JP4641960B2 - Coated small diameter straight neck end mill - Google Patents

Description

  The present invention relates to a coated small-diameter straight neck end mill for use in cutting of a die or the like, in particular, deep engraving.

In recent years, miniaturization of home appliances and machine products has been remarkable, and electronic parts and semiconductor-related parts have become more precise and complicated. Along with this, high precision of the mold to be molded is also required at the same time. A cutting tool is used for such processing. However, particularly in the case of deep engraving that processes deep portions and corners, it is difficult to perform high-precision processing because unstable cutting is forced by bending of the cutting tool. The reason is considered as follows. First, the end mill is easily deflected during cutting, the processing accuracy is lowered, chatter vibration is generated, and shape errors due to these occur. Since machining becomes unstable, problems such as deterioration of finished surface properties, tool breakage, and breakage are likely to occur. Therefore, it is important to reduce the deflection of the cutting tool in order to stably perform the deep cutting with the cutting tool with high accuracy. In order to solve the above problem, the present applicant has previously proposed a small-diameter end mill used for deep machining of a mold, etc., in which a neck is coated in order to suppress neck deflection (patent document) 1). In Patent Document 1, the bending force applied to the end mill is covered by coating a hard film having a residual compressive stress from the blade portion of the tapered neck end mill to the neck portion and covering a portion having a length of 50% or more of the length under the neck. It is disclosed to be able to withstand and suppress the overall deflection of the end mill. Generally, the reason for coating a hard film on a tool is to improve the wear resistance of the blade part, and the hard film coated on the blade part and the neck part has a uniform film thickness or the blade part. The hard coating is thicker and the same coating. The reason why the hard film of the blade part is coated thicker than the neck part is that the blade part located at the tip of the tool has a higher plasma density at the time of coating and ions tend to concentrate.
JP 2002-011611 A

  When performing deep engraving using a small-diameter end mill, it has a straight neck end mill in which the outer diameter of the neck is substantially constant from the tip toward the shank, and a long tapered neck that expands from the tip toward the shank. A taper neck end mill is used. Here, considering the rigidity of the tool, the neck of the taper neck end mill is superior to the neck of the straight neck end mill, and the one described in Patent Document 1 further applies a hard film to the neck of the taper neck end mill. The rigidity is improved and the deflection is reduced. Here, when machining with a taper neck end mill, the wall surface to be machined needs to be an inclined surface so as not to contact the neck of the end mill. However, the finer the machining, the more often the wall surface to be machined is vertical or near vertical. For fine processing, a straight neck end mill must be used. However, in the straight neck end mill, the tool rigidity is insufficient, and a step is inevitably generated at the connection portion between the neck portion and the shank portion, resulting in poor breakage resistance. In view of such conventional circumstances, the present invention is a deep engraving process using a straight neck end mill, which suppresses the deflection of the tool at least as much as a taper neck end mill with a hard coating, improves shape accuracy, and is resistant to breakage. It is an object of the present invention to provide a coated small-diameter straight neck end mill that can improve the performance.

  In order to achieve the above object, the first invention is a coated small-diameter straight neck end mill having a blade diameter of 2 mm or less, wherein the film thickness of the hard film is different between the blade part and the neck part. A film thickness ratio T2 / T1 between the film thickness T1 of the film and the film thickness T2 of the hard film at the neck is 1 <T2 / T1 <20. This reinforces the neck that most affects the amount of deflection of the tool and improves the shape accuracy.

  By applying the invention of the present application, it is possible to provide a coated small-diameter straight neck end mill that can suppress tool deflection in deep engraving processing, and that can improve high-precision shape processing and breakage resistance of the tool. It was.

