JP4320646B2 - Cutting method - Google Patents

Description

The present invention relates to a cutting method suitably used for cutting a material, a raw material, and the like that form a molding die for an optical element and the like.

  There is a technique for cutting a hard material such as cemented carbide or glass by vibrating the tip of a tool such as diamond, which is called vibration cutting. This is because the cutting edge of the tool performs fine cutting at a high speed by vibration, and the cutting edge generates a chip by the vibration, and the cutting process generates less stress on both the tool and the work material. (For example, refer to Patent Documents 1, 2, 3, 4, etc.). By this vibration cutting, the critical cutting amount required in normal ductile mode cutting is improved several times, and difficult-to-cut materials can be cut with high efficiency.

  In such vibration cutting, if the vibration frequency is increased in order to improve the processing efficiency, the above-described effect is increased, and the feed rate of the tool is also increased almost in proportion to the frequency. used. In addition, since this frequency exceeds the human audible range, there is an advantage that the vibrator and the vibrator excited by the vibrator do not produce unpleasant sound.

As a method of generating such high-speed vibration at the tool edge, a standing wave is generated by exciting a member holding the tool by a piezo element or a giant magnetostrictive element, and resonating the member with bending vibration or axial vibration. It has been put to practical use as a stable vibration. In such a method, a member for holding a tool, that is, a vibrating body is fixed to a member connected to an apparatus housing, a tool stand of a processing machine, or the like at a resonance node.
JP 2000-52101 A JP 2000-218401 A Japanese Patent Laid-Open No. 9-309001 JP 2002-126901 A

When performing cutting with the vibration cutting tool as described above placed on a processing machine as it is, the way the tool blade edge touches the surface to be cut, that is, the surface to be processed, may vary depending on the shape of the surface to be processed. For example, when the trajectory of the tool edge is a curve or the surface to be processed is a curved surface, the processing area of the tool edge moves along the edge of the edge of the tool as it is processed, and the vibration surface moves with respect to the cutting direction of the edge. There is a problem in that the effect of vibration cutting is reduced because it is not vertical. This causes an increase in the back component force in the cutting process and a decrease in the scraping effect due to the cutting edge rake face of the chip, and there is a problem that the cutting load is suddenly increased on both the work surface and the cutting edge. It was.
For this reason, when the vibration cutting tool is mounted on the processing machine as described above, the surface roughness of the surface to be processed deteriorates rapidly with the movement of the cutting point of the cutting edge, or the cutting edge wear progresses to improve the machining shape accuracy. This causes a problem of deterioration in processing quality such as lowering, and shortens the life of the vibration cutting tool. In some cases, the cutting edge of the tool is broken and the processing cannot be continued.
Particularly in applications where the machining surface is required to have extremely high shape accuracy and surface roughness, such as an optical surface, the movement of the machining point of the tool edge accompanying vibration cutting as described above is serious, and the vibration surface is the surface to be machined. For example, an optical surface with high shape accuracy and high surface roughness can be created efficiently in the machining area in the center, which is almost perpendicular to the center of the machine. However, the machining point on the tool edge moves and vibrates in the machining area around the work surface. When the surface to be processed forms an angle of 45 ° or more with respect to the surface, the effect of vibration cutting is almost lost, and the shape accuracy and surface roughness of the optical surface are rapidly deteriorated. At the same time, when the cutting material is a hard and brittle material, the critical cutting amount (maximum cutting amount that can be ductile mode cutting) decreases unless the vibration surface is perpendicular to the work surface. In addition, the surface to be processed may not be an optical surface.
In addition, when using a cutting tool with a thin and sharp edge like a sword cutting tool, the above-mentioned problem is further noticeable. Initially, the vibration cutting effect reduces the processing load and gives a deep cut, and the cutting progresses without any problem. However, if the vertical relationship between the vibration surface and the work surface is lost due to movement to the periphery of the work surface, the surface roughness of the work surface will deteriorate rapidly, and the cutting edge may eventually break. It occurred frequently. In other words, when cutting an optical surface having a fine structure such as a diffraction groove with a cutting edge such as a sword tip, depending on the overall shape of the optical surface, it is possible to accurately create a fine structure and to create a tool. It is not compatible with making the blade edge thick and sturdy. This becomes a fatal problem when the vibration cutting tool is directly mounted on the processing machine as described above. Such a problem occurs especially when performing vibration cutting of an optical surface having a fine structure on a deep curved surface with a normal angle of 45 ° or more, that is, the vertical relationship between the vibration surface and the processing surface is greatly broken. It was a big problem.

