Georg Walder | University Of Appleid Scienecs Of Western Switzerland (original) (raw)
Papers by Georg Walder
CIRP Annals, 2008
Following a brief review of EDM and its use on advanced aerospace alloys including workpiece inte... more Following a brief review of EDM and its use on advanced aerospace alloys including workpiece integrity constraints, data are presented after machining Ti–6Al–4V and Inconel 718. Roughing and finishing (multiple trim cut) strategies were employed on two high specification machines with pulse generators designed to provide minimum workpiece integrity damage. Results include productivity, 3D topographic maps of workpiece surfaces, microstructural
Plasma created during electrical discharge machining (EDM) is investigated with fast imaging and ... more Plasma created during electrical discharge machining (EDM) is investigated with fast imaging and with time-and spatially-resolved optical emission spectroscopy. After the breakdown, the plasma develops very fast (< 50ns) and then remains stable. The plasma excites a broad volume around the electrode gap. Typical spectra show a strong H α and continuum radiation, with many lines emitted by impurities coming from electrodes materials. The plasma contamination from the electrodes is mostly concentrated in their vicinity. The electron density reaches 2•10 18 cm-3 at the beginning of the discharge. This extreme density causes merging of lines, strong Stark broadening and shift of the H α line. The density decreases afterwards rapidly with time. The electron temperature remains roughly constant around 0.7eV. The low temperature, the high density measured and other spectroscopic evidences prove that the EDM plasma is non-ideal (Γ ≅ 0.45).
Journal of Physics D, Nov 7, 2005
Plasma Sources Science and Technology, May 1, 2008
Plasma created during electrical discharge machining (EDM) is investigated with fast imaging and ... more Plasma created during electrical discharge machining (EDM) is investigated with fast imaging and with time-and spatially-resolved optical emission spectroscopy. After the breakdown, the plasma develops very fast (< 50ns) and then remains stable. The plasma excites a broad volume around the electrode gap. Typical spectra show a strong H α and continuum radiation, with many lines emitted by impurities coming from electrodes materials. The plasma contamination from the electrodes is mostly concentrated in their vicinity. The electron density reaches 2•10 18 cm-3 at the beginning of the discharge. This extreme density causes merging of lines, strong Stark broadening and shift of the H α line. The density decreases afterwards rapidly with time. The electron temperature remains roughly constant around 0.7eV. The low temperature, the high density measured and other spectroscopic evidences prove that the EDM plasma is non-ideal (Γ ≅ 0.45).
Procedia CIRP
The electrical field within the machining area of a WEDM machine was simulated using COMSOL Multi... more The electrical field within the machining area of a WEDM machine was simulated using COMSOL Multiphysics software. In this document, we share the results of this simulation, in particular the geometry considered Figure 5: Electrical field distribution while machining a) with negative polarity of -10 V, b) with positive polarity of +5 V and c) with positive polarity of +2 V Figure 6: Worktank geometry considered and electrical field distribution during storage with an external applied voltage of -0.5 V. 1) when the WC-Co workpiece is connected to the machine ground with: a) brass wire also connected to the ground and b) wire removed. 2) when the WC-Co workpiece is insulated (floating ground) with the c) wire connected to the ground, d) wire at floating ground and e) wire removed.
The cutting tool is a key element in the material removal process. Cemented carbide tools are wel... more The cutting tool is a key element in the material removal process. Cemented carbide tools are well established as they exist in a large variety of substrate compositions and offer the possibility to deposit a wide range of coating. Surface properties of the cutting edge determine the tool lifetime and coatings can add a significant increase. High Power Impulse Magnetron Sputtering (HiPiMS is a new coating technology able to deposit hard and dense layers. Pico-second LASER machining allows microstructuration of difficult to machine material like cemented carbides without thermal impact. The combination of HiPiMS coating and ps –Laser micro-structuring was applied to the cutting edge of standard cemented carbide turning tools. For different combinations of HiPiMS –coated, ps-LASER structured tools, lifetimes in standard steel turning operation have been studied using and compared to lifetimes of standard coated and uncoated tools. A significant increase of tool lifetime having HiPiMS ...
Procedia CIRP, 2020
The cutting tool is a key element in the milling process; it determines the process performance a... more The cutting tool is a key element in the milling process; it determines the process performance and the quality of the machined pieces. For best performance, cutting fluids are applied as close as possible to the area between the tool and the work piece. Its primary functions are chip evacuation, cooling of the tool and piece as well as lubrication. Recent developments allow the injection of the fluid through the spindle, the tool holder and finally through a central hole in the cutting tool. For tools with large diameters (> 6mm) one or several central straight channels are used. For tools with small diameter ( A 10 pico-second laser was used for drilling the holes in order to avoid thermal impact in the tungsten cobalt (Wc-Co) – hard metal that would occur using other methods like EDM-drilling. For the milling tool of O 1.0 mm, the lateral holes have a diameter of 0.12 mm and, for the milling tool of O 2.5 mm, the lateral holes are O 0.3 mm. The diameter of the central blind ho...
