A DRILL

Abstract: A drill produced from a substantially rod-like blank containing high speed steel has at one end thereof a pointed tip which is intended to penetrate the material to be drilled. The drill is preferably a helical drill having edge parts which extend essentially from the outer part of the drill tip to the periphery of the drill cross-section, and further includes a radially open groove which extends helically along the drill, for the purpose of removing chippings from the drill. The drill is particularly characterized in that the blank, and therewith also the drill, in cross-section includes a central steel part, which is intended to exhibit high compressive strength, and which therewith forms the outer part of the drill tip, and a concentrical outer layer of high-speed steel which is intended to exhibit high thermal stability and which is applied with the aid of a casting technique.

Description: A dr il l . The present invention relates to a drill manufactured from a substantially rod-like blank containing high speed steel. The invention also relates to a method for pro¬ ducing a drill according to the invention. Drills of the kind meant here are intended for drilling primarily metal and are cylindrical in shape and include a pointed tip which is intended to be inserted into the material to be drilled and cutting edge-parts located in the vicinity of said drill tip. In this regard, slightly different requirements are placed on the drill material in the radial direction of the drill cross-section. The centrally located parts of the drill, the drill tip, are required to have a high compression strength and wear resistance. In addition to being wear resistant, the outer parts of the drill are also required to have a high temperature stability, because of the high relative speeds between the outer drill parts and the material being drilled. Drills of this kind are manufactured from high-speed εteel- rόd , although optimum regard is not paid, however, to the aforesaid variation regarding the requisite material prop¬ erties. This will often result in the use of a more ex¬ pensive material than is actually required. The present invention relates to a drill in which the properties of the drill material vary radially in the cross-section of the drill, and . in which the properties of the material have been adapted to occurrent stresses as described hereinafter. According to the invention, at least part of the drill a- terial, with regard to its composition, can be selected with regard to desired material properties and not, as is usual, also with regard to the working properties of the material, primarily the hot working properties thereof. This will also enable very high contents of alloying sub¬ stances to be used. The invention thus relates to a drill produced from a sub¬ stantially ' rod-like blank which contains high speed steel. The drill has at one end thereof a pointed tip which is intended to penetrate the material to be drilled, and is preferably a helical-type drill which includes cutting edges which extend essentially from the centre part of the drill tip to the periphery of the drill cross-section, and also at least one radially open.groove which extends helically along the drill, for the removal of chippings. The inventive drill is particularly characterized in that the blank, and herewith also the drill in cross-section, comprises a steel central part which is adapted to exhibit high compressive strength and which forms the outer part of the drill tip, and a concentric, outer layer of high speed steel which is adapted to exhibit high thermal stability and which is applied by means of a casting technique. The invention also relates to a method for producing a drill in accordance with the invention, essentially in accordance with the following claim 6. The invention will now be described in more detail with reference to an illustrative embodiment thereof. According to the invention the drill blank, and therewith also the drill, includes, in cross-section, a central part which is adapted to exhibit high compressive strength and to form, inter alia, the drill tip. The requirement of thermal stability is not especially accentuated in this case. In the case of slightly. simpler and less expensive drills, the central drill part may comprise carbon steel, i.e. not necessarily high speed steel. In the case of high performance drills, however, it is preferred in many cases to produce the central part of the drill from high speed steel, although not necessarily a high speed steel - which possesses high thermal stability. Furthermore, in accordance with the invention, the said outer layers of the drill comprise high speed steel, al¬ though a somewhat simpler high speed steel can be accepted in the case of simpler and less expensive drills. In the case of high performance drills, a high speed steel pos¬ sessing very high thermal stability is preferably used. The contents recited with regard to material compositions are all in percent by weight. By the expression "up to x %" is meant contents which lack substantially the sub¬ stance concerned or which contain only traces of said substance up to contents of x %. In accordance with one preferred embodiment the aforesaid outer layer will comprise a high speed steel which con¬ tains, in percent by weight, 0.7-2 % C, up to 6 % Cr, up to 10 % Mo, up to 16 % W, up to 3 % V, 5-15 % Co, with the remaining alloying substances being present in essen- tially normally occurring contents, with the remainder consisting of Fe and normally occurring impurities. In this regard, very high -contents are suitably corre¬ sponded by relatively low Mo-contents, since these sub¬ stances can, to a certain extent, be substituted one for the other. hen the aforesaid central drill part comprises high speed steel, the steel will contain, in accordance with one preferred embodiment, in percent by weight, 0.7-2 % C, up to 6 % Cr, up to 10 % Mo, up to 16 % , up to 3 % V, with the remaining alloying substances being present in essen¬ tially normally occurring proportions, with the remainder comprising Fe together with normally occur¬ ring impurities. It is also preferred that casting is effected in an essen¬ tially known manner, i.e. by the direct casting of a metal melt essentially in accordance with Swedish Patent 8003487 -9, where molten metal is caused to run from a container through an outlet port therein and caused to form a con- tinuous wire-like body by stabilizing with the aid of a wire which passes continuously through the outlet port whereafter the continuous jet of- molten metal surrounding the wire is solidified around said wire and collected, there being formed a wire which " includes a core corre- sponding to the stabilizing wire, and a concentrical outer layer corresponding to the molten metal, or alternatively by so-called dip-forming in which a wire is passed through a molten metal bath and a layer of bath metal frozen onto the wire, there being formed a wire which includes a core, corresponding to the wire passing through the molten bath, and a concentrical outer layer, corresponding to the bath metal. The function of the inventive drill and the advantages afforded thereby will be apparent essentially from the aforegoing. Thus, when seen in the radial direction, the material from which the inventive drill is comprised has been adapted to stresses which occur when the drill is in use. Casting of the outer drill layer onto a central core eliminates problems associated with the manufacture of wire from cast ingots or blanks whose cross-sectional size is many times greater than the size of the ultimate wire. Thus, this eliminates problems associated primarily with the hot rolling of high alloyed, high-speed steel type materials. This enables the drill blank to be pro¬ duced at much lower costs than when manufacturing in accordance with traditional methods. The invention has been described in the aforegoing with reference to a number of embodiments thereof. It will be understood, however, that other embodiments are conceiv¬ able and that minor modifications can be made without departing from the scope of the invention. For example, the wire, or rod, forming the central part of the drill can conceivably be produced by casting in the aforedescribed manner. Furthermore, the material from which the central drill part is made and from which the outer drill layer is made can have compositions other than those recited above. The recited proportions in which the various constituents are present are only rough values, since the method for producing the drill blank enables a great deal of freedom with regard to composition, where¬ with compositions which lie outside normally occurring high-speed steel compositions are highly conceivable. It has been said in the aforegoing that the central part of the drill comprises a material which possesses high compressive strength. It is meant by this that the mate- rial either exhibits said high compressive strength or can be brought to a condition of high compressive strength, e.g. by heat treatment. As beforementioned, the invention is particularly suited to the manufacture of helical drills which include edge portions which extend from the outer part of the drill tip to the periphery of the drill cross-section, and which also include at least one radially open groove which ex¬ tends helically along the drill, for the removal of chip- pings. The invention can also conceivably be applied to other types of drill. The invention shall not therefore be considered limited to the aforedescribed and illustrated embodiments, since modifications can be made within the scope of the follow¬ ing claims.

