Method for machining a spiral groove

Abstract

[Task] To improve machining efficiency and machining precision when machining a spiral groove. [Solution] The spiral groove machining method is a spiral groove machining method by which a spiral groove 21 is formed in the outer peripheral surface 22 of a workpiece 2 having a shaft shape by means of a shaft-shaped cutting tool 11 having a cutting blade 112 on the outer peripheral surface.The method for machining a spiral groove includes a cutting preparation step in which the cutting tool 11 is placed in a posture in which its central axis 113 is inclined to a line L1 perpendicular to the central axis 23 of the workpiece 2 by a lead angle A of the spiral groove being machined, and the cutting blade 112 is directed toward the outer peripheral surface 22 of the workpiece 2, and a cutting step in which, after the cutting preparation step, the cutting tool 11 is moved in the direction along the central axis 23 of the workpiece 2 while the cutting blade 112 of the cutting tool 11 abuts against the outer peripheral surface 22 of the workpiece 2 rotating about its central axis 23, so that a spiral groove is formed in the outer peripheral surface 23 of the workpiece 2.

Description

[Technical Field]The present invention relates to a method for machining a spiral groove.[Background Technology]A known example of a component in which a spiral groove is formed is a screw shaft of a ball screw. A screw shaft is generally cylindrical in most cases, and a spiral groove is formed in the outer circumferential surface. Such a screw shaft is produced, for example, by machining. A method of machining a screw shaft by machining is disclosed in, for example, Patent Document 1.Patent Document 1 discloses an example of a machining method using a bit as a cutting tool. In this machining method, a cylindrical workpiece is rotated about its central axis, the tip is fitted to the outer peripheral surface of the workpiece at the time of the trimming, and the trimming is moved in the direction along the central axis of the workpiece. By repeating this cutting into the outer circumferential surface of the workpiece by the tip a plurality of times, a spiral groove is formed.Patent Document 1 also discloses a machining method using an end mill as a cutting tool. In this machining method, an end mill is attached to the outer circumferential surface of a workpiece such that the axial direction of the end mill is along the radial direction of the workpiece. That is, the end mill is disposed such that the axial direction of the end mill forms a right angle to the tangential direction at the machining point of the outer circumferential surface of the workpiece. The workpiece and the end mill are each rotated about their central axis, and the end mill is moved in the direction along the central axis of the workpiece. This forms a spiral groove.[Prior Art Documents][Patent Documents][Patent Document 1] Patent No. JP 4933081 B2[Overview of the Invention][Problems to be Solved by the Invention]In a ball screw, balls are provided in the spiral groove of the screw shaft, and the screw shaft and a ball nut move relative to each other via the balls. It is therefore preferable that the cross-sectional shape of the spiral groove has a semi-circular shape. For machining such a spiral groove by a machining method using a tip, for example, a round tip, i.e., a tip corresponding to the cross-sectional shape of the groove, is used. However, since a particular tip is required for this, the machining cost increases.Further, in a machining method using a tip (rotating), a feed motion is required by which, while the workpiece is rotated at a certain speed, the tip is moved in the direction along the central axis of the workpiece in accordance with the pitch of the spiral groove. Therefore, when turning, the cutting load becomes larger as compared with general thread machining. In addition, in a workpiece machined into a threaded shank, quenching hardening is frequently performed in advance. As a result, the cutting load can become even greater during a rotation. For this reason, in a turning operation, 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 improve the machining efficiency in turning.On the other hand, in a machining method using an end mill (milling), cutting of the workpiece is performed using a base blade provided on the front end surface of the end mill and an outer peripheral blade provided on the outer peripheral side. Since not only the rotation of the workpiece but also the rotation of the tool is used in milling for cutting the workpiece, the rotation speed of the workpiece can be set to a lower speed compared to the rotation. As a result, the feed speed of the tool for matching with the pitch of the spiral groove can also be set to a lower speed. Thereby, the cutting load on the tool can be adjusted appropriately during milling and a spiral groove can be formed by fewer cycles than during turning.However, in a machining method using an end mill, the base blade mainly cuts the workpiece. At this time, a large cutting load acts on the base blade, and vibration and progress of tool wear are easy to occur. Particularly in a component having a spiral groove such as a threaded shaft, the manufacture is often performed by hard turning, by which a workpiece having a high degree of hardness is cut. Therefore, compared with general machining, the described vibrations and progress of tool wear are easy to occur. For this reason, when cutting a spiral groove by the base blade of an end mill, restriction of machining conditions such as the machining speed is difficult, so that improvement of the machining efficiency is difficult.The present invention aims to improve the machining efficiency and the machining precision in machining a spiral groove.