Bit for a twist drill and method for producing a flute in the area of a bit for a twist drill

ES 2 239 136 T3

DESCRIPTION

Drill bit for a twist drill and procedure for the fabrication of a chip receiving groove in the area of ​​the drill tip for a twist drill.

The present invention relates to a drill tip for a twist drill having, joined together by a transverse edge, a plurality of main cutting edges to which, along chip-receiving grooves in the longitudinal direction of the drill bit , follow secondary edges, being found between a tangent adjacent to the inner side of the respective secondary cutting edge and oriented perpendicular to the longitudinal direction of the drill and the radial direction, A secondary rake angle is defined which increases in the longitudinal direction of the drill (see, for example, US-A-5 678 960).

In a drill tip for a conventional twist drill, as a rule the two main cutting edges extend curved over the transverse cutting edge, converging with each other in the manner of an "S". Each of the main edges is followed by a main flank, which is transformed into a chip-receiving slot formed in a helical manner in the longitudinal direction of the drill. In each of the lateral faces of the corresponding chip-receiving groove, the secondary edge is formed, which converges on the main edge, forming a cutting edge. Then, the secondary edge is that edge that extends in a helical fashion along the corresponding chip receiving groove. In this case, a drill tip is understood to be a longitudinal area of ​​the drill, which begins at the front edges (main edges and transverse cutting edge) and has a length that corresponds approximately to twice the diameter of the drill.

The secondary rake angle, as defined above, roughly indicates the geometric orientation of a cutting wedge forming the secondary edge relative to the radial direction, that is, in a direction perpendicular to the longitudinal axis of the bit. A positive angle of attack, that is, an angle greater than 0 °, is used when the cutting wedge converges in the form of a point. Correspondingly, a negative rake angle means that the cutting wedge converges bluntly. In the conventional drill tip with the curved shape of the main cutting edges and the transverse cutting edge, there is a positive secondary rake angle. It is spread with a constant value over the total cutting length of the bit.

The positive secondary rake angle has the advantage that the contact area between the chips detached from the workpiece during the drilling process and the bore wall of the workpiece is as small as possible. Therefore, these chips are evacuated very quickly.

From EP 0 712 343 B1 a twist drill with S-curved main edges is known. In the known twist drill, a positive secondary rake angle and the radius of curvature of the Chip receiving groove increases in the longitudinal direction of the bit.

However, in the area of ​​the main cutting edges the positive secondary rake angle has the disadvantage that the cutting wedge in the area of ​​the cutting edge is comparatively weakened due to its pointed geometry. However, it is precisely on the cutting edge that very large forces arise when drilling. In addition, the load is increased because, when drilling, the cutting edge almost catches in the material. Thus, there is the danger of chipping the drill bit in particular at this location. Furthermore, it is disadvantageous that the detached chip bends, which requires additional force and thus more power for chip removal.

The present invention has the aim of eliminating the mentioned disadvantages.

According to the invention, the object is achieved by means of a drill tip for a twist drill having a plurality of main cutting edges, joined together, through a transverse cutting edge, which are followed by secondary cutting edges, which extend in the longitudinal direction of the bit along chip receiving grooves, where the secondary rake angle increases in the longitudinal direction of the bit and the main cutting edges extend straight towards the secondary cutting edge. The secondary angle of attack is especially 0 ° in the area of ​​the cutting edge. In this way, a particularly good cut with high stability is achieved. In this way, the cutting edge is very robust and resistant.

This configuration is based, on the one hand, on the consideration of having main edges of rectilinear extension to avoid too high a load. In this way, the cutting wedge in the area of ​​the cutting edge is comparatively compact and therefore robust. In this way, it is kept under the danger of an excessive load in this area. However, the secondary rake angle of 0 °, formed on a radially oriented main cutting edge in a straight line, has the essential disadvantage that, on the path over the cutting extension of the drill, the chip is not sufficiently detached. Quick Wall Drill. Under certain circumstances, this leads to unwanted bore wall surface roughness. In addition, when sharpening the bit to form the secondary rake angle of 0 °, a profiled grinding wheel of expensive geometry is required. On the other hand, with a positive secondary rake angle, a so-called standard grinding wheel with a simple geometry can be used, which is comparatively advantageous.

