JP2006334732A - Cutting tool, cutting method, cutting device, mold for forming optical element, optical element and cutting method for mold for forming optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cutting tool used in machining for cutting while oscillating the cutting tool is vibrated with high frequency, a cutting method, a cutting device, a mold for forming an optical element, an optical element formed by the mold, and a cutting method of a mold for forming optical element. <P>SOLUTION: A shank 23b of the cutting tool is formed using material having a density ranging from 1 to 6.2, Young's modulus of 250 GPa, and a coefficient of linear expansion of 5×10<SP>-6</SP>or less, whereby when it is used in oscillating cutting in which the cutting tool 23 is driven at high speed with a frequency of 1 kHz or more, it can follow high-frequency because of its light weight and high rigidity, so that cutting can be performed with high accuracy and at high efficiency. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is a lightweight and high-rigidity cutting tool for moving a tool at high speed and obtaining a good machining surface free from chattering by moving the tool itself, such as vibration cutting or FTS (Fast Tool Servo). The present invention relates to a cutting tool used for cutting that moves the tool itself at a high speed, a cutting method and apparatus using the cutting tool, and an optical element molding die obtained thereby.

  Cutting is generally used for processing the optical element molding die. The processing surface of the mold optical surface needs to be a mirror surface. Therefore, in a general cutting process for obtaining a mirror surface, the cutting tool (bite) is made as rigid as possible to reduce the cutting edge chatter as much as possible.

  By the way, there is known a machining method in which a cutting tool is driven in a cutting direction by a piezo element or a giant magnetostrictive element, and cutting is performed in synchronism with the rotational motion of a workpiece, and this method is called a first tool servo (FTS). And so on. In cutting using this FTS, the work efficiency can be improved by rotating the work piece as fast as possible and driving the cutting tool at a high frequency while synchronizing it. Since a fixed part and a butting member for attaching and detaching are required, the weight of the driven body increases, and the driving frequency band is limited. Therefore, even in an FTS that gives very high frequency vibration, about 5 kHz is the practical upper limit. In order to drive a cutting tool at a higher frequency, it is very important to reduce the weight of the cutting tool. Although attempts have been made to reduce the size of the cutting tool, no other measures have been taken. It was.

  In addition, a processing method called vibration cutting is known. This is a method in which feed cutting is performed using a tool while applying a 1-axis or 2-axis vibration to the tool blade edge. In cutting in which the vibration is synchronized to make the cutting edge vibrate in a circular or elliptical locus, (1) the back component force in cutting is reduced to a normal fraction, and the burden on both the workpiece and the tool cutting edge is reduced. , (2) effective in scraping off chips, (3) can also cut hard brittle materials that could not be cut conventionally, (4) in the ductile mode cutting of hard brittle materials, can maintain a critical cutting amount (ductile mode can be maintained) In recent years, it has attracted attention as an excellent feature that the maximum cutting amount) can be increased.

  In this vibration cutting, these effects become more remarkable as the tool edge is vibrated at a higher speed, and the feed rate of the cutting tool or workpiece can be increased. It is common. Furthermore, when it is vibrated at a frequency of 20 kHz or higher, ultrasonic vibration exceeding the human audible range can be achieved, so that vibration cutting with high machining efficiency can be realized without causing unpleasant sound from the device. ing. However, since the degree of realization increases exponentially as the frequency increases, it is very difficult to vibrate the cutting tool at a frequency of 60 kHz or higher. At present, about 100 kHz is said to be a practical upper limit.

  The cutting tool used for this vibration cutting generally has a structure in which a cutting tool in which a chip having a cutting edge and a shank for fixing the cutting tool are integrated is fixed to a vibrating body by fastening with a screw or the like. The installed cutting tool can be easily replaced.

  Piezo elements, giant magnetostrictive elements, etc. are used as vibrators to vibrate the vibration body attached to the tip of the cutting tool at high speed. This vibration causes excitation of the vibration body to resonate and generate a standing wave. This stabilizes high frequency vibrations. This vibration body resonance uses axial vibration (that is, sound waves) that is the cutting direction of the cutting tool, flexural vibration of the vibration body, etc., but it does not depend on changes in cutting load among various resonance modes. Fixing to a desired frequency is important in achieving the above-described effects and realizing highly accurate and efficient vibration cutting with good reproducibility.

  As described above, in vibration cutting, it is important to vibrate the cutting tool at high speed and with high accuracy in order to realize high-precision and high-efficiency machining. For this purpose, the mass of the cutting tool is kept sufficiently small. This is very important. If the cutting tool is heavy, it will be in the same state as when the weight is applied to the tip of the vibrating body, the tip of the vibrating body will not vibrate, the vibration amplitude of the cutting tool will be greatly reduced, and the desired vibration cutting effect will be obtained. Disappear. In particular, the higher the vibration frequency, the greater the influence of mass, which becomes a problem when performing highly efficient vibration cutting.

  Conventionally, a tool steel called high-speed steel was used as a shank, and a chip having a cutting edge such as diamond or ceramic was brazed to the shank. However, the density of the tool steel is as high as 7.8. As the frequency increases, the size of the shank must be made extremely small, and the size of the tip to be fixed must be reduced accordingly, so that the cutting edge becomes smaller and cut in a narrow area. Since the processing burden has to be borne, the wear of the cutting edge has rapidly progressed and the tool life has been shortened. For this reason, frequent tool changes are required, and the time to interrupt machining increases each time. Eventually, the effect is not reflected even though the frequency is increased to improve machining efficiency. It was.

  Furthermore, since the size of the shank is reduced, the rigidity against cutting load etc. decreases and it bends slightly, so it becomes difficult to maintain the position of the tip of the blade with high accuracy, and vibration such as chatter is caused here. It has also occurred that the surface roughness of the machined surface is deteriorated.

Conventionally, cemented carbide materials have been used in place of high-speed steel as a countermeasure against shank deflection and chatter, but the Young's modulus is very high at 550 GPa, and the countermeasure effect is high. Since it is very heavy at about 14.5, there is a problem that vibration amplitude is greatly attenuated as a side effect.
JP-A-6-155112

  On the other hand, Patent Document 1 discloses a technique for generating a reaction sintered silicon carbide material having a thermal expansion coefficient close to a diamond tip on a shank portion. However, the technique of Patent Document 1 provides a cutting tool that can be used in a high-temperature environment, and neither discloses nor suggests a cutting tool used for vibration cutting or the like.

  The present invention has been made in view of the problems of the prior art, and can be used for cutting while vibrating a cutting tool at a high frequency, a cutting method, a cutting apparatus, and an optical element molding. It aims at providing the cutting method of a metal mold | die, an optical element, and the optical element shaping die.

The cutting tool according to claim 1 is a cutting tool used for cutting while vibrating the cutting tool at a frequency of 1 kHz or more,
It has a chip having a cutting edge and a shank for holding it, and the shank is formed using a material having a density of 1 to 6.2 and a Young's modulus of 250 GPa or more. .

  In cutting with vibration, it is particularly important to select an appropriate material for the shank of the cutting tool, so that the original characteristics of machining with vibration can be utilized up to a high frequency.

