Machine tool

Abstract

To provide a processing route, a processing method, a machine tool and the like, related to processing of a screw reducing a tool load.SOLUTION: A machine tool comprises a drive control part that controls a tool holding part 4 and a workpiece holding part 2 so as to be capable of executing a combination of vibration processing for performing cutting while relatively vibrating a tool 3 along an axis different from a rotation axis of a workpiece W, and non-vibration processing for performing cutting by linearly moving the tool 3 along the rotation axis, when a screw is processed along the rotation axis by adding a code for issuing a command of the vibration processing to an existing NC program for screw processing.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technical field of the present application relates to a method for machining a screw and a machine tool capable of machining a screw. [Background technology]

[0002] Generally, in machine tools that perform turning, the cutting tool and workpiece are rotated relative to each other along the circumferential direction of the workpiece while the workpiece is fed relatively along the rotation axis of the workpiece to machine the workpiece into a desired shape. This type of machining can produce long, continuous chips, which tend to remain in the machining chamber and require regular chip cleaning. This increases the time required to machine the workpiece. Furthermore, if long chips remain in the machining chamber, they may damage the workpiece or other components.

[0003] Therefore, in the machine tool shown in Patent Document 1, chips are broken up by vibrating the machine during turning. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 10610993 (Patent No. 6914840) Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the machining method of Patent Document 1, as shown in FIG. 12, a large load is applied to the tool due to vibration, which increases the frequency of tool replacement. [Means for solving the problem]

[0006] Therefore, the present invention provides a machining path, machining method, machine tool, etc. for thread machining that reduces the load on the tool. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is an explanatory diagram illustrating an example of a schematic configuration of a machine tool. [Figure 2] FIG. 2 is a block diagram showing the configuration of a machine tool. [Figure 3] 10 is a diagram showing an example of a movement trajectory of a machining point of a tool relative to a change in position of the Z axis; [Figure 4] 10 is a diagram showing an example of a movement trajectory of a machining point of a tool relative to a change in position of the Z axis; [Figure 5] 10 is a diagram showing an example of a movement trajectory of a machining point of a tool relative to a change in position of the Z axis; [Figure 6] 10 is a diagram showing an example of a movement trajectory of a machining point of a tool relative to a change in position of the Z axis; [Figure 7] 10 is a diagram showing an example of a movement trajectory of a machining point of a tool relative to a change in position of the Z axis; [Figure 8] 10 is a diagram showing an example of a movement trajectory of a machining point of a tool relative to a change in position of the Z axis; [Figure 9] 10 is a diagram showing an example of a movement trajectory of a machining point of a tool relative to a change in position of the Z axis; [Figure 10] 10 is an explanatory diagram showing an input screen displayed on the display unit of the operation panel by the programming unit. FIG. [Figure 11] FIG. 2 is an explanatory diagram showing an example of an NC program created by a programming unit. [Figure 12] Diagram showing conventional processing method DETAILED DESCRIPTION OF THE INVENTION

[0008] (machine tools) FIG. 1 is a schematic diagram showing the main components of a machine tool 1. This machine tool 1 is an NC lathe that performs turning by rotating a workpiece W and bringing a cutting tool 3 into contact with the workpiece W. Examples of such machining include external diameter machining, internal diameter machining, drilling, profiling taper machining, grooving, end face machining, and thread cutting. FIG. 1 shows a state in which a thread cutting operation is being performed on a machine tool capable of these operations. When performing thread cutting, this machine tool 1 moves the workpiece W and the cutting tool 3 relatively on the Z axis and vibrates the cutting tool 3 in the radial direction of the workpiece W based on program codes.

[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 paper surface of FIG. 1) is defined as the Y axis. In FIG. 1, the radial direction of the workpiece W and the X axis are parallel to each other.

[0010] When applying vibration in thread cutting, it is preferable to vibrate the tool 3a or workpiece parallel to the X-axis, but this is not limitative and vibration may be parallel to the Y-axis or in a direction having components of the X and Y axes. Also, when applying vibration treatment in thread cutting, it is preferable to vibrate in the radial direction of the workpiece W, but any direction including a radial vibration component will do. For example, in the case of Figure 1, vibration may be in a direction having components of the X and Z axes.

