JP2001009624A - End mill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve cutting performance by setting a shaft directional rake angle of a cutting edge of a position corresponding to specific % of an end mill radius from the rotational center to a specific value, and specifying the depth of a chip pocket in this position. SOLUTION: A shaft directional rake angle in a 4% position of an end mill radius from the rotational center is set to 0 deg. to -5 deg., and the depth 3 of a chip pocket is set not less than 5% of the end mill radius. Thus, a remarkable effect is obtained even for removing chips besides imparting cutting performance to a cutting edge 2 in the vicinity of the totational center. That is, the chip pocket houses the chips made by a chisel edge, and a rake angle of a negative angle takes the action for quickly keeping away the chips from a cutting position. Since the chips generated in the vicinity of the rotational center are little but become a cause of welding and abrasion to the cutting edge 2, a corresponding rake angle and the chip pocket are imparted to remove this cause to obtain an effect in both aspects of the tool service life and finishing surface accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an end mill mainly used for a machine tool, and more particularly to a three-dimensional curved surface cutting such as a cavity cutting and a helical cutting.
In particular, the present invention relates to an end mill used in dry cutting for bottom cutting.

[0002]

2. Description of the Related Art A ball end mill shown in FIG. 1 is generally used as an end mill for cutting a three-dimensional curved surface.
Since ball end mills have cutting edges on the spherical surface from the center of rotation to the outer periphery, the cutting edge trajectory can be easily obtained in three-dimensional curved surface cutting in which the feed direction is not fixed, so that the cutting shape can be finished with high accuracy. There are features. Since the ball end mill must maintain the cutting property even at the center of rotation, a cutting edge needs to be present at the center of rotation. For this purpose, a center-tied cutting edge shown in FIG. 2 is employed. On the other hand, it is extremely difficult to tie the cutting edge exactly at the center, and there is a drill-shaped rising edge as shown in FIG. 3 to avoid this. For example, JP-A-10-
No. 249,623 discloses a ball-end mill with a rising edge.

[0003]

In the case of bottom surface cutting in three-dimensional curved surface cutting, the center of rotation mainly plays a cutting action, so that the poor machinability of this portion is a major problem. For this reason, the tool life could not be extended without the use of cutting oil. However, when cutting the bottom of the cavity, etc. in three-dimensional curved surface cutting, the cutting part would sink in the oil even if cutting oil was used in combination. There was a problem that a sufficient cooling effect or a chip removing effect could not be obtained, and instead the chips were easily bitten and the tool life could not be improved. In addition, there is a problem that the performance of the hard material film is reduced by the combined use of a cutting oil.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above background, and has improved cutting performance by improving the blade shape at the center of rotation, thereby enabling three-dimensional operations such as cavity cutting and helical cutting. It is an object of the present invention to provide an end mill which has good finishing accuracy and a long tool life even when cutting a bottom surface by using dry cutting for curved surface cutting.

[0005]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a hard metal-coated ball blade or a curved blade protruding in the axial direction at the center of rotation. In the end mill, the axial rake angle of the cutting edge at a position corresponding to 4% of the end mill radius from the rotation center is 0 ° to
−5 °, wherein the depth of the tip pocket at the position is 5% or more of the radius.

[Action]

In the present invention, the rake angle in the axial direction at a position 4% of the radius of the end mill from the center of rotation is 0 ° to -5.
(4) The reason why the depth of the tip pocket is set to 5% or more of the radius is that not only is the cutting edge provided near the center of rotation imparted with machinability, but also a remarkable effect is achieved in removing chips. In other words, the tip pocket accommodates the chips produced by the chisel edge, and the negative rake angle acts to quickly move the chips away from the cutting position. Even a small amount of chips generated near the center of rotation can cause welding and wear to the cutting edge, so to eliminate them, provide a suitable rake angle and insert pocket to reduce tool life and finish surface accuracy. The effect is obtained on both sides. In finish cutting, a value of 2% of the end mill diameter and a value of about 3% of pick feed are selected for one rotation feed, so the cutting edge at a position 4% of the radius from the center of rotation was used as a reference, and the tip pocket The depth, that is, 5% of the radius, may be considered as a lower limit value at which the rake face functions as a cutting edge.

