Machine tool, control device for machine tool, and variable lead thread cutting method

Abstract

The present invention provides a machine tool capable of accurately forming variable lead thread portions even on long workpieces, a control device for the machine tool, and a variable lead thread cutting method. [Solution] A machine tool 100 that performs variable lead thread cutting to form a variable lead thread portion VL in the longitudinal direction of a workpiece W, comprising a feed means, a rotation means, and a control device 140 for driving and controlling the tool post 130, wherein the variable lead thread cutting includes an Nth thread cutting operation that forms the Nth variable lead thread portion in the Nth machining section (N=1, 2...) of the workpiece W, and an N+1th thread cutting operation that forms the N+1th variable lead thread portion continuous with the Nth variable lead thread portion in the N+1th machining section adjacent to the Nth machining section of the workpiece W, wherein the control device 140 rotates the workpiece W while relatively feeding and moving the workpiece W and the cutting tool T to start the N+1th thread cutting operation from within the Nth machining section.

Description

Technical Field

[0001] The present invention relates to a machine tool, a control device for a machine tool, and a variable lead thread cutting method, and particularly to a machine tool for machining a variable lead thread, a control device for a machine tool, and a variable lead thread cutting method.

Background Art

[0002] Conventionally, as a machine tool for forming a "variable lead screw" in which the lead (the distance advanced per revolution of the screw) changes, a first coefficient device that gives a coefficient command to the head so that the lead of the screw is constant, and a second coefficient device that issues a coefficient command of +1 or -1 each time the workpiece rotates, and an adder that adds the outputs of the first and second coefficient devices and gives a coefficient command that increases or decreases arithmetically to the head are provided. A numerically controlled lathe is known (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] If the workpiece is short, a variable lead screw portion can be accurately formed on the workpiece by the above-described machine tool. However, if the workpiece is long, it is difficult to accurately form a variable lead screw portion on the workpiece due to the influence of the contact rotation of the workpiece.

[0005] Therefore, the present invention solves the problems of the prior art as described above. That is, an object of the present invention is to provide a machine tool, a control device for a machine tool, and a variable lead thread cutting method capable of accurately forming a variable lead screw portion even for a long workpiece.

Means for Solving the Problems

[0006] The invention according to claim 1 is a machine tool that performs variable lead thread cutting to form a variable lead thread portion in the longitudinal direction of the workpiece, comprising: a workpiece holding means for holding a workpiece; a tool post for holding a cutting tool for cutting the workpiece; a feeding means for feeding the cutting tool relative to the workpiece in a predetermined machining feed direction by relative movement between the workpiece holding means and the tool post; a rotating means for rotating the workpiece; and a control device for driving and controlling the feeding means, the rotating means and the tool post, wherein the variable lead thread cutting is performed on the workpiece. The method includes a nth thread cutting process that forms the nth variable lead screw portion in the nth machining section (N=1, 2...) of the workpiece, and an N+1 thread cutting process that forms the N+1 variable lead screw portion continuous with the nth variable lead screw portion in the N+1 machining section adjacent to the nth machining section of the workpiece, wherein the control device rotates the workpiece while relatively feeding and moving the workpiece and the cutting tool to start the N+1 thread cutting process from within the nth machining section, thereby solving the aforementioned problems.

[0007] The invention according to claim 2 solves the aforementioned problems by, in addition to the configuration of the machine tool described in claim 1, the control device rotates the workpiece while relatively feeding and moving the workpiece and the cutting tool, thereby performing a cutting operation along a predetermined spiral cutting path, and when the control device performs the N thread cutting operation, the control device repeats the cutting operation until it reaches the target cutting depth targeted by the variable lead thread cutting operation.

[0008] The invention according to claim 3 solves the aforementioned problems by, in addition to the configuration of the machine tool described in claim 1 or claim 2, the control device changes the feed amount in the feed movement by a predetermined amount each time the workpiece is rotated by 1 / m (m=2, 3, ...) during the thread cutting process of N.

[0009] The invention according to claim 4 is a control device for a machine tool that performs variable lead thread cutting to form a variable lead thread portion in the longitudinal direction of a workpiece, comprising: a workpiece holding means for holding a workpiece; a tool post for holding a cutting tool for cutting the workpiece; a feeding means for feeding the cutting tool relative to the workpiece in a predetermined machining feed direction by relative movement between the workpiece holding means and the tool post; and a rotating means for rotating the workpiece, wherein the variable lead thread cutting includes an Nth thread cutting operation to form an Nth variable lead thread portion in the Nth machining section (N=1, 2...) of the workpiece, and an N+1th thread cutting operation to form an N+1 variable lead thread portion continuous with the Nth variable lead thread portion in the N+1 machining section adjacent to the Nth machining section of the workpiece, and the above-mentioned problems are solved by rotating the workpiece while relatively feeding the workpiece and the cutting tool, thereby starting the N+1th thread cutting operation from within the Nth machining section.

