Machine tool

Abstract

To provide a machine tool capable of preventing a work from being cut too much from a target finish shape.SOLUTION: The machine tool includes target acquisition means, tool path acquisition means, shape acquisition means and cutting control means. The target acquisition means acquires a target finish shape of a work. The tool path acquisition means acquires a tool path in a finishing process performed at least once. The shape acquisition means acquires a measurement shape of the work. The cutting control means for cutting the work by moving a cutting tool along the tool path. When a specific measurement shape, which is the measurement shape of the work after a specific finishing process acquired by the shape acquisition means, does not reach the target finish shape, but a difference between the specific measurement shape and the target finish shape is within a predetermined range, the cutting control means offsets the tool path to the side closer to the work by the value obtained by multiplying the difference by a correction coefficient of less than 1, and performs the finishing process again.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a machine tool. [Background technology]

[0002] Patent Document 1 discloses a method for machining a workpiece in the order of rough machining, semi-finishing machining, and finish machining in a machine tool that cuts the workpiece using a cutting tool (bite). When the machine tool described in Patent Document 1 performs finish machining, it calculates the difference (error) between the target finish shape of the workpiece in semi-finishing machining and the measured shape of the workpiece after semi-finishing machining, and offsets the tool path during finish machining of the workpiece by the difference, so that the workpiece shape after finish machining approaches the target finish shape. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 7-124849 Summary of the Invention [Problem to be solved by the invention]

[0004] In the machine tool described in Patent Document 1, due to various factors such as the difference in the amount of cut during semi-finishing and finishing, and the difference in the environmental temperature around the workpiece, it is considered that the shape of the workpiece will not reach the target finish shape of the finish even after finishing. Therefore, it is considered to perform the finish processing multiple times. However, unless special measures are taken, there is a risk that the workpiece will be cut more than the target finish shape. For example, if the cutting tool during the second finish processing is less sharp than the cutting tool during the first finish processing, a situation will occur in which a large part of the workpiece is cut off during processing during the second finish processing, and there is a risk of overcutting. In addition, for example, the cutting allowance during the second finish processing is smaller than that during the first finish processing, and as a result, the cutting resistance during the second finish processing is smaller than the cutting resistance during the first finish processing, and there is a risk of overcutting.

[0005] The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a machine tool that can prevent a workpiece from being cut beyond a target finished shape. [Means for solving the problem]

[0006] In order to achieve the above object, the present invention comprises a target acquisition means for acquiring a target finished shape of a workpiece, a tool path acquisition means for acquiring a tool path in finish machining which is performed at least once, a cutting control means for cutting the workpiece by moving a cutting tool along the tool path, and a shape acquisition means for acquiring a measured shape of the workpiece, wherein the cutting control means is configured to, when a specific measured shape, which is the measured shape of the workpiece after specific finish machining acquired by the shape acquisition means, does not reach the target finished shape and a difference between the specific measured shape and the target finished shape is within a predetermined range, offset the tool path to a side approaching the workpiece by a value obtained by multiplying the difference by a correction coefficient less than 1, and perform finish machining again, and when the specific measured shape does not reach the target finished shape in a surface direction perpendicular to the longitudinal direction of the cutting tool and a surface direction difference, which is the difference between the specific measured shape and the target finished shape in the surface direction, is within a predetermined range, offset the tool path to a side approaching the workpiece by a value obtained by multiplying the surface direction difference by a correction coefficient less than 1, the cutting control means performs zero cut to perform a second finish machining by moving a cutting tool along the tool path used in the first finish machining when a first measurement shape, which is a measured shape of the workpiece after the first finish machining acquired by the shape acquisition means, does not reach the target finish shape and a first surface direction difference, which is a difference between the first measurement shape and the target finish shape in the surface direction, exceeds a first predetermined value and is less than a second predetermined value; performs a second finish machining by offsetting the tool path by the first surface direction difference toward the workpiece when the first measurement shape does not reach the target finish shape and the first surface direction difference is equal to or greater than a second predetermined value; and performs a second finish machining by offsetting the tool path by the first surface direction difference when the second measurement shape, which is a measured shape of the workpiece after the second finish machining acquired by the shape acquisition means, does not reach the target finish shape and a second surface direction difference, which is a difference between the second measurement shape and the target finish shape in the surface direction, is equal to or greater than a predetermined value.and a machine tool configured to perform a third finishing process by offsetting the tool path toward a workpiece by a value obtained by multiplying the second surface direction difference by a correction coefficient less than 1. 。 Effect of the Invention

