JP4197803B2 - Grinding method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for grinding brittle materials such as optical elements made of glass such as lenses and prisms.
[0002]
[Prior art]
Grinding is performed to produce an optical element such as a lens or a prism from glass (optical glass) which is a brittle material. This grinding includes a curve generating process, which is a rough process for creating a spherical surface or a planar shape on the surface of a brittle material, and a smoothing process by co-rubbing (lapping) with diamond pellets. FIG. 5 shows the curve generating process described in “Optical component processing terminology” (published by the Optical Industry and Technology Association), (a) grinding the convex shape from the optical glass 102, and (b) from the optical glass 102. In this case, the concave shape is ground.
[0003]
The optical glass 102 is affixed to the workpiece holder 103, and the cup-shaped diamond grindstone 101 is tilted and ground at an angle α at which a desired spherical shape can be created with respect to the optical glass 102. The angle α is an angle formed by the grindstone shaft 110 of the grindstone holder 105 and the work shaft 120 of the workpiece holder 103. Creation is performed by rotating both the grindstone 101 and the optical glass 102 while maintaining the angle α.
[0004]
[Problems to be solved by the invention]
In general, the grinding efficiency for grinding an object to be ground and the obtained surface roughness quality are in a contradictory relationship. Therefore, when the grinding efficiency is increased, the obtained surface roughness decreases, and conversely the surface roughness decreases. When improved, the grinding efficiency decreases. That is, in order to improve the grinding efficiency, it is necessary to increase the abrasive grain size of the grindstone to ensure a large cutting amount. However, if the abrasive grain size increases and the depth of cut increases, the surface roughness obtained decreases. In addition, when the cutting depth is large in this way, in a brittle material such as glass, fracture (cracking) occurs and the crack, which is a crack, progresses to the inside of the material, so that the surface roughness further decreases. Have.
[0005]
Accordingly, an object of the present invention is to provide a grinding method capable of simultaneously obtaining a high surface roughness while using a grinding tool having a high grinding efficiency.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the grinding method of the present invention uses an interfacial potential double layer possessed by silica ultrafine particles contained in a colloidal silica liquid, adsorbs silica particles on the surface of a grindstone, and is a brittle material to be processed. A polishing action is performed simultaneously with a grinding action on the surface of an object.
[0007]
That is, the invention of claim 1 is a method of grinding a brittle material such as an optical element with a grindstone, using a grindstone having any one of aluminum, zinc, nickel, magnesium or copper as a bond material, and the grindstone and the brittle material. Between the silica particles containing the silica particles and intercalating the colloidal silica liquid, which is an alkali liquid, and reacting the silica particles forming the interfacial potential double layer in the colloidal silica liquid with the metal ions of the bond material. The gelled product is adhered to the surface of the grindstone, and the brittle material is ground and polished .
[0008]
The silica ultrafine particles contained in the colloidal silica liquid, which is an alkaline liquid, are negatively charged by adsorbing hydroxyl groups, and adsorb on the metal surface although it is extremely weak. On the other hand, it is known that aluminum, zinc, copper, nickel, and magnesium metals are attacked in the alkaline solution. When a grindstone using such a metal as a bond material is ground in a colloidal silica liquid, which is an alkaline liquid, and the brittle material is ground, the bond material of the grindstone is eroded by the alkaline liquid, Elutes as positively charged metal ions. Due to this elution, the ultrafine silica particles that are negatively charged due to the attachment of hydroxyl groups react with metal ions on the surface layer of the grindstone to produce a gelled product (silica gel) and adhere to the grindstone surface.
[0009]
Since this condition occurs on the surface of the grindstone, the grinding action of the ultrafine silica particles adhering to the surface is taken into account in accordance with normal grinding with diamond or cBN abrasive grains of the grindstone. It is possible to obtain a surface roughness higher than that of the normal grinding process.
[0010]
In addition, since silica ultrafine particles adhere to the surface of the grindstone, the amount of abrasive grains protruding from the surface of the grindstone is reduced. Therefore, the cutting depth of the abrasive grains of the grindstone is also reduced, and higher surface roughness can be obtained. At the same time, the ultrafine particle film that has gelled intervenes at the interface between the grindstone and the object to be ground, and also serves as a cushioning material that absorbs vibrations caused by the processing of both, so that a high surface roughness can be obtained. In addition to such an action, even if a gelled film is interposed, the grinding efficiency is not reduced because the grinding with the abrasive grains is not changed.
