Spiral groove processing method

Abstract

To improve processing accuracy and efficiency in processing of a spiral groove.SOLUTION: A spiral groove processing method is a processing method of a spiral groove for forming a spiral groove 21 on an outer peripheral face 22 of a workpiece 2 which has a shaft shape, by a shaft-shaped cutting tool 11 having a cutting blade 112 on its outer peripheral face. The processing method of the spiral groove has: a cutting preparation step for bringing the cutting tool 11 in a posture where a center shaft 113 of the cutting tool is tilted to a line L1 vertical to a center shaft 23 of the workpiece 2 by a lead angle A of the processed spiral groove 21, and directing the cutting blade 112 to the outer peripheral face 22 of the workpiece 2; a cutting step for, after the cutting preparation step, bringing the cutting blade 112 of the cutting tool 11 into contact with the outer peripheral face 22 of the workpiece 2 rotating around its center shaft 23 while moving the cutting tool 11 in a direction of the center shaft 23 of the workpiece 2, for forming the spiral groove 21 on the outer peripheral face 23 of the workpiece 2.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for machining a helical groove.

Background Art

[0002] As an example of a member in which a helical groove is formed, a screw shaft of a ball screw is known. The screw shaft generally has a substantially cylindrical shape, and a helical groove is formed on its outer peripheral surface. Such a screw shaft is manufactured, for example, by cutting. A method for machining a screw shaft by cutting is disclosed, for example, in Patent Document 1.

[0003] Patent Document 1 discloses, as an example, a machining method using a tool bit as a cutting tool. In this machining method, a cylindrical workpiece is rotated around a central axis, and a tip of the tool bit is applied to the outer peripheral surface of the workpiece while the tool bit is moved in a direction along the central axis of the workpiece. By repeating such cutting of the outer peripheral surface of the workpiece by the tip a plurality of times, a helical groove is formed.

[0004] Patent Document 1 also discloses, among other things, a machining method using an end mill as a cutting tool. In this machining method, the end mill is applied to the outer peripheral surface of the workpiece so that the axial direction of the end mill is along the radial direction of the workpiece. That is, the end mill is arranged so that the axial direction of the end mill is perpendicular to the tangent direction at the machining point on the outer peripheral surface of the workpiece. The workpiece and the end mill are rotated around their respective central axes, and the end mill is moved in a direction along the central axis of the workpiece. Thereby, a helical groove is formed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the case of a ball screw, balls are provided in the helical groove of the screw shaft, and the screw shaft and the ball nut perform relative movement via the balls. Therefore, it is desirable that the cross-sectional shape of the helical groove is semi-circular. In order to machine such a helical groove by a machining method using a tip, for example, a circular tip, that is, a tip corresponding to the cross-sectional shape of the groove, is used. However, in this case, a special tip is required, so the machining cost increases.

[0007] Also, in the machining method using a tip (turning), while rotating the workpiece at a predetermined speed, a feeding operation is required to move the tip in the direction along the central axis of the workpiece in accordance with the pitch of the helical groove. Therefore, in turning, the cutting load tends to be higher than that in general screw machining. In addition, the workpiece to be machined on the screw shaft is often subjected to a quenching treatment in advance. Therefore, in turning, the cutting load tends to be even higher. For such reasons, in turning, the cutting of the workpiece is often divided into a plurality of cycles, and the workpiece is gradually cut. As a result, it is difficult to increase the machining efficiency in turning.

[0008] On the other hand, in the machining method using an end mill (milling), the workpiece is cut using the bottom edge provided on the tip surface of the end mill and the outer peripheral edge provided on the outer peripheral surface. In milling, since the workpiece is cut using not only the rotation of the workpiece but also the rotation of the tool, the rotation speed of the workpiece can be set lower compared to turning. Along with this, the feeding speed of the tool for matching the pitch of the helical groove can also be set lower. As a result, in milling, the cutting load on the tool can be appropriately adjusted, and a helical groove can be formed in fewer cycles than in turning.

[0009] However, in the machining method using an end mill, mainly the bottom edge cuts the workpiece. In this case, a large cutting load is applied to the bottom edge, vibration is likely to occur, and tool wear also progresses easily. In particular, members having a helical groove such as a screw shaft are often manufactured by hard turning that cuts a high-hardness workpiece. Therefore, compared with general cutting, the above-mentioned vibration is likely to occur and tool wear also progresses easily. For these reasons, when cutting a helical groove with the bottom edge of an end mill, the constraints on machining conditions such as machining speed become severe, and it is difficult to improve machining efficiency.

[0010] An object of the present invention is to improve machining efficiency and machining accuracy in the machining of a helical groove.

