JP3839297B2 - Grinding method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for grinding an optical element made of glass which is a brittle material such as a lens and a prism, and a grinding wheel used for grinding.
[0002]
[Prior art]
As a grinding method for manufacturing lenses and prisms, curve generating processing (hereinafter referred to as CG processing) for creating a spherical surface or a planar shape is performed. In this CG processing, a cup-shaped diamond grindstone is disposed at an angle that allows creation of a desired spherical shape with respect to the optical glass that is the object to be ground, while rotating both the tool and the optical glass. This is a method of creating a spherical shape.
[0003]
Japanese Patent No. 311557 discloses that a diamond grindstone using aluminum as a binder is used for grinding. FIG. 4 shows an EPD (Electrophoretic Deposition) grinding method described in this publication.
[0004]
The diamond blade 1 as a grindstone uses aluminum as a binder for diamond abrasive grains. As shown in FIG. 4, a conductive diamond blade 1 and a workpiece 5 are arranged in a machining liquid 2 in which ultrafine abrasive grains 12 made of silica are mixed, and a charge is generated between the diamond blade 1 and the machining liquid 2. The workpiece 5 is ground and cut while the abrasive grains 12 are adhered to the diamond blade 1 by charging the ultrafine abrasive grains 12 suspended in the processing liquid 2.
[0005]
[Problems to be solved by the invention]
In CG processing, there is a contradictory relationship between the grinding efficiency for processing a workpiece and the surface roughness quality obtained by grinding. That is, when the grinding efficiency is increased, the obtained surface roughness is reduced, and conversely, if the surface roughness is attempted to be improved, the grinding efficiency is lowered. In order to improve the grinding efficiency, increase the protrusion amount of the abrasive grains of the grinding wheel and ensure a large cutting amount, or increase the strength of the binder that holds the abrasive grains so that it can withstand the large cutting amount. There is a need to.
[0006]
However, as described above, the machining efficiency improves as the cutting depth increases, but the obtained surface roughness decreases. In particular, in brittle materials such as glass, fracture (cracking) occurs in the machining area. As a result, surface roughness is further reduced. On the contrary, if the cutting amount is reduced, the surface roughness is improved, but the removal amount is reduced and the processing efficiency is lowered. At the same time, when trying to improve the surface roughness by reducing the protruding amount of abrasive grains, the abrasive grains that become the blade are small, so a device with high operation accuracy corresponding to the protruding amount is required, and the processing efficiency is low. Nevertheless, expensive equipment is required, resulting in costly processing.
[0007]
Also, if the grindstone structure is softened using resin as a binder, the surface roughness is improved because the protruding amount of the abrasive grains is apparently reduced due to the elastic deformation of the binder, but the abrasive is softer and less rigid. The holding force becomes small, the occurrence of abrasive dropout and the wear of the binding material become severe, the machining efficiency is lowered, the tool is worn early, a shape error occurs on the machined surface of the tool, and the tool life is shortened.
[0008]
In the EPD grinding and cutting method shown in Japanese Patent No. 311557, the processing efficiency and surface roughness can be improved by charging and attaching the ultrafine abrasive grains 12 suspended in the processing liquid 2 to the diamond blade 1. Is going. However, in the EPD grinding and cutting method, an electric charge is positively applied between the diamond blade 1 and the machining fluid 2 by the power supply device, so that it is necessary to add an insulating function and the like in the electrode and the device configuration to the existing grinding machine. The structure and control are complicated.
[0009]
Further, anodic elution due to electrolysis occurs in the diamond blade 1 due to the electric charge supplied from the power supply device. For this reason, in addition to wear due to processing, wear due to elution due to electrolysis of the diamond blade 1 occurs. In order to suppress this, in the above publication, an anode film is formed on the blade surface. In order to perform stable processing, the formation of the anode coating is indispensable, but conversely, it is very difficult to maintain the anode coating stably while securing a certain level of strength, especially the processing conditions between the blade and the cathode. That is, the amount of energization at both poles is affected by fluctuations in the surface condition of the blade, the amount of processing fluid supplied, the pressure, etc., making the machining operation difficult.
[0010]
In order to ensure a stable anode coating, high-purity aluminum is required as a binder for the blade that is the anode. In the above publication, a high-purity binder of 100% aluminum is used. Since aluminum is a softer metal such as bronze, nickel, and iron, which are existing binders, it can be expected to hold diamond abrasive grains in a flexible state, so it has the potential to improve surface roughness. . However, in reality, since the extensibility is higher than expected flexibility, the ability to hold diamond abrasive grains is small, and the diamond abrasive grains are likely to fall out during processing. Therefore, it is not suitable as a binding material for a grindstone.
