JPH05185B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] This invention relates to a porous superfinishing grindstone. [Prior art] In general, in superfinishing, abrasive grain size (JIS-
R6001 (depending on the particle size of the abrasive) ranges from #800 (average of 18 to 22 μm) to #3000 (average of average
A fine particle size of 5.9 to 4.7 μm) is applied, and
The surface of the grinding wheel is intended to be used in surface contact with the workpiece. Therefore, in order to obtain a stable and beautiful finished surface, it is fundamentally important that the grinding wheel structure is uniform and porous to prevent clogging or crushing due to surface contact. It is said that In conventional technology, in order to improve the cutting performance of a grinding wheel with a normal standard structure, the selection criteria is a grinding wheel with a soft bonding degree that is made porous by increasing the pore volume in the grinding wheel. Although the cutting performance of the grindstone is improved, the amount of wear of the grindstone is very large, and it is extremely disadvantageous economically, so it cannot be said that it is preferable. In grinding wheels with such a soft bonding degree, the bonding force that supports the abrasive grains weakens as the binder decreases, resulting in a sharp increase in grinding wheel wear.As a countermeasure, it is necessary to maintain the soft bonding degree. However, as the amount of binder increases, artificial porosity agents such as organic particles are sometimes added to prevent the degree of bonding from becoming hard. (For example, Japanese Patent Application Laid-open No. 161269/1983). In this case, the size of the artificial porosity agent must be smaller than the diameter of the abrasive grains in order to maintain the fine and uniform structure unique to the abrasive grains and binder in fine-grained abrasive wheels used in superfinishing processes. Or, since the equivalent level of fine grains are applied, the surface of the product grindstone is smooth and dense, and the fine pores peculiar to porous grindstones cannot be observed with the naked eye. In other words, since no essential improvements have been made to the intrinsic structure of the grinding wheel, increasing the amount of bonding agent within a range that does not make the bonding degree of the grinding wheel hard will improve the wear resistance of the grinding wheel somewhat, but the effect will not be significant. I can't say that there is. In addition, when using a large amount of fine pore agent, the cross section of the grinding wheel becomes apparently dense before firing, making it more likely to crack, and even during firing, cracks can occur due to the reduction of the abrasive grains as aggregate. This may cause deformation, etc. [Problems to be solved by the invention] As described above, with the conventional technology, it is not possible to obtain a porous superfinishing grindstone with excellent wear resistance without impairing cutting performance during superfinishing. There was a problem. [Means for Solving the Problems] In order to solve the above problems, the present invention uses hard abrasive grains such as aluminum oxide, silicon carbide, diamond, cubic boron nitride, etc. Organic particles consisting of large particles with a particle size of ~50 times the particle size and small particle particles with a particle size of 1.5 to 10 times the abrasive particle size are further blended with vitrified bond, molded and fired. This method uses a porous superfinishing grindstone. The details will be described below. First, the particle size of the hard abrasive grains used in this invention is not particularly limited to a range, but in accordance with the above-mentioned Japanese Industrial Standards, it ranges from #800 (approximately 20 μm) to #3000.
(approximately 5 μm) is most commonly used.
Therefore, in order not to destroy the dense structure inherent in ordinary superfinishing wheels that use hard abrasive grains, the size of the pore agent particles must be 20 μm in average diameter.
The following fine particles are preferred. However, when a large amount of microporous agent is used, as mentioned above, the cross section of the whetstone becomes apparently dense before firing, making it easy to crack, and even during firing, the proportion of abrasive grains as aggregate decreases. This makes them more susceptible to cracking or deformation. On the other hand, when using large particles 20 to 50 times the abrasive grain size alone as a porosity agent,
Large particles, unlike small particles, play a sufficient role as aggregates, so they tend to cause defects such as cracks and deformation not only when they are present in large quantities, but also during manufacturing. When the amount is small, the dispersion within the grinding wheel becomes uneven, making it difficult to achieve a homogeneous pore distribution, which is not preferable. Therefore, in this invention, the particle size of the small-sized particles is set to 50 μm or more in average diameter ( 1.5 to 10 times the abrasive grain diameter) is preferable,
In addition, in order to uniformly disperse relatively large pores with a uniform shape in the grinding wheel, and to make them dotted with the grinding wheel action, large particles must have an average diameter of 100 to 500 μm (the diameter of the abrasive grains).
