JPS6158246B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a drill used for drilling holes in cast iron or steel materials, and particularly to a cemented carbide drill using cemented carbide as a material. <Conventional technology and its problems> High-speed steel drills have traditionally been used for drilling work in general steel materials, cast iron, etc., but recently there has been a strong demand for higher efficiency in drilling work, and drills have become more popular. Increasingly, the number of rotations is increased to meet this demand, and as a result, cemented carbide, which has excellent wear resistance, is increasingly being used as drill material. However, since cemented carbide is not a material with satisfactory strength, such as inferior transverse rupture strength compared to high-speed steel, its uses are limited, and it has not always been sufficient in terms of cutting resistance and wear. The strength of a drill depends on the torsional rigidity and bending rigidity of the material, but the factors that determine the strength are the core thickness C and the groove width ratio B:A shown in FIG. Figure 2 shows the torsional rigidity values when the values were changed. The torsional stiffness ratio is expressed as a ratio of the circular cross section without grooves as 100%. As is clear from Fig. 2, the core thickness C is increased and the groove width ratio B:A
The smaller the , the stronger it will be. However, with the conventional drill shape shown in Figure 1, the core thickness C
If you simply increase the thickness of the groove and decrease the groove width ratio B:A, not only will the cutting resistance (torque, thrust) increase significantly, but it will also be difficult to eject chips, and there are limits to the core thickness and groove width ratio. Generally, the core thickness was set to 15 to 23% of the drill diameter, and the groove width ratio was set to 1 to 1.3:1. Further, one of the reasons for the increase in cutting resistance is that the rake angle _θ 1 in the radial direction is negative at any arbitrary position or point in the radial direction of the cutting edge 1 shown in FIG. In addition, since the distance between the negative position and the opposite groove wall (indicated by l ₁ in Fig. 1) is large in conventional drills, the chips 2 ejected as shown in Fig. 3 are This may also happen if it does not hit the complete groove wall and may reach the machined hole wall. 3 in the diagram
indicates the contact area of the chip 2. <Means for solving the problem> The present invention was made to solve the problem, and the core thickness C in a drill made of ultra-hard material.
25~35% of drill diameter, groove width ratio B:A 0.4~
0.8:1, and at least 2/3 of the drill diameter, the shape of the cutting edge when viewed directly from the outer periphery is set so that the rake angle in the radial direction is -5° to positive, and the groove wall facing the cutting edge 1 When assuming that a perpendicular line is drawn from the outer periphery of the wall to the reference line, with the cutting edge outside at least 2/3 of the drill diameter as the reference line, when the cutting edge tip is viewed directly, The first feature is that the distance between the outer periphery of the cutting edge is 47% or less of the drill diameter. The second feature is that at least 2/3 of the drill diameter is connected with a concave curve so that the rake angle of the cutting edge face directly viewed from the outer periphery is 0° to positive.
It is characterized in that part or all of the cutting edge is coated with a thin film. Additionally, a margin of the outer diameter portion is provided at the cutting edge position, and is also provided on the opposite side of the cutting edge. <Example and its effects> Made of ultra-hard material, the core thickness C is 25 to 35% of the drill diameter, the groove width ratio B:A is 0.4 to 0.8:1, and the above rake angle is at least Connect the cutting edge end face directly viewed from the outer periphery of 2/3 of the drill diameter with a straight line or concave curve so that the rake angle in the radial direction is -5° to positive, and determine the distance between the cutting edge 1 and the opposing groove wall. ,
That is, in Fig. 14A and B, draw a perpendicular line c-d passing through the wall end c of the groove opposite to the reference line connecting point a on the outer periphery and point b, which is 2/3 of the drill diameter on the cutting edge 1. When the distance from a line parallel to the perpendicular line and passing through the outer end point a of the cutting edge is defined as distance l (Fig. 14A), this distance l should be 47% or less of the drill diameter D, and all or part of the cutting edge should be The part is coated with a thin film of TiCN, TiC, Al ² O ₃ or the like. The above distance is defined not as a right-angled cross section of the drill, but as an end view after the tip angle has been applied. The embodiments shown in FIGS. 4 and 5 have a rake angle of 0° in the radial direction, and FIG. 6 shows an example in which the rake angle is a positive angle θ ₂ , contrary to the conventional drill. , Figure 7 shows that the shape of cutting edge 1 is -5 at the outer periphery of the drill.
This is an example of a concave curve having a positive value of ˜°. Further, as shown in FIG. 6, margins on the outer diameter portion are also provided at the cutting edge position 4 and at the opposite side 5 of the cutting edge. Each of the above requirements is based on the following reasons. Figure 8 is a diagram comparing the sharpness achieved by making the rake angle positive in the radial direction and the flow of chips by reducing the distance between the cutting edge and the groove wall facing the cutting edge. When the distance is small, the chips 11 are bent small and do not hit the hole wall 12 and do not damage the hole wall, but as the distances B and C increase, the chips become more bent and hit the hole wall, Also, since it is cut into large pieces, it is not easy to discharge it smoothly. The point angle of conventional drills is generally 118 to 130 degrees, and in this case the rake angle is negative. In the present invention, the tip angle is 135 to 145 degrees, and the rake angle is -5 degrees to positive. The larger the positive angle, the greater the torque reduction effect, but if it is too large, the strength of the cutting edge will decrease. Therefore, from the viewpoint of both sharpness and strength, a range of 0 to 20 degrees is preferable. Fig. 10 shows the differences between examples a', b', c', d' of conventional drill A shown in the left half of Table 1 below and examples a to f of drill B according to the present invention. C is the core thickness expressed as a percentage of the drill diameter, θ is the rake angle, R
indicates the groove width ratio, and in the conventional technology, the rake angle is a negative angle, and it is clear that the groove width ratio and core thickness are all different. Regarding the drill, the overall strength, strength of the outer periphery of the cutting edge, cutting resistance, and chip control are determined by S50C.
The scores obtained by testing steel and evaluating it with the highest score being 10 points, the total score, and the overall evaluation are ◎,
It can be seen that the overall characteristics are good if the ratio of distance l to drill diameter is 47% or less, which is shown in the order of 〇, △, and ×.

