Processing device and processing method

Abstract

To provide a processing device and a processing method which prevent chips from getting tangled, while suppressing regenerative chatter vibration.SOLUTION: A spindle control part 21 controls rotation of a cutting tool 10 or of a spindle 2a mounted with a material 6 to be cut. A movement control part 22 controls a relative movement of the cutting tool 10 with respect to the material 6 to be cut. In a cutting period of time during which the cutting tool 10 cuts the material 6 to be cut, the spindle control part 21 executes first control by which rotation of the spindle 2a is accelerated or decelerated so that a speed variation ratio which is a ratio of a current rotation speed in the same rotation position and a rotation speed before one round rotation is made is out of a range between a first threshold larger than 1 and a second threshold smaller than 1. In a non-cutting period of time during which the cutting tool 10 does not cut the material 6 to be cut, the spindle control part 21 executes second control by which rotation of the spindle 2a is decelerated or accelerated. The spindle control part 21 executes the first control and the second control alternately.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a processing apparatus and a processing method. [Background technology]

[0002] "Regenerative chatter vibration" is a self-excited vibration in which the vibration that occurred during the previous cutting revolution (or the previous blade in the case of a multi-blade tool) remains as an undulation on the machined surface, and this vibration is reproduced as a fluctuation in the chip thickness during the current cutting. "Regenerative chatter vibration" deteriorates the finish accuracy of the machined surface and can be a cause of chipping of the cutting tool.

[0003] In order to suppress regenerative chatter vibration in turning, a rotational speed fluctuation method is known in which the spindle rotational speed is controlled so that the current rotational speed at a certain rotational position (rotational angle) changes from the rotational speed of one rotation before. Patent Document 1 discloses a processing device that suppresses the occurrence of chatter vibration by alternately executing acceleration control, which accelerates the rotation of the spindle so that a speed fluctuation ratio, which is the ratio between the current rotational speed at the same rotational position and the rotational speed of one rotation before, is equal to or greater than a first value greater than 1, and deceleration control, which decelerates the rotation of the spindle so that the speed fluctuation ratio is equal to or less than a second value smaller than 1.

[0004] In cutting, chips that are continuously discharged can often become tangled around the workpiece or tool, which can be a problem. To prevent chips from becoming tangled, chip breakers are generally used, which strongly curl and break the chips. Chips have become brittle due to large plastic deformation, so when chips curled by the chip breaker collide with the workpiece or tool, they are more likely to break due to the excessive deformation that occurs after the collision. However, when the workpiece material is highly ductile or the chip thickness is thin (chip thickness is generally thin in finishing), the chips are difficult to break.

[0005] Aiming to solve the problem of chip entanglement, Non-Patent Document 1 discloses vibration feed cutting, in which the tool is fed at a constant feed rate in the feed direction while vibrating in the feed direction to intermittently cut the workpiece. In vibration feed cutting, by appropriately setting the amplitude and period of the vibration in the feed direction, chips can be reliably cut and the problem of chip entanglement can be solved.

[0006] Fig. 1(a) shows the state of vibration feed cutting. In vibration feed cutting, the tool is vibrated in the feed direction while being fed at a constant feed rate, and periodic non-cutting periods are generated in which the tool retreats from the workpiece in the feed direction and does not cut, thereby achieving intermittent cutting that reliably cuts chips.

[0007] Figure 1(b) shows the relationship between the spindle angle and the axial displacement of the tool cutting edge in oscillatory feed cutting. Line a shows the cutting edge position on the first rotation, line b shows the cutting edge position on the second rotation, and line c shows the cutting edge position on the third rotation. "Feed" indicates the feed rate per rotation (mm / rev), and "Air cutting interval" indicates the non-cutting period during which the cutting edge retreats in the feed direction and does not cut the workpiece. In oscillatory feed cutting, cutting periods in which the tool cuts the workpiece material alternate with non-cutting periods in which the tool does not cut the workpiece, intermittently cutting the workpiece and shearing chips to prevent them from becoming entangled in the workpiece or the tool. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2020 / 31582 [Non-patent literature]

[0009] [Non-Patent Document 1] Eiji Kasahara, "Chip Cutting by Vibration Feed Cutting", Preprint of the 1967 Spring Academic Conference of the Japan Society of Precision Machinery, 119 Summary of the Invention [Problem to be solved by the invention]

[0010] In the method of suppressing regenerative chatter vibration using rotational speed fluctuation (cutting speed fluctuation), the "speed fluctuation ratio," which is the ratio of the current rotational speed to the rotational speed of the previous rotation at the same rotational position, is an important parameter. The further the speed fluctuation ratio is from 1, the greater the effect of suppressing chatter vibration. Conversely, the closer the speed fluctuation ratio is to 1, the more likely chatter vibration will grow.

[0011] If the spindle rotation continues to accelerate during normal continuous turning, the maximum rotation speed may be reached before the end of the cutting process, resulting in excessively high-speed cutting and severe tool wear. Conversely, if the spindle rotation continues to decelerate, the rotation may stop before the end of the cutting process, resulting in reduced machining efficiency. Therefore, methods for suppressing regenerative chatter vibration that utilize rotational speed fluctuations require alternating acceleration and deceleration of the rotation, but when the rotational speed switches between increasing and decreasing, the speed fluctuation ratio approaches 1, which creates the problem of chatter vibration easily growing.