The configuration according to the invention is furthermore based on the reflection that different loads originate at different places along the cutting length of the drill and that different secondary rake angles are advantageous for the different loads, that is, a development variable of the value of the secondary rake angle in the direction of the longitudinal direction of the drill. Thus, due to the formation of the drill tip with increasing secondary rake angle in the longitudinal direction of the drill, for each local load, a site-dependent optimized secondary rake angle is set.

With the substantially increasing secondary rake angle in shape, it is achieved that in the area of ​​the cutting edge the drill tip is comparatively robust, due to a reduced secondary rake angle and that, furthermore, in a further development it is formed Increasing higher positive secondary rake angle, providing fast chip discharge.

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A drill tip formed in this way is preferably manufactured by a continuous sharpening process. But, the drill tip can also be made into a conventional drill tip with a positive secondary rake angle and curved leading edges, by flat sharpening the leading edges in the area of ​​the cutting edge by a separate sharpening operation. However, this has the disadvantage that disturbing transitions, ie edges, can occur in the area of ​​the cutting edges.

Preferably, the secondary rake angle is between + 5 ° and -5 ° on the main edges. Especially, it is between 0 ° and -5 °. This configuration with a reduced secondary angle of attack or with a moderately negative secondary angle of attack makes it possible to guarantee a high resistance of the cutting wedge in the area of ​​the cutting edge. On the other hand, a hooking of the cutting edge is avoided during the attack of the tip of the drill to the material. The choice of the special secondary angle of attack depends, in this case, on the material to be worked. Negative rake angles, i.e. a blunt secondary edge, are used in special cases, for example for soft materials such as light metals or plastic materials.

The cutting edges, especially the secondary cutting edges of the drill bit, are preferably formed without a protective bevel, that is, without chamfering. However, protective bezels can also be provided. In this case, the corresponding main cutting edge does not extend completely in a rectilinear manner to the secondary cutting edge, but only to the protective bevel.

In order to achieve rapid removal of the chips from the bore wall in the further course of the drill cutting length, the secondary rake angle preferably increases to a comparatively high final value of + 25 °.

As the problem of cutting edge breakage only occurs in the contiguous area on the main cutting edges, the final value is preferably already reached at a length, in the longitudinal direction of the corresponding drill, of 0.25 to 1.5 times, especially 1 time, the diameter of the drill bit.

Preferably, the drill tip and especially the entire twist drill have a drill core with a constant or decreasing core diameter in the longitudinal direction of the drill. A twist drill, with a constant core diameter, is especially easy to manufacture. The decreasing core diameter in the direction of the longitudinal axis of the drill has the advantage that, in this way, the chip receiving grooves are deepened and thus more space for chips is available. In this way, better chip discharge is obtained and chip stagnation is prevented. A reduction in the diameter of the core preferably occurs in a range between 10 and 20%, based on a length of approximately 100 mm.

Furthermore, according to the invention, the object is achieved by means of a process for the manufacture of a chip receiving groove in the area of ​​a drill tip for a twist drill, with the characteristics of claim 6.

With such a process, a particularly robust drill is obtained in the area of ​​the main cutting edges and, at the same time, it is ensured that when drilling a rapid discharge of the chips is carried out in the area of ​​the secondary cutting edges and a hole is obtained. of a high surface quality.

For easy and inexpensive manufacturing, the different secondary rake angles are processed in a continuous sharpening process.

For this purpose, during the sharpening process, an abrasive wheel and the drill tip are preferably brought against each other by means of a multidimensional spatial movement. Such a multidimensional spatial movement is achievable with nowadays common CNC machine tools. Thus, the grinding wheel and the drill tip perform relatively complex movements with each other.

