EP2865490B1 - Pierre à aiguiser de superfinition, procédé de superfinition qui utilise cette dernière - Google Patents

Pierre à aiguiser de superfinition, procédé de superfinition qui utilise cette dernière Download PDF

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Publication number
EP2865490B1
EP2865490B1 EP12879575.4A EP12879575A EP2865490B1 EP 2865490 B1 EP2865490 B1 EP 2865490B1 EP 12879575 A EP12879575 A EP 12879575A EP 2865490 B1 EP2865490 B1 EP 2865490B1
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EP
European Patent Office
Prior art keywords
stone
superfinishing
abrasive grains
conforming
inclined surface
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German (de)
English (en)
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EP2865490A1 (fr
EP2865490A4 (fr
Inventor
Takayoshi MINO
Susumu Nakano
Kenji MARUOKA
Takao Ochi
Masanori SAWASHITA
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NSK Ltd
Mizuho Ika Kogyo KK
Mizuho Co Ltd
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NSK Ltd
Mizuho Ika Kogyo KK
Mizuho Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
    • B24B19/00—Single-purpose machines or devices for particular grinding operations not covered by any other main group
    • B24B19/02—Single-purpose machines or devices for particular grinding operations not covered by any other main group for grinding grooves, e.g. on shafts, in casings, in tubes, homokinetic joint elements
    • B24B19/06—Single-purpose machines or devices for particular grinding operations not covered by any other main group for grinding grooves, e.g. on shafts, in casings, in tubes, homokinetic joint elements for grinding races, e.g. roller races
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24D—TOOLS FOR GRINDING, BUFFING OR SHARPENING
    • B24D3/00—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents
    • B24D3/02—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used as bonding agent
    • B24D3/04—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used as bonding agent and being essentially inorganic
    • B24D3/14—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used as bonding agent and being essentially inorganic ceramic, i.e. vitrified bondings

Definitions

  • the present invention relates to a superfinishing stone for the superfinishing of materials to be machined, in particular, a superfinishing stone suitable for superfinishing the raceway grooves of ball bearings, and to a superfinishing method using the stone.
  • superfinishing machines for exclusive use are generally used.
  • the inner ring or outer ring of a ball bearing is superfinished with such a superfinishing machine
  • the inner ring or outer ring is rotated and a stone held by the stone holder is pressed against the raceway groove and rocked.
  • the stone is thereby reciprocated along the raceway groove within a certain range of angles to superfinish the groove.
  • the superfinishing stone in this machining does not undergo a stone shaping step, such as truing or dressing, in preparation for the processing, unlike stones in grinding. It is therefore necessary that the shape of the working surface of the stone should be regulated beforehand so as to conform to the circular-arc curved surface of the raceway groove to be processed.
  • raceway grooves of the ball bearing have been processed beforehand by grinding which precedes the superfinishing, so as to have a circular-arc cross-section.
  • the raceway groove is efficiently mirror-finished, for example, to an Ra of 0.01 ⁇ m less in a short time period while maintaining the accuracy of the shape formed by the pre-processing grinding.
  • a stone 100 which has, in a tip part thereof, a protrudent circular-arc surface 101 having a radial dimension corresponding to the circular-arc curved surface of the raceway groove, as shown in, for example, Fig. 7 .
  • This superfinishing has been conducted in the following manner.
  • the stone 100 is disposed so that the protrudent circular-arc surface 101 conforms to the outer-ring raceway groove 3 of the outer ring 2, and the outer-ring raceway groove 3 is superfinished while rotating the outer ring 2 and rocking the stone 100 along the direction of the rotation axis of the outer ring 2.
  • a tip part of a stone 200 is made to have a shape configured of: a cylindrical surface portion 201 having a radius of curvature slightly larger than the radius of curvature of the raceway groove of the outer ring; and tapered portions 202 which extend respectively to both sides of the cylindrical surface portion 201 along the axial direction thereof.
  • This shape of the stone 200 brings about a decrease in the area of contact between the outer-ring raceway groove and the stone, resulting in an increase in surface pressure to render the abrasive grains apt to shed.
