JPH0669669B2 - Super Abrasive Grain - Google Patents

Description

The present invention relates to a superabrasive grain superfinishing grindstone.

[Conventional technology]

Usually, in the super finishing process, the convex portion of the workpiece and the grindstone come into contact with each other at the initial stage of the machining to increase the contact pressure, and the convex portion is rapidly cut and flattened. As the machining progresses, the grindstone and the machined surface of the workpiece come into a state close to surface contact, the contact pressure decreases, and the cutting action automatically stops.

In this state, chips are not generated and a vanishing action of rubbing is performed, and the surface of the workpiece finally becomes a mirror finish with a black glow.

Conventionally, a grindstone made of aluminum oxide based abrasive grains and cubic boron nitride abrasive grains (hereinafter referred to as CBN abrasive grains) has been used for this series of processing.

Performed using a grindstone made of aluminum oxide-based abrasive grains, for example, super finishing of radial ball bearing raceways is
A few tens of μm for a radius cutting amount of 4 to 6 μm per workpiece
This is done in exchange for the heavy wheel wear.

On the other hand, in the above processing performed using the CBN abrasive grain, the CBN abrasive grain has a hardness about 2.2 times that of the aluminum oxide abrasive grain and is tough and hard to break, so the abrasion of the stone is several μm with respect to the radius cutting amount. Alternatively, it is as small as 1 μm or less. In addition, even with a large cutting force that acts at the beginning of processing, the abrasive grains do not crush, and the number of working abrasive grains increases with the increase of the contact area with the workpiece, and the cutting amount of the grindstone also increases. There is no wear (blindness) or clogging. Since the cutting action does not stop even in the process of finishing the machining, the cutting state of the minute amount is continued. As a result, the surface of the work piece has a finished surface resembling a white surface with low gloss.

[Problems to be Solved by the Invention]

In the conventional super-finishing process, even using any one type of grindstone of the aluminum oxide-based abrasive grains or CBN abrasive grains,
By skillfully utilizing the critical pressure and setting working conditions based on this, it is possible to perform rough, medium, and finishing processing equivalent to that using two or three types of grindstones.

However, when aiming for the highest efficiency, finishing accuracy and economy, there was a limit to the processing with only one kind of grindstone.

In particular, in mirror finishing using unstable and spontaneous clogging, there is a problem in that the accuracy of roughness of the surface of the workpiece after machining becomes uneven.

The present invention has been made to solve such a problem, and provides a superabrasive superfinishing grindstone capable of efficiently performing from rough finishing to accurate mirror finishing in one step in a short time. That is the purpose.

[Means for Solving the Problems]

The superabrasive grain superfinishing grindstone provided by this invention is a superabrasive grain superfinishing grindstone formed by combining diamond abrasive grains and CBN abrasive grains with a binder, and the volume ratio of the diamond abrasive grains in the grindstone is 5 ~ 15%, the volume ratio of the CBN abrasive grains in the grindstone is 1 to 3.6 times the diamond abrasive grains, the particle size of the diamond abrasive grains is almost the same as that of the CBN abrasive grains, the binder is vitrified The binding hardness of the superabrasive superfinishing grindstone was 30 to 80 on the Rockwell hardness scale H scale.

Volume ratio of diamond abrasive grains in the grindstone is 5 to 15%
The reason is that if it is less than 5%, the burnishing effect of the diamond abrasive grains is small and it takes a long time to finish the mirror surface, so that the mirror surface finish cannot be performed efficiently. This is because the cutting performance of the CBN abrasive grains is impaired and mirror finishing can be done quickly, but removal of the machining allowance is delayed (the grindability of the work piece deteriorates).

The reason why the volume ratio of the CBN abrasive grains in the grindstone is 1 to 3.6 times that of the diamond abrasive grains is as follows.

That is, in the one-step processing of the low-speed rocking bead, the effect is large if the mixing ratio of the CBN abrasive grains is increased in order to remove the machining allowance more quickly within the required tolerance of the finished surface roughness. However, if the mixing ratio of diamond abrasive grains and CBN abrasive grains exceeds 1: 3.6, specular gloss is reduced and the quality of appearance is reduced, and it is not possible to secure the necessary amount of binder in the stone. .

On the other hand, in a two-step superfinishing process for the purpose of achieving ultra-precise surface finish roughness with a machining allowance of 1 to 2 μm, if the mixing ratio of diamond abrasive grains and CBN abrasive grains is 1: 1, it will be It is possible to obtain a super-mirror surface of 0.01 μm Rmax or less. However, if the above mixing ratio is less than 1: 1, the stock removal will approach 0 (zero) μm without limit, cutting marks will remain during roughing, and a problem will occur with the finished surface roughness.