[Means for Achieving Object](1) The spiral groove processing method of the present invention is a spiral groove processing method by which a spiral groove is formed in the outer peripheral surface of a workpiece having a shaft shape by means of a shaft-shaped cutting tool having a cutting blade on the outer peripheral surface. The spiral groove processing method includes a cutting preparation step of bringing a cutting tool into a posture in which its central axis is inclined to a line perpendicular to the central axis of the workpiece by an angle of intersection of the spiral groove being processed and directing the cutting blade toward the outer circumferential surface of the workpiece, and a cutting step of, after the cutting preparation step, moving the cutting tool in the direction along the central axis of the workpiece while the cutting blade of the cutting tool abuts against the outer circumferential surface of the workpiece rotating about its central axis, so that a spiral groove is formed in the outer circumferential surface of the workpiece.In this spiral groove machining method, cutting of the workpiece is performed by a cutting blade provided on the outer circumferential surface of a shaft-shaped cutting tool. By cutting the workpiece by a cutting blade provided on the outer circumferential surface, for example, a bending moment loading the cutting tool is reduced as compared with cutting by a base blade of an end mill. This suppresses vibrations of the cutting tool. Consequently, by this helical groove processing method, the processing efficiency and the processing precision in the helical groove processing can be improved.(2) In the method of processing a spiral groove of item (1), the cutting blade of the cutting tool may also be provided in a certain range in the direction along the central axis of the cutting tool. The cutting step may also include a first cutting step in which a first portion of the cutting blade is abutted against the outer circumferential surface of the workpiece and the outer circumferential surface of the workpiece is cut by the first portion, and a second cutting step in which, after the first cutting step, a second portion of the cutting blade is abutted against the outer circumferential surface of the workpiece at a position in the direction along the central axis of the cutting tool other than the first portion, and the outer circumferential surface of the workpiece or the outer circumferential surface of a new workpiece is cut by the second portion.In the spiral groove processing method of item (2), the processing point at which the cutting blade comes into contact with the workpiece differs depending on whether it is a multiple machining of one workpiece or a machining of a new workpiece after the machining of the one workpiece. Therefore, even if there is wear at the first portion, for example, machining can be performed without replacing the tool with the second portion. Consequently, according to the method of machining a spiral groove of item (2), in the machining of a spiral groove, full use can be made of the entire cutting blade in the machining of the spiral groove and the tool life of a single cutting tool can be extended. The transition from the first section as the machining point to the second section can proceed in a form in which the cutting point of action changes over to the second section after the first section has reached its tool life. The tool life may be learned empirically or from a test of the tool.(3) In the method for machining a spiral groove of item (2), a turning / milling center including a tool spindle that holds and rotates an end portion of the cutting tool may also be used. The cutting blade of the cutting tool may also be provided in a certain range of an end portion different from the end portion that the tool spindle holds in the direction along the central axis of the cutting tool. The first portion may also be closer to the tool spindle than the second portion in the direction along the central axis of the cutting tool.In the spiral groove machining method of item (3), for the machining in the cutting blade, the first portion from the base side (tool spindle side) is used. The closer the machining point is to the base side, the shorter the distance between the machining point and the point at which the cutting tool is held becomes, thereby further suppressing warping and bending due to the cutting load. Consequently, by this spiral groove processing method of item (3), processing efficiency and processing precision in the spiral groove processing can be improved.(4) In the method of processing a spiral groove of item (1), the workpiece may also have an outer peripheral surface subjected to quench hardening. In the cutting step, a spiral groove may also be formed in the outer circumferential surface of a workpiece that has been subjected to quench hardening.In a ball screw, for example, friction occurs between the threaded shaft and the balls inserted into the helical groove. Therefore, in a workpiece machined into a threaded shank, quenching hardening can be performed in advance. In cutting a workpiece having such a high degree of hardness, a large load acts on the blade, the tip of the blade is easily worn out, or vibration is easily caused in the cutting tool. In the spiral groove processing method of item (4), cutting of the workpiece is performed by a cutting blade provided on the outer circumferential surface of a cutting tool, so that vibration does not easily occur. Therefore, this machining method is particularly suitable for the machining of a workpiece having a high degree of hardness in which quenching hardening has been performed.(5) The method of machining a spiral groove of item (1) may also include a grinding step of grinding the formed spiral groove after the cutting step.The spiral groove is machined by a feed motion of the cutting tool, so that rough surface roughness of the groove surface may occur due to the machining conditions. In the method of machining a spiral groove of item (5), the spiral groove is ground in a grinding step after the cutting step. Consequently, by the spiral groove processing method of item (5), the processing efficiency and the processing precision in the spiral groove processing can be improved.