[Table] Also, if the rake angle is -5° or less, the cutting resistance will be high and the rigidity will be insufficient, so -5° to positive is suitable, but it is recommended to keep it in the range of 0 to 20° from the viewpoint of both sharpness and strength. desirable. If the core thickness is 30%, the length of the cutting edge will be 1/3 + 1/3 = 2/3 as shown in Figure 9. Therefore, if 1/2 or more of the cutting edge has a positive rake angle, sufficient effect will be exhibited, so we set the condition that the rake angle be at least 2/3 of the drill diameter. Furthermore, if the core thickness C is less than 25% of the drill diameter, the torsional rigidity will be insufficient, and if it exceeds 35%, chip evacuation will be poor. Groove width ratio is also 0.4 to 0.8:
If it is outside the range of 1, the curling and cutting of chips will not go well. In Figure 11, the work material is S50C, H _B 240, and the cutting speed
This is a comparison diagram of the characteristics of the drill of the present invention with a diameter of 8.5 mm at 50 m/min and a conventional drill.The drill of the present invention has torque and thrust similar to the conventional drill, and has a negative rake angle in the radial direction. Compared to a conventional drill with a large core thickness and a large groove width ratio, this shows a marked decrease. The specifications of each of the above drills are shown in Table 2, and the material is cemented carbide (P30), the surface of which is coated with TiN.

