JP2008307628A - Small-diameter cemented carbide endmill - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-diameter cemented carbide endmill having end cutting edges having an outside diameter D1 of 0.5 mm or less, which endmill can improve machining precision and durability by suppressing the deflection and breakage of the tool by improving the stiffness and strength of the cutting edges, and also can be easily treated in resharpening the cutting edges and in a setting-up operation. <P>SOLUTION: A diameter increasing portion 16 for smoothly and continuously increasing the diameter is provided between the cutting edge portion 14 and a shank 12 so as to make a tip end half angle α 15° or larger. Therefore, the projecting length L2 from the shank 12 to the tip end of the cutting edge portion 14 becomes small, and the mechanical strength and the stiffness of the projecting portion including the cutting edge portion 14 become high, and the deflection and breakage of the tool can be suppressed. As a result, the high machining precision can be achieved in a cutting operation, and the durability can be improved. On the other hand, the breakage of the cutting edge portion 14 in resharpening the cutting edge portion 14 and in a setting-up time, etc. for mounting the endmill in a holder can be suppressed. Therefore, the endmill can be easily handled. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a small-diameter carbide end mill, and more particularly, to a long-life small-diameter carbide end mill that can suppress bending deformation and breakage of a tool and obtain high machining accuracy.

A blade portion that is made of a cemented carbide and has a bottom blade and an outer peripheral blade that are coaxially and integrally provided on the front end side of the shank, and has an outer diameter D1 of 0.5 mm or less. Carbide end mills have been proposed. An example of the end mill described in Patent Document 1 is a first taper portion having a linearly smaller diameter dimension, a neck portion having a constant radial dimension, and a first linearly smaller diameter dimension at the front end side of the shank. A small-diameter blade portion is integrally provided through two taper portions.
JP 2006-88229 A

  However, since such a conventional small-diameter carbide end mill has a large protruding dimension from the shank to the blade part, it is difficult to ensure rigidity and mechanical strength, and bending deformation and breakage are liable to occur during cutting, Not only is it difficult to obtain sufficient processing accuracy and durability, but there is a possibility of breakage during grinding of the blade portion or setup during mounting on the holder, and handling is not easy.

  The present invention has been made against the background of the above circumstances, and the object of the present invention is to increase the rigidity and mechanical strength of the blade in a small-diameter carbide end mill having an outer diameter D1 of the bottom blade of 0.5 mm or less. In addition, it is intended to improve processing accuracy and durability by suppressing bending deformation and breakage of the tool, and to facilitate handling at the time of grinding or setting up the blade portion.

  In order to achieve such an object, the first invention is made of a cemented carbide, and a blade portion having a bottom blade and an outer peripheral blade is integrally provided coaxially on the front end side of the shank, and An inclined straight line S connecting a corner connecting the bottom blade and the outer peripheral blade and the outer peripheral edge of the shank is a center line with a small-diameter carbide end mill having an outer diameter D1 of the bottom blade of 0.5 mm or less. As the tip half angle α that is inclined with respect to O is 15 ° or more, it goes from the same outer diameter of the blade portion to the shank until it reaches the same outer diameter as that of the shank between the blade portion and the shank. It is characterized by having a diameter increasing portion in which the diameter dimension increases.

  The second invention is characterized in that, in the small-diameter carbide end mill of the first invention, the diameter-increasing portion has a diameter that is smoothly and continuously increased from the blade portion to the shank.

  According to a third aspect of the present invention, there is provided the small-diameter carbide end mill according to the second aspect, wherein the diameter-increasing portion is (a) linearly larger in diameter from the same outer diameter as the blade portion toward the shank side. (B) The diameter is increased nonlinearly so that the outer contour in the axial direction becomes a concave arc shape. A concave arc-shaped portion which is caused to reach the outer peripheral edge of the tip of the shank is provided between the tapered portion and the shank.

  According to a fourth aspect of the present invention, in the small-diameter carbide end mill according to the third aspect, the concave arcuate portion is curved with a constant radius R in the axial outline.