  As described above, at high vibration frequencies, the mass of the cutting tool attached to the tip of the vibrator greatly affects exponentially, so reducing the material density even if the shank size is the same greatly reduces vibration amplitude. Can be improved. If the density of the material of the shank is 6.2 or less, the weight is reduced, which is advantageous for speeding up. If the density is 1 or more, generally rigidity can be secured. In the present invention, since the density of the conventional high-speed steel is about 7 or 8, the density of 6.2 or less, which is 80% or less, is set as a range where a remarkable difference can be expected. As the minimum density, the smaller the value, the lighter the weight can be. However, since the density is actually larger than water if it is a rigid body, it is set to 1 or more.

  In addition, as described above, it is also important that the cutting tool does not bend or chatter during the cutting process. On the other hand, if the Young's modulus of the shank material is 250 GPa or more, the rigidity is high and the deflection or chatter is not generated. Generation can be effectively suppressed. Further, 250 GPa or more whose Young's modulus is 25% higher than 200 GPa of the high-speed steel was set as a material characteristic range for remarkably preventing this. The upper limit of the Young's modulus is preferably as large as possible. However, since the maximum Young's modulus is 1200 GPa such as diamond, this is the practical upper limit. In particular, the Young's modulus of high-speed steel is quite high as a metal material, so that even if the value is increased by 25%, there is a significant difference in chatter suppression.

  Specific examples of the material for the shank include ceramic materials such as alumina, silicon nitride, silicon carbide, and zirconia, and any of these materials can reduce the aforementioned vibration damping. However, for example, zirconia has a density of 6 and is 25% lighter than high-speed steel, so it is effective in realizing vibration cutting at a high frequency, but from the viewpoint of weight, it is about 2/3 of that. Other weight ceramics such as alumina and silicon nitride are more preferred.

The cutting tool according to claim 2 is characterized in that, in the invention according to claim 1, the linear expansion coefficient of the material of the shank is 5 × 10 ⁻⁶ or less.

  Especially in vibration cutting, etc., the cutting tool vibrates at a high frequency, so that the joints between the parts are displaced slightly to generate friction, and therefore frictional heat may be generated. The cutting tool attached to the tip of the vibrating body by fastening a screw or the like is also abutted against the vibrating body by high-frequency vibration, and friction with the vibrating body is generated on the bottom surface of the shank that is in contact with the cutting tool to generate heat.

  This frictional heat increases the temperature of the shank by about 10 to 30 ° C. from normal temperature in order to directly heat the cutting tool and make the shank shape as small as possible so as not to inhibit vibration. In addition, it depends on the tightening conditions of the cutting tools, the surface roughness of the contact surfaces, the rigidity of the shank material, the friction coefficient, etc., so the reproducibility is poor. To do. For this reason, the shank material undergoes thermal expansion and contraction, and it is difficult to stabilize the cutting edge position of the chip fixed thereto with high accuracy.

  On the other hand, the vibrating body has a larger volume and a much larger heat capacity than the cutting tool, so the temperature rapidly decreases as it moves away from the frictional heat generation surface, and cooling means such as blowing dry air inside is incorporated. In some cases, the overall temperature rise is very small. Therefore, the temperature rise due to this frictional heat is small, and the thermal expansion and contraction of the vibrating body accompanying this is small.

The thermal expansion coefficient of high-speed steel, which is a conventional shank material, is about 11 × 10 ⁻⁶ , but if the length of the shank in the cutting direction is 10 mm, the shank tip position is 3 when the shank temperature rises by 30 ° C. .3 μm. Naturally, the position of the cutting edge of the tip attached to the tip of the shank also drifts to the same extent, and unless such temperature drift is taken into account, it is difficult to obtain a highly accurate machined surface shape. . In particular, the cutting edge position due to this frictional heat is required in a cutting process in which the shape accuracy is required to be 50 nm or less, such as a transfer optical surface of a mold for molding an optical surface of a high-precision optical element. Temperature drift is a very big problem.

  Further, when vibration cutting is performed on hard and brittle materials such as carbide and glass, the cutting depth is often as small as 1 μm or less because the critical cutting depth of the material is small. When temperature drift occurs at the cutting edge position, the depth of cut changes during machining and increases more than three times the original, making ductile mode cutting impossible and brittle fracture mode. It causes a serious problem of disappearing. That is, the temperature drift at the cutting edge position due to the frictional heat is a serious problem as it affects whether or not ductile mode machining can be realized stably.

  Therefore, especially in vibration cutting, it is important to reduce thermal expansion / contraction of the shank material in order to realize high-precision cutting, so it is necessary to select a material with a low linear expansion coefficient for the shank. It can be said that it is important.

The smaller the linear expansion coefficient is, the higher the effect of keeping the position of the blade constant is. However, if the linear expansion coefficient of the shank material is set to 5 × 10 ⁻⁶ or less, the cutting coefficient can be reduced. It is effective in suppressing the influence of thermal expansion. Further, the range of the linear expansion coefficient in which a remarkable effect can be expected as compared with the conventional high-speed steel shank material is 5 × 10 ⁻⁶ , which is 1/2 or less in the above example. This is an absolute value, and therefore includes the range from 0 to -5 × 10 ⁻⁶ . As a result, the temperature drift at the above-mentioned cutting edge position is reduced to about 1.5 μm, so that in the cutting of a material whose critical depth of cut is not so small, the machining range error can be corrected.

Examples of materials whose linear expansion coefficient falls within this range include Invar (1.5 × 10 ⁻⁶ ), Super Invar (1 × 10 ⁻⁶ ), Stainless Invar (1.3 × 10 ⁻⁶ ), Carbide (4 8 to 5 × 10 ⁻⁶ ), quartz (−5 × 10 ⁻⁷ ), silicon nitride (1.3 × 10 ⁻⁶ at room temperature), silicon carbide (4 × 10 ⁻⁶ ), and the like. However, the density of Invar or Super Invar is as large as about 8.1, and the density is as high as 14.5 for carbide. On the other hand, quartz has a low Young's modulus. Therefore, ceramic materials such as silicon nitride and silicon carbide are preferable because they satisfy both the linear expansion coefficient and the density. The linear expansion coefficient here refers to an average linear expansion coefficient at a temperature of 0 ° C. to 50 ° C. at which the shank can actually be used. Incidentally, the average linear expansion coefficient between 0 ° C. and 1000 ° C. is often used for ceramic materials, etc., but especially for silicon nitride, sialon, etc., the value is greatly different from the linear expansion coefficient near room temperature of 20 ° C. It becomes.

  According to a third aspect of the present invention, in the invention according to the first or second aspect, the shank material is mainly composed of silicon nitride.

  Here, the “material mainly composed of silicon nitride” refers to a material containing 50% by weight or more of silicon nitride, and specifically includes commercially available silicon nitride ceramic, sialon, and the like. These have similar physical properties, a density of 3.3, and a Young's modulus of 270 to 300 GPa. Therefore, compared with the high-speed steel which is a conventional shank material, it has a weight of 1/2 or less and a Young's modulus of 1.3 times or more. By using this as the shank material, a high frequency of 1 kHz or more Therefore, it is very advantageous for highly efficient vibration cutting without bending and chatter.

