WORKPIECE MACHINING METHOD AND WORKPIECE MACHINING DEVICE

Abstract

A workpiece machining method for machining a workpiece (5) into a desired shape, comprising: Holding a radial milling cutter (3) in a tool holding unit, the radial milling cutter (3) having a corner portion at a lower end formed into an arc shape in a side view, and rotating about a rotation axis (C0) to perform cutting of the workpiece (5); Detecting a positional deviation between a real contour line (P2), which is a contour line of the radial milling cutter (3), and an ideal contour line (P1), which is a contour line of the radial milling cutter (3) formed into an ideal shape when the radial milling cutter (3) is held by the tool holding unit (9); Calculating a first correction value (#591) configured to make an arc center point (R1) of a first arc portion formed into an arc shape at a corner portion of the ideal contour line (P1) and an arc center point (R2) of a second arc portion formed into an arc shape at a corner portion of the real contour line (P2) identical to each other in a plane perpendicular to the rotation axis (C0); and Correcting a machining point (T1) by the radial cutter (3) using the first correction value (#591) when cutting is performed.

Description

TECHNICAL FIELDThe present invention relates to a workpiece machining method and a workpiece machining apparatus.PRIOR ARTConventionally, a workpiece processing apparatus has been used in which a milling cutter (also, an end mill) moves relative to a workpiece (a material to be processed) using an NC program and the milling cutter is rotated to cut the workpiece.In such a machining apparatus, the end mill is chucked and fixed to a tool holding unit such as a spindle, and the end mill moves relative to the workpiece to machine the workpiece. Therefore, when the end mill is attached to the tool holding unit due to an erroneous clamping or the like, positional deviation may occur. Moreover, an initial shape failure of the end mill may occur. In such a case, there is a problem that the end mill cannot be moved to an accurate cutting position with respect to the workpiece, and high-precision cutting is not possible.Further, JP S63-233 403A discloses that in machining a workpiece with a ball end mill, the position of the ball end mill is corrected in consideration of deterioration of the ball end mill due to wear. That is, JP S63-233 403A discloses that an error of a cutting surface is prevented by calculating a shape error by laser scanning a tool shape that changes as the cutting of the workpiece proceeds through the ball end mill, calculating a correction amount of a tool position based on the calculated shape error, and correcting the tool position.However, the technique disclosed in JP S63-233 403A relates to correction of wear deterioration of the end mill, but not to correction of a shape error of the end mill or an assembly error thereof at the time of positioning. Moreover, JP S63-233 403A shows an example of using a ball end mill (a tool having a hemispherical tip) as an end mill, but does not relate to correction of a radial end mill (a tool forming an arcuate corner at the tip).DE 103 34 035 A1 describes a method for machining workpiece surfaces by means of a milling tool and a milling tool for carrying out the method. In order that a high machining accuracy of the workpiece surface is achieved even in milling cutters with runout deviations, the shape deviations are determined by measurement techniques and taken into account during the subsequent machining by correction movements of the cutting edge.SUMMARYAs described above, in the conventional example disclosed in JP S63-233 403A, when a deviation occurs in an arc center at a corner part formed into an arc shape of a radial milling cutter, this deviation cannot be corrected, thereby causing a problem that an error occurs on the cut surface.The present invention has been made to solve such a conventional problem, and an object of the present invention is to provide a workpiece machining method and a workpiece machining apparatus capable of reducing cutting errors at the time of workpiece machining by correcting an arc center of a radial milling cutter."The object is achieved by a workpiece machining method having the features of claim 1 and by a workpiece machining apparatus having the features of claim 6.The invention enables the reduction of cutting errors in the workpiece machining by correcting the arc centers of the radial milling cutter.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a block diagram schematically showing a configuration of a workpiece processing apparatus according to an embodiment. FIG. 2 is an explanatory diagram schematically illustrating a state in which a radial milling cutter is in contact with a workpiece at the time of cutting. FIG. 3 are explanatory diagrams illustrating positional relationships between an ideal contour line and a real contour line of the radial milling cutter, wherein (a) illustrates a starting position, (b) illustrates arc shapes at a corner portion, (c) illustrates a state in which arc centers are identical in the X-Y plane direction, and (d) illustrates a state in which two arc centers R 1 and R 2 are identical. FIG. 4 is an explanatory diagram showing the shape errors of the arc shapes at the corner point between the ideal contour line and the real contour line of the radial milling cutter. FIG. 5 is an explanatory diagram showing the machining points and the unit normal vectors when the workpiece is machined with the radial milling cutter. FIG. 6 is a diagram showing the coordinates of the machining points of the workpiece by the radial milling cutter set in an NC program. FIG. 7 is a diagram showing arithmetic expressions for correcting the coordinates of the machining points shown in FIG. 6. FIG. 8 is a flowchart showing a method of correcting the machining points by the radial milling cutter. FIG. 9 is an explanatory diagram illustrating a proportional distribution of the correction values in adjacent angular directions.DESCRIPTION OF THE EMBODIMENTS[Description of Configuration of Embodiment]A workpiece processing apparatus according to an embodiment will be described below with reference to the drawings. FIG. 1 is an explanatory diagram schematically illustrating a configuration of a workpiece processing device 1 (hereinafter, simply