[0010] The invention according to claim 5 is a variable lead thread cutting method for forming a variable lead thread portion in the longitudinal direction of a workpiece using a machine tool comprising: a workpiece holding means for holding a workpiece; a tool post for holding a cutting tool for cutting the workpiece; a feeding means for feeding the cutting tool relative to the workpiece in a predetermined machining feed direction by relative movement between the workpiece holding means and the tool post; a rotating means for rotating the workpiece; and a control device for driving and controlling the feeding means, the rotating means and the tool post, wherein the method comprises: an Nth thread cutting step for forming an Nth variable lead thread portion in the Nth machining section (N=1, 2...) of the workpiece; and an N+1th thread cutting step for forming an N+1 variable lead thread portion continuous with the Nth variable lead thread portion in the N+1 machining section adjacent to the Nth machining section of the workpiece, wherein the N+1th thread cutting step is started from within the Nth machining section, thereby solving the aforementioned problems.

[0011] The invention according to claim 6 solves the aforementioned problems by, in addition to the configuration of the variable lead thread cutting method described in claim 5, repeating a cutting process in the N thread cutting step, in which the workpiece is rotated while the workpiece and the cutting tool are relatively fed and moved, and a cutting process is performed along a predetermined helical cutting path, until the target cutting depth targeted by the variable lead thread cutting is reached.

[0012] The invention according to claim 7 solves the aforementioned problems by, in addition to the configuration of the variable lead thread cutting method described in claim 5 or claim 6, changing the feed amount in the feed movement by a predetermined amount each time the workpiece is rotated by 1 / m (m=2, 3, ...) in the thread cutting step N.

[0013] The invention according to claim 8 solves the aforementioned problems by having, in addition to the configuration of the variable lead thread cutting method described in claim 5, the thread cutting step N includes a thread forming substep that forms the variable lead thread portion N, and a groove width expansion substep that expands the thread groove width of the variable lead thread portion N from an expansion start position advanced by a predetermined amount in the feed direction from a reference position in the thread forming substep. [Effects of the Invention]

[0014] According to the machine tool of the invention described in claim 1, the control device rotates the workpiece while relatively feeding and moving the workpiece and the cutting tool, and starts the N+1th thread cutting process from within the Nth processing section. As a result, the variable lead thread portion of the workpiece is formed by multiple thread cutting processes. Therefore, by setting the processing section to a range in which processing accuracy can be ensured, it becomes possible to process the workpiece with a variable lead thread, and even long workpieces can have a variable lead thread portion formed with high accuracy.

[0015] According to the machine tool of the invention of claim 2, in addition to the effects of the machine tool of the invention of claim 1, when the control device performs the Nth thread cutting, the control device repeats the cutting process until it reaches the target cutting depth set by variable lead thread cutting. As a result, the Nth variable lead thread portion of the workpiece is formed by multiple cutting operations, reducing the cutting resistance applied to the cutting tool, extending the life of the cutting tool, and reducing waste, thereby mitigating the environmental burden.

[0016] According to the machine tool of the invention of claim 3, in addition to the effects of the machine tool of the invention of claim 1 or claim 2, the control device changes the feed amount in the feed movement by a predetermined amount each time the workpiece is rotated 1 / m (m=2, 3, ...) during the Nth thread cutting process. As a result, the feed amount of the variable lead screw portion formed on the workpiece changes in stages, making it easier to control the operation of the machine tool compared to the case where the feed amount of the variable lead screw portion formed on the workpiece is continuously changed. This allows for faster processing of the workpiece, reduced processing time, and reduced power consumption.

[0017] According to the control device for a machine tool of the invention described in claim 4, by rotating the workpiece while relatively feeding and moving the workpiece and the cutting tool, the N+1th thread cutting process is started from within the Nth processing section, so that the variable lead thread portion of the workpiece is formed by multiple thread cutting processes. This makes it possible to set a processing section within a range where processing accuracy can be guaranteed, enabling variable lead thread cutting on the workpiece, and allowing for the formation of a variable lead thread portion with high accuracy even on long workpieces.

[0018] According to the variable lead thread cutting method of the invention described in claim 5, since the N+1 thread cutting step is started from within the Nth cutting section, the variable lead thread portion of the workpiece is processed through multiple thread cutting steps. Therefore, it is possible to set a range in which processing accuracy can be ensured as the processing section, and variable lead thread cutting can be performed on the workpiece, making it possible to form a variable lead thread portion with high accuracy even on long workpieces.

[0019] According to the variable lead thread cutting method of the invention of claim 6, in addition to the effects of the variable lead thread cutting method of the invention of claim 5, in the Nth thread cutting step, the cutting process is repeated until the target cutting depth targeted by the variable lead thread cutting is reached, by rotating the workpiece while relatively feeding and moving the workpiece and the cutting tool together, and cutting along a predetermined helical cutting path. As a result, the Nth variable lead thread portion of the workpiece is formed through multiple cutting steps, reducing the cutting resistance applied to the cutting tool, extending the life of the cutting tool, and reducing waste, thereby reducing the environmental burden.

