JP2007301645A - Burnishing tool for forming dimple - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a burnishing tool which forms dimples and performs burnishing by using a simple device. <P>SOLUTION: The burnishing tool 1 has a retainer 5 which is externally fitted to a mandrel 2 in a freely rotatable manner and holds a rolling body for rolling on an outer peripheral surface of the mandrel 2 by the rotation of the mandrel 2. The mandrel 2 is provided with a projection part 23b2 which is engaged with the rolling body and is an approximately polygonal shape in the cross section view on the outer peripheral surface of the mandrel 2. The retainer 5 is inserted so as to face an inner peripheral surface of a workpiece, holds the rolling body in a freely appearing/disappearing manner from the outer peripheral surface of the retainer 5 in the radial direction, engages the projection part 23b2 and the rolling body by the rotation of the mandrel 2, and rolls the rolling body by oscillating it with respect to the inner peripheral surface of the workpiece. The burnishing tool 1 is characterized in that it is equipped with balls 4 as the rolling body. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a burnishing tool, and more particularly to a burnishing tool for forming dimples.

In general, sliding members used under severe conditions such as fluid bearing surfaces represented by engines and hard disk drives have high rotational speeds and high temperatures. A technique for reducing the frictional resistance of the sliding surface by forming fine grooves and dimples is known.
Conventionally, as a technique for forming dimples on a sliding surface, there is a technique using so-called WPC processing (fine particle shot peening) or laser processing.

On the other hand, burnishing is a kind of plastic working that improves surface hardness and surface roughness by rotating while pressing a rolling roller against the work and deforming the work surface of the work. . By subjecting the sliding surface to burnishing, the durability, wear resistance, and reliability can be greatly improved.
And the burnishing tool which vibrates the rolling roller for a burnishing process and performs a peening process and a burnishing process simultaneously is known (patent document 1).

By the way, a sliding member used under severe conditions is often provided with an oil groove or an oil hole on the inner peripheral surface of the sliding bearing in order to supply lubricating oil and improve the lubricating performance. When such an oil hole or the like is processed, burrs are easily formed at the edge portion around the hole, and if this burr adheres to the sliding surface, it causes seizure or galling. For this reason, normally, after the inner peripheral surface of the sliding bearing is processed by grinding or the like, a separate process is provided to replace the processing tool, and deburring of the edge portion such as an oil hole is performed.
Japanese Patent Laying-Open No. 2003-159648 (FIG. 6)

  However, in order to perform WPC processing and laser processing, a dedicated machine facility must be provided and performed at a separate processing station, and there is a problem that the burden is large both in terms of facility cost and processing man-hours. Furthermore, in the case of laser processing, since it is necessary to irradiate laser light perpendicularly to the processing surface, it has been difficult to process, for example, the inner peripheral surface of a sliding bearing.

On the other hand, in peening using a rolling roller for burnishing, it is difficult to form dimples with various shapes and sizes that are required. There was a case.
Further, in the peening process using the rolling roller, the rolling roller is in line contact with the work surface of the workpiece in the axial direction, so that it is not possible to expect a deburring effect on the edge portion such as an oil hole.

  This invention is made | formed in view of such a background, and makes it a subject to provide the dimple formation burnishing tool which forms a dimple with a simple apparatus and performs burnishing.

  In order to solve the above-described problems, the present invention provides a mandrel that is mounted on a processing machine and rotated, and a rolling element that is rotatably fitted to the mandrel and rolls the outer peripheral surface of the mandrel by the rotation of the mandrel. A retainer that rotatably holds the protrusion, and the mandrel is provided with a convex portion that engages with the rolling element and has a substantially polygonal shape in a cross-sectional view on the outer peripheral surface of the mandrel. The rolling element is inserted so as to face the inner peripheral surface of the workpiece, holds the rolling element in a radial direction from the outer peripheral surface of the retainer, and the protrusion and the rolling element are engaged by rotation of the mandrel. A dimple-forming burnishing tool for rolling the rolling element while vibrating the inner circumferential surface of the workpiece, wherein the rolling element includes a ball.

