-1 CONTROLLABLE NANOPARTICLE JET FLOW TRANSPORTATION TYPE MINIMAL QUANTITY LUBRICATION GRINDING EQUIPMENT UNDER MAGNETICALLY ENHANCED ELECTRIC FIELD FIELD OF THE INVENTION [0001] The present invention relates to a minimal quantity lubrication grinding fluid transportation process method and equipment in mechanical grinding processing, and particularly relates to controllable nanoparticle jet flow transportation type minimal quantity lubrication grinding equipment under a magnetically enhanced electric field. BACKGROUND OF THE INVENTION [0002] Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field. [0003] Minimal quantity lubrication technology is also known as MQL (Minimal Quantity Lubrication) technology, which is used for mixing minimal quantity lubricating fluid with compressed air with a certain pressure and atomizing the same to spray to a grinding area, in order to effectively lubricate a contact surface of a grinding wheel and abrasive dust and a contact surface of the grinding wheel and a workpiece. By adopting this technology, on the premise of ensuring effective lubricating and cooling effects, the minimal grinding fluid is used (approximately a few thousandths of the dosage of a traditional pouring lubrication manner) to reduce the cost, the environmental pollution and the human body injury. [0004] Nanoparticle jet flow minimal quantity lubrication is established on the basis of the enhanced heat transfer theory. It can be seen from the enhanced heat transfer theory that the heat transfer capability of solid is much larger than those of liquid and gas. The heat conductivity coefficient of a solid material at room temperature is larger than that of a fluid material for several orders of magnitudes. Solid particles are added in a minimal quantity lubrication medium to significantly increase the heat conductivity coefficient of a fluid medium, improve the convection heat transfer capability and greatly compensate the defect of insufficient minimal quantity lubrication cooling capability. In addition, nanoparticles (referring to ultrafine solid particles with sizes of 1 -1 00nm) also have such special tribological properties as wearing resistance, antifriction, high carrying capacity and the like on lubrication and tribology. In the nanoparticle jet flow minimal quantity lubrication, nano solid particles are added into a -2 minimal quantity lubrication fluid medium to prepare nano fluid, namely, the nanoparticles and a lubricant (oil or oil water mixture) are mixed with high pressure gas and atomized to be sprayed into the grinding area in a jet flow manner. [0005] The inventors have made deep theoretical analysis and experimental verification on a minimal quantity lubrication grinding supply system, related patents have been applied for the research results, the invention patent applied by the invention designer with application number of 201210153801.2 discloses a nanoparticle jet flow minimal quantity lubrication grinding lubricant supply system, in which nano solid particles are added into degradable grinding fluid to be prepared into a minimal quantity lubrication grinding lubricant, the lubricant is converted into pulse droplets with fixed pressure, variable pulse frequency and invariable droplet diameter by a minimal quantity supply device, and the droplets are sprayed into the grinding area in a jet flow manner under the action of an air isolation layer generated by the high pressure gas. However, controllable jet flow ultrafine droplets are not formed in a magnetically enhanced electrostatic atomization manner, and the atomization principle and the droplet control manner are different; the invention patient with application number of 201110221543.2 discloses a nanoparticle jet flow minimal quantity lubrication grinding three phase flow supply system, in which nano fluid is conveyed to a nozzle through a liquid path, meanwhile, the high pressure gas enters the nozzle through a gas path, the high pressure gas is fully mixed with the nano fluid in a nozzle mixing chamber and fully atomized and enters a vortex chamber after being accelerated in an acceleration chamber, meanwhile, compressed gas is taken in through a vent hole of the vortex chamber to further rotationally mix and accelerate the three-phase flow, and then the three-phase flow is jet to the grinding area from the nozzle outlet in an atomized droplet manner. But ultrafine spray droplets with charges are not formed by the magnetically enhanced electrostatic atomization principle in the disclosed technical solution, controllable jet flow cannot be achieved, and the atomization principle and the droplet control manner are different. [0006] Application number 201310042095.9 discloses a nano fluid electrostatic atomization controllable jet flow type minimal quantity lubrication grinding system, in which controllable distribution of the jet spray droplets can be achieved by means of the electrostatics principle to reduce the environmental pollution and provide better health guarantee for workers. A corona charging nozzle is installed on the grinding system, the nozzle body of the corona charging nozzle is connected with a liquid supply system and a gas supply system, a high voltage DC electrostatic generator at the lower part of the nozzle body is connected with the cathode of an adjustable high voltage DC power supply, the anode of the adjustable high voltage DC power -3 supply is connected with a workpiece electrifying device, and the workpiece electrifying device is attached to the non-processed surface of a workpiece; nano fluid grinding fluid is conveyed into the corona charging nozzle by the liquid supply system, meanwhile, the gas supply system conveys compressed air into the corona charging nozzle, the nano fluid grinding fluid is driven by the compressed air to jet out from the outlet of the nozzle body to be atomized and is charged by the high voltage DC electrostatic generator to become controllable jet flow, and the nano fluid grinding fluid is controllably distributed to the grinding area of the processed workpiece under the action of an electric field force and an aerodynamic force. In the disclosed technical solution, minimal quantity lubrication grinding achieved by charging of nanoparticle jet flow droplets and controllable and orderly transportation of spray droplets under the coupling action of a magnetic field, an electric field and atomization is not adopted, controllable jet flow ultrafine droplets are generated, and the atomization principle and the droplet control manner are different. [0007] In the minimal quantity lubrication grinding, if the minimal quantity lubricant cannot be effectively and controllably injected into the grinding area under the carrying action of the high pressure gas, namely, nanoparticle jet flow will be dispersed into the surrounding environment in the wedge-shaped area of the grinding wheel/workpiece interface. Now we are highly concerning about the influence of lubricating fluid and cooling liquid on the health of operators during minimal quantity lubrication processing, for example, the operators will suffer from various diseases of respiratory system including occupational asthma, allergic pneumonia, pulmonary function loss and skin diseases, such as allergy, oil acne and skin cancer, etc. The industrial concern of minimal quantity lubrication is potential health hazard brought by the spray droplets powered by air to the operators. The spray droplets in the spray powered by the compressed air are not constrained after being jet in minimal quantity lubrication, the movement thereof is not controllable anymore, and a series of problems, such as dispersion, drift and the like, will occur. However, the fine spray droplets will be dispersed into the working environment due to these problems, which not only greatly pollutes the environment, but also brings great health harm to the workers. The spray droplets can even cause various occupational diseases if being smaller than 4 pm. According to actual reports, the lung function can be damaged even in case of short-term exposure in this environment. Therefore, the exposure limiting concentration of mineral oil spray droplets suggested by the USA Occupation Safety and Health Research Institute is 0.5mg/m 3 . In order to ensure the health of the workers, the fine droplets must be controlled in the minimal quantity lubrication process to reduce the amount of diffusion. However, from the current retrieval literatures, the research in this area has not been reported, so the research on the above-mentioned -4 problems is extremely urgent. Based on this situation, we have made a research on the controllable distribution of the fine spray droplets in the minimal quantity lubrication process. [0008] The inventors have made deep theoretical analysis and experimental verification on the jet flow controllability of the minimal quantity lubrication grinding supply system, related patents have been applied for the research results, the invention patent applied by the invention designer with application number of 201310042095.9 discloses a nano fluid electrostatic atomization controllable jet flow minimal quantity lubrication grinding system, in which nanoparticle jet flow minimal quantity lubricating fluid is further atomized on the basis of the pneumatic atomization by means of the electrostatic atomization principle, meanwhile, the jet minimal quantity lubricating fluid is charged by means of the electrostatic charging principle, the charged droplets directionally move towards the workpiece under the action of an electric field force to achieve controllable jet flow of nanoparticles. Although directional and controllable jet flow of the nanoparticles is achieved in this solution, under this condition, if the charging capacity of the droplets need to be further increased, the voltage of the DC power supply needs to be continuously increased, but due to the limit of a breakdown voltage, the electrostatic voltage cannot be increased unlimitedly, how to increase the charging capacity of the droplets without increasing the electrostatic voltage becomes the main research direction, and based on this situation, we have made a research on how to increase the charging capacity of the spray droplets without increasing the electrostatic voltage in an electrostatic atomization charging process. SUMMARY OF THE INVENTION [0009] It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative. [0010] More particularly, the present invention seeks to provide controllable nanoparticle jet flow transportation type minimal quantity lubrication grinding equipment under a magnetically enhanced electric field, which is used for improving the charging capacity of droplets by increasing a magnetic field on the surrounding of a corona area. [0011] To this end, a first aspect of the present invention provides controllable nanoparticle jet flow transportation type minimal quantity lubrication grinding equipment under a magnetically enhanced electric field, comprising: a nozzle provided with a high voltage DC electrostatic generator and a magnetic field forming device at the outside; -5 the nozzle is connected with a nanoparticle liquid supply system and a gas supply system; the high voltage DC electrostatic generator is connected with the cathode of an adjustable high voltage DC power supply , and the anode of the adjustable high voltage DC power supply is connected with a workpiece electrifying device which is used for being attached to the non-processed surface of a workpiece , in order to form a negative corona discharge manner; the magnetic field forming device is arranged at the surrounding of an electrostatic discharge corona area; nano fluid grinding fluid is jet out from the spray head of the nozzle to be atomized to become droplets, and the droplets are charged under the action of the high voltage DC electrostatic generator and the magnetic field forming device and are conveyed into a grinding area. [0012] Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to". [0013] The high voltage DC electrostatic generator is installed on the magnetic field forming device, and the magnetic field forming device is installed on the nozzle. [0014] The high voltage DC electrostatic generator is formed by a part of the spray head, and the magnetic field forming device is installed on the nozzle. [0015] The magnetic field forming device is composed of two identical structures, which are fixed in a clamping groove on the periphery of the nozzle close to the spray head through respective fixing plates with semi-circular arcs at the middle parts, and the two fixing plates are connected together; each structure includes: a fixed plate and a movable plate, which are hinged, a T-shaped chute is arranged at the upper part of the fixed plate, one end of an angle adjusting and fixing mechanism is fixed on the movable plate, and the other end of the angle adjusting and fixing mechanism is movably connected with the T-shaped chute for adjusting and fixing an angle; a magnetic box is arranged on the movable plate, a magnetic element is arranged in the magnetic box, an electrode chuck is arranged at the top of the magnetic box, and the high voltage DC electrostatic generator is installed on the electrode chuck.

