JPH0134727B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Industrial application field The present invention relates to a carbide drill mainly used for metal processing, and more specifically, a carbide drill with a specially designed chamfer shape attached to the cutting edge to strengthen the cutting edge. This paper relates to a method for strengthening the cutting edge that enables easy and accurate chamfer processing. (b) Conventional technology and its problems Although carbide drills whose cutting blades are made of cemented carbide can improve 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, a chamfer is generally added to the edge where the rake face and flank face intersect.
This treatment strengthens the cutting edge. This chamfer is attached over the entire cutting edge, but in the conventional one, as shown in Figs. 1 to 3, a reference line P
(This reference line is parallel to the rotation axis in the case of the front cutting edge) A flat surface 3 whose inclination angle θ is in the range of 10 to 45 degrees, and the installation width a occupying the rake face is about 0.03 to 0.3 mm. Since the rounded surface is connected to the rake face and flank face and has a radius of curvature comparable to the diameter and a dimension, it has been difficult to ensure stable performance in drills. That is, FIGS. 4a and 4b 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. Γ Wear-resistant work material: SCM435 (H _s 30) Tool: FN11R-44A, Chip SNG432 Grade T12A Cutting conditions: V (cutting speed) = 170 m/min f (feed) = 0.36 mm/rev d (depth of cut )=2mm T (cutting time)=20min Γ Breakage rate Workpiece: SCM435 grooving tool Tool: Same cutting conditions as above: V=80m/min f=0.172~0.20mm/rev d=2 T=3min f= Each test was repeated three times at 0.172 and 0.20 mm/rev, and the failure rate was determined based on the number of failures and the time until failure. 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, unlike throw-away tips, it is nearly impossible to grind them with a whetstone due to the complexity of the cutting edge shape.For this reason, a handler with diamond abrasive particles attached is used to chamfer a carbide drill. However, the reality is that this is done manually, and as a result, errors (variations) occur in the angle and size of the chamfer, making drill performance unstable. Further, in the case of a drill with a flat chamfer as shown in FIG. 3, sharp edges remain 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 does not have excellent biting properties against the work material. (c) Means for solving the problem The present invention provides a carbide drill that solves the problem and a method for strengthening its cutting edge. The installation width on the rake face side of the attached chamfer is made larger than that on the flank face side, and furthermore, this chamfer is made continuous with a slight roundness to the rake face and flank face, respectively, and the entire chamfer is curved in a convex direction. It is characterized by its surface. 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. Furthermore, the angle of inclination of the chamfer 13 attached to the diagonal intersection of the rake face 11 and the flank face 12 in order to remove acute edges is also approximately the same as the value of θ shown in FIG. That is, Qianhua 13
The installed width a on the rake face side is made larger than the installed width b on the flank side to prevent the angle of the cutting edge from becoming extremely blunt, thereby suppressing deterioration in sharpness. However, unlike the conventional shape, the chamfer 13 has a gently convex arcuate surface as a whole, and its both sides have smaller roundness to form the rake face 11 and flank face 12.
connected to. Note that it is desirable that the size of the chamfer provided on the front cutting edge of the drill be controlled in accordance with the position of the cutting edge. For example, welding defects on the center cutting edge and wear on the outer cutting edge, which are problems specific to drills, can be alleviated by increasing the chamfer size toward the center of rotation and gradually decreasing it toward the outer periphery. can be reduced to width. Adjustment of the size of the chamfer, etc. can be easily and accurately performed by the method of the present invention, which will be described later. Below, the results of a comparative test regarding the cutting performance of the drill of the present invention with the above-mentioned chamfer and a conventional drill will be listed. The drills used in the test, A (conventional drill) and B (drill of the present invention) in Fig. 8, both have a diameter of 10 mm. In addition, the chisel blade 14 of both is thinned.
The width of the front cutting edge 15 is made extremely small, and the front cutting edge 15 is curved in the same direction when viewed from the end. The cutting edge treatment shown in FIG. 3 is applied to the A drill, while the cutting edge treatment shown in FIG. 7 is applied to the B drill. The dimensions of the processing section are shown in Table 1 below.

[Table] Prepare four of each of these two types of drills, and
Holes were drilled on S50C (HB250) using emulsion type water-soluble cutting oil. The measurement results of the cutting torque and thrust force at that time are shown in Table 2, and there was no significant difference between the two.

