Browsing by Author "Stehle, Thomas"

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Open Access
Determination of the shear angle in the orthogonal cutting process
(2022) Storchak, Michael; Stehle, Thomas; Möhring, Hans-Christian
Determination of the shear angle by experimental and analytical methods, as well as by numerical simulation, is presented. Experimental determination of the shear angle was performed by analyzing the chip roots obtained by the method of cutting process quick stop through purposeful fracture of the workpiece in the area surrounding the primary cutting zone. The analytical determination of the shear angle was carried out using the chip compression ratio and was based on the principle of a potential energy minimum. Measurement of the shear angle in the numerical simulation of orthogonal cutting was performed using the strain rate pattern of the machined material at the selected simulation moment. It was analyzed how the parameters of the Johnson-Cook constitutive equation and the friction model affect the shear angle value. The parameters with a predominant effect on the shear angle were determined. Then the generalized values of these parameters were established with a software algorithm based on identifying the intersection of the constitutive equation parameter sets. The use of generalized parameters provided the largest deviation between experimental and simulated shear angle values from 9% to 18% and between simulated and analytically calculated shear angle values from 7% to 12%.
Open Access
Determination of the tool-chip contact length for the cutting processes
(2022) Storchak, Michael; Drewle, Konstantin; Menze, Christian; Stehle, Thomas; Möhring, Hans-Christian
The thermomechanical interaction of the tool with the chip in the most loaded secondary cutting zone depends on the contact length of the tool rake face with the chip. Experimental studies of the dependency of the contact length on the cutting speed, the undeformed chip thickness, and the tool rake angle, performed by the optical method, are used for comparison with the contact length obtained by the FE modeling of the orthogonal cutting process. To determine the parameters of the constitutive Johnson-Cook equation, which serves as a material model of the FE cutting model that has a predominant influence on the contact length, a software-implemented algorithm was developed. This algorithm is based on determining the generalized parameters of the constitutive equation through finding the intersection of these parameter sets. The plurality intersection of the parameter sets of the constitutive equation is determined by means of the design of experiments and refined by subsequent multiple iterations. The comparison of the contact length values, obtained by simulating the cutting process using the generalized parameters of the constitutive equation as a material model with their experimental values, does not exceed 12% for a wide range of cutting speeds and depths of cut, as well as for the tool rake angle.
Open Access
Einsatz von KI bei der Prozessvorhersage für Bandsägen : Einsatz von künstlicher Intelligenz zur Vorhersage von Prozesskräften beim Bandsägen
(2023) Tandler, Tobias; Hirth, Thomas; Eisseler, Rocco; Stehle, Thomas; Möhring, Hans-Christian
Open Access
Influence of a closed-loop controlled laser metal wire deposition process of S Al 5356 on the quality of manufactured parts before and after subsequent machining
(2021) Becker, Dina; Boley, Steffen; Eisseler, Rocco; Stehle, Thomas; Möhring, Hans-Christian; Onuseit, Volkher; Hoßfeld, Max; Graf, Thomas
This paper describes the interdependence of additive and subtractive manufacturing processes using the production of test components made from S Al 5356. To achieve the best possible part accuracy and a preferably small wall thickness already within the additive process, a closed loop process control was developed and applied. Subsequent machining processes were nonetheless required to give the components their final shape, but the amount of material in need of removal was minimised. The effort of minimising material removal strongly depended on the initial state of the component (wall thickness, wall thickness constancy, microstructure of the material and others) which was determined by the additive process. For this reason, knowledge of the correlations between generative parameters and component properties, as well as of the interdependency between the additive process and the subsequent machining process to tune the former to the latter was essential. To ascertain this behaviour, a suitable test part was designed to perform both additive processes using laser metal wire deposition with a closed loop control of the track height and subtractive processes using external and internal longitudinal turning with varied parameters. The so manufactured test parts were then used to qualify the material deposition and turning process by criteria like shape accuracy and surface quality.
Open Access
Influence of the manufacturing parameters of an AlMg5 wire-based hybrid production process on quality and mechanical properties
(2021) Möhring, Hans-Christian; Becker, Dina; Eisseler, Rocco; Stehle, Thomas; Reeber, Tim
Hybrid manufacturing processes are known for combining the advantages of additive manufacturing and more traditional manufacturing processes such as machining to create components of complex geometry while minimising material waste. The trend towards lightweight design, especially in view of e-mobility, gives aluminium materials an important role to play. This study examines the use of aluminium alloys in laser metal wire deposition (LMWD) processes with subsequent subtractive machining, which is considerably more difficult due to the different process-related influences. The investigations are focussed on the influence of the differently controlled laser power on the shape accuracy, the microstructure, and the hardness of the AlMg5 test components after the LMWD process with subsequent subtractive machining by turning. The long-term goal of the investigations is to increase the stability of the hybrid production process of AlMg5 components with defined dimensional accuracy and mechanical properties.
