Numerical control device and numerical control method

Abstract

This numerical control device (1a) controls vibration cutting in which a workpiece is cut by moving a tool and the workpiece relative to each other with vibration along a movement path using a feed shaft provided on the workpiece or the tool. The numerical control device (1a) is provided with: a machining condition input unit (10) that inputs machining conditions (23) including a rotational speed of a main shaft that rotates the workpiece, a main shaft rotational speed, which is a rotational speed of a main shaft that rotates an object to be machined, and machining depth information relating to the difference between first machining and second machining performed after the first machining; a vibration condition determination unit (13) that, on the basis of the machining conditions (23), determines vibration conditions (24) including a radial vibration amplitude and a radial vibration frequency in at least one of the first machining and the second machining, such that vibrating the tool or the workpiece in the radial direction of the central axis of the main shaft to make chip separation; and a machining performing unit (14) that performs cutting using the machining conditions (23) and the vibration conditions (24).

Description

Numerical control device and numerical control method

[0001] The present disclosure relates to a numerical control device and a numerical control method for performing vibration cutting.

[0002] Machine tools used in cutting processes remove material from the surface of a workpiece by moving the workpiece and tool relative to each other while interfering with each other, thereby achieving a desired shape. The removed material is then discharged as chips. Long chips can become entangled with the workpiece and tool, reducing machining accuracy and causing scratches on the machined surface, resulting in machining defects.

[0003] Patent Document 1 discloses that in turning, in which a tool is brought into contact with a rotating workpiece to perform cutting, the axis that drives the tool is vibrated in the direction of the central axis of the spindle, creating a moment when the tool and the workpiece do not interfere with each other and breaking up chips into short pieces.The control device disclosed in Patent Document 1 determines whether chip breaking will occur when a specific axis out of multiple feed axes is vibrated based on tool data, the relative positional relationship between the workpiece and the tool, and movement data for moving the workpiece and the tool relatively, and automatically selects the axis to vibrate.

[0004] International Publication No. 2022 / 269751

[0005] However, according to the technology of Patent Document 1, in order to break the chips into small pieces, it is necessary to vibrate the workpiece or the tool in a direction along the generatrix of the outer peripheral surface of the workpiece. For example, in turning, vibrations including a component in the direction of the central axis of the workpiece are required. If the mechanical structure driven by the feed shaft is heavy, or if vibrations cannot be transmitted because an elastic body such as a belt is interposed between the motor and the structure, the feed shaft cannot be vibrated in a direction parallel to the machining surface of the workpiece, and vibration cutting cannot be performed.

[0006] The present disclosure has been made in consideration of the above, and aims to provide a numerical control device that can achieve chip breaking at a desired chip length during cutting processing, even when the feed axis cannot be vibrated in a direction parallel to the processing surface.

[0007] In order to solve the above-mentioned problems and achieve the object, a numerical control device according to the present disclosure controls vibration cutting, which cuts a workpiece by moving the tool and the workpiece along a movement path while vibrating them relative to each other using a feed axis provided on the workpiece or the tool. The numerical control device includes: a machining condition input unit that inputs machining conditions including a spindle rotation speed, which is the rotation speed of a spindle that rotates the workpiece, and machining depth information related to the difference between a first machining and a second machining performed after the first machining; a vibration condition determination unit that determines vibration conditions, based on the machining conditions, including a vibration amplitude and a vibration frequency in the spindle radial direction for at least one of the first machining and the second machining, so as to vibrate the tool or the workpiece in the spindle radial direction to break up chips; and a machining execution unit that performs cutting using the machining conditions and the vibration conditions.

[0008] According to the numerical control device disclosed herein, even if the feed axis cannot be vibrated in a direction parallel to the machining surface, it is possible to achieve chip breaking at the desired chip length during cutting processing.

[0009] FIG. 1 is a block diagram showing an example of a configuration including a drive unit and a machine tool in which vibration cutting is performed by a numerical control device according to a first embodiment; FIG. 2 is an explanatory diagram of vibration cutting using a machine tool according to a first embodiment; FIG. 3 is a block diagram showing an example of a configuration of a numerical control device according to a first embodiment; FIG. 4 is a diagram showing an example of a machining path in turning processing performed by a numerical control device according to a first embodiment; FIG. 5 is a diagram showing an example of a machining program executed by a numerical control device according to a first embodiment; FIG. 6 is a diagram showing an example of specifying chip length and chip thickness in a machining program executed by a numerical control device according to a first embodiment; 3 is a diagram for explaining the mechanism; FIG. 3 shows the distribution of positions where the minimum cutting thickness is obtained in the numerical control device of embodiment 1; FIG. 3 shows the distribution of positions where the minimum cutting thickness is obtained in the numerical control device of embodiment 1; Schematic diagram showing two machining paths during vibration cutting in the numerical control device of embodiment 2; Schematic diagram showing two other machining paths during vibration cutting in the numerical control device of embodiment 2; Schematic diagram showing two further other machining paths during vibration cutting in the numerical control device of embodiment 2;A diagram showing other time changes in the spindle phase. A block diagram showing an example of the configuration of a numerical control device according to a fifth embodiment. A diagram for explaining machining of a tapered portion in a numerical control device according to a sixth embodiment. A diagram for explaining a first method for dealing with an increase in the X-direction component of the feed rate when machining a tapered portion in a numerical control device according to the sixth embodiment. A diagram for explaining a second method for dealing with an increase in the X-direction component of the feed rate when machining a tapered portion in a numerical control device according to the sixth embodiment. A diagram showing an example of the hardware configuration of a numerical control device according to the first to sixth embodiments.

[0010] A numerical control device and a numerical control method according to an embodiment will be described in detail below with reference to the drawings.

[0011] In the first to sixth embodiments, chip breaking is achieved by vibration cutting in the radial direction of the spindle.

[0012] 1 is a block diagram showing an example of a configuration including a drive unit 2 and a machine tool 3 in which vibration cutting is performed by a numerical control device according to the first embodiment. The machine tool 3 is, for example, a Swiss-type automatic lathe, and includes a spindle 300 that rotates a workpiece 303 as a machining target, and an X-axis and a Z-axis as multiple feed axes that move a tool 304 relative to the workpiece 303. Specifically, the machine tool 3 includes an X-axis drive unit 301 having an X-axis, a spindle motor 302 connected to the spindle 300, an X-axis servo motor 305 connected to the X-axis drive unit 301 and driving the X-axis in the X direction, a Z-axis drive unit 307 having a Z-axis, and a Z-axis servo motor 306 connected to the Z-axis drive unit 307 and driving the Z-axis in the Z direction, which is the direction of the central axis of the spindle 300.

[0013] The drive unit 2 has a spindle servo control unit 201, an X-axis servo control unit 202, and a Z-axis servo control unit 203. The spindle servo control unit 201 performs position control so that the spindle position of the spindle motor 302 of the machine tool 3 coincides with a spindle drive command, and outputs a spindle current. However, if the spindle drive command is a speed command, the spindle servo control unit 201 performs speed control so that the spindle speed coincides with the spindle drive command.

[0014] X-axis servo control unit 202 controls the X-direction position of machine tool 3 by performing position control so that the servo motor position of X-axis servo motor 305 coincides with the X-direction drive command, and outputs a servo motor current. Z-axis servo control unit 203 similarly controls the Z-direction position using Z-axis servo motor 306 that drives in the Z direction.

[0015] For simplicity, FIG. 1 shows only the X-axis and Z-axis as feed axes, but it may also have a Y-axis drive unit and a Y-axis servo control unit that drive the tool in the Y direction, for example, in the vertical direction.

[0016] A tool 304 is attached to the X-axis drive device 301, and a workpiece 303 is placed on the spindle 300. A spindle current generated by the spindle servo control unit 201 of the drive unit 2 based on a spindle drive command is supplied to the spindle motor 302. A servo motor current generated by the X-axis servo control unit 202 of the drive unit 2 based on an X-direction drive command is supplied to the X-axis servo motor 305. A servo motor current generated by the Z-axis servo control unit 203 of the drive unit 2 based on a Z-direction drive command is supplied to the Z-axis servo motor 306. The spindle motor 302 drives the spindle 300 in accordance with the spindle current, the X-axis servo motor 305 drives the X-axis drive device 301 in accordance with the servo motor current, and the Z-axis servo motor 306 drives the Z-axis drive device 307 in accordance with the servo motor current.