Thus, in the present invention, the rolling element to be burnished is a ball, and a convex portion is provided on the outer peripheral surface of the rotating mandrel so as to have a polygonal shape, and this convex portion is engaged with the ball while rotating. Then, the inner peripheral surface of the workpiece is burnished while the ball is bounced and vibrated by the rotational force of the convex portion. For this reason, burnishing can be performed while forming a substantially circular dimple of an appropriate size with a simple device.
In addition, the dimple shape, size, depth, etc., pitch between the dimples, etc. can be set by appropriately setting the number and height of the protrusions, the rotation speed and feed speed of the mandrel, the diameter of the mandrel and the ball, etc. It can be set optimally according to the use conditions required for. Therefore, it is possible to ensure optimum lubrication characteristics and a smooth finished surface that match the use conditions.

  In addition, when the rolling element that performs burnishing is a ball, if holes or grooves are formed in the direction intersecting the inner peripheral surface of the workpiece, such as oil holes or cross holes in the connecting rod, Since the ball collides with or is pressed against the peripheral edge portion such as an oil hole, it is possible to simultaneously deburr the edge portion such as an oil hole.

In the above-described present invention, it is desirable that a roller is further provided as the rolling element.
According to such a configuration, a roller is further provided as a rolling element in addition to the ball, and a finished surface with good surface roughness can be obtained by enlarging the pressing area during the rolling process. The processed surface can be smoothly finished by the rolling action of the roller.

In the present invention described above, it is desirable that the balls and the rollers are alternately arranged along the axial direction of the retainer.
According to such a configuration, since the balls and the rollers are alternately arranged along the axial direction of the retainer, by applying the mandrel, the burnishing by the balls and the rollers is alternately performed. A more uniform and smooth processed surface can be finished while fusing to form dimples.
In other words, the mandrel is fed in the axial direction by a processing machine, and the respective processes of forming dimples by ball vibration and improving the hardness and surface roughness of the processed surface by the rolling action of the roller are alternately fused. Therefore, it is possible to form a smooth and more durable finished surface on which dimples are formed.

  Here, the “alternate arrangement” includes an arrangement such as a ball, a roller, and a ball, and an arrangement such as a roller, a ball, and a roller, in addition to arranging the balls and rollers side by side in the axial direction.

In the above-described present invention, the balls and the rollers can be alternately arranged along the circumferential direction of the retainer.
According to such a configuration, since the balls and the rollers are alternately arranged along the circumferential direction of the retainer, the burnishing by the balls and the rollers is alternately performed. The machined surface can be finished more smoothly.
The term “alternately arranged” has the same meaning as described above.

  In the above-described present invention, the mandrel is provided with a tapered portion whose diameter is reduced as the outer peripheral surface for rolling the rolling element moves toward the axial tip of the mandrel, and the mandrel is externally fitted to the mandrel. It is desirable that a spacer is provided for holding the retainer at a predetermined position in the axial direction of the mandrel with respect to the portion.

  According to such a configuration, the tool machining diameter formed by the circumscribed circle of the rolling element is adjusted by adjusting the position of the retainer in the axial direction with respect to the tapered portion and adjusting the gap between the outer peripheral surface of the mandrel and the rolling element. It can be set appropriately. For this reason, the tolerance of the workpiece diameter can be set in various patterns.

  According to the dimple formation burnishing tool according to the present invention, it is possible to provide a dimple formation burnishing tool that forms dimples by a simple device and performs burnishing.

Embodiments of the present invention will be described in detail with reference to the drawings as appropriate.
In the drawings to be referred to, FIG. 1 is a cross-sectional view for explaining the overall configuration of a dimple formation burnishing tool (hereinafter simply referred to as “burnishing tool”) according to an embodiment of the present invention, and FIG. 2 is an embodiment of the present invention. FIG. 3 is an exploded perspective view of the burnishing tool according to the embodiment, and FIG. 3 is a cross-sectional view taken along line AA of FIG. 1 showing a state where the burnishing tool is inserted into the workpiece.

  As shown in FIG. 1, a burnishing tool 1 according to an embodiment of the present invention includes a mandrel 2 that is mounted on a processing machine such as a lathe (not shown) and rotated, a spacer ring 3 that is externally fitted to the mandrel 2, and a mandrel A retainer 5 that rotatably holds the ball 4 that rolls on the outer peripheral surface, a thrust ring 6 that holds the retainer 5 in the axial direction of the mandrel 2, and a cap nut 8 as a fixture are provided.