  According to the first invention of the present application, the film thickness ratio T2 / T1 is 1 <T2 / T1 <20, where T1 is the thickness of the hard coating on the blade and T2 is the thickness of the hard coating on the neck. Features. This is an important improvement of the present invention in that the thickness of the hard coating on the neck is set to be thicker than the thickness of the hard coating on the blade, and the deflection of the tool can be suppressed by improving the rigidity of the neck. . Since the neck portion is longer in the tool axis direction than the blade portion, the influence on the deflection amount of the entire tool is greater. In the first invention, even if cutting resistance acts on the blade portion during cutting, Since the rigidity of the neck that easily affects the deflection amount of the entire tool is improved, the deflection amount of the tool can be suppressed. Since there is a difference in the film thickness of the hard coating between the blade part and the neck part, it is considered that there is a difference in how the blade part and the neck are bent with respect to the bending force, and the bending force is relaxed and dispersed to prevent breakage. Here, as described above that the film thickness ratio T2 / T1 is 1 or less, the film thickness of the blade part and the neck part is uniform, or the hard film of the blade part is coated thickly to suppress the deflection of the neck part. The amount of deflection of the entire tool increases, and high-precision shape machining cannot be performed. The neck bends uniformly with respect to the bending force, and the bending force cannot be relaxed / dispersed, and breakage easily occurs at the boundary between the neck and the shank. When the value of the film thickness ratio T2 / T1 is 20 or more, the hard coating on the neck becomes brittle, and it becomes difficult to suppress the amount of deflection of the neck. Since the hard coating is brittle, cracks may occur in the hard coating during cutting, which may cause breakage. Furthermore, since a large difference is provided between the film thicknesses of the hard film on the blade part and the neck part, the manufacturing cost is increased, which is not realistic. Accordingly, the value of the film thickness ratio T2 / T1 was set to 1 <T2 / T1 <20. As a more preferable range of the film thickness ratio T2 / T1, 3.5 <T2 / T1 <18 suppresses the amount of deflection of the tool, and more accurate shape processing is possible. The film thickness of the hard coating on the blade is preferably 2 μm or less, and the cutting edge of the blade is kept sharp, the increase in cutting resistance is suppressed, the amount of tool deflection is suppressed, and highly accurate shape processing is possible. is there. If the thickness exceeds 2 μm, the cutting edge may be increased due to a thick hard coating on the cutting edge, and the cutting edge may be rounded to reduce the cutting performance.

  As a further preferred form of the first invention, it is preferable to set the residual compressive stress S of the internal hard coating coated on the neck to 2 GPa ≦ S ≦ 8 GPa. When these configurations are satisfied, the amount of deflection of the neck can be further suppressed. Here, if the residual compressive stress S is less than 2 GPa, the amount of deflection of the tool tends to increase, and high-precision shape processing cannot be performed. When the residual compressive stress S exceeds 8 GPa, the internal hard coating of the neck becomes too brittle, and the effect of suppressing the deflection of the tool is reduced due to cracks in the hard coating of the neck caused by vibration during cutting. A preferable range of residual compressive stress S is 2.5 GPa ≦ S ≦ 5.5 GPa. Furthermore, not only the internal hard film but also the residual compressive stress S of the external hard film coated on the outer peripheral side of the internal hard film at the neck may satisfy the above numerical range, and the neck can be further reinforced.

  As a method of measuring the residual compressive stress in the tool, it can be qualitatively determined from the hard film composition, crystal structure, structure, film hardness, and hard film state at the tip of the blade, but quantitatively determined from micro thin film X-ray diffraction. can do. As a method for measuring the residual compressive stress of a hard coating quantitatively with the highest accuracy, it is preferable to coat the same coating on another test piece and calculate from the deformation amount of the thin plate before and after coating. A measurement method calculated from the deformation amount will be described. For example, the test piece was made of cemented carbide having a length of 8 mm, a width of 25 mm, a thickness of 0.7 mm to 0.9 mm, and was subjected to double-sided mirror finishing with an elastic modulus E of 517.54 GPa and a Poisson's ratio v of 0.238. A thin plate is prepared, and the amount of deformation of the thin plate before the coating treatment is measured in advance. Thereafter, a hard film is coated on one surface of the thin plate, and the deflection amount δ and the film thickness d in the coating treatment are determined from the deformation amount after coating. Then, the test piece thickness D and the measurement length l are measured, and the residual compressive stress S can be calculated from the formula (1).

