Grinding method

Abstract

A work (1) is rotationally symmetric with respect to an axis (L0), and a section of a surface (5) thereof to be polished which is formed by cutting the surface (5) along a virtual plane containing the axis (L0) includes a circular arc (5a) which extends from the intersection with the axis (L0) toward one side of the axis (L0) over an angle exceeding 120°. When polishing the work (1) with a rotating brush (10), the work (1) is rotated around the axis (L0) and, simultaneously therewith, the rotating brush (10) is rotated and pressed against the surface (5) to be polished and is moved along the circular arc (5a) while the rotation axis (L1) of the rotating brush (10) is kept perpendicular to the contact surface of the surface (5) to be polished. The rotational direction (R2) of the rotating brush (10) is opposite to the rotational direction (R1) of the work (1) in the forward side along the moving direction (M1) of the rotating brush (10), when the surface (5) to be polished and the rotating brush (10) are viewed from the rotation axis (L1) direction along the rotation axis (L1).

Description

[Technical Field]

[0001] The present invention relates to a polishing method for polishing a spherical portion of a workpiece using a rotating brush. [Background Art]

[0002] A polishing method for polishing the surface of a rotationally symmetric workpiece with a polishing tool is described in Patent Document 1. In this document, the workpiece is a lens, and the surface to be polished of the workpiece is a curved surface protruding toward one side in the axial direction along the central axis. The polishing tool includes an annular processing working portion in which abrasive grains are embedded in an elastic body. The elastic body is rubber, resin, or sponge. When polishing the surface to be polished, the workpiece is rotated about the central axis. Further, while rotating the polishing tool about the central axis of the processing working portion, the processing working portion is pressed against the surface to be polished and moved along the surface to be polished.

[0003] As a polishing tool, a rotating brush provided with an abrasive bundle is known. The rotating brush described in Patent Document 2 includes a brush body having an abrasive bundle and an abrasive bundle holder that holds the base end portion of the abrasive bundle, and a brush case that surrounds the brush body from the radially outer side. The abrasive bundle is formed by bundling linear abrasives obtained by impregnating an aggregate of inorganic long fibers such as alumina fibers with resin and curing the resin. The brush case holds the brush body in a state where the tip end portion of the abrasive bundle is exposed to the outside. [Prior Art Documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Unexamined Patent Publication No. 2011-36974 [Patent Document 2] Japanese Unexamined Patent Publication No. 2009-50967 [Summary of the Invention] [Problem to be Solved by the Invention]

[0005] It is conceivable to polish the surface of a rotationally symmetrical workpiece using a rotary brush as described in Patent Document 2. For example, it is conceivable to polish a workpiece with a substantially spherical surface using a rotary brush. However, such a polishing method has not been proposed.

[0006] In light of the above problems, no polishing method has been proposed for polishing the spherical portion of a workpiece using a rotating brush. [Means for solving the problem]

[0007] To solve the above problems, the present invention provides a method for polishing a workpiece that is rotationally symmetric about a predetermined axis, and in which the cross-section of the surface to be polished, cut by a virtual plane including the axis, has an arc of more than 120° toward one side of the axis from a reference point where it intersects the axis, a rotary brush is used as the polishing tool, the workpiece is rotated about the axis, the rotary brush is rotated and pressed against the surface to be polished, the rotation axis of the rotary brush is moved along the arc of the cross-section while maintaining the rotation axis of the rotary brush perpendicular to the contact surface of the surface to be polished, and when the surface to be polished and the rotary brush are viewed from the direction of the rotation axis along the rotation axis, the rotation direction of the rotary brush is The moving rotating brush The front side is characterized by being opposite to the direction of rotation of the workpiece.

[0008] In this invention, when polishing the surface of a workpiece, the workpiece and the rotating brush are rotated. The rotating brush is pressed against the surface to be polished, and while maintaining the rotation axis of the rotating brush perpendicular to the contact surface of the surface to be polished, it is moved along the arc of the cross-section. Here, the rotation direction of the workpiece and the rotation direction of the rotating brush are defined as the direction of rotation when viewing the surface to be polished and the rotating brush from the rotation axis along the rotation axis. The moving rotating brush They face each other at the front. In this way, the rotation direction of the workpiece and the rotation direction of the rotating brush are aligned. Moving rotating brush Compared to when the brushes are facing the same direction at the front, the brushes grip the surface being polished more effectively. Therefore, it is easier to polish spherical surfaces.

[0009] In the present invention, the rotating brush is rotated in a first rotational direction and pressed against the surface to be polished, moving along the arc of the cross section from a position offset to the other side of the axis from the reference point, via the reference point, to a vertex that is 90° away from the reference point toward one side of the axis, then the rotating brush is moved away from the surface to be polished, and thereafter the rotating brush is rotated in a second rotational direction opposite to the first rotational direction and pressed against the surface to be polished, moving from the end of the arc of the cross section opposite to the reference point to the vertex.

[0010] Here, if the surface to be polished of a workpiece is formed by cutting by contacting a cutting tool with the outer circumferential surface of the workpiece, which rotates around its axis, the sphericity of the polished portion may decrease beyond a predetermined tolerance range due to the precision of the cutting process. For example, the cross-section of the surface to be polished may be an ellipse shape, with the direction perpendicular to the axis being longer than the direction in which the axis is aligned. In this case, when the rotating brush is moved from the reference point to the end of the arc of the cross-section of the surface to be polished, when the rotating brush passes the apex, the amount of cut on the front side in the direction of movement of the rotating brush decreases compared to the amount of cut on the rear side in the direction of movement of the rotating brush. Therefore, when the rotating brush polishes the area beyond the apex of the arc of the cross-section to the end, the polishing force of the rotating brush on the surface to be polished may decrease. To address this problem, in the present invention, when the rotating brush polishes the area beyond the apex of the arc of the cross-section to the end, the rotation direction of the rotating brush is set to a second rotation direction opposite to the first rotation direction. Furthermore, the direction of movement of the rotating brush is set to move from the end towards the apex, so that the rotation direction of the workpiece and the rotation direction of the rotating brush are opposite each other on the front side of the direction of movement of the rotating brush. This prevents the amount of cutting on the front side of the direction of movement of the rotating brush from being less than the amount of cutting on the rear side of the direction of movement of the rotating brush, thus preventing a decrease in the polishing force of the polished surface by the rotating brush. Therefore, even if the cross-section of the polished surface is an elongated ellipse in the direction perpendicular to the axis, the polishing accuracy can be maintained in the same way as when the cross-section of the polished surface is circular.

