DIMPLE-FORMING BURNISHING TOOL AND DIMPLE-FORMING BURNISHING METHOD

Abstract

A burnishing tool includes a mandrel; and a frame fitted to the mandrel and holding balls contacting an outer peripheral surface on the mandrel. The outer peripheral surface has a contact surface with the balls. The contact surface is at a side of the outer peripheral surface which is closer to the work surface. The contact surface and the work surface have a distance therebetween in a direction normal to the work surface. A distance at a side of the mandrel closer to the processing machine and a distance at the opposite side of the mandrel have a distance difference therebetween. A diameter of the outer peripheral surface on the mandrel is set in such a way that the distance difference with the mandrel flexed during formation of the dimples becomes smaller than that before flexing of the mandrel.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2012-035752 filed on Feb. 22, 2012; the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a dimple-forming burnishing tool and a dimple-forming burnishing method for forming a dimple on a work surface by contacting a ball with the work surface.

2. Description of Related Art

There is a technique of forming fine dimples for keeping a lubricant on a sliding surface of a sliding member such as a bearing to reduce friction resistance of the sliding surface. The surface treatment for forming the dimples on a work surface such as the sliding surface has been known as a dimple-forming by a WPC treatment (fine-particle shot-peening), a dimple-forming by a laser-machining and the like.

The dimple-forming by the WPC treatment is a surface treatment of shooting fine particles, smaller than those for an ordinary peening, at a high speed to be struck on the work surface for forming dimples. The dimple-forming by the laser-machining is a surface treatment of radiating laser beam on the work surface using an exclusive processing machine for forming dimples.

There is proposed another surface treatment for forming dimples on a work surface using a burnishing tool (see, for example, Patent Document 1). The burnishing tool includes a cylindrical frame fitted to a mandrel from the outside. The cylindrical frame holds rotatably rolling elements to come radially out of or into the outer peripheral surface of the frame. With the mandrel fitted to a processing machine rotated, the projections, formed on the outer peripheral surface of the mandrel, engage rolling elements such as balls. The rolling elements vibratingly rotate on the inner peripheral surface of a work as a work surface.

• [Patent Document 1] Japanese Patent Publication NO. 4575899

However, when the surface treatment of forming dimples is applied to the work surface of a narrow portion such as the side surface of the groove portion of a compressor component, the problem has been proposed as follows.

That is, the WPC treatment requires shooting particles at every surface treatment, which raises machining cost, and is not efficient. The laser-machining is difficult to be applied to the work surface of the narrow portion such as a side surface of the groove portion.

The burnishing tool as described in Patent Document 1 is a tool used for the surface treatment to the inner peripheral surface of a hole formed to a work, and is not applied to the surface treatment to a work surface such as a side surface of the groove portion. If the tool is used on the work surface of the narrow portion such as the side surface of the groove portion, a tool diameter becomes smaller, and the tool is flexed during formation of dimples. This causes difficulty in to forming dimples by secure contacting all of the rolling elements on the work surface.

SUMMARY OF THE INVENTION

The invention is directed to a dimple-forming burnishing tool and a dimple-forming burnishing method which efficiently and securely form dimples to a work surface of a narrow portion such as a side surface of a groove portion.

A first aspect of the invention provides a dimple-forming burnishing tool. The dimple-forming burnishing tool includes a mandrel having an end side fitted and fixed to a processing machine for rotating; and a frame fitted to another side of the mandrel from the outside, and holding balls contacting an outer peripheral surface of the mandrel. The balls on the outer peripheral surface contact a work surface with the mandrel and the frame rotated for forming dimples on the work surface. The outer peripheral surface has a contact surface with the balls. The contact surface is at a side of the outer peripheral surface which is closer to the work surface. The contact surface and the work surface have a distance therebetween in a direction normal to the work surface. A distance at a side of the mandrel closer to the processing machine and a distance at the opposite side of the mandrel to said side have a distance difference therebetween. A diameter of the outer peripheral surface on the mandrel is set in such a way that the distance difference with the mandrel flexed during formation of the dimples becomes smaller than that before flexing of the mandrel.

