JPS6260202B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a high-speed steel drill, and particularly to a drill whose strength can be increased as much as possible while suppressing an increase in cutting resistance and a decrease in chip evacuation function. [Technical background of the invention and its problems] High-speed steel has traditionally been used for drilling work in general steel materials and steel. Originally, a drill advances while discharging chips generated by drilling to the outside of the hole through its own groove.
In order for this drilling work to be performed efficiently, it is required that the cutting resistance be small and that the chips be discharged smoothly, and the quality of the chip discharge also affects the increase or decrease in the cutting resistance. affect In particular, the increase in cutting resistance becomes more significant as the drilling depth increases. Further, the drill is required to have sufficient strength to withstand the cutting forces acting on it. However,
Increasing the area of the groove and decreasing the core thickness in order to improve the chip evacuation function inevitably reduces the cutting resistance, especially the thrust, but on the other hand, there is a dilemma that the strength is insufficient. The relationship between the two must be harmonized. Further, the strength of a drill is given not only by the toughness and elasticity of the material itself, but also by the rigidity (bending rigidity and torsional rigidity) that depends on the shape. Therefore, regarding the shape that governs the strength of conventional drills, the shape of the cutting edge when viewed directly from the edge is the first.
This will be explained with reference to the diagram. A portion 1 indicated by a broken line in the figure is a thick core portion, and a land portion 3 is a solid portion in which no groove portion 2 is formed. In other words, as is well known, the drill has a groove portion 2 around a thick core portion 1, which serves as a chip discharge passage.
and a land portion 3, which is a thick wall portion, are formed so as to wrap around each other in a spiral shape. Therefore, the drill diameter D
The ratio of the diameter C of the core thick portion 1 to the diameter C (hereinafter referred to as the core thickness ratio and expressed as a percentage) is involved in the strength of the drill, and the ratio of the circumference B of the groove portion 2 to the circumference A of the land portion 3 is related to the strength of the drill.
The ratio (hereinafter referred to as the groove width ratio and expressed as B:A) similarly affects the strength of the drill. These two factors can be considered to be factors that mainly control the strength of the drill in terms of shape. In other words, the drill strength increases as the core thickness ratio increases and the groove width ratio decreases. Figure 2 is a graph showing this relationship in terms of torsional rigidity ratio at each value of core thickness ratio and groove width ratio. and is expressed as a ratio to that value. In the figure, samples A to D have the shapes of general conventional drills, and the groove width ratio of each sample is 1:1 for A and C, and 1.3:1 for B and D. In addition, samples Ho to Ho are examples in which the core thickness ratio is large and the groove width ratio is small, and the groove width ratio of each sample is 0.4:1 for Ho and F, and 0.8:1 for G and Chi. As shown in the figure, it is clear that the sample hoops show a good torsional stiffness ratio and are excellent in strength. However, simply increasing the core thickness ratio and decreasing the flute width ratio will result in an increase in cutting force and a decrease in chip evacuation function, and the range in which these values can take is inevitably limited. The value is the core thickness ratio
The groove width ratio was 1:1 to 1.3:1. Note that the web taper has a well-known appropriate slope. FIG. 3 shows the shape of a conventional product called a large-core drill, when viewed directly from the incisal end surface, which has been devised to eliminate the above-mentioned general restrictions. In this example, the core thickness ratio is set to be as large as about 50%. In other words, the core thickness ratio is increased to increase strength, but simply increasing the core thickness ratio will reduce the area of the groove, so a tip pocket 4 is provided at the tip of the drill to further reduce shear stress. The heel portion 5 is rounded to prevent concentration and increase torsional rigidity. However, in this case, although the area of the chip pocket 4 is large, the chip pocket has a cross section different from that of the discharged chips, so it cannot be said to be an effective groove shape.
Rather, the rounded portion of the heel portion 5 was clogged with chips, which could cause the drill to break. Therefore, the conditions under which this type of drill can be used are limited to a narrow range due to the shape of the chips. [Object of the Invention] The present invention has been devised in view of the above-mentioned circumstances in order to effectively improve the performance of a drill. Therefore, an object of the present invention is to provide a drill that can increase the strength as much as possible while suppressing an increase in cutting resistance and a decrease in chip evacuation function. [Summary of the Invention] The present invention provides a method in which the diameter of the core thick portion is 25% or more of the drill diameter.
