JP2005271158A - Centerless grinding wheel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a centerless grinding wheel, performing high-accuracy grinding by preventing a step from being caused by a difference in thermal expansion in a joint of a wheel. <P>SOLUTION: This grinding wheel 20 is constructed so that a hard abrasive grain layer 2 is formed on the outer peripheral end of a body 1. In the hard abrasive grain layer 2, the hard abrasive grain layers 2a to 2d provided in the outer periphery of the respective wheels are disposed in the longitudinal direction to come into contact with each other in a joint 3 of the wheel 3. The wheel is formed to have the hard abrasive grain layer 2 composed of two or more areas different in coefficient of linear thermal expansion, whereby a difference in coefficient of linear thermal expansion is set to 5×10<SP>-6</SP>K<SP>-1</SP>or less in the joint 3 of the wheel. Two or more thus constructed wheels are sequentially disposed in the longitudinal direction to vary the coefficient of linear thermal expansion of the hard abrasive grain layer 2 in stages. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a centerless grinding wheel for use in centerless grinding of round or cylindrical workpieces such as needle bearings, carbide pins, motor shafts, and ferrules.

  Centerless grinding is a grinding process suitable for peripheral grinding of small diameter round bars and pipes. In this centerless grinding, as shown in FIG. 3, a grinding wheel 20 for grinding the workpiece W, and an adjusting wheel 21 that faces the grinding wheel 20 in a manner of sandwiching the workpiece W and applies a braking force to the workpiece W. And grinding by a centerless grinding machine provided between the grinding wheel 20 and the adjusting wheel 21 and provided with a blade 22 that supports the workpiece W. As shown by the arrows in the drawing, the grinding wheel 20 and the adjusting wheel 21 are The workpiece W is rotated in the same direction, the workpiece W is rotated in the opposite direction, and the outer periphery of the workpiece W is ground by the grinding wheel 20.

  In this centerless grinding, the adjusting wheel 21 is disposed with its axis inclined with respect to the grinding wheel 20, so that the workpiece W advances in the direction of arrow A while sliding on the top surface 22 a of the blade 22. To do.

  In centerless grinding, since the cutting load can be changed within one wheel, roles such as rough grinding and finish grinding can be shared at each part of the abrasive layer. Therefore, by changing the grain size of the abrasive grains in stages and forming an abrasive grain layer according to the role, the feed rate of the work material can be increased and the machined surface roughness can be improved. Precision and high quality processing is possible.

In recent years, demands for reductions in processing accuracy and processing costs have become stricter, and in response to this, wheels have been changed by changing not only the abrasive grain size but also the presence or absence of abrasive coating, the concentration of abrasive grains, the type of bond, etc. Designed. When the wheel is produced in this manner, the abrasive grain layers having different compositions are adjacent to each other, causing a difference in linear thermal expansion between the abrasive grain layers, which causes a problem that processing accuracy is lowered.

  With respect to this problem, Patent Document 1 uses a vitrified grindstone such as glass having a small coefficient of linear thermal expansion as the base metal material to stabilize the processing accuracy. However, it is not a measure against dimensional changes due to direct heat generation during grinding.

  The level of temperature change of M / C and grinding fluid at the start of M / C, at the start of grinding, and at the time of stable grinding is as small as about 10 to 20 ° C., and the thickness of the abrasive layer is about 3 to 5 mm. The impact of expansion is expected to be small. However, the temperature of the grinding point is said to be 500 ° C. to 1000 ° C. or more, and the outer diameter of the wheel changes between the start of grinding and the grinding stability due to the linear thermal expansion coefficient of the abrasive layer near the heat source. It is expected that.

Also, since the composition of the abrasive layer is different for each part of the wheel, the linear thermal expansion coefficient is different, and the amount of heat generated in each wheel is also different, resulting in a difference in wheel outer diameter, A step due to the difference occurs in the wheel.
In the manufacture of a centerless wheel, the length of the wheel is usually about 50 mm, and when a wheel longer than that is manufactured, it is manufactured by succeeding a wheel of 30 to 50 mm. In this case, since the abrasive grain layer is formed by changing the composition for each wheel, a step due to the difference in linear thermal expansion occurs at the joint of the wheel.

JP-A-57-8077

  As described above, the hard abrasive layer formed using abrasive grains having different particle sizes has a different thermal expansion for each hard abrasive layer due to heat generated by grinding. For example, as shown in FIG. 4A, the hard abrasive grain layer 52 is arranged in the longitudinal direction so that the hard abrasive grains 52a to 52c provided on the outer circumferences of the respective wheels are in contact with the joint 53 of the wheel. When the abrasive grain size is increased in the order of the hard abrasive grain layer 52a to the hard abrasive grain layer 52c, as shown in FIG. 4 (b), which is an enlarged view of a portion surrounded by a circle in FIG. 4 (a), A step due to a difference in thermal expansion occurs at the joint of the wheel. If such a step occurs at the wheel joint, high-precision grinding cannot be performed.

