JP3194624B2 - Grinding method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for grinding highly brittle materials such as glass and ceramics by electrolytic in-process dressing grinding.

[0002]

2. Description of the Related Art Conventionally, a method and an apparatus for grinding a spherical surface of an optical material using an electrolytic in-process dressing grinding method are disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 3-60973. FIG. 5 is a plan view showing a main part of the above-mentioned grinding apparatus in a partial cross section, and shows a cup-shaped conductive member arranged at a swivel angle α with respect to the rotation axis of a work 2 held on a rotatable chuck 1. The abrasive whetstone 4 is provided rotatably. The (+) pole of the DC power supply 6 is electrically connected to the outer periphery of the conductive grindstone 4 via the brush 5. The (−) pole of the DC power supply is connected to the dress electrode 7. The dress electrode 7 is formed in a shape similar to the grinding finish curvature RA of the work 2, and is arranged opposite to the grinding surface 4 a of the conductive grindstone 4 with a small gap L. further,
A nozzle 8 connected to a coolant supply device (not shown) is provided so that a weakly conductive coolant 9 can be supplied to a gap L between the grinding surface 4a of the conductive grindstone 4 and the dress electrode 7.

In the grinding method using the above-described grinding device, the grinding is performed by rotating the conductive grindstone 4 and bringing the grinding surface 4a into contact with the work 2 while rotating the chuck 1 and rotating the work 2. At this time, a voltage is applied to the dress electrode 7 and the brush 5 by the DC power supply 6 while supplying the weakly electric coolant 9 from the nozzle 8 between the grinding surface 4 a and the dress electrode 7.
Grinding of the work 2 is performed while always performing electrolytic dressing on the grinding surface 4a.

Next, the progress of dressing of the grinding surface 4a of the conductive grindstone 4 by electrolytic dressing will be described with reference to FIG. As shown by A, a conductive grindstone 4 having a ground surface 4a formed at the curvature RA of the ground surface of the work 2 is prepared, and a voltage is applied thereto while applying a weakly electric coolant to the ground surface. When the electrolytic dressing 4a is performed, as shown by B, the bond material on the ground surface 4a is electrolytically eluted, and the dressing of the abrasive grains 10 proceeds, and at the same time, the insulating oxide film 11 of the bond material is generated on the ground surface 4a. . When the electrolytic elution of the bond material proceeds and the thickness of the insulating oxide film 11 gradually increases to a certain thickness, the insulating material is in an insulating state, and a current flows between the dress electrode 7 and the conductive grindstone 4. The connection is stopped, the elution of the bond material is stopped, the insulating oxide film 11 is not generated beyond the thickness, and the dressing of the abrasive grains 10 is completed. Since the generated insulating oxide film 11 is lower in hardness than the bond material, the insulating oxide film disappears faster due to the grinding resistance at the time of the grinding process. At the same time, it is removed and thinned. Then, by removing the insulating oxide film 11 to make it thinner, the conductivity between the dress electrode 7 and the conductive grindstone 4 is restored, and the electrolytic dressing of the ground surface 4a is performed.
As the elution of the bond material progresses, a new insulating oxide film 11 is formed below the remaining insulating oxide film 11 so that the ground surface 4a is generated during the grinding of the workpiece. Since the hardness of the insulating oxide film is lower than that of the bonding material, the holding power of the abrasive grains is weakened. As shown in FIG. Is maintained. As described above, the generation and removal of the insulating oxide film 11 having a lower hardness than the bond material and being quickly eliminated by the grinding resistance are repeated, and the bond material on the ground surface 4a is formed by the formation of the insulating oxide film 11 and the electrolytic elution. Will be removed by Therefore, the abrasive grains 10 worn by the grinding process are removed together with the insulating oxide film 11 that has been eliminated more quickly due to the grinding resistance. This allows
The grinding surface 4a is sharpened and can always maintain a processable state.

