Thread milling cutter

Abstract

A thread milling cutter is provided that can reduce the tilting of an internal thread being machined and thus increase the tool life. A thread milling cutter (10) includes a plurality of thread cutting edges (20a, 24, 29) spaced circumferentially apart from one another on one side of the front end (14) of an outer circumference of a tool body (12), as well as a plurality of end cutting edges formed on the front end (14) of the tool body (12). An effective cutting edge section (35), which cuts a workpiece, and a non-effective cutting edge section (36), which is set back towards an axial shank end (13) with respect to a trajectory of the effective cutting edge section (35) when the tool body (12) rotates about an axis (C), are formed on the plurality of end cutting edges.

Description

TECHNICAL AREA

[0001] The present invention relates to a thread milling cutter which can reduce tilting of an internal thread to be machined and thus increase the tool life. STATE OF THE ART

[0002] Conventionally available tools for cutting internal threads in workpieces include thread milling cutters. A thread milling cutter incorporates thread-cutting edges around the outer circumference of the tool body and performs thread cutting by moving it relative to a workpiece while being rotated about an axis by a drive device such as an NC milling machine. One type of such thread milling cutter is provided with end cutting edges on the face of the tool body to eliminate the need for pre-drilling by another tool as a preceding thread-cutting process, and performs drilling and thread cutting simultaneously (Patent Document 1).

[0003] The thread cutting edges of the thread mill disclosed in patent document 1 are formed by a multitude of axially arranged threads. If the thread mill tilts during cutting, a difference in pitch diameter can therefore occur between the beginning and end of the cut internal thread (internal thread tilting). In patent document 1, it is less likely that such internal thread tilting will increase with a growing number of cut internal threads, thus ensuring the service life of the thread mill. DOCUMENT ON THE STATE OF THE TECHNOLOGY PATENT DOCUMENT

[0004] Patent document 1: JP 6692932 B2 SUMMARY OF THE INVENTION PROBLEM TO BE SOLVED BY THE INVENTION

[0005] However, the technique disclosed in patent document 1 is problematic insofar as, under certain cutting conditions, the tilting of the internal thread increases at an early stage with an increasing number of internal threads cut, leading to a shorter tool life. One reason for this is presumably that during a cutting operation with the thread milling cutter, the amount of material removed from the workpiece by one end cutting edge per thread cutting edge of the thread milling cutter is very small for one rotation (hereinafter referred to as "one revolution") of the thread milling cutter around an axis.

[0006] The present invention was made to solve the problem described above, and one objective of the invention is to provide a thread milling cutter that can reduce the tilting of an internal thread being machined, thereby increasing the tool life. MEANS TO SOLVE THE PROBLEM

[0007] To achieve this objective, a thread milling cutter according to the present invention cuts an internal thread into a workpiece by moving relative to the workpiece while rotating about an axis. The thread milling cutter comprises: a tool body comprising an axial front end and a shank end arranged axially opposite the front end and having a shank shape centered about the axis; a plurality of thread cutting edges, each formed by a plurality of axially arranged threads and spaced apart circumferentially on the side of the front end of an outer circumference of the tool body; and a plurality of end cutting edges formed on the front end of the tool body such that each of these is connected to the plurality of thread cutting edges on the side of the front end.An effective cutting edge section that cuts the workpiece and an ineffective cutting edge section that is axially recessed towards the side of the shank end relative to a trajectory of the effective cutting edge section when the tool body performs a rotation about the axis are formed on the plurality of end cutting edges. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0008] In the thread milling cutter according to claim 1, the effective cutting edge section and the ineffective cutting edge section are formed on the plurality of end cutting edges, each of which is connected to the plurality of thread cutting edges. The ineffective cutting edge section is set back towards the axial shank end relative to the trajectory of the effective cutting edge section when the tool body rotates about an axis (during one revolution). Consequently, depending on the cutting conditions, it is less likely that the ineffective cutting edge section will cut the workpiece, while the effective cutting edge section is more likely to do so.Accordingly, the cutting area of ​​the workpiece is increased by an effective cutting edge section during one revolution when the ineffective cutting edge section is present, compared to when no ineffective cutting edge section is present and the multitude of end cutting edges is entirely formed by the effective cutting edge section. Thus, this thread milling cutter makes it possible to reduce tilting of an internal thread being machined and thereby increase the tool life.

[0009] The thread milling cutter according to claim 2 offers the following effect in addition to that achieved by the thread milling cutter according to claim 1. When the effective cutting edge section and the ineffective cutting edge section are formed on a terminal cutting edge, it is difficult to ensure the relief of the ineffective cutting edge section towards the shank end near the intermediate boundary. In contrast, each of the terminal cutting edges of the present thread milling cutter is formed entirely (with the exception of a groove cutting edge described below) either by the effective cutting edge section or the ineffective cutting edge section.Accordingly, the relief of the ineffective cutting edge section towards the shank end can be easily ensured, so that the ineffective cutting edge section is less likely to come into contact with the workpiece during a cutting operation with the thread milling cutter. Consequently, the cutting quantity through the effective cutting edge section during one revolution can be easily ensured.

[0010] The thread milling cutter according to claim 3 offers, in addition to the effect achieved by the thread milling cutter according to claim 1 or 2, the following effect. The rake faces of the plurality of end cutting edges are each formed by the plurality of grooves recessed at the front end of the tool body. Furthermore, each of the grooves comprises a groove surface and a groove base. The groove surface lies circumferentially opposite the corresponding rake face, and the distance between the groove surface and the rake face tapers towards the shank end. The groove base connects the groove surface and the rake face, extends from the axial side of the tool body to its outer circumference, and is inclined towards the shank end.

[0011] The multiple slots are interconnected on the axis side. This creates an edge between the rake face of one of two circumferentially adjacent slots and the slot face of the other slot. This edge is called a slot cutting edge. Each of the multiple slot cutting edges is connected to a multiple of end cutting edges. The trajectories of the multiple slot cutting edges overlap, at least on the end cutting edge side, when the tool body is rotated. When the workpiece is cut not only by the end cutting edges but also by the slot cutting edges on the side of the end cutting edges, each of the multiple slot cutting edges can easily come into contact with the workpiece, and the radial deformation of the tool body corresponding to this contact can be made as uniform as possible in the circumferential direction.Accordingly, it is possible to prevent the occurrence of vibrations caused by such uneven radial deformation, thereby suppressing a reduction in tool life due to such vibrations.

[0012] The thread milling cutter according to claim 4 offers, in addition to the effect achieved by the thread milling cutter according to claim 3, the following effect. Each of the end cutting edges is fully formed (with the exception of the groove cutting edge) either by the effective cutting edge section or the ineffective cutting edge section. Accordingly, as described above, the unloading of the ineffective cutting edge section towards the shank end can be easily ensured, so that the cutting quantity by the effective cutting edge section can be easily ensured during one revolution.

[0013] Since the ineffective cutting edge section is less likely to cut the workpiece, a relatively small amount of chips is collected in the groove forming the rake face of the ineffective cutting edge section. Chips produced by cutting with the effective cutting edge section are primarily collected in the groove forming the rake face of the effective cutting edge section, and therefore a relatively large amount of chips is collected in the groove. The depth of the groove forming the rake face of the effective cutting edge section, from the side of the leading edge to the bottom of the groove, is greater than the depth of the groove forming the rake face of the ineffective cutting edge section, also from the side of the leading edge to the bottom of the groove.This makes it possible to enlarge the internal volume of the groove containing a large amount of chips, while simultaneously reducing the internal volume of the groove containing a small amount of chips. Consequently, it is possible to prevent chip clogging during a thread milling operation and to ensure the rigidity of the tool body, thereby increasing the tool life of the thread mill.

[0014] The thread milling cutter according to claim 5 offers the following effect in addition to that achieved by the thread milling cutter according to any one of claims 1 to 4. The effective cutting edge section and the ineffective cutting edge section are arranged alternately in the circumferential direction. Thus, during a cutting operation, the number of positions in the circumferential direction where the plurality of thread cutting edges come into contact with the workpiece can be approximately half as many as the number of positions where the effective cutting edge section comes into contact with the workpiece. Accordingly, it is possible to reduce the load concentration on a portion of the thread milling cutter in the circumferential direction during cutting and thus increase the tool life.

[0015] The thread milling cutter according to claim 6 offers, in addition to the effect achieved by the thread milling cutter according to any one of claims 1 to 5, the following effect: The plurality of end cutting edges are rotationally symmetrical about the axis. Thus, the effective cutting edge section and the ineffective cutting edge section are arranged rotationally symmetrically, and therefore the reaction force experienced by the effective cutting edge section from the workpiece during a cutting operation can be made as uniform as possible in the circumferential direction. Accordingly, it is possible with the thread milling cutter to reduce the load concentration on a portion of the effective cutting edge sections during cutting and thus increase the tool life.

