KR960010151B1 - Twisting drill - Google Patents

Abstract

The twist drill is designed to complement chipping and rupturing due to the brittleness of a drill and the increase of cutting resistance. The twist drill has : web diameter (T) at an endline being 25 - 40 percent of a drill diameter; distance between an edge (C2) and both cutting blade (C1) being 0.3D - 0.4D; angle between both cutting blades and web cutting blade being 30 - 40 degree; angle with both edges being 30 - 55 degree; and the ratio of cylinders in float part and a rend (A/B) being 0.8 - 1.2.

Description

Twist drill

1 is a top plan view of a tip of a conventional high speed steel twist drill.

2 is a plan view of the distal end of a twist drill made of a conventional hard material.

3 is a plan view of the distal end of the twist drill according to the present invention.

4 is a side view of the drill tip as viewed in the direction A of FIG.

FIG. 5 is a side view of the drill tip as viewed in the direction B of FIG. 3. FIG.

6 is a detailed view of the grinding surface seen in the direction C of FIG.

7 is an enlarged view of the connection portion between the main cutting edge and the web cutting edge.

8 is an enlarged view of the axial cutting surface of the main cutting edge portion.

9 is an enlarged view of an axial cut surface of the web cutting edge portion.

10 is an axial cutaway view of the main cutting blade seen in the direction D of FIG.

11 is a front view of a twist drill in which the entire drill is made of a hard material as an embodiment of the present invention.

12 is a front view of a twist drill in which a hard material is used only in a drill tip including a cutting edge as another embodiment of the present invention.

13 to 17 are chip shapes according to flute shape changes.

18 is a graph showing changes in moment size when drilling holes with different shapes of flute edges.

19 is a graph showing an increase in the axial cutting resistance according to the change in the machining depth when drilling holes with different shapes of pull root edges.

20 is a graph showing the amount of moment increase according to the change in processing depth when drilling holes with different shapes of flute edges.

* Explanation of symbols for main parts of the drawings

1: land part 2: flute

3: web 4: main cutting edge

5: web cutting edge 7: corner portion

8 flute space 9: inclined plane

10: grinding surface

The present invention relates to a twist drill made of a hard material such as cemented carbide or cermet, and more particularly, to the chipping phenomenon of the edge portion due to brittleness, which is one of the characteristics of cemented carbide drills, and an increase in cutting resistance during drilling. The present invention relates to a twist drill that compensates for a breakage caused by a body part.

Twist drills are generally made of relatively low quality materials such as high speed steel or hard materials such as cemented carbide or seamet.

1 is a plan view of a drill tip for explaining a conventional high-speed steel drill, the tip of the drill is a land portion 1, a spiral groove-shaped flute 2 for chip discharge and coolant supply, and a web represented by the size of a central inscribed circle. It consists of (3).

The stiffness of the drill in this configuration is A / B, which is the ratio of the circumferential flute size (A) and the circumferential land portion size (B), and T / D, which is the ratio of the web size (T) and the drill diameter (D). A / B and T / D mentioned above are mainly used as a unit which greatly influences and shows the rigidity of a drill.

For high speed steel drills, A / B ranges from 1.0 to 1.6 and T / D ranges from 0.15 to 0.25.

In addition, the high-speed steel drill having the above-described shape is a long spiral chip due to a wide flute, and due to the flexibility of the high-speed steel, which is not easily broken, it is common that the hole enlargement is rather large.

However, the high-speed steel drill as described above has the weakness of its own rigidity, which makes it difficult to cut strongly and decreases the hole precision due to its flexibility, and it is limited in high-speed cutting due to the limitation of high temperature characteristics and wear resistance, thus separating in terms of productivity.

On the other hand, high hardness materials such as cemented carbide or cermet have a great brittleness compared to high speed steel.

However, when manufacturing a drill having the same shape as a high speed steel drill using the above-mentioned high hardness material, there is no problem in the machining of cast iron, but when drilling a strong workpiece such as steel, chipping damage of the needle line or weak torsional rigidity of the drill body It is easy to be damaged due to the hard machining. Therefore, in recent years, the ferromagnetic hole has been made by a high-speed steel drill, but as described above, since high-speed steel has various problems, it is required to develop a drill that can make steel processing more efficient.

2 is a plan view of the tip of a steel drill with a recently developed cemented carbide, and is designed to have an A / B value of 0.4 to 0.8 and a T / D value of 0.25 to 0.35.

