Patent Application
20250196291
The present disclosure relates to a rotary dresser. The present application claims priority based on Japanese Patent Application No. 2022-052113 filed on Mar. 28, 2022, the entire contents of which are incorporated herein by reference.
WO 2017/145491 (PTL 1) describes increasing life and reducing variations in sharpness and life of a rotary dresser.
A rotary dresser of the present disclosure is a rotary dresser having a super-abrasive grain layer including super-abrasive grains bonded in a single layer to a base metal by a metal binder, in which the super-abrasive grains include first super-abrasive grains having a first average grain diameter, and second super-abrasive grains having a second average grain diameter smaller than the first average grain diameter, a plurality of super-abrasive grains exposed at a surface of the super-abrasive grain layer among the first super-abrasive grains and the second super-abrasive grains have working surfaces formed thereon, and in a region with a highest degree of concentration of the super-abrasive grains, a ratio of a total area of the plurality of working surfaces to an area of an imaginary surface smoothly connecting the working surfaces is 30% or more and 60% or less.
A conventional rotary dresser suffers from short life.
A rotary dresser is used for molding the shape of a grinding surface of a grindstone (truing or dressing). One typical example is a disc-shaped rotary dresser used for truing or dressing of a grindstone for machining gears. In this rotary dresser, a plurality of abrasive grains have working surfaces formed thereon, and a ratio of a total area of the working surfaces on the plurality of abrasive grains to an area of an imaginary surface smoothly connecting these plurality of working surfaces is set to 5 to 30%, to achieve the effect of increasing life and reducing variations in sharpness and life of the rotary dresser.
When configured in this manner, a disc-shaped rotary dresser for gears can achieve the above-described effect. If the above-described features are applied to a forming rotary dresser or the like, however, the dresser still suffers from short life.
To solve the problem described above, the working area of diamonds could be increased, and to do that, the amount of machining for forming working surfaces of the diamonds could be increased, and the abrasive grains could be made denser by filling fine grains between coarse grains.
To that end, the present disclosure relates to a rotary dresser having the following features.
A rotary dresser having a super-abrasive grain layer including super-abrasive grains bonded in a single layer to a base metal by a metal binder, in which the super-abrasive grains include first super-abrasive grains having a first average grain diameter, and second super-abrasive grains having a second average grain diameter smaller than the first average grain diameter, a plurality of super-abrasive grains exposed at a surface of the super-abrasive grain layer among the first super-abrasive grains and the second super-abrasive grains have working surfaces formed thereon, and in a region with a highest degree of concentration of the super-abrasive grains, a ratio of a total area of the plurality of working surfaces to an area of an imaginary surface smoothly connecting the working surfaces is 30 to 60%.
If the total area ratio is less than 30%, there will be too few working surfaces, resulting in reduced life. If the total area ratio is more than 60%, there will be too many working surfaces, resulting in reduced sharpness.
The total area ratio of 30% or more and 60% or less is easily achieved by using super-abrasive grains having a smaller average grain diameter. To improve the sharpness and life of the rotary dresser, it is required to use, for example, larger super-abrasive grains having an average grain diameter of about 0.3 to 0.8 mm. The use of the larger super-abrasive grains is likely to result in a smaller ratio of the total area of the plurality of working surfaces to the area of the imaginary surface. To increase the total area ratio, the amount of grinding for forming the working surfaces on the super-abrasive grains is increased. By combining the second super-abrasive grains having a smaller diameter, the ratio of the total area of the plurality of working surfaces to the area of the imaginary surface can be as large as 30 to 60% even with a small amount of grinding for forming the working surfaces. The life of the rotary dresser is thereby also improved.
When configured in this manner, the rotary dresser can have high wear resistance, and can attain stable sharpness and life.
Since diamonds work during machining, increasing the number of diamonds improves the life.
In a grinding wheel, the degree of concentration (the number of abrasive grains) significantly affects performance such as sharpness. In the case of a rotary dresser, the working area of working diamond portions significantly affects performance, and in particular, abrasive grains having an average grain diameter of about 300 to 800 μm are often used, which exert a pronounced effect on the performance. In the present disclosure, the high working area ratio of the super-abrasive grains can allow for good sharpness and improved life of the dresser.
Preferably, the second average grain diameter is 30% or more and 80% or less of the first average grain diameter. By setting the average grain diameter of the second super-abrasive grains to 30 to 80% of the average grain diameter of the first super-abrasive grains, the second super-abrasive grains can easily fit between the first super-abrasive grains, and the density of abrasive grains is increased, which facilitates increasing the working area ratio of the abrasive grains.
When artificially synthesized diamonds are used as the super-abrasive grains, crystal planes of the diamonds are joined to a joint surface of the base metal in a substantially parallel relationship with the joint surface, because of a shape in which the crystal planes of the diamonds clearly appear. As a result, the super-abrasive grains are densely joined in a stable manner, which can allow for an increase in the working area ratio even with a small amount of grinding for forming the working surfaces on the super-abrasive grains. As a result, the working surfaces can be easily formed, and the super-abrasive grain layer has an increased thickness which leads to improved life.