Therefore, the present invention makes it possible to easily create work surfaces of various shapes with high processing accuracy without losing the advantage of vibration cutting that enables quick and efficient cutting of various materials. It aims at providing the cutting method which can be performed.

In order to solve the above problems, a vibration cutting apparatus suitable for carrying out the cutting method according to the present invention includes (a) a cutting tool, (b) a vibration source for vibrating the cutting tool, and (c) a tip portion. A vibrating body that supports the cutting tool and transmits vibrations from a vibration source to the cutting tool, and (d) a tool drive that supports the vibrating body and can be displaced so that the machining point of the cutting tool becomes the turning center. And a driving device having a section. Here, “the machining point becomes the turning center” means that the machining point that generates chips of the cutting edge of the cutting tool coincides with or is close to the turning center. It means a range in which it can be considered that the cutting edge of the machining point does not substantially move only by changing the direction of the cutting edge of the point. Specifically, this corresponds to a state where the machining point is within a range of, for example, about 10 μm or less from the turning center. In addition, the axis | shaft which rotates a cutting tool, ie, the turning axis which passes a turning center, shall extend in the tangential direction of the to-be-processed surface which should be normally formed in a to-be-processed body.

  In the above apparatus, the tool driving unit supports the vibrating body and displaces so that the machining point of the cutting tool becomes the center of rotation. For example, the cutting surface is arranged so that the vibration surface of the cutting tool is perpendicular to the work surface. Or the vibration surface of the cutting tool can be arranged at a desired angle with respect to the work surface. In other words, the angle control of the cutting edge at the processing point becomes simple and precise, and a workpiece surface with various shapes can be created with high processing accuracy.

  When the cutting tool is attached so that the processing point is the turning center and vibration cutting is performed, for example, the cutting tool can always perform cutting while maintaining the direction of the cutting edge at the processing point constant with respect to the processing surface. The vibration surface at the tip can be maintained perpendicular to the surface to be processed during processing. As a result, it is possible to improve the machining capability and reduce the efficiency of chip removal due to the reduction of the back part, which is a feature of vibration cutting, and to enable mirror cutting of hard and brittle materials and difficult-to-cut materials, resulting in a high machining shape. Precision and machined surface roughness can be obtained, and the tool life can be greatly extended. The cutting tool feeding method at the time of cutting may be a ruling process in which the cutting edge is repeatedly sent in one direction, or a turning process in which a workpiece is rotated to cut mainly a rotationally symmetric shape. Also good.

  In a specific aspect of the present invention, in the vibration cutting device, the tool driving unit is configured to change the posture of the cutting edge provided on the cutting tool with respect to the surface of the workpiece or the workpiece surface to be formed on the workpiece. Adjust. In this case, the workpiece can be efficiently cut by adjusting the posture of the blade edge, and the finish of the workpiece surface can be improved to the expected accuracy.

  In another aspect of the present invention, the drive device includes a workpiece drive unit that supports the workpiece and rotates it around a predetermined rotation axis. In this case, it is possible to cut the work surface while rotating the work body and adjusting its posture.

  In another aspect of the present invention, the driving device rotates the workpiece by the workpiece driving unit, and the cutting tool is rotated with respect to the rotation axis of the workpiece by at least one of the tool driving unit and the workpiece driving unit. To move the workpiece relatively. In this case, since the cutting tool is moved relative to the rotating workpiece, a rotationally symmetric shape can be created efficiently. A vibration cutting device provided with such a drive device is particularly suitable for processing of an optical surface shape that has many rotationally symmetric shapes and requires high accuracy with respect to the processing shape and surface roughness.