referred to as "processing device 1") according to the embodiment. As illustrated in FIG. 1, the processing apparatus 1 includes a bed 19 serving as a base, a table 21 provided on an upper surface of the bed 19, a column 23 disposed from one side of the bed 19 to straddle the bed 19 and shaped in an inverted U-shape in a front view, and a main shaft support 25 disposed near an upper center of the column 23.In the following description, a direction to be set on an upper surface of the bed 19 is defined as an X-axis direction (longitudinal direction), a direction orthogonal to the X-axis direction on the upper surface of the bed 19 is defined as a Y-axis direction (transverse direction), and a direction orthogonal to the upper surface of the bed 19 (i.e., a normal direction) is defined as a Z-axis direction. The X, Y and Z axes are orthogonal coordinate systems.The table 21 includes a workpiece holding unit 7. the workpiece holding unit 7 fixes a workpiece 5 to be machined by the machining apparatus 1, the table 21 is supported on the bed 19 via a linear guide bearing (not illustrated) and movable in the X-axis direction relative to the bed 19 by an actuator (not illustrated) such as a linear motor. That is, by the control of the table 21, the workpiece 5 can be moved relative to a desired position on the X axis on the bed 19.The column 23 is formed integrally with the bed 19. Near the upper center of the column 23, a case-shaped main shaft support 25 is provided. A main shaft case 27 is provided on a lower surface of the main shaft carrier 25.A spindle 29 for fastening and rotating a radial milling cutter 3 is provided at an appropriate position on a lower surface of the main shaft housing 27. As illustrated by reference number 3 in FIG. 2, "radial milling cutter" refers to a cutting tool in which a corner part of a lower end is formed in an arc shape in a side view and rotates about a rotation axis to perform cutting of the workpiece 5. In other words, "radial milling cutter" refers to a cutting tool in which the corner portion of a cutting edge is formed in an arc shape with a constant radius and a lower portion has a flat shape.The spindle 29 is provided with a tool holding unit 9, and the tool holding unit 9 enables attachment and detachment of the radial milling cutter 3.The radial milling cutter 3 is moved in the Z-axis direction (vertical direction) of the spindle 29 relative to a desired position. The spindle 29 is movable in the direction of the Z axis. Accordingly, the radial milling cutter 3 can be moved relative to a position in the Z-axis direction by controlling the spindle 29.The main shaft housing 27 is supported on the main shaft support 25 via a linear guide bearing (not shown). Therefore, the radial milling cutter 3 can be moved in the Y-axis direction by an actuator (not shown), for example, a linear motor. That is, the radial milling cutter 3 can be moved relative to a desired position on the Y axis by controlling the main shaft housing 27.Thus, by controlling the movement of the table 21, the main shaft housing 27, and the spindle 29, the three-dimensional relative position of the workpiece 5 and the radial milling cutter 3 can be adjusted. That is, the workpiece 5 can be cut by abutting the radial milling cutter 3 against a desired machining part of the workpiece 5. The relative movement of the workpiece 5 and the radial milling cutter 3 is only an example, and both the workpiece 5 and the radial milling cutter 3 can be moved on each axis.FIG. 2 is an explanatory diagram schematically showing a state in which the radial milling cutter 3 is in contact with the workpiece 5 at the time of cutting. As illustrated in FIG. 2, the radial milling cutter 3 has a shape in which a side view when rotated is line-symmetrical about a center line C 0. As described above, the corner portion of the radial milling cutter 3 is formed into an arc shape of 1 / 4 circle, i.e., 90 degrees. A bottom of the radial milling cutter 3 has a straight shape. The radial milling cutter 3 is provided on the outer periphery with a cutting edge portion that enables the cutting of the workpiece 5 by the cutting edge portion. The center of the 90-degree arc in the corner portion of the radial milling cutter 3 is defined as C2 and C2'.The radial milling cutter 3 is fixed by clamping an upper end portion (the upper end in the figure) in the tool holding unit 9.The radial milling cutter 3 held by the tool holding unit 9 rotates about the center line (rotation axis) C 0 in the Z-axis direction (vertical direction) to cut the workpiece 5 with the blade.Returning to FIG. 1, the machining apparatus 1 includes a tool shape measuring device 31 for measuring a shape of the radial milling cutter 3. the tool shape measuring device 31 is, for example, a laser measuring device, and measures the shape of the radial milling cutter 3 by irradiating a laser beam from the direction of the side surface of the radial milling cutter 3 and receiving the irradiated laser beam.The machining apparatus 1 includes a control unit 13 for comprehensively controlling the entire machining apparatus 1 including the movement control of the table 21, the main shaft housing 27, and the spindle 29. the control unit 13 includes a positional deviation detection unit 15 for detecting a positional deviation of the radial milling cutter 3, and a memory 14 for storing various data such as data on the dimension and shape of the radial milling cutter 3.The control unit 13 controls a movement of the table 21 that fixes the workpiece 5 and a movement of the spindle 29 that fixes the radial milling cutter 3 based on an NC program described later. Moreover, the control unit 13 controls a rotation of the radial milling cutter 3.The NC program is created by CAM (Computer Aided Manufacturing) 39 on the basis of the CAD data 37 of the workpiece 5. In the NC program, a machining path 41 indicating three-dimensional coordinates when the radial milling cutter 3 is moved relative to the workpiece 5 is set. The NC program set by the CAM 39 is transmitted to the computer 33.The positional deviation detection unit 15 calculates a contour line (a later-described real contour line P 2) of the radial milling cutter 3 on the basis of the shape of the radial milling cutter 3 measured by the tool shape measurement device 31. That is, the positional deviation detection unit 15 