Next, in the hard film coated on the blade, the thickness of the film coated on the flank gradually increases from the outer peripheral blade side toward the center of rotation, and the flank of the cutting blade flank located at a position of 10 ° from the rotation axis. Since the thickness of the coating is 1.5 times or more the thickness of the cutting edge located at an angle of 80 ° from the rotation axis, the effect of protecting the cutting edge can be obtained and wear can be suppressed. Thin film coating of hard material prevents oxidation in high-speed cutting with temperature rise, has the effect of delaying the growth of wear, but when the peripheral speed is low, rubbing wear is the main, so when coating the same material, The coating thickness needs to be changed between the low speed range and the high speed range. The reason for limiting the gradually increasing film thickness to the flank here is that rubbing wear is concentrated on the flank.

In end mill cutting, the cutting temperature rises with the removal of chips, and flank wear usually precedes rake face wear, which causes a service life. Therefore, supplying the cutting oil is a means of delaying the progress of wear and extending the tool life. In the case of dry cutting, the cutting oil is not supplied, so that the tool life is generally shortened. However, in the present invention, the vicinity of the center of rotation of the curved blade is arranged at a position above the center,
In addition, since the range is limited in consideration of the machinability, the value can be cut into the workpiece without rubbing. Further, since the coating layer withstands high temperatures well, it maintains the adhesion to the base material and maintains the machinability for a long time even in dry cutting. In a region having a rake face, rake face wear increases due to the contact pressure between the rake face and the chip, but since the generation of flank wear is slow, the cutting edge itself acts apparently to recede. In the present invention, the hard coating on the flank is particularly thick near the center of rotation, so that the cross section of the coating maintains a sharp edge due to a bank effect for protecting the base material from abrasion, and there is almost no deterioration in sharpness. In this way, maintaining sufficient cutting properties near the center of rotation,
Producing appropriate wear enables long-term continuous use by dry cutting. The flank wear causes the cutting edge to retreat in the axial direction, which causes a change in the processing size due to the wear.In the present invention, the rake face wear is preceded by the effect of the coating, and the rake face wear is caused by the rake face wear. Since the displacement is very small, there is also an effect that the change in the processing size is small even if cutting is performed for a long time.

In the present invention, as an embodiment, the bottom blade may be a ball blade or a curved blade such as an ellipse or a parabola that protrudes in the axial direction at the center of rotation. By arranging it at a position above the center, the rake angle in the rotation direction becomes a negative angle in this portion, and the flank forms a chisel edge because the cutting edges are connected at the center of rotation. These strengthen the cutting edge at the center of rotation and exhibit an effect of withstanding cutting edge friction even at low speed cutting. Further, in the end mill cutting, the bending of the end mill during cutting is inevitable. The angle is changed to the regular angle side, and it does not cause chatter or bluntness.
In addition, in the conventional centering blade ball end mill, since the centering amount is as large as 2% or more, friction at the chisel edge portion increases, wear is accelerated, and the cutting surface is deteriorated. Hereinafter, the present invention will be described with reference to the drawings showing the embodiments.

[0010]

4 to 7 show one embodiment of the present invention, which is a ball end mill having a diameter of 10 mm and a number of blades of 2 made of ultrafine cemented carbide. The center rise amount at the center of rotation is 0.12 mm in width and 4% of the radius from the center of rotation, that is, 0.2%.
The rake angle in the axial direction at a position distant by 4 mm is −4 °, and the chip pocket is formed by deeply cutting the gash and has a depth of 0.6 mm. The coating is applied to the entire blade portion with a thickness of 1.5 μm. As shown in FIG. 8, the conventional product has a width of the rising amount of 0.25 mm, the tip pocket has a shallow gash and a rounded bottom with a rake face, a depth of 0.3 mm, and an axial rake angle. Is-
10 ° or more. The coating is made evenly over the entire blade.
5 μm. The product of the present invention and the conventional product were compared for use in bottom cutting of a three-dimensional curved surface shown in FIG. The cutting was dry cutting using air blow. The cutting depth was 0.3 mm in both the axial and pick directions and the number of revolutions was 10,000 revolutions / min. Therefore, the cutting speed was 107 m / outermost diameter used for cutting.
min, the feed rate is 2 m / min.