[0011]
The invention of claim 2 is characterized in that, in the invention of claim 1, the colloidal silica liquid contains a water-soluble grinding liquid .
[0012]
In this invention, since a water-soluble grinding liquid is mixed in the liquid of colloidal silica, an activation action acts at the interface between the grindstone and the object to be ground, and the discharge of sludge generated by grinding is enhanced. The surface roughness can be improved by preventing the occurrence of scratches (scratches). Also, the grinding resistance can be reduced by the lubricating action of the grinding fluid, vibration and heat generation due to grinding can be suppressed, and higher surface roughness and shape stability can be ensured.
[0013]
The invention of claim 3 is characterized in that, in the invention of claim 1 or 2, the colloidal silica liquid contains a metal ion .
[0014]
In this invention, by including metal ions in the liquid of colloidal silica, the included metal ions and silica ultrafine particles are adhered, and a gel having a size corresponding to the charge and amount of metal ions is generated. Intervene in the liquid. Since this gel further adheres hydroxyl groups in the liquid, it gradually softens and becomes liquid to adhere to the grindstone surface. In this way, by containing metal ions in the colloidal silica liquid in advance, a gel having a certain size is generated, and the gel is attached to the surface of the grindstone, thereby shortening the grindstone in a shorter time. As a result, it is possible to promote the adhesion of the ultrafine silica particles to the surface of the silica, and thus it is possible to ensure the high polishing ability of the ultrafine silica particles.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment 1)
FIGS. 1 and 2 (a) and 2 (b) are the first embodiment of the present invention, and FIG. 2 (a) shows a case where optical glass is ground using a colloidal silica liquid for an aluminum bond grindstone. The surface roughness measurement result is shown in (b), and the surface roughness measurement result when grinding is performed on an aluminum bond grindstone using an existing water-soluble grinding liquid is shown.
[0018]
In this embodiment, as shown in FIG. 1, an aluminum bond grindstone 1 is attached to an existing curve generator (hereinafter referred to as a CG machine), and a colloidal silica liquid 2 is ejected from a nozzle 2a instead of a water-soluble grinding liquid. The optical glass 3 is ground while being applied. The aluminum bond grindstone 1 is a grindstone using diamond abrasive grains and high-purity aluminum as a bond material. In this embodiment, an aluminum bond grindstone (#) manufactured and sold by Nissan Diamond Industries Co., Ltd. 600, concentration 100).
[0019]
The colloidal silica liquid 2 is a Snowtex 30 (trade name, Snowtex is a colloidal silica liquid containing 30% by weight of ultrafine silica particles) manufactured by Nissan Chemical Industries, Ltd., which has high silica purity and is used for polishing semiconductors. The product was diluted to 6% by weight with pure water. The silica ultrafine particles in the silica liquid 2 are negatively charged. Two types of FPL51 (trade name) and BSL7 (trade name) manufactured and sold by OHARA Co., Ltd. were used for the optical glass 3 as the brittle material to be ground.
[0020]
The grinding machine used was an existing curve generator, and in this embodiment, KCG-3 type (trade name) manufactured by Kyoritsu Seiki Co., Ltd. was used. The aluminum bond grindstone 1 is mounted on the grindstone holder 1a of the curve generator, the optical glass 3 is attached to the workpiece holder 3a, and the aluminum bond grindstone 1 and the optical glass 3 are respectively rotated and ground with a total cutting amount of about 1 mm. went. The peripheral speed of the aluminum bond grindstone 1 at this time is 10 m / sec, and the peripheral speed of the optical glass 3 is 0.1 m / sec. In this grinding, colloidal silica liquid 2 was supplied from nozzle 2a.
[0021]
2A and 2B show measurement results of surface roughness when FPL51 is used as the optical glass 3. FIG. The average surface roughness Ra when grinding with the aluminum bond grindstone 1 using the existing water-soluble grinding fluid under the same grinding conditions is 0.320 μm as shown in FIG. On the other hand, when grinding is performed while supplying the colloidal silica liquid 2 to the aluminum bond grindstone 1 of this embodiment, the average surface roughness Ra corresponds to about 1/6 as shown in FIG. It improved to 0.052 micrometer. The same tendency was observed for other optical glasses.
