Control device for a machine tool

Abstract

Control device (100) for a machine tool, which performs coordinated operation of at least one spindle (18) for the relative rotation of a cutting tool (16) and a workpiece (14) and at least one feed axis for moving the cutting tool (16) relative to the workpiece (14) and performs thread cutting, while causing the cutting tool (16) to perform a cutting process on the workpiece (14) several times in a radial direction, wherein the control device (100) comprises: an oscillation operation execution determination unit (102) that determines whether an oscillation operation should be executed, causing the cutting tool (16) to oscillate in the radial direction of the workpiece (14); an oscillation command generation unit (106) that generates an oscillation command for the oscillation operation based on a determination result by the oscillation operation execution determination unit (102); and a control unit (110) that superimposes the oscillation command onto a position command of the feed axis to generate a drive command of the feed axis, wherein the oscillation operation execution determination unit (102) determines to execute the oscillation operation intermittently, and wherein the oscillation instruction generation unit (106) generates an oscillation instruction such that a non-oscillation cutting section of a current cutting operation includes a section where oscillation cutting was performed in a previous cutting operation, or such that an oscillation cutting section of the current cutting operation includes a section where non-oscillation cutting was performed in the previous cutting operation.

Description

BACKGROUND OF THE INVENTION Area of ​​the invention

[0001] The present invention relates to a control device for a machine tool. State of the art

[0002] A technique for performing thread cutting while chip removal is already known. For example, a technique is known in which a back-and-forth vibration of a workpiece and a cutting tool is effected during a predetermined number of times of a thread cutting process, and the vibration pattern is defined for each instance of the thread cutting process that includes the back-and-forth vibration, such that a section that has already been machined by another thread cutting process is partially contained within a section that is to be machined in a predetermined thread cutting process (see, for example, international publication no. WO2016 / 056526).

[0003] Patent document 1: International PCT Publication No. WO2016 / 056526.

[0004] EP 3 213 848 A1 discloses a numerical control device comprising: a drive unit controlling a main shaft rotating a workpiece, a first drive shaft moving a cutting tool relative to the workpiece along a direction perpendicular to a thread direction of a thread formed in a machining operation, and a second drive shaft moving the cutting tool relative to the workpiece along the thread direction; and a vibration unit superimposing a vibration on the movement of the first drive shaft, which is a reciprocating feed motion with a period in a predetermined ratio to a rotation period of the main shaft, and performing a thread cutting operation to form a thread on the workpiece by moving the cutting tool and the workpiece relative to each other and performing a cutting operation more than once on the workpiece.The numerical control device includes a thread cutting vibration adjustment unit that controls the drive unit to shift the vibration phase relative to the main shaft phase by a predetermined vibration phase shift amount for each cutting process performed more than once. SUMMARY OF THE INVENTION

[0005] Since the technique described in the international PCT publication No. WO2016 / 056526 always involves reciprocating vibration of the workpiece and cutting tool (hereinafter also referred to as oscillation operation) during thread cutting, the stress on the machine tool due to this reciprocating vibration is high. Therefore, a control device for a machine tool was desired that could perform thread cutting while reducing the stress on the machine tool due to oscillation operation, without increasing the cycle time, which is important for machining operations.

[0006] Furthermore, in the technique described in international publication no. WO2016 / 056526, the position deviation, which is a discrepancy between a position command and the actual position, is large due to reasons such as reaction delay during oscillation operation, resulting in incomplete cutting (see later description). Fig. 7) Therefore, it is currently difficult to achieve chip crushing during final machining, and thus a control device for a machine tool was desired that can reliably crush chips in a case of non-oscillation operation in the current pass after oscillation operation in the previous pass, as in final machining during thread cutting.

[0007] One aspect of the present disclosure relates to a control device for a machine tool that performs coordinated operation of at least one spindle for the relative rotation of a cutting tool and a workpiece and at least one feed axis for moving the cutting tool relative to the workpiece, and performs thread cutting while causing the cutting tool to repeatedly perform a cutting process on the workpiece in a radial direction, wherein the control device comprises: an oscillation operation execution determination unit that determines whether an oscillation operation should be executed, causing the cutting tool to oscillate in the radial direction of the workpiece; an oscillation command generation unit that generates an oscillation command for the oscillation operation based on a determination result by the oscillation operation execution determination unit;and a control unit that superimposes the oscillation command onto a feed axis position command to generate a feed axis drive command, wherein the oscillation operation execution determination unit determines to execute the oscillation operation intermittently, and wherein the oscillation operation command generation unit generates an oscillation command such that a non-oscillation cutting section of a current cutting operation includes a section where oscillation cutting was performed in a previous cutting operation, or such that an oscillation cutting section of the current cutting operation includes a section where non-oscillation cutting was performed in the previous cutting operation.

