Machine tool

Abstract

To provide a processing route, a processing method, a machine tool and the like related to processing of a screw in which a tool load is reduced.SOLUTION: In execution of screw cutting processing, a machine tool 1 causes a workpiece W and a cutting tool 3 to move relatively to each other on a Z-axis, and causes the cutting tool 3 to vibrate in a radial direction of the workpiece W on the basis of a code of a program.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The technical field of the present application relates to a screw processing method and a machine tool capable of processing screws.

Background Art

[0002] Generally, in a machine tool performing turning, the workpiece is machined into a predetermined shape by relatively rotating a cutting tool and the workpiece along the circumferential direction of the workpiece while relatively feeding and moving along the rotation axis of the workpiece. In such processing, long continuous chips may be generated, but the long continuous chips tend to remain in the processing chamber, and it is necessary to periodically clean the chips. For this reason, the time until the workpiece is machined becomes long. Furthermore, if long chips remain in the processing chamber, there is also a possibility of damaging the workpiece or the like.

[0003] Therefore, in the machine tool shown in Patent Document 1, the chips are divided by vibrating during turning.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the processing method of Patent Document 1, as shown in FIG. 12, since a large load is applied to the tool by vibration, the frequency of tool replacement increases.

Means for Solving the Problems

[0006] Therefore, provided are a machining path, a machining method, a machine tool, etc. related to screw machining with reduced tool load.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Embodiments for Carrying Out the Invention

[0008] (Machine tool) FIG. 1 is a schematic view showing the main part of a machine tool 1. This machine tool 1 is an NC lathe that performs turning operations by rotating a workpiece W and applying a cutting tool 3 to the workpiece W. Examples of machining include outer diameter machining, inner diameter machining, drilling, profiling taper machining, grooving, end face machining, and threading. FIG. 1 shows a state in which threading is being performed on a machine tool capable of these machining operations. When performing threading, this machine tool 1 relatively moves the workpiece W and the cutting tool 3 in the Z-axis direction and vibrates the cutting tool 3 in the radial direction of the workpiece W based on the code of the program.

[0009] In the following description, the rotation axis of the workpiece W is defined as the Z-axis, the vertical direction perpendicular to the Z-axis is defined as the X-axis, and the direction perpendicular to both the X-axis and the Z-axis (the direction perpendicular to the plane of FIG. 1) is defined as the Y-axis. In FIG. 1, the radial direction of the workpiece W is parallel to the X-axis.

[0010] When adding vibration during threading, it is preferable to vibrate the tool 3a or the workpiece parallel to the X-axis, but it is not limited to this, and vibration parallel to the Y-axis or vibration in a direction having components of the X-axis and the Y-axis may also be used. Further, when adding a vibration process during threading, it is preferable to vibrate in the radial direction of the workpiece W, but any vibration in a direction including a radial vibration component may be used. For example, in FIG. 1, vibration may be performed in a direction having components of the X-axis and the Z-axis.

[0011] The machine tool 1 includes a spindle 2 (an example of a workpiece holding part) having a chuck mechanism 6 at its tip, a spindle headstock 5 that rotatably holds the spindle 2, a cutting tool 3, and a tool holding part 4 (for example, a tool post, a tool spindle) that holds the cutting tool 3 so as to be movable in the X-axis, Y-axis, and Z-axis directions. The spindle headstock 5 incorporates a spindle drive unit 11 (FIG. 2) that rotationally drives the spindle 2 and is fixed on the bed of the machine tool 1. The spindle drive unit 11 (FIG. 2) is constituted by, for example, a servo motor. And this spindle drive unit 11 functions as a rotation drive unit that relatively rotates the cutting tool 3 and the workpiece W along the circumferential direction of the workpiece W. In the present embodiment, processing is performed using the drive unit of the existing workpiece holding part and the drive unit of the tool holding part without newly installing a vibration mechanism for applying vibration to the machine tool. That is, while controlling the drive unit of the existing workpiece holding part and the drive unit of the tool holding part to perform processing, the movement of the vibration component is superimposed to relatively move the workpiece holding part and the tool holding part to perform processing. In the processing of Patent Document 1, the runout of vibration is large and the vibration is propagated to the machine tool itself. As it is, the machining quality of the screw is reduced, so the machine tool is mechanically reinforced so that the vibration is not propagated. Alternatively, a separate vibration mechanism that does not transmit vibration is attached to the machine tool. With the processing method of the present embodiment, it is possible to perform processing without attaching a separate vibration mechanism.

[0012] The cutting tool 3 in FIG. 1 is a general-purpose tool 3a for a lathe. And an example in which the tool 3a is held by the tool holding part 4 is shown.

[0013] The tool holding part 4 is driven in each axial direction by a tool feed drive unit 10 (FIG. 2). The tool feed drive unit 10 has an X-axis feed mechanism, a Y-axis feed mechanism, and a Z-axis feed mechanism that perform feed operations on the X-axis, Y-axis, and Z-axis. Each feed mechanism is constituted by, for example, a combination of a ball screw and a servo motor.