[0016] If the displacement of a multitude of end cutting edges from their rotationally symmetric position is 2° or less, this means that the "multitude of end cutting edges is rotationally symmetric about the axis". BRIEF DESCRIPTION OF THE DRAWINGS [ Fig. 1] A front view of a thread milling cutter according to a first embodiment. [ Fig. 2] An enlarged front view of the thread milling cutter, showing section II in Fig. 1 shows. [ Fig. 3] A view of the thread milling cutter from below, in the direction of arrow III in Fig. 1. [ Fig. 4] A cross-sectional view of the thread milling cutter along line IV-IV in Fig. 3. [ Fig. 5] A partially enlarged front view of a thread milling cutter according to a second embodiment. [ Fig. 6] A partially enlarged front view of a thread milling cutter according to a third embodiment. [ Fig. 7] A partially enlarged front view of a thread milling cutter according to a fourth embodiment. [ Fig. 8] Partially enlarged front view of a thread milling cutter according to a fifth embodiment. EMBODIMENTS OF THE INVENTION

[0017] Preferred embodiments are described below with reference to the accompanying drawings. Fig. Figure 1 is a front view of a thread milling cutter according to the first embodiment. A thread milling cutter 10 is a tool for cutting an internal thread into a workpiece by means of a rotational force transmitted by a drive device such as an NC milling machine or a machining center.

[0018] The thread milling cutter 10 is made of carbide, which is obtained by pressing and sintering tungsten carbide or the like. The material of the thread milling cutter 10 is not limited to carbide; for example, the thread milling cutter 10 can be made of high-speed steel.

[0019] The thread milling cutter 10 comprises a tool body 12 with a shank shape centered about an axis C, and a first cutting edge section 20 and a second cutting edge section 30 for cutting a workpiece. In the following description, the direction of axis C is simply referred to as the "axial direction".

[0020] The tool body 12 is a shaft-like part with an axial front end 14 (lower end section in Fig. 1) and a shaft end 13 (upper end section in Fig. 1), which is arranged axially opposite the front end 14. The front end 14 of the tool body 12 also forms a front end of the thread milling cutter 10. On the side of the front end 14 of the tool body 12, the first cutting edge section 20, the second cutting edge section 30 and a plurality of grooves 16 are provided.

[0021] A section of the tool body 12 located on the side of the shank end 13 is called the shank 11, and a section extending from the shank 11 to the front end 14 is called the lower head section. The shank 11 is columnar and has a substantially constant outer diameter along axis C. The lower head section is also columnar and has a substantially constant outer diameter along axis C, except for a connecting section between it and the shank 11. The connecting section of the lower head section is tapered such that its diameter decreases towards the front end 14. Accordingly, the outer diameter of the lower head section on the side of the front end 14 is smaller relative to the connecting section than the outer diameter of the shank 11.

[0022] The shaft 11 and the lower head section can each be cylindrical, and the outer diameter of the lower head section can be greater than or equal to the outer diameter of the shaft 11. The shaft 11 is not restricted to having a substantially constant outer diameter along the axis C, and the shaft 11 can, for example, be tapered such that the outer diameter widens towards the front end 14.

[0023] The shank 11 is held by the drive device. The thread milling cutter 10, whose shank 11 is held by the drive device, cuts an internal thread into a workpiece by utilizing the drive force transmitted by the drive device. The drive force of the drive device rotates (turns) the thread milling cutter 10 about the axis C and feeds the thread milling cutter 10 in a helical motion to move it relative to the workpiece. The helical feed motion enables the thread milling cutter 10 to rotate (circle) around the central axis of the internal thread being formed while the thread milling cutter 10 is fed in the axial direction.

[0024] The grooves 16 are recesses for removing chips formed by the cutting of the workpiece by the first cutting edge section 20 and the second cutting edge section 30. The grooves 16 are formed by partially cutting out the outer circumferential surface of the columnar tool body 12 along axis C from the front end 14 to the shank end 13. The plurality of grooves 16 divides the first cutting edge section 20 into a plurality of (in the present embodiment, four) sections in the circumferential direction of the tool body 12.

[0025] Next, the first cutting edge section 20 and the second cutting edge section 30 are described with reference to the Fig. 2 and Fig. 3 described. Fig. Figure 2 is a partially enlarged front view of the thread milling cutter 10, which represents section II in Fig. 1 shows. Fig. Figure 3 is a view of the thread milling cutter 10 from below, in the direction of arrow III. Fig. 1. The top side of the drawing paper of Fig. 2 corresponds to the side of the shaft end 13.

[0026] As in Fig. As shown in Figure 2, the first cutting edge section 20 is a portion that cuts an internal thread into the inner circumferential surface of a bore formed by the second cutting edge section 30. The first cutting edge section 20 comprises a plurality of threaded sections projecting radially outward from the side of the front end 14 of the outer circumference of the tool body 12. Each of the plurality of threaded sections is formed by two threads, consisting of a front threaded section 21, which forms a thread on the side of the front end 14, and a rear threaded section 26, which forms a thread on the side of the shank end 13. The front threaded sections 21 and the rear threaded sections 26 are arranged between corresponding plurality of grooves 16.

[0027] The front thread sections 21 each include a front rake face 22, a front flank face 23, and a front cutting edge 24, which is formed by an edge between the front rake face 22 and the front flank face 23. The rear thread sections 26 each include a rear rake face 27, a rear flank face 28, and a rear cutting edge 29, which is formed by an edge between the rear rake face 27 and the rear flank face 28.

[0028] The front chip surfaces 22 and the rear chip surfaces 27 are parts that generate and remove chips when a workpiece is cut by the front cutting edges 24 and the rear cutting edges 29, respectively. The front chip surfaces 22 and the rear chip surfaces 27 are located on the front faces of the outer surfaces of the front thread sections 21 and the rear thread sections 26, respectively, in a direction of rotation R (clockwise). Fig. 3) during cutting and are connected to the wall surfaces of the grooves 16.

[0029] The front flank surfaces 23 and the rear flank surfaces 28 are parts that reduce the contact area between the first cutting edge section 20 and a workpiece when the workpiece is cut by the front cutting edges 24 and the rear cutting edges 29, respectively. The front flank surfaces 23 and the rear flank surfaces 28 are located on the outer circumference of the outer surfaces of the front thread sections 21 and the rear thread sections 26, respectively.

[0030] The front cutting edges 24 and the rear cutting edges 29 are parts that cut into a workpiece to slice it. Foot surfaces 20a, which are combs connecting the front cutting edges 24 to the corresponding rear cutting edges 29 in an axial direction, also slice the workpiece. The height from the foot surfaces 20a to the tips 24a of the front cutting edges 24 is less than the height from the foot surfaces 20a to the tips 29a of the rear cutting edges 29.

[0031] A front cutting edge 24, a rear cutting edge 29, and a base surface 20a, as described above, form a thread cutting edge, which is formed from a plurality of axially arranged threads for cutting an internal thread into a workpiece. Hereinafter, when referring to the entire thread cutting edge, it is referred to as a "thread cutting edge 24".

[0032] The thread milling cutter 10, which includes a multitude of circumferentially spaced thread cutting edges 24, is fed helically during turning and thus cuts an internal thread into a workpiece. Specifically, the workpiece is first roughly cut by the front cutting edges 24. The roughly cut sections are then finished by the rear cutting edges 29, thereby providing the workpiece with a thread. This rough and finish cutting reduces the load on the rear cutting edges 29. This results in less wear on the rear cutting edges 29, which in turn increases the cutting accuracy of the thread cutting edges 24.

[0033] As in the Fig. 2 and Fig. As shown in Figure 3, the second cutting edge section 30 is a portion that cuts a bore with a diameter corresponding to the inner diameter of the internal thread. The second cutting edge section 30 is configured at the front end 14 of the tool body 12 such that it is subdivided circumferentially by a plurality of (in the present embodiment, four) grooves 40, 41, which are recessed at the front end 14. The plurality of grooves 40, 41, the details of which are described below, are recesses extending from the side of axis C to the outer circumference of the tool body 12 and each opening towards the plurality of grooves 16.

[0034] The second cutting edge section 30 comprises a plurality of rake faces 31, 32, a plurality of flank faces 33, 34, and a plurality of first end cutting edges 35 and second end cutting edges 36. Edges between the rake faces 31 and the corresponding flank faces 33 form the first end cutting edges 35. Edges between the rake faces 32 and the corresponding flank faces 34 form the second end cutting edges 36.