detects an amount of deviation between the contour line (a later-described ideal contour line P 1) in an ideal state of the radial milling cutter 3 and the real contour line P 2, and stores data of the detected amount of deviation in the memory 14.The computer 33 includes a computing unit 33 a. The calculation unit 33 aincludes a positional deviation correction unit 331 and a memory 332. The positional deviation correction unit 331 performs a process for correcting the machining path 41 included in the NC program when the workpiece 5 is cut by the radial milling cutter 3. The arithmetic unit 33 aacquires the NC program including the machining path 41 from the CAM 39, and further corrects, based on an amount of deviation between the ideal contour line P 1 and the real contour line P 2, the three-dimensional coordinates of the machining path 41 using a first correction value and a second correction value calculated by the machining described later. That is, the arithmetic unit 33 acorrects the NC program on the basis of the first correction value and the second correction value. The memory 332 stores the corrected NC program including a machining path 43.The arithmetic unit 33 atransmits the NC program including the corrected machining path 43 to the control unit 13. therefore, the control unit 13 executes the cutting of the workpiece 5 by the radial milling cutter 3 using the corrected machining path 43.Next, a correction process of the machining pass performed by the positional deviation correction unit 331 will be described. Hereinafter, the contour line in the ideal state of the radial milling cutter 3 is referred to as "ideal contour line P 1" and a real contour line of the radial milling cutter 3 is referred to as "real contour line P 2".When the workpiece 5 is actually machined with the radial milling cutter 3 as described above, an assembly error occurs when the radial milling cutter 3 is attached to the spindle 29, and a shape error exists in the radial milling cutter 3. The presence of the positional deviation causes an error in the cut position of the workpiece 5, thereby lowering the machining accuracy. In this embodiment, a method of correcting the positional deviation generated in the radial milling cutter 3 is performed. Next, the method for correcting the positional deviation generated in the radial milling cutter 3 will be described in detail.[Description of Method for Correcting Positional Deviation]In FIG. 3, (a) is an explanatory diagram showing a shape (ideal shape) of the radial milling cutter 3 and a shape (real shape) of the real radial milling cutter 3. Reference numeral P1 shown in (a) of FIG. 3 denotes a contour line shaped into an ideal shape, i.e., the ideal contour line P1. Reference numeral P2 denotes a real-shape contour line, i.e., the real contour line P2. As described above, there is a positional deviation between the ideal contour line P 1 and the real contour line P 2 due to a mounting error and a shape error. Therefore, the ideal contour line P 1 and the real contour line P 2 are not identical to each other.In order to correct an error of a cutting position caused by the positional deviation, the positional deviation correction unit 331 corrects the above mounting error by executing a first correction process described below, and corrects the above shape error by executing a second correction process.(First Correction Process)The correction is performed to make the positions of an arc center at a corner portion in the ideal contour line P 1 (this is defined as "arc center R 1") and an arc center at a corner portion in the real contour line P 2 (this is defined as "arc center R 2") identical to each other in the X-Y plane direction. Further, if necessary, a process is performed to make the positions of the arc center R 1 at the corner portion in the ideal contour line P 1 and the arc center R 2 at the corner portion in the contour line P 2 identical in the Z-axis direction.(Second Correction Process)A difference between an arc (an arc of 1 / 4 circle) of the ideal contour line P 1 and an arc (an arc of 1 / 4 circle) of the real contour line P 2 is calculated around the arc center R 1 at the corner portion in the ideal contour line P 1, and a method for correcting the difference is performed.As an initial process for performing the first correction process and the second correction process, a real shape of the radial milling cutter 3 is measured using the tool shape measurement device 31 (see FIG. 1 ). Here, an example in which a laser measurement device is used as the tool shape measurement device 31 will be described. The laser measurement device measures the shape of the radial milling cutter 3 by irradiating a laser beam from the direction of the side surface of the radial milling cutter 3 and receiving the irradiated laser beam. As a result, as illustrated in (a) of FIG. 3, the real contour line P 2 of the radial milling cutter 3 is detected. In addition, the data of the ideal contour line P 1 illustrated in (a) of FIG. 3 is stored in the memory 14 in advance. In (a) of FIG. 3, an amount of deviation between the two contour lines P 1 and P 2 is exaggerated.Thereafter, the first correction process is performed. Specifically, as illustrated in (b) of FIG. 3, the positions of the arc center R 1 of the arc (first arc portion) at the corner portion of the ideal contour line P 1 and the arc center R 2 of the arc (second arc portion) at the corner portion of the real contour line P 2 are calculated.As described above, since the data of the ideal contour line P1 is stored in the memory 14, the arc center R1 can be calculated based on the data of the ideal contour line P1. On the other hand, the arc center R 2 may be calculated based on the real contour line P 2 data measured by the laser measurement device, for example, by a method such as the least squares method. FIG. 3, (b) shows an example in which the radius of curvature in the corner region of the ideal contour line P 1 deviates from the radius of curvature in the corner region of the real contour line P 2.Then, the amount of deviation between the arc center R1 and the arc center R2 in the X-Y plane direction, i.e., the horizontal distance between R1 and R2 shown in (b) of FIG. 3, is stored in the memory 14. By decomposing and correcting the amount of deviation into a component in the X-axis and Y-axis directions