  • the shape of the stone comes, in a short period, to conform to the shape of the outer-ring raceway groove and the so-called hit comes to continue.
  • the document states that as a result, the work has no portion left unremoved by the grinding and need not be discarded or reprocessed as a defective due to accuracy failure and that the first bearing processed just after stone replacement can be a non-defective product.
  • patent document 1 a plurality of prior-art documents concerning stones are known (patent documents 2 to 6).
  • the stone described in any of the prior-art documents is unsatisfactory in terms of the ability to be conformed (hereinafter referred to also as conformability), and there has been room for improvement.
  • the conforming operation which is performed by means of the work at the time when a new stone is used first has various problems including a decrease in production efficiency in mass- production steps and the occurrence of percent defective due to insufficient formation of a stone working surface.
  • Vitrified-bond stones which employ superhard cubic boron nitride (CBN) abrasive grains or diamond (SD) abrasive grains are increasingly being put to practical use as superfinishing stones in place of the conventional stones employing white aluminum oxide (WA) abrasive grains or green silicon carbide (GC) abrasive grains.
  • CBN cubic boron nitride
  • SD diamond
  • abrasive grains are increasingly being put to practical use as superfinishing stones in place of the conventional stones employing white aluminum oxide (WA) abrasive grains or green silicon carbide (GC) abrasive grains.
  • vitrified stones containing superhard abrasive grains are extensively selected.
  • superhard abrasive grains are expensive as compared with WA or GC abrasive grains and, hence, the stones are required to have such quality that the wear resistance is high or the stone life is long.
  • the amount of stone wear is extremely slight.
  • the amount of stone wear per work is as small as 1 ⁇ m or less; in the case of WA or GC stones, the wear amount thereof is 20-30 times.
  • An object of the invention which has been achieved in view of the circumstances described above, is to provide a superfinishing stone which can be easily conformed to works to be machined and a superfinishing method in which the stone is used.
  • the present inventors have found out a superfinishing stone which satisfies inconsistent stone requirements, i.e., stone quality that brings about improved conformability and finishing performance, and further found out a superfinishing method in which this stone is used.
  • the invention has been thus achieved.
  • That object of the invention is accomplished with the following configurations.
  • the shape of the stone working surface in the tip part is configured of a first inclined surface and a second inclined surface which meet each other approximately in the shape of the letter V. Consequently, the portion which comes into strong contact with the surface to be machined has an increased contact area, while the portion which comes into weak contact therewith has a reduced contact area. As a result, the stone working surface comes to undergo an overall hit and have improved conformability with a minimum number of works required for conforming. Furthermore, by dispersedly disposing soft abrasive grains, a lubricant layer which is non-abrasive, soft, and weak but is less apt to shed is formed, resulting in a further improvement in conformability and a reduction in stone wear amount. Thus, the inconsistent stone requirements, i.e., stone quality that brings about improved conformability and finishing performance, can be simultaneously satisfied.
  • the present inventors directed attention to that portion of the stone which comes into strong contact with the surface to be machined and that portion thereof which comes into weak contact with the surface.
  • the portion which comes into strong contact is prone to suffer clogging in the case where the stone acts hard, but suffers an increased stone wear amount in the case where the stone acts softly.
  • the inventors hence have found that the conformability of a stone, i.e., the conformability of the whole area of the stone working surface, is improved by increasing the area of the stone working surface of that portion of the stone which comes into strong contact and by reducing the area of the stone working surface of that portion of the stone which comes into weak contact.
  • that portion of the stone in which the stone working surface comes into strong contact with surfaces to be machined has been made to have enhanced stone conformability, and the conformability of the whole stone working surface has been improved thereby.
  • the stone working surface of a stone for superfinishing outer-ring raceway grooves acts in the following manner.
  • a stone central portion thereof which is shown as the hatched part in Fig. 10 , comes into continuous strong contact, while the peripheral portions, i.e., the portions other than the stone central portion, come into intermittent weak contact. Consequently, by increasing the stone contact area of the central portion of a stone, the conformability of the stone is improved.