[0005]

However, in the above-mentioned conventional grinding method and apparatus, current is always applied between the conductive grinding wheel 4 and the dress electrode 7 to apply a voltage, and the eluted bonding material is removed. When the thickness reaches a certain value due to the formation of the insulating oxide film 11, the electrolytic elution of the bond material is stopped. However, the following problem has occurred. That is, in the electrolytic in-process dressing grinding in which a voltage is constantly applied, in order to sufficiently exhibit the grinding ability of the conductive grindstone 4 to be used and to obtain the maximum grinding ratio, the abrasive grains 10 have to be crushed due to abrasion. Immediately before starting, it is essential to set the processing conditions so that the abrasive grains that are likely to be crushed by the removal of the insulating oxide film 11 fall off. In order to obtain such processing conditions, the relationship between the abrasion rate of the abrasive grains 10 and the removal rate of the insulating oxide film (the rate at which the removal occurs due to grinding resistance) is important. However, according to the conventional electrolytic in-process dressing grinding method, for example, when grinding is performed with low-mesh abrasive grains (coarse abrasive grains), the grinding wheel 4 is usually cut into the work 2 at a high speed. The removal rate of the insulating oxide film 11, which has become larger and has a lower hardness than the bond material, increases. When the removal rate of the insulating oxide film 11 is high (large), the speed at which the abrasive grains 10 in the insulating oxide film 11 on the grinding surface 4a side fall off with the elution of the bonding material also increases,
As a result, the abrasive grains 10 that can still be used, although the wear of the abrasive grains 10 by grinding is negligible.
However, even the abrasive grains 10 fall off from the grinding surface 4a,
As a problem before considering the relationship between the abrasion speed and the speed at which the insulating oxide film disappears, it has been difficult to use the grinding wheel 4 effectively. Further, when the grinding of the work 2 is continued, since the processing resistance on the inner and outer circumferences of the cup-shaped conductive grindstone 4 in contact with the work 2 is large, the hardness of the insulating oxide film 11 having a low hardness in this portion is reduced. Removal speed increases. Furthermore, since the spherical surface generating processing is generally performed at a high speed, the contact between the ground surface 4a and the work 2 during the grinding processing makes it easier to remove the insulating oxide film 11 having a low hardness. For this reason, the elution of the bonding material proceeds more than necessary, and the shape of the conductive grindstone 4 is quickly deformed, so that the shape accuracy of the ground surface of the workpiece 2 cannot be maintained.

The present invention has been made in view of the above-mentioned problems in the prior art, and has been developed in the field of spherical processing of an optical element or the like by an electrolytic in-process dressing grinding method while maintaining the shape of a conductive grindstone with a small amount of precision. It is an object of the present invention to provide a grinding method and apparatus capable of stably and continuously processing an optical element or the like with good stability.

[0007]

In order to achieve the above object, a grinding method according to the present invention comprises mounting a conductive grindstone on a grinding device and then rotating the work held by a work holder while rotating the conductive grindstone. The grinding surface is brought into contact with the workpiece by rotating the grinding wheel, and a weak electric coolant is supplied between the grinding surface and the dress electrode from the nozzle, and a (-) voltage is applied to the dress electrode from the power supply device to the conductive grindstone. +) In a grinding method in which a voltage is applied to grind a workpiece while electrolytically dressing the grinding surface of the grindstone, the grinding surface of the conductive grindstone mounted on the grinding device is subjected to electrolytic dressing to perform grinding of the grinding surface. The bond material is electrolytically eluted, and the dressing of the abrasive grains is advanced, and an insulating oxide film of the bond material is formed on the ground surface to hold the abrasive grains with the oxide film. Separate electrolysis Grinding the work with the grindstone in a state where the dressing is not performed, continuing the grinding with the abrasive grains protruding on the grinding surface even after the insulating oxide film has disappeared, and when the abrasive grains have progressed to abrasion, During the grinding process, electrolytic dressing is performed to advance the dressing of the abrasive grains, and at the same time, an insulating oxide film is formed to hold the abrasive grains with the oxide film. Grinding the work with the grindstone in a state where the dressing is not performed, grinding with the abrasive grains protruding from the grinding surface even after the insulating oxide film has disappeared, and electrolytically dressing the grindstone during the grinding of the work. And the state in which electrolytic dressing is not performed is alternately performed. The grinding apparatus according to the present invention includes a rotatable work holder that holds a work, a conductive grindstone that rotates and contacts the surface of the work held by the work holder, and a grinding surface of the conductive grindstone. A dress electrode arranged to maintain a constant distance between the electrodes, a power supply device for applying a (-) voltage to the electrode and applying a (+) voltage to the grindstone, and a weakly electric coolant between the electrode and the grindstone. A nozzle for supplying, and a grinding device having the grinding wheel and the electrode for electrolytic dressing such that the grinding surface of the conductive grinding stone is in a state where abrasive grains are sharpened and held by an insulating oxide film of a bonding material. And a power supply switching means for cutting off the power supply between the grindstone and the electrode in order to prevent the electrolytic dressing from being performed during the work grinding after the electrolytic dressing. .