According to the invention, if the mandrel is flexed during formation of the dimples, the burnishing tool of a smaller diameter enables all of the balls arranged on the outer peripheral surface to be pressed against the work surface with the mandrel flexed. This operation forms the dimples of approximately a uniform depth at a predetermined whole region on the work surface of a narrow portion which is a side surface of, for example, a groove portion.

That is, the dimples are efficiently and securely formed to the work surface of the narrow portion such as a side surface of the groove portion.

Therefore, the work surface is formed with very fine and uniform dimples, and keeps a lubricant in the dimples. This prevents a lubricant from running out, and reduces frictional resistance, thereby enhancing the sliding property.

The dimple-forming burnishing tool is fitted to a generic processing machine (machine tool) such as a machining center, or an NC milling machine for use, and is capable of forming dimples in a shape which is required with ease and at an inexpensive cost.

The mandrel has a first sectional line which is positioned on the outer peripheral surface and at said side of the mandrel closer to the work surface. The first sectional line is defined by sectioning the mandrel by a plane which is normal to the work surface and includes an axis of the mandrel. The work surface has a second sectional line on the work surface. The second sectional line is defined by sectioning the work surface by the plane. The first sectional line and the second sectional line have a parallel degree therebetween. A diameter of the outer peripheral on the mandrel at the opposite side to a side closer to the processing machine is set to be larger than that at said side close to the processing machine, so that the parallel degree with the mandrel flexed during formation of the dimples becomes smaller than that before flexing of the mandrel.

According to the invention, it is applicable to the case where the work surface is a plane. With the mandrel is flexed during formation of the dimples, the sectional line at the side of the outer peripheral surface closer to the work surface is approximately parallel with the sectional line on the work surface. This permits all of the balls arranged on the outer peripheral surface to be pressed against the work surface at a further uniform strength.

The outer peripheral surface of the mandrel has a side shape in a frustum of a circular cone which diverges toward the opposite side to said side closer to the processing machine.

According to the invention, with the mandrel being flexed, the sectional line at a side of the outer peripheral surface closer to the work surface is exactly a curved line, not a straight line. On the other hand, a parallel degree between the sectional line at a side of the outer peripheral surface closer to the work surface and the sectional line on the work surface become sufficiently smaller. Herein, formation of the outer peripheral surface of the mandrel in a side-shape of a frustum of a circular is made by minor change from formation of the mandrel in a side-shape of a straight circular cylinder in the manufacturing process of the mandrel itself.

The balls are spaced apart from each other in a peripheral direction of the frame and in a direction parallel with the axis of the frame.

According to the invention, it is enabled to further efficiently form the dimples on the work surface.

The frame includes: a frame body fitted to the mandrel from the outside and defining first through-holes for the balls to be fitted thereto, respectively; and a frame cover fitted to the frame body from the outside, having the balls projecting radially outward from the outer peripheral surface of the frame, and defining second through-holes which coincide in position with the first through-holes for preventing the balls from dropping out of the first through-holes, respectively.

According to the invention, it facilitates machining such as formation of holes for holding the balls, thereby enhancing manufacturing operability for the dimple-forming burnishing tool.

A second aspect of the invention provides a dimple-forming burnishing method which includes contacting the balls on the work surface to form dimples on the work surface using the dimple-forming burnishing tool according to the first aspect of the invention.

According to the invention, it is capable of serving as the same operation and benefits as those of the first aspect of the invention.

Benefits of the Invention

According to the invention, this enables the dimples to be efficiently and securely formed on the work surface of the narrow portion such as a side surface of the groove portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a half sectional view which shows a whole structure of a dimple-forming burnishing tool according to an embodiment of the invention.

FIG. 2 is a general perspective view of the burnishing tool as show in FIG. 1, which shows an example of working condition.

FIG. 3 is a schematic view of the front periphery of a mandrel before the mandrel is flexed.

FIG. 4 is a schematic view of the front periphery of the mandrel with the mandrel flexed during formation of dimples.

FIG. 5 is a perspective view of the mandrel which schematically shows the front periphery of the mandrel with the mandrel flexed during formation of dimples.

FIGS. 6A and 6B are views which show the state of dimple-forming by a burnishing tool, FIG. 6A is a general view as viewed from the position opposed to the work surface, and FIG. 6B is an enlarged view of the dimples formed on the work surface as shown in FIG. 6A.