  • Fig. 1 is a slant view of the tip part of a superfinishing stone according to one embodiment of the invention
  • Fig. 2A is a view of the tip part of the superfinishing stone viewed from the straddle direction (IIA of Fig. 1 )
  • Fig. 2B is a view of the tip part of the superfinishing stone viewed from the thickness direction (IIB of Fig. 1 ).
  • the superfinishing stone 10 (hereinafter referred to simply as stone 10) according to this embodiment is equipped at a tip part 11 thereof with a first inclined surface 12a and a second inclined surface 12b which, when one of two perpendicular directions is referred to as thickness direction (direction IIB in Fig. 1 ) and the other is referred to as straddle direction (direction IIA in Fig. 1 ) and when the surfaces are viewed from the thickness direction, extend from a central portion respectively toward both sides at an inclination angle ⁇ with the straddle direction (see Fig. 2B ).
  • the first inclined surface 12a and the second inclined surface 12b meet each other at the straddle-direction central portion to form a ridge 13.
  • the ridge 13 has a sharp approximately letter-V shape so that the straddle width gradually decreases toward the tip.
  • the thickness direction corresponds to the direction of the rotation axis of the outer ring 2 of a ball bearing in an operation for superfinishing the outer-ring raceway groove 3 of the outer ring 2 (the operation includes a conforming operation; the same applies hereinafter), while the straddle direction corresponds to the circumferential direction in the operation for superfinishing the outer-ring raceway groove 3 of the ball-bearing outer ring 2 (see Fig. 5 ).
  • the first inclined surface 12a and the second inclined surface 12b each have the shape of a circular arc when viewed from the straddle direction. More specifically, the tip part of the first inclined surface 12a has a circular-arc shape when viewed from one straddle direction, while the tip part of the second inclined surface 12b has a circular-arc shape when viewed from the other straddle direction.
  • the curvature of the circular-arc shape is set in accordance with the work to be machined. In cases when the outer-ring raceway groove of the outer ring of a ball bearing is to be superfinished, the curvature of the circular-arc shape is set so as to be approximately equal to that of the circular arc of the outer-ring raceway groove.
  • the inclination angle ⁇ is set at 3°-5°.
  • the tip part 11 is rendered closely akin in shape to the outer-ring raceway groove and the stone contact area is increased, thereby improving the conformability.
  • the inclination angle ⁇ is less than 3°, the effect of forming an inclined surface is too low.
  • the maximum conforming amount which is explained below, becomes too large and much time is required for the tip part to have a circular-arc shape that conforms to the outer-ring raceway groove.
  • the inclination angle ⁇ is preferably 3.5°-4.5°, more preferably about 4°.
  • the maximum conforming amount d becomes larger in proportion thereto.
  • the maximum conforming amount d has suitable values, it is necessary to reduce the inclination angle ⁇ as the straddle-direction width B increases. Conversely, it is necessary that as the straddle-direction width B decreases, the inclination angle ⁇ should be increased.
  • the conforming operation is easy when the stone working area is less than 10 mm 2 , and is not easy when the area is 10 mm 2 or larger.
  • the maximum conforming amount d is preferably 0.13-0.22 mm, more preferably about 0.175 mm.
  • the stone central portion, of the stone working surface that is always in contact with the surface being processed undergoes accelerated wear, and this not only increases the area of the stone working surface but also rapidly conforms the whole stone.
  • the center of the circular arc of the raceway groove of an outer ring formed by pre-processing grinding in the state of having been attached to a superfinishing machine, does not always coincide with the center line of the stone.
  • the occurrence of even a slight offset might make the stone suffer a deformation, chipping, etc., resulting in troubles such as a decrease in superfinishing accuracy or efficiency, etc.
  • the tip part 11 of this stone 10 can be shaped with a rotary dresser.
  • Figs. 4A and 4B show an example of shaping methods for shaping the tip part 11 of a stone 10 with a rotary dresser.
