Patent Application
20050268748
The invention relates to a tubular blank for the production of drilling tools, the blank having a forming part that can be formed in a non-cutting manner while thereby forming straight or helical chip grooves and coolant channels, and the finished tool being able to be fitted with a shaft for clamping in a machine tool and with a drill tip provided with cutting edges.
It is known from DE-A-198 56 986 to use for the production of a drilling tool a tubular blank which comprises a piece of tube of ductile material with an inside and outside diameter that are constant over its length. For the production of a drill body while thereby forming chip grooves and coolant channels, the blank is formed there in a non-cutting manner by the swaging method and is subsequently fitted at its rear end with a drill shaft for clamping in a machine tool. It is known in this case that the drill shaft is clamped for example on the finished drill body by suitable clamping means (for example screws). For this purpose, a clamping part adjoining the region of the chip groove is required. In the production of actual, operational drills using the known blanks with an inside and outside diameter that are constant over the length, it has been found that, depending on the wall thickness of the blank, either the non-cutting formability in the forming part or the strength in the clamping part leave something to be desired.
Against this background, the invention is based on the object of developing a tubular blank of the type stated at the beginning which allows for the different preconditions in terms of deformation and strength in the forming part and the clamping part of the drill body.
The combination of features specified in patent claim 1 is proposed as a solution for achieving this object. Advantageous configurations and developments of the invention emerge from the dependent claims.
The solution according to the invention is based on the recognition that, for the production of drilling tools, the blank should have a relatively small material wall thickness in the forming part, in order that adequate deformation can take place with few working steps, while thicker-walled material is required in the region of the clamping part, to allow the forces occurring during clamping to be absorbed. The clamping on the drill shaft takes place for example by means of clamping screws, which act against a clamping area in the clamping part, or by thermal shrink-fitting of the tool shaft onto the clamping part. In the first case, the clamping area causes the material to be thinned in places if they are produced by a metal-cutting process. Since the clamping screws press against the zone where the material is thinned, it must be ensured that adequate material remains when the clamping area is produced. The same applies correspondingly if the clamping area is formed by a non-cutting process, for example in a forging operation. In the case of shrink-fitting, it must be taken into account that the clamping chuck is heated up to an elevated temperature, for example to 400° C., and has a relatively high thermal capacity. This leads on contact to heating up of the clamping part and to reduced strength at the moment of clamping. The wall thickness must therefore be chosen such that the clamping part is not plastically deformed during this clamping operation. In order to allow for these conflicting preconditions, the invention proposes a clamping part which is arranged at the shaft-side end of the forming part, is integrally connected to the latter and the tubular wall thickness of which is greater than in the region of the forming part.
According to a preferred configuration of the invention, the outside tube diameter is greater in the region of the clamping part than in the region of the forming part. In principle, it is possible in this case for the inside tube diameter to be equal in the region of the clamping part and the forming part, or for the inside tube diameter to be greater or smaller in the region of the clamping part than in the region of the forming part.
A further advantageous configuration of the invention provides that a preferably planar clamping area is arranged on the outer side of the clamping part, it being possible for the inside tube diameter to be constant or variable over the length of the clamping part and smaller in the region of the clamping area than outside the clamping area. The clamping area may in this case run parallel to the tube axis. It is also possible for the clamping area to run obliquely with respect to the tube axis. In the latter case, the drilling tool can be secured better against pulling out of the tool from its clamping restraint.
It is simplest if both the interior outline and the exterior outline of the blank are circular over the length of the clamping part and over the length of the forming part and have a constant diameter. However, it is also possible in principle for the interior outline to be formed in an oval or elliptical manner, at least over the length of the clamping part, the clamping area expediently being arranged in the region of the smaller inside tube diameter. In this way, the wall thickness, and consequently the strength, of the clamping part can be increased in the region of the clamping area.
A further advantageous configuration of the invention provides that, with a constant outside tube diameter, the inside tube diameter conically diverges at least over part of the length of the forming part toward the free end. This measure allows the cooling channels formed in the forming operation to be widened toward the drill tip. A further modification of the cooling channels over the length of the forming part can be achieved by the interior outline of the blank being formed in an oval or elliptical manner at least over part of the length of the forming part.
A further preferred configuration of the invention provides that a transitional portion which runs conically is provided between the forming part and the clamping part. The transitional portion is advantageously conically formed on the inside between the clamping part and the forming part in the same direction as on the outer side. A step-shaped transitional portion may also be arranged between the clamping part and the forming part. The transitional portion may in this case be formed and dimensioned in such a way that at least one bit seat for receiving a cutting bit can be formed in it there. To improve the flow properties in the cooling channels, it has proven to be particularly advantageous if the flow channel is widened in the transitional portion with respect to the clamping part.
To produce the tubular blank for the non-cutting forming in the production of drilling tools, it is expedient to start with a piece of tube with a constant inside and outside diameter, which is formed, preferably swaged, at least partially over a mandrel from the outside while thereby forming a forming part that has a thinner wall than a clamping part, or is subjected to a metal-cutting operation, preferably drilled or turned on a lathe, on its inner and/or outer surface. The clamping area may be formed into the outer surface of the clamping part by either a metal-cutting operation or a non-cutting operation.
The invention is explained in more detail below on the basis of several preferred exemplary embodiments. In the drawing:
a shows a side view of a finished drilling tool with a helical chip groove, a thickened clamping shaft and an attached drill tip;
b shows a section along the sectional line B-B of
a to d show four exemplary embodiments of tubular blanks for the production of drilling tools;
a shows a tubular blank with a clamping area and an oval inner passage;
b shows a longitudinal section through the blank that is shown in
Represented in
The drilling tool that is shown in
In the case of the exemplary embodiment shown in
The clamping part 16 must absorb clamping forces during the clamping in a tool shaft without thereby undergoing plastic deformation. On the other hand, the blank must be formed in a specific manner by plastic deformation in the region of the forming part 26 to introduce the chip grooves 12. In order to satisfy the conflicting conditions with regard to strength and deformability, the wall thickness of the tubular blank 22 is greater in the clamping part 16 than in the forming part. This can be realized with the inside diameter of the central channel 24 remaining the same by an increased outside diameter in the region of the clamping part 16 (
To produce the tubular blanks 22 that are shown in
The blank expediently consists of a case hardening steel with a phase transition point of from 480 to 650° C. Preferably used for this purpose is a case hardening steel with a chromium content of less than 2%, preferably a 16 MnCr 5 steel. The case hardening steel is hardened, for example by carburizing or nitriding on the surface, and if appropriate on the inner side, after the forming. The hardness profile thereby achieved in the wall of the tool shaft leads to a high load-bearing capacity.
To sum up, the following can be stated: the invention relates to a tubular blank 22 for the production of drilling tools, the blank having a forming part 26 that can be formed in a non-cutting manner while thereby forming chip grooves 12 and coolant channels, and the finished drilling tool being able to be fitted with a shaft for clamping in a machine tool and with a drill tip 20 provided with cutting edges. In order to allow for the conditions in terms of strength and deformability, the tubular blank 22 has a clamping part 16 which is arranged at the shaft-side end of the forming part 26, is integrally connected to the latter and the tubular wall thickness of which is greater than in the region of the forming part 26.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102 55 498.6 | Nov 2002 | DE | national |
| 103 33 666.4 | Jul 2003 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP03/13293 | 11/26/2003 | WO | 5/27/2005 |
