JP3957230B2 - Ball end mill - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a ball end mill mainly used in a machine tool.
[0002]
[Prior art]
In a ball end mill used for three-dimensional curved surface processing of a die or the like, in recent years, there is an increasing need for directly ball-end milling a high-hardness mold material that has been previously quenched. In order to satisfy this requirement, ball end mills made of cemented carbide have become widespread and have been effective in high-speed cutting simultaneously with cutting of hard materials.
In the conventional ball end mill shown in FIG. 1, the rake angle of the ball blade portion is set to a positive value for the purpose of improving the sharpness. (Hereinafter, abbreviated as Conventional Example 1) As an improvement of this, there is one in which the rake angle of the ball blade portion shown in FIG. 2 is set to a negative value. For example, a ball end mill disclosed in JP-A-6-218612 has a rake angle of -20 ° to -40 ° at the center of the ball blade and a rake angle of -15 ° to -35 ° at the outer periphery. And each with a specific clearance angle. (Hereinafter, abbreviated as Conventional Example 2)
[0003]
[Problems to be solved by the invention]
However, if the rake angle is set to a negative value, the resistance applied to the cutting edge during cutting increases due to the dullness of the cutting edge, excessive generation of cutting heat at the cutting point, and thermal wear of the cutting edge, causing tool life. To shorten. The ball end mill has a cutting edge near the center of rotation, but the cutting speed of this part approaches 0 regardless of the number of rotations of the tool. It is a cause of obstruction.
Therefore, when the rake angle of the ball blade is set to a negative value, there is a problem that a cutting-inhibiting factor is superimposed on this portion, and an effect cannot be expected in cutting a hard material.
[0004]
[Object of the present invention]
The present invention has been made in order to solve the above-mentioned problems. In particular, a three-dimensional curved surface machining of a mold is used to cut a hardened material that has been pre-quenched to reduce chipping and obtain a long life. -Provide end mills.
[0005]
[Means for solving problems]
In order to achieve the above object, the present invention provides a solid ball end mill comprising a plurality of outer peripheral cutting edges having a twist and a substantially 1/4 circle arc-shaped ball edge connected to the outer peripheral cutting edge. Based on the position at which the rake angle in the radial cross section from the center of the arc of the ball blade protrudes forward in the rotational direction with respect to the line connecting the outer peripheral cutting edge and the tool axis in the tool end view, volume of the negative value in the portion near the outer peripheral cutting edge from the outermost protruding position, characterized in that Oite was changed to 0 ° ~ + 10 ° to the portion close to the tool axis than the outermost protruding position - It is a le end mill. Further, the ball end mill is characterized in that the negative value is up to -20 ° .
[0006]
[Action]
Ball cutting a three-dimensional curved surface - le end mill, must be guaranteed machinability to any direction for the cutting feed direction is not constant. When cutting in the horizontal direction, cutting is mainly performed at the center of rotation of the cutting edge, that is, the nose part, and the nose is easily rubbed and accompanied by heat generated by friction. Further, in the case of a steeply inclined surface, the outer peripheral portion of the ball blade is cut, and this portion has a high cutting speed. Therefore, if sufficient cutting edge strength is not maintained, chipping and thermal damage are severe and performance is impaired. These are phenomena related to the chip dischargeability as well as the cutting performance of the cutting edge. The direction in which the chips are generated in the ball blade portion is substantially the direction from the ball blade toward the center of the arc on the radiation. If the rake angle near the nose is negative, it will be subject to a large cutting resistance, and the vicinity of the nose will need to maintain the cutting edge strength, so the chip groove will be bent sharply due to the shallow groove depth. It causes wasteful power and heat generation. On the other hand, in the portion close to the outer peripheral cutting edge, the effect of a twisting blade acts, and even if the rake angle is a negative value, the chips are changed in the direction toward the tool axis and discharged.
Therefore, a negative value that increases the cutting edge strength is useful for extending the service life, because the burden of unnecessary force and heat is small.
[0007]