[0008]

According to the grinding method described with reference to the above-described conceptual diagram, the conductive grinding wheel 4 formed in the state shown in FIG.
Is supplied to the ground surface 4a of the grinding wheel 4 from the power supply device 6 for the initial dressing step, thereby performing electrolytic dressing of the ground surface 4a, and electrolytically eluting the bond material. As shown, generation of an insulating oxide film and dressing of the abrasive grains 10 are performed. Next, the power supply from the power supply device is turned off, and the workpiece is processed by a grinding method using a normal grindstone in a state where electrolytic dressing is not performed. As a result, the elution of the bond material due to the electrolytic current is suppressed, and as shown in C, the abrasion of the abrasive grains 10 held by the bond material due to the grinding resistance at the time of grinding the work by the grindstone 4 and the formation of the insulating oxide film 11. Only removal is performed. Accordingly, the useable abrasive grains 10 are prevented from falling off due to the elution of the bond material as in the related art. Then, when the wear of the abrasive grains 10 has progressed, a predetermined amount of electrolytic in-process dressing grinding is performed by energizing from a power supply device, that is, the abrasive grains worn by eluting the bond material on the grinding surface 4a are removed. By making the abrasive grains 10 protrude as shown in D to sharpen the grinding surface 4a as shown in D, the shape of the conductive grinding stone 4 is prevented from being deformed, and stable grinding can be continued. . And in the grinding device of the present invention, the switching means 15 for energization is provided.
By the above operation, the grinding surface of the grindstone can be made into a state in which the abrasive grains are sharpened and held by the insulating oxide film, and a state in which the abrasive grains are held by the bonding material. The grinding wheel can be used effectively because the grinding process can be performed until the glass is blinded. In addition, the elution of the bonding material is reduced, so that the shape of the grinding wheel is slowed down. Also, by retracting the dress electrode 7 from the grinding surface 4a, the grinding surface of the grindstone is changed to a state in which the abrasive grains are sharpened to hold the insulating oxide film and a state in which the abrasive grains are held by the bonding material. As described above, since the grinding process can be performed until the usable abrasive grains on the grinding surface 4a cause blindness as described above, the grinding wheel can be used effectively, and the elution of the bonding material is reduced, so that the grinding wheel can be used. Deformation is also slow.

[0009]

Embodiment 1 FIG. 3 is a plan view showing a grinding apparatus for carrying out a grinding method according to the present invention, with a part cut away. The work 2 is held by the chuck 1 and is rotated by a driving device (not shown). A conductive grindstone 4 provided so as to be able to abut on the work surface 2a of the work 2
Is formed in a cup shape having a swivel angle α with respect to the rotation axis of the work 2, and is driven to rotate about the axis m by a driving device (not shown). Grinding surface 4a of the conductive grinding wheel 4 is formed in the shape of the grinding finishing curvature R _A of the same curvature R _A of the workpiece 2, the grinding portion 4b is
Abrasive grains such as diamond powder (about # 400) and Cu, S
It is formed of a sintered alloy that is specially blended with a metal powder such as n or Fe and heat-treated.