[0014] (Configuration of Machine Tool and Peripheral Devices) As shown in FIG. 2, the machine tool 1 has a first control device 20 that controls the movement of the tool 3a and the work W. The first control device 20 includes a storage unit 21 that stores programs such as a program for executing (interpreting) an NC program and sending drive signals to the spindle drive unit 11 and the tool feed drive unit 10, and a drive control unit 22 that has an OS for functioning the program. The machine tool 1 moves the work W and the tool 3a by the spindle drive unit 11 and the tool feed drive unit 10 that receive signals from the first control device 20.

[0015] The drive control unit 22 of the first control device 20 creates an operation command from the operation code of the NC program by executing (analyzing) the NC program stored in the storage unit 21, and drives the spindle drive unit 11 and the tool feed drive unit 10 based on the operation command. The drive control unit 22 is a functional unit that reads and executes the NC program stored in the storage unit 21. While sequentially reading the NC program, it recognizes (analyzes) the described NC code and performs drive control based on the described program. When the recognized NC code relates to the rotation control of the spindle 2, the drive control unit 22 transmits a corresponding control signal to the spindle drive unit 11. Further, when the recognized NC code relates to the feed control of the tool holder 4, the drive control unit 22 transmits a corresponding control signal to the tool feed drive unit 10.

[0016] The spindle drive unit 11 controls the rotation of the spindle 2, for example, the rotation speed and the forward and reverse rotation directions, according to the control signal transmitted from the drive control unit 22.

[0017] Similarly, the tool feed drive unit 10 controls the operation of the tool holder 4 according to the control signal transmitted from the drive control unit 22, for example, controls the speed (feed speed) at which the tool 3a moves (speed control), and controls the movement position of the cutting edge of the tool 3a (position control).

[0018] Further, the storage unit 21 may store the NC program itself in which a command such as "G985 A10. I0.5 K1.0" is inserted as a code for commanding the thread cutting process of the present embodiment. Also, when executing the NC program in which the thread cutting command is inserted, the storage unit 21 may store parameters (for example, setting the vibration amplitude to 0) for controlling so as not to apply vibration even to the movement path that applies vibration on the NC program. The first control device may sequentially execute the NC program in blocks while checking the values of the parameters stored in the storage unit 21.

[0019] The first control device 20 processes and executes these drive control functions and storage functions by arithmetic means such as a CPU or an LSI.

[0020] The machine tool 1 further includes a second control device 40 that controls the display on the display unit 32 of the operation panel. The second control device 40 includes a storage unit 42 that stores a program for controlling the display on the screen of the operation panel 30, a display control unit 41 that has an OS or the like for causing the program to function, and a programming unit 43 that creates an NC program.

[0021] The storage unit 42 of the second control device 40 stores programs for assisting in NC program creation, programs related to the screen display of the input screen 35 for such creation assistance, and the like. The display control unit 41 of the second control device 40 has an OS that functions these programs, and can assist in creating an NC program on the screen display of the display unit 32 while functioning these programs. The programming unit 43 creates an NC program based on the information set such as conditions from the screen for assisting in creating the NC program. For example, by simply inserting "G985 A10. I0.5 K1.0" into an existing NC program for thread cutting without vibration application, the NC program for thread cutting with vibration of the present embodiment can be easily created. Also, when automatic calculation regarding the root diameter of the thread is selected on the display screen of FIG. 10, the shape data of the same thread shape and the existing NC program for thread cutting of the same thread shape are analyzed, the root diameter of the thread is extracted, and a new NC program for thread cutting including the root diameter of the thread is generated. On the other hand, when an arbitrary numerical value (for example, X coordinate) is input into the input field for the root diameter of the thread, an NC program for thread cutting including the X coordinate is generated. Further, other parameters may be entered in the command format of "G985 A10. I0.5 K1.0". When the value of the root diameter of the thread is put into the command code format as "V_" in the aforementioned "G985 A10. I0.5 K1.0", for example, it becomes "G985 A10. V72.2 I0.5 K1.0". In this case, "V_" is an NC code that defines the execution, non - execution, and vibration direction of vibration. Also, the programming unit 43 may have functions such as directly creating and editing an NC program by directly describing NC codes such as G - codes and M - codes, and functions (code insertion unit 44) for inserting G - codes and M - codes into specific lines or blocks of an NC program.

[0022] The second control device 40 processes and executes these storage functions, display control functions, and programming functions by arithmetic means such as a CPU or LSI different from the arithmetic means of the first control device 20.

[0023] The operation panel 30 is provided with a display unit 32 (e.g., a touch panel) for displaying a program execution button 31, a screen for displaying information on programs and machine tools (e.g., coordinates), etc. An operator can perform various operations related to machining, such as various settings and creation of NC programs, while checking the display on the display unit 32 on the operation panel.

[0024] When the program execution button 31 on the operation panel 30 of the machine tool 1 is pressed, the drive control unit 22 starts the execution of the NC program. The drive control unit 22 reads the NC program stored in the storage unit 21. Then, the drive control unit 22 executes machining by controlling the spindle drive unit 11 and the tool feed drive unit 10 based on the read NC program.

