machine tool

Abstract

Machine tool (1, 21), comprising: a holding device (3) on which a shaft-shaped workpiece (5) is mounted; a tool (19) capable of moving relative to the workpiece (5) in a radial and axial direction of the workpiece (5); a machining control unit (10, 22) that performs a thread cutting process by repeating a tool pass in which the tool (19) cuts the workpiece (5) in the radial direction, moves in a direction parallel to an axis of the workpiece (5), and then moves away from the workpiece (5) in the radial direction while the workpiece (5) and the tool (19) are relatively rotated around the axis of the workpiece (5); a speed control unit capable of changing a speed on a tool pass basis; and a rotational speed calculation section (13) which calculates a relative rotational speed between the workpiece (5) and the tool (19) in each tool pass, the machine tool (1, 21) being characterized in that the machining control unit (10, 22) is capable of executing the thread cutting process in a plurality of types of cutting modes having different cutting methods of the tool (19), the machine tool (1, 21) further comprising: a number-of-same-speed cutting passes calculating section (14) that determines the cutting mode and decides the number of tool passes before the speed is to be changed according to the cutting mode.

Description

[0001] The present invention relates to machine tools, such as lathes, capable of performing, for example, a thread cutting process.

[0002] When machining is performed with a machine tool (particularly machining a workpiece with low rigidity or machining using a tool with low rigidity), strong vibrations known as chatter vibration are often generated during machining. Such chatter vibration causes problems such as chatter marks on the cutting surface, tool breakage, and so on. As a solution to such problems, a technique has been developed to suppress chatter vibration by changing the main spindle speed during a thread cutting cycle, as disclosed in Japanese Patent Application Publication No. 2004-209558 (JP 2004-209558 A).

[0003] The above conventional techniques show, as examples of methods of changing the main spindle speed, a method of changing the main spindle speed for a finishing process, and a method of changing the main spindle speed in each pass. However, the conventional techniques do not show a suitable method of changing the main spindle speed. When a cutting method of the tool passes (hereinafter referred to as "cutting mode") is a so-called alternate flank feed mode, the factor that significantly affects the instantaneous cutting is the cutting surface of two passes before. Accordingly, effective suppression of chatter vibration cannot always be expected using the main spindle speed changed according to the cutting of one pass before.Thus, the operator must decide, according to the cutting mode, etc., a setting of the number of passes in which cutting is continuously performed at the same main spindle speed (hereinafter referred to as the "number of same-speed cutting passes") each time the main spindle speed is changed. Therefore, it is not easy for an unskilled operator to use such machining tools. Prior to the present application, the applicant developed a technique capable of suppressing an increase in cutting load. In this technique, the same lead-out angle is used in all the passes when the main spindle speed is changed on a per-pass basis during a thread cutting cycle (Japanese Patent Application No. 2012-121107 (Publication No.: JP 2013-244576 A)). The present invention was made in consideration of this technique.

[0004] It is an object of the present invention to provide a machine tool in which it is not necessary for the operator to decide the number of same-speed cutting passes each time according to the cutting mode, etc.

[0005] The object is achieved by a machine tool according to claim 1. Advantageous further developments are contained in the dependent claims.

[0006] To achieve the above object, a machine tool according to a first aspect of the present invention includes a holder, a tool, a machining control unit, a rotational speed control unit, and a rotational speed calculation section (hereinafter referred to as "a first calculation section"). A shaft-shaped workpiece is mounted on the holder. The tool is capable of moving relative to the workpiece in a radial and axial direction of the workpiece. The machining control unit performs a thread cutting process by repeating a tool pass in which the tool cuts the workpiece in the radial direction, moves in a direction parallel to an axis of the workpiece, and then moves away from the workpiece in the radial direction while the workpiece and the tool are relatively rotated around the axis of the workpiece.The speed control unit is capable of changing a rotational speed based on a tool pass. The first calculation section calculates a relative rotational speed between the workpiece and the tool in each tool pass. The machining control unit is capable of executing the thread cutting process in a plurality of cutting modes having different cutting methods of the tool. The machine tool further includes a number-of-the-same-speed-cutting-passes calculation section (hereinafter referred to as a "second calculation section") that determines the cutting mode and decides the number of tool passes before changing the rotational speed according to the cutting mode.