[0035] A set consisting of a rake face 31, a flank face 33 and a first end cutting edge 35, and a set consisting of a rake face 32, a flank face 34 and a second end cutting edge 36, are arranged alternately in the circumferential direction. Furthermore, two sets, each containing the first end cutting edge 35, and two sets, each containing the second end cutting edge 36, are provided, and these sets are rotationally symmetrical about the axis C.

[0036] In order to be rotationally symmetrical, the positions of the first end cutting edges 35 and the second end cutting edges 36 in the present description must, for example, be in Fig. 3 not be completely identical to the positions of the first end cutting edges 35 and the second end cutting edges 36 when the thread milling cutter 10 is rotated 180° around the axis from the in Fig. The state shown in Figure 3 is rotated. For example, if the positional shift between the two states is 2° or less, this means that a "multiple number of first end cutting edges 35 and second end cutting edges 36 are rotationally symmetric".

[0037] The chip surfaces 31 and 32 are designed for generating and removing chips when a workpiece is cut by the first end cutting edge 35 and the second end cutting edge 36. The chip surfaces 31 and 32 face the outer surface of the second cutting edge section 30 in the direction of rotation R. The chip surfaces 31 are formed by the grooves 41, and the chip surfaces 32 by the grooves 40.

[0038] The flank surfaces 33, 34 are designed to reduce the contact area between the second cutting edge section 30 and a workpiece when the workpiece is cut by the first end cutting edges 35 and the second end cutting edges 36. The flank surfaces 33 are inclined upwards towards the side of the shank end 13 in a direction that extends circumferentially away from the first end cutting edges 35 (towards the rear in the direction of rotation R). The flank surfaces 34 are inclined upwards towards the side of the shank end 13 in a direction that extends circumferentially away from the second end cutting edges 36. The flank surfaces 33, 34 are formed as sections of the front end 14 of the tool body 12.

[0039] The first end cutting edges 35 are parts that cut into a workpiece to cut the workpiece. The first end cutting edges 35 each include an outer end cutting edge 35a, which is connected to a flank 24b of a front cutting edge 24 on the side of the front end 14, and an inner end cutting edge 35b, which is connected to an outer end cutting edge 35a on the side of the axis C.

[0040] A diameter d2 at the position of a boundary B between the outer end cutting edges 35a of the first end cutting edges 35 and the flanks 24b is greater than or equal to a core diameter d1 of the base surfaces 20a. The core diameter d1 is twice the radial distance from the axis C to the base surfaces 20a. The diameter d2 is twice the radial distance from the axis C to the boundary B. The diameter at the position of the boundary B between the second end cutting edges 36 and the flanks 24b is essentially identical to the diameter d2 (slightly larger than the diameter d2).

[0041] Here, the axial support force generated during cutting in the thread milling cutter 10 is greater on the side of axis C than on the side of boundary B. Accordingly, the axial support force generated in the thread milling cutter 10 can be more easily displaced radially outwards when the diameter d2 is greater than or equal to the core diameter d1 of the base surfaces 20a than when the diameter d2 is smaller than the core diameter d1. Therefore, this support force reduces the probability of the thread milling cutter 10 tilting relative to the central axis of an internal thread being cut. This makes it possible to reduce the pitch diameter difference (tilting of the internal thread) between the start and bottom of an internal thread cut with the thread milling cutter 10, thus increasing the tool life of the thread milling cutter 10.

[0042] The respective pitch diameters of the start and bottom of an internal thread are measured using a known stepped gauge. The difference between these measurements is the "pitch diameter difference between the start and bottom of an internal thread".

[0043] Since the diameter d2 and the core diameter d1 are essentially identical in the present embodiment, the boundary B, which represents the starting point of the flanks 24b of the front cutting edges 24, can be prevented from lying radially outside the base surfaces 20a. This can reduce the load concentration on the flanks of the rear cutting edges 29, which cut sections uncut by the flanks 24b. Consequently, the durability of the thread cutting edges 24, such as the rear cutting edges 29, can be ensured, thus making it possible to increase the tool life of the thread milling cutter 10.

[0044] An angle θ1 between each of the outer end cutting edges 35a and a virtual plane P, which is orthogonal to the axis C, is set to 0° or more and 6° or less (1° in the present embodiment). The angle θ1 is measured on a plane that is orthogonal to the virtual plane P and passes through the outer end cutting edges 35a. The angle θ1 assumes a positive value when the outer end cutting edges 35a are inclined upwards towards the side of the shank end 13 in the direction of the axis C. The angle θ1 can be set to assume a negative value.

[0045] The inner end cutting edges 35b are parts that cut a workpiece while reducing the cutting resistance of the first end cutting edges 35. The inner end cutting edges 35b are inclined more towards the side of the shank end 13 in the direction of axis C than the outer end cutting edges 35a. That is, the angle θ2 between each of the inner end cutting edges 35b and the virtual plane P is larger than the angle θ1. The angle θ2 is measured on a plane that is orthogonal to the virtual plane P and passes through the inner end cutting edges 35b.

[0046] At the start of a cutting operation on a workpiece using the thread milling cutter 10, the outer end cutting edges 35a, which have a smaller angle θ1 relative to the virtual plane P, come into contact with the workpiece essentially linearly first to cut it. Subsequently, as the cutting operation progresses, the inner end cutting edges 35b, which have a larger angle θ2 relative to the virtual plane P, also come into contact with the workpiece, thereby increasing the cutting area of ​​the first end cutting edges 35. The closer the angle θ1 of the outer end cutting edges 35a, which come into contact with the workpiece at the start of a cutting operation with the thread milling cutter 10, is to 0°, the more easily all the outer end cutting edges 35a come into contact with the workpiece essentially at once, and the more wear-resistant the first end cutting edges 35 are.

[0047] The second end cutting edges 36 are parts that do not actually serve as end cutting edges for cutting a workpiece. Hereinafter, a part that does not function as an end cutting edge is referred to as an ineffective cutting edge section, and a part that does function as an end cutting edge is referred to as an effective cutting edge section. This means that the second end cutting edges 36 consist entirely of ineffective cutting edge sections, and the first end cutting edges 35 consist entirely of effective cutting edge sections.

[0048] It should be noted that, depending on the cutting conditions when cutting a workpiece using the thread milling cutter 10 and the degree of wear of the first end cutting edges 35, the second end cutting edges 36 can also function as end cutting edges (cut a workpiece). However, unless otherwise specified, the following describes the conditions under which the second end cutting edges 36 do not function as end cutting edges.

[0049] Fig. Figure 2 shows a case in which the first end cutting edges 35 are located on the left and right sides of the drawing sheet relative to axis C. Additionally, in Fig. 2. The second end cutting edges 36, when the thread milling cutter 10 (tool body 12) is rotated 90° about the axis C from the aforementioned state without being fed helically, are indicated by dashed lines. That is to say, in Fig. 2 are the second end cutting edges 36, which are located on the drawing sheet to the left and right of axis C, represented by dashed lines.

[0050] As in Fig. As shown in Figure 2, the second end cutting edges 36 are set back relative to the first end cutting edges 35 in the direction of the axial shank end 13. More precisely, the second end cutting edges 36 are set back relative to the trajectories of the first end cutting edges 35 in the direction of the axial shank end 13 when the thread milling cutter 10 performs a rotation (during one revolution) about the axis C without being fed helically. Consequently, the second end cutting edges 36 suspend cutting the workpiece, although this depends on the cutting conditions.

[0051] Conventional thread milling cutters are not provided with such second end cutting edges 36, and all of the multiple end cutting edges are formed by the first end cutting edges 35. In a cutting operation using conventional thread milling cutters, the amount of material removed from a workpiece per revolution by a first end cutting edge 35 per thread cutting edge 24 is very small. For this reason, under certain cutting conditions, the tilting of internal threads can increase at an early stage as the number of internal threads cut increases.

[0052] The increase in internal thread tilt becomes significant when the workpiece hardness is 60 HRC or higher. HRC is a unit of Rockwell hardness, which uses a C-scale. The increase in internal thread tilt is also more pronounced when the tool body 12 has a narrower underhead section. In particular, when the underhead section has a tool diameter of 6.2 mm (a core diameter d1 of 4.81 mm) or less, the increase in internal thread tilt becomes significant. The tool diameter is twice the radial distance from axis C to the tip 29a of the rear cutting edge 29.

[0053] The longer the axial dimension of the lower head section of the tool body 12, the more pronounced the increase in the tilt of the internal threads. In particular, the increase in the tilt of the internal threads is pronounced when the axial dimension is greater than three times the minimum nominal diameter of the internal threads that can be cut with the thread milling cutter 10. To cut an internal thread with a large nominal diameter, it is preferable to increase the tool diameter of the tool body 12. Accordingly, it can be said that the increase in the tilt of internal threads is likely to be pronounced when the axial dimension of the lower head section of the tool body 12 is greater than 4 to 4.5 times the tool diameter of the tool body 12.