[0011] In the present invention, the rotating brush is rotated in a first rotational direction and pressed against the surface to be polished, moving along the arc of the cross section from a vertex 90° away from the reference point toward one side of the axis, via the reference point, to a position offset to the other side of the axis from the reference point, then the rotating brush is moved away from the surface to be polished, and thereafter the rotating brush is rotated in a second rotational direction opposite to the first rotational direction and pressed against the surface to be polished, moving from the vertex to the end of the arc of the cross section opposite to the reference point.

[0012] Here, if the surface to be polished of a workpiece is formed by cutting by contacting a cutting tool with the outer circumferential surface of the workpiece, which rotates around an axis, the cross-section of the surface to be polished may have an elliptical shape, with the axial direction being longer than the direction perpendicular to the axis. In this case, when the rotating brush is moved from the reference point to the end of the arc, the amount of cutting on the front side in the direction of movement of the rotating brush decreases compared to the amount of cutting on the rear side in the direction of movement of the rotating brush, from the reference point to the apex. Therefore, when the rotating brush polishes the surface to be polished on the side of the apex of the arc of the cross-section of the surface to be polished that is closer to the reference point, the polishing force of the rotating brush on the surface to be polished may decrease. To address this problem, in the present invention, when the rotating brush polishes the surface of the cross-section that is closer to the reference point than the apex, the rotation direction of the rotating brush is set as the first rotation direction, and the direction of movement of the rotating brush is set as the direction from the apex to the reference point. Furthermore, when the rotating brush polishes the surface of the cross-section that is closer to the end than the apex, the rotation direction of the rotating brush is set as the second rotation direction, and the direction of movement of the rotating brush is set as the direction from the apex to the end. This prevents the amount of cutting at the front of the rotating brush in the direction of movement from decreasing compared to the amount of cutting at the rear of the rotating brush in the direction of movement, thus preventing a decrease in the polishing force of the polished surface by the rotating brush. Therefore, even when the cross-section of the polished surface is an elongated ellipse in the axial direction, the polishing accuracy can be maintained as if the cross-section of the polished surface were circular.

[0013] In the present invention, the rotating brush can be rotated in the first rotational direction and pressed against the surface to be polished, and moved from a position offset to the other side of the axis from the reference point, through the reference point, along the arc of the cross-section, to the end of the arc of the cross-section opposite to the reference point. That is, if the sphericity of the part to be polished is high and the cross-section of the surface to be polished is circular, the amount of cutting in the front side in the direction of movement of the rotating brush does not change even if the rotating brush goes beyond the apex of the arc in the cross-section of the surface to be polished. Therefore, the polishing force of the surface to be polished by the rotating brush can be maintained while keeping the rotational direction of the rotating brush as the first rotational direction and the direction of movement of the rotating brush in the direction from the reference point to the end.

[0014] In the present invention, the rotational speed of the workpiece, which rotates the workpiece around its axis, is lower than the rotational speed of the brush, which rotates the rotating brush around its axis. It is desirable that the brush rotational speed divided by the workpiece rotational speed is not divisible. This prevents the occurrence of striped polishing patterns on the polished surface. That is, if the brush rotational speed is divisible by the workpiece rotational speed, band-shaped polishing marks will occur on the polished surface at equal angular intervals around the axis. In contrast, if the brush rotational speed is not divisible by the workpiece rotational speed, the occurrence of such band-shaped polishing marks can be avoided.

[0015] In the present invention, the rotating brush comprises a bundle of abrasive materials consisting of a plurality of linear abrasive materials, and an abrasive bundle holder that holds the base end portion of the abrasive bundle, wherein the central portion of the tip surface of the abrasive bundle is recessed, and the tip portion of the abrasive bundle can be brought into contact with the surface to be polished. In this way, it is easy to bring the entire tip surface of the abrasive bundle into contact with the surface to be polished, making it easier to ensure the polishing force of the surface to be polished by the rotating brush.

[0016] In the present invention, the rotating brush comprises a plurality of abrasive material bundles arranged in an annular shape, and an abrasive material bundle holder that holds the base ends of the plurality of abrasive material bundles, and each abrasive material bundle comprises a plurality of linear abrasive materials, and the respective tip portions of the plurality of abrasive material bundles can be brought into contact with the surface to be polished. In such a rotating brush, there are no abrasive material bundles at the center of rotation of the brush where the peripheral speed is zero during polishing. Here, when the linear abrasive materials constituting the abrasive material bundles come into contact with the surface to be polished of the workpiece at zero peripheral speed while the brush is pressed against the surface to be polished, the linear abrasive materials are prone to breaking. However, if the rotating brush is equipped with a plurality of abrasive material bundles arranged in an annular shape, the occurrence of such a situation can be avoided.

[0017] In the present invention, the rotating brush comprises an annular abrasive bundle consisting of a plurality of linear abrasives arranged in an annular shape, and an abrasive bundle holder that holds the base end portion of the abrasive bundle, and the tip portion of the abrasive bundle can be brought into contact with the surface to be polished. In such a rotating brush, there are no linear abrasives at the center of rotation of the brush where the peripheral speed is zero during polishing. Here, if a linear abrasive with zero peripheral speed comes into contact with the surface to be polished of the workpiece while the brush is pressed against the surface to be polished, the linear abrasive is prone to breaking. However, if the rotating brush is equipped with an abrasive bundle consisting of a plurality of linear abrasives arranged in an annular shape, the occurrence of such a situation can be avoided.

[0018] In the present invention, the rotating brush comprises a brush body having an abrasive bundle comprising a plurality of linear abrasive materials and an abrasive bundle holder that holds the base end portion of the abrasive bundle, and a sleeve that surrounds the abrasive bundle and the abrasive bundle holder with the tip portion of the abrasive bundle exposed to the outside, and faces the abrasive bundle with a predetermined radial gap, so that the tip portion of the abrasive bundle comes into contact with the surface to be polished. In this way, the sleeve can suppress the spreading of the abrasive bundle outward, making it easier to ensure the polishing force of the surface to be polished by the rotating brush. In addition, since the movement of the linear abrasive materials constituting the abrasive bundle can be suppressed, it is possible to prevent or suppress the formation of scratches on the surface to be polished of the workpiece.

