JP2007307680A - Cutting method, optical element and die - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve surface precision of an optical element or a rotating axis symmetrical type curved surface of a die for this optical element under a cutting method, on the optical element and on the die. <P>SOLUTION: The rotating axis symmetrical shape curved surface of a workpiece 9 is cut and worked while moving a working point of a tool 8 and the workpiece 9 in the crest direction of a cutting blade of the tool 8 by revolving the tool 8 within a specified area under the cutting method to cut and work the rotating axis symmetrical shape curved surface on the workpiece 9 by making the tool 8 a knife edge of which has the circular arc cutting blade contact with the rotated workpiece 9 by rotating the optical element or the die to form this optical element as the work 9. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a cutting method for cutting an optical element or a die having a rotational axis symmetry shape, and an optical element and a die cut by the cutting method, and more particularly to an optical element or a die. The present invention relates to a technique for improving the surface accuracy of a rotationally symmetric curved surface.

  When cutting an optical element or a die having a curved surface having a rotationally symmetric shape, it is common to use a so-called Earl bite-shaped single crystal diamond bit having a circular cutting edge (for example, non-patent document). 1).

  The cutting edge radius r of the above-mentioned round bite-shaped single crystal diamond bit is in the range of several μm to several mm, and particularly 0.5 mm to 1 mm is often used. The wing angle of the tool edge is generally 60 degrees or less. The shape of the cutting edge is appropriately set according to the size of single crystal diamond that can be applied as a tool, the diamond processing technique, the tool shape required in the processing method described later, and the like.

  One of the following methods is applied to the processing of the rotationally symmetrical curved surface with such a tool. As shown in FIG. 8A, one method is a method of machining while simultaneously controlling two linear movement axes (generally X and Z axes) in order to move the workpiece 13 and the tool 14 relative to each other. is there. This method is a simultaneous biaxial control in which the machining action points (contact points with the workpiece on the tool) P1 and P2 are moved along the cutting edge 14a of the tool 14 in accordance with the inclination of the curved surface of the workpiece 13. This is called a cutting method.

  Another method is that, as shown in FIG. 8B, the machining action points Pf and Pf are obtained by simultaneous three-axis control in which a turning axis (generally, B axis) is added as a movement axis of the simultaneous two-axis control cutting method. This is a technique called an SPDT (single point diamond turning) method for processing so as not to move on the cutting edge 14a of the tool 14 (that is, at one point on the cutting edge 14a).

  The former simultaneous two-axis control cutting method can be machined with two axes that are one axis fewer than the SPDT method, but in order to obtain high machining accuracy, extremely high shape accuracy over the entire use area of the cutting edge of the tool Is required. On the other hand, in the SPDT method, the shape accuracy of the cutting edge of the tool is not so necessary, but high control accuracy is required for the processing apparatus to be applied. However, the SPDT method that can stably obtain a high-accuracy machined surface is frequently used due to recent high-precision cutting devices.

  By the way, in order to stably perform the mirror surface cutting (ductile mode cutting) of brittle materials represented by crystal materials for optical elements and glass, the thickness of cut per rotation of the workpiece according to the characteristics of each material. It is necessary to set the processing conditions to reduce the thickness. For example, it is known that a cut-out thickness for uniformly mirror-cutting the entire surface of a fluorite (111) surface used as an optical lens is desirably 85 nm or less (for example, see Non-Patent Document 2). .

  In the example of the SPDT method shown in FIG. 9, the tool 15 having an R bite shape is used under the conditions of the cutting depth a and the tool feed speed f for each rotation of the workpiece 16 (only the machining surface is shown). The cut thickness of the workpiece 16 gradually increases from the tip 15a of the tool 15 to the surface layer 16a of the workpiece 16, and reaches a maximum value hmax near the surface layer of the workpiece 16. According to the above processing principle, in order to mirror-cut a brittle material or the like, it is necessary to set processing conditions so that the maximum value hmax is not more than a value that can be mirror-cut.