FIGS. 7A, 7B and 7C are schematic views of a mandrel which is pressed into the work surface with the pressing-into amount varied, FIG. 7A shows a case of a smaller pressing-into amount, FIG. 7B shows a case of an appropriate pressing-into amount, and FIG. 7C shows a case of a larger pressing-into amount.

In the Figures, the numeral F1 indicates a front direction in a longitudinal direction of the burnishing tool, and the numeral R1 indicates a rear direction in a longitudinal direction of the burnishing tool.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, an embodiment according to the invention will be described with reference to the drawings. FIG. 1 shows a half-sectional view of a dimple-forming burnishing tool (hereafter, referred to as a burnishing tool) according to the embodiment of the invention. In FIG. 1, the upper side of the burnishing tool relative to the axis CL is shown by the sectional view, and the lower side thereof is shown by the side view. It is noted that the front direction F1 and the rear direction R1 of the burnishing tool are set for clear description, as shown in FIG. 1.

As shown in FIG. 1, the burnishing tool 1 includes: a mandrel 2 having a rear end side which is rotatably fitted to a processing machine (not shown in Figs.) such as a machining center or an NC milling machine; and a frame 4 which is fixed to the front end side of the mandrel from the outside and which holds balls 3 contacting the outer peripheral surface 23 on the mandrel 2.

The mandrel 2 is formed in a round bar-shape as a whole. The mandrel 2 includes a shank portion 21 fitted to the processing machine, and a body portion 22 having the frame 4 fitted thereto from the outside. The mandrel 2 is composed of an integral member having the shank portion 21 and the body portion 22 formed integrally with each other, thereby preventing additional vibrations from transmitting, enhancing stiffness, and ensuring stable flexibility.

The shank portion 21 adopts a straight shape as shown in FIG. 1, and, in addition, various shapes such as a taper shape for adapting to a processing machine for fitting. The body portion 22 includes a trunk portion 24 continuous with the shank portion 21; and a front portion 25 which is smaller in diameter than the trunk portion 24 and which has an outer peripheral surface 23 contacting the balls 23. The front portion 25 may not be necessarily smaller in diameter than the trunk portion 24.

The frame 4 is formed in approximately a cylindrical shape as a whole. The frame 4 includes a frame body 41 which is fitted to the mandrel 2 from the outside, and a frame cover 42 which is fitted to the frame body 41 from the outside.

The frame body 41 includes a holding portion 44 which is formed with first through-holes 43 for the balls 33 to be fitted therein. The frame body 41 includes a fitting portion 45 which is larger in diameter than the holding portion 44 for fitting the frame 4 to the mandrel 2. The frame body 41 includes an intermediate portion 46 which connects the holding portion 44 and the fitting portion 45. Each of the first through-holes 43 has an inner diameter slightly larger than the diameter of each ball 3. The respective balls 3 are fitted into the corresponding first through-holes 43 for holding.

The fitting portion 45 of the frame body 41 has, on a rear side thereof, thread-holes 47 (for example, three pieces) which are formed at equal angular intervals on the circular periphery and which extend radially of the frame body 41. The mandrel 2 has the trunk portion 24 which is formed, on the outer peripheral surface, with an annular recessed portion 26 in a V-shaped section. Stopper screws 61 are screwed into the thread-holes 47 to be pressed against the inner surface on the annular recessed portion 26 formed to the trunk portion 24, which fixes the frame 4 to the mandrel 2. Herein, the thread-holes 47 and the annular recessed portion 26 are located in the longitudinal direction in such a way that the distal ends of the stopper screws 61 come in contact with the front oblique surface of the inner surface on the annular recessed portion 26. Therefore, the rear end surface on the intermediate portion 46 of the frame body 41 comes in contact with the front end surface on the trunk portion 24 of the mandrel 2, which securely positioned the frame 4 to the mandrel 2.

The frame body 41 of the frame 4 has a stepped shape in which the holding portion 44 and the fitting portion 45 larger in diameter than the holder portion 44 are connected by the intermediate portion 46, and is fixed to the mandrel 2 at the fitting potion 45 of a larger diameter. This constitution enhances the stiffness compared with a frame in a cylindrical shape having little step, and is capable of rigidly fixing the frame 4 to the mandrel 2. This prevents the distal end side (front side) of the burnishing tool 1 from being displaced, and thereby achieves further stability.

