Processing device and processing method

Abstract

To provide a cutting process technique that maintains a good surface quality of a finished surface by vibration feed cutting.SOLUTION: A main shaft control unit 21 controls rotation of a main shaft 2a to which a cutting tool 10 or a workpiece 6 is mounted. A movement control unit 22 controls relative movement of the cutting tool 10 with respect to the workpiece 6. The movement control unit 22 vibrates the cutting tool 10 in a feeding direction so that a cutting period in which the cutting tool 10 cuts the workpiece 6 and a non-cutting period in which the cutting tool 10 does not cut the workpiece 6 are periodically repeated. The main shaft control unit 21 controls rotation of the main shaft 2a so that a cutting speed during a start period or an end period of the cutting period is higher than a cutting speed during an intermediate period between the start period and the end period.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] In cutting, chips are continuously discharged and can 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. When the chips are curled by the chip breaker and collide with the workpiece or tool, they are easily broken up 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 may not break up even when they collide with the workpiece or tool.

[0003] Non-Patent Document 1 discloses vibration feed cutting, which intermittently cuts a workpiece by vibrating the tool in the feed direction while feeding it at a constant static feed rate in the feed direction. By appropriately setting the amplitude and period of vibration in the feed direction, vibration feed cutting can reliably cut chips and eliminate the problem of chip entanglement.

[0004] Figure 1(a) shows vibration feed cutting. In vibration feed cutting, the cutting tool is vibrated in the feed direction so that cutting periods in which the cutting tool cuts the workpiece and non-cutting periods in which the cutting tool does not cut the workpiece are repeated periodically. By periodically generating non-cutting periods in which the tool is not cutting by retracting the tool in the feed direction from the workpiece, intermittent cutting that reliably cuts chips is achieved.

[0005] Figure 1(b) shows an example of 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 static 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 during which the tool cuts the workpiece (periods in the dotted areas in Figure 1(b)) alternate with non-cutting periods during which the tool does not cut the workpiece. This intermittent cutting of the workpiece intermittently cuts the chips, preventing them from becoming entangled in the workpiece or the tool. [Prior art documents] [Non-patent literature]

[0006] [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]

[0007] Figure 2 shows a photograph of the surface of a workpiece that has been finished using conventional vibration feed cutting. The finished surface shown in Figure 2 is dotted with cloudy streaks. As such, the problem with conventional vibration feed cutting is that the surface quality of the finished surface is prone to deterioration.

[0008] The present disclosure has been made in view of these circumstances, and its purpose is to provide a cutting technique that maintains good surface quality of the finished surface obtained by vibration feed cutting. [Means for solving the problem]

[0009] In order to solve the above problems, one embodiment of the processing device of the present invention is a processing device that 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, wherein the movement control unit vibrates the cutting tool in the feed direction so that cutting periods in which the cutting tool cuts the workpiece and non-cutting periods in which the cutting tool does not cut the workpiece are repeated cyclically, and the spindle control unit controls the rotation of the spindle so that the cutting speed in the start period or end period of the cutting period is higher than the cutting speed in an intermediate period between the start period and the end period.

[0010] Another aspect of the present invention is a method for machining a workpiece with a cutting tool, comprising a step of vibrating the cutting tool in a feed direction so that a cutting period in which the cutting tool cuts the workpiece and a non-cutting period in which the cutting tool does not cut the workpiece are repeated cyclically, and the rotation of the spindle is controlled so that the cutting speed in a start period or an end period of the cutting period is higher than the cutting speed in an intermediate period between the start period and the end period.

[0011] 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]

[0012] [Figure 1] FIG. 10 is a diagram for explaining vibration feed cutting. [Figure 2] This is a photograph of the finished surface obtained by conventional vibration feed cutting. [Figure 3] 1 is a diagram showing a schematic configuration of a processing apparatus according to an embodiment; [Figure 4] Photographs of the finished surface when cutting at different feed rates. [Figure 5] FIG. 10 is a diagram showing the measurement results of the finished surface roughness when cutting at different cutting speeds. [Figure 6] FIG. 10 is a diagram showing the relationship between the spindle rotation angle and the tool position in the feed direction in vibration feed cutting. [Figure 7]10A to 10C are diagrams illustrating examples of control patterns in the machining method of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] FIG. 3 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.