As shown in FIG. 2, the mandrel 2 is formed in a round bar shape as a whole, and a shank 21 mounted on a processing machine (not shown) such as a lathe and an outer peripheral surface formed in a substantially hexagonal shape in a cross-sectional view. And a main body portion 22 having the retainer holding portion 23.
In addition to the straight shape as in the present embodiment, the shank 21 may have various shapes such as a tapered shape so as to be compatible with a processing machine to be mounted.

The main body portion 22 includes a trunk portion 24 that is continuous with the shank 21, and a retainer holding portion 23 that is reduced in diameter relative to the trunk portion 24. The retainer holding part 23 includes a straight part 23a to which the cylindrical spacer ring 3 is attached, a hexagonal part 23b to which the retainer 5 is attached, and a tip part 23c to which the thrust ring 6 is attached. Then, the cap nut 8 is screwed into the end surface 23c1 of the distal end portion 23c of the retainer holding portion 23 to hold the retainer 5 (see FIG. 1).
Further, in the retainer 5, in order to reduce the friction coefficient, the ball 4 is placed so that the end surface 3 a of the spacer ring 3 and the spacer ring-side ball 4 a held on the retainer 5 are in contact with each other. Has been placed.

  Since the mandrel 2, the rolling element ball 4, and the retainer 5 are required to be durable, heat treatment is performed using special alloy steel to improve hardness and toughness. Depending on the use conditions, DLC, TIN Further, durability can be further improved by surface coating treatment such as TICN.

  With this configuration, the retainer 5 is held by the spacer ring 3 and the thrust ring 6 at both ends, and is rotatably fitted to the mandrel 2. And the retainer 5 is arrange | positioned so that it may be located in the hexagonal-shaped part 23b with respect to the axial direction of the mandrel 2. As shown in FIG.

As shown in FIG. 3, the outer peripheral surface of the hexagonal portion 23 b is formed in a substantially hexagonal shape in a sectional view. The hexagonal shape includes a flat portion 23b1 that forms a hexagonal side and a convex portion 23b2 that corresponds to the apex of the hexagonal shape.
The flat part 23b1 is formed so as to scrape off the outer peripheral surface of the round rod-shaped retainer holding part 23 (see FIG. 2) along the axial direction. For this reason, the convex part 23b2 is formed in the position far from the rotation center C of the mandrel 2 with respect to the flat part 23b1. An outer peripheral surface with a gentle curvature is formed from the flat portion 23b1 to the convex portion 23b2 so that the ball 4 can roll smoothly.

  In the present embodiment, the hexagonal portion 23b (see FIG. 2) of the retainer holding portion 23 is formed in a substantially hexagonal shape. However, the present invention is not limited to this. May be. In the present embodiment, the flat portion 23b1 is used. However, the present invention is not limited to this, and the flat portion 23b1 does not necessarily have to be flat and may be formed of a curved surface.

The retainer 5 holds the balls 4 forming the dimples D on the processed surface of the workpiece W so as to be rotatable and swingable so as to vibrate in the radial direction of the retainer 5. The balls 4 are arranged in six equal circumferential directions of the retainer 5 so as to correspond to the hexagonal shape of the retainer holding portion 23 (see FIG. 2).
When the burnishing tool 1 (see FIG. 2) is inserted into the workpiece W, the balls 4 are interposed between the outer peripheral surface of the mandrel 2 and the inner peripheral surface of the workpiece W, as shown in FIG. At this time, each convex part 23b2 or each flat part 23b1 of the retainer holding | maintenance part 23 (refer FIG. 2) and the ball | bowl 4 arranged in 6 equality are each comprised simultaneously.

The operation of the burnishing tool according to this embodiment configured as described above will be described with reference to FIG.
As shown in FIG. 3, the burnishing tool 1 according to the present embodiment is rotatably held by the retainer 5 along the outer peripheral surface of the mandrel 2 when the mandrel 2 is mounted on a processing machine (not shown) and rotated clockwise. The ball 4 rotated (rotates) counterclockwise. At this time, since the workpiece W is fixed, when the ball 4 rotates counterclockwise, the ball 4 revolves clockwise along the inner circumferential surface of the workpiece W and the outer circumferential surface of the mandrel 2.

  In this manner, when the ball 4 revolves around the mandrel 2 in a state where the ball 4 is sandwiched between the inner peripheral surface of the work W and the outer peripheral surface of the mandrel 2, the ball 4 is placed on the outer peripheral surface of the mandrel 2. The projections 23b2 and the flat portions 23b1 that have been formed pass alternately. For this reason, the ball 4 follows the inner peripheral surface of the workpiece W while vibrating in the radial direction of the retainer 5 due to the height difference between the convex portion 23b2 and the flat portion 23b1 (difference in distance from the rotation center C of the mandrel 2). Rolling.

