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PublicationAssessing the Environmental and Economic Impact of Wire-Arc Additive Manufacturing( 2024-05)
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PublicationNumerical Modeling of the Redistribution of Residual Stresses in Deep Rolled Cross Bores in Shafts from GJS700-2( 2024)
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PublicationInfluence on the Bead Geometry in Laser Metal Deposition with Wire( 2023-09-28)Laser metal deposition with wire (LMD-w) is a promising additive manufacturing technology, which attracts interest due to the low waste of material, the flexible application possibilities along the production chain and the improved metallurgical properties compared to powder-based processes. However, the complex handling of the technology and the resulting low process stability inhibit the broad industrial application. In particular, the varying bead geometry prevents automation and series production. To improve the geometric accuracy, it is necessary to understand influencing parameters. For this purpose, a parameter study is carried out in the present work. Different combinations of laser power, wire feed rate, traverse speed and welding angle are set, and the deposited beads are evaluated in terms of height and width. A factorial design experiment with the Box-Behnken was used to analyse and understand the interaction of these parameters on the deposited beads.
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PublicationCoefficient of friction of cemented carbides machined by sinking EDM( 2023)Cemented carbides possess properties that predestine them as a durable tool. However, these properties hinder conventional machining, which is why Electrical Discharge Machining (EDM) is a promising alternative. Three different EDMed cemented carbides were compared with a ground surface in a pin-on-disk test setup. They were evaluated under dry and lubricated conditions with two distinct antibody materials. The tests did not reveal a correlation between the surface roughness of the cemented carbide pins and the coefficient of friction. However, some test sets yielded very different results, which is why particular considerations should be made with new sliding compositions.
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PublicationMonitoring of fluctuating material properties for optimizing sheet-metal forming processes: a systematic literature review( 2023)Material properties can vary both along a sheet-metal coil and from coil to coil despite tight tolerances influencing the process stability of sheet-metal processes and the part quality, which leads to rejects and machine downtime [1]. This significantly affect the economic efficiency of the process. Monitoring fluctuations in material characteristics at regular intervals along sheet-metal coils is enabled directly by non-destructive testing (NDT) before the process offering conclusions on the material properties. Another material monitoring technique arises from monitoring process conditions of the upstream processes, e.g., cold rolling, leading indirectly to insights on material properties. In this work, a systematic literature review (SLR) [2] is conducted to investigate recent approaches for material monitoring and for the utilization of resulting material data for optimizing different sheet-metal forming processes. Existing approaches for different sheet-metal forming processes are critically appraised. Based on the SLR research gaps are revealed and research opportunities, e.g., arising from a potential transfer of existing solutions between different forming processes and recent advances in data-driven methods, are identified.
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PublicationFine blanking of pre-hardened high manganese steel to investigate the sheared surface hardening and part quality( 2023)Fine blanking is a highly productive process for manufacturing of high accuracy sheet metal parts with functional surfaces. The specific process characteristic leads to high forming in the shear zone and an associated strain hardening of the sheared functional surfaces. Utilization of the process-immanent sheared surface hardening can reduce time and resources of downstream heat treatment processes such as case hardening. High Manganese Steels (HMnS) are characterized by a high strain hardening capacity due to the deformation mechanisms of twinning and transformation induced plasticity occurring during forming. As a result of high tensile strengths, HMnS are suitable as lightweight materials, but often exhibit a relatively low yield strength in terms of structural design features. One approach for increasing the strength values without changing the alloy design is a forming-induced strain hardening of the semi-finished sheet metal by means of upsetting. Therefore, this paper deals with an experimental investigation of the influence of pre-hardening on the blanked part properties during fine blanking of HMnS X40MnCrAlV19-2 LY (1.7401). For this purpose, sheet blanks were strain hardened by means of flat coining and subsequently fine blanked with an analog geometry representing tribologically stressed functional surfaces. Relevant functional surfaces were then analyzed by means of microhardness measurements with regard to the sheared surface hardening as well as characterized in terms of the quality-determining attributes die roll and clean-shear area. Due to the deformation mechanism of twinning, fine blanking of pre-hardened HMnS resulted in a combination of process-immanent high sheared surface hardening and increased yield strength with simultaneous optimal functional surface quality.