-6 [0016] The high voltage DC electrostatic generator is composed of a plurality of L-shaped needle electrodes I, a rubber stopper is arranged at the middle of each L-shaped needle electrode 1, and a conducting wire interface is arranged at the tail of each L-shaped needle electrode I; a plurality of electrode slots are arranged at one side of the electrode chuck of the magnetic field forming device, a conducting wire through groove is arranged at the opposite side of the electrode chuck, each electrode slot is communicated with the conducting wire through groove, and the conducting wire interface is located in the conducting wire through groove and is connected with an electrode high voltage conducting wire. [0017] The spray head is flat fan-shaped, and the inner surface of the flat fan-shaped spray head is a hemi-elliptical sphere or a hemisphere; a V-shaped groove is formed in the top end of the hemi-elliptical sphere, and the two inclined planes of the V-shaped groove are symmetrical relative to the axial line of the nozzle and form a long and narrow spray opening with the hemi-elliptical sphere. [0018] The magnetic field forming device is composed of two identical structures, which are fixed in a clamping groove on the periphery of the nozzle close to the spray head through respective fixing plates with semi-circular arcs at the middle parts, and the two fixing plates are connected together; each structure includes: a fixed plate and a movable plate, which are hinged, a T-shaped chute is arranged at the upper part of the fixed plate, one end of an angle adjusting and fixing mechanism is fixed on the movable plate, and the other end of the angle adjusting and fixing mechanism is movably connected with the T-shaped chute for adjusting and fixing an angle; a magnetic box is arranged on the movable plate, a magnetic element is arranged in the magnetic box, and an electrode chuck is arranged at the top of the magnetic box. [0019] The spray head is divided into two parts, namely a spray head body and an electrode nozzle 1, the spray head body is in threaded connection with the electrode nozzle 1, the spray head body is made of a ceramic material, the electrode nozzle I is made of a discharge electrode material to serve as the high voltage DC electrostatic generator, the thickness of the thinner position at the outlet of the electrode nozzle I is 0.3-1.2 mm, and a conducting wire connecting ring I is arranged on the electrode nozzle I for connecting the electrode high voltage conducting wire. [0020] The angle adjusting and fixing device includes an angle positioning ring, an arched chute is arranged on the angle positioning ring, the angle positioning ring is fixedly connected -7 with the movable plate, and the arched chute is movably connected with the fixed plate through a positioning mechanism formed by a slide block screw and a nut for adjusting and fixing the angle. [0021] The magnetic element is a permanent magnet or an electromagnet; when the electromagnet is adopted, an electromagnet conducting wire groove is arranged on the back side face of the magnetic box, and the electromagnet is connected with an adjustable electromagnet power supply through an electromagnet conducting wire. [0022] The nozzle includes a mixing cavity body, and the two ends of the mixing cavity body are hermetically connected with a gas injection pipe and the spray head respectively; the interior of the mixing cavity body is divided into a liquid inlet cavity and a mixing cavity, the liquid inlet cavity and the mixing cavity are isolated by a disk-shaped liquid inlet stopper, and a plurality of liquid inlet holes are arranged on the liquid inlet stopper; a plurality of gas injection holes are arranged on the front part of the gas injection pipe in the mixing cavity, and the gas injection holes are arranged to form two groups of opposite helical lines; a conical acceleration segment is arranged between the mixing cavity and the spray head. [0023] Controllable nanoparticle jet flow transportation type minimal quantity lubrication grinding equipment under a magnetically enhanced electric field includes: a high voltage DC electrostatic generator and a magnetic field forming device are arranged internally to form an integral nozzle; the integral nozzle is connected with a nanoparticle liquid supply system and a gas supply system; the high voltage DC electrostatic generator is connected with the cathode of an adjustable high voltage DC power supply, and the anode of the adjustable high voltage DC power supply is connected with a workpiece electrifying device which is used for being attached to the non-processed surface of a workpiece, in order to form a negative corona discharge manner; the magnetic field forming device is arranged at the surrounding of an electrostatic discharge corona area; nano fluid grinding fluid is jet out from the integral nozzle to be atomized to become droplets, and the droplets are charged under the action of the high voltage DC electrostatic generator and the magnetic field forming device and are conveyed into a grinding area. The integral nozzle includes an integral nozzle body, an integral nozzle gas injection channel is arranged in the integral nozzle, a plurality of gas injection holes are arranged at the -8 lower part of an integral nozzle gas injection pipe wall of the integral nozzle gas injection channel and are communicated with an integral nozzle mixing cavity; the integral nozzle body is further provided with an integral nozzle liquid injection cavity communicated with an integral nozzle liquid injection channel; the integral nozzle liquid injection cavity is communicated with the integral nozzle mixing cavity through an integral nozzle orifice; a fan-shaped nozzle outlet of the integral nozzle is arranged at the bottom of the integral nozzle mixing cavity; an integral nozzle electrode groove is arranged at the lower part of the fan-shaped nozzle outlet of the integral nozzle, and an integral nozzle magnetic box is arranged at the lower part of the integral nozzle electrode groove; the high voltage DC electrostatic generator and the magnetic field forming device are respectively arranged in the integral nozzle electrode groove and the integral nozzle magnetic box. [0024] The integral nozzle includes an integral nozzle body, an integral nozzle gas injection channel is arranged in the integral nozzle, a plurality of gas injection holes are arranged at the lower part of an integral nozzle gas injection pipe wall of the integral nozzle gas injection channel and are communicated with an integral nozzle mixing cavity; the integral nozzle body is further provided with an integral nozzle liquid injection cavity communicated with an integral nozzle liquid injection channel; the integral nozzle liquid injection cavity is communicated with the integral nozzle mixing cavity through an integral nozzle orifice; a spray head body and an electrode nozzle || are arranged at the bottom of the integral nozzle mixing cavity, and the spray head body is in threaded connection with the electrode nozzle 1l; a conducting wire connecting ring II is arranged on the electrode nozzle || for connecting the electrode high voltage conducting wire to serve as the high voltage DC electrostatic generator; an integral nozzle magnetic box is arranged at the lower part of the electrode nozzle 1l; the magnetic field forming device is arranged in the integral nozzle magnetic box. [0025] The high voltage DC electrostatic generator includes: a circular electrode disk, and an annular electrode conducting wire placement groove and a plurality of needle electrode clamping grooves arranged at intervals are arranged on the circular electrode disk; an electrode conducting wire through hole is further arranged in the electrode conducting wire placement groove, the electrode high voltage conducting wire is connected to the outside of the integral nozzle through an electrode conducting wire channel of the integral nozzle after being led out; -9 L-shaped needle electrodes || are inserted in the needle electrode clamping grooves. The magnetic field forming device includes: a magnet, which is placed in the integral nozzle magnetic box and is positioned by a positioning chuck, and a magnet baffle is arranged on the positioning chuck; the magnet is a permanent magnet or an electromagnet; if the magnet is the electromagnet, an electromagnet conducting wire is led out by the electrode conducting wire channel of the integral nozzle. [0026] The workpiece electrifying device is composed of an insulating shell of the workpiece electrifying device, a weight, a pressing permanent magnet and a pressing spring; the pressing permanent magnet is installed on the insulating shell of the workpiece electrifying device, the weight is installed at the middle of the insulating shell of the workpiece electrifying device