As an example, FIG. 10 shows the relationship between the tool cutting depth a and the tool feed f when a convex spherical surface having a curvature radius of 10 mm is cut with a tool having a cutting edge radius of 1 mm with a maximum cutting thickness of 50 nm. The graph of the result calculated | required scientifically is shown. From the figure, it can be seen that when the cutting depth a is 2 μm, the tool feed speed f at which mirror cutting can be performed is a very small value of 0.75 μm / rev. Under machining conditions exceeding this value, the maximum cut thickness hmax is equal to or greater than the limit value inherent to the workpiece that can be mirror-cut, so that brittle mode cutting is performed and a mirror surface cannot be obtained.
Ultra-precision machining and aspherical machining, NTS Corporation, (2004) P219. Journal of Precision Engineering Vol. 70, no. 1, (2004) P106.

  In the above-described principle of mirror cutting of a brittle material, the maximum cutting thickness hmax can be kept minute by using a tool having a large cutting edge radius even if the cutting amount and feeding speed are set to be relatively large. Therefore, high-efficiency mirror cutting can be performed. However, if the tool is used at a fixed position by the SPDT method, it is particularly brittle material with high hardness such as ceramics or cemented carbide, or thermochemical such as glass. When processing an optical element or a die made of a material having a large amount of tool wear due to the action, the tool is severely damaged, and it is difficult to perform highly accurate processing.

  And even when applying the above-mentioned simultaneous biaxial control machining method, which is another machining method, with a tool with a large radius of curvature of the cutting edge, the wing angle becomes narrow due to the limitation of the size of the single crystal diamond that can be applied. Processing of curved surfaces with large angles is not possible. This is because the wing angle of the tool to be applied needs to be larger than the inclination angle of the workpiece due to the principle of the machining method. Furthermore, in the simultaneous two-axis control processing method, as described above, a very high shape accuracy is required over the entire use area of the cutting edge of the tool, and it is difficult to process the optical element or the die with high accuracy. It is.

  SUMMARY OF THE INVENTION In view of the above-described conventional situation, an object of the present invention is to provide a cutting method for increasing the surface accuracy of a rotationally symmetric curved surface of an optical element or a mold for the optical element, and an optical machined by the cutting method. It is to provide an element and a mold.

  In order to solve the above-described problem, the cutting method of the present invention rotates an optical element or a mold for molding the optical element as a workpiece, and the cutting edge of the rotated workpiece has an arc shape. In a cutting method for cutting a rotationally symmetric shape curved surface on the workpiece by contacting a tool having a cutting edge, the tool and the workpiece are rotated by turning the tool within a predetermined range. While the machining action point is moved in the ridge line direction of the cutting edge of the tool, the rotationally symmetrical curved surface of the workpiece is cut.

Preferably, the feed speed of the tool is controlled in accordance with the rotationally symmetrical curved surface of the workpiece so that the change in the cut thickness of the workpiece is not more than a certain amount.
Preferably, the turning speed of the tool is controlled so that the cut thickness of the workpiece is substantially constant regardless of the position of the cutting edge.

Preferably, the arc radius of the cutting edge is 2 mm or more.
Preferably, cutting is performed while vibrating the cutting edge in the cutting direction.
Preferably, the workpiece is any one of optical glass, calcium fluoride, single crystal silicon, and tungsten sintered body.

In order to solve the above-mentioned problems, the optical element of the present invention is configured to be cut by any one of the cutting methods described above.
In order to solve the above problems, the mold according to the present invention has a structure cut by any one of the above cutting methods.

  In the present invention, by rotating the tool within a predetermined range, the processing point of the tool and the workpiece (optical element or mold) is moved in the ridge line direction of the cutting edge of the tool while rotating the workpiece. Axisymmetrically shaped curved surface is cut. Thereby, since the working action point in a tool moves continuously, tool wear is distributed along a cutting edge ridgeline. Therefore, it is possible to suppress a decrease in surface accuracy of the workpiece due to tool wear. Further, by turning the tool, even if the processed surface of the workpiece is a curved surface with a large inclination angle, it can be processed with high accuracy. Therefore, according to the present invention, it is possible to improve the surface accuracy of the rotationally symmetric curved surface of the optical element or the mold for the optical element.