[0017] In this machine tool 3, the spindle 300 and spindle motor 302 are mounted on top of the Z-axis drive unit 307. As a result, the load weight of the Z-axis drive unit 307 is large. In conventional vibration cutting, vibration machining is performed by vibrating the spindle 300 mainly in the Z direction at a frequency of several Hz to several tens of Hz, but when the load weight on the Z axis is large, the responsiveness of the Z axis cannot be improved. Similarly, if the rigidity of the connection is insufficient, such as when the Z-axis drive unit 307 and the Z-axis servo motor 306 are connected by a belt or the like, it is difficult to achieve high responsiveness, and vibration cutting in the Z direction cannot be performed.

[0018] However, in the machine tool 3 shown in FIG. 1 , the configuration of the spindle 300 and the X-axis drive unit 301 is an example of the mechanical configuration of a Swiss-type automatic lathe. For example, instead of the Z-axis drive unit 307 driving the spindle 300, the Z-axis drive unit 307 may be mounted on the X-axis drive unit 301, and the X-axis drive unit 301 and the Z-axis drive unit 307 may drive the tool 304 in the X and Z directions. Furthermore, in the case of turning using a simultaneous five-axis machine tool having a rotary axis, both the rotary table on which the workpiece 303 is placed and the drive axis driving the tool 304 may be driven by the drive unit 2. Furthermore, the machine tool 3 is not limited to a machine that performs turning, but may also be a machine that performs milling. Here, the workpiece 303 mounted on the spindle 300 is configured to rotate, but vibration cutting may also be performed by rotating the tool 304. For example, drilling and milling are methods of cutting the workpiece 303 using a rotating tool 304.

[0019] FIG. 2 is an explanatory diagram of vibration cutting using the machine tool 3 according to the first embodiment. In FIG. 2, the vibration direction is indicated by a solid line with an arrow, and the tool path is indicated by a dashed line with an arrow. The spindle 300 rotates the workpiece 303 at a constant speed in accordance with a spindle drive command. The Z-axis servo motor 306 is controlled by the Z-direction drive command from the Z-axis drive unit 307, thereby moving the spindle 300 and the workpiece 303 in the Z direction along a tool path defined by a machining program (described below) while interfering with the tool 304 and the workpiece 303. However, since cutting is performed by the relative motion between the tool 304 and the workpiece 303, when the workpiece 303 moves in the negative direction of the Z axis, the tool 304 appears to move in the positive direction of the Z axis when viewed from a coordinate system linked to the workpiece 303. For simplicity, the following description will be given using the tool path as viewed from such a coordinate system as an example.

[0020] The X-axis driving device 301 vibrates the tool 304 in the X direction, thereby vibrating the tool 304 in the radial direction perpendicular to the central axis O of the workpiece 303. However, as will be described later in a sixth embodiment, when machining a tapered surface in the XZ direction, a feed amount command and a vibration command for a vibration amplitude and a vibration frequency based on execution vibration conditions, which will be described later, are superimposed on the X-axis servo control unit 202.

[0021] The X-axis driving device 301 vibrates the tool 304, which generates relative vibration between the tool 304 and the workpiece 303, breaking up the chips. Here, the X-axis driving device 301 is used to vibrate the tool 304, but as long as it is possible to generate relative vibration in the radial direction between the tool 304 and the workpiece 303, the workpiece 303 may be vibrated using the spindle 300, or a Y-axis driving device may be used to generate vibration in the radial direction.

[0022] 3 is a block diagram showing an example of the configuration of a numerical control device 1a according to the first embodiment. The numerical control device 1a has a machining program analysis unit 11, a parameter reception unit 12, a machining condition input unit 10, a vibration condition determination unit 13, and a machining execution unit 14. The numerical control device 1a is a control device that drives a machine tool 3. In the first embodiment, chip separation is achieved by rough machining including vibration cutting immediately before finish machining, and the subsequent finish machining not including vibration cutting.

[0023] Each element constituting the numerical control device 1a will be described. In the first embodiment, the finishing machining corresponds to the second machining, and the rough machining including vibration cutting immediately before the finishing machining corresponds to the first machining. The second machining is performed after the first machining. The machining program analysis unit 11 analyzes the machining program 21 and creates machining program analysis information from among the information required for processing in the machining condition input unit 10. The machining program analysis information includes machining path information, feed rate, spindle rotation speed, tool information used, information related to vibration cutting, and the like.

[0024] The machining path information is information about the relative movement path between the tool 304 and the workpiece 303, and includes the coordinate values ​​of a set of start and end points for one path, the interpolation method for the movement path connecting the start and end points (non-interpolation, linear interpolation, circular interpolation, etc.), etc. A movement path defined by a set of start and end points is called a movement block, and one movement block is called one movement block.

[0025] The feed rate is the relative movement speed of the tool 304 with respect to the workpiece 303, and is expressed as the movement amount per unit time (e.g., mm / min) or the movement amount per unit rotation (e.g., mm / rev) synchronized with the rotational speed of the spindle 300.

[0026] The spindle rotation speed is the rotation speed of the spindle 300 and is expressed as the number of rotations per unit time (for example, rev / min, rpm).

[0027] The tool use information includes which tool 304 is to be used when executing the movement block, and information about the tool 304. The information about the tool 304 includes the length of the tool 304, the amount of wear, the tool diameter in the case of a cutting tool, and the radius of the rounded portion of the tool cutting edge (cutting edge radius R) in the case of a turning tool.

[0028] The information related to vibration cutting specifically includes information indicating whether vibration cutting is enabled or disabled, the vibration target axis, the vibration direction, the vibration amplitude, the vibration frequency, the number of vibrations per revolution of the spindle, etc. This information may be changed for each movement block, or, if not otherwise specified, the information specified in the previous movement block may be inherited as is.

[0029] The machining program 21 targeted in the first embodiment may be a program conforming to the Electronic Industries Alliance (EIA) / International Organization for Standardization (ISO) system, or may be a program in a format known as an interactive type.

[0030] Fig. 4 is a diagram showing an example of a machining path in a turning process executed by the numerical control device 1a according to the first embodiment. Fig. 5 is a diagram showing an example of a machining program 21 executed by the numerical control device 1a according to the first embodiment. The turning process shown in Fig. 4 is realized by the machining program 21 shown in Fig. 5. Note that the machining program 21 describes only a part that is essential for the turning process shown in Fig. 4.

[0031] In Fig. 4, the vertical axis corresponds to the X axis, and the horizontal axis corresponds to the Z axis. In Fig. 4, the hatched area and the gray halftone area correspond to the workpiece 303, and the halftone area indicates the area to be turned. In Fig. 4, the solid line with an arrow indicates the machining path.

[0032] In Figure 5, the N at the beginning of each block indicates the block number of the machining program 21. One line of the machining program 21 corresponds to one block. The particularly important contents of each block will be explained below. Block N02 commands the start of rotation of the spindle 300 and the value of the spindle rotation speed. Block N04 includes a command to activate the vibration cutting function. Block N05 is a block for a cutting feed command, and also commands the feed rate at that time.

[0033] The N01, N100, and N101 blocks are fast-forward command blocks that position the tool 304 at a high feed rate to a position immediately before machining. The N102 block is a command to disable the vibration cutting function, and from the cutting feed command block of the N103 block, vibration cutting is disabled and vibration-free finish machining begins.

[0034] 3, the parameter receiving unit 12 acquires setting values ​​of NC (Numerical Control) parameters 22 used for controlling the numerical control device 1a. The NC parameters 22 include parameters for enabling / disabling various functions provided in the numerical control device 1a, parameters for maximum speed and acceleration / deceleration time constants related to acceleration / deceleration control of each motor (spindle motor 302, X-axis servo motor 305, Z-axis servo motor 306), and the like.

[0035] In the first embodiment, the parameter receiving unit 12 acquires information on the target chip length and information on the target chip thickness during finish machining from the NC parameters 22 and transmits them to the machining condition input unit 10. The target chip length may be a single set value, or may be in the form of a table that allows selection and switching of multiple set values ​​for each material of the workpiece 303 or each type of tool. Also, the target chip length may be written and set in the form of a character string and a numerical value in one block of the machining program 21. In this case, the target chip length is analyzed by the machining program analysis unit 11, and the information on the target chip length for that block is included in the machining program analysis information.

[0036] The same applies to the target chip thickness. As will be described later, in the first embodiment, unevenness is created on the machined surface by radial vibration cutting, and the uneven machined surface is machined by non-vibration cutting, thereby causing fluctuations in the chip thickness and making it easier to break up the chips. Then, the vibration conditions 24 are determined so that the minimum value of the chip thickness is equal to or less than the target chip thickness. The target chip thickness may be a single value, or may be in the form of a table that allows selection and switching of multiple setting values ​​for each material of the workpiece 303 and each tool type.