The frame cover 42 in a cylindrical shape is formed with second through-holes 48 which coincide in position with the first through-holes 43, respectively. Each of the second through-holes 48 has an inner diameter smaller than the diameter of each ball 3. The second through-holes 48 allow the balls 3 to project radially outward from the outer peripheral surface of the frame 4, and have function to prevent the balls 3 from dropping out of the first through-holes 43.

The frame cover 42 is fitted to the frame body 41 from the outside with the first through-holes 43 and the second through-holes 48 coinciding in position with each other, and is fixed to the frame body 41 by clamps 5 (for example, two pieces). Each of the clamps 5 in an L-shape includes a fitting portion 51 having a through-hole 53 for a screw member 62 to be inserted therein, and a holding portion 52 having the frame cover 42 held between the holding portion 52 and the frame body 41. The frame body 41 has the fitting portion 45 which has, at the front side, threaded holes 49 (for example, two pieces) formed at equal angular intervals on the circular periphery and extending radially of the frame body 41. The screw member 62 is inserted through the through-hole 53 to be screwed into the threaded hole 49, and thereby the frame cover 42 is held and fixed between the clamp 5 and the frame body 41.

The frame 4 is constituted by two separate members of the frame body 41 and the frame cover 42. This constitution facilitates machining for forming holes for holding the balls 3 held, and enhances manufacturing operability for the burnishing tool 1. It is noted that the frame 4 may be constituted by an integral member having the frame body 41 and the frame cover 42 formed integrally with each other.

The balls 3 are arranged at angular intervals in the peripheral direction of the frame 4, and are arranged at intervals in a direction parallel with the axis CL (referred to as an axial direction) of the frame (common axis with that of the burnishing tool 1). This constitution enables dimples 71 (see FIG. 4) to be more efficient formed on the work surface 7 (see FIG. 2). Herein, the positions of the first through-holes 43 in the frame body 41 and the positions of the second through-holes 48 in the frame cover 42 are determined, depending on the arrangement layout of the balls 3.

In FIG. 1, the balls 3 are axially arranged in ball rows at the respective four peripheral positions which are spaced at intervals of 90 degree in the peripheral direction of the frame 4. The balls 3 in neighboring ball rows are slightly displaced axially from each other. It is noted that the placement number of the balls 3 and the arrangement layout of the balls 3 such as peripheral or axial arrangement intervals of the balls 3 may vary, depending on a size or a material of the work surface 7 (see FIG. 2).

FIG. 2 is a general perspective view of the burnishing tool which shows an example of the use. FIG. 3 is a schematic perspective view of the front periphery of the mandrel before the mandrel is flexed. FIG. 4 is a schematic view of a front periphery of the mandrel with the mandrel flexed during the formation of dimples. FIG. 5 is a perspective view which schematically shows the front periphery of the mandrel with the mandrel flexed during the formation of dimples. In FIGS. 3 and 4, the shape of the mandrel 2 is exaggeratingly drawn for convenient description, and the number of balls 3 is drawn differently from the actual one (FIG. 7 is the same as ones). In FIG. 5, the shape of the mandrel 2 is exaggeratingly drawn for convenient description, and the balls 3 are not shown in the Figure.

As shown in FIG. 2, the burnishing tool 1 is a tool for contacting the balls 3 on the outer peripheral surface 23 (see FIG. 1) with the work surface 7 on the work W with the mandrel 2 and the frame 4 rotating, thereby to form the dimples 71 (see FIG. 4) on the work surface 7. The work surface 7 is a side surface on a groove portion S formed to the work W.

As shown in FIGS. 3 to 5, the burnishing tool 1 is pressed into the work surface 7 by a predetermined press-into amount in a direction of P (see FIG. 2) from the position (see FIG. 3) where the ball 3 at the most distal end side (front side F1) contacts just or slightly the work surface 7 (see FIG. 4). At this time, the mandrel 2 flexes oppositely to the work surface 7 as it extends toward the distal end side, with the axis CL (common axis with that of the burnishing tool 1) having a maximum flexion of δ at the distal end of the mandrel 2, thereby forming the dimples 71 on the work surface 7.

