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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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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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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.
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PublicationNumerical Prediction of the Influence of Process Parameters and Process Set-Up on Damage Evolution during Deep Drawing of Rectangular Cups( 2022)The manufacturing of three-dimensional components by deep drawing is performed using flat sheets. The material properties of the sheets are influenced by the deep drawing process by means of microstructural effects (e.g., anisotropy, residual stresses, voids, lattice defects). The resulting effects, especially voids and lattice defects, influence the component in the form of damage accumulation and evolution. Depending on the process route and parameters, different load paths are created, which lead to different damage evolution scenarios. This paper numerically investigated the influence of process parameter (drawing ring radius) as well as process set-up (multi-step deep drawing and reverse drawing) during deep drawing and the associated load paths on damage evolution in rectangular cups made out dual phase steel DP800.
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PublicationSize and speed of ejected particles from different cemented carbide grades machined with sinking EDM( 2022)The application of cemented carbides is desired in several fields due to their superb mechanical properties. The downside of the large strength and wear resistance occurs upon machining, which, especially for conventional machining, is expensive or even impossible. Hence, Electrical Discharge Machining (EDM) is used since it works independently from the mechanical properties of the workpiece. However, the ED-machining of cemented carbides is also characterised by low productivity and high tool wear when it is compared to the machining of steel. This paper investigates the material removal phenomenon of different cemented carbide grades by means of a high speed video camera. In order to allow observation, the single discharges are conducted in air. A large number of experiments with different energy levels is analysed by an algorithm to identify the particle size, particle speed and the ejection angle. The results can be used to identify the dominant material removal mechanism. This should in the future be used to create a machining technology which is dedicated to the specific cemented carbide grade.
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PublicationDeep Rolling of Bores Using Centrifugal Force( 2022)Deep rolling is a mechanical surface treatment for the specific modification of edge zone properties. In this process, the surface is plastically deformed by a rolling element. The roughness, residual stresses and hardness in particular can be positively influenced. An external pressure unit is usually used to generate the forces required for plastic deformation. The acquisition costs associated with the pressure unit and the space required reduce the attractiveness of deep rolling. In this work, the possibility of generating the required forces by exploiting the rotational speed of machining center spindles for processing bores is shown.
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PublicationThermographic in-situ investigation of precise electrochemical machining( 2022)Modelling of ECM is a powerful tool to improve the cost- and time intensive tool-development process. While different simulation models for DC-ECM have been published and validated, the virtual prediction of the process variant with oscillating cathode is still hindered by its highly transient nature. In order to develop and later validate a model of PECM, high-resolution information on the temperature profile and gas evolution during one oscillation is required. Temperature and gas concentration both increase during the electric pulses and constantly decrease due to flushing. This paper presents a fixture that allows the thermographic analyses of the PECM process. Consequently, the conditions within the electrolyte channel during PECM are captured which allows a deeper understanding of the process.
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PublicationTowards in-process evaluation of the precise electrochemical machining (PECM)( 2022)Increasing environmental and economic concerns have increased the use of high-strength materials and superalloys, such as the well-known nickel-based alloys. Due to their very high strength, such materials push established machining methods to their economic limits. As a result, non-traditional machining methods such as precise electrochemical machining (PECM) are gaining importance. PECM has shown significant advantages such as high material removal rates and lower surface roughness. Despite these advantages, some challenges still need to be overcome, such as the implementation of an in-process monitoring system and the determination of optimal process parameters to achieve maximum material removal rates and good surface roughness. While the analytical determination of the optimal parameters is difficult due to the high complexity of the process, the empirical determination shows better results. However, a hitherto very unused approach in this respect is the data-driven model. Based on process data, such models have shown great results in other fields, especially for highly complex systems. The first step in developing such a model is to figure out what process data are needed. In this paper, the potential of a data driven model for PECM is presented. Furthermore, current waveforms for different PECM setups are analyzed and various parameters for the in-process monitoring of the process are formulated. The ability of these parameters to differentiate between different processes was investigated. It was found that the formulated parameters could be used to monitor the efficiency of flushing in the working gap.
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PublicationEffect of a Single Particle in Abrasive Waterjet Machining on 42CrMo4 Modifications( 2022)Waterjet machining is a powerful tool for processing of a variety of materials from ductile to brittle ones. However, it is a complicated machining process to control and predict its results on the workpiece due to the interaction of high dynamic abrasive particles with the workpiece surface and with each other simultaneously. A proper approach to decrease this complication is to investigate the effect of a single particle on the workpiece surface instead of multiple particles with their complex interactions. Therefore, the aim of this study is to understand the mechanism of abrasive waterjet machining by considering the effect of single particles of different abrasives with different attacking angles on two different microstructural conditions of a steel alloy. Here, 42CrMo4 is selected as the workpiece material for its ability to have different modifications from ductile to brittle characteristics. First, the effect of process parameters on the impact characteristics of the waterjet is studied. In the next step, the effect of particle velocity on the workpiece material modification is investigated. Furthermore, the effect of impact angle on the material modification and shape of the generated footprints is explored. Moreover, the effect of kinetic and kinematic properties of abrasive particle on burr formation in the ductile modification of 42CrMo4 is investigated.