Compared to the first degree high-speed steel drill in the above structure, the value of A / B is smaller and the value of T / D is larger because the smaller the value of A / B and the larger the value of T / D, the higher the bending rigidity of the drill. The increased torsional stiffness can reinforce the fragility of drills made of hard materials.

However, cemented carbide drills as shown in Fig. 2 have the advantage that strong cutting is possible due to the change of A / B and T / D values, while the cross-sectional area of the flute groove is reduced, so that the external coolant to be made at the same time as the discharge of chips Supply is difficult

Therefore, when the depth of the processing hole is deep, the cutting resistance is sharply increased due to the difficulty of supplying the cutting oil, and the hole processing becomes difficult.

In order to solve the above-mentioned problems of chip discharge and coolant supply, the shape of the flute should be improved, and the deeper the cutting depth, the more the cutting resistance increases, so that the shape of the chip is shorter than that of a long spiral chip such as a conventional high speed steel. This is preferred.

An object of the present invention is to improve the shape of the flute so that it is possible to smoothly discharge the chip and supply the coolant while ensuring the precise hole processing and long tool life.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

3 is a plan view of the tip of the twist drill according to an embodiment of the present invention, a relatively large web is formed so as to have a T / D value of 0.25 ~ 0.40 to have a high rigidity.

The flute width W of chip deformation is perpendicular to the straight line connecting the two cutting edge ends, which is the maximum distance of the inner wall of the flute from the straight line passing through the cutting edge C ₁ and increases the drill stiffness to 0.40. Maintaining ~ 0.47D.

On the other hand, the edge of the drill land (1) is provided with an edge portion 7 by a diagonal chamfer for the smooth supply of the cutting oil, the flute space (8) formed by the corner portion is mainly to provide a smooth supply of cutting oil It is for.

The remaining flute space 2 serves to smoothly discharge the chip to the outside, and the flute space provides the coolant drop and the drill rigidity caused by the mutually opposite functions of the discharge of the chip and the supply of cutting oil, which are functions of a common flute. It should be possible to solve the difficulties at the same time.

To this end, in the present invention, the distance F from the straight line connecting the two cutting edges of the corner starting point (C ₂ ) is 0.3 to 0.4D, and the inclination angle (θ ₂ ) of the corner portion formed with the straight line connecting the two cutting edge ends is measured. Was in the range of 30 to 55 °.

In order to ensure smooth discharge of the chip through the limited space flute, a short broken chip must be formed unlike a high-speed steel drill in which a long spiral chip is formed. The formation of the chip is determined by the shape of the flute and the grinding method of the tip. It depends on the shape of the main cutting edge 4 and the shape of the web cutting edge 5 and the flute wall surface 6 determined by the thinning method.

In the present invention, the angle (θ ₁ ) at which the web cutting edge connecting the two cutting edges is formed is in the range of 30 to 40 °, and the angle (θr) at which the major cutting edge C ₁ forms the radial direction at the outer circumference is -5 to It was in the range of 15 ° and the flute width (W) was limited to the range of 0.40 to 0.47D as described above to form a short broken chip.

At this time, the length ratio of the length of the web cutting edge (5) and the main cutting edge (4) is in the range of 0.2 ~ 0.5.

4 is a side view of the drill tip viewed from the direction A in FIG. ₃ , and the inclination angle θ ₃ formed between the drill shaft and the inclined surface 9 is in a range of 0 to 10 degrees.

This is to remove the large negative inclination angle in consideration of the weak cutting function and the self-centering function of the web cutting edge of the conventional high-speed steel drill made a large negative inclination angle during machining.

FIG. 5 is a side view of the drill tip viewed from the direction B of FIG. 3 and the angle (θ ₄ ) formed between the valley 11 and the drill shaft formed by the inclined surface 9 and the grinding surface 10 is in a range of 30 to 50 °. Have

This angle is related to securing the space for the removal of chips formed at the web cutting edge. The larger the angle, the larger the space.

FIG. 6 is a detailed view of the grinding surface viewed from the direction C of FIG. ₅ and the angle θ ₅ formed between the inclined surface 9 and the grinding surface 10 has a size of 90 to 120 °. While the space for discharge is increased, the stiffness of the edge is weakened.

7 is an enlarged view of the connecting portion of the main cutting edge and the web cutting edge, wherein the connecting portion of the main cutting edge 4 and the web cutting edge 5 has a radius γ of 0.05 to 0.1D.