Claims: Cl a i s 1. A drill produced from a substantially rod-like blank containing high speed steel, said drill having at one end thereof a tip or point intended to penetrate the material to be drilled, and said drill preferably being a helical drill which includes edge parts which extend substantially from the outer part of the drill tip to the periphery of the drill cross-section, and which further includes at least one radially open groove which extends helically along the drill for the purpose of transporting chippings, characterized in that the blank, and therewith also the drill, includes in cross-section a central steel part which is intended to exhibit high compressive strength and to form the outer part of the drill tip, and a concen¬ trical outer layer of high speed steel which exhibits high thermal stability and which is applied by a casting operation. 2. A drill according to claim 1, characterized in that both the central drill part and the outer drill layer comprise high speed steel. 3. A drill according to claim 1, characterized in that the central drill part comprises carbon steel. 4. A drill according to claim 1, characterized in that the outer drill layer comprises high speed steel which includes in percent by weight, 0.7-2 % C, up to 6 % Cr, up to 10 % Mo, up to 16 % , up to 3 % V, 5-15 % Co, the remaining alloying substances being present essentially in normally occurring proportions, and the remainder being Fe together with normally occurring impurities. 5.. A drill according to claim 1, 2 or 4, characterized in that said central drill part comprises a high speed steel which includes, in percent by weight, 0.7-2 % C, up to 6 ? Cr, up to 10 % Mo, up to 16 % W, up to 3 % V, the remain¬ ing alloying substances being present in substantially normally occurring proportions and the remainder compris¬ ing Fe together with normally occurring impurities. 6. A method for producing a drill in accordance with any of the preceding claims, characterized in that said cast- ing operation is effected either in the form of a direct casting of a metal melt in which the molten metal is caused to run from a container through an outlet port therein and therewith caused to form a continuous wire¬ like body by stabilizing with the aid of a wire which - passes continuously through the outlet port, whereafter the continuous jet surrounding the wire is caused to solidify around the wire and is collected, there being formed a wire which includes a core, corresponding to the stabilizing wire, and a concentrical outer layer, corre- sponding to the molten metal, or by so-called dip-forming in which a wire is passed through a molten metal bar and a layer of molten metal is frozen onto the wire, there being formed a wire which includes a core, corresponding to the wire passing through the molten metal bath, and a concentrical outer layer, corresponding to the molten metal.

Inventors: EKEROT SVEN, EKEROT, SVEN
Applicants: EKEROT SVEN TORBJOERN, EKEROT, SVEN
Application year: 1988
Main classification: B23B51
IPC codes: B22D19, B23B51