Cylindrical machining method

Abstract

This invention provides a simple method for machining the cylindrical surface of a workpiece using a machine tool with a rotary table, even when the workpiece center is eccentric from the rotary table center. [Solution] A cylindrical machining method is performed by placing a disc-shaped workpiece 1 having a material outline 1c and a finished center 1a on a rotary table 11 that rotates around a table center 11a, calculating the finished eccentric position d which is the position from the table center 11a to the finished center 1a, rotating the rotary table 11 and moving the spindle 15 which is fitted with a rotary tool 17, so that the rotary tool 17 first contacts the workpiece 1 near the furthest point 33a which is the point on the material outline 1c that is furthest from the finished center 1a, based on the finished eccentric position d and the rotation angle θ of the rotary table 11, to cylindrically machine the outer circumference of the workpiece 1 with respect to the finished center 1a.

Description

Technical Field

[0001] The present invention relates to a cylindrical machining method.

Background Art

[0002] A grinding center that integrates the functions of a grinding machine based on a machining center is known. Also, a method of cylindrically grinding the crank pin of a crankshaft with reference to the journal center is known (Japanese Patent Laid-Open No. 11-90799).

Summary of the Invention

Problems to be Solved by the Invention

[0003] An object of the present invention is to provide a method for easily machining the cylindrical surface of a workpiece around the workpiece center even when the workpiece center is eccentric from the center of a circular table by using a machine tool (for example, a grinding center or a machining center) having a circular table.

Means for Solving the Problems

[0004] A first aspect of the present invention is to place a disk-shaped workpiece having a material outer shape and a finish center on a circular table that rotates around the table center, calculate a finish eccentricity position that is the position from the table center to the finish center, rotate the circular table, move a spindle that rotates with a rotating tool mounted thereon, and based on the finish eccentricity position and the rotation angle of the circular table, perform cylindrical machining on the outer periphery of the workpiece around the finish center so that the rotating tool first contacts the workpiece in the vicinity of the farthest point that is the point farthest from the finish center among the material outer shapes. This is a cylindrical machining method.

[0005] The cylindrical machining method is, for example, a cylindrical grinding method or a cylindrical cutting method. The rotating tool is, for example, a rotating grinding wheel or an end mill. A workpiece may have singularities. Singularities are, for example, electrodes, markings, holes, or grooves. The finished center is a virtual center and is determined by the singularities. For example, when singularities are evenly distributed on the circumference of a workpiece, the finished center may be determined from the centroid of the singularities or from the outline of the singularities. The center of the material outline is eccentric from the finished center.

[0006] The outer circumference measurement points may be the positions where the radial lines extending from the center of the finished surface intersect with the outer shape of the material. The radial lines are straight lines passing through the center of the finished surface. The radial lines may be evenly distributed in the circumferential direction. The rotating tool may first make contact with the workpiece near the furthest point. The furthest point does not need to be the exact furthest point. For example, the furthest point may be determined by measuring multiple outer circumference points on the outer circumference of the workpiece and selecting the point that is furthest from those points. When performing cylindrical grinding, the rotary table may rotate at a constant angular velocity. [Effects of the Invention]

[0007] According to the present invention, even when the center of the workpiece is eccentric from the center of the rotary table, the cylindrical surface of the workpiece can be easily machined using a machine tool having a rotary table, with the center of the workpiece as the center. [Brief explanation of the drawing]

[0008] [Figure 1] Right side view of the cylindrical processing apparatus of Embodiment 1 [Figure 2] Flowchart of the cylindrical machining method in Embodiment 1 [Figure 3] Plan view of a workpiece placed on a table in the cylindrical machining method of Embodiment 1 [Figure 4] Plan view showing the method for measuring the workpiece shape in the cylindrical machining method of Embodiment 1. [Figure 5] Plan view showing the cylindrical processing method of Embodiment 1 [Figure 6] Plan view showing the method for measuring the workpiece shape in the cylindrical machining method of Embodiment 2. [Modes for carrying out the invention]

[0009] <Embodiment 1> As shown in Figure 1, the grinding machine (cylindrical processing machine) 10 of this embodiment includes a frame 12, a rotary table 11, a chuck 13, a spindle 15, a moving device 16, a grinding wheel 17, an ATC (tool changer) 18, and a control device 21.