Hereinafter, a cutting method, an optical element, and a mold according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a perspective view showing a cutting apparatus according to an embodiment of the present invention.

  In the figure, a cutting device (lathe) 1 includes a workpiece axis spindle 2, a Z axis slide table 3, an X axis slide table 4, a B axis rotary table 5, a tool table 6, a nozzle 7, and the like. A workpiece 9 mounted on the workpiece shaft spindle 2 is processed by a tool 8 mounted on the workpiece 6. The workpiece 9 is an optical element or a mold, and is, for example, any one of optical glass, calcium fluoride, single crystal silicon, and tungsten sintered body.

  The workpiece axis spindle 2 is installed on a Z-axis slide table 3 that can move in the Z-axis direction, which is the horizontal direction, via a spindle holding portion 3a. A workpiece 9 is rotatably mounted on the workpiece shaft spindle 2. The rotation axis direction of the workpiece axis spindle 2 and the workpiece 9 is the Z-axis direction here.

  On the X-axis slide table 4 that is perpendicular to the Z-axis direction and movable in the X-axis direction that is the horizontal direction, a B-axis rotary table 5 having a vertical turning axis direction is installed. A tool table 6 is installed on the B-axis rotary table 5, and a tool 8 having a cutting edge made of single crystal diamond is mounted on the tool table 6. Here, the B-axis rotary table 5 is turned (turned) within a predetermined angle, and accordingly, the tool 8 is also turned within a predetermined angle. The nozzle 7 supplies coolant or mist for cooling and lubrication of the processing area.

  Next, cutting of the workpiece 9 by the turning apparatus 1 will be described with reference to FIGS. FIG. 2 is an explanatory view showing a tool and a workpiece to be mounted on the cutting apparatus.

  The processing conditions in the present embodiment (feed (feed speed) f [μm / rev] for each rotation of the work 9, cutting depth a of the tool 8, rotation speed of the work 9, etc.) are as follows: Based on the curvature radius R of each machining position in the section of the workpiece 9 in the rotation axis direction, the arc radius r of the cutting edge 8b of the cutting edge 8a, etc., the maximum value hmax of the cutting thickness of the tool 8 relative to the workpiece 9 is Geometrically determined and set so as to be less than or equal to the specular cutting value inherent to the workpiece 9. Note that the workpiece 9 shown in FIG. 2 may be processed in advance into a shape that approximates the target shape before cutting.

  FIG. 3A shows the cutting edge radius (the cutting edge arc radius) r and the maximum cutting thickness when the cutting depth a is 0.5 μm and the tool feed speed is 5 μm / rev, with the rotational axis symmetry plane as the machining condition. The relationship of hmax is shown. As can be seen from this figure, under certain machining conditions, the maximum cutting thickness hmax decreases as the cutting edge radius r of the tool increases. Further, the maximum cutting thickness that can be mirror-cut by the tool is a value specific to the material to be processed, but in most brittle materials, this value is 100 nm or less, and the radius r of the cutting edge of a tool that satisfies this is 2 mm. That's it. Naturally, a tool having a cutting edge radius r of less than 2 mm can be applied because the maximum cutting thickness can be made minute by further reducing the processing conditions. Further, the cutting edge shape of the tool may be a flat surface as long as there is no geometric interference with the shape of the workpiece.

  FIG. 3B shows a tool feed f [μm / rev] and a maximum cutting thickness hmax [nm] when machining a convex spherical shape having a curvature radius R of 10 mm of the workpiece 9 with a cutting depth a of the tool 8 being 2 μm. ] Is shown. For example, in order to process the maximum cutting thickness hmax at 50 nm, the tool feed f when using a tool whose arc radius r of the cutting edge 8a is 2 mm is 1.0 μm / rev or less, and the arc radius of the cutting edge 8a It can be seen that the tool feed f when using a tool with r of 10 mm may be set to 1.8 μm / rev or less.