The manner in which the dimples D are formed by rolling the ball 4 while vibrating and the operational effects of the dimples will be further described with reference to FIGS. FIG. 4 is an enlarged cross-sectional view of the main part of FIG. 3 showing how the dimples are formed. FIG. 5 is an enlarged cross-sectional view of the main part around the ball for explaining the function and effect of the dimple.
The ball 4 rolls while alternately passing through the convex portions 23b2 and the flat portion 23b1 formed on the outer peripheral surface of the mandrel 2, but when the ball 4 is positioned on the convex portion 23b2 of the mandrel 2, FIG. ), The ball 4 is pressed so as to be bounced by the convex portion 23b2 of the mandrel 2, so that a dimple D is formed on the inner peripheral surface of the workpiece W.
On the other hand, when the ball 4 is positioned on the flat portion 23b1, a slight gap is provided between the ball 4 and the inner peripheral surface of the workpiece W as shown in FIG. The inner peripheral surface of W is not pressed.

  In the present embodiment, when the ball 4 is positioned at the flat portion 23b1, a slight gap is provided between the ball 4 and the inner peripheral surface of the workpiece W. However, the present invention is not limited to this. Instead, they may be close or in contact. Further, the ball 4 may be configured to press the inner peripheral surface of the workpiece W.

As described above, the burnishing tool 1 according to the present invention uses the rolling element that performs the burnishing process as the ball 4, and the outer peripheral surface of the rotating mandrel 2 is provided with the convex portion 23b2 so as to have a substantially hexagonal shape, and this convex portion 23b2 By engaging with the ball 4 while rotating, the inner peripheral surface of the workpiece W is burnished while the ball 4 is repelled and vibrated by the rotational force of the convex portion 23b2. For this reason, burnishing can be performed while forming a substantially circular dimple D having an appropriate size with a simple apparatus.
Accordingly, the burnishing tool 1 according to the present invention can be used with a general-purpose cutting machine such as a lathe or a machining center, so that it is possible to form dimples having a required shape easily and inexpensively.

  That is, the burnishing tool 1 according to the present invention appropriately sets the shape and size of the dimple D by appropriately setting the number and height of the convex portions 23b2, the rotation speed and feed speed of the mandrel 2, the diameter of the mandrel 2 and the ball 4, and the like. The size such as the sheath and the depth, the pitch between the dimples D, and the like can be optimally set according to the use conditions required for the workpiece W. Therefore, it is possible to ensure appropriate lubrication characteristics and finished surface accuracy that match the use conditions.

  Therefore, according to the burnishing tool 1 according to the present invention, a very fine dimple D can be formed on the inner peripheral surface of the workpiece W, and lubricating oil can be held in the dimple D. Can be prevented and the sliding characteristics can be improved. Moreover, since the surface hardness of the inner peripheral surface of the workpiece W can be increased by the peening effect, and the compressive residual stress can be applied to the processed surface, the fatigue strength of the processed surface is improved.

  Further, since the rolling element that performs the burnishing process is the ball 4, as shown in FIG. 5, when the oil hole W1 is formed in the direction intersecting the inner peripheral surface of the workpiece W, the oil hole W1 Since the ball collides with or is pressed against the peripheral edge portion W2, it is possible to simultaneously remove the burrs W3 formed on the edge portion W2 of the oil hole W1.

Subsequently, a dimple formation burnishing tool (hereinafter simply referred to as “burnishing tool”) according to another embodiment of the present invention will be described with reference to FIGS. 6 and 7. FIG. 6 is a cross-sectional view for explaining the overall configuration of a burnishing tool according to another embodiment of the present invention, and FIG. 7 is an exploded perspective view of the burnishing tool according to another embodiment of the present invention.
6 and 7 are exaggerated for the sake of convenience of explanation.

As shown in FIG. 6, the burnishing tool 1 ′ according to another embodiment of the present invention has a hexagonal taper of the retainer holding portion 23 ′ of the mandrel 2 ′ so that the tool diameter δ (see FIG. 3) can be adjusted. This is different from the burnishing tool 1 described above in that a portion 23b 'is provided and adjusters 31 to 35 are appropriately arranged so that the axial position of the retainer 5 relative to the mandrel 2' can be adjusted.
Therefore, this difference will be mainly described below, and the same constituent elements as those of the burnishing tool 1 according to the above-described embodiment will be omitted by using the same reference numerals.