[0037] The above-mentioned table can be defined as a target chip length table, for example, with a list of workpiece 303 material information and a list of tool 304 type information in rows and columns, allowing a target chip length setting value to be set for each combination. Similarly, the table can be defined as a target chip thickness table, allowing a target chip thickness setting value to be set. Specifically, for example, if chip shearing is difficult for a particular material, setting the corresponding target chip thickness table value to a smaller value can be expected to facilitate chip shearing. Furthermore, depending on the tool used, chip shearing may be difficult. In such cases, setting the corresponding target chip thickness table value to a smaller value can be expected to facilitate chip shearing. Furthermore, some materials cannot be cut at a high speed. In such cases, the relative movement speed between the tool 304 and the workpiece 303 is not high, and there is room to increase the vibration frequency. Therefore, chip-related problems may be suppressed by setting the corresponding target chip length table value to a smaller value.

[0038] The target chip length and target chip thickness may also be specified in the machining program 21. FIG. 6 is a diagram showing an example of specifying the chip length and chip thickness in the machining program 21 executed by the numerical control device 1a according to the first embodiment. When vibration cutting is enabled in block N04, the target chip length is simultaneously specified as L10.0. In subsequent operations, the vibration conditions 24 in each movement block are calculated so that this target chip length is always satisfied. The target chip length may also be changed in the middle of a movement block using a letter (L) and a numerical value.

[0039] Furthermore, during the finishing cut in block N103 in Figure 6, the target chip thickness is specified as E5.0. As with the target chip length L specification, subsequent operations always use this target chip thickness as the target value, and operate to calculate the vibration condition 24. Also, the target chip thickness may be similarly changed using the letter (E) and a numerical value in the middle of a movement block. Note that the example letters (L) and (E) can be changed as appropriate.

[0040] Returning to Fig. 3, the machining condition input unit 10 calculates the machining conditions 23 using information from the machining program analysis unit 11 and the parameter reception unit 12. The machining conditions 23 include information such as the feed rate for each machining pass, the number of spindle revolutions, machining depth information, the radius of the workpiece 303, the cutting edge radius R, and whether or not radial vibration cutting is performed. The machining depth information includes the cutting depth and the cutting thickness. A specific method for calculating the machining conditions 23 will be described later.

[0041] The vibration condition determination unit 13 calculates vibration conditions 24 for determining a vibration waveform for vibration cutting based on the machining conditions 23. The vibration conditions 24 include vibration amplitude, the number of vibrations I per rotation of the spindle, vibration frequency f, etc. A specific method for calculating the vibration conditions 24 will be described later.

[0042] The machining execution unit 14 performs processes such as generating a vibration waveform for vibration cutting, superimposing the vibration waveform on the movement path, and accelerating and decelerating based on the machining conditions 23 and the vibration conditions 24 determined by the vibration condition determination unit 13, and outputs commands to the spindle motor 302 and the X-axis servo motor 305. Processes such as superimposing on the movement path and accelerating and decelerating are well known techniques to those skilled in the art of the numerical control device 1a, and therefore will not be described here.

[0043] In generating a vibration waveform based on the vibration conditions 24, the vibration waveform is generated based on information on the vibration frequency, vibration period, and phase. At this time, a sinusoidal vibration command may be generated within the numerical control device 1a, or the vibration command may be generated using the response characteristics of the X-axis servo control unit 202 or the like.

[0044] FIG. 7 is a block diagram showing an example of the configuration of the X-axis servo control unit 202 of the numerical control device 1a according to the first embodiment. The generation of a vibration command taking into account the response characteristics of the X-axis servo control unit 202 will be described. The X-axis servo control unit 202 includes a position controller 31 that generates a speed command Vr so that the feedback position coincides with the drive axis command, and a speed controller 32 that generates a torque command Tr so that the speed command Vr coincides with the feedback speed. Generally, the feedback position and feedback speed are determined by the values ​​detected by a detector attached to the motor and the values ​​detected by a position detector attached to the drive axis. The control block shown here is merely an example, and any control system may be used as long as it can control the feedback position in response to the drive axis command.

[0045] In the example of the control block shown in FIG. 7, the response of the feedback position to the drive axis command can be approximated by the transfer function shown in the following equation (1).

[0046]

[0047] In other words, the transfer function is a control system with three poles and one zero, which acts as a filter for high-frequency drive axis commands. Therefore, high-frequency components contained in the vibration command are cut by the response characteristics of the servo control unit, so the response becomes a sinusoidal vibration waveform even without generating a strictly sinusoidal command. For example, waveforms such as triangular wave commands or square wave commands can be input.

[0048] FIG. 8 is a diagram showing an example of a vibration command that takes into account the response characteristics of the X-axis servo control unit 202 of the numerical control device 1a according to the first embodiment. The upper diagram in FIG. 8 shows a triangular wave drive axis command. The lower diagram in FIG. 8 shows a rectangular wave drive axis command. Because the triangular wave and rectangular wave commands are expressed as a Fourier series of a sine wave, high-frequency vibration components are cut off by the characteristics of the X-axis servo control unit 202, resulting in a vibration waveform dominated by first-order sine wave components. By using such triangular wave and rectangular wave commands, the numerical control device 1a can simplify the calculation of command values ​​compared to when a sine wave command is generated.

[0049] Next, we will explain the processing contents of the machining condition input unit 10 and the vibration condition determination unit 13. In the first embodiment, the target is a moving block that performs vibration cutting in the radial direction and a moving block that performs non-vibration cutting on the area machined by this moving block, so it is necessary to identify a pair of these two moving blocks.

[0050] Hereinafter, to make it easier to imagine the actual machining, the moving block that performs the former radial vibration cutting machining will be referred to as the rough machining block, and the moving block that performs the latter non-vibration machining will be referred to as the finish machining block for convenience.

[0051] Fig. 4 shows a machining path in turning. As shown in Fig. 4, in turning, a desired shape is obtained by repeatedly machining in the radial direction (X direction) while feeding in the direction of the central axis O of the workpiece 303 (the Z direction, which is the direction of the central axis of the spindle 300) and deepening the cutting position in the radial direction. Therefore, in turning, the X coordinate changes while repeating approximately the same movement path in the Z direction.

[0052] Furthermore, in turning, all cutting steps except the first are performed on the surface obtained by the previous cutting. Therefore, by analyzing the start and end point information of each moving block, it is possible to identify the rough cutting moving block that will create the machined surface during finish cutting. In other words, among the moving blocks with a start point at approximately the same Z coordinate as the moving block for non-vibration cutting, the moving block for vibration cutting in the radial direction whose X coordinate is closest to the moving block for non-vibration cutting is the rough cutting block that corresponds to the finishing cutting block.

[0053] The machining program analysis unit 11 reads ahead and analyzes a sufficient amount of the machining program 21 in advance, and accumulates machining program analysis information. The machining condition input unit 10 uses the accumulated machining program analysis information to select target movement blocks (pairs of finish machining blocks and rough machining blocks).

[0054] Fig. 9 is a conceptual diagram showing the geometric relationship between the tool 304 and workpiece 303 used in the numerical control device 1a of embodiment 1. Fig. 10 is another conceptual diagram showing the geometric relationship between the tool 304 and workpiece 303 used in the numerical control device 1a of embodiment 1. Methods for calculating various dimensional quantities will be described with reference to Figs. 9 and 10.

[0055] The tip of the cutting edge of the tool 304 is often rounded and radiused. Here, the center point of the radiused portion of the cutting edge is used as the reference point (the point indicated by the coordinate value) of the machining path when considering the movement of the tool 304, and is referred to as the center point of the cutting edge radius Ce. The radius of the circle at the tip of the cutting edge of the tool 304 is referred to as the radius of the cutting edge radius R. In practice, turning tools are structured to include a tip with a cutting edge, a rod-shaped shank that holds the tip, and a tool holder that holds the shank. A reference position set in a mechanical structure, such as the base of the tool holder, is often used as the position indicated by the coordinate value. The numerical control device 1a performs tool compensation based on dimensional information, such as the tool length, of the selected tool 304, thereby controlling the tool cutting edge to move to the position commanded by the machining program 21. This is a well-known technique to those skilled in the art, and can be implemented without problems by shifting the coordinate value to reflect this tool compensation concept in the basic concept described below. Therefore, for simplicity, the center point of the cutting edge radius Ce will be described as the coordinate value of the machining path.