[0025] In thread cutting, the spindle 2 holding the workpiece W is rotated around the Z axis by the spindle drive unit 11. Then, by specifying the position of the tool holder 4 on the X axis on the NC program by the tool feed drive unit 10, the cutting amount of the tool 3a on the X axis can be set to a predetermined value. In this state, the tool feed drive unit 10 feeds and drives the tool holder 4 in the Z axis direction to relatively move the tool 3a on a line parallel to the rotation axis of the workpiece W. In FIG. 1, the movement path (tool path) of the cutting edge of the tool 3a is shown by a broken line. As shown in FIG. 1, in thread cutting, after the cutting edge of the tool 3a is positioned at the start position (Xa, Za), it moves at a predetermined feed rate to the first cutting position (X1, Za) in the X axis direction at a predetermined cutting feed rate, and then moves to the position (X1, Z1) at a feed rate (mm / rev) per revolution according to the thread pitch to perform thread cutting on the workpiece W. Then, after moving to the relief position (Xa, Zb), it returns to the start position (Xa, Za) to complete the first thread cutting. Next, while cutting the tool 3a into the workpiece W with a predetermined cutting amount, the tool 3a is moved along the same path to perform thread cutting on the workpiece W a plurality of times. In this example, as an example, thread cutting is performed 7 times. The tool paths for multiple thread cuttings are as follows. a) First thread cutting (the first thread cutting) (Xa, Za) → (X1, Za) → (X1, Z1) → (Xa, Zb) → (Xa, Za) b) Second threading process (Second threading) (Xa, Za) → (X2, Za) → (X2, Z2) → (Xa, Zb) → (Xa, Za) c) Third threading process (Third threading) (Xa, Za) → (X3, Za) → (X3, Z3) → (Xa, Zb) → (Xa, Za) d) Fourth threading process (Fourth threading) (Xa, Za) → (X4, Za) → (X4, Z4) → (Xa, Zb) → (Xa, Za) e) Fifth threading process (Fifth threading) (Xa, Za) → (X5, Za) → (X5, Z5) → (Xa, Zb) → (Xa, Za) f) Sixth threading process (Sixth threading) (Xa, Za) → (X6, Za) → (X6, Z6) → (Xa, Zb) → (Xa, Za) g) Seventh threading process (Seventh threading) (Xa, Za) → (X7, Za) → (X7, Z7) → (Xa, Zb) → (Xa, Za) Thus, in thread cutting, the relative movement of the tool 3a is executed multiple times. The dotted line in Fig. 1 shows the movement locus of the machining point of the tool 3a. Thus, the operation of cutting the tooth surface of the screw is performed multiple times along different cutting paths that are not the same. That is, a program is not created such that the movement locus of the machining point becomes the same cutting path. The dotted line in Fig. 1 is on a straight line and is the movement locus of the machining point of the tool 3a in the conventional thread cutting. In Patent Document 1, since a vibration component is added to this machining, it is necessary to newly set the cutting position as well. This is because it only focuses on not generating long chips. On the other hand, in the present embodiment, since the load on the tool and the machine tool is considered, a vibration component is added or not added to this movement locus. Therefore, when vibration is added to the straight-line movement locus like the dotted line in Fig. 1, for example, it becomes the movement locus of the first, third, and fifth vibration cutting in Fig. 3. On the other hand, the second, fourth, and sixth machining in Fig. 3 are straight-line cutting without the addition of a vibration component. Also, the first machining and the second machining in Fig. 3 relatively move the tool 3a in the Z-axis direction from the same cutting position. Similarly, the third machining and the fourth machining in Fig. 3 relatively move the tool 3a in the Z-axis direction from the same cutting position.

[0026] Repeatedly, in the conventional thread cutting, assuming that one round of the thread machining portion of the dotted line in Fig. 1 is one cut, during the execution of one cut machining (thread machining portion), the cutting amount of the tool 3a in the X-axis (work diameter direction) with respect to the work W is kept constant.

[0027] In contrast, the NC program for thread cutting in the present embodiment creates an NC program including a code for changing the cutting amount of the tool 3a in the X-axis (radial direction) during the execution of one cut machining. In particular, it is preferable to include G-codes and M-codes in which the cutting amount changes periodically, such as the first vibration cutting in Fig. 3, in the NC program. Even if it is not a G-code or an M-code, it may be a code of a combination of symbols and numbers such as "#20240327", or a code related to vibration, such as the name of a function like "vibration frequency" or "frequency".

[0028] (NC Program) An overview for creating an NC program including codes related to vibration is described. Specifically, the creation of an NC program for thread cutting is described.

[0029] Figure 3 is a diagram showing the machining path of thread cutting when the NC program created in this embodiment is executed by the machine tool 1. The vertical axis of the figure indicates the cutting position of the thread on the X-axis of the machining point of the tool 3a, and the horizontal axis indicates the amount of movement (position of the machining point of the tool 3a) on the Z-axis of the machining point of the tool 3a, shown by the rotational speed of the work spindle. In the case of existing thread cutting without vibration, the thread can be machined by performing the linear machining on the straight line in Figure 3 three times. Even if the finishing machining is increased by one time, the thread can be machined by four times of linear machining.

