JP3840659B2 - Ball end mill and processing method thereof - Google Patents

Description

  The present invention relates to a ball end mill excellent in the sphericity of a ball blade used for three-dimensional machining of a mold and the like, and a manufacturing method thereof.

As a ball end mill used for three-dimensional machining of molds, etc., a ball end mill having a clearance angle larger toward the center of rotation than the clearance angle on the outer peripheral edge side of the ball blade in order to improve chip discharge performance of the ball end mill (Patent Document 12) ) In addition, a multi-blade ball end mill having three or more blades is used to perform high-efficiency machining, and each land of a parent-child blade type having a main cutting edge and a secondary cutting edge (Patent Document 3). There is a shaft centering type structure in which all the edges of the ball blade are in contact with the center of the apex of the entire bottom blade (Patent Document 4), and a nose portion of the ball blade is provided with a substantially V-shaped notch (Patent Document 5). . In the parent and child blade type of Patent Document 1, cutting is performed only with the parent blade near the axis, and the feed speed cannot be increased. If the feed speed is increased, the burden on the parent blade increases, and the axis of the secondary cutting edge, that is, the blade axis. Chipping and loss occurred due to the edge at the center side. The shaft centering type of Patent Document 2 is very difficult to manufacture. In particular, the ball blade provides a predetermined clearance angle, so that the vicinity of the shaft center portion is located in the shaft center portion in order to avoid grinding stone interference or grinding wheel interference with the next blade. Protrusion remains and rounding accuracy near the shaft center is difficult to obtain, and those with a notch of Patent Document 3 have a large rounding accuracy at the notch, and the rounding accuracy of the ball end mill itself is not obtained, and there is a problem in machining accuracy. there were. In finishing with a ball end mill, machining accuracy is important and good sphericity of the ball blade's rotation trajectory is required. However, in order to give a predetermined clearance angle to the ball blade, there are two blades near the shaft center. The radius accuracy is greatly reduced due to the clearance angle, and in the case of three or more blades, the wheel cannot be passed over the center of the shaft to avoid interference with the next blade. However, the sphericity of the rotation trajectory of the ball blade could not be obtained, and there was a problem with the rounded accuracy.
JP 2002-52412 A JP-A-6-218612 JP-A-6-155126 JP-A-10-128611 JP-A-11-216608

  An object of the present invention is to provide a ball end mill capable of improving the sphericity of the rotation trajectory of the ball blade and obtaining good roundness accuracy and obtaining good machining accuracy.

The present invention relates to a ball end mill having a plurality of ball blades at the end of the end mill, and a clearance angle in the vicinity of the axial center between the vicinity of the axial center of 20% or less of the radius of the ball blade and the vicinity of the other outer peripheral portion. the provided less than around 該Gaishu section, the flank width of the near axial eccentric part is a ball end mill, wherein the expansion gel toward the shaft center, the processing method, contact the processing method of the ball end mill In the first step, the vicinity of the outer periphery of the ball blade is ground toward the axis while providing a predetermined clearance angle on the flank face toward the axis, before the grinding stone interferes with the next blade. In the second step, the clearance angle is smaller than the vicinity of the outer periphery and the track is shifted toward the rake face by the rotation angle around the end mill axis, and from the outer periphery near the axis. performs a grinding toward the axial center, in the vicinity of the shaft heart unit The lower surface width processing method of the ball end mill, characterized in that processing to so that spread toward the axis is.

  By applying the present invention, it is possible to provide a ball end mill that can improve the sphericity of the rotation trajectory of the ball blade and obtain good roundness accuracy and good machining accuracy, and a method for manufacturing the same.