[0007] According to the present invention, it is possible to provide a machine tool that can prevent a workpiece from being cut beyond a target finished shape. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic overall configuration diagram of a machine tool in a first embodiment. [Diagram 2] FIG. 2 is a flowchart illustrating a process of machining a workpiece performed by a machine tool in the first embodiment. [Diagram 3] FIG. 3 is a schematic diagram showing the shape of the workpiece after the first finish machining in the first embodiment. [Figure 4] FIG. 4 is a plan view of the workpiece 6 after the first finish machining for explaining the second correction of the tool path in the first embodiment. [Diagram 5] FIG. 5 shows the relationship between the difference ΔR after each of the first to third finish machining operations and the subsequent processing in the first embodiment. [Figure 6] FIG. 6 is a flowchart illustrating a process of machining a workpiece performed by a machine tool in the second embodiment. [Figure 7] FIG. 7 is a schematic cross-sectional view of a workpiece after a first finish machining in the second embodiment. [Figure 8] FIG. 8 shows the relationship between the difference ΔL after each of the first to third finish machining operations and the subsequent processing in the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [First embodiment] A first embodiment of the present invention will be described with reference to Figures 1 to 5. Note that the embodiment described below is shown as a preferred specific example for carrying out the present invention, and while there are some parts that specifically exemplify various technical matters that are technically preferable, the technical scope of the present invention is not limited to this specific embodiment.

[0010] (Configuration of machine tool 1) 1 is a schematic overall configuration diagram of a machine tool 1 according to the present embodiment. In this embodiment, the vertical direction of the machine tool 1 in use is referred to as the Z direction. In addition, hereinafter, the expressions "upper" and "lower" refer to the vertical direction of the machine tool 1 in use.

[0011] The machine tool 1 in this embodiment is, for example, a three-axis vertical machining center equipped with a control device 2 that controls the movement of a cutting tool 3 attached to a spindle 16 and the like in accordance with an NC program. However, the machine tool 1 is not limited to this, and other machine tools 1 such as a vertical machining center with four or more axes including the rotation direction of the table 13 and the spindle 16, a horizontal machining center, a turning center, etc. The machine tool 1 includes a bed 11, a saddle 12, a table 13, a column 14, a spindle head 15, a spindle 16, a cutting tool 3, and a control device 2.

[0012] A guide surface 111 extending in a Y direction perpendicular to the Z direction is provided on the upper surface of the bed 11. The guide surface 111 guides the saddle 12 arranged on the bed 11 in the Y direction. A guide surface 121 extending in an X direction perpendicular to both the Y direction and the Z direction is provided on the upper surface of the saddle 12. The guide surface 121 guides the table 13 arranged on the saddle 12 in the X direction. The Y direction moving means of the saddle 12 relative to the bed 11 and the X direction moving means of the table 13 relative to the saddle 12 can be realized using, for example, a ball screw and a servo motor (not shown), and the amount of movement of the table 13 is output to the control device 2 from an encoder provided on the output shaft of the servo motor.

[0013] A column 14 is provided at the end of the upper surface of the bed 11 in the Y direction. In this embodiment, the column 14 is fixed to the bed 11. Hereinafter, the side of the bed 11 on which the column 14 is provided in the Y direction is referred to as the rear, and the opposite side is referred to as the front. The column 14 has a portion erected upward from the upper surface of the bed 11 and a portion protruding from the upper end of the portion toward the tip side, and is approximately L-shaped. A guide surface 141 extending in the Z direction is provided on the front surface of the column 14. The guide surface 141 guides the spindle head 15 arranged in front of the column 14 in the Z direction. The Z direction movement means of the spindle head 15 relative to the column 14 can be realized using, for example, a ball screw and a servo motor, and the movement amount of the spindle head 15 is output to the control device 2 from an encoder provided on the output shaft of the servo motor. Based on the movement amounts of various movement means output from the encoder, the control device 2 obtains the position of the reference point of the spindle head 15 and is able to control the movement of the cutting tool 3 attached to the spindle 16. The reference point of the spindle head 15 is a coordinate point acquired by the control device 2, and in this embodiment, is the lower end position of the spindle head 15 in the Z direction, and is the position where the central axis of the spindle 16 exists in the X and Y directions.

[0014] The spindle head 15 is provided with a spindle 16 to which a cutting tool 3 such as an end mill or a drill is attached. The spindle 16 is configured to detachably hold the cutting tool 3 and to rotate the held cutting tool 3. The spindle 16 is also called a spindle or a shaft.

[0015] The control device 2 controls the movement of the saddle 12 in the Y direction relative to the bed 11, the movement of the table 13 in the X direction relative to the saddle 12, and the movement of the spindle head 15 in the Z direction relative to the column 14, thereby controlling the movement of the spindle head 15. When the machine tool 1 processes a workpiece 6 (see Figs. 3 and 4 described later), the control device 2 moves the cutting tool 3 attached to the spindle 16 along a tool path 71 (CL: Cutter Location) as shown in Figs. 3 and 4, which is generated by a CAM device 5 having a CAM (Computer Aided Manufacturing) function based on a target finish shape 60 (see Figs. 3 and 4 described later) of the workpiece 6 created using, for example, a CAD device 4 having a CAD (Computer Aided Design) function. The control device 2 performs post-processing to convert the tool path data generated by the CAM device 5 into an NC (Numerical Control) program that can be read by the machine tool 1.

