JP2023060913A - end mill - Google Patents

Abstract

An object of the present invention is to provide an end mill for hole drilling by helical drilling, which has a small thrust force and is capable of drilling with high drilling efficiency.
SOLUTION: An end mill 1 has a configuration specialized for hole machining by helical machining, and a center base angle α indicating a medium-to-low gradient of a bottom cutting edge is formed to be 15° or more and 45° or less. When the center base angle α is increased, the contact area of the bottom cutting edge 11 with respect to the workpiece becomes narrower, and the area near the center of the bottom cutting edge 11 where the peripheral speed is low is not used for machining. If machining is performed in a region where the peripheral speed is low, the thrust force increases. However, in the present invention, the region near the center of the bottom cutting edge 11 where the peripheral speed is low is not used for machining, so the thrust force can be reduced.
[Selection drawing] Fig. 1

Description

The present invention relates to an end mill for hole drilling by helical machining.

Conventionally, drills are mainly used for drilling holes in metal materials and the like. In some cases, an end mill is used to drill holes by helical machining.

Here, helical machining means rotating the end mill around its axis of rotation while revolving horizontally so that the axis of rotation revolves around an orbit such as a circle. This is a processing method for drilling (for example, Patent Document 1).

JP-A-10-94914

Both drills and end mills have a large axial reaction force (thrust force) due to the tool during machining. If the thrust force is large, it is necessary to increase the pressing force of the tool against the workpiece, but deformation such as bending occurs when processing a member with low rigidity such as an aluminum plate or a plastic plate. Therefore, it is necessary to slow down the machining speed so as not to deform the workpiece, which makes it difficult to increase the machining efficiency.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an end mill for helical drilling that is capable of drilling holes with a small thrust force and high machining efficiency.

As a result of diligent research and development, the applicant found that the thrust force can be reduced by forming a large mid-base angle indicating a mid-to-low slope of the bottom cutting edge, which is formed to about several degrees in conventional end mills. Found it.

In order to achieve the above object, the invention according to claim 1 is an end mill used for hole drilling by helical machining, wherein the center base angle is formed to be 15° or more and 45° or less. Using technical means.

Here, helical machining means rotating the end mill around its axis of rotation while revolving horizontally so that the axis of rotation revolves around an orbit such as a circle. This is a processing method for drilling.

According to the second aspect of the invention, in the end mill according to the first aspect, a technical means is used, wherein the center base angle is 25° or more and 45° or less.

According to a third aspect of the invention, in the end mill according to the first or second aspect, the end mill employs the technical means that the helix angle of the peripheral cutting edge is 15° or more and 45° or less.

According to the fourth aspect of the invention, the end mill according to any one of the first to third aspects is provided with a coolant introduction hole along the axis.

According to the end mill of the present invention, the thrust force can be made extremely small. As a result, it is possible to suppress deformation of a material having low rigidity or a thin plate-shaped member during helical processing, and it is possible to quickly perform hole processing of a workpiece, which has been difficult to improve processing efficiency. In addition, since the thrust force is small, the feed speed in the axial direction of the end mill can be increased, so that highly efficient drilling is possible. An end mill with coolant inlet holes can increase the cooling efficiency of the workpiece and the end mill. In addition, the chip discharge efficiency can be improved.

FIG. 1(A) is an explanatory side view of the vicinity of the cutting edge of the end mill of the present invention. FIG. 1(B) is an explanatory front view of the end mill of the present invention as viewed from the cutting edge side. FIG. 4 is an explanatory view schematically showing the relationship between the bottom cutting edge and the workpiece during helical machining at different center base angles. FIG. 2A shows a case where the center base angle is small, and FIG. 2B shows a case where the center base angle is large. FIG. 4 is an explanatory diagram of an end mill provided with a coolant introduction hole; FIG. 10 is an explanatory diagram showing the relationship between the midbase angle and the ramping angle at which helical processing was possible; FIG. 5 is an explanatory diagram showing the thrust force when helical drilling is performed by the end mills of the example and the comparative example.

An embodiment of the present invention will be described below with reference to FIGS.

Here, an example in which the end mill 1 of the present invention is applied to a radius end mill having three blades will be described.

The end mill 1 consists of a shank (not shown) and a blade.