Means for Solving the Problem

[0011] (1) The method for machining a helical groove of the present invention is a method for machining a helical groove in which a helical groove is formed on the outer peripheral surface of a workpiece having an axial shape by an axial cutting tool having a cutting edge on the outer peripheral surface. The method for machining a helical groove includes a cutting preparation step of tilting the cutting tool to a posture inclined by the lead angle of the helical groove to be machined with respect to a line perpendicular to the central axis of the workpiece and directing the cutting edge toward the outer peripheral surface of the workpiece, and after the cutting preparation step, while bringing the cutting edge of the cutting tool into contact with the outer peripheral surface of the workpiece rotating around its central axis, moving the cutting tool in a direction along the central axis of the workpiece to form a helical groove on the outer peripheral surface of the workpiece.

[0012] In the above method for machining a helical groove, the workpiece is machined by a cutting edge provided on the outer peripheral surface of the axial cutting tool. By cutting the workpiece with the cutting edge provided on the outer peripheral surface, the bending moment applied to the cutting tool is reduced compared with the case of cutting with the bottom edge of an end mill, for example. As a result, the vibration of the cutting tool is suppressed. Therefore, according to the above method for machining a helical groove, it is possible to improve machining efficiency and machining accuracy in the machining of a helical groove.

[0013] (2) In the method for machining the helical groove of (1) above, the cutting edge of the cutting tool may be provided in a predetermined range in the direction along the central axis of the cutting tool. The cutting process may include a first cutting process in which a first portion of the cutting edge is applied to the outer peripheral surface of the workpiece and the outer peripheral surface of the workpiece is cut by the first portion, and after the first cutting process, a second portion of the cutting edge, which has a different position from the first portion in the direction along the central axis of the cutting tool, is applied to the outer peripheral surface of the workpiece, and a second cutting process in which the outer peripheral surface of the workpiece or the outer peripheral surface of a new workpiece is cut by the second portion.

[0014] In the method for machining the helical groove of (2) above, when machining a workpiece multiple times or when machining a new workpiece after machining a certain workpiece, the machining points where the cutting edge and the workpiece are in contact are different. Therefore, even if, for example, the first portion is worn, machining can be performed with the second portion without replacing the tool. Thus, according to the method for machining the helical groove of (2) above, in machining the helical groove, the entire cutting edge can be used up for machining the helical groove, and the tool life when viewed with one cutting tool can be extended. Note that the transition from the first portion, which is the machining point, to the second portion can be in a mode where the cutting action position is shifted to the second portion after the first portion reaches the tool life. The tool life can be known empirically or by inspecting the tool.

[0015] (3) The method for machining the helical groove of (2) above may use a composite machine tool including a tool spindle that holds and rotates the end of the cutting tool. The cutting edge of the cutting tool may be provided in a predetermined range of an end portion different from the end portion held by the tool spindle in the direction along the central axis of the cutting tool. The first portion may be closer to the tool spindle than the second portion in the direction along the central axis of the cutting tool.

[0016] In the method for machining the helical groove of (3) above, machining is performed starting from the first portion on the root side (tool spindle side) of the cutting edge. The closer the machining point is to the root side, the shorter the distance between the machining point and the point where the cutting tool is held, and vibrations and deflections due to the cutting load are further suppressed. Therefore, according to the method for machining the helical groove of (3) above, in the machining of the helical groove, the machining efficiency and machining accuracy can be improved.

[0017] (4) In the method for machining the helical groove of (1) above, the workpiece may have an outer peripheral surface that has been quenched. In the cutting process, a helical groove may be formed on the outer peripheral surface of the quenched workpiece.

[0018] For example, in a ball screw, the screw shaft rubs against the balls fitted into the helical groove. Therefore, the workpiece to be machined on the screw shaft may be quenched in advance. When machining such a workpiece having a high hardness, a large load is applied to the cutting edge, the cutting edge is likely to wear, and vibrations are likely to occur in the cutting tool. In the method for machining the helical groove of (4) above, since the workpiece is machined by the cutting edge provided on the outer peripheral surface of the cutting tool, vibrations are less likely to occur. Therefore, this machining method is particularly suitable for machining a high-hardness workpiece that has been quenched.

[0019] (5) The method for machining the helical groove of (1) above may further include a grinding process for grinding the formed helical groove after the cutting process.

[0020] Since the helical groove is machined by the feeding operation of the cutting tool, the surface roughness of the groove surface may become rough depending on the machining conditions. In the method for machining the helical groove of (5) above, the helical groove is ground by the grinding process after the cutting process. Therefore, according to the method for machining the helical groove of (5) above, in the machining of the helical groove, the machining efficiency and machining accuracy can be improved.