[0016] The control device 2 includes a control unit 21 having a CPU (arithmetic processing unit) and a RAM that serves as a calculation area when the CPU is operating, and a storage unit 22 including a ROM. The storage unit 22 stores programs and the like for realizing various functions performed by the control device 2. The control unit 21 includes a target acquisition means 211, a machining condition acquisition means 212, a cutting control means 213, and a shape acquisition means 214, and the CPU executes the programs stored in the storage unit 22 to realize various functions.

[0017] The target acquisition means 211 acquires a target finished shape 60 (see FIGS. 3 and 4) after finish machining of the workpiece 6 from the CAM device 5, and stores it in the storage unit 22. The target acquisition means 211 acquires the target finished shape 60 of the workpiece 6 at each machining stage from the CAM device 5 via an interface that communicates with the CAM device 5 by wired or wireless communication means.

[0018] The machining condition acquisition means 212 acquires machining conditions such as the type and shape (diameter, length) of the cutting tool 3 to be used, the feed speed of the cutting tool 3 relative to the workpiece 6, and the rotation speed of the cutting tool 3 during machining from the CAM device 5, and stores them in the storage unit 22. The machining condition acquisition means 212 also has a function of acquiring a tool path 71 (see Figs. 3 and 4) during machining of the workpiece 6 from the CAM device 5 as one of the machining conditions of the workpiece 6, and stores it in the storage unit 22, and serves as a tool path acquisition means 212a. The machining condition acquisition means 212 acquires the above-mentioned machining conditions from the CAM device 5 via an interface that communicates with the CAM device 5 by wired or wireless communication means.

[0019] The cutting control means 213 performs cutting of the workpiece 6 by moving the cutting tool 3 along the tool path. Although details will be described later, the cutting control means 213 is configured to appropriately correct the method of correcting the tool path according to the stage of processing (e.g., whether it is the first finishing process, the second finishing process, the third finishing process, etc.) in order to prevent cutting the workpiece 6 excessively smaller than the target finishing shape of the workpiece 6, and to gradually drive in the workpiece 6 with a plurality of finishing processes.

[0020] The shape acquisition means 214 acquires the measured shape of the workpiece 6. The shape acquisition means 214 only needs to be able to acquire the measured shape of the workpiece 6, and may, for example, measure the shape of the workpiece 6 by contacting each part of the workpiece 6 with a touch probe attached to a tool magazine (not shown) of the machine tool 1, or may measure the workpiece 6 using a camera and then perform image processing to measure the shape of the workpiece 6.

[0021] (Machining work by machine tool 1) 2 is a flow chart for explaining the machining process of the workpiece 6 performed by an end mill as the cutting tool 3 attached to the spindle 16 of the machine tool 1 of this embodiment. In this embodiment, for convenience, it is assumed that the shape of the workpiece 6 is annular with a through hole penetrating in the longitudinal direction (Z direction) of the cutting tool 3, and the inner and outer circumferential surfaces of the workpiece 6 are cut by the cutting tool 3 (end mill) to machine the inner and outer diameters of the workpiece 6. In this embodiment, an example will be described in which the tool path acquired from the CAD device 4 is corrected in a plane direction perpendicular to the Z direction, that is, so-called tool diameter correction is performed.

[0022] First, in step S1, the workpiece 6 is subjected to undercutting. In the undercutting, the workpiece 6 is machined to have a target intermediate shape larger than the target finished shape 60 in a plane direction perpendicular to the Z direction. That is, the workpiece 6 after undercutting is formed to have an inner diameter slightly smaller than the target finished shape 60 and an outer diameter slightly larger than the target finished shape 60.

[0023] Next, in step S2, the workpiece 6 after the preliminary machining is cleaned and measured. The cleaning of the workpiece 6 is performed to improve the accuracy of the shape measurement of the workpiece 6 by removing cutting powder and the like that adhered to the workpiece 6 during the preliminary machining in step S1 from the surface of the workpiece 6. The cleaning of the workpiece 6 can be realized by, for example, spraying air, coolant, and the like onto the workpiece 6 to remove cutting powder and the like. After the workpiece 6 is cleaned, the shape of the workpiece 6 is acquired by a touch probe as the shape acquisition means 214.

[0024] Next, in step S3, the value of a variable i is initialized to 1. The variable i is a variable for counting the number of times finishing processing is performed in step S5 described below.

[0025] Next, in step S4, the tool path during the finish machining acquired from the CAD device 4 is corrected based on the difference in the surface direction perpendicular to the Z direction between the target intermediate shape in the back machining and the measured shape of the workpiece 6 after the back machining. The correction here is performed with the aim of making the shape of the workpiece 6 slightly larger than the target finished shape 60 so that the workpiece 6 after the first finish machining performed next is not over-cut.