  In another aspect of the present invention, the drive device moves the cutting tool relative to the rotation axis of the workpiece at least two-dimensionally. In this case, processing of any rotationally symmetric shape is possible.

  In another aspect of the invention, the cutting tool has a diamond cutting edge. Cutting with a diamond cutting edge can achieve extremely high shape accuracy and minute surface roughness, and is therefore very suitable for optical surface creation. Especially in vibration cutting, the cutting stress is remarkably reduced for both the work piece and the cutting edge, so that a deep cutting depth is obtained and the life of the diamond cutting edge is extended. The optical surface can be created and processed efficiently.

  In another aspect of the present invention, the cutting edge of the cutting tool has a sword-like cutting edge shape. In this case, it becomes easy to create and process a fine structure such as a diffraction groove on the surface of the workpiece. Also, by performing vibration cutting so that the blade edge of the sword tip becomes the machining point, the vibration surface can be made perpendicular to the work surface facing the machining point at all times during machining, so that the cutting back force is reduced. Reduces tool edge wear and breakage. In addition, the surface roughness and shape accuracy of the surface to be processed can be increased.

  In another aspect of the present invention, the cutting edge of the cutting tool has a half-moon shaped cutting edge shape. In this case, it becomes easy to create a fine structure such as a diffraction groove on the surface of the processing surface. In addition, when the surface to be processed is a curved surface, the surface roughness can be made smaller than that of the blade of the sword using an arc-shaped cutting edge, and a smooth optical surface can be created. Furthermore, by performing vibration cutting so that the half-moon shaped cutting edge becomes the machining point, the vibration surface can be made perpendicular to the work surface facing the machining point at all times during machining, so that the cutting back force is reduced. Reduces tool edge wear and breakage. In addition, the surface roughness and shape accuracy of the surface to be processed can be increased.

  In another aspect of the present invention, the cutting edge of the cutting tool has an arcuate cutting edge shape. In this case, since the arcuate cutting edge is used as a whole, the cutting trace on the surface to be processed becomes smooth and the surface roughness can be lowered. Therefore, when an optical surface is created, the specularity is increased and the quality of the optical surface to be processed can be improved.

  In another aspect of the present invention, the processing point of the cutting tool is disposed on the extension of the tool axis of the vibrating body. Here, the tool axis extends in the cutting depth direction of the cutting tool and becomes the center of the lateral vibration of the vibrating body. When the vibration surface of the cutting tool is arranged so that it is perpendicular to the work surface at the machining point, for example, the tool axis extends perpendicular to the tangential plane of the work surface facing the machining point. Become. In this case, the cutting edge of the cutting tool is displaced about the extension line of the tool axis, and the symmetry of vibration is improved on the tool axis. Therefore, the surface to be processed is cut more smoothly, and the processing accuracy can be improved. Moreover, it is easy to grasp the arrangement of the cutting tool and the tip of the vibrating body with respect to the surface to be processed, and the workability of processing by the vibration cutting device can be improved.

  A cutting method according to the present invention is a cutting method for transmitting vibration from a vibration source to a cutting tool supported on a tip portion of the vibrating body via the vibrating body, and supporting the vibrating body of the cutting tool. The machining point is displaced so as to be the center of rotation.

  In the above method, the vibrating body is supported and displaced so that the machining point of the cutting tool becomes the center of rotation. For example, the vibration surface of the cutting tool can be arranged at a desired angle with respect to the workpiece surface. In addition, the angle control of the cutting edge at the machining point becomes simple and precise, and a workpiece surface with various shapes can be created with high machining accuracy.