[0008] According to the present disclosure, it is possible to create a control device for a machine tool that is capable of performing thread cutting while the load on the machine tool is reduced due to oscillation operation, without increasing the cycle time. Furthermore, it is possible to create a control device for a machine tool that can reliably crush chips in a case of non-oscillation operation in the current pass after oscillation operation in the previous pass, as in the final machining stage of thread cutting. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a functional block diagram showing the configuration of a control device for a machine tool according to one aspect of the present disclosure; Fig. 2 is a diagram showing a screw produced by thread cutting; Fig. Figure 3 shows a workpiece during thread cutting; Fig. Figure 4 is a diagram to illustrate the operation of thread cutting by the control device for the machine tool according to one aspect of the present disclosure; Fig. Figure 5 is a diagram to illustrate the operation of thread cutting by the control device for the machine tool according to one aspect of the present disclosure; Fig. Figure 6 is a diagram to illustrate the operation of thread cutting by the control device for the machine tool according to one aspect of the present disclosure; Fig. 7 is a diagram showing a finished machining process in the final pass of conventional thread cutting; and Fig. Figure 8 is a diagram showing the finishing process in the final pass of thread cutting by the control device for the machine tool according to one aspect of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0009] Below, one aspect of the present revelation is described in detail with reference to the drawings.

[0010] A control device for a machine tool according to one aspect of the present disclosure performs a coordinated operation of at least one spindle for the relative rotation of a cutting tool and a workpiece and at least one feed axis for moving the cutting tool relative to the workpiece and performs thread cutting, while causing the cutting tool to perform a cutting process on the workpiece several times in the radial direction.

[0011] Fig. Figure 1 is a functional block diagram showing a configuration of a control device 100 for a machine tool according to one aspect of the present disclosure. As in Fig. As shown in Figure 1, the control device 100 issues a drive command to carry out coordinated operation of these axes on a motor 120, which drives at least one spindle for relative rotation of a cutting tool and a workpiece, and at least one feed axis for moving the cutting tool relative to the workpiece.

[0012] Before explaining the configuration of the control device 100, a description of thread cutting with reference to Fig. 2 and Fig. 3 given. Here is Fig. 2 a diagram showing a screw 12 produced by thread cutting. Fig. Figure 3 shows a workpiece 14 during thread cutting.

[0013] As in Fig. As shown in Figure 2, the screw 12 produced by thread cutting has a threaded groove 10 of sufficient depth, which is formed in a helical shape on its outer circumferential surface. The control device 100 for the machine tool according to one aspect of the present disclosure rotates the cutting tool and the workpiece relative to each other and moves the cutting tool relative to the workpiece to perform cutting, thereby forming the threaded groove 10.

[0014] As indicated by the arrow P in Fig. As specified in Figure 3, a cutting tool 16 performs the cutting action to form the threaded groove 10 on the workpiece 14 several times along a predetermined path 10a (i.e., the location of the threaded groove 10) on the workpiece 14. The path 10a is present in a spiral pattern around the entire circumference of the outer surface of the workpiece 14. Fig. Figure 3 shows the state immediately after the start of the cutting process, where the thread groove 10 is still shallow. By repeating the cutting process several times, a deep thread groove 10 is created, as shown in Figure 3. Fig. 2 shown, trained to complete the final screw 12.

[0015] In Fig. In step 3, the workpiece 14 is attached to the spindle 18 and is controlled to rotate it in the direction indicated by arrow C. The axis of rotation indicated by arrow C is called the C-axis. In other words, the C-axis corresponds to angular coordinates that specify an angle around the spindle 18.

[0016] The cutting tool 16 moves along path 10a on the surface of the workpiece 14, which rotates to cut the thread groove 10. Therefore, the cutting tool 16 is synchronized with the rotation of the C-axis direction of the workpiece 14 and is controlled to move along the Z-axis, which is a coordinate axis of the workpiece 14 in the longitudinal direction.

