KR940011215B1 - Twist drill - Google Patents

Abstract

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Description

Twist drill

1 to 3 are views showing a first embodiment of the present invention,

1 is an end view in the axial direction showing a drill.

FIG. 2 is a side view of II of FIG. 1.

3 is an end view in the axial direction showing a modification of the above-described drill.

4 to 12 show other embodiments,

4 (a) is an end view in the axial direction showing the drill.

4 (b) is an enlarged view of the portion indicated by arrow A in FIG. 4 (a).

Fig. 5 (a) and Fig. 5 (b) are front end views of the V-direction in Fig. 4 (a).

6 is a cross-sectional view taken along the line VI-VI of FIG. 4 (a).

7 is a sectional view along the VII direction of FIG. 5 (a).

8 is a distal end view of the VIII direction of FIG. 5 (a).

9 and 10 are enlarged views showing chisel portions.

11 and 12 show an example of the change in the honing shape shown in FIG.

13 is an axial distal end view showing a conventional drill.

14 is a perspective view showing a chip.

* Explanation of symbols for main parts of the drawings

10: drill body 11: torsion groove

12: cutting edge 13a: thinning blade

14: intersection portion 15: tip polishing surface

16: slope 17: goal line

18: the first free side 19: the second free side

20 Chisel 21 Honil

21a: inner ridge 21b: end

22: oil hole O: axis

L: vertical line

The present invention relates to a twist drill (hereinafter abbreviated as drill) configured as cemented carbide or cermets, and in particular to a technique for reducing cutting resistance.

Recently, cemented carbide drills are being used a lot. Such drills are excellent in wear resistance and can be subjected to high speed cutting or heavy cutting. However, they are inferior in mechanical strength such as anti-cutting force due to their low toughness. Therefore, they have a larger center thickness and a smaller groove width ratio than those of high speed steel drills. You must make up the intensity. Fig. 13 shows an example presented above as such a drill (Japanese Patent Laid-Open No. 61-30845). The drill shown in this drawing has two torsion grooves 2 formed on the outer circumference of the drill body 1 made of cemented carbide and a cutting edge 3 formed at the free end of the wall facing the direction of rotation of the torsion groove 2. will be. At this time, the center thickness T of the drill body 1 is set at 20-35% of the drill diameter, and the groove width ratio A / B is set at 0.4-0.8.

The shape of the torsion groove 2 at the tip end portion of the drill in the axial direction connects the corner Q with the axis of the drill body 1 to the outer circumferential corner Q of the cutting edge 3. When the vertical line L orthogonal to one straight line N is drawn, it becomes concave shape with respect to this vertical line L. FIG. However, the above-described drill has a problem that chipping is easy when heavy cutting or high speed cutting is performed. That is, since the chip generated by the cutting edge 3 has a faster growth rate than the inner circumferential side, the chip is grown as if the fan is unfolded and the tip of the chip is grown at the bottom 2a of the torsion groove 2. ), That is, bent by the periphery of the portion where the distance from the vertical line L is the maximum, and a fracture occurs at the root portion of the chip due to the resistance at that time, and as shown in FIG. It is called a form.

By the way, in the said drill, as a result of trying to raise the torsional rigidity, the distance W from the said vertical line L to the bottom part 2a of the torsion groove 2 becomes short. For this reason, the chip receives the resistance from the bottom portion 2a of the torsion groove 2 directly in the direction opposite to the growth direction of the chip, and a chip having a thick and compressed thickness is produced. In addition, when the chip is subjected to strong compression, a large cutting torque or thrust load is applied to the drill body 1. Furthermore, the above-described drill has a short distance W from the vertical line L to the bottom portion 2a of the torsion groove 2, so that the cross-sectional area of the cross section orthogonal to the axis of the torsion groove 2, that is, the discharge area of the chip It is inevitably small and clogging of the chip is likely to occur, whereby chipping of the drill is more likely to occur when high-speed cutting or heavy cutting is performed.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and can reduce thrust loads, cutting torques, etc., as well as prevent chip clogging, by roughly curling the chips without forcibly compressing them. An object of the present invention is to provide a drill capable of preventing the occurrence of chipping in high speed cutting or heavy cutting.