In particular, in the present invention, the vibration from the vibration source is transmitted to the cutting tool supported on the tip of the vibrating body through the vibrating body, and the workpiece is turned around the rotation axis and turned with the cutting tool. A method for cutting a symmetric workpiece surface, wherein the cutting tool is displaced in a plane orthogonal to the cutting direction by supporting the vibrating body and having the machining point of the cutting tool as a turning center, and the displacement is caused by the vibration. The vibration surface is kept perpendicular to the work surface being cut.
In a specific aspect of the present invention, in the cutting method, when the cutting tool is turned, the cutting tool is formed on the surface of the workpiece or on the workpiece surface to be formed on the workpiece. Adjust the posture of the blade edge.

  The molding die according to the present invention has an optical surface created by machining using the vibration cutting device. In this case, a mold having a concave surface and other various optical surfaces can be efficiently and simply processed with high accuracy.

  The optical element according to the present invention is molded by the molding die. In this case, a high-precision optical element can be obtained with a high-precision mold.

[First Embodiment]
Hereinafter, a vibration cutting apparatus suitable for carrying out the cutting method according to the first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram conceptually illustrating the structure of a vibration cutting apparatus that processes an optical surface of a molding die for molding an optical element such as a lens.

  As shown in FIG. 1, the vibration cutting device 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 is a vibration cutting tool in which a cutting tool 23 is 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 supports the workpiece W via the chuck 37. 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, 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).

  The vibrator driving device 50 is for supplying electric power to a vibration source built in the vibration cutting unit 20, and the tip of the tool unit 21 is controlled by the main controller 70 by a built-in oscillation circuit or PLL circuit. It can be vibrated at a desired frequency and amplitude. 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 has a diamond tip cutting edge 23a, and vibrates 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 is possible to prevent the axial vibration and the bending vibration from being hindered.

  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.

  Returning to FIG. 2, the axial vibrator 83 is a vibration source that is formed of a piezo element (PZT), a giant magnetostrictive element, or the like and is connected to the end face on the base side of the vibrating body 82, and is connected via a connector or the like not shown. Are connected to the vibrator driving device 50 of FIG. 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 casing 86 is a member having a cylindrical inner space, and is a part 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 a super hard material, a ceramic material, high-speed steel, or the like, and is difficult to bend while being lightweight. The processing tip 23c is a diamond tip, and is fixed to the tip of the shank 23b by brazing or the like. 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 firmly fixed to the distal end portion 21a so as to be detachable. Specifically, fixing screws 25 and 26 are sequentially screwed into fixing holes 21h and 21g that penetrate between 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 tip 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. The fixing screws 25 and 26 are preferably formed of a material having a specific gravity substantially equal to the specific gravity of the material of the vibrating body 82 from the viewpoint of not giving noise or the like to the vibration of the vibrating body 82. Specifically, although depending on other processing conditions, about 0.75 to 1.25 times the specific gravity 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 high speed, for example, in the YZ plane as already described. 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.

  Here, in the vibration cutting apparatus of this embodiment, the cutting edge 23 of the cutting tool 23 is supported so as to be rotatable around the turning axis PX, and the reason why the vibration surface OS and the tool axis AX are held perpendicular to the surface SA to be processed. explain. In the case of the vibration cutting apparatus of the present embodiment, the cutting edge 23r of the cutting tool 23 is rotated to an arbitrary angular position around the turning axis PX by the second movable portion 36, so that the machining area of the cutting edge 23r is changed during cutting. It is possible to perform the ductile mode cutting process without fixing, and it is possible to perform the process not affected by the shape accuracy of the cutting edge ridge line of the blade edge 23r. On the other hand, in the case of creating an optical surface by conventional turning (machining without using the pivot axis PX), the machining area of the cutting edge 23r moves on the edge of the cutting edge simultaneously with the progress of turning. If the diamond constituting the cutting edge 23r includes a crystal orientation that is easily worn or chipped, the cutting edge 23r may easily wear at that portion or chipping may occur. When wear progresses as in the former, a shape error corresponding to the wear occurs in that portion, and when chipping occurs as in the latter, brittle mode machining occurs in that portion and a mirror surface cannot be obtained. On the other hand, in the case of a vibration cutting device that appropriately rotates the blade edge 23r around the pivot axis PX as in the present embodiment, the processing region of the blade edge 23r can be fixed, so the crystal orientation of the diamond to be used is also fixed, It is possible to realize cutting that can avoid the above-described shape error and degradation of the machined surface quality. Furthermore, since the machining region is fixed, high machining shape accuracy can be easily realized and machining of the cutting tool 23 can be achieved if the diamond crystal orientation of that portion is fixed to the crystal orientation with the least wear. The life due to wear of the cutting tip 23c can be greatly extended.