[0007] According to a second aspect of the present invention, the machine tool in the first aspect of the present invention further includes a vibration detection unit, a vibration direction determination section, and a cutting mode decision section. The vibration detection unit detects vibrations generated in a rotation axis direction and a feed direction. The vibration direction determination section determines a direction in which the vibrations are more likely to be generated based on the detected vibrations. The cutting mode decision section decides one cutting mode from among the plurality of types of cutting modes.The cutting mode decision section decides a cutting mode according to the direction in which vibrations are more likely to be generated, and the machining control unit performs machining in the cutting mode decided by the cutting mode decision section.

[0008] According to a third aspect of the present invention, in the first or second aspect of the present invention, a radial feed mode, a flank feed mode, and an alternate flank feed mode are set as the cutting modes.

[0009] According to the present invention, the machine tool includes the second calculation section that determines the cutting mode and, according to the cutting mode, decides the number of tool passes before changing the rotational speed. Accordingly, the second calculation section determines the cutting mode of the thread cutting process based on the set machining program, etc., and automatically decides an optimal number of same-speed cutting passes according to the cutting mode. For example, the second calculation section decides to change the rotational speed in every pass when the cutting mode is the radial feed mode, or decides to change the rotational speed every two passes when the cutting mode is the alternate flank feed mode. Thus, even an inexperienced operator can easily suppress chatter vibration and use the machine tool with ease.

[0010] According to the second aspect of the present invention, the cutting mode in which chatter vibrations are less likely to be generated is decided according to the vibrations, and machining is performed in this cutting mode. Therefore, chatter vibrations can be further suppressed. Fig. 1 is a diagram showing an overall configuration of a lathe. Fig. 2 is a diagram showing an example of a tool pass in a thread cutting cycle using the lathe. Fig. 3 is a diagram showing a manner in which the main spindle rotation is changed during a thread cutting cycle. Fig. 4A to 4C are diagrams showing paths of the tool and the width which are affected by the preceding cutting surface in the three types of cutting modes, namely a radial feed mode, a flank feed mode and an alternate flank feed mode. Fig. 5 is a diagram showing a manner in which the main spindle speed is changed so that cutting is performed in the last tool pass at the high speed. Fig. 6 is a diagram showing an overall configuration of a lathe according to a modified embodiment.

[0011] A machine tool according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0012] First, the overall configuration of a machine tool 1 is described with reference to Fig. 1. The lathe 1 includes a clamping device 3 having a claw 4 at the distal end of a main spindle 2, and capable of holding a shaft-shaped workpiece 5 by the clamping device 3. A motor 7, which rotates the main spindle 2, and an encoder 6, which detects the rotational speed of the main spindle 2, are contained in the headstock 8, which supports the main spindle 2 so that the main spindle 2 rotates.

[0013] A main spindle control section 9 monitors the rotational speed of the main spindle 2 through the encoder 6 and controls the rotational speed of the main spindle 2. A lathe control section 10 controls the entire behavior of the lathe 1 and is connected to the main spindle control section 9, an input unit 11, a storage section 12, a rotational speed calculation section 13 (a first calculation section), a number-of-same-speed cutting passes calculation section 14 (a second calculation section), and a first-pass rotational speed calculation section 15 (hereinafter referred to as "a third calculation section"). The input unit 11 sets the cutting mode and sends a command to change the main spindle rotational speed. The storage section 12 stores a machining program, etc. The first calculation section 13 calculates the main spindle rotational speed.The second calculation section 14 decides the number of same-speed cutting passes (i.e., the number of passes in which cutting is continuously performed at the same main spindle speed). The third calculation section 15 calculates the main spindle speed in the initial pass (first pass) so that cutting in the final tool pass is performed at a high speed. The lathe 1 controls the rotational speed of the workpiece 5 (i.e., the main spindle speed) via the main spindle control section 9. Further, the lathe 1 controls the machining operation so that a tool 19 cuts the peripheral surface of the rotating workpiece 5 and the workpiece 5 or the tool 19 is fed in the rotation axis direction and the radial direction using a well-known configuration.

[0014] An example of a tool pass in a thread cutting cycle as a machining form of the lathe 1 will be described with reference to Fig. 2 described.

[0015] The lathe 1 carries out a thread cutting process by repeating a cycle which, according to the machining program stored in the storage section 12, consists of the following multiple tool passes (in Fig. 2 (shown by arrows). In the tool passage, the motor 7, controlled by the main spindle control section 9, is supplied with electric power to rotate the main spindle 2 at a predetermined main spindle speed, and the workpiece 5 rotates around the axis. Furthermore, under the control of the lathe control section 10, the tool 19 mounted on a tool holder 20 cuts the workpiece 5 in the radial direction and is advanced in the longitudinal direction (the rotation axis direction) to machine a threaded portion A, and then moves away from the workpiece 5 in the radial direction.