[0020] According to the variable lead thread cutting method of the invention of claim 7, in addition to the effects of the variable lead thread cutting method of the invention of claim 5 or claim 6, in the Nth thread cutting step, by changing the feed amount in the feed movement by a predetermined amount each time the workpiece is rotated 1 / m (m=2, 3, ...), the feed amount of the variable lead thread portion formed on the workpiece changes in stages. Therefore, compared to the case where the feed amount of the variable lead thread portion formed on the workpiece is continuously changed, the operation control of the machine tool becomes easier, the workpiece can be processed at a higher speed, the processing time can be shortened, and power consumption can be reduced.

[0021] According to the variable lead thread cutting method of the invention of claim 8, in addition to the effects of the variable lead thread cutting method of the invention of claim 5, the nth thread cutting step includes a thread forming substep for forming the nth variable lead thread portion and a groove width expansion substep for expanding the thread groove width of the nth variable lead thread portion from an expansion start position advanced by a predetermined amount in the feed direction from a reference position in the thread forming substep. As a result, the thread groove width of the variable lead thread portion is expanded, and a male screw-shaped variable lead thread portion can be formed on the workpiece. [Brief explanation of the drawing]

[0022] [Figure 1] A diagram illustrating the configuration of a machine tool, which is a first embodiment of the present invention. [Figure 2A]A side view of the workpiece showing the first machining example of the workpiece by the machine tool shown in FIG. 1. [Figure 2B] An enlarged view of IIB in FIG. 2A [Figure 3A] A flowchart showing the variable lead thread cutting method in the first machining example. [Figure 3B] A flowchart showing each thread cutting step shown in FIG. 3A [Figure 3C] A flowchart showing the cutting process shown in FIG. 3B [Figure 4] A diagram explaining some parameters in the thread cutting step of the first machining example. [Figure 5] A side view of the workpiece showing the tool path in the first thread cutting step. [Figure 6] An enlarged view of part VI shown in FIG. 5 in the first thread cutting step. [Figure 7] A side view of the workpiece showing the machining result by the first thread cutting step. [Figure 8] A side view of the workpiece showing the tool path in the second thread cutting step. [[ID=二十八]] [Figure 9] A side view of the workpiece showing the second machining example of the workpiece by the machine tool shown in FIG. 1. [Figure 10] A diagram explaining some parameters in the thread cutting step of the second machining example. [Figure 11] A flowchart showing the thread cutting steps in the second machining example. [Figure 12] A flowchart showing the groove width expansion sub-step in the second machining example. [Figure 13] A side view of the workpiece showing the tool path in the second thread cutting step of the second machining example. [Figure 14] A side view of the workpiece showing the third machining example of the workpiece by the machine tool shown in FIG. 1. [Figure 15] A device configuration diagram of the machine tool which is the second embodiment of the present invention.

Mode for Carrying Out the Invention

[0023] The present invention relates to a machine tool that performs variable lead thread cutting to form a variable lead thread portion in the longitudinal direction of a workpiece, comprising: a workpiece holding means for holding a workpiece; a tool post for holding a cutting tool for cutting the workpiece; a feeding means for feeding the cutting tool relative to the workpiece in a predetermined machining feed direction by relative movement between the workpiece holding means and the tool post; a rotating means for rotating the workpiece; and a control device for driving and controlling the feeding means, the rotating means and the tool post, wherein the variable lead thread cutting is performed with respect to the Nth machining section (N=1, 2...) of the workpiece. The method includes a nth thread cutting process to form a variable lead screw portion, and an n+1th thread cutting process to form a variable lead screw portion continuous with the nth variable lead screw portion in the n+1th machining section adjacent to the nth machining section of the workpiece, wherein the control device rotates the workpiece while relatively feeding and moving the workpiece and the cutting tool to start the n+1th thread cutting process from within the nth machining section, and the specific embodiment can be anything as long as it is possible to accurately form a variable lead screw portion even in a long workpiece. [Examples]

[0024] Hereinafter, a machine tool 100, a control device 140 equipped with the machine tool 100, and a variable lead thread cutting method using the machine tool 100 will be described based on Figures 1 to 14.

[0025] <1. Overview of Machine Tools> First, based on Figure 1, which is a diagram of the device configuration of a machine tool that is one embodiment of the present invention, we will explain the overview of the machine tool 100, which is an automatic lathe.

[0026] The machine tool 100 includes at least a spindle (workpiece holding means) 110 for holding a workpiece W, a spindle feed mechanism (feeding means) 120 for moving the spindle 110 in the longitudinal direction of the workpiece W (machining feed direction; Z-axis direction as shown in Figure 1), a tool post 130 for holding a cutting tool T for cutting the workpiece W, such as a threading tool, and a control device 140 for controlling the spindle 110, the spindle feed mechanism 120, and the tool post 130.