[0022]
Explaining this reason, when a colloidal silica liquid having negatively charged silica ultrafine particles is supplied to the aluminum bond grindstone 1, the silica ultrafine particles are adsorbed to the aluminum bond grindstone, although they are extremely weak. Further, since the colloidal silica liquid 2 is an alkaline liquid, aluminum is attacked and trivalent aluminum ions are eluted. In this elution, the silica ultrafine particles adsorbed in a negatively charged state with a hydroxyl group adsorbed more strongly with aluminum ions on the surface layer, gelled, and adhered on the surface of the grindstone. Since this state occurs on the surface of the grinding wheel, in addition to the normal grinding process with diamond abrasive grains in the grinding wheel, polishing of the attached silica ultrafine particles acts, and more than the normal grinding process using water-soluble grinding fluid The surface roughness can be obtained.
[0023]
Therefore, since the polishing action of the ultrafine particles acts as compared with the surface roughness when processing is performed with a normal water-soluble grinding liquid not containing silica ultrafine particles, a better surface roughness can be obtained. Further, since silica ultrafine particles adhere to the surface of the grindstone, the amount of diamond abrasive grains protruding from the surface of the grindstone becomes small. For this reason, the cutting depth of the abrasive grains of the aluminum bond grindstone itself is also reduced, and higher surface roughness can be obtained.
[0024]
In this embodiment, the aluminum bond grindstone 1 is used. However, any grindstone using a bond material made of a metal that is eluted with an alkaline solution may be used, and any one of zinc, copper, nickel, and magnesium is used. can do. Moreover, although the colloidal silica liquid 2 having a content of ultrafine silica particles of 6% by weight was used, the concentration is not limited to this, and the concentration can be appropriately selected within the range of 3 to 30% by weight. . The selection in this case can be determined in consideration of the workability of processing and the degree of influence such as damage to the CG machine.
[0025]
In such an embodiment, since grinding is performed by adding the polishing action of silica ultrafine particles, a ground surface with higher surface roughness can be obtained.
[0026]
(Embodiment 2)
FIGS. 3A and 3B are Embodiment 2 of the present invention. FIG. 3A is a measurement result of the surface roughness obtained by the grinding method of this embodiment, and FIG. 3B is grinding. The increase of the electric current value of the motor which rotates the aluminum bond grindstone 1 in process is shown. In the characteristic diagram of FIG. 3B, each lens is ground based on the current value of the motor on the grindstone side (motor that rotates the grindstone) when grinding is not performed on the vertical axis (during so-called idling) (0.00). The amount of increase in motor current is plotted, and the number of lenses ground (the number of lenses ground when 30 lenses are created by grinding optical glass) is plotted on the horizontal axis. Characteristic curve A in (b) shows a grinding process using only a colloidal silica liquid, and B shows a grinding process when a colloidal silica liquid and a grinding liquid are mixed.
[0027]
A feature of this embodiment is that a slightly water-soluble grinding liquid is mixed in the colloidal silica liquid 2. That is, in this embodiment, the aluminum bond grindstone 1 is attached to an existing curve generator (GC machine) similar to that in the first embodiment for grinding, but in the colloidal silica liquid 2 supplied during this grinding process. The optical glass 3 is ground using a slightly mixed water-soluble grinding liquid. As the colloidal silica liquid 2, a liquid obtained by diluting Snowtex 30 of Nissan Chemical Industries, Ltd. with pure water to 6% by weight was used.
[0028]
In this embodiment, the aluminum bond grindstone 1, the colloidal silica liquid 2, the optical glass 3, and the curve generator are the same as those in the first embodiment. As the water-soluble grinding fluid, Green Cut (trade name) sold by Mabuchi S & T Co., Ltd. was used, and this grinding fluid was added to the colloidal silica liquid 2 at a concentration of 1.5 vol%. If the colloidal silica liquid 2 is diluted to 6 vol% or more with a water-soluble grinding liquid, it is difficult to obtain the effect of the polishing action by the ultrafine silica particles, and the surface roughness during grinding using only the water-soluble polishing liquid is close. The desired result was not obtained.