[0011] The machine tool 1 includes a spindle 2 (an example of a workpiece holder) having a chuck mechanism 6 at its tip, a headstock 5 that rotatably holds the spindle 2, a cutting tool 3, and a tool holder 4 (e.g., a tool rest or tool spindle) that holds the cutting tool 3 movably along the X-, Y-, and Z-axes. The headstock 5 incorporates a spindle drive unit 11 (FIG. 2) that rotates the spindle 2 and is fixed to the bed of the machine tool 1. The spindle drive unit 11 (FIG. 2) is formed, for example, by a servo motor. The spindle drive unit 11 functions as a rotation drive unit that rotates the cutting tool 3 and the workpiece W relative to each other in the circumferential direction of the workpiece W. In this embodiment, machining is performed using the existing drive units of the workpiece holder and the tool holder without installing a new vibration mechanism for applying vibration to the machine tool. In other words, machining is performed by controlling the existing drive units of the workpiece holder and the tool holder, while the workpiece holder and the tool holder are moved relative to each other with the vibration movement superimposed thereon. The machining method disclosed in Patent Document 1 has large vibration swings that propagate to the machine tool itself, which, if left unchecked, reduces the quality of thread machining. Therefore, the machine tool is mechanically reinforced to prevent the vibration from propagating. Alternatively, a separate vibration mechanism that prevents vibration from propagating is attached to the machine tool. However, the machining method of this embodiment makes it possible to perform machining without the need to attach a separate vibration mechanism.

[0012] 1 is a general-purpose tool 3a for a lathe, and an example is shown in which the tool 3a is held by a tool holder 4.

[0013] The tool holder 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 configured, for example, by combining a ball screw and a servo motor.

[0014] (Configuration of machine tools and peripheral devices) As shown in Fig. 2, machine tool 1 has a first control device 20 that controls the movement of tool 3a and workpiece W. First control device 20 has a memory unit 21 that stores programs and the like for executing (interpreting) NC programs and sending drive signals to spindle drive unit 11 and tool feed drive unit 10, and a drive control unit 22 that has an OS and the like that makes the programs function. In machine tool 1, spindle drive unit 11 and tool feed drive unit 10 receive signals from first control device 20 and move workpiece W and tool 3a.

[0015] The drive control unit 22 of the first control device 20 executes (analyzes) the NC program stored in the memory unit 21 to create operation commands from the operation codes of the NC program, and drives the spindle drive unit 11 and the tool feed drive unit 10 based on the operation commands. The drive control unit 22 is a functional unit that reads and executes the NC program stored in the memory unit 21, and while sequentially reading the NC program, recognizes (analyzes) the written NC code and controls the drive based on the written program. If the recognized NC code relates to rotation control of the spindle 2, the drive control unit 22 transmits a corresponding control signal to the spindle drive unit 11. Furthermore, if the recognized NC code relates to 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 / reverse direction of rotation, in accordance with a control signal sent from the drive control unit 22.

[0017] Similarly, the tool feed drive unit 10 controls the operation of the tool holding unit 4 in accordance with a control signal transmitted from the drive control unit 22, for example, controls the speed (feed speed) at which the tool 3a is moved (speed control), and also controls the movement position of the cutting edge of the tool 3a (position control).

[0018] The storage unit 21 may also store the NC program itself into which a command such as "G985 A10. I0.5 K1.0" is inserted as a code for commanding thread cutting according to this embodiment. The storage unit 21 may also store parameters (for example, setting the vibration amplitude to 0) for controlling the NC program so that vibration is not applied even to a movement path that applies vibration in the NC program when the NC program is executed. The first control device may be configured to execute the NC program sequentially in block order while checking the values ​​of the parameters stored in the storage unit 21.

[0019] The first control device 20 performs these drive control functions and storage functions by processing them using a calculation means such as a CPU or an LSI.

[0020] The machine tool 1 further has a second control device 40 that controls the display on the display unit 32 of the operation panel. The second control device 40 has a memory unit 42 that stores programs and the like that control the display on the screen of the operation panel 30, a display control unit 41 that has an OS and the like that makes the programs function, and a programming unit 43 that creates NC programs.

[0021] The memory unit 42 of the second control device 40 stores programs for supporting NC program creation and programs related to the display of the input screen 35 for supporting NC program creation. The display control unit 41 of the second control device 40 has an OS that runs these programs and can support NC program creation on the screen display of the display unit 32 while running these programs. The programming unit 43 creates an NC program based on information set using the NC program creation support screen. For example, simply inserting "G985 A10. I0.5 K1.0" into an existing NC program for thread machining without vibration application can easily create an NC program for thread machining with vibration according to this embodiment. Furthermore, selecting "automatic calculation of thread root diameter" on the display screen of Figure 10 analyzes the shape data of the same thread shape or an existing NC program for thread machining with the same thread shape, extracts the thread root diameter, and generates a new NC program for thread machining that includes the thread root diameter. On the other hand, entering an arbitrary value (e.g., X coordinate) in the input field for the thread root diameter generates an NC program for thread machining that includes the X coordinate. Furthermore, other parameters may be entered into the command format of "G985 A10. I0.5 K1.0." Entering the value of the thread root diameter as "V_" into the command code format for the aforementioned "G985 A10. I0.5 K1.0" results in, for example, "G985 A10. V72.2 I0.5 K1.0." In this case, "V_" is an NC code that defines whether vibration is to be performed, not performed, and the vibration direction. The programming unit 43 may also have a function for directly entering NC codes such as G-codes and M-codes to directly create and edit NC programs, and a function for inserting G-codes and M-codes into specific lines or blocks of an NC program (code insertion unit 44).