[0012] On the other hand, in vibration feed cutting, which prevents chip entanglement, non-cutting periods are set periodically during the cutting period, which tends to reduce machining efficiency, and because the feed rate fluctuates, the finished surface roughness tends to vary depending on the cutting location. In order to keep the finished surface roughness below the allowable value, it is sufficient to reduce the feed rate per revolution, but reducing the feed rate per revolution leads to a decrease in machining efficiency.

[0013] The present disclosure has been made in view of these circumstances, and its purpose is to provide a cutting processing technology that effectively suppresses regenerative chatter vibration while preventing entanglement of chips. [Means for solving the problem]

[0014] To solve the above problems, a processing apparatus according to one embodiment of the present disclosure includes a spindle control unit that controls the rotation of a spindle to which a cutting tool or a workpiece is attached, and a movement control unit that controls the relative movement of the cutting tool with respect to the workpiece. During a cutting period in which the cutting tool cuts the workpiece, the spindle control unit executes a first control that accelerates or decelerates the rotation of the spindle so that a speed fluctuation ratio, which is the ratio of the current rotational speed to the rotational speed of the previous rotation at the same rotational position, falls outside the range between a first threshold value greater than 1 and a second threshold value less than 1. During a non-cutting period in which the cutting tool is not cutting the workpiece, the spindle control unit executes a second control that accelerates or decelerates the rotation of the spindle. The spindle control unit alternates between the first control and the second control.

[0015] Another aspect of the machining method of the present disclosure is a machining method for cutting a workpiece, which alternately performs a first step of accelerating or decelerating the rotation of the spindle during a cutting period in which the cutting tool cuts the workpiece, so that a speed fluctuation ratio, which is the ratio between the current rotational speed at the same rotational position and the rotational speed one rotation ago, becomes a value outside the range between a first threshold value greater than 1 and a second threshold value less than 1, and a second step of accelerating or decelerating the rotation of the spindle during a non-cutting period in which the cutting tool is not cutting the workpiece.

[0016] Any combination of the above components and conversion of the expressions of the present disclosure into methods, devices, systems, etc. are also valid aspects of the present disclosure. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 10 is a diagram for explaining vibration feed cutting. [Figure 2] 1 is a diagram showing a schematic configuration of a processing apparatus according to an embodiment; [Figure 3] FIG. 1 is a diagram for explaining a conventional technique. [Figure 4] FIG. 1 is a diagram for explaining a conventional technique. [Figure 5] FIG. 4 is a diagram for explaining a control pattern according to the embodiment. [Figure 6]FIG. 10 is a diagram for explaining another example of a control pattern according to the embodiment. [Figure 7] 10A and 10B are diagrams for comparing the processing technique of the embodiment with a conventional technique. [Figure 8] FIG. 10 is a diagram showing analysis results. [Figure 9] FIG. 10 is a diagram for explaining another example of a control pattern according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] FIG. 2 shows a schematic configuration of a processing apparatus 1 according to an embodiment. The processing apparatus 1 is a cutting apparatus that performs turning by cutting the cutting edge of a cutting tool 10 into a workpiece 6. The processing apparatus 1 includes a headstock 2 and a tailstock 3 that rotatably support the workpiece 6, and a tool rest 4 that supports the cutting tool 10, all mounted on a bed 5. A rotation mechanism 8 has an electric motor and is provided inside the headstock 2 to rotate a spindle 2a to which the workpiece 6 is attached. A feed mechanism 7 has an electric motor, a ball screw, and the like, and is provided on the bed 5 to move the cutting tool 10 relative to the workpiece 6. In this processing apparatus 1, the feed mechanism 7 moves the tool rest 4 in the X-, Y-, and Z-axis directions, thereby moving the cutting tool 10 relative to the workpiece 6. Here, the X-axis direction is the horizontal cutting direction perpendicular to the axial direction of the workpiece 6, the Y-axis direction is the vertical cutting direction, and the Z-axis direction is the feed direction parallel to the axial direction of the workpiece 6.

[0019] The control unit 20 includes a spindle control unit 21 that controls the rotation of the spindle 2a by the rotation mechanism 8, and a movement control unit 22 that controls the relative movement of the cutting tool 10 with respect to the workpiece 6. While the spindle 2a is rotating, the movement control unit 22 drives the feed mechanism 7 to cause the cutting tool 10 to cut into the workpiece 6, thereby machining the workpiece 6. The machining device 1 may be an NC machine tool. The rotation mechanism 8 and the feed mechanism 7 each have an actuator such as an electric motor, and the spindle control unit 21 and the movement control unit 22 adjust the power supplied to the actuator, respectively, to control the behavior of the rotation mechanism 8 and the feed mechanism 7.

[0020] In the processing device 1 of the embodiment, the workpiece 6 is attached to the spindle 2a and rotated by the rotation mechanism 8, but in another example, the cutting tool 10 may be attached to the spindle 2a and rotated by the rotation mechanism 8. The feed mechanism 7 only needs to move the cutting tool 10 relative to the workpiece 6, and it is sufficient if it has a mechanism for moving at least one of the cutting tool 10 and the workpiece 6.

