Gear cutting tool and manufacturing method thereof

Abstract

To solve the problem that, when using hard film of high hardness as thick film on a surface of a gear cutting tool, compression stress of the hard film becomes excessive, so that the hard film may be self-destructed and peeled, and that precision of a tooth profile is considerably impaired in such cases, and further, that the self-destructed portion exposes its parent material, whereby abrasion resistance deteriorates.SOLUTION: In a gear cutting tool, a plurality of cutting edges are annularly arranged with a rotation axis as the center, and hard film is coated on a surface. In the gear cutting tool, a thickness of the hard film at a rake face of the cutting edge is 0.8 times or greater relative to a thickness of the hard film at a flank of the cutting edge.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to gear cutting tools for machining gears, in particular skiving cutters used in power skiving, in which a cutting tool with cutting edges on its circumference is rotated synchronously with a gear to be machined and the gear is machined by slippage that occurs when the rotation axis of the tool and the gear to be machined are inclined at a predetermined angle, and to gear cutting tools such as pinion cutters used in shaper machining, in which cutting is performed by moving relatively in the tooth trace direction of the gear to be machined synchronously with the gear to be machined, and methods for manufacturing such tools. [Background technology]

[0002] In recent years, skiving (power skiving) has become increasingly common in the manufacture of gears. The cutter used in skiving is also called a skiving cutter, and its shape is almost identical to that of the pinion cutter used in shaping.

[0003] However, it is characterized by having a different helix angle from the gear to be manufactured, and the difference in helix angle causes the gear to be cut and the cutter to rotate synchronously, which causes slippage in the tooth trace direction to be generated and cut.Moreover, the surface of most skiving cutters is covered with a ceramic film (hard film) represented by TiAlN, AlCrN, etc. (see Patent Documents 1 and 2).

[0004] In hobbing or shaping, which are also methods for machining gears, a hard TiN coating may be used, particularly when wet cutting using cutting oil and the cutting speed is less than 200 m / min, or the rake face may be re-ground to remove the ceramic coating from the rake face before use.

[0005] On the other hand, in the case of skiving cutters, the cutting face is re-ground and then coated with a ceramic hard film, i.e., recoating is performed. Note that before recoating, a process of removing the hard film (de-coating) is sometimes carried out to remove the old hard film remaining on the flank face, and in other cases, the old hard film is simply coated over the old hard film.

[0006] The difference between hobbing, shaping and skiving is that in skiving, the rake angle changes continuously during cutting, and the effective rake angle takes a large negative value (-20 to -30°). This causes significant deformation of the chips and, since there is no escape route, the temperature of the rake face is likely to rise. If cutting is performed without a TiN hard coating or ceramic hard coating, which has low heat and oxidation resistance, the tool life will be drastically reduced.

[0007] Therefore, since the ceramic hard coating applied to the skiving cutter requires high heat resistance and oxidation resistance, a nitride coating containing chromium, aluminum or silicon is preferable, and AlCrN is more preferable. When applied to hobbing, this is the same as the characteristics of the hard coating required for high-speed (250 m / min or more) dry cutting, and many skiving cutters are coated with the same hard coating as hobs for high-speed dry cutting. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 4950276 [Patent Document 2] Patent Publication No. 2022-74210 Summary of the Invention [Problem to be solved by the invention]

[0009] However, although Patent Document 1 discloses the thickness of an oxidation-resistant coating layer and a high-hardness coating layer for gear cutting tools including a hob, pinion cutter, and broach, it does not disclose or suggest anything about the thickness of the rake face and flank face. Patent Document 2 also discloses machining using a skiving cutter coated with an AlCrN film or an AlTiCrN film, but it also does not particularly mention the ratio of film thicknesses on the rake face and flank face.

[0010] In general high-speed dry hobbing, wear known as crater wear occurs on the rake face slightly away from the tooth tip, whereas in skiving, wear occurs mostly at the cutting edge. For this reason, skiving cutters have a short life compared to hobs, and tool costs are high.