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

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

[0024] The drive control unit 22 starts executing the NC program when the program execution button 31 on the operation panel 30 of the machine tool 1 is pressed. The drive control unit 22 reads the NC program stored in the memory unit 21. Then, the drive control unit 22 controls the spindle drive unit 11 and the tool feed drive unit 10 based on the read NC program to perform machining.

[0025] In thread cutting, the spindle 2 holding the workpiece W is rotated around the Z axis by the spindle drive unit 11. Then, the position of the tool holder 4 on the X axis is specified in the NC program by the tool feed drive unit 10, so that the cutting depth 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, moving the tool 3a relatively along a line parallel to the rotation axis of the workpiece W. In Figure 1, the movement path (tool path) of the cutting edge of tool 3a is indicated by a dashed line. As shown in Figure 1, in thread cutting, the cutting edge of tool 3a is positioned at a start position (Xa, Za), and then moves at a predetermined cutting feed rate in the X-axis direction to a first cutting position (X1, Za). Then, at a feed rate per revolution (mm / rev) corresponding to the thread pitch, tool 3a moves to a position (X1, Z1) to cut the thread into the workpiece W. Tool 3a then moves to a relief position (Xa, Zb) and returns to the start position (Xa, Za), completing the first thread cutting. Next, tool 3a is moved along the same path while cutting into the workpiece W by a predetermined cutting depth, and thread cutting is performed on the workpiece W multiple times, for example, seven times in this example. The tool path for multiple thread cutting is as follows: a) First thread cutting (first thread cutting) (Xa,Za)→(X1,Za)→(X1,Z1)→(Xa,Zb)→(Xa,Za) b) Second thread cutting (secondary thread cutting) (Xa,Za)→(X2,Za)→(X2,Z2)→(Xa,Zb)→(Xa,Za) c) Third thread cutting (third thread cutting) (Xa,Za)→(X3,Za)→(X3,Z3)→(Xa,Zb)→(Xa,Za) d) Fourth thread cutting (fourth thread cutting) (Xa,Za)→(X4,Za)→(X4,Z4)→(Xa,Zb)→(Xa,Za) e) Fifth thread cutting (fifth thread cutting) (Xa,Za)→(X5,Za)→(X5,Z5)→(Xa,Zb)→(Xa,Za) f) 6th thread cutting (6th thread cutting) (Xa,Za)→(X6,Za)→(X6,Z6)→(Xa,Zb)→(Xa,Za) g) Seventh thread cutting (7th thread cutting) (Xa,Za)→(X7,Za)→(X7,Z7)→(Xa,Zb)→(Xa,Za) As described above, in thread cutting, the tool 3a moves relative to the tool 3a multiple times. The dotted line in FIG. 1 indicates the movement trajectory of the tool 3a's processing point. In this way, the thread tooth flank is cut multiple times using different cutting paths. In other words, the program is not designed to ensure that the movement trajectory of the processing point is the same cutting path. The dotted line in FIG. 1 is a straight line, representing the movement trajectory of the tool 3a's processing point in conventional thread cutting. In Patent Document 1, a vibration component is added to all of this cutting, so the cutting depth must also be newly set. This is because the focus is solely on preventing the generation of long chips. In contrast, in this embodiment, a vibration component is sometimes added to this movement trajectory and sometimes not, taking into account the load on the tool and machine tool. Therefore, if vibration is added to a linear movement trajectory like the dotted line in FIG. 1, it results in the movement trajectories of the first, third, and fifth vibration cutting passes shown in FIG. 3. On the other hand, the second, fourth, and sixth cutting passes shown in FIG. 3 are linear cuts without the addition of a vibration component. In addition, the tool 3a is moved relatively along the Z axis from the same cutting position in the first and second machining operations in Fig. 3. Similarly, the tool 3a is moved relatively along the Z axis from the same cutting position in the third and fourth machining operations in Fig. 3.

[0026] To reiterate, in conventional thread cutting, if the thread cutting portion of one revolution of the dotted line in Figure 1 is considered to be one cut, the amount of cut of the tool 3a on the X-axis (radial direction of the workpiece) into the workpiece W is kept constant while one cut is being performed (thread cutting portion).

[0027] In contrast, the NC program for thread cutting in this embodiment is an NC program that includes code for changing the amount of cutting in the X-axis (radial) direction of the tool 3a during one cutting operation. In particular, it is preferable to include G code or M code in the NC program, in which the amount of cutting periodically changes, as in the first vibration cutting in Figure 3. Instead of G code or M code, codes related to vibration, such as a code combining symbols and numbers like "#20240327" or the name of a function like "vibration frequency" or "frequency", can also be used.