[0021] In such a processing device 1, it is known that regenerative chatter vibrations do not grow if the current rotational speed at a certain rotational position of the spindle 2a is made sufficiently different from the rotational speed one rotation ago. Hereinafter, the ratio between the current rotational speed at the same rotational position and the rotational speed one rotation ago will be referred to as the "speed fluctuation ratio." Speed fluctuation ratio = (current rotation speed / previous rotation speed)

[0022] Below, we will explain the control patterns for the rotation mechanism 8 and the feed mechanism 7 that achieve cutting that effectively suppresses regenerative chatter vibration while preventing chip entanglement. Before that, we will explain, as comparative examples, two conventional methods for suppressing regenerative chatter vibration. Figure 3 is a diagram for explaining Conventional Method 1, which uses a typical triangular wave fluctuation pattern in the spindle rotation speed fluctuation method, and Figure 4 is a diagram for showing Conventional Method 2, which uses the fluctuation pattern of the spindle rotation speed proposed in Patent Document 1.

[0023] <Conventional method 1> FIG. 3(a) shows a triangular wave fluctuation pattern of the spindle rotation speed. In the triangular wave fluctuation pattern, acceleration periods in which rotation is accelerated and deceleration periods in which rotation is decelerated are repeated alternately. The spindle rotation speed changes linearly from a minimum value to a maximum value during the acceleration period, and changes linearly from a maximum value to a minimum value during the deceleration period. The lengths of the acceleration period and the deceleration period are set to be equal.

[0024] FIG. 3(b) shows the time progression of the speed fluctuation ratio in the triangular wave fluctuation pattern, and FIG. 3(c) shows the change in the vibration magnitude of chatter vibration. Chatter vibration occurs in the "chatter vibration occurrence region" where the speed fluctuation ratio is close to 1. According to conventional method 1 using the triangular wave fluctuation pattern, when the speed fluctuation ratio falls below the first threshold value Th_h near the maximum value of the spindle rotation speed, the chatter vibration displacement begins to increase, and when the speed fluctuation ratio falls below the second threshold value Th_l, the chatter vibration begins to converge. FIG. 3(c) shows how chatter vibration grows during the period Ih-l between the time when the speed fluctuation ratio reaches the first threshold value Th_h and the time when the speed fluctuation ratio reaches the second threshold value Th_l.

[0025] <Conventional method 2> FIG. 4(a) shows the fluctuation pattern of the spindle rotation speed proposed in Patent Document 1. In the fluctuation pattern of the spindle rotation speed shown in FIG. 4(a), acceleration periods in which rotation is accelerated and deceleration periods in which rotation is decelerated are alternately repeated. The spindle rotation speed fluctuates from a minimum value to a maximum value during the acceleration periods, and fluctuates from a maximum value to a minimum value during the deceleration periods. The lengths of the acceleration periods and the deceleration periods are set to be equal. The fluctuation pattern proposed in Patent Document 1 solves the problem of the triangular wave fluctuation pattern in Conventional Method 1.

[0026] 4(b) shows the time transition of the speed fluctuation ratio in the rotation speed fluctuation pattern proposed in Patent Document 1. In Conventional Method 2, acceleration control, which accelerates the rotation of the spindle so that the speed fluctuation ratio becomes a first value (V1) greater than 1, and deceleration control, which decelerates the rotation of the spindle so that the speed fluctuation ratio becomes a second value (V2) less than 1, are alternately and repeatedly executed.

[0027] Chatter vibration occurs in a "chatter vibration occurrence region" where the speed fluctuation ratio is close to 1. In this example, the chatter vibration occurrence region is defined as a range equal to or less than a first threshold value Th_h greater than 1 and equal to or greater than a second threshold value Th_l less than 1. The first threshold value Th_h and the second threshold value Th_l may be calculated by simulation, derived by experiment, or may be empirical values. In the variation pattern of the spindle rotation speed proposed in Patent Document 1, the speed fluctuation ratio (V1) in acceleration control is set higher than the first threshold value Th_h, and the speed fluctuation ratio (V2) in deceleration control is set lower than the second threshold value Th_l, thereby realizing machining that suppresses the growth of regenerative chatter vibration.

[0028] However, as shown in Figure 4(b), even in the fluctuation pattern proposed in Patent Document 1, although the period during which the speed fluctuation ratio falls within the chatter vibration occurrence region is very short, it occurs immediately after the timing at which acceleration and deceleration switch, and there is room for improvement.In addition, the fluctuation pattern proposed in Patent Document 1 is premised on its use in machining in which chips are continuously discharged, and does not solve the problem of chips entangled in the workpiece material or tool.

[0029] Therefore, in this embodiment, we propose a machining method that can more effectively suppress regenerative chatter vibration while preventing chip entanglement. The proposed machining method is characterized by varying not only the spindle rotation speed but also the feed rate. This machining method suppresses regenerative chatter vibration by performing cutting only during either the acceleration period or the deceleration period, and achieves intermittent cutting that periodically cuts chips by providing periods during the machining period when the cutting tool 10 does not cut the workpiece 6.