[0027] The spindle 110 comprises a spindle body 111, a chuck 112 provided at the tip of the spindle body 111, and a headstock 113 that supports the spindle body 111 at its rear end.

[0028] The spindle body 111 rotates by rotating a spindle motor (not shown). This spindle motor is a conventionally known built-in motor or the like, formed between the spindle body 111 and the headstock 113.

[0029] The chuck 112 grips the workpiece W and rotates together with the spindle body 111. Therefore, the spindle motor functions as a means of rotation for rotating the workpiece W.

[0030] The headstock 113 is mounted on the bed (not shown) of the machine tool 100 so as to be movable in the Z-axis direction (axis direction of the spindle 110) by the spindle feed mechanism 120.

[0031] The spindle feed mechanism 120 includes a base 121 fixed to the machine tool 100, a Z-axis feed table 122 on which the headstock 113 is mounted, a guide rail 123 provided on the base 121 that restricts the feed direction of the Z-axis feed table 122, and a linear servo motor 124 provided between the Z-axis feed table 122 and the guide rail 123 that moves the Z-axis feed table 122 along the guide rail 123. The linear servo motor 124 is formed from a movable element 124a provided on the Z-axis feed table 122 and a stator 124b provided on the base 121. Therefore, the Z-axis feed table 122 is able to slide freely on the guide rail 123. With the spindle feed mechanism 120 configured in this way, the spindle 110 and the tool post 130 move relative to each other. This relative movement causes the cutting tool T to move relative to the workpiece W in the machining feed direction.

[0032] The tool post 130 includes a tool holder 131 for holding the cutting tool T, an X-axis feed mechanism 132 mounted on the bed of the machine tool 100 for moving the tool holder 131 in the X-axis direction (direction perpendicular to the Z-axis direction; cutting direction), and a Y-axis feed mechanism (not shown) mounted on the bed (not shown) of the machine tool 100 for moving the tool holder 131 in the Y-axis direction (direction perpendicular to the Z-axis direction and the X-axis direction).

[0033] The X-axis feed mechanism 132 includes a base 132a fixed to the machine tool 100, an X-axis feed table 132b on which the tool holder 131 is placed, a guide rail 132c provided on the base 132a to restrict the feed direction of the X-axis feed table 132b, and a linear servo motor 132d provided between the X-axis feed table 132b and the guide rail 132c to move the X-axis feed table 132b along the guide rail 132c. The linear servo motor 132d is formed from a movable element 132d1 provided on the X-axis feed table 132b and a stator 132d2 provided on the base 132a. Therefore, the X-axis feed table 132b is able to slide freely on the guide rail 132c.

[0034] The control device 140 is electrically connected to the spindle motor (not shown) of the spindle 110, the linear servo motor 124 of the spindle feed mechanism 120, the X-axis feed mechanism 132 (linear servo motor 132d) and Y-axis feed mechanism of the tool post 130, etc., based on the stored NC program, and drives and controls them. In other words, the control device 140 drives and controls the tool post 130.

[0035] <2. Example of first processing of the workpiece> Next, based on Figures 2A and 2B, we will describe workpiece W1, which is a first example of workpiece processing performed by the machine tool 100 described above. Figure 2A is a side view of a workpiece showing a first machining example of the workpiece using the machine tool shown in Figure 1, and Figure 2B is an enlarged view of Figure 2A, IIB.

[0036] As shown in FIG. 2A, on the work W1, a female-threaded variable lead screw portion VL with a pitch increasing toward the rear end side of the work W1 (P1 < P2 < P3 < ···) is formed. Here, in the first machining example, the "pitch" means the center-to-center distance of the bottom valleys for each rotation in the variable lead screw portion VL, as shown in FIG. 2A.

[0037] Furthermore, in the variable lead screw portion VL in the first machining example, the center-to-center distance of the bottom valleys (center-to-center distance of the bottom valleys) increases every 1 / 4 rotation. That is, if the center-to-center distance of the bottom valleys from 0 degrees to 90 degrees (1 / 4 rotation) is p1a, from 90 degrees (1 / 4 rotation) to 180 degrees (2 / 4 rotation) is p1b, from 180 degrees (2 / 4 rotation) to 270 degrees (3 / 4 rotation) is p1c, and from 270 degrees (3 / 4 rotation) to 360 degrees (1 rotation) is p1d, then as shown in FIG. 2B, P1 = p1a + p1b + p1c + p1d the relationship holds and p1a < p1b < p1c < p1d the relationship holds.

[0038] In this machining example, the center-to-center distance of the bottom valleys is increased every 1 / 4 rotation, but the interval for expanding the center-to-center distance of the bottom valleys is not limited to 1 / 4 rotation. That is, the center-to-center distance of the bottom valleys may increase every 1 / m rotation (m = 2, 3 ···).