as shown in (c) of FIG. 3, the real contour line P 2 acan be shifted to the real contour line P 2 bafter the correction before the correction, and the positional deviation between the arc center R 1 and the arc center R 2 in the X-Y plane direction is corrected. In (c) of FIG. 3, the positions of the arc center R 1 and the arc center R 2 in the direction of the X-Y plane are identical to each other.Further, the amount of deviation in the vertical direction (Z-axis direction) between the arc center R 1 and the arc center R 2 is calculated, and the amount of deviation is stored in the memory 14. By correcting the amount of deviation between the arc center R 1 and the arc center R 2 in the vertical direction, the real contour line P 2 bmay be shifted to the real contour line P 2 c, as illustrated in (d) of FIG. 3, and the coordinates of the arc center R 1 and the arc center R 2 in the vertical direction are corrected. That is, the mounting error is corrected. A correction value of the amount of deviation in the X-Y plane direction at this time is stored as a reference code #591 in the memory 332 shown in FIG. 1. Moreover, a correction value of the deviation amount in the Z-axis direction (vertical component) is stored as the reference code #592.Next, the second correction process is performed. That is, after the three-dimensional coordinates of the arc center R 1 and the arc center R 2 are corrected to be identical to each other in the first correction process, and the three-dimensional machining points of the radial milling cutter 3 are corrected to correct a shape error of the radial milling cutter 3. The correction of the three-dimensional machining points of the radial milling cutter 3 will be described in detail below.The position correction of the radial milling cutter 3 is performed on the basis of a unit normal vector V 1 with respect to the machining surface at a machining point T 1 (described in detail later with reference to FIG. 5 ) of the radial milling cutter 3 and the shape error of the radial milling cutter 3. Thus, the three-dimensional position of the radial milling cutter 3 can be corrected in at least one of the X-axis, Y-axis and Z-axis directions. The directions of the X, Y and Z axes are determined by the unit normal vector V1.FIG. 4 is an explanatory diagram showing the relationship between the angles of the arc (0 degrees to 90 degrees) at the corner part of the radial milling cutter 3 and the correction values for correcting the shape error. FIG. 4 illustrates the ideal contour line P 1 at the corner part of the radial milling cutter 3 and the real contour line P 2 cafter the arc center R 1 and the arc center R 2 are identical to each other.In FIG. 4, the vertical direction (Z-axis direction) is set to an angle of 0 degrees and the horizontal direction is set to an angle of 90 degrees. As an example, FIG. 4 shows a shape in which the real contour line P 2 cprotrudes outward from the ideal contour line P 1 in a range of 0 degrees to 45 degrees with respect to the arc center R 1, and the real contour line P 2 cis recessed more deeply than the ideal contour line P 1 in a range of 45 degrees to 90 degrees.As described above, the corner portion at a tip of the radial milling cutter 3 is formed into an arc shape of 1 / 4 circle, i.e., 90 degrees. Then, an arc center point of the 90-degree arc in the ideal contour line P 1 is defined as R 1, and a line passing through the arc center point R 1 and parallel to the center line C 0 (see FIG. 2 ) is defined as an "axial direction line C 1.". The arc center R 1 illustrated in FIG. 4 is the arc center R 1 of the ideal contour line P 1 illustrated in (d) of FIG. 3. Since the three-dimensional coordinates of the arc center R 1 of the ideal contour line P 1 and the arc center R 2 of the real contour line P 2 care corrected to be identical by the above-described first correction process, the arc center R 1 and the arc center R 2 in FIG. 4 are identical.Then, as illustrated in FIG. 4, ten straight lines L 00 to L 90 extending from the arc center R 1 toward the outer shape of the 90-degree arc of the radial milling cutter 3 are set at 10-degree intervals. Specifically, the cutting angle between the axial direction line C 1 of the radial milling cutter 3 and the straight line L 00 is 0 degrees. That is, the straight line L 00 and the axial direction line C 1 are parallel to each other (collinear).An intersecting angle between the axial direction line C 1 and the straight line L 10 is 10 degrees. Similarly, an intersection angle between the axial direction line C 1 and the lines L 20 to L 90 is 20 degrees to 90 degrees. That is, the direction parallel to the axial direction line C 1 is 0 degrees, the direction orthogonal to the axial direction line C 1 is 90 degrees, and respective straight lines are set for each angle direction of 10 degrees.Here, an intersection point between the straight line L 00 and the ideal contour line P 1 is defined as an intersection point Q 00 a. Similarly, the intersections of the respective straight lines L10, L20,..., and L90 and the ideal contour line P1 are defined as intersections Q10a, Q20a,..., and Q90a, respectively. The intersections of the respective straight lines L00, L10, L20,..., and L90 with the real contour line P2c are defined as intersections Q00b, Q10b, Q20b,..., and Q90b. Since a distance (i.e., a difference) between the two intersection points in each straight line is a form error, this value is set as a correction value (second correction value) in the second correction method. For example, in the straight line L 10, "Q 10 b-Q 10 a" is set as the second correction value.Thereafter, the second correction values in the respective angular directions are stored as reference codes #500, #510,..., and #590 in the memory 14 of the control unit 13 shown in FIG. 1. Specifically, "#500=Q00b-Q00a", "#510=Q10b-Q10a",..., and "#590=Q90b-Q90a" are stored.Although FIG. 4 shows an example in which the second correction value is calculated in the respective straight lines L 00, L 10,..., and L 90 at intervals of 10 degrees in order to avoid complications, the second correction value is actually set to finer angular intervals (e.g., every 1 degree). Therefore, the second correction value for each 1-degree angle interval is stored in the memory 14 as reference codes #500, #501, #502,..., #589 and #590.In