Preferably, a ratio of a maximum grain diameter to a minimum grain diameter of the first super-abrasive grains and the second super-abrasive grains (a maximum grain diameter D1 of the first super-abrasive grains/a minimum grain diameter D3 of the second super-abrasive grains) is 1.3 to 4.
Preferably, the first average grain diameter is 300 μm or more and 800 μm or less. To dress a grindstone with a rotary dresser, an abrasive grain diameter of the grindstone is about 100 μm to 200 μm, and an abrasive grain diameter of the rotary dresser must be larger than the abrasive grain diameter of the grindstone so as to prevent degradation of dressing performance of the rotary dresser. Thus, the first average grain diameter is set to 300 μm or more. In addition, a forming shape of the super-abrasive grain layer of the rotary dresser has an R of up to about 400 μm, and it is preferable for the average grain diameter of the first abrasive grains to be 800 μm or less to accommodate this shape.
Preferably, the super-abrasive grains are artificially synthesized diamonds.
Preferably, when a cross section of the super-abrasive grain layer is viewed, an average value of distances between the respective first super-abrasive grains and the base metal is smaller than an average value of distances between the respective second super-abrasive grains and the base metal within a certain range.
Preferably, the rotary dresser of the present disclosure is fabricated by a process including the following steps.
As described above, the rotary dresser is fabricated with an inverse method (or an inverse plating method).
When the rotary dresser of the present disclosure is fabricated with the inverse method as described above, both the first super-abrasive grains and the second super-abrasive grains are present on the surface side of the abrasive grain layer of the rotary dresser. Thus, the total area ratio of the working surfaces formed on the plurality of super-abrasive grains can be easily increased, and the life is also improved. In addition, when performing dressing with the rotary dresser of the present disclosure, the second super-abrasive grains having a smaller average grain diameter can also work effectively for the dressing. Thus, the total area ratio of the working surfaces formed on the plurality of super-abrasive grains can be increased even with a reduced overall number of the super-abrasive grains.
In the rotary dresser fabricated with this method, the distances from the lowermost ends of the first super-abrasive grains and the second super-abrasive grains to the base metal vary randomly with each super-abrasive grain and are not uniform. This cored bar may or may not be the base metal. When the cored bar is not the base metal, a configuration for joining the cored bar and the base metal to each other is further provided.
A method of measuring working surfaces is described.
Base metal 103 is made of, for example, stainless steel. Base metal 103 has a cylindrical shape, and a super-abrasive grain layer 101 is provided on an outer circumferential surface of base metal 103. Diamonds are fixed as super-abrasive grains to super-abrasive grain layer 101. Note that CBN (cubic boron nitride) may be used instead of diamond. Furthermore, diamond and cubic boron nitride may be mixed.
A groove 102 extending in a circumferential direction is formed in super-abrasive grain layer 101. This groove 102 is formed along the shape of a workpiece. Such diamond rotary dresser 100 is used for dressing a so-called forming grindstone.
Measuring machine: VR-5000 manufactured by Keyence Corporation. The measurement principle is a “light-section method.” Analysis procedure: (1) Perform three-dimensional measurement. (2) Planarize the shape by one or both of the following A and B. A: Waviness removal (cutoff process), which planarizes waviness of a certain wavelength or more. B: Quadratic curve correction, which planarizes an arc shape obtained by fitting of the entire shape with a quadratic curve. (3) Set a threshold value and calculate a working area.
A setting is made to exclude unnecessary portions. In a minute region exclusion setting, a lower limit value for noise removal is set to [0.01 mm2], and any region having a smaller area than this lower limit value is removed from the total area.
The total area of working surfaces 205 and the area ratio (55.2%) of working surfaces 205 to the area of the trimmed region are calculated using the threshold value and the lower limit value for noise removal.
That is, in the region with the highest degree of concentration of super-abrasive grains 204, the ratio of the total area of the plurality of working surfaces 205 to the area of an imaginary surface 206 smoothly connecting working surfaces 205 is calculated in the step of
Working surface 205 of super-abrasive grain 204 is formed by grinding or polishing of super-abrasive grain 204. The area of working surface 205 can be adjusted by varying an amount of time of the grinding or polishing of super-abrasive grain 204.
The grain diameters of super-abrasive grains 204 are measured with Morphologi, an imaging grain size distribution apparatus manufactured by Malvern. As a result of the measurement, there are at least two peaks P1 and P2. A boundary 401 is drawn at a valley between peaks P1 and P2, and the side of a larger diameter than boundary 401 is defined as first super-abrasive grains, and the side of a smaller diameter than boundary 401 is defined as second super-abrasive grains.
A maximum grain diameter of the first super-abrasive grains is D1, a minimum grain diameter of the first super-abrasive grains is D2, a maximum grain diameter of the second super-abrasive grains is D2, and a minimum grain diameter of the second super-abrasive grains is D3.
An average grain diameter of each of the first super-abrasive grains and the second super-abrasive grains can be measured with Morphologi, an imaging grain size distribution apparatus manufactured by Malvern.