[0039] <3. Machining Method of the First Machining Example of the Work> Next, based on FIGS. 3A to 8, the machining method (variable lead screw cutting method) of the work W1 shown in FIGS. 2A and 2B will be described. Figure 3A is a flowchart showing the variable lead thread cutting method in the first machining example, Figure 3B is a flowchart showing each thread cutting step shown in Figure 3A, Figure 3C is a flowchart showing the cutting process shown in Figure 3B, Figure 4 is a diagram explaining some of the parameters in the thread cutting step of the first machining example, Figure 5 is a side view of the workpiece showing the tool trajectory in the first thread cutting step, Figure 6 is an enlarged view of part VI shown in Figure 5 in the first thread cutting step, Figure 7 is a side view of the workpiece showing the machining result from the first thread cutting step, and Figure 8 is a side view of the workpiece showing the tool trajectory in the second thread cutting step.

[0040] <3.1. Overview of Variable Lead Thread Cutting Method> In the first example of workpiece machining, the variable lead thread cutting method, as shown in Figure 3A, involves performing tip machining followed by a thread cutting step (thread cutting) a predetermined number of times (Nmax). Here, the "nth thread cutting step (N=1, 2...)" is the step of forming the nth variable lead thread portion in the nth machining section of the workpiece W.

[0041] In tip machining, as shown in Figure 4, the outer diameter of the tip side of the workpiece W1 where the variable lead screw portion VL is not formed is made smaller than the outer diameter φD of the rear end side, which is φd. Note that in Figure 4, the relationship "φd < φD - u × 2" holds true, but φd only needs to be smaller than φD.

[0042] For each thread cutting process, at least the following parameters related to the thread cutting process (partially shown in Figure 4) are given in advance. Depth of cut per pass: r [mm] Total cutting depth: u [mm] Spindle rotation speed: s [rpm] Reference position:z[mm] Reference feed rate: f [mm / revolution] Machining rotation speed: w [revolutions] The unit angle for changing the feed rate is d [degrees]. Variable feed rate per workpiece rotation: k [mm] Connection position: c [rotation] Approach rotations: a [rotations] X-axis displacement during approach: b [mm]

[0043] "Total depth of cut" refers to the target depth of cut in a thread cutting process. The "reference position" is the starting position for thread cutting (the distance from the leading edge of the workpiece W1). "Reference feed rate" refers to the feed rate at the reference position PS. "Machining rotation speed" refers to the number of times the workpiece W1 is rotated from the reference position PS to the completion of the thread cutting process. The "connection position" refers to the number of rotations the workpiece W1 undergoes from the reference position PS to the start of the thread cutting process. "Approach rotational speed" refers to the number of rotations required to move the tip of the cutting tool T from the initial position PI to the reference position PS, and also the number of rotations required to completely detach the tip of the cutting tool T from the workpiece W1. "X-axis movement during approach" refers to the amount of movement of the tip of the cutting tool T in the X-axis direction from the initial position PI to the reference position PS.

[0044] <3.2. First thread cutting step> Next, we will explain the first threading step (threading process). In the first thread cutting step, as shown in Figures 3B and 6, the cutting process S10 with a single cutting depth r is repeated until the total cutting depth u is reached, forming a variable lead thread portion in the first machining section MA1 as shown in Figure 7. In the first thread cutting step, c=0.

[0045] As shown in Figure 3C, the cutting process S10 sequentially executes the approach motion (S100), machining (S110), and release motion (S120).

[0046] (S100) In the approach operation, as shown in Figure 5, the cutting tool T is moved from the initial position PI, determined by the parameters described above, to the reference position PS. Here, the initial position PI can be determined from the reference feed rate f, approach rotation speed a, variable feed amount k per workpiece rotation, and X-axis movement amount b during approach.

[0047] (S110) Subsequently, the spindle 110 is moved in the Z-axis direction and rotated by w[rotations] so that the cutting tool T passes through the spiral tool trajectory PL1 shown in Figure 5, which was determined from the parameters described above, and the workpiece W is cut with the cutting tool T. In this cutting process, the feed rate in the feed movement is changed by a predetermined amount (k / m) each time the workpiece W is rotated by a unit angle d (i.e., every 1 ÷ (360 ÷ d) rotations). In other words, the tool path PL1 changes with each unit angle d. For the sake of explanation, Figure 5 uses the values ​​w=3, a=1, and d=90.

[0048] (S120) In the detachment operation, the depth of cut is reduced from the wath rotation to detach the cutting tool T from the workpiece W.

[0049] Therefore, once the first thread cutting step described above is completed, as shown in Figure 7, the first variable lead thread portion VL1 will consist of a completed cutting region M cut with a total cutting amount u, and an intermediate cutting region S with a cutting amount smaller than the cutting amount in the completed cutting region M.

[0050] <3.3. From the second thread cutting step onward> The second thread cutting step also involves repeating the cutting process S100 with a single cutting depth r until the total cutting depth u is reached, thereby forming the second variable lead thread portion VL2 as shown in Figure 8.