[0017] Furthermore, the cutting tool 16 gradually moves vertically with respect to the surface of the workpiece 14, i.e., in the X-axis direction, which is the coordinate axis in the radial direction, each time the cutting is performed. Therefore, the cutting tool 16 is controlled to perform the cutting in a gradually deeper position with respect to the workpiece 14.

[0018] Next, a configuration of the control device 100 for the machine tool according to one aspect of the present disclosure is described. As in Fig. As shown in Figure 1, the control device 100 comprises an oscillation operation execution determination unit 102, an oscillation condition calculation unit 104, an oscillation instruction generation unit 106, an adder 108 and a control unit 110.

[0019] A numerical controller is used, for example, as the control device 100. The control device 100 is implemented, for example, by causing a computer with a CPU, memory, or the like to load a program according to the present embodiment.

[0020] The oscillation operation execution determination unit 102 determines whether the oscillation operation for oscillating the cutting tool 16 in the radial direction (X-axis direction) of the workpiece 14 should be executed. This determination is made based on a machining program that is entered externally. The oscillation operation execution determination unit 102 according to one aspect of the present disclosure is characterized in that it determines whether the oscillation operation should be executed intermittently. That is, the oscillation operation execution determination unit 102 determines the execution of the intermittent oscillation operation, such that the oscillation operation for performing a relative back-and-forth vibration between the cutting tool 16 and the workpiece 14 and the non-oscillation operation for not performing the back-and-forth oscillation are repeated alternately.Consequently, the oscillation mode and the non-oscillation mode are repeatedly executed alternately in the same processing pass.

[0021] It is preferred that the oscillation operation execution determination unit 102 determines the execution of the oscillation operation in order to perform the oscillation cutting in the current cutting operation in a position that differs from the section in which the oscillation cutting was performed in the previous cutting operation. Since it is possible to more reliably include the section in the current cutting operation where the cutting was previously performed, a so-called idle run is consequently generated more reliably, thereby reducing the size of the chips more reliably.

[0022] Furthermore, it is preferred that the oscillation operation execution control unit 102 determines whether the cutting is performed intermittently by the oscillation operation, and then whether the cutting is performed by the non-oscillation operation in the next pass. Consequently, in a case where the non-oscillation cutting is performed in the final pass after the oscillation cutting, it is possible, for example, to reliably crush chips. This will be described in detail later.

[0023] It is also preferred that the oscillation operation execution determination unit 102 determines whether to perform non-oscillation cutting until the position deviation, which is a deviation between the position command and the actual position, becomes equal to or less than a predetermined threshold in a non-oscillation cutting section performed by the intermittent oscillation operation. Consequently, it is possible to reliably crush chips in the non-oscillation cutting section performed by the intermittent oscillation operation. This will be described in detail later.

[0024] The oscillation condition calculation unit 104 calculates the oscillation operation condition to be output to the oscillation command generation unit 106, based on the machining program, the machining parameter, and / or the feedback value from the machine tool. As described in Fig. As shown in Figure 1, the oscillation condition calculation unit 104, for example, calculates conditions such as the interval of oscillation operation (the distance between adjacent vertices in the oscillation waveform, as shown in Figure 1). Fig. 4 shown, which will be described later), the amplitude and the cycle based on the externally entered processing program.

[0025] It is preferred that the oscillation condition calculation unit 104 changes the interval of the oscillation operation. In particular, the oscillation condition calculation unit 104 can change the interval of the oscillation operation between different processing passes. Furthermore, the oscillation condition calculation unit 104 can change the interval of the oscillation operation within the same processing pass. Alternatively, the oscillation condition calculation unit 104 can change the interval of the oscillation operation between different processing passes and can change the interval of the oscillation operation within the same processing pass.

[0026] Furthermore, the oscillation operation calculation unit 104 can change the oscillation operation interval according to the diameter of the workpiece 14. For example, the oscillation operation interval is set to be longer if the diameter of the workpiece 14 becomes smaller, i.e., if the number of cutting operations increases. Conversely, the oscillation operation interval can be set to be shorter if the diameter of the workpiece 14 becomes smaller, i.e., if the number of cutting operations increases. The setting of the oscillation operation interval is described in detail later.