The fifth aspect of the invention is the small-diameter carbide end mill of the fourth aspect, wherein the tip half angle α is in the range of 15 ° to 35 °, and the taper half angle β of the tapered portion is in the range of 5 ° or more and less than 20 °. It is characterized by that.
The taper half angle β is ½ of the taper angle.

  In such a small-diameter carbide end mill, since the diameter increasing portion is provided between the blade portion and the shank so that the tip half angle α is 15 ° or more, the protruding dimension from the shank to the tip of the blade portion is small. It becomes small and the mechanical strength and rigidity of the protrusion part including a blade part become high, and the bending deformation and breakage of a tool are suppressed. As a result, high machining accuracy can be obtained during cutting and durability can be improved. On the other hand, breakage during grinding of the blade portion or setup during mounting on the holder is suppressed, and handling is facilitated.

  In the second invention, since the diameter of the diameter-increased portion is increased smoothly and continuously, stress concentration due to a sudden change in the diameter is prevented, and breakage during cutting is more effective. To be suppressed.

  In the third invention, since the diameter increasing portion includes the tapered portion and the concave arc-shaped portion, the tip half angle α is easily set to 15 ° or more while preventing stress concentration due to a sudden change in the diameter. Strength and rigidity can be improved.

  In the fourth invention, since the concave arc-shaped portion is curved with a constant radius R, its design and processing are easy, and the concave arc-shaped portion can be processed with high dimensional accuracy.

  In the fifth invention, since the taper half angle β of the taper portion is less than 20 °, stress concentration at the boundary portion with the blade portion due to a sudden change in diameter is prevented, while the taper half angle β is 5 ° or more. Therefore, the tip half angle α can be made to be 15 ° or more by the concave arc-shaped portion while enjoying the stress concentration preventing action by the tapered portion. Moreover, since the tip half angle α is set to 35 ° or less, the diameter can be increased to the same outer diameter as the shank by the concave arc-shaped portion having a constant radius R while ensuring a predetermined length as the tapered portion. .

  The small-diameter cemented carbide end mill of the present invention only needs to have an outer diameter D1 of the bottom blade of 0.5 mm or less, and an end mill of a straight blade having an outer peripheral blade having the same constant diameter as the outer diameter D1, Is suitably applied to a tapered blade end mill that linearly increases from the outer diameter D1, but can also be applied to other end mills such as a ball end mill in which a bottom blade is provided on a hemispherical surface. While the present invention is preferably applied to an end mill having an outer diameter D1 of 0.1 mm or less, an end mill having an outer diameter D1 larger than 0.5 mm can be configured in the same manner as the present invention.

  In the blade portion, a chip discharging groove is formed, an outer peripheral blade is provided along the groove, and a bottom blade is provided so as to be continuous with the outer peripheral blade. As the groove, a twisted groove is desirable, but a straight groove that can be easily processed may be employed. Since the number of grooves, that is, the number of blades, is very small, two (two blades) are appropriate. However, one (one blade) or three (three blades) can be used.

  If the tip half angle α is smaller than 15 °, the projecting dimension from the shank to the tip of the blade becomes large, and it becomes difficult to obtain mechanical strength and rigidity. Therefore, the diameter increasing portion so that the tip half angle α is 15 ° or more. Need to be configured. When the diameter increasing portion is constituted by a tapered portion connected to the blade portion and a concave arc-shaped portion having a certain radius R connected to the shank, it is necessary to secure a tapered portion having a predetermined length dimension. In addition, it is desirable to configure the diameter increasing portion in the range where the tip half angle α is 35 ° or less.

  Although it is desirable for the diameter-increasing portion to increase the diameter dimension smoothly and continuously as in the second aspect of the invention, when the first aspect of the invention is carried out, the cylindrical part having a constant diameter dimension and the rate of change in the diameter dimension are inconsequential. You may provide the discontinuous change part etc. which are changing continuously. In the second aspect of the invention, it is sufficient that the diameter dimension in the diameter-increasing part is increased smoothly and continuously. At the boundary between the blade part and the diameter-increasing part, or at the boundary between the diameter-increasing part and the shank, The rate of change of may change discontinuously.

