wbk

German Gonzalez Fernandez, M.Sc.

  • 76131 Karlsruhe
    Kaiserstraße 12

German Gonzalez Fernandez, M.Sc.

Forschungs- und Arbeitsgebiete:

  • Simulation von Fertigungsprozessen
  • Einstellung von Randschichtzuständen bei der Zerspanung
  • Verschleißkompensation

 

Projekte:

  • Verschleißkompensierende Einstellung von nanokristallinen Randschichten bei der Zerspanung mittels ortsaufgelöster Temperatur- und Verschleißmessung

 

Lebenslauf:

Seit 06/2018

wissenschaftlicher Mitarbeiter am Institut für Produktionstechnik (wbk) des Karlsruher Instituts
für Technologie (KIT)

10/2016 - 05/2018

Projektingenieur bei IK4 IDEKO – DanobatGroup.
Abteilung Schwingungen und Ratterunterdrückung.

10/2014 - 03/2016

Erasmus Mundus Masterstudiengang Mechatronik und Micro-Mechatronik Systeme - EU4M an der Universität Oviedo und an der Hochschule Karlsruhe – Technik und Wirtschaft

10/2010 - 03/2014

Studium des Maschinenbaus an der Universität Oviedo

04/10/1992

Geboren in Gijon (Spanien)

Veröffentlichungen

[ 1 ] Iglesias, A.; Dombovari, Z.; Gonzalez Fernandez, G.; Munoa, J. & Stepan, G. (2018), „Optimum Selection of Variable Pitch for Chatter Suppression in Face Milling Operations“, materials, Band 112, S. 1. http://dx.doi.org/10.3390/ma12010112
Abstract
Cutting capacity can be seriously limited in heavy duty face milling processes due to self-excited structural vibrations. Special geometry tools and, specifically, variable pitch milling tools have been extensively used in aeronautic applications with the purpose of removing these detrimental chatter vibrations, where high frequency chatter related to slender tools or thin walls limits productivity. However, the application of this technique in heavy duty face milling operations has not been thoroughly explored. In this paper, a method for the definition of the optimum angles between inserts is presented, based on the optimum pitch angle and the stabilizability diagrams. These diagrams are obtained through the brute force (BF) iterative method, which basically consists of an iterative maximization of the stability by using the semidiscretization method. From the observed results, hints for the selection of the optimum pitch pattern and the optimum values of the angles between inserts are presented. A practical application is implemented and the cutting performance when using an optimized variable pitch tool is assessed. It is concluded that with an optimum selection of the pitch, the material removal rate can be improved up to three times. Finally, the existence of two more different stability lobe families related to the saddle-node and flip type stability losses is demonstrated.

[ 2 ] González Fernández, G.; Segebade, E.; Zanger, F. & Schulze, V. (2019), „FEM-based comparison of models to predict dynamic recrystallization during orthogonal cutting of AISI 4140“. Procedia CIRP 82, Elsevier, S. 154-159. 10.1016/j.procir.2019.04.061
Abstract
Machining processes induce a thermo-mechanical load collective on the surface layer, which leads to grain refinement of varying depths depending on several factors apart from the workpiece. The size relation of the cutting edge radius to the cutting depth (relative roundness) as well as the cutting edge microgeometry influence the generation of nanocrystalline layers. In this work several models to predict dynamic recrystallization during orthogonal cutting of AISI 4140 are compared using 2D FEM-models considering both, relative roundness and cutting edge microgeometry.

[ 3 ] Gonzalez Fernandez, G.; Plogmeyer, M.; Zanger, F.; Biehl, S.; Bräuer, G. & Schulze, V. (2020), „Effect of tool coatings on surface grain refinement in orthogonal cutting of AISI 4140 steel“. 5th CIRP Conference on Surface Integrity (CSI 2020), Hrsg. Arrazola, P. J., Elsevier, S. 176-180. 10.1016/j.procir.2020.02.113
Abstract
Recrystallization mechanisms leading to the generation of ultrafine grains (UFG) by surface severe plastic deformation (S2PD) at low temperatures (< 0.5Tm (melting temperature)) have been investigated over the last years. Material removal processes like broaching impose large plastic strains along the shear plane during chip formation, leading in many cases to changes in the workpiece subsurface microstructure. In this work the influence of the cutting material on surface grain recrystallization were studied on broaching of AISI 4140q&t steel. Orthogonal cutting tests were carried out in dry conditions on a broaching machine using tools with different coatings. Uncoated cemented carbide inserts were geometrically prepared using fixed abrasive grinding processes and then coated by physical vapor deposition (PVD) with Al2O3 and CrVN thin films. Workpiece subsurface layers were analyzed after machining by Focused Ion Beam (FIB-SEM) and X-ray diffraction (XRD). The presented results show the influence of the cutting material on the final microstructure of the machined workpieces through the determination of the final grain sizes and dislocation densities.