In addition, since the material mainly composed of silicon nitride has a linear expansion coefficient as small as 1.3 × 10 ⁻⁶ near room temperature, the thermal expansion / contraction amount is 1/8 or less that of conventional high-speed steel, Since a very stable cutting edge position can be maintained during machining, it is also suitable for high-precision cutting.

  In particular, when cutting a molding optical surface of an optical element molding die (referred to as a surface on which an optical surface of an optical element is transferred), both high surface roughness and shape accuracy can be achieved, and high speed is achieved. It is very preferable because it can be processed efficiently.

Furthermore, in a material mainly composed of silicon nitride, the fracture toughness value is 6.0 MN / m ^3/2 , which is high and difficult to break in ceramic materials. For example, when fixing a cutting tool to a vibrating body, There is no fear of cracking even if it is strongly tightened with a screw or the like, and there is no fear of sudden breakage during ultrasonic vibration due to microcracks generated on the surface during shank processing. In that respect, it can be said that it is easier to use as a shank material than silicon carbide having a fracture toughness value of 3.5.

  The cutting tool according to claim 4 is the invention according to any one of claims 1 to 3, wherein the cutting edge of the tip is diamond.

  In cutting and vibration cutting using FTS, it is important to use a cutting edge with low wear so that the cutting edge can reliably correspond to the machining surface in order to obtain a highly accurate machining surface. . In order to obtain highly accurate shape accuracy and surface roughness, it is preferable to use a chip having the hardest diamond cutting edge.

  The cutting tool according to claim 5 is the invention according to any one of claims 1 to 3, wherein the cutting edge of the tip is formed of a material containing 98% by weight or more of boron nitride. To do.

  Since boron nitride (BN) is very hard and has low reactivity, the cubic polycrystalline sintered body is widely used as a cutting tool. When the cutting edge is formed of diamond, wear may progress rapidly due to the exhaustion of the cutting edge combined with oxygen in the atmosphere due to the heat generated during cutting, or diffusion of carbon in the workpiece. For example, when cutting glass, it is well known that the thermal conductivity of glass is very poor, so when diamond is used as the cutting edge, it is well known that wear is significant. When cutting ferrous metals, diamond carbon is the material to be processed. It is known to diffuse and wear.

  When performing cutting or vibration cutting using FTS on such materials, it is better to cut with a cutting edge using boron nitride than when using diamond as the cutting edge. A machined surface with high surface roughness and high shape accuracy can be obtained by reflecting the effect of the light weight, high rigidity, and low thermal expansion / contraction shank of the present invention with little wear on the blade edge.

  In addition, when sintering the cubic powder of boron nitride to the size of a chip, an auxiliary agent such as a binder is usually used. However, this auxiliary agent is not as hard as boron nitride and has poor wear properties. Chips made of boron nitride, which contains a large amount of agent, have a large amount of wear during cutting and cannot take advantage of their characteristics. Therefore, it is more preferable to manufacture the chip with a material having high purity of boron nitride, and numerically, boron nitride should occupy 98% by weight or more of the material.

  A cutting tool according to a sixth aspect is characterized in that, in the invention according to any one of the first to fifth aspects, a tip having the cutting edge is fixed to the shank by an active metal method.

  In cutting and vibration cutting using FTS, in order to widen the frequency band of the position control of the cutting tool and to keep the vibration amplitude of the cutting tool attached to the tip of the vibrating body large, the cutting tool has been made smaller conventionally. As described above, the mass has been reduced.

  Even in the cutting tool using the shank of the present invention, reducing the size of the shank is effective for enhancing the above-described effect, and if the shank is made small, the size of the chip placed and fixed on it is reduced. Inevitably smaller. If the insert is made too small, the tool life will be shortened, so there is a limit. However, in processing using FTS and vibration cutting, there are important issues to be solved in reducing this shank.

  That is, since the bonding area for fixing the chip having the cutting edge to the shank is small, the chip fixing force may be weakened. In cutting and vibration cutting using FTS, the cutting tool is vibrated at a high speed, especially in vibration cutting, and sometimes vibrates at several tens of kHz, so the joint surface between the tip and the shank easily peels off during machining. It can happen that the chip is removed. In other words, it is very important to make the bonding between the chip and the shank robust in order to perform efficient processing at a high frequency.

  Usually, a diamond tip is joined to a carbide shank by silver brazing or the like, but the tip is securely joined to a shank having the characteristics of light weight, high rigidity and low expansion and contraction as in the present invention. In some cases, such a bonding method may not be sufficient.

  When joining a shank of a ceramic material as used in the present invention and a chip such as diamond, a joining method called an active metal method is performed, which is stronger and more robust than conventional silver brazing. It is preferable that the chip can be bonded to the shank.

  This method is activated by sandwiching a thin sheet of a brazing material containing a high-temperature active metal such as Ag, Cu or Ti at a place to be joined and placing it in a vacuum atmosphere or an inert gas atmosphere at about 1000 ° C. for several hours. Metals such as titanium diffused and bonded to the ceramic material, resulting in a stronger bond than brazing that relies solely on normal wettability.

  Examples of the active metal brazing material include Ag-Cu-Ti, Cu-Sn-Ti, Co-Ti, Ni-Ti, and aluminum alloy, which are commercially available. A brazing material may be used. In general, the Ag—Cu—Ti brazing material is most frequently used, which is obtained by adding titanium in the range of 1 to 3 wt% to the silver brazing composition.

  As the active metal method, a method using a thin sheet of brazing material has been described, but the shank or chip is bonded to the shank or chip joint surface by sputtering or vapor deposition, or by applying a paste such as fine particles or amalgam. And the chip may be melt-diffused by heat treatment in a vacuum atmosphere or an inert gas atmosphere. The supply method of the brazing material is not limited here, and the active metal method is sufficient.

  As another bonding method, there is a method of brazing after metallization by the Mo-Mn method or the like, but the active metal method is simple and reliable, and the strength is not inferior. Furthermore, according to the active metal method, brazing is performed in a vacuum or in an inert gas, not in the air so that the active metal is not oxidized, so that wetting defects such as bubbles do not occur on the joint surface, and the entire joint surface There is also a feature that the raw material is spread and reliable bonding is possible.

  A cutting tool according to a seventh aspect is characterized in that, in the invention according to any one of the first to sixth aspects, a cutting edge shape of the cutting edge of the tip is a sword tip shape.

  When the cutting edge of the tip is pointed like a sword, the shank also has an elongated shape so as not to interfere with the work piece, so the rigidity is low, and it is easy to bend or generate chatter vibration due to the cutting load. In addition, since a screw or the like for fixing requires a desired size, it is necessary to make the tip of the shank thin and the base of the shank thick, so that the shank shape becomes long and the volume increases. Therefore, if the shank material is selected within the range described in claim 1, the rigidity becomes high, the deflection and chatter vibration are suppressed, and the weight is reduced. Therefore, in the cutting process using FTS, the driving frequency band is set. The control accuracy can be increased and vibration cutting can obtain a sufficient amplitude even at a high frequency, so that the effect is greater than cutting tools of other shapes.