[0028] (NC program) This article provides an overview of how to create an NC program that includes vibration-related code. Specifically, it explains how to create an NC program for thread machining.

[0029] 3 is a diagram showing a machining path for thread cutting when the NC program created in this embodiment is executed by the machine tool 1. The vertical axis of the diagram indicates the thread cutting position on the X axis of the machining point of the tool 3a, and the horizontal axis indicates the movement amount on the Z axis of the machining point of the tool 3a (the position of the machining point of the tool 3a) in terms of the rotation speed of the work spindle. With existing vibration-free screw machining, screws can be machined by performing the linear machining shown in Figure 3 three times. Even if finishing machining is added by one time, screws can be machined with four linear machining operations.

[0030] In contrast, as shown in this figure, the drive control unit 22 of this embodiment executes the NC program seven times to machine a thread by controlling the relative movement between the workpiece W and the tool 3a. For example, by simply inserting one command code block ("G985 A10. I0.5 K1.0;") into an existing vibration-free NC program for thread machining, a machine tool can perform three linear machining operations, each with vibration applied. This allows existing NC programs for thread machining to be used as is. The machining method of Patent Document 1 simply applies vibration to an existing NC program for thread machining, which can place a strain on the tool and machine tool and reduce the quality of the thread. It is also impossible to create a machining program that properly overlaps two wave machining paths simply by looking at the NC program.

[0031] Based on the NC program, the drive control unit 22 moves the tool holder 4 in the Z-axis direction relative to the workpiece while vibrating it in the X-axis direction (the workpiece radial direction) during the first, third, and fifth cuts (vibration machining). As a result, the machining point trajectory of the tool 3a held by the tool holder 4 (the trajectory of the tip of the tool 3a in FIG. 1) traces a sinusoidal vibration waveform on the XZ plane. Based on the NC program, the drive control unit 22 only moves the tool holder 4 in the Z-axis direction relative to the workpiece at a constant speed without vibrating it in the X-axis direction (the workpiece radial direction) during the second, fourth, and sixth cuts (non-vibration machining). In FIG. 3, the second, fourth, and sixth cuts are performed by moving the tool holder 4 in the Z-axis direction from the same cut position as the first, third, and fifth cuts, respectively. In this case, macro programming is performed using the G code and M code of the NC program to perform six cutting operations that alternate between vibration machining and non-vibration machining (linear machining), and the machining path is as shown in Figure 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 executing the seventh (final) cutting command code of the NC program, the drive control unit 22 only moves the tool holder 4 in the Z-axis direction but does not vibrate the tool holder 4. In other words, the NC program command code for the seventh (final) cutting is processed by setting the address value related to the vibration amplitude 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 finish thread machining block (which may be NC code with only the X-coordinate) is loaded in the NC program, the first control device can also control the spindle drive unit and the tool feed drive unit so that they do not vibrate relative to each other on the X-axis. Then, the NC program command code for the seventh (final) cutting sets the X-coordinate address, which sets the position of the tool holder 4, to a constant value so that the position of the tool 3a in the X-axis direction is maintained constant. For example, if the X-coordinate position of the cutting in the NC program corresponding to the seventh (final) infeed machining is the same as the root diameter position of the thread, control can be performed so that vibration is not applied to the movement trajectory of the machining point during thread machining at that X-coordinate position. As a result, the trajectory of the machining point of the tool 3a held by the tool holder 4 will trace a straight line (a trajectory without vibration in the X-axis direction) in the XZ plane, with a constant position on the X-axis. This prevents a decrease in the shape accuracy of the finished surface due to vibration of the tool 3a. Note that this finishing pass without vibration in the X-axis direction may be performed multiple times, rather than just the last of multiple infeed machining passes. Furthermore, in this embodiment, since the first half of the thread machining is performed with vibration and the second half is not, it is not necessary to disable vibration application. For example, if the X-coordinate position of the cutting in the NC program is the same as the root diameter position of the thread, control can be performed so that the lower limit of the movement trajectory is the X-coordinate of the root diameter position, as in the fifth (vibration) thread machining pass in which vibration is applied. Furthermore, the finishing pass may be a zero cut. In this embodiment, a thread cutting program can also be created by inserting the program code from the code insertion unit 44 of the programming unit 43 of the machine tool's second control device 40. The input screen 35 shown in FIG. 10 is a screen for supporting the creation of a thread cutting program. On this screen, enter the X coordinate of the finish cut position in the thread root diameter input field 35t and press the NC program button. The "G985" G-code, which contains numerical and symbolic information related to the thread root diameter, is inserted into the machining program. For example, "G985 A10. V72.2 I0.5 K1.0." Here, "G985" is an example of an NC code that defines thread cutting with vibration. If "Enable" is selected in the chip breaking input field 35c on the program creation support input screen 35, the NC code "G985 A10." is output. "A10" is the NC code that defines the chip breaking cycle as enabled. Furthermore, "I_" is the NC code that defines the frequency magnification of the vibration operation, and "K_" is the NC code that defines the vibration amplitude magnification. The amplitude magnification K can be set arbitrarily, but in Figure 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 machining program. Increasing the vibration frequency magnification factor I or the vibration amplitude magnification factor K increases the load on the tool and machine tool. Therefore, as shown in the input screen in Figure 10, it is preferable to set values ​​in the range of 0.5 to 2.5, from "NORMAL" (I = 0.5) for the chip length to "VERY SHORT" (I = 2.5). The input screen also allows for arbitrary input of values, such as 1.3 or 1.4. For example, suppose the threshold value is set to 2.5, and a value greater than 2.5, such as 3.0, is entered. The first control device reads 3.0, but because it is greater than the predetermined value of 2.5, it may change both the vibration frequency magnification factor and the vibration amplitude magnification factor to 2.5 and perform thread machining. The NC program may also contain the NC code "G985 A10. I0.5 K3.0." In this case, the first control device reads the NC program and finds that "K3.0" is greater than 2.5, so although the NC program states that the value is 3.0, it can control the value at 2.5. This allows the load on the tool and machine tool to be kept within a certain range, maintaining the thread machining accuracy. Furthermore, to reduce the chance of incorrectly inputting the vibration operation frequency multiplier I and vibration amplitude multiplier K, it is preferable to input them as decimal values. Furthermore, since arbitrary input is possible, there is a chance that the input may be forgotten, resulting in the vibration operation frequency multiplier I and vibration amplitude multiplier K not being set. In such a case, the first control device continues to use the previously set vibration operation frequency multiplier I and vibration amplitude multiplier K to execute and control the vibration thread machining.