[0054] Unlike the thread milling cutter 10, with an end mill that does not perform thread cutting, the axial feed rate can be increased during a revolution to increase the amount of material removed by the end cutting edges during that revolution. In contrast, for the thread milling cutter 10, which performs thread cutting and axial cutting simultaneously, the axial feed rate must be adjusted according to the thread form, and therefore there is a limit to the amount of material that can be removed by an end cutting edge.

[0055] However, in the thread milling cutter 10 according to the present embodiment, the second end cutting edges 36 do not cut any workpiece, so that the cutting amount of the workpiece is increased by a first end cutting edge 35 during one revolution compared to conventional thread milling cutters where all end cutting edges are the first end cutting edges 35. According to the thread milling cutter 10, it is possible to reduce the tilting of an internal thread to be cut and thus increase the tool life.

[0056] Each of the second end cutting edges 36 is formed in a straight line from the boundary B between the flank 24b of the corresponding front cutting edge 24 to the axis C. An angle θ3 between the second end cutting edge 36 and the virtual plane P is larger than the two angles θ1 and θ2. The angle θ3 is measured on a plane that is orthogonal to the virtual plane P and passes through the second end cutting edge 36.

[0057] With such a relationship between the angle θ3 and the angles θ1 and θ2, the second end cutting edge 36 can easily be offset back towards the shank end 13 over the entire length of the first end cutting edge 35. Consequently, it can be prevented that the second end cutting edge 36 partially comes into contact with the workpiece, thus ensuring that the first end cutting edge 35 cuts the intended amount during one revolution.

[0058] The first end cutting edges 35, consisting of the effective cutting edge sections, and the second end cutting edges 36, consisting of the ineffective cutting edge sections, are arranged alternately in the circumferential direction. Thus, during a circumferential cutting operation, the number of positions where the first end cutting edges 35 contact the workpiece can be approximately half the number of positions where the multitude of thread cutting edges 24 contact the workpiece. This makes it possible to reduce the load concentration on a portion of the thread milling cutter 10 in the circumferential direction during a cutting operation and thus increase the tool life of the thread milling cutter 10.

[0059] The multitude of first end cutting edges 35 and second end cutting edges 36 are arranged rotationally symmetrically around the axis C. Thus, the reaction force absorbed by the first end cutting edges 35 from the workpiece during a cutting operation can be made as uniform as possible in the circumferential direction.

[0060] Furthermore, the respective thread cutting edges 24 are connected to both the first end cutting edges 35 and the second end cutting edges 36 described above, and therefore the multitude of thread cutting edges 24 are also arranged rotationally symmetrically around the axis C. Thus, the reaction force that the thread cutting edges 24 absorb from the workpiece during a cutting operation can be easily made as uniform as possible in the circumferential direction. This makes it possible to reduce the load concentration on a portion of the first end cutting edges 35 and the thread cutting edges 24 during a cutting operation with the thread milling cutter 10, thereby increasing the tool life of the thread milling cutter 10.

[0061] If both the effective cutting edge section and the ineffective cutting edge section are formed on an end cutting edge (for example, in the case of the first end cutting edges 62, 72 and the second end cutting edges 52, 63, 74 of the second to fourth embodiments), it is difficult to ensure a reset of the ineffective cutting edge section towards the shank end 13 near the boundary between the effective cutting edge section and the ineffective cutting edge section.

[0062] In contrast, in the thread milling cutter 10 according to the present embodiment, the first end cutting edges 35 are formed entirely by the effective cutting edge sections, and the second end cutting edges 36 are formed entirely by the ineffective cutting edge sections. Accordingly, the retraction of the second end cutting edges 36 (ineffective cutting edge sections) towards the shank end 13 can be easily ensured, so that the second end cutting edges 36 are less likely to come into contact with the workpiece during a cutting operation using the thread milling cutter 10. Consequently, the cutting quantity by the first end cutting edges 35 (effective cutting edge sections) can be easily ensured during one revolution.

[0063] The second end cutting edges 36 are set back from the boundary B towards the shank end 13 relative to the first end cutting edges 35. This means that the multitude of thread cutting edges 24 located radially outside the boundary B have essentially identical shapes. Accordingly, the load exerted on the multitude of thread cutting edges 24 during a cutting operation using the thread milling cutter 10 can be easily standardized, thereby increasing the service life of the thread milling cutter 10.

[0064] In the present embodiment, the boundary B between each of the second end cutting edges 36 and the corresponding flank 24b is located slightly radially further outward than the boundary B between each of the first end cutting edges 35 and the corresponding flank 24b. For example, the radial distance between the boundaries B is preferably less than or equal to half the radial dimension of the flanks 24b. Such a positional relationship between the boundaries B can further prevent the second end cutting edges 36 from contacting the workpiece.

[0065] Next, grooves 40 and 41 will be described with reference to the Fig. 2 to 4 described. Fig. Figure 4 is a cross-sectional view of the thread milling cutter 10, along line IV-IV in Fig. 3.

[0066] As in the Fig. 2 and Fig. Figure 3 shows a plurality of grooves 40, 41 recesses formed at the front end 14 of the tool body 12. Each of the grooves 40 includes the rake face 32 described above, a groove surface 42 opposite the rake face 32 in the circumferential direction, and a groove base 44 connecting the groove surface 42 and the rake face 32. Similarly, each of the grooves 41 includes the rake face 31 described above, a groove surface 43 opposite the rake face 31 in the circumferential direction, and a groove base 45 connecting the groove surface 43 and the rake face 31. The groove surfaces 42, 43 are located on the rear side (in the direction of rotation R, the rear side of the flank surfaces 33, 34) of the surfaces formed by the grooves 40, 41.

[0067] The side of axis C of a groove 40 is in contact with the rake face 31 of the groove 41, which adjoins this groove 40 on its front side in the direction of rotation R. Similarly, the side of axis C of a groove 41 is in contact with the rake face 32 of the groove 40, which adjoins this groove 41 on its front side in the direction of rotation R.

[0068] Thus, an edge is formed between the groove surface 42 and the groove base 44 of the groove 40 and the rake face 31 of the groove 41. This edge is referred to as the groove cutting edge 46. The groove cutting edge 46 is connected to one end of the first end cutting edge 35 on the side of axis C. Similarly, the groove cutting edge 47, formed by the edge between the groove surface 43 and the groove base 45 and the rake face 32, is connected to one end of the second end cutting edge 36 on the side of axis C. Fig. 2 is the groove cutting edge 47, which is connected to the second end cutting edge 36, also represented by a dashed line.

[0069] The groove bases 44, 45 are essentially flat surfaces extending from the radially inner side of the tool body 12 (side of axis C) to the outer circumference of the tool body 12 and inclined at a constant angle towards the shank end 13. Although not shown, the angle of inclination of the groove bases 44, 45 relative to the virtual plane P is a groove angle. In the present embodiment, the groove angle of the groove base 44 and the groove angle of the groove base 45 are identical. It should be noted that the groove base 44 and the groove base 45 can have different groove angles.

[0070] The width W1 of a groove base 44 is the dimension in a direction perpendicular to the direction of the inclination of the groove base 44. The width W2 of a groove base 45 is the dimension in a direction perpendicular to the direction of the inclination of the groove base 45. Fig. Figure 2 schematically shows the width W1 of the groove base 44 at the groove cutting edge 46 and the width W2 of the groove base 45 at the groove cutting edge 47.

[0071] Fig. Figure 4 shows a cross-section parallel to the direction of the width W1 and perpendicular to the inclination of the groove base 44. As in this cross-section, the opposite distance between the rake face 32 and the groove surface 42 towards the shank end 13 (groove base 44) is smaller. Furthermore, the angle between the rake face 32 and the groove surface 42 is smaller in the section shown. Fig. The cross-section shown in Figure 4 is defined as the groove opening angle θ4. The groove opening angle θ4 is also an angle between the rake face 32, which extends in the direction of axis C, and a portion of the groove cutting edge 46. Accordingly, the cross-section shown in Figure 4 is defined as the groove opening angle θ4. Fig. 2 schematically the groove opening angle θ4.

[0072] The same applies to the groove 41. In particular, in a cross-section parallel to the width W2 and perpendicular to the inclination of the groove base 45, the opposite distance between the rake face 31 and the groove surface 43 decreases towards the shank end 13 (groove base 45). Furthermore, the groove opening angle θ5, which is an angle between the rake face 31 and the groove surface 43 in a cross-section perpendicular to the inclination of the groove base 45, is also an angle between the rake face 31, extending in the direction of axis C, and the groove cutting edge 47. Accordingly, Fig. 2 schematically the groove opening angle θ5.