summary, when an assembly error occurs in the radial milling cutter 3, the first correction process is performed such that the arc centers R 1 and R 2 are identical. Specifically, as described in (a) to (d) of FIG. 3, an assembly error, which is an amount of deviation, is calculated to make the positions of the arc center R 1 at the corner portion of the ideal contour line P 1 and the arc center R 2 at the corner portion of the real contour line P 2 identical in the horizontal direction (X-Y plane direction) and to make the positions in the vertical direction (Z axis direction) identical. The components of the correction value (first correction value) of the calculated mounting error in the X-Y plane are stored in the memory 14 as reference code #591, and the components in the vertical direction are stored as reference code #592.The first correction value is used to make the correction so that the positions of the two arc centers R 1 and R 2 in the X-Y plane are identical to each other. Specifically, the amount of deviation in the X-Y plane is decomposed into an X-axis component and a Y-axis component to calculate a correction value in the X-axis direction and a correction value in the Y-axis direction. In addition, a correction value in the Z-axis direction is calculated. The arc center R 2 is corrected by the correction values (first correction values) in the respective directions. Thereby, the positions of the arc center R 1 and the arc center R 2 in the X-Y plane direction and the Z axis direction are identical to each other.Thereafter, the straight lines L00 to L90 are drawn from the arc center R1 of the ideal contour line P1 shown in FIG. 4 at every angle of 1 degree, and the second correction value is calculated on each straight line. That is, the second correction process is performed. The calculated second correction values are stored in the memory 14 as the reference codes #500 to #590.The three-dimensional coordinates of the NC program are corrected using the reference codes #591 and #592 calculated by the first correction process and the reference codes #500 to #590 calculated by the second correction process. Thereby, the mounting error and the shape error between the ideal contour line P 1 and the real contour line P 2 cmay be corrected.Next, the processing for correcting the three-dimensional coordinates of the processing path included in the NC program using the first correction value and the second correction value will be described.[Description of Three-Dimensional Coordinate Correction]First, the unit normal vector V 1 at a desired machining point (defined as T 1) of the workpiece 5 is calculated based on the CAD data (data illustrating the shape of the workpiece 5 as a finished product) 37 shown in FIG. 1 and the NC program created in the CAM 39, i.e., the NC program for machining the workpiece with the radial milling cutter 3 in an ideal shape. This is performed by the arithmetic unit 33 aof the computer 33.FIG. 5 is an explanatory diagram showing a movement of the radial milling cutter 3 according to the machining path when the workpiece 5 is machined with the radial milling cutter 3. As illustrated in FIG. 5, a point at which the radial milling cutter 3 contacts the workpiece 5 is the machining point T 1 when the workpiece 5 is cut by the radial milling cutter 3. A unit normal vector (defined as V1) at the machining point T1 is calculated. This processing is performed by the computer 33, for example. The three-dimensional coordinates of the machining point T 1 can be obtained from the NC program or by actually moving the ideal end mill along the machining path when the ideal end mill is mounted.When the workpiece 5 is machined with the radial milling cutter 3, the radial milling cutter 3 moves in at least one of the X-axis, Y-axis, and Z-axis directions with respect to the workpiece 5.A surface of the workpiece 5 around the machining point T 1 is planar or curved. However, if the surface is limited to an extremely small area, this area can be regarded as a plane even if it is a curved surface.The unit normal vector V 1 is a vector orthogonal to the above-described minute region (plane), and has a component in each direction of the X axis, the Y axis, and the Z axis. The scalar magnitude of the unit normal vector V1 is "1". In other words, when the respective numerical values that are the components of the unit normal vector V 1 in the X, Y, and Z directions are squared and added and the square root (root) thereof is calculated, the solution is "1".In the embodiment, the correction values (the difference between the ideal contour line P1 and the real contour line P2) stored as the above reference codes #500, #501,..., #589, and #590 are set as the deviation amounts in the respective angular directions. Then, the unit normal vector V 1 is vectorially decomposed into a component in the three-dimensional directions of the X-axis, the Y-axis, and the Z-axis, and a deviation amount in each direction is calculated. Hereinafter, a specific description will be given with reference to the arithmetic expressions shown in FIGS. 6 and 7.FIG. 6 shows three-dimensional coordinates when a cutting position of the radial milling cutter 3 moves in the order of the machining points f 51->f 52->f 53->f 54->f 55. The three-dimensional coordinates indicate the coordinates when the radial milling cutter 3 is formed into an ideal shape. That is, the three-dimensional coordinates of the machining path originally set in the NC program are illustrated.In the embodiment, the three-dimensional coordinates of the machining path are corrected based on the unit normal vector V 1 and the respective reference codes described above. Specifically, the coordinates of the respective machining points f 51, f 52, f 53, f 54, and f 55 illustrated in FIG. 6 are corrected to the coordinates of the respective machining points f 61, f 62, f 63, f 64, and f 65 illustrated in FIG. 7. That is, the arithmetic expressions shown in FIG. 7 are stored in the memory 332, and the coordinates of the machining points are corrected by the arithmetic expressions.Specifically, for example, the three-dimensional coordinates of the machining point f51 shown in FIG. 6 are X=-1.60657, Y=-0.42583, and Z=-1.09809. On the other hand, when the real contour line P2 deviates from the ideal contour line P1, the coordinates are corrected to the