  • a stone 10 is disposed so that the center line Y thereof is offset from a perpendicular line X which is perpendicular to the central axis O of a rotary dresser 50. Specifically, while the center line Y of the stone 10 is kept parallel with the perpendicular line X, the stone 10 is disposed in such a position that the center line Y has shifted upward in the straddle direction by a distance equal to, for example, a half (T/2) of the straddle width (T) of the stone 10.
  • This offset amount is set so that the first inclined surface 12a to be formed has an inclination angle of 3°-5°.
  • the stone 10 in this state is moved parallel with the perpendicular line X toward the rotary dresser 50 and pressed against a dressing groove 51 of the rotary dresser 50, thereby shaping the tip part.
  • first plunge processing is conducted.
  • that surface 16 of the tip part 11 of the stone 10 which is on one side is shaped into a circular-arc shape and a first inclined surface 12a is formed in the tip part 11 on said one side.
  • the stone 10 is reversed with respect to the straddle direction, and this stone 10 is disposed in the same position relative to the rotary dresser 50.
  • the stone 10 is disposed so that the center line Y of the stone 10 coincides with the position shifted upward in the straddle direction from the perpendicular line X perpendicular to the central axis O of the rotary dresser 50 by a distance equal to a half (T/2) of the straddle width (T) of the stone 10.
  • T/2 half of the straddle width
  • This offset amount also is set so that the second inclined surface 12b to be formed has an inclination angle of 3°-5° and that this inclination angle is equal to that of the first inclined surface 12a.
  • the grinding stone 10 in this state is moved parallel with the perpendicular line X toward the rotary dresser 50 and pressed against the dressing groove 51 of the rotary dresser 50, thereby shaping the tip part.
  • second plunge processing is conducted.
  • that surface 18 of the tip part 11 of the stone 10 which is on the other side is also shaped into a circular-arc shape and a second inclined surface 12b is formed in the tip part 11 on said other side.
  • a stone 10 is produced.
  • the first inclined surface 12a and the second inclined surface 12b are curved so as to be slightly recessed due to the curvature of the rotary dresser, as shown in Fig. 3 .
  • the inclination angles ⁇ in this case are, as shown in Fig. 3 , the angle formed by the straddle direction and a line which connects the top of the ridge 13 to the end of the one-side surface 16 and the angle formed by the straddle direction and a line which connects the top of the ridge 13 to the end of the other-side surface 18, when the tip part 11 is viewed from the thickness direction.
  • the stone 10 is a composite-superabrasive-grain vitrified-bond stone obtained by binding composite superabrasive grains including soft abrasive grains having no abrasive properties and hard abrasive grains having abrasive properties, with a vitrified bond.
  • the hard abrasive grains are cubic boron nitride (CBN), diamond (SD) (each having a new Moh's hardness of 14 or 15), etc.
  • the soft abrasive grains are cerium oxide (CeO 2 ; hardness, 4-5), barium sulfate (BaSO 4 ; hardness, 3-4), zirconium oxide (ZrO 2 ; hardness, 8-9), silicon oxide (SiO 2 ; hardness, 7-8), etc.
  • the abrasive-grain mixture may have such a volume ratio that the proportion of the hard abrasive grains is 60-90% and that of the soft abrasive grains is 10-40%. A more suitable volume ratio in the mixture is that the proportion of the hard abrasive grains is 70-80% and that of the soft abrasive grains is 20-30%.
  • the binder 10 to be used for the stone 10 of the invention is a binder regulated so as to have a softening temperature not higher than a given value, so that the soft abrasive grains, which have chemical reactivity, are not chemically or thermally altered. It is preferable that the binder should be configured of 80-95% by weight low-melting inorganic glass and 5-20% by weight high-melting inorganic mineral.
  • the stone 10 may be produced by evenly mixing the abrasive grains, the binder, and ingredients including a pore-forming agent and other aids and then subjecting the mixture to powder regulation, molding, drying, and burning.
  • the burning temperature for stone formation may be 750°C.
  • the soft abrasive grains are (A) BaSO 4 (average particle diameter, 6.0 ⁇ m), (B) CeO 2 (average particle diameter, 1.4 ⁇ m), (C) ZrO 2 (average particle diameter, 1.0 ⁇ m), and (D) SiO 2 (average particle diameter, 5.0 ⁇ m).