[0011]
Furthermore, when the purity of aluminum increases, the strength also decreases, resulting in insufficient strength as a grindstone and insufficient wear resistance. For this reason, it is difficult to perform processing without forming a strong anode coating with a high-purity binder of 100% aluminum.
[0012]
Further, when an electrically strong anode coating is formed, the surface of the grindstone is hardened and the strength is increased, but at the same time, the insulating property is increased and colloidal silica fine particles are difficult to adhere. Actually, the anode film formed by energization is removed by grinding processing force, and the electroconductivity is restored again because the electroconductivity is obtained again. As a result, the anode film is formed again, and this process is repeated in the machining region. However, it is difficult to secure this cycle stably in the processing area, and the state of film formation is affected by slight environmental changes such as the amount and pressure of colloidal silica liquid to be supplied, the direction of supply, etc., and stable film formation In other words, it is very difficult to obtain a stable processing.
[0013]
The present invention has been made in consideration of such conventional problems, and a grinding method capable of simultaneously establishing three points of high grinding efficiency, good surface roughness, and high wear resistance. And it aims at providing a grinding wheel.
[0014]
[Means for Solving the Problems]
To achieve the above object, the grinding method of the invention of claim 1, using a grinding wheel having a powder of at least one of powder and silicon aluminum and aluminum oxide as abrasive grains of the binder, the silicon oxide particles The workpiece is ground while the silicon oxide particles are adhered to the surface of the grinding wheel by a zeta potential difference by supplying a working fluid that is dispersed and has a pH value of 3 to 9.
[0017]
[Name embodiment]
First, before describing specific embodiments of the present invention, an outline of the present invention will be described. The outline of the present invention uses a binder containing at least one of aluminum and aluminum oxide powder and silicon powder, and combines the softness of aluminum with the strength (abrasion resistance) generated by the silicon content. In addition to using the grinding wheel possessed by the process, the processing solution pH supplied during processing is in the range of 3 to 9, so that silicon oxide (SiO ₂ ) fine particles (hereinafter referred to as silicon oxide) and the grinding wheel surface in the processing solution By using the electrophoretic phenomenon due to the zeta potential of aluminum oxide (Al ₂ O ₃ ) formed by oxidation, silicon oxide is adsorbed on the surface of the grindstone while the power supply device is unnecessary. As the processing liquid, a colloidal silica liquid which is a colloidal solution in which silicon oxide is dispersed is used.
[0018]
In the present invention, the aluminum used for the binder is close to the aluminum alloy material having an alloy number of 4000 based on JIS. By adding silicon (Si) to aluminum, the aluminum has higher wear resistance than pure aluminum. It has an enhanced structure.
[0019]
The zeta potential of the metal oxide (aluminum oxide) is the potential of the sliding surface between the charged surface and the liquid in the electrokinetic phenomenon, and is determined from the migration speed of particles in the electrophoresis phenomenon. Since it is impossible to actually measure the surface potential of particles, the only zeta potential that can be measured is used as a substitute characteristic when discussing the electrical equalization property.
[0020]
In addition, by setting the pH of the colloidal silica liquid supplied to the grinding area within the range of 3 to 9, the zeta potential of silicon oxide (SiO ₂ ) , which is fine particles in the liquid, is negatively charged and formed on the surface of the grindstone. The aluminum oxide (Al ₂ O ₃ ) to be charged can be positively charged. This is shown in the text “Technology for Utilizing New Fine Particles” distributed at the 3rd Open Symposium hosted by the Japan Society for Abrasive Technology on September 29, 2000.
[0021]
FIG. 1 is a graph published in “Fine Particle Dispersion Technology” in this text, where the horizontal axis represents the pH value and the vertical axis represents the See evening potential. As shown in FIG. 1, the zeta potential of the metal oxide changes depending on the pH, and when the pH is in the range of 3 to 9, the silicon oxide (SiO ₂ ) present in the colloidal silica liquid becomes negative, and the surface of the grindstone The aluminum oxide (Al ₂ O ₃ ) formed on the surface is positively charged. Accordingly, the silicon oxide negatively charged in the colloidal silica liquid is electrically adsorbed by the grinding wheel having aluminum oxide, which is positively charged in the liquid, as a surface layer.