As a more preferable form of the first invention, the half width H in at least one X-ray diffraction among the internal hard film and the external hard film coated on the neck is 0.8 ° <H <2. It is 4 °. By satisfying these requirements, the amount of deflection of the neck can be further reduced, high-precision shape processing can be performed, and stable cutting can be performed. If the value of H is 0.8 ° or less, the amount of deflection of the tool may not be sufficiently suppressed, and the shape processing accuracy is not sufficient. When the angle is 2.4 ° or more, the hard coating on the neck tends to become brittle, and cracks occur in the hard coating on the neck due to vibration during cutting or the like, and the effect of suppressing the amount of deflection of the tool decreases. For these reasons, it is preferable to define the value of the half width H in the above range. In X-ray diffraction, when it has a crystal structure of B1 structure, it is preferable to make it a half width of (200) plane. Further, in the first invention, the film thickness of the internal hard film of the neck may be changed from the blade part side of the neck part to the shank part side. It is better to increase the film thickness. Thereby, the neck part taper part vicinity which is a connection part of the neck part used as a bending node and a shank part can be reinforced, and the deflection amount of the whole tool can be suppressed. It is possible to reinforce the neck while suppressing the difference in film thickness between the hard coating on the blade and the internal hard coating on the blade side of the neck, so the hard coating at the boundary between the blade and the neck is less likely to crack, and the neck It is possible to coat the hard film stably. When the thickness of the internal hard coating is changed in stages, the way the neck bends changes at the position where the thickness changes, and the bending force applied to the entire tool is relaxed and dispersed to suppress chatter vibration. , Finished surface properties are improved. It is thought that breakage can be prevented. With these improvements, tool deflection can be greatly suppressed, chatter vibration can be reduced, finishing can be performed more stably, and high-precision machining with less shape error can be realized.
The above-described coating of the hard film on the neck cannot be achieved by a general coating process, and is intentionally coated with a thick hard film on the neck.

As a method of manufacturing a coated small-diameter straight neck end mill coated with a hard film having different film thicknesses at the blade part and the neck part, before the first coating process, the neck part, the shank is attached to the tool member which is the material of the straight neck end mill. And forming a cutting edge at the tip of the tool member, and then coating the inner hard film on the tip and the neck located opposite to the shank of the tool member. A tool shape having a neck portion and a shank portion is completed. In the second coating step, the hard film of the blade part and the external hard film of the neck part are coated, and the film thickness ratio T2 / the film thickness T1 of the hard film of the blade part and the film thickness T2 of the hard film of the neck part. A coated small-diameter straight neck end mill with a T1 of 1 <T2 / T1 <20 can be obtained, and a coated small-diameter straight neck end mill capable of suppressing the amount of bending and breakage of the tool and achieving high-precision shape accuracy can be provided. Here, in the first coating step, hard coatings with different compositions may be laminated a plurality of times, and in the second coating step, hard coatings with different compositions may be laminated a plurality of times, The hard coating in the first coating step and the second coating step may have different compositions. In order to increase the film thickness of the internal hard film on the shank part side of the neck part in the first coating step, a method of masking the blade part side of the neck part can be considered. By the above manufacturing method, in the first coating step, a hard film for improving the rigidity of the neck and suppressing the amount of deflection, for example, TiSiN can be applied, and the cutting force is reduced on the blade. It is possible to coat a hard film according to the purpose, such as applying a lubricating film for suppressing the amount of deflection of the tool, such as CrSiN.