[0030] 5 shows an example of a control pattern in the machining method of the embodiment. In the machining method of the embodiment, a period in which the cutting tool 10 bites into the workpiece 6 and cuts the workpiece 6 is called a "cutting period," and a period in which the cutting edge of the cutting tool 10 does not bite into the workpiece 6 and does not cut the workpiece 6 is called a "non-cutting period."

[0031] FIG. 5(a) shows the displacement of the cutting edge position fed by the feed mechanism 7, FIG. 5(b) shows the fluctuation pattern of the spindle rotation speed, and FIG. 5(c) shows the transition of the speed fluctuation ratio during the cutting period. Note that the speed fluctuation ratio is the ratio between the current rotation speed at a certain rotation position and the rotation speed of the previous rotation. Since the speed fluctuation ratio for the first rotation of the spindle 2a cannot be calculated, the speed fluctuation ratio for the first rotation is not shown in FIG. 5(c). Also, in FIG. 5(c), a first threshold value Th_h greater than 1 is the upper limit of the speed fluctuation ratio that causes chatter vibration, and a second threshold value Th_l less than 1 is the lower limit of the speed fluctuation ratio that causes chatter vibration. As described above, the first threshold value Th_h and the second threshold value Th_l may be calculated by simulation, derived by experiment, or based on empirical values.

[0032] <Control during cutting period> During the cutting period, the movement control unit 22 causes the cutting edge of the cutting tool 10 to bite into the workpiece 6, and the spindle control unit 21 executes first control to accelerate the rotation of the spindle 2a so that the speed fluctuation ratio becomes a value outside the range between the first threshold value Th_h and the second threshold value Th_l (the chatter vibration generation region). By the spindle control unit 21 controlling the rotation of the spindle 2a so that the speed fluctuation ratio becomes a value outside the "chatter vibration generation region," the occurrence of chatter vibration during the cutting period can be suppressed. In this embodiment, the spindle control unit 21 executes acceleration control during the cutting period from time 0 to t2, and in this example, the speed fluctuation ratio is maintained at "1.03," which is greater than the first threshold value Th_h. The spindle control unit 21 changes the rotational speed of the spindle 2a from a first speed (here, 500 rpm) to a second speed (here, 600 rpm) so that the speed fluctuation ratio becomes a value outside the chatter vibration occurrence region, thereby making it possible to effectively suppress chatter vibration.

[0033] At time t1, just before the end of the cutting period, the movement control unit 22 reverses the direction of the feed motion of the cutting tool 10 by the feed mechanism 7, specifically, retracts the cutting tool 10 in the opposite direction to the feed direction. After time t1, the area where the tool cutting edge contacts the workpiece 6 (the area of the contact region as seen in the cutting direction, called the "cutting cross-sectional area") gradually decreases, and when the cutting cross-sectional area reaches zero at time t2, the chips are cut off, and the cutting period ends. Thus, according to the machining method of the embodiment, the chips are cut off by retracting the tool cutting edge in the feed direction and reducing the area where the cutting edge contacts the workpiece 6 (cutting cross-sectional area) to zero.

[0034] During the cutting period up to time t1 when the direction of the feed motion is reversed, the movement control unit 22 preferably controls the relative movement of the cutting tool 10 with respect to the workpiece 6 so that the feed rate per spindle rotation is constant, thereby maintaining a constant finished surface roughness. In other words, the movement control unit 22 increases the absolute value of the feed rate in accordance with the rate of increase in the spindle rotation speed, thereby controlling the feed rate per rotation to maintain a constant. By controlling the feed rate in this way, the movement control unit 22 can achieve a constant finished surface roughness.

[0035] <Control during non-cutting periods> When the cutting period ends at time t2, the non-cutting period begins. During the non-cutting period, the movement control unit 22 maintains the cutting edge of the cutting tool 10 away from the workpiece 6 in the feed direction, preventing the cutting edge of the cutting tool 10 from cutting the workpiece 6. In other words, the movement control unit 22 prevents the cutting edge of the cutting tool 10 from digging into the workpiece 6 during the non-cutting period, reducing the cutting cross-sectional area to zero. FIG. 5(a) shows the cutting tool 10 moving in the opposite direction to the feed direction during the non-cutting period, then reversing its movement direction approximately in the middle of the non-cutting period and moving again in the feed direction. However, the cutting tool 10 does not need to be continuously moved and may be stationary in a position where it is not cutting the workpiece 6. In either case, during the non-cutting period, the movement control unit 22 controls the relative movement between the cutting tool 10 and the workpiece 6 so that the cutting edge of the cutting tool 10 does not dig into the workpiece 6.

[0036] During the non-cutting period, the spindle control unit 21 executes second control to decelerate the rotation of the spindle 2a. In the second control, the spindle control unit 21 changes the rotational speed of the spindle 2a from the second speed (600 rpm) to the first speed (500 rpm). To improve machining efficiency, it is preferable that the non-cutting period be as short as possible. Therefore, it is preferable that the spindle control unit 21 executes deceleration control at full power to reduce the rotational speed of the spindle 2a to 500 rpm, which is the speed at the start of the cutting period. In other words, it is preferable that the non-cutting period be set sufficiently shorter than the cutting period to improve machining efficiency. Ideally, the non-cutting period is set to the shortest time required to change the rotational speed of the spindle 2a from the second speed (600 rpm) at the end of a cutting period to the first speed (500 rpm) at the start of the next cutting period. In the example shown in FIG. 5, the non-cutting period ends at time t3 when the rotational speed of the spindle 2a is returned to the first speed, and the next cutting period resumes. At time t3, cutting may be resumed from the rotational position where cutting was interrupted at time t2.