Here, the flow of chips is affected by the groove depth of the outer peripheral cutting edge or the core thickness of the end mill. A ball blade of a ball end mill of a twisted blade always protrudes forward in the rotational direction with respect to a line segment connecting the outer peripheral cutting edge and the tool axis in the end view. The most protruding part is usually close to the part where the outer peripheral cutting edge has the deepest groove depth, that is, the outer peripheral side from this part is convenient for chip removal because the ball blade is open in the tool axis direction. Good. On the other hand, on the axial center side, since the cutting edge strength needs to be maintained as described above, the depth of the cutting groove becomes shallow, and it is desirable to increase the rake angle in order to secure the cutting groove. Taking these into consideration, the cutting edge strength is strengthened with a negative value, preferably up to -20 ° , in the portion closer to the outer peripheral cutting edge, with the position that protrudes most forward in the rotational direction as the reference. By having a portion that is not negative in the near portion, preferably a portion that is 0 ° to + 10 °, the chip removal is facilitated and the machinability is improved.
[0008]
Here, the rake angle is determined in consideration of the machinability and the cutting edge strength, and the portion close to the outer peripheral cutting edge may be selected within the range of -20 ° from the balance with the helix angle. In the portion close to the center, the blade groove depth is shallow near the axial center, and the rake angle must approach 0, so + 10 ° may be changed as a limit. If the rake angle of the nose portion is a negative value, a force that pushes the end mill in the axial direction acts, so that the vibration in the axial direction is excited and the cut surface is deteriorated. In the present invention, this vibration is also reduced and it has characteristics suitable for high-speed cutting.
[0009]
【Example】
FIGS. 3 and 4 show an embodiment of the present invention. As Example 1 of the present invention, a ball of 10 mm diameter, 15 mm blade length, 100 mm overall length, 2 blades and a twist angle of 30 ° made of ultrafine cemented carbide. In the end mill, the rake angle near the tool axis is 0 °, and the rake angle near the peripheral cutting edge is −15 °. Furthermore, as Example 2 of the present invention, a rake angle of the portion near the tool axis was set to + 3 ° at the maximum, and a rake angle near the outer peripheral cutting edge was set to −10 °.
FIG. 5 shows a change in the rake angle. The present invention example 1 changes as shown by a solid line a by taking the above configuration, and similarly, the present invention example 2 shows a broken line b, and FIG. The conventional example 1 shown is at the position of the thin lines d and e, and the conventional example 2 shown in FIG.
The above tool was subjected to three-dimensional cutting using a machining center.
The SKD61 material tempered to a hardness of 42 HRC was selected as the work material, and the concave curved surface was scanned and cut at a rotational speed of 6000 rpm, a feed rate of 2000 mm / min, and a cutting depth of 0.3 mm. Despite the curved cutting of the high-hardness work material, the cutting edge wear of the ball blades of Examples 1 to 3 of the invention was a normal wear form without abnormal damage such as chipping or chipping.
The ball end mill of Conventional Example 1 used for comparison produced chipping particularly in a portion close to the outer peripheral cutting edge, leading to an early tool life. Further, in the case of the conventional example 2, chipping is not recognized, but the cutting surface is severely peeled due to rubbing wear due to the influence of the cutting property deterioration due to the negative rake angle in the portion near the tool axis. Was presented.
[0010]
【The invention's effect】
As described above, according to the present invention, as a result of improvement in the ball end mill for high-hardness materials particularly used for three-dimensional curved surface processing such as a mold, the generation of unnecessary force and heat near the nose. A ball end mill was obtained that reduced tool wear, had good chip discharge near the outer peripheral cutting edge, high cutting edge strength, low chipping, and long tool life.
[Brief description of the drawings]
FIG. 1 is a front view of an example of a conventional product.
FIG. 2 is a partially enlarged view for displaying a rake angle as an example of another conventional product.
FIG. 3 shows a partially enlarged view for displaying a rake angle according to an embodiment of the present invention.
FIG. 4 shows a bottom view of FIG.
FIG. 5 is an explanatory diagram showing changes in the rake angle of the ball blades of the present invention and a comparative example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Main body 2 Blade part 3 Peripheral blade 4 Ball blade 5 Nose 6 Rake angle of a ball blade 7 Rake angle 8 of an outer peripheral blade

Claims (2)

In a solid ball end mill comprising a plurality of outer peripheral cutting edges having a twist and a substantially 1/4 circular arc-shaped ball edge connected to the outer peripheral cutting edge, a radial direction from the arc center of the ball edge is provided. In the portion where the rake angle in the cross section is closer to the outer peripheral cutting edge than the most protruding position with reference to the position that protrudes most forward in the rotational direction with respect to the line segment connecting the outer peripheral cutting edge and the tool axis in the tool end view. from a negative value, volume, characterized in that Oite was changed to 0 ° ~ + 10 ° to the portion close to the tool axis than the outermost protruding position - le end mill. 2. The ball end mill according to claim 1, wherein the negative value is up to -20 [deg .].

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