(6) In the method for machining a spiral groove of item (1), a turning / milling center including a tool spindle that holds and rotates a cutting tool, a workpiece spindle that holds a first end portion of a workpiece and rotates the workpiece, and an auxiliary workpiece spindle that supports a second end portion different from the first end portion may also be used.In the method of machining a spiral groove of item (6), the workpiece is rotated about its central axis. Further, in the above spiral groove machining methods, the cutting blade provided on the outer circumferential surface of the cutting tool is arranged to match the lead angle of the spiral groove, and the cutting tool is moved in the direction along the central axis of the workpiece. As compared with these machining methods, in the method of machining a spiral groove of item (6), a turning / milling center having a lathe function and a machining center function is used. Consequently, according to this machining method, a spiral groove can be formed in the workpiece with a single machine tool, and the machining efficiency can be improved.(7) In the spiral groove processing method of item (1), a spiral groove may also be formed in the outer peripheral surface of a workpiece by, in the cutting step, applying the cutting blade of a cutting tool to the outer peripheral surface of the workpiece and moving the cutting tool in the direction along the central axis of the workpiece while vibrating (reciprocating) the cutting tool in the direction along the central axis thereof.For example, the screw shaft is an elongated component whose length direction is in the direction along the central axis. If a spiral groove is formed in an elongated workpiece, a long, continuing chip is easily formed. When the chip comes into contact with the workpiece during machining, there is a possibility that the workpiece is damaged. In the spiral groove processing method of item (7), during processing, the cutting tool is vibrated at a certain amplitude and frequency of vibration, so that chips are more easily cut in the middle and a long, continuing chip is difficult to form. Further, by changing the processing point at which the cutting blade and the workpiece come into contact due to the vibrations, wear of a specific portion of the cutting blade can be suppressed, so that uniform wear can be provided in a specific range of the cutting blade corresponding to the vibrations.(8) According to the above-described spiral groove machining method of the present invention, a spiral groove can be formed in the outer circumferential surface of a workpiece having a shaft shape. By any of the methods for machining a spiral groove from (1) to (7), a shaft component having a spiral groove can be produced. Thus, a method of making a shaft component having a helical groove is encompassed within the scope of the present invention.(9) A spiral groove processing machine of the present invention is a spiral groove processing machine by which a spiral groove is formed in the outer circumferential surface of a workpiece having a shaft shape by means of a shaft-shaped cutting tool having a cutting blade on the outer circumferential surface, comprising a control device for controlling the position or posture of the cutting tool and the position or posture of the workpiece, wherein the control device is configured such that a cutting preparation processing is performed in which the cutting tool is brought into a posture in which its central axis is inclined to a line perpendicular to the central axis of the workpiece by an angle of intersection of the spiral groove being processed, and the cutting blade is directed toward the outer circumferential surface of the workpiece, and a cutting processing is performed, in which, after the cutting preparation processing, the cutting tool is moved in the direction along the central axis of the workpiece while the cutting blade of the cutting tool abuts on the outer circumferential surface of the workpiece rotating about its central axis, so that a spiral groove is formed in the outer circumferential surface of the workpiece.(10) A program for a spiral groove processing machine of the present invention is a program used for a spiral groove processing machine by which a spiral groove is formed in the outer circumferential surface of a workpiece having a shaft shape by means of a shaft-shaped cutting tool having a cutting blade on the outer circumferential surface, and is configured such that cutting preparation processing is performed in which the cutting tool is brought into a posture in which its central axis is inclined to a line perpendicular to the central axis of the workpiece by an angle of intersection of the spiral groove being processed and the cutting blade is directed toward the outer circumferential surface of the workpiece, and cutting processing is performed in which after the cutting preparation processing the cutting tool is moved in the direction along the central axis of the workpiece while the cutting blade of the cutting tool abuts on the outer circumferential surface of the workpiece, rotating about its central axis, so that a spiral groove is formed in the outer circumferential surface of the workpiece.[Effects of the Invention]As mentioned above, according to the method of machining a spiral groove of the present invention, the machining efficiency and the machining precision in machining a spiral groove can be improved.[Brief Description of Drawings][FIG. 1 ] FIG. 1 is a schematic view showing the main structure of a turning / milling center by which the spiral groove of the present embodiment is processed.