8 and 9 are enlarged axial cutting planes of negative land, which are corners having negative inclination angles by honing to protect main cutting edges and web cutting edges. Since chipping of edges occurs well, the width (t) of the negative land was set to a uniform size of 0.05 to 0.30 mm regardless of the drill size.

Moreover, the angle (alpha) of a negative land has a range of 20-30 degrees with respect to an axial direction.

FIG. 10 is an axial cutaway view of the main cutting edge viewed from the direction D of FIG. 3, where the primary clearance angle (β ₁ ) in the range of 9 to 13 ° and the secondary clearance angle (β ₂ ) in the range of 18 to 23 ° are shown. Have

The width T of the primary clearance surface 13 has a size of 0.1 to 0.14D, and the secondary clearance surface has TiC, TiCN in order to improve wear resistance and high thermal properties of the drill head and the fluted body portion. And a film layer made of Al ₂ O ₃ by physical vapor deposition.

FIG. 11 shows an example in which the entire twist drill is made of a hard material such as cemented carbide or cermet. In FIG. 12, only the tip of the drill is made of a hard material and the rest of the drill tip is formed. The body part is an example of welding made of steel.

In the case of a twist drill as shown in FIG. 12, a hole for lubrication of cutting oil is installed in the drill body portion, and one injection hole size is formed in the range of 20 to 40% of the body cross section, and the discharge hole is 10 to 20 on the grinding surface 10. Two are formed in the size of%.

Example

To compare the formation of chips according to the difference in cross-sectional shape of the drill tip, flute width (W), which directly affects chip formation, and the angle (θr) of the main cutting edge in the radial direction are different from those of Table 1 The drill of the present invention and the conventional hole processing were performed.

The removal is steel of SCM ₄ (HRC 24-25), the rotational speed (V) of the drill is 37.4m / min, and the feed amount per revolution (f) is 0.25mm.

Table 1

As in the above embodiment of each drill, as the flute width W decreases, the deformation radius of the chip decreases, and the chip having the small deformation radius is formed together with the chip.

In addition, in the conventional high speed steel drill, as the flute width W increases, the deformation radius of the chip increases and the continuous chip (FIG. 17) gradually occurs, and the rigidity of the drill decreases. The drills B and C of the present invention are used. It can be seen that the chip of the shape is easier to discharge than the conventional drill (D and E) is formed.

And the appropriate flute width (W) is in the range of 0.40 ~ 0.47d, the shape of the appropriate edge in the limited flute width (W) as described above is appropriate when the radial inclination angle at the blade edge is in the range of -5 ~ -15 ° Chips are formed.

On the other hand, for precise and powerful hole work, the smooth supply of cutting oil and the smooth supply of cutting oil should be made during machining, so that there is no increase in cutting resistance. In the present invention, the edge portion at the tip of the drill bit as shown in FIG. 3 for the smooth supply of cutting oil. (7) was installed.

In Table 2, three types of drills with different corner sizes and positions are presented as sampling. When cutting the 3D, 4D, 5D, and 6D hole depths using the respective drills, the axial cutting force ( Fz) and moment (Mz) were measured.

Table 2

The measured values of the moments when drilling holes with a depth of 6D using the respective drills are shown in FIG.

As shown in FIG. 18, the difference between the cutting resistance at the initial entry and the cutting depth at the final machining depth is largely determined by the chip discharge and the coolant supply. You can see that it depends.

In FIG. 19 and FIG. 20, the change of the axial cutting resistance Fz and the moment Mz is indicated in the hole depth when the hole is drilled with each of the drills shown in Table 2 above. It can be seen that a sharp increase in cutting resistance during machining is largely dependent on the values of F and A: B representing the size of the edge portion 7.

Furthermore, the lower the strength, the higher the heat generation during machining, and the workpiece that reacts sensitively to the state of lubrication of cutting oil, the effect of the edge portion is greater, it is advantageous to check the size of the edge portion.

However, the larger the edge, the weaker the drill's stiffness and the more likely the chip cutting of the proper shape is to be made. Therefore, the distance f between the straight line connecting the _two edges and the starting point C ₂ is 0.3 to 0.4D. The angle (θ ₂ ) of the corner portion formed with this straight line was limited to the range of 30 to 55 °.

The range of the flute width W presented above, the size range of F and θ ₂ , which are the shape of the corner portion, and the ratio of the size ratio of the circumference of the tip portion circumference of the flute portion 2 and the land portion 1 by the thinning method. The value ranges from 0.8: 1 to 1.2: 1.