[0016] During thread cutting cycle machining with the lathe 1, the main spindle speed is changed to a low speed or a high speed at a predetermined period. A manner in which the main spindle speed is changed during thread cutting cycle machining is briefly described below.

[0017] S0 represents a reference speed, and W represents a change in the main spindle speed. These values ​​S0, W are input in advance by the operator via the input unit 11. The first calculation section 13 calculates a high speed SH and a low speed SL based on these parameters using the following equations (1), and the main spindle speed is changed to either the high speed SH or the low speed SL in each pass ( Fig. 3). This can suppress an increase in chatter vibration compared to the case where cutting is performed in all these passes at a constant main spindle speed. SH=(1+W200)S0SL=(1−W200)S0 SH High-speed side main spindle speed [min -1 ] SL low-speed side main spindle speed [min -1 ] S0 Reference speed [min -1 ] W Change in main spindle speed [%]

[0018] A decision of the number of same-speed cutting passes by the second calculation section 14 will be described. The three types of cutting modes, namely a radial feed mode, a flank feed mode, and an alternate flank feed mode, can be set as an embodiment of the cutting mode (ie, a cutting method of the tool pass) in the lathe 1. Fig. 4A to 4C are diagrams showing paths of the tool and the width affected by the preceding cutting surface (later referred to as “regenerative width”) in the three types of cutting modes, respectively.

[0019] The Fig. The radial feed mode shown in Figure 4A is a cutting mode in which cutting is performed with cutting edges on both the right and left sides (right and left sides in Fig. 2) of the blade cutting insert of the tool 19. The smallest V-shaped surface in Fig. 4A corresponds to the path of the tool of the first pass. As machining progresses, the path of the tool gradually changes to a larger V-shaped surface, and the largest V-shaped surface corresponds to the path of the tool of the tenth pass. Accordingly, in the radial feed mode, a cut of the nth pass is only affected by the cutting surface of the (n-1)th pass. When cutting the tenth pass, Fig. 4A the regenerative width from one pass before bd1a.

[0020] The Fig. The flank feed mode shown in Fig. 4B is a cutting mode in which cutting is performed with the cutting edge on the left side of the blade insert of the tool 19. The small V-shaped surface in Fig. 4B, on the far right, corresponds to the tool path of the first pass. As machining progresses, the tool path gradually changes to a V-shaped surface containing an inclined surface to the left, and the large V-shaped surface containing the inclined surface on the far left corresponds to the tool path of the tenth pass. Accordingly, even in the flank feed mode, a cut of the nth pass is only affected by the cutting surface of the (n-1)th pass. When cutting the tenth pass, Fig. 4B the regenerative width from one pass before bd1b.

[0021] The Fig. The alternating flank feed mode shown in Figure 4C is a cutting mode in which cutting is performed by alternately using the left and right cutting edges of the tool 19 in each pass. The smallest V-shaped surface in Fig. 4C corresponds to the path of the tool of the first pass. As machining progresses, the path of the tool alternately changes to a V-shaped surface containing a right or left inclined surface. The V-shaped surface containing the largest right and left inclined surface corresponds to the path of the tool of the tenth pass. Accordingly, in the alternating flank feed mode, a cutting of the nth pass is influenced by the cutting surface of the (n-1)th pass and the cutting surface of the (n-2)th pass. In the cutting of the tenth pass, Fig. 4C the regenerative width from one pass before bd1c and the regenerative width from two passes before is in Fig. 4C bd2c. Regarding the relationship between the regenerative width and chatter, the larger the regenerative width, the more chatter is likely to be generated due to the influence of the previous cutting surface. In the alternating flank feed mode, chatter is more likely to be influenced by the cutting surface from two previous passes because the regenerative width of two previous passes is larger than that of one previous pass.

[0022] In view of the above, in the lathe 1, the second calculation section 14 determines the cutting mode of the thread cutting process based on the set machining program, etc., and sets the number of same-speed cutting passes to “2” when the alternate flank feed mode is set as the cutting mode, and sets the number of same-speed cutting passes to “1” when the radial feed mode or the flank feed mode (namely, any mode other than the alternate flank feed mode) is set as the cutting mode.

[0023] A calculation of the main spindle speed of the first pass through the third calculation section 15 is described. Fig. 5 is a diagram showing a manner in which the main spindle speed is changed so that cutting is performed in the last tool pass at the high speed.

