JP2015193074A - High frequency vibration incorporated plasma discharge grinding device and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high frequency vibration incorporated plasma discharge grinding device that is superior in surface roughness accuracy for a hard-to-cut material, enables grinding work suitable for shape machining, and improves grinding work accuracy and its efficiency while reforming a machining surface.SOLUTION: A plasma discharge grinding device includes a grinding wheel formed by bonding abrasive particles with electrically-conductive bonding materials, a grindstone spindle and vibration means for making high frequency vibration thereof, and a high frequency pulse power supply for generating plasma. An interval between a workpiece and a rotational grinding wheel is determined by a projection height of the abrasive particles, and the grinding wheel is made to have high frequency vibration to a workpiece surface in an axial direction. Thereby, microbubbles by the cavitation are generated in the water between electrodes where the workpiece comes into contact with the abrasive particles of the grinding wheel, and the relatively large air bubbles generated by the electrolysis of the water are transformed into the microbubbles. A high frequency pulse current is applied between the electrodes to generate plasma, and the workpiece is subjected to etching to generate a reforming layer improved in machinability, and thereby the abrasive particles of the grinding wheel grind.

Description

  The present invention relates to a grinding device that propagates high-frequency vibrations to a grinding wheel and grinds the workpiece, and in particular, the high-frequency vibration, plasma, and grinding are suitably used to improve the processing surface of the workpiece. To grind difficult-to-cut materials efficiently and with high accuracy, or to create functional interfaces by modifying the work surface of the workpiece according to applications such as low friction and improved wear resistance. The present invention relates to a high frequency vibration assisted plasma discharge grinding apparatus and a method thereof.

2. Description of the Related Art Conventionally, there is an electrolytic grinding apparatus that applies electrolytic voltage between a grinding wheel and a surface of a workpiece via an electrolytic solution to electrolytically grind the surface of the workpiece (see Patent Document 1).
This electrolytic grinding apparatus applies electrolytic voltage between a grinding wheel and a workpiece via an electrolytic solution to perform electrolytic grinding. The grinding (kinetic energy of abrasive grains) and the electrolytic (electric energy to the workpiece) It is a processing technology that combines the two elements of >>.

However, in this electrolytic grinding apparatus, in order to stabilize the electrolytic reaction, it is necessary to set the distance between the electrodes, that is, the distance between the conductive binder, which is the base material of the grindstone, and the work piece to 0.02 mm or more. Is 0.04 mm or more, and with this particle size, the grinding accuracy until the workpiece is mirror-finished cannot be obtained.
Therefore, by reducing the size of the abrasive grains and grinding them by propagating high-frequency vibrations to the grindstone so that the electrolytic reaction is induced or promoted even when the distance between the electrodes is less than 0.02 mm, A high-frequency vibration-assisted electrolytic grinding apparatus that induces or promotes an electrolytic reaction by propagating high-frequency vibration to a grindstone even when the distance between electrodes is less than 0.02 mm, where stable electrolytic reaction did not occur in the apparatus and method. Devised. As a result, the machining accuracy is improved and the workpiece can be mirror-finished (see Patent Document 2).

JP-A-3-251317 JP 2014-14915 A

The above-described electrolytic grinding apparatus using high-frequency vibration has enabled unprecedented high-precision grinding. However, in conventional grinding of small diameter inner peripheral surfaces, even if it is possible to satisfy the surface roughness accuracy, a tool due to a large machining resistance in the case of difficult-to-cut materials such as titanium alloys. Due to deformation, it is not possible to perform shape processing such as eliminating core runout on the inner peripheral surface of the material, and it is difficult to control the processing direction due to the isotropic nature of electrolytic action in electrolytic processing. Since the ability to correct the shape error of the workpiece is low, it is also unsuitable to perform shape processing such as eliminating core runout.
On the other hand, in the electric discharge machining, although the direction of material removal can be controlled more accurately than in the electrolytic machining, there is a problem that a deteriorated layer is generated due to heat as the machining surface becomes rough.

