JPH023374Y2 - - Google Patents

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a ball end mill, in particular, which not only prevents chatter during cutting and improves machining accuracy, but also reduces chip discharge resistance and improves chip removal. The present invention relates to a ball end mill that not only improves ejection performance and thereby improves workability and productivity, but also significantly extends tool life.

<Conventional technology> Ball end mills have traditionally been used for engraving molds, etc., but mainly due to the arrangement of the cutting blades,
There were some unsatisfactory points in terms of machinability.

That is, as shown well in Figure 3,
Generally, the cutting edge of a conventional ball end mill a has a bottom cutting edge b and a circumferential cutting edge c arranged point-symmetrically with respect to the axial center for reasons of tool manufacturing.
The bottom cutting edge b and the peripheral cutting edge c are formed by arranging them at equal dividing angles.

For example, in the case of a type in which the bottom cutting edge b and the circumferential cutting edge c each have two blades, the bottom cutting edge b makes an angle of 180° to each other, and the circumferential cutting edge c makes an angle of 180° to each other.
180°, and each blade is
They are arranged at 90° angles.

Therefore, the cycle of the cutting force applied to the workpiece by the cutting edge is always constant at the same cutting speed (same rotational speed). Therefore, if the period matches the natural frequency of the cutting tool or the natural frequency of the workpiece, a resonance phenomenon occurs and the depth of cut becomes unstable due to the so-called chatter phenomenon (irregular small oscillations). Due to regular fluctuations, the machined surface becomes wavy, which not only reduces the precision of the machined surface, but also causes damage such as chipping of each cutting edge of the ball end mill.

Furthermore, since the angles formed by the bottom cutting blade and the peripheral cutting blade are equal, the sizes of the tip pocket d for the bottom cutting blade and the tip pocket 6 for the peripheral cutting blade are regulated, which improves chip evacuation. Not only is this unsatisfactory, but it also has the disadvantage of easily causing chipping of the cutting edge.

Therefore, due to these drawbacks, the cutting speed is suppressed to a low level, resulting in not only low productivity but also
There is a problem in that the machining accuracy of the cutting surface is poor.

On the other hand, in conventional spiral end mills,
The leads of each cutting blade formed in a spiral shape on the circumferential surface of the cutter body are formed at different angles (for example, ±5 degrees around 45 degrees), and the pitch of the cutting blades in each cross section is set at different angles (for example, around 60 degrees). ±2°) (Special Publication Publication No. 30-5244
issue). However, what is formed unevenly is the lead of the cutting blade which is spirally formed on the circumferential surface of the cutter body, and the leads have different inclinations, and the angles between the rays from the central axis to the cutting blade are different. By tightening and eliminating periodicity,
The purpose of this is to suppress the chatter phenomenon, and the pitch of each cutting edge is not actively made to be unequal by making the leads unequal, but by passively making the pitch of each cutting edge unequal. The angles between each cutting edge in any cross section are not necessarily unequal, and depending on the cross section, the angle between each cutting edge may be equally divided or approximate to equally divided parts. (for example, the mutual angles of the cutting blades with leads of 45°, 40°, and 50° in Figure 3 of the above publication are the same), which deviates from the applicable setting conditions. There was a problem that the objective could not be achieved.

<Problems to be solved by the invention> In view of these conventional drawbacks, the main purpose of the present invention is to increase the feed rate by preventing chatter and improving chip evacuation, thereby expanding the machining range. Furthermore, cutting resistance is significantly reduced, machinability is improved, cutting speed is increased, and it can be used in a wide range of rotation speeds, resulting in high productivity, excellent machining accuracy, and extended tool life. Our goal is to provide ball end mills that can be used.

<Means for solving the problem> According to the present invention, this purpose is to improve the angle between the bottom cutting edge and the circumferential cutting edge, or the angle between each bottom cutting edge or each circumferential cutting edge. At least one of the angles formed is divided by angles that are not equally divided, and the circumferential cutting edge is separated from the bottom cutting edge in the rotation direction side, and the circumferential cutting edge is separated from the bottom cutting edge in the rotation direction side. This is achieved by providing a ball end mill characterized in that the angle at the angle is larger than the equal division angle.