  Further, since the amount of thermal expansion and contraction due to frictional heat and the like increases due to the elongated shank shape, the use of the low linear expansion material as described in claim 2 further stabilizes the cutting edge position and provides a highly accurate fine shape. The optical surface can be cut.

  In addition, since the bonding area between the chip and the shank is difficult to be secured, when the above-described active metal method is used for bonding the chip and the shank, the chip can be firmly bonded and peeling of the chip can be prevented.

  Here, as shown in FIG. 5, the sword-shaped blade edge shape includes a first edge RB1 of the rake face 23r, a second edge RB2 extending in a direction intersecting the first edge RB1, An angle A defined by the third edge RB3 connecting the end of the first edge RB1 and the end of the second edge RB2 and formed by the first edge RB1 and the second edge RB2. Is 10 ° ≦ A ≦ 45 °, and when the third edge RB3 is an arc, the radius r is 0.05 μm ≦ r ≦ 3 μm, and the third edge RB3 is a non-arc. In this case, 0.1 μm ≦ b ≦ 5 μm is set, where b is a distance connecting the end portions of the third edge portion RB3 with a straight line.

  A cutting method according to an eighth aspect is characterized in that the cutting tool according to any one of the first to seventh aspects is cut while being vibrated at a frequency of 1 kHz or more.

  A cutting device according to a ninth aspect includes the cutting tool according to any one of the first to seventh aspects, and a driving device capable of vibrating the cutting tool at a frequency of 1 kHz or more. .

  The optical element molding die according to claim 10 has a molded optical surface processed by cutting the cutting tool according to any one of claims 1 to 7 while vibrating at a frequency of 1 kHz or more. Features.

  An optical element according to an eleventh aspect is characterized by being molded using the optical element molding die according to the tenth aspect.

  According to a twelfth aspect of the present invention, there is provided a method for cutting an optical element molding die, wherein the molding optical surface of the optical element molding die is cut using the cutting device according to the ninth aspect.

  According to the present invention, a cutting tool, a cutting method, a cutting apparatus, an optical element molding die, an optical element formed thereby, and an optical element that can be used for cutting while vibrating the cutting tool at a high frequency A method for cutting a molding die can be provided.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram conceptually illustrating the structure of a cutting apparatus that processes a molding optical surface of an optical element molding die for molding an optical element such as a lens. The cutting tool according to the embodiment of the present invention can be used in the cutting apparatus or the cutting method shown in FIG.

  As shown in FIG. 1, a cutting apparatus 10 includes a vibration cutting unit 20 for cutting a workpiece W that is a workpiece, an NC drive mechanism 30 that supports the vibration cutting unit 20 with respect to the workpiece W, A drive control device 40 for controlling the operation of the NC drive mechanism 30; a vibrator drive device 50 for applying desired vibration to the vibration cutting unit 20; a gas supply device 60 for supplying a cooling gas to the vibration cutting unit 20; And a main controller 70 that controls the overall operation of the apparatus.

  The vibration cutting unit 20 has a cutting tool 23 embedded at the tip of a tool portion 21 extending in the Z-axis direction, and efficiently cuts the workpiece W by high-frequency vibration of the cutting tool 23. Details of the vibration cutting unit 20 will be described later.

  The NC drive mechanism 30 is a drive device having a structure in which a first stage 32 and a second stage 33 are placed on a pedestal 31. Here, the first stage 32 supports the first movable part 35, and the first movable part 35 indirectly receives the workpiece W, which is a material of the optical element molding die, via the chuck 37. I support it. The first stage 32 can move the workpiece W, for example, to a desired position along the Z-axis direction at a desired speed. The first movable portion 35 can rotate the workpiece W around the horizontal rotation axis RA parallel to the Z axis at a desired speed. On the other hand, the second stage 33 supports the second movable part 36, and the second movable part 36 supports the vibration cutting unit 20. The second stage 33 supports the second movable part 36 and the vibration cutting unit 20 and can move them to a desired position along, for example, the X-axis direction or the Y-axis direction at a desired speed. Further, the second movable portion 36 can rotate the vibration cutting unit 20 at a desired speed by a desired angular amount around the vertical turning axis PX parallel to the Y axis. In particular, the vibration cutting unit 20 is positioned at its tip by arranging the tip point of the vibration cutting unit 20 on the vertical pivot axis PX by appropriately adjusting the fixed position and angle of the vibration cutting unit 20 with respect to the second movable portion 36. It can be rotated around the point by a desired angle.

  In the NC drive mechanism 30 described above, the first stage 32 and the first movable unit 35 constitute a workpiece drive unit that drives the workpiece W, and the second stage 33 and the second movable unit 36 are A tool driving unit that drives the vibration cutting unit 20 is configured.

  The drive control device 40 enables high-precision numerical control, and drives the motor, the position sensor, and the like built in the NC drive mechanism 30 under the control of the main control device 70, thereby allowing the first and first control. The two stages 32 and 33 and the first and second movable parts 35 and 36 are appropriately operated to a target state. For example, the first and second stages 32 and 33 follow a predetermined locus in which the machining point at the tip of the cutting tool 23 provided at the tip of the tool portion 21 of the vibration cutting unit 20 is set at a low speed in a plane parallel to the XZ plane. Thus, the workpiece W can be rotated around the horizontal rotation axis RA at a high speed by the first movable portion 35 while moving (feeding operation) relative to the workpiece W. As a result, the NC drive mechanism 30 can be utilized as a highly accurate lathe under the control of the drive control device 40. At this time, the second movable portion 36 can appropriately rotate the tip of the cutting tool 23 around the vertical turning axis PX around the processing point corresponding to the tip of the cutting tool 23, Thus, the tip of the cutting tool 23 can be set to a desired posture (tilt).

  A vibrator driving device (also referred to as a driving device) 50 is for supplying electric power to a vibration source incorporated in the vibration cutting unit 20, and the tip of the tool unit 21 is mainly controlled by a built-in oscillation circuit or PLL circuit. It can be vibrated at the desired frequency and amplitude under the control of the device 70. Although details will be described later, the tip of the tool portion 21 is capable of bending vibration perpendicular to the axis (that is, the tool axis extending in the cutting depth direction) and axial vibration along the axis. Fine and efficient machining with the tip of the tool portion 21, that is, the cutting tool 23, directed to the surface of the workpiece W is enabled by simple vibration or three-dimensional vibration.

  The gas supply device 60 is for cooling the vibration cutting unit 20, and passes a gaseous fluid source 61 for supplying pressurized dry air and the pressurized dry air from the gaseous fluid source 61. Are provided with a temperature adjusting unit 63 as a temperature adjusting unit for adjusting the temperature of the gas and a flow rate adjusting unit 65 as a flow rate adjusting unit for adjusting the flow rate of the pressurized dry air that has passed through the temperature adjusting unit 63. Here, the gaseous fluid source 61 dries air by, for example, sending the air to a dryer using a thermal process, a desiccator, or the like, and pressurizes the dry air to a desired pressure with a compressor. Although not shown, the temperature adjustment unit 63 includes, for example, a flow path in which the refrigerant is circulated around and a temperature sensor provided in the middle of the flow path. By adjusting the temperature and supply amount of the refrigerant, The pressurized dry air passed through the flow path can be adjusted to a desired temperature. Furthermore, the flow rate adjusting unit 65 has, for example, a valve and a flow controller (not shown), and can adjust the flow rate when supplying pressurized dry air whose temperature is adjusted to the vibration cutting unit 20. Yes.