[0073] Depending on the cutting conditions (for example, if the inner diameter of a bore for an internal thread to be cut is less than or equal to 1.5 times the core diameter d1), the slot cutting edges 46, 47, which are connected to the first end cutting edge 35 and the second end cutting edge 36, can cut the workpiece even during a cutting operation with the thread milling cutter 10. However, on sections other than the groove bases 44, 45, the slot cutting edge 47 is set back towards the shank end 13 and radially outwards with respect to the slot cutting edge 46, as is the case with the second end cutting edge 36 with respect to the first end cutting edge 35. Accordingly, it is less likely that the slot cutting edge 47 will cut the workpiece.

[0074] This is because the depths (distance from the front end 14 to the groove bottoms 44, 45) of the grooves 40, 41 are essentially identical, and the groove opening angle θ5 at groove 41 (groove cutting edge 47) and the width W2 of the groove bottom 45 are each larger than the groove opening angle θ4 at groove 40 (groove cutting edge 46) and the width W1 of the groove bottom 44. It should be noted that if the groove opening angles θ4, θ5 are identical and the width W2 is increased relative to the width W1, the groove cutting edge 47 is also less likely to cut the workpiece. Conversely, if the widths W1, W2 are identical and the groove opening angle θ5 is increased relative to the groove opening angle θ4, it is also less likely that the groove cutting edge 47 will cut the workpiece.As in these cases, conditions in which at least one of the groove opening angles θ5 and the width W2 are large are collectively referred to as the “condition in which the groove 41 is enlarged relative to the groove 40” or as the “condition in which the groove cutting edge 47 is set back from the groove cutting edge 46”.

[0075] In a state where the slot cutting edge 47 is recessed relative to the slot cutting edge 46, the amount of material cut by the slot cutting edge 46 during one revolution can be increased, since the slot cutting edge 47 is less likely to cut the workpiece compared to the slot cutting edge 46, as in the case of the first end cutting edge 35. Accordingly, the tool life of the thread milling cutter 10 can be increased.

[0076] The grooves 40 and 41 form chip spaces for receiving chips produced during cutting of the workpiece. Since groove 41 is larger than groove 40, the chip space formed by groove 41 can be widened. This makes it possible to prevent chip clogging during a cutting operation with the thread milling cutter 10.

[0077] The chip space formed by the groove 41 can be further widened by increasing the width W2 relative to the width W1, compared to a case where the groove opening angle θ5 is simply increased relative to the groove opening angle θ4. Accordingly, in this case, it is possible to further prevent clogging with chips during a cutting operation using the thread milling cutter 10.

[0078] Next, a second embodiment will be described with reference to Fig. 5 described. The first embodiment describes a case in which each of the second end cutting edges 36 consists entirely of the ineffective cutting edge section. In contrast, the second embodiment describes a case in which part of each of the second end cutting edges 52 is formed by an effective cutting edge section 52a and another part thereof by an ineffective cutting edge section 52b. Sections identical to those described in the first embodiment are identified by identical reference numerals, and descriptions thereof have been omitted.

[0079] Fig. Figure 5 is a partially enlarged front view of a thread milling cutter 50 according to the second embodiment. The top side on the drawing sheet of Fig. 5 corresponds to the side of the shaft end 13. Furthermore, it shows Fig. 5 a case in which the first end cutting edges 35 are located on the left and right sides of the drawing sheet relative to axis C. Additionally, in Fig. 5 the second end cutting edges 52, when the thread milling cutter 50 (tool body 12) is rotated by 90° about the axis C from the aforementioned state without being fed in a helical manner, are indicated by dashed lines.

[0080] The second cutting edge section 51 of the thread milling cutter 50 is a part that cuts a bore hole with a diameter corresponding to the inner diameter of the internal thread. Similar to the first embodiment, the second cutting edge section 51 is designed at the front end 14 of the tool body 12 such that it is subdivided circumferentially by a plurality (a total of four) grooves 40, 41 which are recessed at the front end 14.

[0081] The dimensions of the grooves 40, 41 in the second embodiment differ partially from those of the grooves 40, 41 in the first embodiment, but are designated with identical reference numerals in both embodiments to simplify the description of the grooves 40, 41. The same applies to the third to fifth embodiments described below.

[0082] The second cutting edge section 51 includes a plurality of rake faces 31, 32, a plurality of flank faces 33, 34, and a plurality of first end cutting edges 35 and second end cutting edges 52. Edges between the rake faces 32 and the corresponding flank faces 34 form the second end cutting edges 52. The first end cutting edges 35 and the second end cutting edges 52 are arranged alternately in the circumferential direction and are rotationally symmetrical about the axis C.

[0083] The second end cutting edges 52 are parts whose sections cut into a workpiece to cut the workpiece. The second end cutting edges 52 each comprise an effective cutting edge section 52a, which is connected to a flank 24b of the front cutting edge 24, and a non-effective cutting edge section 52b, which is connected to the side of the axis C of the effective cutting edge section 52a.

[0084] The effective cutting edge sections 52a are identical to the outer end cutting edges 35a of the first end cutting edges 35 and the radially outer sections of the inner end cutting edges 35b. That is, the effective cutting edge sections 52a overlap the trajectories of the first end cutting edges 35 when the thread milling cutter 50 rotates about the axis C without being fed helically. Accordingly, the effective cutting edge sections 52a cut the workpiece during a cutting operation using the thread milling cutter 50.

[0085] The ineffective cutting edge sections 52b are parts that are recessed towards the shank end 13 relative to the effective cutting edge sections 52a. The ineffective cutting edge sections 52b are recessed towards the axial shank end 13 relative to the trajectories of the first end cutting edges 35 when the thread milling cutter 50 rotates about the axis C without being fed helically. Consequently, depending on the cutting conditions, the ineffective cutting edge sections 52b no longer cut into the workpiece.

[0086] Thus, the cutting area of ​​the workpiece during one revolution is increased by portions (sections on the side of axis C) of the first end cutting edges 35 that correspond to the ineffective cutting edge sections 52b. Consequently, with the thread milling cutter 50, it is possible to reduce the tilting of an internal thread to be cut and thus increase the tool life.

[0087] Since the thread milling cutter 50 cuts a workpiece by rotation while being fed helically, the amount of material cut during one revolution on the side of the axis C of the first end cutting edges 35 is less than on the radially outer side if no second end cutting edges 52 are present. In contrast, if second end cutting edges 52 are present, the amount of material cut by the first end cutting edges 35 during one revolution is increased by the ineffective cutting edge sections 52b of the second end cutting edges 52 on the side of the axis C, while it is maintained by the effective cutting edge sections 52a on the radially outer side. That is, with the second end cutting edges 52, the amount of material cut by the first end cutting edges 35 during one revolution can be made uniform in the radial direction.Consequently, with the thread milling cutter 50 it is possible to further reduce the tilting of an internal thread to be cut, thereby further increasing the tool life of the thread milling cutter 50.

[0088] A groove cutting edge 54, formed by an edge between the groove surface 43 and the groove base 45 of a groove 41, and the rake face 32 of a groove 40 are connected to the ends of a second end cutting edge 52 and a non-effective cutting edge section 52b on the side of axis C. Fig. The groove cutting edge 54, connected to the second end cutting edge 52, is shown by a dashed line. Additionally, the following is shown: Fig. 5 similar to Fig. 2 schematically the width W2 of the groove base 45 of the groove 41 and the groove opening angle θ5 of the groove 41.

[0089] In the present embodiment, the width W1 of the groove base 44 of the groove 40 and the width W2 of the groove base 45 are identical. However, the groove opening angle θ5 of the groove 40 is larger than its groove opening angle θ4. Accordingly, the groove cutting edge 54 is recessed relative to the groove cutting edge 46 in the direction of the shank end 13 and radially outwards in sections other than the groove bases 44 and 45, so that the groove cutting edge 54 is less likely to cut the workpiece. Consequently, the amount of workpiece cut by the groove cutting edge 46 during one revolution can be increased, potentially increasing the tool life of the thread milling cutter 50.

[0090] The widths W1 and W2 are identical, and the groove opening angle θ5 is larger than the groove opening angle θ4. Accordingly, the thickness of the tool body 12 can be easily standardized circumferentially at a position radially outside the grooves 40, 41 at the groove base 44, 45 of the grooves 40, 41. This makes it possible to uniformly adjust the rigidity of the tool body 12 circumferentially at this position, thereby increasing the service life of the thread milling cutter 50.