[0056] The definitions of each dimension will be explained. FIGS. 9 and 10 show a previous machining surface Wn-1, which is the previous (n-1) machining surface, and a current machining surface Wn, which is the current (n) machining surface. The tool 304 shown by the dashed line in FIG. 10 indicates the position at the time of the previous (n-1) cutting, while the tool 304 shown by the solid line in FIGS. 9 and 10 indicates the position at the time of the current (n) cutting. The path of the center point Ce of the cutting edge R during the previous machining is called the previous machining path Pn-1, and the path of the center point Ce of the cutting edge R during the current machining is called the current machining path Pn. As shown in FIG. 10, the current machining is performed on the previous machining surface Wn-1, so dimensions such as the cutting depth D and the cutting thickness H can be formulated based on the relationship between the current machining and the previous machining.

[0057] The cutting depth D is the difference between the coordinate Xn-1 of the vibration center locus of the previous machining path Pn-1 and the coordinate Xn of the vibration center locus of the current machining path Pn, and as the vibration center locus, the coordinate of the center point Ce of the cutting edge R is used as described above. The cutting depth Dn at the nth cutting is calculated by the following formula (2): Dn=Xn-Xn-1 (2)

[0058] The difference between the previous machining surface Wn-1 and the current machining surface Wn is called the cutting thickness H. If the cutting edge R radius at the n-1th cutting is Rn-1 and the cutting edge R radius at the nth cutting is Rn, the cutting thickness Hn at the nth cutting is calculated by the following formula (3): Hn = Dn + Rn - Rn-1 (3)

[0059] Here, if this is the first cutting, and there is no previous machining, then if Rn-1 = 0 and Xn-1 = the X coordinate of the outer circumferential surface of the workpiece 303 (= the radius r of the workpiece 303), then the cutting depth D1 and the cutting thickness H at the first cutting can be calculated using equations (2) and (3), as shown in Figure 9. The radius r of the workpiece 303 can be found from the X coordinate Xc of the start point of rough machining (the previous machining) and the cutting edge R radius Rn-1 of the tool 304. Alternatively, the radius r of the workpiece 303 may be found by adding the X coordinate of the start point of the current machining path Pn + the cutting depth Dn of the current machining path Pn - the cutting edge R radius Rn-1 of the previous machining path Pn-1.

[0060] Using the above concept, if the nth cutting is considered as the finishing block and the (n-1)th cutting is considered as the roughing block, the cutting depth Dn in the finishing process can be calculated. The feed rate, spindle speed, cutting edge radius R of the tool 304, and whether or not radial vibration cutting is performed in each movement block are included in the processing program analysis information.

[0061] As described above, the machining condition input unit 10 sets information including the feed rate in each moving block, the spindle rotation speed, the cutting depth D, the cutting thickness H, the radius r of the workpiece 303, the cutting edge radius R, and whether or not radial vibration cutting is performed as machining conditions 23 and inputs this information to the vibration condition determination unit 13.

[0062] Next, a description will be given of the processing in the vibration condition determination unit 13. The vibration condition determination unit 13 determines the vibration amplitude A in rough machining required to achieve the target chip thickness H in finish machining, and the number of vibrations I per revolution of the spindle in rough machining required to break the chips to the target chip length.

[0063] When vibration cutting is performed in the radial direction, unevenness is formed on the machined surface due to fluctuations in the cutting thickness H. In finish processing, in order to generate the surface of the final product or part, it is necessary to achieve the surface quality (surface roughness) specified in the drawing, etc., and vibration cutting in the radial direction cannot be performed. However, by creating unevenness on the machined surface to be finished and then performing finish processing using non-vibration cutting, the thickness of the chips generated can be changed periodically, making the chips more likely to break up.

[0064] In the first embodiment, the vibration condition determining unit 13 determines the vibration amplitude A of the rough-machined block so that the minimum cutting thickness Hmin, which is the minimum value of the cutting thickness H of the finish-machined block, is equal to or smaller than the first threshold value.

[0065] FIG. 11 is a conceptual diagram showing the geometric relationship between the tool 304 and the workpiece 303 during vibration cutting by the numerical control device 1a of embodiment 1. The vertical axis of FIG. 11 represents amplitude, and the horizontal axis represents time. FIG. 11 shows the previous machining path Pn-1, previous machining surface Wn-1, and cutting edge R radius Rn-1 from the previous (n-1th) vibration cutting, and the current machining path Pn, current machining surface Wn, and cutting edge R radius Rn from the current (nth) non-vibration cutting. FIG. 11 also shows the continuous cutting section Tf. The continuous cutting section Tf is the section during which the tool 304 comes into contact with the workpiece 303 and performs cutting during one cycle.

[0066] As can be seen from Figure 11, the minimum chip thickness Hmin in the current non-vibration cutting is expressed as Hmin = Dn - A + (Rn - Rn - 1) using the cutting depth Dn in the current non-vibration cutting, the vibration amplitude A in the previous vibration cutting, and the cutting edge R radii Rn-1 and Rn. Therefore, if the minimum value of the target chip thickness H is H'min, the vibration amplitude A in the previous vibration cutting (rough machining) can be calculated using the following equation (4): A = Dn - H'min + (Rn - Rn - 1) (4)

[0067] For ease of explanation, the locus of the command for the movement path before vibration is added will be referred to as the center of vibration hereinafter, but the top dead center or bottom dead center of vibration may also be referred to as the locus of the movement path. More specifically, when a position is commanded using the movement path + vibration component, for example, if the position command is Z + A sin θ, the method of overlapping the vibration component with the locus of the movement path can be adjusted by offsetting it up or down, such as Z + A (1 - sin θ) or Z + A (1 + sin θ).

[0068] FIG. 12 is a diagram illustrating the mechanism by which chip shedding occurs during finish cutting in the numerical control device 1a of the first embodiment. FIG. 12 shows the previous machined surface Wn-1, which is the rough-machined surface on which vibration cutting is performed; the current machined surface Wn, which is the finished surface on which non-vibration cutting is performed; the chips Wp after shedding; and the minimum chip thickness Hmin. If the tool 304 is vibrated during finish cutting, the vibration trajectory is transferred to the current machined surface Wn, which is the finished surface, deteriorating the appearance of the workpiece 303. For this reason, non-vibration cutting without vibration is required during finish cutting. In the first embodiment, unevenness is already present on the machined surface during rough cutting. Therefore, when finish cutting is performed, the chip thickness H of the chips Wp fluctuates due to the influence of the unevenness of the rough-machined surface, even in a non-vibration state. In this case, the chip thickness H is also the thinnest during finish cutting at the position where the chip thickness H was set to be minimum during rough cutting.

[0069] If the minimum cutting thickness Hmin is set to 0, the cutting thickness H during finish machining will be 0 at this position, causing the chips Wp to become discontinuous and resulting in fragmented chips Wp. On the other hand, if the cutting thickness H is set to exactly 0, no finishing cutting will be performed at the position where the cutting thickness H is 0, leaving streaks on the machined surface and resulting in an unsatisfactory appearance. If the minimum cutting thickness Hmin is set to a value greater than 0, the chips Wp will be continuous even at the position of the minimum cutting thickness Hmin, but stress will be concentrated at the position k1 of the minimum cutting thickness Hmin due to machining. Due to this stress concentration, the chips Wp will be fragmented and discharged at the position of the minimum cutting thickness Hmin. The conditions for chip fragmentation due to stress concentration vary depending on the material and physical properties of the workpiece 303, the machining conditions 23, and the combination of the tool 304 and the workpiece 303. Therefore, the minimum cutting thickness Hmin may be input by the user when setting the vibration conditions, or may be automatically set using a database predefined for the processing conditions 23, the physical properties of the material, etc.