35%, and the flute width ratio is set within the range of 0.4:1 to 0.8:1, and the radial rake angle of the cutting edge located at least 2/3 of the drill diameter on the outer peripheral side is -5%. The above object is achieved by setting the cutting edge to be within a positive range, and by bringing the relative positional relationship between the cutting edge and the groove walls facing each other closer to each other. [Embodiments of the Invention] A preferred embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 4 is a side view showing the cutting edge end face of the drill according to the present invention when viewed directly, and FIG. 5 is a perspective view showing the schematic structure of the tip thereof. In the figure, the diameter C of the thick core portion 1 (indicated by a broken line)
is set within a range of 25% to 35% of the drill diameter D. Furthermore, the ratio of the circumference B of the groove portion 2, which is the space portion, to the circumference length A, which is the thick portion, of the land portion 3 is 0.4:1.
It is set within the range of ~0.8:1. That is, compared to conventional drills, the core thickness ratio is large and the groove width ratio is small. Next, the cutting edge 6 located on the outer peripheral side of at least 2/3 of the drill diameter has a rake angle θ ₁ in the radial direction set within a range of −5° to positive, and the cutting edge shape is a concave arc. is formed. Also, a point with respect to an imaginary reference line connecting a point P ₁ at the outer peripheral end of the cutting edge 6 and a point P ₂ on the cutting edge 6 that is 2/3 of the radius from the center and closer to the outer periphery. _P1
The distance L (hereinafter referred to as relative distance) from the point P ₃ of the outer peripheral end of the groove wall 7 facing the cutting edge 6 to the upper perpendicular line is set to 47% or less of the drill diameter D. In addition, since the core thickness ratio is large, the flank surface 8 of the cutting edge 6
As shown in FIG. 5, about half of the rear side of the drill in the rotating direction is ground down by thinning to form a cutting edge 9 in the thick core portion. Thinning is performed axially symmetrically with respect to the axis O of the drill,
This forms a rake face 10 of the cutting edge 9 and an adjacent ground surface 11 adjacent thereto. This type of thinning is called cross thinning, and the cutting edge 9 in the thick core part is aligned with the axis O as shown in Fig. 4.
They are formed in straight lines 180° from the opposite sides.
The width of the chisel where the cutting edge 9 is not formed is set within the range of 0 mm to 0.4 mm, and the closer it is to 0 mm, the better. In addition, the angle θ ₂ between the direction of the straight line connecting the point P ₁ on the outer peripheral edge of the cutting edge 6 and the axis O and the direction in which the cutting edge 9 in the core thickness section extends is set within the range of 35° to 45°. has been done. Rake face 10 formed by thinning
is its axial rake angle θ ₃ (as shown in Fig. 7)
is set within the range of -5° to +5°. Further, as shown in FIG. 6, the length of the rake face 10 in the axial direction is 0 mm at the axial center O, and gradually increases as it goes outward in the radial direction. The angle θ ₄ formed between the valley line 12 formed by the intersection of the rake face 10 and the adjacent ground surface 11 and the axis O of the drill is set within the range of 25° to 60°. This angle is set at an angle that ensures a sufficient axial length of the rake face 10 so that the chips cut by the cutting edge 9 do not hit the adjacent polished surface 11 and increase the thrust. and is set so as to obtain a sufficient breaking effect on chips. In addition, it is set so that sufficient strength can be obtained. In addition, the angle θ ₅ (shown in FIG. 7) between the rake face 10 and the adjacent ground surface 11 is set within the range of 90° to 110° to prevent an increase in thrust due to chips and to ensure sufficient braking action. It is set so that it can be obtained. FIG. 8 is a perspective view showing an embodiment of the drill in which the tip portion of the drill is configured as described above, and further includes an oil supply hole for chip oil. As shown in the figure, inside the land portion 3 and the shank 13, which are solid thick portions from the tip to the rear end of the drill, a spiral cut is made along the helix angle of the groove portion 2. Two oil supply holes 14 are formed. Discharge port 1 of each oil supply hole 14
5 is opened in the flank 8 of the cutting blade 6, and the suction port 16 is opened in the bottom surface 17 of the rear end. Oil supply hole 14
The number of 2 is equal to the number of stripes of the land section 3 formed.