Preferably, during the sharpening process a grinding wheel is used, formed as a standard grinding wheel to be applied to multiple types of drill bits. Drill types in this case are twist drills, for example, with different rake angle developments. An abrasive wheel of this type, for example, is equally suitable for the manufacture of a twist drill of the conventional type, which has a constant positive secondary rake angle along the cutting edge and in which the main cutting edges extend curved over the cutting edge. transverse edge in the manner of an S.

As an alternative to sharpening for the production of different secondary rake angles, they can advantageously also be produced by injection molding. The advantage of such an injection molding is that it is possible to quickly and easily produce complex drill point geometries as well. The complexity of the geometry is limited only by technical constraints of the injection molding, as well as by constructive constraints of the molds for the drill bit.

A drill tip produced in this way is formed, for example, as a separate part which can be inserted as a spare part in a drill base body which is suitably shaped and which at least partially encompasses the secondary cutting edges. Alternatively, the drill tip is formed as an integral component of a twist drill, ie, in one piece therewith. In integral shaping, immediately after sharpening the chip receiving groove in the area of ​​the drill tip, the entire chip receiving groove, or the entire length of the cutting edge, is simply and quickly grinded. Complete drill bit is injection molded.

An example of embodiment of the invention is explained in detail below on the basis of the figures which, in each case, by means of schematic representations show:

Figure 1, a plan view of a drill tip of a conventional drill with curved main edges, Figure 2, a plan view of a tip according to the invention, with rectilinear main edges, Figures 3a to 3c, schematic sections of a drill tip, according to figure 2, in different longitudinal positions along the longitudinal direction of the drill, figure 4, a side view of a drill bit in a housing relative to an abrasive wheel, for explanation of the sharpening process, figure 5, a representation, according to figure 4, in a plan view, figure 6, an enlarged representation of the par3

ES 2 239 136 T3 is marked with a circle in figure 5, in the area of ​​contact between the grinding wheel and the drill tip, figure 7, a sectional view, by way of example, of a standard grinding wheel, Figures 8a to 8c, schematic sectional views of a drill tip at constant drill lengths at different times of the sharpening process, and Figure 9, a side view of a drill with indication of the cutting position, according to the figures 8a8c.

In the figures, the pieces of equal action are indicated with the same references.

The conventional twist drill 2, shown in Figure 1, abbreviated as a drill, has at the front end of its drill tip 3 two main cutting edges 4 connected to each other by means of a transverse cutting edge 6. The main cutting edges 4, as well as the transverse edge 6 are spirally formed, approximately S-shaped. Each of the two main edges 4 is followed by a main flank 8 which each becomes a chip receiving groove 10.

Both main cutting edges 4 extend approximately in the radial direction of the drill 2. Each of the main flanks 8 has cooling fluid holes 9 through which the drill 2 can be cooled during the drilling process. At each of the two main edges 4, it follows at its ends, forming at each cutting edge 12, a secondary edge 14 that extends in the longitudinal direction L, that is, it penetrates the paper plane. The longitudinal direction L of the drill bit is represented in FIG. 1 with a cross enclosed in a circle.

Due to the curved conformation of the main edges 4, a positive rake angle γ is formed in the area of ​​the cutting edge 12. It is defined as the angle between a tangent T adjacent to the inner side 16 of the secondary edge 14 and the radial direction R. Both the tangent T and the radial direction R extend perpendicular to the longitudinal direction L of the drill and meet thus on a common plane. The definition of secondary angle of attack γ can best be seen in Figure 3c. The cut plane perpendicular to the longitudinal direction of the drill represented therein is, at the same time, the common plane for the tangent T and the radial direction R.

The angle of attack γ is designated as positive when, as in the case of FIG. 1, the cutting edge 12 ends in a point, that is, when the cutting edge 12 especially protrudes from the center of the drill. Otherwise, a negative secondary rake angle γ occurs when a blunt cutting edge 12 is formed. Along the secondary edges 14 a protective chamfer 13 may be arranged, indicated by lines as a chamfer.

