JP2002361543A - Internal grinding device - Google Patents

Abstract

(57) [Problem] To provide an inner surface grinding device capable of processing a circular inner surface of a workpiece such as a cylindrical part with high accuracy in a short time. SOLUTION: This inner surface grinding device 10 has a grinding wheel 16-2.
0, a grinding wheel shaft 13, a driving unit that supports the grinding wheel shaft at one end thereof and rotationally drives it, a support unit that rotatably supports the grinding wheel shaft at the other end, and the workpiece 1 having the circular inner surface 1 a. And a holding unit 14 for holding.
The grindstone shaft is penetrated into the circular inner surface of the workpiece, both ends of the grindstone shaft are supported and rotated, and the circular inner surface is ground with the grindstone.
Further, another internal grinding device is a first grinding device in which a first grinding wheel is fixed.
A first drive unit that supports and rotates the grindstone shaft;
A second drive unit that supports and rotates a second grindstone shaft to which a second grindstone is fixed;
And a second grinding wheel shaft is arranged from the other end, and the inner surface of the circular shape is simultaneously ground with the first and second grinding wheels.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inner surface grinding apparatus capable of processing a circular inner surface of a workpiece such as a cylindrical part with high precision.

[0002]

2. Description of the Related Art Conventionally, flight control for aircraft
It is an important functional part of the actuator and has high hardness (HRc5
(0 or more) of a cylindrical component, a distortion (bending), which is considered to be caused by non-uniformity of the material structure / residual processing stress, sometimes occurred in the heat treatment step. In particular, L /
2 for a large D (length / diameter) ratio (L / D ≧ 15)
A bend of as much as 00 μm may occur. In order to remove such a bend and satisfy the cylindricity requirement (for example, 1 μm) of the inner diameter, the following processing has been performed so far.

Honing processing Honing processing is performed while repeating measurement, and a portion having poor cylindricity is corrected, and post-processing is unnecessary. In this honing process, the honing grindstone moves in accordance with the bending of the work (workpiece), so that a sophisticated skill is required for the correction, and the processing takes a great deal of time, resulting in poor productivity. For example, a processing amount of 450 μm may require about 15 hours. The cylindricity refers to the nonuniform size of the diameter at two or more places in the cylindrical portion, and is the sum of the values of straightness at the center of the cylinder, roundness of the cylindrical cross section, and axial dimensional deviation of the cylindrical cross section diameter. Is defined by

[0004] Electric discharge machining is performed by planetary movement of a cylindrical electrode on the inner surface of the sleeve. In this electric discharge machining,
The concentricity of the inner and outer diameters is liable to occur, and a great amount of processing time is required. For example, it may take about 8 hours at a removal amount of 200 μm. Further, a step (honing processing) of removing a deteriorated layer (heat-affected layer) generated by electric discharge machining in a later step is required. In addition, since the heat-affected layer has a very high hardness, the processing time is twice as long as usual. That is all. As described above, much time is required for the entire processing, and the productivity is not good.

[0005]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present invention provides an internal grinding apparatus capable of processing a circular inner surface of a workpiece such as a cylindrical part with high precision in a short time. The purpose is to provide.

[0006]

In order to achieve the above object, a first internal grinding apparatus according to the present invention comprises a grinding wheel shaft on which a grinding wheel is fixed, and a driving unit which supports the grinding wheel shaft at one end thereof and rotationally drives it. And a support unit that rotatably supports the grinding wheel shaft at the other end, and a holding unit that holds a work piece having a circular inner surface, wherein the work piece held by the holding unit has a circular shape. The grinding wheel shaft is penetrated into the inner surface, and both ends of the grinding wheel shaft are supported by the drive unit and the support unit, and the circular inner surface is ground by the grindstone while being rotated by the drive unit.

According to this internal grinding apparatus, the circular inner surface of the workpiece is ground by the grinding wheel fixed to the grinding wheel shaft while supporting the grinding wheel shaft at both ends. The shaft is less likely to bend, and the circular inner surface of the workpiece can be machined with high precision. In addition, since the grinding process is performed using a grindstone, a heat-affected layer is not generated, and post-processing (for example, honing) is facilitated and time is not required. . Also,
Since straightness is corrected at the time of grinding, cylindricity can be machined with high accuracy. Further, even a work piece having a large (length / diameter) ratio can be machined with higher precision than the conventional cantilever support.