In the present invention, the ball blade has a clearance angle that is smaller in the vicinity of the axial center of the end mill than in the vicinity of the outer peripheral portion. can Earl accuracy in the vicinity of heart unit obtaining, improving mill tip overall Earl accuracy. At the time of cutting, there is an effect that it is possible to suppress wear near the shaft center, and high-precision machining can be continued.
Processing method of the present invention, Oite the processing method of the ball end mill, the first step, the vicinity of the outer peripheral portion of the ball cutting edge, while providing a predetermined relief angle flank towards the axis, toward the axis Grinding is performed, and the grinding wheel is released before the grinding wheel interferes with the next blade. In the second step, the clearance angle is set smaller than the vicinity of the outer peripheral portion, and the rake face side is rotated at the rotation angle about the end mill axis. in shifting trajectory, perform grinding from the outer peripheral side in the vicinity of the shaft eccentric part toward the axis, and wherein processing the flank width of the near axial eccentric part, to so that spread toward the axis It is a processing method of a ball end mill that can improve the sphericity and obtain a good roundness accuracy.

As a form of the present invention, by setting the clearance angle near the axis of the end mill to an angle of 5 ° or less, the radius accuracy of the entire end mill is further improved, and wear near the axis is suppressed in the cutting process. The effect that can be improved. If it exceeds 5 °, it will be easy to produce convex protrusions because it will avoid interference with the grindstone at the end of the end mill, and it will be difficult to obtain rounded accuracy. Becomes worse. Preferably it is 3 ° or less. The reason why the ball blade is a bottom blade such as a center cut is that the cutting load can be distributed to each ball blade, there is no difference in the cutting edge length of the ball blade, the machining surface becomes regular, and a good machining surface is obtained. The effect of improving the radius accuracy is great because it is easy to cause interference of the grindstone at the tip. The reason why the number of ball blades is 3 or more is to increase the feed rate and improve the machining efficiency by increasing the number of blades, but due to the interference of the grindstone at the tip of the end mill with the conventional multi-blade. Since the protrusions are formed, they cannot be used for finish cutting, and the effect of improving the radius accuracy is very large. Unequal division can reduce cutting resistance and suppress chatter vibration as compared with a normal equal division product, and can perform highly efficient and highly accurate machining. The reason why the vicinity of the shaft center is in the range of 20% or less of the ball radius centered on the shaft center when the end mill is viewed from the bottom is that the cutting ability of the ball blade tends to be inferior if it is larger than 20%. The following is desirable. In order to suppress the amount of abrasion at the end mill end, 5% or more is desirable. The reason why the diameter of the circumscribed circle is 0.03 mm to 0.3 mm in the remaining part of the center is that the strength in the vicinity of the shaft center is improved while maintaining the roundness accuracy and the cutting ability, and high-precision machining can be further continued. If it is smaller than 0.02 mm, the strength of the central part is not sufficient and wear cannot be suppressed, and the rounding accuracy of the remaining part cannot be maintained during cutting, and if it exceeds 0.3 mm, the remaining part is not machinable. Therefore, cutting resistance and wear at the tip end increase, chattering and stuffiness occur, and the difference in cutting state between the ball blade and the remaining part of the core is conspicuous and the machined surface deteriorates. Preferably it is 0.08 mm-0.2 mm. The remaining portion may have a chisel edge-shaped ridge, and the chisel edge-shaped ridge can reduce the contact portion with the workpiece, thereby reducing cutting resistance and enabling highly efficient and highly accurate machining. Hereinafter, the present invention will be described in detail based on examples.

Example 1
FIG. 1 and FIG. 2 show Example 1 of the present invention, which is a solid ball end mill coated with 3 μm of a TiAlN coating made of an ultrafine particle cemented carbide having a ball radius of 2 mm and 3 blades.
The ball blade 1 is obtained by grinding the flank face of the ball blade in the following procedure with a clearance angle of 17 ° in the normal direction and 1 ° in the vicinity 2 of the axial center of the end mill.
a. A predetermined clearance angle of 17 ° is provided on the flank surface near the outer periphery of the ball blade toward the axis, and grinding is performed to the vicinity of the axis.
b. Relieve grinding before grinding interferes with the next cutting edge, the relief angle trajectories which are shifted in 3 ° rake face side in the rotational angle around the set end mill axis to 1 °, from the outer peripheral side in the vicinity of the shaft eccentric part Grinding toward the axis .
c. Flank width near axial eccentric part is processed into a so that spread toward the axis.
The accuracy of the ball blade was within a range of ± 0.0032 mm with respect to the ball radius of 2 mm including the vicinity of the axial center.