[Table] Also, cutting conditions V = 50m/min, f = 0.3mm/
When 800 holes with a depth of 30 mm were drilled using rev, as shown in Figure 8, minute chipping C was observed on the cutting edge of all four A drills, but B
No abnormality was found in the drill. this is,
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 Next, further tests were conducted using the same drill, and the results shown in FIG. 9 were obtained. That is, three of the four samples of drill A broke out and reached the end of its life before reaching 1200 holes, but drill B could continue to be used even after drilling 1200 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, a brush or an elastic buffing wheel is impregnated with or contains high hardness abrasive grains, and this is pressed against a drill cutting edge to define a grinding surface. It is characterized in that a chamfer having the above-mentioned shape is attached by moving it in a different direction. An example of this method is shown in FIGS. 10 and 11. Reference numeral 20 in the figure is a rotating brush preferably made of 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. Press this brush against the cutting edge of the drill 10 held by a chuck 30 or the like as shown in the figure, and hold the brush so that the grinding part, that is, the bristles of the brush move from the rake face 11 to the flank face 12 side or in the opposite direction. When the bristles are rotated, a chamfer in the shape shown in FIG. 7 is formed due to the bending of the tips 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 moved repeatedly in a linear manner, and the 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 buffing stone instead of a brush. According to this method, a brush or the like can be pressed against a cutting edge with a complicated shape, so the grinding tool such as a brush and a drill are mechanically held and the positions and angles of both are controlled while grinding is carried out. By doing
A highly accurate chamfer can be applied efficiently. Furthermore, by changing the plunge angle and plunge amount of the cutting blade into the grinding tool, it is also possible to change the size of the chamfer at the center of the cutting blade and the outer periphery of the cutting blade, the basic angle with respect to the reference line, etc. (d) 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. . Furthermore, the method of the present invention makes it possible to mechanize chamfer machining, which conventionally had to be done manually, and thus greatly contributes to reducing the cost of drills.Mechanization also prevents variations in chamfer size, etc. This has the effect of further improving drill performance. It goes without saying that the scope of application of the present invention includes:
This includes all drills whose cutting edges are partially or entirely made of cemented carbide.

[Brief explanation of drawings]

Fig. 1 is a side view showing an example of a conventional carbide drill, Fig. 2 is a front view thereof, and Fig. 3 is a side view showing an example of a conventional carbide drill.
An enlarged cross-sectional view taken along the X-ray, a and b in Fig. 4 are graphs showing changes in toughness and wear resistance by changing the size and angle of chamfer in a turning tool, and Fig. 5 is a graph showing changes in toughness and wear resistance of the carbide of the present invention Side view showing an example of a drill, No. 6
The figure shows its front view, Figure 7 is an enlarged sectional view taken along the Y-Y line in Figure 6, and Figure 8 shows the properties of the front cutting edge of conventional drill A and drill B of the present invention used in the test. FIG. 9 is a graph showing the durability of the same drill as above, FIG. 10 is a plan view showing an example of the method of the present invention, and FIG. 11 is a front view thereof. 10... Carbide drill, 11... Rake face, 12
... Flank surface, 13 ... Chisel blade, 15 ... Front cutting blade, 20 ... Rotating brush, 2
1...High quality abrasive grain, 30...Chick.

Claims (1)

[Scope of Claims] 1. A carbide drill in which the cutting edge is strengthened by removing the diagonal edges of the rake face and flank face by attaching a chamfer of a minute width that intersects both faces, the rake face side of the chamfer being The width of the chamfer is larger than that on the flank side, and the chamfer is continuous with a slight roundness to the rake face and the flank face, respectively, and the entire chamfer is curved in a convex direction. Carbide drill. 2. The carbide drill according to claim 1, wherein the chamfer is large on the rotation center side and gradually becomes smaller toward the outer periphery. 3 A rotary brush, a brush that moves linearly repeatedly, or an elastic buffing wheel is attached to and impregnated with or contains high-hardness abrasive grains, and is pressed against the drill cutting edge, so that the grinding surface of the brush or buffing wheel is pressed against the cutting edge. By moving from the rake face side to the flank face side or in the opposite direction, the installation width on the rake face side is larger than that on the flank face side and a minute roundness is created on the edge part where the rake face and flank face diagonally intersect. A method for strengthening the cutting edge of a carbide drill, which is characterized by attaching a chamfer that is curved in a convex direction and connected to the rake face and flank face. 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.