[0019] In the present invention, the workpiece is an artificial joint, the rotating brush includes an abrasive bundle composed of a plurality of linear abrasive materials, and the linear abrasive material may include an aggregated yarn of inorganic long fibers and a resin impregnated into the aggregated yarn. A rotating brush provided with such a bundle of linear abrasive materials has high grinding power. Therefore, when such a rotating brush is used, an artificial joint made of cobalt, chromium, titanium alloy or the like can be polished. [BRIEF DESCRIPTION OF THE DRAWINGS]

[0020] [Figure 1] FIG. 1 is a side view of a workpiece that is an object of the polishing method of the present invention. [Figure 2] FIG. 2 is a perspective view of a rotating brush used for polishing a workpiece. [Figure 3] FIG. 3 is a cross-sectional view of the rotating brush. [Figure 4] FIG. 4 is an explanatory view of a first polishing method. [Figure 5] FIG. 5 is an explanatory view showing the rotation direction of a workpiece, the rotation direction of a rotating brush, and the moving direction of the rotating brush in the first polishing method. [Figure 6] FIG. 6 is an explanatory view of a second polishing method. [Figure 7] FIG. 7 is an explanatory view showing the rotation direction of a workpiece, the rotation direction of a rotating brush, and the moving direction of the rotating brush in the second polishing method. [Figure 8] FIG. 8 is an explanatory view of problems that occur when the first polishing method is adopted. [Figure 9] FIG. 9 is an explanatory view of a third polishing method. [Figure 10] FIG. 10 is an explanatory view showing the rotation direction of a workpiece, the rotation direction of a rotating brush, and the moving direction of the rotating brush in the third polishing method. [Figure 11] FIG. 11 is an explanatory view of problems that occur when the first polishing method is adopted. [Figure 12] FIG. 12 is an explanatory view of another example of a rotating brush. [Figure 13] FIG. 13 is an explanatory view of still another example of a rotating brush. [MODE FOR CARRYING OUT THE INVENTION]

[0021] The polishing method according to an embodiment of the present invention will be described below with reference to the drawings. Figure 1 is a side view of a workpiece to which the polishing method of the present invention is applied. Figure 2 is a perspective view of a rotating brush used for polishing the workpiece. Figure 3 is a cross-sectional view of the rotating brush.

[0022] (Work) The workpiece 1 to be polished in this example is an artificial joint. More specifically, workpiece 1 in this example is an artificial hip joint. Workpiece 1 is made of metal, consisting of cobalt, chromium, titanium alloy, etc. As shown in Figure 1, workpiece 1 has a shape that is rotationally symmetric about a predetermined axis L0. Workpiece 1 has a rod-shaped portion 2, a disc portion 3, and a spherical portion 4 in this order, moving from one side to the other in the axial direction X along axis L0. The surface 5 to be polished of workpiece 1 is the outer circumferential surface of the spherical portion 4. The cross section obtained by cutting the surface to be polished 5 with a virtual plane including axis L0 has an arc 5a exceeding 120° from a reference point P1 where the surface to be polished 5 and axis L0 intersect toward one side of axis L0. Here, the cross section obtained by cutting workpiece 1 with a virtual plane including axis L0 has the same shape as the side view shown in Figure 1.

[0023] In this example, the diameter of the spherical portion of workpiece 1 ranges from 20 mm to 40 mm. The arc 5a, formed by cutting the surface to be polished 5 with a virtual plane, extends from the reference point P1 to a position 135° in the direction toward one side of the axis L0. When polishing the surface to be polished 5, the rod-shaped portion 2 of the workpiece is chucked to the spindle of the machine tool.

[0024] (Rotating brush) In the polishing method of this example, the polishing tool used to polish the workpiece 1 is a rotary brush 10. As shown in Figures 2 and 3, the rotary brush 10 comprises a brush body 11 and a brush case 12 that holds the brush body 11. The rotary brush 10 also includes fixing screws 13 for securing the brush body 11 to the brush case 12.

[0025] The brush body 11 has an abrasive material bundle 15 and an abrasive material bundle holder 16 that holds the base end portion of the abrasive material bundle 15. The abrasive material bundle 15 is made by bundling together a plurality of linear abrasive materials 17. The linear abrasive material 17 is made by impregnating and hardening a binder resin into a bundle of inorganic long fibers. That is, the linear abrasive material 17 comprises a bundle of inorganic long fibers such as alumina long fibers and a resin that impregnates the bundle of fibers. The inorganic long fibers are alumina long fibers, silicon carbide fibers, boron fibers, or glass fibers.

[0026] As shown in Figure 3, the abrasive bundle holder 16 comprises a cylindrical portion 18 that surrounds the base end portion of the abrasive bundle 15 from the outer circumference, and a bottom portion 19 that seals one opening of the cylindrical portion 18. The bottom portion 19 is disc-shaped. The inner circumference of the cylindrical portion 18 and the end face of the bottom portion 19 on the side of the cylindrical portion 18 constitute an abrasive bundle holding hole 31 that holds the base end portion of the abrasive bundle 15. The end of the abrasive bundle 15 inserted into the cylindrical portion 18 abuts against the bottom portion 19. The abrasive bundle 15 is fixed to the abrasive bundle holder 16 by adhesive injected into the abrasive bundle holding hole 31. The abrasive bundle 15 becomes a circular bundle when held in the abrasive bundle holding hole 31. The bottom portion 19 is provided with a screw hole 20 that penetrates the bottom portion 19 radially. The screw hole 20 is used to fix the brush body 11 to the brush case 12.

[0027] In this example, the abrasive bundle 15 has a concave central portion of its tip surface 15a. Therefore, as shown in Figure 3, when the abrasive bundle 15 is cut along the rotation axis L1 of the rotating brush 10, the tip surface 15a has a cross-sectional shape of an arc 5a that is concave towards the base end of the abrasive bundle 15. The curvature of the arc 5a corresponds to the curvature of the polishing surface 5 of the workpiece 1. It is desirable that the diameter of the abrasive bundle 15 be greater than 1 / 3 and less than or equal to 1 / 2 of the diameter of the spherical portion 4 of the workpiece 1.