[0010] The rotary table 11 is positioned on the frame 12. The rotary table 11 has a table center 11a. The chuck 13 is positioned on the rotary table 11. The chuck 13 is, for example, a vacuum chuck or an electrostatic chuck. The workpiece 1 is placed on the chuck 13. The table center 11a extends in the vertical direction (Z direction). The rotary table 11 and the chuck 13 rotate together around the table center 11a. The direction of rotation around the Z axis is defined as the C axis.

[0011] The spindle 15 is positioned on the frame 12. The spindle 15 is positioned on the moving device 16. The spindle 15 has a spindle center 15a and a spindle hole (spindle tapered hole) 15b.

[0012] The moving device 16 is positioned on the frame 12. The moving device 16 allows the spindle 15 to move freely in the vertical direction (Z direction), the forward and backward direction (Y direction), and the left and right direction (X direction) relative to the rotary table 11. The moving device 16 has a spindle head 16a and a camera (imaging device) 16b.

[0013] The ATC18 is positioned on the frame 12. The ATC18 holds multiple tools. The ATC18 exchanges tools with the spindle 15. The tools include a grinding wheel 17 and a touch probe 19.

[0014] The grinding wheel 17 has a tapered shank 17a and a rotating grinding wheel 17b. The tapered shank 17a is mounted in the spindle hole 15b. The rotating grinding wheel 17b is a straight cylinder.

[0015] The touch probe 19 has a tapered shank 19a and a tip sphere 19b. The tapered shank 19a is substantially the same as the tapered shank 17a.

[0016] The control device 21 is a numerical control device. The control device 21 numerically controls the circular table 11, the spindle 15, the moving device 16, and the ATC 18. Also, the control device 21 controls the chuck 13 and the camera 16b. The control device 21 receives a signal from the touch probe 19 and reads the coordinates of the spindle 15 when the tip sphere 19b contacts the workpiece 1.

[0017] As shown in FIG. 3, the workpiece 1 has a finishing center 1a, a singular point 1b, and a material outer shape 1c. The singular point 1b is, for example, an electrode, a marking, or a notch. The finishing center 1a has no entity and is defined by the singular point 1b. In FIG. 3, four singular points 1b are evenly arranged in the circumferential direction near the material outer shape 1c. The intersection of two straight lines connecting the centers of gravity of the opposing singular points 1b is taken as the finishing center 1a. The material outer shape 1c is a straight circular cylinder. The center of the material outer shape 1c (not shown) is eccentric from the finishing center 1a. The outer shape after grinding is the finished outer shape 1d. The finished outer shape 1d is centered on the finishing center 1a. The finished outer shape 1d is a circle with a diameter slightly smaller than the inscribed circle of the material outer shape 1c.

[0018] As shown in FIG. 2, in the processing method of this embodiment, first, the workpiece 1 is placed on the circular table 11 (step S1). Next, the finishing center 1a is determined (step S2). Next, the maximum distance (maximum outer peripheral distance) Ra and the minimum distance (minimum outer peripheral distance) Rb are determined (step S3). Then, the workpiece 1 is cylindrically ground on a cylindrical surface centered on the finishing center 1a (step S4).

[0019] As shown in FIG. 3, in step S1, the workpiece 1 is placed and fixed on the chuck 13 by a robot or an operator. For example, the workpiece 1 is placed on the chuck 13 such that the center of the outer shape 1c of the material and the finish center 1a substantially coincide with the table center 11a. When an operator places the workpiece 1, it is not easy to accurately place the workpiece 1 on the chuck 13. Even when the position of the finish center 1a is measured in advance and then the workpiece 1 is placed on the chuck 13, there are measurement errors and placement errors. As a result, the finish center 1a is eccentric from the table center 11a.