  Even with a tool whose arc radius r of the cutting edge 8a is 2 mm, by setting the concave workpiece 9 having a small curvature radius R as a processing target, or setting the cutting depth a and the feed speed f of the tool 8 to be small. Thus, it is possible to perform mirror cutting, but by setting the arc radius r of the cutting edge 8a to a large radius of 2 mm or more, a large cutting depth a and a maximum cutting thickness hmax are maintained. Since it can be set to a fast feed speed f, highly efficient machining is possible.

  When the workpiece 9 is machined by the cutting apparatus 1 shown in FIG. 1, the workpiece shaft spindle 2 is first rotated under the above-described machining conditions, and the tool 8 cuts into the workpiece 9 as shown in FIG. Cutting is performed by giving the depth a and moving the tool 8 from the outer periphery to the center of the workpiece 9 or in the opposite direction.

  At this time, the movement of the tool 8 is such that a machining action point (actually not a point but a certain width) P with the workpiece 9 on the tool 8 is arbitrarily moved on the ridge line of the tool cutting edge 8a. To. Specifically, the tool 8 is swung within such a range that the machining action point P moves within the use area (that is, the cutting edge 8b) of the tool cutting edge 8a, and the machining action point between the tool 8 and the workpiece 9 is obtained. While moving P in the ridge line direction of the cutting edge of the tool 8, the rotationally symmetrical curved surface of the workpiece 9 is cut. In this case, the X, Z, and B axis control by the X axis slide table 3, the Z axis slide table 4, and the B axis rotary table 5 is performed at a contact angle (machining) at the processing point P with the tool 8 on the workpiece 9. The coordinates of the tool position are geometrically determined from the normal to the machining surface of the workpiece 9 set at the action point P and the angle formed by the rotation axis of the workpiece 9 and the radius r of the arc of the tool cutting edge. Good. In addition, when moving the processing action point P in the ridgeline direction of the cutting edge of the tool 8, the tool 8 may be continuously swung within a predetermined range, but may be swung intermittently at predetermined angles. .

  In FIG. 4A, when the workpiece 9 has a rotationally symmetric aspherical shape, the workpiece radius position from the workpiece rotation axis and the curvature radius R of each machining position in the section in the rotation axis direction of the workpiece 9 An example of the relationship is shown. FIG. 4B shows a setting example of the tool feed speed f in FIG. 4A. In FIGS. 4A and 4B, the rotational axis symmetry of the workpiece 9 is convex with a radius of curvature of 8.1 to 20 mm in a convex shape using a tool having a 6 mm arc radius of the cutting edge 8a. This is an example of processing a spherical shape with a cutting depth a of 1 μm and a maximum cutting thickness hmax of 50 nm.

  As shown in FIGS. 4A and 4B, the amount of change in the maximum cut thickness hmax is constant by changing the feed rate f of the tool in response to the change in the radius of curvature R of the cross section in the rotational axis direction of the workpiece 9. It becomes possible to maintain below the amount.

  Further, as shown in FIG. 5, the B-axis rotary table 5 (X) so that the amount of movement of the machining action point P in the tool 8 increases corresponding to the workpiece radial position from the rotation axis of the workpiece 9. Since the axial slide table 3 and the Z-axis slide table 4) are controlled by a control means (not shown) and the tool 8 is moved, the cutting distance of each machining action point P of the tool 8 can be made constant. The amount of wear of the tool 8 is uniform over the entire point of action P.

  FIG. 6 is a shape accuracy evaluation result of a glass for an optical lens having a diameter of 10 mm that is mirror-cut using a tool 8 having an arc radius r of the cutting edge 8b of the cutting edge 8a of 10 mm based on the configuration of the present embodiment. to Valley) was able to obtain a highly accurate mirror surface of 0.98 μm.