  • the superabrasive (hard abrasive) grains used as comparative abrasive grains are (E) CBN (average particle diameter, 3.0 ⁇ m).
  • the grainstones are as follows. The same vitrified bond is used, and the binder amount is constant at 0.35 parts by weight per unit abrasive-grain amount. Furthermore, the molding conditions and the burning conditions also are the same.
  • Table 1 are shown the RH hardness values of the various stones. The RH hardness is determined by the Rockwell test method using scale H in accordance with JIS R6240. Minus (-) values of the hardness indicate the case where the stone is soft and the longer indicator passes by the set point 30 and by 0 and then stops.
  • the machining oil is a water-insoluble oil based on a sulfurized fatty oil.
  • the working surface of each stone is shaped into a protrudent circular-arc surface having a radius corresponding to the circular-arc cross-sectional shape of the inner surface of the groove.
  • the pores have been filled with a high-melting wax.
  • the numbers of works required for conforming the soft-abrasive-grain stones do not differ much from that for the CBN (hard-abrasive-grain) stone although smaller than that. It is rather noted that although the soft-abrasive-grain stones have minus (-) values of RH hardness and are exceedingly soft as compared with the CBN stone, there is little difference therebetween in the number of works for conforming. Furthermore, the average stone wear amount is as small as about 1/2 that of the CBN stone. Namely, the stone layer constituted of soft abrasive grains forms a substance layer which has a soft and weak stone friction surface but is less apt to shed or wear, i.e., a clean layer, thereby bringing about a reduction in stone wear.
  • Figs. 6A to 6E are views which show photographs of the working surfaces of the test stones; Fig. 6A shows the case of the BaSO 4 abrasive grains (A), Fig. 6B shows the case of the CeO 2 abrasive grains (B), Fig. 6C shows the case of the ZrO 2 abrasive grains (C), Fig. 6D shows the case of the SiO 2 abrasive grains (D), and Fig. 6E shows the case of the CBN abrasive grains (E).
  • the soft abrasive grains which do not have an abrading action, mitigate stone clogging or dulling without being directly affected by bond erosion due to chips, thereby serving as a lubricating surface layer to bring about a reduction in stone wear.
  • the vitrified stone which includes the composite abrasive grains selected in accordance with the invention, has a higher Pc than conventional stones which contain no soft abrasive grains. This is because the soft abrasive grains do not readily shed or wear upon an increase in the pressure applied to the stone surface and do serve as a lubricating surface layer to contribute to a decrease in stone wear. Namely, it can be seen that the soft abrasive grains form a layer of a substance which has a soft and weak stone friction surface but is less apt to shed or wear, i.e., a layer of a lubricating substance.
  • the hard abrasive grains in sections 1 to 9 are cubic boron nitride (CBN), while the soft abrasive grains in sections 1 to 3, 6, and 7 are cerium oxide (CeO 2 ).
  • the particle diameter of the CBN in sections 1 to 5 is 4-8 ⁇ m (2,500 mesh), and that of the CBN in sections 6 to 9 is 2-4 ⁇ m (4,000 mesh).
  • the materials in section 1 and section 3 are of the same quality.
  • the binder for each stone is a vitrified bond based on R 2 O-RO-Al 2 O 3 -SiO 2 -B 2 O 3 .
  • the stones were examined also for wear property, which relates to the number of works for conforming, and for the volume ratio (%) of stone constituent elements (content of hard abrasive grains, Vgl; content of soft abrasive grains, Vg2; porosity Vp; and binder content Vb) and critical stone pressure Pc (MPa), which both may affect finishing performance.
  • Vgl hard abrasive grains
  • Vg2 content of soft abrasive grains
  • Vb porosity Vp
  • binder content Vb binder content
  • MPa critical stone pressure
  • the stone has a rectangular stick shape having a stone straddle width of 5.5 mm and a thickness of 5.5 mm.