[0020] In step S2, the moving device 16 moves the spindle head 16a, and the camera 16b photographs the outer shape of the singular point 1b. The control device 21 performs image processing and extracts the outer shape of the singular point 1b. Then, the control device 21 calculates the centroid position of the singular point 1b with respect to the table center 11a from the position of the spindle head 16a and the extracted outer shape of the singular point 1b. The control device 21 calculates the finish eccentricity position d from the position of the centroid of the singular point 1b. Here, the finish eccentricity position d is a vector quantity. The finish eccentricity position d is defined in (X, Y, C) coordinates. The eccentricity amount |d| is the distance from the table center 11a to the finish eccentricity position d.

[0021] Note that one or more cameras 16b may be fixed to the frame 12. When one camera 16b is arranged, the control device 21 may rotate the circular table 11 so as to accommodate the singular point 1b within the viewing angle of the camera 16b and calculate the position of the singular point 1b.

[0022] In step S3, first, the ATC 18 attaches the touch probe 19 to the spindle 15. As shown in Figure 4, the control device 21 moves the touch probe 19 along the search trajectory 51 and brings the tip sphere 19b into contact with the material outline 1c. Multiple (eight in Figure 4) rays 31 extend evenly in the circumferential direction from the finish center 1a. The search trajectory 51 is a straight line trajectory from the outside of the material outline 1c toward the workpiece 1, along the rays 31 extending from the finish center 1a. When the tip sphere 19b contacts the material outline 1c, the touch probe 19 emits a contact signal to the control device 21. The control device 21 reads the XYZ coordinates of the spindle 15 at the time of contact as the coordinates of the outer circumference measurement point 33. The coordinates of the outer circumference measurement point 33 are read sequentially from the direction of all the rays 31.

[0023] The control device 21 calculates the distance R1 from all outer circumference measurement points 33 to the finished center 1a. The outer circumference measurement point 33 furthest from the finished center 1a is defined as the furthest point 33a. The distance R1 at the furthest point 33a is defined as the maximum distance Ra. The outer circumference measurement point 33 closest to the finished center 1a is defined as the nearest point 33b. The distance R1 at the nearest point 33b is defined as the minimum distance Rb.

[0024] Step S4 will be explained with reference to Figure 5. The XY coordinates are taken with respect to the table center 11a. Next, the rotary table 11 is rotated at a constant angular velocity ω. Next, the control device 21 mounts the grinding wheel 17 on the spindle 15 and rotates the spindle 15. The angle of the finished eccentric position d from the X axis is defined as the rotation angle θ. The control device 21 controls the spindle 15 so that the XY coordinates of the spindle 15 with respect to the rotation angle θ satisfy the following equation. X=0 Y=|d|sinθ+K θ = ωt K = K0 - ap·n = Ra + r - ap·n (where K > Rb - Rd + r) Here, |d|[mm]: Eccentricity θ [rad]: Rotation angle ω[rad / s]: Angular velocity t[s]: Time elapsed since the start of processing K[mm]: Cutting distance K0 [mm]: Cutting start distance. Maximum distance + grinding wheel radius. Ra[mm]: Maximum distance r[mm]: Grinding wheel radius ap[mm]: Cutting depth Rb[mm]:Minimum distance Rd[mm]: Reach length from minimum distance n[-]: Number of rotations since the start of cutting. Quotient of θ / 2π.

