JP2002263995A - Method and device for grinding spherical surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for grinding ceramics, a hard and breakage material compared with metal, to be a smoother and more precise spherical surface than metal. SOLUTION: A grinding step (A) and an electrolytic dressing step (B) are implemented alternately. In the grinding step (A), a work 1 with a spherical surface 1a is driven to rotate around the rotation axis (z) passing the center O of the spherical surface and orthogonally crossing a horizontal axis (y) while oscillating around the horizontal axis (y) passing the center O. At the same time, a conductive grinding stone 14 with a recessed spherical surface 14a engaged with the spherical surface 1a of the work is supported oscillatably along the spherical surface 1a of the work to apply a constant load to the work, and the work is ground by driving/rotating the grinding stone 14 around a vertical axis passing the center of the recessed spherical surface 14a. In the electrolytic dressing step (B), the position of a cathode 17 is determined with a prescribed gap between the cathode and the recessed spherical surface 14a while the conductive grinding stone 14 is driven/rotated around the vertical axis passing the center of the recessed spherical surface 14a, and the recessed spherical surface 14a is electrolytically dressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grinding method and apparatus for making a ceramic spherical surface highly smooth and highly accurate.

[0002]

2. Description of the Related Art The wear resistance of an artificial joint is an important factor that most affects the life of the artificial joint. However, at present, the life of the prosthesis is shorter than the remaining life of the patient due to wear, and the patient must be re-operated. Therefore, there is an urgent need to improve its wear resistance.

FIG. 9 is a schematic view showing the structure of an artificial joint. The spherical head 1 is fixed to the stem 2, and the portion of the head 1 having a convex spherical surface comes into contact with the concave spherical surface of the socket 3 to form a sliding surface of the joint. However, due to long-term relative sliding,
A slack occurs between the sliding surfaces, and this slack governs the life of the artificial joint.

In order to extend the life of the artificial joint, it is essential to optimize the materials of the socket 3 and the head 1 and to improve the surface roughness and the shape accuracy. At present, materials for artificial joints mainly use a combination of a polyethylene socket and a metal head. Polyethylene is a polymer material that deforms according to the load, has the advantage of not exerting a significant effect even if it is not precisely molded, and has the impact resistance, making it the optimal material for sockets. ing.

[0005] Table 1 compares metals and ceramics as head material. As is clear from this table, the ceramic head has less wear on the socket than the metal head, and is superior in compatibility with the living body, stability in the living body (for example, corrosion resistance), hardness, friction coefficient, and the like. Yes,
The development of ceramic heads instead of metal heads is expected to prolong the life of artificial joints.

[0006]

[Table 1]

[0007]

FIG. 10 shows an example of the shape and dimensions of the head of a bone constituting an artificial joint. As shown in this figure, the head 1 has a spherical shape, and it is necessary to finish almost the entire outer peripheral surface thereof (in the range of 250 degrees in the figure) with high smoothness and high accuracy. However, as shown in Table 1,
Ceramics have lower workability than metals, and conventional processing means have a surface roughness of 0.5 to Rmax (Ry).
Only about 0.8 μm and a roundness of about 1 to 2 μm could be achieved.

That is, the conventional metal head is (A) cut with a lathe or the like and then finished with a buff or the like, or (B) is sandwiched between two working disks like a ball for a bearing and rolled. It was moving and processing. However, in any case, as described above, sufficient high smoothness and high accuracy cannot be achieved, and there is a problem that the life of an artificial joint using the same is short. In addition, there is a problem in that it is unsuitable for multi-product small-quantity production which needs to be adapted to each individual like an artificial joint, and it is difficult to process ceramics.

The present invention has been made to solve such a problem. That is, an object of the present invention is to provide a grinding method and apparatus capable of processing ceramics, which are hard and brittle materials compared to metals, into spherical surfaces with higher smoothness and higher precision than metals.