through the pressing spring in a penetration manner, and a conducting wire connecting ring and a cotter pin slot are arranged at the end part exposed from the insulating shell of the workpiece electrifying device. [0027] The present invention has the following beneficial effects: the controllable nanoparticle jet flow transportation type minimal quantity lubrication grinding equipment under the magnetically enhanced electric field is provided for improving the charging capacity of droplets by increasing the magnetic field on the surrounding of the corona area. Under a magnetically enhanced corona discharge condition, free electrons form Larmor movement under the coaction of a coulomb force and a Lorentz force, and the movement locus of the free electrons is prolonged. That is, since the free electrons make the Larmor movement, the collision probability of the free electrons with air molecules and minimal quantity lubrication grinding fluid particles is greatly increased, thus resulting in more intense electron avalanche, enhancing air ionization and ensuring more sufficient particle charging. Due to the existence of the magnetic field, the corona inception voltage of corona discharge is reduced. By means of the coupling action of the magnetic field, the electric field and atomization, minimal quantity lubrication grinding is achieved by charging of nanoparticle jet flow droplets and controllable and orderly transportation of spray droplets. BRIEF DESCRIPTION OF THE DRAWINGS [0028] One or more preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: - 10 [0029] Fig.1 is an axonometric drawing of assembly in the first and third embodiments; [0030] Fig.2 is an axonometric drawing of assembly in the second and fourth embodiments; [0031] Fig.3 is a schematic diagram of liquid path and gas path systems in the first, second, third and fourth embodiments; [0032] Fig.4 is a block diagram of a circuit system in the first, second, third and fourth embodiments; [0033] Figs.5a and b are a sectional view and a top view of a workpiece electrifying device in the first, second, third and fourth embodiments; [0034] Fig.6 is a sectional view of a nozzle body in the first and second embodiments; [0035] Fig.7 is a local axonometric drawing of a gas injection pipe in the first and third embodiments; [0036] Fig.8 is a sectional view of a spray head in the first embodiment; [0037] Fig.9 is an axonometric drawing of assembly of an electromagnetic device in the first and third embodiments; [0038] Fig.10 is a schematic diagram of assembly of a nozzle and an electromagnetic device in the first and third embodiments; [0039] Fig.1 1 is an axonometric drawing of a fixed plate in the first and third embodiments; [0040] Fig.12 is an axonometric drawing of a movable plate in the first and third embodiments; [0041] Fig.13 is an axonometric drawing of a magnetic box in the first and third embodiments; [0042] Fig.14 is an axonometric drawing of an electrode chuck in the first and third embodiments; - 11 [0043] Fig.15 is an axonometric drawing of a fixing plate in the first and third embodiments; [0044] Fig.16 is a top view of an angle positioning ring in the first and third embodiments; [0045] Fig.17 is an axonometric drawing of an L-shaped needle electrode and a rubber stopper in the first embodiment; [0046] Fig.18 is a sectional view of an integral nozzle in the second embodiment; [0047] Fig.19 is a top view of an integral nozzle in the second and fourth embodiments; [0048] Fig.20 is a sectional view of assembly of an integral nozzle and an electromagnetic device in the second embodiment; [0049] Figs.21a and b are a top view and a revolved sectional view of a circular electrode groove in the second embodiment; [0050] Fig.22 is a top view of a positioning chuck in the second and fourth embodiments; [0051] Fig.23 is a sectional view of an electrode spray head in the third embodiment; [0052] Fig.24 is a sectional view of an integral nozzle in the fourth embodiment; wherein, 1-grinding wheel, 2-grinding machine part worktable, 3-insulating board, 4-workpiece, 5-magnetic suction cup, 6-grinding wheel cover, 7-compressed air conveying coiled pipe, 8 nano fluid conveying coiled pipe, 9-adjustable high voltage DC power supply, 10-electrode high voltage conducting wire, 11-workpiece electrifying device, 12-nozzle, 13-electromagnetic device, 14-electromagnet conducting wire, 15-adjsutable electromagnet power supply, 16 mixing cavity body, 17-gas injection pipe, 18-spray head, 19-left nozzle nut, 20-liquid inlet threaded pipe, 21-right nozzle nut, 22-liquid inlet stopper, 23-sealing washer I, 24-sealing washer II, 25-liquid inlet cavity, 26-mixing cavity, 27-acceleration segment, 28-fan-shaped nozzle outlet, 29-clamping groove, 30-positioning threaded hole, 31 -air compressor, 32-nano fluid storage tank, 33-gas storage tank, 34-hydraulic pump, 35-filter, 36-pressure gauge, 37 throttle valve 1, 38- turbine flowmeter I, 39- turbine flowmeter II, 40-throttle valve 1l, 41 pressure regulating valve 1, 42-pressure regulating valve 1l, 43-overflow valve, 44-nano fluid recycling box, 45-fixed plate, 46-movable plate, 47-angle positioning ring, 48-screw I, 49-screw II, 50-slide block screw, 51-electrode chuck, 52-magnetic box, 53-nut, 54-screw Ill, 55-screw IV, 56-T-shaped chute, 57-through hole 1, 58-positioning block, 59-fixing plate insertion -12 opening, 60-magnetic box fixing block, 61 -through hole 1l, 62-threaded hole 1, 63-hexagonal counter bore, 64-through hole Ill, 65-threaded through hole, 66-threaded hole 1l, 67 electromagnet conducting wire groove, 68-electrode slot, 69-through hole IV, 70-conducting wire through groove, 71-fixing plate, 72-through hole V, 73-through hole VI, 74-through hole VII, 75-arched chute, 76-cotter pin slot, 77-insulating shell of workpiece electrifying device, 78 weight, 79-pressing permanent magnet, 80-pressing spring, 81 -conducting wire connecting ring, 82-rubber stopper, 83-L-shaped needle electrode 1, 84-conducting wire interface, 85 integral nozzle body, 86-integral nozzle gas injection channel, 87-integral nozzle gas injection channel joint, 88-integral nozzle liquid injection channel, 89-integral nozzle liquid injection channel joint, 90-integral nozzle liquid injection cavity, 91 -integral nozzle orifice, 92-integral nozzle mixing cavity, 93-integral nozzle acceleration segment, 94-fan-shaped nozzle outlet of integral nozzle, 95-integral nozzle electrode conducting wire channel, 96-integral nozzle electrode groove, 97-integral nozzle magnetic box, 98-electromagnet conducting wire channel of integral nozzle, 99-integral nozzle fixing threaded hole, 100-integral nozzle gas injection pipe wall, 101-circular electrode disk, 102-L-shaped needle electrode 1l, 103-magnet, 104 positioning chuck, 105-electrode conducting wire through hole, 106-needle electrode clamping groove, 107-electrode conducting wire placement groove, 108-positioning through hole, 109 magnet baffle, 110-integral nozzle, 111-spray head body, 112-electrode nozzle 1, 113 conducting wire connecting ring I, 114-electrode nozzle 1l, 115-electrode wiring space, 116 conducting wire connecting ring II. DETAILED DESCRIPTION OF THE EMBODIMENTS [0053] A further illustration of the present invention will be given below in combination with accompanying drawings and embodiments. Embodiment 1: [0054] As shown in Fig.1 and Fig.3 to Fig.1 7, the first embodiment of the present invention provides a magnetically enhanced electric field induced nanoparticle jet flow droplet charging mechanism and controllable and orderly spray droplet transportation minimal quantity lubrication grinding process method and equipment. [0055] As shown in Fig.1, in the first embodiment, an insulating board 3 (this novel material has magnetic conductivity but no electric conductivity to ensure the installation of a workpiece 4 and ensure that a stable electric field can be formed between a nozzle 12 and the workpiece 4) is covered on a grinding machine part worktable 2. The workpiece 4 is placed on the -13 insulating board 3, the workpiece 4 is clamped and positioned during magnetization of a grinding machine, and a magnetic suction cup 5 is adsorbed on the side face of a grinding wheel cover 6 for fixing a nano fluid conveying coiled pipe 8, a compressed air conveying coiled pipe 7 and a cathode conducting wire in an electrode high voltage conducting wire 10. One end of the nano fluid conveying coiled pipe 8 is connected with a liquid inlet threaded pipe 20, and the other end of the nano fluid conveying coiled pipe 8 is connected with a turbine flowmeter II 39. One end of the compressed air conveying coiled pipe 7 is connected with a gas injection pipe 17, and the other end of the compressed air conveying coiled pipe 7 is connected with a turbine flowmeter 1 38. One end of the cathode conducting wire in the electrode high voltage conducting