  FIG. 6 is an enlarged view for explaining a processing state of the cutting tool 23 by the processing tip 23c. The cutting edge 23r of the machining tip 23c has an arcuate rake face RB, and the rake face RB is shown as viewed from above (unprocessed face side). The rake face RB includes a linear first edge RB1, a second edge RB2 extending in a direction intersecting the first edge RB1, a first edge RB1 and a second edge RB2. And / or a third edge RB3 having a non-circular arc. The angle h formed by the first edge RB1 and the second edge RB2 is 30 ° ≦ h ≦ 60 °. When the third edge RB3 is a circular arc, the radius r is set to 0.003 mm ≦ r ≦ 5 mm. When the third edge RB3 is a non-arc curve, the approximate arc radius r that minimizes the square-square error is set to 0.003 mm ≦ r ≦ 5 mm.

  As described above, the cutting tool 23 having the cutting edge 23r having the arc-shaped rake face RB is called an R bite. This is a process of creating the cutting edge shape into an arc, and it is relatively easy to finish roundness with high accuracy. There is an advantage that it is easy. Therefore, when an R cutting tool having such a rake surface RB is incorporated into a vibration cutting device and processed, a high-precision optical surface can be obtained easily and efficiently with high blade edge shape accuracy. In the case of creating an optical surface by conventional turning (processing that does not use the turning axis PX), the processing region (or processing point) is changed as the normal angle of the processing surface changes as the cutting progresses. Moves along the arc edge of the cutting edge 23r, and once chipping occurs, the ductile mode cutting becomes brittle processing and the cutting resistance increases and becomes unstable. It continues to be damaged and eventually the arc ridges of the cutting edge 23r after the occurrence of chipping are all destroyed and become unusable. In this way, since the range of the edge of the cutting edge that is damaged by chipping is often widened with the R bite, it is difficult to select and use a portion where no chipping has occurred, and the cutting tool 23 itself has finished its life in a short period of time. Therefore, it tends to be very expensive cutting. On the other hand, as in the present embodiment, the blade edge 23r is rotatably supported around the turning axis PX, and the vibration surface OS and the tool axis AX are held perpendicularly to the tangent line SA ′ in the tool trajectory direction of the workpiece surface SA. For example, chipping can be greatly reduced, and damage to the cutting edge 23r over a wide area as described above can be significantly reduced.

  In the present embodiment, turning is used to create the work surface SA. Turning is a processing method with less load on the cutting tool 23 because once the cutting edge 23r of the cutting tool 23 is cut into the workpiece W, the processing proceeds continuously until the cutting is completed. Therefore, by combining with the cutting tool 23 having the R cutting tool, that is, the arcuate cutting edge 23r, the chipping of the cutting edge 23r can be remarkably suppressed, the life of the cutting tool 23 can be extended, and a highly accurate optical surface can be obtained. The mirror surface can be obtained easily and inexpensively. In addition, the vibration cutting apparatus itself can be configured with a movable shaft, and the vibration cutting apparatus can be manufactured at a low cost. Therefore, machining of the axially symmetric optical element molding die can be realized at low cost.