In this case, the plurality of grinding wheels are fixed to the grinding wheel shaft in the rotation axis direction, and the circular inner surface is controlled while moving the grinding wheel shaft relative to the workpiece in the rotation axis direction. By configuring to perform grinding, grinding can be performed efficiently in a short time, and productivity is improved.

A second internal grinding apparatus according to the present invention includes a first grinding wheel shaft having a first grindstone fixed on the tip end side, a second grinding wheel shaft having a second grindstone fixed on the tip end side, The first
A first drive unit that supports and rotates the grindstone shaft;
A second drive unit that supports and rotates the second grindstone shaft; and a holding unit that holds a workpiece having a circular inner surface, wherein a circle of the workpiece held by the holding unit is provided. The first grindstone shaft is arranged from one end within the shape inner surface, and the second grindstone shaft is arranged from the other end, and the first and second while being rotated by the first and second drive units. Each of the circular inner surfaces is ground with a grindstone.

According to this internal grinding device, the circular inner surface can be simultaneously ground with the first grinding stone and the second grinding stone by about 1/2 of the length of the workpiece, and the workpiece is held by the holding unit. Since the replacement work is not required, the grinding can be efficiently performed in a short time, and the productivity is improved. Since each of the first and second grindstones only needs to perform grinding processing of about １ ／ of the length of the workpiece, the length of each of the first and second grindstone shafts can be made shorter than in the past, and it is difficult to bend. Thus, the circular inner surface of the workpiece can be machined with high precision. In addition, since the grinding process is performed using a grindstone, a heat-affected layer is not generated, and post-processing (for example, honing) is facilitated and time is not required. Thus, the entire processing time of the workpiece can be reduced, and productivity can be improved. . Also,
Since the straightness is corrected during the grinding process, the cylindricity can be accurately processed.

In this case, the circular inner surface may be ground while controlling the first and second grindstone shafts to relatively move in the direction of their rotational axes. Thereby, each of the first and second grindstones can simultaneously perform the grinding of about １ ／ of the length of the workpiece. The grinding near the center of the workpiece can be performed by using one of the other grinding wheel shafts after pulling out and retracting one of the grinding wheel shafts.

Further, in each of the above-mentioned inner surface grinding apparatuses, a dresser unit having a rotating portion for dressing the grindstone while rotating is further provided, and the rotating portion of the dresser unit is retracted with the holding unit retracted from the grinding wheel shaft. It is preferable that the grindstone is rotated to dress (dress) the grindstone fixed to the grindstone shaft.

In each of the above-described internal grinding apparatuses, the workpiece may be rotatably held by the holding unit, and the grinding may be performed while rotating the workpiece. In addition, the above-mentioned grindstone refers to a rotary tool in which abrasive grains are bonded with a binder.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an internal grinding apparatus according to a first embodiment of the present invention;

<First Embodiment>

FIG. 1 is a perspective view showing the entire internal grinding device of the first embodiment, FIG. 2 is a front view of the internal grinding device of FIG. 1, and FIG. 3 is a top view of the internal grinding device of FIG. FIG. 4 is an enlarged front view showing a main part of the internal grinding device of FIG. 2, and FIG. 5 is a top view showing a dressing state by a dresser unit in the internal grinding device of FIG.

As shown in FIGS. 1 to 5, an inner surface grinding apparatus 10 according to the present embodiment comprises a drive unit 11 which fixes a plurality of grindstones 16 to 20 and supports a rotating grindstone shaft 13 at one end thereof to rotate and drive. And a support unit 12 that rotatably supports the grinding wheel shaft 13 at the other end, and a cylindrical body 1 that is a workpiece that is disposed between the drive unit 11 and the support unit 12 and that has a circular inner surface 1a. A work holding unit 14 that is driven to rotate while being held, and a dresser unit 15 having a rotating disk unit 15a for dressing (dressing) the grindstones 16 to 20 fixed to the grindstone shaft 13 are placed on the grinding machine 2. In preparation.

The plurality of grindstones 16 to 20 are formed in a cylindrical shape, are fixed to the grindstone shaft 13 at substantially equal intervals in the direction of the rotation axis, and rotate integrally with the grindstone shaft 13. Grinding is performed while hitting the circular inner surface 1a.

The drive unit 11 includes a rotating shaft 11a driven to rotate by a motor (not shown) and a rotating shaft 1
And a chuck shaft 11b which is connected to 1a and chucks and fixes the grinding wheel shaft 13 at one end, and is fixed on the grinding machine 2, and its fixed position can be adjusted in the horizontal direction h in the figure. .