[0024] In Fig. 5, C represents the number of same-speed cutting passes and N represents the total number of cutting operations. In the Fig. 5 shown edits is C=2 and N=6. In Fig. 5, P represents the period with which the main spindle speed is changed, (n) represents the sequence of cutting passes in the period P, and s(n) (n=1, 2, ..., P) represents the main spindle speed in the cutting pass in the period P. In this example, the main spindle 2 is rotated at the high speed SH in s(1) to s(C), while the main spindle 2 is rotated at the low speed SL in s(C+1) to s(P). In this case, the third calculation section calculates the main spindle speed ss in the first pass using the following equations (2) to (4). That is, the third calculation section 15 decides whether the high speed SH in s(1) to s(C) or the low speed SL in s(C+1) to s(P) in the first pass should be the main spindle speed ss. P=2×C nm=(N−1)mod P ss=s(P−nm+1)

[0025] The total number of cutting operations N can be calculated by dividing the total cutting amount by the cutting amount per pass.

[0026] The lathe 1 includes the second calculation section 14, which determines the number of cutting passes at the same speed. The second calculation section 14 determines the cutting mode of the thread cutting process based on the set machining program, etc., and automatically determines the optimal number of cutting passes at the same speed according to the cutting mode. Thus, even an inexperienced operator can easily suppress chatter vibrations and use the machine tool with ease.

[0027] The lathe 1 includes the third calculation section 15. The third calculation section 15 automatically decides whether the main spindle speed in the first pass should be the high speed SH or the low speed SL, so that cutting in the last pass is performed at the high speed. Therefore, cutting in the last tool pass at the low speed can be reliably prevented.

[0028] The machine tool according to the present invention is not limited to the form of the above embodiment in any respect, and not only the overall configuration of the machine tool but also the manner in which the main spindle speed is changed, etc., can be appropriately modified as necessary without departing from the spirit and scope of the invention.

[0029] For example, although the cutting mode is manually set in the lathe 1 of the above embodiment, a cutting mode more likely to suppress vibrations may be automatically set in response to detection of vibrations generated on the main spindle. A lathe 21 according to such a modified embodiment is constructed based on Fig. 6. In Fig. 6 are the same components as those in Fig. 1 shown lathe 1 is designated by the same reference numerals.

[0030] The lathe 21 has a configuration similar to that of the lathe 1, but a vibration sensor 18 that detects vibrations generated on the main spindle 2 is included near the main spindle 2 in the headstock 8. A vibration direction determining section 16 and a cutting mode deciding section 17 are connected to a lathe control section 22 that controls the overall behavior of the lathe 21. The vibration direction determining section 16 determines the direction in which vibrations are more likely to be generated according to the output of the vibration sensor 18. The cutting mode deciding section 17 decides the cutting mode based on this direction.

[0031] In the lathe 21, after the radial feed mode is automatically selected to start machining, the vibration sensor 18 detects vibrations generated on the main spindle 2 in both the feed direction and the axial direction. The vibration direction determining section 16 determines that the direction of larger vibrations is the direction in which vibrations are more likely to be generated. If vibrations are more likely to be generated in the feed direction, the cutting mode deciding section 17 selects the flank feed mode or the alternate flank feed mode.In either the flank feed mode or the alternate flank feed mode, the cutting width in the feed direction is smaller, and therefore the cutting cross-sectional area is less likely to change, and the proportion of the feed direction component (thrust force) of the combined cutting force is smaller compared to the radial feed mode. The cutting mode decision section 17 then changes the cutting mode from the radial feed mode to the flank feed mode or the alternate flank feed mode to continue machining. When vibration is more likely to be generated in the axial direction, the cutting mode decision section 17 selects the radial feed mode.In the radial feed mode, the cutting width in the axial direction is smaller, and therefore the cutting cross-sectional area is less likely to change, and the proportion of the axial component (feed force) of the combined cutting force is smaller compared to the flank feed mode and the alternate flank feed mode. The cutting mode decision section 17 then continues machining without changing the cutting mode. When the cutting mode is changed, the third calculation section 15 sets N to the number of remaining cutting operations rather than the total number of cutting operations. Then, the third calculation section 15 calculates the main spindle speed ss in the first pass after changing the cutting mode using equations (2) to (4).Whether the flank feed mode or the alternate flank feed mode is selected when the cutting mode is changed can be preset by the operator or can be automatically decided based on the machining program, etc.

[0032] The same advantages as those of lathe 1 can be expected from this lathe 21. For example, even inexperienced operators can easily suppress chatter vibrations, and cutting at the low speed in the last tool pass can be reliably prevented.

