JP2001096414A - Twist drill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stable twist drill of cemented carbide or of TiCN system cermet that excellently resists cutting edge chipping, coating flaking and the like by virtue of an improved end cutting edge and chip evacuating flute. SOLUTION: The twist drill made of cemented carbide or of TiCN system cermet has in a sectional view taken perpendicularly to the axis thereof an S shape spreading from that portion of a chip evacuating flute which is just off the web thickness to a land side. The chip evacuating flute has a concave root and a convex 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 abbreviated as "drill"). It relates to improvement of the cooling effect.

[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.

[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 discharge groove is formed by preventing chipping at the time of chip discharge when the chip is caught and by promoting the penetration of the cutting oil into the chip discharge groove. The purpose of the present invention is to provide a tool with safety at the time of tool handling by giving lubrication to the inner wall of a machining hole and generated chips and further giving a curvature to a heel portion.

[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, and the tip blade and the thinning blade have a diameter of the drill. A twist drill characterized by being connected by an arc of more than 0.15 times and not more than 0.50 times.

[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.

[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. Further, the roundness of the heel portion may be viewed as a circle having a drill diameter of about 0.05 to 0.25, and further, the top of the heel portion and the end of the land portion on the side of the chip discharge groove may have various shapes. Can be taken. 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. Hereinafter, the present invention will be specifically described based on examples.

[0008]

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.
Using 10 twist drills of 35 times, cutting speed = 60 m / min, feed amount per rotation = 0.2 mm /
rev, machining depth = 24 mm, under the condition of wet cutting, SC
M440 (HB250-300) was processed into 100 holes, and the state of the drill heel portion after processing was observed. In addition, a cutting test was performed on the present invention example by coating with a TiAlN film. For comparison, ten drills were similarly tested with a conventional drill having a connection with the tip blade having a curvature of 0.1 times, and the results are also shown in Table 1.

[0009]

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

From Table 1, it can be seen that in a drill in which the groove shape of the heel portion is S-shaped and the arc of the tip blade is enlarged as in the example of the present invention, 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.

[0012]

[Table 2]

According to Table 2, when the number of drilled holes is up to 2,000, in the present invention, chipping of the tip blade is less likely to occur, and the cutting edge can be cooled by promoting penetration of the cutting oil, so that the amount of wear is reduced. 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.

[0014]

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 Perimeter blade 3 Tip blade 4 Chip discharge groove 5 Land part 6 S-shape 7 Thinning blade 8 Arc (connection part of 3 and 7) D Diameter W Core thickness O Shaft center

Claims (2)

[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, and the tip blade is provided in a straight line as viewed from the end face of the twist drill. A twist drill characterized by being connected by an arc of 0.50 times or less. 2. The twist drill according to claim 1, wherein an arc connecting the tip blade and the thinning blade has a diameter of 0.25 to 0.40 times a drill diameter.