[0037] As described above, the spindle control unit 21 executes the first control during the cutting period and the second control during the non-cutting period, and alternately executes the first control and the second control repeatedly to machine the workpiece 6. The spindle control unit 21 and the movement control unit 22 synchronously control the rotation mechanism 8 and the feed mechanism 7, respectively, thereby suppressing chatter vibration and effectively achieving intermittent cutting that cuts chips.

[0038] 5(c), in the cutting period starting at time t3, the speed fluctuation ratio for the first rotation is calculated as the ratio between the rotational speed for that rotation and the rotational speed for the final rotation in the cutting period ending at time t2. Therefore, in the cutting period starting at time t3, the speed fluctuation ratio for the first rotation is calculated to be approximately 0.86. This speed fluctuation ratio is smaller than the second threshold value Th_l, and therefore, even in the cutting period starting at time t3, the speed fluctuation ratio is outside the chatter vibration occurrence region, and chatter vibration is suppressed.

[0039] 5, the spindle control unit 21 executes a first control for accelerating the rotation of the spindle 2a during the cutting period, and executes a second control for decelerating the rotation of the spindle 2a during the non-cutting period. In a modified example, the spindle control unit 21 may execute a first control for decelerating the rotation of the spindle 2a during the cutting period so that the speed fluctuation ratio becomes a value outside the chatter vibration generation region, and execute a second control for accelerating the rotation of the spindle 2a during the non-cutting period. In this way, when the rotation of the spindle 2a is accelerated in the first control, the spindle control unit 21 may decelerate the rotation of the spindle 2a in the second control, and when the rotation of the spindle 2a is decelerated in the first control, the spindle control unit 21 may accelerate the rotation of the spindle 2a in the second control.

[0040] FIG. 6 shows another example of a control pattern in the machining method of the embodiment. Fig. 6(a) shows the displacement of the cutting edge position fed by the feed mechanism 7, Fig. 6(b) shows the fluctuation pattern of the spindle rotation speed, and Fig. 6(c) shows the transition of the speed fluctuation ratio during the cutting period. In Fig. 6(c), a first threshold value Th_h greater than 1 is the upper limit of the speed fluctuation ratio that causes chatter vibration, and a second threshold value Th_l smaller than 1 is the lower limit of the speed fluctuation ratio that causes chatter vibration. The first threshold value Th_h and the second threshold value Th_l may be calculated by simulation, or may be derived by experiment, or may be empirical values.

[0041] <Control during cutting period> During the cutting period, the movement control unit 22 causes the cutting edge of the cutting tool 10 to bite into the workpiece 6, and the spindle control unit 21 executes first control to accelerate the rotation of the spindle 2a so that the speed fluctuation ratio is a value outside the range between the first threshold value Th_h and the second threshold value Th_l (the chatter vibration generation region). The speed fluctuation ratio for the first rotation during the cutting period is maintained at 0.91, which is smaller than the second threshold value Th_l, and the speed fluctuation ratio from the second rotation during the cutting period is maintained at 1.09, which is larger than the first threshold value Th_h. The spindle control unit 21 changes the rotational speed of the spindle 2a from the first speed (500 rpm) to the second speed (600 rpm) so that the speed fluctuation ratio is a value outside the chatter vibration generation region, thereby making it possible to effectively suppress chatter vibration.

[0042] Just before the end of the cutting period, the movement control unit 22 reverses the direction of the feed motion of the cutting tool 10 by the feed mechanism 7 and causes the cutting tool 10 to retreat in the opposite direction to the feed direction. Thereafter, when the area where the tool cutting edge contacts the workpiece 6 (cutting cross-sectional area) becomes zero, the chips are cut off and the cutting period ends. During the cutting period up until the time when the direction of the feed motion is reversed, the movement control unit 22 preferably controls the relative movement of the cutting tool 10 with respect to the workpiece 6 so that the feed amount per spindle rotation is constant, thereby maintaining a constant finished surface roughness.

[0043] <Control during non-cutting periods> When the cutting period ends, a non-cutting period begins. During the non-cutting period, the movement control unit 22 maintains the cutting edge of the cutting tool 10 away from the workpiece 6 in the feed direction, so that the cutting edge of the cutting tool 10 does not cut the workpiece 6.

[0044] During the non-cutting period, the spindle control unit 21 executes second control to decelerate the rotation of the spindle 2a. In the second control, the spindle control unit 21 changes the rotation speed of the spindle 2a from the second speed (600 rpm) to the first speed (500 rpm). To improve machining efficiency, it is preferable that the non-cutting period be as short as possible, and therefore it is preferable that the spindle control unit 21 executes deceleration control at full power to lower the rotation speed of the spindle 2a to 500 rpm, the speed at the start of the cutting period. In other words, it is preferable that the non-cutting period be set sufficiently shorter than the cutting period to improve machining efficiency.