[Second Embodiment]
Hereinafter, a vibration cutting apparatus suitable for carrying out the cutting method according to the second embodiment will be described. The vibration cutting apparatus according to the second embodiment is a partial modification of the vibration cutting apparatus according to the first embodiment. Parts that are not particularly described are common to the apparatus according to the first embodiment, and are common in the drawings. Are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 7 is an enlarged view for explaining a machining state by the machining tip 123c of the cutting tool 23 in the second embodiment. The cutting edge 123r of the machining tip 123c has a half-moon rake face RB, and the rake face RB extends in a direction intersecting the linear first edge HB1 and the first edge HB1. The second edge HB2 and the first edge HB1 are smoothly connected, and the second edge HB2 is an angled arc and / or non-arc third edge HB3. Is outlined. An angle f formed by the first edge HB1 and the second edge HB2 is 0 ° <f <90 °. Further, when the third edge HB3 is a circular arc, the radius r is set to 0.1 μm ≦ r ≦ 5 mm. When the third edge HB3 is a non-circular arc, 0.1 μm ≦ g ≦ 5 mm is set, where g is a distance connecting the end portions with a straight line. Note that a fourth edge HB4 made of a convex arc or straight line may be provided between the second edge HB2 and the third edge HB3. Further, the second edge HB2 can have a predetermined inclination angle with respect to the vibration surface OS and the tangent line SA ′ in the tool trajectory direction of the processing surface SA, and in this case, the step processing portion of the processing surface SA. Can be adjusted.

  As described above, the cutting tool 23 in which the cutting edge 123r has the half-moon rake face RB is referred to as a half-moon bite. When such a half-moon tool is incorporated into a vibration cutting device and processed, it is not limited to a simple mirror surface, and high-precision processing of molds with fine shapes (such as diffraction grooves) that could not be processed due to breakage of the cutting edge. It becomes possible to do. If it is a half-moon tool, the aspherical part of the workpiece W can be processed by the curved R part of the cutting edge 123r, and a smooth optical surface can be processed. Light scattering on the optical surface is reduced. Further, the fine structure portion such as the step, the phase structure, and the diffraction structure of the workpiece W can be processed by a sharp portion of the blade edge 123r, and a decrease in diffraction efficiency can be reduced. By using a molding die for optical elements processed with a half-moon tool, a blazed diffraction structure can be transferred and molded, making it resistant to environmental changes, widening the range of design, and making excellent aberration correction for multiple wavelengths. And an optical element made of plastic.

[Third Embodiment]
Hereinafter, a vibration cutting apparatus suitable for carrying out the cutting method according to the third embodiment will be described. The vibration cutting apparatus according to the second embodiment is obtained by partially changing the vibration cutting apparatus according to the first embodiment, and parts that are not particularly described are common to the apparatus according to the first embodiment.

  FIG. 8 is an enlarged view for explaining a machining state of the cutting tool 23 by the machining tip 223c in the third embodiment. The cutting edge 223r of the processing tip 223c has a sword-shaped rake face RB, and the rake face RB extends in a direction intersecting the linear first edge RB1 and the first edge RB1. The second edge RB2 and the third edge RB3 connecting the end of the first edge RB1 and the end of the second edge RB2 are contoured. The acute angle a formed by the first edge RB1 and the second edge RB2 is 10 ° ≦ a ≦ 45 °. When the third edge RB3 is an arc, the radius r is 0.05 μm ≦ r ≦ 3 μm. When the third edge RB3 is a non-circular arc, the distance connecting the ends of the third edge RB3 with a straight line is defined as b, and 0.1 μm ≦ b ≦ 5.0 μm.

  As described above, the cutting tool 23 in which the blade edge 223r has a rake-like rake face RB is referred to as a sword tip bite. Since the tip of the blade edge 223r is sharply thin and has a shape that is easy to break, a sword tip tool suitable for fine processing is suitably incorporated in the vibration cutting apparatus of this embodiment. That is, if the cutting edge 223r is rotatably supported around the turning axis PX and the vibration surface OS and the tool axis AX are held perpendicularly to the tangent line SA ′ in the tool trajectory direction of the workpiece surface SA, the low profile by vibration cutting is reduced. Since the effects of increasing the component force and critical cutting depth can be maximized, not only chipping but also breakage of the cutting edge can be greatly reduced. The optical surface of the molding die for optical elements made of a hard material having a high hardness can be processed with high accuracy and ease. By using the molding die for optical elements, it is possible to transfer and mold fine structures on the optical surface such as diffractive structures and phase structures in optical glass and plastic molding. An optical element made of glass that can be satisfactorily corrected for a plurality of wavelengths can be obtained.

