The invention relates to a drilling tool for machine tools of the generic type specified in the precharacterizing clause of claim 1, and to a method for the production of a drilling tool such as this.
A drilling tool of this type is known (EP-B-0883455), which has a drill body, a cutting head which is arranged thereon at the end, and a shank which is arranged thereon at the end. The drill body has two chip flutes which are bounded on their flanks by ribs curved in a helical shape. Furthermore, the cutting head has two cutting inserts which are arranged at different radial distances from the drill axis, with mutually partially overlapping working areas in in each case one recessed inset seat. In addition, at its end remote from the cutting head, the drill body has a drill shank which has no ribs and contains a central coolant supply channel, and coolant channels are arranged in the ribs of the drill body. The coolant channels pass in a helical shape there through the drill body and open into the central supply channel. The ribs which are located between the chip flutes are helical with the same pitch in the known drills. Their width is the same over the drill length. It has admittedly already been proposed that the chip flutes have variable pitches along the drill body. However, the mutual separation between the chip flutes and the width of the ribs located between them remain essentially the same.
It has been found that the quality of a drilling tool is substantially dependent on physical features. Fundamentally, it is possible to influence the removal behavior, the oscillation behavior, the bending behavior, the chip formation and the chip removal behavior of a drill in a positive manner by suitable design measures.
Against this background, the invention is based on the object of improving the behavior of the drilling tool during the drilling process in terms of oscillation, bending and twisting in the area of the drill body. A further object is to provide a method which is particularly highly suitable for the production of the tools according to the invention.
The combinations of features specified in patent claim 1 and in the independent method claims have been proposed in order to solve this problem. Advantageous refinements and developments of the invention are specified in the dependent claims.
The invention essentially consists in that the chip flutes associated with the various cutters have different pitches in their profile over the drill body. This results in different cross sections or widths, which are at the same time variable over the length, of the ribs which are located between the chip flutes and have a significant influence on the bending and torsional response of the drill body. In the ideal case, the aim is for the neutral line of the drill bending to coincide with the central axis. In this case, the bending forces are canceled out, as a result of which only torsion forces now act on the drill body. On the other hand, the torsion can be compensated for or eliminated by appropriate stiffening in the torsional direction, that is to say in the circumferential direction. For this purpose, it is advantageous for the cross section of the ribs to be varied permanently over the length of the drill shank. The aim of this variation is to damp torsional oscillations.
In order to achieve this, it is proposed that, on a drill body with two chip flutes which are bounded on their flanks by ribs, the first chip flute is curved in a helical shape, while a second chip flute is not helical or is curved in a helical shape with a pitch which differs from that of the first chip flute, and runs in the same rotation direction.
At least one cutter is in each case advantageously arranged at the cutting-head end of each chip flute and, for example, may in each case be formed by a cutting insert or by a drill bit which is arranged detachably on the drill body.
In the case of cutting inserts, it is advantageous for these to be arranged at different radial distances from a central axis of the drill body in the individual chip flutes, wherein the outer cutting edge of an outer cutting insert projects radially beyond the circumference of the drill body, and the inner cutting edge of an inner cutting insert projects radially beyond the central axis, and wherein the chip flute which is associated with the inner cutting insert is more helical than the chip flute associated with the outer cutting insert. In these considerations, it should be remembered that the outer cutting insert and the associated outer groove have a greater influence on the oscillation behavior, since the cutting forces which occur there and the amount of material removed there are several times greater than on the inner cutting insert and in the area of the inner chip flute. One important aim of the invention is therefore to stiffen the ribs in the area of the outer groove. This can be achieved by the outer groove being less helical than the inner groove. In a corresponding manner, according to one preferred refinement of the invention, the rib to which the outer cutting insert is fitted has a profile which becomes broader from the cutting head to the drill shank, and the rib to which the inner cutting insert is fitted becomes narrower. In a generalized form, this means that a first of the ribs which are arranged between the chip flutes has a profile which becomes broader from the cutting head toward the shank, and in that a second of the ribs which are arranged between the chip flutes has a profile which becomes narrower from the cutting head toward the shank.
A further preferred refinement of the invention provides that coolant channels are arranged in the ribs of the drill body, extend from the shank end to the cutting-head end of the drill body, and have an outlet opening at the cutting-head end, wherein the coolant channels which are arranged in the various ribs are differently helical or are not helical. In this case, the outlet openings of the coolant channels are advantageously arranged within in each case one of the chip flutes, wherein the outlet openings preferably communicate via a non-helical channel end piece with one of the coolant channels which are arranged in the ribs. In this case, the outlet openings expediently have an oval or egg-shaped outline which is elongated in the direction of the chip flutes. In order to avoid blockages and to improve the way in which the chips are carried away, the outlet openings may form a groove which runs along the chip flutes, or open into such a groove.