[0029]
As shown in FIG. 3A, when grinding is performed while supplying a colloidal silica liquid 2 in which a water-soluble grinding liquid is mixed to the aluminum bond grindstone 1, the aluminum bond grindstone shown in FIG. It can be seen that 0.043 μm, which is a high surface roughness accuracy of about 1/8, is secured compared to 0.320 μm when grinding is performed while supplying only the water-soluble grinding fluid. In addition, as shown in FIG. 3 (b), the current flowing in the motor that rotates the grinding wheel during grinding is reduced to about 1/3 to 1/5 by mixing water-soluble grinding fluid into the colloidal silica liquid. Can be made.
[0030]
According to such an embodiment, like the first embodiment, the polishing action of the attached silica ultrafine particles is taken into account, and at the same time, the surface activity of the grinding fluid is obtained by mixing a small amount of water-soluble grinding fluid. The effect of an effect | action is acquired and more favorable surface roughness can be obtained. In addition, the colloidal silica liquid itself (containing colloidal silica liquid containing 30% by weight of silica ultrafine particles or diluted 5 times as in the first embodiment) contains silica ultrafine particles as an abrasive, but is originally ground. Since it does not have an action as a liquid, it is very low in the action of discharging ground glass sludge and the lubricating action in the grinding area between the workpiece and the grindstone.
[0031]
As shown in FIG. 3 (b), the current value of the motor that rotates the aluminum bond grindstone 1 each time a lens is obtained during the grinding process to obtain 30 lenses continuously is cut into colloidal silica liquid 2. When a small amount of the grinding fluid is mixed (characteristic curve B), it becomes about 1/3 to 1/5 when grinding is performed only with the colloidal silica liquid 2 (characteristic curve A). This is because the grinding fluid is mixed in the grinding area in this embodiment compared with the first embodiment, but the amount of grinding fluid is mixed, so that sludge discharge and lubricity in the machining area are improved. The resistance force during grinding is reduced, and the value of the current flowing through the motor is reduced.
[0032]
As a result, in this embodiment, while obtaining a good surface roughness due to the polishing action of the ultrafine silica particles, the surface-active action of the water-soluble grinding fluid improves the discharge of sludge generated by grinding, and always The grinding / polishing action of the diamond grindstone of the grindstone and the adhered silica ultrafine particles can be stably secured, and high surface roughness can be obtained. Therefore, better surface roughness can be obtained by the polishing action by the ultrafine silica particles and the surface active action of the grinding fluid.
[0033]
(Embodiment 3)
In this embodiment, a trace amount of metal ions is added and contained in the colloidal silica liquid 2 of the first embodiment. When copper ions are mixed in the colloidal silica liquid 2 at a concentration of 1 vol% and an aluminum bond grindstone is immersed in the liquid, ultrafine silica particles contained in the colloidal silica liquid are deposited on the surface of the aluminum material of the aluminum bond grindstone. It was observed. This is because when the aluminum bond grindstone is immersed in a colloidal silica liquid containing copper ions, the copper ions react with the hydroxyl groups adhering to the surface of the silica ultrafine particles, resulting in a gelled product on the surface of the aluminum bond grindstone. The gelled product gradually softens and becomes liquid, and further adheres with hydroxyl groups and binds to aluminum ions eluted with alkali, whereby aggregates of silica ultrafine particles are formed on the surface of the aluminum bond grindstone. It adheres.
[0034]
Also in this embodiment, when the optical glass 3 is ground using the same aluminum bond grindstone 1 as in the first embodiment and colloidal silica liquid in which copper ions are mixed at 1 vol%, the surface roughness is shown in FIG. Thus, Ra was 0.048 μm, and the surface roughness was significantly improved from the surface roughness Ra of 0.320 μm when the existing water-soluble grinding fluid was used for grinding.
[0035]
According to such an embodiment, the deposition rate of silica ultrafine particles can be increased by adding a small amount of copper ions to the colloidal silica liquid 2. The contained copper ion reacts with the hydroxyl group adhering to the surface of the silica ultrafine particles to produce a gelled product. Further, the gelled product is formed on the surface of the aluminum bond grindstone 1 and aluminum ions eluted with alkali. It is for reacting and depositing copper, and attaching a silica ultrafine particle to the aluminum bond grindstone surface.