In the embodiment, with the mandrel 2 flexed during formation of the dimples 71 (see FIGS. 4 and 5), the diameter of the outer peripheral 23 on the mandrel 2 is set so as to vary along the axis CL depending on the shape of the work surface 7. Therefore, in relation to the distance L between the contact surface 23a of the outer peripheral surface 23 on a side closer to the work surface 7 and the work surface 7 and normal to the work surface 7, the distance difference between the side closer to the processing machine (processing machine side or rear side) and the opposite side (front side) to the processing machine side becomes smaller than that before flexing of the mandrel 2 (see FIG. 3). To be specific, the distance L between the contact surface 23a and the work surface 7 at the front side is smaller than that at the rear side before flexing of the mandrel 2 (see FIG. 3). With the mandrel 2 flexed (see FIGS. 4 and 5), the front side of the outer peripheral surface 23 has approximately the same distance as that of the rear side thereof. Herein, the mandrel 2 before being flexed is a mandrel 2 without being flexed, if the work surface 7 is assumed not to apply reaction force.

The diameter of the outer peripheral surface 23 on the mandrel 2 at the opposite side (front side) to the processing machine side is set to be greater than that at the processing machine side (rear side). Therefore, a parallel degree between the sectional line 27 and the sectional line 72 with the mandrel 2 flexed during formation of the dimples 71 becomes smaller than that before flexing of the mandrel 2. The sectional line 27 on the outer peripheral surface 23 is defined by sectioning the outer peripheral surface 23 by the plane M and is positioned on a side of the outer peripheral surface 23 closer to the work surface 7 (work surface side). The plane M includes the axis CL of the mandrel 2 and is normal to the work surface 7. The sectional line 72 on the work surface 7 is defined by sectioning the work surface 7 by the plane M. The work surface 7 is a conception that means a plane which is not only the work surface 7 itself but also includes the work surface 7. To be specific, the sectional line 27 on the outer peripheral surface 23 at the work surface 7 side and the sectional line 72 on the work surface 7 get closer to each other toward the front side F1, not being parallel with each other, while they are approximately parallel with each other with the mandrel 2 being flexed (see FIG. 4). This parallel degree defines a magnitude of deviation (error) from a straight line which is to be parallel with the standard straight line.

This constitution is applied to the case in which the work surface 7 of the embodiment is a plane. With the mandrel 2 flexed during formation of the dimples 71, the sectional line 27 on the outer peripheral surface 23 at the work surface 7 side and the sectional line 72 on the work surface 7 are approximately parallel with each other, which enables all of the balls 3 arranged on the outer peripheral surface 23 to be pressed against the work surface 7 at a more uniform strength.

In the embodiment, the mandrel 2 has the front portion 25 having the outer peripheral surface 23 in a side-shape of a frustum of a circular cone which diverges in diameter toward the opposite side (front side) relative to the processing machine side. That is, the outer peripheral surface 23 of the mandrel 2 is formed in a taper shape having a thick distal end, which has a predetermined inclined angle (for example, 10 minutes, or ⅙ degree).

According to this constitution, the sectional line 27 at the work surface 7 side of the outer peripheral surface 23 with the mandrel 2 flexed becomes strictly a curved line, not a straight line, the parallel degree between the sectional line 27 at the work surface 7 side of the outer peripheral surface 23 and the sectional line 72 on the work surface 7 is enabled to become sufficiently smaller. Formation of the outer peripheral surface 23 of the mandrel 2 in a side-shape of a frustum of a circular is made by minor modification from formation of the mandrel 2 in a side-shape of a straight circular cylinder in the manufacturing process of the mandrel 2 itself.

The mandrel 2, the balls 3 and the frame 4 are required to have durability, are composed of a special alloy steel, and are heat-treated for enhancing hardness and toughness. They may be treated by surface coating such as DLC, TIN or TICN for enhancing durability, depending on working condition. The mandrel 2 and the balls 3 may be composed of a material such as cemented carbide or a ceramic material.