[0028] As shown in Figure 2, the brush case 12 comprises a sleeve 21, a circular sealing portion 22 that seals the rear end of the sleeve 21, and a shank 23 that extends from the center of the sealing portion 22 toward the opposite side of the sleeve 21. The sleeve 21 is provided with an elongated hole 24 that extends in the axial direction X. The axis of the shank 23 is the rotation axis L1 of the rotating brush.

[0029] When holding the brush body 11 in the brush case 12, the brush body 11 is inserted inside the sleeve 21, and the sleeve 21 surrounds the abrasive bundle 15 and the abrasive bundle holder 16. The tip portion of the abrasive bundle 15 is exposed to the outside of the sleeve 21 by a predetermined distance. In this state, the fixing screw 13 is screwed into the screw hole 20 of the abrasive bundle holder 16 of the brush body 11 through the elongated hole 24 of the sleeve 21.

[0030] As shown in Figure 3, when the fixing screw 13 is screwed into the screw hole 20, the fixing screw 13 penetrates the abrasive bundle holder 16 in a direction perpendicular to the axis L0, and its tip abuts against the opposing surface portion on the inner circumferential wall surface of the sleeve 21 that faces the elongated hole 24. If the fixing screw 13 is screwed in further from this state, the abrasive bundle holder 16 is pressed against the circumferential wall portion on the inner circumferential wall surface of the sleeve 21 that faces the opposing surface (the circumferential wall portion including the opening edge of the elongated hole 24). As a result, the brush body 11 is fixed to the brush case 12. Once the brush body 11 is fixed to the brush case 12, the sleeve 21 faces the abrasive bundle 15 with a predetermined gap in the radial direction.

[0031] Here, the rotating brush 10 is rotated around the rotation axis L1 when polishing the workpiece 1. If the abrasive bundle 15 of the rotating brush 10 wears down due to polishing the workpiece 1, the fixing screw 13 is loosened and the brush body 11 is moved to the opposite side of the brush case 12 from the shank 23, exposing the tip of the abrasive bundle 15 from the sleeve 21 by a predetermined distance. After that, the fixing screw 13 is screwed in to fix the brush body 11 to the brush case 12.

[0032] (polishing method) Next, a method for polishing the workpiece 1 using a rotating brush 10 will be described. Figure 4 is an explanatory diagram of the first polishing method. Figure 5 is an explanatory diagram of the relationship between the rotation direction of the workpiece 1, the movement direction of the rotating brush 10, and the rotation direction of the rotating brush 10 in the first polishing method. Figure 6 is an explanatory diagram of the second polishing method. Figure 7 is an explanatory diagram of the relationship between the rotation direction of the workpiece 1, the movement direction of the rotating brush 10, and the rotation direction of the rotating brush 10 in the second polishing method. Figure 8 is an explanatory diagram of the problems that occur when the first polishing method is adopted when the workpiece 1 has an elongated elliptical shape in the direction perpendicular to the axis L0. Figure 9 is an explanatory diagram of the third polishing method. Figure 10 is an explanatory diagram of the relationship between the rotation direction of the workpiece 1, the movement direction of the rotating brush 10, and the rotation direction of the rotating brush 10 in the third polishing method. Figure 11 is an explanatory diagram of the problems that occur when the first polishing method is adopted when the workpiece 1 has an elongated elliptical shape in the axial direction X.

[0033] As shown in Figures 4 and 7, when polishing the workpiece 1, the rod-shaped portion 2 of the workpiece 1 is chucked on the spindle of the machine tool and rotated around the axis L0. The rotating brush 10's shank 23 is chucked on the head of the machine tool and rotated around the rotation axis L1. The rotating brush 10 is also pressed against the polishing surface 5 of the workpiece 1 by the machine tool, and moved along the arc 5a of the cross-section of the polishing surface 5 while maintaining the rotation axis L1 perpendicular to the contact surface of the polishing surface 5.

[0034] Here, rotating the rotating brush 10 and pressing it against the surface to be polished 5 means bringing the abrasive bundle 15 of the rotating brush 10 into contact with the surface to be polished 5 with a predetermined depth of cut. The rotation direction R1 of the workpiece 1 and the rotation direction R2 of the rotating brush 10 face each other on the front side of the direction of movement M of the rotating brush 10 when viewing the surface to be polished 5 and the rotating brush 10 from the rotation axis direction Y along the rotation axis L1.

[0035] The rotational speed of the workpiece 1 around its axis L0 is lower than the rotational speed of the rotating brush 10 around its axis L1. Furthermore, the brush rotational speed and the workpiece rotational speed have an indivisible relationship when the brush rotational speed is divided by the workpiece rotational speed. Here, the greater the speed difference between the workpiece rotational speed and the brush rotational speed, the better. The feed rate for moving the rotating brush 10 along the arc 5a is set based on the workpiece rotational speed, etc. The feed rate is constant.

[0036] In this example, the workpiece rotation speed is 300 revolutions / minute. The rotation speed of the rotating brush 10 is 10,000 revolutions / minute. Therefore, when the brush rotation speed is divided by the workpiece rotation speed, the result is not whole. The feed rate of the rotating brush 10 is 0.4 mm / rev relative to the workpiece rotation speed.

[0037] Here, the polishing method for polishing the workpiece 1 using the rotating brush 10 includes a first polishing method in which the direction of movement M1 and the direction of rotation R2 of the rotating brush 10 are not changed during the polishing of the surface to be polished 5, and first and second polishing methods in which the direction of movement M1 and the direction of rotation R2 of the rotating brush 10 are changed during the polishing of the surface to be polished 5. In all of the first polishing direction, second polishing method, and third polishing method, the workpiece rotation speed, the rotating brush rotation speed, and the feed speed of the rotating brush 10 are the same.