[0030] On the contrary, as shown in this figure, the drive control unit 22 of this embodiment controls the relative movement between the work W and the tool 3a based on the NC program, and executes seven times to machine the thread. For example, by simply inserting one block of command code (\"G985 A10. I0.5 K1.0;\") into the NC program of existing thread cutting without vibration, the machining that imparts vibration to each of the three linear machinings and machines again can be executed by the machine tool. Therefore, the existing NC program for thread cutting can be used as it is. The machining method of Patent Document 1 may cause a load on the tool and the machine tool and a deterioration in the quality of the thread in a program that simply imparts vibration to the existing NC program for thread cutting. It is also impossible to create a machining program that appropriately overlaps two waves of machining paths just by looking at the NC program.

[0031] The drive control unit 22, based on the NC program, moves the tool holding unit 4 in the Z-axis direction relative to the workpiece at a constant speed when performing the first, third, and fifth incisions, while vibrating it in the X-axis direction (workpiece radial direction) (vibration machining). As a result, the machining point trajectory of the tool 3a held by the tool holding unit 4 (the tip trajectory of the tool 3a in FIG. 1) draws a sine-wave vibration waveform on the XZ plane. Then, based on the NC program, the drive control unit 22, based on the NC program, only moves the tool holding unit 4 in the Z-axis direction relative to the workpiece at a constant speed when performing the second, fourth, and sixth incisions, without vibrating it in the X-axis direction (workpiece radial direction) (non-vibration machining). In FIG. 3, the second, fourth, and sixth incisions are performed by moving the tool holding unit 4 in the Z-axis direction from the same incision position as the first, third, and fifth incisions, respectively. In this case, the G code and M code of the NC program are macro-programmed to perform six cutting processes by repeating vibration processing and non-vibration processing (straight line processing), and the processing path is as shown in Fig. 3. In other words, the drive control unit 22 accurately executes the contents of the command codes of the NC program.

[0032] On the other hand, when the drive control unit 22 executes the command code for the seventh (last) plunge cutting of the NC program, it only moves the tool holding unit 4 in the Z-axis direction and does not vibrate the tool holding unit 4. That is, the command code of the NC program for the seventh (last) plunge cutting performs processing such as setting the value of the address related to the amplitude of the vibration of the tool 3a to 0, deleting the address related to the vibration of the tool 3a, or ignoring the address related to the vibration of the tool 3a. When the parameter value in the first control device is set to 0 and a block for finish threading (which may be an NC code with only the X coordinate) is read in the NC program, the first control device can also perform control not to vibrate the spindle drive unit and the tool feed drive unit relative to each other on the X-axis. Then, the command code of the NC program for the seventh (last) plunge cutting sets the address of the X coordinate that sets the position of the tool holding unit 4 so that the position of the tool 3a in the X-axis direction is maintained constant. For example, when the cutting X coordinate position on the NC program corresponding to the seventh (last) plunge cutting is the same as the root diameter position of the thread, it is possible to control so that vibration is not imparted to the movement locus of the machining point in the threading at that X coordinate position. As a result, the locus of the machining point of the tool 3a held by the tool holding unit 4 will draw a straight line with a constant position on the X-axis (a locus that does not vibrate in the X-axis direction) in the XZ plane. Thereby, it is possible to prevent the shape accuracy of the finish surface from deteriorating due to the vibration of the tool 3a. Incidentally, the finish path without vibration in the X-axis direction may be performed not only for the last one of multiple plunge cuttings but also for multiple times. Also, in the threading of this embodiment, since the first half is machining with vibration and the second half is machining without vibration, it is not necessary to invalidate the vibration application. For example, when the cutting X coordinate position on the NC program is the same as the root diameter position of the thread, it may be controlled so that the lower limit of the movement locus is the X coordinate of the root diameter position, like the fifth (vibrating) threading with vibration applied. Also, the finish path may be a zero cut. The thread cutting program can also be created in this embodiment by inserting it from the code insertion section 44 of the programming section 43 of the second control device 40 of the machine tool. The input screen 35 shown in FIG. 10 is a screen for assisting in creating the thread cutting program. On this screen, by entering the X coordinate of the finish cutting position in the input field 35t for the thread valley diameter and pressing the button for the NC program, the G-code "G985" with numerical values and symbols related to the thread valley diameter described therein is inserted into the machining program. For example, it is "G985 A10. V72.2 I0.5 K1.0". Here, "G985" is an example of an NC code that defines thread cutting with vibration. If "effective" is selected in the input field 35c for chip breaking on the input screen 35 for program creation assistance, the NC code "G985 A10." is output. "A10" is an NC code that defines enabling the chip breaking cycle. Also, "I_" is an NC code that defines the frequency magnification of the vibration operation, and "K_" is an NC code that defines the amplitude magnification of the vibration. The amplitude magnification K can be set arbitrarily, but in FIG. 3, it is set to K = 1.0. Therefore, for example, a code such as "G985 A10. I0.5 K1.0" is inserted into the thread cutting program. Increasing the frequency multiplication factor I of the vibration operation or the amplitude multiplication factor K of the vibration increases the load on the tool and the machine tool. Therefore, for example, as shown in the input screen shown in FIG. 10, it is preferable to set the value in the range of 0.5 to 2.5 of the chip length from "NORMAL" (I = 0.5) to "VERY SHORT" (I = 2.5). On the input screen, the value can also be arbitrarily input. Therefore, arbitrary settings such as 1.3 and 1.4 are also possible. Also, for example, when the threshold value is set to 2.5, assume that 3.0, a number larger than 2.5, is arbitrarily input. The first control device reads 3.0, but since it is larger than the predetermined value of 2.5, control may be performed to change both the frequency multiplication factor of the vibration operation and the amplitude multiplication factor of the vibration to the set value of 2.5 and perform thread machining. Also, there may be a case where the NC program includes an NC code of "G985 A10. I0.5 K3.0". In this case, since the first control device reads the NC program and "K3.0" is larger than 2.5, although it is 3.0 on the NC program, it is possible to control it with 2.5. Thereby, the load on the tool and the machine tool can be suppressed within a certain range, and the machining accuracy of the thread can be maintained. Furthermore, in order to reduce the misinput of the frequency multiplication factor I of the vibration operation and the amplitude multiplication factor K of the vibration, it is preferable to set the input to a value with a decimal point. Furthermore, since arbitrary input is possible, there may be a case where the input is forgotten, and the frequency multiplication factor I of the vibration operation and the amplitude multiplication factor K of the vibration may not be set. In such a case, the first control device continuously uses the previously set frequency multiplication factor I of the vibration operation and the amplitude multiplication factor K of the vibration to execute and control the vibration thread machining.