In the super finishing process performed under the surface contact condition of the grindstone and the workpiece,
It is necessary to prevent inconvenient grindstone clogging and finish the surface of the workpiece with a uniform mirror surface without scratches. As a binder for this purpose, a virified binder having a large abrasive grain support strength and bond rigidity and capable of forming a grindstone structure with pores is optimal.

Since diamond abrasive grains are thermally unstable and damaged in the air in a high temperature range of about 650 ° C. or higher, low temperature firing is required. Therefore, for CBN wheels containing diamond abrasive grains, a vitrified binder containing glass frit as a main component is selected. However, the object of the present invention can be achieved even with a binder other than the vitrified binder, which is metallic or organic.

It is preferable that the CBN abrasive grains and the diamond abrasive grains have substantially the same diameter. When the diamond abrasive grains are made finer than the CBN abrasive grains, the porous effect of the vitrified superfinishing stone is lost due to the filling effect, and the cross section of the stone becomes dense, which is not preferable. On the other hand, if the particles are made coarser, the minute amount of uniform wear-removing action on the working surface of the grindstone is impaired, which adversely affects the finishing performance such as the grindstone wear amount, the finished surface roughness, and the machinability.

In the super finishing process, if the grindstone is too hard, the machinability is poor, and grinding marks remain on the pre-processed surface, making it difficult to achieve a uniformly smooth mirror finish.On the contrary, if the grindstone is too soft, it becomes a white surface. Mirror finishing requires, for example, a long time under lower pressure conditions.

Therefore, the bonding hardness of the superfinishing stone according to the present invention uses a Rockwell hardness tester and a 1/16 ″ steel ball as an indenter,
The range of 65 to 90 is most preferable in the indicated value on the dial scale (red) when the test load is 20 kg. This number is normal
The HRH hardness (Rockwell hardness meter H scale, 1/8 "steel ball indenter, test load 60 kg, dial scale red) corresponds to a range of approximately 30 to 70. However, an upper limit of 80 is a practical range and is a preferable range. .

[Action]

Since the diamond abrasive grains are mixed with the CBN abrasive grains in the above ratio, it is possible to achieve a mirror finish with a finished surface roughness of 0.10 μm Rmax or less without causing the abrasive grains to be clogged or the grindstone to be clogged.

It is not necessary to sacrifice machinability and perform mirror-finishing by utilizing the crushing of the abrasive grains and the clogging of the grindstone as in the conventional case.
According to the present invention, the machinability and the mirror finishing ability can be simultaneously satisfied. Further, the hardness of the grindstone, which is a factor that affects the performance of the superfinishing grindstone, is, for example, around 80 in Rockwell hardness (1/16 ″ steel ball pressure, test load 20 kg). Therefore, according to the grindstone of the present invention, The single-step processing enables efficient processing in a short time from rough finishing to mirror finishing.

〔Example〕

 An embodiment of the present invention will be described.

Borazon CBN micron powder from G, E, USA, for grade number G3, micron grade 2 to 4 μm CBN abrasive grains,
Similarly, diamond abrasive grains having a micron grade of 2 to 4 μm manufactured by G and E were blended.

The total amount of CBN abrasive grains and diamond abrasive grains was 100 parts, and the amount of the vitrified bond binder to be mixed was constant at 45 parts.

Also, the degree of bonding of the grindstone after firing is Rockwell hardness (1/1
80 in 6 ″ steel ball indenter, test load 20kg, dial scale red)
The volume ratio of the pores was set to 48.0% so that the values were almost the same in the vicinity, and the bulk specific gravity of the raw grindstone was adjusted so that the combined volume ratio of CBN abrasive grains and diamond abrasive grains was constant at 30.0% (concentration C120). Based on the above, each compounding ratio and molding pressure were determined and molding was performed.

Table 1 shows the abrasive grain composition and the degree of bonding of the stones after firing the four types of sample stones in which the compounding composition of the CBN abrasive grains and the diamond abrasive grains was changed and the control stone composed of the CBN abrasive grains alone.

As the virified bond binder, for the comparative grindstone, a high-melting bond (softening point 1105 ° C) according to JP-B-57-49351 is used, and the maximum temperature is 1220 ° C in an inert gas atmosphere. The firing was completed after holding for 1 hour and the required time of 32 hours.

The sample grindstone uses a low-melting bond (softening point 720 ° C) whose main component is glass frit. Similarly, the maximum temperature of 980 ° C is maintained for 0.3 hours in an inert gas atmosphere, and firing is completed in 15 hours. did.