wire 10 penetrates through a conducting wire through groove 70 to be sequentially connected with the tail ends of the needle electrodes, and the other end of the cathode conducting wire is connected with the cathode output end of an adjustable high voltage DC power supply 9. One end of the anode conducting wire in the electrode high voltage conducting wire 10 is connected with a conducting wire connecting ring 81, and the other end of the anode conducting wire is connected with the anode output end of the adjustable high voltage DC power supply 9 and is grounded. A workpiece electrifying device 11 is adsorbed on the non-processed surface of the workpiece, such that the workpiece 4 is connected with the anode of the adjustable high voltage DC power supply 9, an electromagnet coil is connected with an adjustable electromagnet power supply 15 through an electromagnet conducting wire 14, and an electromagnetic device is fixed on a nozzle 12 through a fixing plate 71. [0056] As shown in Fig.3, in the first embodiment, the nozzle 12 is a pneumatic atomization nozzle, and compressed air and nano fluid are mixed in the nozzle 12. The gas path of the nozzle 12 is composed of an air compressor 31, a filter 35, a gas storage tank 33, a pressure regulating valve 1 41, a throttle valve 1 37 and the turbine flowmeter 1 38, which are connected in sequence. The liquid path of the nozzle 12 is composed of a nano fluid storage tank 32, a hydraulic pump 34, a pressure regulating valve II 42, a throttle valve II 40 and a turbine flowmeter II 39, which are connected in sequence. The compressed air generated by the air compressor 31 enters the gas storage tank 33 through the filter 35 and flows by the turbine flowmeter 1 38 to enter the gas injection pipe 17 through the pressure regulating valve 1 41 and the throttle valve 1 37; the hydraulic pump 34 pumps out the nano fluid in the nano fluid storage tank 32, and the nano fluid flows by the turbine flowmeter II 39 to enter a liquid inlet threaded pipe 20 through the pressure regulating valve II 42 and the throttle valve II 40. Wherein, an overflow valve 43 and a nano fluid recycling box 44 form a protection loop, and a pressure gauge 36 is used for monitoring the gas pressure of the gas storage tank 33.

-14 [0057] As shown in Fig.4, in the first embodiment, the adjustable high voltage DC power supply 9 is composed of an AC power supply input unit, a DC voltage stabilizing unit V1, a DC voltage stabilizing unit V2, a self excited oscillation circuit, a power amplification circuit, a high frequency pulse booster, a voltage doubling rectifying circuit and a constant current automatic control circuit. [0058] As shown in Figs.5a and b, in the first embodiment, the workpiece electrifying device 11 is composed of an insulating shell 77 of the workpiece electrifying device, a weight 78, a pressing permanent magnet 79 and a pressing spring 80. When the workpiece electrifying device is close to the non-pressed surface of the workpiece, the pressing permanent magnet 79 will generate a suction force with the workpiece 4 to compress the pressing spring 80, meanwhile, the pressing spring 80 provides a counterforce to ensure the firm connection of the weight 78 and the workpiece 4. A cotter pin slot 76 is formed on the weight 78 and is used for insertion of a cotter pin to ensure that the weight 78 and the pressing spring 80 will not drop from the insulating shell 77 of the workpiece electrifying device when the workpiece electrifying device 11 is not adsorbed on the workpiece 4. The conducting wire connecting ring 81 is arranged at the tail end of the weight 78 for facilitating connection of a conducting wire. [0059] As shown in the sectional view of the nozzle body, the local axonometric drawing of the gas injection pipe 17 and the sectional view of the spray head in Fig.6, Fig.7 and Fig.8, in the first embodiment, it can be seen that the nozzle 12 designed and used in the embodiment is a minimal quantity lubrication atomization nozzle, the minimal quantity lubrication atomization nozzle is composed of a left nozzle nut 19, the gas injection pipe 17, a sealing washer 1 23, the liquid inlet threaded pipe 20, a liquid inlet stopper 22, a right nozzle nut 21, a sealing washer || 24, a spray head 18 and a mixing cavity body 16, and the assembly thereof is as shown in Fig.6. It can also be seen from the figure that the nozzle 12 further includes a liquid inlet cavity 25, a mixing cavity 26, an acceleration segment 27 and a fan-shaped nozzle outlet 28. The compressed air and the nano fluid respectively enter the mixing cavity 26 through the gas injection pipe 17 and the liquid inlet cavity 25 for mixing, the liquid inlet stopper 22 is disk-shaped, 4-8 liquid inlet holes may be symmetrically distributed on the surrounding according to demand for limiting the amount of the nano fluid entering the mixing cavity 26, so as to ensure an enough mixing space for the compressed air and the nano fluid in the mixing cavity 26. The compressed air and the nano fluid are fully mixed in the mixing cavity 26 to form subsonic speed three-phase (compressed air, liquid lubricating base oil and solid nanoparticles) bubble flow. After the bubble flow enters the acceleration segment 27, the flow space of the three-phase bubble flow is reduced due to the conical structure of the -15 acceleration segment 27, such that the pressure and the flow rate of the three-phase bubble flow are increased and the diameter of the bubble is decreased. Meanwhile, when flowing by the acceleration segment 27, the three-phase bubble flow is extruded to become unstable and broken into smaller bubbles and droplets, thus increasing the number of the spray droplets and improving the atomization effect. Meanwhile, after being accelerated, the three-phase bubble flow is jet out at the fan-shaped nozzle outlet 28 at a speed close to the sonic speed, thus accelerating the jet speed, since the pressure suddenly reduces to the atmospheric pressure, the bubbles will urgently expand to burst to form liquid atomization power, meanwhile, the surrounding bubbles will be impacted to burst and mutually collide to change the atomized particles into ultrafine ones. Gas injection holes are formed on the gas injection pipe 17, the gas injection holes are distributed in the form of two opposite helical lines, which is more conducive to full mixing and collision of the three-phase bubble flow in the mixing cavity 26, meanwhile, inclination angles of 15-35 degrees are formed between the central axial lines of the gas injection holes distributed along the helical lines in the axial direction of the gas injection pipe 17 and the central axial lines of the nozzle gas injection pipe, which is conducive to flowing of the three-phase bubble flow in the mixing cavity 26 to the acceleration segment 27 for propulsion, an axial gas injection hole is arranged at the top end of the gas injection pipe 17 for further accelerating the three-phase bubble flow in the acceleration segment 27. A clamping groove 29 and positioning threaded holes 30 are used for connecting the fixing plate 71, and multiple groups of positioning threaded holes 30 are arrayed in the clamping groove 29 along the circumferential direction. It can be seen from Fig.6 that the spray head 18 is a flat fan-shaped spray head. The inner surface of the flat fan-shaped spray head is generally a hemi-elliptical sphere or a hemisphere. A V-shaped groove is formed in the top end of the hemi-elliptical sphere, and the two inclined planes of the V-shaped groove are symmetrical relative to the axial line of the nozzle and form a long and narrow spray opening with the hemi elliptical sphere. This spray head can generate fan-shaped uniform flat jet flow, the impact force of the jet flow is uniform, the impact range is large, the divergence angle can also be adjusted within a larger range, and the cleaning capacity is particularly excellent. In the figure, a refers to the length of the major semi-axis of the ellipse, b refers to the length from the center of the ellipse to the bottom of the V-shaped groove, c refers to the diameter of the injection section of the nozzle, and arefers to a half of the angle of the V-shaped groove. [0060] As shown in Fig.9 to Fig.17, they are an axonometric drawing of total assembly of the electromagnetic device and views of the components, in the first embodiment, two opposite electromagnetic devices are arranged, and one group is shown in Fig.9. As shown in the figure, a screw II 49 penetrates through a through hole 1 57 arranged on a fixed plate 45 and -16 two through holes Ill arranged on a movable plate 46, one end of the screw II 49 sinks into a hexagonal counter bore 63, a nut is screwed on the other end of the screw II 49, so that the movable plate 46 and the fixed plate 45 are interconnected and may rotate relatively. A slide