As a result, in the product of the present invention, after cutting 530 m or more, the cutting edge of the ball edge portion was retreated in the rotating direction, but the cutting edge maintained a sharp edge and cutting was continued. . The rake face had scratches from the ball blade to the innermost edge on the rotation center side, indicating that chips had been generated. The cut surface has a smooth surface with regular rotation marks created by chisel edges,
Chisel edges were creating chips. As for the dimensional accuracy of the finished surface, in the case of the product of the present invention, the sharpness of the nose and the ball blade is good because the amount of upset is small, there is almost no uncut or excessive cutting due to deflection during cutting, and the dimensions as set can be obtained. did it. The conventional product was worn so that the cutting edge was rounded by cutting the same distance. The chip pocket was small, and large friction marks and chip welding were found on the chisel edge. The cut surface was roughened due to irregularly peeled rotation marks, but the sharpness near the chisel edge was poor, the resistance increased, and the bending force increased. This is considered to be the result of the superposition of sharpness reduction. This rotation mark is considered to be caused by the eccentric rotation caused by the galling of the cutting edge, and appeared in a size exceeding the pick feed amount, and the dimensional accuracy was a value outside the setting.

From the above results, it is possible to use a coating composition in which only the high-temperature characteristics are combined with the tool base material, so that the coating composition can be used as a means of changing the coating composition to enhance cutting performance.
Although the embodiment has been described as applied to a ball end mill, similar effects can be obtained as long as the bottom blade is a curved blade protruding in the axial direction at the center of rotation as illustrated in FIGS. If an end mill with a coolant hole is used, the chips can be discharged more smoothly by blowing off the chips. Further, the coating may be applied to the entire blade portion with a uniform thickness. However, if the flank of the ball blade is coated so that the thickness increases toward the center of rotation, the tool life can be further increased. For example, 2.5 μm at 10 ° from the ball center and 1.2 μm at 80 °
What is necessary is just to change the film thickness like m.

[0013]

As described above, according to the present invention, cutting performance is improved by improving the blade shape at the center of rotation, and three-dimensional curved surface cutting such as cavity cutting and helical cutting is performed by dry cutting. Also, the end mill with good finishing accuracy, beautiful appearance, and long tool life can be obtained.

[Brief description of the drawings]

FIG. 1 shows a front view of an example of a conventional product.

FIG. 2 shows a side view of FIG. 1;

FIG. 3 shows a side view of another example of a conventional product.

FIG. 4 is an enlarged front view of one embodiment of the present invention.

FIG. 5 is an enlarged view of a curved blade portion of FIG. 4;

FIG. 6 shows a side view of FIG. 5;

FIG. 7 shows the bottom surface of FIG. 4;

FIG. 8 shows an enlarged side view of FIG. 3;

FIG. 9 is an explanatory diagram of bottom processing of a three-dimensional curved surface by an end mill.

FIG. 10 is an enlarged front view of another embodiment of the present invention.

FIG. 11 is an enlarged front view of another embodiment of the present invention.

[Explanation of symbols]

 1 Body 2 Ball blade 3 Tip pocket depth 4 Rake angle 5 Curved blade

Claims (2)

[Claims] 1. A cemented carbide ball coated with a hard material.
In the case of an edge mill or a curved edge end mill that projects in the axial direction at the center of rotation, the axial rake angle of the cutting edge at a position corresponding to 4% of the end mill radius from the center of rotation is 0 ° to −−.
5 °, the depth of the tip pocket at that position is
% Or more. 2. The end mill according to claim 1, wherein in the hard composition film coated on the blade portion, the thickness of the film on the flank gradually increases from the outer peripheral blade side toward the center of rotation, and the contact point between the curved blade and the outer peripheral blade is changed. The thickness of the coating on the flank of the cutting edge located at 10 ° from the rotation axis about the intersection of the passing radius and the rotation axis is 1.5 times the thickness of the flank coating at 80 ° from the rotation axis.
An end mill characterized by being at least twice as large.