JPH09239644A - Grinding method of cbn tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To grind a CBN tool at a high accuracy of form by holding a diamond harder than the CBN solidly, and reducing the abrasion of a grinding wheel. SOLUTION: In a grinding method of CBN tool to finish a material which consists of CBN into a tool with a desired form, the grinding is carried out by using a grinding wheel 1 formed by covering the surface with a diamond film 3 synthesized by a vapor phase growth.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to cubic boron nitride (C) used for forming dies for optical elements, turning tools and the like.
The present invention relates to a grinding method of a CBN tool for finishing a material of (BN) into a tool having a desired shape.

[0002]

2. Description of the Related Art Conventionally, a processing method has been known in which a tool edge is ground with a resin bond diamond grindstone using a CBN single crystal as a material (Academic Lecture Meeting of the Precision Engineering Society of 1986, P.373). This processing method is C
In order to grind and polish a BN single crystal, diamond abrasive grains having a hardness higher than that of CBN are held by a resin bond, and this grindstone mechanically grinds the CBN single crystal.

[0003]

However, in the conventional grinding method for the CBN tool described above, although the diamond abrasive grains harder than CBN are used for processing, the diamond abrasive grains are held by the resin bond. Is small, and diamond abrasive grains come off during the grinding process. That is, the strength of the resin bond itself is weak with respect to the grinding resistance force generated between the CBN single crystal and the diamond abrasive grains during the grinding process, and the resin bond is broken during the CBN single crystal grinding process to cause the diamond abrasive grains. Will be dropped out. Therefore, even if a diamond abrasive grain harder than a CBN single crystal is used for processing, since the holding force and strength of the bond material for holding the diamond abrasive grain are weak, diamonds drop off one after another during the grinding process, resulting in a resin bond diamond grindstone. The shape of the CBN tool collapses and wears and wears quickly, making it difficult to grind the CBN tool into a desired shape.

Particularly, in the case where an optical element molding die for softening and pressing a glass material by heating is to be highly accurately ground into a spherical or aspherical shape, it is essential to maintain the shape of the grindstone. It was necessary to prevent the shape of the grindstone from collapsing due to the falling of grains.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the invention according to claim 1, 2 or 3 is to firmly hold a diamond harder than CBN and reduce abrasion of the grindstone. , CBN tools with high shape accuracy.

[0006]

In order to solve the above-mentioned problems, the invention according to claim 1, 2 or 3 is a method for grinding a CBN tool for finishing a material made of CBN into a tool having a desired shape. The feature is that grinding is performed by using a grinding wheel whose surface is coated with a diamond film synthesized by phase growth.

With the operation of the invention according to claim 1, 2 or 3,
Covers the surface with a diamond film synthesized by vapor phase epitaxy.
By grinding with the covered grinding wheel, the resin
Resin bond grinding with a structure in which diamond is embedded in the bond
Compared to stones, diamond film grindstones retain diamond
Is high, the wear of the grindstone is extremely small and the shape of the grindstone is
maintain. In the operation of the invention according to claim 2, in the above operation,
In addition, Cr is added to the processed part during grinding. _TwoO_ThreeGrinding fluid containing
By grinding while flowing over, Cr_TwoO_ThreePolishing
The Cr component of the material acts chemically to improve the surface roughness.
You. In the operation of the invention according to claim 3, in addition to the above operation,
CBN tool is a mold for optical element molding
It is possible to finish inverted shapes such as surfaces and aspherical surfaces with high accuracy.
Wear.

[0008]

1 to 5 show Embodiment 1 of the invention, FIG. 1 is a front view of a main part of a grinding machine, FIG. 2 is a plan view of a main part of the grinding machine, and FIG. 3 is a grinding wheel. 4 is a vertical cross-sectional view, FIG. 4 is a chart for comparing the abrasion amounts of the grinding wheels, and FIG. 5 is a chart for comparing the surface roughness according to the type of grinding fluid.

First, the grinding device will be described. 1 and 2, the grindstone shaft 4 and the work shaft 7 are rotatably attached to a grinding device (not shown). The grindstone shaft 4 and the work shaft 7 are configured to be movable in the vertical direction and the horizontal direction, respectively. As shown in FIG. 3, a male screw 6 is threaded on the tip of the grindstone shaft 4, the diamond film grindstone 1 is fitted to the small-diameter portion 4 a, and fixed by a nut 5. The diamond film grindstone 1 is a disc-shaped base material 2 having a V-shaped cross-section on its outer peripheral portion, and a diamond film 3 formed on the outer peripheral portion of the base material 2 by vapor phase growth.
It is composed of The base material 2 is made of dungsten carbide (WC), silicon carbide (SiC), or the like, and the diamond film 3 provided on the outer peripheral portion heats a hydrocarbon gas or the like to thermally decompose it on the surface of the base material 2. The film is formed by a CVD method (chemical vapor phase synthesis method) in which it is deposited by a method or a plasma CVD method in which electrons are deposited by applying high energy with microwaves or high frequencies to generate positive ions from a hydrocarbon gas. is there.