[0033] Note that the form in which the tool holding part 4 moves in the Z-axis direction may not be adopted, and the form in which the work holding part moves in the Z-axis direction may be adopted. The tool path for the threading process in Fig. 3 is as follows. Assuming X0 is the outer diameter position of the thread (thread pitch X coordinate), the depth of cut is X0 - X1 (= X1 - X3 = X5 - X3). Also, the root diameter position of the thread becomes the thread finishing position (thread finishing X coordinate). Additionally, since "Standard (no vibration)" is selected in the input field 35n of the input screen, no vibration is applied during the relief operation and the tool return operation for threading. These settings can also reduce the load on the tool and the machine tool. a) First threading process (First threading operation) (Xa, Za) → (X1, Za) → With vibration → (X1, Z1) → Without vibration → (Xa, Zb) → (Xa, Za) b) Second threading process (Second threading operation) (Xa, Za) → (X1, Za) → Without vibration → (X1, Z2) → Without vibration → (Xa, Zb) → (Xa, Za) c) Third threading process (Third threading operation) (Xa, Za) → (X3, Za) → With vibration → (X3, Z3) → Without vibration → (Xa, Zb) → (Xa, Za) d) Fourth threading process (Fourth threading operation) (Xa, Za) → (X3, Za) → Without vibration → (X3, Z4) → Without vibration → (Xa, Zb) → (Xa, Za) e) Fifth threading process (Fifth threading operation) (Xa, Za) → (X5, Za) → With vibration → (X5, Z5) → Without vibration → (Xa, Zb) → (Xa, Za) f) Sixth threading process (Sixth threading operation) (Xa, Za) → (X5, Za) → Without vibration → (X5, Z6) → Without vibration → (Xa, Zb) → (Xa, Za) g) Seventh threading process (Seventh threading operation) (Xa, Za) → (X5, Za) → Without vibration → (X5, Z7) → Without vibration → (Xa, Zb) → (Xa, Za)

[0034] Here, when performing the grooving process, the NC program is programmed so that a point where the vibration waveform (vibration machining) drawn by the tip of the tool 3a in the XZ plane contacts a straight line (non-vibration machining) can be formed. In FIG. 3, the NC program is programmed so that the waveform showing the change in the cutting amount of the tool 3a on the X axis with respect to the position change on the Z axis contacts the vibration waveform in the XZ plane when performing the grooving process for the previous and subsequent passes (the previous and subsequent straight machining paths).

[0035] For example, it will be described with reference to the vibration waveform of the tool tip during the execution of the third plunge cutting and the straight line which is the movement locus of the tool tip during the execution of the fourth plunge cutting that is one execution order later. Note that the third and fourth times are cutting from the same cutting position (X coordinate) with respect to the radial direction (X axis) of the screw. For example, the command value of the X coordinate in the NC program is the same. Therefore, these two screw machining operations may be programmed as one pair. That is, for the movement loci of two linear machining operations from the same cutting position, a process may be performed in which vibration is added to one linear machining operation and vibration is not added to the other linear machining operation. The valley portion of the vibration waveform during the third plunge cutting and the straight line of the linear machining during the fourth plunge cutting are in contact with each other. The vibration waveform is triangular, but may also be arc-shaped or wave-shaped. Also, the vibration waveforms of the first, third, and fifth times are in the same phase. That is, the phase difference between the waveforms in FIG. 3 is 0°. The phase difference is not limited to this, and there may be a phase difference between the vibration waveforms. For example, the phase difference may be 180°, or may be set within a range of 90° to 270°, for example. Also, although the waveforms of the first and second times have the same period, it is not necessary for them to have the same period waveforms either. If the movement loci of the two tools 3a in vibration machining and linear (non-vibration machining) are in contact with each other at at least one location, there is an effect of separating the chips. In Patent Document 1, an idle movement path where no cutting is performed at all is created. However, if an idle movement path where the tool does not perform cutting is provided in this way, since no cutting is being performed, the movement of the tool is accelerated. And since it collides with the workpiece again in the accelerated state, the impact at that time also becomes large, and it is considered that the wear of the tool becomes faster. Therefore, it is preferable to create an NC program that sets the movement path of the tool tip to provide a contact point or an overlap of the tangent line level that can separate the chips.