The rake angle of the blade portion of the coated small-diameter straight neck end mill of the present invention is preferably positive, and the cutting resistance can be reduced to further suppress the deflection amount of the entire tool. In particular, since the deflection amount of the tool is easily affected by the cutting resistance from the direction perpendicular to the tool, it is more effective to make the rake angle of the outer peripheral edge positive. For the same reason, when the coated small-diameter straight neck end mill is a ball end mill, the normal direction rake angle on the outer peripheral side of the ball blade is preferably positive. In order to suppress the amount of deflection of the blade portion itself, the core thickness is preferably in the range of 70% to 80% with respect to the blade diameter, and the amount of deflection of the tool can be suppressed by increasing the rigidity of the blade portion. As a further preferred form of the present invention, in the coating small diameter straight neck end mill coated with a hard film, at least one layer of the hard coating to be coated on the neck is, Al, Si, Ti, Cr, at least one or more selected from Nb Nitrides, carbides, oxides, borides, or one or more solid solutions thereof are preferred. Particularly preferably, at least one layer of a hard film to be coated is effective with two or more nitrides selected from Al, Si, Ti, Cr, and Nb. In particular, by coating at least one layer of TiSi nitride as the internal hard coating on the neck, the amount of deflection of the tool is remarkably suppressed. The present invention is particularly effective for a coated small-diameter straight neck end mill having a low rigidity of a straight neck end mill having a blade diameter of 2 mm or less, that is, a neck portion of less than 2 mm. The internal hard coating of the neck may be coated on the neck taper portion between the neck and the shank, and the amount of deflection of the entire tool can be suppressed. It is preferable that the present invention is used for deep cutting with a tool protrusion ratio L / D of a tool protrusion length L from the tip of the tool to the front surface of the shank gripping position with respect to the blade diameter D of the tool being 3 or more, When the tool sticking ratio L / D is 10 or more, the effect of the present invention appears more remarkably. Hereinafter, the present invention will be described based on examples.

Example 1
Invention Example 1 uses an ultrafine cemented carbide having a Co content of 8 weight percent and a WC average particle size of 0.4 to 0.6 μm as a base material. As shown in FIG. 1, the blade portion 1 is provided with a ball blade and an outer peripheral blade, the number of blades is two blades, the blade diameter is 2 mm, that is, the ball blade radius is 1 mm, and the normal rake angle of the ball blade is the tip. The angle is set to 0 ° in the vicinity, 5 ° on the outer peripheral side, the rake angle of the outer peripheral blade is 5 °, the twist angle is 20 °, the core thickness is 1.5 mm corresponding to 75% of the blade diameter, and the effective blade length is 3 mm. A neck portion 2 and a neck taper portion 3 are connected to the blade portion 1, and a neck relief having a neck portion diameter of 1.92 mm, which is slightly smaller than the blade diameter, is provided. The length under the neck, which is the end mill axial direction distance from the end mill tip to the boundary between the neck 2 and the neck taper portion 3, is 10 mm, and the diameter of the shank portion 4 is 4 mm. Invention Example 1 is a hard film in which the blade part 1 is coated with TiAlN with a film thickness of 2 μm, the inner hard film of the neck part 2 is coated with TiAlN with a film thickness of 4 μm, and the outer periphery of the internal hard film is coated on the blade part 1. The same TiAlN as that of the hard film was coated to 2 μm, so that the thickness of the hard film at the neck was 6 μm in total. The film thickness ratio T2 / T1 of Example 1 of the present invention is 3.
As a coating method of the hard coating, first, after manufacturing a tool member having a shape in which the pre-processing blade portion, the neck portion 2 and the shank portion 4 are the portions where the blade portion shape is to be formed, the first coating step Then, TiAlN was coated on the neck as an internal hard film with a film thickness of 4 μm. Then, the grinding process for forming a blade part shape in the said front blade part is performed, TiAlN coat | covered by the said front blade part is scraped off, and the said tool member is finished in an end mill shape. Then, as the second coating step, TiAlN was coated with a film thickness of 2 μm on the blade and neck. By coating the hard film by the above coating method, the film thickness of the hard film at the blade portion was set to 2 μm, and the film thickness of the hard film at the neck portion was set to 6 μm.
For comparison, as Comparative Example 2, an end mill having the same specifications as Example 1 of the present invention, in which only the blade portion was coated with TiAlN with a film thickness of 2 μm, that is, the film thickness ratio T2 / T1 was 0, Comparative Example 3 As described above, TiAlN with the same specifications as Example 1 of the present invention and with a hard film thickness of the blade portion of 2 μm and a hard film thickness of the neck portion of 1 μm, that is, the film thickness ratio T2 / T1 is 0.5. I made something. Measurement of the film thickness of the hard coating on the blade part and the neck part was made for each of Example 1 and Comparative Examples 2, 3 each, one of which was an end mill shaft at 2 mm and 5.5 mm from the end mill tip. The thickness of the hard coating on the outer peripheral flank face of the blade and the thickness of the hard coating on the neck were measured at the cut surface. The film thickness of the internal hard film at the neck was a value obtained by subtracting the film thickness of the hard film at the blade from the film thickness of the entire hard film at the neck. In the cutting test, SUS420J2 having a hardness of HRC52 was used for the work material, a reference surface having an inclination angle of 0.5 ° with respect to the end mill axis direction was provided on the work material, and the work material was formed from the upper surface to the lower surface. A finished surface having the same inclination as the reference surface is created by contour cutting toward the surface. Cutting conditions are as follows: the rotational speed is 10,000 min-1, the feed speed in the end mill radial direction is 1 m / min, the finishing mill allowance is set to 0.1 mm for the end mill radial cutting depth of the machine tool, and the end mill axial direction per run Dry cutting was performed with a cut amount of 0.1 mm. As an evaluation method, a machining step between the reference surface at a cutting length of 200 m and a finished surface created by the cutting test is measured using a contact-type shape measuring device in a cross-sectional view perpendicular to the reference surface, and is a finishing machining allowance. The shape error obtained by subtracting the value of the processing step from 0.1 mm was evaluated. The results are shown in Table 1.