The blade portion of the end mill 1 is formed at a portion connecting the outer peripheral helical cutting edge 10, which has a right-handed thread when viewed from the shank toward the tip, the bottom cutting edge 11 having a medium-to-low slope, and the outer helical cutting edge 10 and the bottom cutting edge 11. The corner R edge 12 is provided.

Hole (circular hole) machining by helical machining using the end mill 1 will be described. The end mill 1 is driven by a device such as a milling machine (not shown), and rotates (rotates) to the right when viewed from the shank toward the tip. While rotating the end mill 1, it is rotated (revolved) so that the rotation axis forms a circular orbit so as to have a predetermined ramping angle γ. During this rotation, feed is applied in the axial direction, and the peripheral helical edge 10 cuts the side surface of the hole and the bottom edge 11 simultaneously cuts the surface of the hole, thereby drilling the hole.

The ramping angle γ is an angle determined from the distance H of movement in the axial direction when the distance of one revolution of the axis center is converted into a linear distance L1.

(Number 1)
tan γ = H/L1

The end mill 1 has a configuration specialized for hole drilling by helical machining, and the center base angle α, which is an angle indicating the mid-to-low gradient of the bottom cutting edge, is formed to be 15° or more and 45° or less.

FIG. 2 shows the relationship between the bottom cutting edge and the workpiece during helical machining at different center base angles. Here, the case where the ramping angle γ is greater than 2 to 3° that is employed in machining with a normal end mill is shown.

As shown in FIG. 2A, when the center base angle is small, the contact area S of the bottom cutting edge 11 with respect to the workpiece is wide, and the bottom cutting edge 11 contacts the workpiece up to the vicinity of the center. In particular, when the center base angle α is greater than the ramping angle γ, the entire bottom cutting edge 11 comes into contact with the workpiece.

On the other hand, if the center base angle α is increased as in the present invention, as shown in FIG. .

Since the vicinity of the center of the bottom cutting edge 11 is not used for machining, the area where the peripheral speed is low is not used for machining. If machining is performed in a region where the peripheral speed is low, the thrust force increases. However, in the present invention, the region near the center of the bottom cutting edge 11 where the peripheral speed is low is not used for machining, so the thrust force can be reduced.

By setting the center base angle α to 15° or more, the machining state shown in FIG. be able to. In addition, since the use area of the bottom cutting edge 11 is reduced, the cutting resistance can be further reduced, and the machining efficiency can be improved. By setting the center base angle α to 45° or less, the strength of the bottom cutting edge 11 can be maintained.

In order to reduce the contact area S, the ramping angle γ is required to be smaller than the center base angle α. With the end mill 1, since the center base angle α is large, the ramping angle γ can be made larger than in helical machining using a conventional end mill. As the ramping angle γ increases, the depth of machining per revolution increases, so machining efficiency can be improved.

When the ramping angle γ is large, the depth of cut in the axial direction becomes large, and the contact area of the peripheral helical edge 10 becomes large. As a result, the force for lifting the workpiece is increased, and this force offsets the reaction force, making it possible to reduce the thrust force.

In particular, for the end mill 1, which is used for drilling holes in materials with low rigidity such as soft aluminum materials, resin materials, and flexible plate-like members, the center base angle α should be set to 25° to 45° so that the thrust force is sufficiently reduced. It is preferable to:

The twist angle β of the outer peripheral twist edge 11 is set to 15° or more and 45° or less.

By setting the helix angle α to 15° or more, chips can be properly discharged upward.
This has the effect of additionally reducing the thrust force. Moreover, if the helix angle α exceeds 45°, the chips will not be discharged well.

Since the conventional end mill cuts in a region where the peripheral speed is low, the thrust force becomes large. On the other hand, since the end mill 1 does not cut in the region where the peripheral speed is low, it is not necessary to form a cutting edge in the central portion. This simplifies the design of the end mill and makes it easy to manufacture.

Moreover, since it is not necessary to form a cutting edge in the central portion, the coolant introduction hole 13 can be formed in the center of the shaft as shown in FIG. The end mill 1 having such a configuration can increase the cooling efficiency of the workpiece and the end mill. In addition, the chip discharge efficiency can be improved.

(Change example)
The configuration of the present invention can also be applied to end mills of other shapes such as square end mills and radius end mills with different numbers of teeth.