The support unit 12 has a rotating shaft 12a which rotates in accordance with the rotation of the rotating shaft 11a of the drive shaft 11.
And a chuck shaft 12b which is connected to the rotating shaft 12a and chucks and fixes the grinding wheel shaft 13 at the other end. The chuck shaft 12b is fixed on the grinding machine 2 and its fixed position can be adjusted in the horizontal direction h. Has become. The rotation shaft 12a may be fixed, and the chuck shaft 12b may be driven to rotate.

The rotating shaft 11a of the drive unit 11 and the rotating shaft 12a of the support unit 12 are movable in the direction of the rotating shaft, and the two rotating shafts 11a, 12a are integrally rotated while rotating the grinding wheel shaft 13. By moving the workpiece with respect to the cylindrical body 1 in the direction, the entire inner surface 1a of the circular shape can be ground.

As shown in FIG. 4, the work holding unit 14 has a fixing portion 14a for fixing the cylindrical body 1 of the workpiece on its outer surface, and a main body for rotatably supporting the fixing portion 14a via a bearing 14b. 3 and a rotating part 14c that is rotated by a motor (not shown) and is connected to the fixed part 14a to rotate the fixed part 14a. The rotating part 14c is fixed on the grinding machine 2, and is fixed in the direction g in FIG. It is movable. The fixing portion 14a is a state in which the cylindrical body 1 is fixed, and
And rotate in the opposite direction.

The diameter of the cylindrical grindstones 16 to 20 is made smaller than the diameter of the circular inner surface 1a of the cylindrical body 1, so that the rotating shaft 11a of the driving unit 11, the rotating shaft 12a of the support unit 12, and the work holding unit 14 is adjusted in the direction perpendicular to the rotation axis, and the grindstone shaft 13 is adjusted.
By setting such that the rotation center axis of the cylindrical body 1 and the rotation center axis of the cylindrical body 1 are eccentric by a predetermined amount, the grinding wheels 16 to 20 perform grinding while reliably hitting the circular inner surface 1a of the cylindrical body 1. I have.

The dresser unit 15 is located near the work holding unit 14 as shown in FIG. 3 during normal grinding, and after the work holding unit 14 moves and retreats in the direction g as shown in FIG. 5 during dressing. In the direction g, and dresses each of the grindstones 16 to 20 fixed to the grindstone shaft 13 at the end face of the rotating disk portion 15a.

The internal grinding device 10 shown in FIGS.
Will be described. First, the work holding unit 1
The grinding wheel shaft 13 is made to penetrate through the cylindrical body 1 in a state where the cylindrical body 1 which is the workpiece is fixed in the fixing portion 14a of the grinding wheel 4 and one end of the grinding wheel shaft 13 is connected to the drive unit 11 as shown in FIGS. , And the other end is connected to the chuck shaft 12b of the support unit 12. Thereby, the grinding wheel shaft 13
Are supported at both ends by the chuck shaft 11b of the drive unit 11 and the chuck shaft 12b of the support unit 12.

Next, the rotary shaft 11a of the drive unit 11 is driven to rotate, the grindstone shaft 13 to which the grindstones 16 to 20 are fixed is rotated, and the fixing portion 14 of the work holding unit 14 is fixed.
The cylindrical body 1 fixed at a is rotated in the reverse rotation direction with respect to the grinding wheel shaft 13. The circular inner surface 1a of the cylindrical body 1 and the grinding wheel shaft 1
The relative rotation of each of the grindstones 16 to 20 causes the respective grindstones 16 to 20 to rotate.
To 20 contact the circular inner surface 1a of the cylindrical body 1 to grind the circular inner surface 1a.

The rotation shaft 11a of the drive unit 11
By rotating the rotation shaft 12a of the support unit 12 integrally with the grinding wheel shaft 13 in the direction a of FIG. 4 or the direction a 'opposite thereto, the entire inner surface 1a of the cylindrical body 1 is ground. The amount of movement in the direction a or the direction a 'may be slightly larger than the interval between the plurality of grindstones 16 to 20 and may be smaller in accordance with the number of grindstones than in the case of a single grindstone. The time required can be greatly reduced.

When dressing the cylindrical grindstones 16 to 20, the work holding unit 14 is retracted and the dresser unit 15 is moved in the direction g as shown in FIG. Wheel unit 13 is the drive unit 1
Each of the grindstones 1 fixed to the grindstone shaft 13 with the end face of the rotating disk portion 15a being supported by the
Dressing while abutting on 6-20. Thereby, the grinding performance of each grindstone can be maintained constant even if grinding is performed for a long time.

