wbk Institut für Produktionstechnik

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 — Open Access Journal , S. 1-21.
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, Hrsg. Elsevier B.V., S. 154-159.
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“, Procedia CIRP 87, S. 176-180.
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 [30.11.-1].
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“, Technisches Messen, 10.1515/teme-2020-005 [30.11.-1].
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.