The first feature of the present invention is to drill the maximum value of the distance from the vertical line to the wall surface of the torsion groove when drawing a vertical line perpendicular to the straight line connecting the corner and the center of rotation of the drill body to the outer corner of the cutting edge. It is set to 45-65% of the diameter.

The second feature of the present invention is to form a thinning blade extending in the circumferential direction from the axis portion to the center thickness portion of the drill body by thinning, and to make the shape of the cutting edge and the thinning edge in the axial direction of the cutting edge in a straight shape. In addition, the shape at the distal end portion of the cross section of the thinning edge and the cutting edge in the axial direction is an arc shape. As described above, when the tip of the grown chip is bent at the bottom of the torsion groove, the chip receives resistance in the opposite direction to the growth direction, but in this case, when the length of the chip is relatively long, the degree of freedom of the chip is The large and therefore the resistance acting on the chip is distributed by forces such as causing the chip to bend or bend. In view of the advantages, the inventors have conducted a number of experiments and found that when the distance from the vertical line to the bottom of the torsion groove is 45% or more of the drill diameter, the resistance directly acting on the chip is significantly reduced. The 1st table | surface and the 2nd table | surface show the thickness of the chip | tip produced by the drill which set the ratio with respect to the drill diameter of the said distance to various values. Again, the cutting conditions were as follows, and the thickness of the chip was measured as indicated by the point S in FIG.

Drill diameter: 12mm

Tip angle: 140 °

Radial inclination angle of cutting edge: -15 °

Cutting speed: 65m / min

Feed (mm / rev): At the top of the table

[Table 1]

Workpiece: SCM440, Hardness: H _B 300-350

[Table 2]

Workpiece: SCM440, Hardness: H _B 100

In the above experimental results, it is found that the thickness of the chip is significantly thinned when the distance from the vertical line to the bottom of the torsion groove is 45% or more of the drill diameter. This means that the resistance acting on the chip is small. As a result, the first feature of the present invention is that the distance from the vertical line to the bottom of the torsion groove is 45% or more of the drill diameter, which can significantly reduce the resistance acting on the chip.

In addition, since the distance from the vertical line to the bottom of the torsion groove is long enough, the cross-sectional area of the cross section orthogonal to the axis of the torsion groove, that is, the discharge area of the chip, is also inevitably large, so that it can be discharged smoothly without causing chip blockage. It becomes possible. However, when the above distance exceeds 65% of the drill diameter, the thickness between the wall of the lower side of the torsion groove and the land of the outer periphery becomes thin, and defects or cracks are easily generated in the part, and the torsional rigidity of the drill is also reduced. do.

In addition, the second feature of the present invention is the thinning of the chisel width and the thrust load, as well as the cutting edge and the seed, since the thinning forms a thinning blade extending from the axis portion to the circumferential direction in the center thickness portion of the drill body. Since the shape of the ning blade is linear, the thickness of the chip is likely to be constant in the width direction thereof. For this reason, when the chip is bent, the bending and the like as described above are likely to occur, and the chip can be curled without the strong compression. In addition, since the intersection of the cutting edge and the thinning edge is arc-shaped, it is difficult to separate the chip at the intersection, which prevents chipping and prevents chipping of the drill.

An embodiment which is a first feature of the present invention will be described below with reference to FIGS. 1 and 2.

1 is an end view in the axial direction showing a drill as an example. The drill shown in this drawing has two torsion grooves 11 formed on the outer periphery of the drill body 10 made of cemented carbide and a cutting edge 12 at the free end of the wall facing the rotation direction of the torsion groove 11. ), And the center thickness T of the drill body 10 is set to 20-35% of the drill diameter, and the groove width ratio A / B is set to 0.5-0.9. Further, the shape of the torsion groove 11 at the tip end of the drill body 10 in the axial direction is rotated by the corner Q and the drill body 10 in the outer peripheral corner Q of the cutting edge 12. When the vertical line L orthogonal to the straight line N connected to the center is drawn, it becomes concave shape with respect to this vertical line L. As shown in FIG. In addition, the rear portion of the drill body 10 is cut off at the rear part thereof, and an X-type thinning 13 is formed therein, and a thinning edge 13a extending in the circumferential direction from the axis portion at the center thickness portion is formed on the cutting edge 12. It continues to form.