  • a first inclined surface and a second inclined surface which each had a protrudent circular-arc shape with a radius of 3.5 mm that corresponded to the recessed circular-arc cross-section of the raceway groove of an outer ring were formed in the working surface of each stone so that the working surface, when viewed from the direction of the rotation axis of the outer ring as a work to be machined, inclined from the central portion thereof toward both side surfaces of the stone so as to form the shape of the letter V having an angle within the given range.
  • the same shape as in the embodiment described above, which is shown in Fig. 1 was imparted (hereinafter this shape is often referred to as "two-direction R-curved-surface shape").
  • the outer-ring raceway groove had a groove bottom diameter of 35.75 mm.
  • the conditions for conforming which were common between the Examples and the Comparative Examples, included: a surface roughness resulting from pre-processing grinding of 0.25-0.30 ⁇ m Ra (center-line average roughness); a groove-bottom surface velocity of 5 m/s; a stone pivoting frequency of 13.3 Hz; a conforming period of 4 seconds; and a water-insoluble oil based on sulfurized fatty oil was used as a machining oil.
  • Completion of the conforming of a stone working surface is determined in such a manner that the stone working surface is colored with an oil-based paint and the time when the coloration has disappeared is used as an index to the completion.
  • the conforming pressure was set at 3.0 MPa, which was not higher than the critical stone pressures shown in Table 2.
  • the number of specimens for each stone is 3-4.
  • the inclination angle in the Example classified as section 1 was changed in the range of 3°-5°. As a result, the number of works for conforming was as small as 1-3. Meanwhile, in the Comparative Example classified as section 3, which was equal in quality to the Example classified as section 1, the inclination angle was further reduced to 2° and further increased to 6° and to 8° and the effects thereof were examined. As a result, in the case where the inclination angle was as small as 2°, the state of that surface of the stone which was in contact with the work being machined was the same as that of ordinary stones. Namely, the effect of the stone working surface of the Example wherein that portion of the stone working surface which comes into strong contact with the surface being machined has enhanced conformability was not produced. In the case where the inclination angle was increased beyond 5°, the maximum conforming amount increased and it was necessary that a large number of works for conforming be used for imparting a circular-arc shape conforming to the raceway groove of the outer ring.
  • This test relates to the number of works for conforming with respect to the shape of the stone working surface.
  • the number of works for conforming in the case where the stone working surface has been made to have the two-direction R-curved-surface shape according to the invention is about 1/5 or less the number of works for conforming in the case of the conventional one-direction R-curved-surface shape. That surface shape according to the invention made it possible to reduce the number of works for conforming to 1, which is the minimum number.
  • sections 1 and 7 as which composite-superabrasive-grain stones including both soft abrasive grains and hard abrasive grains were classified, were clearly smaller in the number of works for conforming than sections 4 and 9, in which the abrasive grains consisted only of hard abrasive grains.
  • Section Inclination angle (°) Number of works for conforming Comparative Example 1 - 16 7 - 20 Comparative Example 4 - 22 9 - 27
  • This test relates to the setting of stone pressure in a conforming operation according to the invention. Namely, the stone pressure was set at values lower than the critical stone pressure or set at a value higher than the critical stone pressure, and the resultant changes in the number of works for conforming were determined. Furthermore, the stone working surfaces obtained by the conforming operations were used to ascertain the finishing performance thereof.
  • the Example classified as section 7, which was stably small in the number of works for conforming in ⁇ Conforming Test 1>, and the Comparative Example classified as section 9 were used as specimens.
  • the stone shape in either case was the two-direction R-curved-surface shape having an inclination angle of 4°.
  • the outer-ring raceway groove of the outer ring of a ball bearing was superfinished.
  • the surface velocity of the work to be machined is 5 m/sec in both rough machining and finishing.
  • the stone rocking frequencies are 13.3 Hz for rough machining and 2.0 Hz for finishing.
  • the processing periods are 8 seconds for rough machining and 2 seconds for finishing. With respect to each stone, ten works were processed and average values were determined therefrom.
  • the stone surface pressure for both rough machining and finishing is set at a value lower than the conforming pressures, that is, set at 2.5 MPa, which is less than 0.8Pc.