block screw 50 slides into a T-shaped chute 56 to enable a screw above the slide block screw 50 to penetrate through an arched chute 75 on an angle positioning ring 47, and the upper side of the slide block screw 50 is screwed by a nut 53. A screw I 48 is screwed on a threaded hole 1 62 by penetrating through a through hole VII 74 on the angle positioning ring 47, the screw I 48 is adjusted to enable the angle positioning ring 47 to rotate around the same, the nut 53 is unscrewed to enable the slide block screw 50 to slide in the T-shaped chute 56 so as to adjust the relative angle of the fixed plate 45 and the movable plate 46, then the screw I 48 and the nut 53 are screwed to lock the angle positioning ring 47 for fixing the angles of the movable plate 46 and the fixed plate 45, and scales are arranged on the angle positioning ring 47 for conveniently adjusting a quantitative angle. A permanent magnet or an electromagnet is put in a magnetic box 52, an electrode chuck 51 is arranged above the magnetic box 52, a threaded hole II 66 is aligned with a through hole IV 69, the magnetic box 52 is connected with the electrode chuck 51 through a screw Ill 54, if the electromagnet is installed in the magnetic box 52, the coil conducting wire of the electromagnet can be introduced into a conducting wire through groove 70 through an electromagnet conducting wire groove 67, a rubber stopper 82 is inserted in an electrode slot 68 (interference fit), an L-shaped needle electrode 1 83 is inserted in the rubber stopper 82 (interference fit), the tail end of the L-shaped needle electrode 1 83 extends to the conducting wire through groove 70, and a conducting wire interface 84 is arranged at the tail end of the L-shaped needle electrode 1 83. An electromagnet coil conducting wire and an electrode conducting wire may be led out of the device through the conducting wire through groove 70 to be connected with a power supply. The fixing plate 71 is placed in the clamping groove 29, and a through hole VI 73 is aligned with the positioning threaded holes 30 and is connected with the same through screws. Two groups of opposite electromagnetic devices are arranged, the fixing plate 71 is inserted in a fixing plate insertion opening 59 on a positioning block 58, and the screws are inserted into the through holes V72 on the two groups of fixing plates 71 and are locked by nuts to fix the entire electromagnetic device. Since multiple groups of positioning threaded holes 30 are arrayed in the clamping groove 29 along the circumferential direction, and the relative angle of the fixed plate 45 and the movable plate 46 is adjustable, a multi-angle magnetic field in front of the nozzle is formed. Embodiment 2: [0061] Fig.2 to Fig.5 and Fig.18 to Fig.22 are the second embodiment of the present -17 invention, in the second embodiment, the nozzle 12 and the electromagnetic device 13 in the first embodiment are replaced with an integral nozzle 110. [0062] As shown in Fig.2, an insulating board 3 (this novel material has magnetic conductivity but no electric conductivity to ensure the installation of a workpiece and ensure that a stable electric field can be formed between a nozzle and the workpiece) is covered on a grinding machine part worktable 2. The workpiece 4 is placed on the insulating board 3, the workpiece 4 is clamped and positioned during magnetization of a grinding machine, and a magnetic suction cup 5 is adsorbed on the side face of a grinding wheel cover 6 for fixing a nano fluid conveying coiled pipe 8, a compressed air conveying coiled pipe 7 and a cathode conducting wire in an electrode high voltage conducting wire 10. One end of the nano fluid conveying coiled pipe 8 is connected with an integral nozzle liquid injection channel joint 89, and the other end of the nano fluid conveying coiled pipe 8 is connected with a turbine flowmeter II 39. One end of the compressed air conveying coiled pipe 7 is connected with an integral nozzle gas injection channel joint 87, and the other end of the compressed air conveying coiled pipe 7 is connected with a turbine flowmeter 1 38. The cathode conducting wire in the electrode high voltage conducting wire 10 penetrates through an integral nozzle electrode conducting wire channel 95 to be sequentially connected with the tail ends of the needle electrodes, and the other end of the cathode conducting wire is connected with the cathode output end of an adjustable high voltage DC power supply 9. One end of the anode conducting wire in the electrode high voltage conducting wire 10 is connected with a conducting wire connecting ring 81, and the other end of the anode conducting wire is connected with the anode output end of the adjustable high voltage DC power supply 9 and is grounded. A workpiece electrifying device 11 is adsorbed on the non-processed surface of the workpiece, such that the workpiece 4 is connected with the anode of the adjustable high voltage DC power supply 9, and an electromagnet coil is connected with an adjustable electromagnet power supply 15 through an electromagnet conducting wire 14. [0063] As shown in Fig.3, in the second embodiment, the integral nozzle 110 is a pneumatic atomization nozzle, and compressed air and nano fluid are mixed in the integral nozzle 110. The gas path of the integral nozzle 110 is composed of an air compressor 31, a filter 35, a gas storage tank 33, a pressure regulating valve 1 41, a throttle valve 1 37 and the turbine flowmeter 1 38, which are connected in sequence. The liquid path of the integral nozzle 110 is composed of a nano fluid storage tank 32, a hydraulic pump 34, a pressure regulating valve II 42, a throttle valve II 40 and a turbine flowmeter II 39, which are connected in sequence. The compressed air generated by the air compressor 31 enters the gas storage tank 33 through -18 the filter 35 and flows by the turbine flowmeter 1 38 to enter an integral nozzle gas injection channel 86 through the pressure regulating valve 1 41 and the throttle valve 1 37; the hydraulic pump 34 pumps out the nano fluid in the nano fluid storage tank 32, and the nano fluid flows by the turbine flowmeter II 39 to enter an integral nozzle liquid injection channel 88 through the pressure regulating valve II 42 and the throttle valve II 40. Wherein, an overflow valve 43 and a nano fluid recycling box 44 form a protection loop, and a pressure gauge 36 is used for monitoring the gas pressure of the gas storage tank 33. [0064] As shown in Fig.4, in the second embodiment, the adjustable high voltage DC power supply 9 is composed of an AC power supply input unit, a DC voltage stabilizing unit V1, a DC voltage stabilizing unit V2, a self excited oscillation circuit, a power amplification circuit, a high frequency pulse booster, a voltage doubling rectifying circuit and a constant current automatic control circuit. [0065] As shown in Figs.5a and b, in the second embodiment, the workpiece electrifying device 11 is composed of an insulating shell 77 of the workpiece electrifying device, a weight 78, a pressing permanent magnet 79 and a pressing spring 80. When the workpiece electrifying device is close to the non-pressed surface of the workpiece, the pressing permanent magnet 79 will generate a suction force with the workpiece 4 to compress the pressing spring 80, meanwhile, the pressing spring 80 provides a counterforce to ensure the firm connection of the weight 78 and the workpiece 4. A cotter pin slot 76 is formed on the weight 78 and is used for insertion of a cotter pin to ensure that the weight 78 and the pressing spring 80 will not drop from the insulating shell 77 of the workpiece electrifying device when the workpiece electrifying device 11 is not adsorbed on the workpiece 4. The conducting wire connecting ring 81 is arranged at the tail end of the weight 78 for facilitating connection of a conducting wire. [0066] As shown in Fig.18 to Fig.22, in the second embodiment, the used nozzle is the integral nozzle 110, the integral nozzle 110 is made of a ceramic material through a quick forming method and includes an integral nozzle body 85, the integral nozzle gas injection channel 86, the integral nozzle gas injection channel joint 87, the integral nozzle liquid injection channel 88, the integral nozzle liquid injection channel joint 89, an integral nozzle liquid injection cavity 90, an integral nozzle orifice 91, an integral nozzle mixing cavity 92, an integral nozzle acceleration segment 93, a fan-shaped nozzle outlet 94 of the integral nozzle, an integral nozzle electrode conducting wire channel 95, an integral nozzle electrode groove 96, an integral nozzle magnetic box 97, an electromagnet conducting wire channel 98 of the -19 integral nozzle, an integral nozzle fixing threaded hole 99 and an integral nozzle gas injection pipe wall 100. Compressed air enters the integral nozzle mixing cavity 92 through the