The conductive grindstone 4 is electrically connected to the (+) pole of the power supply 6 via a brush 5 at the outer periphery. (+) A power supply 6 is provided between the pole and the brush 5.
There is provided a changeover switch 20 for turning on and off the supply of power from the power supply. On the other hand, the (−) pole of the power supply 6 is connected to the dress electrode 7. The dress electrode 7
The workpiece 2 is formed in a shape approximate to the grinding finish curvature _RA ,
The conductive grindstone 4 is disposed to face the grinding surface 4 a with a small gap L. Further, a nozzle 8 connected to a coolant supply device (not shown) is provided, so that the weakly electric coolant 9 can be supplied to the gap L between the grinding surface 4a and the dress electrode 7.

Next, an embodiment of the grinding method of the present invention using the apparatus having the above configuration will be described. First, after attaching the conductive grindstone (the grinding surface is in the state of FIG. 2A) 4 to the grinding device,
The conductive grindstone 4 is rotated by a driving device (not shown), and while the weakly conductive coolant 9 is supplied from the nozzle 8, a voltage is applied to the conductive grindstone 4 from the power supply 6 via the dress electrode 7 and the brush 5 to perform initial electrolysis. Dressing (initial dressing step) is performed. Thereby, the grinding surface 4 of the conductive grindstone 4
a is subjected to electrolytic dressing, and the abrasive grains are projected (the abrasive grains are sharpened) so that the spherical surface can be formed (FIG. 2).
B state).

When the initial dressing is completed, the changeover switch 20 is turned off, and the supply of power from the power supply device 6 to the conductive grindstone 4 is stopped. While the conductive whetstone 4 and the work 2 are being rotated while being in contact with the surface 2a, the spherical work of the work 2 is performed. When the conductive grinding stone 4 having # 400 abrasive grains is used, in this ordinary grinding process,
In the grinding process of creating a spherical surface performed by rotating the grindstone 4 and the work 2 without supplying electricity to the conductive grindstone 4, continuous processing of about several hundred works 2 can be stably performed. In such ordinary grinding, the friction of the abrasive grains and the removal of the insulating oxide film of the bond material progress. During this progress, the grinding surface of the grindstone 4 is in the state of FIG.
The abrasive grains 10 are held by a high-hardness bonding material.

In this grinding step, the changeover switch 20 is turned on immediately before the spherical surface forming of a predetermined number of the workpieces 2 is completed, or immediately before the abrasive grains are blinded due to wear, and the brush 5 and the power supply device are turned on. 6 to restart the power supply to the conductive grindstone 4 and perform electrolytic in-process dressing grinding (that is, while processing the work 2, electrolytic grinding without removing the grindstone 4 from the grinding device, Grinding the work 2) is performed on several works 2. Then, in this electrolytic in-process dressing grinding step, the bonding material is electrolytically eluted by the electrolytic dressing, and the dressing state of the abrasive grains on the grinding surface 4a of the conductive grindstone 4 is restored (to the state shown in FIG. 2D). Thereafter, grinding of a large number of works 2 is performed while alternately performing normal grinding and electrolytic in-process dressing grinding.

In the present embodiment, after the initial dressing step, the cycle of the normal grinding step → the electrolytic in-process dressing grinding step → the normal grinding step → the electrolytic in-process dressing grinding step is repeated, and the bonding material forming the conductive grindstone 4 is formed. Since stable processing can be continued while preventing unnecessary elution, the shape of the conductive grindstone 4 can be prevented, and the shape accuracy of each of the ground surfaces of the plurality of works 2 can be maintained with high accuracy. Further, before the abrasive grains are destroyed by wear, the ability of the abrasive grains can be fully utilized to switch from normal grinding to electrolytic in-process dressing grinding. Prevent unnecessary elution,
Since a fall of the still usable abrasive grains can be prevented, a high grinding ratio can be obtained.