[0022]
That is, by setting the pH value of the colloidal silica liquid supplied to the grinding region to be in the range of 3 to 9, fine particles of silicon oxide floating in the liquid adhere to the surface of the grinding wheel due to the electrophoresis phenomenon due to the zeta potential difference. . Since this is adhesion due to a potential difference, it is more strongly adsorbed by increasing the difference between the zeta potential of silicon oxide and the zeta potential of aluminum oxide. For this reason, the pH value of colloidal silica liquid has the best range of 5-8, and can exhibit an adsorption | suction effect quickly.
[0023]
In addition, since aluminum and aluminum oxide are used as a binding material, an aluminum oxide film that is bonded to oxygen in the air is always formed on the surface of the grindstone without applying a charge to the grindstone. Abrasive fine particles adhere.
[0024]
Next, specific embodiments of the present invention will be described with reference to the drawings. FIG. 2 shows a blending ratio when the silicon content in the grinding wheel used in the embodiment of the present invention is changed, and FIG. 3 shows a change in the surface roughness of the workpiece due to the silicon content. FIG. 3 also shows the surface roughness when processed with an existing bronze bond grindstone for comparison. The grinding ratio is an index indicating how much the grindstone is worn to grind and remove the glass as the workpiece, and is a value obtained by dividing the total grinding removal amount of the glass by the total wear amount of the grindstone.
[0025]
In this embodiment, a grinding grindstone containing diamond as abrasive grains and aluminum and silicon as a binder is used for processing while supplying colloidal silica liquid adjusted to a pH of 3 to 9, and a grinding apparatus As such, existing equipment was used.
[0026]
The grinding wheel is formed by using aluminum alloy powder as a binder for diamond abrasive grains, and molding and sintering . Aluminum alloy powder of this is to add dissolved elemental silicon in a high purity aluminum is obtained by the alloy used was triturated to the alloy an average particle size of about 10 to 50 [mu] m. When silicon element is added and dissolved, the volume ratio is 0.5% (not pure aluminum but contains almost no silicon), 10%, 20%, and 40%. Four types of binders were produced. Diamonds as abrasive grains were blended so that the grain size of # 600 would be a concentration degree of 100 for any grindstone.
[0027]
As the colloidal silica liquid supplied during processing, a trade name “COMPOL120” (manufactured by Fujimi Incorporated) was used. The colloidal silica solution, approximately 40 wt% silicon oxide concentrations, the average particle size of about 70～95A, since the intact and has a strongly alkaline pH 10, about 8 by neutralization with an acidic Substance Used at pH. As the object to be ground, BSL7, which is optical glass, was used.
[0028]
Further, as a comparison object, processing using a bronze bond diamond grindstone (hereinafter referred to as bronze bond grindstone) used in existing lens grinding was also performed. The existing curve generator (CG machine) was used as the processing apparatus.
[0029]
As shown by the grinding ratio of the grindstone with respect to the silicon content in FIG. 2, the grindstone containing 10, 20, 40% silicon with respect to the 0.5% grindstone having the smallest silicon content has a high grinding ratio (largely It has become. In the experiment, it was confirmed that a high grinding ratio was obtained by setting the silicon content to 20% or more.
[0030]
It is known that when silicon is contained in aluminum, it becomes close to an alloy material of 4000 series specified by JIS, and exhibits high wear resistance compared to the case of aluminum alone. It could also be confirmed as a binder. As a JIS 4000 series aluminum alloy, there is an alloy number 4032, which has a silicon content of 11.0 to 13.5%, and is widely used as a die-forged product and used for a piston of an internal combustion engine. The wear resistance is better. As a grinding wheel used in this embodiment, a high grinding ratio is confirmed in a region where the silicon content is higher than that of alloy number 4032. In particular, as shown in FIG. 2, a high grinding ratio, that is, high wear resistance is exhibited at a silicon content of 20% or more.
[0031]
Grinding wheels with a silicon content of 0.5% do not fall under pure aluminum, but with pure aluminum with a silicon content of about 0.1%, it is difficult to process due to insufficient strength as a grinding wheel. Therefore, it was used as a substitute for pure aluminum.