[FIG. 2 ] FIG. 2 is a flowchart of a spiral groove processing method of the present embodiment.[FIG. 3] FIG. 3 is a view for explaining a cutting preparation step in the spiral groove processing method according to the present embodiment.[FIG. 4] FIG. 4 is a view for explaining a cutting step in the spiral groove processing method according to the present embodiment.[FIG. 5 ] FIG. 5 is a flowchart of the method for processing a spiral groove according to a modified example of the present embodiment.[FIG. 6 ] FIG. 6 is a view for explaining a first cutting step in the spiral groove processing method according to the modified example of the present embodiment.[FIG. 7 ] FIG. 7 is a view for explaining a second cutting step in the spiral groove processing method according to the modified example of the present embodiment.[Forms for Carrying Out the Invention]Hereinafter, forms for carrying out the present invention will be explained based on the drawings. In the present embodiment, a method of machining a spiral groove formed in a screw shaft in a ball screw will be explained. Further, in the present embodiment, machining of the spiral groove of the screw shaft by a turning / milling center which is an NC (Numerically Controlled Machine Tool) machine will be explained.<Rotation / Milling Center>FIG. 1 is a schematic view showing the main structure of a turning / milling center by which the spiral groove of the present embodiment is processed. A spiral groove 21 is formed in the outer circumferential surface of a workpiece 2 by a turning / milling center 1. In the figure, a screw shaft in which the spiral groove 21 is formed is shown as the workpiece 2 for explanation. The turning / milling center 1 includes a tool spindle 12 that holds a cutting tool 11, a workpiece spindle 13, and an auxiliary workpiece spindle 14. The X-axis direction, the Y-axis direction, and the Z-axis direction are orthogonal to each other.The cutting tool 11 has a cylindrical shape as a kind of shaft shape. The cutting tool 11 in the present embodiment is an end mill. The cutting tool 11 includes a cutting blade 111 and a cutting blade 112. The cutting blade 111 is provided on the front end surface of the cutting tool 11. The cutting blade 111 is also referred to as a base blade. The cutting blade 112 is provided on the outer circumferential surface of the front end side of the cutting tool 11. The cutting blade 112 is provided in the direction of a center axis 113 of the cutting tool 11 in a certain range of the outer circumferential surface from the front end. The cutting blade 112 is also referred to as an outer circumferential blade. The cutting blade 112 is provided to be connected to the cutting blade 111. The cutting blade 112 has a spiral shape (thread shape) extending in the direction along the central axis of the cutting tool 11. The cutting tool 11 may also include a plurality of cutting blades 111 and a plurality of cutting blades 112. The cutting tool 11 has, in a cross section perpendicular to its central axis, a shape corresponding to the cross-sectional shape of the spiral groove to be formed.More specifically, the tool spindle 12 holds the cutting tool 11. The tool spindle 12 holds a base portion of the cutting tool 11, that is, an end portion different from the front end portion where the cutting blade 111 and the cutting blade 112 are provided. The tool spindle 12 is configured such that various tools accommodated in a tool magazine provided at a certain position can be attached and detached. Attachment of the various tools to the tool spindle 12 or replacement is performed by a tool changer provided at a tool changing position near the tool magazine. By an unillustrated X-axis feed mechanism, Y-axis feed mechanism, and Z-axis feed mechanism, the tool spindle 12 is formed movably in the X-axis direction, Y-axis direction, and Z-axis direction, respectively. Furthermore, the tool spindle 12 can rotate the cutting tool 11 held in front of it. More specifically, the tool spindle 12 can rotate the cutting tool 11 about its central axis. Further, the tool spindle 12 is configured to be rotatable about a rotation axis parallel to the Y axis (hereinafter, such a rotation axis is also referred to as a B axis).The workpiece spindle 13 holds an end portion of the workpiece 2, and the workpiece spindle 13 includes a chuck 131 that grips the workpiece 2. The workpiece spindle 13 carries the workpiece 2 such that the workpiece 2 runs along the Z axis. The workpiece spindle 13 is configured to be rotatable about a rotation axis parallel to the Z axis. The workpiece spindle 13 is configured such that the workpiece 2 can rotate about an axis of rotation parallel to the Z axis (hereinafter, such an axis of rotation is also referred to as a C axis), that is, about a central axis 23 of the workpiece 2.The auxiliary work spindle 14 is provided opposite to the work spindle 13. The auxiliary work spindle 14 supports the other end portion of the workpiece 2, and the auxiliary work spindle 14 includes a chuck 141 that grips the workpiece 2. The auxiliary workpiece spindle 14 carries the workpiece 2 such that rotation of the workpiece 2 is permitted. The auxiliary work spindle 14 is configured to be movable in the Z-axis direction.The turning / milling center 1 is provided with other various functions such as an anti-vibration unit by which the workpiece 2 is clamped and eccentricity of the central axis of the workpiece 2 during cutting is suppressed, or a measurement device that measures dimensions of the workpiece such as the outer diameter, etc., with illustration omitted. The turning / milling center 1 further comprises a control device, not shown. The control device controls the position or posture of the respective parts of the turning / milling center. The control device is formed from a computer and comprises a CPU, a RAM, a ROM, etc. The control device executes a computer