[0015]

Second Embodiment FIG. 4 is a plan view showing a second embodiment of a grinding apparatus for carrying out a grinding method according to the present invention, partially cut away. The grinding device of the present embodiment connects the dress electrode 21 formed in the same manner as in the first embodiment to the air cylinder 22,
Arrangement and grinding surface 4 of conductive grindstone 4 facing grinding surface 4a
Able to move back and forth so as to be able to evacuate from a (direction of arrow Y in the figure)
It is provided in. That is, the air cylinder 22 can retract the dress electrode 21 during the grinding process, and can arrange the dress electrode 21 to face the grinding surface 4a during the non-grinding process. The other configuration is the same as that of the first embodiment except that the configuration is not provided with the changeover switch 20.

In this embodiment, by increasing the distance between the dress electrode 21 and the grinding surface 4a of the conductive grindstone 4, no current flows between the grinding surface 4a and the dress electrode 21, and the grinding surface 4a No more dressing. That is, by driving the air cylinder 22 to move the dress electrode 21, the same state as the ON / OFF of the voltage application is performed.

Next, an embodiment of a grinding method using the grinding apparatus having the above configuration will be described. In the embodiment, a work 2 having a size approximately equal to the curvature of the conductive grindstone 4 is used.
Was ground. First, before the work 2 is mounted on the grinding device, the conductive grindstone 4 is mounted on the grinding device.
To rotate. The dress electrode 2 is formed by the air cylinder 22.
1 is brought closer to the grinding surface 4a, a weakly electric coolant 9 is supplied between the dress electrode 21 and the grinding surface 4a, and the conductive grindstone 4 is electrolytically dressed (initial dressing step). When the initial dressing for the ground surface 4a is completed, the dress electrode 21 is retracted by the air cylinder 22. As a result, the dress electrode 21 is ground
As a result, the current supply between the dress electrode 21 and the conductive grindstone 4 is stopped, and the electrolytic dressing of the grinding surface 4a is not performed.

After the retreat of the dress electrode 21 is completed, the work 2 is mounted on the work holder 1 of the grinding device, and the conductive grindstone 4 is brought into contact with the work 2 to perform normal grinding. Thereafter, a plurality of workpieces 2 mounted on the work holder 1 of the grinding apparatus are sequentially subjected to grinding processing, and after finishing grinding processing of a predetermined number of spherical surfaces, or immediately before the abrasive grains are worn out due to abrasion. Then, the normal grinding is finished. After finishing the normal grinding, the work 2 is removed from the work holder 1 of the grinding device, the dress electrode 21 is advanced by the air cylinder 22, and is brought close to the grinding surface 4a of the conductive grindstone 4, and the same as the above-mentioned initial dressing, Electrolytic dressing of the grinding surface 4a of the conductive grindstone 4 is performed. Thereafter, the above-described electrolytic in-process dressing grinding and normal grinding are repeated to grind a large number of works 2.

In the present embodiment, after the initial dressing, the normal grinding and the electrolytic in-process dressing grinding are repeated to stably prevent the abrasive grains and the bond material constituting the conductive grinding stone 4 from flowing out unnecessarily. Since the processing can be maintained, the shape accuracy of the ground surface of the workpiece 2 can be maintained with high accuracy.

In the case of grinding the work 2 having a curvature almost equal to the size of the conductive grindstone 4 as in the present embodiment, or when the curvature of the work 2 for forming a spherical surface is very small, or when forming a spherical surface, For example, when the curvature of the work 2 to be formed is very large, it is impossible to arrange the dress electrode 21 close to the grinding surface 4a of the conductive grindstone 4 in advance during the processing of the work 2 as in the first embodiment. However, in such a case, the conductive grindstone 4 cannot be electrolytically dressed while the work 2 is being processed.
However, in the present embodiment, when the curvature of the work for generating a spherical surface is very small, or when the shape of the work 2 is large compared to the conductive grindstone 4, the air cylinder 22 is moved after the initial electrolytic dressing is completed. By driving and retracting the dress electrode 21 to a position where the dress electrode 21 does not interfere with the work 2, it is possible to perform a stable spherical generation grinding process regardless of the shape of the work 2.