Because in the conventional drill 2, according to FIG. 1, the cutting edge 12 protrudes from the center of the drill, only a limited loading of the cutting edge 12 is possible because it is relatively thin. Because, due to the helical chip-receiving groove 10, the cutting edge 12 forms a cantilevered projection both in the radial direction R and also in the longitudinal direction L of the drill. The cutting edge 12 is the place where the drill bit 2 with its front part attacks the workpiece, so that very high loads appear there.

The secondary rake angle γ, according to FIG. 1, extends in the conventional drill 2 constantly over the entire secondary edge 14. This leads to the fact that the chip-receiving groove has a convexity that causes the dislodged chips to be removed very quickly from the hole wall of the workpiece. The curvature of the chip receiving groove 10 in connection with the secondary edge 14 further causes the chips to form a radius of curvature that essentially matches the radius of curvature of the chip receiving groove 10.

Contrary to what happens with the drill tip 3 shown in figure 1, the drill tip 3 shown in figure 2 always has rectilinear main edges 4, which extend essentially radially in the direction of the transverse edge 6. Consequently, the secondary angle of attack γ is, in this case, 0 ° in the main edges 4. In this way, the cutting edge 12 is substantially more robust, so that higher forces can be absorbed, without the danger of breakage. In order to achieve, at the same time, in the extension of the secondary edges 14 in the longitudinal direction L of the drill the positive effect of a positive secondary rake angle γ, the secondary rake angle γ increases especially continuously in the longitudinal direction L of the drill bit.

The continuous increase in the secondary rake angle γ in the longitudinal direction L of the drill can best be seen in Figures 3a to 3c. Each of these figures comprises two parts, a cross-section by the drill tip 3 being represented in the upper part of the image and immediately below, the position of the cross-section with a view to the longitudinal direction L of the drill. For this purpose, each one shows a drill 2 in a schematic side view, which in its front part has a cutting area 18. The position of the cross section is indicated by a vertical line. Figure 3a shows a section AA immediately following the main cutting edges 4, that is, immediately in the area of ​​the cutting edge 12. Figure 3b shows a section BB through the drill 2, immediately behind the cutting edge 12 and Figure 3c a section CC through the drill, in a longitudinal position A in which the secondary rake angle γ already reaches a value of γ_η. In each of the figures, the core of the drill 19 is indicated by dashes. It has a constant core diameter K in the longitudinal direction L of the drill. It can alternatively also decrease from the tip of the drill 3 in the longitudinal direction L of the drill.

As can be seen from FIG. 3a, the main cutting edges 4 initially extend rectilinear, that is, in a radial direction to the center of the drill. The secondary angle of attack γ therefore assumes a value of 0 °.

As can be seen from Figures 3b and 3c, the value of the secondary rake angle γ increases continuously, so that the chip receiving groove 10 is increasingly curved, so that the secondary edge 14 is held by the groove chip catcher 10. For this reason, chip catcher groove 10 is concavely curved towards secondary edge 14.

The final value γη of the secondary rake angle γ is preferably approximately 25 ° and is reached with the length A, which corresponds to 0.25 to 1.5 times the diameter of the drill. Preferred4

ES 2 239 136 T3 mind, the final value γ_η is achieved with 1 times the diameter of the drill D.

Based on Figures 4 to 7, a sharpening procedure for the manufacture of a drill tip 3 with a secondary rake angle γ is explained below._η growing. According to Figures 4 and 5, the drill bit 2 is clamped in a housing 20, especially of a CNC machine tool. The housing 20 is movable along an adjusting axis Z. Additionally, the housing 20 is laterally mounted movably along a lateral axis X. Furthermore, the drill bit 2 can rotate about an axis of rotation C which extends in the longitudinal direction L of the drill. For sharpening, the drill bit 2 approaches a grinding wheel 22, shaped as a standard grinding wheel, rotatable on an axis of rotation S. The grinding wheel 22 can be moved closer to or away from the axis of rotation C of the drill bit 2 in one direction of lateral displacement Y. Consequently, the direction of displacement Y is oriented perpendicularly to the axis of rotation S, which in turn is oriented perpendicularly to the axis of rotation C of the drill 2. Additionally, as can be seen in figure 5, the abrasive wheel 22 is pivotable on a pivoting axis B. Each of the different directions of movement of the different axes B, C, X, Y, Z are designated with a + or well a -.