[0010]

According to the present invention, the workpiece (1) having the spherical surface (1a) is swung about the horizontal axis y passing through the center O of the spherical surface while passing through the center O to the horizontal axis y. The conductive grindstone (14) having the concave spherical surface (14a) fitted to the spherical surface (1a) of the work is simultaneously driven to rotate around the orthogonal rotation axis z and oscillated along the spherical surface (1a) of the work. A grinding step (A) of supporting the workpiece, applying a constant load to the workpiece, and rotating the vertical axis passing through the center of the concave spherical surface (14a) to grind the workpiece; While rotating (14) about a vertical axis passing through the center of the concave spherical surface (14a), the concave spherical surface (1
4a), a cathode (17) is positioned with a certain gap therebetween, and an electrolytic dressing step (B) for electrolytically dressing the concave spherical surface (14a). The grinding step (A) and the electrolytic dressing step (B) is alternately performed, and a spherical grinding method is provided.

Further, according to the present invention, the work (1) having the spherical surface (1a) is swung about the horizontal axis y passing through the center O of the spherical surface while rotating, and the rotation axis passing through the center O and orthogonal to the horizontal axis y. Work swing rotation device that rotates around z (12)
And a concave spherical surface (14) fitted to the spherical surface (1a) of the work.
a) a conductive grindstone (1), and the conductive grindstone (1);
4) is swingably supported along the spherical surface (1a) of the work, a constant load is applied to the work, and the concave spherical surface (14
a) a grinding wheel rotation driving device (16) for rotating and driving about a vertical axis passing through the center of (a); and a concave spherical surface (14) of the grinding wheel (14).
a cathode (17) fitted with a) and having a certain gap between them
An electrolytic dressing device (18) for electrolytically dressing a concave spherical surface (14a) with the cathode, a grinding position for grinding a workpiece with the grindstone, and a dressing position for electrolytically dressing a grindstone with the cathode. Position shift device (2) for moving the grindstone or workpiece and cathode
0) is provided.

According to the method and apparatus of the present invention, in the grinding step (A), the work swing rotation device (1) is used.
The combination of the grinding wheel rotation drive device (16) and the grinding wheel rotating drive device (16) allows the spherical surface (1a) of the work (1) to be fitted to the concave spherical surface (1).
Grinding can be performed with the conductive grinding wheel (14) having 4a). Further, in the electrolytic dressing step (B), the concave spherical surface (1) of the grindstone (14) is formed by the combination of the grindstone rotation drive device (16) and the electrolytic dressing device (18).
4a) can be electrolytically dressed using the cathode (17). Further, the grinding step (A) and the electrolytic dressing step (B) are alternately performed by moving the grindstone or the work and the cathode between the grinding position and the dressing position by the position shift device (20). Can be. Therefore, ceramics, which are hard and brittle materials compared to metals, can be processed into a smoother and more accurate spherical surface than metals by a combination of grinding and electrolytic dressing.

According to a preferred embodiment of the present invention, the conductive grindstone (14) has a concave spherical surface (14a) fitted to a spherical surface (1a) of a work, and the concave spherical surface (14a) and the vertical axis. And a liquid groove (1) provided through the recess (14b) from the recess (14b) to the outer periphery.
4c). With this configuration, it is possible to smoothly supply a machining liquid and an electrolytic solution necessary for machining and electrolytic dressing to the machining surface and the dressing surface through the concave hole (14b) and the liquid groove (14c) during grinding and electrolytic dressing. it can.

The grinding wheel rotation driving device (16) includes a flexible joint (16a) for supporting the conductive grinding stone (14) so as to be able to swing along the spherical surface (1a) of the work, and a work joint on the flexible joint (16a). And a drive shaft (16b) for applying a constant load toward the shaft and rotating and driving about a vertical axis passing through the center of the concave spherical surface (14a). With this configuration, the flexible joint (16a) allows the conductive grindstone (14) to swing along the spherical surface (1a) of the work, thereby performing automatic alignment. Further, since the rotary drive is performed while applying a constant load by the drive shaft (16b), the entire spherical surface (1a) of the work can be machined under substantially the same conditions.

The work swinging rotation device (12) includes a rotation drive device (12a) that rotates around a rotation axis z passing through the center O of the spherical surface of the work (1) and orthogonal to the horizontal axis y;
A swing mechanism (12b) for swinging the rotary drive device about a horizontal axis y passing through the center O of the spherical surface. With this configuration, the work can be swung about the horizontal axis y while the work is rotationally driven about the rotation axis z by the rotation drive device (12a).