[Effects of Embodiment]
According to the end mill 1 of the present invention, the thrust force can be made extremely small. As a result, it is possible to suppress deformation of a material having low rigidity or a thin plate-shaped member during helical processing, and it is possible to quickly perform hole processing of a workpiece, which has been difficult to improve processing efficiency. In addition, since the thrust force is small, the axial feed speed of the end mill can be increased even with a small-sized machine having low rigidity, so that hole machining with high machining efficiency is possible. Furthermore, it is possible to machine multiple diameter holes with a single end mill. An end mill with coolant inlet holes can increase the cooling efficiency of the workpiece and the end mill. In addition, the chip discharge efficiency can be improved.

As an end mill, a three-bladed radius end mill with an end mill diameter of 6 mm and a helix angle of 45° was prepared. As an example, an end mill having a bottom cutting edge with a center base angle of 30° was prepared, and as a comparative example, end mills with a center base angle of 1° and 15° were prepared.

A machined hole having a diameter of 10 mm and a depth of 10 mm was formed in the aluminum alloy A5082, which was a work piece, and the reaction forces during helical machining of oblique cutting were measured and compared. Here, the reaction force was measured in the vertically upward thrust direction.

While the ramping angle of a general end mill is 2 to 3°, the ramping angle of this embodiment is 5° and 7°. Hole processing was performed by helical processing at 10.5° and 14°. Main processing conditions are shown below.

Peripheral speed: 350 (mm/min)
Rotation speed: 18568 (rpm)
Feed amount: 0.04 (mm/touch)
Feeding speed: 2228 (mm/min)

FIG. 4 shows the relationship between the center base angle and the ramping angle at which helical processing was possible. The points plotted with 〇 in the figure are the conditions under which helical processing was possible, and the points plotted with ● are the conditions under which helical processing could not be performed due to end mill welding or the like. It is believed that the area below the solid line in the drawing indicates the ramping angle at which helical machining can be performed under the machining conditions of the embodiment. There is a tendency that the larger the center base angle, the larger the ramping angle at which helical processing can be performed. It was found that at a center base angle of 30°, helical processing can be performed at a very large ramping angle of 14°. .

In general, standard machining conditions for end mills recommend that the feed rate for helical machining be 70 to 80% of the feed rate for grooving. Also, the feed rate in helical machining uses a value obtained by subtracting the tool diameter from the machining diameter and dividing it by the machining diameter. In this example,
(10-6)/10=0.4 (40%)
Therefore, the recommended feed rate for helical machining is 50 to 70% of the feed rate for grooving.

Although the feed rate of this embodiment is 1.4 to 2.7 times the feed rate for grooving, hole machining is possible.

Furthermore, it is possible to drill holes at much larger ramping angles, whereas typical ramping angles are 2-3°. For example, the ratio of machining depth per revolution is tan10°/tan3°≈3.4
is. As described above, hole drilling can be performed with high processing efficiency.

FIG. 5 shows the thrust force depending on the center base angle and ramping angle. The positive side of the thrust force is the reaction force on the end mill side.

An end mill with a center base angle of 15° (comparative example) produced a large thrust force, and it was observed that the thrust force tended to increase as the ramping angle increased. Moreover, it was impossible to process at a ramping angle of 10.5°. On the other hand, in the case of the end mill (example) with a center base angle of 30°, the thrust force was almost 0, and no increase in thrust force was observed even when the ramping angle was increased.

As described above, according to the end mill of the present invention, it was confirmed that the reaction force in the thrust direction could be made extremely small, and the machining efficiency could be improved.

REFERENCE SIGNS LIST 1 End mill 10 Peripheral helical edge 11 Bottom edge 12 Corner R edge 13 Coolant introduction hole α Middle base angle β Helix angle γ Ramping angle S Contact area

Claims (4)

An end mill for use in hole drilling by helical machining, characterized in that the center base angle is formed to be 15° or more and 45° or less. 2. The end mill according to claim 1, wherein the midbase angle is 25° or more and 45° or less. 3. The end mill according to claim 1, wherein the end mill has a peripheral cutting edge with a helix angle of 15° or more and 45° or less. 4. The end mill according to any one of claims 1 to 3, characterized by having a coolant introduction hole along the axis.

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