program stored in a storage medium, whereby the respective steps of the method for machining a spiral groove, which steps are described below, are realized.By the spiral groove machining method of the present embodiment using the turning / milling center 1 having this configuration, the spiral groove 21 having a lead angle A is formed in an outer circumferential surface 22 of the workpiece 2 having a shaft shape. The angle of intersection is an angle of base and hypotenuse if, in the case of a right-angled triangle with the length of one revolution of the spiral groove and the pitch of the spiral groove as an candidate, the pitch of the spiral groove is the base. The angle of intersection is expressed by the following equation (1):θ: angle of attackL: Pitch of the spiral grooveD: Effective diameter of the spiral grooveThe pitch L of the spiral groove denotes the distance in the central axis direction between a point of the spiral groove and a point reached from the point concerned after one revolution of the spiral groove. The effective diameter D of the spiral groove denotes the diameter of a virtual cylinder in which the length of the vertices of the spiral groove in the central axis direction and the length of the valleys of the spiral groove in the central axis direction are equal.The method of machining a spiral groove will be explained below.<Method for Machining a Spiral Groove>FIG. 2 is a flowchart of the method for processing a spiral groove according to the present embodiment. The spiral groove processing method includes, in order of execution, a heat treatment step S 11, a cutting preparation step S 12, a cutting step S 13, and a grinding step S 14.In the heat treatment step S 11, the workpiece 2 having a cylindrical shape is subjected to heat treatment. The heat treatment is, for example, quench hardening. The workpiece 2 is made of, for example, iron or an alloy having iron as a main component. In the present embodiment, by subjecting the workpiece 2 to heat treatment, the degree of hardness of the workpiece 2 improves. the workpiece 2 has a solid cylindrical shape, but the workpiece 2 may also have a hollow cylindrical shape. That is, it suffices if the workpiece 2 has a shaft shape. The shaft shape is not limited to a cylindrical shape. The shaft shape also includes a shape having a step such as a flange. The shaft shape also includes an asymmetric shape. It is sufficient if the shaft shape has a shape having a center axis as a rotation center.FIG. 3 is a view for explaining the cutting preparation step in the spiral groove processing method according to the present embodiment. In the figure, (A) is a front view of a turning / milling center, and (B) is a view viewed along the direction of the central axis of a workpiece. With reference to FIG. (A) In the cutting preparation step S 12, first, the workpiece 2 is attached to the turning / milling center 1. One end portion of the workpiece 2 is gripped by the chuck 131 of the workpiece spindle 13, and the other end portion is gripped by the chuck 141 of the auxiliary workpiece spindle 14.Next, the cutting tool 11 is placed in a posture in which its center axis 113 is inclined to a line L 1 perpendicular to the center axis 23 of the workpiece 2 by the lead angle A of the spiral groove 21 being machined, and the cutting blade 112 is directed toward the outer circumferential surface 22 of the workpiece 2. More specifically, the perpendicular line L 1 is orthogonal to both the central axis 23 and the perpendicular of the workpiece 2. The cutting tool 11 is placed in a posture in which its central axis 113 is inclined to the perpendicular by the gate angle A in a plane defined by the central axis 23 of the workpiece 2 and the perpendicular orthogonal to the central axis 23. As viewed from the Y-axis direction, the tool spindle 12 is rotated about a rotation axis parallel to the Y-axis, so that the center axis 113 of the cutting tool 11 is inclined to the X-axis direction by the gate angle A. In still other words, the tool spindle 12 is rotated such that the angle formed by a reference axis parallel to the radial direction axis (line L 1) orthogonal to the central axis 23 of the workpiece 2 and the central axis 113 of the cutting tool 11 to the workpiece 2 gives the gate angle A of the helical groove to be formed. In this embodiment, the reference state of the tool spindle 12 is a state in which the central axis thereof is directed to the perpendicular so that the tool spindle 12 is rotated by the lead angle A about the B axis. With reference to FIG. (B) The tool spindle 12 is suitably moved in the X-axis direction, the Y-axis direction, and the Z-axis direction so that the cutting blade 112 is opposed to the outer circumferential surface 22 of the workpiece 2. In the present embodiment, the tool spindle 12 is moved so that the cutting blade 112 is positioned at a position spaced a certain distance in the Y-axis direction (plus side or minus side) from the outer circumferential surface of the workpiece 2. The order of the rotational movement of the tool spindle 12 and the translational movement of the tool spindle 12 is not subject to any particular restriction. After the cutting blade 112 faces the outer circumferential surface of the workpiece 2, for example, by rotating the tool spindle 12, the angle between the central axis 113 of the cutting tool 11 and the X-axis direction can be made to be equal to the gate angle A. In addition, the rotation and the translation movement of the tool spindle 12 can also take place simultaneously.FIG. 4 is a view for explaining a cutting step in the spiral groove processing method according to the present embodiment. In the figure, (A) is a front view of a turning / milling center, and (B) is a view viewed along the direction of the central axis of a workpiece. First, reference is made to FIG. (B) In the cutting step S 13, milling by the cutting tool 11. More