  As shown in Table 1, Example 1 of the present invention was able to suppress the shape error to 0.01 mm. Further, the finished surface has almost no chatter surface and exhibits a good finished surface property, which suppresses the amount of deflection of the tool and enables highly accurate shape processing. On the other hand, Comparative Example 2 had a large shape error of 0.025 mm, and a chatter surface was observed as a finished surface. In Comparative Example 3, the shape error was 0.022 mm, which was slightly smaller than that in Comparative Example 2, but a chatter surface was observed on the finished surface. From these results, in Comparative Examples 2 and 3 where the film thickness ratio T2 / T1 is outside the scope of the present invention, the deflection amount of the tool was not suppressed, and the shape accuracy was not obtained.

(Example 2)
Next, with the same specifications as Example 1 of the present invention, as Examples 4 to 9, the film thickness of the neck is 3 to 36 μm, that is, the value of T2 / T1 is in the range of 1.5 to 18, and Comparative Example 10 And 42 μm, that is, a T2 / T1 value of 21 was subjected to the same test as in Example 1. The test results are shown in Table 2.

  As shown in Table 2, in the inventive examples 4 to 9, the shape error was 0.004 mm to 0.012 mm, and the shape error was small and good. Among them, Example 7 of the present invention having a film thickness ratio T2 / T1 of 6 was particularly excellent with a small shape error of less than 0.005 mm and a finished surface with no chatter surface. This is considered to be because the deflection of the neck was further suppressed. However, the inventive examples 8 and 9 having a large thickness ratio of the hard coating on the blade part and the neck part slightly increased in shape error as compared with the inventive example 7. This is presumably because the neck hard coating occupies a large proportion and the neck surface is brittle, so that micro cracks occur in the neck internal hard coating during cutting, and the tool deflection suppressing effect is reduced. On the other hand, in Comparative Example 10 in which the film thickness ratio T2 / T1 is 22, the shape error is 0.02 mm or more and the shape accuracy is not obtained, and the internal hard film of the neck has already cracked since the start of cutting. This is thought to be due to the lack of reinforcement. FIG. 2 shows the relationship between the value of T2 / T1 and the shape error created based on the test results of Example 1 of the present invention and Comparative Examples 2 to 3 of Example 1, and Examples 4 to 9 of Example 2 and Comparative Example 10 of Example 2. It can be seen that the shape error in the range of T2 / T1 in the range of 1 to 20 is as good as 0.015 mm or less. In addition, as shown in FIG. 2, it can be seen that when T2 / T1 is in the range of 3.5 to 18, the shape error is 0.010 mm or less and processing can be performed with more preferable shape accuracy.