[0033] It is also possible to adopt a configuration in which the workpiece holder moves in the Z-axis direction, rather than the tool holder 4 moving in the Z-axis direction. The tool path for thread cutting in Figure 3 is as follows. If X0 is the external position of the thread (thread X coordinate), the depth of cut is X0 - X1 (= X1 - X3 = X5 - X3). Also, the root diameter position of the thread is the thread finish position (thread finish X coordinate). Also, because standard (no vibration) is selected in input field 35n on the input screen, no vibration is applied during the escape operation or tool return operation during thread cutting. These settings also reduce the load on the tool and machine tool. a) First thread cutting (first thread cutting) (Xa,Za) → (X1,Za) → with vibration → (X1,Z1) → without vibration → (Xa,Zb) → (Xa,Za) b) Second thread cutting (secondary thread cutting) (Xa,Za) → (X1,Za) → No vibration → (X1,Z2) → No vibration → (Xa,Zb) → (Xa,Za) c) Third thread cutting (third thread cutting) (Xa,Za) → (X3,Za) → with vibration → (X3,Z3) → without vibration → (Xa,Zb) → (Xa,Za) d) Fourth thread cutting (fourth thread cutting) (Xa,Za) → (X3,Za) → No vibration → (X3,Z4) → No vibration → (Xa,Zb) → (Xa,Za) e) Fifth thread cutting (fifth thread cutting) (Xa,Za) → (X5,Za) → with vibration → (X5,Z5) → without vibration → (Xa,Zb) → (Xa,Za) f) 6th thread cutting (6th thread cutting) (Xa,Za)→(X5,Za)→No vibration→(X5,Z6)→No vibration→(Xa,Zb) →(Xa,Za) g) Seventh thread cutting (7th thread cutting) (Xa,Za) → (X5,Za) → No vibration → (X5,Z7) → No vibration → (Xa,Zb) → (Xa,Za)

[0034] Here, when performing cutting, the NC program is programmed so that there is a point where the vibration waveform (vibration machining) drawn by the tip of the tool 3a on the XZ plane comes into contact with the straight line (non-vibration machining). In Figure 3, the NC program is programmed so that the waveform showing the change in the cutting amount on the X axis of the tool 3a relative to the position change on the Z axis comes into contact with the vibration waveform on the XZ plane when cutting is performed before and after that (before and after the straight line machining pass).