According to the internal grinding device 10 described above, the circular inner surface 1a of the cylindrical body 1, which is a workpiece, is fixed to the grinding wheel shaft 13 with the grinding wheel shaft 13 supported at both ends. Since grinding is performed at 20, the grinding wheel shaft 13 is less likely to bend than in the case of cantilever support, and the circular inner surface 1a of the cylindrical body 1 can be machined with high precision.

Further, in the inner diameter machining of a cylindrical part such as a sleeve having a high hardness (HRc50 or more), the grinding stone can easily remove the heat treatment strain in a short time without following the bending of the work. Highly accurate cylindricity (including roundness and straightness) within the range can be realized. Further, since no heat-affected layer is generated on the surface to be processed, post-processing such as honing processing becomes easy and time is not required, so that the entire processing time of the work can be reduced, and productivity can be improved. In addition, the (length /
Even when the diameter ratio is as large as 15 or more, processing can be performed with higher precision than in the conventional cantilever support.

Further, by configuring the above-described inner surface grinding apparatus under CNC control (computer numerical control), the above-described grinding processing can be performed without requiring a high skill.

The number of grindstones fixed to the rotating shaft can be appropriately changed according to the length and the like of the workpiece, and may be only one.

<Second Embodiment>

FIG. 6 is a perspective view showing the entire internal grinding device of the second embodiment, FIG. 7 is a front view of the internal grinding device of FIG. 6, and FIG. 8 is a top view of the internal grinding device of FIG. 9 is an enlarged front view showing a main part of the internal grinding device of FIG. 7, and FIG. 10 is a top view showing a dressing state by a dresser unit in the internal grinding device of FIG.

The internal grinding apparatus 30 according to the present embodiment shown in FIGS. 6 to 10 simultaneously grinds the circular inner surface 1a of the cylindrical body 1 as a workpiece from two ends by using two drive units 31 and 32. Fig. 1 to Fig. 5
The same reference numerals are given to the same parts as those of the internal grinding device 10 shown in FIG.

As shown in FIGS. 6 to 10, the inner surface grinding device 30 is provided with a first grindstone shaft 33 having a first grindstone 34 fixed to the tip thereof, connected to a rotating shaft 31a to support and rotate the first grindstone shaft 33a.
And a second drive unit 32 that connects and supports a second grindstone shaft 35 with a second grindstone 36 fixed to the tip thereof to a rotating shaft 32a to rotate and drive the first grindstone shaft 35. The work holding unit 14 and the dresser unit 15 arranged between the second drive unit 32 and the second drive unit 32 are provided on the grinding machine 2.

The first and second grindstones 34 and 36 are formed in a cylindrical shape, rotate integrally with the first and second grindstone shafts 33 and 35, respectively, enter the cylindrical body 1 from both ends, and grind the grindstone 34. , 36 are circular inner surfaces 1 of the cylindrical body 1.
Grinding is performed while hitting a.

The above-mentioned first and second drive units 31,
Reference numeral 32 denotes a rotating shaft 31a, 32a which is rotationally driven by a motor (not shown) to chuck and connect the grinding wheel shafts 33, 35, and is fixed on the grinding machine 2, respectively. The fixed position can be adjusted in the horizontal direction h in the figure.

The rotating shafts 31a and 32a of the driving units 31 and 32 are independently movable in the direction of the rotating shaft, and are processed in the rotating shaft direction while rotating the grinding wheel shafts 33 and 35. The entire surface of the circular inner surface 1a can be ground by moving the cylindrical body 1 with respect to the body.

The diameter of each of the cylindrical grinding wheels 34, 36 is made smaller than the diameter of the circular inner surface 1a of the cylindrical body 1, and each of the rotating shafts 31a, 32a of each of the drive units 31, 32 and the work holding unit 14. Is adjusted in a direction orthogonal to the rotation axis so that the rotation center axes of the grinding wheel shafts 33 and 35 and the rotation center axis of the cylindrical body 1 are eccentric by a predetermined amount. Grinding is performed while each of the grindstones 34 and 36 reliably contacts the circular inner surface 1a of the cylindrical body 1.

The internal grinding device 3 shown in FIGS.
The operation of 0 will be described. First, as shown in FIGS.
The cylindrical body 1 as a workpiece is fixed in the fixing portion 14a of the work holding unit 14, the grinding wheel shaft 33 is connected to the rotation shaft 31a of the first driving unit 31, and the grinding wheel shaft 35 is connected to the second driving unit 32. To the rotating shaft 32a.

