JP2004114172A - Method and apparatus of electric discharge truing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of in-situ electric discharge truing for an electrically conductive grinding wheel, by which very high machining accuracy can be obtained by preventing the deterioration of the form accuracy of the wheel. <P>SOLUTION: An electrode 6 is formed into a required shape by a tool 7 fixed to a machine. Next, an electrically conductive grinding wheel 9 having a highly accurate cross-section is manufactured by transferring the required shape on the surface of the wheel by scanningly tracing the surface of the electrode, while turning the electrically conductive wheel 9. Highly accurate machined surfaces can be achieved by machining a workpiece using the wheel 9. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a discharge truing of a conductive grindstone for grinding an ultra-precision workpiece such as an optical element.
[0002]
[Prior art]
Conventionally, on-machine electric discharge truing performed on a processing machine is well known in Japanese Patent Application Laid-Open No. 63-283861. FIG. 10 shows a conventional on-machine discharge truing method. A rotating electrode 6 is attached to a rotating shaft 2 provided on the machine. The cylindrical outer peripheral portion of the electrode 6 is created in advance by machining with a tool provided on the machine or machining outside the machine.
[0003]
A conductive metal bond grindstone 9 serving as a workpiece is rotated and brought close to the electrode 9 while supplying a processing liquid 11. Although not shown in FIG. 10, a DC voltage required for electric discharge machining is impressed between the grindstone 9 and the electrode 6, and when approaching a predetermined distance, a discharge current controlled in a pulsed manner. Flows and processing proceeds. As a result, the cross-sectional shape of the grindstone 9 is transferred to the inverted shape of the cross-sectional shape of the electrode 6.
[0004]
In order to prevent the transfer of an accurate shape due to the consumption of the electrode 6, it has been proposed to regenerate the electrode 6 after rough discharge truing and perform discharge truing under finishing conditions.
[0005]
[Problems to be solved by the invention]
It seems that this on-machine discharge truing method can obtain sufficient accuracy for processing general mechanical parts. However, in the above-described on-machine electric discharge truing method using a form-rotating electrode, the consumption of the electrode proceeds at the same time as the start of electric discharge machining. Therefore, when the discharge truing is completed, the consumed electrode shape is transferred to the grindstone. Even if the discharge truing is divided into rough machining and finish machining, there is no guarantee that the electrode will be formed in exactly the same shape as before when the electrode is reworked.
[0006]
In the first place, it is said that the electrodes are created on the machine, but there is no description on how to make the electrodes with high precision.
[0007]
Generally, in the field of optical elements such as lenses and mirrors and mold processing for molding them, shape accuracy on the order of submicrons is required.
[0008]
An object of the present invention is to improve the accuracy in an on-machine electric discharge truing method and apparatus for a conductive grindstone for grinding an ultra-precision workpiece such as an optical element.
[0009]
[Means for Solving the Problems]
In order to achieve this object, the electric discharge truing method of the present invention is to form an electrode attached to a processing machine into a predetermined shape with a cutting tool, and to rotate the conductive grindstone to form a predetermined shape. The conductive grindstone can be processed into a predetermined shape with high precision by transferring a predetermined shape of the electrode surface to a grindstone surface by scanning along the electrode surface in a state of being attached to the surface.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
The invention according to claim 1 of the present invention is directed to a method of discharging and truing a conductive grindstone, wherein an electrode attached to a processing machine is formed into a predetermined shape by a cutting tool, and the predetermined shape is formed while rotating the conductive grindstone. It is a discharge truing method of a conductive grindstone, wherein a predetermined shape of the electrode surface is transferred to a grindstone surface by scanning along the electrode surface attached to the processing machine. By performing the processes from electrode formation to discharge truing on one machine, truing can be performed with high accuracy without causing an error or the like due to mounting.
[0011]
According to a second aspect of the present invention, in the first aspect of the present invention, a processing machine capable of numerically controlling at least three axes or more is used. Is eliminated, and a complicated shape defined mathematically can be automatically operated by a program, thereby enabling highly accurate truing.