[0091] Next, a third embodiment will be described with reference to Fig. 6. The first embodiment describes a case in which the first end cutting edges 35 consist entirely of effective cutting edge sections and the second end cutting edges 36 consist entirely of ineffective cutting edge sections. In contrast, the third embodiment describes a case in which effective cutting edge sections 35a, 62a, 63b and ineffective cutting edge sections 62b, 63a are partially present in a first end cutting edge 62 and a second end cutting edge 63, respectively. Parts identical to those described in the first embodiment are identified by identical reference symbols, and their description has been omitted.

[0092] Fig. Figure 6 is a partially enlarged front view of a thread milling cutter 60 according to the third embodiment. The top side on the drawing sheet of Fig. 6 corresponds to the side of the shaft end 13. Furthermore, it shows Fig. 6 a case in which the first end cutting edges 62 are located on the left and right sides of the drawing sheet relative to axis C. Additionally, in Fig. 6 the second end cutting edges 63 when the thread milling cutter 60 (tool body 12) is rotated by 90° about the axis C from the above-mentioned state without being fed in a helical manner, are indicated by dashed lines.

[0093] A second cutting edge section 61 of the thread milling cutter 60 is a part that cuts a bore hole with a diameter corresponding to the inner diameter of the internal thread. Similar to the first embodiment, the second cutting edge section 61 is designed at the front end 14 of the tool body 12 such that it is subdivided circumferentially by a plurality (a total of four) grooves 40, 41 which are recessed at the front end 14.

[0094] The second cutting edge section 61 comprises a plurality of rake faces 31, 32, a plurality of flank faces 33, 34, and a plurality of first end cutting edges 62 and second end cutting edges 63. Edges between the rake faces 31 and the corresponding flank faces 33 form the first end cutting edge 62. Edges between the rake faces 32 and the corresponding flank faces 34 form the second end cutting edge 63. The first end cutting edges 62 and the second end cutting edges 63 are arranged alternately in the circumferential direction and are rotationally symmetrical about the axis C.

[0095] Both the first end cutting edge 62 and the second end cutting edge 63 are parts that partially cut into a workpiece to perform the cutting action. Sections of the first end cutting edge 62 that project towards the axial front end 14 relative to the trajectories of the second end cutting edge 63 when the thread milling cutter 60 completes one revolution about the axis C without helical feed are formed by the effective cutting edge sections 35a, 62a, and the sections recessed towards the axial shank end 13 are formed by the ineffective cutting edge sections 62b.

[0096] The effective cutting edge sections 35a are identical to the outer end cutting edges 35a in the first embodiment. The effective cutting edge sections 62a and the ineffective cutting edge sections 62b are identical to the inner end cutting edges 35b in the first embodiment. The boundary B1 between the first end cutting edge 62 and the corresponding thread cutting edges 24 is identical to the boundary B in the first embodiment.

[0097] From the second end cutting edge 63, sections that project towards the axial front end 14 relative to the trajectories of the first end cutting edges 62 when the thread milling cutter 60 performs one revolution about the axis C without helical feed are formed by the effective cutting edge sections 63b, and sections that are recessed towards the axial shank end 13 are formed by the ineffective cutting edge sections 63a.

[0098] The ineffective cutting edge sections 63a are connected to the flanks 24b of the corresponding front cutting edges 24. The effective cutting edge sections 63b are connected to the corresponding ineffective cutting edge sections 63a on the side of axis C. The ineffective cutting edge sections 63a and the effective cutting edge sections 63b are formed in a straight line in the direction of axis C from the boundary B2 between the second end cutting edges 63 and the corresponding thread cutting edges 24 and run parallel to the virtual plane P (see Fig. 2), which is orthogonal to axis C.

[0099] Boundary B2 is located radially outside boundary B1 and in the direction of the shank end 13. This means that the thread cutting edges 24, which are connected to the corresponding second end cutting edges 63, are formed by cutting sections located on the side of the front end 14 relative to the thread cutting edges 24, which are connected to the corresponding first end cutting edges 62. This further prevents the second end cutting edges 63 from coming into contact with the workpiece.

[0100] In the thread milling cutter 60, as described above, the cutting area of ​​the workpiece is increased by the effective cutting edge sections 35a, 62a, 63b during one revolution due to the presence of the ineffective cutting edge sections 62b, 63a, compared to conventional thread milling cutters where a multitude of end cutting edges consist entirely of effective cutting edge sections. Consequently, it is possible to reduce the tilting of an internal thread to be cut by the thread milling cutter 60, thereby increasing the tool life of the thread milling cutter 60.

[0101] In the present embodiment, the effective cutting edge sections 35a, 62a, 63b and the ineffective cutting edge sections 62b, 63a are partially present on the first end cutting edge 62 and the second end cutting edge 63, respectively. Accordingly, it is possible to protect only one of the first end cutting edge 62 and the second end cutting edge 63 from wear caused by cutting with the thread milling cutter 60.

[0102] The groove cutting edge 64, which is formed by an edge between the groove surfaces 43 and the groove base 45 of a groove 41 and the rake surface 32 of a groove 40, is connected at one end on the side of the axis C of the effective cutting edge section 63b of a second end cutting edge 63. Fig. 6 is the groove cutting edge 64, which is connected to the second end cutting edge 63, indicated by a dashed line. Additionally, it shows Fig. 6 similar to Fig. 2 schematically the width W2 of the groove base 45 of the groove 41 and the groove opening angle θ5 of the groove 41.

[0103] In the present embodiment, the width W1 of the groove base 44 of the groove 40 and the width W2 of the groove base 45 are identical. Furthermore, the groove opening angle θ4 and the groove opening angle θ5 of the groove 40 are identical. It should be noted that, in this case as well, the side of the second end cutting edge 63 of the groove cutting edge 64 extends towards the front end 14 with respect to the groove cutting edge 46 connected to the first end cutting edge 62. Accordingly, it is less likely that the groove cutting edge 46 will cut the workpiece. Consequently, the amount of material removed from the workpiece by the groove cutting edge 64 during one revolution can be increased, potentially increasing the tool life of the thread milling cutter 60.

[0104] Furthermore, the trajectories of the multiple slot cutting edges 46, 64 overlap when the thread milling cutter 60 (tool body 12) completes one revolution about the axis C. When the workpiece is cut not only by the first end cutting edges 62 and the second end cutting edges 63, but also by the slot cutting edges 46, 64, each of the multiple slot cutting edges 46, 64 can easily be brought into contact with the workpiece, and the radial deformation of the thread milling cutter 60 can be made as uniform as possible in the circumferential direction, according to the nature of such contact. Accordingly, it is possible to prevent the occurrence of vibrations caused by such uneven radial deformation in the thread milling cutter 60, thereby suppressing a reduction in the tool life of the thread milling cutter 60 due to such vibrations.

[0105] Next, a fourth embodiment will be described with reference to Fig. 7. The first embodiment describes a case in which the first end cutting edges 35 consist entirely of effective cutting edge sections and the second end cutting edges 36 consist entirely of ineffective cutting edge sections. In contrast, the fourth embodiment describes a case in which effective cutting edge sections 35a, 72b, 72d, 74b, 74d and ineffective cutting edge sections 72a, 72c, 74a, 74c, 74e are provided alternately at a first end cutting edge 72 and a second end cutting edge 74, respectively. Parts identical to those described in the first embodiment are designated with identical reference numerals, and descriptions thereof have been omitted.

[0106] Fig. Figure 7 is a partially enlarged front view of a thread milling cutter 70 according to the fourth embodiment. The top side on the drawing sheet of Fig. 7 corresponds to the side of the shaft end 13. Furthermore, it shows Fig. 7 a case in which the first end cutting edges 72 are located on the left and right sides of the drawing sheet relative to axis C. Additionally, in Fig. 7 the second end cutting edges 74, when the thread milling cutter 70 (tool body 12) is rotated by 90° about the axis C from the above-mentioned state without being fed in a helical manner, are indicated by dashed lines.

[0107] The second cutting edge section 71 of the thread milling cutter 70 is a part that cuts a bore hole with a diameter corresponding to the inner diameter of the internal thread. Similar to the first embodiment, the second cutting edge section 71 is designed at the front end 14 of the tool body 12 such that it is subdivided circumferentially by a plurality (a total of four) grooves 40, 41 which are recessed at the front end 14.

[0108] The second cutting edge section 71 comprises a plurality of rake faces 31, 32, a plurality of flank faces 33, 34, and a plurality of first end cutting edges 72 and second end cutting edges 74s. Edges between the rake faces 31 and the corresponding flank faces 33 form the first end cutting edge 72. Edges between the rake faces 32 and the corresponding flank faces 34 form the second end cutting edge 74. The first end cutting edges 72 and the second end cutting edges 74 are arranged alternately in the circumferential direction and are rotationally symmetrical about the axis C.