  In the third aspect of the invention, the diameter-increased portion includes the tapered portion connected to the blade portion and the concave arc shape portion connected to the shank. Consists of a shape part and a taper part connected to the shank, or a taper part connected to the blade part, an intermediate concave arc shape part, and a taper part connected to the shank, or a concave arc Various modes are possible, such as a configuration with only the shape portion.

  In the fourth invention, the concave arc-shaped portion is curved with a constant radius R. However, in implementing other inventions, the curvature changes, for example, the curvature continuously increases toward the shank. A concave arc-shaped portion can also be employed.

  In the fifth aspect of the invention, the taper half angle β of the taper portion is 5 ° or more and less than 20 °. When the taper half angle β is 20 ° or more, stress concentration is likely to occur at the boundary portion with the blade portion. However, it is not always necessary to set the taper half angle β within the range of 5 ° or more and less than 20 ° when implementing other inventions.

  As the shank, for example, a cylindrical straight shank having a constant outer diameter is preferably used. However, it is possible to adopt a taper shank whose diameter is linearly changed, and at least the tip portion has a circular shape. It should be.

  The outer diameter D2 of the tip portion of the shank is appropriately determined according to the standard of the holder that holds the shank, while the projecting dimension L2 from the shank to the tip of the blade portion is the tip half angle α and the outer diameter D2 of the shank. For example, if D2≈4 mm and the tip half angle α≈15 °, the protruding dimension L2 is about 7.4 mm, and the diameter increasing portion is configured so that the protruding dimension L2 is 7.4 mm or less. You may do it. If D2≈5 mm and the tip half angle α≈15 °, the protrusion dimension L2 is about 9.3 mm. If D2≈10 mm and the tip half angle α≈15 °, the protrusion dimension L2 is about 18.6 mm. However, since the rigidity and mechanical strength decrease as the protrusion dimension L2 increases, it is desirable to increase the tip half angle α as the outer diameter D2 of the shank increases. For example, the tip half angle α may be set so that the protruding dimension L2 is a predetermined value (eg, 7.4 mm) or less regardless of the outer diameter D2 of the tip of the shank.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing a two-blade small-diameter carbide end mill 10 according to an embodiment of the present invention, where (a) is an enlarged front view seen from a direction perpendicular to the center line O, and (b) is a front end portion. The front view further enlarged, (c) is a front view showing the blade portion 14 further enlarged, and (d) is a perspective view of the blade portion 14 further enlarged and seen from the oblique tip side. The small-diameter carbide end mill 10 is made of a cemented carbide alloy, and has a cylindrical shank (straight shank) 12, a blade portion 14 provided on the tip side of the shank 12, and a space between them. The diameter increasing portion 16 is integrally provided on the common center line O. The blade portion 14 functions as an end mill of a straight blade, and a pair of twist grooves 18 are provided by grinding with a grindstone so as to reach the tip portion of the diameter increasing portion 16, and the diameter along the twist groove 18 is An outer peripheral blade 20 having a constant dimension is formed, and a bottom blade 22 is provided continuously at the distal end in the axial direction. The outer diameter D1, that is, the tool diameter of the bottom blade 22 is 0.5 mm or less, 0.05 mm in this embodiment, and the blade length L1 is 0.075 mm. The outer diameter D2 of the shank 12 is 4 mm.