[0026] Next, in step S5, the cutting control means 213 moves the cutting tool 3 along the tool path corrected in step S4 to perform the first finish processing of the workpiece 6. FIG. 3 shows an example of the state of the workpiece 6 after the first finish processing. In FIG. 3, the two-dot chain line is the target finish shape 60 acquired from the CAD device 4, and FIG. 3 shows an example in which the shape (measured shape) of the workpiece 6 after the first finish processing is larger than the target finish shape 60. In FIG. 3, the difference between the measured shape and the target finish shape 60 in the planar direction perpendicular to the Z direction is shown as ΔR [μm]. The difference ΔR is the length between the measured shape and the target finish shape 60 in the direction perpendicular to both the Z direction and the tool path (see the path indicated by the arrow in FIG. 4 described later) (in this embodiment, the radial direction of the workpiece 6).

[0027] Next, as shown in FIG. 2, in step S6, the workpiece 6 is cleaned and measured in the same manner as in step S2.

[0028] Next, in step S7, it is determined whether or not the difference ΔR between the target finish shape 60 and the measured shape in the surface direction perpendicular to the Z direction is within an allowable range. The determination in step S7 is performed based on the criteria shown in Fig. 5. Fig. 5 shows the relationship between each of the differences ΔR after the first to third finish machining operations and the subsequent processing. Since the current time is i=1 after the first finish machining operation, the row i=1 in Fig. 5 is referenced.

[0029] The process after the first finishing process shown in the row i=1 in FIG. 5 will be described. (A-1) If the difference ΔR is 5 μm or more, the tool path is offset by 100% of the difference ΔR (that is, the correction amount C=ΔR×1) toward the workpiece 6 (next step S4). (A-2) If the difference ΔR is more than 2.5 μm and less than 5 μm, the correction amount calculated in the previous step S4 is used as is in the next finish processing (next step S4), and zero cut is performed in the next finish processing (next step S5). (A-3) If the difference ΔR is equal to or greater than −10 μm and equal to or less than 2.5 μm, finish machining is terminated (end). (A-4) If the difference ΔR is less than −10 μm, a message is output to the effect that the workpiece 6 has been cut beyond the dimensional tolerance of the product after machining the workpiece 6, and machining is terminated (end). In this embodiment, it is assumed that the dimensional tolerance of the final product formed by machining the workpiece 6 is ±10 μm.

[0030] Then, as shown in FIG. 2, in step S7, it is determined whether the difference ΔR is within the allowable range of -10 μm or more and 2.5 μm or less. If the difference ΔR is within the allowable range, the finishing process is terminated (A-3 above), and if the difference ΔR is not within the range, the process proceeds to step S8.

[0031] In step S8, it is determined whether the difference ΔR is less than -10 μm. If the difference ΔR is less than -10 μm, a message is output to a display (not shown) of the machine tool 1 indicating that the workpiece 6 has been cut to the extent that the dimensional tolerance of the final product formed by machining the workpiece 6 is exceeded, and machining is terminated (A-4 above). If the difference ΔR is not less than -10 μm, the process proceeds to step S9.

[0032] In step S9, it is determined whether i is 3 or more, and if it is 3 or more, an alarm for tool wear is generated. In other words, if finish machining has already been performed three times with the same cutting tool 3, an alarm is generated so that finish machining is not performed more than three times with the same cutting tool 3.

[0033] Next, in step S10, i is incremented by 1 to become i=2, and the process returns to step S4. That is, in step S10, preparations are made for starting the second finishing process, and the process proceeds to step S4 for the second time.

[0034] Fig. 4 is a plan view of the workpiece 6 after the first finish machining for explaining the correction of the second tool path. In the second step S4, the correction amount C is calculated according to the standard shown in A-1 or A-2, and as shown in Fig. 4, the finishing tool path 71 (i.e., the uncorrected tool path, which is shown by the dashed arrow in Fig. 4) acquired from the CAM device 5 is corrected by the calculated correction amount C toward the side approaching the workpiece 6, and a corrected tool path 72 (shown by the solid line in Fig. 4) is calculated.

[0035] Next, as shown in FIG. 2, in step S5 for the second time, the cutting control means 213 moves the cutting tool 3 along the tool path corrected in step S4 for the second time to perform a second finish machining of the workpiece 6.

[0036] Next, in step S6, the workpiece 6 is cleaned and measured in the same manner as in step S2.

[0037] Next, in step S7 for the second time, it is determined whether or not the difference ΔR between the target finish shape 60 and the specific measurement shape, which is the measurement shape of the workpiece 6 after the second finish machining, is within an allowable range. The determination in step S7 for the second time is performed according to the row i=2 in FIG.

[0038] The process after the second finishing process shown in the row i=2 in FIG. 5 will be described. (B-1) If the difference ΔR exceeds 2.5 μm, the tool path is offset toward the workpiece 6 by 80% of the difference ΔR (i.e., the correction amount C=ΔR×0.8) (next step S4). (B-2) If the difference ΔR is equal to or greater than −10 μm and equal to or less than 2.5 μm, the finishing process is terminated (end). (B-3) If the difference ΔR is less than −10 μm, a message is output to the effect that the workpiece 6 has been cut beyond the dimensional tolerance of the product after machining the workpiece 6, and machining is terminated (END).

