JPS60221208A - Very hard drill and method of strengthening cutting edge thereof - Google Patents

Abstract

PURPOSE:To strengthen the cutting edge of a very hard drill, by improving the form of the chamfered surface of the cutting portion of the drill. CONSTITUTION:A very hard drill is provided with a chamfered surface 13 so as to remove the acute-angle edge of the drill. The chamfered surface 13 is located at the oblique intersection of the rake face 11 and relief face 12 of the drill. A dimension (a) at the chamfered surface 13 and the rake face 11 is made larger than a dimension (b) at the chamfered surface 13 and the relief face 12, so that the angle of the cutting edge of the drill is kept from being made extremely large or blunt. The cutting sharpness of the drill is thus precluded from decreasing. The chamfered surface 13 is a convex arc-shaped surface slowly curving as a whole and extends with a small roundness at each of both the side edges to the rake face 11 and the relief face 12. As a result, the cutting performance of the drill is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a carbide drill mainly used for metal processing, and more particularly, to a chamfer (for strengthening the cutting edge) attached to the cutting edge.
This invention relates to a carbide drill with a specially designed chamfered surface and a method for strengthening the cutting edge of the drill for easily and accurately chamfering the drill.

(b) Conventional technology and the gap between carbide drills whose cutting blades are made of cemented carbide, while making it possible to increase the efficiency of drilling operations, they do not suffer from chipping of the cutting blades due to their low transverse rupture strength. Easy to occur. Therefore, in order to compensate for the brittleness of cemented carbide, the rake face and this chamfer are applied over the entire cutting edge.
As shown in Figure 1, at the diagonal intersection of rake face 1 and flank face 2,
The diagonal depth θ with respect to the reference line P (this reference line is parallel to the rotational axis in the case of the front cutting edge) is in the range of 10 to 45, and the installation a occupying the rake face is 0.03 to 0.3 mm. It was difficult to ensure stable performance in drills because it was considered to be a rounded surface connected to the rake face and flank face with a radius of curvature similar to the flat surface 3 or dimension a.

That is, FIG. 4 (a), tb) and t show changes in toughness and wear resistance by changing the angle and size of chamfering with a carbide turning tool. The numerical values in the figure were determined under the following test conditions.

0 wear-resistant work material: SCM435 (I (s30) tool:
FNIIR-44A, Tip 5NG432 (3) Grade 17'12A Cutting conditions: ■ (Cutting speed) -170m/m1nf (Feed) = 0.36mm/ r evd (Depth of cut) -2m
m T (cutting time) -2Qmin O breakage rate Work material: SCM435 Groove tool: Upper I Same cutting conditions: V-80m/m1n f =0.172~0.20mm1 r evd=2r
nm 1-3m1n f=0.172 Each test was repeated three times at 0.20 mm/rev, and the breakage rate was determined based on the number of breakages and the time until breakage.

As can be seen from this figure, it is very important to uniformly control the angle and size of the chamfer of the cutting edge of a carbide cutting tool in order to obtain stable performance.

However, in the case of drills, it is almost impossible to grind them with a grindstone due to the complexity of the cutting edge shape, such as the throw away thickness (4). The reality is that this is done manually using the attached hunt wrapper, and as a result, there is a 1-degree error (variation) in the angle and size of the chamfer, making the drilling performance unstable.

Further, in the case of a drill with a flat chamfer as shown in FIG. 3, a sharp edge remains at the intersection of the rake face and the flank face, resulting in chipping of the cutting edge, which reduces the life of the drill.

On the other hand, when the rake face 1 and the flank face 2 are connected by a curved radius surface, chipping is reduced, but the cutting edge is not excellent in biting into the work material.

(c) Means for solving the problem of cutting edge The present invention provides a carbide drill that solves the problem of cutting edge and a method for strengthening its cutting edge. The length of the chamfer attached to the rake face side is made larger than that on the flank face side, and the chamfer is roughly continuous with each of the rake face and flank face with a slight roundness.