  FIG. 2 is a cross-sectional view illustrating the structure of the vibration cutting unit 20. The vibration cutting unit 20 includes a cutting tool 23, a vibrating body 82, an axial vibrator 83, a bending vibrator 84, a counter balance 85, and a housing 86.

  Here, the cutting tool 23 is fixed so as to be embedded in the distal end portion 21 a of the tool portion 21 that is the distal end side of the vibrating body 82. As will be described in detail later, the cutting tool 23 includes a cutting edge 23c of a diamond tip at the tip and a shank 23b, and vibrates together with the vibrating body 82 as an open end of the vibrating body 82 in a resonance state. That is, the cutting tool 23 generates a vibration that is displaced in the Z direction with the vibration of the vibrating body 82 in the axial direction, and a vibration that is displaced in the Y-axis direction (or the X-axis direction) with the bending vibration of the vibrating body 82. . As a result, the tip of the cutting tool 23 is displaced at high speed, for example, exaggeratingly drawing an elliptical orbit EO as illustrated.

The vibrating body 82 is made of a material having a linear expansion coefficient of 6 × 10 ⁻⁶ or less. Specifically, silicon nitride, sialon, carbide, invar material, stainless invar material, or the like is preferably used. The vibrating body 82 has a thin outer diameter at the tool portion 21 on the distal end side, and a thick outer diameter on the root side. A first fixing flange 87, which is a plate-like portion, is formed at an appropriate location on the side surface of the vibrating body 82, and the vibrating body 82 is fixed to the housing 86 via the first fixing flange 87 with, for example, screws 93. Has been. The vibrating body 82 is oscillated by the axial vibrator 83 and enters a resonance state in which a standing wave that is locally displaced in the Z direction is formed. The vibrating body 82 is vibrated by the flexural vibrator 84 and enters a resonance state in which a standing wave is locally displaced in the Y-axis direction (or X-axis direction). Here, the position of the first fixing flange 87 is a common node for the vibrating body 82 in the axial vibration and the bending vibration, and by fixing the vibrating body 82 via the first fixing flange 87, It can prevent that an axial direction vibration and a bending vibration are prevented.

  FIG. 3 illustrates the shape of the first fixing flange 87. The first fixing flange 87 shown in FIG. 3A is a perfect disk-shaped fixing member, and the outer peripheral portion is fixed to the casing 86 of FIG. It has no structure. The first fixing flange 87 shown in FIG. 3B is a fixing member having a plurality of openings 87a, and even if the outer peripheral portion is fixed to the housing 86 in FIG. It is like that. The first fixing flange 87 shown in FIG. 3C is a fixing member having a supporting member 87b extending in three directions at an equal angle, for example. Even if the tip of the supporting member 87b is fixed to the casing 86 in FIG. Sufficient ventilation inside and outside the body 86 can be secured.

  In FIG. 2, an axial vibrator 83 is a drive source that is formed of a piezo element (PZT), a giant magnetostrictive element, or the like and is connected to the root-side end face of the vibrating body 82. 1 to the vibrator driving device 50. The axial vibrator 83 operates based on a drive signal from the vibrator driving device 50 and gives a longitudinal wave to the vibrating body 82 by stretching and vibrating at a high frequency. The axial vibrator 83 is displaceable in the Z direction but is not displaced in the XY direction.

  The bending vibrator 84 is a vibration source that is formed of a piezo element, a giant magnetostrictive element, or the like and is connected to the base side surface of the vibrating body 82. The bending vibrator 84 is connected to the vibrator driving device 50 of FIG. It is connected. The bending vibrator 84 operates based on a drive signal from the vibrator driving device 50, and applies a transverse wave, that is, a vibration in the Y direction in the illustrated example, to the vibrating body 82 by vibrating at a high frequency.

  The counter balance 85 is connected to the opposite side of the vibrating body 82 with the axial vibrator 83 interposed therebetween. A second fixing flange 88 is formed at an appropriate position on the side surface of the counter balance 85, and the counter balance 85 is fixed to the housing 86 via the second fixing flange 88. The shape of the second fixing flange 88 is the same as that of the first fixing flange 87 shown in FIG. Note that the counter balance 85 is in a resonance state in which a standing wave that is vibrated by the axial vibrator 83 and locally displaced in the Z direction is formed. Here, the position of the second fixing flange 88 is a node of axial vibration for the counter balance 85, and the axial vibration of the vibrating body 82 is prevented by fixing the second fixing flange 88 via the second fixing flange 88. Can be prevented. The counter balance 85 is also formed of the same material as that of the vibrating body 82.

  The housing 86 is a member having a cylindrical inner space, and is a portion that supports and fixes the vibrating body 82 and the counter balance 85 via the first and second fixing flanges 87 and 88. The first fixing flange 87 is attached to one end of the housing 86 so as to close the opening, and an air supply pipe 92 connected to the opening on the end surface is provided on the other end. The air supply pipe 92 is connected to the gas supply device 60 of FIG. 1, and is supplied with pressurized dry air set to a desired flow rate and temperature.

  In the vibration cutting unit 20 described above, the vibrating body 82, the axial vibrator 83, and the counter balance 85 are joined and fixed to each other by brazing so that the axial vibrator 83 can be vibrated efficiently. It has become. In addition, a through-hole 91 is formed in the shaft center of the vibrating body 82, the axial vibrator 83, and the counter balance 85 so as to pass through these joint surfaces. Of pressurized dry air flows. That is, the through-hole 91 is a supply path for sending pressurized dry air, and constitutes a cooling means for cooling the vibration cutting unit 20 from the inside together with the gas supply device 60 and the air supply pipe 92. The front end portion of the through hole 91 is also used as a holding hole for inserting and fixing the cutting tool 23, and the pressurized dry air introduced into the through hole 91 can be supplied to the periphery of the cutting tool 23. Yes. Further, the tip of the through hole 91 leaves a gap even when the cutting tool 23 is fixed, and pressurized dry air is jetted at a high speed from the opening 91a formed adjacent to the cutting tool 23, and cutting is performed. Not only can the machining point at the tip of the tool 23 be efficiently cooled, but also the machining point and chips adhering to the periphery of the machining point can be reliably removed by an air flow.

  4A is a side view of the tip of the tool part 21 shown in FIG. 2, and FIG. 4B is a plan view of the tip of the tool part 21. As shown in FIG.