The above point is substantially the same as the conventional drill described above. However, the maximum value W of the distance from the vertical line L to the bottom portion 11a of the torsion groove 11, that is, the distance from the vertical line L to the wall surface of the torsion groove 11, at the tip portion in the axial direction. Is set to 45-65% of the drill diameter. As a result, the torsion groove 11 has a shape in which the wall surface toward the bottom portion 11a enters deeply in the rotational direction as shown in FIG. In such a drill, the chips produced as the cutting edges 12 reach the bottom 11a of the torsion groove 11 and are bent, and are dispersed into chips of the transition cutting type as shown in FIG. In this case, since the distance (W) from the vertical line (L) to the bottom portion (11a) of the torsion groove is 45% or more of the drill diameter, as described above, the chip can be curled without excessive compression and thrust load is applied. However, the cutting torque can be significantly reduced. The third and fourth tables set the distance W to 53%, and the radial inclination angle of the cutting edge 12 in the outer circumferential corner Q of the cutting edge 12 is described in more detail with reference to the specific experimental example. When the drill and the distance (W) of the embodiment at -15 ° are 41% and the radial inclination angle is plastic (+), the drilling is performed by the conventional drill with all other conditions identical to those of the drill of the embodiment. In thrust load, cutting torque, cutting power, and the maximum value of the vibration amplitude of the main shaft during the drilling of the processing device with the drill are displayed. Again cutting conditions are as follows.

Drill diameter: 12mm

Tip angle: 140 °

Cutting speed: 65m / min

Feed (mm / rev): At the top of the table

[Table 3]

Workpiece: SCM440, H _B 300-350

[Table 4]

Workpiece: SCM440, H _B 100

In the above experimental results, it can be seen that the thrust load, the cutting torque, and the cutting power are significantly reduced as compared with the conventional drill, although the drill of the embodiment has a negative inclination in the radial direction. As described above, the above-mentioned drill can be curled without excessive compression, so that the resistance acting on the chip can be reduced, thereby greatly reducing cutting resistance such as thrust load. In addition, since the distance W from the vertical line L to the bottom portion 11a of the torsion groove 11 is 65% or less of the drill diameter D, the wall surface and the outer circumference of the torsion groove 11b side The thickness between (10a) can be sufficiently secured and the occurrence of defects and cracks can be prevented, as well as the torsional rigidity of the drill can be improved. In addition, since the drill has a small cutting resistance, the vibration amplitude of the main shaft, which is a punching machine, is small as shown in the experimental results, thereby preventing chipping of the cutting edge and improving the processing precision. In addition, since the wall surface of the torsion groove 11 enters deeply in the rotational direction, the cross-sectional area of the torsion groove 1 is large, so that the chip is easily discharged and the blockage of the chip can be prevented. Again, the drill of the above-described embodiment is formed so that the cutting edge 12 is so-called above the center, but as shown in FIG. 3, the same effect can be obtained even when applied to the drill formed below the center.

By the way, the present invention is not limited to the above cemented carbide, and even if it is constituted by cermet, the above-described effects can be obtained. In general, cermet is extremely unsuitable for drills because of its extremely high hardness and excellent abrasion resistance, but low toughness, low cutting force of 130kg / m㎡, and low torsional rigidity compared to cemented carbide (anti-cutting force of 200kg / m㎡). It was. In other words, when the drill is configured by a cermet, the cutting torque or thrust load is repeatedly received, and thus fatigue failure is easily generated and chipping is performed in a very short time. Therefore, the drill cannot be used for drilling.

However, in the present invention, the cutting torque and thrust load can be reduced while improving the torsional rigidity, so that even if the drill body is constituted by a cermet, the drilling can be performed without any trouble. Tables 5 and 6 above are constructed by cermets including TiC, TiCN, and the like, and the distance W is 53% of the drill diameter D, and the radial inclination angle is -15 °. The experimental result in the case of performing a punching process by the conventional drill which made the drill and the distance W 41% the structure, and made all other conditions the same as the drill of this invention is shown. In addition, the cutting conditions are as follows. In the fifth table, the cutting length means the length obtained by adding the thicknesses of all the workpieces subjected to the perforation processing.

