Cutting tap after nitriding treatment and method for manufacturing the same

Abstract

A cutting tap is provided which suppresses breakage and wear of a blade during tapping and has high durability. In a nitriding treatment step (P2), a nitrogen diffusion layer in which nitrogen atoms contained in an atmosphere gas diffuse from the surface of a tool base material of the cutting tap under heating is formed, and then, in a honing treatment step (P3), an abrasive particle is made to collide with a cutting blade portion of the tool base material of the cutting tap to round the cutting blade portion and remove a blade tip. The cutting blade portion is made to have a thick nitrogen diffusion layer in advance by diffusion from a rear clearance face and diffusion from a front rake face, and the nitrogen concentration and hardness of the blade tip of the cutting blade portion are relatively high and mechanically brittle. Therefore, by removing the mechanically brittle blade tip, wear and breakage of the cutting blade portion of the cutting tap are reduced, and a tool performance capable of maintaining good cutting performance for a long period of time can be obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to a cutting tap and a manufacturing method thereof, and particularly relates to a technology for improving the life of a cutting tap after nitriding treatment. BACKGROUND

[0002] For example, for a cutting tap such as a straight flute tap, a helical flute tap, a point flute tap, a pipe tap, a thread milling cutter, and the like having a cutting edge, it is desirable to have a tool performance that can maintain good cutting properties for a long period of time without wear of the cutting edge and breakage of the cutting edge. A cutting tap having such a tool performance can reduce the number of tool replacements of a machining machine tool such as a machining center and improve machining efficiency.

[0003] In relation thereto, in Patent Literature 1, a cutting tap is proposed in which an incomplete mountain shape that is cut from the top as the thread of the thread cutting portion of the tapered cutting-in portion becomes a complete mountain shape from the front end of the cutting-in portion toward the full thread portion is sectioned in the circumferential direction by a helical groove or a straight groove, and the thread of the sectioned thread has a cutting edge formed along the helical groove or the straight groove at one end portion thereof, that is, one end surface formed by the sectioning. In this cutting tap, in order to suppress the occurrence of a chipped edge (a small notch in the cutting edge) in the cutting edge during cutting, a chamfer is applied to the cutting edge. However, in the cutting edge to which the chamfer is applied, the hardness is insufficient and the durability of the cutting tap cannot be sufficiently obtained.

[0004] In relation thereto, in Patent Literature 2, a technology is described in which, although it is not a cutting tap, in order to suppress breakage or chipping of a cutting edge of a tool (broach) having a cutting edge, after surface hardening treatment (gas nitriding) of a thickness d of about 50 μm that is greater than a height difference h between cutting edges adjacent to each other in the cutting direction is applied to the cutting edge, in a subsequent process, a micro shot blasting process is used to remove a white layer on the surface in order to prevent peeling of a hard coating film of the coating layer.

[0005]

Prior Art Literature

[0006]

Patent Literature

[0007]

Patent Literature 1

[0008]

Patent Literature 2

[0009]

Problem to be Solved by the Invention

[0010] However, even if the process of applying the surface hardening treatment based on gas nitriding described in Patent Document 2 and the micro-blast treatment to the entire surface after the surface hardening are applied to the cutting tap, a notch of the cutting edge is easily generated, and the durability of the cutting tap cannot be sufficiently obtained.

[0011] The present application has been made in view of the above-described circumstances, and aims to provide a cutting tap in which the cutting edge is less worn and damaged, and tool performance in which excellent cutting performance is maintained for a long period of time is obtained.

[0012]

Means for Solving the Problem

[0013] As a result of various studies repeatedly conducted by the present inventors and the like in view of the above-described circumstances, it was noted that, when a cross section of a cutting tap including a cutting edge is observed using an etching liquid, and the state in which etching of a nitrogen diffusion layer is promoted is observed using a metal microscope, the nitrogen diffusion layer is represented by black, and the cutting edge portion that receives diffusion from a clearance face and a rake face has a thicker nitrogen diffusion layer than other surface layers. Generally, the nitrogen diffusion layer has a property in which a gradient of nitrogen concentration and hardness is formed from a surface toward an inner side. At a tip of the cutting edge portion, the nitrogen concentration and hardness are higher than those of other portions, and thus it is conceivable that the tip is more brittle, and thus it was found that, if the tip portion of the cutting edge is removed using a honing treatment after a surface hardening treatment based on gas nitriding is performed on the cutting tap, the cutting tap exhibits an extremely high durable life compared to a case in which the surface hardening treatment based on gas nitriding is performed after the honing treatment. The present application has been made based on the above-described insight.

