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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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PublicationImproved lifetime estimation of shot-peened shaft bores using a numerical approach( 2024)
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PublicationReduction of Taper Angle and Jet Trailback in Waterjet Cutting of Complex Geometries by a Revised Model of the Process Control( 2023)The high-pressure waterjet is a flexible and powerful tool for machining of high-performance products with reduced manufacturing time and costs. However, waterjet machining of complex geometries is difficult to handle because of the complication in controlling and adjusting the process. Therefore, the goal of this study is to improve a process control method to adjust the waterjet tool orientation and to optimize the waterjet cutting process in a simple and efficient manner. As a result, a method is developed which is based on constant feed rate and a distinction between concave and convex curvature of the workpiece geometry.
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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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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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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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PublicationModel Based Prediction of the Heat Affected Zone in a Steel Workpiece Induced by an EDM Single Discharge( 2023)Setting a determined microstructure within the rim zone of a manufactured workpiece without cost-intensive trial and error experiments is essential to meet the increasing requirements of the industry. The most promising approach to predict the final functional properties is to simulate the microstructure evolution and to build an inverse approach of the manufacturing process. Thermal load based microstructure evolution models with an artificial initial structure and temperature gradients up to 1·106K/s have been published in previous works presented by the authors. In this work, an existing heat transfer model was extended to predict the actual temperature gradients for a single discharge during electrical discharge machining (EDM). These calculated temperature gradients were then used to simulate the microstructure evolution of a 42CrMo4 steel. The initial structure was derived from a cross sectional SEM image. Therefore, the presented model is able to simulate the actual microstructure evolution within the heat affected zone of an EDM'ed workpiece.
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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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PublicationMechanism-driven fine blanking of high manganese steels( 2023)Fine blanking is used in industrial processes for mass production of high accuracy sheet metal parts. The process characteristic leads to a strain hardening of the sheared surface. Utilization of the process-immanent surface hardening can reduce time and energy consumption of downstream heat treatment processes like case hardening. Substituting High Strength Low Alloy (HSLA) steels by High Manganese Steels (HMnS) increases strain hardening during fine blanking and may replace the necessary heat treatment. This work investigated the mechanism-driven behavior of HMnS (1.7401) during fine blanking and its influencing factors, changing the part properties. Based on a characterization of the material properties of HMnS, the influence of the initial sheet temperature, blanking velocity and blank holder force on the sheared surface hardening and quality was analyzed. Due to enhanced strain hardening of HMnS, higher surface hardness with softer core was achieved compared to S700MC (1.8974) HSLA-steel. In addition, the sheared surface hardening was increased by a decrease in blanking velocity and an increase in blank holder forces. Taking into account the alloy design, fine blanking of HMnS offers the potential to achieve a high sheared surface hardening by targeted activation of the deformation mechanisms with simultaneous high quality and strength.