The feature is that the entire surface is curved in a convex direction.

5 to 7 show examples in which the chamfer is attached to a typical carbide drill. As shown in the figure, the external shape of the carbide drill 10 is almost the same as that of a conventional drill.

Further, the bevel angle of the chamfer 13, which has an oblique intersection I between the rake face 11 and the flank face 12, is also close to the value of θ shown in FIG. 3 in order to remove an acute edge. In other words, the setting height 3 on the rake face side of the chamfer 13 is made larger than the setting height 3 on the flank face side to prevent the angle of the cutting edge from becoming extremely blunt, thereby suppressing a decrease in sharpness. However, unlike the conventional shape, the chamfer 13 has a slightly convex arcuate surface as a whole, and both sides thereof are connected to the rake face 11 and the flank face 12 with an even smaller roundness.

Note that it is desirable that the size of the chamfer provided at the front cutting edge of the drill be controlled in accordance with the position of the cutting edge. For example, to prevent welding defects on the center cutting edge and wear on the outer cutting edge, which are common problems of drills, it is necessary to increase the size of the chamfer near the center of rotation and gradually reduce it toward the outer periphery. can be reduced to The size of the chamfer can be easily and accurately adjusted by the method of the present invention, which will be described later.

Below, we will list the results of a comparative test regarding the cutting performance of the drill of the present invention with the chamfer described above and the conventional drill.

The drills used in the test are A (conventional drill) and B in Figure 8.
(drill of the present invention) and both have a diameter of 10vrm.

Further, in both cases, the diameter 11 of the chisel blade 14 was made extremely small compared to the thinning process 1, and the front cutting blade 15 was curved in the same direction when viewed from the end. A drill 1 is shown in Figure 3.
On the other hand, one B drill has the cutting edge treated as shown in FIG. The various dimensions of the processing section are shown in Table 1 below.

Table 1 Four of these two types of drills were prepared, and the work material was 550C (H
B250) was drilled using an emulsion type water-soluble cutting oil. The measurement results of cutting torque and thrust force at that time are shown in Table 2, and there was no significant difference between the two.

Table 2 Also, cutting conditions V=50m/min, f=0.
When 800 holes with a depth of 30 mm were drilled at 3 nm/rev, as shown in Figure 8, all four A drills had minute chipping C on the cutting edge, as shown in Figure 1. No abnormalities were found in Drill B. This is because, in the case of the A drill, the intersection of the chamfer, flank face, and rake face is sharp, whereas the B drill has no sharpness in this area and the thickness of the cutting edge is somewhat thicker than that of the A drill. This can be thought of as a result of the fact that it is also thicker.

Next, after further tests using the same drill, Figure 9 1
We obtained the following results. That is, three of the four samples of the A drill were broken and reached the end of their service life before reaching 1,200 holes, but all of the B drills could be used continuously even after drilling 1,200 holes. This is considered to be the result of minute chipping and the presence or absence of variations in dimensions a and b.

Next, in the method which is the second object of the present invention, high hardness abrasive grains are attached to a brush or an elastic puff abrasive stone.

One feature is that a chamfer having the above-mentioned shape is formed by impregnating or containing the material, pressing it against a drill cutting edge, and moving the grinding surface in a predetermined direction.

An example of this method is shown in FIGS. 10 and 11. Reference numeral 20 in the figure is a rotating brush made of material, preferably a compound material such as a metal or nylon having good wear resistance, and hard abrasive grains 21 such as diamond or silicon carbide are attached to this brush. This brush is pressed against the cutting edge part of the drill 10 held by a chuck 30 or the like as shown in the figure, and the grinding part, that is, the tip of the brush moves from the rake surface 11 to the relief surface 12 side or once in the opposite direction. When the brush is rotated to do so, a chamfer in the shape shown in FIG. 7 is formed due to the bending of the tip of the bristles.

Note that the material of the brush and the type of hard abrasive grains may be appropriately selected in consideration of the grinding time and amount of grinding.