[0035] For example, the vibration waveform of the tool tip during the third infeed cut and the linear movement path of the tool tip during the fourth infeed cut, which is executed one step later, will be described. The third and fourth infeed cuts are performed from the same infeed position (X coordinate) relative to the radial direction of the thread (X axis). For example, the X coordinate command value in the NC program is the same. Therefore, these two thread cuts may be programmed as a pair. In other words, for the movement paths of two linear cuts from the same infeed position, vibration may be added to one linear cut and not to the other linear cut. The valley of the vibration waveform during the third infeed cut is located at the point where it intersects with the linear cut of the fourth infeed cut. The vibration waveform is triangular, but it may also be arc-shaped or wavy. The vibration waveforms for the first, third, and fifth infeed cuts are in phase. In other words, the phase difference between the waveforms in Figure 3 is 0°. The phase difference is not limited to this; 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°. Although the first and second waveforms have the same cycle, this does not necessarily have to be the case. The chip-breaking effect is achieved as long as the movement trajectories of the two tools 3a in vibration machining and linear (non-vibration machining) contact at least one point. Patent Document 1 creates a path of no-cutting motion. However, creating a path of no-cutting motion accelerates the tool movement because no cutting occurs. The tool then collides with the workpiece again in an accelerated state, increasing the impact and resulting in rapid tool wear. Therefore, it is preferable to create an NC program that sets a path of the tool tip that provides a point of contact or tangent overlap sufficient to break the chip.

[0036] If an NC program is created in this way, when cutting is performed with the tool 3a, there is no workpiece to be cut in this cutting, although it is a point at the contact point with the previous cutting. Therefore, the cutting operation of the workpiece with the tool 3a ends, and chips are generated by the time of completion. Compared to conventional chips, this can be said to be a break in the chips. In other words, a non-cutting point is created where no cutting is performed by the tool 3a. The existence of a non-cutting area means that the cutting point (cutting edge) of the tool 3a is in contact with the workpiece but is not able to cut it, so the chips are broken. In response to this, the first control device reads a machining program including a command code corresponding to a first cutting position (for example, the position of the first and second cutting in FIG. 3 ) and acquires information about the first cutting position. Then, when the first control device determines that this first cutting position is (i) closer to the thread root diameter position than the thread outer diameter position, and (ii) the same position as the thread root diameter position or a position closer to the thread outer diameter position than the thread root diameter position, it performs first thread machining (first machining in FIG. 3 ) in which the tool is vibrated relatively along the rotation axis of the workpiece, on an axis different from the rotation axis, to cut the workpiece. When the first control device determines that this first cutting position is (i) closer to the thread root diameter position than the thread outer diameter position, and (ii) closer to the rotation axis than the same position as the thread root diameter position, it performs linear machining without applying vibration.

[0037] As shown in Figure 4, by making the maximum cutting depth the same for each machining run, the load on the tool can be made uniform. As can be seen from Figure 4, by making the cutting depth (depth) the same for vibration machining (waveform) and non-vibration machining (straight line), the load on the tool can be made the same for each machining run, and the usable life of a single tool can be extended. This reduces the number of tool changes, reducing the time when thread machining cannot be performed due to tool changes, and therefore improves machining efficiency. Furthermore, with the machining shown in Figure 4, the maximum cutting depth can be adjusted simply by adjusting the amplitude, making it easier to predict tool wear and the timing and frequency of tool replacement, thereby improving setup efficiency. Furthermore, existing thread machining programs can be used as is, and editing them to the machining program of this embodiment is easy. FIG. 11 shows an example of an NC program of this embodiment. The X coordinates of the thread cutting path are N107 (X72.47), N108 (X72.26), and N109 (X72.2). In the thread cutting of FIG. 4, the second command is N107 (X72.47), the fourth command is N108 (X72.26), and the sixth command is N109 (X72.2). These three thread strokes are required to cut the workpiece. In an existing thread machining program, threads can be machined by executing these three blocks. In this embodiment, thread machining with vibration is possible simply by inserting the start command "G985 A10. V72.2 I0.5 K1.0;" and the end command "G985 A30.;" into an existing thread machining program. As shown in Figure 11, by inserting a cutting command between the start command and the end command, one thread stroke is divided into two, as shown in Figure 4, and machining with vibration applied (first stroke) is performed in the first half, and normal machining without vibration applied (second stroke) is performed in the second half, in a block with the same X coordinate (X72.47).

[0038] In this way, if an NC program including vibration-related code can be created, there is no need to install a separate high-pressure coolant device to break up chips, as was previously required. Furthermore, since the load on the tool when machining threads with vibration can be reduced, the tool can be used for a longer period of time than before, and the frequency of tool replacement can be reduced. This leads to reduced tool costs. Furthermore, because the tool replacement time is reduced, more time can be secured for machining threads with the machine tool than before. Furthermore, if the value of the thread root diameter is entered incorrectly, the NC program may contain NC code such as "G985 A10. V72.21 I0.5 K1.0;". The NC program also contains command N109 (X72.2), which is the X coordinate close to the rotation axis. In this case, the first control device can control the thread machining at the coordinate of command N109 (X72.2) to perform linear machining without applying vibration.