[0109] Both the first end cutting edge 72 and the second end cutting edge 74 are parts that partially cut into a workpiece to perform the cutting action. When the thread milling cutter 70 completes one revolution about the axis C without being fed helically, sections of the first end cutting edge 72 that project towards the axial front end 14 relative to the trajectories of the second end cutting edge 74 are formed from the effective cutting edge sections 35a, 72b, 72d, and the sections set back towards the axial shank end 13 are formed by the ineffective cutting edge sections 72a, 72c.

[0110] The effective cutting edge sections 35a are identical to the outer end cutting edges 35a of the first embodiment. A non-effective cutting edge section 72a, an effective cutting edge section 72b, a non-effective cutting edge section 72c, and an effective cutting edge section 72d are connected in this order from an effective cutting edge section 35a in the direction of axis C. Sections that are set back towards the shank end 13 with respect to the inner end cutting edge 35b in the first embodiment are formed by the non-effective cutting edge sections 72a and 72c, and sections that are identical to the inner end cutting edge 35b are formed by the effective cutting edge sections 72b and 72d.

[0111] From the second end cutting edge 74, sections that project towards the axial front end 14 in relation to the trajectories of the first end cutting edge 72 when the thread milling cutter 70 performs a rotation about the axis C without helical feed are formed from the effective cutting edge sections 74b, 74d and the sections set back towards the axial shank end 13 are formed from the ineffective cutting edge sections 74a, 74c, 74e.

[0112] A non-effective cutting edge section 74a, an effective cutting edge section 74b, a non-effective cutting edge section 74c, an effective cutting edge section 74d, and a non-effective cutting edge section 74e are connected in this order from the boundary B between the second end cutting edge 74 and the thread cutting edge 24 in the direction of axis C. In the first embodiment, the sections set back towards the shank end 13 relative to the first end cutting edge 35 are formed by the non-effective cutting edge sections 74a, 74c, and 74e, and the sections identical to the first end cutting edge 35 are formed by the effective cutting edge sections 74b and 74d.

[0113] In the thread milling cutter 70, as described above, the cutting area of ​​the workpiece is increased by the effective cutting edge sections 35a, 72b, 72d, 74b, 74d during one revolution due to the presence of the ineffective cutting edge sections 72a, 72c, 74a, 74c, 74e, compared to conventional thread milling cutters where a multitude of end cutting edges are entirely formed by effective cutting edge sections. Consequently, it is possible to reduce the tilting of an internal thread to be cut by the thread milling cutter 70, thereby increasing the tool life of the thread milling cutter 70.

[0114] In the present embodiment, the effective cutting edge sections 35a, 72b, 72d, 74b, 74d and the ineffective cutting edge sections 72a, 72c, 74a, 74c, 74e are alternately provided at the first end cutting edge 72 and the second end cutting edge 74, respectively. Thus, the ineffective cutting edge sections 72a, 72c, 74a, 74c, 74e function as notches, so that the chips produced by the effective cutting edge sections 35a, 72b, 72d, 74b, 74d can be reduced to fine pieces. Consequently, it is possible to prevent chips produced during a cutting operation with the thread milling cutter 70 from becoming stuck.

[0115] The groove cutting edge 76, which is formed by an edge between the groove surface 43 and the groove base 45 of the groove 41 and the rake surface 32 of the groove 40, is connected to the end of the ineffective cutting edge section 74e of a second end cutting edge 74 located on the side of the axis C. Fig. 7 is the groove cutting edge 76, which is connected to the second end cutting edge 74, shown by a dashed line. Additionally, it shows Fig. 7 similar to Fig. 2 schematically the width W2 of the groove base 45 of the groove 41 and the groove opening angle θ5 of the groove 41.

[0116] In the present embodiment, the groove opening angle θ4 and the groove opening angle θ5 of the groove 40 are identical. However, the width W2 of the groove base 45 of the groove 40 is greater than the width W1 of the groove base 44. Accordingly, the groove cutting edge 76 is recessed at sections other than the groove bases 44 and 45 towards the shank end 13 and radially outwards relative to the groove cutting edge 46, and is less likely to cut the workpiece. Consequently, the amount of workpiece cut by the groove cutting edge 46 during one revolution can be increased, potentially increasing the tool life of the thread milling cutter 70.

[0117] Furthermore, in the present embodiment, the width W2 is increased relative to the width W1. Accordingly, as also described in the first embodiment, it is possible to extend the chip space formed by the groove 41 further than in a case where the groove opening angle θ5 is simply increased relative to the groove opening angle θ4. Therefore, in this case, it is possible to prevent chip build-up during a cutting operation using the thread milling cutter 70.

[0118] Next, a fifth embodiment will be described with reference to Fig. 8. The first to fourth embodiments describe cases in which the depths of the grooves 40 and 41 are identical. In contrast, the fifth embodiment describes a case in which the depth of the groove 41 is greater than the depth of the groove 40. Parts identical to those described in the first embodiment are identified by identical reference symbols, and their descriptions have been omitted.

[0119] Fig. Figure 8 is a partially enlarged front view of a thread milling cutter 80 according to the fifth embodiment. The top side on the drawing sheet of Fig. 8 corresponds to the side of the shaft end 13. Furthermore, it shows Fig. 8 a case in which the first end cutting edges 35 are located on the left and right sides of the drawing sheet relative to axis C. Additionally, in Fig. 8 the second end cutting edges 36 and part of the groove 41 when the thread milling cutter 80 (tool body 12) is rotated 90° around the axis C from the above-mentioned state without being fed in a helical manner, are indicated by dashed lines.

[0120] The second cutting edge section 81 of the thread milling cutter 80 is a part that cuts a bore with a diameter corresponding to the inner diameter of the internal thread. Similar to the first embodiment, the second cutting edge section 81 is configured at its front end 14 such that it is subdivided circumferentially by a plurality of (in the present embodiment, four) grooves 40, 41, which are recessed at the front end 14 of the tool body 12. The second cutting edge sections 81 are identical to those of the first embodiment, except that the dimensions of the grooves 41 are different.

[0121] On the second cutting edge section 81, a groove cutting edge 84, formed by an edge between the groove surface 43 and the groove base 45 of a groove 41 and the rake surface 32 of a groove 40, is connected to one end of the second end cutting edge 36 on the axis C. Fig. 8 is the groove cutting edge 84, which is connected to the second end cutting edge 36, shown by a dashed line. Additionally, the Fig. 8 similar to the Fig. 2 schematically the width W2 of the groove base 45 of the groove 41 and the groove opening angle θ5 of the groove 41.

[0122] In the present embodiment, the groove opening angle θ4 and the groove opening angle θ5 of groove 40 are identical. On the other hand, the width W2 of the groove base 45 is smaller than the width W1 of the groove base 44 of groove 40. Furthermore, the depth of groove 41 is greater than the depth of groove 40. It should be noted that the widths W1, W2, and the depths of grooves 40, 41 are set such that, when the thread milling cutter 80 (tool body 12) completes one revolution about the axis C, the trajectories of the plurality of groove cutting edges 46, 84 overlap on the side of the first end cutting edge 35 and the side of the second end cutting edge 36. Accordingly, as in the third embodiment, it is possible to suppress a reduction in the tool life of the thread milling cutter 80 due to uneven radial deformation.

[0123] Here, chips produced by cutting with the first end cutting edges 35 are mainly collected in the grooves 41 (chip spaces) formed by the chip surfaces 31 of the first end cutting edges 35. Additionally, chips produced by cutting with the second end cutting edges 36 are mainly collected in the grooves 40 (chip spaces) formed by the chip surfaces 32 of the second end cutting edges 36.

[0124] Since the second end cutting edges 36, which consist of the ineffective cutting edge sections, are less likely to cut the workpiece, a relatively small amount of chips is collected in the grooves 40. On the other hand, the workpiece is primarily cut by the first end cutting edges 35, which consist of the effective cutting edge sections, and therefore a relatively large amount of chips is collected in the grooves 41. Because the depth of the grooves 41 is greater than the depth of the grooves 40, it is possible to increase the internal volume of the grooves 41, where a large amount of chips is collected, while decreasing the internal volume of the grooves 40, where a smaller amount of chips is collected. Accordingly, it is possible to prevent chip clogging during a cutting operation with the thread milling cutter 80 and to ensure the rigidity of the tool body 12, thereby increasing the tool life of the thread milling cutter 80.

[0125] Next, a durability test of a thread milling cutter is described. For this durability test, a thread milling cutter according to an example with specific dimensions and a thread milling cutter according to a comparison example, obtained by partially modifying the thread milling cutter according to the example, were used. The example was configured based on thread milling cutter 80, with the depth of the flutes 40 and the depth of the flutes 41 set identically, and the width W1 of the flute bases 44 and the width W2 of the flute bases 45 set identically. The remaining configuration of the example was identical to that of thread milling cutter 80.