Further, the brush may be one that can be repeatedly moved about once in a straight line, and one brush may also contain or be impregnated with hard abrasive grains.

Furthermore, a chamfer having the same shape can be formed by using a grinding tool in which hard abrasive grains are attached to or contained in an elastic puff grindstone instead of a brush.

According to this method, the brush etc. can be pressed against the cutting edge of a complex shape, so the grinding tool such as the brush and the drill are held in a mechanized bend and the position and precision of both are controlled while grinding. By doing this, it is possible to efficiently apply a chamfer with high precision. In addition, by changing the plunge angle and plunge amount of the cutting blade against the grinding tool, it is also possible to change the size of the chamfer at the center of the cutting blade and the outer circumference of the cutting blade, and the basic usage with respect to the reference line. be.

←) Effects As explained above, the present invention reduces chipping of the cutting edge without reducing sharpness by devising the chamfer shape, so it is possible to provide a high-performance carbide drill with a long life.

In addition, the method of the present invention makes it possible to mechanize chamfer machining, which conventionally had to be done by hand, and thus greatly contributes to reducing the cost of drills. Since variations can be prevented, drill performance can be further improved.

Needless to say, the scope of the present invention includes all drills whose cutting blades are partially or entirely made of cemented carbide.

[Brief explanation of drawings]

Figure 1 is a side view showing an example of a conventional carbide drill; Figure 2 is a side view showing an example of a conventional carbide drill;
The figure is a front view, FIG. 3 is an enlarged cross-sectional view taken along the line X-X in FIG. 2, and fa) (1)) in FIG.
Graph showing changes in toughness and wear resistance by changing the size and angle of the chamfer in the groove, FIG. 5 is a side view showing an example of the carbide drill of the present invention, FIG. 6 is a front view thereof, and FIG. 7 is an enlarged sectional view taken along the Y-Y line 1 in Fig. 6, Fig. 8 is a perspective view showing the properties of the front cutting edge of the conventional drill A and the drill B of the present invention used in the test, and Fig. 9 is the same as above. A graph showing the durability of the drill, FIG. 10 is a plan view showing an example of the method of the present invention,
FIG. 11 is a front view thereof. 10... Carbide drill, 11... Rake face, 12...
- Flank surface, 13... Chamfer, 14... Chisel blade, 15... Front cutting blade, 20... Rotating brush, 21...
・High quality abrasive grains. 30...Chuck same agent sickle 1) sentence ni*zif ¥- ku hexa curtain (=) f JP-A-Sho GO-221208 (5) fit in hat) hill U ÷ bow H (gu niece

Claims (4)

[Claims] (1) In a carbide drill in which the cutting edge is strengthened by removing the oblique edges of the rake face and flank by attaching a small to medium-sized chamfer that intersects one point on both sides, the chamfer is installed at one point on the rake face side. ) is larger than that on the flank side, and the chamfer is continuous with a slight roundness on the rake face and the flank face, respectively, and the entire chamfer is a curved surface in a convex direction. Drill. (2) The chamfer is larger on the rotation center side, and the outer circumference is 1
The cemented carbide drill according to claim 1, characterized in that the diameter of the cemented carbide drill is reduced accordingly. (3) High-hardness abrasive particles are adhered to or impregnated into a rotating brush, a brush that is repeatedly moved in a straight line, or an elastic puff whetstone, and this is pressed against a drill cutting edge, so that the grinding surface of the brush or puff whetstone is From the rake face side of the cutting blade to the flank side 1
To move in this direction or in the opposite direction: 1) At the edges where the rake face and flank intersect, the rake face and flank face are placed so that the rake face side is larger than the flank face side and has a slight roundness. A method for strengthening the cutting edge of a carbide drill, which is characterized by adding a chamfer that is curved in a convex direction. (4) The method for strengthening the cutting edge of a carbide drill according to claim (3), characterized in that diamond or silicon carbide abrasive grains are used as the high-hardness abrasive grains.