Next, a dimple-forming burnishing method using the above-structured burnishing tool 1 is described with reference to FIGS. 1 to 5 and FIGS. 6 and 7.

FIGS. 6A and 6B are views which show formation of dimples by the burnishing tool. FIG. 6A is a general view as viewed from the position opposed to the work surface. FIG. 6B is an enlarged view of the dimples formed on the work surface as shown by FIG. 6A. FIGS. 7A, 7B and 7C are schematic views of the burnishing tool and the work surface when the burnishing tool is pressed into the work surface with the press-into amount varied. FIG. 7A shows a case of a smaller press-into amount; FIG. 7B shows a case of an appropriate press-into amount; and FIG. 7C shows a case of a larger press-into amount.

Firstly, an electric source (not shown in Figs) is started to permit the burnishing tool 1, fitted to a processing machine (not shown in Figs), for example, an NC milling machine, to rotate at a predetermined rotational speed in a direction of R2 (see FIG. 2). At this time, the frame 4 is fixed to the mandrel 2, and the mandrel 2 and the frame 4 rotate integrally with each other.

Subsequently, as shown in FIGS. 2 and 6, with the press-into amount for pressing the balls 3 into the work surface 7 set to a predetermined value, the burnishing tool 1 is fed at a predetermined feed rate in a direction of the arrow Q, or an extension direction of the grove portion S.

As shown in FIG. 6, this operation permits the balls 3, held by the frame 4 on the outer peripheral surface 23 of the mandrel 2 rotating, to intermittently contact the work surface 7 corresponding to a side surface on the groove portion S of the work W, thereby forming dimples 71 over a whole predetermined region of the work surface 7. The depths of the dimples 71 become smaller than the press-into amounts of the balls 3 due to a repulsion force from the work W and the like.

The dimples 71 are formed on the work surface 7 at intervals of a horizontal arrangement-pitch P1 in a peripheral direction of the mandrel 2 or a direction of the arrow Q and at intervals of a vertical arrangement-pitch P2 in an axial direction parallel with the axis CL of the mandrel 2 (see FIG. 6B). The horizontal arrangement-pitch P1 corresponds to a feed rate in a direction of the arrow Q per a rotation of the burnishing tool 1. The vertical arrangement-pitch P2 corresponds to each axial displacement between the balls 3 in each of the ball arrangements neighboring at intervals of 90 degree on the circular periphery of the frame 4.

When forming the dimples 71 on the work surface 7 is finished, the burnishing tool 1 is separated apart from the work W to be stopped from rotating.

Herein, the previous experiment determined said press-into amount by which the burnishing tool 1 is further pressed into the work surface 7 from the position for the ball 3 at the most distal end side (front side) to contact just and slightly the work surface 7.

As shown in FIG. 7A, if the press-into amount is too small, a flexion of the mandrel 2 becomes smaller. The balls 3, located at the front side on the outer peripheral surface 23 diverging toward the distal end side (front side), are pressed against the work surface 7 more strongly than the balls 3 located at the rear side. Therefore, the dimples 3 formed at the front side become deeper than the dimples 71 formed at the rear side. In the worst case, there is some possibility of not forming the dimples 71 at the rear side. As shown in FIG. 7C, if the press-into amount is too large, flexion of the mandrel 2 becomes larger. The balls 3 located at the rear side on the outer peripheral surface 23 are pressed against the work surface 7 more strongly than those located at the front side. Therefore, the dimples 3 formed at the rear side become deeper than the dimples 71 formed at the front side. In the worst case, there is some possibility of not forming the dimples 71 at the front side. On the other hand, as shown in FIG. 7B, if a press-into amount is appropriate, the sectional line 27 on the work surface 7 side of the outer peripheral surface 23 and the sectional line 72 on the work surface 7 become approximately parallel with each other with the mandrel 2 flexed. The balls 3 located at the front side of the outer peripheral surface 23 and the balls 3 located at the rear side are pressed against the work surface 7 at a further uniform strength. This operation permits the depths of the dimples 71 formed at the front side and the depths of the dimples 71 at the rear side to become approximately uniform.

Therefore, as shown in FIG. 7B, the experiment determined the press-into amount for forming the dimples 71 of approximately a uniform depth on the work surface 7.