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PublicationChevron cracking during full forward impact extrusion of aluminum alloy EN AW 7075 in dependence of heat treatment condition and tribological system( 2023)In addition to the growing demand for energy efficiency, the current and future legal emission limits in the transport sector lead to an increasing demand for weight-reduced components. By substituting conventional materials with weight-reduced components, such as the aluminum alloy EN AW 7075 (AlZn5.5MgCu), emissions during vehicle service life can be reduced. Chevron cracks, also called internal cracks, can be caused by a variety of reasons during cold extrusion processes and pose a great, non-visible challenge for product quality [1]. However, the cause effect relations between the heat treatment condition and the tribological system in regard to damage development have not yet been sufficiently analyzed. In order to examine these relations, the first forming step of a ball pivot was investigated using full forward impact extrusion. Experiments with different tribological systems were investigated by varying lubricant and die treatment with regard to friction and wear reduction. In addition, the effect of the workpiece formability on crack formation was examined by comparing the T6 and soft annealed state of EN AW 7075 as workpiece materials. During this study, the microstructure of both conditions was investigated to highlight differences. A validated FE process simulation using the simulation software Forge NxT 3.2 accompanied the process in order to evaluate the stress state during the full forward impact extrusion process and its relation to the occurrence of chevron crack formation. In the experiments conducted during this study, chevron cracking occurred during full forward impact extrusion of EN AW 7075 in state T6, while in soft annealed condition none appeared. Unlike the heat treatment condition, the tribological system had no impact on the occurrence of chevron cracking but on the severity of the cracks.
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PublicationSurface Grinding of Borosilicate Crown Glass Optics via a Robotic Approach Based on Superposed Trajectories( 2023)The production of large-sized optical components with complex shapes requires several phases, including surface finishing. Currently, mainly skilled workers can correctly perform this operation, divided into the successive steps of grinding and polishing, leading to long production times, poor reproducibility of results, and exposure to human error. For this reason, the industry is trying to move towards automation involving, for example, high-precision machine tools and machining centers. However, these solutions require high investment costs and long setup times. Using robotic cells helps to reduce these expenses, manufacture larger components, and increase the flexibility in the production chain. In this research, we present an unconventional approach to the robot-assisted grinding of optical samples made of borosilicate crown glass. The samples were guided by a six-degree-of-freedom industrial robot on a rotating grinding disc while imposing to them different trajectories with complex geometry. We avoided regular grinding patterns, which are easily recognizable by human eyes and affect the quality assessment, by superposing multiple relative movements between the machined surface and the abrasive grains. The ground surfaces of the samples were characterized based on average roughness values, profile error data, and surface topography images. Finally, we selected the best robotic grinding procedure matching the trajectory and strategy with optimal surface quality, processing time, and productivity. The suggested methodology not only shortens the manufacturing sequence by eliminating manual methods but also provides components with optical properties within the required specifications for subsequent polishing steps.
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PublicationA Model Calculation of CO2 Emissions Saving Potential for Fine Blanking of Inductively Heated Sheet Metal with Comparison of the Product Variants( 2023)The steel processing industry must increasingly question itself with regard to environmental aspects, especially for automobile production. As a consequence of the resulting lightweight construction requirements in the automotive sector, manufacturing processes of industrial relevance must deal with high-strength steels. In case of fine blanking, the process faces its limits already when processing medium-high tensile strength steels because of high tool wear or failure. A promising approach to overcome these process limits is the introduction of heat into the processed metal sheet in order to lower the flow stress of the steel. In order to estimate the sustainability of a fine blanking process with inductively heated sheets, the energy input during heating is investigated in this work. An energy balance is drawn for fine blanking of inductively heated sheets. A further component of the work is the subsequent use phase of the components produced in this way. A consideration of the greenhouse gas emissions savings potential by fine blanking in the German automotive production shows possible future perspectives for manufacturing. It could be found that by substituting standard fine blanking process by inductively heated fine blanking of higher strength steels greenhouse gas emissions can be decreased.
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PublicationInfluence of process parameters and process set-up on damage evolution during stretch drawing of u-shaped profiles( 2023)The damage state in the form of voids and lattice defects of a sheet metal component has a substantial impact on the performance of a component in service regarding fatigue or crash behaviour. Therefore, managing the damage evolution during forming, especially the accumulation and distribution of damage, by targeted changes of the process parameters and set-up enables to improve component performance by influencing the stress-strain state [1]. The evolution of the stress-strain state during the forming process and along the process route represents the most significant factor influencing the resulting damage state. This paper focuses on the influence of the damage state of sheet metal components in order to improve the performance of a component regarding fatigue and crash behavior. Considering a variation of the process parameter (drawing die radius) and change in process set-up (singlestep, multistep, reverse stretch drawing) the damage accumulation and distribution within the component is analyzed using a calibrated LEMAITRE damage model. For the consideration of this paper, an u-shaped geometry of dual phase steel DP800, which is often found as an element in vehicle body construction, is used.