[Fourth Embodiment]
The molding die according to the fourth embodiment will be described below. FIG. 9 is a diagram for explaining a molding die (optical element molding die) manufactured by using the vibration cutting unit 20 of the first to third embodiments, and FIG. FIG. 9B is a side sectional view of the first mold 2A, and FIG. 9B is a side sectional view of the movable mold, that is, the second mold 2B. The optical surfaces 3a and 3b of both molds 2A and 2B are finished by the vibration cutting apparatus shown in FIGS. That is, the base material (the material is, for example, cemented carbide) of both molds 2A and 2B is fixed to the chuck 37 as a workpiece W, and the standing wave is formed in the vibration cutting unit 20 by operating the vibrator driving device 50 and the like. The cutting tool 23 is vibrated at high speed. In parallel with this, the drive control device 40 is appropriately operated to arbitrarily move the tip of the tool portion 21 of the vibration cutting unit 20 in three dimensions with respect to the workpiece W. Thereby, the optical surfaces 3a and 3b of the molds 2A and 2B are not limited to spherical surfaces and aspheric surfaces, but can be step surfaces, phase structure surfaces, and diffraction structure surfaces.

  FIG. 10 is a cross-sectional view of a lens L press-molded using the mold 2A of FIG. 9A and the mold 2B of FIG. 9B. Although not shown, when the optical surfaces 3a and 3b of the molds 2A and 2B have a step surface, a phase structure surface, a diffractive structure surface, etc., the molding optical surface of the lens L is also a step surface, a phase structure surface, and a diffractive structure. It has a surface. Furthermore, the material of the lens L is not limited to plastic, but may be glass or the like. In addition, the lens L can also be directly produced by the vibration cutting apparatus of the first to third embodiments.

  As described above, the present invention has been described according to the embodiment, but the present invention is not limited to the above embodiment. For example, in the vibration cutting unit 20, the tip shapes of the processing chips 23 c, 123 c, and 223 c are not limited to those illustrated in FIGS. 6 to 8, but depend on the shape of the processing surface SA to be formed on the workpiece W, etc. Can be changed as appropriate.

  In the vibration cutting unit 20, the overall shape and dimensions of the vibrating body 82 and the axial vibrator 83 can be appropriately changed according to the application. Further, the second fixed flange 88 extending from the counter balance 85 can be omitted. Moreover, although the through-hole 91 is provided in axial centers, such as the vibrating body 82, and pressurized dry air is distribute | circulated, the supply method of pressurized dry air is not restricted to the air supply pipe 92 illustrated in FIG. For example, it is possible to supply pressurized dry air around the vibrating body 82 from the side surface of the housing 86. In addition, when the vibration cutting unit 20 is not heated so much, it is not necessary to worry about the dimensional change of the vibrating body 82, and therefore supply of pressurized dry air is not necessary. In addition, in the gas supply device 60 of FIG. 1, instead of air, a gaseous fluid added as a solvent or particles in which oil or other lubricating elements are misted, an inert gas such as nitrogen gas, or the like can be used.

