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PublicationAssessing the Environmental and Economic Impact of Wire-Arc Additive Manufacturing( 2024-05)
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PublicationSurrogate modeling for multi-objective optimization in the high-precision production of LiDAR glass optics( 2024-04-24)
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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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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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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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PublicationModification of the surface integrity of powder metallurgically produced S390 via deep rolling( 2023)Fine blanking is an economical process for manufacturing sheet metal workpieces with high sheared surface quality. When machining high-strength steels, material fatigue leads to increased punch wear, which reduces the economic efficiency of the process. This fatigue of the cutting edge and lateral punch surface can be counteracted by mechanical surface treatments. Deep rolling has proved particularly useful for such surface modification, as it allows both: machining of the lateral punch surface and the application of the cutting edge rounding required for fine blanking. For the precise design of the fine blanking punch contour especially the macroscopic deformation of the workpiece is decisive. In this paper, the possibility of specifically modifying the surface integrity of hardened and powder metallurgically produced S390 by means of the incremental surface treatment process deep rolling is investigated. By varying the decisive process parameters rolling pressure, ball diameter and step over distance, their influence on surface integrity is determined. The surface integrity is afterwards characterized by macro hardness, surface topography and residual stress state and microstructural images.
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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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PublicationOrthogonal cutting with additively manufactured grooving inserts made from HS6-5-3-8 high-speed steel( 2023)Additive manufacturing (AM) of cutting materials such as high-speed steel (HSS) is very challenging. So far, the impact of the layer-by-layer manufacturing technique onto the AM tool performance during machining is widely unknown. In this study, the performance characteristics of AM grooving inserts manufactured from HS6-5-3-8 (ASP 2030) in AM Laser Powder Bed Fusion (LPBF) process were investigated in fundamental cutting experiments. Six different workpiece materials were analyzed and two different parameter sets for the LPBF process investigated. All AM grooving inserts withstood the thermal and mechanical stresses during machining of the investigated materials. Based on these results, AM threading tools manufactured from HS6-5-3-8 will be investigated in a next step, using the geometrical freedom of the AM process for an adapted channel and outlet nozzle design of the internal cutting fluid supply.
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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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