[0045] As described above, the spindle control unit 21 executes the first control during the cutting period and the second control during the non-cutting period, and alternately executes the first control and the second control repeatedly to machine the workpiece 6. The spindle control unit 21 and the movement control unit 22 synchronously control the rotation mechanism 8 and the feed mechanism 7, respectively, thereby suppressing chatter vibration and effectively achieving intermittent cutting that cuts chips.

[0046] Comparing the spindle rotation speed fluctuation pattern shown in Fig. 5(b) with the spindle rotation speed fluctuation pattern shown in Fig. 6(b), the speed fluctuation ratio during the cutting period is different, but the length of the non-cutting period (deceleration during non-cutting) and the rotation speed range during the cutting period (500 rpm to 600 rpm) are the same. As mentioned above, it is preferable that the non-cutting period be as short as possible to improve machining efficiency, so the non-cutting period in both fluctuation patterns is shown as the period when deceleration is at the limit value of deceleration.

[0047] The present inventors performed a time domain analysis of the machining method of the embodiment (hereinafter referred to as "this machining method") by keeping the magnitude of the deceleration during non-cutting and the range of rotational speed constant, and varying the speed fluctuation ratio during the cutting period (the speed fluctuation ratio from the second rotation onwards in one cutting period). The specific cutting resistance and modal parameter values used in the analysis are shown in Table 1. [Table 1]

[0048] In order to compare with the analysis results of this machining method, we also analyzed normal cutting without rotational speed fluctuations (hereinafter referred to as "normal cutting"), and a cutting method in which rotational speed fluctuations are performed using a triangular wave fluctuation pattern (the method explained as conventional method 1; hereinafter referred to as "triangular wave fluctuation cutting"). In this machining method and triangular wave fluctuation cutting, the rotational speed range was 500 rpm to 600 rpm, and the acceleration during the acceleration period and the deceleration during the deceleration period in triangular wave fluctuation cutting were set to the same absolute values as the deceleration limit value during the non-cutting period in this machining method.

[0049] Fig. 7 is a diagram for comparing the control patterns of the machining method of the embodiment and triangular wave fluctuation cutting. Fig. 7 shows the control pattern of the machining method of the embodiment when the speed fluctuation ratio from the second rotation onwards during the cutting period is 1.03. Figure 7(a) shows the displacement of the cutting edge position, Figure 7(b) shows the fluctuation pattern of the spindle rotation speed, and Figure 7(c) shows the transition of the speed fluctuation ratio during the cutting period. The control pattern of this machining method shown in Figure 7 is the same as the control pattern shown in Figure 5 (a control pattern in which the speed fluctuation ratio from the second rotation onwards during the cutting period is 1.03. Note that the speed fluctuation ratio for the first rotation during the cutting period is affected by the speed of the last rotation in the previous cutting period). Note that in triangular wave fluctuation cutting, there are no non-cutting periods, so in Figure 7(c), the transition of the speed fluctuation ratio during triangular wave fluctuation cutting is shown continuously.

[0050] The rotational speed for normal cutting was set to 561 rpm, at which point chatter vibration stability is highest within the 500-600 rpm range. For this machining method, normal cutting, and triangular wave fluctuation cutting, the feed rate during cutting (feed rate per revolution) was set to 0.05 (mm / rev). Under these conditions, a time domain analysis was performed by changing the speed fluctuation ratio during the cutting period for this machining method (the speed fluctuation ratio from the second revolution onwards in one cutting period), and the stability limit value was calculated and compared with the analytical values for triangular wave fluctuation cutting and normal cutting.

[0051] Figure 8(a) shows the analysis results showing the rate of increase from triangular wave fluctuation cutting, and Figure 8(b) shows the analysis results showing the rate of increase from normal cutting. The horizontal axis shows the speed fluctuation ratio during the cutting period of this machining method. In Figures 8(a) and (b), the plotted circles indicate the rate of increase in the stability limit, and crosses indicate the rate of increase in machining efficiency. It can be seen that as the speed fluctuation ratio of this machining method increases, both the stability limit and machining efficiency increase.

[0052] According to the machining method of the embodiment, when the speed fluctuation ratio during the cutting period is 1.09, for example, the chatter vibration stability limit increases by more than 30 times compared to triangular wave fluctuation cutting and by approximately 80 times compared to normal cutting. Furthermore, when the speed fluctuation ratio during the cutting period is 1.09, the machining efficiency improves by approximately 20 times compared to triangular wave fluctuation cutting and by more than 40 times compared to normal cutting. As described above, it has been confirmed that this machining method significantly improves the chatter vibration stability limit and machining efficiency compared to triangular wave fluctuation cutting and normal cutting. Note that this calculation of machining efficiency takes into account the decrease in efficiency due to the existence of non-cutting periods in this machining method, meaning that the significant increase in efficiency more than compensates for this decrease.

[0053] The present disclosure has been described above based on the embodiments. This embodiment is merely an example, and it will be understood by those skilled in the art that various modifications are possible in the combination of each component and each treatment process, and that such modifications are also within the scope of the present disclosure. In the embodiment, the speed fluctuation ratio is constant during the cutting period, but the speed fluctuation ratio does not necessarily have to be constant as long as it is outside the chatter vibration generation region.

