Browsing by Author "Möhring, Hans-Christian"

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Open Access
Assessment of the heat transfer conditions in the cavity of a rotating circular saw
(2024) Stegmann, Jan; Baumert, Moritz; Kabelac, Stephan; Menze, Christian; Ramme, Johannes; Möhring, Hans-Christian
To improve machining processes concerning the usage of lubricants, knowledge of the thermo-mechanical and thermo-fluid interactions at the cutting zone is of great importance. This study focuses on the description of the convective heat transfer which occurs during circular sawing when the lubricant is provided via an internal coolant supply. The highly complex flow field inside the cavity of the sawing process is separated into two distinct flow forms, an impingement and a channel flow. With the aid of experimental and numerical studies, the heat transfer characteristics of these two flow forms have been examined for water and a lubricant used in the circular sawing process. Studies have been conducted over a wide range of Reynolds numbers (impingement flow: 2×103
Open Access
Augmented reality to visualize a finite element analysis for assessing clamping concepts
(2024) Maier, Walther; Möhring, Hans-Christian; Feng, Qi; Wunderle, Richard
This paper presents the development of an innovative augmented reality application for evaluating clamping concepts through visualizing the finite element analysis. The focus is on transforming the traditional simulation results into immersive, holographic displays, enabling users to experience and assess finite element analysis in three dimensions. The application development process involves data processing by MATLAB, visualization in the software Unity, and displaying holograms through Microsoft’s Hololens2. The most significant advancement introduces a new algorithm for rendering different finite elements in Unity. The application targets not only university engineering students but also vocational students with limited background in finite element analysis and machining, aiming to make the learning process more interactive and engaging. It was tested in a real machining environment, demonstrating its technical feasibility and potential in engineering education.
Open Access
Cutting tool condition monitoring using eigenfaces : tool wear monitoring in milling
(2022) König, Wolfgang; Möhring, Hans-Christian
Effective monitoring of the tool wear condition within a machining process can be very challenging. Depending on the sensors used, often only a part of the relevant wear information can be detected. In the case of milling processes data acquisition is made even more difficult by the fact that the process working point is inaccessible for sensor applications due to the physical tool, the machining process itself, the chipping and used cooling-lubricants. By using a variety of sensors and different measuring principles, sensor data fusion strategies can counteract this problem. An approach to this is the eigenface algorithm. This approach, a face recognition technique, is tested for its suitability on tool condition monitoring in milling processes by using multi-sensor process data.
Open Access
A data-driven approach for cutting force prediction in FEM machining simulations using gradient boosted machines
(2024) Reeber, Tim; Wolf, Jan; Möhring, Hans-Christian
Cutting simulations via the Finite Element Method (FEM) have recently gained more significance due to ever increasing computational performance and thus better resulting accuracy. However, these simulations are still time consuming and therefore cannot be deployed for an in situ evaluation of the machining processes in an industrial environment. This is due to the high non-linear nature of FEM simulations of machining processes, which require considerable computational resources. On the other hand, machine learning methods are known to capture complex non-linear behaviors. One of the most widely applied material models in cutting simulations is the Johnson-Cook material model, which has a great influence on the output of the cutting simulations and contributes to the non-linear behavior of the models, but its influence on cutting forces is sometimes difficult to assess beforehand. Therefore, this research aims to capture the highly non-linear behavior of the material model by using a dataset of multiple short-duration cutting simulations from Abaqus to learn the relationship of the Johnson-Cook material model parameters and the resulting cutting forces for a constant set of cutting conditions. The goal is to shorten the time to simulate cutting forces by encapsulating complex cutting conditions in dependence of material parameters in a single model. A total of five different models are trained and the performance is evaluated. The results show that Gradient Boosted Machines capture the influence of varying material model parameters the best and enable good predictions of cutting forces as well as deliver insights into the relevance of the material parameters for the cutting and thrust forces in orthogonal cutting.