machining point f61 shown in FIG. 7.The machining points f 51 and f 61 are machining points at which an angle of the machining position by the radial milling cutter 3 illustrated in FIG. 4 is 64 degrees. Therefore, the second correction value stored as the reference code #564 is read from the memory 14, and the second correction value is decomposed in each direction of the X-axis, the Y-axis and the Z-axis based on the unit normal vector, whereby the correction value is calculated in each axial direction. The three-dimensional coordinates of the machining point f 51 before correction are corrected by the correction value, and the three-dimensional coordinates of the machining point f 61 illustrated in FIG. 7 are calculated.Next, the arithmetic expression of the machining point f61 shown in FIG. 7 will be described in detail. By dividing the unit normal vector V1 at the machining point f61 into a component of the X axis, the Y axis and the Z axis, for example, (X, Y, Z) = (-0.89101, 0.11528, -0.4391). Since an angle of the machining point is 64 degrees, the second correction value stored as the reference code #564 is adopted.That is, [-0.89101*#564] which is a correction value of the X coordinate represented by "f61" in FIG. 7 is a numerical value obtained by multiplying the second correction value set as the reference code #564 by "-0.89101", which is a component in the X-axis direction of the unit normal vector V 1. Moreover, [0.11528*#564], which is a correction value of the Y coordinate, is a numerical value obtained by multiplying the second correction value set as the reference code #564 by "0.11528", which is a component in the Y axis direction of the unit normal vector V 1. Moreover, [-0.4391*#564] which is a correction value of the Z coordinate is a numerical value obtained by multiplying the second correction value set as the reference code #564 by "-0.4391" which is a component in the Z axis direction of the unit normal vector V1.Further, in "f61" of FIG. 7, "-0.9917* #591" which is a component in the X-axis direction of the reference code #591 indicating the first correction value is added to the X coordinate, and "0,1283*#591"which is a component in the Y-axis direction of the reference code #591 indicating the first correction value is added to the Y coordinate. Moreover, the reference code #592 indicating the first correction value is added to the Z coordinate. That is, the deviation amount on the X-Y plane calculated in the first correction is decomposed into an X-axis direction component and a Y-axis direction component, and added to the respective coordinates. In addition, the value of #592 is added to a component in the direction of the Z axis. "-0.9917" is an example of the component in the X axis direction, and "0.1283" is an example of the component in the Y axis direction. The components in the X-axis direction and the Y-axis direction are determined by a horizontal component unit vector of the normal vector of the work surface at the machining point.Therefore, the three-dimensional coordinates shown at the machining point f 61 in FIG. 7 are coordinates reflecting the first correction value calculated in the first correction process and the second correction value calculated in the second correction process. By driving the radial milling cutter 3 on the basis of the coordinates, the influence of the error can be avoided even if a shape error occurs between the ideal contour line P 1 and the real contour line P 2 to perform machining with high accuracy. That is, by correcting the three-dimensional coordinates of the machining point f 51 illustrated in FIG. 6 to the three-dimensional coordinates of the machining point f 61 illustrated in FIG. 7, it is possible to perform cutting of the workpiece 5 by bringing a desired portion of the radial milling cutter 3 into contact with the machining point of the workpiece 5.Further, the memory 332 mounted in the arithmetic unit 33 aof the computer 33 stores arithmetic expressions for correcting the machining points on the basis of the first correction values and the second correction values. Thereafter, the positional deviation correction unit 331 corrects the machining points by the radial milling cutter 3 using the arithmetic expressions, whereby it is possible to reduce the arithmetic load at the time of machining.In the embodiment (d) of FIG. 3, an example of the three-dimensional coordinates of the arc center R 1 of the ideal contour line P 1 and the arc center R 2 of the real contour line P 2 are identical to each other is illustrated. That is, by the first correction process, the Z-axis coordinates of the arc center R 1 and the arc center R 2 are made identical. However, a deviation in the Z-axis direction often does not pose a great problem in the machining of the workpiece 5. That is, when a deviation occurs in the Z-axis direction (the direction of the axial direction line C 1 illustrated in FIG. 4 ), the machining point of the workpiece 5 is completely deflected in the Z-axis direction due to the deviation, but this deviation does not necessarily need to be corrected.That is, a relative deviation of the shape of the workpiece 5 in the Z-axis direction does not often cause a great problem in the machining of the workpiece 5. Therefore, as illustrated in (c) of FIG. 3, correction may be performed to make the arc center R 1 and the arc center R 2 identical in the X-Y plane direction, and the second correction may be performed in a state where a deviation occurs in the Z-axis direction. That is, in the first correction process, the first correction may be performed to make the arc center R 1 and the arc center R 2 identical in the X-Y plane direction, and in a state where a deviation in the Z axis direction occurs in the second correction process, that is, the second correction may be performed in a state where the arc center R 1 and the arc center R 2 illustrated in FIG. 4 are not identical.That is, in the first correction process, the respective centers of the first arc portion formed into an arc shape at the corner part of the ideal contour line P 1 and the second arc portion formed into an arc shape at the corner part of the real contour line P 2 are made to be identical to each other in a plane (X-Y plane) orthogonal to the rotation axis (center line C 0 illustrated in FIG. 2 ).