[0070] The chip length L is expressed as π×r / I, where r is the radius of the workpiece 303. Therefore, the number of vibrations I per one rotation of the spindle to achieve the desired chip length L is given by the following equation (5): I=π×r / L (5)

[0071] The chip length L can also be set by changing the position at which the minimum chip thickness Hmin is achieved. FIG. 13 shows the distribution of the positions q at which the minimum chip thickness Hmin is achieved in the numerical control device 1a of the first embodiment. FIG. 14 shows the distribution of the positions q at which the minimum chip thickness Hmin is achieved in the numerical control device 1a of the first embodiment. In FIG. 13, the positions q extend parallel to the Z direction. In FIG. 14, the positions q do not extend parallel to the Z direction. The shapes of the rough-machined surface Wn-1, which is the pre-machined surface, are different between FIG. 13 and FIG. 14. When the chip length L and the circumferential distance are an integer multiple, i.e., when the spindle rotation speed and the vibration frequency are an integer multiple, the position q at which the minimum chip thickness Hmin is achieved is consistent regardless of the position in the Z direction, as shown in FIG. 13. In such cases, the angle at which stress concentration occurs always occurs at the same position, and slight streaks may be observed on the finished machined surface. Therefore, by changing the position q at which the minimum cutting thickness Hmin is achieved depending on the position in the Z direction, such streaky patterns can be made less noticeable. For example, when the chip length L and the circumferential distance are non-integer multiples, that is, when the spindle rotation speed and the vibration frequency are non-integer multiples, the positions q at which the minimum cutting thickness Hmin is achieved will not be aligned. Therefore, the vibration condition determination unit 13 determines the vibration frequency so that the ratio between the spindle rotation speed and the vibration frequency is not an integer multiple.

[0072] In this way, the vibration condition determination unit 13 determines the vibration amplitude A of the rough-machined block so that the minimum chip thickness Hmin of the finish-machined block is equal to or less than the first threshold. The vibration condition determination unit 13 also calculates the number of vibrations I per spindle revolution to achieve the desired chip length L according to equation (5). The vibration condition determination unit 13 inputs vibration conditions 24, including the calculated vibration amplitude A of the rough-machined block, the number of vibrations I per spindle revolution, and the vibration frequency, to the machining execution unit 14. As described above, the machining execution unit 14 performs processes such as generating a vibration waveform for vibration cutting, superimposing the vibration waveform on the movement path, and accelerating / decelerating, based on the vibration conditions 24 determined by the vibration condition determination unit 13, and outputs commands to the spindle motor 302 and the X-axis servo motor 305.

[0073] Up to this point, an example of machining in which the tool moves only in the Z direction has been shown. However, this may also be applied to machining shapes in which the Z and X axes are moved simultaneously, such as tapered shapes. When the Z and X axes move simultaneously, the axial ratio, which is the ratio of the amount of movement in each axial direction, can be used to calculate the position at which the minimum uncut thickness Hmin occurs from the amount of change in radius after one rotation and the movement distance. Therefore, the vibration frequency may be determined so that the position at which the minimum uncut thickness Hmin occurs is located at a desired position. Alternatively, the vibration direction of the machined surface may be changed to a desired direction by vibrating in the X direction in addition to the Z direction. In other words, the vibration condition determination unit 13 may also use the axial ratio, which is the ratio of the amount of radial movement when vibration is not performed to the amount of axial movement of the spindle, to determine at least one of the vibration conditions of the vibration direction, vibration frequency, and vibration amplitude so that chip separation occurs.

[0074] In the above, an example was described in which the mass of the Z axis is heavy and vibration cutting in the Z direction is not possible, but by performing vibration cutting in the X direction in a situation in which vibration cutting in the Z direction is possible, it is possible to achieve both chip breakability and surface quality during finish machining by non-vibration cutting, which are difficult to achieve with vibration cutting in the Z direction. Furthermore, by combining vibration cutting in the Z direction with vibration cutting in the X direction (radial direction), it is possible to achieve both chip breakability during rough machining and chip breakability by non-vibration cutting during finish machining. Furthermore, as long as vibration cutting and non-vibration cutting are performed consecutively, the first embodiment can be applied without necessarily being limited to rough machining and finish machining.

[0075] As described above, according to embodiment 1, the vibration conditions 24 during rough machining are determined so that chip breaking occurs during finish machining using non-vibration cutting, and machining is then performed, so that chip breaking can be achieved without using vibration cutting during finish machining.

[0076] Second Embodiment In the second embodiment, vibration cutting is performed in the radial direction when rough cutting is repeated, and chips are broken. Specifically, in the second embodiment, the phases of the vibration waveforms are shifted between the previous and next cutting operations so that the vibration waveforms intersect between the previous and next cutting operations. The configuration of the numerical control device 1a according to the second embodiment is the same as that of the numerical control device 1a according to the first embodiment shown in FIG. 1. Normally, when performing turning, a cylindrical raw material is machined into its final shape. At this time, it is difficult to reach the final shape in a single cutting operation, so as shown in FIG. 4, rough cutting is repeated multiple times while changing the tool position in the radial direction.

[0077] In the second embodiment, in the rough machining in which the radial vibration cutting is repeated multiple times, the chips are broken by overlapping the previous and next machining passes so that they intersect. However, for convenience, any two consecutive machining passes during the multiple repeated rough machining will be referred to as the previous machining pass and the current machining pass in the description, but the current machining pass will become the previous machining pass in the next rough machining, and the vibration cutting of the next surface will be repeated by the new current machining pass. In the second embodiment, the machining of the current machining pass corresponds to the second machining, and the machining of the previous machining pass corresponds to the first machining. The second machining is performed after the first machining.

[0078] The second embodiment will be described in accordance with the flow of calculation of the vibration conditions 24. In the first embodiment, the finish machining path, which is the current machining path, is a path for non-vibration cutting, but in the second embodiment, the finish machining path, which is the current machining path, is set to a machining path for vibration cutting in the radial direction, so that two machining paths can be specified using the same concept as in the first embodiment.

[0079] FIG. 15 is a schematic diagram showing two machining paths during vibration cutting by the numerical control device 1a of the second embodiment. The vertical axis of FIG. 15 represents amplitude, and the horizontal axis represents time. FIG. 15 also shows a previous machining path Pn-1 and a current machining path Pn. FIG. 15 also shows a continuous cutting section Tf and a separation section Tg. The separation section Tg is a section in which the tool 304 is not in contact with the workpiece 303 during one cycle, and no cutting is performed. First, as described above, the cutting depth Dn of the current machining path Pn is calculated, and the vibration amplitude A of the previous machining path Pn-1 and the vibration amplitude A of the current machining path Pn are made to match the calculated cutting depth Dn.

[0080] In the second embodiment, a vibration start phase Φ is newly added as a post-machining vibration condition 24. The vibration start phase Φ is information that determines the phase by which the start of vibration is delayed after the moving block starts moving. Normally, the vibration start phase Φ is 0, in which case the vibration cutting operation with the vibration waveform superimposed starts simultaneously with the start of movement of the moving block.

[0081] In Fig. 15, the vibration start phase Φ is set to π / 2. As a result, as shown in Fig. 15, the continuous cutting section Tf in the current machining path Pn is determined to be Φc = 3π / 2 when the vibration phase Φc is used. Since the chip length L is expressed as L = Φc × r / I, the number of vibrations I per one rotation of the spindle is I = L / (Φc × r). In this case, the separation section Tg in which the tool 304 does not come into contact with the workpiece 303 during one cycle and no cutting is performed is determined to be Φd = π / 2 when the vibration phase Φd is used.

[0082] The radius r of the workpiece 303 is calculated, for example, by the start point X coordinate of the current machining path Pn + the cutting depth Dn of the current machining path Pn - the cutting edge R radius Rn-1 of the previous machining path Pn-1. At this time, if the tool path of the previous machining path Pn-1 and the tool path of the current machining path Pn are in contact with each other, or if the previous machining path Pn-1 is located below the current machining path Pn at the same spindle rotation angle position, the material at that position has been cut away by the previous machining, so in the current machining path Pn, the tool 304 does not come into contact with the workpiece 303 and misses, and the miss breaks up the chips.

[0083] In Fig. 15, an example was explained in which A = Dn and Φ = π / 2, but these values ​​can be changed arbitrarily. Fig. 16 is a schematic diagram showing two other machining paths during vibration cutting by the numerical control device 1a of embodiment 2. Fig. 17 is a schematic diagram showing two further other machining paths during vibration cutting by the numerical control device 1a of embodiment 2. In Fig. 16, A > Dn and Φ = π / 2. In Fig. 17, A = Dn and Φ = π. The vertical axis of Figs. 16 and 17 represents amplitude, and the horizontal axis represents time.

[0084] Once the number of vibrations per spindle revolution I is determined, the vibration frequency f can be calculated by f = S × I / 60, where S is the spindle rotation speed. The larger the vibration amplitude and vibration frequency of vibration cutting, the greater the load on the tool 304, machine structure, feed axis, and motor. Therefore, there is a need to determine vibration conditions 24 that will achieve chip breaking at the desired chip length L within the range of predetermined vibration conditions 24 (vibration amplitude A, vibration frequency f, or number of vibrations I per spindle revolution).