The thinning method is determined by the magnitude of θ ₁ indicating the position of the web cutting edge and the inclination angle θ ₄ , θ ₅ which determines the inclination angle of the grinding surface 10. The larger the θ ₄ , the larger the value of A: B and the web. The chip pocket of the edge portion becomes small.

On the contrary, as θ ₅ increases, the value of A: B decreases, the space for chip processing generated in the web edge increases, and the strength of the edge decreases.

In view of the above, in the present invention, the value of θ ₄ is in the range of 30 to 50 ° and the value of θ ₅ is in the range of 90 to 120 °.

In addition, the rigidity of the drill is determined by the rigidity of the body portion, in the present invention, the size of the body web in the range of 0.25D ~ 0.4D, the ratio of the circumferential size of the flute portion and the body portion of 1.2: 1 ~ 1.7: 1 It was set as the range of.

Claims (17)

In a twist drill in which a spiral groove-shaped flute is formed in the trill body for discharging chips and supplying coolant, the web diameter at the tip of the drill (T) is set to 25 to 40% of the drill diameter (D). The distance (F) between the edge (C ₂ ) starting from the second flute wall on the opposite side of the blade and the straight line connecting the two cutting edges (C ₁ ) is 0.3D to 0.4D, and the two cutting edges are connected. The angle (θ ₁ ) between the straight line and the web cutting edge is in the range of 30 to 40 °, the angle (θ ₂ ) between the straight line connecting the edges of the edge part is in the range of 30 to 55 °, and the circle of the flute part is A twist drill in which the ratio of columnar size to the circumferential size of the land is in the range of 0.8 to 1.2. The twist drill according to claim 1, wherein a distance W perpendicular to a straight line connecting the two cutting edge ends and passing through the cutting edge C ₁ to a maximum depth of the flute is in the range of 0.40 to 0.47 D. The twist drill according to claim 1, wherein the inclination angle? R formed in the radial direction at the outer peripheral portion of the main cutting edge is -5 ° to -15 °. The twist drill according to claim 1, wherein the shape of the flute portion and the edge portion at the drill tip portion is connected to the drill body portion. The twist drill according to claim 4, wherein a ratio between the circumferential size of the flute portion and the circumferential size of the land portion in the drill body portion is in the range of 1.2 to 1.7. The twist drill according to claim 1, wherein the ratio (L ₁ / L | ₂ ) of the length L ₁ of the web cutting edge portion to the length L ₂ of the main cutting edge is in the range of 0.2 to 0.5. 2. The grinding according to claim 1, wherein the inclined surface 9 by thinning passes through the drill center and the web cutting edge and forms an angle θ ₃ with an axial cross section of 0 ° to -10 ° and differs from the inclined surface 9 during thinning. Twist the angle (θ ₅ ) with the surface 10 in the range of 90 to 120 °, and the angle (θ ₄ ) between the line 11 where the two slopes meet and the center axis of the drill in the range of 30 to 50 °. drill. The twist drill according to claim 1, wherein the clearances of the main cutting edge (4) and the web cutting edge (5) are two-stage planes. The twist drill according to claim 8, wherein the first clearance angle of the clearance surface is in the range of 9 to 13 ° in the cross section perpendicular to the main cutting edge, and the secondary clearance angle is in the range of 18 to 23 °. The twist drill according to claim 8, wherein the line where the primary clearance surface (13) and the secondary clearance surface (14) meet is parallel to the major cutting edge and has a width in the range of 0.1 to 0.14D. The twist drill according to claim 1, wherein the cutting edges (4) and the web cutting edges (5) have a negative slope. 12. The twist drill according to claim 11, wherein the inclined surface of the edge portion has a width in the range of 0.05 to 0.3 mm and the inclination angle formed in the drill axial direction is in the range of 20 to 30 degrees. The twist drill according to claim 1, wherein the drill material is made of cemented carbide or cermet, which is made of a hard material. The twist drill according to claim 13, wherein the drill is entirely made of cemented carbide or cermet. The twist drill according to claim 13, wherein only the tip portion including the drill cutting edge portion is made of cemented carbide or cermet, and the remaining body portion is made of general steel. The twist drill according to claim 15, having a coolant internal oil supply hole in a drill body portion made of ordinary steel. The twist drill according to claim 1, wherein the drill body portion including the drill tip and the flute is coated with components of TiC, TiCN, TiC, and AL ₂ O ₃ .