[0038] The first, second, and third polishing methods are described in detail below. In the following description, the point where the polishing surface 5 of workpiece 1 intersects with the axis L0 is defined as the reference point P1. Furthermore, the vertex P2 of the polishing surface 5 is defined as the position 90° away from the reference point P1 in one direction X along the arc 5a of the cross-section of the polishing surface 5. In addition, the end of the arc 5a of the cross-section of the polishing surface 5 opposite to the reference point P1 is defined as the end P3 of the polishing surface 5.

[0039] (First polishing method) The first polishing method is used when polishing multiple workpieces 1 in succession, and it has been confirmed in advance that the spherical portion 4 of all workpieces 1 has a high degree of sphericity. That is, it is used when the cross-section of the polishing surface 5 of the workpiece 1 has a circular shape that is within or below a predetermined tolerance range.

[0040] As shown in Figure 4, in the first polishing method, the workpiece 1 is rotated in a predetermined rotational direction R1. The rotating brush 10 is also rotated in the first rotational direction R2(1) and pressed against the polishing surface 5 of the rotating workpiece 1, and moved along the arc 5a of the cross-section from a position offset to the other side of the axis L0 from the reference point P1 on the polishing surface 5 of the workpiece 1, through the reference point P1, to the end point P3 (polishing process ST1). As shown in Figure 5, in the polishing process ST1, when the polishing surface 5 and the rotating brush 10 are viewed from the direction of the rotation axis L1 along the rotation axis L1 of the rotating brush 10, the first rotational direction R2(1) of the rotating brush 10 is opposite to the rotational direction R1 of the workpiece 1 on the front side of the movement direction M1 of the rotating brush 10 (the side where the vertex P3 is located).

[0041] Subsequently, polishing step ST1 is repeated a predetermined number of times. This completes the polishing of workpiece 1.

[0042] (Effects and Benefits) In this example, when polishing the surface 5 of workpiece 1, both workpiece 1 and the rotating brush 10 are rotated. The rotating brush 10 is pressed against the surface 5, and the rotation axis L1 of the rotating brush 10 is kept perpendicular to the contact surface of the surface 5, while moving along the arc 5a of the cross-section. Here, the rotation direction R1 of workpiece 1 and the rotation direction R2 of the rotating brush 10 are opposite to each other in front of the direction of movement M1 of the rotating brush 10 when viewed from the direction of rotation axis L1 along the rotation axis L1 of the workpiece 1 and the rotating brush 10 in front of the direction of movement M1 of the rotating brush 10. In this way, the brush bites into the surface 5 more firmly compared to when the rotation direction R1 of workpiece 1 and the rotation direction R2 of the rotating brush 10 are in the same direction in front of the direction of movement M1 of the rotating brush 10. Therefore, it is easy to polish the spherical surface 5.

[0043] In this example, polishing is started from a position offset by 5° from the reference point P1 to the other side of the axis L0. Therefore, the reference point P1 and its surroundings, where the peripheral speed is zero on the surface to be polished 1, can be polished sufficiently.

[0044] Furthermore, the rotational speed of the workpiece 1 around its axis L0 is lower than the rotational speed of the rotating brush 10 around its axis L1, and the brush rotational speed cannot be divided evenly by the workpiece rotational speed. This prevents the formation of striped polishing patterns on the polishing surface 5. In other words, when the brush rotational speed is divisible by the workpiece rotational speed, band-shaped polishing marks are formed at equal angular intervals around the axis L0 on the polishing surface 5. Conversely, when the brush rotational speed is not divisible by the workpiece rotational speed, the formation of such band-shaped polishing marks can be avoided.

[0045] In this example, the rotating brush 10 comprises a single abrasive bundle 15 consisting of multiple linear abrasive materials 17, and an abrasive bundle holder 16 that holds the base end portion of the abrasive bundle 15. The abrasive bundle 15 has a concave central portion of its tip surface 15a. The rotating brush 10 brings the tip portion of the abrasive bundle 15 into contact with the surface to be polished 5. This makes it easy to bring the entire tip surface 15a of the abrasive bundle 15 into contact with the surface to be polished 5, thus making it easier to ensure sufficient polishing force on the surface to be polished 5 by the rotating brush 10.

[0046] Furthermore, the rotating brush 10 includes a brush body 11 having an abrasive bundle 15 comprising a plurality of linear abrasive materials 17 and an abrasive bundle holder 16 that holds the base end portion of the abrasive bundle 15, and a sleeve 21 that surrounds the abrasive bundle 15 and the abrasive bundle holder 16 with the tip portion of the abrasive bundle 15 exposed to the outside, and faces the abrasive bundle 15 with a predetermined radial gap. The rotating brush 10 brings the tip portion of the abrasive bundle 15 into contact with the surface to be polished 5. In this example, the sleeve 21 can suppress the spreading of the abrasive bundle 15 outward, making it easier to ensure the polishing force of the surface to be polished 5 by the rotating brush 10. In addition, since the linear abrasive materials 17 constituting the abrasive bundle 15 can be suppressed from moving around, it is possible to prevent or suppress the formation of scratches on the surface to be polished 5 of the workpiece 1.

[0047] Furthermore, workpiece 1 is an artificial joint. The rotating brush 10 is equipped with a bundle of abrasive materials 15 consisting of multiple linear abrasive materials 17, and the linear abrasive material 17 comprises a bundle of inorganic long fibers and a resin impregnating the bundle of fibers. The rotating brush 10 equipped with such a bundle of linear abrasive materials 17 has high grinding power. Therefore, it can polish artificial joints made of cobalt, chromium, titanium alloy, etc.

[0048] (Second polishing method) When the polishing surface 5 of workpiece 1 is formed by cutting by contacting a cutting tool with the outer circumferential surface of workpiece 1, which rotates around the axis L0, the sphericity of the spherical portion 4 may decrease beyond a preset tolerance range due to the precision of the cutting process. Furthermore, when the sphericity decreases due to the precision of the cutting process, the cross-section of the polishing surface 5 of workpiece 1 tends to become an ellipse shape, with the Y direction perpendicular to the axis L0 being longer than the axial direction X. The second polishing method is used when polishing multiple workpieces 1, and there is a possibility that some of them may have such a shape.

