.