  The diameter-increasing portion 16 has a tapered portion 30 whose diameter is linearly increased from the same outer diameter (outer diameter D1 of the bottom blade 22) as the blade portion 14 from the blade portion 14 toward the shank 12 side. In addition to being continuously provided, the diameter dimension is increased nonlinearly so that the taper portion 30 and the shank 12 are smoothly connected to the taper portion 30 and the axial outline becomes a concave arc shape. The concave arc-shaped portion 32 reaching the outer peripheral edge of the tip of the shank 12 is provided, and the diameter is smoothly and continuously increased from the blade portion 14 to the shank 12. The concave arc-shaped portion 32 has an axial outline curved with a certain radius R, and the tangent of the arc coincides with the outer peripheral surface (taper generatrix) of the tapered portion 30 at the boundary with the tapered portion 30. Yes. The tapered portion 30 and the concave arc-shaped portion 32 are such that an inclined straight line S connecting the corner C1 connecting the bottom blade 22 and the outer peripheral blade 20 and the outer peripheral edge C2 of the shank 12 with respect to the center line O The tip half angle α that inclines is within the range of 15 ° to 35 °, and the taper half angle β of the tapered portion 30 is within the range of 5 ° or more and less than 20 °. In the present embodiment, the taper half angle β = 10 °, the radius R = 3 mm, and the tip half angle α is designed to be 20 °, and the protruding dimension L2 from the shank 12 to the tip of the blade portion 14 is about 5. At 5 mm, the diameter D3 of the boundary between the tapered portion 30 and the concave arc-shaped portion 32 is about 1.2 mm.

  FIG. 2 is an electron micrograph of the tip portion of the small-diameter carbide end mill 10 of the present embodiment, (a) is an enlarged photograph of the tip side portion of the shank 12, and (b) is a portion surrounded by a white circle of (a). (C) is an enlarged photograph of the part surrounded by the white circle in (b), (d) is an enlarged photograph of the part surrounded by the white circle in (c), (e) is the blade part 14 from the oblique tip side. It is a photograph taken. (A), (d), and (e) in FIG. 2 correspond to (b), (c), and (d) in FIG. 1, respectively.

  According to the small-diameter carbide end mill 10 of this embodiment, since the diameter increasing portion 16 is provided between the blade portion 14 and the shank 12 so that the tip half angle α is 15 ° or more, the shank 12 The protrusion dimension L2 from the blade edge 14 to the tip of the blade portion 14 is reduced, the mechanical strength and rigidity of the protrusion portion including the blade portion 14 are increased, and the bending deformation and breakage of the tool are suppressed. As a result, high machining accuracy can be obtained during cutting and durability can be improved. On the other hand, breakage during grinding of the blade portion 14 or setup during mounting on the holder is also suppressed, and handling is facilitated.

  Further, in this embodiment, the diameter of the diameter increasing portion 16 is increased smoothly and continuously, so that stress concentration due to a sudden change in the diameter is prevented, and breakage at the time of cutting or the like is further reduced. Effectively suppressed.

  Further, since the diameter increasing portion 16 includes the tapered portion 30 and the concave arc-shaped portion 32, the tip half angle α is easily set to 15 ° or more while preventing stress concentration due to a sudden change in the diameter. Strength and rigidity can be improved.

  Further, since the concave arc-shaped portion 32 is curved with a constant radius R, the design and processing are easy, and the concave arc-shaped portion 32 can be processed with high dimensional accuracy.

  Further, since the taper half angle β of the taper portion 30 is less than 20 °, stress concentration at the boundary portion with the blade portion 14 due to a sudden change in diameter is prevented, while the taper half angle β is 5 ° or more. Therefore, while enjoying the stress concentration preventing effect by the tapered portion 32, the protruding dimension L2 can be reduced by the concave arc-shaped portion 32 so that the tip half angle α becomes 15 ° or more.

  Further, since the tip half angle α is set to 35 ° or less, the diameter of the tapered portion 30 is ensured to the same outer diameter D2 as the shank 12 by the concave arc-shaped portion 32 having a constant radius R while ensuring a predetermined length. Can be increased.