[0011] In addition, to extend the life of a skiving cutter, it is effective to increase the film thickness on the rake face, but in the conventional method, the film thickness on the flank face, i.e., the tooth profile, also increases, which causes a problem of poor precision of the tooth profile. In particular, when a high-hardness hard coating is made thick, the compressive stress of the hard coating becomes excessive, and the hard coating may self-destruct and peel off. In such cases, not only is the precision of the tooth profile significantly impaired, but the base material is exposed in the self-destructed part, causing a problem of reduced wear resistance.

[0012] Therefore, an object of the present invention is to provide a gear cutting tool that improves the tool life by increasing the film thickness on the rake face of the cutting edge while suppressing self-destruction of the hard coating coated on the surface. [Means for solving the problem]

[0013] As a result of intensive research, the inventors of the present application have come to the following findings: Ceramic coatings (hard coatings) generally have compressive stress, which is a major factor in improving the hardness (strength) of the coating and, in turn, its wear resistance. When the inventors of the present application observed the initial wear of the skiving cutter, they found that damage to the skiving cutter progressed gradually from the tip of the teeth on the rake face.

[0014] It was also confirmed that wear progresses rapidly from the portion where the hard coating is self-destructing. In other words, in order to improve the wear resistance of the rake face while suppressing the self-destruction of the hard coating, the inventors discovered that maintaining a specific relationship between the film thickness on the rake face and the film thickness on the flank face is extremely useful in improving the tool life.

[0015] Therefore, in the present invention, in a gear cutting tool having a plurality of cutting edges arranged in an annular shape around a rotation axis and having a hard coating on the surface, the thickness of the hard coating on the rake face of the plurality of cutting edges is set to 0.8 times or more, preferably 1.5 times or less, more preferably less than 1.1 times, of the thickness of the hard coating on the flank face.

[0016] In addition, with regard to the invention of a method for manufacturing a gear cutting tool, the coating process for coating a hard film on a gear cutting tool material includes a first coating process for coating a hard film on the surface of the gear cutting tool material, and a second coating process for further coating a hard film on the surface of the gear cutting tool material after the first coating process, with a jig that covers the flank surface of the cutting edge of the gear cutting tool material being placed.

[0017] The hard coating applied to the surface of the gear cutting tool (skiving cutter or pinion cutter) may be a hard coating such as a nitride, carbonitride, boronitride, oxynitride, etc., containing two or more metal components including aluminum.

[0018] The film thickness on the rake face side of the cutting edge can be measured at a position 1.0 mm radially from the apex of the tooth tip toward the rake face toward the tooth base. The film thickness on the flank side of the cutting edge can be measured at a position 1.0 mm radially from the apex of the tooth tip toward the flank face toward the tooth trace. These film thicknesses preferably have a relationship of 0.8Tf≦Tr≦1.5Tf, where Tr is the film thickness on the rake face side and Tf is the film thickness on the flank side. Effect of the Invention

[0019] The gear cutting tool of the present invention has the effect of improving the service life of the gear cutting tool by providing a predetermined thickness for each hard coating on the rake face and flank face of the cutting edge or providing a predetermined distribution. [Brief description of the drawings]

[0020] [Figure 1] FIG. 2 is a schematic cross-sectional view of the inside of a film-forming device during a first coating step of the gear cutting tool of the present invention. [Diagram 2] FIG. 4 is a schematic cross-sectional view of the inside of a film-forming device during a second coating step of the gear cutting tool of the present invention. [Diagram 3] 1 is an electron microscope photograph of the rake face side of a skiving cutter used in a cutting test. [Figure 4] 1 is an electron microscope photograph of the rake face side of a skiving cutter used in a cutting test. [Diagram 5] 1 is an electron microscope photograph of the rake face side of a skiving cutter used in a cutting test. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The manufacturing method of the gear cutting tool of the present invention will be described with reference to the drawings. Fig. 1 shows a schematic cross-sectional view of the inside of a film-forming device during a first coating (film-forming) step of coating the surface of the gear cutting tool of the present invention with a hard film, and Fig. 2 shows a schematic cross-sectional view of the inside of the film-forming device during a second coating step.