Drill diameter: 12.5mm

Tip angle: 140 °

Workpiece: SCM440 H _RC 30

Cutting speed: 50m / min

Feed: 0.3mm / rev

[Table 5]

[Table 6]

As shown in Table 5, although the drill of the present invention does not show any strange thing even if the drilling is performed at 20 m, the conventional drill is chipped by the drilling at 7 m. The present invention is constructed by the cermet drill body. It can be seen that the drilling process can be carried out without any problems. This is because, as shown in Table 6, the present invention drill significantly reduces the cutting torque and the like, even though the inclination angle in the radial direction is negative (-). Since the drill body can be configured as a cermet in the present invention as described above, the excellent wear resistance possessed by the cermet can be revitalized and the drill life can be extended. Next, Fig. 4 (a) and Fig. 4 (b) show an embodiment which is a second feature of the present invention. The drill shown in these figures makes the shape at the tip of the thinning edge 13a and the cutting edge 12 formed by the X-type thinning 13 in the axial direction linear, and the thinning edge 13a. Is a circular arc shape at the leading end portion in the axial direction which is the intersection 14 with the cutting edge 12.

r

0.15D로 되어 있다. 곡률반경(r)이 0.15D를 상회하면 비틀림홈(11)의 비틀림각에 따르는 경사각을 가지고 있는 절삭날(12)의 유효부분의 비율이 적게 되므로 절삭저항이 크게 되기 때문이다. 한편 곡률반경(r)이 0.05D를 하회하면 교차부분(14)에 있어서 칩핑이나 칩의 분리가 발생하기 쉽게 되기 때문이다. 역시 전기한 제1실시예에 있어서 절삭날(12) 및 씨닝날(13a)을 제2실시예와 같은 모양으로 구성해도 동일한 효과를 얻을 수 있는 것은 물론이다.Since the chisel width is narrowed by the X-type thinning 13 as such a drill, the thrust load is reduced, as well as the shape of the cutting edge 12 and the thinning edge 13a is linear, so that the thickness of the chip is in the width direction thereof. It is easy to become constant in. For this reason, when the chip is bent, buckling is likely to occur, and curling can be performed without compressing the chip. In addition, since the intersection portion 14 of the cutting edge 12 and the thinning edge 13a has an arc shape, it is difficult to separate the chip at the intersection portion 14, which prevents chipping and prevents chipping of the drill. To prevent it. At this time, the radius of curvature r of the intersection portion 14 shown in FIG. 4 (b) is 0.05D when the drill diameter is D.

r

It is 0.15D. This is because when the radius of curvature r exceeds 0.15D, the ratio of the effective portion of the cutting edge 12 having the inclination angle according to the torsion angle of the torsion groove 11 decreases, thereby increasing the cutting resistance. On the other hand, if the radius of curvature r is less than 0.05D, chipping or chip separation at the intersection 14 is likely to occur. In the first embodiment described above, the same effect can be obtained even if the cutting edge 12 and the thinning edge 13a have the same shape as in the second embodiment.

Next, another embodiment of the present invention will be described with reference to FIGS. 4 to 13. The twist drill in this embodiment is a linear shape of the cutting edge 12 and the thinning edge 13a in the axial distal end portion, and has the following characteristics in addition to the configuration requirements of the first or second embodiment. .

(1) The angle α at the distal end portion of the axial direction formed by the thinning edge 13a with respect to the straight line N extending from the axis O to the outer peripheral corner Q of the cutting edge is set to 20 ° -40 °. . The range of the angle α is a range in which the chip evacuation can be improved and the blockage of the chip can be reliably prevented. In other words, the chips generated by the thinning edge 13a and the chips generated by the cutting edge 12 interact with each other by the difference in their growth speeds to mutually constrain the growth direction. By stretching towards the side. However, when the angle between the thinning edge 13a and the straight line N exceeds 40 °, the growth direction of the chip generated by the thinning edge 13a and the cutting edge 12 is greatly changed, so that the chip is thinning edge 13a. It becomes easy to separate in the part corresponding to the intersection part 14 with the cutting edge 12. FIG. In addition, since the angle α + δ between the thinning edge 13a and the cutting edge 12 becomes small, defects are likely to occur at their intersections 14. On the other hand, when the angle between the thinning edge 13a and the straight line N is less than 20 °, the ratio of the length of the thinning edge 13a to the length of the cutting edge 12 becomes large, so that the thinning edge 13a in the growth direction of the chip. As a result, the generated portion is greatly affected and the chip interaction is not properly performed. In addition, an increase in the length of the thinning edge 13a causes an increase in cutting resistance.