The cathode (17) has a hemispherical surface (17a) facing the concave spherical surface (14a) of the grinding wheel (14), and a liquid for supplying a conductive liquid from the center toward the center of the grinding wheel. And a flow path (17b). According to this configuration, the hemispherical surface (17a) is positioned at an interval from the concave spherical surface (14a) of the grindstone (14), and the conductive liquid is supplied from the liquid flow path (17b), during which the conductive liquid is necessary for electrolytic dressing. The electrolyte can be smoothly supplied to the dressing surface.

The electrolytic dressing device (18) includes a conductive liquid supply device (19) for supplying a conductive liquid between the conductive grindstone and the cathode, a positively applied conductive grindstone, and a negatively applied cathode. Power supply device (18a).
With this configuration, while the conductive liquid flows between the conductive grindstone and the cathode, the conductive grindstone can be positively applied and the cathode can be negatively applied to electrolytically dress the concave spherical surface (14a) of the conductive grindstone. .

The position shift device (20) includes a moving table on which a work swinging rotation device (12) and an electrolytic dressing device (18) are mounted at an interval, and moving the moving table in at least the xz axis direction. And an NC drive device for numerical control. With this configuration, while the grindstone is rotated at a fixed position by the grindstone rotation driving device (16), the NC
The work table and the cathode can be moved between the grinding position where the work is ground by the grindstone and the dressing position where the grindstone is electrolytically dressed by the cathode by numerically controlling the moving table in the xz axis direction by the driving device. .

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram of a spherical grinding apparatus according to the present invention. As shown in this figure, the spherical grinding apparatus of the present invention includes a work swing rotating device 12, a conductive grinding wheel 14, a grinding wheel rotation driving device 16, an electrolytic dressing device 18, and a position shifting device 20.

Work 1 to which the method and apparatus of the present invention are applied
Is, for example, the head shown in FIGS. 9 and 10 and having at least a part of a spherical surface 1a having a center O. Further, the material of the work is preferably a ceramic which is a hard and brittle material, in particular, zirconia ceramics, alumina, alumina / zirconia composite ceramics (for example, ZTA), ceramics containing yttrium or yttrium oxide, and the like. . Note that the present invention is not limited to these materials, and may be directed to the same metals as conventional metal bone heads.

FIG. 1A shows a grinding step. As shown in FIG.
It comprises a rotary drive device 12a and a swing mechanism 12b. The rotation driving device 12a is driven to rotate about a rotation axis z passing through the center O of the spherical surface of the work 1 and orthogonal to the horizontal axis y, and a non-processed portion of the work 1 is fixed to one end of the rotation shaft 12c. The rotation drive device 12a includes, for example, an electric motor and a reduction gear, and can continuously rotate the work 1 around the rotation axis z at a predetermined rotation speed (for example, 30 to 200 rpm in an embodiment described later).

The oscillating mechanism 12b oscillates the rotary driving device 12a about the horizontal axis y passing through the center O of the spherical surface of the work together with the work 1. This swing mechanism 12
b includes, for example, a moving table (not shown) in which the rotary driving device 12a is attached together with the work 1, and an NC driving device (not shown) for numerically controlling the moving table in at least the xz-axis direction. By combining the movement in the x-axis direction and the movement in the z-axis direction, it is possible to swing about a horizontal axis y passing through the center O of the spherical surface. Further, the rotary drive device 12a is mounted on a swing table (not shown) supported by a horizontal axis y passing through the center O of the spherical surface, and is swung by another swing drive device (for example, a linear motion cylinder and a link mechanism). The moving table may be swung.

With the above-described structure, the work 1 having the spherical surface 1a is rotationally driven about the rotational axis z passing through the center O and orthogonal to the horizontal axis y while swinging about the horizontal axis y passing through the center O of the spherical surface. be able to.

The conductive grindstone 14 has a concave spherical surface 14a fitted to the spherical surface 1a of the work 1. This whetstone will be described in detail with reference to FIG.