  FIG. 3 is a diagram for specifically explaining the shape when the diameter increasing portion 16 is designed by variously changing the tip half angle α, and the taper half angle β of the taper portion 30 is 10 °. FIG. 3A shows a case where the tip half angle α = 18 °, the radius R = 3 mm, the protrusion dimension L2 is about 6 mm, and the boundary diameter dimension D3 is about 1.5 mm. (b) is the case where the tip half angle α = 23 °, the radius R = 3 mm, the protruding dimension L2 is about 4.7 mm, and the boundary radial dimension D3 is about 1 mm. (c) is the case where the tip half angle α = 30 °, the radius R = 3 mm, the protrusion dimension L2 is about 3.4 mm, and the boundary diameter dimension D3 is about 0.5 mm. (d) is the case where the tip half angle α = 37 °, the radius R = 2.5 mm, the protrusion dimension L2 is about 2.6 mm, and the boundary diameter dimension D3 is about 0.3 mm. In this (d), the tapered portion 30 exists temporarily, but its length dimension is short, and the effect of the tapered portion 30 to prevent stress concentration due to a sudden change in the radial dimension is not necessarily sufficiently obtained. The tip half angle α is preferably 35 ° or less, although it varies depending on the outer diameter D2.

Moreover, FIG. 4 is a figure explaining the result of having investigated the durability to breakage by changing taper half angle (beta) of the taper part 30 in the range of 5 degrees-20 degrees. That is, three small-diameter carbide end mills 10 (No. 1 to No. 3) each having a taper half angle β = 5 °, 10 °, 15 °, and 20 ° are prepared, and groove cutting is performed under the following processing conditions. The cutting distance until the tool breakage was examined. The tool specifications other than the taper half angle β are the same, the tool diameter, that is, the outer diameter D1 of the bottom blade 22, D2 = 0.05 mm, the number of blades, the blade length L1 = 0.075 mm, the tip half angle α = 25 °, The radius R of the concave arc-shaped portion 32 is 3 mm.
"Processing conditions"
-Work material: Pre-hardened steel (HRC40)
Work material dimensions: 100mm x 30mm, plate thickness 5mm
・ Rotation speed: 40000 min ^-1
・ Incision: 0.002mm
・ Feeding: 50mm / min
・ Processed groove shape: length 100mm, width 0.05mm, depth 0.05mm
・ Machining method: Groove 100mm in length (cut) step by 0.002mm

  The cutting distance in FIG. 4 is the total cutting distance of the step machining. For example, when the cutting distance is 220 mm, the groove machining with a depth of 0.002 mm and a length of 100 mm is performed twice, and then the third grooving process is in progress ( 20 mm) means that the tool is broken. In the evaluation column, “◯” indicates pass, “x” indicates failure, “◯” indicates that the average cutting distance is 200 mm or more, and “X” indicates less than 200 mm.

  As is apparent from the results of FIG. 4, when the taper half angle β is 5 ° to 15 °, the average cutting distance is 200 mm or more in all cases, whereas when the taper half angle β is 20 °, the average cutting distance is The distance is 125.7 mm, which is about half of the taper half angle β = 5 ° to 15 °. This is presumably because when the taper half angle β is 20 °, stress concentration occurs at the boundary portion with the blade portion 14 due to a sudden change in the diameter dimension, and breakage easily occurs. Therefore, it is desirable that the taper half angle β is less than 20 °.

  FIG. 5 is a diagram for explaining the result of examining the machining accuracy of the groove by changing the tip half angle α in the range of 10 ° to 30 °. That is, three small-diameter carbide end mills 10 (No. 1 to No. 3) each having a tip half angle α = 10 °, 15 °, 20 °, 25 °, and 30 ° are prepared, and a groove is cut to a depth of 0.002 mm. Processing was performed and the groove width was measured with a microscope, and compared with the actual blade diameter (outer diameter D1) before processing. The processing conditions were the same as those in the durability test of FIG. 4, but the groove width was measured by performing groove processing only once with a notch of 0.002 mm. Moreover, the measurement accuracy of the measuring microscope for measuring the groove width and the blade diameter (outer diameter D1) is 0.2 μm. The tool specifications other than the tip half angle α are the same, the tool diameter, that is, the outer diameter D1 of the bottom blade 22, 0.05 mm, the number of blades, the blade length L1 = 0.075 mm, the taper half angle β = 10 °, The radius R of the concave arc-shaped portion 32 is 3 mm.

