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Benedict Stampfer, M.Sc.

  • 76131 Karlsruhe
    Kaiserstraße 12

Benedict Stampfer, M.Sc.

Area of Research:

  • Surface Engineering of AISI 4140 QT
  • Modeling, multi-sensor-application and process control
  • Cooling strategies in machining
    • Minimum Quantity Lubrication
    • Cryogenic machining with liquid nitrogen
  • Machining of Ti-6Al-4V
  • Machining simulation by means of the Finite-Element-Method (FEM)
  • Organisation of DFG SPP 2086

 

Projects:

  • DFG: Investigations on thermally induced distortions during machining of Ti-6Al-4V by using local cryo-genic machining
  • DFG SPP 2086: In-process softsensor for surface-conditioning during longitudinal turning of AISI 4140

 

Test benches:

 

Publications

[ 1 ] Stampfer, B.; Zanger, F. & Schulze, V. (2018), "In-Process Analysis of Minimum Quantity Lubrication during Drilling of AISI 4140". Advances in Production Research, eds. Schmitt, R. & Schuh, G., pp. 541-550. 10.1007/978-3-030-03451-1_53
Abstract
Minimum quantity lubrication (MQL) is an established concept to meet high ecological and economical demands in metal machining. Compared to flood cooling, MQL massively reduces the efforts associated with the supply and disposal of the lubricants and the handling of emulsion contaminated chips. At the same time, MQL can reach a similar tool life. The mechanisms that have an influence on this effect are a matter of ongoing research. For this work, aerosol was generated by a 1-channel MQL system and supplied to a drilling process with AISI 4140 specimen. The drilling torque, feed force and workpiece temperatures are evaluated under different MQL air input pressures and tool cooling channel lengths. The results are interpreted by the help of flood cooling reference tests and high speed camera recordings, which reveal the open-jet atomisation of lubrication ligaments at the tool exit, arising from different MQL operation parameters.

[ 2 ] Stampfer, B.; Golda, P.; Zanger, F.; Schießl, R.; Maas, U. & Schulze, V. (2019), "Thermomechanically coupled numerical simulation of cryogenic orthogonal cutting". 17th CIRP Conference on Modelling of Machining Operations (17th CIRP CMMO), eds. Ozturk, E.; Mcleay, T. & Msaoubi, R., pp. 438-443. 10.1016/j.procir.2019.04.036
Abstract
During machining of Ti-6Al-4V, high thermal loads arise, which demand for advanced cooling concepts, such as the application of liquid nitrogen. An efficient approach to analyze the thermomechanical mechanisms which influence the tool life and the workpiece distortions is the usage of coupled numerical simulations. In this work, the Finite -Element-Method was used to simulate the tool-workpiece-interaction and the chip formation, whereas the detailed treatment of the nitrogen fluid flow and its heat transfer is solved by an in-house program using the Finite-Difference-Method. Both simulations are coupled by appropriate boundary conditions, which are updated iteratively during the calculation.

[ 3 ] Stampfer, B.; Böttger, D.; Gauder, D.; Zanger, F.; Häfner, B.; Straß, B.; Wolter, B.; Lanza, G. & Schulze, V. (2020), "Experimental identification of a surface integrity model for turning of AISI4140". Procedia CIRP 87, pp. 83-88. 10.1016/j.procir.2020.02.067
Abstract
In this work an experimental study of the turning of AISI4140 is presented. The scope is the understanding of the workpiece microstructure and hardness-depth-profiles which result from different cutting conditions and thus thermomechanical surface loads. The regarded input parameters are the cutting velocity (vc = 100, 300 m/min), feed rate (f = 0.1, 0.3 mm), cutting depth (ap = 0.3, 1.2 mm) and the heat treatment of the workpiece (tempering temperatures 300, 450 and 600?C). The experimental data is interpreted in terms of machining mechanisms and material phenomena, e.g. the generation of white layers, which influence the surface hardness. Hereby the process forces are analyzed as well. The gained knowledge is the prerequisite of a workpiece focused process control.