[0036] By creating the NC program in this way, when performing plunge cutting with the tool 3a, with respect to the contact point with the previous plunge cutting, although it is a point, in this plunge cutting, there is no workpiece to be cut. Therefore, since the operation of cutting the workpiece with the tool 3a ends, chips are generated up to the end point. From the perspective of conventional chips, this can be said to have divided the chips. That is, non-cutting points where the plunge by the tool 3a is not performed are created. Due to the existence of a non-cutting area, although the cutting point (cutting edge) of the tool 3a is in contact with the workpiece but cannot be cut, the chips are divided. In contrast, the first control device reads a machining program including a command code corresponding to the first plunge position (for example, the positions of the first and second machining in FIG. 3), and acquires information regarding the first plunge position. Then, when the first control device determines that this first plunge position is (i) a position on the minor diameter side of the screw from the outer diameter position of the screw and (ii) the same position as the minor diameter position of the screw or a position on the outer diameter side of the screw from the minor diameter position of the screw, it executes a first screw machining (the first machining in FIG. 3) in which the tool is vibrated relatively on an axis different from the rotation axis along the rotation axis of the workpiece to cut the workpiece. When the first control device determines that this first plunge position is (i) a position on the minor diameter side of the screw from the outer diameter position of the screw and (ii) at a position from the rotation axis that is more than the same position as the minor diameter position of the screw, it does not perform vibration machining with vibration applied and executes straight machining.

[0037] As shown in FIG. 4, in each machining, by making the maximum plunge amount approximately the same, the load applied to the tool can be made uniform. As can also be seen from FIG. 4, by making the plunge amounts (depths) of the vibration machining (waveform) and the non-vibration machining (straight line) the same, and making the load applied to the tool the same in each machining pass, the service life of a single tool can be extended. As a result, the number of tool changes is reduced, so the time when screw machining cannot be performed due to tool change is reduced, and the machining efficiency also increases. Also, for the machining shown in FIG. 4, since the maximum plunge amount can be adjusted only by adjusting the amplitude of the vibration, it becomes easier to predict tool wear, and it also becomes easier to predict the tool change timing and frequency, so the setup efficiency is improved. In addition, the existing threading processing program can be used as it is, and it is easy to edit the existing processing program into the processing program of the present embodiment. FIG. 11 is an example of the NC program of the present embodiment. The X coordinates of the threading cutting path are three: N107(X72.47), N108(X72.26), and N109(X72.2). In the threading process of FIG. 4, they are the second command N107(X72.47), the fourth command N108(X72.26), and the sixth command N109(X72.2). The thread stroke for cutting the workpiece is three times. For an existing threading program, a thread can be processed by executing these three blocks. In the present embodiment, by simply inserting the start command "G985 A10. V72.2 I0.5 K1.0;" and the end command "G985 A30." into the existing program for threading, threading with vibration becomes possible. As shown in FIG. 11, by sandwiching the cutting command between the start command and the end command, as shown in FIG. 4, one thread stroke is divided into two, and the machining with vibration applied to the first half (the first stroke) is executed, and the normal machining without vibration applied to the second half (the second stroke) are executed in blocks with the same X coordinate (X72.47).

[0038] In this way, if an NC program including codes related to vibration can be created, there is no need to separately provide a high-pressure coolant device for cutting chips as in the prior art. Furthermore, since the load on the tool during conventional vibration machining of threads can be reduced, the tool can be used for a longer period than before, and the frequency of tool replacement can be decreased. This leads to a reduction in tool costs. Furthermore, since the tool replacement time is reduced, the time for machining threads on the machine tool can be ensured to be longer than before. Also, when an incorrect value of the thread root diameter is entered or the like, the NC program may include an NC code such as "G985 A10. V72.21 I0.5 K1.0;". The NC program also includes a command N109(X72.2) which is the X coordinate close to the rotary axis. In this case, the first control device can also control to perform linear machining without imparting vibration in the thread machining at the coordinate of the command N109(X72.2).