[0032]
In the grinding surface roughness in FIG. 3, BSL7, which is an optical glass, is used by using a grindstone in which the content of silicon with respect to aluminum is set to 0.5, 10, 20, and 40% in the same manner as the grinding ratio. Was ground. In any case, the average surface roughness Ra is as good as 0.1 μm or less.
[0033]
Among these, when the silicon content is 0.5% which is extremely low and 40% where the silicon content is high, the surface roughness is slightly reduced. When the content is 0.5%, since it is a binder close to pure aluminum, the diamond abrasive grains are frequently shattered due to insufficient strength as a grindstone and insufficient holding ability of diamond abrasive grains, and stable grinding is performed. It is difficult. As can be seen from the small grinding ratio shown in FIG. 2, when the content ratio is 0.5%, the wear of the grinding wheel in the grinding surface is large because the grinding wheel wear is large due to the detachment of the diamond abrasive grains and the abrasion of the binder. Many products (diamond abrasive grains, binder particulate matter, etc.) intervene, which causes large scratches (scratches) on the workpiece, which is presumed to have caused a reduction in surface roughness. On the other hand, when the silicon content is 40%, the holding power of the diamond abrasive grains becomes strong, but it becomes hard and brittle. And while a diamond abrasive grain retention force is too strong, the elastic deformation of a grindstone becomes small and the damage to a workpiece becomes large. In other words, since the diamond abrasive grains are firmly supported, it causes a large brittle fracture of the work piece, and at the same time, when the binder breaks, a hard discharge greater than 0.5% is generated. However, it is presumed that the surface roughness was reduced due to this intervening in the processed part.
[0034]
In the bronze grindstone in FIG. 3 as a comparative example, even when the colloidal silica liquid was supplied to an existing CG machine and grinding was performed, the average surface roughness Ra was at a level of 0.3 to 0.4 μm. The zeta potential of bronze, which is a binder for the bronze grindstone, is unknown at this time, but it is considered that it does not have a positive potential because the silicon oxide fine particles in the colloidal silica liquid do not adhere. Accordingly, the silicon oxide fine particles are only sandwiched and rubbed at the grinding interface with the BSL 7 that is the workpiece, and the fine particles are not fixed by the electric adhesion force. Can't get.
[0035]
In the grinding wheel of this embodiment, since the silicon oxide fine particles adhere to and accumulate on the surface of the grinding wheel, the protruding amount of the diamond abrasive grains is apparently reduced. For this reason, the cutting depth of a diamond abrasive grain also becomes small and higher surface roughness can be obtained. Normally, the amount of protrusion is small, resulting in a clogged state, where the binding material and the lens that is the workpiece are in contact and contact with each other. Since the silicon oxide fine particles are adhered and deposited, the silicon oxide fine particle layer acts as a buffer material, so that problems such as seizure do not occur. Rather, since silicon oxide fine particles as an abrasive are sandwiched, a large polishing force acts to obtain a good processed surface.
[0036]
In this embodiment, aluminum is used as the binder, but instead of this, aluminum oxide may be used, and a stable zeta potential can be obtained thereby, so that the oxidation in the colloidal silica liquid is performed. Silicon particles can be reliably adsorbed.
[0037]
【The invention's effect】
According to the invention of claim 1, since the silicon oxide particles in the working fluid are adsorbed to the surface of the grindstone by the zeta potential and processed, the grinding efficiency of the workpiece can be increased, and the surface roughness can be improved. can do.
[0038]
In addition , since a binder containing silicon in addition to aluminum or aluminum oxide is used, a grinding wheel with high wear resistance can be obtained.
[0039]
According to invention of Claim 3, it can be set as the grinding wheel which has favorable grinding efficiency and favorable surface roughness.
[Brief description of the drawings]
FIG. 1 is a characteristic diagram showing the relationship between zeta potential and pH of a metal oxide.
FIG. 2 is a characteristic diagram showing a grinding ratio with respect to a silicon content in a binder in the embodiment.
FIG. 3 is a characteristic diagram showing average surface roughness with respect to silicon content in a binder.
FIG. 4 is a cross-sectional view showing EPD grinding cutting.

Claims (1)

Aluminum with beam and grinding wheel comprising a powder of at least one of powder and silicon as an abrasive bonding material aluminum oxide, silicon oxide particles are dispersed and the pH value is to supply the working fluid in the range of 3-9 Thus , the grinding method is characterized in that the workpiece is ground while the silicon oxide particles are adhered to the surface of the grinding wheel by a zeta potential difference .

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