Next, the respective drive shafts 31 and 32 rotate the respective rotating shafts 31a and 32a to rotate the respective grindstone shafts 33 and 35 on which the grindstones 34 and 36 are fixed, respectively. Is rotated in the reverse rotation direction with respect to the grindstone shafts 33, 35. The circular inner surface 1a of the cylindrical body 1 and the grinding wheel shafts 33, 3
The relative rotation of each of the grindstones 34 and 36 of FIG.
4 and 36 grind the circular inner surface 1a while contacting the circular inner surface 1a of the cylindrical body 1. At this time, as shown in FIG. 9, while the rotating shaft 31a moves in the direction b together with the grinding wheel shaft 33, the circular inner surface 1a of the cylindrical body 1 is
Grind from the side. At the same time, the rotating shaft 32a is
While moving in the direction b ', the circular inner surface 1a of the cylindrical body 1 is ground by the grindstone 36 from the other end 1c side.

As described above, each of the grindstones 34 and 36 is connected to each end 1
By moving in the directions b and b ′ from b and 1c respectively, the circular inner surface 1a of the cylindrical body 1 can be ground.
When the grindstone 34 and the grindstone 36 move about half the length of the cylindrical body 1 and approach to a certain distance as shown by the broken line in FIG. 9, a sensor (not shown) detects this state, and for example, the second drive unit On the 32nd side, the rotary shaft 32a is pulled in the direction opposite to the direction b 'in FIG. 9 and retracted, and the entire surface of the circular inner surface 1a is ground by moving the rotary shaft 31a in the direction b on the first drive unit 31 side. Process. As described above, the amount of movement of each of the grinding wheel shafts 33, 35 in the direction b or the direction b 'may be about half the length of the cylindrical body 1, so that the time required for grinding can be reduced to about half.

When dressing (dressing) the cylindrical grindstones 34 and 36, the work holding unit 14 is retracted and the dresser unit 15 is retracted as shown in FIG.
Is moved in the direction g, the rotating shaft 32a of the second unit 31, for example, is extended, and the grindstone 36 is dressed while being in contact with the end face of the rotating disk portion 15a at the position shown by the broken line in FIG. Thereby, the grinding performance of each grindstone can be maintained constant even if grinding is performed for a long time.

According to the internal grinding device 30 described above, the circular inner surface 1a of the cylindrical body 1 is fixed to the grinding wheel shafts 33, 35 while supporting the grinding wheel shafts 33, 35 in a cantilever state.
Grinding is performed at 36. Since the grinding wheels 34 and 36 only need to move about half the length of the cylindrical body 1, the grinding wheel shafts 33 and 35 are used.
Is made shorter than before so that the grinding wheel shafts 33, 3
5 hardly bends, and the circular inner surface 1a of the cylindrical body 1 can be machined with high precision. In the conventional apparatus, the inner surface grinding device 3
Grinding can be performed with the same accuracy by using a grinding wheel shaft having the same length as the grinding wheel shafts 33 and 35 of 0, but the cylindrical body 1 must be replaced by the work holding unit 14, and if the subsequent grinding time is included. In this case, it takes more than twice as long as the case using the inner surface grinding device 30.

Further, in processing the inner diameter of a cylindrical part such as a sleeve having a high hardness (HRc 50 or more), it is possible to easily remove the heat treatment strain in a short time without the whetstone following the bending of the work. Highly accurate cylindricity (including roundness and straightness) within the range can be realized. Further, since no heat-affected layer is generated on the surface to be processed, post-processing such as honing processing becomes easy and time is not required, so that the entire processing time of the work can be reduced, and productivity can be improved. In addition, the (length /
Even when the diameter ratio is as large as 15 or more, the grinding wheel shaft can be made shorter than in the conventional case, so that high-precision machining can be performed.

Further, by configuring the above-described inner surface grinding apparatus under CNC control (computer numerical control), the above-described grinding processing can be performed without requiring a high level of skill.