[0039] Then, in step S7, it is determined whether the difference ΔR is within the allowable range of -10 μm or more and 2.5 μm or less. If the difference ΔR is within the allowable range, the finishing process is terminated (B-2 above); if the difference ΔR is not within the range, the process proceeds to step S8.

[0040] Step S8 and the following step S9 are the same as those in the first time. If the determination in both step S8 and step S9 is No, the process proceeds to step S10.

[0041] In step S10, i is incremented by 1 to i=3, and the process returns to step S4. That is, in step S10, preparations are made for starting the third finishing process. Then, the process proceeds to step S4 for the third time.

[0042] In the third step S4, a correction amount C (=ΔR×0.8) is calculated according to the standard shown in B-1 above, and the finishing tool path acquired from the CAM device 5 (i.e., the uncorrected tool path) is corrected toward the workpiece 6 by the calculated correction amount C. Then, the next third step S5 and step S6 are performed in the same manner as the second step S4, step S5, and step S6.

[0043] Then, in the third step S7, it is determined whether or not the difference ΔR between the target finish shape 60 and the measured shape of the workpiece 6 after the third finish machining is within the allowable range. The determination in the third step S7 is performed according to the row i=3 in FIG.

[0044] The process after the third finishing process shown in the row i=3 in FIG. 5 will be described. (C-1) If the difference ΔR exceeds 10 μm, it is determined that the number of times the same cutting tool 3 can be used has reached its limit and an alarm is issued (step S11). (C-2) If the difference ΔR is equal to or greater than −10 μm and equal to or less than 10 μm, the finishing process is terminated (end). (C-3) If the difference ΔR is less than −10 μm, a message is output to the effect that the workpiece 6 has been cut beyond the dimensional tolerance of the product after machining the workpiece 6, and machining is terminated.

[0045] 2, in step S7, it is determined whether the difference ΔR is within the allowable range of -10 μm or more and 10 μm or less, and if the difference ΔR is within the allowable range, the finish processing is terminated (C-2 above), and if the difference ΔR is not within the range, the process proceeds to step S8. Step S8 is the same as the first and second times.

[0046] In step S9, it is determined whether i is 3 or more. This time, i=3, and finish machining has already been performed three times. Therefore, the process proceeds to step S11, an alarm is issued, and machining is terminated (C-1 above). Note that, in this embodiment, an alarm is issued when finish machining has been performed three times, but the number of times can be changed appropriately depending on the strength of the cutting tool 3, the hardness of the workpiece 6, etc.

[0047] (Functions and Effects of the First Embodiment) The cutting control means 213 is configured to offset the tool path toward the workpiece 6 by a value (correction amount C) obtained by multiplying the difference ΔR between the specific measurement shape and the target finish shape 60 by a correction coefficient less than 1 (0.8 in this embodiment) to perform the finish processing again (for the third time in this embodiment) when the specific measurement shape, which is the shape of the workpiece 6 after the specific finish processing (the second finish processing in this embodiment) acquired by the shape acquisition means 214, does not reach the target finish shape 60 and the difference between the specific measurement shape and the target finish shape 60 is within a predetermined range (exceeding 2.5 μm in this embodiment). Therefore, it is possible to prevent the workpiece 6 from being cut more than the target finish shape 60. Here, since the cutting allowance is small and the cutting resistance is reduced after the finish processing, there is a risk of overcutting in the second finish processing performed after the finish processing. Therefore, according to this configuration, in the second finish processing, the tool path acquired from the CAM device 5 is corrected using a correction amount obtained by multiplying the difference ΔR by a correction amount less than 1, so that it is possible to prevent the workpiece 6 from being cut more than the target finish processing during the second finish processing.

[0048] Moreover, the correction coefficient less than 1 by which the difference R is multiplied when calculating the correction amount C is preferably 0.5 or more and 0.9 or less. If the correction coefficient is less than 0.5, the difference ΔR between the specific measurement shape of the workpiece 6 after the second finish processing and the target finish shape 60 of the workpiece 6 is unlikely to fall within the allowable range, and there is a concern that the number of times the workpiece 6 is processed will increase. If the correction coefficient exceeds 0.9, there is a risk that the workpiece 6 will be overcut in the second finish processing. From the same viewpoint, the correction coefficient is more preferably 0.7 or more and 0.8 or less.