[Description of Processing Operation of Embodiment]Next, a processing method for correcting the processing points by the radial milling cutter 3 by executing the computer program according to the embodiment will be described with reference to the flowchart illustrated in FIG. 8. The process shown in FIG. 8 is performed by the computer 33 shown in FIG. 1. The method presented below is stored as a computer program in the memory 332 (see FIG. 1 ) of the computer 33.First, in step S 11 shown in FIG. 8, an NC program serving as a machining path for the radial milling cutter 3 is created by the CAM 39 shown in FIG. 1. The machining path at this time is a machining passage (machining path 41 illustrated in FIG. 1 ) in the case where the radial milling cutter 3 is accurately mounted on the spindle 29 of the tool holding unit 9 and there is no shape error of the radial milling cutter 3.In step S 12, the positional deviation detection unit 15 of the control unit 13 detects the ideal contour line P 1 of the radial milling cutter 3. That is, the memory 14 stores the dimension and shape data of the radial milling cutter 3, whereby it is possible to acquire the ideal contour line data P 1 from the dimension and shape data of the radial milling cutter 3.In step S 13, the positional deviation detection unit 15 calculates the real contour line P 2 of the radial milling cutter 3.In step S 14, the positional deviation detection unit 15 calculates the arc center R 1 at the corner portion of the ideal contour line P 1 and the arc center R 2 at the corner portion of the real contour line P 2. The arc center R1 can be obtained from the data of the ideal contour line P1 stored in the memory 14. Further, the arc center R 2 can be calculated by a method such as the least squares method based on the real contour line data P 2.In step S 15, the positional deviation correction unit 331 of the computer 33 calculates an assembly error that is an amount of deviation between the two arc centers R 1 and R 2. Specifically, the amount of deviation between the arc center R 1 and the arc center R 2 in the direction of the X-Y plane is calculated. Further, an amount of deviation between the arc center R 1 and the arc center R 2 in the Z-axis direction is calculated. A correction value for correcting the amount of deviation between the arc center R1 and the arc center R2 in the X-Y plane direction is set to the reference code #591 of the memory 332. In addition, a correction value for correcting the amount of deviation between the arc center R1 and the arc center R2 in the Z-axis direction is set to the reference code #592.In step S 16, the positional deviation correction unit 331 calculates second correction values for respective angular directions of the arc at the corner portion of the radial milling cutter 3 based on the ideal contour line P 1 and the real contour line P 2 cafter making the arc center R 1 and the arc center R 2 identical to each other, and sets the calculated second correction values to the respective reference codes #500 to #590.In step S 17, the positional deviation correction unit 331 performs correction to make the three-dimensional coordinates of the arc center R 1 of the ideal contour line P 1 and the arc center R 2 of the real contour line P 2 identical to each other by the first correction values set to the reference codes #591 and #592.The positional deviation correction unit 331 further calculates the unit normal vector V 1 at the machining point T 1 of the workpiece 5 by the radial milling cutter 3, and further corrects the coordinates of the machining points in the respective directions of the X axis, the Y axis, and the Z axis using the reference codes. More specifically, the second correction value set to, for example, the reference code #564 is acquired based on the angular direction (angle from 0 degrees to 90 degrees) of the machining point T1 by the radial milling cutter 3. Further, the unit normal vector V 1 is decomposed into a component in the X-axis direction, the Y-axis direction, and the Z-axis direction, and the coordinates of the machining points in the X-axis direction, the Y-axis direction, and the Z-axis direction are corrected by multiplying the second correction values.As a result, the three-dimensional coordinates of the machining points shown in FIG. 6 can be corrected to the three-dimensional coordinates shown in FIG. 7. Then, the control unit 13 performs the machining of the workpiece 5 by the radial milling cutter 3 on the basis of the machining path of the corrected three-dimensional coordinates, thereby enabling machining of the workpiece 5 with high accuracy.[Description of Effects of Embodiment]In the workpiece processing apparatus 1 for processing a workpiece by executing the computer program according to the present embodiment, first, the first correction value is calculated. More specifically, in the case where a deviation is generated between the ideal contour line P 1 and the real contour line P 2 of the radial milling cutter 3, when the workpiece 5 is machined using the radial milling cutter 3, an installation error, which is an amount of deviation between the arc center R 1 at the corner portion of the ideal contour line P 1 and the arc center R 2 at the corner portion of the real contour line P 2, is calculated. The first correction value, which is a correction value for correcting the mounting error, is calculated. Then, based on the first correction value, correction is performed to make the coordinates of the arc center R1 and the arc center R2 in the direction of the X-Y plane coincide with each other. Further, correction is performed to make the coordinates of the arc center R 1 and the arc center R 2 identical in the Z-axis direction.Further, the second correction value, which is a correction value for correcting the amount of deviation in each angular direction (0 degrees to 90 degrees), is calculated, and the three-dimensional coordinates of the machining point of the radial milling cutter 3 are corrected based on the second correction value. Therefore, even if there is an assembly error in the assembly of the radial milling cutter 3 to the spindle 29 or a shape error in the radial milling cutter 3, the machining path is corrected by the radial milling cutter 3 to eliminate these errors, thereby making it possible to machine the workpiece 5 with high accuracy.As illustrated in FIG. 7, the arithmetic expressions