WO2025252671A1

WO2025252671A1 - Electric discharge machining methods and systems

Info

Publication number: WO2025252671A1
Application number: PCT/EP2025/065200
Authority: WO
Inventors: Davide MELIS; Massimo Arcioni; Dario CLORI; Emanuele PICIOLLO; Lorenzo Fabbri
Original assignee: Nuovo Pignone Technologie SRL
Current assignee: Nuovo Pignone Technologie SRL
Priority date: 2024-06-04
Filing date: 2025-06-02
Publication date: 2025-12-11
Anticipated expiration: 2026-12-04

Abstract

The innovative electric discharge machining method allows to produce particles of smaller size and to assist the material in floating within the dielectric fluid and reaching the machine filtering system more efficiently through an electrical discharge machining system (1000); machining comprises application of electricity to a workpiece (1040) through an electrode (1050) and generation of metal particles (1090) by micro-fusion of the workpiece (1040) due to electric sparks; the workpiece (1040) is made of metal; the electrode (1050) is at a distance from the workpiece (1040); the workpiece (1040) to be machined is immersed in a liquid (1080) contained in a tub (1010) during machining; the liquid (1080) is essentially made by a dielectric material. Graphene particles (1095) are added to the liquid (1080) before starting machining and the liquid (1080) is circulated outside the tub (1010) during machining so that agglomerates comprising graphene particles (1095) and metal particles (1090) are filtered out of the circulated liquid, and graphene particles (1095) are also supplemented to the liquid (1080) during machining.

Description

TITLE

ELECTRIC DISCHARGE MACHINING METHODS AND SYSTEMS

DESCRIPTION

TECHNICAL FIELD

[0001] The subject matter disclosed herein relates to an electrical discharge machining method and more particularly, but not exclusively, to a so-called electrical discharge machining (EDM) sinking method utilised in order to remove material from a workpiece and to manage the particles produced during the removal process. The subject matter disclosed herein relates also to a corresponding electrical discharge machining system.

BACKGROUND ART

[0002] In general, the physical principle of EDM machining consists of a series of very high frequency, controlled, non-stationary electrical discharges, between the electrode and the piece causing local micro fusion of the metal of the workpiece and generation of metal particles by microfusion of the workpiece. These micro fusions, when of big size, tend to precipitate to the working tank bottom. This leads to a reduced filtering capability of the EDM system as the micro fusions do not reach the machine filtering system.

[0003] In particular, sinking EDM is utilised with regard to processing of workpieces by spark erosion. The workpiece (usually made of conductive material such as metal) and the electrode (usually made of graphite, copper or brass) are generally presented with a dielectric fluid between them and are connected to a DC power supply (EDM generator) delivering periodic pulses of electric energy, such that sparks erode the workpiece by melting and vaporization and so create a cavity or hole or otherwise shape in the workpiece. In order to provide for spark erosion, the workpiece and the electrode must have no physical contact and a gap is maintained typically through appropriate sensors and servo motor control. Erosion debris must be removed from the erosion site, and this usually necessitates a retraction cycle during conventional electrical discharge machining.

[0004] Currently, sinking EDM method generates large and heavy particles, especially during the roughing phase. These particles can accumulate on the component itself, gather at the bottom of the tank, or remain in the working area, failing to reach the machine filtration system. Consequently, they end up contaminating the dielectric fluid. Therefore, it would be desirable a method able to remove particles form a workpiece that can reach the machine filtering system more efficiently.

[0005] Innovative methods are able to produce particles of smaller size with improved buoyancy into dielectric fluid, in order to help the material (microfusions and agglomerations) in floating within the dielectric fluid and reaching the machine filtering system more efficiently. In particular, this is achieved through introduction of graphene into the dielectric fluid.

[0006] It is to be noted that graphene has already been used as a coating of aluminum (Al) electrode to reduce the manufacturing cost of electrodes, as disclosed in the scientific article “ Influence of graphene coating in electrical discharge machining with an aluminum electrode" by Kamlesh Paswan, Somnath Chattopadhyaya and Anil Dube published on 28 Giugno 2023.