A three-blade ball end mill with the same dimensions is manufactured with the parent and child blade described in Patent Document 3 as Conventional Example 2, the shaft alignment described in Patent Document 4 as Conventional Example 3, and the notch described in Patent Document 5 as Conventional Example 4. A cutting test was carried out after measuring the radius accuracy.
The radius accuracy of Conventional Example 2 is ± 0.005 mm, which is substantially equivalent to Example 1 of the present invention, Conventional Example 3 is +0.025 mm, and Conventional Example 4 has a significantly reduced radius accuracy at the notch portion.

(Example 2)
Using invention example 1, conventional examples 2 and 3, pre-hardened steel with a hardness of HRC 40, work speed of 8000 min ⁻¹ , feed rate of 2400 mm / min, cutting amount, 0.2 mm in the end mill axial direction, pick direction The finishing accuracy of the three-dimensional shape was performed by wet cutting using a water-soluble cutting fluid, and the processing accuracy and surface were investigated. Conventional Example 4 did not perform a cutting test because of poor roundness accuracy.
In Example 1 of the present invention, the amount of wear in the vicinity of the axial center is almost as small as about 0.005 mm even when the cutting length is 500 m, and the form error of the three-dimensional shape is 5 μm or less, and the machining surface is rough. The maximum height surface roughness Rz was as good as 3 μm. In Conventional Example 2, chipping and chipping occurred in the initial stage of cutting, and the machining accuracy and surface roughness were not obtained, resulting in a life. Conventional Example 3 had a foam error exceeding 30 μm due to the foam error and caused deep scratches on the processed surface, and the processed surface roughness was inferior to 37 μm at the maximum height surface roughness Rz.

Example 3
As Example 5 of the present invention, the same specification as Example 1 of the present invention, the clearance angle in the vicinity of the axial center of the end mill is 0.1 °, Example 6 of the present invention is 0.5 °, Example 7 of the present invention is 3 °, Example of the present invention 5 ° was prepared as 8 and 7 ° was manufactured as Example 9 of the present invention.
Examples 5 to 7 of the present invention have good rounding accuracy of ± 0.0030 mm, and even in the cutting test, the amount of wear near the shaft center is almost not at the cutting length of 100 m, and is about 0.005 mm even at the cutting length of 500 m. The form error of the three-dimensional shape was 5 μm or less, and the processed surface roughness was good with a maximum height surface roughness Rz of 3 μm. Invention Example 8 was slightly inferior at ± 0.0050 mm, but the abrasion amount was 0.008 mm when the cutting length was 500 m, and the foam error was 10 μm or less. Invention Example 9 had inferior radius accuracy of +0.012 mm, a foam error of 15 μm, scratched on the processed surface, and the processed surface roughness was inferior at 22 μm in terms of the maximum height surface roughness Rz.

Example 4
As Example 10 of the present invention, the diameter of the circumscribed circle with the same specification as that of Example 1 of the present invention is 0.01 mm, 0.02 mm as Example 11 of the present invention, and 0.02 mm as Example 12 of the present invention. 04 mm, 0.06 mm as Invention Example 13, 0.08 mm as Invention Example 14, 0.1 mm as Invention Example 15, 0.15 mm as Invention Example 16, and 0.15 as Invention Example 17. 2 mm, 0.25 mm as Invention Example 18, 0.3 mm as Invention Example 19, 0.35 mm as Invention Example 20, and 0.35 mm as Invention Example 20 were measured. It was.
Inventive Examples 10 to 20 have good radius accuracy of ± 0.0025 to 0.0050 mm, and the wear amount in the vicinity of the axial center is as small as 0.006 mm or less even when the cutting length is 500 m. 11 to 13 were 0.0050 mm or less, Invention Examples 14 to 20 were 0.0032 mm or less, and the foam error was 5 μm or less. The machined surface roughness was good at 5 μm or less except that Examples 18 and 19 of the present invention produced a slight stagnation, and Example 20 of the present invention was slightly inferior with a maximum height surface roughness Rz of 7 to 12 μm due to mushy chatter. there were.