[0085] For example, to reduce the vibration frequency f, it is necessary to reduce the number of vibrations I per one rotation of the spindle, and reducing the number of vibrations I per one rotation of the spindle increases the chip length L, as can be seen from L = Φc × r / I. Therefore, in order to reduce the chip length L, it is necessary to further shorten the length of the continuous cutting section Tf.

[0086] The continuous cutting section Tf can be shortened as the vibration start phase Φ is increased. Therefore, as shown in Figure 17, by setting the vibration start phase Φ to a value greater than π / 2, for example π, the continuous cutting section Tf can be lengthened to Φc = 4π / 3. Also, as shown in Figure 16, if A > Dn and Φ = π / 2, even with the same vibration start phase Φ, by setting A > Dn, the continuous cutting section Tf can be shortened to Φc < 3π / 2. Therefore, by increasing the vibration amplitude A, it is possible to approach the desired vibration condition 24.

[0087] Furthermore, when the vibration amplitude A is reduced, the continuous cutting section Tf is extended, which is the opposite of the above, and therefore the chip length L. As another example, the chip length L may be adjusted by increasing the number of vibrations I per rotation of the spindle.

[0088] As described above, according to the second embodiment, the phase of the vibration waveform is shifted between the previous and next machining processes so that the vibration waveforms have an intersection between the previous and next machining processes, thereby making it possible to achieve chip cutting at a desired chip length.

[0089] Third Embodiment. The third embodiment deals with the case where radial vibration cutting is performed on an unmachined surface or a machined surface machined by non-vibration cutting. That is, the third embodiment deals with machining of a machined surface on which no irregularities have been generated by radial vibration cutting, for example, the first machining. As described above, turning typically involves machining a cylindrical material, so the surface of the workpiece 303 has no irregularities at the start of the first vibration cutting. Alternatively, even when a workpiece 303 machined in a different process is attached to a lathe and machined, the machined surface has no irregularities at the start of vibration cutting. The configuration of the numerical control device 1a according to the third embodiment is the same as that of the numerical control device 1a according to the first embodiment shown in FIG. 1.

[0090] The third embodiment will be described in accordance with the flow of calculation of the vibration conditions 24 described above. What is required in the third embodiment is the cutting thickness H of the target radial vibration cutting path. In the case of a machining surface machined by non-vibration cutting, by using the previous machining path Pn-1 in the second embodiment as a non-vibration cutting path, the previous machining path Pn-1 can be identified and the cutting thickness H can be calculated using the same concept as in the second embodiment.

[0091] In the case of initial machining, the initial machining path can be determined by the fact that there is no previous machining path for the target machining path, that is, there is no machining path whose X coordinate is in the opposite direction to the cutting direction. In the case of initial machining, if the coordinates of the outer peripheral surface of the workpiece 303 are known, the cutting depth D can be calculated using the coordinate values ​​of the outer peripheral surface as the coordinate values ​​of the previous machining surface, and the cutting edge radius R can be set to 0, thereby performing the same calculation as described above. If the coordinate values ​​of the outer peripheral surface are unknown, the cutting thickness H can be obtained by specifying the initial cutting depth D or cutting thickness H using a combination of a character string and a numerical value on the machining program 21.

[0092] 18 is a diagram showing an example of specifying the initial cutting depth D and the initial cutting thickness H in the machining program 21 executed by the numerical control device 1a according to the third embodiment. In the upper diagram of FIG. 18, D5.0 is added to the N05 block to specify the initial cutting depth D. In the lower diagram of FIG. 18, E5.0 is added to the N05 block to specify the initial cutting thickness H. The above operations are performed by the machining condition input unit 10 according to the third embodiment.

[0093] Next, the operation of the vibration condition determination unit 13 in the third embodiment will be described. FIG. 19 is a diagram showing the positional relationship between the tool 304 and the workpiece 303 during vibration cutting in the numerical control device 1a of the third embodiment. As can be seen from FIG. 19, if the relationship between the cutting depth D, the cutting edge radius R of the tool 304, and the vibration amplitude A satisfies D≦A−R, then the cutting edge of the tool 304 will be separated from the workpiece 303 at least at the top dead center of the vibration. Therefore, by making A≧D+R, it is possible to achieve chip breaking.

[0094] For example, if the vibration amplitude A is set equal to D+R, chip separation occurs for each vibration cycle. Since the chip length L is expressed as π×r / I, it can be seen that the desired chip length L can be achieved by setting I=L / (π×r). In this way, the vibration conditions 24 for causing chip separation at the desired chip length L are determined.

[0095] Fig. 20 is a diagram showing the relationship between the machining path and the tool separation position, and the time change of the spindle phase, in the numerical control device 1a of embodiment 3. Fig. 21 is a diagram showing the relationship between the machining path and the tool separation position, and another time change of the spindle phase, in the numerical control device 1a of embodiment 3. Fig. 22 is a diagram showing another relationship between the machining path and the tool separation position, and another time change of the spindle phase, in the numerical control device 1a of embodiment 3. Fig. 23 is a diagram showing another relationship between the machining path and the tool separation position, and another time change of the spindle phase, in the numerical control device 1a of embodiment 3.

[0096] In Figures 20 and 21, the tool separation position Uc in the vibration direction is positioned at the vibration center of the vibration machining path (Uc = 0). In Figures 22 and 23, the tool separation position Uc is positioned on the tool 304 side (upper side) of the vibration center of the vibration machining path (Uc > 0). Figures 20 to 23 show the vibration phase e1 and the spindle phase e2. In Figures 20 and 22, the number of vibrations per spindle rotation is I = 1.5, and in Figures 21 and 23, I = 2.0.

[0097] If the vibration amplitude A is made larger than D + R, the tool 304 will be separated in the sections before and after the top dead center, and the chip length can be made even shorter than when A = D + R. For example, as shown in Figures 20 and 21, in a situation where the tool 304 is separated at the center of the vibration amplitude A, the continuous cutting section Tf where chips are generated in a continuous manner will occupy half of one vibration cycle.

[0098] The chip length L is determined by the phase change of the rotation of the spindle 300 in the continuous cutting section Tf. That is, if the spindle phase change, which is the phase change of the rotation of the spindle 300 in the continuous cutting section Tf, is ΔS, the chip length is ΔS × r. The unit of ΔS is radian. The spindle phase change ΔS is expressed as ΔS = 2π × Tc / I using the ratio Tc of the continuous cutting section Tf to the vibration period and the number of vibrations I per spindle rotation. For example, in Figure 20, Tc = 0.5 and I = 1.5, so ΔS = 2π / 3.

[0099] 22 and 23, when the tool separation position Uc is closer to the tool 304 than the center of amplitude, the continuous cutting section Tf becomes longer. Therefore, the corresponding spindle phase change ΔS also becomes larger, which results in a longer chip length L. Furthermore, as shown in Figures 21 and 23, when I is set to 2.0, the spindle phase change ΔS in the continuous cutting section Tf becomes shorter even for the same tool separation position Uc.

[0100] From the above, it is possible to shorten the chip length L by making the vibration amplitude A larger than D+R and moving the tool separation position Uc toward the workpiece 303, or by increasing the number of vibrations I per rotation of the spindle, and it is possible to determine the vibration condition 24 that achieves chip breaking at the desired chip length L.

[0101] As described above, according to the third embodiment, when performing radial vibration cutting on a surface on which no unevenness is formed due to radial vibration cutting, chip breaking can be achieved at the desired chip length.

[0102] Fourth Embodiment In a fourth embodiment, a case where vibration is stopped in one movement block of vibration cutting in the radial direction will be described.

[0103] In radial vibration cutting, vibration is applied perpendicular to the movement path during non-vibration cutting, which has a greater impact on the shape than vibration cutting, which vibrates in a direction along the movement path. Therefore, there are cases where it is desirable to stop vibration, for example, near the end point or in an arc shape. In the case of radial vibration, if the amplitude is not 0 at the end point of the block, uncut material may be left. Below, we will explain the matters required to achieve vibration stopping operation. The machining conditions 23 in embodiment 4 include information on the distance to the target stop position. This can be determined by calculating the distance from the start point of the block to the target stop position.

[0104] The target stop position, for example, at the end point, is calculated from the movement path information. Also, in the case of an arbitrary position within one movement block, it can be specified, for example, as a location where an axis reversal occurs, or by the coordinate values ​​of a specific axis. In the former case, it is determined from the movement path information, and in the latter case, it is possible to specify the specific axis and coordinate values ​​by parameters provided in the numerical control device 1a that can be arbitrarily changed by the user.