The grindstone rotary drive unit 16 has a flexible joint 16a on which the grindstone 14 is mounted below, and a drive shaft 16b for rotating the flexible joint 16a while pressing the upper end thereof downward. The flexible joint 16a supports the conductive grindstone 14 in a swingable manner along the spherical surface 1a of the work, and swings the conductive grindstone (14) along the spherical surface (1a) of the work so as to perform self-alignment. Has become. This flexible joint 16
The swing angle of “a” may be about 5 degrees in all directions.

The drive shaft 16b is connected to a drive unit (for example, an electric motor and a speed reducer) and a biasing unit (for example, an air cylinder and a spring), not shown, to apply a constant load to the flexible joint 16a toward the work. And it is designed to rotate around a vertical axis passing through the center of the concave spherical surface 14a. This rotation speed is 5 in the embodiment described later.
0 to 200 rpm, and the constant load is, for example, 4.9 to 49.
About N.

With the above-described structure, the conductive grindstone 14 is swingably supported along the spherical surface 1a of the work 1,
, And can be driven to rotate about a vertical axis passing through the center of the concave spherical surface 14a.

FIG. 2 is a perspective view of a grindstone used in the apparatus of the present invention. As shown in this figure, the conductive grindstone 14 has a concave spherical surface 14a fitted to the spherical surface 1a of the workpiece 1 and a concave spherical surface 1a.
A concave hole 14b provided at the intersection of the vertical axis 4a and the vertical axis, and a liquid groove 14c provided penetrating from the concave hole 14b to the outer peripheral portion.
And With this configuration, when the work 1 is ground by the grindstone 14, the working fluid from the working fluid nozzle 15 provided outside the grindstone is smoothly supplied to the work surface of the work through the liquid groove 14c and the concave hole 14b. can do.

FIG. 1B shows an electrolytic dressing step. As shown in this figure, the cathode 17 is
4 has a semi-spherical surface 17a facing the concave spherical surface 14a, and a liquid flow path 17b for supplying a conductive liquid from the center to the center of the grindstone 14. The electrolytic dressing device 18 includes a conductive liquid supply device 19 that supplies a conductive liquid between the conductive grindstone 14 and the cathode 17, and a power supply device 18 a that applies the conductive grindstone 14 to the positive side and applies the cathode to the negative side.
And In this figure, 18b is a brush, 18b
c is a power supply line. With this configuration, the cathode 1 fitted with the concave spherical surface 14a of the grindstone 14 and having a certain gap therebetween.
Electrolytic dressing of the concave spherical surface 14a of the grindstone 14 can be performed while the conductive liquid flows between the groove 7 and the concave spherical surface 14a of the grindstone 14. Also, at the time of this electrolytic dressing, the conductive liquid processing liquid from the liquid flow path 17b provided at the center of the cathode 17 is passed through the concave hole 14b and the liquid groove 14c of the grindstone 14,
It can be supplied to the processing surface of the grindstone 14 smoothly.

The position shift device 20 includes a moving table (not shown) in which the work swinging rotation device 12 and the electrolytic dressing device 18 are mounted at an interval, and numerical control of the moving table in at least the xz-axis direction. And an NC drive device (not shown) for moving the grindstone or the workpiece and the cathode between a grinding position for grinding the work with the grindstone and a dressing position for electrolytically dressing the grindstone with the cathode. .

In the spherical grinding method of the present invention using the above-described apparatus, the grinding step (A) and the electrolytic dressing step (B) are performed alternately. That is, in the grinding step (A), the workpiece 1 is swung about the horizontal axis y passing through the center O of the spherical surface while passing through the center O while the horizontal axis y
, And at the same time, supports the conductive grindstone 14 swingably along the spherical surface 1a of the work, applies a constant load to the work, and generates a concave spherical surface 14a.
Grinds the workpiece by rotating around a vertical axis passing through the center of the workpiece. Further, in the electrolytic dressing step (B), while the conductive grindstone 14 is rotationally driven around a vertical axis passing through the center of the concave spherical surface 14a, a constant gap is provided between the conductive grindstone 14 and the concave spherical surface 14a, and the cathode 17 is moved. Positioning, concave spherical surface 14a
Is subjected to electrolytic dressing.