[0054] In the embodiment, the ratio of the rotation speed to the feed speed is controlled to be constant during the cutting period, thereby keeping the feed marks remaining on the finished surface constant (maintaining constant roughness of the finished surface). FIG. 9 shows another example of a control pattern in the machining method of the embodiment. FIG. 9(a) shows the displacement of the cutting edge position fed by the feed mechanism 7, FIG. 9(b) shows the fluctuation pattern of the spindle rotation speed, and FIG. 9(c) shows the transition of the speed fluctuation ratio during the cutting period. In this example, the rotation speed range is expanded to 500 to 1200 rpm. FIG. 9(a) shows that the cutting edge position displaces nonlinearly rather than linearly, but by controlling the feed rate during the cutting period in accordance with the speed fluctuation ratio of the spindle rotation speed, it is possible to maintain a constant finished surface roughness. If it is not necessary to maintain a constant finished surface roughness, it is not necessary to control the ratio of the rotation speed to the feed speed to a constant value.

[0055] In the embodiment, an example is shown in which the movement control unit 22 reverses the direction in which the cutting tool 10 is fed when switching from a cutting period to a non-cutting period (when cutting is interrupted), but the movement control unit 22 may also move the cutting tool 10 backward in the feed direction while at the same time moving it in a direction that reduces the depth of cut (in a direction that moves it away from the finishing surface) so that the cutting tool 10 does not scrape against the finishing surface during the non-cutting period.

[0056] When switching the spindle rotation from acceleration to deceleration, it actually takes a short amount of time for the acceleration to decrease and the rotation to deceleration to begin. During this period when acceleration / deceleration is switched, the speed fluctuation ratio approaches 1, so it is preferable to include the period when acceleration / deceleration is switched in the non-cutting period. In this case, the spindle control unit 21 may execute a first control during the cutting period to accelerate the rotation of the spindle 2a so that the value falls outside the chatter vibration generation region, and may execute a second control during the non-cutting period to reduce the acceleration of the rotation of the spindle 2a and then decelerate the rotation of the spindle 2a.

[0057] Even when the spindle rotation is switched from deceleration to acceleration, it actually takes a short time for the deceleration rate to decrease and the rotation to accelerate. During this switching period, the speed fluctuation ratio approaches 1. However, if the speed fluctuation ratio of the first rotation of the cutting period (first step), which is the ratio of the speed fluctuation ratio to the last rotation of the previous cutting period, is originally far enough from 1 (e.g., as in Figure 5), sufficiently high chatter vibration stability can be ensured even if the speed fluctuation ratio approaches 1 slightly. Therefore, all or part of this switching period can be included in the first rotation of the cutting period. Note that all or part of this switching period may also be included in the non-cutting period. On the other hand, if the speed fluctuation ratio of the first rotation of the cutting period is not originally far enough from 1 (e.g., as in Figure 6), it is preferable to include the period during which acceleration / deceleration is switched in the non-cutting period to prevent chatter vibration stability from being lower than in other cutting periods due to the speed fluctuation ratio approaching 1 at the beginning of the cutting period.

[0058] In addition, when the spindle control unit 21 executes the first control to decelerate the rotation of the spindle 2a during the cutting period, it may execute the second control to reduce the deceleration of the rotation of the spindle 2a and then accelerate the rotation of the spindle 2a during the non-cutting period.

[0059] Although the embodiment shows an example of turning, this machining method may also be applied to milling. In this case, as described in the embodiment, milling is performed while accelerating, the feed motion is reversed to interrupt cutting, and then the milling is rapidly decelerated during a non-cutting period, after which the milling is performed again while accelerating, thereby significantly improving chatter vibration stability. Note that, although chip entanglement is rarely a problem with intermittent machining methods such as milling, as described above, the improvement in efficiency obtained by providing a non-cutting period more than compensates for the decrease in machining efficiency, so it is well worth applying this machining method to milling just for the purpose of improving chatter vibration stability.

[0060] In the machining method of the embodiment, there are many parameters, such as the fluctuation profile of the rotational speed, feed rate, and depth of cut during cutting and non-cutting periods, as well as the amplitude and period, but these can be determined taking into consideration the performance of the machine tool (maximum acceleration of the spindle and feed axis), the range of rotational speed and feed rate desired for machining, the required chatter vibration stability and frequency of chip breakage, etc. Furthermore, while only chatter vibration stability and machining efficiency were evaluated in the comparison with conventional methods, the machining method of the embodiment also simultaneously achieves prevention of entanglement due to chip breakage, and also makes it possible to overcome the decline in machining efficiency that is an issue in vibration feed cutting to prevent entanglement by not generating chatter vibration even when the depth of cut is increased.

[0061] The outline of the aspects of the present disclosure is as follows. A machining apparatus according to one embodiment of the present disclosure includes a spindle control unit that controls the rotation of a spindle to which a cutting tool or a workpiece is attached, and a movement control unit that controls the relative movement of the cutting tool with respect to the workpiece. During a cutting period in which the cutting tool cuts the workpiece, the spindle control unit executes a first control that accelerates or decelerates the rotation of the spindle so that a speed fluctuation ratio, which is the ratio of the current rotational speed to the rotational speed of the previous rotation at the same rotational position, falls outside the range between a first threshold value greater than 1 and a second threshold value less than 1. During a non-cutting period in which the cutting tool is not cutting the workpiece, the spindle control unit executes a second control that accelerates or decelerates the rotation of the spindle. The spindle control unit alternately executes the first control and the second control.