of the corrected machining path are stored in the memory 332 of the computer 33. The three-dimensional coordinates are corrected by replacing the reference codes #500 to #590 and the reference codes #591 and #592 in the arithmetic expressions, thereby making it possible to reduce the arithmetic load at the time of machining. This enables shortening of the machining time of the workpiece 5.Further, the unit normal vector of the workpiece 5 is calculated by the radial milling cutter 3, the correction value is calculated by vectorial decomposition of the second correction value in the three-dimensional direction of the unit normal vector, and the three-dimensional coordinates of the machining point are corrected by the radial milling cutter 3, thereby making it possible to improve the accuracy of the correction.It should be noted that in the above-described embodiment, the second correction value is calculated for each 1 degree of the arc-shaped range at the corner portion of the radial milling cutter 3 within a range of 0 degrees to 90 degrees, but in the case of an angle of 63.7 degrees, as illustrated in FIG. 9, the second correction value may be acquired by proportionally distributing the reference code #563 of 63 degrees and the reference code #564 of 64 degrees that are close to the angle of 63.7 degrees through 3 to 7. This method makes it possible to perform the processing of correcting the machining point with higher accuracy.Although the embodiments of the present invention have been described above, it should not be understood that the statements and drawings that form a part of this disclosure are intended to limit the present invention. Various alternative embodiments, examples, and operating techniques will be apparent to those skilled in the art from this disclosure.

Claims

A workpiece machining method for machining a workpiece (5) into a desired shape, comprising: holding a radial milling cutter (3) in a tool holding unit, the radial milling cutter (3) having a corner portion at a lower end formed into an arc shape in a side view, and rotating about a rotation axis (C0) to perform cutting of the workpiece (5); detecting a positional deviation between a real contour line (P2) that is a contour line of the radial milling cutter (3) and an ideal contour line (P1) that is a contour line of the radial milling cutter (3) formed into an ideal shape when the radial milling cutter (3) is held by the tool holding unit (9); calculating a first correction value (#591) configured to make an arc center point (R1) of a first arc portion formed into an arc shape at a corner portion of the ideal contour line (P1) and an arc center point (R2) of a second arc portion formed into an arc shape at a corner portion of the real contour line (P2) identical to each other in a plane perpendicular to the rotation axis (C0); and correcting a machining point (T1) by the radial milling cutter (3) using the first correction value (#591) when the cutting is performed.The workpiece machining method according to claim 1, further comprising: correcting, by the radial milling cutter, the machining point using the first correction value (#591), which is a correction value configured to make the positions of the arc center (R1) of the first arc portion and the arc center (R2) of the second arc portion identical to each other in a direction of the rotational axis (C0) in addition to a position on the plane perpendicular to the rotational axis (C0).The workpiece machining method according to claim 1 or 2, further comprising: calculating a second correction value (#500, #510... #590) configured to correct a positional deviation between the first arc portion and the second arc portion in multiple angular directions with respect to the arc center (R1) of the first arc portion, the respective centers in the plane perpendicular to the rotational axis being identical to each other; and correcting a machining point by the radial milling cutter (3) using the second correction value (#500, #510... #590) in addition to the first correction value (#591) at the time of cutting.The workpiece machining method according to claim 3, further comprising: calculating, by the radial milling cutter, a unit normal vector of the machining point of the workpiece; decomposing the unit normal vector (V1) into components in each direction of an X axis, a Y axis, and a Z axis that are orthogonal coordinate systems; and correcting coordinates in each direction of the X axis, the Y axis, and the Z axis using correction values obtained by multiplying the components in each of the axis directions by the second correction value (#500, #510... #590).The workpiece machining method according to claim 4, further comprising calculating the second correction value (#500, #510... #590) when a position of the machining point (T1) is not identical to one of the plurality of angular directions by proportionally distributing the second correction value (#500, #510... #590) in two angular directions adjacent to the position of the machining point (T1).A workpiece processing apparatus (1) for processing a workpiece (5) into a desired shape, comprising: a radial milling cutter (3) in which a corner part of a lower end is formed in an arc shape in a side view and rotates about a rotation axis (C0) to cut the workpiece (5); a tool holding unit (9) configured to hold the radial milling cutter (3); a positional deviation detection unit (15) configured to detect a positional deviation between a real contour line (P2) which is a contour line of the radial milling cutter (3) and an ideal contour line (P1) which is a contour line of the radial milling cutter (3) formed into an ideal shape when the radial milling cutter (3) is held by the tool holding unit (9); A positional deviation correction unit (331) configured to correct the positional deviation; wherein the positional deviation correction unit (331) calculates a first correction value configured to make an arc center (R1) of a first arc portion formed into an arc shape at a corner portion of the ideal contour line (P1) and an arc center (R2) of a second arc portion formed into an arc shape at a corner portion of the real contour line (P2) identical to each other in a plane perpendicular to the rotation axis, and corrects a machining point (T1) by the radial milling cutter (3) using the first correction value.

Images