[0021] (6) The method for machining the helical groove in (1) above may use a multi-functional machine tool including a tool spindle that holds and rotates a cutting tool, a work spindle that holds the first end of the workpiece and rotates the workpiece, and an auxiliary work spindle that supports the second end different from the first end.

[0022] In the method for machining the helical groove in (6) above, the workpiece is rotated around its central axis. Also, in the method for machining the helical groove above, the cutting edge provided on the outer peripheral surface of the cutting tool is arranged to match the lead angle of the helical groove, and the cutting tool is moved in the direction along the central axis of the workpiece. For such a machining method, in the method for machining the helical groove in (6) above, a multi-functional machine tool including a lathe function and a machining center function is used. Therefore, according to this machining method, a helical groove can be formed on the workpiece with one machine tool, and the machining efficiency can be improved.

[0023] (7) In the method for machining the helical groove in (1) above, in the cutting process, while bringing the cutting edge of the cutting tool into contact with the outer peripheral surface of the workpiece and vibrating (reciprocating) the cutting tool in the direction along its central axis, the cutting tool may be moved in the direction along the central axis of the workpiece to form a helical groove on the outer peripheral surface of the workpiece.

[0024] For example, a screw shaft is a long member with the direction along the central axis as the longitudinal direction. When forming a helical groove on a long workpiece, continuous long chips are likely to be generated. If the chips come into contact with the workpiece during machining, the workpiece may be damaged. In the method for machining the helical groove in (7) above, since the cutting tool is vibrated at a predetermined amplitude and frequency during machining, the chips are likely to be cut in the middle, and continuous long chips are less likely to be generated. Also, since the machining point where the cutting edge and the workpiece come into contact varies due to the vibration, wear of a specific part of the cutting edge can be suppressed, and wear in a predetermined area of the cutting edge corresponding to the vibration can be made uniform.

[0025] (8) According to the above method for machining the spiral groove, a spiral groove can be formed on the outer peripheral surface of a workpiece having a shaft shape. By the method for machining the spiral groove according to any one of the above (1) to (7), a shaft member having a spiral groove can be manufactured. Therefore, the method for manufacturing a shaft member having a spiral groove is also included in the scope of the present invention.

[0026] (9) The spiral groove machining machine of the present invention is a spiral groove machining machine for forming a spiral groove on the outer peripheral surface of a workpiece having a shaft shape by means of a shaft-shaped cutting tool having a cutting edge on its outer peripheral surface, and is provided with a control device for controlling the position or posture of the cutting tool and the position or posture of the workpiece. The control device positions the cutting tool in a posture inclined by the lead angle of the spiral groove to be machined with respect to a line perpendicular to the central axis of the workpiece, and directs the cutting edge toward the outer peripheral surface of the workpiece in a cutting preparation process. After performing the cutting preparation process, the control device moves the cutting tool in a direction along the central axis of the workpiece while pressing the cutting edge of the cutting tool against the outer peripheral surface of the workpiece rotating around its central axis, thereby performing a cutting process for forming a spiral groove on the outer peripheral surface of the workpiece.

[0027] (10) The program for the spiral groove machining machine of the present invention is a program used for a spiral groove machining machine for forming a spiral groove on the outer peripheral surface of a workpiece having a shaft shape by means of a shaft-shaped cutting tool having a cutting edge on its outer peripheral surface. The program positions the cutting tool in a posture inclined by the lead angle of the spiral groove to be machined with respect to a line perpendicular to the central axis of the workpiece, and directs the cutting edge toward the outer peripheral surface of the workpiece in a cutting preparation process. After performing the cutting preparation process, the program moves the cutting tool in a direction along the central axis of the workpiece while pressing the cutting edge of the cutting tool against the outer peripheral surface of the workpiece rotating around its central axis, thereby performing a cutting process for forming a spiral groove on the outer peripheral surface of the workpiece.

Advantages of the Invention

[0028] As described above, according to the method for machining the spiral groove of the present invention, in the machining of the spiral groove, the machining efficiency and the machining accuracy can be improved.

Brief Description of the Drawings

[0029]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

MODE FOR CARRYING OUT THE INVENTION

[0030] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, a method for processing a spiral groove formed on a screw shaft of a ball screw will be described. Further, in the present embodiment, a case where the spiral groove of the screw shaft is processed using a complex processing machine which is a NC machine tool (Numerically Controlled Machine Tool) will be described.