[0049] As shown in Figure 6, in the second polishing method, first, the workpiece 1 chucked on the spindle of the machine tool is rotated in the rotational direction R1, and the rotating brush 10 chucked on the head of the machine tool is rotated in the first rotational direction R2(1). The rotating brush 10 is pressed against the polishing surface 5 of the rotating workpiece 1 and moved along the arc 5a of the cross-section of the polishing surface 5, from a position offset to the other side of the axis L0 from the reference point P1, through the reference point P1, to the vertex P2 (first polishing step ST11). In the second polishing direction, the rotational direction R1 of the workpiece 1 is the same as in the first polishing method.

[0050] Here, while the rotating brush 10 is moving, the rotation axis L1 of the rotating brush 10 is maintained perpendicular to the contact surface of the polishing surface 5. Also, as shown in Figure 7(a), the second rotation direction R2(2) of the rotating brush 10 is opposite to the rotation direction R1 of the workpiece 1 on the front side of the movement direction M1 of the rotating brush 10 (the side where the vertex P2 exists) when viewing the polishing surface 5 and the rotating brush 10 from the direction of the rotation axis L1 along the rotation axis L1 of the rotating brush 10.

[0051] Next, the rotating brush 10 is moved away from the polishing surface 5 (setting change step ST12).

[0052] Subsequently, the rotating brush 10 is rotated in the second rotation direction R2(2), which is opposite to the first rotation direction R2(1), and pressed against the surface to be polished 5, moving from the end P3 of the arc 5a to the apex P2 (second polishing step ST13). Therefore, the direction of movement M2 of the rotating brush 10 is opposite to the direction of movement M1 in the first polishing step. Note that the rotation direction R1 of the workpiece 1 remains unchanged.

[0053] Here, while the rotating brush 10 is moving, the rotation axis L1 of the rotating brush 10 is maintained perpendicular to the contact surface of the surface to be polished 5. Also, as shown in Figure 7(b), the second rotation direction R2(2) of the rotating brush 10 is opposite to the rotation direction R1 of the workpiece 1 on the front side of the movement direction M1 of the rotating brush 10 (the side where the vertex P2 is located) when viewing the surface to be polished 5 and the rotating brush 10 from the direction of the rotation axis L1 along the rotation axis L1 of the rotating brush 10.

[0054] Subsequently, the first polishing process ST11, the setting change process ST12, and the second polishing process ST13 are repeated a predetermined number of times. This completes the polishing of workpiece 1.

[0055] (Effects of the second polishing method) In the second polishing method, even if the cross-section of the surface to be polished 5 is an elliptical shape in which the direction Y perpendicular to the axis L0 is longer than the direction X perpendicular to the axis, due to the machining accuracy of the workpiece 1, the polishing accuracy can be maintained as in the case where the cross-section of the surface to be polished 5 is circular. This effect will be explained with reference to Figure 8. In Figure 8, the cross-section of the surface to be polished 5 of the workpiece 1 is an elliptical shape in which the direction Y perpendicular to the axis L0 is longer than the direction X perpendicular to the axis.

[0056] For example, suppose the cross-section of the surface to be polished 5 is an elongated ellipse in the direction Y perpendicular to the axis L0, and the first polishing method is adopted, in which the rotating brush 10 is moved from the reference point P1 to the end point P3 of the arc 5a to perform polishing. In this case, as shown in the simplified Figure 8, when the rotating brush 10 moving from the reference point P1 to the end point P3 of the arc 5a exceeds the vertex P2, the rear part of the abrasive bundle 15 in the direction of movement M1 contacts the surface to be polished 5, and the front part of the abrasive bundle 15 in the direction of movement M1 cannot contact the surface to be polished 5 to the same depth as the rear part. Therefore, the amount of cutting in the front part of the rotating brush 10 in the direction of movement decreases compared to the amount of cutting in the rear part of the rotating brush 10 in the direction of movement. Thus, when the rotating brush 10 polishes the area on the end point P3 side of the vertex P2 of the arc 5a of the cross-section, the polishing force on the surface to be polished 5 by the rotating brush 10 may decrease.

[0057] In contrast, in this example, when the rotating brush 10 polishes the area on the terminal side P3 rather than the vertex P2 in the arc 5a of the cross-section, the rotation direction R2 of the rotating brush 10 is set to the second rotation direction R2(2), which is opposite to the first rotation direction R2(1). Furthermore, the movement direction M1 of the rotating brush 10 is set to the direction from terminal P3 toward vertex P2, so that the rotation direction R1 of the workpiece 1 and the rotation direction R2 of the rotating brush 10 are opposite each other on the front side of the movement direction M1 of the rotating brush 10. This prevents the amount of cutting on the front side of the movement direction of the rotating brush 10 from decreasing compared to the amount of cutting on the rear side of the movement direction of the rotating brush 10, thus preventing a decrease in the polishing force on the polishing surface 5 by the rotating brush 10. Therefore, even if the cross-section of the polishing surface 5 is elliptical, the polishing accuracy can be maintained.

[0058] Furthermore, the second polishing method can achieve the same effects as the first polishing method.

[0059] (Third polishing method) When the polishing surface 5 of workpiece 1 is formed by cutting by contacting a cutting tool with the outer circumferential surface of workpiece 1, which rotates around the axis L0, the sphericity of the spherical portion 4 may decrease beyond a preset tolerance range due to the precision of the cutting process. Furthermore, when the sphericity decreases due to the precision of the cutting process, the cross-section of the polishing surface 5 of workpiece 1 may tend to become an elliptical shape with a longer axial direction X compared to the Y direction perpendicular to the axis L0. The third polishing method is used when polishing multiple workpieces 1 and there is a possibility that some of them have such a shape.

[0060] As shown in Figure 9, in the third polishing method, first, the workpiece 1 chucked on the spindle of the machine tool is rotated in rotational direction R1, and the rotating brush 10 chucked on the head of the machine tool is rotated in the first rotational direction R2(1). The rotating brush 10 is pressed against the polishing surface 5 of the rotating workpiece 1 and moved along the arc 5a of the cross-section of the polishing surface 5 from the apex P2, via the reference point P1, to a position offset to the other side of the axis L0 from the reference point P1 (first polishing step ST21). In the third polishing direction, the rotational direction R1 of the workpiece 1 is the same as in the first and second polishing methods. The first rotational direction R2(1) in the third polishing direction is the opposite rotational direction to the first rotational direction R2(1) in the second polishing method. Also, the movement direction M1 of the rotating brush 10 in the third polishing direction is the opposite direction to the movement direction M1 of the rotating brush 10 in the third polishing direction.