[ 4 ] Plogmeyer, M.; Gonzalez Fernandez, G.; Schulze, V. & Bräuer, G. (2020), „Development of thin-film based sensors for temperature and tool wear monitoring during machining“, Technisches Messen, 10.1515/teme-2020-0058
Abstract
The development of thin-film sensors for temperature and wear measurement in machining operations is presented in this work. A functional thin-film system, consisting of an Al2O3 insulation layer, a chromium sensor layer structured by photolithography and an Al2O3 wear-protection and insulation layer, is deposited by physical vapor deposition (PVD) processes onto the surface of cemented carbide cutting inserts. First specimen of the sensors are successfully fabricated and tested in laboratory experiments as well as in machining operations to demonstrate their functionality. These tool-integrated sensors can be used as an in-process monitoring device to determine the temperatures on the rake face at or close to the tool-chip contact area and to measure the progress of the flank-wear land width. The knowledge of these important process parameters opens up the possibility to develop new in-process control mechanisms in order to modify and improve the surface integrity of manufactured components. Thereby, their performance and lifetime can be enhanced.

[ 5 ] Schwär, D.; Gonzalez Fernandez, G.; Segebade, E.; Zanger, F. & Heizmann, M. (2020), „Evaluation of the acoustic emission caused by the chip segmentation frequency during machining of titanium alloy“, tm - Technisches Messen, 10.1515/teme-2020-0056
Abstract
This work investigates the relationship between acoustic emission and chip segmentation frequency of Ti-6Al-4V at the external longitudinal turning process. Therefore, several sensors like structure borne sensors, microphones and a force dynamometer have been installed in a vertical turning machine. To induce a change of the segmentation frequency, several experiments with different feed rates have been carried out. From each experiment the acoustic emissions have been recorded and the generated chips have been analyzed. Since the chips get stretched or compressed during the chip formation the change in the length is calculated to get an estimation of the segmentation frequency. The comparison of the spectral analysis of the acoustic emission signals and the chip analysis has shown that both methods show the same tendency. The segmentation frequency decreases with increasing feed.

[ 6 ] Diaz Ocampo, D.; Gonzalez Fernandez, G.; Zanger, F. & Heizmann, M. (2021), „Schätzung der Segmentspanbildungsfrequenz mithilfe von Körperschallsignalen“. De Gruyter, S. 1-5. hrrps://doi.org/10.1515/teme-2021-0059
Abstract
Da die Spansegmentierungsfrequenz bei der Zerspanung hochfester Materialien in direktem Zusammenhang mit dem Eigenspannungszustand des Werkstücks steht, ist sie eine wichtige Kenngröße. Bei bisherigen Methoden kommt hauptsächlich, zur Schätzung der Segmentspanbildungsfrequenz mithilfe von Körperschallsignalen beim orthogonalen Schnitt, die Fourier-Transformation zum Einsatz, welche jedoch bei den im Außenlängsdrehen vorkommenden, stark unharmonischen Signalen ungeeignet ist. Es wird eine Methode vorgestellt, welche die Periodizität der Körperschallsignale im Zeitbereich ermittelt und daraus die Segmentierungsfrequenz schätzt. Dazu werden zeitvariante Merkmale vorgestellt, welche die Segmentspanbildungsfrequenz approximieren. Im Anschluss wird die Methode mit beim orthogonalen Schnitt eingesetzten Methoden verglichen, wobei gezeigt werden kann, dass die hier vorgestellte Methode grundsätzlich robuster gegenüber Störeinflüssen ist, bei den zeitvarianten Merkmalen jedoch noch Potenzial zur Verbesserung besteht.

[ 7 ] Plogmeyer, M.; Gonzalez Fernandez, G.; Biehl, S.; Schulze, V. & Bräuer, G. (2021), „Wear-resistive thin-film sensors on cutting tools for in-process temperature measurement“, S. 85-88. hrrps://doi.org/10.1016/j.procir.2021.02.011
Abstract
In-process control of machining operations allows to develop strategies to modify and improve the surface integrity of manufactured components and thereby enhancing their performance and lifetime. These control strategies require reliable real-time data like cutting forces, process temperatures and tool wear. In this work, a wear-resistive thin-film sensor is developed to measure temperature of the cutting tool surface during machining. A multi-layer sensor system is applied on the tool surface by physical vapor deposition (PVD). The tool-sensors are subsequently tested for their functionality and durability in turning operations of AISI 4140q&t steel.

[ 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, Band 5, Nr. 3, S. 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 ] Gonzalez Fernandez, G.; Diaz Ocampo, D.; Segebade, E.; Heizmann, M. & Zanger, F. (2021), „Chip segmentation frequency based strategy for tool condition monitoring during turning of Ti-6Al-4V“, Procedia CIRP , Band 102, S. 276-280. 10.1016/j.procir.2021.09.047
Abstract
Tool condition monitoring in machining reduces downtimes, maximizes productivity rate and improves the quality of the end-product. However, it still poses a challenge due to the complex non-stationary character of the tool wear and the several uncertainties coming from the machining processes. Recent studies provide new strategies for indirect tool monitoring. Unfortunately due to the unbalance between big amounts of data, low accuracy and high complexity they are not feasible in an industrial environment. The present research work proposes a strategy for tool condition monitoring during turning of Ti-6Al-4V using acoustic emission signals and the chip segmentation frequency as measurement variable. Three different approaches for wear estimation using different AE-data processing methods are presented. Through their combination, a strategy for qualitative and quantitative tool wear monitoring is proposed.

[ 10 ] 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 , Band 102, S. 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.