[0014] That is, the gist of the first application is a manufacturing method of a cutting tap having a nitrogen diffusion layer, including: a nitriding treatment step in which a nitrogen diffusion layer in which nitrogen atoms contained in an atmosphere gas under heating diffuse from a surface of a base material of the cutting tap is formed in a thickness of 10 μm to 30 μm; and a honing treatment step in which an abrasive particle collides with a cutting edge portion of the base material of the cutting tap that has undergone the nitriding treatment step to round the cutting edge portion, so that a difference between a thickness of the nitrogen diffusion layer of the cutting edge portion and a thickness of the nitrogen diffusion layer of a clearance face and a rake face that hold the cutting edge portion is within 5 μm.

[0015] In addition, the gist of the second application is a cutting tap having a nitrogen diffusion layer on a rake face and a clearance face that hold a cutting edge portion, in which a difference between a thickness of the nitrogen diffusion layer at the cutting edge portion and a thickness of the nitrogen diffusion layer at other portions of the rake face and the clearance face other than the cutting edge portion is within 5 μm.

[0016]

Effects of the Invention

[0017] The manufacturing method of the nitrided cutting tap according to the first invention includes: a nitriding treatment step in which a nitrogen diffusion layer in which nitrogen atoms contained in an atmosphere gas diffuse from a surface of a base material of the cutting tap under heating is formed at a thickness of 10 μm to 30 μm; and a honing treatment step in which an abrasive particle collides with a cutting edge portion of the base material of the cutting tap subjected to the nitriding treatment step to partially round the cutting edge portion so that a difference between a thickness of the nitrogen diffusion layer of the cutting edge portion and a thickness of the nitrogen diffusion layer of a relief surface and a rake surface that hold the cutting edge portion is within 5 μm. The cutting edge portion is thickened by diffusion from the relief surface and diffusion from the rake surface, and the cutting edge portion has a relatively high nitrogen concentration and hardness, and is mechanically brittle. Therefore, by removing the mechanically brittle cutting edge portion, the difference between the thickness of the nitrogen diffusion layer of the cutting edge portion and the thickness of the nitrogen diffusion layer of the relief surface and the rake surface that hold the cutting edge portion is within 5 μm, and thus wear and breakage of the cutting edge portion of the cutting tap are reduced, and a tool performance capable of maintaining a good cutting property for a long period of time can be obtained, and the thickness of the nitrogen diffusion layer is uniformized.

[0018] The cutting tap according to the second invention has a nitrogen diffusion layer on a rake surface and a relief surface that hold a cutting edge portion, and a difference between a thickness of the nitrogen diffusion layer at the cutting edge portion and a thickness of the nitrogen diffusion layer at other portions of the rake surface and the relief surface other than the cutting edge portion is within 5 μm. Therefore, the nitrogen concentration and the hardness of the cutting edge portion are not too high, and the mechanical brittleness is not too different, and thus wear and breakage of the cutting edge portion of the cutting tap are reduced, and a tool performance capable of maintaining a good cutting property for a long period of time can be obtained.

[0019] Here, it is preferable that, in the nitriding treatment step, the nitriding treatment of the base material of the cutting tap is performed in an atmosphere furnace in which an atmosphere of ammonia gas is maintained at a temperature of 500°C or higher and 550°C or lower.

[0020] Further, it is preferable that, in the honing treatment step, the abrasive particle collides with the cutting edge portion using compressed air, and thus the cutting edge portion is removed.

[0021] Further, it is preferable that, in the honing treatment step, the thickness of the nitrogen diffusion layer at the cutting edge portion is reduced to be close to the thickness of the nitrogen diffusion layer formed on a surface other than the cutting edge portion by removing the cutting edge portion.

[0022] In addition, it is preferable that the thickness of the nitrogen diffusion layer formed on the surface of the cutting tap after the tip of the cutting blade portion is removed by the honing treatment process be 10 μm or more and 30 μm or less, and the surface hardness of the cutting tap be 950 HV or more and 1050 HV or less.