[0105] The vibration condition determination unit 13 calculates the time Tb required to reach the target stop position using the distance PL to the target stop position included in the machining conditions 23, the feed rate F, and the spindle rotation rate S, and calculates the number of vibrations N required to reach the target stop position using the vibration frequency f and the following equation (6).

[0106] Tb=PL / (F×S)×60 N=Tb×f=PL / (F×S)×60×f...(6)

[0107] Since the number of vibrations N is not necessarily an integer, an integer value m that satisfies m≦N<m+1 is found, and this integer value m is set as the number of vibrations until vibration stops.

[0108] In reality, the machine does not always operate at the feed rate (F x S), and the time to reach the target stop position is longer than Tb due to acceleration and deceleration. Therefore, even if m = N, it is possible to stop the vibration before reaching the target stop position.

[0109] The number of vibrations N until vibration stops is included in the vibration conditions 24, and when the vibration waveform is calculated in the processing execution unit 14, the number of vibrations N is counted, and the vibration in the block is stopped when the number of vibrations N reaches m, thereby achieving the desired operation.

[0110] A similar approach can be used to restart vibration. By specifying the target vibration restart position in the same way as the target stop position, the distance to the target vibration restart position can be calculated. The number of vibrations N for the target vibration restart position can be substituted by the number of times the movement amount is output, the number of times the movement path is interpolated, or the like.

[0111] As described above, according to the fourth embodiment, the radial vibration can be stopped at any position, and by converging the vibration near the end point, problems such as remaining uncut portions at the end point of the block can be solved.

[0112] Fifth Embodiment Fig. 24 is a block diagram showing an example of the configuration of a numerical control device 1b according to a fifth embodiment. In the numerical control device 1b of the fifth embodiment, a machining condition determination unit 15 is added to the numerical control device 1a of Fig. 3.

[0113] In the first to fourth embodiments, the vibration conditions 24 are set by combining machining using vibration cutting. However, in actual machining, machining of raw material before cutting, efficient removal of material by multiple rough machining operations, and finish machining to obtain a good surface after rough machining are often included in a single part machining process.

[0114] The machining condition determination unit 15 uses information such as the movement path of each block included in the machining conditions 23, whether vibration cutting is enabled or disabled, and the feed rate to determine which pattern the machining to be performed falls into: initial machining, rough machining, or finish machining.

[0115] The vibration condition determination unit 13 selects a calculation method for the vibration conditions 24 for each block based on the judgment result of the machining condition judgment unit 15. That is, it judges which cutting mode applies to each stage of the machining process described in the first to third embodiments, and selects the vibration cutting mode to be used. Based on this selection result, the vibration condition determination unit 13 determines the vibration conditions 24 for each case, and machining is performed using the vibration conditions 24 of each pattern.

[0116] Although the above describes an embodiment for general turning, embodiment 5 may also be applied to turning cycles for lathes, such as threading cycles, cutting cycles, rough cutting cycles, finishing cycles, etc., and to combined turning cycles.

[0117] By applying the first and fifth embodiments, for example, when a turning cycle is performed, the vibration condition determination unit 13 determines the vibration period and vibration frequency in the processing run immediately prior to the finishing process using the processing conditions related to the processing depth so that the minimum cutting thickness Hmin during the finishing process of the turning cycle is equal to or less than the first threshold value.

[0118] One example of a turning cycle is a thread cutting cycle, which expresses a series of operations for specific machining such as thread cutting in NC machining code such as a simple G code, making it easy to create a machining program 21. A thread cutting cycle can execute machining by describing machining conditions 23 such as end point coordinates, thread pitch, thread depth, thread angle, thread radius, and taper depth (in the case of a tapered thread) as a short machining program 21 of one or two lines.

[0119] In the thread cutting cycle, an external thread and an internal thread are cut radially multiple times using a thread cutting tool. The machining condition determination unit 15 analyzes the machining cycle command and determines whether the current machining corresponds to an initial machining, rough machining, or finish machining pattern.

[0120] The vibration condition determination unit 13 uses processing conditions 23 that can be converted into thread pitch and thread depth to determine the vibration period and vibration frequency in the processing run immediately before the finishing process so that the minimum cutting thickness Hmin during finishing of the thread cutting cycle is equal to or less than the first threshold value.

[0121] In order to realize the thread shape specified in the thread cutting cycle, the machining execution unit 14 performs machining multiple times along the pitch of the thread using the machining pattern determined by the machining condition judgment unit 15 and the vibration conditions 24 including the vibration period and vibration frequency determined by the vibration condition determination unit 13.

[0122] As described above, according to the fifth embodiment, by changing the vibration conditions 24 in radial vibration cutting according to the characteristics of the machining path, chip breaking at the desired chip length can be generally achieved.

[0123] Sixth Embodiment In the sixth embodiment, a case where a tapered portion is machined will be described. The configuration of the numerical control device 1a according to the sixth embodiment is the same as that of the numerical control device 1a according to the first embodiment shown in FIG. 1. FIG. 25 is a diagram for explaining machining of a tapered portion in the numerical control device 1a according to the sixth embodiment. As shown in FIG. 25, in machining a tapered portion, two axes, the X-axis and the Z-axis, for driving in the radial direction, operate simultaneously to machine a movement path having a taper angle θ with respect to the central axis O of the spindle 300. FIG. 25 shows the feed rate F, the Z-direction component Fz of the feed rate F, the X-direction component Fx of the feed rate F, the radial (X-direction) thickness Hr of the workpiece 303, and the cutting thickness H.

[0124] In machining the tapered portion, the radial thickness Hr of the workpiece 303 increases in accordance with the taper angle θ relative to the cutting thickness H, as expressed by Hr = H / cos θ. To accommodate this, the vibration condition determination unit 13 in the sixth embodiment replaces the cutting thickness H with H / cos θ to calculate the vibration conditions 24.

[0125] The taper angle θ is calculated in the machining condition input unit 10 by, for example, finding the arc tangent from the ratio of the movement amounts of each axis of the block, and is added to the machining conditions 23, making it available to the vibration condition determination unit 13.

[0126] With the above-described configuration, the concepts of the first to fifth embodiments can be applied to taper machining as they are, and the effect of breaking up chips can be obtained in taper machining as well.

[0127] However, as can be seen from FIG. 25, in taper machining, movement in the radial direction (X direction) occurs even when vibration is not applied, and therefore, by superimposing the vibration component, the X direction component Fx of the feed rate F increases further.

[0128] Specifically, Fx = F sin θ and Fz = F cos θ. Assuming that the thickness in the radial direction Hr is reached at the top dead center of the vibration as shown in Figure 25, the feed rate is 4A x I [mm / rev] because the movement is equal to the vibration amplitude A x 2 in half the vibration period. The vibration amplitude A is expressed as (H / cos θ) + (30F sin θ / S x I).

[0129] Two methods for dealing with an increase in the X-direction component Fx of the feed rate F will be described.

[0130] 26 is a diagram illustrating a first method for dealing with an increase in the X-direction component Fx of the feed rate F during machining of a tapered portion in the numerical control device 1a of the sixth embodiment. In the first method, a vibration component in the axial direction of the spindle 300 is added, so that the vibration direction is perpendicular to the tapered surface. As a result, as shown in FIG. 26, the radial feed amount caused by the vibration can be reduced.

[0131] Specifically, the vibration locus can be obtained by rotating a movement path (non-tapered path) that moves only in the direction of the central axis of the spindle 300 by a taper angle θ. For example, we will explain how a vibration path with a taper angle θ is expressed using a case where the Z coordinate of the non-tapered path is expressed as F×t using a composite feed rate F and the X coordinate is expressed as A sinωt. t is time. In this case, the vibration amplitude A is the cutting thickness H / 2. The vibration period is not important in the sixth embodiment, so it is simply expressed as ω, which is an arbitrary period.

[0132] When the non-tapered path is rotated by θ around the ZX coordinate, the Z coordinate becomes Fcosθ×t−A sinθ×sinωt, and the X coordinate becomes Fsinθ×t+A cosθ×sinωt.

[0133] As a result, as shown in Figure 26, the movement amount per time period of 1 / 2 the vibration period, i.e., the radial feed amount from the valley to the peak of the vibration, changes from the original H / cosθ to Hcosθ, and since θ<90° in the tapered path, it can be seen that the radial movement speed has indeed been reduced.

[0134] The above calculation is performed in the vibration condition determination unit 13, and the vibration amplitude A is included as the vibration condition 24 of the vibration waveform that is superimposed on the movement amount in the X-axis and Z-axis, thereby making it possible to break up the chips while reducing the radial movement speed.