When super-abrasive grains 204 protrude only to a small extent, the peaks of the load curve shown in
The area ratio of super-abrasive grains 204 is measured in groove 102 in this embodiment. However, diamond rotary dresser 100 may not have groove 102 and have a constant height in the X direction of
When a cross section of super-abrasive grain layer 101 is viewed, an average value of distances between respective first super-abrasive grains 1204 and base metal 103 is smaller than an average value of distances between respective second super-abrasive grains 2204 and base metal 103 within a certain range.
To confirm the performance difference due to variation in the working area ratio, rotary dressers of specifications shown in Table 1 were fabricated, and a dressing test for a grindstone was conducted. The unit of average grain diameters of coarse grains and fine grains is μm, which is applicable to other tables as well. The grindstone diameter was 300 mm, the grindstone circumferential speed was 19.1 m/s, the grindstone rotation speed was 1216 rpm, the rotary dresser diameter was 70 mm, the rotary dresser circumferential speed was 8.8 m/s, the rotary dresser rotation speed was 2400 rpm, the circumferential speed ratio was 0.46, the cutting speed was 0.3 μm/rev, the dress-out was 3 sec, and the grindstone was a vitrified bond wheel including CBN abrasive grains.
In Table 1, the life index and the dressing resistance index indicate ratios of the life and the dressing resistance of each sample number when the life and the dressing resistance of Sample No. 3 are 1. The “grinding depth of super-abrasive grain layer surface” is measured in units of μm, and represents an amount corresponding to H in
In addition, it took a considerable amount of time and effort to manufacture a sample having a working area ratio of more than 60%, which also resulted in a low yield. In other words, a sample having a working area ratio of 65% with a large grinding depth of the super-abrasive grain layer was manufactured with time and effort, but resulted in high dressing resistance and chatter vibration.
Furthermore, one type of samples having an average abrasive grain diameter of 650 μm were fabricated for comparison with a conventional rotary dresser. Samples with different working area ratios were fabricated as shown in Sample Nos. 10 to 16, and compared with Sample Nos. 1 to 9. As a result, although there was no significant difference in the life and the dressing resistance, it took a considerable amount of time and effort to fabricate the rotary dressers and adjust the working area ratios, which made mass production difficult.
Next, a test was conducted for the difference due to variation in grain diameter ratio of the first abrasive grains and the second abrasive grains, and variation in ratio of maximum and minimum abrasive grain diameters.
Preferred ranges for these grain diameter ratios were set mainly due to issues in manufacturing a high-quality rotary dresser rather than performance issues of the rotary dresser.
In this test, the average grain diameter of the first abrasive grains was maintained at 650 μm and the average grain diameter of the second abrasive grains was varied, to confirm the difference due to the variation in grain diameter ratio and the variation in ratio of maximum and minimum abrasive grain diameters. Furthermore, the life and the dressing resistance were evaluated using the obtained rotary dressers.
Sample No. 21 to 50 that were manufactured in this Example 2 are shown in Tables 2 and 3.
In this test, a rotary dresser was fabricated, and the surface of a super-abrasive grain layer was ground with a grindstone in order to form working surfaces on abrasive grains. The “grinding depth of super-abrasive grain layer surface” is measured in units of μm, and represents an amount corresponding to H in
As a result, in samples having a ratio of average grain diameters outside the range of 30 to 80%, the working area of the second super-abrasive grains was 0% or very small at any stage. In contrast, in samples having a ratio of average grain diameters within the range of 30 to 80%, it was confirmed that the ratio of the working surfaces formed on the second super-abrasive grains as well was increased. It can therefore be seen that adding the second super-abrasive grains facilitates control of increasing the working area ratio, and facilitates fabrication of a high-quality rotary dresser.
In addition, from the viewpoint of the variation in ratio of maximum and minimum abrasive grain diameters, in samples having a maximum grain diameter/minimum grain diameter value outside the range of 1.3 to 4, the working area of the second abrasive grains was 0% at any stage. In samples having a maximum grain diameter/minimum grain diameter value within the range of 1.3 to 4, the working surfaces were formed on the second abrasive grains as well. It can therefore be seen that adding the second super-abrasive grains facilitates control of increasing the working area ratio, and facilitates fabrication of a high-quality rotary dresser.
A dressing test for a grindstone was then conducted using Sample Nos. 21 to 50 under the same conditions as in Example 1. The results are shown in Tables 4 and 5.
In Tables 4 and 5, the life index and the dressing resistance index indicate ratios of the life and the dressing resistance of each sample number when the life and the dressing resistance of Sample No. 3 are 1. From Tables 4 and 5, it was found that the same tendency appeared as in Table 1 of Example 1.
It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the meaning and scope equivalent to the terms of the claims.
100 diamond rotary dresser; 101 super-abrasive grain layer; 102 groove; 103 base metal; 105 trimmed region; 202 low-melting-point alloy; 203 plated layer; 204 super-abrasive grain; 205 top surface; 280 reference surface; 401 boundary; 1204 first super-abrasive grain; 2204 second super-abrasive grain.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-052113 | Mar 2022 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2023/011441 | 3/23/2023 | WO |