[0031] <Complex processing machine> FIG. 1 is a schematic view showing the main configuration of a composite processing machine for processing a helical groove according to the present embodiment. The composite processing machine 1 forms a helical groove 21 on the outer peripheral surface of a workpiece 2. In the figure, a screw shaft with a helical groove 21 formed thereon is shown as the workpiece 2 for the sake of explanation. The composite processing machine 1 includes a tool spindle 12 that holds a cutting tool 11, a workpiece spindle 13, and an auxiliary workpiece spindle 14. Here, when the composite processing machine 1 is viewed from the front, the vertical direction is the X-axis direction, the front-rear direction is the Y-axis direction, and the left-right direction is the Z-axis direction. The X-axis direction, the Y-axis direction, and the Z-axis direction are perpendicular to each other.

[0032] The cutting tool 11 has a cylindrical shape which is a kind of shaft shape. In the present embodiment, the cutting tool 11 is an end mill. The cutting tool 11 includes a cutting edge 111 and a cutting edge 112. The cutting edge 111 is provided on the tip surface of the cutting tool 11. The cutting edge 111 is also referred to as a bottom edge. The cutting edge 112 is provided on the outer peripheral surface of the tip side of the cutting tool 11. The cutting edge 112 is provided on the outer peripheral surface within a predetermined range from the tip in the direction of the central axis 113 of the cutting tool 11. The cutting edge 112 is also referred to as an outer peripheral edge. The cutting edge 112 is provided so as to be connected to the cutting edge 111. The cutting edge 112 has a helical shape (twisted shape) with an extending direction along the central axis of the cutting tool 11. The cutting tool 11 may include a plurality of cutting edges 111 and a plurality of cutting edges 112. The cutting tool 11 has a shape corresponding to the cross-sectional shape of the helical groove to be formed in a cross-section perpendicular to its central axis.

[0033] The tool spindle 12 holds the cutting tool 11. More specifically, the tool spindle 12 holds the cutting tool 11 via a tool holder (not shown). The tool spindle 12 holds the base portion of the cutting tool 11, that is, the end portion different from the tip portion where the cutting edges 111 and 112 are provided. The tool spindle 12 is configured to be detachable from various tools housed in a tool magazine provided at a predetermined position. The attachment and replacement of various tools to the tool spindle 12 are performed by a tool changing device provided at a tool changing position near the tool magazine. The tool spindle 12 is configured to be movable in the X-axis direction, Y-axis direction, and Z-axis direction by an X-axis feed mechanism, a Y-axis feed mechanism, and a Z-axis feed mechanism (not shown), respectively. Further, the tool spindle 12 can rotate the held cutting tool 11. More specifically, the tool spindle 12 can rotate the cutting tool 11 around its central axis. Also, the tool spindle 12 is configured to be rotatable around a rotation axis parallel to the Y-axis (hereinafter, such a rotation axis is also referred to as the B-axis).

[0034] The work spindle 13 holds one end of the work 2. The work spindle 13 includes a chuck 131 that grips the work 2. The work spindle 13 holds the work 2 such that the work 2 is along the Z-axis. The work spindle 13 is configured to be rotatable around a rotation axis parallel to the Z-axis. The work spindle 13 is configured to be rotatable around a rotation axis parallel to the Z-axis (hereinafter, such a rotation axis is also referred to as the C-axis), that is, around the central axis 23 of the work 2, of the work 2.

[0035] The auxiliary work spindle 14 is provided so as to face the work spindle 13. The auxiliary work spindle 14 supports the other end of the work 2. The auxiliary work spindle 14 includes a chuck 141 that grips the work 2. The auxiliary work spindle 14 supports the work 2 so as to allow the rotation of the work 2. The auxiliary work spindle 14 is configured to be movable in the Z-axis direction.

[0036] Although illustration is omitted, the multi - tasking machine 1 also has various functions such as a vibration - damping unit that clamps the workpiece 2 and suppresses the eccentricity of the central axis of the workpiece 2 during cutting, and a measuring device that measures the dimensions of the workpiece such as the outer diameter. Further, the multi - tasking machine 1 is provided with a control device (not shown). The control device controls the position or posture of each part of the multi - tasking machine. The control device is composed of a computer including a CPU, a RAM, a ROM, etc. The control device realizes each step of the spiral groove processing method described later by executing a computer program stored in a recording medium.

[0037] By the spiral groove processing method of the present embodiment using the multi - tasking machine 1 having such a configuration, a spiral groove 21 having a lead angle A is formed on the outer peripheral surface 22 of the workpiece 2 having a shaft shape. Here, the lead angle refers to the angle formed by the base and the hypotenuse in a right - angled triangle having the length of one rotation of the spiral groove and the lead of the spiral groove as adjacent sides, when the lead of the spiral groove is the base. The lead angle is represented by the following formula (1). tanθ = L / (πD) (1) θ: Lead angle L: Lead of the spiral groove D: Effective diameter of the spiral groove Note that the lead L of the spiral groove refers to the distance in the central axis direction between a point on the spiral groove and the point that starts from the said point and reaches after going around the spiral groove once. The effective diameter D of the spiral groove refers to the diameter of a virtual cylinder where the length of the center axis direction of the crest of the spiral groove is equal to the length of the center axis direction of the trough of the spiral groove. Hereinafter, the spiral groove processing method will be described.