(2) The radial inclination angle δ at the outer circumferential corner of the cutting edge 12 is -10 ° to -20 °, and an extension line at the distal end portion of the cutting edge 12 in the axial direction between the cutting edge 12 and the thinning edge 13a. ratio of the length (L ₁₎ to the length (L ₂₎ to the cutting edge outer corner (Q) of the intersection point (P) to the axis (O) intersecting point (P) from when the intersecting point between a P (L ₁ / L ₂ ) is set to 0.4-0.7:. It is a range that can reliably prevent chipping and reduce cutting resistance. That is, when the ratio L ₁ / L ₂ is less than 0.4, a narrow chip is generated by the thinning edge 13a, and the cutting edge 12 is caused by the large resistance received when the chip continues to come out into the torsion groove 11. Is separated from the chip.

On the other hand, if the ratio (L ₁ / L ₂ ) exceeds 0.7, the growth direction of the chip is greatly influenced by the portion generated as the thinning edge 13a, and the chip is not normally transition-cut as shown in FIG. It tends to increase. Increasing the ratio of the thinning edge 13a causes an increase in cutting resistance. In addition, if the radial inclination angle δ exceeds -10 °, the angle α + δ between the cutting edge 12 and the thinning edge 13a inevitably becomes small, and chip interaction is not properly performed. In addition, it causes a decrease in the edge strength of the cutting edge 12 in the outer circumferential corner Q. On the other hand, if the inclination angle δ in the radial direction is less than -20 °, the angle α + δ between the cutting edge 12 and the thinning edge 13a becomes large, so that the chip is cut into the cutting edge 12 and the thinning edge 13a. At the intersection 14 with), it becomes easy to separate and the cutting resistance becomes large.

(3) The inclination angle [theta] in the axial direction of the thinning edge 13a is set to 0 to -5 degrees (FIG. 6). Since the angle of inclination θ of the thinning edge 13a is a negative angle, the polishing surface can be left as an inclined surface by thinning when regrinding the drill, and the regrinding can be easily performed. In addition, it is possible to increase the blade tip strength of the thinning blade (13a). However, when the inclination angle θ in the axial direction becomes negative at the extreme, the cutting resistance at the thinning edge 13a increases, and therefore it is necessary to set it to -5 ° or more.

(4) The angle? Between the tip polishing surface 15 formed by thinning and the inclined surface 16 along the thinning edge 13a is set to 95 degrees to 115 degrees (Fig. 7). The chip generated as the thinning edge 13a reaches the tip polishing surface 15 of the thinning and continues to come out of the torsion groove 11 therefrom, so that the chip is subjected to great resistance at that time. When the angle λ is less than 95 °, the resistance acting on the chip of the thinning edge 13a becomes too large, making it easy to separate from the chip of the cutting edge 12. In addition, a large resistance to the chip increases the thrust load. On the other hand, when the angle λ exceeds 115 °, the portion of the drill body 10 is sharply shaved, and as a result, it becomes difficult to bend the chip into the torsion groove 11.

⑤ The angle ø formed between the tip polishing surface 15 formed by thinning and the slope 17 between the inclined surface 16 along the thinning edge 13a and the axis O is set to 30 ° -40 °. (Figure 5 (a)). When the angle? Exceeds 40 °, the frictional resistance between the chip generated as the thinning edge 13a and the tip polishing surface 15 is increased, and the thrust load is increased in addition to the above-described problem of chip separation. However, if the angle ø is made too small, it is necessary to make it 30 ° or more because the portion of the drill 11 has a large side of the hile 11b. By setting the angle ø to 30 ° -40 °, it is possible to prevent separation of the chip generated as the thinning edge 13a and to reduce the thrust load.