  The present invention has been made in view of the circumstances described above, and its purpose is to improve the machining accuracy and increase the efficiency of the small-diameter inner peripheral surface of a difficult-to-cut material, and to perform grinding processing. The object is to provide a high-frequency vibration-assisted plasma discharge grinding apparatus and method capable of creating a functional interface by modifying the surface according to the application.

As a result of diligent research in view of the above-mentioned problems, the inventor has performed grinding that is excellent in surface roughness accuracy and suitable for shape processing even for small-diameter inner peripheral surfaces of difficult-to-cut materials that have been difficult to grind until now The inventors have devised a high-frequency vibration-assisted plasma discharge grinding apparatus and method capable of machining.
A feature of the present invention is that when a voltage applied electrode, that is, a grinding wheel and a workpiece are brought close to each other, even pure water with low conductivity is electrolyzed to generate hydrogen and oxygen bubbles between the electrodes. This bubble is transformed into microbubbles by applying high-frequency vibration in the axial direction, and a high-frequency pulse current is passed through the electrodes to create a uniform plasma phase between the electrodes (because plasma is easily generated in the gas phase) ), The microbubbles are crushed and active oxygen such as OH radicals are generated, which uniformly improves the processed surface and facilitates grinding.
Functions of the high-frequency vibration include changing bubbles generated between the electrodes into microbubbles, quickly discharging processing waste, and cleaning the electrode surface to keep the processing efficiency constant.
That is, the high-frequency vibration-assisted plasma discharge grinding apparatus of the present invention comprises a grinding wheel formed by bonding and solidifying non-conductive abrasive grains with a conductive binder, a grinding wheel spindle that rotationally drives the grinding wheel, and the grinding wheel spindle as a shaft. And a high-frequency pulse power source that outputs a high-frequency pulse current that generates plasma via a machining fluid between the grinding wheel and the workpiece, 10 μm in a state where the workpiece and the abrasive grains of the grinding wheel are in contact with each other by causing the grinding wheel to be high-frequency vibrated in the axial direction along the surface of the workpiece by setting the distance between the grinding wheel and the rotating grinding wheel to the minimum size. The bubbles generated by electrolysis of water between the following narrow electrodes are changed to minute microbubbles, and the workpiece and the abrasive grains of the grinding wheel are in contact with each other A plasma is generated by applying a high-frequency pulse current from the high-frequency pulse power source between the electrodes, and the plasma etches the workpiece, thereby improving the machinability on the local processing surface. A layer is generated, and the modified layer is ground by the abrasive grains of the grinding wheel.
With such a configuration, even in difficult-to-cut materials such as titanium alloys, grinding can be performed only locally between the tool and the work material, so that the shape accuracy after processing can be improved.

Further, the grinding wheel is characterized in that the machining fluid is supplied to the grinding zone through the machining fluid at the center of the shaft.
Thereby, even if it is the inner peripheral surface of the to-be-processed object of a small diameter and a blind hole, a processing liquid can be supplied suitably to a grinding region.

  The high-frequency vibration-assisted plasma discharge grinding method of the present invention includes a grinding wheel formed by bonding and solidifying non-conductive abrasive grains with a conductive binder, a grinding wheel spindle that rotationally drives the grinding wheel, and the grinding wheel spindle. High-frequency vibration comprising vibration means for high-frequency vibration at 20 kHz or more in the axial direction, and a high-frequency pulse power source that outputs a high-frequency pulse current that generates plasma through the machining fluid between the grinding wheel and the workpiece. In an assisting plasma discharge grinding apparatus, the workpiece and the grinding wheel are vibrated at a high frequency in the axial direction along the workpiece surface by setting the distance between the workpiece and the rotating grinding wheel to a minimum size of the abrasive grains. While changing the bubbles generated by the electrolysis of water between the narrow electrodes of 10 μm or less in the state of contact with the abrasive grains, to micro-bubbles, A plasma is generated by applying a high-frequency pulse current from the high-frequency pulse power source between the electrodes in a state where the workpiece and the abrasive grains of the grinding wheel are in contact, and the plasma etches the workpiece. A modified layer with improved machinability is generated on the local processed surface, and the modified layer is ground by the abrasive grains of the grinding wheel.