[0007] Scientific article ‘54 Comprehensive Analysis of the Effect of Graphene- Based Dielectric for Sustainable Electric Discharge Machining of Ti-6Al-4V” by Kashif Ishfaq, Muhammad Asad, Saqib Anwar Catalin I. Pruncu, Mustafa Saleh, Shafiq Ahmad, published on 23 December 2020 discloses the potentiality of kerosene-based dielectric with graphene nanoparticles, revealing a material removal rate (MRR) higher of titanium alloys.

[0008] It is to be noted that the introduction of graphene has been used in order to solve issues of lower material removal rate (MRR) and tool wear (TWR) in the use of EDM, but the introduction of graphene into dielectric fluid to enhance dielectric filtering capabilities by electric sparks to create smaller agglomerates of graphene and metal particles appear undisclosed.

[0009] Accordingly, and more specifically, it would be desirable a method wherein the graphene particles are supplemented to the dielectric liquid in a tub during machining and that the concentration of graphene in the dielectric liquid in the tub is measured at least during machining.

SUMMARY

[00010] According to a first aspect, the subject-matter disclosed herein relates to an innovative electric discharge machining method wherein the liquid is circulated outside the tub during machining and agglomerates comprising graphene and metal are filtered out of the circulated liquid, and wherein graphene is supplemented to the liquid during machining.

[00011] According to a second aspect, the subject-matter disclosed herein relates to an innovative electric discharge machining system configured to carry out the innovative method.

BRIEF DESCRIPTION OF THE DRAWINGS.

[00012] A more complete appreciation of the disclosed embodiments of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: Fig. 1 illustrates a schematic view of a first embodiment of an innovative electric discharge machining system;

Fig. 2 illustrates a schematic view of a second embodiment of an innovative electric discharge machining system;

Fig. 3 illustrates a schematic view of a portion of the system of Fig. 1;

Fig. 4 illustrates a schematic view of a portion of the system of Fig. 2; and

Fig. 5 illustrates a flow chart of an embodiment of an innovative electric discharge machining method.

DETAILED DESCRIPTION OF EMBODIMENTS

[00013] The electrical discharge machining (EDM) allows for exceptional precision and accuracy in machining operations. However, a problem that arises with EDM is that the sparks generated during EDM lead to big microfusions that tend to precipitate to the working tank bottom. This leads to a reduced filtering capability as the micro-fusions do not reach the machine filtering system.

[00014] According to the subject matter disclosed herein, an innovative electric discharge machining method wherein the graphene particles are supplemented to the liquid during machining through an innovative electric discharge machining system. By incorporating graphene into the liquid, the sparks generated during EDM lead to smaller micro-fusions and the formation of agglomerates comprising graphene and metal particles. The reduced size of micro-fusions and agglomerations assist the material in floating within the dielectric fluid and reaching the machine filtering system more efficiently.

[00015] According to the innovative method, before starting machining, graphene particles are added in the liquid in the working tank. The concentration of graphene particles in the liquid in the working tank is measured at least during machining and graphene particles are supplemented to the liquid during machining. The concentration of graphene in the liquid is preferably maintained within a predetermined concentration range; more preferably, the concentration is maintained substantially constant.

[00016] Referring now to drawings, Fig.1 and Fig. 2 show an innovative electric discharge machining system 1000 and 2000 suitable for carrying out an innovative method (see e.g. flow chart 3000 in Fig. 5), to produce particles of smaller size and to assist the material in floating within the dielectric fluid and reaching the machine filtering system more efficiently.

[00017] The discharge machining comprises application of electricity to a workpiece 1040, 2040 through an electrode 1050, 2050 and generation of metal particles 1090, 2090 by micro-fusion of the workpiece 1040, 2040 due to electric sparks 1110, 2110 (see Fig. 3 and Fig. 4).

[00018] Advantageously the electrode 1050, 2050 is at a distance from the workpiece 1040, 2040 and the workpiece 1040, 2040, preferably a metal workpiece, to be machined is immersed in a liquid 1080, 2080 contained in a tub 1010, 2010 during machining.

[00019] Graphene particles 1095, 2095 are added to liquid 1080, 2080 before starting machining, wherein liquid 1080, 2080 is essentially made by a dielectric material, preferably hydrocarbon dielectric material or ester dielectric material. Liquid 1080, 2080 is circulated outside the tub 1010, 2010 during machining and agglomerates comprising graphene particles 1095, 2095 and metal particles 1090, 2090 are filtered out of the circulated liquid 1080, 2080.