(6) The distance (l) in the axial direction between the outer peripheral corner Q of the cutting edge 12 and the tip edge of the hedge 11b of the torsion groove is set to 0.3-1.0 times the drill diameter. The flow path of the cutting oil is secured to the cutting part by making the distance l more than 0.3 times the drill diameter. However, if the distance l exceeds 1.0 times of the drill diameter, the portion of the drill 11 of the drill body 10 is not secured.

⑦ As shown in FIG. 8, the front end surface of the drill body 1 is provided with a clearance angle β ₁ of 7 ° -15 ° and a flat first clearance surface 18 along the cutting edge 12. In addition, a second free surface 19 in which the clearance angle β ₂ is larger than the clearance angle β _{1 in} a range of 15 ° to 25 ° and a flat second clearance surface 19 is formed in accordance with the first clearance surface 5 described above. An edge F intersecting the first free surface 18 and the second free surface 19 is parallel to the cutting edge 12 and also intersects the axis O. As shown in FIG. The second free surface 19 is formed to prevent frictional wear (so-called second contact) between the free surface and the bottom of the processing hole, to secure the flow path of the cutting oil, and to enhance the lubrication and cooling effect of the cutting portion by the cutting oil. Can be. Therefore, it is said to be an extremely important effect for a carbide drill that performs heavy cutting.

In addition, since the first and second free surfaces 18 and 19 are formed flat, the first and second free surfaces 18 and 19 can be regrind by a planar grinding process. Compared to lead grinding, the surface roughness of the grinding surface can be improved. In addition, it is easy to grind and prevent the occurrence of minute grinding defects in the ridges such as the cutting edge 12, prolong the life of the drill, and can prevent significant problems such as initial chipping. Moreover, the first relief angle (β ₁₎ of the clearance surface 18, it is possible to effectively prevent the flank wear because it is more than 7 °. This effect is particularly remarkable in the case of high speed cutting. However, when the clearance angle β ₁ is greater than 15 °, the wedge angle ρ of the cutting edge 12 is reduced, and chipping or defects are likely to occur on the cutting edge 12.

Also it can ensure a passage for supplying cutting oil to the cutting portion being sufficient to increase the lubricating and cooling effect by the coolant is incidentally, because the clearance angle (β ₂₎ is more than 15 ° of the second clearance surface (19). However, in order to secure the blade tip rigidity, the clearance angle β ₂ is preferably 25 ° or less. By the way, the edge F in which the 1st, 2nd free surfaces 18 and 19 cross | intersect is parallel with the cutting edge 12, and the crossing edge F intersects with the axis O for the following reason. By. In other words, when the intersecting edge F is inclined in the so-called center-up direction with respect to the cutting edge 12, the width of the first free surface 18 becomes narrow in the outer peripheral portion, and the blade tip rigidity in the outer peripheral portion decreases. In addition, when the intersection portion F is inclined downwardly with respect to the cutting edge 12, the first free surface 18 becomes wider, so that a second contact at the first free surface 18 is more likely to occur. to be. In addition, when the intersecting edge F is located above the center, as shown in FIG. 9, a chisel 20 having a large chisel angle γ is formed at the boundary between the second free surfaces 19 and the chisel 20 ) Mechanical strength is reduced. Therefore, it is preferable that the intersecting edges F pass through the axis O or beneath the center, but if the intersection portion F is in the shape intersecting the axis O, the first and second free surfaces when re-polishing ( 18) This is because the shape of (19) can be more accurately reproduced.

(8) The honing 21 is formed in the thinning edge 13a and the cutting edge 12 as shown in FIG. In addition, the distance C between the virtual extension line and the inner ridge line 21a of the other honing 21 when the virtual extension line is drawn along the inner ridge line 21a of one honing 21 is 0-0.3mm. Chisels 20 are formed between the end portions 21b of the honing 21. When the honing 21 intersects with the axis portion, two sticking points are generated during cutting, and defects are likely to occur. For this reason, it is necessary to separate the ends 21b of the honings 21 from each other. At this time, the interval C is set to 0.3 mm or less in order to reduce the thrust load with the chisel width G being a predetermined value or less. Again, the ends 21b of the honing 21 may be configured to be in rough contact with each other, but in this case, the chisel must be formed even slightly.