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
Development of a multi-sensor concept for real-time temperature measurement at the cutting insert of a single-lip deep hole drilling tool
(2022) Ramme, Johannes; Wegert, Robert; Guski, Vinzenz; Schmauder, Siegfried; Möhring, Hans-Christian
The mechanical energy resulting from cutting processes is turned almost completely in thermal energy, which encourages thermal procedures, such as diffusion, leading to higher wear in the cutting tool and thus to higher temperatures. Furthermore, high temperatures influence the properties of the marginal zones in the workpiece. In this presented work, the in-process temperature of a cutting insert during single-lip deep hole drilling (SLD) is investigated. Therefore, a sensor-integrated tool with resistance temperature detectors (RTD) placed beneath the cutting insert is developed. First, the thermal properties of the cutting insert are adjusted to fit the assembled tool. Afterwards, a CEL-Simulation is obtained to examine the temperature distribution at the cutting edge of the SLD-tool. The temperatures calculated by simulation can be compared to the in-process temperatures of the sensor integrated tool. Because of the usage of a cooling lubricant, simulated temperatures can be varied with a factor to fit the experimentally measured temperature curves. The highest temperature during the process appears at the outer edge of the cutting insert. By knowing the thermal properties, the maximum process temperatures for the deep hole drilling operation are to be calculated. The results represent a contribution to an interdisciplinary research project “Surface Conditioning in Machining Processes” (SPP 2086) of the German Research Foundation (DFG).
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
Evaluation of methods for measuring tool-chip contact length in wet machining using different approaches (microtextured tool, in-situ visualization and restricted contact tool)
(2022) Ellersiek, Lars; Menze, Christian; Sauer, Florian; Denkena, Berend; Möhring, Hans-Christian; Schulze, Volker
The contact length is one of the most important factors to evaluate the chip formation process and the mechanical loads in metal cutting. Over the years, several methods to identify the contact length were developed. However, especially for wet cutting processes the determination of the contact length is still challenging. In this paper, three methods to identify the contact length for dry and wet processes in cutting of Ti6Al4V and AISI4140 + QT are presented, discussed and analyzed. The first approach uses tools with a microtextured rake face. By evaluating the microstructures on the chip, a new method to identify the contact length is established. The second approach applies high speed recordings to identify the contact length. The challenge is thereby the application of high-speed recordings under wet conditions. In the third approach, tools with restricted contact length are used. It is shown that with all three methods the contact length is reduced using metal working fluid.
Open Access
Flow visualisation and evaluation studies on metalworking fluid applications in manufacturing processes : methods and results
(2023) Fritsching, Udo; Buss, Lizoel; Tonn, Teresa; Schumski, Lukas; Gakovi, Jurgen; Hatscher, Johnson David; Sölter, Jens; Avila, Kerstin; Karpuschewski, Bernhard; Gerken, Julian Frederic; Wolf, Tobias; Biermann, Dirk; Menze, Christian; Möhring, Hans-Christian; Tchoupe, Elio; Heidemanns, Lukas; Herrig, Tim; Klink, Andreas; Nabbout, Kaissar; Sommerfeld, Martin; Luther, Fabian; Schaarschmidt, Ingo; Schubert, Andreas; Richter, Markus
Metalworking operations rely on the successful application of metalworking fluids (MWFs) for effective and efficient operation. Processes such as grinding or drilling often require the use of MWFs for cooling, lubrication, and chip removal. Electrochemical machining processes require electrolyte flow to operate. However, in those machining operations, a fundamental understanding of the mode of action of MWF is lacking due to the unknown flow dynamics and its interaction with the material removal during the process. Important information on the behaviour of MWFs during machining can be obtained from specific experimental flow visualisation studies. In this paper, promising flow visualisation analysis techniques applied to exemplary machining processes (grinding, sawing, drilling, and electrochemical machining) are presented and discussed. Shadowgraph imaging and flow measurements, e.g., particle image velocimetry, allow the identification of typical flow and MWF operating regimes in the different machining processes. Based on the identification of these regimes, efficient machining parameters and MWF applications can be derived. In addition, detailed experimental analyses of MWFs provide essential data for the input and validation of model development and numerical simulations within the Priority Programme SPP 2231 FluSimPro.
Open Access
Generalizable process monitoring for FFF 3D printing with machine vision
(2023) Werkle, Kim Torben; Trage, Caroline; Wolf, Jan; Möhring, Hans-Christian
Additive manufacturing has experienced a surge in popularity in both commercial and private sectors over the past decade due to the growing demand for affordable and highly customized products, which are often in direct opposition to the requirements of traditional subtractive manufacturing. Fused Filament Fabrication (FFF) has emerged as the most widely-used additive manufacturing technology, despite challenges associated with achieving contour accuracy. To address this issue, the authors have developed a novel camera-based process monitoring method that enables the detection of errors in the printing process through a layer-by-layer comparison of the actual contour and the target contour obtained via G-Code processing. This method is generalizable and can be applied to different printer models with minimal hardware adjustments using off-the-shelf components. The authors have demonstrated the effectiveness of this method in automatically detecting both coarse and small contour deviations in 3D-printed parts.
