JP2001105220A - Twist drill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the deforming action of chip and provide an easy discharge of a curled chip in a twist drill having a thinning generally called X shape. SOLUTION: When a drill body 1 is seen in side view in a direction almost perpendicular to a ridge line 13 appearing in a flank face in the tip view of the drill body 1, a tip point 12 of a heel 11 is included within a circular arc drawn about a chisel point 9 by a radius R equal to a distance between the chisel point 9 and a cutting edge corner 10. In this case, a thinning face 6 is formed of a concavely curved surface when the drill body 1 is seen in side view in a direction almost perpendicular to a thinning cutting edge 7 in tip view.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a twist drill, and more particularly, to a thinning shape and a core thickness called an X-shape.

[0002]

2. Description of the Related Art Usually, a chisel is provided at the center of the tip of a twist drill, which has an extremely large negative angle that cannot be recognized as a rake angle. At the center of the drill, the drilling is performed while forcibly crushing the work material with the chisel edge, so that the cutting resistance increases, and the chip condition becomes unsuitable, and the drill performance deteriorates. The thinning is performed to solve such a problem. In particular, the thinning referred to as an X-shape forms a thinning blade almost reaching the axis of the drill. It is considered an effective thinning.

FIGS. 7 to 9 show an example of a conventional twist drill in which an X-shaped thinning is formed, showing only a tip portion of a drill main body 1, and the same portions as those of an embodiment of the present invention described later. The code is attached.

[0004] The X-shaped thinning is provided to the third flank 5 so that one end thereof is close to the axis O, and is characterized in that a thinning blade 7 reaching near the axis O is formed. . As a result, the chisel edge is eliminated and cutting resistance is improved. However, conventionally, since the thinning surface 6 is formed in a flat shape, in order to prevent chip clogging, FIG.
As shown in (2), the inclination angle α of the thinning surface 6 with respect to the axis O is reduced so that chip pockets are secured in the thinning portion. As a result, as shown in FIG. 8, as shown in FIG. 8, the tip point 12 of the heel 11 is located outside the arc drawn with the radius R from the chisel point 9 on the axis O to the cutting edge corner 10. Will be done.

[0005]

The chips generated by the cutting blades 4 and the thinning blades 7 flow out substantially following the arc of the radius R, but are cut away along the line EE in FIG. As shown in FIG. 10, the heel 1
Since the shape of the chip 1 is missing, the function of restraining and deforming the chip flowing out does not work sufficiently, and the chip has a large curl radius and a long length before cutting. Chips having such a shape are not preferable in terms of chip discharge.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and relates to a twist flank having a thinning blade formed by X-shaped thinning at the center of the tip. When the twist drill is viewed sideways from a direction substantially perpendicular to the intersection ridge line with the third flank, the tip point of the heel is within the arc drawn with the radius to the cutting edge corner centered on the chisel point. As included, the thinning surface of the thinning is formed by a curved surface that is concave when the twist drill is viewed from the side from a direction substantially perpendicular to the thinning cutting edge in a front view, and The core thickness at the base end side of the drill is smaller than the core thickness at the tip end side of the arc drawn with the radius from the chisel point as the center and the distance to the corner. Characterized in that it is formed.

That is, in order to generate finely divided chips having a small curl radius, a heel portion having a function of restraining the chips and promoting deformation is provided at a position where the chips flow out. It is composed. On the other hand, the heel is extended in the tip direction, so that the chip pockets become smaller and the chips generated by the thinning blade do not clog the chips. The pocket volume is secured. Further, the core thickness is made large at the distal end portion so as to exert the chip binding force, and the core thickness is made small at the base end portion side so as to easily discharge the chips.

[0008]

Next, an embodiment of the present invention will be described with reference to the drawings. 1 to 3 show only the tip portion of the twist drill of the present invention. The drill body 1 is provided with two chip discharge grooves 2 with a twist around an axis O. At the intersection ridge line of the tip with the second flank 3, the cutting edge 4
Are formed.

A third flank 5 is further provided behind the second flank 3 in the rotation direction, and a thinning surface 6 having one end close to the axis O is attached to the third flank 5. X
A thinning blade 7 reaching the vicinity of the axis O is formed by this, and a rake face 8 having a rake angle of about 0 ° is formed on the thinning blade 7, so that cutting resistance is reduced. A greatly improved twist drill.