In the finishing performance test of the sample grindstone, the material is bearing steel (SUJ2, hardness H
RC 58/64), and a square grindstone (10 mm long in the vibration direction of the grindstone, 3 mm wide in the rotating direction of the work) is machined on the end face of the ring-shaped workpiece (outer diameter 45 mm, inner diameter 22 mm) that rotates at 406 times / min. Press the surface, and the vibration (1140 times / min) and amplitude (inside 2.
Plunge cut plane super finishing was performed while giving 1 mm).

As the processing oil, a mixed oil of 5 parts of magnetized fatty oil and 95 parts of mineral oil was used.

The pre-working roughness was also superfinished with a WA # 800 grindstone, and the maximum height surface roughness was kept constant at about 0.8 μm Rmax.

The cutting direction angle (maximum tilt angle) of the sine wave, which is the movement trajectory of the abrasive grains on the surface of the workpiece under the superfinishing conditions, is 10 °.

Further, the grindstone surface pressure in accordance with the 15~20kg / cm ² practical range, constant at 18 kg / cm ^2, in particular, pressurizing method, the electrical resistance wire affixed to the elastic ring of the grindstone holder portion by spring pressure Tests were carried out by using a strain gauge while the pressing force was kept constant throughout the experiment with a processing time of 2 minutes.

Table 2 shows the test results of the use surface condition of the four types of sample grindstones in which the composition of the CBN abrasive grains and the diamond abrasive grains were changed and the comparative grindstone composed of the CBN abrasive grains alone.

From this test result, a comparative control grindstone consisting of CBN abrasive grains alone that does not contain diamond grits, and a rough surface finish also gives a white finished surface in a cutting state, but a sample grindstone containing diamond grits is either a mirror surface or The finished surface was in a semi-cut state with a partly glossy surface.

Sample 1 with a diamond abrasive grain composition of less than 5% and a CBN abrasive grain ratio of 25% or more (CBN abrasive grain concentration C100 or more)
Since the whetstone of No. 2 has excellent machinability, it does not easily become a perfect mirror surface within the test time.

Further, in the case of the grindstone of Sample 4 in which the diamond abrasive grain exceeds 15% and the CBN abrasive grain ratio is 12.5% or less (concentration C50 or less),
Although it becomes a mirror surface state, the roughness of the pre-machined surface cannot be completely removed due to the insufficient cutting amount, and the roughness of the finished surface also becomes rough.

That is, the volume ratio of the CBN abrasive grains in the grindstone is 5 to 15
%, The grinding stones of Samples 2 and 3 mixed with diamond abrasive grains satisfy a cutting ratio of 30 or more without impairing the finishing performance such as the cutting amount and the abrasion loss of the grinding stone, and the finished surface roughness is
As small as 0.2 μm Rmax or less, beautiful mirror finishing is possible in a short time.

As in the conventional case, in mirror finishing using unstable and naturally occurring clogging, the roughness accuracy of the surface of the workpiece after machining may become uneven. For example, the roughness of the finished surface when using the CBN abrasive grains alone in the finishing process in a cutting state of a small amount is 0.20 μmRmax or less, which is a white-like surface with poor gloss.

On the other hand, the grindstones of the examples can provide a mirror finish with a finished surface roughness of 0.10 μm Rmax or less without causing crushing or clogging. In other words, it is possible to satisfy both the machinability and the mirror finish at the same time, rather than the conventional mirror finish that uses the crushing of the abrasive grains and the clogging of the grindstone at the sacrifice of the machinability.

In addition, the superabrasive grain superfinishing stone of the example has a Rockwell hardness indicating value of about 80, which is within a preferable hardness indicating value range. Therefore, according to the grindstone of the embodiment, it is possible to efficiently perform from the rough finishing to the mirror finishing in a short time by one-step processing.

〔The invention's effect〕

As described above, according to the superabrasive grain superfinishing grindstone of the present invention, since it has the above-described configuration, the machinability, the wear resistance and the like performance is not impaired, and the accuracy is improved from the rough finish in one-step processing. It is possible to efficiently and efficiently finish mirror finish.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-58-82677 (JP, A)

Claims (2)

[Claims] 1. A superabrasive superfinishing grindstone in which diamond grits and cubic boron nitride grits are bonded with an engaging agent, wherein the volume ratio of the diamond grits in the grindstone is 5 to 15.
%, And the volume ratio of the cubic boron nitride abrasive grains in the grindstone is 1 to 3.6 times that of the diamond abrasive grains, and the particle diameter of the diamond abrasive grains is substantially the same as that of the cubic boron nitride abrasive grains. As a vitrified binder, and the bond hardness of the superabrasive grain superfinishing stone is set to 30 to 80 on a Rockwell hardness scale H scale. 2. The superabrasive superfinishing whetstone according to claim 1, wherein the binder is a metallic or organic binder.