Various method variants are proposed according to the invention for the production of the drilling tools according to the invention.
According to a first method variant, the following method steps are proposed:
These measures result in the two chip flutes being curved with a different pitch and the same rotation direction, such that a first rib, which is arranged between the chip flutes, becomes broader in its profile from the cutting head to the shank, and the other becomes narrower. In principle, it is possible for the prefabricated blank to be twisted in a helical shape in a rotation direction in the opposite sense to the helical shape of the second groove. This means that one of the two chip flutes in the finished drill body runs in a straight line, or even runs in a helical shape in the opposite direction to the rotation direction.
According to a second method variant of the invention, the following method steps are proposed:
In this way, it is also possible to produce a drill body with chip flutes with different helical shapes.
In all the above cases, one preferred refinement of the invention proposes that a deep-hole bore is incorporated into the ribs, which remain between the grooves during the milling process, before the twisting of the blank, and is made helical during the twisting of the blank, forming the coolant channel. In the second method variant, it is in this case advantageous for the first deep-hole bore to be incorporated after the introduction of the first straight groove, and for the second deep-hole bore to be incorporated after the introduction of the second straight groove.
According to the invention, a third method variant provides the following method steps:
These measures mean that the chip flutes which are incorporated after the twisting can have different helical pitches, thus ensuring that the deep-hole bores likewise have different helixes and are located in the ribs between the chip flutes.
Furthermore, these measures make it particularly simple to mill the deep-hole bores on the cutting head side in an untwisted, preferably straight, area, forming outlet openings which open into the chip flutes. In addition, seating depressions for holding cutting inserts can be incorporated into the cutting-head end of the ribs, in the immediate vicinity of the outlet openings. The deep-hole bores on the cutting head side are expediently shaped in their untwisted straight area with an oval or egg-shaped outline, forming outlet openings, in which case the deep-hole bores on the cutting head side can be shaped to create grooves which are open at the edge.
The invention will be explained in more detail in the following text with reference to the drawings, in which:
a and b each show a side view of a rotationally symmetrical blank, which has been turned to a drill body contour, with and without a clamping surface;
a and b show a side view and a plan view of the blank provided with deep-hole bores, as shown in
a and b show a side view and a plan view of the blank as shown in
a and b show a side view and a plan view of the blank as shown in
a to d show three side views and one plan view of the drilling tool produced from the blank as shown in
a to d show a side view and three diagrammatic illustrations of the drilling tool shown in
a and b show a diagrammatic illustration and a plan view of a drilling tool with a straight outer chip flute and a helical inner chip flute.
The drilling tools illustrated in
In the exemplary embodiment shown in
The coolant channels 32, 34 must be placed within the drill body 14, before or after the introduction of the chip flutes 24, 26, such that they are completely embedded in the ribs 28, 30 between the chip flutes 24, 26.
Various method variants are proposed for the production of the described drilling tools.
In a first method step, a base material body is always turned by machining to a drill body contour, forming a rotationally symmetrical first blank 38 (
In the procedure indicated in
In a second method step as shown in
In a third method step as shown in
In a final method step, the blank as shown in
The exemplary embodiment shown in
A further possible way to produce helical chip flutes 24, 26 with a different pitch is to introduce them in two steps. First of all, a first non-helical or helical flute is incorporated in the blank before it is twisted. The blank is then subjected to a first twisting process. A second chip flute is then milled in, which may be non-helical or helical. If straight chip flutes are in each case provided initially, a second twisting process is expediently also carried out, thus producing two differently helical chip flutes 24, 26. One of the deep-hole bores 32′, 34′ can in each case be incorporated before the twisting steps, which bores are provided with different helical shapes during the further machining process, together with the chip flutes 24, 26 and the ribs 28, 30 arranged between them.
In summary, the following statement can be made: the invention relates to a drilling tool for machine tools. The drilling tool comprises a drill body 14, a cutting head 16 arranged thereon at the end, and a shank 12 arranged thereon at the end, wherein the drill body 14 has two chip flutes 24, 26 which are bounded on their flanks by ribs 28, 30 and of which a first chip flute 24 is curved in a helical shape. One special feature of the invention is that a second chip flute is not helical or is curved in a helical shape with a pitch which is not the same as the first chip flute 24 but preferably runs in the same rotation direction.
Number | Date | Country | Kind |
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10 2007 042 280.8 | Sep 2007 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2008/059921 | 7/29/2008 | WO | 00 | 2/22/2010 |