[00020] In addition, graphene particles 1095, 2095 are supplemented to the liquid 1080, 2080, preferably graphene particles in the liquid are supplemented gradually and intermittently. In a more particular embodiment graphene particles in the liquid are supplemented pulsatingly.

[00021] Advantageously, graphene particles 1095, 2095 are supplemented to the liquid 1080, 2080 during machining and the concentration of graphene in the liquid 1080, 2080 in the tub 1010, 2010 is measured at least during machining. The concentration of graphene in the liquid 1080, 2080, with this method, may be maintained within a predetermined concentration range, preferably substantially constant. The concentration of graphene in the liquid may be controlled by means of a dispenser with a graphene particle reservoir and a particle counter.

[00022] Preferably, graphene particles 1095, 2095 are supplemented to the liquid 1080, 2080 in the tub 1010, 2010 and/or to circulated liquid 1080, 2080 after filtering.

[00023] Liquid 1080, 2080 is extracted from a lower region 1011, 2011 of the tub 1010, 2010 before filtering, and is introduced in the tub 1010, 2010 after filtering.

[00024] In addition, liquid 2080 is extracted from an upper region 2013 of the tub 2010 before filtering.

[00025] Referring to Fig. 3 and Fig. 4 during machining, a flow of liquid containing graphene particles 1095, 2095 is created at least in a region 1100, 2100 where the electric sparks 1110, 2110 occur, wherein the flow of liquid containing graphene particles 1095, 2095 is configured so to create turbulence, in particular local turbulence in a spark gap 1300, 2300 between the electrode 1050, 2050 and the workpiece 1040, 2040.

[00026] Fig. 1 and Fig. 2 show a schematic view of an embodiment of an electric discharge machining system 1000, 2000, comprising devices configured to carry out innovative methods.

[00027] In particular, the electric discharge machine system 1000, 2000 comprise:

- the tub 1010, 2010 configured to be filled by liquid 1080, 2080 and to house the workpiece 1040, 2040 to be machined; a tub drain 1020, 2020 disposed in the tub 1010,2010, preferably is disposed in the lower region 1011, 2011 of the tub 1010,2010; an outer piping 1030, 2030 with a pump 1031, 2031 and a filter 1032,2032 disposed downstream of the pump 1031, 2031, preferably the filter 1032, 2032 is fluidly coupled to the pump 1031, 2031;

- the electrode 1050, 2050 configured to be located close to the workpiece 1040, 2040 to be machined; and

- an electric control device 1200, 2200, configured to maintain (d, e) a gap 1300, 2300 between the workpiece 1040, 2040 and the electrode 1050, 2050 and to supply (c, f) electric power to the electrode 1050, 2050.

[00028] Advantageously, the outer piping 1030, 2030 comprises a pipe 1033, 2033 that extends from a base of the tub 1010, 2010 to the pump 1031, 2031.

[00029] The outer piping 1030, 2030 may comprise further: a first pipe 1034, 2034 that extends from the filter 1032, 2032 to a portion of the tub 1010, 2010 different from the base of the tub 1010, 2010; a second pipe 1035, 2035 that extends from the filter 1032, 2032 to the electrode 1050, 2050; a third pipe 1036, 2036 that extends from the filter 1032, 2032 to the upper region 1013, 2013 of the tub 1010, 2010;

[00030] The third pipe 1036, 2036 is configured to carry filtered liquid in the upper region 1013, 2013 of the tub 1010, 2010 through a flushing nozzle 1060, 2060.

[00031] The second pipe 1034, 2034 carries filtered liquid to a lateral region 1012, 2012 of the tub 1010, 2010.

[00032] Referring to Fig. 2, the electric discharge machining system 2000 may comprise further a second tub drain 2070 disposed in the upper region 2013 of the tub 2010.

[00033] Advantageously, in the second embodiment of the electric discharge machining system 2000, the first pipe 2033 is provided with a first portion of pipe 2033a that carries liquid 2080 containing graphene particles 1095, 2095 from the upper region 2013 of the tub 2010 to filter 2032, and a second portion of pipe 2033b that carries liquid 2080 containing graphene particles 1095, 2095 from the lower region 2011 of the tub 2010, through tub drain 2020, to the filter 2032.

