JP2000015511A - Twist drill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a chip discharge groove wider by making the core thickness of a drill main body to the specific % of a drill diameter and also the thickness of a land to the specific % or less of the drill diameter. SOLUTION: The core thickness is 15-30% of a drill diameter D for the drill diameter D of the twist drill made of a super particulate cemented carbide. The thickness (d) of a land is made to 40% or less of the drill diameter D. Thus, in the edge groove for chip discharge, the distance from an edge top can be made longer by thinning the thickness of the land and the edge groove 2 itself can be made in slender. Therefore, a bigger numerical value is used to the arc of the bottom of the edge groove 2 or the arc with a different curvature can be provided on a heel further. The curvature radius of the cross section orthogonally crossing with the axis of the bottom periphery of a twisted groove is made in the range of 0.2D-0.5D, when the drill diameter is D.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cemented carbide twist drill used for drilling and the like.

[0002]

2. Description of the Related Art Various shapes of twist drills made of cemented carbide have been proposed, but there is a major problem in discharging chips generated in drilling. The chip discharge is related to the chip shape, and the shape that is most easily discharged is a form called “transition break type”. This chip form is curled in the drill blade groove, formed into a substantially conical shape, sent to the shank side in the twist groove, and discharged. In order to obtain this chip form, the shape of the tip blade, the blade groove, particularly the arc shape at the bottom of the blade groove, the heel portion, and the like are related. As an example of these, there is Japanese Patent No. 2674124 in which the radius of the blade groove bottom is specified. When defining the shape of the chips, they are formed in a chip form in which the curl diameter is made as small as possible in order to break the chips in consideration of the cutting resistance, and in particular, the core thickness and the circular arc at the bottom of the blade groove are defined.

[0003] With respect to the rigidity, the core thickness is the most important factor, and it is particularly preferable that the core thickness is larger in a drill for cutting in the axial direction. However, these are mainly discussed based on high-speed steel, and It is not a discussion of cermets. As is well known, compared to high-speed steel, carbide has an elastic modulus of 3 times or more, and cermet has an elastic modulus of 2 times or more. For example, regarding torsional rigidity, Galloway shows an inscribed circle diameter ratio d / D (d: thickness of a land portion) and a sectional torsional rigidity ratio, as shown in FIG. , D / D = 0.4, torsional rigidity ratio =
0.10, d / D = 0.5, torsional rigidity ratio of section = 0.
28, the land portion has a large thickness of about 0.3 to 0.5.

[0004]

As described above, various proposals have been made for the core thickness as described in the prior art. However, it is only recognized that a relatively thick land portion is better.
The core thickness is important in determining the rigidity of the drill, but it is possible to increase the rigidity in other configurations. There is no problem in terms of rigidity even when the blade is used. By expanding the chip discharge groove further to the land side, the shape of the chip can be defined and widened, so that a sufficient space can be taken and a more flexible chip processing can be performed. In the case where a large amount of chips are generated as in the case of high feed machining, a tool provided with a chip form having good dischargeability and a wide blade groove is provided.

[0005]

Therefore, in the present invention,
In a twist drill made of cemented carbide and / or cermet, the core thickness of the drill body is set to 15 mm of the drill diameter.
% To 30%, and the thickness of the land is 40% or less of the drill diameter. First, the core thickness was set slightly thinner as a carbide or cermet twist drill. However, FIG. The cemented carbide has a modulus of about 600 MPa and the cermet has a modulus of about 400 MPa, while the elastic modulus of the speed steel is 200 MPa. Further, by reducing the thickness of the core and the thickness of the land portion, the blade groove used for chip discharge can be widened.

[0006]

Secondly, as shown in FIG. 1, the distance between the cutting edge and the cutting edge can be made longer by reducing the thickness of the land, as shown in FIG. Can be Therefore, the arc at the bottom of the blade groove can be used in various ways such as a larger numerical value, or an arc having a different curvature is provided in the heel portion. In detail, the radius of curvature R in a cross section orthogonal to the axis around the bottom of the twist groove is in the range of 0.2D ≦ R ≦ 0.5D where D is the drill diameter. Further, by making the heel portion concavely curved, chips can be guided without difficulty.

Third, a thinning blade is formed in the core thick portion by the thinning so as to extend in the outer peripheral direction from the axis portion, and the shape of the thinning blade and the cutting blade as viewed from the front in the axial direction is linear. By making the tip blade straight, the cutting resistance is reduced, and the shape is made to supplement the settings of the core thickness, land thickness, and the like. In addition, the shape of the intersection of the thinning blade and the cutting blade in the axial front view is arc-shaped, because the carbide, cermet becomes too sharp when crossed in a straight line, providing an appropriate roundness, This is to reduce chipping or the like during cutting. Preferably, the size is 0.05 to 0.50 times the drill diameter. A larger value may be used for a work material having high strength, and a smaller value may be used for a work material having low strength.

Fourthly, the drill body is provided with a coolant hole which forms a spiral along the torsion groove, and is opened at the flank of the tip blade. As for the opening position, the second flank of the tip blade is good, and by opening the second flank, coolant is supplied to the entire cutting edge as the drill rotates. As the coolant, a water-soluble cutting oil is used, but mist or compressed air whose temperature is controlled is used.