<Operation> In this way, by proactively dividing the angle between each cutting edge unequal, the period of the cutting force is made indeterminate, and the period of the natural frequency of the cutting tool or workpiece material is continuous with the cutting period. This prevents the occurrence of resonance phenomena, prevents the chattering phenomenon that occurs due to the equal division angle between the cutting edges of conventional ball end mills, and improves the accuracy of the machined surface. I will do it.

Furthermore, the circumferential cutting edge is separated from the bottom cutting edge in the direction of rotation, and the angle of the circumferential cutting edge in the rotational direction with respect to the bottom cutting edge is formed at an angle that is larger than the equal division angle. The chip pocket for the bottom cutting blade is enlarged to enlarge the chip discharge space, thereby reducing the chip discharge resistance and resulting in extremely good chip discharge performance.

Therefore, the cutting speed is significantly increased, productivity is greatly improved, chatter is prevented, machining accuracy is significantly improved, and the life of the cutting tool is also significantly extended.

Embodiments Specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

1 and 2, a ball end mill 1 has a ball end mill main body 3 having a shank 2 at the rear end, and a tip 4 of the ball end mill main body 3 having a hemispherical shape.

The tip portion 4 is provided with a pair of bottom cutting blade tip pockets 5 and a peripheral cutting blade tip pocket 6 facing each other in the intersecting direction when viewed from the bottom.

A bottom cutting blade tip 7 is fixed to the rear side in the rotational direction of the bottom cutting blade tip pocket 5 by means such as brazing, and a peripheral cutting blade is attached to the rear side of the peripheral cutting blade tip pocket 6 in the rotational direction. A chip 8 for use is fixed by means such as brazing.

The bottom peripheral cutting edge tip 7 has a bottom cutting edge 9 at the tip in the rotational direction.

The bottom cutting blade 9 is formed into an arc shape with a radius of curvature R that allows the starting end 9a to be located near the rotation center (axis center) and to cut the workpiece material while making point contact with the workpiece material when viewed from the bottom. , the radius R is substantially the same over the entire length of the circular arc, and the curve is convex in the direction of rotation. Further, the blade 9 has a starting end 9a and a terminal end 9b located on the same radiation line from the shaft center, and a distance Le between the terminal ends 9b is approximately 80% of the diameter D of the ball end mill body 3. Moreover, it is formed in a circular arc shape, with the tip end (apex) of the blade 9 in the rotational direction located in the vicinity of 1/2 circle of the diameter D of the ball end mill main body 3. The above radius of curvature is approximately 25% to 75% of the diameter D of the ball end mill body 3.
(1/4 to 3/4), and this may be changed depending on the material of the workpiece, the material of the bottom cutting edge 9, and other conditions.

On the other hand, the circumferential cutting edge tip 8 has a circumferential cutting edge 10 at its tip.

The circumferential cutting edge 10 has a distance Lr between starting ends 10a in the vicinity of about 70% of the diameter D of the ball end mill main body 3 when viewed from the bottom, and a terminal end 10b is on the outer periphery of the ball end mill main body 3 and has an axis passing through the starting end 10a. Located at the rear of the rotation direction from the radiation from the center,
As clearly shown in FIG. 1, the terminal end 10b is formed at a right-handed twist angle (positive rake angle) located rearward than the starting end 10a when viewed from the side.

Therefore, the terminal end of the bottom cutting blade 9 and the starting end of the peripheral cutting blade 10 are in a state in which they each overlap (Lo) in the radial direction by about 5% of the diameter D of the ball end mill body 3 on the rotation locus. is formed.

The angle between the bottom cutting blades 9 in one direction (for example, the rotational direction) is 180° + α°, and the angle in the other direction (for example, the counter-rotational direction) is 180° - α°, so that the angle between the bottom cutting blades 9 is 180° + α°. They are divided and arranged so that the mutual angle in one direction (for example, counter-rotation direction) is slightly deviated from the dividing angle of 180°.

Similarly, the circumferential cutting edges 10 have an angle of 180° + β° in one direction (for example, the counter-rotation direction), and an angle of 180° - β° in the other direction (for example, the rotational direction). They are arranged so that the mutual angle in one direction (for example, rotational direction) is slightly deviated from the equal dividing angle of 180° by 180°.

Furthermore, the mutual angles between the bottom cutting edge 9 and the peripheral cutting edge 10 are θ1=90°−(α+β)°, θ2=90°+(α+
β + r) °, θ3 = 90 ° - (β + r) °, θ4 = 90 ° + r
All angles are divided and arranged at different angles at a ratio of 90°, which is an equal dividing angle.

