JP2001096416A - Twist drill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stable twist drill of cemented carbide or of TiCN cermet that excellently resists cutting edge chipping, coating peeling and the like by virtue of an improved end cutting edge and a chip evacuating groove. SOLUTION: The twist drill made of cemented carbide or of TiCN cermet has in a sectional view taken perpendicularly to the axis thereof as S shape spreading from that portion of a chip evacuating groove which is just off the web thickness of the land side. The chip evacuating groove has a concave root and a protrusion heel. In the end face view of the twist drill, an end cutting edge is formed straight and is connected to a web thinning edge by an arc 0.15 to 0.50 times as long as the drill diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a twist drill made of cemented carbide or cermet (hereinafter simply referred to as "drill"). The present invention relates to a drill capable of improving the cooling effect and enhancing the chipping resistance at the time of drilling by strengthening the cutting edge to obtain excellent stability and centripetality.

[0002]

2. Description of the Related Art In recent years, twist drills made of cemented carbide have been widely used. Carbide drills are excellent in wear resistance and can perform high feed cutting and heavy cutting, but they are inferior in mechanical strength such as bending strength due to low toughness, and therefore, compared to high speed steel drills The core thickness must be increased and the ratio of the groove width to the land width must be reduced to compensate for the strength. For example, in Japanese Patent Publication No. Sho 61-30845,
Two chip discharge grooves are formed on the outer periphery of a drill body made of cemented carbide, and a cutting edge is formed at a tip ridge portion of a wall surface of the chip discharge groove that faces in the rotation direction. Here, the core thickness of the drill body is relatively large, 20 to 35% of the drill diameter,
The ratio A / B of the groove width A to the land width B in a cross section orthogonal to the axis of the drill body is set to a relatively small value of about 0.6. Further, as an improvement of the above-mentioned patent, Japanese Patent No. 2674124 proposes a twist drill having an increased groove width ratio. In both cases, the shape of the chip discharge groove is such that the outer peripheral edge Q of the cutting blade and the edge Q
When a perpendicular L that is perpendicular to a straight line N connecting the axis L is drawn, the shape is concave with respect to the perpendicular L. This is designed so that the chips are not forcibly bent with a small radius of curvature so that the chips do not rub against the inner wall surface of the processing hole. Also, it is disclosed that the chipping resistance at the time of drilling is improved by strengthening the cutting edge.
No. 4124.

[0003]

Heretofore, since the toughness of the cemented carbide is low, the mechanical strength such as the transverse rupture strength is inferior.
The core thickness was increased and the ratio of the groove width to the land width was reduced to supplement the strength. However, when the cause of the breakage was examined, it was found that the breakage was caused by chipping of a sharp portion at the tip, biting of chips, and shortage of cutting oil. Therefore, by expanding the chip discharge groove in an S-shape toward the land portion, the chip is prevented from being chipped when the chip is discharged, and the chip is discharged by promoting penetration of the cutting oil into the chip discharge groove. Measures the lubrication of grooves, inner walls of drilled holes, and generated chips, and furthermore, provides curvature to the heel to provide safety when handling tools, and hones the cutting edge of the cutting edge, especially in the low-speed region. An object of the present invention is to provide a tool which is provided large and has excellent stability.

[0004]

Therefore, the present invention provides
In a twist drill made of a cemented carbide or a TiCN-based cermet, in a cross section perpendicular to the axis of the twist drill, a portion from the vicinity contacting the core thickness of the chip discharge groove to the land portion side
The bottom of the chip discharge groove is concave, the heel is convex, and the tip blade is provided in a straight line when viewed from the end face of the twist drill. A twist drill characterized by being connected by an arc of not less than 15 times and not more than 0.50 times, and a honing width of the arc portion being larger than other portions.