Further, in FIGS. 1 and 2, a CBN mold 6 for heating and softening a glass material to obtain an optical element by press-molding the glass material is vacuum-adsorbed or fitted (tight fit) at the tip of the work shaft 7. ) And so on. CB
The tip of the N-type 6 forms a spherical or aspherical molding surface portion 9 created by the diamond film grindstone 1. Further, a polishing liquid mixed with an abrasive containing Cr ₂ O ₃ as a main component is poured from a nozzle 8 from above onto the molding surface portion 9 of the CBN mold 6 created by the diamond film grindstone 3.

Next, the CBN by the grinding device having the above-mentioned structure
The grinding operation of the mold 6 will be described. While the diamond film grindstone 1 is being rotated, the axis Y of the grindstone shaft 4 is moved in the direction of the arrow X, and in conjunction with this movement, the CBN type 6
The forming surface portion 9 is created by rotating the workpiece shaft 7 holding the workpiece in the direction of the arrow Z.
For the interlocking movement of the grindstone shaft 4 and the work shaft 7, the coordinate position of each axis is calculated based on a circle equation or an aspherical surface by a computer (not shown), and the position of each axis is calculated based on this. It is controlled by NC or the like. As a result, the diamond film grindstone 1 is a CBN type because the grinding grains to be ground are diamonds that are harder than CBN, the diamond grain holding force is higher than that of the resin bond grindstone, and the V-shaped outer peripheral portion is maintained. The molding surface portion 6 of 6 is ground with high shape accuracy.

FIG. 4 is a table showing a comparison of the amounts of wear of the resin bond grindstone and the diamond film grindstone. The horizontal axis shows the total grinding amount when the CBN type 6 is ground to an aspherical surface, that is, the total cutting amount when grinding is performed,
The vertical axis represents the reduction amount of the outer diameter of the grindstone at the time when the grinding by each cut is completed. As can be seen, in the diamond film grinding wheel, the change in the grinding wheel outer diameter due to the grinding process of CBN was observed to be smaller than when the resin bond grinding wheel was used,
It can be seen that there is little wear.

Further, during the grinding operation, a grinding liquid mixed with an abrasive containing Cr ₂ O ₃ as a main component is poured over a working portion where CBN and diamond are in contact with each other. For this reason, in the processed portion, a chemical action on CBN by Cr ₂ O ₃ occurs, and a ground surface having a better surface roughness can be obtained. However, if the required accuracy of surface roughness is low, C
The grinding operation can be performed by using a general grinding liquid without flowing r ₂ O ₃ . FIG. 5 shows chromium oxide (Cr
₂ is a chart showing a comparison of surface roughness of a ground surface when a polishing liquid containing ₂ O ₃ ) and a polishing liquid not containing ₂ O ₃ ) are used. The horizontal axis shows the presence or absence of Cr ₂ O ₃ , and the vertical axis shows the CBN type 6 under each condition.
The value of the surface roughness when grinding is shown. As can be seen from this, the surface roughness of the ground surface is improved by pouring the grinding liquid containing Cr ₂ O ₃ . It is considered that this is because the Cr (chromium) component generated a chemical action with respect to CBN, so that the grinding resistance force generated between the diamond film grindstone 1 and the CBN mold 6 during grinding decreased.

Although the mechanism of the action of Cr is unknown at present, since the effect as shown in FIG. 5 could not be confirmed with an abrasive such as Si ₂ O ₃ , the chemical action of Cr on CBN is not found. Is considered to have occurred. In addition, Cr ₂ O ₃ acts as a cushion by the presence of Cr ₂ O ₃ in the processed portion where CBN and diamond contact each other, and prevents cracks generated on the CBN ground surface and prevents surface roughness. It is thought that the improvement of the quality is obtained.

Further, after the cutting by the grinding process is completed, the forming surface portion 9 is scanned again without cutting the diamond film grindstone 1, and each of the CBN type 6 and the diamond film grindstone 1 has a slight amount. The irregular shape due to the elastic deformation can be corrected, and higher shape accuracy can be obtained.

According to the first embodiment of the present invention, a CBN die for forming an optical element having a high shape accuracy is obtained by performing a grinding process using a diamond film grindstone that firmly holds a diamond harder than CBN. You can Further, a grinding surface having good surface roughness can be obtained by pouring a grinding liquid mixed with an abrasive containing Cr ₂ O ₃ as a main component to the processed portion.