Procedia CIRP, 2016
Metallurgical modifications of machined metal surfaces are created by nearly all machining proces... more Metallurgical modifications of machined metal surfaces are created by nearly all machining processes based on thermal and or mechanical processes. The EDM-electro-discharge machining-creates a so called "white layer" or "heat affected zone" (HAZ) having a thickness ranging from a few hundred micro-meters (for roughing operation) down to a few micrometers (for finishing). This remaining HAZ is a problem for many industrial applications: the presence of micro-cracks and metallurgic inhomogeneity inherent to thermal stresses reduces part lifetime of tools, etc. due to fatigue stress. The study presents a method to remove the HAZ created by Die-sinking EDM on warm working steel (W300) by cold ablation with a picosecond LASER. Technologies & strategies for Laser machining have been developed. The laser machined samples have been metallurgical analysed to prove the removal of the white layer and assure that no heat impact due the LASER machining was created, eg. only cold ablation took place. Fatigue test samples have been prepared by EDM machining and either EDM finished or finished by pico-second LASER in order to compare the lifetime both kind of samples © 2016 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the organizing committee of 18th CIRP Conference on Electro Physical and Chemical Machining (ISEM XVIII).
Journal of Materials Processing Technology, 2004
The power balance of EDM systems for discharge pulses of the order of a microsecond was found to ... more The power balance of EDM systems for discharge pulses of the order of a microsecond was found to be strongly related to cathode material properties [Investigations of physical processes in wire-EDM by means of single and multiple discharge measurements and analysis, Proc. ...
Procedia CIRP, 2018
Wire EDM is a time consuming process which requires several, (cost significant), consumables like... more Wire EDM is a time consuming process which requires several, (cost significant), consumables like wire, filters or deionization resin. Based on machining history and sensor inputs a developed model, e.g. an intelligent software, allows to predict the status & future capacity of consumables and wear parts and thus avoid down-times of machine. The use of a predictive model for estimation of the lifetime of consumable and wear parts will be a significant step in the automation of (wire EDM) machines.
Journal of Materials Processing Technology, 2004
CIRP Annals, 2008
Following a brief review of EDM and its use on advanced aerospace alloys including workpiece inte... more Following a brief review of EDM and its use on advanced aerospace alloys including workpiece integrity constraints, data are presented after machining Ti–6Al–4V and Inconel 718. Roughing and finishing (multiple trim cut) strategies were employed on two high specification machines with pulse generators designed to provide minimum workpiece integrity damage. Results include productivity, 3D topographic maps of workpiece surfaces, microstructural
Plasma created during electrical discharge machining (EDM) is investigated with fast imaging and ... more Plasma created during electrical discharge machining (EDM) is investigated with fast imaging and with time-and spatially-resolved optical emission spectroscopy. After the breakdown, the plasma develops very fast (< 50ns) and then remains stable. The plasma excites a broad volume around the electrode gap. Typical spectra show a strong H α and continuum radiation, with many lines emitted by impurities coming from electrodes materials. The plasma contamination from the electrodes is mostly concentrated in their vicinity. The electron density reaches 2•10 18 cm-3 at the beginning of the discharge. This extreme density causes merging of lines, strong Stark broadening and shift of the H α line. The density decreases afterwards rapidly with time. The electron temperature remains roughly constant around 0.7eV. The low temperature, the high density measured and other spectroscopic evidences prove that the EDM plasma is non-ideal (Γ ≅ 0.45).
Journal of Physics D, Nov 7, 2005
Plasma Sources Science and Technology, May 1, 2008
Plasma created during electrical discharge machining (EDM) is investigated with fast imaging and ... more Plasma created during electrical discharge machining (EDM) is investigated with fast imaging and with time-and spatially-resolved optical emission spectroscopy. After the breakdown, the plasma develops very fast (< 50ns) and then remains stable. The plasma excites a broad volume around the electrode gap. Typical spectra show a strong H α and continuum radiation, with many lines emitted by impurities coming from electrodes materials. The plasma contamination from the electrodes is mostly concentrated in their vicinity. The electron density reaches 2•10 18 cm-3 at the beginning of the discharge. This extreme density causes merging of lines, strong Stark broadening and shift of the H α line. The density decreases afterwards rapidly with time. The electron temperature remains roughly constant around 0.7eV. The low temperature, the high density measured and other spectroscopic evidences prove that the EDM plasma is non-ideal (Γ ≅ 0.45).