In the description with reference to FIGS. 6 to 10, the grinding wheels 34, 36 are respectively connected to the ends 1b, 1b, 1
The grinding starts from c and the grinding wheel shafts 33 and
Although the pattern in which 35 moves was used, the present invention is not limited to this.
Other movement patterns may be used. For example, at the start of grinding, the grindstone 34 is located near the center of the circular inner surface 1a of the cylindrical body 1 in the direction of the rotation axis, and one end 1b is opposite to the direction b in FIG.
, While the grindstone 36 starts grinding from the other end 1c and moves in the direction b ′. At the start of grinding, both the grindstone 34 and the grindstone 36
The pattern may be located near the center of the circular inner surface 1a and move toward the ends 1b and 1c so as to be away from each other. In addition, a plurality of grinding wheels may be provided on both or one of the grinding wheel shafts 33 and 35.
The grinding time can be further reduced.

Although the present invention has been described with reference to the embodiment, the present invention is not limited to the embodiment.
Various modifications are possible within the scope of the technical idea of the present invention. For example, the inner surface grinding apparatus according to the present invention can be applied to the entire inner diameter precision finishing of a cylindrical part such as a sleeve, and the outer surface of the workpiece does not necessarily have to be circular. In addition, although the workpiece is rotated by the work holding unit, the grinding may be performed while the workpiece is fixed.

[0050]

According to the inner surface grinding apparatus of the present invention, the circular inner surface of a workpiece such as a cylindrical part can be machined with high precision, and can be machined in a short time to improve productivity.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an entire internal grinding device according to a first embodiment.

FIG. 2 is a front view of the internal grinding device of FIG. 1;

FIG. 3 is a top view of the internal grinding device of FIG. 1;

FIG. 4 is an enlarged front view showing a main part of the internal grinding device of FIG. 2;

FIG. 5 is a top view showing a dressing state by a dresser unit in the internal grinding device of FIG. 3;

FIG. 6 is a perspective view illustrating an entire internal grinding device according to a second embodiment.

FIG. 7 is a front view of the internal grinding device of FIG. 6;

FIG. 8 is a top view of the internal grinding device of FIG. 6;

FIG. 9 is an enlarged front view showing a main part of the internal grinding device of FIG. 7;

FIG. 10 is a top view showing a dressing state by a dresser unit in the internal grinding device of FIG. 8;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylindrical body, to-be-processed body, and workpiece 1a Circular inner surface of cylindrical body 1b One end of cylindrical body 1c The other end of cylindrical body 1, 30 Internal grinding device 11 Drive unit 11a Rotary axis 12 Support unit 12a Rotary axis 13 Grinding stone Axis 14 Work holding unit 15 Dresser unit 15a Rotating disk unit 16-20 Grinding stone 31 First driving unit 31a Rotating shaft 32 Second driving unit 32a Rotating shaft 33 First grinding stone shaft 34 First grinding stone 35 Second grinding stone Shaft 36 Second whetstone

Claims (5)

[Claims] 1. A grindstone shaft to which a grindstone is fixed, a drive unit that supports the grindstone shaft at one end thereof and rotationally drives it, a support unit that rotatably supports the grindstone shaft at the other end, and a circular inner surface. And a holding unit for holding the workpiece, wherein the grinding wheel shaft is penetrated into a circular inner surface of the workpiece held by the holding unit, and the grinding wheel shaft is driven by the drive unit and the support unit. And grinding the circular inner surface with the whetstone while rotating by the drive unit. 2. A grinding machine for fixing the plurality of whetstones in the direction of a rotation axis to the whetstone shaft, and grinding the circular inner surface while controlling the whetstone shaft to move relative to the workpiece in the direction of the rotation axis. The internal grinding apparatus according to claim 1, wherein the internal grinding is performed. 3. A first grindstone shaft having a first grindstone fixed to the tip end side, a second grindstone shaft having a second grindstone fixed to the tip end side, and a rotary drive for supporting the first grindstone shaft. A first drive unit that supports and rotates the second grindstone shaft, and a holding unit that holds a workpiece having a circular inner surface, wherein the holding unit holds the workpiece. The first grindstone shaft is arranged from one end within the circular inner surface of the processed workpiece, and the second grindstone shaft is arranged from the other end, and is rotated by the first and second drive units. The inner surface grinding device, wherein the first and second grindstones respectively grind the circular inner surface. 4. The grinding machine according to claim 3, wherein the circular inner surface is ground while controlling the first grinding wheel axis and the second grinding wheel axis to relatively move in the direction of their rotation axes. Internal grinding device as described. 5. A dresser unit having a rotating unit for dressing the grindstone while rotating, wherein the rotating unit of the dresser unit rotates while the holding unit is retracted from the grindstone shaft, and the dresser unit rotates the grindstone shaft. The internal grinding apparatus according to any one of claims 1 to 4, wherein the fixed whetstone is dressed.