[0005]

The operation will be described with reference to FIGS. First, by making the shape of the chip discharge groove in the cross section perpendicular to the axis of the twist drill into a substantially S-shape from the vicinity of contact with the core thickness to the heel portion, the chip generated at the cutting edge is While rubbing the inner wall of the processing hole, it is discharged to the outside along the chip discharge groove.At this time, the flow of some chips changes due to friction with the inner wall of the processing hole, causing the chip to bite. It has been found that chipping occurs when the force is applied to the thin heel tip. The substantially S-shape represents the shape from the vicinity in contact with the core thickness of the drill to the heel, but the upper part of the S-shape is formed by the blade groove bottom. The lower part of the S-shape is formed by giving the heel a convex roundness without extending the blade groove bottom as it is. In this way, by expanding in an S-shape from the vicinity in contact with the core thickness of the chip discharge groove toward the land portion, first, the upper part of the S-shape, that is, the bottom of the chip discharge groove,
Since the chips are curled (strongly compressed), an appropriate curvature (about 0.10 D to 0.30 D) is provided, but the contact length is hardly considered. In the present invention, the length of contact is shortened by providing the curvature of the heel portion, and the curved surface is changed from a concave surface to a convex surface at 30 to 120 degrees from the vicinity of contact with the core thickness. Accordingly, the chips are sufficiently curled and discharged to the outside along the discharge grooves. More desirably, it is 45 to 90 degrees from the vicinity in contact with the core thickness.

Further, in the conventional drill, the chips are discharged when the chip discharge groove is full, and the cutting fluid cannot be sufficiently supplied to the tip of the drill.
The direction of some chips changes. Therefore, the lubrication of the chip discharge groove can be supplemented because the cutting oil penetrates and is supplied in the S-shape, particularly the space below the S-shape. Furthermore, the roundness of the heel is 0.05-
Although a circle of about 0.25 may be seen, the top of the heel and the end of the land on the chip discharge groove side may take various forms. In FIG. 3, it is connected to the end of the land part by making use of the curvature as it is. It may be connected linearly in order to further expand the space of this portion, or may be connected in a concave shape. In all of these cases, the penetration of the cutting oil or the like is more effective.

[0007] When the tip blade is provided in a straight line, the thinning blade and the tip blade are straight, and the joint tends to suffer defects such as chipping at the beginning of use and peeling of the coating film. Does not show wear. Therefore, in the present application, the tip blade and the thinning blade have a drill diameter of 0.
By making the arc more than 15 times and not more than 0.50 times, the load applied to the connecting portion is dispersed, and it is possible to prevent minute chipping and chipping which are likely to occur in the initial stage of use, and to reduce, in particular, peeling of the film. There is action. Therefore, if the size of the arc is less than 0.15 times the diameter of the drill, the above-mentioned effect is not obtained. If the size of the arc exceeds 0.50 times, the thinning blade cannot be kept substantially in a straight line. Is 0.15 to 0.50 times, more preferably 0.25 to 0.40 times the drill diameter.

The honing shape is particularly likely to occur in a low-speed region due to the low mechanical strength of a carbide drill, and therefore, in the present invention, the honing amount of the arc portion at the joint between the thinning blade and the tip blade is determined by the thinning blade and the tip blade. The honing amount is larger than the honing amount. By making the arc large and the honing of the arc part large, the mechanical impact can be reduced, and the peeling of the film on the arc part and minute chipping or chipping of the cutting edge can be reduced. Also, by forming the tip blade so that the width gradually increases from the outer peripheral side toward the axial center side, the tip blade is most likely to peel off the film at the center of rotation and chipping of the cutting edge,
By increasing the width and angle of the honing toward the axis, the width is increased, and the angle is increased to the minus side, thereby synergistically with the size of the arc portion, thereby improving the peeling of the coating and the chipping resistance of the cutting edge. it can. Also, since the cutting speed is higher on the outer peripheral side than on the axial center side, the honing width of the cutting edge may be set to more than 0.005 and 0.05 or less of the drill diameter. If it is less than 0.005, the edge strength is insufficient, and damage to the coating and chipping cannot be prevented. If it exceeds 0.01, the generation of chips is hindered, and smooth cutting is not performed. 0.05 or less.
Also, the honing angle of the cutting edge is more than 5 degrees and 4
It may be provided at 0 degrees or less. If it is less than 5 degrees, the edge strength is insufficient, and damage and chipping of the coating cannot be prevented. If it exceeds 40 degrees, the generation of chips is hindered, and smooth cutting is not performed. And Hereinafter, the present invention will be specifically described based on examples.