In the burnishing tool 1 ′ according to another embodiment of the present invention, as shown in FIG. 7, the retainer holding portion 23 ′ of the mandrel 2 ′ is directed to the axial tip of the mandrel 2 ′ (the left side in the figure). A hexagonal tapered portion 23b 'having a reduced diameter is provided.
Specifically, the main body portion 22 ′ includes a trunk portion 24 that is continuous with the shank 21, and a retainer holding portion 23 ′ whose diameter is reduced with respect to the trunk portion 24. The retainer holding portion 23 'includes a straight portion 23a' to which the cylindrical end ring 3 'is attached, a hexagonal tapered portion 23b' to which the retainer 5 is attached, and a tip portion 23c to which the thrust ring 6 is attached. It is equipped with. And the cap nut 8 is screwed into the end surface 23c1 of the front-end | tip part 23c of the retainer holding | maintenance part 23, and the retainer 5 is hold | maintained (refer FIG. 6).

The adjusters 31 to 35 are disposed on both sides of the retainer 5 with the retainer 5 interposed therebetween, and are mounted between the end ring 3 ′ and the thrust ring 6.
Specifically, the end ring 3 ′ is held in contact with the end surface 24 a of the body portion 24, and the adjust rings 31, 32, 33, 34 are attached from the end ring 3 ′ adjacent to the end ring 3 ′. Further, the retainer 5, the adjuster string 35, and the thrust ring 6 are sequentially attached and fixed by the cap nut 8.

  For example, the adjusters 31 to 35 having different thicknesses of about 1 to 5 mm, for example, are used, and the arrangement of the adjusters 31 to 35 is rearranged so that the tool diameter is 0.02 per 0.0025 mm. It can be adjusted within a range of about 0.05.

  Next, another embodiment of the retainer according to the present invention will be described with reference to FIG. FIG. 8 is a view for explaining another embodiment of the retainer according to the present invention, wherein (a) is a cross-sectional view showing a first embodiment of the retainer according to the present invention, and (b) is a cross-sectional view of (a). A perspective view and (c) are perspective views showing a 2nd example of a retainer concerning the present invention.

  The rolling elements in the retainer 5 in each of the above-described embodiments are configured by the balls 4 arranged in the circumferential direction 6 equally, but the retainers 51 and 52 according to the first and second examples are shown in FIG. As shown, the ball 41 and 43 and rollers 42 and 44 are provided.

  In the retainer 51 according to the first embodiment, in the axial direction of the retainer 51, one ball 41 is arranged on the tip side (left side in the figure) of the mandrel 2, and on the rear side (right side in the figure) of the mandrel 2. One roller 42 is arranged. Then, in the circumferential direction of the retainer 51, as in the above-described embodiment, the retainer 51 is arranged in six circumferential directions corresponding to the hexagonal shape of the retainer holding portion 23 (see FIG. 2) (FIG. 3). reference).

According to this configuration, since the balls 41 and the rollers 42 are alternately arranged along the axial direction of the retainer 51, the ball 41 and the rollers 42 are alternately burned by feeding the mandrel 2. Therefore, it is possible to finish the processing surface more uniformly and smoothly while forming the dimple D (see FIG. 3) by fusing both processing characteristics.
That is, by feeding the mandrel 2 in the axial direction by a processing machine, the respective processes of forming dimples by the vibration of the ball 41 and improving the hardness and surface roughness of the processing surface by the rolling action of the roller 42 are alternately fused. Therefore, it is possible to form a smooth and highly durable finish surface on which the dimples D are formed.

In the retainer 52 according to the second embodiment, only the ball 43 or the roller 44 is configured in the axial direction of the retainer 52. In the circumferential direction of the retainer 52, the balls 43 and the rollers 44 are alternately arranged along the circumferential direction of the retainer 52.
According to this configuration, since the balls 43 and the rollers 44 are alternately arranged along the circumferential direction of the retainer 52, the burnishing by the balls 43 and the rollers 44 is performed alternately. The processed surface can be finished more smoothly while forming the dimple D (see FIG. 3).