[0126] In the example, the tool diameter was set to 3.1 mm, the axial dimension of the lower head section of the tool body 12 to 18 mm, the widths W1, W2 to 0.09 mm, the angle θ1 to 1°, the angle θ2 to 10°, the angle θ3 to 12°, and the groove opening angles θ4, θ5 to 30°. The comparison example was configured in the same way as the example, except that all second end cutting edges 36 were changed to first end cutting edges 35.

[0127] The durability test assessed how many internal threads were formed in SKD11 (60HRC) workpieces from each of the example and comparison examples, held by a horizontal machining center (drive device). The internal threads to be cut had a nominal diameter of M4 × 0.7, a thread length of 12 mm (3D), and were of quality grade 6H as defined by the ISO standard.

[0128] More precisely, the tool radius offset was adjusted so that a stepped taper with a pitch diameter of +0.080 could advance 1.5 turns or more into the internal threads, while a stepped taper with a pitch diameter of +0.100 could not advance more than one turn. The durability test was then started. The durability test was aborted if a stepped taper with a pitch diameter of +0.020 could not advance 17 turns, and the durability test was restarted after the tool radius correction. The number of passes was set to one. Additionally, air was used as a coolant, the cutting speed was 45 m / min, and the feed rate per edge was 0.02 mm / t.

[0129] The durability test was terminated if the pitch diameter difference (tilt of the internal threads) between the bore entrance and the bore root of the formed internal threads was 0.1 mm or more. Furthermore, the durability test was also terminated if the tool broke and no further tool radius correction was possible.

[0130] The results of the durability test are described. The example confirmed that a total of 74 internal threads were formed. Conversely, the comparison example confirmed that a total of 30 internal threads were formed. Accordingly, it was shown that, compared to the comparison example, which does not include a second end cutting edge 36, the example with the second end cutting edge 36 reduced the tilting of the internal threads and thus made it possible to increase the tool life.

[0131] In the comparison example, the cutting quantity (feed per edge) of the workpiece by a thread cutting edge 24 during one revolution was 0.02 mm, and the cutting quantity (feed per edge) of the workpiece by a first end cutting edge 35 during one revolution was approximately 0.001114 mm. In contrast, in the example, the cutting quantity by the thread cutting edge 24 was identical to that of the comparison example, while the cutting quantity by the first end cutting edge 35 was approximately twice that of the comparison example.

[0132] Although the present invention has been described with reference to the embodiments and examples, it can readily be inferred that the invention is not limited to these embodiments and that various modifications can be made without departing from the scope of the invention. For example, the numerical values ​​used in the embodiments and examples are merely examples and can, of course, be replaced by other numerical values, and the relative magnitudes of the numerical values ​​can be changed appropriately.

[0133] For example, angles θ1 and θ2 can be identical. Angles θ2 and θ3 can be identical, and angle θ3 can be smaller than angle θ2. Core diameters d1 and d2 can be different. Width W1 can be larger than width W2. Groove opening angle θ4 can be larger than groove opening angle θ5.

[0134] The foregoing embodiments describe cases in which the front threaded sections 21 each have one thread and the rear threaded sections 26 each have one thread. However, the present invention is not necessarily limited thereto. For example, the rear threaded sections 26 may each have two or more threads. Furthermore, the shape of the front threaded sections 21 and the shape of the rear threaded sections 26 may be identical.

[0135] The foregoing embodiments describe a case in which each of the first cutting edge sections 20 and the second cutting edge sections 30, 51, 61, 71, 81 is subdivided circumferentially into four sections by a plurality of grooves 16 and grooves 40, 41. However, the present invention is not necessarily limited thereto. For example, each of the first cutting edge sections 20 and the second cutting edge sections 30, 51, 61, 71, 81 can be subdivided circumferentially by the plurality of grooves 16 and grooves 40, 41 into two sections, three sections, or five or more sections.

[0136] The foregoing embodiments describe cases in which the first end cutting edges 35, 62, 72 and the second end cutting edges 36, 52, 63, 74 are arranged alternately in the circumferential direction. However, the present invention is not necessarily limited to this. Two or more first end cutting edges 35, 62, 72 and two or more second end cutting edges 36, 52, 63, 74 can be arranged consecutively in the circumferential direction. End cutting edges that differ from the first end cutting edges 35, 62, 72 and the second end cutting edges 36, 52, 63, 74 can also be provided. The plurality of end cutting edges is preferably rotationally symmetrical about the axis C, but need not be.

[0137] Some of the configurations of one of the preceding embodiments can be applied to the other embodiments. For example, the ineffective cutting edge sections on the first end cutting edges 35, 62, 72 and the second end cutting edges 36, 52, 74 of the first, second, fourth, and fifth embodiments can be formed by removing some of the thread cutting edges 24 as in the third embodiment. Furthermore, the notches described in the fourth embodiment can be formed on the first end cutting edges 35, 62, 72 and the second end cutting edges 36, 52, 63, 74 of the first through third and fifth embodiments.

[0138] As in the fifth embodiment, the depth of the groove 41 in the first to fourth embodiments can be greater than the depth of the groove 40. The depths of the grooves 40 and 41 can also be identical in the fifth embodiment. Furthermore, the depth of the groove 40 can be greater than the depth of the groove 41 in each of the embodiments. DESCRIPTION OF REFERENCE NUMBERS 10, 50, 60, 70, 80 thread milling cutters 12 tool bodies 13 Shaft end 14 front end 20a Foot surface (part of the thread cutting edge) 24 front cutting edge (part of the thread cutting edge) 29 rear cutting edge (part of the thread cutting edge) 35 First end cutting edge (effective cutting edge section) 62, 72 first end cutting edge 36 Second end cutting edge (non-effective cutting edge section) 52, 63, 74 second end cutting edge 35a, 52a, 62a, 63b, 72b, 72d, 74b, 74d effective cutting edge section 52b, 62b, 63a, 72a, 72c, 74a, 74c, 74e ineffective cutting edge section 40, 41 Nut 42, 43 Grooved surface 44, 45 Groove 46, 47, 54, 64, 76, 84 Groove cutting edge C axis QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 6692932 B2

[0004]

Claims

[1] A thread milling cutter that cuts an internal thread in a workpiece by moving relative to the workpiece while rotating about an axis, the thread milling cutter comprising: a tool body including an axial front end and a shank end disposed axially opposite the front end and having a shank shape centered about the axis; a plurality of thread cutting edges each formed by a plurality of axially arranged threads and spaced apart from each other in the circumferential direction on the front end side of an outer periphery of the tool body; and a plurality of end cutting edges formed on the front end of the tool body so as to be respectively connected to the plurality of thread cutting edges on the front end side, wherein an effective cutting edge portion that cuts the workpiece and a non-effective cutting edge portion that is axially recessed toward the axial shank end relative to a trajectory of the effective cutting edge portion when the tool body rotates about the axis are formed on the plurality of end cutting edges. [2] The thread milling cutter according to claim 1, wherein each of the end cutting edges is completely formed by either the effective cutting edge portion or the non-effective cutting edge portion. [3] The thread milling cutter according to claim 1 or 2, further comprising a plurality of grooves recessed at the front end to respectively form rake surfaces of the plurality of end cutting edges and communicating with each other on the side of the axis thereof, each of the grooves including: a groove surface opposite the corresponding rake face in the circumferential direction and whose opposite distance to the rake face tapers towards the shank end; and a groove bottom connecting each of the groove surfaces and the corresponding rake surface, extending from the axis side to the outer circumference of the tool body and inclined towards the shank end, an edge between the rake face of one of the two grooves which are circumferentially adjacent to each other and the groove face of the other of the two grooves forms a plurality of groove cutting edges which are each connected to the plurality of end cutting edges, and the trajectories of the plurality of groove cutting edges when the tool body is caused to rotate about the axis, which overlap each other at least on the side of the end cutting edge. [4] The thread milling cutter according to claim 3, wherein each of the end cutting edges is completely formed by either the effective cutting edge portion or the ineffective cutting edge portion and a depth of the groove from the front end side to the groove bottom forming the rake face of the effective cutting edge portion is greater than a depth of the groove from the front end side to the groove bottom forming the rake face of the non-effective cutting edge portion. [5] The thread milling cutter according to any one of claims 1 to 4, wherein the effective cutting edge portion and the non-effective cutting edge portion are arranged alternately in the circumferential direction. [6] The thread milling cutter according to any one of claims 1 to 5, wherein the plurality of end cutting edges are rotationally symmetrical about the axis.

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