  Note that the cutting apparatus 1 shown in FIG. 1 is merely an example, and the cutting method of the present invention can be performed by another cutting apparatus. In the present embodiment, the optical element or mold as the workpiece 9 is selected from optical glass, calcium fluoride, single crystal silicon, and tungsten sintered body as preferable examples. When the workpiece is an optical element, any material that can be used as a lens, prism, mirror, or the like may be used. When the workpiece is a mold, the optical element (lens, prism, mirror, etc.) is used. Any material can be used as long as it can be used for molding.

  In the present embodiment, the tool 8 is swung within a predetermined range by the B-axis rotary table 5, so that the processing action point P between the tool 8 and the workpiece (optical element or mold) 9 is set to the cutting edge of the tool 8. The rotationally symmetrical curved surface of the workpiece 9 is cut while moving in the ridge line direction 8a. Thereby, since the processing action point P in the tool 8 continuously moves, tool wear is dispersed along the ridgeline of the cutting edge 8a. Therefore, it is possible to suppress a decrease in surface accuracy of the workpiece 9 due to wear of the tool 8. Further, by turning the tool 8, even if the processing surface of the workpiece 9 is a curved surface having a large inclination angle, it can be processed with high accuracy. Therefore, according to the present embodiment, the surface accuracy of the rotationally symmetrical shape curved surface of the workpiece 9 (the optical element or the mold for the optical element) can be increased.

  Further, by controlling the feed speed of the tool 8 in accordance with the rotational axis symmetrical shape curved surface of the workpiece 9 so that the change in the maximum cut thickness hmax of the workpiece 9 is a certain amount or less, a so-called rotational axis is obtained. Even when a workpiece 9 having a symmetric aspherical shape is processed, it is possible to perform cutting while maintaining the maximum cut thickness hmax to be equal to or less than a specular cutting value unique to the workpiece. Therefore, the surface accuracy of the rotationally symmetrical shape curved surface of the workpiece 9 can be effectively increased.

  Further, the tool 8 is controlled by controlling the turning speed of the tool 8 by the B-axis rotary table 5 so that the cutting distance at each working point of the tool 8 is substantially constant regardless of the radial position of the workpiece 9. The amount of wear of the tool 8 can be made uniform over the entire processing action point P. Therefore, it is possible to more effectively suppress a reduction in surface accuracy of the workpiece 9 due to wear of the tool 8, and it is possible to further increase the surface accuracy of the rotationally symmetrical curved surface of the workpiece 9.

  Further, by setting the arc radius of the cutting edge 8b to 2 mm or more, even when the cutting depth a of the tool 8 is increased or the feed speed f of the tool 8 is increased, the maximum cutting thickness hmax is increased. Can be suppressed. Therefore, the surface accuracy can be further enhanced while processing the rotationally symmetrical curved surface of the workpiece 9 with high efficiency.

FIG. 7 is an explanatory view showing a tool and a workpiece according to another embodiment of the present invention.
The cutting apparatus according to the present embodiment is provided with a vibration means capable of vibrating the tool 12 being machined, and the tool 12 is held on the tool table 6 shown in FIG. Since it has the same configuration as the cutting apparatus 1 shown in FIG. 1 except for the points described above, detailed description of the cutting apparatus is omitted.

  As the vibration means, a coolant 10a to which ultrasonic vibration is added from the ultrasonic water supply nozzle 10 is used by using an ultrasonic water supply device (not shown) that is generally used as a flowing water type ultrasonic cleaning device. Irradiating the tool 12 causes the tool 12 to vibrate slightly. Further, the shank 11 holding the tool 12 is in a horizontal direction so that the vibration direction of the tool 12 is inclined with respect to the XY plane (the plane extending in the vertical direction and the depth direction in the figure). The angle γ is set in the range of 0 to 20 degrees.

  The processing conditions in the present embodiment are the same as those described above except that the coolant 10a is supplied during the cutting of the workpiece 9 and the cutting edge of the tool 12 is vibrated in the cutting direction in the range of 10 kHz to 3 MHz. The same as the form.