integral nozzle gas injection channel 86, and meanwhile, nano fluid enters the integral nozzle liquid injection cavity 90 through the integral nozzle liquid injection channel 88 and enters the integral nozzle mixing cavity 92 to be mixed with the compressed air after being throttled by the integral nozzle orifice 91. The integral nozzle orifice 91 is used for limiting the amount of the nano fluid entering the integral nozzle mixing cavity 92, so as to ensure an enough mixing space for the compressed air and the nano fluid in the integral nozzle mixing cavity 92. The compressed air and the nano fluid are fully mixed in the integral nozzle mixing cavity 92 to form subsonic speed three-phase (compressed air, liquid lubricating base oil and solid nanoparticles) bubble flow. After the bubble flow enters the integral nozzle acceleration segment 93, the flow space of the three-phase bubble flow is reduced due to the conical structure of the integral nozzle acceleration segment 93, such that the pressure and the flow rate of the three-phase bubble flow are increased and the diameter of the bubble is decreased. Meanwhile, when flowing by the integral nozzle acceleration segment 93, the three-phase bubble flow is extruded to become unstable and broken into smaller bubbles and droplets, thus increasing the number of the spray droplets and improving the atomization effect. Meanwhile, after being accelerated, the three-phase bubble flow is jet out at the fan-shaped nozzle outlet 94 of the integral nozzle at a speed close to the sonic speed, thus accelerating the jet speed, since the pressure suddenly reduces to the atmospheric pressure, the bubbles will urgently expand to burst to form liquid atomization power, meanwhile, the surrounding bubbles will be impacted to burst and mutually collide to change the atomized particles into ultrafine ones. Gas injection holes are formed on the integral nozzle gas injection pipe wall 100, the gas injection holes are distributed in the same way as that in the first embodiment, this arrangement is more conducive to full mixing and collision of the three-phase bubble flow in the integral nozzle mixing cavity 92, meanwhile, inclination angles of 15-35 degrees are formed between the central axial lines of the gas injection holes and the central axial lines of the nozzle gas injection pipe, which is conducive to flowing of the three-phase bubble flow in the integral nozzle mixing cavity 92 to the integral nozzle acceleration segment 93 for propulsion, an axial gas injection hole is arranged at the top end of the integral nozzle gas injection pipe wall 100 for further accelerating the three-phase bubble flow in the integral nozzle acceleration segment 93, and the design of the fan-shaped nozzle outlet 94 of the integral nozzle is the same as that in the first embodiment. In the figure, the circular electrode disk 101 is made of a rubber material and has certain elasticity, 4-8 needle electrode clamping grooves 106 are arrayed on the circumference thereof, an electrode conducting wire placement groove 107 is arranged on the circular electrode disk 101, an electrode conducting wire through hole 105 is arranged in - 20 the electrode conducting wire placement groove 107 for conveniently leading out the electrode conducting wire, and the electrode conducting wire is led out of the integral nozzle 100 through the integral nozzle electrode conducting wire channel 95 after being led out. An L-shaped needle electrode 11 102 is inserted in each needle electrode clamping groove 106 (interference fit). The circular electrode disk 101 with a connected electrode is put in the integral nozzle electrode groove 96, a magnet 103 is placed in the integral nozzle magnetic box 97, the positioning as shown in Fig.20 is performed by a positioning chuck 104, and a magnet baffle 109 is arranged on the positioning chuck 104 for limiting the magnet. After penetrating through a positioning through hole 108, a screw is connected to the integral nozzle fixing threaded hole 99 for fixing the positioning chuck 104. The magnet 103 can be a permanent magnet and can also be an electromagnet, and if the magnet 103 is the electromagnet, the electromagnet conducting wire is led out by the electromagnet conducting wire channel 98 of the integral nozzle. Embodiment 3: [0067] The third embodiment of the present invention is as shown in Fig.1, Fig.3 to Fig.5, Fig.6, Fig.7, Fig.9 to Fig.16 and Fig.23, in the third embodiment of the present invention, except that the arrangement of the electrode and the design of the spray head are different from those in the first embodiment, the designs of others are the same as those in the first embodiment. In the third embodiment, the manner of adding the discharge electrode is changed, the L-shaped needle electrode 1 83 is no longer arranged in the electrode slot 68 on the electrode chuck 51 in the original first embodiment, and the electrode chuck 51 is merely used as the box cover of the magnetic box 52 in the third embodiment. In the third embodiment, the spray head 18 in the first embodiment is designed again, the design solution is as shown in Fig.23, the spray head 18 in the original first embodiment is detached into two parts, namely a spray head body 111 and an electrode nozzle 1 112, the spray head body 111 is in threaded connection with the electrode nozzle 1 112, the spray head body 111 is made of a ceramic material, the electrode nozzle I 112 is made of a discharge electrode material, the thickness of the thinner position at the outlet of the electrode nozzle 1 112 is 0.3-1.2 mm, and a conducting wire connecting ring I 113 is arranged on the electrode nozzle I 112 for conveniently connecting the conducting wire. Embodiment 4: [0068] The fourth embodiment of the present invention is as shown in Fig.2 to Fig.5, Fig.19, -21 Fig.22 and Fig.24, in the fourth embodiment of the present invention, except that the arrangement of the electrode and the design of the nozzle outlet are different from those in the second embodiment, the designs of others are the same as those in the second embodiment. In the fourth embodiment, the integral nozzle electrode groove 96 in the original second embodiment is removed in the fourth embodiment, such that the circular electrode disk 101 and the L-shaped needle electrode 11 102 are no longer used in the fourth embodiment. The fan-shaped nozzle outlet 94 of the integral nozzle in the original second embodiment is processed to the shape as shown in Fig.24 and is provided with internal threads to form threaded connection with an electrode nozzle II 114 with external threads, an electrode wiring space 115 as shown in Fig.24 is arranged in the integrally formed nozzle, and meanwhile, a conducting wire connecting ring || 116 is arranged on the electrode nozzle II 114 for conveniently connecting the electrode conducting wire. [0069] The specific working process of the solution is as follows: with the first embodiment as an example, the nano fluid enters the liquid inlet threaded pipe 20 through the liquid path: the nano fluid storage tank 32, the hydraulic pump 34, the pressure regulating valve II 42, the throttle valve II 40 and the turbine flowmeter II 39, and the compressed air enters the gas injection pipe 17 through the gas path: the air compressor 31, the filter 35, the gas storage tank 33, the pressure regulating valve 1 41, the throttle valve 1 37 and the turbine flowmeter 1 38. The liquid inlet stopper 22 is arranged between the liquid inlet cavity 25 and the mixing cavity 26 for ensuring a sufficient mixing space in the mixing cavity 26. The nano fluid and the compressed air enter the mixing cavity 26 at the same time, since two groups of opposite gas injection holes arranged in helical lines are formed on the gas injection pipe 17, the three-phase bubble flow is fully mixed and collided in the mixing cavity 26 to form vortex. Meanwhile, inclination angles of 15-85 degrees are formed between the central axial lines of the gas injection holes distributed along the helical lines in the axial direction of the gas injection pipe 17 and the central axial lines of the nozzle gas injection pipe, which is conducive to flowing of the three-phase bubble flow in the mixing cavity 26 to the acceleration segment 27 for propulsion, the axial gas injection hole is arranged at the top end of the gas injection pipe 17 for further accelerating the three-phase bubble flow in the acceleration segment 27, the accelerated three-phase bubble flow is jet out after entering the fan-shaped nozzle outlet 28, since the pressure suddenly reduces to the atmospheric pressure, the bubbles will urgently expand to burst to form liquid atomization power, and meanwhile, the surrounding bubbles will be impacted to burst and mutually collide to change the atomized particles into ultrafine ones, therefore pneumatic atomization is achieved.