[0012]
According to a third aspect of the present invention, in the first aspect of the present invention, the cutting tool for forming the electrode is a single crystal or polycrystalline diamond cutting tool, and the cutting edge has an arc shape, and has high contour accuracy. This has the effect of forming the contour of the electrode with the same accuracy as the contour accuracy of the cutting tool.
[0013]
The invention described in claim 4 is characterized in that, in the invention described in claim 1, the numerical control is performed so that the cutting shape by the cutting tool is an arc, a non-arc, a V-shape, a polygonal shape, and the like. It is also possible to form an electrode having a complicated cross-sectional shape.
[0014]
According to a fifth aspect of the present invention, in the first aspect of the present invention, the electrode surface is formed along the electrode surface in a direction perpendicular to a generatrix direction of the electrode tip portion having a cylindrical, non-cylindrical, or square tip shape. In order to form a grindstone having a predetermined cross-sectional shape by scanning the conductive grindstone while numerically controlling the conductive grindstone, the conductive grindstone and the electrode are mainly subjected to electric discharge machining at only one point, so the electrode Can be used efficiently without deforming all at once.
[0015]
According to a sixth aspect of the present invention, in the invention of the fifth aspect, after the discharge truing, the conductive grindstone is moved by a required amount in the axial direction of the electrode to form the conductive grindstone with a new electrode surface. Even if the electrode at the place where discharge truing is worn out and loses its shape, by moving the place, it becomes possible to continue discharge truing with the electrode having the same cross-sectional shape and achieve a highly accurate shape. Has the effect of being able to form a whetstone having
[0016]
The invention according to claim 7, a processing machine capable of numerically controlling three or more processing axes, an electrode attached to the processing machine, a cutting tool provided in the processing machine, and a cutting tool for cutting the electrode, A power supply unit including a discharge circuit for discharging and truing the grindstone by scanning the grindstone along the cut surface of the electrode on the processing machine cut into the predetermined shape by the cutting tool. This is a discharge truing device, and can perform high-precision machining by performing high-precision electrode formation to on-machine discharge truing.
[0017]
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
[0018]
FIG. 1 shows the steps of the present invention.
[0019]
In the first stage shown in FIG. 1A, the electrode 6 is processed by the diamond cutting tool 7 provided on the processing machine. Although not shown, numerical control is performed by an arbitrary program.
[0020]
In the second stage shown in FIG. 1 (b), the conductive grindstone 9 which is also mounted on the grinding spindle provided on the machine and is rotating, and has the same position as the first stage shown in FIG. 1 (a). The electrode 6 attached to the electrode 6 is approached, and the grindstone 9 is scanned along the surface of the electrode 6 according to a predetermined program along the surface of the electrode 6, and the sectional shape of the grindstone 9 is adjusted to a predetermined shape using the discharge circuit 20. Thus, the electric discharge machining is performed by the electric discharge circuit 20.
[0021]
In the third stage shown in FIG. 1C, the workpiece 15 is ground by using a grindstone 9 formed in a predetermined shape. If the cross-sectional shape of the grinding wheel is deformed after the grinding, the process may be returned to the second stage again. Similarly, if the electrode 6 loses its shape, it returns to the first stage. In any of the processes, since it can be performed on the same processing machine without changing the mounting position of the electrode 6, it is characterized in that it can be freely moved to any stage by returning to the original coordinate values.
[0022]
FIG. 2 shows an electric discharge truing apparatus as a processing machine for realizing the process of the present invention shown in FIG. The X table has three axes of a Y table 13 and a Z table 14 provided on the X table, and can be driven with a precision of nanometer order by a numerical controller (not shown). On the Y table 13, a diamond cutting tool 7 for processing the electrode 6, a grinding spindle 11, and a conductive grindstone 9 at its tip are provided. On the Z table 14, the electrode 6 and the workpiece 15 are installed. The discharge circuit 20 shown in FIG. 1A for discharge truing, a discharge liquid supply nozzle, and the like are omitted.
[0023]
3 and 4 show an example of forming and processing the electrode 6 using the diamond cutting tool 7 which is the first stage of the present invention.
[0024]
FIG. 3 shows an example in which the electrode 6 is processed by feeding the diamond cutting tool 7 in the X-axis direction using the discharge truing apparatus shown in FIG. Needless to say, the processing surface of the electrode 6 is completely parallel to the X axis of the processing machine.