  According to the present embodiment, in addition to the effects of the above-described embodiments, the turning tool 12 vibrates during machining, so that cooling at the working point is efficiently performed and damage to the tool 12 is suppressed. Therefore, it is possible to more effectively increase the surface accuracy of the curved surface of the rotational axis symmetry of the optical element or the mold for the optical element.

  In addition, you may apply the vibration cutting apparatus which can vibrate the tool 12 directly to a single axis | shaft or a multi-axis direction as a vibration means. In this case, the workpiece shaft rotation speed and the tool cutting depth may be appropriately set as machining conditions generally applied in vibration cutting.

It is a perspective view which shows the cutting apparatus which concerns on one embodiment of this invention. It is explanatory drawing which shows the tool with which the said cutting apparatus is mounted | worn, and a to-be-processed object. It is a graph which shows the relationship between the cutting edge radius (arc radius of cutting edge) r of a tool and the maximum cutting thickness hmax on the rotational axis symmetry plane. It is a graph which shows the example of the relationship between the tool feed f and the cutting thickness hmax in the said cutting device. Example of relationship between workpiece radius position from workpiece rotation axis and radius of curvature R at each machining position in cross section in rotation axis direction of workpiece when workpiece is rotationally symmetric aspherical It is a graph which shows. It is a graph which shows the example of a setting of the tool feed speed f in the case of FIG. 4A. It is a graph which shows the relationship between the workpiece radial position from the rotating shaft of the said workpiece, and the moving amount | distance of the machining action point in the said tool. It is a figure which shows the shape accuracy evaluation result of an example (glass for optical lenses of (phi) 10 mm) cut into the said workpiece in this Embodiment. It is explanatory drawing which shows the tool and workpiece based on other embodiment of this invention. It is explanatory drawing which shows the conventional simultaneous biaxial control cutting system. It is explanatory drawing (the 1) which shows the conventional SPDT (single point diamond turning) system. It is explanatory drawing (the 2) which shows the conventional SPDT (single point diamond turning) system. It is a graph which shows the example of the relationship between the tool cutting depth and tool feed in the conventional SPDT (single point diamond turning) system.

Explanation of symbols

1 Cutting device (Lathe)
2 Workpiece axis spindle 3 Z-axis slide table 3a Spindle holding part 4 X-axis slide table 5 B-axis rotary table 6 Tool base 7 Nozzle 8 Tool 8a Cutting blade 8b Cutting edge 9 Workpiece 10 Ultrasonic water supply nozzle 10a Coolant 11 Shank 12 tool

Claims (8)

An optical element or a mold for molding the optical element is rotated as a work piece, and a tool having a cutting edge with an arc-shaped cutting edge is brought into contact with the rotated work piece. In a cutting method of cutting a rotationally symmetrical shape curved surface,
By rotating the tool within a predetermined range, the rotationally symmetric curved surface of the workpiece is cut while moving the machining action point of the tool and the workpiece in the ridge line direction of the cutting edge of the tool. A cutting method characterized by processing.   The feed rate of the tool according to claim 1, wherein the feed rate of the tool is controlled in accordance with a rotationally symmetrical curved surface of the workpiece so that a change in the cut thickness of the workpiece is not more than a certain amount. Cutting method.   The cutting method according to claim 1 or 2, wherein the turning speed of the tool is controlled so that the cut thickness of the workpiece is substantially constant regardless of the position of the cutting edge.   The cutting method according to any one of claims 1 to 3, wherein an arc radius of the cutting edge is 2 mm or more.   The cutting method according to any one of claims 1 to 4, wherein the cutting blade is cut while being vibrated in a cutting direction.   The cutting work according to any one of claims 1 to 5, wherein the workpiece is any one of optical glass, calcium fluoride, single crystal silicon, and a tungsten sintered body. Method.   An optical element cut by the cutting method according to any one of claims 1 to 6.   A metal mold cut by the cutting method according to any one of claims 1 to 6.