[0061] Here, while the rotating brush 10 is moving, the rotation axis L1 of the rotating brush 10 is maintained perpendicular to the contact surface of the surface to be polished 5. Also, as shown in Figure 10(a), the first rotation direction R2(1) of the rotating brush 101 is opposite to the rotation direction R1 of the workpiece 1 on the front side of the movement direction M1 of the rotating brush 10 (the side where the reference point P1 exists) when viewing the surface to be polished 5 and the rotating brush 10 from the direction of the rotation axis L1 along the rotation axis L1 of the rotating brush 10.

[0062] Next, the rotating brush 10 is moved away from the polishing surface 5 (setting change step ST22).

[0063] Subsequently, the rotating brush 10 is rotated in a second rotation direction R2(2), opposite to the first rotation direction R2(1), and pressed against the surface to be polished 5, moving from the apex P2 to the end P3 (second polishing step ST23). Here, the second rotation direction R2(2) in the third polishing direction is the opposite rotation direction to the second rotation direction R2(2) in the second polishing method. The movement direction M2 of the rotating brush 10 in the third polishing direction is the opposite direction to the movement direction M1 of the rotating brush 10 in the third polishing direction, and is the same direction as the movement direction M1 in the first polishing method. There is no change in the rotation direction R1 of the workpiece 1.

[0064] Here, while the rotating brush 10 is moving, the rotation axis L1 of the rotating brush 10 is maintained perpendicular to the contact surface of the polishing surface 5. Also, as shown in Figure 10(b), the second rotation direction R2(2) of the rotating brush 10 is opposite to the rotation direction R1 of the workpiece 1 on the front side of the movement direction M1 of the rotating brush 10 (the side where the end P3 is located), when viewing the polishing surface 5 and the rotating brush 10 from the direction of the rotation axis L1 along the rotation axis L1 of the rotating brush 10.

[0065] Subsequently, the first polishing process ST21, the setting change process ST22, and the second polishing process ST23 are repeated a predetermined number of times. This completes the polishing of workpiece 1.

[0066] (Effects of the third polishing method) In the third polishing method, even if the cross-section of the surface to be polished 5 is an elliptical shape with an elongated axial direction X due to the machining accuracy of the workpiece 1, the polishing accuracy can be maintained as if the cross-section of the surface to be polished 5 were circular. This effect will be explained with reference to Figure 11. In Figure 11, the cross-section of the surface to be polished 5 of the workpiece 1 is an elliptical shape with an elongated axial direction X compared to the direction Y perpendicular to the axis L0.

[0067] For example, suppose the cross-section of the surface to be polished 5 is an ellipse shape that is elongated in the axial direction X, and the first polishing method is adopted, and the rotating brush 10 is moved from the reference point P1 to the end point P3 of the arc 5a to perform polishing. In this case, as shown in the simplified Figure 11, between the reference point P1 and the vertex P2 of the arc 5a, when the rear part of the abrasive bundle 15 in the direction of movement M1 contacts the surface to be polished 5, the front part of the abrasive bundle 15 in the direction of movement M1 cannot contact the surface to be polished 5 to the same depth as the rear part. Therefore, the amount of cutting in the front part of the rotating brush 10 in the direction of movement is less than the amount of cutting in the rear part of the rotating brush 10 in the direction of movement. Consequently, when the rotating brush 10 polishes the area closer to the reference point P1 than to the vertex P2, the polishing force on the surface to be polished 5 by the rotating brush 10 may decrease.

[0068] In contrast, in this example, when the rotating brush 10 polishes the area closer to the reference point P1 than to the vertex P2, the direction of movement M1 of the rotating brush 10 is set to move from the vertex P2 toward the reference point P1. Furthermore, the rotation direction R1 of the workpiece 1 and the rotation direction R2 of the rotating brush 10 are set to be opposite directions in front of the direction of movement M1 of the rotating brush 10. This prevents the amount of cutting on the front side of the rotating brush 10 in the direction of movement from decreasing compared to the amount of cutting on the rear side of the rotating brush 10 in the direction of movement, thus preventing a decrease in the polishing force on the polishing surface 5 by the rotating brush 10. Therefore, even if the cross-section of the polishing surface 5 is elliptical, the polishing accuracy can be maintained.

[0069] Furthermore, the third polishing method can achieve the same effects as the first polishing method.

[0070] (modified version) The rotating brush 10 does not necessarily have to have a sleeve 21. For example, the brush body 11 can be used as the rotating brush.

[0071] Alternatively, when polishing the workpiece 1, the rotating brush 10 may be attached to the head of the machine tool via a floating holder, thereby pressing the rotating brush 10 against the polishing surface 5 with a predetermined biasing force.

[0072] (Another example of a rotating brush) Figure 12 is an explanatory diagram of another rotary brush used in the polishing method of this example. Figure 13 is an explanatory diagram of yet another rotary brush used in the polishing method of this example. The rotary brush 10A shown in Figure 12 comprises a plurality of abrasive material bundles 15 arranged in an annular shape, and an abrasive material bundle holder 16 that holds the base end portion of each of the plurality of abrasive material bundles 15. Each abrasive material bundle 15 comprises a plurality of linear abrasive materials 17. The abrasive material bundle holder 16 has a disc portion 32 with a plurality of abrasive material bundle holding holes 31 arranged in an annular shape on its front surface, and a shank portion 33 extending rearward from the center of the disc portion 32. Each abrasive material bundle 15 has its base end portion inserted into each abrasive material bundle holding hole 31 and is fixed to the abrasive material bundle holder 16 with adhesive. When polishing the workpiece 1, the tip portions of each of the plurality of abrasive material bundles 15 are brought into contact with the surface to be polished 5.