[0025] The cutting length Rd is, for example, 0.5 mm to 1 mm. The cutting length Rd is the length by which the distance between the grinding wheel 17 and the finishing center 1a is cut further from the minimum distance Rb so that the outer shape 1c of the material is not exposed in the vicinity of the nearest point 33b. The distance K is reduced by the cutting amount ap each time the rotary table 11 rotates. While the rotary table 11 rotates, the Y coordinate takes the form of a sine wave with respect to time. That is, as the rotary table 11 rotates, the spindle 15 undergoes simple harmonic motion only in the Y direction, following the Y coordinate of the finishing center 1a.

[0026] The grinding wheel 17 first makes contact with the workpiece 1 near the furthest point 33a. In the first rotation, the grinding wheel 17 grinds only near the furthest point 33a. When moving to the next rotation, it cuts in the Y-axis direction by a depth of cut ap. Then, it grinds a slightly longer distance than the previous rotation. By repeating this process, the outer shape 1c of the material is gradually ground in a concentric pattern around the finished center 1a. When the distance from the finished center 1a to the grinding wheel 17 reaches Rb, grinding of almost the entire circumference of the workpiece 1 is completed. By further grinding by Rd, the remaining grinding of the outer shape 1c of the material can be eliminated.

[0027] After cylindrical grinding is complete, orientation flats, notches, grooves, holes, etc., may be machined. At this time, the ATC18 may change the spindle 15 and the tool as needed.

[0028] In the grinding method of this embodiment, the grinding wheel 17 first contacts the workpiece 1 near the furthest point 33a, and the grinding range gradually expands from the vicinity of the furthest point 33a. When the grinding wheel 17 contacts the workpiece 1 from a part other than the furthest point 33a and grinds, the processing reaction force applied to the workpiece 1 becomes large, and the position of the workpiece 1 may shift on the chuck 13. In this embodiment, the processing reaction force is suppressed to a small extent, and the displacement of the workpiece 1 is suppressed.

[0029] Furthermore, according to this embodiment, the workpiece 1 does not need to be repositioned while steps S1 to S4 are being executed. The process of photographing the singularity 1b, measuring the finished center 1a, and cylindrical grinding the workpiece 1 can all be performed on a single grinding machine 10. Therefore, errors in the placement, measurement, and processing of the workpiece 1 can be suppressed.

[0030] In step S3, the maximum distance Ra and minimum distance Rb are measured in advance. Then, in step S4, cylindrical grinding is started with the distance from the finished center 1a to the grinding wheel 17 set as the maximum distance Ra. If the position where the workpiece 1 and the grinding wheel 17 begin to make contact is unknown, it is necessary to approach the grinding wheel 17 from a position sufficiently far from the workpiece 1. However, since grinding is started from the maximum distance Ra, there is no wasted movement and the processing time can be reduced.

[0031] During cylindrical grinding, the spindle 15 is not moved in the X direction, but is only moved in the Y direction based on the rotation angle θ, causing simple harmonic motion of the spindle 15. This simplifies the control of the spindle 15. For example, the spindle 15 can be controlled to trace a circle in the θ-Y plane of the rotation angle θ and the Y coordinate.

[0032] <Embodiment 2> The cylindrical grinding method of this embodiment differs from the cylindrical grinding method of Embodiment 1 in step S3. Step S3 will be explained with reference to Figure 6.

[0033] First, a touch probe 19 is attached to the spindle 15. Next, three or more outer circumference measurement points 41 are determined. Preferably, the outer circumference measurement points 41 are arranged almost evenly in the circumferential direction on the outer shape 1c of the material. The spindle 15 searches along a search trajectory 51 from the radially outer side of the workpiece 1 of the outer circumference measurement points 41 toward the finished center 1a. When the tip sphere 19b contacts the outer shape 1c of the material, the touch probe 19 emits a contact signal. The control device 21 measures the XYZ coordinates at this time. The control device 21 determines the outer shape base circle 43 that passes through the coordinates of each outer circumference measurement point 41. The center of the outer shape base circle 43 is defined as the base circle center 43a. The radius of the outer shape base circle 43 is defined as the outer shape radius Rc. The distance from the finished center 1a to the outer shape base circle 43 is defined as the outer shape eccentricity dd. The control device 21 calculates the maximum distance Ra and the minimum distance Rb using the following formula. Ra = Rc + dd Rb = Rc - dd Here dd[mm]: External eccentricity Rc[mm]:Outer radius

[0034] According to this embodiment, when the material's outer shape 1c is close to a perfect circle, the maximum distance Ra and the minimum distance Rb can be calculated accurately.