[ 4 ] Stampfer, B.; Golda, P.; Schießl, R.; Maas, U. & Schulze, V. (2020), "Cryogenic orthogonal turning of Ti-6Al-4V", The International Journal of Advanced Manufacturing Technology, vol. 111, pp. 359-369. 10.1007/s00170-020-06105-z
Abstract
Cooling of machining operations by liquid nitrogen is a promising approach for reducing cutting temperatures, increasing tool life and improving the workpiece surface integrity. Unfortunately, the cooling fluid tends to evaporate within the supply channel. This induces process variations and hinders the use of nitrogen cooling in commercial applications. In this work, the coolant is applied via the tool?s rake face during orthogonal turning of Ti-6Al-4V. The effect of a nitrogen supply pressure adjustment and a subcooler usage ? proposed here for the first time for machining ? is analyzed in terms of process forces, tool temperatures and wear patterns, taken dry cutting as a reference. Thereby, reliable cooling strategies are identified for cryogenic cutting.

[ 5 ] Golda, P.; Schießl, R.; Stampfer, B.; Schulze, V. & Maas, U. (2020), "Experimental determination of the cooling performance of liquid nitrogen for machining conditions", International Journal of Heat and Mass Transfer, vol. 164, pp. 120588 (1-11). 10.1016/j.ijheatmasstransfer.2020.120588
Abstract
This paper presents an experimental investigation of cryogenic cooling with liquid nitrogen. A thermal imaging camera is used to measure the temperature distribution of a pre-heated titanium alloy (Ti-6Al- 4V) specimen interacting with a flow of liquid nitrogen. The main objective of this work is to determine the surface heat transfer in a robust way. A new method, the so-called inverse global integration method (IGIM), is introduced which allows the calculation of the heat transfer from a solid body to the cryo- genic medium using all available pixel points of a thermogram. Reproducible and accurate results could be achieved by ensuring well-defined initial and boundary conditions during the execution of the exper- iment. The parameters with the highest impact on the heat transfer are the surface temperature, nozzle distance, as well as the working pressure in the nitrogen tank. The work is completed by performing curve fitting on the experimental results in order to compare the cooling performance and to simplify the technical application.

[ 6 ] Schulze, V.; Zanger, F.; Stampfer, B.; Seewig, J.; Uebel, J.; Zabel, A.; Wolter, B. & Böttger, D. (2020), "Surface conditioning in machining processes", tm - Technisches Messen, vol. 87, no. 11, pp. 661-673. 10.1515/teme-2020-0044
Abstract
The new field of surface conditioning in machining requires a common terminology, which needs to be established. Therefore participants of the DFG priority programme 2086 (SPP 2086) created a Glossary focussing on its Task Forces Modelling and Simulation and Measurements and Control. The terms and explanations were also harmonized with the DFG Collaborative Research Centre 926 Microscale Morphology of Component Surfaces and the Collaborative Research Centre 136 Process Signatures in order to reach the goal of an universal terminology. The Glossary is divided into General terms, Modelling and simulation, Measurement and control and Specific measurement techniques.

[ 7 ] Böttger, D.; Stampfer, B.; Gauder, D.; Straß, B.; Häfner, B.; Lanza, G.; Schulze, V. & Wolter, B. (2020), "Concept for soft sensor structure for turning processes of AISI4140", tm - Technisches Messen, vol. 87, no. 12, pp. 745-756. 10.1515/teme-2020-0054
Abstract
During turning of quenched and tempered AISI4140 surface layer states can be generated, which degrade the lifetime of manufactured parts. Such states may be brittle rehardened layers or tensile residual stresses. A soft sensor concept is presented in this work, in order to identify relevant surface modifications during machining. A crucial part of this concept is the measurement of magnetic characteristics by means of the 3MA-testing (Micromagnetic Multiparameter Microstructure and Stress Analysis). Those measurements correlate with the microstructure of the material, only take a few seconds and can be processed on the machine. This enables a continuous workpiece quality control during machining. However specific problems come with the distant measurement of thin surface layers, which are analyzed here. Furthermore the scope of this work is the in-process-measurement of the tool wear, which is an important input parameter of the thermomechanical surface load. The availability of the current tool wear is to be used for the adaption of the process parameters in order to avoid detrimental surface states. This enables new approaches for a workpiece focused process control, which is of high importance considering the goals of Industry 4.0.