[0027] The oscillation command generation unit 106 generates an oscillation command for the oscillation operation based on the determination result by the oscillation operation execution determination unit 102. Furthermore, the oscillation command generation unit 106 generates an oscillation command for the oscillation operation according to the oscillation condition calculated by the oscillation condition calculation unit 104. According to one aspect of this disclosure, the oscillation command generation unit 106 generates an oscillation command such that the non-oscillation cutting section of the current cutting operation includes a section where oscillation cutting was performed in the previous cutting operation.Alternatively, the oscillation command generation unit 106 generates the oscillation command so that the oscillation cutting section of the current cutting operation includes a section where non-oscillation cutting was performed in the previous cutting operation. This makes it possible to generate a so-called idle run more reliably and to crush chips more reliably.

[0028] The adder 108 calculates a position deviation, which is the difference between a position feedback based on position detection by an encoder (not shown) intended for the motor 120 and a position command from the feed axis. The feed axis position command and the position deviation are input to the control unit 110, which will be described later.

[0029] The control unit 110 superimposes the oscillation command generated by the oscillation command generation unit 106 onto the feed axis position command and the position deviation, thereby generating a drive command for the motor 120, which drives the feed axis. It should be noted that in one aspect of the present disclosure, the feed axis position command is generated once, and the oscillation command is superimposed onto the generated position command; however, the present disclosure is not limited to this. The oscillation command can be superimposed in advance, and the feed axis position command can be generated.

[0030] Next, the operation of the thread cutting by the control device 100 for the machine tool according to one aspect of the present disclosure will be described in detail with reference to Fig. 4, Fig. 5 to Fig. 6 described here Fig. 4, Fig. 5 to Fig. Six diagrams illustrating the operation of the thread cutting operation by the control device 100 for the machine tool according to one aspect of the present disclosure. These figures correspond to Part A of Fig. 3, viewed in the Z-axis direction from the side where the cutting starts. In particular, Fig. 4 a diagram showing an example of a case in which the interval of the oscillation operation is constant in each processing pass (hereinafter referred to simply as a pass). Fig. Figure 5 is a diagram showing an example of a case where the interval of the oscillation operation is increased when the diameter of the workpiece 14 decreases. Fig. Figure 6 is a diagram showing an example of a case in which the oscillation operation in each pass is not in a direction of cutting into the workpiece 14, but rather in a direction in which it is separated from the workpiece 14.

[0031] It should be noted that the C-axis, the Z-axis, and the X-axis in Fig. 4, Fig. 5 to Fig. 6 in the same definition as the C-axis, the Z-axis and the X-axis as described above Fig. 3 can be used. Furthermore, in Fig. 4, Fig. 5 to Fig. 6 the section surrounded by a dashed line, a section which, during the current cutting, includes the section where the cutting was previously carried out, and consequently indicates the section where the so-called idle time takes place and chips are crushed.

[0032] In the Fig. In the operating example shown in Figure 4, any one of the passes from the first to the fourth pass is to perform an intermittent oscillation operation, and a linear non-oscillation cutting operation and an oscillation cutting operation, which is a deep cutting operation in a curved shape, are performed alternately and repeatedly. Furthermore, in any one of the first to fourth passes, the interval L of the oscillation operation, which is defined in Fig. As shown in Figure 4, the constant. Regarding the final pass, since it is the finished processing stage, it is simply a non-oscillating cut without oscillation and is therefore a completely linear cut.

[0033] Here, the spacing L of the oscillation operation, i.e., the distance between adjacent vertices in the oscillation waveform, can be determined as in Fig. As shown in Figure 4, the permissible chip length is set accordingly. The permissible chip length is set to a length that does not impede cutting by chips that become entangled in the cutting tool 16 during cutting, for example. Consequently, it is possible to crush the chips without hindering the cutting process. The permissible chip length can be set by a G-code, a parameter, or the like, so that the interval L of the intermittent oscillation operation can be defined.

[0034] In the Fig. The operational example shown in point 5 is intended to be similar to the one in Fig. In the operating example shown in Figure 4, any of the passes from the first pass to the fourth pass performs intermittent oscillation operation, and linear non-oscillation cutting and oscillation cutting, which is deep cutting in a curved shape, are performed alternately and repeatedly. As shown in Fig. As shown in Figure 5, the interval of the oscillation operation differs for each pass from the first to the fourth pass. Regarding the final pass, since it is the finishing process, it is simply a non-oscillation cutting operation without oscillation and is therefore a completely linear cut.