[0051] The machining parameters in the second threading step are equal to those in the first threading step, except for c and w, in order to make the first variable lead thread portion VL1 and the second variable lead thread portion VL2 continuous. As an example, c = 2 and w = 5. That is, the second threading starts within the first machining section MA1.

[0052] Since the second threading step itself is the same as the first threading step, the description thereof is omitted.

[0053] Similarly hereinafter, by repeating the third threading step, the fourth threading step, and so on, even when the workpiece W1 is long, the variable lead thread portion VL can be accurately formed.

[0054] <4. Second machining example of workpiece> Next, based on FIG. 9 which is a side view showing a second machining example of a workpiece by the machine tool shown in FIG. 1, a workpiece W2 which is a second machining example of the workpiece by the above-described machine tool 100 will be described.

[0055] As shown in FIG. 9, a male-threaded variable lead thread portion VL is formed on the workpiece W2, where the pitch increases toward the rear end side of the workpiece W1 (P1 < P2 < P3 < ···). And for the variable lead thread portion VL of the workpiece W2, the distance between the centers of the bottom valleys also increases every 1 / m rotation (m = 2, 3 ···; in this embodiment, m = 4).

[0056] <5. Machining method for the second machining example of workpiece> Next, based on FIGS. 10 to 13, the machining method (variable lead threading method) of the workpiece W2 shown in FIG. 9 will be described. Figure 10 is a diagram illustrating some of the parameters in the thread cutting step of the second machining example, Figure 11 is a flowchart showing the thread cutting step in the second machining example, Figure 12 is a flowchart showing the groove width expansion substep in the second machining example, and Figure 13 is a workpiece side view showing the tool path in the second thread cutting step in the second machining example.

[0057] <5.1. Overview of Variable Lead Thread Cutting Method> In workpiece W2, as in the first machining example (i.e., as shown in Figure 3A), after machining the tip, the thread cutting step (thread cutting) is performed a predetermined number of times (Nmax). The tip processing is the same as in the first processing example, so it will be omitted.

[0058] In addition to the parameters given in the first machining example, the thread cutting process involves at least the parameters shown in Figure 10 below. Screw groove width standard expansion amount: h [mm] Number of times to expand the screw thread: q [times]

[0059] "Screw groove width standard expansion amount" refers to the amount by which the screw groove width is expanded in the Z-axis direction from the reference position PS when expanding the screw groove. "Thread groove expansion count" refers to the number of times the thread groove is expanded. Note that Figure 10 shows the case where q=4 as an example.

[0060] <5.2. First thread cutting step> Next, we will explain the first threading step (threading process). The first thread cutting step is performed in the following order, as shown in Figure 11: thread forming substep S1, groove width expansion substep S2.

[0061] The thread-forming substep S1 is a step in which, similar to the first machining example, a cutting step S10 with a single cutting depth r is repeated until the total cutting depth u is reached, thereby forming the first variable lead thread portion VL1 as shown in Figure 7. The plunge step in the second machining example is the same as that in the second machining example, so the description is omitted.

[0062] When the thread forming sub-step S1 ends, the groove width expansion sub-step S2 is executed. In the groove width expansion sub-step S2, as shown in FIG. 12, from the expansion start position advanced by h / q [mm] in the Z-axis direction from the reference position PS until reaching the thread groove expansion number q, the plunge step S10 with a single plunge amount r is repeated until reaching the total plunge amount u, so that the groove width of the first variable lead thread portion VL1 is expanded as shown in FIG.

[0063] <5.3. After the second threading step> The second threading step also repeatedly performs the plunge step S100 with a single plunge amount r until reaching the total plunge amount u to form the second variable lead thread portion VL2. In addition, in the thread forming sub-step in the second threading step, it is continuous with the cutting path by the thread forming sub-step in the first threading step, and in the groove width expansion sub-step in the second threading step, it is continuous with the cutting path by the groove width expansion sub-step in the first threading step.

[0064] Similarly hereinafter, by repeating the third threading step, the fourth threading step,... even when the workpiece W1 is long, a male-threaded variable lead thread portion VL can be accurately formed.

[0065] <5. Third machining example of the workpiece> Next, based on FIG. 14 which is a side view showing the third machining example of the workpiece by the machine tool shown in FIG. 1, the workpiece W3 which is the third machining example of the workpiece by the above-described machine tool 100 will be described.

[0066] As shown in FIG. 14, the workpiece W3 also has a male-threaded variable lead thread portion VL formed therein with a pitch increasing toward the rear end side of the workpiece W1 (P1 < P2 < P3 < ···). Furthermore, the distance between the centers of the roots of the variable lead screw portion VL of the workpiece W3 also increases by 1 / m rotation (m=2, 3...; in this embodiment, m=4). Furthermore, in workpiece W3, the diameter of the variable lead screw portion VL increases towards the rear end of workpiece W. In other words, the variable lead screw portion Vl of the workpiece W3 is tapered.