specifically, the workpiece 2 is rotated by rotating the workpiece spindle 13 holding the workpiece 2 about its central axis 23. In this embodiment, in the cutting step S 13, the workpiece 2 is rotated. However, the workpiece 2 may be rotated before the cutting step S 13 is performed. The workpiece 2 may also be rotated during the cutting preparation step S 12. The workpiece 2 may also be rotated before the execution of the cutting preparation step S 12. In short, the workpiece 2 should be rotated before the workpiece 2 is machined in the cutting step S 13. Further, the cutting tool 11 is rotated by rotating the tool spindle 12 about its center axis 113. The cutting tool 11 may also be rotated before the cutting step S 13. The cutting tool 11 should be rotated before machining the workpiece 2. Subsequently, the tool spindle 12 is moved in the Y-axis direction, and the cutting blade 112 of the rotary cutting tool 11 is abutted to the outer circumferential surface of the rotary workpiece 2 so that the cutting tool 11 cuts into the workpiece 2. Here, the central axis 113 of the cutting tool 11 becomes parallel to the tangential direction at the machining point where the cutting blade 112 and the workpiece 2 come into contact on the outer circumferential surface of the workpiece 2 as viewed in the direction along the central axis of the workpiece 2. This is referred to in the drawing. (A) Cut the outer peripheral surface of the workpiece 2 by the cutting blade 112. Subsequently, 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 step S 13, cutting of the workpiece is performed from the start to the end of the cutting processing by the cutting blade 112 provided on the outer circumferential surface of the cutting tool 11. In the cutting step S 13, the spiral groove is formed from its start point to its end point by the cutting blade 112 provided on the outer circumferential surface of the cutting tool 11. Thereby, the spiral groove 21 is formed in the outer circumferential surface of the workpiece 2.According to the spiral groove machining method of the present embodiment, cutting of the workpiece 2 is performed by the cutting blade 112 provided on the outer circumferential surface of the cutting tool 11 having a cross-sectional shape corresponding to the cross-sectional shape of the spiral groove. Therefore, in one-time machining, that is, by one-time movement of the cutting tool 11 in the Z-axis direction in the region where the spiral groove is formed, a spiral groove is formed in the outer circumferential surface of the workpiece 2. Further, cutting of the workpiece 2 is performed by the cutting blade 112 provided on the outer circumferential surface without using the cutting blade 111 provided on the base surface of the cutting tool 11. Therefore, compared with cutting by the cutting blade 111, occurrence of a bending moment on the cutting tool 11 is suppressed, and vibration is less likely to occur. Consequently, by the spiral groove processing method of the present embodiment, processing efficiency in the spiral groove processing can be improved.< Example>FIG. 5 is a flowchart of a method for processing a spiral groove according to the modified example of the present embodiment. Hereinafter, a method of processing a spiral groove according to a modified example of the present embodiment will be explained, and duplicate explanation of the above explanation will be omitted as appropriate. The spiral groove machining method according to the modified example is different from the above-described embodiment in a change in the machining point at which the cutting tool 11 and the workpiece 2 come into contact. In this spiral groove machining method, the cutting step S 13 includes a first cutting step S 131 and a second cutting step S 132 performed after the first cutting step S 131.FIG. 6 is a view for explaining the first cutting step in the spiral groove processing method according to the modified example of the present embodiment. In the first cutting step S 131, a first portion 1121 of the cutting blade 112 abuts on the outer circumferential surface 22 of the workpiece 2, and the outer circumferential surface 22 of the workpiece 2 is cut by the first portion 1121. When the cutting blade 112 approaches the workpiece 2 in which no spiral groove is formed, the first portion 1121 corresponds to the point (machining point) of the cutting blade 112 that first impinges on the outer circumferential surface 22 of the workpiece 2. The first portion 1121 is provided at a position a certain distance from the end on the base side of the cutting blade 112 (end of the tool spindle 12 side) in the direction along the center axis of the cutting tool 11. The predetermined distance is, for example, less than or equal to half the length of the cutting blade 112 in the direction along the central axis. Preferably, the determined distance is less than or equal to one quarter of the length of the cutting blade 112 in the direction along the central axis. By performing the first cutting step S 131, the spiral groove 21 is formed in the workpiece 2.After the execution of the first cutting step S 131, the workpiece in which the spiral groove 21 has been formed is taken out from the turning / milling center 1, and a new workpiece in which no spiral groove is formed is inserted into the turning / milling center 1. Subsequently, the second cutting step S 132 is performed.FIG. 7 is a view for explaining the second cutting step in the spiral groove processing method according to the modified example of the present embodiment. In the second cutting step S 132, a second portion 1122 of the cutting blade 112 different from the first portion 1121 abuts on the outer circumferential surface of the workpiece 2, and the outer circumferential surface of a new workpiece 2 is cut by the second portion 1122. When the cutting blade 112 approaches the workpiece 2 in which no spiral groove is