It is explanatory drawing which shows the high frequency vibration assistance plasma discharge grinding apparatus of this invention. It is principal part explanatory drawing which shows the high frequency vibration assistance plasma discharge grinding apparatus of this invention. It is explanatory drawing which shows the process between the grindstone and the electrode of a to-be-processed object in the high frequency vibration assistance plasma discharge grinding apparatus of this invention. It is explanatory drawing which shows the process between the grindstone and the electrode of a to-be-processed object in the high frequency vibration assistance plasma discharge grinding apparatus of this invention. It is explanatory drawing which shows the process between the grindstone and the electrode of a to-be-processed object in the high frequency vibration assistance plasma discharge grinding apparatus of this invention.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for implementing a high-frequency vibration-assisted plasma discharge grinding apparatus according to the present invention will be described in detail with reference to the accompanying drawings. 1 to 5 are diagrams illustrating embodiments of the present invention. In these drawings, the same reference numerals denote the same components, and the basic configuration and operation are the same. To do.
<Configuration>
As shown in FIG. 1, a high-frequency vibration-assisted plasma discharge grinding apparatus 1 of the present invention includes a grinding wheel spindle 3 that rotationally drives a grinding wheel 2, and a high-frequency vibration high frequency for applying high-frequency vibration in the axial direction of the grinding wheel spindle 3. Processing that provides a pulse power supply 4, a plasma discharge high-frequency pulse power supply 5 for generating plasma discharge between the grinding wheel 2 and the workpiece, and a grinding fluid and plasma discharge machining fluid 6 in the grinding region. Liquid supply means 7.
The grinding wheel spindle 3 is provided with a fine hole at the center of the shaft together with the grinding wheel 2, and supplies it to the grinding zone through the machining liquid 6 from the machining liquid supply means 7. By using the grinding wheel 2 as a liquid passing type, grinding can be performed while suitably supplying the processing liquid even on the inner peripheral surface of the workpiece having a small diameter and a blind hole. Then, by operating the high-frequency pulse power supply 4 for high-frequency vibration, the grindstone spindle 3 reciprocates (oscillates) in the Z-axis direction with high-frequency vibration in the axial direction, that is, the Z-axis direction in FIG. However, the inner peripheral surface of the workpiece W is ground.
The Y table 8 on which the workpiece W is placed and fixed is movable in the Y axis direction, and the X table 9 on which the Y table 8 is placed is movable in the X axis direction. And the control means (not shown) for controlling the grinding process by the high frequency vibration assistance plasma discharge grinding apparatus 1 including the X table 9, the Y table 8 and each pulse power source is separately provided.

  FIG. 2 is a processing example different from that in FIG. 1, and schematically shows a state where the grinding wheel 2 is grinding the inner peripheral surface Wa of the chucked workpiece W. The grinding wheel 2 is formed by bonding and solidifying non-conductive abrasive grains such as diamond abrasive grains with a conductive binder. In a state where the abrasive grains protruding from the surface of the grinding wheel 2 grind the workpiece W, the protruding height of the abrasive grains from the conductive binder is the distance between the electrodes of the grinding wheel 2 and the workpiece W. In the case of the present embodiment, in order to perform high-precision grinding, it is preferable that the protrusion height of the abrasive grains is less than 20 μm, preferably less than 10 μm.

The high frequency pulse power supply 4 for high frequency vibration vibrates the grinding wheel spindle 3 provided with the grinding wheel 2 in the axial direction at a frequency of 20 kHz or more, preferably 40 kHz or more, and an amplitude of several μm to several tens of μm.
The plasma discharge high-frequency pulse power supply 5 determines the protrusion height of the abrasive grains between the grinding wheel 2 (more precisely, the conductive binder) and the workpiece W as a preset plasma discharge voltage. And a high-frequency pulse current having a pulse width of 1 microsecond or less (sub-microsecond) level is applied.