[0039] Furthermore, in the thread cutting process shown in Figure 12, the vibration waveform has two peaks and three valleys during one rotation of the workpiece spindle, and the vibration is high-speed. Therefore, when performing the thread cutting process shown in Figure 12 with a conventional machine tool, the machine tool itself vibrates, resulting in a decrease in the quality of the thread. Therefore, when performing the thread cutting process shown in Figure 12 with a conventional machine tool, it was necessary to reinforce the structure to be resistant to vibration. Alternatively, measures such as installing a vibration mechanism that has vibration countermeasures on the machine tool were required. In the thread machining shown in Figure 5, the vibration waveform has two peaks and three valleys per four rotations of the workpiece spindle. Because the vibration is slower than in the thread machining shown in Figure 12, it is possible to prevent vibration from being transmitted to the machine tool itself. This makes it possible to create an NC program for the thread cutting shown in Figure 5 and execute that NC program on a current machine tool without having to take measures such as reinforcing the machine tool. It should be noted that the shape shown in Figure 5 is not the only possible shape, and as long as the waveform has one or fewer peaks or one or fewer valleys per rotation of the workpiece spindle, the impact of vibration can be reduced compared to the machining shown in Figure 12. Furthermore, while the vibration waveform is triangular, it is not limited to this and may be arc-shaped or wavy.

[0040] In Figure 6, the peak of the amplitude of the first vibration machining is above the outer shape of the workpiece. Therefore, the maximum cutting depth in the first vibration machining can be designed to be smaller than the maximum cutting depths in the third to sixth machining passes. In addition, the maximum cutting depth in the second non-vibration machining (linear machining) is set to the same as the maximum cutting depth in the first vibration machining pass. By doing this, the maximum cutting depth for the first and second times can be reduced.

[0041] In Figure 7, the cutting path is such that the peak of the tool movement trajectory for the third vibration cutting protrudes above the tool movement trajectory for the second linear cutting. By doing this, the maximum cutting depth for the third and fourth cuttings can be made smaller than the maximum cutting depth for the first cutting, reducing the load on the tool. By combining the machining path concept in Fig. 6 with the machining concept in Fig. 7, it is possible to design the maximum cutting depths to be the same for the first through sixth passes. It is also possible to design the difference between the maximum cutting depths for the first and second passes and those for the fourth through sixth passes to be small. Therefore, it is desirable to provide a function on the operation screen to adjust the distance between the peak of the crest and the straight line. The degree of tool wear can be measured in advance according to the material quality, maximum cutting depth, and cutting time, and stored as data. When the operator is preparing to process the screw, the function can calculate the timing for tool replacement from the tool wear and display the maximum cutting depth and tool replacement timing, allowing the operator to operate intuitively.

[0042] Of the NC programs that include codes related to vibration, it is preferable that the NC program for thread machining further includes a command code that decreases the vibration amplitude in the X-axis direction of the tool holder 4 as the cutting operation is performed later. The vibration amplitude of the vibration waveform at the tool tip decreases. In the thread machining shown in Figure 8, the amplitude of the tool tip at the first, third, and fifth cutting operations is expressed as A 1、 A 3、 When A1 is A5, it can be seen that the magnitude of the amplitude satisfies the relationship A1>A3>A5.

[0043] According to this, the vibration amplitude of the tool 3a decreases as the cutting process is performed later (i.e., as the cutting process moves from the rough cutting process to the finish cutting process). Therefore, in the finish cutting process, which requires shape accuracy, the vibration amplitude of the tool 3a can be reduced to improve the thread cutting accuracy by the tool 3a.