According to the method and apparatus of the present invention described above,
In the grinding step (A), the work swing rotation device 1
2 and the grinding wheel rotation drive unit 16, the work 1
Can be ground with a conductive grindstone 14 having a concave spherical surface 14a fitted to the spherical surface 1a. Also, in the electrolytic dressing step (B), the grinding wheel rotation driving device 1
With the combination of 6 and the electrolytic dressing device 18, the concave spherical surface 14 a of the grindstone 14 can be electrolytically dressed using the cathode 17. Further, the grinding step (A) and the electrolytic dressing step (B) can be performed alternately by moving the grindstone or the work and the cathode between the grinding position and the dressing position by the position shift device 20. . Therefore, ceramics, which are hard and brittle materials compared to metals, can be processed into spherical surfaces with higher smoothness and higher precision than metals by a combination of grinding and electrolytic dressing.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below.
The means for alternately performing grinding and dressing in the above-described method and apparatus of the present invention is simply referred to as an interval ELID method in the present invention.

(Experimental method) (Fixed abrasive grain finishing method by interval ELID method)
Ceramics are hard and brittle materials, and it is more difficult to achieve high efficiency and high quality processing than metals. In the abrasive processing of ceramics,
Diamond is most often used to increase processing efficiency. Conventional abrasive grain processing methods include polishing using loose abrasive grains and grinding using fixed abrasive grains. In polishing, it is difficult to reliably supply abrasive grains between the polisher and the processing surface, and there is a problem of insufficient processing efficiency due to insufficient abrasive grains. In particular, when processing a convex surface having a large curvature, the abrasive grains cannot remain on the processing surface in the polishing process, and processing while supplying the abrasive grains requires a large amount of expensive diamond, which increases the processing cost. Would. On the other hand, grinding using fixed abrasive
With the development and spread of dressing, fine abrasive grains that could not be applied to conventional grindstones can be used, and high quality processing can be realized.

In ordinary ELID dressing, dressing is performed simultaneously with processing by using a grindstone as an anode and adding a dedicated cathode. At this time, the installation space of the cathode is an indispensable condition. Therefore, in the processing of the bone head, the installation of the cathode is impossible because the entire work surface of the grindstone comes into contact with the workpiece. Therefore, in the present invention, a means for performing dressing and processing alternately (interval ELID method) is applied.

(Experimental System) The workpiece has a shape and dimensions as shown in FIG. 10 and is a head of an artificial hip joint made of zirconia ceramics. Zirconia ceramics have higher toughness than alumina ceramics and are advantageous in preventing fracture of the head due to cracks. There are four types of whetstones that differ only in particle size, # 4000, # 8000,
# 40000, # 120,000 (each having an average particle size of 4.
1, 1.8, 0.3, 0.13 μm). The grindstone shown in FIG. 2 was used. The outer diameter of the working surface of the grindstone is 23 mm, and the inner diameter is 10 mm. The reason why the hole 14b is provided at the center is to stabilize the contact state between the grindstone and the workpiece and to improve the machining efficiency. This also saves expensive diamonds. With the working surface shape and the concave spherical surface, the radius of curvature was 12.5 mm, which is the same value as the nominal radius of the workpiece. 4mm width at 4 places to supply grinding fluid effectively during processing
Of the groove 14c. The bonding material used was a composite bonding material in which copper and resin were mixed at a volume ratio of 7: 3.

(Relative Movement of Grinding Stone and Workpiece) As shown in FIG. 1, the head 1 was bonded to a jig (12c) with wax and fixed to the center of a rotary table. The grindstone was attached to the lower end of the spindle 16b via a freely tiltable adapter (flexible joint 16a), and was pressed against the processing surface of the head with a constant pressure by an air cylinder (not shown). The processing was performed by rotating the bone head to the left and right on the XZ plane using a rocking table while rotating the grindstone and the bone head in opposite directions. The minimum tilt angle of the rocking table for contacting the entire processing surface is calculated based on the size of the artificial head and the outer diameter of the grinding wheel working surface.
Since the center of the head does not coincide with the center of the swing table in the Z direction, a positional shift occurs in the X direction and the Z direction as the workpiece swings. This is followed by the vertical movement of the grindstone and the simultaneous movement of the X-axis table.