In the present invention, the thinning surface 6 is formed as follows. That is, regarding the intersection ridge line 13 between the second flank surface 3 and the third flank surface 5 shown in FIG. 1, a chisel point on the axis O in FIG. The distal end point 12 of the heel 11 is arranged closer to the distal end side so as to be included in an arc drawn with a radius R from the center 9 to the cutting edge corner 10.

On the other hand, in order to prevent the chip pocket on the tip end side of the thinning surface 6 from becoming small due to the above-mentioned shape and causing chip clogging, in the present invention, the thinning blade 7 shown in FIG. In FIG. 3, which is a side view (specifically, a side view including a cross section along the line AA) from a direction perpendicular to the direction, formed by, for example, a cylindrical surface having a radius r or a concave curved surface formed by a part of a conical surface. As a result, the volume of the chip pocket is increased.

Next, the present invention is characterized in that the core thickness is changed between the distal end side and the proximal end side of the drill with a point at which the arc drawn by the radius R intersects the axis O as a substantially boundary. 4 and FIG. 5 are respectively a BB line and a C- line in FIG.
The cross section along the line C is shown. The line BB is on the distal side of the radius R, and the line CC is on the proximal side. The core thickness φC is formed smaller than the core thickness φB.

The chips generated by the cutting blades 4 and the thinning blades 5 flow out substantially following the arc of the radius R, are restrained at the tip of the extended heel 11, undergo a deformation action, and curl. Chips that are curled and cut to an appropriate size are discharged together with the cutting fluid through the chip discharge groove 2 to the outside of the machining hole. The part has a thickness that allows chips to pass easily.

The above-described configuration is very convenient for a brazing type twist drill as shown in FIG. 6, for example. This drill is formed by grooving the tip of a steel shank 14 and inserting a cemented carbide tip 15 having a length substantially equal to the radius R into the groove and brazing. It is possible to easily manufacture an alloy chip having a core thickness different from that of the shank portion.

[0015]

The twist drill of the present invention makes use of the low cutting resistance of the X-shaped thinning, and generates a chip shape that can be easily discharged and a chip discharge groove that is easy to discharge by the shape and the core thickness of the thinning surface. Can be obtained.

[Brief description of the drawings]

FIG. 1 is a front view of a tip portion of a twist drill according to the present invention.

FIG. 2 is a bottom view of FIG.

FIG. 3 is a cross-sectional view taken along line AA of FIG.

FIG. 4 is a sectional view taken along the line BB of FIG. 2;

FIG. 5 is a sectional view taken along line CC of FIG. 2;

6 shows a brazing type twist drill according to the present invention, wherein (a) is a front view and (b) is a side view. FIG.

FIG. 7 is a front view showing an example of a tip portion of a conventional twist drill.

FIG. 8 is a bottom view of FIG. 7;

FIG. 9 is a sectional view taken along the line DD in FIG. 7;

FIG. 10 is a sectional view taken along the line EE in FIG. 8;

[Explanation of symbols]

 2 chip discharge groove 4 cutting edge 6 thinning surface 7 thinning edge 9 chisel point 10 cutting edge corner 11 heel 12 (heel) tip point O axis φB, φC core thickness

Claims (2)

[Claims] 1. A drill body having a round bar shape is provided with two twisted chip discharge grooves with a twist around an axis, and a cutting edge is formed at a tip ridge at a tip angle, and further at a tip center part. In a twist drill having a thinning blade formed by X-shaped thinning, when the twist drill is side-viewed from a direction substantially orthogonal to an intersection ridge line of a second flank and a third flank in a front view, a chisel point is formed. As the center point and the distance to the cutting edge corner are drawn as a radius, the tip point of the heel is included in the arc, so that the twist drill is concave when viewed from the side from a direction substantially perpendicular to the thinning cutting edge in the front view. A twist drill, wherein a thinning surface of the thinning is formed by a curved surface. 2. A core thickness on the base end side of the drill from the arc drawn with the radius from the chisel point as the center to the corner is formed smaller than the core thickness on the tip side. Item 2. The twist drill according to item 1.