[0014] 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.

[0015] 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 the spindle control unit 21 may control the rotation of the spindle 2a to which the cutting tool 10 is attached. Furthermore, the feed mechanism 7 may move the cutting tool 10 relative to the workpiece 6, and may have a mechanism for moving at least one of the cutting tool 10 and the workpiece 6.

[0016] In the processing device 1 of the embodiment, the movement control unit 22 vibrates the cutting tool 10 in the feed direction so that cutting periods in which the cutting tool 10 cuts the workpiece 6 and non-cutting periods in which the cutting tool 10 does not cut the workpiece 6 are periodically repeated. In other words, the processing device 1 of the embodiment is a vibration feed cutting device that periodically generates non-cutting periods in which the cutting tool 10 moves away from the workpiece 6 in the feed direction and does not cut, thereby achieving intermittent cutting that reliably cuts chips.

[0017] As shown in Figure 2, the surface of a workpiece that has been finish-machined using conventional vibration feed cutting may have scattered areas that resemble cloudy streaks. The present inventors conducted the experiments described below to investigate the cause of the deterioration of the properties of the finished surface caused by conventional vibration feed cutting.

[0018] First, the present inventors used a microscope to observe the finished surface to investigate the relationship between the machining traces left on the finished surface and the locations where the problematic streaks occurred. As a result, they found that the streaks occurred at the location where cutting and non-cutting transitions took place. The present inventors speculated that the cause of the streaks was that, because the uncut thickness is smaller at the location where cutting and non-cutting transitions, the cutting temperature at that location dropped, creating conditions that made it easier for the metal workpiece material to adhere to the tool.

[0019] To verify the above speculation, the present inventor fixed the cutting speed V at 100 m / min, set the feed rate F per revolution in the range of 0.01 to 0.08 mm / rev, performed longitudinal turning of steel, and observed the finished surface at each feed rate. Note that in this experiment, normal turning (turning without vibrating the tool in the feed direction) was performed, rather than vibration feed cutting.

[0020] Figure 4 shows photographs of the finished surfaces when turning at different feed rates. It also shows the finished surfaces when turning with feed rates (F) set to 0.01 mm / rev, 0.02 mm / rev, 0.03 mm / rev, 0.04 mm / rev, 0.05 mm / rev, 0.06 mm / rev, 0.07 mm / rev, and 0.08 mm / rev. The photographs in Figure 4 reveal that a high-gloss surface is obtained when the feed rate (F) is 0.04 mm / rev or higher. However, when the feed rate (F) is 0.03 mm / rev or lower, the amount of adhesion of the workpiece material to the tool increases as the feed rate decreases, resulting in a hazy, whitish finished surface.

[0021] Next, the present inventor fixed the feed rate per revolution F at 0.01 mm / rev and set multiple cutting speeds V in the range of 100 to 240 m / min, performed longitudinal turning of steel, and measured the finished surface roughness at each cutting speed. Note that in this experiment, normal turning was performed instead of vibration feed cutting.

[0022] Figure 5 shows the measurement results of the finished surface roughness when cutting at different cutting speeds. In Figure 5, the vertical axis represents the unevenness of the finished surface, and the horizontal axis represents the position in the feed direction. Figure 5 also shows the measurement results of the surface roughness of the finished surface when turning was performed at cutting speeds V of 100 m / min, 120 m / min, 140 m / min, 160 m / min, 180 m / min, 200 m / min, 220 m / min, and 240 m / min. The measurement results shown in Figure 5 confirm that when the cutting speed V is 180 m / min or higher, the surface roughness is small and a good finished surface can be obtained, but when the cutting speed V is 160 m / min or lower, the surface roughness is large and a good finished surface cannot be obtained.