That is, the angles θ2 and θ4 formed by the circumferential cutting edge 10 on the rotational direction side with respect to the bottom cutting edge 9 are such that the circumferential cutting edge 10 is separated in the rotational direction side and becomes larger than the equal division angle. Along with this, the distance between the peripheral cutting edge 10 and the bottom cutting edge 9 in the rotational direction has also increased, and the tip pocket 5 for the bottom cutting edge has been enlarged compared to the same pocket with the conventional equally divided angle. It is formed.

As mentioned above, the angle between the bottom cutting blades 9 and
By dividing the angle between each circumferential cutting edge 10 and the angle between each bottom cutting edge 9 and the circumferential cutting edge 10 by angles that are not equally divided, each cutting edge 9, 10
Therefore, the period of the cutting force applied to the workpiece always differs even at the same cutting speed (same rotational speed).

Therefore, even if the period matches the natural frequency of the cutting tool, the natural frequency of the workpiece, or the natural frequency of the cutting machine, it is only between the single cutting edges 9 and 10. and each cutting edge 9, 10
Since the angles formed by each other are different, the period becomes irregular in one rotation, and the natural frequencies do not match continuously.

As a result of this, resonance phenomena are prevented, and as a result, occurrence of chatter phenomena is also prevented.

In addition, as mentioned above, there is a tip pocket 5 for the bottom cutting blade.
As a result of being enlarged, the chip discharge space is enlarged, so the chip discharge resistance is reduced and the chip discharge performance is improved.

In this embodiment, the angle between the bottom cutting edges 9, the angle between the circumferential cutting edges 10, and the angle between the bottom cutting edge 9 and the circumferential cutting edge 10 are all equally divided. What is divided by an angle that is not
Although shown as being optimal in terms of preventing chatter, the angle between the bottom cutting edges 9 or the circumferential cutting edge 10
Even if only one of the mutual angles is divided by an angle that is not equally divided, it is suitable for preventing the occurrence of chatter.

The material for the bottom cutting edge tip 7 and the peripheral cutting edge tip 8 is preferably a cemented carbide whose main component is tungsten carbide (WC), but this may vary depending on the material of the workpiece and other conditions. In addition, the material may be appropriately selected from among high-speed steel (high speed steel), cermet, ceramic, and other materials.

Furthermore, in this embodiment, these tips 7 and 8 are fixed to the ball end mill body 3 with brazing, but the tips 7 and 8 can be detachably attached to the body 3 with a crank bolt or the like. It may also be a throw-away type.

Further, in this embodiment, the bottom cutting blade 9 and the peripheral cutting blade 10 are each of two-blade type, but the cutting blades 9 and 10 may be of single-blade type or three-blade type. It can also be applied to multi-blade types with more than one blade.

Further, in this embodiment, the starting end 9a of the bottom cutting blade 9 is slightly spaced apart from the axial center of the ball end mill main body 3, but it may be aligned with the coaxial center.

Further, in this embodiment, each circumferential cutting edge 9 is formed point-symmetrically with respect to the axial center of the ball end mill main body 3, but even if it is formed eccentrically with respect to the coaxial center, good.

Furthermore, in this embodiment, the terminal end 9b of the bottom cutting blade 9
Although the ball end mill body 3 is positioned inside the diameter D of the ball end mill body 3, the present invention can also be applied to a machine in which the terminal end 9b extends to the outer periphery of the body 3.

Next, an experimental example of this embodiment will be explained.

A comparative cutting test between the conventional example and this example was conducted using a vertical milling machine using the following tool specifications and work material specifications.

(1) Tool specifications Diameter of ball end mill: D=50mm Angle between each cutting edge in conventional example: Equal division angle Angle between each bottom cutting edge in this example: Angle that is not evenly divided Angle between each circumferential cutting edge in this example: Angle that is not evenly divided Conventional radius of curvature: r=50mm Curvature radius of this example: R=50mm Distance between bottom cutting edge starting end and shaft center: 1=1mm Bottom cutting blade type: 2-flute type Peripheral cutting blade type: 2-flute type Installing the tip for the bottom cutting blade: Fixed with brazing Material of conventional bottom cutting edge and peripheral cutting edge: Cemented carbide M20 Material of bottom cutting blade in this example: Cemented carbide M20 Material of peripheral cutting edge in this example: Cemented carbide M20 (2) Work material specifications Material: FC−25 The results of the above cutting test are as follows.