<Method of free-cutting difficult-to-cut materials>
The high frequency vibration assisted plasma discharge grinding method of the present invention having such a configuration will be described in detail below.
First, FIG. 3 shows a state of a grinding zone before processing, and a conductive binding material obtained by bonding and protruding abrasive grains, that is, an electrode grindstone 10 and a workpiece W, that is, abrasive grains. A machining fluid 6 mainly composed of water is supplied between the protruding height electrodes.

Next, FIG. 4 shows a state in which the electrode grindstone 10 vibrates at a high frequency of 20 kHz or more in the left-right direction of the figure by operating the high-frequency pulse power supply 4 for high-frequency vibration.
In this state, the machining fluid 6 between the workpiece grindstone 9 and the workpiece W supplied from the machining fluid supply means 7 through the grinding wheel spindle 3 and the grinding stone 2 is electrolyzed even if pure water having low conductivity is used. As a result, bubbles of several hundred μm are generated.
The bubbles are broken by high-frequency vibration between narrow electrodes and changed to microbubbles 11 which are uniform microbubbles of several μm or less. Phase) and the air (gas phase) of the microbubbles 11 are uniformly and densely mixed to form a liquid phase / gas phase mixed state. And it becomes easy to generate a plasma phase by flowing a high frequency pulse current.
Moreover, since the microbubble 11 produces | generates active oxygens, such as OH radical which has high oxidizing power, with the energy at the time of crushing, it exhibits an effect in modification | reformation of a process surface.

In addition to the state of FIG. 4 in which the electrode grindstone 9 vibrates at a high frequency, the plasma discharge high-frequency pulse power source 5 is operated, and as shown in FIG. An environment in which uniform plasma 12 is generated by fine discharge is formed between the electrodes where the electrode grindstone 9 and the workpiece W are in contact with each other.
When a voltage is applied between the electrodes by the plasma discharge high-frequency pulse power supply 5, bubbles of non-uniform size are generated between the electrodes due to the electrolysis of water, which is also broken by the high-frequency vibration between the narrow electrodes. To microbubbles 11.
The voltage applied by the plasma discharge high-frequency pulse power source 5 between the electrode grindstone 9 and the workpiece W is not short-circuited between the electrode grindstone 10 and the workpiece W, and an excessive spark discharge. A high frequency pulse is set so as not to cause arc discharge. Then, in a state where the machining fluid 6 between the electrode grindstone 10 and the workpiece W is atomized by high-frequency vibration and microbubbles 11 are generated by cavitation, the electrode grindstone 10 side is placed between the electrodes, the negative electrode, By applying a high frequency pulse voltage with the workpiece W side as a positive electrode, the uniform plasma 12 shown in FIGS. 2 and 5 is locally generated at a location where the electrode grindstone 10 and the workpiece W are in contact with each other.

This plasma 12 ionizes the water of the machining fluid 6 located there, thereby further generating active oxygen such as OH radicals having a high oxidizing power, and the active oxygen is in contact with the workpiece W with which the grinding wheel contacts. The modified layer 13 with improved machinability is generated by locally etching the surface of the film. Then, the modified layer 13 can be suitably ground with a grinding wheel at a low processing pressure and without accompanying tool deformation.
Since the generation site of the plasma 12 and the generation site of the microbubbles 11 due to cavitation are local, and the active oxygen such as OH radicals has a short life, the generated modified layer 13 is a workpiece. Since it does not extend over the inner peripheral surface Wa of W and is limited only to the contact portion of the electrode grindstone 10, it does not etch other than the processed surface unlike the electrolytic processing.
And although the processing waste 14 which generate | occur | produces when a grinding wheel grinds and removes the modified layer 13 is scattered finely between electrodes, these are discharged | emitted out of a grinding region by high frequency vibration. Also, the surface of the electrode is always cleaned and kept activated.