[00034] In particular, the first portion of pipe 2033a and the second portion of pipe 2033b get together in a third portion of pipe 2033c of the second embodiment of the electric discharge machining system 2000, and preferably the tub 2010 is an infinity tub, i.e. an overflow tub with an overflow design at the edges that allows liquid to flow over freely.

[00035] Fig. 5 illustrates a flow chart of an embodiment of the innovative electric discharge machining method 3000 to produce particles of smaller size and to assist the material in floating within the dielectric fluid and reaching the machine filtering system more efficiently. The flow chart has a start-block 3010 and an end-block 3040; the steps between block 3010 and block 3040 are typically repeated several times during electric discharge machining. According to this embodiment of the innovative method, these steps are: introducing 3011 liquid 1080, 2080 in the tub 1010, 2010; immersing 3012 the workpiece 1040, 2040 in the tub 1010, 2010; adding 3013 graphene particles 1095, 2095 to liquid 1080, 2080; starting machining process 3014 with generation of metal particles 1090, 2090 by micro-fusion of the workpiece 1040, 2040 due to electric sparks 1110, 2110 through application of electricity to the workpiece 1040, 2040; extracting 3015 liquid 1080, 2080 from a lower region 1011, 2011 of the tub 1010, 2010 and/or from an upper region 2013 of the tub 2010; circulating 3016 liquid with agglomerates comprising graphene particles 1095, 2095 and metal particles 1090, 2090 outside the tub 1010, 2010 through outer piping 1030, 2030; filtering 3017 out of the circulated liquid agglomerates comprising graphene particles 1095, 2095 and metal particles 1090, 2090; introducing 3018 liquid 1080, 2080, in the tub 1010, 2010 after filtering 3017; measuring and evaluating 3020 a value of the concentration of graphene particles 1095, 2095 in the liquid 1080, 2080; if the value of the concentration of graphene particles 1095, 2095 calculated is less 3021 than a predetermined concentration of graphene particles range, supplementing 3023 graphene particles 1095, 2095 in the liquid 1080, 2080; continuously evaluating 3025 of the concentration of graphene particles 1095, 2095 in the liquid 1080, 2080; if the value of the concentration calculated is contained 3022 within the predetermined concentration range, continuing 3022 machining process of workpiece 1040, 2040; evaluating 3030 a workpiece shaped during machining process of workpiece 1040, 2040; if workpiece shaped obtained is close to a predetermined shaped 3031, the machining process is terminated 3040; if workpiece shaped obtained is not close to the predetermined shaped 3032, the steps from 3014 to 3030 are iterated.

[00036] As is well known, in an Electrical Discharge Machining (EDM) process, material removal occurs through electrical discharges generated between an electrode and a metal workpiece, both immersed in a dielectric fluid. This fluid plays a crucial role: on one hand, it electrically insulates the electrode from the workpiece until the moment of discharge; on the other, it cools the system and aids in the removal of metallic debris generated during machining, also known as eroded particles.

[00037] In the present patent application, the dielectric fluid has been enriched with graphene particles, with the aim of improving the dispersion of metallic debris and facilitating its removal. Thanks to its high electrical conductivity and large specific surface area, graphene not only helps stabilize the erosion process but also actively binds to the metallic debris, forming agglomerates that remain suspended and can be easily filtered.

[00038] This behavior was experimentally confirmed during testing. In the first phase, eight different types of graphene, six mixing techniques, and two concentrations (high at 4 g/L and low at 0.5 g/L) were evaluated, along with four dispersing agents to improve suspension stability.

[00039] The parameters considered to assess dispersion quality included apparent volume, sedimentation time, particle size (D90), and the fluid’s insulation resistance. The latter was measured by applying a 250 V voltage only to dispersions classified as medium or high quality. The results allowed the selection of the most promising samples, particularly the combinations G99Mix2, G3Mix2, and G2Mix2, which were further investigated in the second phase.

[00040] In this subsequent phase, the focus was on determining the concentration at which each type of graphene caused the breakdown of the dielectric’s insulation. Tests were conducted with G3 and a mix of G2 and G3, specifically observing the dielectric’s behavior in terms of conductivity. After testing, the samples were vacuum-filtered and subjected to a selective dissolution process of the metallic content using two approaches: one aggressive (strong) and one milder (mild). The results showed that, in the strong dissolution case, over 80% of the total recovered material weight consisted of metal, while the mild dissolution still exceeded 50%.