(Example 3)
As Examples 11-16 of the present invention, those having a residual compression stress S of 1.5 GPa to 9.1 GPa of the internal hard coating of the neck with the same specifications as those of Example 1 of the present invention were prepared. Went. Here, the value of each residual compressive stress S is a value calculated from the deformation amount of the thin plate before and after coating in the first coating step. The test results are shown in Table 3.

  As shown in Table 3, all of Examples 11 to 16 of the present invention had a small shape error of 0.015 mm or less, suppressed the amount of tool deflection, and were able to perform highly accurate shape processing. In particular, Examples 12 to 14 of the present invention showed extremely excellent results with a shape error of 0.01 mm or less. This is presumably because high residual compressive stress was applied to the neck, the hard coating resisted the bending force generated at the neck during cutting, and the amount of deflection of the tool was suppressed. The finished surfaces of Invention Examples 11 to 16 all showed good results, but in particular, Invention Examples 13 and 14 were clean surface properties having no chatter surface. FIG. 3 is a diagram showing the relationship between the residual compressive stress S and the shape error of Examples 11 to 16 of the present invention. When the residual compressive stress S is in the range of 2 GPa to 8 GPa, the shape error is as good as 0.01 mm or less. It turns out that it is. Furthermore, as shown in FIG. 3, it can be seen that the shape error is as good as 0.006 mm or less in the range of 3 GPa to 6.5 GPa.

Example 4
With the same specifications as Example 1 of the present invention, the composition of the neck internal hard film and the blade part and the neck external hard film were changed as Invention Examples 17 to 20, and the internal hard film of the neck as Comparative Examples 21 and 22. The same composition of the blade part and the neck external hard film was prepared, and the same test as in Example 1 was performed. Table 4 shows the specifications and test results of Examples 17 to 20 of the present invention and Comparative Examples 21 and 22.

  As shown in Table 4, Examples 17 to 20 of the present invention had a small shape error of 0.01 mm or less and could be processed with high accuracy. The finished surface property was good with no chatter surface observed. This increases the rigidity of the neck by the internal hard coating of the neck and suppresses the amount of deflection of the tool, while the film thickness of the hard coating of the blade can be suppressed to 2 μm or less, the cutting resistance does not increase, This is thought to be because the amount of deflection could be suppressed. Particularly, Examples 19 and 20 of the present invention in which the blade portion was coated with a hard film containing Cr had a smaller shape error of 0.005 mm or less, and the deflection amount of the tool could be further suppressed. This is thought to be because the cutting resistance applied to the tool blade edge in addition to the neck reinforcement could be reduced by the lubricating action of the hard coating. In Comparative Examples 21 and 22, the shape error was as large as 0.015 mm or more, and the shape accuracy deteriorated. This is because the film thickness of the hard coating on the blade is equivalent to the film thickness of the hard coating on the neck, and the cutting edge of the tool is rounded by a thick hard coating, the cutting resistance increases, and the deflection of the neck increases. Conceivable.

(Example 5)
With the same specifications as in Invention Example 1, hard films having different half-value widths H of the hard film on the neck were coated as Invention Examples 23 to 28, and the same tests as in Example 1 were performed. Table 5 shows the specifications of the inventive examples 23 to 28 and the test results.