[0039] Furthermore, in the thread cutting shown in Fig. 12, during one rotation of the workpiece spindle, there are two peaks and three valleys in the vibration waveform, and it is vibrating at high speed. Therefore, when performing the thread cutting shown in Fig. 12 on a conventional machine tool, the machine tool itself vibrates, and as a result, the machining quality of the thread deteriorates. Therefore, when performing the thread cutting shown in Fig. 12, in the case of a conventional machine tool, it is necessary to reinforce the structure to be vibration-resistant. Or, measures such as attaching a vibration mechanism with vibration countermeasures to the machine tool are necessary. In the thread machining shown in Fig. 5, during four rotations of the workpiece spindle, the peaks of the vibration waveform come twice and the valleys come three times. In order to vibrate more slowly than the thread machining shown in Fig. 12, vibration can be prevented from being transmitted to the machine tool itself. As a result, without taking measures such as reinforcement on a conventional machine tool, an NC program for the thread cutting shown in Fig. 5 can be created, and machining can be enabled by executing the NC program on the current machine tool. Note that not limited to the form shown in Fig. 5, if the number of peaks of the waveform is 1 or less or the number of bottom points of the valley is 1 or less during one rotation of the workpiece spindle, the influence of vibration can be reduced compared to the machining in Fig. 12. Also, the vibration waveform is triangular, but it is not limited to this and may be arc-shaped or so-called wavy.

[0040] In Fig. 6, the peak of the amplitude of the first vibration machining is above the outer shape of the workpiece. Therefore, the maximum cutting amount by the first vibration machining can also be designed to be smaller than the maximum cutting amount in the machining from the third to the sixth times. Also, the maximum cutting amount by the second non-vibration machining (linear machining) is the same as the maximum cutting amount by the first vibration machining. By doing so, the maximum cutting depths for the first and second times can be reduced.

[0041] In FIG. 7, the peak portion of the movement locus of the tool in the third vibration machining protrudes above the movement locus of the tool in the second straight machining, resulting in a machining path. By doing so, the maximum cutting depths for the third and fourth times can be made smaller than the maximum cutting depth in the first machining, and the load on the tool can be reduced. When combining the machining path concept in FIG. 6 and the machining concept in FIG. 7, it is also possible to design the maximum cutting depths from the first to the sixth times to be the same. Also, it is possible to design to reduce the difference between the maximum cutting depths for the first and second times and the maximum cutting depths from the fourth to the sixth times. Therefore, it is also appropriate to provide a function on the operation screen to adjust the distance from the peak to the straight line. According to the material of the material, the maximum cutting depth, and the cutting time, the wear degree of the tool is measured in advance and stored as data. When the operator sets up the threading machining, if there is a function to calculate the tool replacement timing from the tool wear and display the maximum cutting depth and the tool replacement timing, the operator can also operate intuitively.

[0042] Among the NC programs for threading that include codes related to vibration, it is preferable that the NC program for threading further includes a command code for reducing the vibration amplitude in the X-axis direction of the tool holder 4 as the execution order of the cutting machining is later. The vibration amplitude of the vibration waveform at the tool tip decreases. In the threading machining shown in FIG. 8, when the amplitudes of the tool tip at the first, third, and fifth cutting machinings are A 1、 A 3、 A 5 , it can be seen that the relationship of the amplitude magnitudes satisfies A 1 > A 3 > A 5 .

[0043] According to this, the later the execution order of the grooving process is (that is, the closer the grooving process is from the rough machining process to the finishing process), the smaller the vibration amplitude of the tool 3a becomes. Therefore, in the finishing process where shape accuracy is required, the vibration amplitude of the tool 3a can be reduced to improve the threading accuracy by the tool 3a.