  As apparent from the figure, the tip 21a provided on the tool portion 21 has a tapered shape, and has a frustoconical shape that is rotationally symmetric about the tool axis AX extending in the cutting depth direction. Have. The cutting tool 23 held at the tip of the tip 21a includes a shank 23b having a triangular tip and a plate-like shape as a whole, and a machining tip 23c fixed to the tip of the shank 23b. Among these, the shank 23b is formed of silicon nitride ceramic or the like, and is light in weight but is not easily bent and has a configuration advantageous for vibration. The processing tip 23c is a diamond tip, and is fixed to the tip of the shank 23b by brazing using an active metal method. The cutting tool 23 itself is fixed so as to be embedded in the end surface 21d of the tip 21a, and the tip of the processing tip 23c is disposed on the extension of the tool axis AX. Further, the processing tip 23c and the shank 23b that supports the processing tip 23c are accommodated in a conical space in which the side surface shape of the distal end portion 21a is extended. Here, the taper angle θ of the tip portion 21a is in the range of 15 ° to 90 °, and preferably in the range of 30 ° to 90 °. When the taper angle θ is 15 ° or more, the bending strength or the like of the distal end portion 21a is secured, and in particular, sufficient strength is secured at 30 ° or more. Further, when the taper angle θ is 15 ° or more, the tendency of the vibration mode to change in the vicinity of the tip 21a can be suppressed, and the cutting accuracy by the cutting tool 23 is particularly effective by avoiding unintended vibrations when the cutting tool 23 is 30 ° or more. Tend to improve. On the other hand, when the taper angle θ of the distal end portion 21a is 90 ° or less, the distal end portion 21a is less likely to interfere with the workpiece surface SA of the workpiece W, so that the machining shape is more optional.

  The cutting tool 23, that is, the fixed portion 23e of the shank 23b is inserted into the hole 21f drilled along the tool axis AX from the end surface 21d of the tip 21a, and is formed of the same material as the material of the tool 21. The two fixing screws 25 and 26 are detachably fixed to the distal end portion 21a. Specifically, the fixing screws 25 and 26 are sequentially screwed into and fixed to the fixing holes 21h and 21g penetrating the upper and lower side surfaces of the tip 21a. These fixing holes 21h and 21g extend, for example, in the Y-axis direction, and the tightening direction of both is orthogonal to the tool axis AX. Both the fixing holes 21h and 21g have different inner diameters, and the inner diameter of the fixing hole 21g is larger than the inner diameter of the fixing hole 21h. Both fixing holes 21h and 21g are filled by screwing both fixing screws 25 and 26. That is, deep concave portions are not left or high convex portions are not formed at the positions of the fixing holes 21h and 21g. One fixing screw 25 screwed into the fixing hole 21h is a fastening member for fixing the cutting tool 23, and is a Torx screw including a male screw portion 25b and a head portion 25a. By screwing the head portion 25a with an appropriate tool while the male screw portion 25b is inserted into the fixing hole 21g, the male screw portion 25b passes through the opening 23h formed in the fixing portion 23e, and the fixing hole 21g It is screwed with a female screw on the inner surface of the fixing hole 21h formed at the back. At this time, the fixing portion 23e of the cutting tool 23 is clamped between the head portion 25a and the inner surface of the hole 21f, and the fixing portion 23e is fixed from the upper surface side. Is secured. The other fixing screw 26 screwed into the fixing hole 21g is a female screw having a protruding portion with a reduced diameter at the tip, and functions as a locking member for preventing the fixing screw 25 from coming off. The fixing screw 26 is screwed into the fixing hole 21g by being screwed into the female screw on the inner surface of the fixing hole 21g by turning the upper end to the fixing hole 21g and turning the upper end with an appropriate tool, thereby filling the fixing hole 21g. . The fixing screw 25 is tightened from the upper end by the protruding portion of the fixing screw 26 screwed in this way, and the fixing screw 25 is prevented from loosening, so that the cutting tool 23 can be fixed more reliably, and the vibration of the cutting tool 23 can be reduced. Looseness can be reduced.

  The fixing screws 25 and 26 for fixing the cutting tool 23 to the distal end portion 21 a of the vibrating body 82 are desirably made of a material having a linear expansion coefficient similar to that of the vibrating body 82. Specifically, although depending on other processing conditions, about 0.75 to 1.25 times the linear expansion coefficient of the vibrating body 82 is practical. In this case, the tool portion 21 and the fixing screws 25 and 26 are similarly expanded, and the cutting tool 23 can be fixed stably and reliably regardless of the temperature change. Further, as the material of the fixing screws 25 and 26, considering the ease of processing and the like, a ceramic material, a high-speed steel, etc. are suitable in addition to a cemented carbide material like the shank 23b, but silicon nitride, sialon, invar material, A stainless invar material or the like can also be used. In addition, the fixing screws 25 and 26 are preferably formed of a material having a density substantially equal to the density of the material of the vibrating body 82 from the viewpoint of not giving noise or the like to vibration of the vibrating body 82. Specifically, although depending on other processing conditions, about 0.75 to 1.25 times the density of the vibrating body 82 is practical. In general, the fixing screws 25 and 26 and the vibrating body 82 are made of the same material, but the fixing screws 25 and 26 and the vibrating body 82 can also be formed of different materials.

  The inner dimension of the hole 21f into which the fixed part 23e of the cutting tool 23 is inserted is slightly larger than the outer dimension of the fixed part 23e of the cutting tool 23 with respect to the thickness in the Y-axis direction. Further, on the side of the inner wall of the hole 21f that does not support the fixed portion 23e of the cutting tool 23, a semi-cylindrical groove 21k in which the through hole 91 is extended as it is is formed. The end portion of the groove 21k is an opening 91a for discharging the pressurized dry air fed from the through hole 91 to the tip portion 21a of the tool portion 21. Thereby, the upper side surface of the cutting tool 23 can be directly and efficiently cooled from the fixed portion 23e side embedded and supported in the tip portion 21a. Further, since the pressurized dry air is injected from the opening 91a near the processing point on the workpiece W toward the tip of the cutting tool 23, the temperature rise of the workpiece W can be suppressed and the processing accuracy can be improved. Moreover, the airflow cross section in the groove 21k is smaller than the airflow cross section in the through hole 91, and the flow rate of the pressurized dry air can be increased at the groove 21k. As a result, since the pressurized dry air of sufficient momentum can be injected to the processing point on the workpiece W, the workpiece W can be reliably cooled, and the chips adhering to the processing point of the workpiece W and the vicinity thereof. Can be removed quickly, and the processing accuracy of the cutting tool 23 can be increased.