[0035] In particular, the interval of the oscillation operation is set to a longer duration when the diameter of the workpiece becomes smaller, i.e., when the number of cutting operations increases. As in Fig. As shown in Figure 5, the interval L2 of the oscillation operation of the fourth pass is therefore set to a longer duration than the interval L1 of the oscillation operation of the first pass. Consequently, it is possible to keep the chip length constant by setting the interval of the oscillation operation to a longer duration, thus avoiding a situation in which the circumferential length of the workpiece 14 becomes shorter as the number of cutting passes increases.

[0036] In the Fig. The operational example shown in section 6 is intended to be similar to the one in Fig. In the operating example shown in Figure 4, any one of the passes from the first to the fourth pass performs intermittent oscillation operation, and linear non-oscillation cutting and oscillation cutting in a curved shape are performed alternately and repeatedly. Furthermore, in any one of the passes from the first to the fourth pass, the interval L of the oscillation operation is as shown in Figure 4. Fig. The operating example shown in section 4 is constant. However, in each of the first four passes, the oscillation is not in the direction of cutting into the workpiece 14, but rather in the direction in which it is separated from the workpiece 14. In other words, compared to the operating examples of Fig. 4 and Fig. 5 indicates the opposite direction of oscillation.

[0037] If the oscillation operation is carried out here in the direction of cutting into the workpiece 14, as in Fig. 4 and Fig. As shown in Figure 5, in order to determine the oscillation amplitude so that the cutting depth in the next pass covers a section where cutting has already been performed in the current pass, the cutting depth in the next pass depends on the oscillation amplitude of the current pass. Therefore, it is necessary to anticipate this in the machining program using the control device 100, such as a numerical controller. In contrast, by reversing the oscillation direction, as in the figure shown in Figure 5, the cutting depth in the next pass depends on the oscillation amplitude of the current pass. Fig. In the operating example shown in Figure 6, the oscillation amplitude of the next pass no longer differs from the oscillation amplitude of the current pass. Therefore, it is not necessary to anticipate the machining program using the control device 100, such as a numerical controller.

[0038] Next, a finishing operation in the final pass of thread cutting by the control device 100 for the machine tool is described in accordance with one aspect of the present disclosure with reference to Fig. 7 and Fig. 8 described in detail. Here is Fig. Figure 7 shows a diagram illustrating the final processing stage of a conventional thread cutting process. Fig. Figure 8 is a diagram showing the finishing process in the final pass of thread cutting by the control device 100 of the machine tool according to one aspect of the present disclosure. The C-axis, Z-axis, and X-axis in Fig. 7 and Fig. 8 are defined with the same definition as the C-axis, Z-axis and X-axis in the above described Fig. 3 is used. Furthermore, the section that is marked by a dashed line in Fig. 8 is surrounded by a section which, during the current cutting, includes the section where the cutting was previously carried out, and consequently indicates the section where the so-called idle time takes place and chips are crushed.

[0039] In conventional thread cutting, in a case where the cutting operation without oscillation in the final pass is carried out after the cutting operation with oscillation in a single pass immediately before the final pass, it is assumed that, as indicated by the dashed line 72 in Fig. Figure 7 shows a location where a machined section in the final pass includes a section where machining in the pass was carried out immediately before the final pass (i.e., the location where the dashed line 72 overlaps with the straight line of the final pass, which is a valley section of the dashed line 72 and is a so-called idle section), consequently chipping. In practice, as shown by the solid line 71 in Fig. As specified in point 7, however, there is no location where a machined section in the final pass does not include a section where machining was performed in the pass immediately before the final pass (i.e., the location where the solid line 71 overlaps with the straight line of the final pass), consequently, chips cannot be crushed. This is due to the position deviation, which is the difference between the position command and the actual position in oscillation operation.

[0040] In contrast, one aspect of the present revelation, as indicated by the dotted line 82 in Fig. 8 indicates a location where the processed section in the final pass includes a section where the processing in the pass was carried out immediately before the final pass, ideally created and in practice as by the solid line 81 and the dashed line drawn from a circle in Fig.As specified, a location is created where the machined section in the final pass encompasses a section where machining was performed immediately before the final pass, thus reducing the size of the chips. This is because the positional deviation in non-oscillation operation converges by providing for both oscillation and non-oscillation operation in the same pass. This enables reliable chip reduction in the final pass.