[0135] 27 is a diagram for explaining a second method for dealing with an increase in the X-direction component Fx of the feed rate F when machining a tapered portion in the numerical control device 1a of embodiment 6. In the second method, radial vibration is realized using not only the X-axis but also the Y-axis.

[0136] 27, the amplitude of the vibration component in the X direction can be reduced by applying vibration in the Y direction as well, which can be said to change the vibration direction within the XY plane.

[0137] Specifically, in FIG. 27, the X component of the radial feed amount in the case of vibration in only the X direction is H / cos θ. In contrast, if the tilt angle in the Y direction is φ, the X component of the radial feed amount in the case of vibration in the X and Y directions is H / cos θ × cos φ - (1 - cos φ) × (R + r). The first term reduces H / cos θ by cos φ, and this is further reduced by the second term. Note that the Y component of the radial feed amount in the case of vibration in the X and Y directions is (H / cos θ + R + r) × sin φ. These movement amounts are the amplitudes from the valley to the peak of the vibration. Furthermore, there is no difference between the vibration frequency described in the previous embodiments and that in embodiment 6, so a description thereof will be omitted.

[0138] The above calculation is performed in the vibration condition determination unit 13, and the vibration waveform for the X axis is superimposed on the original movement amount, and for the Y axis, since there is no original movement command, only the vibration waveform is output, which is included in the vibration condition 24, thereby realizing synchronized vibration operation of the X axis and Y axis in the processing execution unit 14.

[0139] As described above, according to the sixth embodiment, chip breaking can be achieved by vibration in the radial direction even in a tapered path. Furthermore, chip breaking in a tapered path can be achieved while suppressing an increase in the radial feed rate.

[0140] Here, the hardware configuration of the numerical control devices 1a and 1b will be described. FIG. 28 is a diagram showing an example of the hardware configuration of the numerical control devices 1a and 1b according to the first to sixth embodiments. The numerical control devices 1a and 1b can be realized by a processor 401, a memory 402, and an interface circuit 403 shown in FIG. 28. An example of the processor 401 is a CPU (Central Processing Unit, also referred to as a central processing unit, processing unit, arithmetic unit, microprocessor, microcomputer, processor, or DSP (Digital Signal Processor)) or a system LSI (Large Scale Integration). An example of the memory 402 is a RAM (Random Access Memory) or a ROM (Read Only Memory).

[0141] The numerical control devices 1a and 1b are realized by the processor 401 reading and executing a program for executing the operations of the numerical control devices 1a and 1b, which is stored in the memory 402. It can also be said that this program causes the computer to execute the procedures or methods of the numerical control devices 1a and 1b. The memory 402 is also used as a temporary memory when the processor 401 executes various processes. Note that the functions of the numerical control devices 1a and 1b may be partially realized by dedicated hardware and partially realized by software or firmware.

[0142] The configurations shown in the above embodiments are examples of the contents of the present disclosure, and may be combined with other known technologies, or embodiments may be combined with each other, and some of the configurations may be omitted or modified within the scope of the gist of the present disclosure.

[0143] 1a, 1b Numerical control device, 2 Drive unit, 3 Machine tool, 10 Machining condition input unit, 11 Machining program analysis unit, 12 Parameter reception unit, 13 Vibration condition determination unit, 14 Machining execution unit, 15 Machining condition judgment unit, 21 Machining program, 22 NC parameters, 23 Machining conditions, 24 Vibration conditions, 31 Position controller, 32 Speed ​​controller, 201 Spindle servo control unit, 202 X-axis servo control unit, 203 Z-axis servo control unit, 300 Spindle, 301 X-axis drive unit, 302 Spindle motor, 303 Workpiece, 304 Tool, 305 X-axis servo motor, 306 Z-axis servo motor, 307 Z-axis drive unit, 401 Processor, 402 Memory, 403 Interface circuit, A Vibration amplitude, Ce Cutting edge R center point, D, D1, Dn Depth of cut, e1 Vibration phase, e2 spindle phase, f vibration frequency, H cutting thickness, Hmin minimum cutting thickness, Hr thickness, I number of vibrations per spindle rotation, N number of vibrations, O central axis, Pn current machining path, Pn-1 previous machining path, R, Rn, Rn-1 cutting edge R radius, r radius, Tf continuous cutting section, Tg separation section, Uc tool separation position, Wn current machining surface, Wn-1 previous machining surface, Wp chip, ΔS spindle phase change, Φ vibration start phase, θ taper angle.

Claims

1. A numerical control device that controls vibration cutting, which cuts a workpiece by moving the tool and the workpiece along a movement path while vibrating the tool relative to the workpiece using a feed axis provided on the workpiece or the tool, comprising: a machining condition input unit that inputs machining conditions including a spindle rotation speed, which is the rotation speed of a spindle that rotates the workpiece, and machining depth information related to the difference between a first machining and a second machining performed after the first machining; a vibration condition determination unit that determines vibration conditions including a vibration amplitude and a vibration frequency in the spindle radial direction for at least one of the first machining and the second machining based on the machining conditions, so as to vibrate the tool or the workpiece in the spindle radial direction to break up chips; and a machining execution unit that performs cutting using the machining conditions and the vibration conditions.

2. The numerical control device described in claim 1, characterized in that vibration cutting is performed in the radial direction of the spindle during the first machining and vibration cutting is not performed during the second machining, and the vibration condition determination unit determines the vibration conditions for the first machining so that the minimum cutting thickness during the second machining is equal to or less than a first threshold value.

3. A numerical control device according to claim 2, characterized in that the minimum cutting thickness is determined based on at least one of the material of the workpiece, the shape of the tool, the spindle rotation speed, and the wavelength of vibration.

4. A numerical control device according to claim 2 or 3, characterized in that the vibration condition determining unit determines the vibration frequency so that the ratio of the spindle rotation speed to the vibration frequency is not an integer multiple.

5. The numerical control device according to claim 1, characterized in that the vibration condition determination unit determines the vibration conditions for the second machining so that the machining path of the first machining and the machining path of the second machining have an intersection.

6. The numerical control device according to claim 5, wherein the machined surface by the first machining is an unmachined surface or a machined surface machined by non-vibration cutting.

7. A numerical control device as claimed in any one of claims 1 to 4, characterized in that the vibration condition determination unit further uses an axial ratio, which is the ratio between the radial movement amount when no vibration is performed and the axial movement amount of the main spindle, to determine at least one of the vibration conditions of vibration direction, vibration frequency and vibration amplitude so that chip breaking occurs.

8. A numerical control device as described in any one of claims 1 to 7, characterized in that the vibration condition determination unit calculates the number of vibrations until the vibration is stopped using a stop target position at which the vibration is stopped, and adds the calculated number of vibrations to the vibration conditions, and the processing execution unit stops the vibration at the number of vibrations.

9. A numerical control device as described in claim 2 or 3, characterized in that when a turning cycle is performed, the vibration condition determination unit determines the vibration conditions including the vibration period using machining conditions related to the machining depth so that the minimum cutting thickness during the second machining of the turning cycle is equal to or less than the first threshold value.

10. The numerical control device described in claim 9, characterized in that when a thread cutting cycle is performed, the vibration condition determination unit determines the vibration conditions including the vibration period using machining conditions that can be converted into thread pitch and thread depth so that the minimum cutting thickness during the second machining of the thread cutting cycle is equal to or less than the first threshold value.

11. A numerical control device as described in any one of claims 1 to 10, characterized in that the vibration condition determination unit determines vibration conditions in the spindle radial direction and spindle axial direction so that the vibration direction is perpendicular to the tapered surface when machining a tapered portion.

12. A numerical control device according to any one of claims 1 to 10, characterized in that the vibration condition determination unit drives two feed axes to vibrate in the radial direction of the spindle when machining a tapered portion.

13. A numerical control method for cutting a workpiece by moving the tool and the workpiece along a movement path while vibrating the tool relative to the workpiece using a feed axis provided on the workpiece or the tool, the method comprising: a machining condition input step for inputting machining conditions including a spindle rotation speed, which is the rotation speed of a spindle that rotates the workpiece, and machining depth information related to the difference between a first machining and a second machining performed after the first machining; a vibration condition determination step for determining vibration conditions including a vibration amplitude and a vibration frequency in the spindle radial direction for at least one of the first machining and the second machining based on the machining conditions, so that the tool or the workpiece is vibrated in the spindle radial direction to break up chips; and a machining execution step for performing cutting using the machining conditions and the vibration conditions.

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