[00041] These findings indicate that the suspended graphene effectively sequestered a significant amount of metallic particles, forming stable, easily suspendable metal-graphene clusters. Furthermore, particle size analysis revealed that after metal dissolution, the aggregate sizes were smaller than those observed before treatment, suggesting that the metallic particles acted as bridges between graphene flakes. The size reduction compared to the original G3 paste also suggests possible degradation of the graphene due to the electric arc generated during EDM.

[00042] However, the addition of graphene introduces a critical issue: concentration. Each type of graphene — whether exfoliated, reduced, or oxidized — has different conductive properties. If the concentration in the dielectric exceeds a certain threshold, known as the percolation threshold, continuous conductive paths may form within the fluid. This phenomenon compromises the dielectric’s electrical insulation, which is essential to ensure that discharges occur only at the desired points and in a controlled manner.

[00043] When insulation fails, uncontrolled discharges may occur at unintended points in the system. This can lead to local short circuits between the electrode and the workpiece or between different areas of the workpiece itself, negatively affecting machining quality. The workpiece may suffer from issues such as uneven erosion, microcracks, or loss of dimensional accuracy. Additionally, insulation degradation accelerates the chemical and thermal aging of the dielectric, reducing its service life and compromising the overall efficiency of the EDM process. The electrode may wear out more quickly, and the surface finish of the workpiece may deteriorate.

[00044] For these reasons, it is essential to optimize the concentration of graphene in the dielectric fluid. The goal is to maintain a critical balance: adding enough graphene to ensure effective agglomeration of debris and process stability, but not so much as to compromise the insulating properties of the fluid. Only in this way can an efficient, stable, and safe EDM process be achieved.

[00045] Therefore, identifying an optimal graphene concentration value to achieve a functional balance between metallic debris agglomeration and the maintenance of the dielectric fluid’s insulating properties is not obvious. In particular, based on the available technical knowledge, the use of graphene in EDM processes has been known solely for its electrical conductivity, and not as a functional agent for forming suspendable and easily removable metalgraphene clusters. This enables the controlled use of graphene to facilitate the selective removal of eroded material without compromising the dielectric’s insulation, representing a non-obvious and innovative approach compared to the current state of the art.

Claims

1. An electric discharge machining method (3000), wherein machining comprises application of electricity to a workpiece (1040, 2040) through an electrode (1050, 2050) and generation of metal particles (1090, 2090) by micro-fusion of the workpiece (1040, 2040) due to electric sparks (1110, 2110), wherein the workpiece (1040, 2040) is made of metal, wherein the electrode (1050, 2050) is at a distance from the workpiece (1040, 2040), wherein the workpiece (1050, 2050) to be machined is immersed (3012) in a liquid (1080, 2080) contained in a tub (1010, 2010) during machining, wherein the liquid (1080, 2080) is essentially made of a dielectric material, wherein graphene particles (1095, 2095) are added (3013) to the liquid (1080, 2080) before starting machining, wherein the liquid (1080, 2080) is circulated (3016) outside the tub (1010, 2010) during machining and agglomerates comprising graphene particles (1095, 2095) and metal particles (1090, 2090) are filtered (3017) out of the circulated liquid, wherein graphene particles (1095, 2095) are supplemented (3023) to the liquid during machining.

2. The electric discharge machining method of claim 1, wherein concentration of graphene in the liquid (1080, 2080) is maintained within a predetermined concentration range.

3. The electric discharge machining method of claim 2, wherein concentration of graphene in the liquid (1080, 2080) is maintained substantially constant.

4. The electric discharge machining method of claim 1, wherein the dielectric material is a hydrocarbon dielectric material.

5. The electric discharge machining method of claim 1, wherein the dielectric material is ester dielectric material.

6. The electric discharge machining method of claim 1 or 3, wherein graphene particles (1095, 2095) in the liquid (1080, 2080) are supplemented gradually and intermittently.

7. The electric discharge machining method of claim 1, wherein liquid is extracted from an upper region (2013) of the tub (2010) before filtering (3017).