  The present invention has been made to solve such problems, and provides a centerless grinding wheel capable of high-precision grinding by suppressing generation of a step due to a difference in thermal expansion at a wheel joint. Objective.

In order to solve the above-described problems, the present invention provides a grinding wheel for grinding a workpiece, an adjusting wheel for sandwiching the workpiece and facing the grinding wheel to apply a braking force to the workpiece, and the grinding A centerless grinding wheel used for grinding by a centerless grinding machine provided with a blade that is installed between a grinding wheel and the adjusting wheel and supports a workpiece, and has a plurality of linear thermal expansion coefficients different in one wheel. A wheel having a hard abrasive layer composed of a region is formed, and a plurality of wheels are sequentially arranged in a longitudinal direction so that a difference in linear thermal expansion coefficient is 5 × 10 ⁻⁶ K ⁻¹ or less at the joint of the wheel. A centerless grinding wheel disposed.

By forming a wheel by integrally forming a hard abrasive grain layer composed of a plurality of regions having different linear thermal expansion coefficients in one wheel, although a difference in thermal expansion occurs in one wheel, it was formed continuously. Since it is a difference in thermal expansion in the abrasive layer, the work material is not caught. In addition, since the difference in coefficient of linear thermal expansion is 5 × 10 ⁻⁶ K ⁻¹ or less at the wheel seam, it is possible to suppress the occurrence of a step due to the thermal expansion difference at the wheel seam. Therefore, according to the configuration of the present invention, it is possible to perform rough grinding to finish grinding with a single grinding wheel, and it is possible to suppress the step within a certain range at the joint of the wheel, so that the work material is not caught, Processing accuracy can be improved.

  According to the present invention, it is possible to perform rough grinding to finish grinding with one grinding wheel, and since no step is generated at the joint of the wheel, the work material is not caught and the processing accuracy can be improved.

  Fig.1 (a) shows the structure of the grinding wheel which concerns on embodiment of this invention. The workpiece W is sandwiched between the grinding wheel 20 and the adjustment wheel 21 and ground.

  The grinding wheel 20 of the present embodiment has a hard abrasive grain layer 2 formed on the outer peripheral end of the main body 1. The hard abrasive layer 2 is formed using diamond, cBN or the like according to the processing conditions and the material of the material to be ground. The hard abrasive layer 2 is formed by arranging the hard abrasive layers 2a to 2d provided on the outer periphery of each wheel in the longitudinal direction so as to be in contact with the joint 3 of the wheel.

The details of the hard abrasive layer 2 are shown in FIG. In the present invention, a wheel having a hard abrasive grain layer 2 composed of a plurality of regions having different linear thermal expansion coefficients is formed, and the difference in linear thermal expansion coefficient is 5 × 10 ⁻⁶ K ⁻¹ or less at the joint 3 of the wheel. Thus, a plurality of wheels are sequentially arranged in the longitudinal direction to change the linear thermal expansion coefficient of the hard abrasive grain layer 2 stepwise.
For example, the linear thermal expansion coefficient of the hard abrasive layer 2 is as follows. The linear thermal expansion coefficient for each hard abrasive layer is the same in all regions in the hard abrasive layer 2a. Of the hard abrasive layer 2b, the difference between the linear thermal expansion coefficient of the region 2b ₁ in contact with the hard abrasive layer 2a across the joint 3 is 5 × 10 ⁻⁶ K with respect to the linear thermal expansion coefficient of the hard abrasive layer 2a. It is set to be ^-1 or less.
Thus, the difference in the linear thermal expansion coefficient between the hard abrasive layers adjacent to each other with the joint 3 interposed therebetween can be set to 5 × 10 ⁻⁶ K ⁻¹ or less, for example, by the following method.

As an example of forming a hard abrasive layer using abrasive grains having different particle sizes, when the abrasive layer A is formed with cBN having a particle size # 1000 and the abrasive layer B is formed with cBN having a particle size # 1500, the particle size # There is currently no 1500 cBN abrasive coated metal, so the abrasive layer A and the abrasive layer B usually produce a linear thermal expansion coefficient difference of 5 × 10 ⁻⁶ K ⁻¹ or more. . An example of the details of the composition of the abrasive grain layer A and the abrasive grain layer B is shown in Table 1.
On the other hand, as in the abrasive layer C in Table 1, the difference in linear thermal expansion coefficient between the abrasive layer A and the abrasive layer C is 5 × by adding Ni powder and adjusting the blending ratio of the filler. It can be adjusted to be a small value of 10 ⁻⁶ K ⁻¹ or less.