[0025]
FIG. 4 is a diagram showing how electrodes are formed in the YZ section in the discharge truing apparatus shown in FIG. In the example of this figure, the diamond tool 7 is pitch-fed using the Y-axis every time the diamond tool 7 is moved and machined in the X-axis direction, so that the electrode cross-sectional shape becomes a predetermined shape via the control device by the NC program. You can process it. In the present embodiment, an example is shown in which the shape of the tip of the electrode is formed in a cylindrical shape that is easy to process, but it goes without saying that a non-arc shape, a V-shape, or the like that is mathematically defined may be used. Similarly, a convex or concave electrode may be manufactured.
[0026]
The important points in the electrode forming process of the first stage of the present invention are as follows. In other words, the electrode is mounted at the same position in both cases during electrode formation and discharge truing, and assuming that there is no processing-related error, the shape error of the diamond bite is the same as the shape of the electrode surface. It is an error. For example, for a high-precision single crystal diamond tool, a tool having a contour of a tip nose radius of 50 nm or less is commercially available. If the electrode is processed with such a diamond bite, the shape accuracy of the formed electrode surface is also reduced to 50 nm or less.
[0027]
FIGS. 5, 6, and 7 show a discharge truing process of the conductive grindstone 9, which is the second stage of the present invention.
[0028]
FIG. 5 is a diagram illustrating a state in which the conductive grindstone 9 is brought close to the electrode 6 that has been processed with high precision at a predetermined number of revolutions. The grinding wheel 9 and the electrode 6 are connected by a discharge circuit 20. A discharge liquid (not shown) is also supplied. The table is driven based on the NC program so that the grindstone 9 scans the surface of the electrode 6 as if it traces. If necessary, it is cut in the Z direction in FIG.
[0029]
FIG. 6 shows a method of performing discharge truing with high accuracy. When the position in the X-axis direction is fixed at one place and the discharge truing is performed by driving along the arrow 22 in the Y-axis and Z-axis directions, discharge marks as shown by 6a in FIG. If the discharge marks 6a become large, the cross-sectional shape accuracy of the truing grindstone 9 deteriorates. In this case, discharge truing is performed by the same NC program while being shifted by a certain distance in the direction of arrow 21 parallel to the X axis. The shape of the electrode surface shifted in the direction of arrow 21 is exactly the same as the shape of the electrode surface at the initial position at the original position, and the work can be continued with high accuracy. Further, needless to say, by changing the position in the X direction, the electrode 6 manufactured in the first stage can be effectively used.
[0030]
FIG. 7 shows an example in which the conductive grindstone 9 can be trued into various cross-sectional shapes. It goes without saying that the grinding wheel shape may be a circular arc, a mathematically defined non-circular arc, a V-shape, a convex shape or a concave shape. In this grinding wheel forming step, it is also possible to easily produce a full-shaped grinding wheel in which the shape to be processed is inverted.
[0031]
The important points in the discharge truing step, which is the second step of the present invention, are as follows. That is, assuming that there is no error at the time of electric discharge machining or an error caused by driving the machining machine, the shape error of the electrode shape becomes the shape error of the cross section of the grindstone as it is. For example, if the shape error of the electrode surface is 50 nm, the same applies to the error of the grinding wheel cross-sectional shape.
[0032]
8 and 9 show an example of a grinding step which is the third stage of the present invention.
[0033]
FIG. 8 shows a state in which the workpiece 15 is machined under predetermined grinding conditions. Traverse grinding is performed in the X-axis direction, and pitch-feeding is performed in the Y direction to perform processing into a predetermined shape.
[0034]
FIG. 9 shows an example in which a non-arc surface whose cross-sectional shape is mathematically defined is ground and traversed in the X-axis direction as shown in FIG. For example, a non-circular cylindrical lens mold which is a kind of optical component is an example. By sequentially feeding the grindstone 9 from the machining start point to the respective positions indicated by 9a, 9b, and 9c, a predetermined shape accuracy can be obtained. It goes without saying that numerical control is performed by the NC program.