[0038] <Spiral groove processing method> Figure 2 is a flowchart of the spiral groove processing method of the present embodiment. The spiral groove processing method includes a heat treatment step S11, a cutting preparation step S12, a cutting step S13, and a grinding step S14 in the order of execution.

[0039] In the heat treatment step S11, a workpiece 2 having a cylindrical shape is heat-treated. The heat treatment is, for example, quenching. The workpiece 2 is made of, for example, iron or an alloy mainly composed of iron. By heat-treating the workpiece 2, the hardness of the workpiece 2 is improved. In the present embodiment, the workpiece 2 has a solid cylindrical shape, but the workpiece 2 may have a hollow cylindrical shape. That is, the workpiece 2 only needs to have an axial shape. The axial shape is not limited to a cylindrical shape. The axial shape includes a shape having a step such as a flange. The axial shape includes an asymmetric shape. The axial shape only needs to be a shape having a central axis that is the center of rotation.

[0040] FIG. 3 is a diagram for explaining a cutting preparation step in the method for machining the spiral groove of the present embodiment. In the figure, (A) is a view seen from the front of the multi-functional machine, and (B) is a view seen along the direction along the central axis of the workpiece. Referring to FIG. (A), in the cutting preparation step S12, first, the workpiece 2 is attached to the multi-functional machine 1. One end of the workpiece 2 is gripped by the chuck 131 of the workpiece spindle 13, and the other end is gripped by the chuck 141 of the auxiliary workpiece spindle 14.

[0041] Next, the cutting tool 11 is set in a posture inclined by the lead angle A of the spiral groove 21 to be machined with respect to a line L1 perpendicular to the central axis 23 of the workpiece 2, and the cutting edge 112 is directed toward the outer peripheral surface 22 of the workpiece 2. More specifically, the perpendicular line L1 is orthogonal to both the central axis 23 of the workpiece 2 and the vertical axis. The cutting tool 11 is set in a posture inclined by the lead angle A with respect to the vertical axis within a plane defined by the central axis 23 of the workpiece 2 and the vertical axis orthogonal to the central axis 23. When viewed from the Y-axis direction, the tool spindle 12 is rotated around a rotation axis parallel to the Y-axis so that the central axis 113 of the cutting tool 11 is inclined by the lead angle A with respect to the X-axis direction. More specifically, the tool spindle 12 is rotated so that the angle formed by a reference axis parallel to the radial axis (line L1) orthogonal to the central axis 23 of the workpiece 2 and the central axis 113 of the cutting tool 11 becomes the lead angle A of the spiral groove to be formed with respect to the workpiece 2. In this embodiment, since the reference state of the tool spindle 12 is such that its central axis is directed in the vertical direction, the tool spindle 12 is rotated around the B-axis by the lead angle A. Referring to FIG. (B), the tool spindle 12 is appropriately moved in the X-axis direction, Y-axis direction, and Z-axis direction so that the cutting edge 112 faces the outer peripheral surface 22 of the workpiece 2. In this embodiment, the tool spindle 12 is moved so that the cutting edge 112 is disposed at a position a predetermined distance away from the outer peripheral surface of the workpiece 2 in the Y-axis direction (+ side or - side). Note that the order of the rotational movement of the tool spindle 12 and the translational movement of the tool spindle 12 is not particularly limited. For example, after the cutting edge 112 is opposed to the outer peripheral surface of the workpiece 2, the tool spindle 12 may be rotated so that the angle formed by the central axis 113 of the cutting tool 11 and the X-axis direction becomes the same angle as the lead angle A. In addition, the rotation and translational movement of the tool spindle 12 may be performed simultaneously.