  The tip portion 21a of the tool portion 21 vibrates at a high speed, for example, at a frequency of 1 kHz or more in the YZ plane during the cutting process. Further, the tip end portion 21a of the tool portion 21 is gradually moved by the NC drive mechanism 30 in FIG. 1 while drawing a predetermined trajectory in the XZ plane, for example, with respect to the workpiece W as a workpiece. That is, the feeding operation of the tool unit 21 is performed. Further, the workpiece W, which is a workpiece, is rotated at a constant speed around a rotation axis RA parallel to the Z axis by the NC drive mechanism 30 in FIG. 1 (see FIG. 4). As a result, the workpiece W can be turned, and the workpiece SA is rotationally symmetric about the rotation axis RA with respect to the workpiece W, for example, a curved surface such as an uneven spherical surface or an aspheric surface, a phase element surface, or the like. Can be formed. At this time, by using the second stage 33, the tip (that is, the blade edge 23r) of the cutting tool 23 of the tool portion 21 is rotated around the turning axis PX parallel to the Y-axis direction, as shown in FIG. The vibration surface OS at the tip of the cutting tool 23 is set to be substantially perpendicular to the workpiece surface SA to be formed on the workpiece W. Thereby, the processing accuracy of the processing surface SA can be increased, and the processing surface SA can be made smoother. Further, during the processing of the workpiece W, since the pressurized dry air is injected at high speed from the opening 91a at the tip of the tool portion 21 toward the tip of the cutting tool 23, the cutting tool 23 and the work surface SA can be efficiently cooled. Not only can the temperature of the cutting tool 23 and the surface SA to be processed be within a certain range depending on the temperature and flow rate of the pressurized dry air. The pressurized dry air is introduced through a through hole 91 that penetrates the axis of the tool portion 21 and flows inside the vibrating body 82, the axial vibrator 83, the counter balance 85, and the like. The temperature can be adjusted by the temperature and flow rate of the pressurized dry air. As described above, the temperature of the vibrating body 82 can be stabilized by adjusting the temperature of the pressurized dry air. As a result, the temperature drift of the cutting edge position of the cutting tool 23 held at the tip thereof is reduced. Therefore, a highly accurate and highly reproducible cutting surface can be obtained.

  In the above, the vibrators 83 and 84 and the vibrating body 82 are cooled by the pressurized dry air. However, since the dry air is inexpensive and can be easily obtained and supplied, and there is no moisture that causes electric leakage, etc., it is safe. It is. The dry state is preferably 10% or less in terms of relative humidity because the risk of condensation is avoided. Further, when the cutting oil is supplied in the form of mist and mixed with pressurized dry air, the heat capacity is increased, so that the cooling effect can be further enhanced and the tool edge wear at the processing point can be reduced, which is convenient.

According to the present embodiment, the shank 23b of the cutting tool 23 is made of a material having a density of 1 or more and 6.2 or less, a Young's modulus of 250 GPa or more, and a linear expansion coefficient of 5 × 10 ⁻⁶ or less. Since it is lightweight and highly rigid when used for vibration cutting that drives the cutting tool 23 at a frequency of 1 kHz or higher, it can follow a high frequency and perform highly accurate and highly efficient cutting. It can be carried out. By using an optical element molding die having a molding transfer surface that has been subjected to vibration cutting using such a cutting tool, an optical element having a highly accurate optical surface can be molded.

Example 1
FIG. 6 is a perspective view of an ultra-precise machine that is a cutting machine used in the test conducted by the present inventors. In FIG. 6, an X-axis table 2 driven in the X-axis direction by a control device (not shown) is disposed on a pedestal 1. A turning table 2a is placed on the X-axis table 2, and a diamond tool 23 shown in FIG. 7 is mounted thereon. A Z-axis table 4 driven in the Z-axis direction by a control device (not shown) is disposed on the base 1. On the Z-axis table 4, a main shaft (swivel axis) 5 that is rotationally driven by a control device (not shown) is attached. The main shaft 5 can be attached with an optical element molding die (not shown in FIG. 6) having a transfer optical surface to be processed. A diamond tool 23 that is a cutting tool is supported on the X-axis table 2 via a vibration cutting unit 20. The vibration cutting unit 20 including the diamond tool 23 is the same as that shown in FIG.

  The inventor manufactured a mold for optical surface molding. First, as a pre-processing, the workpiece W is made of a Co-containing super hard material, which is roughed by a general-purpose grinding machine to create an approximate shape of the optical surface, and a more precise axial motion. An aspheric optical surface shape was created with a grinding error machine with a shape error of 1 μm.

  For finishing cutting, an ultra-precision machine having an axis resolution of 1 nm and having a spindle 5 shown in FIG. 6 was used. The workpiece W is attached to the main shaft 5 on the Z-axis slider and is rotated and held, and the vibration cutting unit 20 is attached to the swivel tool table 2a on the X-axis table 2 and flexural vibration of the vibration body at a frequency of 40 kHz. And the shaft vibration are resonated in synchronism with each other, and an elliptical vibration having an amplitude of 2 μm in a cutting direction and an amplitude of 3 μm in a direction perpendicular thereto is given to the diamond tool 23.

  Although the workpiece W is subjected to elliptical vibration cutting by turning, the tool cutting edge of the diamond tool 23 changes its direction so as to always maintain the perpendicular to the processing surface (molding optical surface) by the turning tool base 2a. The elliptical vibration surface is always perpendicular to the machining surface, and the effects of elliptical vibration cutting, such as low back force, chip scooping, and deep critical depth of cut, are maintained from the outermost periphery to the center of the transfer optical surface. proceed.

  The aspherical processed shape to be finished as a molded optical surface is a concave surface with a central radius of curvature of 1.8 mm, an effective diameter of 3.8 mm, and a normal angle of the molded optical surface at the outermost periphery of 68.4 °, which is very deep. For this reason, the apex angle of the shank of the diamond tool 23 is narrowed to 35 ° so as to have an elongated shape so that there is no interference during processing.

  The diamond tool 23 attached to the tip of the vibration cutting unit 20 is an artificial diamond tip, and the cutting edge rake face shape is an R bit with an arc. The arc radius is 0.8 mm. As for the shank, there were prepared a conventional carbide brazed one and a silicon nitride shank according to the present invention obtained by diffusion bonding of an Ag—Cu—Ti active raw material in a vacuum.

  First, cutting of the molding optical surface of the workpiece W was started from the outermost periphery with a cutting depth of 1 μm using a conventional carbide shank artificial diamond R bite. When the elliptical vibration cutting is not used, the critical cutting amount is less than 0.1 μm, and therefore, the machining conditions for cutting with 10 times higher efficiency. When the cutting tool was sent from the outermost circumference to 1 mm, the diamond tip suddenly disappeared and machining was impossible. A careful search revealed that the artificial diamond tip had fallen on the base surface under the tool table and was detached from the shank. Further, as a result of observing this peeled surface, it was confirmed that the brazing material used for brazing did not spread over the entire joining surface, and there was a gap in the center. In addition, as a result of observing the cutting surface, which is only the outer peripheral portion, it was found that countless streak patterns were seen in the radial direction, and minute chatter was generated. Interpreted. For the time being, the cut surface was a mirror surface, but it was not a good optical surface with an average surface roughness Ra of 10 nm.

  Since the shank material is cemented carbide, its Young's modulus is not as small as 550 GPa, so it is unlikely that chatter vibration was generated by this shank material. This is because the amplitude of the actual elliptical vibration is smaller than the setting because the weight of the shank is large, and the cutting load has not been reduced since the beginning of cutting. It can be inferred that the shank thermally expanded due to frictional heat with the body, the amount of cutting increased, the cutting load increased further, and chatter occurred. The artificial diamond chip was peeled off by normal silver brazing that was originally performed in the atmosphere, so that the entire joint surface was imperfectly wet with the brazing material, so it could withstand the rapidly increasing cutting load. It seems that it peeled.