[Table] Figures 12 and 13 of the attached drawings are curves showing the effect of the coating layer in the present invention. S48C, H _B
The results of drilling holes in 2.20 material at V = 50 m/min are shown for comparison. As can be understood from the figure, it has been shown that the cutting force provided with the coating layer is suppressed and wear is reduced. With the above configuration, the following effects can be obtained. (1) As shown in Figure 2, torsional rigidity is greatly improved. The same applies to bending rigidity. (2) Figure 11 shows an example in which the work material is S50C, H _B 240, and a φ8.5 drill is used at a cutting speed of 50 m/min. Compared to a conventional drill with a radial rake angle, a large core thickness, and a large groove width ratio, the torque and thrust are significantly lower. (3) By making the distance between the cutting edge and the groove wall at the outer periphery of the drill close as shown in Figure 14A (B is a conventional drill), chips can be cut and discharged only within the drill groove. This will improve drainage performance. The embodiments shown in FIGS. 4 and 5 are for the case where the rake angle θ in the radial direction is 0°,
FIG. 6 shows an example in which θ ₂ has a positive rake angle, contrary to the conventional drill. The effect further enhances the above-mentioned effect. Further, FIG. 7 shows a case in which the cutting edge is formed in a concave curved shape with an angle of −5° to positive at the outer periphery of the drill. In this case, the generation of chips is shared by the longer cutting edge, so it is carried out smoothly, and the longer cutting edge length reduces the amount of work per unit length of the cutting edge, improving wear resistance. It becomes possible. Further, Fig. 6 shows an embodiment with a double margin, that is, margin parts 4 and 5, which not only improves hole accuracy but also prevents chips from flowing into the second part of the outer periphery. , cutting can be done smoothly. However, these effects are due to the fact that the cutting edge is TiCN, TiC,
By being coated with a thin film such as Al ₂ O ₃ , it is more effective and the advantages of the superhard alloy are fully utilized. Coating generally improves wear resistance and durability, and has the effect of improving welding resistance on the finished surface and reducing cutting resistance, but when slicing and turning, the cutting speed is relatively low. It is large, so welding problems are unlikely to occur, and the magnitude of cutting resistance does not matter much. However, in the case of a drill, it is important to increase its overall strength, and in addition to increasing the absolute strength of the drill itself in terms of shape, coating reduces the cutting resistance that acts on the drill and improves its strength and durability.

[Brief explanation of the drawing]

Figure 1 is an end view of the drill, Figure 2 is a curve showing the relationship between core thickness and groove width ratio on torsional rigidity, Figure 3 is an explanatory diagram showing the state of chips in a conventional drill, and Figure 4. is an end view of the drill of the present invention, No. 5
The figure is a side view of Figure 4, Figures 6 and 7 are end views of other embodiments, Figure 8 is a comparison diagram showing the flow of chips, and Figure 9 is a diagram showing the drill diameter and cutting edge length. FIG. 10 is a comparison diagram showing the differences between a conventional drill and the drill of the present invention. FIG. 11 is a comparison diagram of test results showing the relationship between thrust, torque, and feed in drills of various shapes. Figure 12 is an experimental comparison diagram showing the relationship between thrust, torque and feed with and without a coating layer, Figure 13 is an experimental comparison diagram showing the relationship between the outer circumferential margin and the number of holes drilled, and Figure 14 is an explanatory diagram of the distance l. , in the same figure, A is the case of the present invention, and B is the conventional drill. R... Groove width ratio B: A, C... Core thickness, D... Drill diameter, θ... Rake angle, l... Distance, 1... Cutting edge, 4, 5... Margin.

Claims (1)

[Claims] 1. In a drill made of an ultra-hard material, the core thickness is 25 to 35% of the drill diameter, the groove width ratio is 0.4 to 0.8:1, and the radial rake angle of the cutting edge when viewed directly from the end is at least as large as the drill diameter. -5° to positive outside 2/3 of
Assuming that a perpendicular line is drawn from the outer periphery of the groove wall to the reference line using the cutting edge that is at least 2/3 outside of the drill diameter when viewed directly from the cutting edge as a reference line, the relationship between the perpendicular line and the outer periphery of the cutting edge is The distance is 47% or less of the drill diameter, and part or all of the cutting edge is coated with one or more of TiN, TiC, TiCN, or Al ₂ O ₃ directly or through another layer. A drill characterized by: 2. The shape of the cutting edge in direct view from the core thickness to the outer periphery of the drill is connected by a concave curve so that the rake angle in the radial direction of the cutting edge outside of at least 2/3 of the drill diameter is between 0° and positive. The drill according to claim 1, characterized in that: 3. The drill according to claim 1 or 2, characterized in that the margin of the outer diameter portion is provided at the cutting edge position and also provided on the opposite side of the cutting edge. 4. The drill according to claim 1, 2, or 3, wherein a portion of the coated cutting edge is at least a rake face or a margin.