formed, the second portion 1122 corresponds to the point of the cutting blade 112 that hits the outer circumferential surface 22 of the workpiece 2 first. The second portion 1122 is provided further on the front end side of the cutting tool 112 (opposite side to the tool spindle 12 side) 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 a certain distance from the end of the front end side of the cutting blade 112 (end of the side opposite to the tool spindle 12 side) in the direction along the central axis of the cutting tool 11. The predetermined distance is, for example, less than half of the length of the cutting blade 112 in the direction along the central axis. Preferably, the determined distance is less than or equal to one quarter of the length of the cutting blade 112 in the direction along the central axis. By performing the second cutting step S 132, the spiral groove 21 is formed in the new workpiece 2.The second portion 1122 should be located at a different location than the first portion 1121 in the direction along the central axis of the cutting tool 11. The second portion 1122 may also be provided further on the base side of the cutting blade 112 (tool spindle 12 side) than the first portion in the direction along the central axis of the cutting tool 11. Furthermore, in the first cutting step S 131 and in the second cutting step S 132, machining can also be carried out on the same workpiece. That is, in cutting and forming a spiral groove on a workpiece a plurality of times, meanwhile, the machining point at which the cutting blade 112 and the workpiece 2 come into contact may be changed.Except for this, in the above-described embodiment, the case where the heat treatment step S 11 is performed before the cutting preparation step S 12 has been explained. However, no heat treatment step S 11 can be carried out. That is, a spiral groove may also be formed in a workpiece that has not been subjected to heat treatment. Further, a workpiece in which a heat treatment is performed at a position other than that of the machining, that is, a workpiece that has been subjected to a heat treatment in advance, and in this workpiece, the cutting preparation step S 12 and the cutting step S 13 are performed, may also be provided. Further, in the above-described embodiment, the case where the grinding step S 14 is performed after the cutting step S 13 has been explained. However, no grinding step S 14 can be carried out. That is, the grinding step of the spiral groove may be appropriately performed if necessary or performed at a location other than that of the machining.Further, in the above-described embodiment, the case where, in the cutting step S 13, the cutting of the workpiece 2 is performed by exclusively moving the cutting tool 11 in the Z-axis direction while rotating about its central axis has been explained. However, in the cutting step S 13, the cutting tool 11 may be moved in the Z-axis direction (direction along the central axis of the workpiece 2) while being vibrated (reciprocating) in the direction along the central axis thereof. As an aspect in which the cutting tool 11 is vibrated in the direction along its central axis, it is conceivable to form the tool spindle 12 as a generating axis in the direction along its central axis (i.e., in the direction along the central axis of the cutting tool 11) and vibrate (reciprocatingly move) the tool axis 12 along this generating axis by a combined movement due to an X-axis feed mechanism and Z-axis feed mechanism in the example shown in FIG. 4(A). Then, a motion composed of this oscillating motion and the feed motion in the Z-axis direction is added to the tool spindle 12.Further, in the above-described embodiment, the case where a spiral groove is formed in the workpiece 2 by a universal turning / milling center 1 has been explained. However, in the method for machining a spiral groove, a machine tool other than a turning / milling center may be used. As another machine tool, there is, for example, a 5-axis machine tool. Further, a special machining apparatus for carrying out the method for machining a spiral groove according to the present invention may also be used.Further, in the above-described embodiment, the case where a spiral groove is formed by milling in which the cutting tool 11 is rotated about its central axis and machining of the workpiece 2 is performed has been explained. However, the spiral groove may be formed by rotating in which the workpiece 2 is cut without rotating the cutting tool 11 about its central axis.Further, in the above-described embodiment, the case where the workpiece 2 is machined into a screw shaft of a ball screw has been explained. However, the method for machining a spiral groove of the present embodiment is not limited thereto. By the spiral groove machining method, the workpiece 2 can also be machined into a shaft component having a spiral oil groove, for example. In short, the workpiece 2 can also be machined into a shank component having a helical groove by the helical groove machining method.As stated above, the explanation of the above-described embodiments is given in all points by way of example, without being limited thereto. Suitable modifications and changes will be possible by those skilled in the art. The scope of the present invention is not shown in the above-described embodiments but in the claims. Further, the scope of the present invention includes modifications of embodiments within the same scope as the claims.[Explanation of Reference Numerals]1 Turning / milling center 11 Cutting tool 111, 112 Cutting blade 1121 First portion 1122 Second portion 113 Center 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 Center axis A Lead angleReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedJP 4933081 B2

[0005]

Claims