[0023] It is known that adhesion, where a part of the workpiece material adheres to the cutting edge, does not occur once the cutting point temperature exceeds a certain value determined by the relationship between the workpiece material and the cutting edge material. While adhesion is likely to occur in a temperature range lower than this cutting point temperature, the work-hardened state cannot be maintained in a temperature range higher than the cutting point temperature, and therefore adhesion of the adhered material does not persist.

[0024] The temperature at the cutting point increases with increasing chip thickness and / or cutting speed. The observation results shown in Figure 4 confirm that a good glossy surface can be obtained when the feed rate (F), which correlates with chip thickness, is 0.04 mm / rev or higher. The measurement results shown in Figure 5 confirm that a good surface finish can be obtained when the cutting speed (V), which correlates with chip thickness, is 180 m / min or higher. Comparing the effects of cutting speed and chip thickness on the temperature at the cutting point, the effect of cutting speed is greater. Therefore, in the two experiments described above, similar changes in the finished surface (gouging) were observed even though the range of change in feed rate (correlated with chip thickness) was 8 times (0.01 to 0.08 mm / rev) compared to the range of change in cutting speed (2.4 times (100 to 240 m / min)).

[0025] From the above demonstration experiments, the present inventors have found that in conventional vibration feed cutting, the instantaneous feed rate F decreases near the transition between cutting and non-cutting, causing the cutting point temperature to drop to a temperature range that causes adhesion, making the workpiece more likely to adhere to the cutting tool and resulting in poor finished surface roughness. Based on this understanding of the phenomenon, the processing apparatus 1 of the present disclosure compensates for the decrease in cutting point temperature during vibration feed cutting by increasing the cutting speed (rotational speed), thereby suppressing the decrease in cutting point temperature and reducing or suppressing deterioration of the finished surface (e.g., ripping or adhesion of the workpiece to the cutting tool). Specifically, the processing apparatus 1 increases the cutting speed (rotational speed) near the timing when the cutting period switches to the non-cutting period during vibration feed cutting, thereby reducing or suppressing deterioration of the finished surface.

[0026] Figure 6 shows the relationship between the spindle rotation angle and the tool position (cutting edge position) in the feed direction during vibration feed cutting. Line a shows the cutting edge position at the (N-3)th rotation, line b shows the cutting edge position at the (N-2)th rotation, line c shows the cutting edge position at the (N-1)th rotation, and line d shows the cutting edge position at the Nth rotation. "Feed" indicates the static feed amount per rotation.

[0027] In the machining apparatus 1, the movement control unit 22 feeds the cutting tool 10 in the feed direction at a static feed rate while vibrating the cutting tool 10 in the feed direction so that a cutting period during which the cutting tool 10 cuts the workpiece 6 and a non-cutting period during which the cutting tool 10 does not cut the workpiece 6 are periodically repeated. In the vibration pattern of the cutting tool 10 shown in FIG. 6, the cutting tool 10 vibrates in the feed direction 2.5 times per rotation of the spindle 2a. During the cutting period, the area between line d and line c or line b (the dotted area in FIG. 6) represents the dynamically changing instantaneous feed rate. As described above, the instantaneous feed rate is correlated with the chip thickness. Therefore, an increase in the instantaneous feed rate increases the chip thickness, while a decrease in the instantaneous feed rate decreases the chip thickness.

[0028] As shown in Figure 6, the cutting period is divided into a start period T1, an intermediate period T2, and an end period T3. The start period T1 is the period between rotation angle P1, which indicates the start of the cutting period, and rotation angle P2, which indicates the first intersection of line c and line b. During the start period T1, the instantaneous feed rate gradually increases from the start of cutting. The intermediate period T2 is the period between rotation angle P2 and rotation angle P3, which indicates the next intersection of line b and line c. During the intermediate period T2, the instantaneous feed rate remains constant. The end period T3 is the period between rotation angle P3 and rotation angle P4, which indicates the end of the cutting period. During the end period T3, the instantaneous feed rate gradually decreases toward the end of cutting.