[0022] First, in the coating process carried out when manufacturing the gear cutting tool according to the present invention, as shown in Fig. 1, a rotating jig 3 of a coating device (film-forming device) is passed through the central hole of a bell-shaped skiving cutter 1, and these are stacked in several stages, with a spacer 4 and a masking jig 5 placed on them, and then a film is formed while rotating in a predetermined rotation direction 6 in the coating device. In a general coating device used, particularly when forming a ceramic coating containing two or more types of metals such as an AlCrN film, the film is formed by an arc method using a solid target or by sputtering. 4 Spacer 5 Masking jig 6 Rotation Direction

[0023] For this reason, the target (evaporation source) 2 is located at a position radially away from the rotation axis, and the components 2a that will become the coating fly in approximately perpendicular to the rotation axis. As a result, in the skiving cutter 1, the ceramic coating on the flank facing the evaporation source becomes thicker, and the coating thickness on the rake face not facing the evaporation source becomes thinner than that of the flank.

[0024] Next, as shown in Fig. 2, the cover 2 attached during the second coating preferably has a uniform shape in the circumferential direction. This is because the thickness of the film on the flank 1a varies in the circumferential direction of the skiving cutter 1, which causes uneven wear and affects the pitch accuracy of the gear to be machined. Therefore, it is preferable that the film thickness ratio on the flank 1a of the gear cutting tool is less than 1.1 times each other for each tooth. Also, if the film thickness of each tooth on the rake face 1b differs, the wear becomes uneven, which also leads to deterioration of the gear pitch accuracy and vibration during machining, so the film thickness ratio is preferably less than 1.1 times.

[0025] Moreover, the first coating step is performed for about half the time of a normal coating step, and the second coating step is performed for the remaining half of the time using the spacer 4 and masking jig 5 shown in Fig. 1, and then with a cover 21 that covers the flank 1a. In this way, the increase in film thickness on the flank 1a is suppressed during the latter half of the second coating step, and as a result, the film thickness on the rake face 1b side can be increased while the overall film thickness can be suppressed.

[0026] The above-mentioned coating process is merely an example, and other coating methods may be used as long as the film thickness on the rake face of the skiving cutter is 0.8 times or more that on the flank face. For example, after coating the rake face and flank face, the tooth profile may be ground to remove the hard film on the flank face, and then coating may be performed again.

[0027] The hard coating may be AlCrN, AlTiCrN, or a nitride obtained by adding 5% or less of another metal component to the hard coating. When the hard coating is AlCrN, the atomic ratio (atm %) of the elements Al and Cr constituting the hard coating is preferably Al:Cr=60-75%:25-40%.

[0028] When the hard coating is AlTiCrN, the atomic ratio (atm%) of each of the elements Al, Ti, and Cr constituting the hard coating is preferably Al:Ti:Cr=60-65%:30-35%:5-10%. Note that it is sufficient that at least one layer of each of the AlCrN and AlTiCrN hard coatings is coated on the skiving cutter. In other words, hard coatings of different compositions, such as TiN, may be formed on the upper and lower layers of these hard coatings.

[0029] Alternatively, hard coatings having completely different chemical components may be formed in the first and second coating steps. For hard coatings with a single metal component, such as TiN, coating can be performed using a crucible. In this case, if the rake face of the skiving cutter is placed facing downward, the rake face faces the crucible, so the film thickness on the rake face side can be made thicker even with conventional methods. EXAMPLES

[0030] Example 1 In this embodiment, when a hard coating was applied to the surface of a gear cutting tool (skiving cutter), the thickness ratio of the hard coating on the rake face and flank of the cutting edge was verified in the form shown in FIG. 1 or FIG. 2. The verification results will be described. First, the film thickness on the rake face of the skiving cutter coated only with the film formation form shown in FIG. 1 was 1.7 μm, and the film thickness on the flank was 2.7 μm. As a result, the film thickness ratio on the rake face / flank (the value obtained by dividing the film thickness on the rake face side by the film thickness on the flank face side) was 0.63. In addition, even when the film formation time was increased (doubled), the film thickness on the rake face of the gear cutting tool (skiving cutter) was 4.3 μm, and the film thickness on the flank was 6.6 μm, and the film thickness ratio on the rake face / flank was 0.65.