20 to 50 times) is preferable, and since the shape of the pores is uniform, it can be said that it is preferable that the ratio of the major axis and the minor axis or the diameter and height be close to 1, since the shape of the pores is uniform. In the present invention, large particles having a particle diameter of 20 to 50 times the abrasive grain size and small particle particles having a particle diameter of 1.5 to 10 times the abrasive grain diameter are mixed. The most preferable mixing ratio is 1 large particle size particle and 1 part large particle size particle.
2 to 5 parts by volume of small particle size particles per part by volume. Here, if the large grain size particles are small, less than 20 times the abrasive grain size, it is difficult to easily soften the degree of bonding with the grinding wheel, resulting in poor machinability, whereas if the large grain size is more than 50 times the abrasive grain diameter, This is because the particle size is undesirable because it tends to cause cracks, deformation, etc. during the production of the grindstone, and the structure of the grindstone becomes a coarse mesh-like discontinuous structure, which increases the amount of wear of the grindstone. In addition, if the small particle size is less than 1.5 times the abrasive grain size, it will have a dense structure unique to the grinding wheel, and will not be effective as a porous grinding wheel base.
In addition, when the particle size is more than 10 times larger, the formation of large-sized pores increases as they approach the pores of coarse particle sizes.
As a result, the amount of wear on the grinding wheel increases, resulting in the same result as the porous grinding wheel made of only large-sized particles as described above, and the effect is reduced, which is not preferable. moreover,
In the mixing ratio of large-sized particles and small-sized particles of the present invention, if the latter is in a small amount of less than 2 parts by volume, the base of the grinding wheel becomes dense, cutting performance decreases, and clogging or crushing occurs. On the other hand, if the amount exceeds 5 parts by volume, the amount of wear on the grinding wheel will increase.
The effect of adding it decreases, which is not preferable. In this invention, organic particles having the above-mentioned particle size distribution are used as a pore agent. Generally, porosity agents are burned away when a shaped whetstone is fired, forming pores within the whetstone structure, so the organic particles in this invention include, for example, styrene resin, acrylic resin, polyester resin, and modified polyphenylene. It is preferable to use a substance that can be completely burned out, such as oxide or epoxy resin. Furthermore, the vitrified bond used in this invention is commonly used and is not particularly limited. [Function] In this invention, the porous structure formed by the large-sized particles can be used without reducing the abrasive grain volume ratio, compared to the dense structure inherent in the grinding wheel, which has a small amount of wear and has high wear resistance. A soft bond can be easily obtained, and it exhibits the effect of imparting excellent cutting performance without impairing the wear resistance of the grinding wheel. In addition, in this invention, the porous structure formed on the grinding wheel base by small-sized particles is cut into relatively large-sized pores scattered on the working surface of the grinding wheel formed by large-sized particles. This prevents debris from accumulating and allows uniform discharge of cutting debris over the entire working surface of the grinding wheel.
Good cutting action can be maintained with an extremely small amount of grindstone wear. [Example] Granular styrene resin with a particle size of 400 μm as a large particle size particle and a particle size of 65 μm as a small particle size particle was prepared, and the average particle size was Japanese Industrial Standard #1200 (13 μm).