On the basis of the enlarged representation according to FIG. 6, in the area of ​​the drill tip 3, it appears that at the beginning of the sharpening process, the main edge 4 is machined with the lateral face 24 of the grinding wheel 22 forming in this way a rectilinear main cutting edge 4. The front face 26 of the grinding wheel 22 extends at an angle and becomes, forming a curvature 30, the side face 24. The curvature 30 of the abrasive wheel 22 essentially defines the radius of curvature of the chip-receiving groove 10. In figure 7 a typical geometry of the abrasive wheel 22 is shown in an enlarged section, shaped as standard grinding wheel. Only the left side of the cross section is shown with respect to the axis of rotation of the grinding wheel 22. The abrasive wheel 22 has essentially a trapezoidal cross section, where the upper part of both parallel trapezoidal sides form the lateral face 24 which, forming the curvature 30, integrates with the front side 26. An abrasive wheel 22 of this type usually finds application in sharpening a drill bit 2, as described with reference to figure 1.

In order for such a grinding wheel 22 to obtain the desired different secondary rake angles γ, a multidimensional spatial relative movement is required between the grinding wheel 22 and the drill bit 2.

For the sharpening of the drill bit 2 the housing 20 is approximated along the axis of approach Z during the entire sharpening process. At the beginning of the sharpening process there is no or only negligible rotation about the axis of rotation C. The axis of rotation C corresponds to the longitudinal axis of the drill 2. Firstly, the grinding wheel 22 is continuously displaced in the positive Y direction, whereby, at the same time, the housing 20 is also displaced in the same positive direction of the lateral axis X. A pivotal movement of the grinding wheel 22 about the pivot axis B about the pivot point B ', specifically in the negative direction of the pivot axis B.

In such a sharpening process, first the main edge 4 is sharpened with the lateral face 24 of the grinding wheel 22, in such a way that the main edge 4 extends straight. Then, for the formation of the positive rake angle, the grinding wheel 22 is pivoted towards the bit 2, in such a way that the front face 26 of the grinding wheel 22 conforms the radius of curvature of the chip-receiving groove 10 following the secondary edge 6, as can be seen from figure 3c.

The development of the sharpening process in the immediate area of ​​the main edges 4 for different sharpening instants, can be seen from Figures 8a to 8c each of Figures 8a to 8c represent a section VIII-VIII through the drill tip 3 ( see figure 9). For this reason, in these three figures, each of the main cutting edges 4 extend rectilinearly. As the sharpening process proceeds, the geometry of the chip receiving groove 10 is essentially altered. At the beginning of the sharpening process, the drill tip 3 is formed according to FIG. 8a. The geometry of the chip-receiving groove 10 here essentially corresponds to the geometry of the cross-section of the grinding wheel 22, according to FIG. 7. With progressive advancement, the grinding wheel 22 is progressively brought in the direction of the center of the drill, as can be seen from figure 8b. During the following development, by means of the pivotal movement of the abrasive wheel 22 about the pivoting axis B, the lateral zone 32 of the chip receiving groove 10 opposite the main cutting edge 4 is formed.

List of reference signs

Drill

Drill tip

Main cutting edge

Cross cutting edge 8 Main flank

Chip receiving slot

Cutting edge

Protective bezel

Secondary edge 16 Internal face

Cutting area

Drill core

Housing 22 Grinding wheel 24 Side face

Front face 30 Curvature 32 Lateral zone γ Secondary rake angle γ_η Final value A Length B Pivoting axis

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B 'Pivot point

C Axis of rotation D Drill diameter K Core diameter L Drill longitudinal direction R Radial direction

S axis of rotation

T Tangent

Y Direction of travel Z Approach axis X Lateral axis