A size, a depth, an arrangement-pitch and an arrangement aspect of the dimples 71 may be modified by varying a machining condition (a rotation rate of the burnishing tool 1 and a feed rate); a diameter, an arrangement layout, the number, the arrangement layout and the mass of the balls 3; an inclined angle (taper angle) of the outer peripheral surface 23 on the mandrel 2; a force of pressing the balls 3 against the work surface 7 and the like. Following this, a material property (hardness) of the work surface 7 on the work W may be considered.

The burnishing tool 1 is structured so as to be applied to formation of the dimples 71 on the work surface 7 corresponding to the side surface of the groove portion S that has a depth of about 20 mm to about 50 mm and a width of about 20 mm. If the burnishing tool 1 is applied to another groove portion S of a different size and the like, the measure may be taken by fabricating a burnishing tool 1 of a different size in diameter and length at the design stage or by removing the frame 4 and the balls 3 from the mandrel 2 to be exchanged to ones of a different specification.

As describe above, the burnishing tool 1 of the embodiment includes: the mandrel 2 having a rear end side fitted to the processing machine for rotating; and the frame 4 fitted and fixed to the front end side of the mandrel 2 from the outside to hold the balls 3 that contact the outer peripheral surface 23 on the mandrel 2. With the mandrel 2 and the frame 4 rotating, the balls 3 on the outer peripheral surface 23 contact with the work surface 7, thereby forming the dimples 71 on the work surface 7. Herein, the diameter of the outer peripheral on the mandrel 2 is set in such a way that in relation to the distance L between the contact surface 23a with the balls 3 on the work surface 7 side of the outer peripheral surface 23 and the work surface 7 and normal to the work surface 7, the distance difference between the front side and the rear side with the mandrel 2 flexed during formation of the dimples 71 becomes smaller than that before flexing of the mandrel 2.

According to this embodiment, if the mandrel 2 is flexed during formation of the dimples 71 due to the burnishing tool 1 of a smaller diameter, all of the balls 3 arranged on the outer peripheral surface 23 are pressed against the work surface 7 at a further uniform strength with the mandrel 2 being flexed. This operation forms the dimples 71 of approximately a uniform depth, for example, on the whole predetermined region on the work surface 7 of a narrow portion such as a side surface of the groove portion S. That is, the dimples 71 are enabled to be efficiently and securely formed on the work surface 7 of the narrow portion such as the side surface of the groove portion S.

Therefore, the work surface 7 on the work W is formed with very fine and uniform dimples 71, which are capable of keeping lubricant. This function prevents oil from running out on the work surface 7, and reduces frictional resistance, thereby enhancing the sliding property.

The burnishing tool 1 is fitted to a generic processing machine (a machine tool) such as an NC milling machine, and is capable of forming dimples in a shape which is required at ease and an inexpensive price.

As described above, though the embodiment of the invention is explained, the invention is not limited to the constitution as described in the embodiment. Although the invention has been described above by reference to the embodiment, the invention is not limited to the embodiments described above. Appropriate modifications and variations of the constitution may be made within the purpose of the invention, including appropriate combination and selection of the constitutions as described in the embodiment.

For example, the embodiment explains that the burnishing tool 1 is fitted to a processing machine of a vertical type with the axis CL extending in a vertical direction. However, the invention is not limited to this aspect, and, for example, the burnishing tool 1 may be fitted to a machining tool of a horizontal type with the axis CL extending in a horizontal direction for use.

Although the above-described embodiment explains that the work surface 7 is a plane parallel with a vertical axis, the present invention is not limited to this aspect. For example, the present invention is applicable to the case where work surface 7 is curved in a section which is defined by sectioning the work surface 7 by a horizontal plane (planar view). To be specific, the invention is applicable to the case where the work surface 7 is a side surface of a scroll groove in a compressor component or the case where the work surface 7 is an inner peripheral surface 7 of a hole formed to the work W and the like. The invention is applicable to the case where the work surface 7 is a plane inclined to the vertical axis.