[0035]
The important points in the grinding step, which is the third step of the present invention, are as follows. That is, if there is no error caused by driving the processing machine, the error of the shape of the grindstone becomes the error of the sectional shape of the workpiece as it is. For example, if the error in the cross-sectional shape of the grindstone is 50 nm, the same applies to the shape error of the workpiece.
[0036]
Further, in the present embodiment shown in FIG. 9, an example is shown in which a non-circular cross section is machined by feeding the grinding wheel 9 having an arc-shaped cross section at a pitch in the Y-axis direction. It goes without saying that a grinding wheel may be manufactured by discharge truing in the present embodiment, and a predetermined shape may be obtained by a feeding method along the X-axis direction shown in FIG.
[0037]
【The invention's effect】
As described above, according to the present invention, an electrode is formed in a predetermined shape on the processing machine by using a cutting tool mounted on the processing machine, and while the conductive grindstone is rotated, the electrode mounted on the processing machine is maintained. An excellent on-machine discharge truing method and apparatus capable of obtaining a very high-precision shape accuracy by transferring a predetermined shape to a grindstone surface by scanning the electrode surface as if to trace.
[Brief description of the drawings]
FIG. 1A is a diagram showing a first stage process of a discharge truing method according to an embodiment of the present invention; FIG. 1B is a diagram showing a second stage process in the embodiment; FIG. FIG. 2 is a perspective view showing a discharge truing apparatus according to an embodiment of the present invention. FIG. 3 is a view showing electrode processing on the discharge truing apparatus. FIG. 4 is an electrode shown in FIG. FIG. 5 is a view for explaining the operation of a cutting tool in machining. FIG. 5 is a view showing a position of a grindstone in discharge truing. FIG. 6 is a view showing movement of an electrode use position in discharge truing. (B) A diagram showing a grindstone that has been subjected to a discharge arc in a concave arc shape by an electrode. (C) A diagram showing a grindstone that has been discharged in a non-arc shape by an electrode. FIG. 8 is a view showing a grindstone subjected to discharge truing. FIG. 8 is a view showing a grinding state of a workpiece by a grindstone. FIG. 9 is a view showing machining of a non-circular surface of the workpiece by a grindstone. FIG. 10 is a conventional discharge truing method. [Explanation of symbols]
6 Electrode 7 Diamond tool 9 Conductive grindstone 12 X table 13 Y table 15 Workpiece 20 Discharge circuit

Claims (7)

In the method of discharging and truing the conductive grindstone, an electrode attached to the processing machine is formed in a predetermined shape by a cutting tool, and the conductive grindstone is formed in a predetermined shape while rotating the conductive grindstone, and is attached to the processing machine. The method according to claim 1, wherein a predetermined shape of the electrode surface is transferred to a grindstone surface by scanning along the electrode surface. 2. The electric discharge truing method according to claim 1, wherein a machining machine capable of numerically controlling at least three axes is used. 2. The discharge truing method according to claim 1, wherein the cutting tool for forming the electrode is a single-crystal or poly-crystal diamond cutting tool, the cutting edge has an arc shape, and the contour accuracy is high. 2. The discharge truing method according to claim 1, wherein numerical control is performed so that the cutting shape by the cutting tool is an arc, a non-arc, a V shape, a polygonal shape, or the like. Cylindrical, non-cylindrical, along the electrode surface in a direction perpendicular to the generatrix direction of the electrode tip having a square tip shape, by scanning the conductive grindstone while numerically controlling the electrode surface as if following this electrode surface, 2. The discharge truing method according to claim 1, wherein a grindstone having a predetermined sectional shape is formed. 6. The on-machine discharge truing according to claim 1, wherein after performing the discharge truing by the method according to claim 5, the conductive grindstone is formed by a new electrode surface by moving the conductive grindstone by a required amount in the axial direction of the electrode. Method. A processing machine capable of numerically controlling three or more processing axes, an electrode attached to the processing machine, a cutting tool provided on the processing machine for cutting the electrode, and a predetermined cutting by the cutting tool; A power truing device comprising: a power supply unit including a discharge circuit for discharging and truing the grindstone by scanning the grindstone along a cutting surface of the electrode on the processing machine formed into a shape.

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