  In this embodiment, the rollers 42 and 44 are of a straight cylindrical shape. However, when the mandrel 2 has a tapered shape, the tapered roller can be adapted to the tapered shape of the mandrel 2. Can be used. That is, if the mandrel 2 has a tapered shape with a reduced diameter on the tip side (left side in the figure), for example, the roller can adopt a tapered shape with a diameter enlarged on the tip side. According to such a configuration, since the rollers are evenly brought into contact with the inner peripheral surface of the workpiece, the surface roughness of the finished surface can be improved.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and can be implemented with appropriate modifications.
For example, in the present embodiment, the balls 4 are arranged in a uniform manner in the circumferential direction 6 of the retainer 5 so as to correspond to the hexagonal shape of the retainer holding portion 23. However, the present invention is not limited to this. It is not necessary to correspond to the position and number of the convex portions 23b2 formed on the mandrel 2. Therefore, the mandrel can be provided with a convex portion having an octagonal shape, and the balls can be evenly distributed in the circumferential direction of the retainer.

  In the embodiment of the present invention, a ball and a roller are provided as rolling elements, and the burnishing process is performed while vibrating the rolling element. However, as a reference example of the present invention, only the ball is vibrated and dimple processing is performed. It is also possible to perform burnishing without vibrating the rollers.

It is sectional drawing for demonstrating the whole structure of the burnishing tool which concerns on embodiment of this invention. It is a disassembled perspective view of the burnishing tool which concerns on embodiment of this invention. It is. It is AA sectional drawing of FIG. 2 which shows the state which inserted the burnishing tool which concerns on embodiment of this invention in the workpiece | work. FIG. 4 is an enlarged cross-sectional view of a main part of FIG. 3 showing a state where dimples are formed. It is a principal part expanded sectional view around the ball | bowl for demonstrating the effect of a dimple. It is sectional drawing for demonstrating the whole structure of the burnishing tool which concerns on other embodiment of this invention. It is a disassembled perspective view of the burnishing tool which concerns on other embodiment of this invention. It is. It is a figure for demonstrating the other Example of the retainer which concerns on this invention, (a) is sectional drawing which shows 1st Example of the retainer which concerns on this invention, (b) is a perspective view of (a), c) is a perspective view showing a second embodiment of a retainer according to the present invention.

Explanation of symbols

1,1 'burnishing tool (dimple forming burnishing tool)
2,2 'Mandrel 3 Spacer ring 4 Ball 5 Retainer 6 Thrust ring 8 Cap nut W1 Oil hole W2 Edge part W3 Burr 21 Shank 22 Main body part 22' Main body part 23b Hexagonal part 23, 23 'Retainer holding part 23b Hexagonal part 23b 'taper part 31-35 adjustment string (spacer)
41, 43 Ball 42, 44 Roller 51, 52 Retainer 23b1 Flat part 23b2 Convex part C Center of rotation D Dimple W Workpiece

Claims (5)

A mandrel that is mounted on a processing machine and rotated,
A retainer that is rotatably fitted to the mandrel and rotatably holds a rolling element that rolls the outer peripheral surface of the mandrel by the rotation of the mandrel;
The mandrel is provided with a convex portion that engages with the rolling element and has a substantially polygonal shape in a sectional view on the outer peripheral surface of the mandrel,
The retainer is inserted so as to face the inner peripheral surface of the workpiece, and holds the rolling element in a radial direction from the outer peripheral surface of the retainer,
A dimple formation burnishing tool that rolls while causing the rolling element to vibrate with respect to the inner peripheral surface of the workpiece by the rotation of the mandrel, and the protrusion and the rolling element are engaged.
A dimple forming burnishing tool comprising a ball as the rolling element.   The dimple formation burnishing tool according to claim 1, further comprising a roller as the rolling element.   The dimple-forming burnishing tool according to claim 2, wherein the balls and the rollers are alternately arranged along the axial direction of the retainer.   The dimple-forming burnishing tool according to claim 2, wherein the balls and the rollers are alternately arranged along a circumferential direction of the retainer. The mandrel is provided with a tapered portion whose diameter is reduced as the outer peripheral surface for rolling the rolling element is directed to the tip in the axial direction of the mandrel,
5. The spacer according to claim 1, further comprising a spacer that is fitted on the mandrel and holds the retainer at a predetermined position in an axial direction of the mandrel with respect to the tapered portion. The dimple forming burnishing tool described.

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