[0049] In addition, when the specific measurement shape does not reach the target finish shape 60 in a plane direction perpendicular to the longitudinal direction of the cutting tool 3, and the difference between the specific measurement shape and the target finish shape 60 is within a predetermined range, the cutting control means 213 is configured to offset the tool path toward the workpiece 6 in the plane direction by a value (correction amount C) obtained by multiplying the difference ΔR between the specific measurement shape and the target finish shape 60 in the plane direction by a correction coefficient less than 1, and perform finish processing again. That is, in this embodiment, the cutting tool 3 cuts the workpiece 6 from the plane direction, and corrects the tool path in the plane direction in finish processing, that is, performs so-called tool diameter correction. Therefore, it is even easier to suppress overcutting of the workpiece 6 after the second finish processing. That is, when the cutting tool 3 cuts the workpiece 6 from a direction perpendicular to its longitudinal direction, there is a concern that the cutting tool 3 will bend to escape due to the hardness of the workpiece 6, particularly in the first finish processing, and the cutting amount will be reduced more than expected. In the second finishing process, the cutting allowance of the workpiece 6 is reduced by the previous finishing process, and the cutting resistance is likely to decrease accordingly. In this situation, if the tool path is offset toward the workpiece 6 by, for example, the difference ΔR between the specific measurement shape of the workpiece 6 after the previous finishing process and the target finishing shape 60 in the second finishing process, there is a risk that the workpiece 6 will be overcut. Therefore, according to the configuration of this embodiment, when the cutting tool 3 cuts the workpiece 6 from a direction perpendicular to its longitudinal direction in the finishing process, the effect of suppressing overcutting is further enhanced.

[0050] Moreover, the cutting control means 213 is configured to perform zero cut to perform a second finish machining by moving the cutting tool 3 along the tool path at the first finish machining, when the first measurement shape, which is the measured shape of the workpiece 6 after the first finish machining acquired by the shape acquisition means 214, does not reach the target finish shape 60, and when the first surface direction difference, which is the difference between the first measurement shape in the surface direction perpendicular to the longitudinal direction of the cutting tool 3 and the target finish shape 60 (i.e., the difference ΔR in the workpiece 6 after the first machining), exceeds a first predetermined value (2.5 μm) and is less than a second predetermined value (5 μm). Furthermore, the cutting control means 213 is configured to perform a second finish machining by offsetting the tool path by the first surface direction difference to the side approaching the workpiece 6, when the first measurement shape does not reach the target finish shape 60, and when the first surface direction difference is equal to or greater than the second predetermined value (5 μm). In this way, when the first surface direction difference is equal to or greater than the second predetermined value (5 μm), the cutting allowance of the workpiece 6 is relatively large, and the cutting resistance is relatively large even in the second finishing process, so that there is little risk of overcutting. Therefore, the tool path is offset by the first surface direction difference toward the side approaching the workpiece 6 to perform the second finishing process, and the workpiece 6 having a large cutting allowance can be sufficiently cut. Also, when the first surface direction difference is greater than the first predetermined value (2.5 μm) and less than the second predetermined value (5 μm), the machining accuracy of the first finishing process is high, and therefore, in the second finishing process, the possibility of warping (escape) of the cutting tool 3 due to the hardness of the workpiece 6 during the first finishing process is taken into consideration, and zero cut is performed, so that the workpiece 6 can be easily brought closer to the target finished shape 60 by the second finishing process. With this configuration, it is possible to prevent overcutting of the workpiece 6 while suppressing a decrease in the cutting efficiency of the workpiece 6.

[0051] Furthermore, the cutting control means 213 is configured to perform the third finishing process by offsetting the tool path toward the workpiece 6 by a value obtained by multiplying the second surface direction difference by a correction coefficient (0.8) less than 1 when the second measurement shape as a specific measurement shape, which is the measurement shape of the workpiece 6 after the second finishing process acquired by the shape acquisition means 214, does not reach the target finishing shape 60 and the second surface direction difference, which is the difference between the second measurement shape in the surface direction and the target finishing shape 60, is equal to or greater than a predetermined value (2.5 μm). In this embodiment, since the accuracy of the second finishing process is improved as described above, in the unlikely event that the second measurement shape of the workpiece 6 after the second finishing process does not reach the target finishing shape 60 and the second surface direction difference is equal to or greater than a predetermined value, it is considered that the remaining cutting allowance is considerably small. Therefore, when the second measured shape does not reach the target finished shape 60, and the second surface direction difference, which is the difference between the second measured shape and the target finished shape 60 in the surface direction, is a predetermined value (2.5 μm) or more, the tool path is offset toward the workpiece 6 by an amount obtained by multiplying the second surface direction difference by a correction coefficient (0.8) that is less than 1, and then the third finishing process is performed, which makes it easy to prevent the workpiece 6 from being over-cut in the third finishing process.

[0052] As described above, according to this embodiment, it is possible to provide a machine tool 1 that can prevent the workpiece 6 from being cut beyond the target finished shape 60.

[0053] [Second embodiment] This embodiment is an embodiment in which a tool path acquired from a CAD device 4 is corrected in the Z direction, that is, a so-called tool length correction is performed. For convenience, this embodiment will be described assuming that an end mill is attached as a cutting tool 3 to a spindle 16 of a machine tool 1, and a groove of a predetermined depth is formed in a block. Note that, among the symbols used in this embodiment and the following embodiments, the same symbols as those used in the previous embodiments represent the same components, etc. as those in the previous embodiments, unless otherwise specified.

[0054] 6 is a flow chart for explaining the machining process of the workpiece 6 performed by the end mill as the cutting tool 3 attached to the spindle 16 of the machine tool 1 of this embodiment. In the pre-machining of step S1a of this embodiment, the workpiece 6 is machined to have a target intermediate shape that is larger in the Z direction than a target finished shape 60 (see FIG. 7 described later). In other words, the workpiece 6 after pre-machining is formed so that the groove is shallower than the target finished shape 60. The subsequent steps S2a and S3a are similar to steps S2 and S3 in the first embodiment.