[0073] In the rotary brush 10A of this example, there is no abrasive material bundle 15 at the rotation center where the peripheral speed is zero during polishing. Here, when the brush is pressed against the surface to be polished 5, the linear abrasive material 17 constituting the abrasive material bundle 15 contacts the surface to be polished 5 of the workpiece 1 at zero peripheral speed, the linear abrasive material 17 is prone to breaking. However, if the rotary brush 10A is equipped with multiple abrasive material bundles 15 arranged in a ring shape, this situation can be avoided. In addition, the rotary brush 10A can also be equipped with a sleeve 21 that surrounds the multiple abrasive material bundles 15 and the abrasive material bundle holder 16 with the tip portions of each abrasive material bundle 15 exposed to the outside.

[0074] The rotating brush 10B shown in Figure 13 comprises an annular abrasive bundle 15 consisting of multiple linear abrasive materials 17 arranged in a ring, and an abrasive bundle holder 16 that holds the base end portion of the abrasive bundle 15. The abrasive bundle holder 16 has a disc portion 32 with a single annular abrasive bundle holding hole 31 on its front surface, and a shank portion 33 extending rearward from the center of the disc portion 32. The base end portions of the abrasive bundles 15 are inserted into each abrasive bundle holding hole 31 and fixed to the abrasive bundle holder 16 with adhesive. During polishing, the respective tip portions of the multiple abrasive bundles 15 are brought into contact with the surface to be polished 5.

[0075] With the rotary brush 10B, there are no linear abrasives 17 at the rotation center where the peripheral speed is zero during polishing. Therefore, it is possible to suppress the occurrence of breakage due to contact between the linear abrasive 17 at zero peripheral speed and the polishing surface 5 of the workpiece 1. Furthermore, if the rotary brush 10B is equipped with an annular abrasive bundle 15, the abrasive bundle 15 will continuously contact the polishing surface 5. Therefore, compared to the rotary brush 10A, in which multiple linear abrasives are arranged in an annular shape and the abrasive bundle 15 intermittently contacts the polishing surface 5 during polishing, it is easier to improve the surface roughness of the polishing surface 5 after polishing. In addition, the rotary brush 10B can also be equipped with a sleeve 21 that surrounds multiple abrasive bundles 15 and abrasive bundle holder 16 with the tip portions of each abrasive bundle 15 exposed to the outside.

Claims

1. In a method for polishing a workpiece that is rotationally symmetric about a predetermined axis, and in which the cross-section of the surface to be polished, cut by a virtual plane including the axis, has an arc exceeding 120° toward one side of the axis from a reference point where it intersects the axis, Using a rotating brush as a polishing tool, The workpiece is rotated around the axis, The rotating brush is rotated and pressed against the surface to be polished, and while maintaining the rotation axis of the rotating brush perpendicular to the contact surface of the surface to be polished, it is moved along the arc of the cross-section. A polishing method characterized in that, when the surface to be polished and the rotating brush are viewed from the direction of the rotation axis along the rotation axis, the direction of rotation of the rotating brush is opposite to the direction of rotation of the workpiece on the front side of the moving rotating brush.

2. The rotating brush is rotated in a first rotational direction and pressed against the surface to be polished, and moved along the arc of the cross section from a position offset to the other side of the axis from the reference point, via the reference point, to a vertex that is 90° away from the reference point toward one side of the axis, Next, the rotating brush is moved away from the surface to be polished. The polishing method according to claim 1, characterized in that the rotating brush is then rotated in a second rotation direction opposite to the first rotation direction and pressed against the surface to be polished, and moved from the end of the arc of the cross-section opposite to the reference point to the vertex.

3. The rotating brush is rotated in a first rotational direction and pressed against the surface to be polished, and moved along the arc of the cross section from a point 90° away from the reference point toward one side of the axis, via the reference point, to a position offset to the other side of the axis from the reference point, Next, the rotating brush is moved away from the surface to be polished. The polishing method according to claim 1, characterized in that the rotating brush is then rotated in a second rotation direction opposite to the first rotation direction and pressed against the surface to be polished, and moved from the apex to the end of the arc of the cross-section opposite to the reference point.

4. The polishing method according to claim 1, characterized in that the rotating brush is rotated in a first rotational direction and pressed against the surface to be polished, and is moved from a position offset to the other side of the axis from the reference point, through the reference point, along the arc of the cross-section, to the end of the arc of the cross-section opposite to the reference point.

5. The rotational speed of the workpiece that rotates the workpiece around the axis is lower than the rotational speed of the brush that rotates the rotating brush around the axis of rotation. The polishing method according to claim 1, characterized in that when the brush rotation speed is divided by the workpiece rotation speed, the result is not a whole number.

6. The rotating brush comprises a bundle of abrasive materials consisting of multiple linear abrasive materials, and a bundle of abrasive materials holder that holds the base end portion of the bundle of abrasive materials. The aforementioned abrasive material bundle has a recess in the central part of its tip surface. The polishing method according to claim 1, characterized in that the tip portion of the abrasive bundle is brought into contact with the surface to be polished.

7. The rotating brush comprises a plurality of abrasive material bundles arranged in an annular shape, and an abrasive material bundle holder that holds the base end portions of the plurality of abrasive material bundles. Each abrasive bundle comprises multiple linear abrasive materials, The polishing method according to claim 1, characterized in that the tip portions of each of the multiple abrasive material bundles are brought into contact with the surface to be polished.

8. The rotating brush comprises an annular abrasive bundle consisting of a plurality of linear abrasive materials arranged in a ring, and an abrasive bundle holder that holds the base end portion of the abrasive bundle. The polishing method according to claim 1, characterized in that the tip portion of the abrasive bundle is brought into contact with the surface to be polished.

9. The rotating brush comprises a brush body having an abrasive bundle comprising a plurality of linear abrasive materials and an abrasive bundle holder that holds the base end portion of the abrasive bundle, and a sleeve that surrounds the abrasive bundle and the abrasive bundle holder with the tip portion of the abrasive bundle exposed to the outside, and faces the abrasive bundle with a predetermined gap in the radial direction, The polishing method according to claim 1, characterized in that the tip portion of the abrasive bundle is brought into contact with the surface to be polished.

10. The aforementioned workpiece is an artificial joint, The aforementioned rotating brush is equipped with a bundle of abrasive materials consisting of multiple linear abrasive materials, The polishing method according to claim 1, characterized in that the linear abrasive material comprises a bundle of inorganic long fibers and a resin impregnating the bundle of fibers.

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