Procedia CIRP
The electrical field within the machining area of a WEDM machine was simulated using COMSOL Multi... more The electrical field within the machining area of a WEDM machine was simulated using COMSOL Multiphysics software. In this document, we share the results of this simulation, in particular the geometry considered Figure 5: Electrical field distribution while machining a) with negative polarity of -10 V, b) with positive polarity of +5 V and c) with positive polarity of +2 V Figure 6: Worktank geometry considered and electrical field distribution during storage with an external applied voltage of -0.5 V. 1) when the WC-Co workpiece is connected to the machine ground with: a) brass wire also connected to the ground and b) wire removed. 2) when the WC-Co workpiece is insulated (floating ground) with the c) wire connected to the ground, d) wire at floating ground and e) wire removed.
The cutting tool is a key element in the material removal process. Cemented carbide tools are wel... more The cutting tool is a key element in the material removal process. Cemented carbide tools are well established as they exist in a large variety of substrate compositions and offer the possibility to deposit a wide range of coating. Surface properties of the cutting edge determine the tool lifetime and coatings can add a significant increase. High Power Impulse Magnetron Sputtering (HiPiMS is a new coating technology able to deposit hard and dense layers. Pico-second LASER machining allows microstructuration of difficult to machine material like cemented carbides without thermal impact. The combination of HiPiMS coating and ps –Laser micro-structuring was applied to the cutting edge of standard cemented carbide turning tools. For different combinations of HiPiMS –coated, ps-LASER structured tools, lifetimes in standard steel turning operation have been studied using and compared to lifetimes of standard coated and uncoated tools. A significant increase of tool lifetime having HiPiMS ...
Procedia CIRP, 2020
The cutting tool is a key element in the milling process; it determines the process performance a... more The cutting tool is a key element in the milling process; it determines the process performance and the quality of the machined pieces. For best performance, cutting fluids are applied as close as possible to the area between the tool and the work piece. Its primary functions are chip evacuation, cooling of the tool and piece as well as lubrication. Recent developments allow the injection of the fluid through the spindle, the tool holder and finally through a central hole in the cutting tool. For tools with large diameters (> 6mm) one or several central straight channels are used. For tools with small diameter ( A 10 pico-second laser was used for drilling the holes in order to avoid thermal impact in the tungsten cobalt (Wc-Co) – hard metal that would occur using other methods like EDM-drilling. For the milling tool of O 1.0 mm, the lateral holes have a diameter of 0.12 mm and, for the milling tool of O 2.5 mm, the lateral holes are O 0.3 mm. The diameter of the central blind ho...
Procedia CIRP, 2016
Metallurgical modifications of machined metal surfaces are created by nearly all machining proces... more Metallurgical modifications of machined metal surfaces are created by nearly all machining processes based on thermal and or mechanical processes. The EDM-electro-discharge machining-creates a so called "white layer" or "heat affected zone" (HAZ) having a thickness ranging from a few hundred micro-meters (for roughing operation) down to a few micrometers (for finishing). This remaining HAZ is a problem for many industrial applications: the presence of micro-cracks and metallurgic inhomogeneity inherent to thermal stresses reduces part lifetime of tools, etc. due to fatigue stress. The study presents a method to remove the HAZ created by Die-sinking EDM on warm working steel (W300) by cold ablation with a picosecond LASER. Technologies & strategies for Laser machining have been developed. The laser machined samples have been metallurgical analysed to prove the removal of the white layer and assure that no heat impact due the LASER machining was created, eg. only cold ablation took place. Fatigue test samples have been prepared by EDM machining and either EDM finished or finished by pico-second LASER in order to compare the lifetime both kind of samples © 2016 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the organizing committee of 18th CIRP Conference on Electro Physical and Chemical Machining (ISEM XVIII).
Journal of Materials Processing Technology, 2004
The power balance of EDM systems for discharge pulses of the order of a microsecond was found to ... more The power balance of EDM systems for discharge pulses of the order of a microsecond was found to be strongly related to cathode material properties [Investigations of physical processes in wire-EDM by means of single and multiple discharge measurements and analysis, Proc. ...
Procedia CIRP, 2018
Wire EDM is a time consuming process which requires several, (cost significant), consumables like... more Wire EDM is a time consuming process which requires several, (cost significant), consumables like wire, filters or deionization resin. Based on machining history and sensor inputs a developed model, e.g. an intelligent software, allows to predict the status & future capacity of consumables and wear parts and thus avoid down-times of machine. The use of a predictive model for estimation of the lifetime of consumable and wear parts will be a significant step in the automation of (wire EDM) machines.
Journal of Materials Processing Technology, 2004