[0035] The present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. All technical matters included in the technical concept described in the claims are covered by the present invention. The embodiments described above are preferred examples, but those skilled in the art can realize various alternatives, modifications, variations, or improvements from the contents disclosed herein, and these are included in the technical scope described in the appended claims. [Explanation of Symbols]

[0036] 1 Work 1a Finishing focus 1c Material outline 11-yen table 11a Table center 15 Spindle 17. Grinding wheels (rotary tools) 33a Farthest point d Shishangりeccentric position θ return angle

Claims

1. A disc-shaped workpiece having an outer shape and a center of finish is placed on a circular table that rotates around the center of the table. The finished eccentric position, which is the position from the center of the table to the center of the finished product, is calculated. The rotary table is rotated, and the spindle, which is fitted with a rotary tool and rotates, is moved so that the rotary tool first contacts the workpiece near the furthest point, which is the point on the outer shape of the material that is furthest from the finished center, and the outer circumference of the workpiece is cylindrically machined around the finished center, based on the finished eccentric position and the rotation angle of the rotary table. Cylindrical machining method.

2. Furthermore, The coordinates of multiple positions on the outer shape of the material from the center of the table are measured, and the maximum outer perimeter distance to the furthest point is determined. From the starting cutting distance, which is the sum of the radius of the rotating tool and the maximum outer circumference distance, the tool is cut toward the center of the table. The cylindrical processing method according to claim 1.

3. Furthermore, The coordinates of multiple outer circumference measurement points from the center of the table are measured, The maximum outer circumference distance is determined to be the largest distance among the distances from the outer circumference measurement point to the finished center. The cylindrical processing method according to claim 2.

4. Furthermore, The coordinates of three or more outer circumference measurement points of the material's outer shape are measured from the center of the table. The center of the outer circumference base circle, which is the center of the outer circumference base circle passing through the aforementioned outer circumference measurement point, and the radius of the material outline, are determined. Based on the aforementioned finished eccentric position and the material radius, the maximum outer circumference distance is determined. The cylindrical processing method according to claim 2.

5. Furthermore, The minimum outer circumference distance is determined, which is the distance from the finished center of the material's outer shape to the nearest point, The cutting of the tool is terminated at the distance from the finished center to the minimum outer circumference distance. A cylindrical processing method according to any one of claims 1 to 4.

6. Furthermore, The coordinates of multiple outer circumference measurement points from the center of the table are measured, The smallest distance from the aforementioned outer circumference measurement point to the aforementioned finished center is determined as the minimum outer circumference distance. The cylindrical processing method according to claim 5.

7. Furthermore, The center of the base circle, which is the center of the outer shape base circle passing through the aforementioned outer circumference measurement point, and the material radius, which is the radius of the material's outer shape, are determined. Based on the aforementioned finished eccentric position and the material radius, the minimum outer circumference distance is determined. The cylindrical processing method according to claim 5.

8. When machining a cylinder, the X-coordinate of the spindle is made to coincide with the center of the table, and the Y-coordinate of the spindle traces a sinusoidal trajectory with amplitude equal to the distance from the center of the table to the finished eccentric position, with respect to the rotation angle. A cylindrical processing method according to any one of claims 1 to 7.

9. When machining a cylinder, each time the rotary table rotates, a certain amount of cutting is performed to cut the Y coordinate of the main spindle toward the center of the table. The cylindrical processing method according to claim 8.

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