[0023] In addition, it is preferable that the angle between the clearance face and the rake face of the cutting blade portion be an acute angle. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a view showing a three-blade tap to which the present application is properly applied.

[0025] Figure 2 is a II-II sectional view showing the cross section perpendicular to the center line of rotation of the tap of Figure 1 .

[0026] Figure 3 is a view showing the cutting blade portion of the tap of Figure 1 before being honed.

[0027] Figure 4 is a metal microscope photograph showing the cutting blade portion of the tap of Figure 1 before being honed.

[0028] Figure 5 is a view showing the cutting blade portion of the tap of Figure 1 after being honed.

[0029] Figure 6 is a metal microscope photograph showing the cutting blade portion of the tap of Figure 1 after being honed.

[0030] Figure 7 is a process diagram showing the main part of the manufacturing process of the tap of Figure 1 .

[0031] Figure 8 is a chart showing the results of cutting test 1 using a plurality of types of tap.

[0032] Figure 9 is a coordinate graph showing the results of the cutting test of Figure 8 in a manner that the number of cuts can be compared for each test material.

[0033] Figure 10 is a metal microscope photograph showing the cutting blade portion of test material 2 of Figure 8 enlarged.

[0034] Figure 11 is a graph showing the results of cutting tests 2 performed using a plurality of types of screw taps.

[0035] Figure 12 is a coordinate graph showing the results of the cutting tests 2 of the respective samples in a manner that the number of cuts can be compared. Figure 11 DETAILED DESCRIPTION

[0036] Hereinafter, an embodiment of the present application will be described in detail with reference to the drawings. Note that in the following embodiment, the drawings are appropriately simplified or modified, and the dimensional ratios and shapes of the parts, etc. are not necessarily accurately depicted.

[0037]

EMBODIMENT

[0038] Figure 1 is a drawing showing a three-fluted screw tap 10 to which the present application is appropriately applied. Figure 2 is a cross section of a leading portion 22 of the screw tap 10 of Figure 1 is a II-II cross-sectional view of Figure 1 The screw tap 10 is cited as an example of a cutting tap, and integrally has a shank portion 12, a neck portion 14, and a thread portion 16 in that order on a rotational center line CL. An external thread having a thread groove shape corresponding to an internal thread to be machined is provided in the thread portion 16, and three helical grooves 20 are formed at equal intervals around the rotational center line CL in a manner of dividing the external thread.

[0039] The thread portion 16 has a leading portion 22 formed by removing the thread teeth 18 of the external thread in a tapered manner in the axial direction, and a full tooth portion 24 having the thread teeth 18 of a full shape provided continuously with the leading portion 22. A cutting edge portion 28 is formed in the thread teeth of the leading portion 22 and the thread teeth of the full tooth portion 24 and the ridge line portion of the helical groove 20, that is, the ridge line portion on the rotational direction Al side of the thread teeth. In the present embodiment, the helical groove 20 is right-handed, and is provided across the thread portion 16 to substantially the entire region of the neck portion 14. As shown in Figure 2 the cutting edge portion 28 formed in the leading portion 22 is a front end portion in a region in which a concave circular-arc-shaped rake face 30 and a convex circular-arc-shaped relief face 32 are sandwiched, and a front end angle a is an acute angle.

[0040] Figure 3 is an enlarged cross-sectional view of the cutting edge portion 28 of the screw tap 10 after a nitriding treatment (a nitriding treatment process P2 described later) and before a honing treatment (a honing treatment process P3 described later), Figure 4 is an enlarged photograph of the cutting edge portion 28 after the nitriding treatment and before the honing treatment. Also, Figure 5 is an enlarged cross-sectional view of the cutting edge portion 28 of the screw tap 10 after the nitriding treatment and after the honing treatment, Figure 6 ​is an enlarged photograph of the cutting edge portion 28 after the nitriding treatment and the honing treatment. Note that, Figure 4 and Figure 6 is a photograph of an enlarged image of a cross section of the tap 10 taken by corroding the cross section of the tap 10 with an etching solution and enlarging the image with a metal microscope. In Figure 4 and Figure 6 , the nitrogen diffusion layer 38 is more easily corroded than the tool base material 36, and appears relatively dark in the metal microscope photograph.