FIG. 11 shows a modified example of the honing shape shown in FIG. 10. The ends of the honing 21 are brought into contact with each other, but the outer ridge line 21c of the honing 21 is near the axis O. They form an arc shape and intersect on the axis O. As a result, the chisel is formed and stuck to the point of the axis O portion only slightly. In addition, as shown in FIG. 12, the honing shape may be gradually narrowed from the outer circumference toward the axis O. As shown in FIG. Such a honing shape can prevent the occurrence of chipping on the outer circumferential side of the thinning blade 13a having a high cutting speed. Of course, since the cutting edge 12 is a straight line, there is little dispersion in the shape of the honing 21.

⑨ The chisel width (G) is 0-0.4mm. The chisel 20 acts to push the workpiece to the left and right, so if the chisel width G is wider, the thrust load increases and the cutting speed is increased at the end of the chisel 20. This is likely to occur. Therefore, the chisel width G is better to be close to zero and can be 0.44 mm or less, thereby eliminating such defects and improving stuck stability.

In the drill body 10, an oil hole 22 is formed in a spiral shape along the torsion groove 11 (figure 5 (b)). Such a drill can not only change the position of the oil hole 22 even if re-polishing, but can always perform cutting under constant conditions. However, since the oil hole 22 is spiral, the torsional rigidity of the drill is less likely to be impaired. . For this reason, the above-mentioned drill interacts with the distance W shown in FIG. 1 at 45% or more of the drill diameter D to reduce the cutting resistance, so that the drill W can be used on the heavy cutting side. Again, this effect can be obtained even if the shape of the cutting edge 12 and the thinning edge 13a is not a linear shape, and the same also applies to the following.

A chamfer along the torsion groove 11 is formed at the intersection between the torsion groove 11 and the land 10a of the outer circumference, that is, the hile 11b. This chamfer surface is about 0.5 mm in width. Also, instead of the chamfer surface, a round honing surface with a radius of curvature of about 0.5 mm may be formed. Such a chamfer surface can prevent generation | occurrence | production of a defect and a crack by the chip | tip of the part.

표면 On the surface of the drill body 10, a coating layer such as TiC, TiN, TiCN, Al ₂ O ₃ is provided. The coating layer can improve the heat resistance and abrasion resistance of the drill, and can reduce the frictional resistance with the chip and further reduce the cutting torque and thrust load because the coating layer as described above has a small coefficient of friction.

As described above, the first feature of the present invention is the maximum value of the distance from the vertical line to the wall surface of the torsion groove when a vertical line perpendicular to the straight line connecting the corner and the center of rotation of the drill body is drawn in the outer corner of the cutting edge. In the second feature, thinning blades extending from the axial part to the circumferential direction are formed in the center thickness of the drill body by thinning, The shape at the tip end in the axial direction of the intersection between the thinning blade and the cutting edge is an arc shape. Therefore, the thrust load and cutting torque can be made without roughly compressing the chips without excessive compression. Etc., as well as to reduce chipping and prevent chipping in high-speed cutting and heavy cutting. It is very promising as it can be used for heavy cutting and high speed cutting. In addition, since the drill body can be configured by a cermet having excellent wear resistance, the drill life can be improved.

Claims (17)

The torsion groove 11 is formed on the outer circumference of the cemented carbide or cermet drill body 10 which is rotated about the axis, and the cutting edge is formed at the free end of the wall surface in the direction of rotation of the torsion groove 11. 12), the center thickness T of the drill body 10 is set to 20% to 35% of the drill diameter D, and the torsion groove 11 at the distal end portion of the drill in the axial direction. When the shape is drawn on the outer peripheral corner Q of the cutting edge 12 described above, the vertical line L orthogonal to the straight line N connecting the corner Q and the above-described axis line, this vertical line L is In the twist drill concave with respect to the shape, the maximum value W of the distance from the vertical line L to the wall of the torsion groove 11 is set to 45% to 65% of the drill diameter D, In addition, the ratio A / B of the groove width A to the land width B in the cross section orthogonal to the axis of the drill body 10 is 0.9 to 1.2, and the center thickness T is obtained. When the torsion groove 11 in contact with the virtual circumference to be formed has a radius of curvature R in the cross section orthogonal to the axis around the bottom, the drill diameter is D, 0.15D.