A book is preferable, but one book is also acceptable. Further, the inner diameter of the oil supply hole 14 is preferably several percent to 20% of the drill diameter D in view of the strength of the drill. The oil supply hole 14 of this drill is made by forming two holes to serve as oil supply holes along the axial direction in a high-speed steel material formed in a plate-shaped bar member, and then holding the plate-shaped bar member under high temperature. It can be formed by being plastically deformed by twisting. Furthermore, drills configured in each of the above shapes have TiC, TiCN, and TiN on their surfaces.
A coating layer may be formed using one or a combination of two or more of Al ₂ O 3 and Al 2 O ₃ . Also,
The coating layer is formed into a dense thin layer by ion plating or chemical vapor deposition. Next, the operation of the embodiment of the present invention will be explained based on experimental data in comparison with the conventional example. Table 1 below shows drills with common configurations (conventional products).
1) Data from experiments conducted on three types of samples: a drill with a simply increased core thickness ratio and decreased groove width ratio to increase strength (conventional product-2), and a drill according to the present invention (invented product). It shows. In addition, in order to make the effect of thinning constant, all samples were subjected to the same thinning as the invention product. The thinning shape of the test sample is as follows: chisel width = 0.1mm, θ ₂
= 40°, θ ₃ = 0°, θ ₄ = 38°, and θ ₅ = 100°. Drill diameter is 8.5mm, material is SKH9, H _RC
It is 63. The work material is S50C, H _B 250, and the cutting conditions are: cutting speed V = 15 m/min, feed rate per rotation f = 0.25 mm/rotation, and drilling depth 40 mm.
The cutting oil was an emulsion type and was supplied externally.

[Table] As is clear from Table 1, the conventional product-2, which has a small groove width ratio and a large core thickness ratio, and the invented product have a cross section of 2.
Both the moment of order and the torsional stiffness ratio are increased, and the effect of increasing strength is significant. By the way, although such an effect is well predicted, the reason why a drill like Conventional Product-2 has not been adopted in the prior art is as already stated. As shown in the data values of torque and thrust that indicate cutting resistance in Table 1, the product of the present invention has a slight increase in thrust, but not as much as the conventional product-2, and in terms of torque. is suppressed to the same value as conventional product-1. Moreover, the strength has increased sufficiently. That is, this effect is obtained by increasing the rake angle of the cutting edge 6 in the radial direction. Another feature of the present invention is that it suppresses deterioration in chip evacuation function. The quality of the chip evacuation function is influenced by the shape of the chips generated and their movement within the groove 2. Figure 9 is conventional product-2
FIG. 3 is a schematic diagram showing the movement of chips caused by the drill.
The chips 18 cut out from the cutting edges 6 and 9 are formed in a curled shape along the groove wall 7 and flow from the center side to the outer circumferential side of the drill. At this time,
If the distance between the cutting edge 6 and the groove wall 7 is large, chips 1
8 becomes larger, and the chips 18 tend to become clogged in the groove 2. Also, the chips 18 are removed from the hole wall 1.
It breaks when it hits point 9, making the finished surface rough. One of the important factors governing the movement of the chips 18 is the relative relationship between the shape (curvature) of the cutting edge 6 and the shape (curvature) of the groove wall 7. Therefore, in order for the chips 18 to pass through the groove portion 2 and be smoothly discharged, there is an appropriate shape relationship between the cutting edge 6, the groove walls 6, and the groove walls 7. If the shape is expressed using some index, the relative positional relationship of the groove wall 7 to the cutting edge 6 or the cutting edge 6 to the groove wall 7 can be expressed by the distance (relative distance) between them. Expression is effective as one display method. Therefore, it is possible to define the relative distance L as one index, and express the quality of the chip evacuation function by the ratio of the relative distance L to the drill diameter D. That is, in the example shown in FIG. 9, the relative distance L is large, so that the narrow groove portion 2 cannot sufficiently perform the chip discharge function. Next, the performance will be compared among three types: the conventional drill shown in FIG. 3, the conventional drill 1 shown in Table 1, and the drill of the present invention. In this case, the thinning shown in Figure 3 was also the same as for the other drills. As shown in Table 1, the torque and thrust of the Conventional-1 drill are almost stable. In the conventional drill shown in Figure 3, the normal torque is 85Kgfcm and the thrust is 330Kgf, but when the hole depth is near 30mm, the torque increases to 130Kgfcm and 380Kgf, respectively.