[0067] <6. Machining method for the third example of workpiece processing> Next, we will explain the machining method (variable lead thread cutting method) for the workpiece W3 shown in Figure 14. When machining workpiece W3, in addition to the parameters shown in the second machining example, a taper amount t [mm] is given as a parameter for each thread cutting operation, and the tool path PL is determined by taking this taper amount t into account.

[0068] <7. Effects of the machine tool 100 in this embodiment> The first embodiment of the present invention, consisting of a machine tool 100, a control device 140, and a variable lead thread cutting method, as described above, provides the following effects.

[0069] The control device 140 rotates the workpiece W while relatively feeding and moving the workpiece W and the cutting tool T, starting the N+1 thread cutting process from within the Nth machining section MAN (N=1, 2, ...). As a result, the variable lead thread portion VL of the workpiece W is formed by multiple thread cutting processes. Therefore, by setting the machining section to a range in which machining accuracy can be guaranteed, variable lead thread machining can be performed on the workpiece W, and even long workpieces can have their variable lead thread portions formed with high accuracy (First to Third Machining Examples).

[0070] Furthermore, when the control device 140 performs the Nth thread cutting, it repeats the cutting process until it reaches the total cutting depth u, which is the target cutting depth for variable lead thread cutting. As a result, the Nth variable lead thread portion VLN of the workpiece W is formed through multiple cutting operations, reducing the cutting resistance applied to the cutting tool T, extending the life of the cutting tool, and reducing waste, thereby mitigating the environmental burden. (Examples 1 to 3 of the machining process).

[0071] Furthermore, in the Nth thread cutting operation, the control device 140 changes the feed rate in the feed movement by a predetermined amount each time the workpiece W is rotated by 1 / m (m=2, 3, ...). As a result, the feed rate of the variable lead thread portion VL formed on the workpiece W changes in stages. This makes it easier to control the operation of the machine tool 100 compared to the case where the feed rate of the variable lead thread portion VL formed on the workpiece W is continuously changed, allowing for faster workpiece processing, reduced processing time, and reduced power consumption. (Examples 1 to 3 of the machining process).

[0072] Furthermore, since the Nth thread cutting step includes a thread forming substep for forming the Nth variable lead thread portion VLN, and a groove width expansion substep for expanding the thread groove width of the Nth variable lead thread portion VLN from an expansion start position advanced by a predetermined amount in the feed direction from a reference position in the thread forming substep, the thread groove width of the variable lead thread portion VL is expanded, and a male screw-shaped variable lead thread portion VL can be formed on the workpiece W (third machining example). [Examples]

[0073] Hereinafter, a machine tool 200, a control device 240 equipped with this machine tool 200, and a variable lead thread cutting method using this machine tool 200 will be described based on Figure 15, which is a device configuration diagram of a machine tool according to a second embodiment of the present invention. Furthermore, the machine tool 200 of the second embodiment is a modified version of the machine tool 100 of the first embodiment, and many elements are common to the machine tool 100 of the first embodiment. Therefore, detailed explanations of common items are omitted, and only a code in the 200s, with the last two digits being common, is assigned.

[0074] As shown in Figure 15, the machine tool 200 is provided with a guide bush 250 for holding the workpiece W on the base 221 of the spindle feed mechanism 220. In the machine tool 200, in addition to the spindle 210, the guide bush 250 also functions as a workpiece holding means. Therefore, by performing the same drive control in the machine tool 200 as in the machine tool 100 of the first embodiment, the machine tool 200 can also process the workpieces W1 to W3 described above.

[0075] <Variation> Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above.

[0076] For example, in each of the embodiments described above, the spindle 110 was moved relative to the tool post 130 by the spindle feed mechanism 120. However, if the spindle 110 and the tool post 130 move relative to each other, the spindle 110 may be fixed and the tool post 130 may be moved in the Z-axis direction, or both the spindle 110 and the tool post 130 may move in the Z-axis direction. [Explanation of Symbols]

[0077] 100, 200... Machine tools 110, 210... Main spindle (workpiece holding means) 111, 211... Spindle body 112, 212... Chuck 113, 213... Headstock 120, 220... Spindle feed mechanism (feeding means) 121, 221... Base 122, 222... Z-axis feed table 123, 223... Guide rails 124, 224... Linear servo motor 124a, 224a... Mover 124b, 224b...Stator 130, 230... Tool rest 131, 231... Tool holder 132, 232... X-axis feed mechanism 132a, 232a... Base 132b, 232b... X-axis feed table 132c, 2322 ··· Guide rail 132d, 232d... Linear servo motor 132d1, 232d1... Mover 132d2, 232d2... Stator 140, 240... Control device 250 ··· Guide bush (workpiece holding means) T... Cutting tool W, W1~W3 ··· Work VL... Variable lead screw section VL1 ··· First variable lead screw section MA1 ··· First processing section MA2 ··· Second processing section PL1 ··· Tool path in the first thread cutting step PL2 ··· Tool path in the first thread cutting step P1~P4 ··· Pitch p1a~p1d ··· Distance between valley bottom centers φd ··· Outer diameter of the workpiece tip φD ··· Outer diameter of the rear end of the workpiece M... Machining completed area S... Area in progress of machining PI Initial position PS ··· Base position