White aluminum oxide (abbreviated as WA) abrasive grain 100
Large particle size particles 4.5 parts by weight as shown in the table
sample 1 in which 13.5 parts by volume and small particle size particles were blended, sample 2 in which 13.5 parts by volume of small particle size particles were blended with 100 parts by weight of WA abrasive grains and no large particle size particles were blended; Sample 3 was prepared in which no particulate steely resin was added. And the sample grindstone is

[Table] In addition to WA abrasive grains and granular steel resin, vitrified bond (15 parts by weight per 100 parts by weight of WA abrasive grains)
(parts by weight) and 30% concentration dextrin liquid (5 parts by volume) are stirred and mixed, and the volume of the abrasive grains, bond, and pores is divided by the volume of the grindstone using a fired grindstone (%).
However, the bulk specific gravity of the raw grindstone is calculated in advance so that the abrasive grain ratio is 42.5%, the bond ratio is 7.5%, and the porosity is 50.0%, and each compounding ratio and molding are determined based on this bulk specific gravity. The conditions (pressure) were determined and a square grindstone was formed. After that, the obtained raw whetstone was dried, and after being kept in an electric furnace at a maximum temperature of 1240°C for 1 hour, it was fired under conditions such that the total time required was 32 hours. Amount of wear, amount of cutting, and finished surface roughness were measured. Each measurement method is as follows. Hardness (RH): Based on the value indicated on Dial B when using a Rockwell hardness type steel ball with a diameter of 1/8 inch and a load of 60 kg. In addition, minus (-)
The hardness is the soft hardness when the long hand passes the set point of 30, then passes the 0 point and stops. Grinding wheel wear amount, cutting amount, and finished surface roughness: Using processing oil (90% mineral oil, 10% sulfurized fatty oil) with a super finishing machine (manufactured by Seibu Jidoki Co., Ltd.), bearing steel (SUJ type 2, Rockwell C scale) was used. 58/62)
The outer surface of the inner cylinder (outer diameter 14.5 mm, width 12 mm) was plunge-cut superfinished using a grindstone working surface (circumferential width 3 mm, axial width 11 mm). The main superfinishing conditions at this time were: a grinding wheel frequency of 1400 cpm;
The maximum inclination angle that gives the shape of the sinusoidal motion trajectory of the abrasive grains at a grinding wheel amplitude of 2 mm and a workpiece rotation speed of 406 rpm.
It was set to 25°. In addition, the pre-processing of the workpiece was ground to a surface roughness of 1.0S, and the super-finishing time was 2.
Each measured value is the average value for four test pieces. From the results shown in the table, it can be seen that the grinding wheel wear amount of Sample 1 (based on this invention) containing both large and small particles of granular steel resin is lower than that of Sample 2 containing only small particles. 1/4, and about 1/5 of Sample 3, which does not contain any granular styrene resin, which is extremely low.
Moreover, the cutting amount of sample 1 did not decrease compared to other samples 2 and 3, but rather increased.
In addition, Sample 1 showed a small value in terms of finished surface roughness, and was clearly superior to Samples 2 and 3. [Effects] As is clear from the above, the porous superfinishing grindstone of the present invention overturns the conventional wisdom that the amount of cutting is increased or the finished surface roughness is obtained at the expense of the amount of wear of the grinding wheel, and Even if the amount of wear is drastically reduced to about 1/4 to 1/5, the machinability does not deteriorate, and at the same time, the finished surface roughness also improves. It can be said that the contribution to processing is extremely large.

Claims (1)

[Scope of Claims] 1. Hard abrasive grains such as aluminum oxide, silicon carbide, diamond, cubic boron nitride, etc., and large particles and abrasive grains having a particle size 20 to 50 times the abrasive grain size. 1. A porous superfinishing whetstone characterized by blending organic particles consisting of small-sized particles having a particle size 1.5 to 10 times larger than the average particle diameter, and further containing vitrified bond, molded and fired. 2. Amount (capacity) of small particle size particles in organic particles
The porous superfinishing grindstone according to claim 1, wherein the amount of the large-sized particles is 2 to 5 times the amount (capacity) of the large-sized particles.