[0044] FIG. 9 shows a machining path that combines the concept of FIG. 8 and the concept of FIG. 7. Depending on the type of screw, it is also conceivable to perform cutting with a machining path as shown in FIG. 9. For the fourth threading in FIG. 9, non-vibrating machining is performed in response to a command for the first cutting position (for example, X72.26). Thereafter, for the fifth threading, vibrating machining is performed in response to a command for the second cutting position (for example, X72.2) which is deeper than the fourth cutting position. The vibration vibrates in a direction where the cutting depth becomes shallower with the second cutting position as the base. Therefore, the machining path of the fifth threading becomes like a triangular wave with peaks connected. The peak of the wave is at a position (for example, X72.28) where the cutting depth is shallower than the first cutting position (for example, X72.26). Above the first cutting position, since there is no workpiece, chips are generated where it is cut. On the other hand, the deepest position of the wave in the machining path of the fifth threading is at the second cutting position (for example, X72.2). This is because if the cutting depth is deeper than this, the surface quality of the screw changes. Thereafter, for the sixth threading, machining is performed without applying vibration in response to a command for the second cutting position (for example, X72.2). On the machining program, since the machining paths overlap at points, short chips are generated. Although there may be some errors depending on the performance of the machine tool and the chips may remain connected, since they are in a very thin state, the chips may break and be separated. From these, for example, the following machine tools and the like can be provided. Of course, it is also possible to provide a control method for a machine tool, a control device for a machine tool, a machining program editing device for threading, a machining program editing method for threading, a machining method for a screw, and the like. (1) Machine tool A A tool holding part for holding a tool, A work holding part for holding a work, (i) From a first cutting position on an axis orthogonal to the rotation axis of the work, along the rotation axis of the work, a screw machining for cutting the work along the rotation axis, which is a first screw machining for cutting the work by vibrating the tool relatively on an axis different from the rotation axis, and (ii) a second screw machining for linearly cutting the work along the rotation axis of the work from the first cutting position along the rotation axis of the work, and a drive control unit for driving and controlling the tool holding part and the work holding part so as to perform the above, a machine tool. (1) Control device A of a machine tool A control device for a machine tool including a tool holding part for holding a tool and a work holding part for holding a work, (i) From a first cutting position on an axis orthogonal to the rotation axis of the work, along the rotation axis of the work, a screw machining for cutting the work along the rotation axis, which is a first screw machining for cutting the work by vibrating the tool relatively on an axis different from the rotation axis, and (ii) a second screw machining for linearly cutting the work along the rotation axis of the work from the first cutting position along the rotation axis of the work, and a control device for a machine tool for controlling the above. (2) Machine tool B A tool holding part for holding a tool, A work holding part for holding a work, (i) From a first cutting position on an axis orthogonal to the rotation axis of the work, along the rotation axis of the work, a first screw machining for cutting the work by vibrating the tool relatively on an axis different from the rotation axis, and (ii) a second screw machining for linearly cutting the work along the rotation axis of the work from a second cutting position on an axis orthogonal to the rotation axis of the work, and driving and controlling the tool holding part and the work holding part so as to perform the above, and reading a machining program including a command code corresponding to the first cutting position, and when the first cutting position read from the machining program is (i) a position on the minor diameter side of the screw from the outer diameter position of the screw and (ii) the same position as the minor diameter position of the screw or a position on the outer diameter side of the screw from the minor diameter position of the screw, a control device for executing the first screw machining, a machine tool. (3) Machine tool C A tool holding part for holding a tool, A work holding part for holding a work, (i) From a first cutting position on an axis orthogonal to the rotation axis of the work, along the rotation axis of the work, a first thread cutting for cutting the work by vibrating the tool relatively on an axis different from the rotation axis; and (ii) a second thread cutting for linearly cutting the work along the rotation axis of the work from a second cutting position on an axis orthogonal to the rotation axis of the work. A control device that drives and controls the tool holding part and the work holding part to perform the above operations, reads a machining program including an amplitude magnification factor K, and when the amplitude magnification factor K read from the machining program is larger than a predetermined value, changes the amplitude magnification factor K to a predetermined value and executes the first thread cutting. A machine tool comprising the above components. (4) Machine tool D A tool holding part for holding a tool, A work holding part for holding a work, (i) From a first cutting position on an axis orthogonal to the rotation axis of the work, along the rotation axis of the work, a first thread cutting for cutting the work by vibrating the tool relatively on an axis different from the rotation axis; and (ii) a second thread cutting for linearly cutting the work along the rotation axis of the work from a second cutting position on an axis orthogonal to the rotation axis of the work. A control device that drives and controls the tool holding part and the work holding part to perform the above operations, and when the amplitude magnification factor of vibration is not set, uses the set value of the previously set amplitude magnification factor K to execute the first thread cutting. A machine tool comprising the above components. (5) Machine tool E A tool holding part for holding a tool, A work holding part for holding a work, (i) From a first cutting position on an axis orthogonal to the rotation axis of the workpiece, along the rotation axis of the workpiece, a first threading operation of cutting the workpiece by vibrating the tool relatively on an axis different from the rotation axis; and (ii) from a second cutting position on an axis orthogonal to the rotation axis of the workpiece, along the rotation axis of the workpiece, a second threading operation of cutting the workpiece linearly. A control device drives and controls the tool holding part and the workpiece holding part so as to perform the above operations. When the frequency multiplication factor I of the vibration operation is not set, the control device uses the previously set value of the frequency multiplication factor I to execute the first threading operation. A machine tool comprising the control device. (6) Machine tool F A tool holding part for holding a tool; A workpiece holding part for holding a workpiece; (i) From a first cutting position on an axis orthogonal to the rotation axis of the workpiece, (i-1) relatively move the tool along the rotation axis of the workpiece by a first distance, and (i-2) after moving the first distance, while continuously relatively moving the tool along the rotation axis, vibrate the tool relatively on an axis different from the rotation axis to cut the workpiece, which is the first threading operation; and (ii) (ii-1) from a second cutting position on an axis orthogonal to the rotation axis of the workpiece, relatively move the tool along the rotation axis of the workpiece by a first distance, and (ii-2) after moving the first distance, linearly cut the workpiece along the rotation axis, which is the second threading operation. A control device drives and controls the tool holding part and the workpiece holding part so as to perform the above operations. A machine tool comprising the control device.

Explanation of reference numerals

[0045] W Workpiece 1 Machine tool 2 Spindle (workpiece holding part) 3a Thread cutting tool (tool) 4 Tool holding part 10 Tool feed drive part (feed drive part) 11 Spindle drive part (rotation drive part) 23 Drive control part (thread cutting control part)

Claims

[Claim 1] A tool holding portion for holding a tool; A workpiece holder that holds the workpiece; a drive control unit that drives and controls the tool holding unit and the work holding unit to perform: (i) a first thread machining operation in which the workpiece is cut along the rotation axis of the workpiece from a first cutting position on an axis perpendicular to the rotation axis of the workpiece, the first thread machining operation being performed by vibrating a tool relatively on an axis different from the rotation axis to cut the workpiece; and (ii) a second thread machining operation in which the workpiece is cut in a straight line along the rotation axis of the workpiece from the first cutting position.

Images