[0041] In the cutting edge portion 28, chamfering based on honing (R-honing) processing is performed, as shown in the enlarged cross-sectional view of Figure 5 and the enlarged photograph of Figure 6 At the time of the forming process based on grinding or the like, the sharp tip 34 formed in the tool base material 36 is removed, as shown in the enlarged cross-sectional view of Figure 5 and the enlarged photograph of Figure 6 The difference between the thickness tl of the nitrogen diffusion layer 38 at the cutting edge portion 28 and the thickness t2 of the nitrogen diffusion layer 38 at other portions (the clearance face 32 or the rake face 30) other than the cutting edge portion 28 is within 5 μm. The thickness tl of the nitrogen diffusion layer 38 at the cutting edge portion 28 is a value measured in the direction of the half angle (a / 2) of the front end angle a, and the thickness t2 of the nitrogen diffusion layer 38 at the clearance face 32 or the rake face 30 is a value in the direction perpendicular to the clearance face 32 or the rake face 30.

[0042] Figure 7 Main portions of the manufacturing process of the tap 10 are shown. In the tap grinding process Pl, the thread 18 based on thread grinding is formed in a bar-shaped tool base material 36 made of high-speed tool steel, for example, the spiral flute 20 is formed by groove grinding, and the chisel portion 22 is formed by tooth-removing grinding. Also, quenching is performed on the tool base material 36 as necessary.

[0043] Next, in the nitriding treatment process P2, gas nitriding is performed in an atmosphere furnace in which the temperature is maintained at 500°C or higher and 550°C or lower in an ammonia atmosphere, for example, whereby the nitrogen diffusion layer 38 is formed on the surface of the tool base material 36 at a thickness of about 10 μm to 30 μm, as shown in the enlarged cross-sectional view of Figure 3 and the enlarged photograph of Figure 4 The surface hardness of the tool base material 36 in which the nitrogen diffusion layer 38 is formed is 950 HV or higher and 1050 HV or lower (JIS Z 2244:2009), for example. In the measurement of the Vickers hardness HV, a pressure load of 0.3 Kgf is used.

[0044] Also, in the honing process P3, abrasive particles such as Al2O3, SiC, and the like are partially sprayed from the nozzle N toward the tip of the cutting edge portion 28, i.e., the cutting tip 34 after the nitriding treatment, together with compressed air, and the cutting tip 34 is removed to round the tip of the cutting edge portion 28. Thus, the difference between the thickness tl of the nitrogen diffusion layer 38 of the cutting edge portion 28 and the thickness t2 of the nitrogen diffusion layer 38 of the clearance face 32 or the rake face 30, or the like is set to be within 5 μm. That is, honing is performed. Figure 5 The enlarged cross-sectional view and Figure 6 The enlarged photograph shows this state. The direction of the above-mentioned nozzle N is preferably the direction of the half angle (a / 2) of the tip angle a of the cutting tip 34.

[0045] [Cutting Test 1]

[0046] The present inventors produced test pieces 1 to 6, which are the same in material and shape as the screw tap 10 but differ in surface treatment and honing, as shown in Table 2. For each of the two test pieces, cutting (internal thread machining) was performed under the cutting test conditions shown in Table 1 below, and the damage state was observed for each tool (test piece) per 100 holes to grasp and evaluate the damage state. Also, based on the presence or absence of damage or the size of the wear, the point in time at which it was judged that the tool could not be used any longer was judged to be the point at which the life was reached, and the value of the number of machined holes at that time was recorded.

[0047] (Table 1)

[0048] Workpiece material: S45C

[0049] Screw size: M10 x pitch 1.5 mm

[0050] Machine used: vertical machining center BT50

[0051] Cutting oil: water-soluble cutting oil (10 times dilution)

[0052] Cutting speed: 15 m / min

[0053] Machining length of lower hole: 20 mm (limit hole)

[0054] (Table 2)

[0055] Pre-treatment honing surface Nitriding treatment post-treatment honing

[0056]

[0057] Figure 8 The test results of the cutting test 1 are shown in Figure 9 are coordinate graphs showing the number of machined holes according to the test results of each test piece. Also, Figure 8 Figure 10 ​is a metal microscope photograph showing the cutting edge portion 28 of the test material 2, which is an example of a broken cutting edge, in an enlarged manner.