(Experimental Result) (Dressing of Grinding Stone) The grinding stone was attached to the upper spindle 16b via the adapter 16a, and the cathode 17 made of carbon was installed immediately below. The electrolyte was allowed to be uniformly injected into the gap between the electrode and the grindstone through the hole 17a at the center of the cathode. Table 2 shows the conditions of the interval dressing according to the present invention. The electrolytic dressing was performed under the conditions of a pulse current on / off time of 2 μs, a no-load voltage of 60 V, a pick current of 5 A, and a gap between the grindstone and the cathode of 0.5 mm. Further, in order to reduce unevenness of the gap due to the center deviation between the grinding wheel and the cathode, the grinding wheel 14 was rotated at a rotation speed of 30 rpm. When both the power supply voltage and the current became stable, the dressing was completed, and the time was about 4 minutes.

[0039]

[Table 2]

(Processed Surface Properties and Surface Roughness) In the preceding step as a forming step, ELID grinding was performed using a # 4000 cast iron bond diamond grindstone. While observing with a three-dimensional surface structure microscope, the surface roughness was measured using a surface roughness measuring device. The machined surface has an anisotropic surface texture due to the simple creation movement of the grinding wheel and the workpiece, and the roughness in the wheel feeding direction is about 0.19 μmRa. FIG. 3 shows an example of the roughness profile.

In the finishing step, first, with the aim of removing the destructive layer in the forming step, processing was performed with a # 4000 composite bond grindstone. After that, # 8000, # 40000, # 1
Grinding stones were applied in the order of 20,000 and the effect of abrasive grain size on surface roughness was examined. For all three types of grindstones, dressing was performed every 60 minutes, and the total processing time was 240 minutes. In addition, the rotation speed of the grindstone and the workpiece are set to 150 rpm and 100 rpm, respectively, and the processing load is set to 40 rpm.
N, the reciprocating rotation of the swing table was set to 2 for 60 minutes. FIG. 4 shows a change in the surface roughness with respect to the abrasive grain size. The roughness data in the figure was measured with a three-dimensional surface structure microscope, and did not use a filter. From FIG.
Although the surface roughness tended to be smoother as the size of the abrasive grains became smaller, there was no significant difference because the processing conditions were the same as shown in the figure. When a low-frequency cut-off filter of 0.08 mm was applied to the result processed in # 120,000, the surface roughness was about 4 nm. FIG. 5 shows an example.

In the range of this experiment, processing by constant pressure cutting and E
Compared to LID grinding, it can be seen that the surface roughness obtained with a # 4000 grindstone of similar size is much better with the former. In order to increase efficiency, it is considered that rough finishing should use larger abrasive grains than grinding.

(Working surface roundness) In a forced cutting method such as grinding, the processing accuracy is greatly affected by the accuracy of the machine. On the other hand, in the machining method using constant-pressure cutting, the machining accuracy depends on the uniformity of machining conditions such as speed, pressure, and machining time during machining, in addition to the shape accuracy and tool shape accuracy in the previous process. In this experiment, the rotation speed, the load, and the angular velocity of the swing table were kept constant with respect to the entire swing range of the swing table. The roundness measurement was performed on three parallel surfaces using a roundness measuring machine. 2CR for the filter
A cutoff of 75,50 peaks / revolution was used. FIG. 6 shows the measurement results. From this figure, it can be seen that the roundness could be attained to 0.5 μm or less.

(Effect of Grinding Stone Diameter on Contact State of Grinding Stone and Workpiece) In the processing of a spherical surface, it is difficult to form a tool having a spherical surface into a radius of curvature similar to that of the workpiece. In polishing using an elastic polisher, the polisher is deformed in accordance with pressure and conforms to a processing surface, so that the influence of a difference in tool shape is reduced. In contrast, in fixed abrasive processing using a non-deformable grindstone, the difference in the radius of curvature between the workpiece and the grindstone has a great effect on the processing.