In this case, the burnishing tool 1 is fitted to, for example, the five axis processing machine, and is used with the axis CL being parallel with the work surface 7. That is, considering a shape and an angle of the work surface 7, a movement control and a rotation (rotary motion) control are combined and performed to form the dimples 71 on the work surface 7 of the work W. The movement control is a control of moving in three axis directions, the X axis, the Y axis and the Z axis orthogonal to each other, of a machining head (not show in Figs) for fitting the burnishing tool 1. The rotation control is a control of rotating about two axis, or the A/B axis and the C axis, of a work-fixing portion (not shown in Figs) for fixing the work W.

In addition, the present invention is applicable to the case where the work surface 7 is curved in a section (as viewed from the front) which is defined by sectioning the work surface 7 by, for example, the vertical plane. In this case, with the mandrel 2 flexed during the formation of the dimples 71, the diameter of the outer peripheral surface 23a varies along the axis CL, depending on a shape of the curved work surface 7, and is set in such a way that the distance L between the contact surface 23a and the work surface 7 at the front side of the outer peripheral surface on the mandrel 2 becomes approximately the same as that at the rear side thereof.

In the above-described embodiment, although a ball 3 is fitted to a circular through-hole formed to the frame 4, the present invention is not limited to this. The frame 4 may be formed with elongated circular through-holes, to which a plurality of balls 3 are fitted.

EXPLANATION OF REFERENCE NUMERALS

• 1 dimple-forming burnishing tool
• 2 mandrel
• 23 outer peripheral surface
• 23a contact surface
• 27 cutting-plane line
• 3 ball
• 4 frame
• 41 frame body
• 42 frame cover
• 43 first through-hole
• 48 second through-hole
• 7 work surface
• 71 dimple
• 72 cutting-plane line
• CL axis
• L distance
• M plane

Claims

1. A dimple-forming burnishing tool comprising:

a mandrel having an end side fitted to a processing machine for rotating; and

a frame fitted and fixed to another side of the mandrel from the outside, and holding balls contacting an outer peripheral surface of the mandrel,

wherein the balls on the outer peripheral surface contact a work surface for forming dimples on the work surface with the mandrel and the frame rotated,

wherein the outer peripheral surface has a contact surface with the balls and,

wherein the contact surface is at a side of the outer peripheral surface which is closer to the work surface,

wherein the contact surface and the work surface have a distance therebetween in a direction normal to the work surface,

wherein a distance at a side of the mandrel closer to the processing machine and a distance at the opposite side of the mandrel have a distance difference therebetween,

wherein a diameter of the outer peripheral surface on the mandrel is set in such a way that the distance difference with the mandrel flexed during formation of the dimples becomes smaller than that before flexing of the mandrel.

2. The dimple-forming burnishing tool according to claim 1,

wherein the mandrel has a first sectional line which is positioned on the outer peripheral surface and at said side closer to the work surface,

wherein the first sectional line is defined by sectioning the mandrel by a plane which is normal to the work surface and includes an axis of the mandrel,

wherein the work surface has a second sectional line on the work surface,

wherein the second sectional line is defined by sectioning the work surface by the plane,

wherein the first sectional line and the second sectional line have a parallel degree therebetween,

wherein a diameter of the outer peripheral surface on the mandrel at the opposite side to said side closer to the processing machine is set to be larger than that at the side closer to the processing machine, so that the parallel degree with the mandrel flexed during formation of the dimples becomes smaller than that before flexing of the mandrel.

3. The dimple-forming burnishing tool according to claim 2,

wherein the outer peripheral surface of the mandrel has a side shape in a frustum of a circular cone which diverges toward the opposite side to said side closer to the processing machine.

4. The dimple-forming burnishing tool according to claim 1, wherein the balls are spaced apart from each other in a peripheral direction of the frame and in a direction parallel with the axis of the frame.

5. The dimple-forming burnishing tool according to claim 1,

wherein the frame comprising:

a frame body fitted to the mandrel from the outside and defining first through-holes for the balls to be fitted thereto, respectively; and

a frame cover fitted to the frame body from the outside, having the balls projecting radially outward from the outer peripheral surface of the frame, and defining second through-holes which coincide in position with the first through-holes for preventing the balls from dropping out of the first through-holes, respectively.

6. A dimple-forming burnishing method comprising: contacting the balls on the work surface to form dimples on the work surface using the dimple-forming burnishing tool according to claim 1.