[0042] FIG. 4 is a diagram for explaining a cutting process in the method for machining a spiral groove according to the present embodiment. In the figure, (A) is a view seen from the front of the machining center, and (B) is a view seen along the direction along the central axis of the workpiece. First, referring to FIG. (B), in the cutting process S13, milling is performed using the cutting tool 11. More specifically, the workpiece 2 is rotated around its central axis 23 by rotating the workpiece spindle 13 holding the workpiece 2. In this embodiment, the workpiece 2 is rotated during the cutting process S13. However, the workpiece 2 may be rotated before the execution of the cutting process S13. The workpiece 2 may be rotated during the cutting preparation process S12. The workpiece 2 may be rotated before the cutting preparation process S12. In short, the workpiece 2 may be rotated before machining the workpiece 2 in the cutting process S13. Further, by rotating the tool spindle 12, the cutting tool 11 is rotated around its central axis 113. However, the cutting tool 11 may be rotated before the cutting process S13. The cutting tool 11 only needs to be rotated before machining the workpiece 2. Thereafter, the tool spindle 12 is moved in the Y-axis direction, and the cutting edge 112 of the rotating cutting tool 11 is brought into contact with the outer peripheral surface of the rotating workpiece 2, and the cutting tool 11 is cut into the workpiece 2. At this time, the central axis 113 of the cutting tool 11 is parallel to the tangential direction at the machining point where the cutting edge 112 and the workpiece 2 are in contact with each other on the outer peripheral surface of the workpiece 2 as seen in the direction along the central axis of the workpiece 2. As a result, referring to FIG. (A), the outer peripheral surface of the workpiece 2 is cut by the cutting edge 112. Thereafter, the tool spindle 12 is moved in the Z-axis direction, that is, the cutting tool 11 is moved in the direction along the central axis of the workpiece 2. That is, in the cutting process S13, the workpiece is cut with the cutting edge 112 provided on the outer peripheral surface of the cutting tool 11 from the start to the end of the cutting process. In the cutting process S13, from the start end to the end end of the spiral groove is formed by the cutting edge 112 provided on the outer peripheral surface of the cutting tool 11. As a result, a spiral groove 21 is formed on the outer peripheral surface of the workpiece 2.

[0043] According to the spiral groove machining method of the present embodiment in this way, the workpiece 2 is machined by the cutting edge 112 provided on the outer peripheral surface of the cutting tool 11 having a cross-sectional shape corresponding to the cross-sectional shape of the spiral groove. Therefore, in one cutting process, that is, in the range where the spiral groove is formed, the spiral groove is formed on the outer peripheral surface of the workpiece 2 only by moving the cutting tool 11 once in the Z-axis direction. Further, the workpiece 2 is machined by the cutting edge 112 provided on the outer peripheral surface without using the cutting edge 111 provided on the bottom surface of the cutting tool 11. Therefore, compared with the case of cutting by the cutting edge 111, the bending moment generated in the cutting tool 11 is suppressed, and vibration is less likely to occur. Therefore, according to the spiral groove machining method of the present embodiment, the machining efficiency can be improved in the machining of the spiral groove.

[0044] <Modification example> FIG. 5 is a flowchart of a spiral groove machining method according to a modification example of the present embodiment. Hereinafter, the spiral groove machining method according to the modification example of the present embodiment will be described, but descriptions overlapping with the above description will be omitted as appropriate. The spiral groove machining method according to the modification example is different from the above-described embodiment in that the machining point where the cutting tool 11 and the workpiece 2 are in contact is changed. In this spiral groove machining method, the cutting process S13 includes a first cutting process S131 and a second cutting process S132 executed after the first cutting process S131.

[0045] FIG. 6 is a diagram for explaining a first cutting step in a method for machining a spiral groove according to a modified example of the present embodiment. In the first cutting step S131, a first portion 1121 of the cutting edge 112 is brought into contact with the outer peripheral surface 22 of the workpiece 2, and the outer peripheral surface 22 of the workpiece 2 is cut by the first portion 1121. The first portion 1121 corresponds to a point (machining point) on the cutting edge 112 that first contacts the outer peripheral surface 22 of the workpiece 2 when the cutting edge 112 is brought close to the workpiece 2 on which no spiral groove is formed. The first portion 1121 is provided at a position that is a predetermined distance from the root side end (the end on the tool spindle 12 side) of the cutting edge 112 in the direction along the central axis of the cutting tool 11. The predetermined distance is, for example, 1 / 2 or less of the length of the cutting edge 112 in the direction along the central axis. Preferably, the predetermined distance is 1 / 4 or less of the length of the cutting edge 112 in the direction along the central axis. By performing the first cutting step S131, a spiral groove 21 is formed in the workpiece 2.

[0046] After the first cutting step S131 is executed, the workpiece on which the spiral groove 21 is formed is taken out from the composite machining machine 1, and a new workpiece on which no spiral groove is formed is attached to the composite machining machine 1. Thereafter, the second cutting step S132 is executed.