FIGS. 7 and 8 illustrate the effect of the case where the grindstone diameter is larger (FIG. 7) and smaller (FIG. 8). In the case of FIG. 7, at the beginning of machining, the inner edge of the grinding wheel working surface contacts the workpiece with a line (A). As the processing progresses, the grindstone gradually wears, and the contact area between the two expands to the outer edge to form an annular band (B). Workpiece (C)
By tilting to the angle shown in (1), a portion corresponding to the outside of the grinding wheel working surface cannot be machined. In the processing in the previous step, a part other than the finishing range was not processed, so that part protrudes from the spherical surface. Therefore, when the workpiece is further inclined, as shown in (D), the workpiece and the grindstone come into a bad state in which they are in point contact with each other, and the non-uniformity of the pressure distribution due to this may deteriorate the shape accuracy. Can be

On the other hand, when a grindstone having a curvature slightly smaller than the diameter of the workpiece is used (FIG. 8), when the machining starts,
The outer edge of the grinding wheel working surface contacts the workpiece (E). As the processing proceeds, the contact zone extends to the center of the grinding wheel (F). In such a contact state, processing in a required finishing range can be realized (G).

Comparing the two cases, the latter case (when using a grindstone having a curvature slightly smaller than the diameter of the work) not only can process the whole work, but also increases the actual processing speed of the grindstone and increases efficiency. Improvement can be achieved. Also, when the workpiece is completely formed into a spherical surface in the molding step, the inclination angle required for the workpiece is reduced. However, it should be noted that the center of the workpiece cannot be machined.

As described above, in the embodiment of the present invention, the finishing of the zirconia ceramic artificial hip joint head by cutting at a constant pressure was attempted using the fixed abrasive processing method. As a result, (1) Within the experimental conditions, # 4000, # 8000,
# 40000, # 120,000 (each having an average particle size of 4.
For the four types of diamond grindstones (1, 1.8, 0.3, 0.13 μm), the machined surface roughness showed a better tendency as the size of the abrasive grains became smaller, but the difference was not large. Was. (2) The final result is a surface roughness of 4 nmRa and a roundness of 0.
Good results of 5 μm were obtained. (3) The magnitude of the radius of curvature of the concave spherical grindstone with respect to the convex processing surface has a great influence on the state of contact between them. The use of a grindstone with a radius of curvature allows the entire processing surface to be machined, and also improves efficiency.

It should be noted that the present invention is not limited to the above-described embodiment, and may be variously modified without departing from the gist of the present invention.

[0050]

As described above, according to the method and apparatus for grinding a spherical surface of the present invention, the grinding step (A) and the electrolytic dressing step (B) are performed alternately, so that the grinding step (A) and the electrolytic dressing step (B) are performed in comparison with the metal. Ceramics, which are hard and brittle,
It has excellent effects such as processing into a spherical surface with higher smoothness and higher precision than metal.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a spherical grinding apparatus according to the present invention.

FIG. 2 is a perspective view of a grindstone used in the apparatus of the present invention.

FIG. 3 is a roughness profile according to the embodiment of the present invention.

FIG. 4 is a diagram showing a change in surface roughness with respect to an abrasive grain size.

FIG. 5 is a diagram showing an example of the obtained surface roughness.

FIG. 6 is a diagram showing the results of roundness measurement.

FIG. 7 is a diagram showing a processing state when a grindstone diameter is larger than a workpiece diameter;

FIG. 8 is a diagram showing a processing state when a grindstone diameter is smaller than a workpiece diameter;

FIG. 9 is a schematic view showing the structure of an artificial joint.

FIG. 10 is a diagram showing an example of the shape and dimensions of a head constituting an artificial joint.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Head (work), 1a spherical surface, 2 stems, 3 sockets, 12 work swing rotation device, 12a rotation drive device, 12b swing mechanism, 14 conductive grindstone, 14a
Concave spherical surface, 14b concave hole, 14c liquid groove, 16 grinding wheel rotation drive device, 16a flexible joint (adapter), 16b drive shaft (spindle), 17 cathode, 1
7a hemispherical surface, 17b liquid flow path, 18 electrolytic dressing device, 18a power supply device, 18b brush, 18c
Power supply line, 19 conductive liquid supply device, 20 position shift device