A helical groove machining method by which a helical groove is formed in the outer peripheral surface of a workpiece having a shaft-shaped shape by means of a shaft-shaped cutting tool having a cutting blade on the outer peripheral surface, comprising a cutting preparation step in which a cutting tool is placed in a posture in which its central axis is inclined to a line perpendicular to the central axis of the workpiece by an angle of intersection of the helical groove being machined and the cutting blade is directed toward the outer peripheral surface of the workpiece, and a cutting step in which after the cutting preparation step, the cutting tool is moved in the direction along the central axis of the workpiece while the cutting blade of the cutting tool abuts on the outer peripheral surface of the workpiece rotating about its central axis, so that a helical groove is formed in the outer peripheral surface of the workpiece.The spiral groove processing method according to claim 1, wherein the cutting blade of the cutting tool is provided in a certain range in the direction along the central axis of the cutting tool, and the cutting step includes a first cutting step in which a first portion of the cutting blade is abutted against the outer circumferential surface of the workpiece and the outer circumferential surface of the workpiece is cut by the first portion, and a second cutting step in which, after the first cutting step, a second portion of the cutting blade is abutted against the outer circumferential surface of the workpiece at a position in the direction along the central axis of the cutting tool other than the first portion, and the outer circumferential surface of the workpiece or the outer circumferential surface of a new workpiece is cut by the second portion.The helical groove machining method according to claim 2, wherein in the helical groove machining method, a turning / milling center is used that includes a tool spindle that holds and rotates an end portion of the cutting tool, and the cutting blade of the cutting tool is provided in the direction along the central axis of the cutting tool in a specific range of an end portion different from the end portion that the tool spindle holds.The method for processing a spiral groove according to claim 1, wherein the workpiece has an outer circumferential surface that has been subjected to quench hardening, and in the cutting step, the spiral groove is formed in the outer circumferential surface of the workpiece that has been subjected to quench hardening.The helical groove machining method according to claim 1, wherein the helical groove machining method further comprises a grinding step of grinding the formed helical groove after the cutting step.The spiral groove machining method according to claim 1, wherein the spiral groove forming method uses a turning / milling center including a tool spindle that holds and rotates a cutting tool, a workpiece spindle that holds a first end portion of a workpiece and rotates the workpiece, and an auxiliary workpiece spindle that supports a second end portion of the workpiece different from the first end portion.The spiral groove machining method according to claim 1, wherein a spiral groove is formed in the outer circumferential surface of a workpiece by applying the cutting blade of the cutting tool to the outer circumferential surface of the workpiece and moving the cutting tool in the direction along the central axis of the workpiece while vibrating the cutting tool in the direction along the central axis thereof in the cutting step.A method of manufacturing a shaft component having a helical groove, by which a shaft component having a helical groove is manufactured by means of one of the methods of machining a helical groove according to any one of claims 1 to 7.A machining machine for a helical groove by which a helical groove is formed in the outer peripheral surface of a workpiece having a shaft shape by means of a shaft-shaped cutting tool having a cutting blade on the outer peripheral surface, comprising a control device for controlling the position or posture of the cutting tool and the position or posture of the workpiece, wherein the control device is configured such that a cutting preparation processing is performed in which the cutting tool is brought into a posture in which its central axis is inclined to a line perpendicular to the central axis of the workpiece by an angle of intersection of the helical groove being machined, and the cutting blade is directed toward the outer peripheral surface of the workpiece, and a cutting processing is performed in which, after the cutting preparation processing, the cutting tool is moved in the direction along the central axis of the workpiece, while the cutting blade of the cutting tool abuts on the outer circumferential surface of the workpiece rotating about its central axis, so that a spiral groove is formed in the outer circumferential surface of the workpiece.A program for a spiral groove processing machine, by which a spiral groove is formed in the outer peripheral surface of a workpiece having a shaft shape by a shaft-shaped cutting tool having a cutting blade on the outer peripheral surface, configured such that cutting preparation processing is performed in which the cutting tool is placed in a posture in which the center axis thereof is inclined to a line perpendicular to the center axis of the workpiece by an angle of intersection of the spiral groove being processed and the cutting blade is directed toward the outer peripheral surface of the workpiece, and cutting processing is performed in which after the cutting preparation processing, the cutting tool is moved in the direction along the center axis of the workpiece while the cutting blade of the cutting tool abuts on the outer peripheral surface of the workpiece rotating about the center axis thereof, so that a spiral groove is formed in the outer peripheral surface of the workpiece.

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