In addition to the above methods, instead of Ni powder, general abrasive grains such as SiC and Al ₂ O ₃ , metals such as copper, metal compounds such as meteorite, cryolite and glass, metal oxides Etc. can be added to the bond in consideration of the target grinding performance to adjust the linear thermal expansion coefficient.

Further, in the hard abrasive layer 2c, the linear thermal expansion coefficient of the region 2c ₁ in contact with the hard abrasive layer 2b across the seam 3 is different from the linear thermal expansion coefficient of the region 2b ₂ by 5 × 10 ⁻⁶ K. It is set to be ^-1 or less. In the hard abrasive layer 2d, the linear thermal expansion coefficient in all regions is set so that the difference from the linear thermal expansion coefficient in the region 2c ₂ is 5 × 10 ⁻⁶ K ⁻¹ or less.
In the grinding wheel 20 described above, the average grain size of the abrasive grains is reduced by changing the abrasive grain size in the order from the hard abrasive grain layer 2a to the hard abrasive grain layer 2d. .

In order not to cause a step in the wheel seam 3, it is best to make the compositions of two hard abrasive layers adjacent to each other across the seam 3 equal. In the embodiment of the present invention, as a result of investigating the size of a step that can be allowed to suppress the catching of the work material at the joint 3 of the wheel, the lines of two hard abrasive layer layers adjacent to each other with the joint 3 interposed therebetween. The difference in thermal expansion coefficient is 5 × 10 ⁻⁶ K ⁻¹ or less. The reason will be described below.
In the resin bond wheel, the linear thermal expansion coefficient of the hard abrasive layer is usually set in the range of 3 × 10 ^{−6 to} 25 × 10 ⁻⁶ K ⁻¹ . For example, a hard abrasive layer (abrasive layer A) having a linear thermal expansion coefficient of 5 × 10 ⁻⁶ K ^{−1 and} a hard abrasive layer (abrasive layer) having a linear thermal expansion coefficient of 10 × 10 ⁻⁶ K ⁻¹ B) are adjacent to each other with the joint 3 interposed therebetween, and the wheel is formed with the thickness of the hard abrasive layer being 0.1 mm.
Assuming that the distance from the grinding point is 0.1 mm and the temperature at the grinding point is 500 ° C. or higher, the thickness of the abrasive layer A is 0 when the temperature of the hard abrasive layer changes by 100 ° C. .05 μm and the thickness of the abrasive layer B expands by 0.10 μm. As a result, a step of 0.05 μm is generated between the abrasive layer A and the abrasive layer B.

On the other hand, the grain size of the abrasive grains in order from the inlet side to the outlet side is, for example, # 270, # 600, # 1500, and when the length of each hard abrasive grain layer is 50 mm, the cutting amount in centerless grinding is Each hard abrasive layer has a thickness of about 3 μm, which is 0.06 μm / mm per length of the abrasive layer. Considering the actual usage situation in centerless grinding, if a step exceeding the same depth as the cutting amount per length of the abrasive layer occurs at the wheel seam, the catch of the work material at the wheel seam is remarkable. As a result, the processing accuracy decreases. For this reason, the difference in linear thermal expansion coefficient between two hard abrasive grain layers adjacent to each other with the joint 3 being 5 × 10 ⁻⁶ K ⁻¹ or less can reduce the size of the step, Occurrence of catching of the work material at the joint of the wheel is suppressed.

As described above, the hard abrasive layer 2b and the hard abrasive layer 2c are formed by integrally forming a hard abrasive layer composed of a plurality of regions having different linear thermal expansion coefficients. Although there is a difference in expansion, since it is a difference in thermal expansion within the continuous abrasive grain layer, the work material is not caught.
Further, since the difference in the linear thermal expansion coefficient between the adjacent hard abrasive layers 2 is set to 5 × 10 ⁻⁶ K ⁻¹ or less at the wheel seam 3, the thermal expansion difference at the wheel seam 3 is set. The step due to can be suppressed within a certain range.

  Since the step can be suppressed within a certain range at the wheel seam 3, the material to be ground is not caught by the step, the surface accuracy of the material to be ground is not lowered, and the processing accuracy is improved.

  In addition, said embodiment shows an example of the grinding wheel of this invention, and this invention is not limited to said embodiment, The whole shape of a grinding stone, the shape of a hard abrasive grain layer, the number, etc. Can be appropriately changed.