[0058] In Figure 8 and Figure 9 , the test material 1 is the most general specification of a tap and has been used up to now, and no honing processing and nitriding treatment are performed. In this test material 1, a slight chipping occurs at the tip 34, and the wear increases from this as a starting point. The first life (number of processes) is 700, and the second life (number of processes) is 600.

[0059] The test material 2 is a test material on which the same nitriding treatment as the nitriding treatment process P2 is performed in order to improve the wear resistance of the test material 1. This test material 2 has a broken tip 34 of the cutting edge portion 28 and a broken cutting edge before the wear resistance is exerted, and thus the life is greatly shortened compared with the test material 1.

[0060] The test material 3 is a test material on which honing processing is performed as a countermeasure against chipping of the test material 1. According to this test material 3, although chipping is suppressed, initial wear occurs from the time of the new product due to the honing processing, and thus the wear increases compared with the test material 1, and the durability is poor.

[0061] The test material 6 is a test material on which honing processing and nitriding treatment are performed similarly to the test material 5, but differs from the test material 5 in that the nitriding treatment is performed after the honing processing. In this test material 6, although the tip 34 of the cutting edge portion 28 is removed, since the nitriding treatment is performed after the removal of the tip 34, the thickness tl of the nitrogen diffusion layer 38 of the cutting edge portion 28 is greater than the thickness t2 of the other rear flanks 32 or rake faces 30, and in the surface of the cutting edge portion 28, the nitrogen concentration and hardness are high and brittle, and thus the suppression effect of the defect is limited. Since the nitrogen concentration and hardness change exponentially from the surface, it is presumed that even a relatively small difference in the thickness of the nitrogen diffusion layer 38 has a large effect.

[0062] On the other hand, the test material 4 and the test material 5, on which the nitriding treatment is performed before the honing processing, have no damage to the cutting edge portion 28 even after 900 processes, and the wear is small, and thus it is judged that the processes can be continued, and the cutting test is ended at this 900 times. This case is a case in which the tip 34 of the cutting edge portion 28, which is relatively high in nitrogen concentration and hardness and mechanically brittle, is removed by the honing processing after the nitriding treatment, and thus the nitrogen diffusion layer 38 is uniformized, and thus the cutting edge portion 28 of the tap 10 has no wear or broken cutting edge, and it is presumed that the cutting performance can be maintained in a good state for a long period.

[0063] [Cutting Test 2]

[0064] Next, the inventors of this application prepared samples A, B, C, D, and E, which are made of the same material and shape as the spiral tap 10, subjected to the aforementioned nitriding and honing processes, and varied the difference Δt (=│t1-t2│) between the thickness t2 of the nitrogen diffusion layer 38 on the surface of the tool base material 36 (other parts different from the cutting edge 28) and the thickness t1 of the nitrogen diffusion layer 38 on the surface of the cutting edge 28. For each pair of samples, cutting (internal thread machining) was performed under the cutting test conditions shown in Table 1, and the tool (sample) was observed every 100 holes to understand and evaluate the damage state. Furthermore, based on the presence or absence of defects or the degree of wear, the tool was judged to have reached the end of its service life at the point when it was determined to be unusable, and the number of holes machined at that time was recorded. It should be noted that the "thickness difference" item in Table 3 represents t1-t2.

[0065] (Table 3)

[0066] The difference in thickness between pretreatment honing, surface nitriding, and posttreatment honing.

[0067]

[0068] Figure 11 The results of cutting test 2 are shown. Figure 12 It is expressed according to the fact that each sample can be compared. Figure 11 The coordinate graph of the number of processes shown in the test results.

[0069] exist Figure 11 and Figure 12 In this study, sample 1 is a standard spiral tap of the most common specifications and has been used consistently without honing or nitriding. In sample 1, minor chipping occurs at the cutting edge 34, leading to increased wear starting from this point. The life (number of machining passes) of the first sample is 700, and that of the second sample is 600.

[0070] Sample 2 was subjected to the same nitriding treatment as sample 1 in the nitriding process P2 to improve the wear resistance of sample 1. The difference Δt between thickness t1 and thickness t2 was 13 μm. Before the wear resistance of sample 2 was achieved, the cutting edge 34 of the cutting edge 28 was damaged or broken, so its lifespan was significantly shortened compared to sample 1.

[0071] Sample A was a sample that underwent slight honing as a subsequent treatment of Sample 2. As a result, the difference Δt between thickness t1 and thickness t2 was 9 μm. Due to insufficient honing as a subsequent treatment, Sample A suffered breakage and tool breakage.