[0044] Figure 9 shows a machining path that combines the concepts of Figure 8 and Figure 7. Depending on the type of screw, it may be possible to perform cutting using the machining path shown in Figure 9. In Figure 9, the fourth thread cutting is performed without vibration in response to a command for the first cutting depth position (e.g., X72.26). Then, the fifth thread cutting is performed with vibration in response to a command for the second cutting depth position (e.g., X72.2), which is deeper than the fourth thread cutting. The vibration is generated in the direction of shallower cutting, with the second cutting depth position as the base. Therefore, the cutting path for the fifth thread cutting resembles a triangular wave with a series of peaks. The peak of the wave is at a position (e.g., X72.28) where the cutting depth is shallower than the first cutting depth position (e.g., X72.26). Since there is no workpiece above the first cutting depth position, chips are generated there. Meanwhile, the deepest point of the wave in the cutting path for the fifth thread cutting is at the second cutting depth position (e.g., X72.2). Cutting deeper than this would affect the quality of the thread surface. After that, the sixth thread cutting is performed without applying vibration to the command for the second cutting depth position (for example, X72.2). In the cutting program, the cutting paths overlap at points, resulting in short chips. There are some errors depending on the performance of the machine tool, so the chips may remain connected, but because they are quite thin, they break and are broken into pieces. From these, for example, it is possible to provide the following machine tools, etc. Of course, it is also possible to provide a machine tool control method, a machine tool control device, a thread machining program editing device, a thread machining program editing method, a thread machining method, etc. (1) Machine tool A 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 a 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 a workpiece is cut in a straight line along the rotation axis of the workpiece from the first cutting position. (1) Machine tool control device A A control device for a machine tool including a tool holding unit that holds a tool and a workpiece holding unit that holds a workpiece, A control device for a machine tool that controls: (i) a first thread machining step in which a 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 step 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 step in which a workpiece is cut in a straight line along the rotation axis of the workpiece from the first cutting position. (2) Machine tool B a tool holding portion for holding a tool; a workpiece holder that holds the workpiece; a control device 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 by oscillating the tool relatively on an axis different from the rotation axis from a first cutting position on an axis perpendicular to the rotation axis of the workpiece; and (ii) a second thread machining operation in which the workpiece is cut linearly along the rotation axis of the workpiece from a second cutting position on an axis perpendicular to the rotation axis of the workpiece; and that reads a machining program including a command code corresponding to the first cutting position, and performs the first thread machining if the first cutting position read from the machining program is (i) a position closer to the thread root diameter position than the outer diameter position of the thread, and (ii) the same position as the thread root diameter position or a position closer to the outer diameter position of the thread than the outer diameter position of the thread. (3) Machine tool C a tool holding portion for holding a tool; a workpiece holder that holds the workpiece; a control device 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 by oscillating the tool relatively on an axis different from the rotation axis from a first cutting position on an axis perpendicular to the rotation axis of the workpiece; and (ii) a second thread machining operation in which the workpiece is cut linearly along the rotation axis of the workpiece from a second cutting position on an axis perpendicular to the rotation axis of the workpiece; and that reads a machining program including an amplitude magnification factor K, and, if the amplitude magnification factor K read from the machining program is greater than a predetermined value, changes the amplitude magnification factor K to the predetermined value and performs the first thread machining operation. (4) Machine tool D a tool holding portion for holding a tool; a workpiece holder that holds the workpiece; a control device 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 by vibrating the tool relatively on an axis different from the rotation axis from a first cutting position on an axis perpendicular to the rotation axis of the workpiece; and (ii) a second thread machining operation in which the workpiece is cut in a linear fashion along the rotation axis of the workpiece from a second cutting position on an axis perpendicular to the rotation axis of the workpiece, and that, if a vibration amplitude magnification factor K is not set, performs the first thread machining operation using a previously set value of the amplitude magnification factor K. (5) Machine tool E a tool holding portion for holding a tool; a workpiece holder that holds the workpiece; a control device 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 by vibrating the tool relatively on an axis different from the rotation axis from a first cutting position on an axis perpendicular to the rotation axis of the workpiece; and (ii) a second thread machining operation in which the workpiece is cut linearly along the rotation axis of the workpiece from a second cutting position on an axis perpendicular to the rotation axis of the workpiece, and that, if a frequency multiplier I of the vibration operation is not set, performs the first thread machining operation using a previously set value of the frequency multiplier I. (6) Machine tool F a tool holding portion for holding a tool; a workpiece holder that holds the workpiece; a control device that drives and controls the tool holding unit and the work holding unit to perform the following: (i) a first thread machining operation, in which, from a first cutting position on an axis perpendicular to the rotation axis of the work, (i-1) the tool is moved relatively a first distance along the rotation axis of the work, and (i-2) after the movement of the first distance, the tool is continued to be moved relatively along the rotation axis while oscillating the tool relatively on an axis different from the rotation axis to cut the work; and (ii) (ii-1) from a second cutting position on an axis perpendicular to the rotation axis of the work, the tool is moved relatively a first distance along the rotation axis of the work, and (ii-2) after the movement of the first distance, the work is continued to be cut in a straight line along the rotation axis. [Explanation of symbols]

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

Claims

1. a tool holding portion for holding a tool; a workpiece holder that holds the workpiece; a drive control unit that controls the tool holding unit and the work holding unit so that, when machining threads along the rotation axis of a workpiece, a combination of vibration machining, in which cutting is performed by vibrating the tool relatively along an axis different from the rotation axis, and non-vibration machining, in which cutting is performed by moving the tool linearly along the rotation axis, can be performed by adding code that commands vibration machining to an existing NC program for thread machining in driving the tool holding unit and the work holding unit.

2. A control device for a machine tool including a tool holding unit that holds a tool and a workpiece holding unit that holds a workpiece, A drive control means is provided for controlling the tool holding unit and the work holding unit so that, by adding a code for commanding vibration machining to an existing NC program for thread machining, it is possible to combine vibration machining, in which cutting is performed by vibrating the tool relatively along an axis different from the rotation axis when machining a thread along the rotation axis of a workpiece, and non-vibration machining, in which cutting is performed by moving the tool linearly along the rotation axis, The drive control means is a control device for a machine tool that controls the presence or absence of vibration of the tool, the vibration direction, the frequency magnification and the amplitude magnification based on a vibration command code included in the NC program.

Images