[0047] FIG. 7 is a diagram for explaining a second cutting step in a method for machining a spiral groove according to a modified example of the present embodiment. In the second cutting step S132, a second portion 1122 different from the first portion 1121 of the cutting edge 112 is brought into contact with the outer peripheral surface of the workpiece 2, and the outer peripheral surface of the new workpiece 2 is cut by the second portion 1122. The second portion 1122 corresponds to a point on the cutting edge 112 that first contacts the outer peripheral surface 22 of the workpiece 2 when the cutting edge 112 is brought close to the workpiece 2 on which the spiral groove is not formed. The second portion 1122 is provided on the tip side (opposite to the tool spindle 12 side) of the cutting edge 112 rather than the first portion 1121 in the direction along the central axis of the cutting tool 11. The second portion 1122 does not overlap with the first portion 1121. The second portion 1122 is provided at a position at a predetermined distance from the end on the tip side (the end opposite to the tool spindle 12 side) of the cutting edge 112 in the direction along the central axis of the cutting tool 11. The predetermined distance is, for example, less than 1 / 2 of the length in the direction along the central axis of the cutting edge 112. Preferably, the predetermined distance is 1 / 4 or less of the length in the direction along the central axis of the cutting edge 112. By executing the second cutting step S132, a spiral groove 21 is formed in the new workpiece 2.

[0048] However, the second portion 1122 may be at a position different from the first portion 1121 in the direction along the central axis of the cutting tool 11. The second portion 1122 may be provided on the base side (tool spindle 12 side) of the cutting edge 112 rather than the first portion in the direction along the central axis of the cutting tool 11. Also, the same workpiece may be cut in the first cutting step S131 and the second cutting step S132. That is, when forming a spiral groove by performing cutting on a certain workpiece a plurality of times, the machining point where the cutting edge 112 contacts the workpiece 2 may be changed during that process.

[0049] In addition, in the above-described embodiment, the case where the heat treatment step S11 is executed before the cutting preparation step S12 has been described. However, the heat treatment step S11 may not be executed. That is, a helical groove may be formed in a workpiece that has not been heat-treated. Further, a workpiece that has been heat-treated at a location different from the cutting process, that is, a workpiece that has been heat-treated in advance, may be prepared, and the cutting preparation step S12 and the cutting step S13 may be executed on the workpiece. Also, in the above-described embodiment, the case where the grinding step S14 is executed after the cutting step S13 has been described. However, the grinding step S14 may not be executed. That is, the grinding step of the helical groove may be appropriately executed as necessary, and may also be executed at a location different from the cutting process.

[0050] In addition, in the above-described embodiment, in the cutting step S13, the case where the cutting tool 11 is moved only in the Z-axis direction while rotating around its central axis to machine the workpiece 2 has been described. However, in the cutting step S13, the cutting tool 11 may be moved in the Z-axis direction (the direction along the central axis of the workpiece 2) while vibrating (reciprocating) in the direction along its central axis. As an aspect of vibrating the cutting tool 11 in the direction along its central axis, in the example shown in FIG. 4(A), a generation axis in the direction along its central axis (that is, the direction along the central axis of the cutting tool 11) is configured by a combined operation of the X-axis feed mechanism and the Z-axis feed mechanism, and the tool spindle 12 is vibrated (reciprocated) along this generation axis. Then, an operation in which this vibration operation is combined with the feed operation in the Z-axis direction is applied to the tool spindle 12.

[0051] In addition, in the above-described embodiment, the case where a helical groove is formed in the workpiece 2 using the general-purpose machining center 1 has been described. However, as the method for machining the helical groove, other machine tools other than the machining center may be used. The other machine tool is, for example, a 5-axis machining center. Also, a dedicated machining tool for implementing the method for machining the helical groove according to the present invention may be used.

[0052] In the above-described embodiment, the case where the spiral groove is formed by milling in which the cutting tool 11 is rotated around its central axis to machine the workpiece 2 has been described. However, the spiral groove may be formed by turning in which the workpiece 2 is machined without rotating the cutting tool 11 around its central axis.

[0053] In the above-described embodiment, the case where the workpiece 2 is machined into the screw shaft of the ball screw has been described. However, the method for machining the spiral groove of the present embodiment is not limited thereto. For example, the workpiece 2 may be machined into a shaft member having a spiral oil groove. In short, the method for machining the spiral groove may be to machine the workpiece 2 into a shaft member having a spiral groove.

[0054] Although it is repetitive, the descriptions of the above-described embodiments are illustrative in all respects and are not restrictive at all. Modifications and changes are appropriately possible for those skilled in the art. The scope of the present invention is indicated not by the above-described embodiments but by the scope of the claims. Further, the scope of the present invention includes modifications from the embodiments within the scope equivalent to the scope of the claims.