[0031] In contrast, a skiving cutter that was coated in the film formation form shown in Figure 1 (first coating process) and then coated for the same period of time in the film formation form shown in Figure 2, i.e., with the cover 21 attached (second coating process), had a film thickness of 2.7 μm on the cutting face and 3.0 μm on the flank, resulting in a film thickness ratio of 0.9.

[0032] Example 2 In the same manner as in Example 1 described above, the coating time of the first coating step and the coating time of the second coating step were changed, and the skiving cutter was coated. One of the cutters had a rake face thickness of 3.6 μm, a flank thickness of 4.4 μm, and a rake face / flank thickness ratio of 0.81, and the other had a rake face thickness of 6.0 μm, a flank thickness of 5.4 μm, and a rake face / flank thickness ratio of 1.10. In this way, since the rake face / flank thickness ratio is set to 0.8 or more in the present invention, a skiving cutter with a long life can be provided.

[0033] The above test results show that when coating a gear cutting tool with a hard coating, coating in the film formation form shown in Figure 1 (first coating process) and then coating in the film formation form shown in Figure 2 (second coating process) will result in a film thickness ratio on the rake face / flank face (the film thickness on the rake face side divided by the film thickness on the flank face side) of 0.8 or more.

[0034] Although the present invention has been described with respect to a skiving cutter, which has a particularly large coating effect on the rake face, it goes without saying that the present invention is also effective for a pinion cutter, which has almost the same shape as a skiving cutter and is used in shaping. In particular, the present invention has a certain effect on pinion cutters when the workpiece is a difficult-to-cut material, such as one with high hardness.

[0035] Example 3 Next, a skiving cutter, described later, was manufactured using powdered high speed steel (surface hardness: Rockwell C scale 66HRC) as the substrate. The specifications of the skiving cutter were module: 2.3, pressure angle: 20°, number of tool teeth: 36, and twist angle: 5°. The surface of the skiving cutter was coated in the film formation form shown in Fig. 1, and then coated for the same period of time with the cover 21 shown in Fig. 2 attached, to cover it with an AlCrN film. The film thickness on the rake face of this skiving cutter was 2.7μm, the film thickness on the flank face was 3.0μm, and the film thickness ratio on the rake face / flank face was 0.90.

[0036] After that, a gear cutting test was conducted using this skiving cutter. The gear specifications were: material: S45C (annealed material), module: 2.3, pressure angle: 20°, number of teeth: 84, helix angle: 15°, tooth thickness: 20mm. The cutting conditions were: cross angle: 20°, cutting speed: 200m / min, cutting depth: 0.8mm / pass, feed: 0.25mm / rev, cutting length: 1.3m / tooth. An electron microscope photograph (backscattered electron composition image: 200x magnification) of the tooth tip of the skiving cutter used in this test is shown in Figure 3. As shown in Figure 3, the wear amount of the tooth tip (exposed amount of the rake face base material) was minor, less than 0.1mm.

[0037] Comparative Example 1 As a comparative example, a skiving cutter of the same material and shape as in the example was coated with an AlCrN coating in the form of coating shown in Figure 1. The rake face film thickness of this skiving cutter was 1.7 μm, the flank film thickness was 2.7 μm, and the rake face / flank film thickness ratio was 0.63. A gear cutting test was carried out using this skiving cutter under the same conditions as in the example. Figure 4 shows an electron microscope photograph (backscattered electron composition image: 200x magnification) of the tip of the skiving cutter after the cutting test. As shown in Figure 4, the base material was exposed over a width of 0.2 mm or more and a length of 0.1 mm or more on the rake face side of the skiving cutter used, and it was clear that the wear was greater than in the example.

[0038] Comparative Example 2 An AlCrN coating was applied to a skiving cutter of the same shape in the same manner as in Comparative Example 1. However, the coating time was doubled. This skiving cutter had a rake face film thickness of 4.3 μm and a flank film thickness of 6.6 μm, with a rake face / flank film thickness ratio of 0.65. A cutting test was carried out using this skiving cutter under the same conditions as in the example. An electron microscope photograph (backscattered electron composition image: 200x magnification) of the tooth tip after machining is shown in FIG. 5. As shown in FIG. 5, wear had progressed from the tooth tip of the skiving cutter used, and it was confirmed that the coating film had self-destructed on the cutting edge ridge other than the tooth tip.