Claims

1. A machine tool for performing variable lead thread cutting, which forms a variable lead thread portion in the longitudinal direction of a workpiece, comprising: a workpiece holding means for holding a workpiece; a tool post for holding a cutting tool for cutting the workpiece; a feeding means for feeding the cutting tool relative to the workpiece in a predetermined machining feed direction by relative movement between the workpiece holding means and the tool post; a rotating means for rotating the workpiece; and a control device for driving and controlling the feeding means, the rotating means and the tool post, wherein the machine tool performs variable lead thread cutting, which forms a variable lead thread portion in the longitudinal direction of the workpiece, The variable lead thread cutting process includes an Nth thread cutting process that forms an Nth variable lead thread portion in the Nth machining section (N=1, 2...) of the workpiece, and an N+1 thread cutting process that forms an N+1 variable lead thread portion continuous with the Nth variable lead thread portion in the N+1 machining section adjacent to the Nth machining section of the workpiece. A machine tool characterized in that the control device rotates the workpiece while relatively feeding and moving the workpiece and the cutting tool, thereby starting the N+1 thread cutting process from within the N processing section.

2. The control device moves the workpiece and the cutting tool relative to each other, while rotating the workpiece to perform a cutting operation along a predetermined spiral cutting path. The machine tool according to claim 1, characterized in that when the control device performs the thread cutting process N, the control device repeats the cutting process until it reaches the target cutting depth targeted by the variable lead thread cutting process.

3. The machine tool according to claim 1 or 2, characterized in that the control device changes the feed amount in the feed movement by a predetermined amount each time the workpiece is rotated 1 / m (m = 2, 3, ...) in the thread cutting process N.

4. A control device for a machine tool that performs variable lead thread cutting, which forms a variable lead thread portion in the longitudinal direction of a workpiece, comprising: a workpiece holding means for holding a workpiece; a tool post for holding a cutting tool for cutting the workpiece; a feeding means for moving the cutting tool relative to the workpiece in a predetermined machining feed direction by relative movement between the workpiece holding means and the tool post; and a rotating means for rotating the workpiece, wherein the feeding means, the rotating means, and the tool post are driven and controlled. The variable lead thread cutting process includes an Nth thread cutting process that forms an Nth variable lead thread portion in the Nth machining section (N=1, 2...) of the workpiece, and an N+1 thread cutting process that forms an N+1 variable lead thread portion continuous with the Nth variable lead thread portion in the N+1 machining section adjacent to the Nth machining section of the workpiece. A control device for a machine tool, characterized in that it rotates the workpiece while relatively feeding and moving the workpiece and the cutting tool, thereby starting the N+1 thread cutting process from within the N processing section.

5. A variable lead thread cutting method for forming a variable lead thread portion in the longitudinal direction of a workpiece using a machine tool comprising: a workpiece holding means for holding a workpiece; a tool post for holding a cutting tool for cutting the workpiece; a feeding means for feeding the cutting tool in a predetermined machining feed direction relative to the workpiece by relative movement between the workpiece holding means and the tool post; a rotating means for rotating the workpiece; and a control device for driving and controlling the feeding means, the rotating means and the tool post, wherein a variable lead thread portion is formed in the longitudinal direction of the workpiece. The process comprises: an Nth thread cutting step for forming an Nth variable lead screw portion in the Nth machining section (N=1, 2...) of the workpiece; and an N+1 thread cutting step for forming an N+1 variable lead screw portion continuous with the Nth variable lead screw portion in the N+1 machining section adjacent to the Nth machining section of the workpiece. A variable lead thread cutting method characterized in that the N+1 thread cutting step is started from within the N cutting section.

6. The variable lead thread cutting method according to claim 5, characterized in that, in the N thread cutting step, the workpiece and the cutting tool are relatively fed and moved while the workpiece is rotated and a cutting step is performed along a predetermined helical cutting path, and this cutting step is repeated until the target cutting depth targeted in the variable lead thread cutting is reached.

7. The variable lead thread cutting method according to claim 5 or 6, characterized in that, in the thread cutting step N, the amount of feed in the feed movement is changed by a predetermined amount each time the workpiece is rotated by 1 / m (m = 2, 3, ...).

8. The variable lead thread cutting method according to claim 5, characterized in that the thread cutting step N comprises a thread forming substep for forming the variable lead thread portion N, and a groove width expansion substep for expanding the thread groove width of the variable lead thread portion N from an expansion start position advanced by a predetermined amount in the feed direction from a reference position in the thread forming substep.

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