  As is clear from the results of FIG. 5, when the tip half angle α is 15 ° to 30 °, the average of the difference was 0.001 mm or less in all cases, whereas when the tip half angle α = 10 °, The average of the differences is 0.0032 mm, which is three times or more of the case where the tip half angle α = 15 ° to 30 °. This is because the protrusion dimension L2 from the shank 12 increases as the tip half angle α decreases, and the protrusion dimension L2≈11 mm when the tip half angle α = 10 °. It is expected to expand. In the evaluation column, “◯” means pass, “x” means fail, and “◯” means that the average difference is 0.001 mm or less, and “×” means it exceeds 0.001 mm.

  As mentioned above, although the Example of this invention was described in detail based on drawing, this is an embodiment to the last, and this invention implements in the aspect which added various change and improvement based on the knowledge of those skilled in the art. Can do.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure explaining the small diameter carbide end mill to which this invention was applied, (a) is the enlarged front view seen from the direction perpendicular to the center line O, (b) is the front view which expanded and showed the tip part further. (c) is a front view showing the blade portion further enlarged, and (d) is a perspective view of the blade portion further enlarged and seen from the oblique tip side. Fig. 2 is an electron micrograph of the tip of the small-diameter carbide end mill shown in Fig. 1, where (a) is a photograph showing the tip side of the shank, and (b) is an enlarged photograph of the part surrounded by white circles in (a). , (C) is an enlarged photograph of the part surrounded by the white circle in (b), (d) is an enlarged photograph of the part enclosed by the white circle in (c), and (e) is an enlarged photograph of the blade part taken from the oblique tip side. It is. The figure which shows specifically the shape at the time of designing the diameter increase part by changing the tip half angle α variously, (a) when α = 18 °, (b) when α = 23 °, (c) Is the case where α = 30 °, and (d) is the case where α = 37 °. It is a figure explaining the result of having investigated durability to breakage using several types of test goods from which taper half angle (beta) differs. It is a figure explaining the result of having investigated processing accuracy using a plurality of kinds of test goods from which tip half angle alpha differs.

Explanation of symbols

  10: Small diameter carbide end mill 12: Shank 14: Blade portion 16: Diameter increasing portion 20: Outer peripheral blade 22: Bottom blade 30: Tapered portion 32: Concave arc shape portion S: Inclined straight line O: Center line α: Tip half angle β: Tapered half angle

Claims (5)

A small portion having a bottom blade and an outer peripheral blade that are made of cemented carbide, are integrally provided coaxially on the front end side of the shank, and has an outer diameter D1 of 0.5 mm or less. A carbide end mill,
The inclined straight line S connecting the corner connecting the bottom blade and the outer peripheral blade and the outer peripheral edge of the shank is such that the tip half angle α inclined with respect to the center line O is 15 ° or more. A small-diameter portion having a diameter-increasing portion that increases in diameter as it goes toward the shank from the same outer diameter as the blade portion to the same outer diameter as the shank between the blade portion and the shank. Carbide end mill. 2. The small-diameter carbide end mill according to claim 1, wherein the diameter-increasing portion has a diameter that is smoothly and continuously increased from the blade portion to the shank. The diameter increasing portion is
The taper portion is continuously provided with a taper portion in which the diameter dimension increases linearly from the same outer diameter as the blade portion toward the shank side, and
A concave arc-shaped portion that is smoothly connected to the tapered portion and whose diameter is increased nonlinearly so that the axial outline is a concave arc shape and reaches the outer peripheral edge of the shank. The small-diameter carbide end mill according to claim 2, further comprising a taper portion and the shank. The small-diameter carbide end mill according to claim 3, wherein the concave arcuate portion is curved with a constant radius R in the axial outline. 5. The small-diameter carbide end mill according to claim 4, wherein the tip half angle α is in a range of 15 ° to 35 °, and the taper half angle β of the tapered portion is in a range of 5 ° or more and less than 20 °. .

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