[0072] The sample B and the sample C are samples in which honing processing (honing processing step P3) is appropriately performed as a subsequent process to the sample 2, and the difference Δt between the thickness t1 and the thickness t2 is 5 μm and 1 μm, respectively. The sample B and the sample C do not have damage of the cutting edge portion 28 even after 900 times of processing, and have little wear, and thus it is judged that the processing can be continued, and the cutting test is ended at 900 times.

[0073] The sample D is a sample in which honing processing is slightly excessively performed as a subsequent process to the sample 2, and as a result, the difference Δt between the thickness t1 and the thickness t2 is 5 μm (t1-t2=-5 μm). Although the sample D does not have damage of the cutting edge portion 28 after 900 times of processing, the wear is large, and thus it is judged that the processing cannot be continued any more, but the wear resistance is superior to that of the sample 1. It is presumed that the reason is that the blade tip 34 of the cutting edge portion 28, which is relatively high in nitrogen concentration and hardness and mechanically brittle, is removed by honing processing after the nitriding treatment, the difference Δt (absolute value) between the thickness t1 and the thickness t2 is within 5 μm, and thus the nitrogen diffusion layer 38 is uniformized, and thus the cutting edge portion 28 of the cutting tap does not have wear and damage of the blade, and it is presumed that the cutting performance can be maintained in a good state for a long period of time.

[0074] The sample E is a sample in which honing processing is excessively performed as a subsequent process to the sample 2, and as a result, the difference Δt between the thickness t1 and the thickness t2 is 9 μm (t1-t2=-9 μm). In the sample D, the wear resistance is insufficient, and similarly to the sample 1, the wear becomes excessively large when exceeding 700 times.

[0075] As described above, according to the manufacturing method of the twist drill (cutting tap) 10 of the present embodiment, in the nitriding treatment step P2, the nitrogen diffusion layer 38 in which nitrogen atoms contained in an atmosphere gas diffuse from the surface of the tool base material 36 of the cutting tap under heating is formed, and thereafter, in the honing treatment step P3, the cutting edge portion 28 of the tool base material 36 of the cutting tap is rounded by colliding abrasive particles with the cutting edge portion 28 to remove the blade tip 34. In the cutting edge portion 28, the nitrogen diffusion layer 38 is formed thick in advance due to diffusion from the clearance face 32 and diffusion from the rake face 30, and the blade tip 34 of the cutting edge portion 28 is relatively high in nitrogen concentration and hardness and mechanically brittle. Thus, by removing such mechanically brittle blade tip 34, wear and damage of the blade at the cutting edge portion 28 of the cutting tap are reduced, and it is possible to obtain a tool performance in which the cutting performance can be maintained in a good state for a long period of time, and the thickness of the nitrogen diffusion layer 38 is uniformized.

[0076] In addition, according to the spiral tap (cutting tap) 10 of the present embodiment, the difference Δt (absolute value) between the thickness t1 of the nitrogen diffusion layer 38 at the cutting edge portion 28 of the spiral tap 10 and the thickness t2 of the nitrogen diffusion layer 38 at other portions (the clearance face 32 or the rake face 30) other than the cutting edge portion 28 is within 5 μm. Therefore, the nitrogen concentration and the hardness of the cutting edge portion 28 are not so high, and the mechanical brittleness is not so different, so that the wear and the breakage of the cutting edge at the cutting edge portion 28 of the spiral tap 10 are reduced, and a tool performance capable of maintaining a good cutting property for a long period of time can be obtained.

[0077] The above describes the embodiment of the present application in detail based on the drawings, but the present application is also applicable to other modes.

[0078] For example, the cutting tap (spiral tap 10) of the above-described embodiment is formed with the spiral groove 20, but the shape of the groove can be a straight groove or a spiral point groove. Also, the cutting tap of the present application can be a straight flute tap, a spiral flute tap, a thread milling cutter, or the like, as long as it is a rotary cutting tool having a cutting edge.

[0079] In addition, the cutting tap (spiral tap 10) of the above-described embodiment is composed of three edges, but the number of edges is not particularly limited. Also, the cutting tap of the present application can be composed of various tool materials (tool base material 36) such as high-speed tool steel, super-hard alloy steel, or the like, and a hard coating film such as AlCrN or the like can be formed on the nitrogen diffusion layer 38 as needed.