(Example 5)
As shown in FIGS. 3 and 4, the inventive example 21 is provided with a chisel edge-shaped ridge 6 that extends in the direction of the axial center part 2 in the direction of the axial center part 2 in the remnant part 5 in the same specification as the inventive example 15 as shown in FIG. A cutting test was performed after measuring the radius accuracy in the same manner as in the example. The roundness accuracy was good, the cutting state was further stabilized, and the machining accuracy and the surface roughness were further improved.

(Example 6)
As Example 22 of the present invention, three ball blades having the same specifications as Example 1 of the present invention were arranged in unequal divisions at 115 °, 120 °, and 125 ° division angles, respectively, and the R accuracy was measured in the same manner as in the example. A cutting test was conducted. The rounding accuracy is in the range of ± 0.003 mm, which is good rounding accuracy equivalent to Example 1 of the present invention, and the cutting state is very stable with less cutting resistance and no chatter / vibration. The roughness was further improved.

(Example 7)
Invention Example 23 was the same as Invention Example 1, and the flank face of the ball blade was ground by the following procedure.
a. In the first step, a predetermined clearance angle is provided on the flank face near the outer peripheral portion of the ball blade toward the axis, and grinding is performed to the vicinity of the axis.
b. The shaft center is a track shifted gradually to the rake face side by 3 ° with the rotation angle about the end mill axis so that the clearance angle becomes 1 ° at the shaft center. Grinding is performed from the outer peripheral side near the shaft center.
c. Flank width near axial eccentric part is processed into a so that spread toward the axis.
These grinding processes result in a continuous ground surface and improved sphericity, and the radius accuracy is in the range of ± 0.002 mm with respect to the ball radius of 2 mm including the vicinity of the shaft center. Better machining accuracy and machined surface roughness than in Example 1 were obtained.

FIG. 1 is a bottom view of Example 1 of the present invention. FIG. 2 shows an enlarged view of the main part of FIG. FIG. 3 shows a bottom view of Example 21 of the present invention. FIG. 4 shows an enlarged view of the main part of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ball blade 2 Shaft center part 3 Relief surface near the outer peripheral part of a ball blade 4 Relief face near the shaft center part of a ball blade 5 Remaining part 6 Chisel edge-shaped edge

Claims (9)

In a ball end mill having a plurality of ball blades at the end of the end mill, a clearance angle near the shaft center portion is set between the vicinity of the shaft center portion of 20% or less of the radius of the ball blade and the other outer periphery portion. less than near provided, the flank width of the near axial eccentric part, a ball end mill, wherein the expansion gel towards the axis. 2. The ball end mill according to claim 1, wherein a clearance angle in the vicinity of the axial center portion is set to 5 ° or less. 3. The ball end mill according to claim 1 or 2, wherein the ball blade is a center cut and an equal bottom blade. 4. The ball end mill according to claim 1, wherein the number of blades is three or more. The ball end mill according to claim 1 or 4, wherein the ball blades are arranged in unequal divisions. The ball end mill according to any one of claims 1 to 5 , wherein a center-remaining portion is provided in an axial center portion of the end mill, and a diameter of a circumscribed circle of the center-remaining portion is 0.03 mm to 0.3 mm. Ball end mill. 7. The ball end mill according to claim 6 , wherein a chisel edge-shaped ridge is provided in the center-remaining portion. Oite the processing method of the ball end mill, the first step, the vicinity of the outer peripheral portion of the ball cutting edge, while providing a predetermined relief angle flank towards the axis performs a grinding toward the axis, following The grinding wheel is released before the grinding wheel interferes with the blade. In the second step, the clearance angle is set smaller than the vicinity of the outer peripheral portion, and the shaft is shifted to the rake face side by the rotation angle around the end mill axis. perform grinding from the outer peripheral side in the vicinity of eccentric part toward the shaft center, a flank width near axial eccentric part, the processing method of the ball end mill, characterized in that processing to so that spread toward the axis. In the processing method of the ball end mill of claim 8 wherein the relief angle in the vicinity of the outer peripheral portion of the ball cutting edge, the processing method of the ball end mill being characterized in that gradually decreases toward the axial center of the end mill.

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