-22 [0070] 1-5 L-shaped needle electrodes I 83 can be installed on the electrode slot of the electrode chuck 51 according to the condition. The radius of the discharge tip of each L shaped needle electrode 1 83 is about 0.3-1.5 mm. The conducting wire interface 84 at the tail end of each L-shaped needle electrode 1 83 is connected with the electrode high voltage conducting wire 10, and the electrode high voltage conducting wire 10 is led out of the electromagnetic device through the conducting wire through groove 70 and is connected with the cathode output end of the adjustable high voltage DC power supply 9. Since the corona inception voltage of negative corona discharge is low while the breakdown voltage is high during corona discharge, the L-shaped needle electrode 1 83 is connected with the cathode of the power supply, and the anode output end of the adjustable high voltage DC power supply 9 is connected with the workpiece electrifying device 11 through the electrode high voltage conducting wire 10 and is grounded. [0071] Since the area of the workpiece 4 is large, the L-shaped needle electrode 1 83 and the workpiece 4 form a needle-plate structure. Therefore, a very non-uniform electric field (corona discharge conditions) is formed. Multi-pole needle discharge is adopted in the electrostatic corona spray, since the relative distance of the tips of the pole needles is larger, mutual corona inception voltage is not affected, but the concentration of electrons and ions between the electrode and the workpiece will be greatly increased by the simultaneous corona discharge of the pole needles, such that the charging efficiency of the spray droplets can be increased. Moreover, after the electric fields of the pole needles are compounded, the electric field force applied to the spray droplets is enhanced, which is more conducive to directional movement of the spray droplets. Because the adjustable voltage range of the adjustable high voltage DC power supply 9 is 1-150 KV, and pd is larger than 26.66kpa - cm (p refers to the external atmospheric pressure of the working conditions and d refers to the distance between the needle plate electrodes) in the working conditions, we make an analysis by using the stream theory instead of the Townsend theory. [0072] When a higher voltage lower than the breakdown voltage is applied to both ends of the L-shaped needle electrode I 83, if the electric field (local electric field) near the electrode surface is very strong, then the gaseous medium near the electrode is locally broken down to generate the corona discharge phenomenon. The gas pressure of the gas herein is about 105 Pa. When the radius of curvature of the electrode is very small, because of its particularly high field intensity nearby, the electrode is prone to generate corona discharge. [0073] In the very non-uniform electric field, before an air gap is completely broken down, -23 corona discharge occurs near the electrode, resulting in dark blue halation. This particular halation is generated in a discharge process in an ionization area on the surface of the electrode. Molecules in the ionization area generate excitation and ionization under the action of external ionization factors (e.g., light source) and an electric field to form a large amount of electron avalanche. At this time, a reversible process of excitation and ionization, namely, compounding is generated as well. In the compounding process, light radiation will be generated to form the halation, and this is corona. The current intensity of corona discharge is determined by external voltage, electrode shape, electrode spacing, gas properties and density and the like. [0074] When the potential difference between the two electrodes is gradually increased from zero, silent non-self-sustaining discharge occurs firstly, at this time, the current is very weak, and when the voltage is increased to a certain numerical value Vs, the corona discharge occurs. The voltage Vs is called a corona inception voltage or the threshold voltage of the corona discharge, and the numerical value thereof is characterized by the sudden increase (from about 10-14 to 10-6 A) of the current between the electrodes and the occurrence of hazy glow at the electrode with a smaller radius of curvature. [0075] The calculation formula of the threshold field intensity is: (E,), = Em [1+ K / (&r)" (1) in the formula, (Er), refers to the threshold field, Eo = 31 00kV/m (this value is equivalent to the spark field intensity in a uniform field with discharge gap of 1 cm in the air at a standard state), m refers to a coefficient describing the surface state of a conductor (0.6 <m <1), 5 refers to the relative density of air: 6= 2. 94 *10-3P / (273 + T) (Pa is the unit of P, when P is 101 325Pa and T is 25 DEG C, 5 is 1), K = 3. 08*10- 2 m 1

/

2 , and r refers to the radius of the electrode end. For electrodes with different curvatures, for example, the needle-plate electrode, the calculation formula is: (E), EK 1 2 (r / 2) (2) the numerical values of Eo and K herein are the same as those in formula (1), and m and 5 are 1. The above-mentioned formula is applicable to cathodes or anodes with small radiuses of curvature. Calculation of threshold voltage: - 24 [0076] (3) Parabolic needle-plane gap, the radius of the needle tip is r, the gap distance is d, V is the actual voltage applied to the needle electrode, then the electric field intensity at a distance x away from the needle tip along the axial center of the gap is: Ex =2V (r + 2x)ln[(r + 2d)/r] (3) the threshold voltage is: V, = (E,), (r / 2)ln [(r + 2d) /r] according to the working conditions of the grinding machine, when the tip radius of the L shaped needle electrode 1 83 is 0.5mm, the electrode spacing is 20-30cm (when the distance is larger than 30cm, the electric field force effect begins to decline). The range of corona inception voltage is 15.3-16.2KV, which is calculated according to the formula (4). [0077] During grinding processing, when the angle of the nozzle is kept at 30 degrees and the distance between the nozzle and the workpiece is kept at 20 cm, the minimum distance between the nozzle and the workpiece is 20sin30 =10cm (the vertical distance between the nozzle and the workpiece). When the atmospheric pressure p of the working environment is air of 10 5 pa, it can be obtained by looking up a table that when d is 10 cm, the spark breakdown voltage is 265KV, and when d is 20 cm, the spark breakdown voltage is 510KV. Thus, the spark breakdown voltage is very high. Electrostatic droplet atomization mechanism: [0078] Electrostatic atomization is a phenomenon that electrostatic force overcomes the surface tension of liquid to break the liquid into fine spray droplets. Due to the corona discharge effect, a large amount of charges with the same polarity are applied to the surfaces of the droplets under a skin effect, thus increasing the surface activity of the liquid to generate significant directional arrangement of molecules on the surface layer and reduce the surface tension. Under the condition of an invariable droplet volume, with the increase of the charge quantity, the surface tension will be decreased gradually, the surface instability is increased, and finally a Taylor cone is formed. When the surface tension is not large enough to bind the liquid, the liquid will form fine water silk under the repulsive interaction of the charges with the same polarities on the surface and the surface disturbance of the liquid caused by the external force, the fine water silk is continuously increased and is finally broken into fine spray droplets. At this time, the radius of curvature at the tip of the Taylor cone formed on the droplet surface - 25 is smaller than that at the tip of the electrode, thus a stronger electric field is formed at the tip of the Taylor cone, meanwhile, the mass of the liquid molecules is much larger than that of the air molecules, so the liquid molecules are easier to accumulate near the corona area to form a spatial electric field consistent with the external electric field, and this is very conducive to the ionization of the corona area. Thus, the charging effect of electrostatic atomization corona charging is obviously better than that of the traditional electrostatic corona discharge. [0079] When the relative speed between the droplet and the surrounding gas is quite high, the division of the droplet is controlled by a pneumatic pressure, surface tension and a viscous force. For the liquid with lower viscosity, the breakup of the droplet is mainly determined by the pneumatic pressure and the surface tension. The pneumatic pressure applied to the large droplet isO.5pAV 2 , wherein p, refers to gas density, and AV refers to gas-liquid relative speed. However, the cohesive force generated by the surface tension will hinder the deformation and breakup of the droplet, the cohesive force can be expressed as 40-/D , o refers to the inherent surface tension of the liquid, and D refers to the initial droplet diameter. [0080] When the diameter of the droplet is decreased, the cohesive force is increased, when the cohesive force is balanced with the tensile stress caused by the pneumatic pressure, the droplet remains stable, and if the two cannot counteract each other, the droplet will be deformed or broken. According to the principle that the tensile stress caused by the pneumatic force generated on the droplet is balanced with the cohesive force generated by the surface tension, a non-dimensional number can be obtained: We PAV 2 D ~ we= =8 o~ (5) therefore, when the Weber number is larger than 8, the stress of the droplet is unbalanced, resulting in deformation. In addition, the maximal steady state droplet diameter corresponding to AV can be figured out according to (5): D =80 am

AV

2 P" (6) under the action of the coulomb repulsion of the charged droplet, the surface tension is weakened, and the weakened surface tension value is: 2 q2 3 64rcr 3 (7) wherein, r refers to the radius of the droplet, q refers to the charging capacity of the droplet and - 26 e refers to a dielectric constant of surrounding air. It can be obviously seen from the formula that when the charge q is increased, the surface tension is reduced, thus surface charging of the droplet is beneficial for atomization. [0081] At this time, the We of the charged droplet can be expressed as: pWAV 2 D 1282T 2