[0036]
Therefore, a local battery is formed between the copper ion and the surface layer of the aluminum bond grindstone 1 eluted with an alkali due to the precipitation of copper ions by a reduction reaction, which is higher than the electric energy obtained only by the elution of the aluminum bond. A potential can be obtained, and silica ultrafine particles can be adhered and grown faster and more strongly. Even if this copper ion is added to the colloidal silica liquid at less than 1 vol% (for example, 0.8 vol%, 0.4 vol%), the precipitation rate of silica ultrafine particles can be increased on the surface of the grindstone. When processed by using, the surface roughness is improved more than the surface roughness by grinding using an existing water-soluble grinding fluid. In this embodiment, copper ions are used as metal ions, but calcium ions and sodium ions have the same effect.
[0037]
In this embodiment, metal ions such as copper ions are included in order to ensure strong adhesion of ultrafine silica particles and to ensure a high growth rate. However, the water-soluble grinding fluid shown in Embodiment 2 is also used. By making it contain simultaneously, the surface active effect | action by a water-soluble grinding fluid can be obtained. That is, as described in the second embodiment, since there is an effect of improving the working force in the polishing process due to the surface active action of the grinding liquid, the precipitation rate of the silica ultrafine particles can be obtained by adding the grinding liquid. In addition, the action of reducing the grinding resistance force by the grinding fluid is added, so that the workpiece can be processed quickly.
[0038]
In this embodiment, the copper material is mixed in the colloidal silica liquid 2 and the aluminum material of the aluminum bond grindstone is eluted by immersing the aluminum bond grindstone in the liquid. An aluminum block material is immersed in the colloidal silica liquid to elute aluminum ions from the block material, and then an aluminum bond grindstone is immersed in the colloidal silica liquid to adhere agglomerates of silica ultrafine particles to the surface of the aluminum bond grindstone. Also good.
[0039]
According to such an embodiment, stronger adhesion of silica ultrafine particles and faster growth can be performed, and a highly efficient polishing action can be ensured.
[0040]
In each of the above embodiments, as a method for interposing the colloidal silica liquid on the surface of the brittle material, the colloidal silica liquid is sprayed from the nozzle. Grinding may be performed by interposing a colloidal silica liquid between them.
[0041]
【The invention's effect】
According to the first aspect of the present invention, grinding is performed by adding the polishing action of the ultrafine silica particles, so that a ground surface with higher surface roughness can be obtained.
[0042]
According to the second aspect of the present invention, better surface roughness can be obtained by the polishing action by the ultrafine silica particles and the surface active action of the grinding fluid.
[0043]
According to the invention of claim 3, stronger adhesion of silica ultrafine particles and faster growth can be performed, and a highly efficient polishing action can be ensured.
[Brief description of the drawings]
FIG. 1 is a partially cutaway front view of an apparatus for processing.
FIGS. 2A and 2B are characteristics diagrams of average surface roughness when grinding is performed. FIG. 2A shows the first embodiment, and FIG. 2B shows the case of an existing grinding fluid.
3A is a characteristic diagram of average surface roughness when grinding is performed according to Embodiment 2, and FIG. 3B is a characteristic diagram of a current value of a motor at the time of grinding.
FIG. 4 is a characteristic diagram of average surface roughness when grinding is performed according to Embodiment 4;
FIGS. 5A and 5B are front views showing a conventional grinding process. FIGS.
[Explanation of symbols]
1 Aluminum bond whetstone 2 Colloidal silica liquid 3 Optical glass

Claims (3)

In a method of grinding a brittle material such as an optical element with a grindstone,
Using a grindstone having any of aluminum, zinc, nickel, magnesium or copper as a bond material,
Between the grindstone and the brittle material, a colloidal silica liquid that contains silica particles and is an alkaline liquid is interposed,
The silica particles that form an interfacial potential double layer in the colloidal silica liquid and the gelled product obtained by reacting the metal ions of the bond material are attached to the surface of the grindstone,
A grinding method characterized by grinding and polishing the brittle material . The grinding method according to claim 1, wherein the colloidal silica liquid contains a water-soluble grinding liquid. The grinding method according to claim 1 or 2, wherein the colloidal silica liquid contains metal ions.

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