The test results are shown below.
FIG. 2 shows the configuration of the wheel used in the test. FIG. 2 (a) is a conventional product, and the linear thermal expansion coefficient of the hard abrasive grain layer 2a is 5 × 10 ⁻⁶ K ⁻¹ and the linear thermal expansion coefficient of the hard abrasive grain layer 2b with the wheel joint 3 interposed therebetween. ^Is 10 × 10 ⁻⁶ K ⁻¹ , and the linear thermal expansion coefficient of the hard abrasive layer 2 c is 20 × 10 ⁻⁶ K ⁻¹ .

Inventive product 1 has an abrasive grain layer having the structure shown in FIG. 2 (b), the linear thermal expansion coefficient of hard abrasive grain layer 2a ₁ is 5 × 10 ⁻⁶ K ⁻¹ , and the hard abrasive grain layer 2a ₂ line. The thermal expansion coefficient is 10 × 10 ⁻⁶ K ⁻¹ , the linear thermal expansion coefficient of the hard abrasive grain layer 2b ₁ formed across the joint 3 is 10 × 10 ⁻⁶ K ⁻¹ , and the hard abrasive grain layer 2b ₂ The linear thermal expansion coefficient is set to 20 × 10 ⁻⁶ K ⁻¹ .
Invention 2 has an abrasive grain layer having the structure shown in FIG. 2 (b), the hard abrasive grain layer 2a _{1 has} a linear thermal expansion coefficient of 5 × 10 ⁻⁶ K ⁻¹ , and the hard abrasive grain layer 2a _{2 has} a line. The thermal expansion coefficient is 10 × 10 ⁻⁶ K ⁻¹ , the linear thermal expansion coefficient of the hard abrasive grain layer ₂ b ₁ formed with the joint 3 interposed is 15 × 10 ⁻⁶ K ⁻¹ , and the hard abrasive grain layer ₂ b ₂ The linear thermal expansion coefficient is set to 20 × 10 ⁻⁶ K ⁻¹ .
The comparative product has an abrasive layer having the configuration shown in FIG. 2B, the linear thermal expansion coefficient of the hard abrasive layer 2a ₁ is 5 × 10 ⁻⁶ K ⁻¹ , and the linear heat of the hard abrasive layer 2a ₂ . The expansion coefficient is 10 × 10 ⁻⁶ K ⁻¹ , the linear thermal expansion coefficient of the hard abrasive layer 2b ₁ formed across the joint 3 is 18 × 10 ⁻⁶ K ⁻¹ , and the hard abrasive layer 2b ₂ line. The thermal expansion coefficient is 20 × 10 ⁻⁶ K ⁻¹ .

Test conditions are shown below.
M / C Centerless grinding machine Wheel size 400 ^D × 150 ^T
Work material SUJ-2, Diameter 3 x Length 10
Feeding speed 8m / min
Stock removal 40μm (20μm on one side)

FIG. 2 (c) shows the test results.
The processing time (dressing interval) until the surface roughness of the work material becomes Ra 0.1 μm is 80 hours for the conventional product, 200 hours for the invention product 1, 170 hours for the invention product 3, and 100 hours for the comparison product. It was. From this result, it can be seen that the dress interval is improved by setting the difference in coefficient of linear thermal expansion of the hard abrasive layer at the joint of the wheel within 5 × 10 ⁻⁶ K ⁻¹ .

  INDUSTRIAL APPLICABILITY The present invention can be used as a centerless grinding wheel used when centerless grinding a round bar-like or cylindrical workpiece.

It is a figure which shows the centerless grinding wheel which concerns on embodiment of this invention. It is a figure which shows the structure of the abrasive grain layer of the centerless grinding wheel used for the test, and a test result. It is a figure which shows a mode that it grinds using a centerless grinding wheel. It is a figure which shows an example of the conventional centerless grinding wheel.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Main body 2 Hard abrasive grain layer 2a-2d Hard abrasive grain layer 3 Seam 20 Grinding wheel 21 Adjustment wheel 22 Blade W Workpiece

Claims (1)

A grinding wheel that grinds the workpiece, an adjustment wheel that sandwiches the workpiece and faces the grinding wheel to impart a braking force to the workpiece, and a workpiece that is installed between the grinding wheel and the adjustment wheel A centerless grinding wheel used in grinding by a centerless grinder equipped with a blade for supporting an object, wherein a wheel having a hard abrasive layer composed of a plurality of regions having different linear thermal expansion coefficients is formed in one wheel. A centerless grinding wheel in which a plurality of wheels are sequentially arranged in the longitudinal direction so that the difference in coefficient of linear thermal expansion is 5 × 10 ⁻⁶ K ⁻¹ or less at the joint of the wheels.

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