[0029] FIG. 7 shows an example of a fluctuation pattern in a machining method according to an embodiment. FIG. 7(a) shows the fluctuation of the tool position in the feed direction, FIG. 7(b) shows the fluctuation of the instantaneous feed rate f, and FIG. 7(c) shows the fluctuation of the spindle rotation speed. In the vibration feed cutting shown in FIG. 7, the fluctuation period of the feed rate per spindle rotation is 1.5, the amplitude is 0.05 mm, and the static (average) feed rate per rotation is 0.05 mm / rev. The instantaneous feed rate f shown in FIG. 7(b) corresponds to the chip thickness.

[0030] As shown in FIG. 7(b), the instantaneous feed rate f remains constant at a maximum value fmax during the intermediate period. Therefore, the chip thickness is maximized during the cutting period. However, since the instantaneous feed rate f during the start and end periods is smaller than the instantaneous feed rate fmax during the intermediate period, if the spindle rotation speed n is kept constant during the cutting period as in the past, the cutting point temperature during the start and end periods would be lower, potentially making the workpiece 6 more likely to adhere to the cutting tool 10. Therefore, in the machining apparatus 1 of this embodiment, the spindle control unit 21 controls the rotation of the spindle 2a so that the cutting speed during the start or end period of the cutting period is higher than the cutting speed during the intermediate period between the start and end periods. Preferably, the spindle control unit 21 controls the rotation of the spindle 2a so that the cutting speed during both the start and end periods is higher than the cutting speed during the intermediate period. Specifically, the spindle control unit 21 sets the spindle rotation speed during both the start and end periods to be higher than the spindle rotation speed during the intermediate period.

[0031] In this embodiment, the spindle control unit 21 sets the spindle rotation speed during the intermediate period to a constant value (400 rpm). During the start period, the spindle control unit 21 sets the spindle rotation speed to the maximum value (800 rpm) at the start of cutting, and gradually linearly decreases the spindle rotation speed until the start period ends (until the intermediate period begins). Here, the maximum value of the spindle rotation speed is set to a speed that does not cause adhesion of the workpiece 6 at the start of the cutting period. Furthermore, during the end period, the spindle control unit 21 gradually linearly increases the spindle rotation speed from the spindle rotation speed during the intermediate period (400 rpm) to the maximum value (800 rpm) at the end of cutting.

[0032] As described above, the spindle control unit 21 controls the rotation speed of the spindle 2a, thereby suppressing increases and decreases in the cutting point temperature due to fluctuations in the chip thickness, and reducing fluctuations in the finished surface properties.

[0033] 7(c), the spindle control unit 21 linearly varies the spindle rotation speed, but may vary it sinusoidally, exponentially, or polymorphically. The spindle control unit 21 keeps the spindle rotation speed constant in the intermediate section, but it does not necessarily have to be constant; it may be any speed that does not cause adhesion of the workpiece 6 in the intermediate section. The spindle control unit 21 sets the spindle rotation speed at the cutting start timing to its maximum value in the start period, and sets the spindle rotation speed at the cutting end timing to its maximum value in the end period, but the spindle rotation speeds at the cutting start timing and the cutting end timing may be different.

[0034] In the machining apparatus 1 of the embodiment, the spindle control unit 21 increases the cutting speed to prevent the cutting point temperature from dropping to a temperature at which the workpiece material adheres due to a decrease in the instantaneous feed rate during the start period and / or end period, thereby suppressing or reducing the drop in the cutting point temperature. In other words, during the start period and / or end period in which the finished surface may deteriorate, the spindle control unit 21 rotates the spindle 2a at a rotational speed that can prevent or reduce deterioration of the finished surface.