[0055] Next, in step S4a, the tool path during the finish machining acquired from the CAD device 4 is corrected based on the difference in the Z direction between the above-mentioned target intermediate shape in the back machining and the measured shape (hereinafter, sometimes simply referred to as the measured shape) of the groove 61 (see FIG. 7 described later) formed in the workpiece 6 after the back machining. The correction here is performed with the aim of making the shape of the workpiece 6 slightly shallower than the target finished shape 60 so that the workpiece 6 after the first finish machining performed next is not over-cut.

[0056] Next, in step S5a, the cutting control means 213 moves the cutting tool 3 along the tool path corrected in step S4a to perform the first finish machining of the workpiece 6. An example of the state of the workpiece 6 after the first finish machining is shown in Fig. 7. In Fig. 7, the two-dot chain line is the target finish shape 60 acquired from the CAD device 4, and shows an example in which the groove 61 in the workpiece 6 after the first finish machining is shallower than the target finish shape 60. In Fig. 7, the difference in the Z direction between the measured shape and the target finish shape 60 is shown as ΔL [μm].

[0057] Next, as shown in FIG. 6, in step S6a, the workpiece 6 is cleaned and measured in the same manner as in step S2.

[0058] Next, in step S7a, it is determined whether or not the difference ΔL in the Z direction between the target finish shape 60 and the measured shape is within an allowable range. The determination in step S7 is performed based on the criteria shown in Fig. 8. Fig. 8 shows the relationship between each difference ΔL after the first to third finish machining operations and the subsequent processing.

[0059] The process after the first finishing process described in the row i=1 in FIG. 8 will be described. (D-1) If the difference ΔL is 8 μm or more, the tool path is offset by 100% of the difference ΔL (that is, the correction amount C=ΔL×1) toward the workpiece 6 (next step S4a). (D-2) If the difference ΔL is more than 5 μm and less than 8 μm, the tool path is offset toward the workpiece 6 by 80% of the difference ΔL (i.e., the correction amount C=ΔL×0.8) (next step S4a). (D-3) If the difference ΔL is equal to or greater than −10 μm and equal to or less than 5 μm, the finishing process is terminated (end). (D-4) If the difference ΔL is less than −10 μm, a message is output to the effect that the workpiece 6 has been cut beyond the dimensional tolerance of the product after machining the workpiece 6, and machining is terminated (END). Here, in this embodiment as well, it is assumed that the dimensional tolerance of the product after machining of the workpiece 6 is ±10 μm.

[0060] Then, as shown in FIG. 6, in step S7a, it is determined whether the difference ΔL is within the allowable range of -10 μm or more and 5 μm or less. If the difference ΔL is within the allowable range, the finishing process is terminated (D-3 above), and if the difference ΔL is not within the range, the process proceeds to step S8a.

[0061] In step S8a, it is determined whether the difference ΔL is less than -10 μm. If the difference ΔL is less than -10 μm, a message is output to a display (not shown) of the machine tool 1 indicating that the workpiece 6 has been cut to an extent that exceeds the dimensional tolerance of the machined product, and the machining is terminated (D-4 above). If the difference ΔL is not less than -10 μm, the process proceeds to step S9a. Steps S9a and S10 are the same as steps S9 and S10 in the first embodiment.

[0062] In the second step S4a, the correction amount C is calculated according to the criteria shown in D-1 or D-2, and as shown in Figure 4, the finishing tool path obtained from the CAM device 5 (i.e., the uncorrected tool path) is corrected by the calculated correction amount C toward the side closer to the workpiece 6.

[0063] Steps S5a to S10a for the second time are the same as those for the first time, and steps S4a to S6a for the third time are the same as those for the second time.

[0064] The process after the third finishing process described in the row i=3 in FIG. 8 will be described. (E-1) If the difference ΔL exceeds 10 μm, it is determined that the number of times the same cutting tool 3 can be used has reached its limit and an alarm is issued (step S11). (E-2) If the difference ΔL is equal to or greater than −10 μm and equal to or less than 10 μm, the finishing process is terminated (end). (E-3) If the difference ΔL is less than −10 μm, a message is output to the effect that the workpiece 6 has been cut beyond the dimensional tolerance of the product after machining the workpiece 6, and machining is terminated.

[0065] 6, in step S7, it is determined whether the difference ΔL is within the allowable range of -10 μm or more and 10 μm or less, and if the difference ΔL is within the allowable range, the finish processing is terminated (E-2 above), and if the difference ΔL is not within the range, the process proceeds to step S8a. Step S8a is the same as the first and second times.