[0041] The period of non-oscillation operation can be easily determined by a predetermined value with respect to time or distance, or it can be determined based on whether the positional deviation is equal to or less than a predetermined threshold. Furthermore, the above explanation was described using the final machining step of thread cutting as an example; however, the present invention is not limited to this and can be applied to all cases in which the non-oscillating cutting operation is performed in the next pass after the oscillating cutting operation.

[0042] In summary, according to one aspect of the present revelation, the following effects can be achieved. (1) A control device 100 for a machine tool, which performs coordinated operation of at least one spindle 18 for the relative rotation of a cutting tool 16 and a workpiece 14 and at least one feed axis for moving the cutting tool 16 relative to the workpiece 14 and performs thread cutting while causing the cutting tool 16 to repeatedly perform a cutting process on the workpiece 14 in a radial direction (X-direction), wherein the control device 100 comprises: an oscillation operation execution determination unit 102, which determines whether an oscillation operation is to be performed, causing the cutting tool 16 to oscillate in the radial direction (X-direction) of the workpiece 14; an oscillation command generation unit 106,which generates an oscillation command for oscillation operation based on a determination result by the oscillation operation execution determination unit 102; and a control unit 110 that superimposes the oscillation command onto a feed axis position command to generate a feed axis drive command. Furthermore, the oscillation operation execution determination unit 102 determines that the oscillation operation is executed intermittently, and the oscillation command generation unit 106 generates an oscillation command such that a non-oscillation cutting section of a current cutting operation includes a section where oscillation cutting was performed in a previous cutting operation, or such that an oscillation cutting section of the current cutting operation includes a sectionwhere non-oscillation cutting was performed in the previous cutting operation. Consequently, compared to conventional technology, it is possible to reliably crush chips by performing intermittent oscillation operation without increasing the cycle time. Since the number of oscillation operation cycles can be reduced, it is also possible to reduce the load on the machine tool caused by the oscillation operation. Furthermore, in conventional technology, there may be a case where incomplete cutting occurs due to a large positional deviation caused by reaction delay or the like during oscillation operation, as a result of which chips cannot be crushed. However, since, according to the present disclosure, the positional deviation converges during the non-oscillation operation, it is possible to reliably crush the chips.when the non-oscillation operation in the current pass is executed after the oscillation operation in the previous pass. (2) The oscillation operation execution determination unit 102 is configured to determine the execution of an oscillation operation in order to perform the oscillation cutting in the current cutting operation in a position different from a section where oscillation cutting was performed in a previous cutting operation. Since it is possible to more reliably include a section where cutting was previously performed in the current cutting operation, it is thus possible to generate the so-called idle time more reliably and to reduce chips more reliably. (3) The control device 100 further comprises an oscillation condition calculation unit 104, which calculates a condition for an oscillation operation to be output to the oscillation command generation unit 106, based on a machining program, a machining parameter and / or a feedback value from the machine tool, and the oscillation condition calculation unit 104 is configured to change an interval of the oscillation operation. Consequently, it is possible to calculate conditions such as the interval, amplitude and cycle of the oscillation operation, and thus it is possible to reduce chips more reliably. In particular, it is possible to adjust the chip length by changing the interval of the oscillation operation. (4) The oscillation condition calculation unit 104 is configured to change the interval of the oscillation operation between different machining passes. Consequently, it is possible to reduce chips more reliably and to adjust the chip length. (5) The oscillation condition calculation unit 104 is configured to change the interval of the oscillation operation within the same machining pass. Consequently, it is possible to reduce chips more reliably and to adjust the chip length. (6) The oscillation condition calculation unit 104 is configured to change the interval of the oscillation operation according to the diameter of the workpiece 14. Consequently, it is possible to keep the chip length constant by setting a longer interval of the oscillation operation, thus avoiding a situation in which the circumferential length of the workpiece 14 becomes shorter as the number of cutting passes increases, thereby making it possible to carry out more efficient and uniform thread cutting. (7) The oscillation operation execution determination unit 102 is configured to determine whether to perform the cutting operation intermittently using an oscillation operation, and then to perform the cutting operation using a non-oscillation operation in a subsequent pass. Consequently, it is possible to reliably reduce chips when the non-oscillation cutting is performed in the next pass after the oscillation cutting operation. For example, it is possible to reliably reduce chips even in the final processing stage of the last pass. (8) The oscillation operation execution determination unit 102 is configured to determine whether to perform non-oscillation cutting until a positional deviation in a non-oscillation cutting section caused by intermittent oscillation operation becomes equal to or less than a predetermined threshold. Consequently, it is possible to reduce chips in the non-oscillation cutting section more reliably by means of intermittent oscillation operation.