[0035] In the embodiment, an example has been shown in which the movement control unit 22 vibrates the tool cutting edge in a sinusoidal wave, but the vibration locus is not limited to a sinusoidal wave, and various vibration loci may be applied, such as a triangular wave, a square wave, a trapezoidal wave, etc. Whichever vibration locus is applied, the instantaneous feed rate decreases in the boundary region between the cutting period and the non-cutting period, and therefore, by increasing the cutting speed (rotational speed) in the boundary region to suppress or reduce the resulting decrease in cutting point temperature, deterioration of the finished surface is prevented or reduced.

[0036] The present disclosure has been described above based on the embodiments. These embodiments are merely examples, and it will be understood by those skilled in the art that various modifications are possible in the combination of the respective components and the respective treatment processes, and that such modifications are also within the scope of the present disclosure.

[0037] In the embodiment, an example has been shown in which the spindle control unit 21 controls the rotation of the spindle 2a in longitudinal turning, in which the diameter of the workpiece 6 does not change. In end face turning, in which the diameter of the workpiece 6 changes gradually, constant peripheral speed control may be performed, in which the rotation speed is increased on the side with a smaller diameter to suppress changes in the cutting speed. Even in such end face turning, the spindle control unit 21 may control the rotation of the spindle 2a so that the cutting speed in the start period or end period of the cutting period is higher than the cutting speed in the intermediate period between the start period and the end period.

[0038] The outline of the present disclosure is as follows. A machining apparatus according to one aspect 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. The movement control unit vibrates the cutting tool in the feed direction so that a cutting period in which the cutting tool cuts the workpiece and a non-cutting period in which the cutting tool does not cut the workpiece are periodically repeated. The spindle control unit preferably controls the rotation of the spindle so that the cutting speed in the start period or end period of the cutting period is higher than the cutting speed in an intermediate period between the start period and the end period.

[0039] The spindle control unit controls the rotation of the spindle so that the cutting speed in the start period or end period of the cutting period is higher than the cutting speed in the intermediate period, thereby preventing or reducing deterioration of the finished surface.

[0040] The spindle control unit may control the rotation of the spindle so that the cutting speed in the start period and the end period is higher than the cutting speed in the intermediate period. The spindle control unit may set the spindle rotation speed at the start timing and / or the end timing of the cutting period to the maximum value in the cutting period.

[0041] A machining method according to another aspect of the present disclosure is a method for machining a workpiece with a cutting tool, comprising a step of oscillating the cutting tool in a feed direction so that a cutting period in which the cutting tool cuts the workpiece and a non-cutting period in which the cutting tool does not cut the workpiece are cyclically repeated. In this machining method, it is preferable to control the rotation of the spindle so that the cutting speed in a start period or a finish period of the cutting period is higher than the cutting speed in an intermediate period between the start period and the finish period.

[0042] By controlling the rotation of the spindle so that the cutting speed in the start or end period of the cutting period is higher than the cutting speed in the middle period, it is possible to prevent or reduce deterioration of the finished surface. [Explanation of symbols]

[0043] 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 relative movement of a cutting tool with respect to a workpiece, wherein the movement control unit vibrates the cutting tool in a feed direction so that a cutting period in which the cutting tool cuts the workpiece and a non-cutting period in which the cutting tool does not cut the workpiece are periodically repeated, the spindle control unit controls the rotation of the spindle so that a cutting speed in a start period and / or an end period of the cutting period is higher than a cutting speed in an intermediate period between the start period and the end period. A processing device characterized by:

2. the spindle control unit sets the spindle rotation speed at the start timing and / or end timing of the cutting period to a maximum value during the cutting period.

2. The processing device according to claim 1.

3. A machining method for machining a workpiece with a cutting tool, comprising: a step of vibrating the cutting tool in a feed direction so that a cutting period in which the cutting tool cuts the workpiece and a non-cutting period in which the cutting tool does not cut the workpiece are periodically repeated; controlling the rotation of the spindle so that the cutting speed in the start period and / or the end period of the cutting period is higher than the cutting speed in an intermediate period between the start period and the end period; A processing method characterized by:

4. The spindle rotation speed at the start timing and / or end timing of the cutting period is set to the maximum value during the cutting period. The processing method according to claim 3 .

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