R

Twist drill, characterized in that set to 0.2D. The cutting edge (12) according to claim 1, wherein the thinning edge (13) is formed in the center thickness (T) portion by the thinning portion (13) extending in the circumferential direction from the axis portion. The twist drill which made the shape in the front-end | tip part of the axial direction with the straight line shape. The twist drill according to claim 2, wherein the shape of the tip portion in the axial direction at the intersection of the thinning edge (13a) and the cutting edge (12) described above is an arc shape. The twist drill according to claim 3, wherein the radius of curvature (r) of the intersection between the thinning edge (13a) and the cutting edge (12) is 0.5 to 0.15 times the drill diameter (D). The twist drill according to any one of claims 2 to 4, wherein the radial inclination angle δ in the outer peripheral corner Q of the cutting edge 12 is -10 ° to -20 °. . The intersection point from the axis O in any one of Claims 2-4 when the point where the extension line in the axial direction front-end | tip of the thinning edge 13a and the cutting edge 12 which were mentioned above was made into P is P. characterized in that set to 1: length (L ₁₎ and the intersection (P) the ratio of the length (L ₂₎ to the outer corner (Q) of the one cutting edge 12 from 0.4 to 0.7 to the (P) Twist drill. The axially distal end portion according to any one of claims 2 to 4, wherein the thinning edge 13a formed with respect to the straight line N extending from the axis O to the outer peripheral corner Q of the cutting edge 12 forms. The twist α is set to an angle α of 20 ° to 40 °. The cutting edge (1) according to any one of claims 2 to 4, wherein the first clearance surface (18) having a clearance angle (beta) ₁ of 7 ° to 15 ° and a flat edge is formed on the tip end surface of the drill body 10 described above. 12, the clearance angle β ₂ is greater than the clearance angle β ₁ of the first clearance surface 18 and is in the range of 15 ° to 25 ° and the second clearance surface 19 is flat. Twist drill, characterized in that the intersection edge (F) between the clearance surface (18) and the second clearance surface (19) is parallel to the cutting edge (12) and crossed with the axis (O). The honing 21 is formed in the cutting edge 12 and the thinning edge 13a which were mentioned above, and the inner ridge 21a of one honing in the vicinity of an axis is defined in any one of Claims 2-4. When a virtual extension line is drawn, the distance C between the virtual extension line and the inner ridge 21a of the other honing is 0 to 0.3 mm, and a chisel (between the ends 21b of the honing 21) is formed. 20) Twist drill, characterized in that formed. 10. The twist drill as set forth in claim 9, wherein the chisel width (G) of said chisel (20) is 0 to 0.4 mm. The twist drill according to any one of claims 2 to 4, wherein the angle of inclination (θ) in the axial direction of the thinning blade (13a) described above is set to 0 ° to 5 °. The angle? Of the tip polishing surface 15 constituted by the thinning 13 described above and the inclined surface 16 along the thinning edge 13a is 95. Twist drill characterized in that it was set to ° to 115 °. The bone line 17 according to any one of claims 2 to 4, wherein the line 17 of the tip polishing surface 15 formed by the thinning 13 described above and the inclined surface 16 along the thinning edge 13a is the axis O. Twist drill, characterized in that the angle (ø) formed to intersect with) is 30 ° to 40 °. The distance (L) according to any one of claims 2 to 4, wherein the distance (L) in the axial direction between the outer circumferential corner Q of the cutting edge 12 described above and the edge of the edge 11b of the torsion groove 11 of the torsion groove 11. Twist drill, characterized in that 0.3 to 1.0 times the drill diameter (D). The twist drill according to any one of claims 1 to 4, wherein an oil hole (22) spirally formed along the torsion groove (11) is provided in the drill body (10). The chamfered surface or rounded shape according to any one of claims 1 to 4, formed at the intersection of the wall surface of the torsion groove 11 described above and the outer peripheral land 10a of the drill body 10. The twist drill which formed the honing surface. The twist drill according to any one of claims 1 to 4, wherein a coating layer of TiC, TiN, TiCN, or the like is provided on the surface of the drill body (10).

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