In the first embodiment of the present invention, grinding is performed using a diamond film grindstone having a V-shaped cross section at the outer peripheral portion. Instead of this, a flat grindstone having a cylindrical outer peripheral surface or a cross section is used. Even if a circular whetstone with an arc is used, the same effect can be obtained. Further, in the first embodiment of the present invention, the case of grinding the CBN mold for optical element molding with the diamond film grindstone is shown, but it is also applied to the case of grinding another CBN tool, for example, a CBN forming tool. Since the diamond film grindstone wears less, it is possible to finish an accurate profile.

[0018]

Second Embodiment FIG. 6 shows a second embodiment of the invention, FIG. 6 is a configuration diagram of a main part of a grinding apparatus, and FIG. 7 is a perspective view of a grinding wheel. The second embodiment of the present invention has the same basic configuration as that of the first embodiment of the invention, and the same portions are denoted by the same reference numerals and the description thereof will be omitted.

In FIG. 6, the grinding apparatus according to the first embodiment of the present invention is a spherical surface generating apparatus called a curve generator. In this grinding apparatus, the work shaft 7 is the same as that of the first embodiment of the invention, but the grindstone shaft 14 is configured to be rotatable in the direction of arrow θ around a point on the rotation axis of the work shaft 7. There is. A diamond film grindstone 11 is attached to the tip of the grindstone shaft 14. As shown in FIG. 7, the tip portion of the diamond film grindstone 11 is formed in a cup shape with the center inside 11a depressed, and the diamond film 13 is formed on the cup-shaped end surface by the CVD method. Further, similarly to the first embodiment of the invention, the molding surface portion 9A of the CBN mold 6 is
From the nozzle 8 from above, a polishing liquid containing an abrasive containing Cr ₂ O ₃ as a main component is flowed.

Similar to the spherical surface creation of the convex lens, the work axis 7
The cup-shaped diamond film grindstone 11 tilted at the turning angle θ is rotated with respect to the axis of the CBN type 6 by rotating the workpiece shaft 7 holding the CBN type 6 in the direction of the arrow W. A spherical surface can be created on the molding surface 9A. When the forming surface 9A of the CBN mold 6 is created using the cup-shaped diamond film grindstone 11, the contact between the grindstone and the grinding surface is not a point contact but a line contact, so that the wear life of the grindstone is long. Become.

According to the second embodiment of the present invention, in addition to the effect of the first embodiment of the present invention, the wear life of the diamond film grindstone is extended, so that a high shape accuracy can be ensured in generating a spherical surface. it can. Further, there is an advantage that a general curve generator can be used.

In the second embodiment of the present invention, the case of grinding the CBN mold having the convex spherical molding surface has been described.
It is natural that the curve generator can be applied to a CBN type having a concave spherical molding surface, because the curve generator can create spherical surfaces on both the concave and convex sides.

[0023]

According to the invention according to claim 1, 2 or 3, the diamond film grindstone has a higher diamond holding force than the resin bond grindstone having a structure in which the diamond is embedded in the resin bond. Since it is made extremely small and the shape of the grindstone is maintained, the CBN tool can be ground with high shape accuracy. According to the invention of claim 2, in addition to the above effect, the Cr component of the Cr ₂ O ₃ abrasive acts chemically to improve the surface roughness, so that the surface of the component etc. processed by the CBN tool is Make it smooth. According to the invention of claim 3, in addition to the above effect, the inverted shape of the spherical surface, the aspherical surface or the like is finished with high accuracy, so that the shape accuracy of the optical element such as the glass lens to be press-molded can be improved.

[Brief description of drawings]

FIG. 1 is a front view of a main part of a grinding device according to a first embodiment of the invention.

FIG. 2 is a plan view of a main part of the grinding device according to the first embodiment of the invention.

FIG. 3 is a vertical cross-sectional view of the grinding wheel according to the first embodiment of the invention.

FIG. 4 is a chart comparing the wear amounts of the grinding wheels of the first embodiment of the invention.

FIG. 5 is a table for comparing surface roughness according to types of grinding fluid according to the first embodiment of the invention.

FIG. 6 is a configuration diagram of a main part of a grinding device according to a second embodiment of the invention.

FIG. 7 is a perspective view of a grinding wheel according to a second embodiment of the invention.

[Explanation of symbols]

 1 Diamond film grindstone 3 Diamond film 4 Grindstone shaft 6 CBN type 7 Work shaft 9 Forming surface

Claims (3)

[Claims] 1. A grinding method for a CBN tool for finishing a material made of CBN into a tool having a desired shape, characterized in that grinding is carried out by using a grinding wheel whose surface is coated with a diamond film synthesized by vapor phase growth. Grinding method for CBN tools. 2. The grinding method for a CBN tool according to claim 1, wherein grinding is performed while pouring a grinding liquid containing Cr ₂ O ₃ over a working portion during grinding. 3. The grinding method for a CBN tool according to claim 1, wherein the CBN tool is an optical element molding die.