It becomes Kgf. In contrast, with the drill of the present invention,
As shown in Table 1, it is stable at a low value. Next, as a result of a continuous drilling test, the resistance of the conventional drill shown in Figure 3 increased as the hole depth increased, and the drill broke at the 33rd hole. The conventional-1 drill in Table 1 was able to cut stably, but it broke at the 350th hole. Observation of the drill revealed that the maximum wear width on the flank surface reached 0.7mm, and it was assumed that the breakage occurred due to increased resistance. On the other hand, Table 1
The drill of the present invention experienced the same level of wear as the conventional -1 drill after drilling 400 holes, and had the same strength as the conventional -1 drill. FIG. 10 is a schematic diagram showing the movement of chips by the drill of the present invention. The relative distance L is the drill diameter D.
Since it is set to 47% or less, the chips 18 are curled along the groove wall 7, broken into short pieces, and formed into a shape that is easy to flow in the groove 2, that is, easily discharged. Furthermore, by setting the angle θ ₂ shown in FIG. The parts to be curled are formed in different directions, and are cut into a shape that is easy to curl.
If this angle θ ₂ is too small, the chip 18 will have a nearly flat shape and will be difficult to curl, while if it is too large, the proportion of the area cut by the cutting blade 9 to the whole will be small and the chip will not be curled. It becomes difficult. The angle θ ₃ corresponds to the rake angle at the center, and as is well known, the larger the angle is positive, the less the resistance will be, but the strength will also be lower, and if it is negative, the opposite effect will occur. If the angle θ ₃ is in the range of −5° to +5°, the sharpness and strength can be maintained. Further, if the angle θ ₃ is not close to 0°, the amount of re-grinding per time during re-grinding will become large. The angle θ ₄ influences the evacuation of chips in the center and the magnitude of the resistance. That is, if the angle θ ₄ is small, the resistance will be small, but the chip breaking effect will be poor, and if the angle θ ₄ is large, the opposite effect will occur. Experimentally, the angle θ ₄ is 25
It can be set within the range of 35° to 41°.
° is desirable. The angle θ ₅ , together with the angle θ ₄ , influences the chip evacuation performance. The setting range of angle θ ₅ is 90
It is possible within a range of 110°, but 100° is preferable.
As is well known, the chisel is the part to be cut, and the key is how narrow it is to make the cutting edge all the way to the center.
The chisel width is preferably in the range of 0 to 0.4 mm. Next, the effect when the cutting oil supply hole 14 is formed will be explained. Suction port 1 of oil supply hole 14
When cutting oil is press-fitted from 6 through the drill holder, the cutting oil is supplied to the cutting edge 6 from the outlet 15 at the tip through the oil supply hole 14, and the cutting edge can be effectively cooled. Further, the returning cutting oil passes through the groove 2 and is discharged to the outside of the hole, and at this time, it promotes the discharge of chips and also cools the workpiece. Therefore, cutting resistance is stable and breakage accidents can be prevented. As for the size of the oil hole, the larger the hole, the more effective the oil discharge will be, but if it is too large, the cross-sectional area of the drill will become smaller, resulting in a decrease in strength. A few percent of the drill diameter
~20% is desirable, but since the groove width is set narrow and the core thickness is set large, the area of the land portion 3 becomes larger than that of a conventional drill. Therefore, even if a large oil supply hole is made, there will be less decrease in strength. Furthermore, although these drills may be made only of high-speed steel, TiC,
By forming a coating layer made of one or a combination of two or more of TiCN, TiN, and Al ₂ O ₃ , the heat resistance of the drill itself can be increased and its wear can be further prevented. Further, since these coating materials have a small coefficient of friction, the thrust and torque can be further reduced. In addition, when the drill wears out, it is re-ground to regenerate the cutting edge. However, even if the base material is exposed on the flank 8 of the drill during this regrinding, the outer circumferential surface of the rake face and margin area is coated. The layer remains and the cutting forces can remain small. [Effects of the Invention] As is clear from the above description, the present invention provides the following excellent effects. In other words, by increasing the core thickness ratio and decreasing the groove width ratio, the strength of the drill can be increased, and by increasing the radial rake angle of the cutting edge, an increase in cutting resistance can be suppressed, and the relative distance can be reduced. By reducing the size, it is possible to suppress the deterioration of the chip evacuation function.