Explanation of Reference Numerals

[0055] 1: Composite machine tool 11: Cutting tool 111, 112: Cutting edges 1121: First portion 1122: Second portion 113: Central axis 12: Tool spindle 13: Workpiece spindle 131: Chuck 14: Auxiliary workpiece spindle 141: Chuck 2: Workpiece 21: Spiral groove 22: Outer peripheral surface 23: Central axis A: Lead angle

Claims

1. A method for machining a helical groove by forming a helical groove on the outer peripheral surface of a workpiece having a shaft shape with a shaft-shaped cutting tool having a cutting edge on its outer peripheral surface, a cutting preparation step of setting the cutting tool in a posture inclined by the lead angle of the helical groove to be machined with respect to a line perpendicular to the central axis of the workpiece and directing the cutting edge toward the outer peripheral surface of the workpiece; and after the cutting preparation step, a cutting step of moving the cutting tool in a direction along the central axis of the workpiece while bringing the cutting edge of the cutting tool into contact with the outer peripheral surface of the workpiece rotating around its central axis to form a helical groove on the outer peripheral surface of the workpiece. A method for machining a helical groove.

2. The method for machining a helical groove according to claim 1, wherein the cutting edge of the cutting tool is provided in a predetermined range in a direction along the central axis of the cutting tool, and the cutting step includes a first cutting step of bringing a first portion of the cutting edge into contact with the outer peripheral surface of the workpiece and cutting the outer peripheral surface of the workpiece with the first portion; and after the first cutting step, a second cutting step of bringing a second portion of the cutting edge, which is different in position from the first portion in a direction along the central axis of the cutting tool, into contact with the outer peripheral surface of the workpiece and cutting the outer peripheral surface of the workpiece or a new outer peripheral surface of the workpiece with the second portion. A method for machining a helical groove.

3. The method for machining a helical groove according to claim 2, wherein the method for machining the helical groove includes using a composite machining machine including a tool spindle that holds and rotates an end portion of the cutting tool, wherein the cutting edge of the cutting tool is provided in a predetermined range of an end portion different from the end portion held by the tool spindle in a direction along the central axis of the cutting tool, and the first portion is closer to the tool spindle than the second portion in a direction along the central axis of the cutting tool. A method for machining a helical groove.

4. The method for machining a helical groove according to claim 1, wherein the workpiece has an outer peripheral surface that has been quenched, and in the cutting step, a helical groove is formed on the outer peripheral surface of the workpiece that has been quenched. A method for machining a helical groove.

5. The method for machining a helical groove according to claim 1, wherein the method for machining the helical groove further includes a grinding step of grinding the formed helical groove after the cutting step. A method for machining a helical groove.

6. The method for machining a helical groove according to claim 1, wherein the method for machining the helical groove is A method for machining a helical groove using a compound machine tool including a tool spindle that holds and rotates the cutting tool, a work spindle that holds the first end of the work and rotates the work, and an auxiliary work spindle that supports the second end of the work different from the first end.

7. The method for machining a helical groove according to claim 1, wherein in the cutting step, while bringing the cutting edge of the cutting tool into contact with the outer peripheral surface of the work and vibrating the cutting tool in a direction along its central axis, the cutting tool is moved in a direction along the central axis of the work to form a helical groove on the outer peripheral surface of the work.

8. A method for manufacturing a shaft member having a helical groove by the method for machining a helical groove according to any one of claims 1 to 7.

9. A helical groove machining machine for forming a helical groove on the outer peripheral surface of a shaft-shaped work by means of a shaft-shaped cutting tool having a cutting edge on its outer peripheral surface, comprising a control device for controlling the position or posture of the cutting tool and the position or posture of the work, wherein the control device sets the cutting tool in a posture inclined by the lead angle of the helical groove to be machined with respect to a line perpendicular to the central axis of the work, and performs a cutting preparation process of directing the cutting edge toward the outer peripheral surface of the work, and after executing the cutting preparation process, while bringing the cutting edge of the cutting tool into contact with the outer peripheral surface of the work rotating around its central axis, the cutting tool is moved in a direction along the central axis of the work to perform a cutting process for forming a helical groove on the outer peripheral surface of the work.

10. A program for use in a helical groove machining machine for forming a helical groove on the outer peripheral surface of a shaft-shaped work by means of a shaft-shaped cutting tool having a cutting edge on its outer peripheral surface, wherein the cutting tool is set in a posture inclined by the lead angle of the helical groove to be machined with respect to a line perpendicular to the central axis of the work, and a cutting preparation process of directing the cutting edge toward the outer peripheral surface of the work is performed, and after executing the cutting preparation process, while bringing the cutting edge of the cutting tool into contact with the outer peripheral surface of the work rotating around its central axis, the cutting tool is moved in a direction along the central axis of the work to perform a cutting process for forming a helical groove on the outer peripheral surface of the work.

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