Open Access
Numerical modeling of cutting characteristics during short hole drilling : modeling of kinetic characteristics
(2023) Storchak, Michael; Stehle, Thomas; Möhring, Hans-Christian
Analyzing the cutting process characteristics opens up significant opportunities to improve various material machining processes. Numerical modeling is a well-established, powerful technique for determining various characteristics of cutting processes. The developed spatial finite element model of short hole drilling is used to determine the kinetic characteristics of the machining process, in particular, the components of cutting force and cutting power. To determine the component model parameters for the numerical model of drilling, the constitutive equation parameters, and the parameters of the contact interaction between the drill and the machined material on the example of AISI 1045 steel machining, the orthogonal cutting process was used. These parameters are determined using the inverse method. The DOE (Design of Experiment) sensitivity analysis was applied as a procedure for determining the component models parameters, which is realized by multiple simulations using the developed spatial FEM model of orthogonal cutting and the subsequent determination of generalized values of the required parameters by finding the intersection of the individual value sets of these parameters. The target values for the DOE analysis were experimentally determined kinetic characteristics of the orthogonal cutting process. The constitutive equation and contact interaction parameters were used to simulate the short hole drilling process. The comparison of experimentally determined and simulated values of the kinetic characteristics of the drilling process for a significant range of cutting speed and drill feed changes has established their satisfactory coincidence. The simulated value deviation from the corresponding measured characteristics in the whole range of cutting speed and drill feed variation did not exceed 23%.
Open Access
Numerical modeling of cutting characteristics during short hole drilling : part 2 - modeling of thermal characteristics
(2024) Storchak, Michael; Stehle, Thomas; Möhring, Hans-Christian
The modeling of machining process characteristics and, in particular, of various cutting processes occupies a significant part of modern research. Determining the thermal characteristics in short hole drilling processes by numerical simulation is the object of the present study. For different contact conditions of the workpiece with the drill cutting inserts, the thermal properties of the machined material were determined. The above-mentioned properties and parameters of the model components were established using a three-dimensional finite element model of orthogonal cutting. Determination of the generalized values of the machined material thermal properties was performed by finding the set intersection of individual properties values using a previously developed software algorithm. A comparison of experimental and simulated values of cutting temperature in the workpiece points located at different distances from the drilled hole surface and on the lateral clearance face of the drill outer cutting insert shows the validity of the developed numerical model for drilling short holes. The difference between simulated and measured temperature values did not exceed 22.4% in the whole range of the studied cutting modes.
Open Access
Optimization of a clamping concept based on machine learning
(2021) Feng, Qi; Maier, Walther; Stehle, Thomas; Möhring, Hans-Christian
Fixtures are an important element of the manufacturing system, as they ensure productive and accurate machining of differently shaped workpieces. Regarding the fixture design or the layout of fixture elements, a high static and dynamic stiffness of fixtures is therefore required to ensure the defined position and orientation of workpieces under process loads, e.g. cutting forces. Nowadays, with the increase in computing performance and the development of new algorithms, machine learning (ML) offers an appropriate possibility to use regression methods for creating realistic, rapid and reliable equivalent ML models instead of simulations based on the finite element method (FEM). This research work introduces a novel method that allows an optimization of clamping concepts and fixture design by means of ML, in order to reduce manufacturing errors and to obtain an increased stiffness of fixtures and machining accuracy. This paper describes the preparation of a dataset for training ML models, the systematic selection of the most promising regression algorithm based on relevant criteria, the implementation of the chosen algorithm Extreme Gradient Boosting (XGBoost) and other comparable algorithms, the analysis of their regression results, and the validation of the optimization for a selected clamping concept.
Open Access
SmartLab vernetzt Produktionsmaschinen : Aufbau einer digitalen Prozesskette in einer bestehenden Produktionsumgebung
(2023) Schneider, Matthias; Meier, Veronika; Stehle, Thomas; Möhring, Hans-Christian
Open Access
Werkzeugmaschinen mit Beinen - die Hexapod-Maschinen
(2002) Heisel, Uwe; Stehle, Thomas; Maier, Walther
Kaum eine andere Entwicklung im Werkzeugmaschinenbau hat das Aussehen und die konstruktive Struktur der Maschinen so sehr verändert wie die Einführung einer neuen Kinematik, die nicht mehr auf den gewohnten, seit jeher unverändert kartesisch zueinander angeordneten Maschinenachsen beruht, sondern auf einem Bewegungsgebilde aus miteinander verbundenen Antriebsstreben und Gelenkstäben, den „Vielbeinern“ oder – wie sie in der Fachwelt genannt werden – den Tripoden beziehungsweise den Hexapoden. Die Bezeichnung Hexapod hat sich inzwischen im internationalen Sprachgebrauch zum Oberbegriff der gesamten Maschinengattung entwickelt. Die neuen Maschinen bieten völlig neue Perspektiven in der Bewegungsflexibilität und Dynamik und eröffnen bezüglich der Bemühungen um die Verbesserung und Weiterentwicklung der Werkzeugmaschinen weitreichende Perspektiven.