[0033] The lathe 21 is provided with the vibration sensor 18 that detects vibrations generated on the main spindle 2, the vibration direction determining section 16 that determines the direction in which vibrations are most likely to be generated, and the cutting mode deciding section 17 that decides the cutting mode based on the direction in which vibrations are most likely to be generated. Thus, the cutting mode in which chatter vibrations are least likely to be generated is determined according to the direction in which vibrations are more likely to be generated, and machining is performed in this cutting mode. Therefore, chatter vibrations can be further suppressed.

[0034] For example, the above embodiment and the modified embodiment are configured such that cutting is performed in the last tool pass at the high speed. However, another modification may be configured such that cutting is performed in a specific tool pass rather than in the last tool pass at the high speed because chatter vibrations tend to be caused, etc. In this case, N represents the pass in which cutting is desired to be performed at the high speed (or the number of remaining cutting operations until that pass), and the main spindle speed ss in the first pass (or the first pass after the change of the cutting mode) is calculated using equations (2) to (4).

[0035] Control of the thread cutting process in the above embodiment and the modified embodiment is applicable to an internal thread cutting process of a cylindrical portion, etc., as well as an external thread cutting process.

[0036] In the above embodiment and the modified embodiment, the three types of cutting modes, namely the radial feed mode, the flank feed mode, and the alternate flank feed mode, can be set as the cutting mode. However, other cutting modes can also be set in the present invention. Alternatively, only two types of cutting modes including the alternate flank feed mode can be set in the present invention.

[0037] In the case where the cutting mode can be manually input and was manually input in the modified embodiment, machining may be started by the input cutting mode rather than the radial feed mode, or the cutting mode may not be changeable.

[0038] Although the vibration sensor 18 is included in the spindle box 8 in the modified embodiment, the vibration sensor 18 may be placed on the tool holder 20 to detect vibrations generated on the workpiece 5.

[0039] The embodiment and the modified embodiment are described with respect to the lathe that rotates a workpiece as one embodiment of the machine tool. However, the present invention may be applicable to other machine tools, such as a machining center, that perform the same machining by relatively rotating a tool and a workpiece through a feed shaft rather than rotating the main spindle.

[0040] It is explicitly stated that, regardless of the arrangement of features in the embodiments and / or claims, all features in the description and / or claims are intended to be separate and independent of each other for the purpose of original disclosure as well as for the purpose of limiting the claimed invention. It is explicitly stated that all ranges of values ​​or indications of groups of instances disclose every possible intermediate value or intermediate instance for the purpose of original disclosure as well as for the purpose of limiting the claimed invention, in particular as limits of ranges of values.

Claims

[1] Machine tool (1, 21), comprising: a holding device (3) on which a shaft-shaped workpiece (5) is mounted; a tool (19) capable of moving relative to the workpiece (5) in a radial and axial direction of the workpiece (5); a machining control unit (10, 22) that performs a thread cutting process by repeating a tool pass in which the tool (19) cuts the workpiece (5) in the radial direction, moves in a direction parallel to an axis of the workpiece (5), and then moves away from the workpiece (5) in the radial direction while the workpiece (5) and the tool (19) are relatively rotated around the axis of the workpiece (5); a speed control unit capable of changing a speed on a tool pass basis; and a speed calculation section (13) which calculates a relative speed between the workpiece (5) and the tool (19) in each tool pass, wherein the machine tool (1, 21) characterized by is that the machining control unit (10, 22) is capable of executing the thread cutting process in a plurality of types of cutting modes having different cutting methods of the tool (19), the machine tool (1, 21) further comprising: a number-of-same-speed cutting passes calculating section (14) that determines the cutting mode and decides the number of tool passes before the speed is to be changed according to the cutting mode. [2] Machine tool (1, 21) according to claim 1, further comprising: a vibration detection unit (18) that detects vibrations generated in a rotation axis direction and a feed direction; a vibration direction determining section (16) which determines a direction in which the vibrations are more likely to be generated based on the detected vibrations; and a cutting mode decision section (17) which decides a cutting mode from the plurality of types of cutting modes, wherein the cutting mode decision section (17) decides a cutting mode according to the direction in which the vibrations are more likely to be generated, and the machining control unit (10, 22) executes machining in the cutting mode decided by the cutting mode decision section (17). [3] A machine tool (1, 21) according to claim 1 or 2, wherein a radial feed mode, a flank feed mode and an alternate flank feed mode are set as the cutting modes.

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