ER

4 pgAV 2 We q 2 64xT2ER3O_ -9q2 642Er (8) it can be seen from formula (8) that, the breakup of the charged droplet in high speed gas flow is closely related to the gas-liquid relative speed, the gas-liquid physical property parameters and the charging field. In addition, if the droplet reaches a steady state in the gas flow, after electrostatic electricity is charged, the We number is increased, the surface tension of the liquid is reduced and is not enough to resist the pneumatic pressure, the droplet will be further deformed and broken, so under the same gas-liquid parameter, the particle size of the spray droplet is smaller after being charged with the electrostatic electricity. As a result, the purpose of thinning the spray droplet particles is achieved, and meanwhile, the same charges on the surfaces of the droplets can ensure more uniform distribution of the droplets. Droplet charging mechanism: [0082] When negative corona discharge occurs on the tip of the L-shaped needle electrode 1 83, a large number of ions will be generated in the corona area, the positive ions will move towards the cathode of the electrode and are electrically neutralized, while the negative ions and electrons will move towards the anode and enter a drift area to collide with the droplet in the drift area so as to be attached to the droplet, such that the droplet becomes a charge carrier and carries charges with the same polarity as the electrode. [0083] The calculation formula of the charging capacity of spray droplet corona charging is as follows: q= f 1+2 k-1 4TEEr 2 1 k+ 2_ (9) - 27 NeKi -- t f =4co in the formula (9), NeKit+1 4so (10) q refers to the charging capacity of the spray droplet, C; k refers to a dielectric constant of the spray droplet; 60 refers to a dielectric constant of the air and is about 8.85 *10-42 c 2 /nm 2 E refers to the electric field intensity formed by corona discharge, V/M; r refers to the radius of the spray droplet, pm. N refers to charging ion concentration, particle number /m 2 e refers to electron charge, 1.6*10-19 , C; Ki refers to charging ion migration rate, m 2 /(V. s) t refers to charging residence time, s. [0084] The droplet is sprayed from the nozzle and accelerates to move towards the workpiece under the action of the aerodynamic force and the electric field force, and the speed is about 50 m/s to 70 m/s. The distance from the nozzle to the workpiece is 20-30 cm, and the movement time is within 0.01s. However, the necessary spray droplet charging time is merely 10-7 S to 10-6S, thus oil spray sprayed from the nozzle is fully charged before arriving at the workpiece. [0085] After being charged, the spray droplet sprayed from the nozzle directionally moves under the action of the electric field force to cover the surface of the workpiece to the maximum. In the charging process, since the surface of the nanoparticle is relatively large, the surface polarity is strong, after being charged, the charge-to-mass ratio thereof is larger than that of the spray droplet, thus the nanoparticle tends to arrive at the workpiece earlier to cover the lower layer of the oil film, in this way, the ideal heat exchange capability thereof can be better utilized. An electrostatic embracing effect exists in the electrostatic field, so when moving to the workpiece, the spray droplet and the nanoparticle are easier to enter the depression of the surface with certain roughness of the workpiece, thus expanding the relative coverage area to achieve better lubrication and heat exchange effects. [0086] It can be seen from Fig.3 that the adjustable high voltage DC power supply 9 is composed of the self excited oscillation circuit, the power amplification circuit, the high frequency pulse booster, the voltage doubling rectifying circuit, the DC voltage stabilizing unit - 28 V1, the DC voltage stabilizing unit V2 and the constant current automatic control circuit. The working principle is that the input end is connected to an AC power supply, and the DC voltage stabilizing unit V1 and the DC voltage stabilizing unit V2 provide DC voltage. The DC voltage stabilizing unit V1 is used as the working voltage of the self excited oscillation circuit. The DC voltage stabilizing unit V2 is a main energy source for power conversion, the high frequency pulse booster is rectified by the voltage doubling rectifying circuit to obtain high voltage electrostatic electricity, a base pulse signal is obtained by the self excited oscillation circuit, amplified by the power amplification circuit and boosted by the high frequency pulse booster to finally output a high voltage signal, and DC high voltage is output from the voltage doubling rectifying circuit. [0087] The power supply is characterized by generating a higher electrostatic voltage, and the supply current is small and is typically not more than 500 PA. The constant current automatic control circuit automatically samples the electrostatic working current of the voltage doubling rectifying circuit, in the case of constant current, when the workload is normally increased, the working current will not be increased. When an external load exceeds the allowable current, the self excited oscillation circuit stops oscillating and the high voltage is interrupted, this property is safe and reliable to the operator, once approaching or touching the high voltage end, the caused shock current is very weak, and meanwhile, high voltage output is interrupted, so there is no life risk. [0088] In order to further increase the controllability of minimal quantity lubrication, the electric field intensity is generally increased to increase the charging efficiency of electrostatic spraying minimal quantity lubrication, to increase the charging capacity of the particles. But due to the limit of the breakdown voltage, the electric field intensity cannot be unlimitedly increased, and larger electric energy consumption will be caused by increasing the electric field intensity. In the case of invariable voltage, the discharge current is increased by adding magnetic fields at the two sides of the electrode in the present invention, so as to increase the charging efficiency of the particles. Under the external magnetic fields, the increase amount of the discharge current is mainly determined by the average magnetic flux density in the corona area and is irrespective to the magnetic field intensity of the non-corona area, so the magnetic fields should be arranged at the two sides of the corona area. In the electric field of traditional corona discharge, free electrons move along the electric field line direction under the action of the coulomb force, and under the condition of magnetically enhanced corona discharge, the free electrons form Larmor movement under the coactions of the coulomb force and the Lorenz force. The movement locus of the free electrons is changed into a complicated helical - 29 line from the original straight line, the rotation center of the helical line is vertical to an electric line of force and a magnetic line of force, since the free electrons will generate elastic and non elastic collision with the air molecules and the minimal quantity lubrication grinding fluid particles during the movement, the movement locus of the free electrons becomes particularly complicated, but regardless of the shape of the specific movement locus of the free electrons, compared with the traditional corona discharge, the movement locus of the free electrons is prolonged in corona discharge under the action of the magnetic field. That is, since the free electrons make the Larmor movement, the collision probability of the free electrons with the air molecules and the minimal quantity lubrication grinding fluid particles is greatly increased, thus resulting in more intense electron avalanche, enhancing air ionization and ensuring more sufficient particle charging. [0089] In the corona area, the ionization degree is determined by two factors, one is the average energy of the free electrons, the other is the collision time of the free electrons, if the energy of the free electrons is smaller than the minimum ionization energy, no matter how many times the free electrons collide, under the condition of invariable magnetic field intensity, the gyration radius of the free electrons will be increased by increasing the electric field intensity, thus reducing the collision of the free electrons and inducing no ionization, if the energy of the free electrons is very high, but the collision time is quite less, the ionization will be very weak. Therefore, it can be known that the relative increase of the collision time of the free electrons with the air molecules in the corona area is opposite to the change direction of the average free energy of the free electrons, thus the relative increase of the discharge current has a maximum value. Due to the application of the magnetic field, the corona inception voltage of negative corona discharge is reduced, the reason lies in that during negative corona discharge, the free electrons quickly fly out of the corona area under the action of the coulomb force, the mass difference of the free electrons and the positive ions is very large, thus when the free electrons fly out of the corona area, the positive ions scarcely move and are accumulated near the corona area. When the magnetic field acts on the surrounding of the corona area, the collision probability of the free electrons and the air molecules is increased, so more positive ions are accumulated near the corona area. The electric field direction of the space charges of the positive ions near the corona area is consistent with the direction of an external electric field, thus enhancing the electric field in the corona area, ensuring more intense ionization and reducing the corona inception voltage. [0090] In summary, the electrostatic atomization minimal quantity lubrication with an external magnetic field is a combination of atomization corona discharge and magnetic field -30 corona discharge, which can further increase the discharge current, enhance the charging effect and reduce the corona inception voltage. [0091] Although the invention has been described with reference to specific examples it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.