The present invention uses a high-frequency vibration and plasma discharge to locally modify a workpiece between electrodes to perform grinding, remove material, remove chips, and clog a grindstone. In addition to the physical effect of preventing the above, active oxygen generated at the time of the generation of plasma or the collapse of bubbles due to cavitation generated by high-frequency vibration is used.
Cavitation generated by high-frequency vibrations concentrates energy during the adiabatic compression process, and forms a high-temperature and high-pressure local field of 5,000 to several tens of thousands of degrees and thousands of atmospheric pressures when the bubbles are crushed. In a high-temperature reaction field caused by cavitation crushing that occurs when high-frequency water or aqueous solution is irradiated, water molecules are decomposed to generate OH radicals and the like. The generated OH radical disappears in a short time, but has a high oxidizing action, and therefore exhibits an action of modifying the surface of the workpiece.

  The high frequency vibration-assisted plasma discharge grinding apparatus and method of the present invention can be used in the processing industry for precisely grinding various materials such as metals.

DESCRIPTION OF SYMBOLS 1 ... High frequency vibration assisted plasma discharge grinding apparatus 2 ... Grinding wheel 3 ... Grinding wheel spindle 4 ... High frequency pulse power source for high frequency vibration 5 ... High frequency pulse power source for plasma discharge 6 ... Working fluid 7 ... Working fluid supply means 8 ... Y table 9 ... X Table 10 ... Electrode grinding wheel 11 ... Micro bubble 12 ... Plasma 13 ... Modified layer 14 ... Processing waste W ... Workpiece

Claims (4)

A grinding wheel formed by bonding and solidifying non-conductive abrasive grains with a conductive binder;
A grinding wheel spindle that rotationally drives the grinding wheel;
Vibration means for vibrating the grinding wheel spindle at a high frequency of 20 kHz or more in the axial direction;
A high-frequency pulse power source that outputs a high-frequency pulse current that generates plasma via a machining fluid between the grinding wheel and the workpiece,
The distance between the workpiece and the rotating grinding wheel is set to the minimum size of the abrasive grains, and the grinding wheel is vibrated in the axial direction along the surface of the workpiece so that the workpiece and the abrasive grains of the grinding wheel come into contact with each other. In the state, the bubbles generated by electrolysis of water between narrow electrodes of 10 μm or less are changed to minute microbubbles,
A plasma is generated by applying a high-frequency pulse current from the high-frequency pulse power source between the electrodes in a state where the workpiece and the abrasive grains of the grinding wheel are in contact, and the plasma etches the workpiece. Generate a modified layer with improved machinability on the local processing surface,
A high-frequency vibration-assisted plasma discharge grinding apparatus, wherein the modified layer grinds the abrasive grains of the grinding wheel.   2. The high frequency vibration assisted plasma discharge grinding apparatus according to claim 1, wherein the grinding wheel supplies the machining fluid to the grinding zone through the machining fluid at the center of the shaft. A grinding wheel formed by bonding and solidifying non-conductive abrasive grains with a conductive binder;
A grinding wheel spindle that rotationally drives the grinding wheel;
Vibration means for high-frequency vibration of the grinding wheel spindle in the axial direction;
A high-frequency vibration-assisted plasma discharge grinding apparatus comprising: a high-frequency pulse power source that outputs a high-frequency pulse current that generates plasma between a grinding wheel and a workpiece via a machining fluid;
The interval between the workpiece and the rotating grinding wheel is set to the minimum size of the abrasive grains, and the grinding wheel is vibrated at a high frequency of 20 kHz or more along the workpiece surface in the axial direction. While changing the bubbles generated by the electrolysis of water between narrow electrodes of 10 μm or less in a state of contact with each other into micro-bubbles,
A plasma is generated by applying a high-frequency pulse current from the high-frequency pulse power source between the electrodes in a state where the workpiece and the abrasive grains of the grinding wheel are in contact, and the plasma etches the workpiece. Generate a modified layer with improved machinability on the local processing surface,
A high frequency vibration assisted plasma discharge grinding method, wherein the modified layer is ground by the abrasive grains of the grinding wheel.   4. The high frequency vibration assisted plasma discharge grinding method according to claim 3, wherein the grinding wheel supplies the machining fluid to the grinding zone through the machining fluid at the center of the shaft.