[0066] In step S9a, it is determined whether i is 3 or more. This time, i=3, and finish machining has already been performed three times. Therefore, the process proceeds to step S11a, an alarm is issued, and machining is terminated (E-1 above). Note that, in this embodiment, an alarm is issued when finish machining has been performed three times, but the number of times can be changed appropriately depending on the strength of the cutting tool 3, the hardness of the workpiece 6, etc.

[0067] (Functions and Effects of the Second Embodiment) In this embodiment, when the specific measurement shape, which is the shape of the workpiece 6 after the specific finish processing (in this embodiment, each of the first finish processing and the second finish processing) acquired by the shape acquisition means 214, does not reach the target finish shape 60, and when the lengthwise difference ΔL, which is the difference between the specific measurement shape in the longitudinal direction of the cutting tool 3 and the target finish shape 60, is within a predetermined range, the cutting control means 213 is configured to offset the tool path toward the workpiece 6 in the longitudinal direction by a value obtained by multiplying the lengthwise difference ΔL by a correction coefficient (0.8) less than 1, and perform the finish processing again. Therefore, when the finish processing is performed again after the finish processing, it is possible to prevent the workpiece 6 from being cut deeper than the target finish shape 60. Here, the front end of the column 14 of the machine tool 1 may fall downward due to thermal deformation, and in this case, it is considered that the workpiece 6 may be cut deeper than the target finish shape 60 when the finish processing is performed again. Therefore, according to this embodiment, in the second finishing process, the tool path obtained from the CAM device 5 is corrected using a correction amount obtained by multiplying the longitudinal difference ΔL by a correction amount less than 1 (0.8), so that over-cutting of the workpiece 6 can be prevented during the second finishing process.

[0068] (Additional Note) Although the present invention has been described above based on the embodiment, the invention according to the claims is not limited to the embodiment. It should be noted that not all of the combinations of features described in the embodiment are necessarily essential to the means for solving the problems of the invention.

[0069] Furthermore, the present invention can be implemented in various ways, such as by omitting some components or adding or substituting components, without departing from the spirit of the invention.

[0070] For example, if the cutting control means 213 is configured to offset the tool path toward the workpiece 6 by an amount obtained by multiplying the difference by a correction coefficient less than 1 and perform finish machining again when the specific measurement shape of the workpiece 6 after specific finish machining does not reach the target finish shape 60 and the difference between the specific measurement shape and the target finish shape 60 is within a predetermined range, it is also possible to modify the process shown in Fig. 5 or 8. In other words, the processes shown in Fig. 5 and 8 are merely examples and can be modified as appropriate depending on, for example, the type, diameter, and hardness of the cutting tool 3, the hardness of the workpiece 6, the cutting allowance, etc. [Explanation of symbols]

[0071] 1…Machine tool 211…Target shape acquisition means 212a...Tool path acquisition means 213...Cutting control means 214…Shape acquisition means 3…Cutting tools 6. Work 60…Target finished shape

Claims

1. A target acquisition means for acquiring a target finished shape of the workpiece; A tool path acquisition means for acquiring a tool path in a finishing process performed at least once; a cutting control means for moving a cutting tool along the tool path to cut a workpiece; A shape acquisition means for acquiring a measured shape of the workpiece, the cutting control means is configured to, when a specific measurement shape, which is a measurement shape of the workpiece after the specific finish processing acquired by the shape acquisition means, does not reach the target finish shape and a difference between the specific measurement shape and the target finish shape is within a predetermined range, offset the tool path toward the workpiece by a value obtained by multiplying the difference by a correction coefficient less than 1, and perform finish processing again; the cutting control means is configured to, when the specific measurement shape does not reach the target finish shape in a plane direction perpendicular to the longitudinal direction of the cutting tool, and when a plane direction difference, which is a difference between the specific measurement shape and the target finish shape in the plane direction, is within a predetermined range, offset the tool path in the plane direction toward the workpiece by a value obtained by multiplying the plane direction difference by a correction coefficient less than 1, and perform finish machining again; The cutting control means includes: When a first measurement shape, which is a measured shape of the workpiece after the first finish machining, acquired by the shape acquisition means, does not reach the target finish shape, and a first surface direction difference, which is a difference between the first measurement shape and the target finish shape in the surface direction, exceeds a first predetermined value and is less than a second predetermined value, a zero cut is performed to perform a second finish machining by moving a cutting tool along the tool path used in the first finish machining; When the first measured shape does not reach the target finish shape and the first surface direction difference is equal to or greater than a second predetermined value, the tool path is offset by the first surface direction difference toward a side approaching a workpiece, and a second finish machining is performed; When a second measurement shape as the specific measurement shape, which is the measurement shape of the workpiece after the second finishing process acquired by the shape acquisition means, does not reach the target finishing shape, and a second surface direction difference, which is the difference between the second measurement shape and the target finishing shape in the surface direction, is equal to or greater than a predetermined value, the tool path is offset toward the workpiece by an amount obtained by multiplying the second surface direction difference by a correction coefficient less than 1, and a third finishing process is performed. Machine tools.

2. The correction coefficient is equal to or greater than 0.7 and equal to or less than 0.

9. The machine tool according to claim 1.

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