Cutting speed Feed (m/min) (mm/rev) This example 135 1610 Conventional example 126 700 From the results of the cutting test above, this example
It has been found that, compared to conventional products, chatter is prevented during cutting, cutting resistance is reduced, and chips are smoothly discharged. As a result,
The cutting speed and feed amount can be significantly increased without causing any problems, the tool life can be significantly extended, and the machining accuracy of the cutting surface can be significantly improved.

<Effects of the invention> As described above, according to the invention, by proactively dividing the angle between each cutting edge unequal, the period of the cutting force is made irregular, and the natural frequency of the cutting tool or workpiece is adjusted. This prevents continuous matching between the period of the cutting period and the cutting period.
Prevents the occurrence of resonance phenomena, prevents the chattering phenomenon that occurs due to the equally divided angles between the cutting edges of conventional ball end mills, improves the precision of the machined surface, and improves machining accuracy. There are advantages.

In addition, the circumferential cutting edge is separated from the bottom cutting edge in the rotational direction, and the angle of the circumferential cutting edge in the rotational direction with respect to the bottom cutting edge is formed at an angle that is larger than the equal division angle. The tip pocket for the bottom cutting blade is enlarged to expand the chip evacuation space and reduce the ejection resistance of the chips, resulting in extremely good chip evacuation, which improves cutting speed and productivity. There is.

As a result, the cutting speed and feed rate can be significantly increased by more than double without any problems, the machining range is greatly expanded, and the need for tool changes due to the material of the workpiece is reduced. In combination with this, there is an advantage that productivity is significantly improved to more than double.

In addition, the generation of wavy cut surfaces due to chatter is prevented, which not only significantly improves the machining accuracy of the workpiece surface, but also prevents the cutting edge of the cutting tool from chipping, significantly extending the tool life by more than doubling. It has the great effect of being able to expand.

[Brief explanation of the drawing]

FIG. 1 is a side view of a ball end mill provided with a bottom cutting edge and a peripheral cutting edge based on the present invention. FIG. 2 is a bottom view of FIG. 1. FIG. 3 is a bottom view of a conventional ball end mill with a bottom cutting blade. 1...Ball end mill, 2...Shank, 3
... Ball end mill body, 4 ... Tip part, 5 ...
...Tip pocket for bottom cutting blade, 6...Tip pocket for circumferential cutting blade, 7...Tip for bottom cutting blade, 8...Tip for circumferential cutting blade, 9...Bottom cutting blade, 9a...Starting end, 9b
...Ending end, 10...Peripheral cutting edge, 10a...Starting end, 1
0b...Terminal, D...Ball end mill body, R
...Radius of curvature of the bottom cutting blade, Le...Distance between the ends of the bottom cutting blade, Lr...Distance between the starting ends of the bottom cutting blade, Lo...
Overlap in the radial direction between the end of the bottom cutting edge and the beginning of the peripheral cutting edge on the rotation trajectory.

Claims (1)

[Claims for Utility Model Registration] (1) In a ball end mill in which a bottom cutting blade is provided at the tip of the ball end mill body and a circumferential cutting blade is provided from the outer periphery of the main body to the tip, At least one of the angles formed by the blade and the peripheral cutting edges, the angles formed by each of the bottom cutting blades, or the angles formed by each of the peripheral cutting blades is divided by an angle that is not equally divided,
Moreover, the circumferential cutting edge is separated from the bottom cutting edge in the rotational direction, and the angle of the circumferential cutting edge in the rotational direction with respect to the bottom cutting edge is an angle that is larger than the equal division angle. Ball end mill. (2) The ball end mill according to claim 1, wherein the angle between the bottom cutting blades is divided by angles that are not equally divided. (3) The ball end mill according to claim 1, wherein the angle between the circumferential cutting blades is divided by angles that are not equally divided. (4) The ball end mill according to claim 1, wherein the angle between the bottom cutting edge and the peripheral cutting edge is divided by angles that are not equally divided. (5) The utility model registration claim set forth in paragraph 1, characterized in that the angles formed by each bottom cutting edge and the angles formed by each circumferential cutting edge are divided by angles that are not equally divided. ball end mill.