Open Access
Improving machinability of additively manufactured components with selectively weakened material
(2021) Maucher, Clemens; Teich, Heiko; Möhring, Hans-Christian
Part design and the possibilities of production are disrupted by the increased usage of additive manufacturing (AM). Featuring excellent creative freedom due to the layer-by-layer buildup of components, AM leads to profound changes in future part design and enables previously impossible geometries. Laser powder bed fusion (LPBF) technology already allows to manufacture small quantities of parts with high productivity and material efficiency. Due to the specific process characteristics, the resulting surface finish of these parts is insufficient for a wide range of applications, and post-processing is usually unavoidable. Specifically for functional surfaces, this post-processing is often done by machining processes, which can pose challenges for intricate and complex AM parts due to excessive machining forces. In the present paper, the influence and the possibilities of the LPBF process parameters on the subtractive post-processing are shown. A novel weakened structure is developed to selectively reduce the strength of the material and improve the cutting conditions. Chip formation, cutting forces and vibrations during drilling as well as cutting forces during an orthogonal cut are examined. To quantify the differences, a comparison of the machinability between bulk material, standard support structures and the weakened structure is carried out.
Open Access
In-process approach for editing the subsurface properties during single-lip deep hole drilling using a sensor-integrated tool
(2024) Wegert, Robert; Guski, Vinzenz; Schmauder, Siegfried; Möhring, Hans-Christian
Single-lip deep-hole drilling (SLD) is characterized by high surface quality and compressive residual stress in the subsurface of the drill hole. These properties depend significantly on the thermomechanical conditions in the machining process. The desired subsurface properties can be adjusted in-process via process monitoring near the cutting zone with a sensor-integrated tool and closed loop control when the thermomechanical conditions are maintained in the optimum range. In this paper, a method is presented to control the thermomechanical conditions to adjust the properties in the subsurface. The process model integrated in the controller is implemented as a soft sensor and takes into account the residual stresses, the roughness, the hardness and the grain size in the surface as well as in the subsurface depending on the process control variables, such as the feed rate and cutting speed. The correlation between the process variables, the thermomechanical conditions of the cutting process and the subsurface properties are investigated both experimentally and by finite element (FE) simulations. Within a justified process parameter range, characteristic fields for the soft sensor were established for each property. In addition, the procedure of controller design and the employed hardware and interfaces are presented.
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
Inverse determination of Johnson-Cook parameters of additively produced anisotropic maraging steel
(2021) Eisseler, Rocco; Gutsche, Daniel; Maucher, Clemens; Möhring, Hans-Christian
In powder bed-based additive manufacturing (AM), complex geometries can be produced in a layer-wise approach. Results of material science experiments regarding material property identification, e.g., tensile strength, show interdependencies between the test load direction and the layer orientation. This goes hand-in-hand with the measured cutting force, changing with the relative angle between cutting direction and layer orientation in orthogonal cutting tests. However, due to the specific process characteristics, the layer orientation results in anisotropic material properties. Therefore, during machining, the material behaves depending on the buildup direction, which influences the cutting process. To predict this behavior, a simplified inverse approach is developed to determine the buildup direction-dependent parameters of a modified Johnson-Cook model for cutting simulation. To qualify these cutting models, mainly the cutting force and additionally the chip formation examined during orthogonal cuts are used. In the present paper, the influence of the laser-powder-bed-fusion (LPBF) process parameters on subtractive post-processing are shown. A good agreement between verification experiments and simulations is achieved.
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
Simulation study on single-lip deep hole drilling using design of experiments
(2021) Fandino, Daniel; Guski, Vinzenz; Wegert, Robert; Möhring, Hans-Christian; Schmauder, Siegfried
Single-lip deep hole drilling (SLD) is characterized by a high surface quality and compressive residual stress in the subsurface of the drill hole. These properties are strongly dependent on the cutting parameters of the SLD process and the actual geometry of the insert and the guide pads. In the present work, full 3D FE simulations of the SLD process were carried out to analyze the thermo-mechanical as-is state in the drilling contact zone by evaluating the feed force, the temperature, as well as the residual stress in the drill hole subsurface. An extensive simulation study was conducted on the effect of the process parameters on the properties using design of experiments (DoE). For the simulations, the Johnson-Cook (JC) constitutive law and the element elimination technique (EET) were applied to represent the material behavior of the workpiece, including chip formation. In-process measurements as well as results from the hole-drilling method to determine residual stresses were conducted to verify the numerical results. By means of DoE and analysis of variance (ANOVA), regression models were developed to describe the effect of the feed rate, cutting speed, and guide pad height on the temperature, feed force, and residual stress in the subsurface.