[0080] In addition, the nitriding treatment process P2 of the above-described embodiment is performed by gas nitriding, but in addition to the gas nitriding, gas soft nitriding, ion nitriding, salt bath nitriding, plasma nitriding, or the like can be used.

[0081] In addition, in the honing treatment process P3 of the above-described embodiment, the edge tip 34 of the cutting edge portion 28 is removed by locally performing plasma treatment using abrasive grains on the cutting edge portion 28, but plasma treatment using glass beads can be performed, and plasma treatment using other materials such as steel beads or the like can be performed.

[0082] In addition, in the honing treatment process P3, the abrasive particles can be sprayed together with compressed air, but can be sprayed together with a liquid, and barrel honing can be performed in a barrel tank together with an abrasive sheet. The barrel honing is not local honing, but the sharp edge tip 34 of the spiral tap 10 is preferentially removed. Also, the abrasive particles can be abrasive grains such as Al2O3, SiC, or the like, and glass particles, steel balls, or the like can be used.

[0083] Note that the above is only one embodiment, and the present application can be implemented in various modes to which various changes and modifications are applied based on the knowledge of those skilled in the art.

[0084] [Legend]

[0085] 10: spiral point (cutting tap) 28: cutting edge portion 30: rake face (other portion than cutting edge portion) 32: relief face (other portion than cutting edge portion) 36: tool base material (base material) 38: nitrogen diffusion layer Δt: difference

Claims

1. A manufacturing method of a nitriding-treated cutting tap (10) having a nitrogen diffusion layer (38), characterized by comprising: a nitriding treatment step (P2) in which a nitrogen diffusion layer (38) is formed in a thickness of 10 μm to 30 μm in a base material (36) of the cutting tap (10) by diffusing nitrogen atoms contained in an atmosphere gas inward from a surface of the base material (36) of the cutting tap (10) at the time of heating; and a honing treatment step (P3) in which a cutting edge portion (28) of the base material (36) of the cutting tap (10) subjected to the nitriding treatment step (P2) is partially collided with abrasive grains to round the cutting edge portion (28) so that a difference (Δt) between a thickness (tl) of the nitrogen diffusion layer (38) of the cutting edge portion (28) and a thickness (t2) of the nitrogen diffusion layer (38) of a relief surface (32) and a rake surface (30) that hold the cutting edge portion (28) is within 5 μm, the thickness (tl) of the nitrogen diffusion layer (38) of the cutting edge portion (28) being a thickness in a direction of a half angle (α / 2) of a front end angle (α) of the cutting edge portion (28), and the thickness (t2) of the nitrogen diffusion layer (38) at the relief surface (32) and the rake surface (30) being a thickness in a direction perpendicular to a surface of the relief surface (32) and the rake surface (30).

2. The manufacturing method of the nitriding-treated cutting tap (10) according to claim 1, characterized in that the honing treatment step (P3) uses a nozzle (N) that sprays the abrasive grains toward the cutting edge portion (28) from a direction of the half angle (α / 2) of the front end angle (α) of the cutting edge portion (28).

3. A nitriding-treated cutting tap (10) having a nitrogen diffusion layer (38) on each of a rake surface (30) and a relief surface (32) that hold a cutting edge portion (28), characterized in that a difference (Δt) between a thickness (tl) of the nitrogen diffusion layer (38) at the cutting edge portion (28) of the cutting tap (10) and a thickness (t2) of the nitrogen diffusion layer (38) at the rake surface (30) and the relief surface (32) is within 5 μm, the thickness (tl) of the nitrogen diffusion layer (38) at the cutting edge portion (28) being a thickness in a direction of a half angle (α / 2) of a front end angle (α) of the cutting edge portion (28), and the thickness (t2) of the nitrogen diffusion layer (38) at the rake surface (30) and the relief surface (32) being a thickness in a direction perpendicular to a surface of the rake surface (30) and the relief surface (32).

4. The nitriding-treated cutting tap (10) according to claim 3, wherein the thickness (tl) of the nitrogen diffusion layer (38) at the cutting edge portion (28) is within 5 μm of the thickness (t2) of the nitrogen diffusion layer (38) at the rake surface (30) and the relief surface (32). ​ ​ ​ ​ ​

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