  In the above vibration cutting apparatus, turning has been mainly described. However, the vibration cutting apparatus shown in FIG. 1 can be modified for ruling. The ruling process is a processing method for creating the processing surface SA by superimposing the trajectory while reciprocating the cutting tool 23. In particular, even a concave surface with a strong curvature or a complicated machining shape can be machined with high accuracy without the cutting tool 23 interfering with the machining surface. In the ruling process, since the cutting edges 23r, 123r, and 223r of the cutting tool 23 do not rotate, the cutting amount is the same from the start of one cutting to the end of cutting. Therefore, at the time of the first cutting, the cutting edges 23r, 123r, and 223r are changed. Large cutting resistance works. In this processing method, chipping is most often generated at the cutting edges 23r, 123r, and 223r at the beginning of normal cutting, and no ruling is adopted for high hardness materials. However, the vibration cutting device of the present embodiment, that is, the blade edges 23r, 123r, and 223r are rotatably supported around the turning axis PX, and the vibration surface OS or the like is perpendicular to the tangent line SA ′ in the tool trajectory direction of the work surface SA. In the case of a vibration cutting apparatus that holds the tool axis AX, chipping can be suppressed by ruling and cutting of a free-form surface can be performed even with a high-hardness material. In addition, since the tool shape, tool wear, and elastic deformation of the tool are completely irrelevant as compared with the conventional grinding process, it is possible to easily obtain a highly accurate machining shape and mirror surface in which the motion accuracy of the machining apparatus is transferred.

It is a block diagram explaining the vibration cutting apparatus of 1st Embodiment. It is a longitudinal cross-sectional view explaining the structure of the vibration cutting unit integrated in the vibration cutting apparatus of FIG. (A)-(c) is an end elevation which illustrates the shape of the 1st fixed flange used for the vibration cutting unit of FIG. (A), (b) is the side sectional drawing and plane sectional drawing of a tool part front-end | tip. It is a top view explaining the movement and turning of a tool part front-end | tip. It is an enlarged view explaining the processing state by the chip | tip for a process. It is an enlarged view for demonstrating a part of structure of the vibration cutting unit in 2nd Embodiment, and shows the modification of FIG. It is an enlarged view for demonstrating a part of structure of the vibration cutting unit in 3rd Embodiment, and shows the modification of FIG. (A), (b) is a sectional side view of the molding die concerning a 4th embodiment. FIG. 10 is a side sectional view of a lens formed by the molding die of FIG. 9.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Vibration cutting apparatus, 20 ... Vibration cutting unit, 21 ... Tool part, 21a ... Tip part, 21d ... End face, 21f ... Hole, 21k ... Groove, 23 ... Cutting tool, 23b ... Shank, 23c ... Chip for processing, 23e DESCRIPTION OF SYMBOLS ... Fixed part, 25 ... Fixed screw, 26 ... Fixed screw, 30 ... Drive mechanism, 32 ... First stage, 33 ... Second stage, 35 ... First movable part, 36 ... Second movable part, 37 ... Chuck, 40 DESCRIPTION OF SYMBOLS ... Drive control apparatus, 50 ... Vibrator drive apparatus, 60 ... Gas supply apparatus, 61 ... Gaseous fluid source, 63 ... Temperature control part, 65 ... Flow control part, 70 ... Main control apparatus, 82 ... Vibrating body, 83, 84 ... Vibrator, 85 ... Counter balance, 86 ... Housing, 91 ... Through-hole, 91a ... Opening, 92 ... Air supply pipe, AX ... Tool axis, EO ... Elliptical orbit, RA ... Rotary axis, SA ... Work surface , W …work

Claims (2)

A linear first edge supported by a tip of the vibrating body via a vibrating body, a second edge extending in a direction intersecting the first edge, and An arc-shaped third edge connecting the ends of the first and second edges, and the angle formed by the first edge and the second edge is transmitted to a cutting tool having an acute cutting edge shape. A method of cutting a work surface consisting of a continuous curved surface without a rotationally symmetric step , turning with the cutting tool while rotating the work body around a rotation axis,
Supporting the vibrating body and displacing the cutting tool in a plane perpendicular to the cutting direction with the processing point of the cutting tool as a turning center,
The cutting method according to claim 1, wherein a vibration surface passing through a processing point of the third edge portion of the cutting tool due to the vibration is kept perpendicular to a surface to be processed during cutting.   When turning the cutting tool, the posture of the cutting edge formed on the cutting tool is adjusted with respect to the surface of the workpiece or a surface to be formed on the workpiece. Item 2. The cutting method according to Item 1.

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