  • the Examples are highly abrasive, show a smaller stone wear amount, and attained a lower surface roughness than the Comparative Examples. Consequently, the Examples had a large value of finishing ratio and were clearly high-performance stones.
  • the conforming pressure exceeds the critical stone pressure (Pc)
  • the stone wear amount (W) increases and a deterioration in finished surface (Ra) or a decrease in finishing ratio (T/W) results, although the number of works for conforming (N) decreases.
  • the conforming pressure is not higher than the critical stone pressure (Pc)
  • the number of works for conforming (N) increases and the stock removal (T) decreases although the surface roughness is low due to a decrease in grinding wear amount (W).
  • a preferred conforming pressure is in the range of 0.8Pc to 1.0Pc.
  • the conforming pressure should be 0.85Pc to 0.95Pc (90 ⁇ 5%).
  • Example Comparative Example Example Comparative Example Example Comparative Example Section 7 9 7 9 7 9 Number of works for conforming 0.8Pc 0.9Pc 1.05Pc N (number of works) 1-2 3-5 1-2 2-4 1-2 2-3 Removal amount T ( ⁇ m/work) 8.9 8.2 9.2 8.6 11.6 10.0 Stone wear amount W ( ⁇ m/work) 0.57 0.90 0.58 0.95 0.75 1.14 Surface roughness Ra ( ⁇ m) 0.021 0.025 0.026 0.029 0.033 0.034 Finishing ratio T/W 15.6 9.1 15.9 9.1 15.5 8.8
  • the shape of the stone working surface in the tip part is configured of a first inclined surface and a second inclined surface which meet each other approximately in the shape of the letter V, the portion which comes into strong contact with the surface to be machined has an increased contact area, while the portion which comes into weak contact therewith has a reduced contact area.
  • the stone working surface comes to undergo an overall hit and have improved conformability with a minimum number of works required for conforming.
  • a lubricant layer which is non-abrasive, soft, and weak but is less apt to shed is formed, resulting in a further improvement in conformability and a reduction in stone wear amount.
  • the inconsistent stone requirements i.e., stone quality that brings about improved conformability and finishing performance, can be simultaneously satisfied.
  • the superfinishing stone of the invention is reduced in stone wear amount and can be prevented from having a shortened life due to stone shape deformation. Desired surface accuracy can hence be obtained therewith. Consequently, although the superfinishing of the raceway grooves of outer rings has limitations on stone length (stone use amount) and hence has had problems in that the stone life is short and the frequency of stone replacement is high, it is possible to prolong the stone life by using the vitrified-bond stone in which superhard cubic boron nitride (CBN) abrasive grains or diamond (SD) abrasive grains are used.
  • CBN cubic boron nitride
  • SD diamond
  • the superfinishing stone and superfinishing methods using the stone were explained with respect to use thereof as superfinishing stones suitable for the outer-ring raceway groove of a ball bearing equipped with an inner ring, an outer ring, and a plurality of balls freely rollably disposed between the inner and outer rings.
  • the superfinishing stone of the invention can be applied not only to outer-ring raceway grooves but also to inner-ring raceway grooves and other works to be machined.
  • the hard abrasive grains are not limited to cubic boron nitride (CBN) and diamond (SD), and use may be made of other hard abrasive grains such as white aluminum oxide (WA) or silicon carbide (GC) abrasive grains.
  • CBN cubic boron nitride
  • SD diamond
  • other hard abrasive grains such as white aluminum oxide (WA) or silicon carbide (GC) abrasive grains.
  • abrasive grains of white aluminum oxide (WA) and silicon carbide (GC) may be used.