8. The electric discharge machining method of claim 1, wherein liquid is extracted (3015) from a lower region (1011, 2011) of the tub (1010, 2010) before filtering (3017).

9. The electric discharge machining method of claim 1, wherein liquid is introduced (3018) in a region of the tub (1010, 2010) after filtering (3017).

10. The electric discharge machining method of claim 1, wherein graphene particles (1095, 2095) are supplemented to the liquid (1080, 2080) in the tub (1010, 2010) and/or to circulated liquid after filtering (3017).

11. The electric discharge machining method of claim 1, wherein concentration of graphene in the liquid (1080, 2080) in the tub (1010, 2010) is measured (3020) at least during machining.

12. The electric discharge machining method of claim 1, wherein during machining, a flow of liquid containing graphene particles (1095, 2095) is created at least in a region (1100, 2100) where the electric sparks (1110, 2110) occur.

13. The electric discharge machining method of claim 11, wherein the flow of liquid containing graphene particles (1095, 2095) is configured so to create turbulence, in particular local turbulence.

14. An electric discharge machining system (1000, 2000) comprising devices configured to carry out the method according to any preceding claims.

15. The electric discharge machining system (1000, 2000) of claim 14 comprising:

- the tub (1010, 2010) configured to be filled by the liquid (1080, 2080) and to house the workpiece (1040, 2040) to be machined; a tub drain (1020, 2020) disposed in the tub (1010, 2010); an outer piping (1030, 2030) with a pump (1031, 2031) and a filter (1032, 2032) disposed downstream of the pump (1031);

- the electrode (1050, 2050) configured to be located close to the workpiece (1040, 2040) to be machined; an electric control device (1200, 2200) configured to maintain (d, e) a gap (1300, 2300) between the workpiece (1040, 2040) and the electrode (1050, 2050) and to supply (c, f) electric power to the electrode (1050, 2050).

16. The electric discharge machining system (1000, 2000) of claim 14, wherein the tub drain (1020, 2020) is disposed in the lower region (1011, 2011) of the tub (1010, 2010).

17. The electric discharge machining system (1000, 2000) of claim 14, wherein the outer piping (1030, 2030) comprises a pipe (1033, 2033) that extends from a base of the tub (1010, 2010) to the pump (1031, 2031).

18. The electric discharge machining system (1000, 2000) of claim 17, wherein the outer piping (1030, 2030) comprises further: a first pipe (1034, 2034) that extends from the filter (1032, 2032) to a portion of the tub (1010, 2010) different from the base of the tub (1010, 2010); a second pipe (1035, 2035) that extends from the filter (1032, 2032) to the electrode (1050, 2050); a third pipe (1036, 2036) that extends from the filter (1032, 2032) to the upper region (1013, 2013) of the tub (1010, 2010);

19. The electric discharge machining system (1000, 2000) of claim 18, wherein the third pipe (1036, 2036) is configured to carry filtered liquid in the upper region (1013, 2013) of the tub (1010, 2010) through a flushing nozzle (1060, 2060).

20. The electric discharge machining system (1000, 2000) of claim 18, wherein the second pipe (1034, 2034) carries filtered liquid to a lateral region (1012, 2012) of the tub (1010, 2010).

21. The electric discharge machining system (1000, 2000) of claim 15, wherein the filter (1032, 2032) is fluidly coupled to the pump (1031, 2031).

22. The electric discharge machining system (2000) of claim 14, comprising a second tub drain (2070) disposed in the upper region (2013) of the tub (2010).

23. The electric discharge machining system (2000) of claim 17, wherein the first pipe (2033) is provided with a first portion of pipe (2033a) that carries liquid (2080) containing graphene particles (2095) from the upper region (2013) of the tub (2010), through the second tub drain (2070), to the filter (2032), and a second portion of pipe (2033b) that carries liquid (2080) containing graphene particles (2095) from the lower region (2011) of the tub (2010), through tub drain (2020), to the filter (2032).

24. The electric discharge machining system (2000) of claim 23, wherein the first portion of pipe (2033 a) and the second portion of pipe (2033b) get together in a third portion of pipe (2033c).

25. The electric discharge machining system (2000) of claim 14 wherein the tub (2010) is an overflow tub.