  As shown in Table 6, in Inventive Examples 23 to 28, the shape error was less than 0.015 mm, and good results were obtained. Particularly, in Examples 24-27 of the present invention, the shape error was as good as 0.01 mm or less, the amount of tool deflection was suppressed, and highly accurate shape processing became possible. FIG. 4 is a diagram showing the relationship between the half width H created based on the test results of the inventive examples 23 to 28 and the shape error. From FIG. 4, the half width H is 0.8 ° <H <2.4 °. It can be seen that the shape error is as good as 0.01 mm or less in the range.

(Example 6)
With the same specifications as Example 1 of the present invention, various hard coatings having different compositions as Invention Examples 29 to 38 were coated, and the same test as in Example 1 was performed. Table 6 shows the specifications and test results of Examples 29 to 38 of the present invention.

  As a result, in Inventive Examples 29 to 38, the shape error was less than 0.015 mm, and good results were obtained. In particular, the inventive examples 29 to 35 coated with two or more nitrides selected from Al, Si, Ti, Cr, and Nb have a smaller shape error of 0.01 mm or less, and are effective in suppressing the amount of deflection of the tool. Met.

(Example 7)
As Example 7, the same specifications as in Example 1 of the present invention were compared, but the thickness of the internal hard film at the neck was changed. The film thickness is measured at the neck by 5.5 mm, 7 mm, and 8.5 mm from the cutting edge along the end mill axis direction, that is, 25%, 50%, and 75% of the length of the neck, respectively. I went there. Inventive Examples 39 to 41 are produced by changing the thickness of the internal hard coating on the neck in two stages, and Inventive Examples 42 to 44 are produced by changing the thickness of the internal hard coating on the neck in three stages. Then, the same test as in Example 1 was performed. Table 7 shows the specifications and test results of Examples 39 to 44 of the present invention.

  As shown in Table 7, Examples 39 to 44 of the present invention had good results with less shape error of less than 0.02 mm compared to Comparative Examples 2 and 3 of Example 1. In particular, the present invention examples 39 to 40 and the present invention examples 42 to 43 in which the entire length of the neck is covered with an internal hard film is good with a shape error of 0.01 mm or less, suppressing the amount of tool deflection, and high accuracy. Accurate shape accuracy is obtained. Furthermore, it can be seen that the shape error is smaller as the ratio of the thick inner hard coating on the neck is increased, and the shape accuracy of the present invention example 40 is better than that of the present invention example 39. It can be seen that the larger the rate of increase in the thickness of the internal hard coating at the neck portion as it goes toward the shank portion, the smaller the shape error and the better the shape accuracy of Invention Example 43 than Invention Example 42. Inventive Examples 42 to 44 in which the thickness of the internal hard coating of the neck portion was changed in three stages from Inventive Examples 39 to 41 were smaller in shape error, and the amount of deflection of the tool could be suppressed. I understand that.

FIG. 1 is a schematic view of a coated small-diameter ball end mill according to the present invention. FIG. 2 is a relationship diagram between the film thickness ratio T2 / T1 and the shape error. FIG. 3 is a relationship diagram between the residual compressive stress S and the shape error. FIG. 4 is a relationship diagram between the half width H and the shape error.

Explanation of symbols

1: Blade part 2: Neck part 3: Neck taper part 4: Shank part

Claims (2)

  It is a coated small-diameter straight neck end mill having a blade diameter of 2 mm or less and having a hard film thickness different between the blade part and the neck part, and the hard film thickness T1 of the blade part and the hard film film of the neck part The coated small-diameter straight neck end mill, wherein the film thickness ratio T2 / T1 to the thickness T2 is 1 <T2 / T1 <20.   The coated small-diameter straight neck end mill according to claim 1, wherein the inner hard coating on the neck is thicker on the shank side of the neck than on the blade side of the neck. End mill.

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