Fifth, a coating layer of a hard film and / or a lubricating film is provided on the surface of the drill body. As the hard coating, a coating intended for abrasion resistance such as TiN or TiAlN, a coating coated with a lubricating coating such as MoS, TaS, or a combination thereof is applied. In particular, in the case of twist drills, chips are discharged through the drill groove because of the balance with chip processing.
It is effective to apply a film having a low coefficient of friction to the cutting groove for a long period of time when the chip contacts the cutting groove. In particular, MoS has a coefficient of friction three orders of magnitude lower in dry air, and is more effective when combined with dry cutting such as dry air or cold air from the coolant hole. Hereinafter, the present invention will be described in detail based on examples.

[0010]

EXAMPLE A material of ultrafine-grain cemented carbide was manufactured by a usual powder metallurgy method, and a two-edged twist drill having a drill diameter of 8 mm was manufactured. FIG. 2 is a front view thereof, and FIG.
Shown in Note that an alloy having a Co content of 8%, that is, an elastic modulus of 590 MPa was used as the ultrafine-particle cemented carbide. The coating was a hard coating. As cited in the prior art, a drill was manufactured in which the core thickness W and the land thickness d were changed as shown in Table 1 with respect to the drill diameter D, and the shape of the blade groove was variously changed.

[0011]

[Table 1]

Using the drills of the present invention and the comparative examples shown in Table 1, the work material SCM440 (annealed material) was used as the cutting data.
Cutting speed 60m / min, feed speed 500m
A hole having a depth of 24 mm (three times the drill diameter) was machined at a speed of m / min using a water-soluble cutting oil. The life was determined while observing the shape of chips and the like, and checking the damage state of the cutting edge for each fixed number of processing holes. The results are also shown in Table 1.

According to Table 1, the twist drills of Examples 1 to 4 of the present invention, which are thinner in core thickness and land thickness, can perform smooth hole drilling, and have a sufficient space for chip generation and discharge. The form was a transition break type, and the discharge was smooth. In addition, cutting can be performed in the same manner in Examples 5 to 8 of the present invention in which both the core thickness and the land portion are slightly increased, and the feed rate is 500 mm / mi.
In this test of n, the chips could be discharged without any problem. Further, in Comparative Example 9 in which the core thickness was reduced, in the high feed test, a slight vibration occurred and the chip was broken. Further, in Comparative Examples 10 and 11, since the land portion was thick, the blade groove was restricted, and there was a problem in chip discharge. Next, in Comparative Example 12 in which the core thickness was increased and the land portion was reduced, the shape of the blade groove, particularly the heel portion, could not be obtained, and the curl of the chip became indefinite, causing a problem in chip discharge. Was.

Next, the radius of curvature R in a section orthogonal to the axis around the bottom of the twist groove is 0.8, 1.6, 2..
4, 3.2, 4.0, and 4.8 mm were prepared. Cutting was performed using the same cutting specifications as in the above-described example, and the forms of the chips were compared. First, the radius of curvature 0.2D (R =
(1.6 mm), it was able to be guided without difficulty by the transition breaking type chip. If it is smaller than 0.8 mm, the braking is strong and the curl diameter becomes small.
At each radius of curvature of 3.2, 4.0, and 4.8 mm, the curl diameter was large, and at 4.8 mm, the chip was in the form of an elongated chip, and was discharged but bulky.

[0015]

According to the twist drill of the present invention, the thickness of the land portion can be made smaller and the blade groove can be further expanded toward the land portion, so that the chip discharge groove can be made wider. Was. In addition, it shows excellent performance in cutting that generates and discharges a large amount of chips at high speeds and high feeds.

[Brief description of the drawings]

FIG. 1 shows the torsional stiffness of a drill by Galloway.

FIG. 2 shows a front view of an example of the present invention.

FIG. 3 shows a sectional view of FIG. 2;

[Brief description of reference numerals]

 1 Twist drill body 2 Groove width d Land width D Drill diameter

Claims (8)

[Claims] 1. A twist drill made of cemented carbide and / or cermet, wherein the core thickness of the drill body is 15% to 30% of the drill diameter and the thickness of the land is 40% or less of the drill diameter. A twist drill characterized by the following. 2. The twist drill according to claim 1, wherein a radius of curvature R in a cross section orthogonal to an axis around a bottom of the twist groove is 0.2 when a drill diameter is D.
A twist drill, wherein D ≦ R ≦ 0.5D is set. 3. The twist drill according to claim 1, wherein the heel portion of the blade groove is formed on a concave curved surface. 4. The twist drill according to claim 1, wherein a thinning blade extending from the axis portion to the outer peripheral direction is formed in the thick core portion by thinning, and the shape of the thinning blade and the cutting blade in the axial front view. Twist drill characterized by having a linear shape. 5. The twist drill according to claim 1, wherein an intersection of the thinning blade and the cutting blade has an arc shape as viewed from the front end in the axial direction. 6. The twist drill according to claim 5, wherein a radius of curvature of an intersection between the thinning blade and the cutting blade is
A twist drill characterized in that the diameter is 0.05 to 0.50 times the drill diameter. 7. The twist drill according to claim 1, wherein the drill body is provided with a helical coolant hole along a torsion groove, and is opened in a flank of a tip blade. Twist drill. 8. The twist drill according to claim 1, wherein a coating layer of a hard film and / or a lubricating film is provided on a surface of the drill body.