[ 8 ] Stampfer, B.; Gonzalez Fernandez, G.; Gerstenmeyer, M. & Schulze, V. (2021), "The Present State of Surface Conditioning in Cutting and Grinding", Journal of manufacturing and materials processing, vol. 5, no. 3, pp. 1-17. doi.org/10.3390/jmmp5030092
Abstract
All manufacturing processes have an impact on the surface layer state of a component, which in turn significantly determines the properties of parts in service. Although these effects should certainly be exploited, knowledge on the conditioning of the surfaces during the final cutting and abrasive process of metal components is still only extremely limited today. The key challenges in regard comprise the process-oriented acquisition of suitable measurement signals and their use in robust process control with regard to the surface layer conditions. By mastering these challenges, the present demands for sustainability in production on the one hand and the material requirements in terms of lightweight construction strength on the other hand can be successfully met. In this review article completely new surface conditioning approaches are presented, which originate from the Priority Program 2086 of the Deutsche Forschungsgemeinschaft (DFG).

[ 9 ] Stampfer, B.; Gonzalez Fernandez, G.; Segebade, E.; Gerstenmeyer, M. & Schulze, V. (2021), "Material parameter optimization for orthogonal cutting simulations of AISI4140 at various tempering conditions", Procedia CIRP , vol. 102, pp. 198-203. 10.1016/j.procir.2021.09.034
Abstract
The mechanical parameters of quenched and tempered AISI4140 and the machining process characteristics are depending on the material?s tempering state. The process characteristics of practical relevance are not only the cutting forces and the tool wear, but also the surface layer states of the machined part. In order to predict and to improve these characteristics efficiently, chip forming simulation via finite element method (FEM) is commonly applied. However, an issue in machining simulation which is often addressed is choosing appropriate material parameters for the flow stress model. This especially accounts for AISI4140 with various tempering conditions, as in many cases the precise heat treatment is not supplied in detail, even in scientific literature. In this work, orthogonal cutting of AISI4140 with tempering temperatures of 300?C, 450?C and 600?C is investigated by experiments and FE simulations. The Johnson-Cook flow stress model is used in the FE simulation. The referring material parameters for the tempering conditions are iteratively adapted via numerical optimization to fit experimental cutting forces. The obtained parameters are compared to literature values in order to prepare a common ground for the cutting simulation of AISI4140. This contributes to an enhanced process modelling when machining AISI4140 with use-case adapted heat treatments.

[ 10 ] Böttger, D.; Stampfer, B.; Gauder, D.; Lanza, G.; Schulze, V.; Straß, B. & Wolter, B. (2021), "Working point determination of 3MA micromagnetic NDT-technique for production integrated detection of white layer during turning of AISI4140". Elsevier, doi.org/10.1016/j.procir.2021.02.002
Abstract
High strength steels are important in terms of lightweight, safety and economical aspects for mobility concepts of the future. In fact, machined surfaces and its characteristics are essential for the entire product-lifecycle. In the presented work, the capability of micromagnetic nondestructive-testing (NDT) techniques combined in 3MA, and optimal working point determination to detect critical surface states such as white layer (WL) associated to hardness increase and its characteristics is discussed. An outlook is given how in terms of Industry 4.0 production-integrated determination of material characteristics can enable in-line monitoring and closed-loop control for an optimization of production processes.

[ 11 ] Gauder, D.; Biehler, M.; Gölz, J.; Stampfer, B.; Böttger, D.; Häfner, B.; Wolter, B.; Schulze, V. & Lanza, G. (2021), "Development of a methodical approach for uncertainty quantification and meta-modeling of surface hardness in white layers of longitudinal turned AISI4140 surfaces", tm - Technisches Messen, doi.org/10.1515/teme-2021-0037
Abstract
The formation of thermally and mechanically induced near-surface microstructures in the form of white layers leads to different hardness properties in these areas. Therefore, this paper conducts systematic surface hardness measurements and uncertainty quantification utilizing the Monte Carlo Method (MCM) in accordance with the Guide to the Expression of Uncertainty in Measurement (GUM). Furthermore, several meta-models describing the hardness course in relationship to the material depth are used to model this nonlinear relationship via machine learning. The evaluation and selection of the optimal model considers the trade-off between measurement uncertainty and prediction quality in terms of mean squared error (MSE). The resulting measurement uncertainty is to be used for the calibration of a non-destructive micromagnetic material sensor. This will then be implemented for in-process monitoring in the outer diameter longitudinal turning process. This should make it possible to detect white layers during machining and to avoid them accordingly by controlling the machine parameters. By means of a soft sensor, the corresponding target value is to be derived from the micromagnetic material sensor measurement.