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  • Chemical & Material Sciences (AREA)
  • Mechanical Engineering (AREA)
  • Ceramic Engineering (AREA)
  • Inorganic Chemistry (AREA)
  • Polishing Bodies And Polishing Tools (AREA)
  • Finish Polishing, Edge Sharpening, And Grinding By Specific Grinding Devices (AREA)
  • Grinding And Polishing Of Tertiary Curved Surfaces And Surfaces With Complex Shapes (AREA)

Claims (6)

  1. Pierre de superfinition (10) équipée à une partie d'extrémité (11) de celle-ci d'une première surface inclinée (12a) et d'une seconde surface inclinée (12b), chacune ayant un forme d'un arc de cercle lorsqu'observée depuis une seconde direction, caractérisée en ce que
    la première surface inclinée (12a) et la seconde surface inclinée (12b), lorsqu'observées depuis une première direction, s'étendent depuis une partie centrale respectivement vers les deux côtés à un angle d'inclinaison allant de 3° à 5° avec la seconde direction qui est perpendiculaire à la première direction et se rejoignent l'une et l'autre pour former une arête ayant approximativement la forme de la lettre V, et en ce que la pierre de superfinition est obtenue en liant des grains abrasifs composites à l'aide d'une liaison vitrifiée, les grains abrasifs composites comprenant des grains abrasifs tendres qui ont une réactivité chimique avec un matériau à usiner mais ne possèdent pas de propriétés abrasives à l'encontre de celui-ci et des grains abrasifs durs qui ont des propriétés abrasives à l'encontre du matériau à usiner.
  2. Pierre de superfinition selon la revendication 1, caractérisée en ce que, lorsque la longueur dans la seconde direction qui est la longueur le long de la seconde direction est exprimée par B (mm) et l'angle d'inclinaison de la première surface inclinée (12a) et de la seconde surface inclinée (12b) est exprimé par α (°), alors la quantité conformation maximale d représentée par l'équation suivante (I) est de 0,13 à 0,22 mm d = B / 2 × tan ⁢ α
    Figure imgb0005
  3. Pierre de superfinition selon la revendication 1 ou 2, caractérisée en ce que les grains abrasifs composites comprennent 10 à 40 % des grains abrasifs tendres et 60 à 90 % des grains abrasifs durs, en termes de rapport volumique dans le mélange.
  4. Pierre de superfinition selon l'une quelconque des revendications 1 à 3, caractérisée en ce que les grains abrasifs durs sont des grains abrasifs durs d'au moins un type choisi parmi des grains abrasifs de nitrure de bore cubique et des grains abrasifs de diamant et les grains abrasifs tendres sont des grains abrasifs tendres d'un ou plusieurs types choisis parmi de l'oxyde de cérium, du sulfate de baryum, de l'oxyde de silicium, et de l'oxyde de zirconium.
  5. Procédé de superfinition qui comprend la superfinition de la gorge de chemin de bague extérieure de la bague extérieure d'un roulement à billes en utilisant la pierre de superfinition (10) selon l'une quelconque des revendications 1 à 4, caractérisé en ce que
    la pierre de superfinition est disposée de telle sorte que la première direction est parallèle à la direction de l'axe de rotation de la bague extérieure et la seconde direction coïncide avec la direction circonférentielle de la bague extérieure et
    une opération de conformation de la pierre de superfinition est effectuée avant l'opération de superfinition à une pression qui est égale à 90±5 % de la pression critique de la pierre.
  6. Procédé de superfinition selon la revendication 5, caractérisé en ce que l'opération de superfinition est effectuée à une pression de surface de pierre qui est inférieure à la pression utilisée lors de l'opération de conformation.
EP12879575.4A 2012-06-21 2012-08-29 Pierre à aiguiser de superfinition, procédé de superfinition qui utilise cette dernière Active EP2865490B1 (fr)

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JP6409474B2 (ja) * 2014-10-03 2018-10-24 株式会社ジェイテクト 砥石、砥石面形状の決定方法、及び、砥石の製造方法
CN105252437A (zh) * 2015-10-09 2016-01-20 芜湖市鸿坤汽车零部件有限公司 一种铈、钛前驱复合树脂砂轮及其制备方法
US10384326B2 (en) * 2015-12-21 2019-08-20 General Electric Company Surface treatment of turbomachinery
JP7340254B2 (ja) * 2020-01-23 2023-09-07 株式会社ミズホ ビトリファイド超仕上げ砥石
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EP2865490A4 (fr) 2015-04-29
JP5961457B2 (ja) 2016-08-02
CN103648719A (zh) 2014-03-19

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