[0043] It should be noted that the present invention is not limited to the above embodiments and that variations and improvements within a scope that can achieve the object of the present invention are included in the present invention. EXPLANATION OF REFERENCE MARKS 10 threaded groove 12 screws 14 workpieces 16 cutting tools 18 spindles 100 Control device 102 Oscillation operation execution determination unit 104 Oscillation condition calculation unit 106 Oscillation command generation unit 108 Adders 110 Control unit 120 engine X X-axis Z Z-axis C C-axis L, L1, L2 oscillation interval

Claims

[1] Control device (100) for a machine tool, which performs coordinated operation of at least one spindle (18) for the relative rotation of a cutting tool (16) and a workpiece (14) and at least one feed axis for moving the cutting tool (16) relative to the workpiece (14) and performs thread cutting, while causing the cutting tool (16) to perform a cutting process on the workpiece (14) several times in a radial direction, wherein the control device (100) comprises: an oscillation operation execution determination unit (102) that determines whether an oscillation operation should be executed, causing the cutting tool (16) to oscillate in the radial direction of the workpiece (14); an oscillation command generation unit (106) that generates an oscillation command for the oscillation operation based on a determination result by the oscillation operation execution determination unit (102); and a control unit (110) that superimposes the oscillation command onto a position command of the feed axis to generate a drive command of the feed axis, wherein the oscillation operation execution determination unit (102) determines to execute the oscillation operation intermittently, and wherein the oscillation instruction generation unit (106) generates an oscillation instruction such that a non-oscillation cutting section of a current cutting operation includes a section on which oscillation cutting was performed in a previous cutting operation, or such that an oscillation cutting section of the current cutting operation includes a section on which non-oscillation cutting was performed in the previous cutting operation. [2] Control device (100) for the machine tool according to claim 1, wherein the oscillation operation execution determination unit (102) determines the execution of an oscillation operation in order to perform the oscillation cutting in a current cutting operation in a position that is different from a position in which the oscillation cutting was performed in a previous cutting operation. [3] Control device (100) for the machine tool according to claim 1 or 2, which further comprises an oscillation condition calculation unit (104) which calculates a condition of an oscillation operation, which is to be output to the oscillation command generation unit (106), on the basis of a machining program, a machining parameter and / or a feedback value from the machine tool, where the oscillation condition calculation unit (104) modifies an interval of the oscillation operation. [4] Control device (100) for the machine tool according to claim 3, wherein the oscillation condition calculation unit (104) changes the interval of the oscillation operation between different machining passes. [5] Control device (100) for the machine tool according to claim 3 or 4, wherein the oscillation condition calculation unit (104) changes the interval of the oscillation operation within an equal machining pass. [6] Control device (100) for the machine tool according to one of claims 3 to 5, wherein the oscillation condition calculation unit (104) changes the interval of the oscillation operation according to a diameter of the workpiece (14). [7] Control device (100) for a machine tool, which performs coordinated operation of at least one spindle (18) for the relative rotation of a cutting tool (16) and a workpiece (14) and at least one feed axis for moving the cutting tool (16) relative to the workpiece (14) and performs thread cutting, while causing the cutting tool (16) to perform a cutting process on the workpiece (14) several times in a radial direction, wherein the control device (100) comprises: an oscillation operation execution determination unit (102) that determines whether an oscillation operation should be executed, causing the cutting tool (16) to oscillate in the radial direction of the workpiece (14), wherein the oscillation operation execution determination unit (102) determines to perform the cutting intermittently by an oscillation operation, and then to perform the cutting by a non-oscillation operation in a subsequent pass. [8] Control device (100) for the machine tool according to one of claims 1 to 7, wherein the oscillation operation execution determination unit (102) determines to perform non-oscillation cutting until a position deviation in a non-oscillation cutting section due to intermittent oscillation operation becomes equal to or less than a predetermined threshold value.

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