[Brief explanation of the drawing]

Figure 1 is a side view showing the shape of a conventional drill when viewed directly from the cutting edge, Figure 2 is a graph showing the relationship between the torsional rigidity ratio, core thickness ratio and groove width ratio of the drill, and Figure 3 is another conventional drill. FIG. 4 is a side view showing the shape of the cutting edge of the drill as viewed directly from the cutting edge of the example drill, FIG. A perspective view showing a schematic configuration of the tip portion, FIG. 6 is a side view as seen from the direction of the arrow in FIG. 5, FIG. 7 is a side view as seen from the direction of the arrow in FIG. 5, and FIG. FIG. 9 is a schematic diagram showing the movement of chips in the conventional drill, and FIG. 10 is a schematic diagram showing the movement of chips in the drill of the present invention. In addition, in the figure, 1 is the core thick part, 2 is the groove part, 3 is the land part,
6 is the cutting edge, 7 is the groove wall, 9 is the cutting edge in the core thickness section, 10 is the rake face of the cutting edge in the core thickness section, 11 is the adjacent ground surface, 12 is the valley line, 14 is the oil supply hole, P ₁ is The point at the outermost edge of the cutting edge, P ₂ is a point on the cutting edge that is 2/3 of the radius from the center and closer to the outer periphery, P ₃ is the point at the outermost edge of the groove wall, is a virtual reference It is a line.

Claims (1)

[Claims] 1. A drill made of high-speed steel, wherein the diameter of the core thickness is set to 25% to 35% of the drill diameter, and the groove width ratio is set within the range of 0.4:1 to 0.8:1. and the rake angle in the radial direction of the cutting edge located at least 2/3 of the drill diameter on the outer peripheral side is set to −5° to positive in the shape of the cutting edge when viewed directly from the cutting edge, and The outermost point and the point on the cutting edge that is 2/2 of the radius from the center.
The outermost periphery of the groove wall facing the cutting blade across the space of the groove from the virtual reference line connecting the points from the outer periphery with a straight line to the perpendicular line passing through the point at the outermost periphery of the cutting blade. A drill characterized in that the distance from the end point is set to 47% or less of the drill diameter. 2 In the shape of the cutting edge when viewed directly from the end surface, the cutting edge located on the outer peripheral side of at least 2/3 of the drill diameter is
The drill according to claim 1, wherein the drill is formed into a concave arc so that the rake angle in the radial direction is set between 0° and positive. 3. The shape of the thick core portion formed by thinning is such that the chisel width is set within the range of 0 mm to 0.4 mm, and in the shape viewed directly from the end surface of the cutting blade, the shape is radially outward from the axis of the thick core portion. The respective cutting edges extending toward each other are formed linearly with respect to each other, and the direction in which the cutting edge of the core thickness section extends and the outermost edge of the cutting edge extending further toward the outer periphery from the outer circumferential end of the cutting edge of the core thickness section are formed. The drill according to claim 1 or 2, wherein an angle formed by a point on the outer peripheral end and a direction extending from the axis intersects each other on the axis is set within a range of 35° to 45°. . 4. The rake face of the cutting edge of the core thick portion formed by thinning has an axial rake angle of −5° to
The valley formed by the intersection of the rake face and the adjacent ground surface formed by thinning at the same time, with the length in the axial direction set within the range of +5° and 0 mm at the axial center position of the drill. 4. A drill according to claim 3, wherein the line is formed at an angle of inclination within the range of 25° to 60° with respect to the axis of the drill. 5. The drill according to claim 4, wherein the angle between the rake face of the thick core portion and the adjacent ground surface is set within a range of 90° to 110°. 6. The drill according to claim 1, which has a cutting oil supply hole twisted along a helix angle in the shank from the rear end to the tip of the drill and in the land portion of the main body. 7. Part or all of the surface of the drill, including at least the rake face of the cutting edge and the outer peripheral surface of the margin, is one or a combination of two or more selected from the group consisting of TiC, TiCN, TiN, and Al ₂ O ₃ . A drill according to claim 1, which is coated with.