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Weimin Hayashi 2-1 Hirosawa, Wako-shi, Saitama Pref. RIKEN (72) Inventor Toshio Kasai 323-37 Tsukamoto, Urawa-shi, Saitama Pref. 4-3-8 Bessho, Urawa-shi, Iwate F-term (reference) 3C047 AA25 3C049 AA02 AA11 AA16 AA19 AB01 AB06 BA09 BC01 BC02 CB01

Claims (8)

[Claims] 1. A work (1) having a spherical surface (1a) is rotationally driven about a rotation axis z passing through the center O and orthogonal to the horizontal axis y while swinging about a horizontal axis y passing through the center O of the spherical surface. At the same time, a conductive grindstone (14) having a concave spherical surface (14a) fitted to the spherical surface (1a) of the work is swingably supported along the spherical surface (1a) of the work and fixed toward the work. A grinding step (A) of applying a load and rotating around a vertical axis passing through the center of the concave spherical surface (14a) to grind the workpiece; Dressing step of positioning the cathode (17) by providing a constant gap between the concave spherical surface (14a) and rotating the concave spherical surface (14a) while rotating around a vertical axis passing through the center of the electrode. (B), wherein the grinding Step (A) and electrolytic dressing implementing steps (B) alternately, grinding method sphere, characterized in that. 2. A work (1) having a spherical surface (1a) is rotated about a rotational axis z passing through the center O and orthogonal to the horizontal axis y while swinging about a horizontal axis y passing through the center O of the spherical surface. A work oscillating rotation device (12), and a concave spherical surface (14a) fitted to the spherical surface (1a) of the work.
A conductive grindstone (14) having the following formula: and the conductive grindstone (14) is swingably supported along the spherical surface (1a) of the work, applies a constant load toward the work, and has a concave spherical surface (14a). A grindstone rotation drive device (16) that rotates around a vertical axis passing through the center of the wheel, and a cathode (17) that fits with the concave spherical surface (14a) of the grindstone (14) and has a certain gap therebetween. An electrolytic dressing device (18) for electrolytically dressing a concave spherical surface (14a) with the cathode; and a grinding wheel or a workpiece between a grinding position for grinding a workpiece with the grinding wheel and a dressing position for electrolytically dressing a grinding stone with the cathode. And a position shift device (20) for moving the cathode. 3. The conductive grindstone (14) has a concave spherical surface (14a) fitted to a spherical surface (1a) of a work, and a concave surface provided at an intersection of the concave spherical surface (14a) and the vertical axis. The spherical grinding apparatus according to claim 1, further comprising a hole (14b) and a liquid groove (14c) penetrating from the concave hole (14b) to an outer peripheral portion. 4. A flexible joint (16a) for supporting a conductive grindstone (14) so as to swing along a spherical surface (1a) of a work, said flexible joint (16a). And a drive shaft (16b) that applies a constant load toward the workpiece and rotates around a vertical axis passing through the center of the concave spherical surface (14a).
The grinding apparatus for a spherical surface according to claim 1, wherein: 5. A rotation drive device (12a) for rotating the work swing rotation device (12) about a rotation axis z passing through the center O of the spherical surface of the work (1) and orthogonal to the horizontal axis y.
The spherical grinding apparatus according to claim 1, further comprising: a swing mechanism (12b) for swinging the rotary drive device about a horizontal axis y passing through the center O of the spherical surface. 6. The grinding wheel (14), wherein the cathode (17) is
A concave hemispherical surface (17a) facing the concave spherical surface (14a), and a liquid flow path (17b) for supplying a conductive liquid from the center toward the center of the grindstone. Item 2. A spherical grinding device according to Item 1. 7. The electrolytic dressing device (18) comprises:
A conductive liquid supply device (19) for supplying a conductive liquid between the conductive grindstone and the cathode, and a power supply device (18a) for applying the conductive grindstone to the plus and applying the cathode to the minus. The grinding apparatus for a spherical surface according to claim 1, wherein: 8. The position shift device (20) includes a work swing rotation device (12) and an electrolytic dressing device (18).
2. The spherical grinding apparatus according to claim 1, wherein the grinding table comprises a moving table mounted at a distance and an NC drive unit for numerically controlling the moving table in at least the xz-axis direction.