[0039] From these test results, in the case of Comparative Example 2, even if an attempt is made to suppress the wear of the rake face by increasing the film thickness, the hard film self-destructs as the film thickness on the flank face increases, and the wear resistance of the tooth tip decreases. On the other hand, in the skiving cutter of the present invention, since only the film thickness on the rake face is increased, it is possible to obtain a skiving cutter with a long life. The results of the above gear cutting tests (listed) are shown in Table 1.

[0040] [Table 1]

[0041] From the above test results, it was found that with regard to the thickness of the hard coating coated on the surface of a gear cutting tool (such as a skiving cutter) used in gear machining, it is effective in extending the life of the gear cutting tool by making the thickness of the hard coating on the rake face of the cutting edge 2.0 μm or more and the thickness of the hard coating on the flank of the cutting edge 3.0 μm or more (in particular, making the thickness of the hard coating on the rake face of the cutting edge 0.8 times or more and less than 1.1 times the thickness of the hard coating on the flank of the cutting edge). [Explanation of symbols]

[0042] 1 Skiving cutter 1a Flank 1b Scooping face 2. Target 2a Film components 3 Rotating Jig 4 Spacer 5 Masking jig 6 Rotation Direction 21 Cover

Claims

1. A gear cutting tool having a plurality of cutting edges arranged in a circular ring shape centered on a rotation axis and having a hard coating coated on its surface, characterized in that the thickness of the hard coating on the rake face of the cutting edges is 0.8 times or more the thickness of the hard coating on the relief face of the cutting edges.

2. 2. The gear cutting tool according to claim 1, wherein the thickness of the hard coating on the rake face of the cutting edge is 0.8 to 1.5 times the thickness of the hard coating on the flank face of the cutting edge.

3. 3. The gear cutting tool according to claim 2, wherein the thickness of the hard coating on the rake face of the cutting edge is 0.8 to less than 1.1 times the thickness of the hard coating on the flank face of the cutting edge.

4. 4. The gear cutting tool according to claim 1, wherein the hard film contains at least two kinds of metallic elements.

5. The gear cutting tool according to claim 4, wherein the gear cutting tool is either a skiving cutter or a pinion cutter.

6. 2. A method for manufacturing a gear cutting tool according to claim 1, wherein the coating step of coating the gear cutting tool material with the hard coating comprises a first coating step of coating the hard coating on a surface of the gear cutting tool material, and a second coating step of further coating the hard coating on the surface of the gear cutting tool material with a jig that covers a flank face of a cutting edge of the gear cutting tool material after the first coating step.

7. 3. A method for manufacturing a gear cutting tool according to claim 2, wherein the coating step of coating the gear cutting tool material with the hard coating comprises a first coating step of coating the hard coating on a surface of the gear cutting tool material, and a second coating step of further coating the hard coating on the surface of the gear cutting tool material with a jig that covers a flank face of a cutting edge of the gear cutting tool material after the first coating step, in a state where the jig is installed.

8. 4. A method for manufacturing a gear cutting tool according to claim 3, wherein the coating step of coating the gear cutting tool material with the hard coating comprises a first coating step of coating the hard coating on a surface of the gear cutting tool material, and a second coating step of further coating the hard coating on the surface of the gear cutting tool material with a jig that covers a flank face of a cutting edge of the gear cutting tool material after the first coating step.

9. 5. A method for manufacturing a gear cutting tool according to claim 4, wherein the coating step of coating the gear cutting tool material with the hard coating comprises a first coating step of coating the hard coating on a surface of the gear cutting tool material, and a second coating step of further coating the hard coating on the surface of the gear cutting tool material with a jig that covers a flank face of a cutting edge of the gear cutting tool material after the first coating step.

10. 6. A method for manufacturing a gear cutting tool according to claim 5, wherein the coating step of coating the gear cutting tool material with the hard coating comprises a first coating step of coating the hard coating on a surface of the gear cutting tool material, and a second coating step of further coating the hard coating on the surface of the gear cutting tool material with a jig that covers a flank face of a cutting edge of the gear cutting tool material after the first coating step, in a state where the jig is installed.

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