  Next, cutting was performed under the same conditions with a cutting tool having exactly the same shape in which an artificial diamond chip was joined to a silicon nitride shank material by an active metal method. As a result, cutting progressed without any problem from the outermost periphery to the center of the molded transfer surface. Furthermore, when the processed aspherical optical surface shape was measured and processed once to correct the error, the shape accuracy was 80 nm PV and the average surface roughness Ra 2.3 nm. There wasn't.

  In addition, elliptical vibration cutting was continuously performed on six surfaces of the same shape of the cemented carbide die with the same cutting tool, but since the second and subsequent machining was performed with a correction amount in advance, the shape of 75 to 90 nm PV was obtained by one finishing process. Errors and average surface roughness Ra of 2.2 to 2.6 nm were obtained with good reproducibility. In such a case, very stable cutting is realized without chatter vibration, and the amount of cut is 10 times that of normal, and the longer the tool life that can process 7 or more surfaces of cemented carbide is, the more elliptical vibration The advantages of the present invention became clear as the characteristics of cutting were exhibited.

(Example 2)
In the same manner as in Example 1, finishing of the optical surface mold using a CVD-SiC material, which was roughed with a shape error of 1 μm or less, was performed by turning using the same ultraprecision processing machine.

  The aspherical optical surface shape finished as a molded optical surface is a deep concave surface having a central radius of curvature of 1.2 mm, an effective optical surface diameter of 2.5 mm, and a normal angle of the optical surface at the outermost periphery of 68.4 degrees. Furthermore, 40 blazed steps having a depth of 1.56 μm are provided as diffraction grooves on the molded optical surface.

  The cutting tools used were a single-crystal diamond tip with a tip of a sword with an apex angle of 25 degrees and a silver-plated high-speed steel, and a single-crystal diamond tip with the same tip shape in a sialon shank with Ag-Cu -Ti raw material joined by active metal method was prepared.

The CVD-SiC material is extremely high in hardness (HV2200) and has a small fracture toughness value of 3.5 MN / m ^3/2 , so the critical depth of cut is very small (<0.03 μm) and is easily chipped. It is the most difficult material for optical surface cutting. In other words, it is extremely difficult to create a molded optical surface by ordinary cutting.

  For the vibration cutting unit 20 of the tool table 2a attached to the swivel axis on the X-axis table 2, an elliptical vibration cutting with an amplitude of 1 μm in a cutting direction and an amplitude of 2 μm in a direction perpendicular to the cutting direction is performed. Went.

  First, cutting was started from the outer periphery using a single crystal diamond tool having a sialon shank as a cutting tool. Since the step of the diffraction groove is more than three times deeper than the cut depth of one cut, it was finished by cutting four times. Cutting was completed to the end, and a good optical mirror surface with a shape error of 67 nm PV and an average surface roughness Ra of 2.6 nm was obtained.

  Further, when the step portion of the blaze groove was evaluated in detail, the bottommost portion of the step where the shape of the tool edge was transferred as it was was a concave arc shape of about 0.3 μm. Although this portion does not have an acute angle shape, there is a possibility that the diffraction efficiency is lowered by about 1%.

  It should be noted that a step shape can be created with a sharp cutting edge with a cutting depth of 0.5 μm with a CVD-SiC material that was thought to be impossible to cut even on a smooth optical surface. is there.

  Subsequently, the same optical surface shape was subjected to vibration cutting under exactly the same conditions using a single crystal diamond tool having a high-speed steel shank as a cutting tool. When the cutting edge touched the outer periphery of the molded optical surface to be processed, the tip of the cutting edge was broken, and processing was impossible. This can be inferred that elliptical vibration could not be realized at the cutting edge due to the cutting load because of the low shank rigidity made of high-speed steel.

It is a block diagram which illustrates notionally the structure of the cutting apparatus which processes the shaping | molding optical surface of the shaping die for optical elements for shape | molding optical elements, such as a lens. 3 is a cross-sectional view illustrating the structure of a vibration cutting unit 20. FIG. FIG. 6 is a diagram illustrating the shape of a first fixing flange 87. 4A is a side view of the tip of the tool part 21 shown in FIG. 2, and FIG. 4B is a plan view of the tip of the tool part 21. As shown in FIG. It is a figure which shows the state which is processing the workpiece | work W with the rake face of the cutting tool. It is a perspective view of the ultraprecision processing machine used for the Example. It is the top view (a) and side view (b) of the cutting tool used for the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Cutting device 20 Vibration cutting unit 21 Tool part 21a Tip part 21d End surface 21f Hole 21g Fixing hole 21h Fixing hole 21k Semi-cylindrical groove 23 Cutting tool 23b Shank 23c Cutting edge 23c Cutting tip 23e Fixing part 23h Opening edge 23r Cutting edge 25r Fixed screw 25a Head portion 25b Male screw portion 26 Fixed screw 30 Drive mechanism 31 Base 32 First stage 33 Second stage 35 First movable portion 36 Second movable portion 37 Chuck 40 Drive control device 50 Transducer drive device 60 Gas supply device 61 Gaseous fluid source 63 Temperature adjusting unit 65 Flow rate adjusting unit 70 Main controller 82 Vibrating body 83 Vibrator 84 Vibrator 85 Counter balance 86 Housing 87 Fixed flange 87a Open 87b Support member 88 Fixed flange 91 Through hole 91a Open 92 Supply Qi pie 93 screws

Claims (12)

A cutting tool used for cutting while vibrating the cutting tool at a frequency of 1 kHz or more,
It has a chip having a cutting edge and a shank for holding it, and the shank is formed using a material having a density of 1 to 6.2 and a Young's modulus of 250 GPa or more. Cutting tools. The cutting tool according to claim 1, wherein a linear expansion coefficient of the material of the shank is 5 × 10 ⁻⁶ or less.   The cutting tool according to claim 1 or 2, wherein the shank material contains silicon nitride as a main component.   The cutting tool according to any one of claims 1 to 3, wherein the cutting edge of the tip is diamond.   The cutting tool according to any one of claims 1 to 3, wherein the cutting edge of the tip is formed of a material containing 98% by weight or more of boron nitride.   The cutting tool according to any one of claims 1 to 5, wherein a tip having the cutting edge is fixed to the shank by an active metal method.   The cutting tool according to any one of claims 1 to 6, wherein a cutting edge shape of the cutting edge of the tip is a sword tip shape.   A cutting method, wherein the cutting tool according to claim 1 is cut while being vibrated at a frequency of 1 kHz or more.   A cutting apparatus comprising: the cutting tool according to claim 1; and a drive device capable of vibrating the cutting tool at a frequency of 1 kHz or more.   An optical element molding die having a molded optical surface processed by cutting the cutting tool according to claim 1 while vibrating at a frequency of 1 kHz or more.   An optical element formed using the optical element molding die according to claim 10. A cutting method for an optical element molding die, wherein the molding optical surface of the optical element molding die is cut using the cutting device according to claim 9.

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