[0009]

EXAMPLE As an example of the present invention, a drill having a drill diameter of 8 mm made of ultra-fine-grain cemented carbide was used, and it was formed into an S-shape as shown in FIG. 3.
With a honing width of 100 microns, a honing angle of 20 degrees, and a twisting arc with a honing width adjusted to a maximum of 120 microns at the connecting arc, cutting speed = 60 m / min, 1 Feed amount per rotation = 0.2 mm / rev, machining depth = 24 mm,
Under the conditions of wet cutting, SCM440 (HB250-30)
0) was processed into 100 holes, and the state of the tip blade, the outer peripheral blade, and the heel portion after processing was observed. In the present invention, TiAlN
The film was coated and a cutting test was performed. For comparison, a conventional drill having a joint with the tip blade having a curvature of 0.1 times and a honing width of 100 microns and a constant was also subjected to one test.
0 runs were performed, and the results are also shown in Table 1.

[0010]

[Table 1] Note) ○: Drill without chipping and chipping at heel, tip blade, and outer cutting edge ×: Drill with chipping and chipping at heel, tip blade, and outer cutting edge

From Table 1, it can be seen that, as in the example of the present invention, in a drill in which the groove shape of the heel portion is S-shaped and the arc of the tip blade is enlarged, chipping of the tip blade and the heel portion is 1/10.
While there is no chipping of the outer peripheral blade caused by this, in the conventional example, 9/10 occurs in the heel portion, and chipping also occurs in the outer peripheral blade portion.

Further, drilling was continued under the same cutting conditions. Maximum flank wear after machining 2000 holes VBmax
(Mm) is shown in Table 2. However, 2000
In the case where the life has been reached or the machine cannot be machined without drilling, it is indicated by the number of drilled holes.

[0013]

[Table 2]

According to Table 2, when the number of drilled holes is up to 2,000, in the present invention, the tip blade is less likely to be chipped or the like, and the cutting edge can be cooled by promoting the penetration of the cutting oil, thereby reducing the wear amount. However, in the conventional example, the maximum wear of the flank on the flank due to chipping, chipping and the like of the tip blade became large, and the 2,000 holes could not be machined, and the life was shortened. In addition, entanglement of chips and the like increases, and it is necessary to continue drilling while removing entangled chips and the like.

[0015]

According to the present invention, the shape of the tip blade of the drill and the groove of the drill can be further expanded toward the land, so that the chip discharge groove can be made wider and stable cutting performance can be obtained. Became possible.

[Brief description of the drawings]

FIG. 1 shows a front view of a drill according to an embodiment of the present invention.

FIG. 2 is a front view in the axial direction of the drill according to the embodiment of the present invention.

FIG. 3 shows a cross-section perpendicular to the axis of FIG. 1;

FIG. 4 is a sectional view taken along a line perpendicular to the axis of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Drill main body 2 Outer edge 3 Tip blade 4 Chip discharge groove 5 Land part 6 S-shape 7 Thinning blade 8 Arc (joining part of 3 and 7) 9 Honing (tip blade) 10 Honing (arc part) D diameter W core Thick O axis

Claims (3)

[Claims] 1. A twist drill comprising a cemented carbide or a TiCN-based cermet, wherein in a cross section perpendicular to the axis of the twist drill, the twist drill is expanded in an S-shape from a portion in contact with a core thickness of a chip discharge groove to a land portion side, The bottom of the chip discharge groove is concave, the heel is convex, the tip blade is provided in a straight line when viewed from the end face of the twist drill, and the tip blade and the thinning blade exceed 0.15 times the diameter of the drill. A twist drill connected by an arc of not more than 50 times and a honing width of the arc portion being larger than other portions. 2. The twist drill according to claim 1, wherein the honing has a gradual width from an outer peripheral side to an axial center side at a cutting edge of a tip blade from an outer peripheral edge to a shaft center portion through a vicinity of a center thickness. A twist drill characterized in that it is formed so as to be wider. 3. The twist drill according to claim 1, wherein the honing is formed such that a negative angle gradually decreases from an outer peripheral side toward an axial center side.