[0062] According to this aspect, the spindle control unit executes the first control to vary the rotation of the spindle during the cutting period so that the speed fluctuation ratio falls outside the range between the first threshold value and the second threshold value, thereby effectively suppressing the occurrence of regenerative chatter vibration. Also, by providing a non-cutting period, chips can be cut off.

[0063] During the cutting period, the movement control unit causes the cutting edge of the cutting tool to dig into the workpiece, and during the non-cutting period, the movement control unit sets the cutting cross-sectional area to zero. During the cutting period, the movement control unit may control the relative movement of the cutting tool with respect to the workpiece so that the feed rate per rotation of the spindle is constant. By controlling in this manner, it is possible to maintain a constant finished surface roughness.

[0064] The first threshold value may be an upper limit value of the speed fluctuation ratio that causes chatter vibration, and the second threshold value may be a lower limit value of the speed fluctuation ratio that causes chatter vibration. The first threshold value and the second threshold value may be determined by experiment or simulation. The spindle control unit may execute a first control that changes the spindle rotation speed from a first speed to a second speed, and execute a second control that changes the spindle rotation speed from the second speed to the first speed. If the spindle rotation is accelerated in the first control, the spindle control unit may decelerate the spindle rotation in the second control, and if the spindle rotation is decelerated in the first control, the spindle control unit may accelerate the spindle rotation in the second control. It is preferable that the non-cutting period be shorter than the cutting period.

[0065] Another aspect of the machining method of the present disclosure is a machining method for cutting a workpiece, which alternately performs a first step of accelerating or decelerating the rotation of the spindle during a cutting period in which the cutting tool cuts the workpiece, so that a speed fluctuation ratio, which is the ratio between the current rotational speed at the same rotational position and the rotational speed one rotation ago, becomes a value outside the range between a first threshold value greater than 1 and a second threshold value less than 1, and a second step of accelerating or decelerating the rotation of the spindle during a non-cutting period in which the cutting tool is not cutting the workpiece.

[0066] According to this aspect, by performing the first step of varying the rotational speed of the spindle so that the speed fluctuation ratio falls outside the range between the first threshold and the second threshold, the occurrence of regenerative chatter vibration can be effectively suppressed. Also, by providing a non-cutting period, chips can be cut off. [Explanation of symbols]

[0067] 1··· Machining device, 2a··· Spindle, 6··· Workpiece, 7··· Feed mechanism, 8··· Rotation mechanism, 10··· Cutting tool, 20··· Control unit, 21··· Spindle control unit, 22··· Movement control unit

Claims

1. a spindle control unit that controls the rotation of a spindle to which a cutting tool or a workpiece is attached; a movement control unit that controls the relative movement of the cutting tool with respect to the workpiece, The spindle control unit executes a first control for accelerating or decelerating the rotation of the spindle so that a speed fluctuation ratio, which is a ratio between a current rotational speed at the same rotational position and a rotational speed one rotation before, becomes a value outside a range between a first threshold value greater than 1 and a second threshold value less than 1, during a cutting period in which the cutting tool cuts the workpiece; performing a second control for decelerating or accelerating the rotation of the spindle during a non-cutting period in which the cutting tool is not cutting the workpiece; The machining device, wherein the spindle control unit alternately executes first control and second control.

2. During the cutting period, the movement control section causes the cutting edge of the cutting tool to bite into the workpiece, During a non-cutting period, the movement control unit sets the cutting cross-sectional area to zero.

2. The processing device according to claim 1.

3. During the cutting period, the movement control unit controls the relative movement of the cutting tool with respect to the workpiece so that the feed amount per rotation of the spindle is constant.

3. The processing device according to claim 2.

4. The first threshold value is an upper limit value of the speed fluctuation ratio that causes chatter vibration, and the second threshold value is a lower limit value of the speed fluctuation ratio that causes chatter vibration.

4. The processing device according to claim 1, wherein the processing device is a processing device for processing a substrate.

5. the spindle control unit executes a first control for changing the spindle rotation speed from a first speed to a second speed, and executes a second control for changing the spindle rotation speed from the second speed to the first speed; 2. The processing device according to claim 1.

6. The spindle control unit When the rotation of the spindle is accelerated in the first control, the rotation of the spindle is decelerated in the second control, When the rotation of the spindle is decelerated in the first control, the rotation of the spindle is accelerated in the second control.

2. The processing device according to claim 1.

7. The non-cutting period is shorter than the cutting period.

2. The processing device according to claim 1.

8. A processing method for cutting a workpiece, comprising: a first step of accelerating or decelerating the rotation of the spindle so that a speed fluctuation ratio, which is a ratio between a current rotational speed at the same rotational position and a rotational speed one rotation before, becomes a value outside a range between a first threshold value greater than 1 and a second threshold value less than 1 during a cutting period in which the cutting tool cuts a workpiece; a second step of decelerating or accelerating the rotation of the spindle during a non-cutting period in which the cutting tool is not cutting the workpiece;

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