[0021]

As described above, according to the grinding method and apparatus of the present invention, while supplying a weakly electric coolant, an insulating oxide film is formed simultaneously with the dressing of the abrasive grains on the ground surface of the conductive grindstone by electrolytic dressing. Electrolytic in-process dressing grinding and normal grinding are performed such that the state of holding the abrasive grains by the insulating oxide film and the state of holding the abrasive grains by the bond material are present during the grinding of the work by the grindstone. As a result, the abrasive grains can be dressed well, and very little abrasive grains can be used without removing them from the ground surface. Can be reduced. This allows
Since the grinding can be performed continuously while maintaining the shape accuracy and the dressing state of the ground surface of the conductive grindstone, a highly accurate optical element or the like can be stably processed.

[Brief description of the drawings]

FIG. 1 is a conceptual view exemplifying a grinding apparatus for performing a grinding method of the present invention.

FIG. 2 is a cross-sectional view schematically showing a state of electrolytic dressing of a ground surface of a conductive grindstone.

FIG. 3 is a plan view showing Embodiment 1 of a grinding apparatus for performing a grinding method according to the present invention.

FIG. 4 is a plan view showing Embodiment 2 of a grinding apparatus for performing a grinding method according to the present invention.

FIG. 5 is a plan view showing a conventional grinding device.

FIG. 6 is a cross-sectional view schematically showing a state of electrolytic dressing of a ground surface of a conductive grindstone.

[Explanation of symbols]

 Reference Signs List 1 chuck 2 work 4 conductive grindstone 4a grinding surface 6 power supply device 7 21 dress electrode 9 coolant 15 switching means 20 switching switch 22 air cylinder

Claims (2)

(57) [Claims] After a conductive grindstone is mounted on a grinding device, the conductive grindstone is rotated while rotating a work held by a work holder, and a grinding surface is brought into contact with the work. While supplying between the grinding surface and the dress electrode, a (−) voltage is applied to the dress electrode from the power supply device, a (+) voltage is applied to the conductive grindstone, and the work is performed while the grinding surface of the grindstone is electrolytically dressed. In the grinding method of performing the grinding process, the grinding surface of the conductive grindstone mounted on the grinding device is subjected to electrolytic dressing, the bond material on the grinding surface is electrolytically eluted, and the abrasive grains are sharpened and the grinding surface is advanced. The insulating oxide film of the bond material is generated and the abrasive grains are held by the oxide film.Then, the power is turned off from the power supply device or the dress electrode is separated to grind the workpiece with the grindstone in a state where the electrolytic dressing is not performed. , Even after the insulating oxide film disappears, the grinding process is continued with the abrasive particles protruding from the ground surface, and when the abrasive particles have progressed to abrasion, electrolytic dressing is performed during grinding of the workpiece to advance the setting of the abrasive particles. Along with forming an insulating oxide film and holding the abrasive grains with the oxide film, thereafter, turning off the power supply or separating the dress electrode and grinding the work with the grindstone in a state where electrolytic dressing is not performed, Grinding with abrasive grains protruding on the grinding surface even after the insulating oxide film has disappeared, and electrolytic dressing of a grindstone during the grinding of the work,
A grinding method characterized by alternately performing a state in which electrolytic dressing is not performed. 2. A rotatable work holder for holding a work, a conductive grindstone abutting on the surface of the work held on the work holder and rotating, and a fixed distance from a ground surface of the conductive grindstone. Dress electrode maintained and arranged,
A grinding apparatus comprising: a power supply device that applies a (−) voltage to the electrode and applies a (+) voltage to the grinding wheel; and a nozzle that supplies a weakly conductive coolant between the electrode and the grinding wheel. In order to electrolytically dress the ground surface of the abrasive whetstone so that the abrasive grains are sharpened and held by the insulating oxide film of the bond material, the whetstone and the electrode are energized, and during the work grinding after the electrolytic dressing. A grinding device, characterized in that a current-switching means is provided for turning off the current between the grindstone and the electrode in order to prevent electrolytic dressing from being performed.