Drilling tool

Abstract: The invention relates to a drilling tool including a shaft (1) having a front end to which a cutting body provided with cutting edges (2) is detachably connected. In the front end of the shaft (1), a seat is formed which is delimited by spaced-apart protrusions (4, 5) between which there is a bottom surface. In the protrusion (4), there is a threaded hole for a screw (8), which alone guarantees the fixing of the cutting body and which is of such a nature that it on tightening it applies pre-stressing forces to the cutting body. On the inside of the opposite protrusion (5), there is a supporting shoulder (15) against which the cutting body is pressed when the screw is tightened and applies a lateral pre-stressing force to the cutting body. Characteristic of the invention is also that the protrusions (4, 5) are laterally displaced in relation to each other in order to freely expose the screw (8) beside the protrusion (5).

Description: Technical Field of the Invention This invention relates to a drilling tool of the type that comprises a shaft having a front end to which a cutting body provided with cutting edges is detachably connected by means of a screw joint. Prior Art Recently, it has become common to manufacture not only drilling tools but also other types of chip forming tools, such as shaft-type cutters, thread cutters and the like, from two separate components, namely on the one hand, a shaft, which most often has a long narrow, cylindrical shape, and on the other hand an cutting body provided with cutting edges which can be detachably connected to a front end of the shaft. In modern machine tools, the tool shafts are so sophisticated and expensive that they, for economic reasons, cannot be integrated with the wearing part of the tool, namely the cutting body, to form a single tool which has to be discarded when the cutting body has worn out. In other words, it is profitable to make the actual cutting body as a detachable unit, which can be replaced, while the expensive shaft may be used for a long time. Generally, the cutting bodies of the tools are assembled on the shafts by means of screw joints. In certain tools, such as milling tools (see e.g. US 5 607 263 and DE 3 448 086), simple screws are used which are screwed fast into a threaded hole in the front end of the shaft via a through hole in the cutting body. A serious disadvantage with this design, however, is that chip-forming edges cannot be formed in the area of the front end of the cutting body, and therefore the cutting body cannot be designed for drilling purposes. For this reason, previously known drilling tools having replaceable cutting bodies are structurally complicated and demand a plurality of details, such as screws, springs or drawbars for the fastening of the cutting body. This means, in practice, that the assembly as well as the disassembly of the cutting body become complicated and time-consuming at the same time as difficulties arise to centre the cutting body in relation to the shaft in an exact manner. Furthermore, the fixation becomes unreliable inasmuch as the cutting body may be dislodged from an initially centred position during operation. Aims and Features of the Invention The present invention aims at obviating the above-mentioned shortcomings of previously known drilling tools having replaceable cutting bodies and at providing an improved drilling tool. Therefore, a primary aim of the invention is to provide a drilling tool which with simple and few means can safeguard the cutting body of the tool on the shaft in a centred state which in a reliable manner is retained during the cutting operation. An additional aim is to create a drilling tool, the cutting body of which can be assembled and disassembled, respectively, in a simple and fast manner. Another aim is to create a drilling tool, the cutting body of which is self-centring inasmuch as the cutting body in connection with the drilling operation is brought automatically to assume the correct position also in such cases as when the cutting body is assembled initially in an incorrect manner. In one particular aspect, the invention also aims at providing a drilling tool having an improved cooling ability. Document US-A-4 744 704 discloses a drilling tool with the features of the preamble of claim 1. According to the invention, at least the primary aim is attained by the combination of features defined in claim 1. Preferred embodiments of the invention are furthermore defined in the dependent claims. Brief Description of the Appended Drawings Of the drawings: Fig 1 is a partial perspective view of a drilling tool according to the invention, whereby a cutting body is shown located in a seat in a free end of a shaft, Fig 2 is an analogous perspective view showing the same tool from the opposite side, Fig 3 is a perspective view showing only the actual shaft of the tool from the same side as in fig 1, Fig 4 is an analogous perspective view showing the shaft from the same side as in fig 2, Fig 5 is a perspective view of the same shaft as seen at a steeper angle than in fig 3 and 4, Fig 6 is a perspective view of a cutting body according to the invention seen from a first side, Fig 7 is a perspective view showing the same cutting body from the opposite side, Fig 8 is a perspective view of the same cutting body seen obliquely from the front, Fig 9 is a perspective view showing the cutting body obliquely from behind, Figs 10-13 are four perspective views corresponding to figs 6-9 showing an alternative embodiment of a cutting body, and Figs 14-17 are analogous perspective views showing an additional alternative embodiment of the cutting body. Detailed Description of Preferred Embodiments of the Invention A front end of a drilling tool which includes a shaft 1 and a cutting body in its entirety designated 2 is shown from opposite directions in figs 1 and 2. In a conventional manner, the shaft 1 has an elongated cylindrical basic shape and two opposing chip channels 3, 3' extending helicoidally along the shaft in the rearward direction from the cutting body. The cutting body 2 is assembled on a seat formed in a front end of the shaft 1 which seat will be described closer with reference being made to figs 3-5. Said seat, which by those skilled in the art is denominated cutting seat, is delimited by two spaced-apart, axially projecting protrusions 4, 5. The front or outer portion of the cutting body 2 has one or more chip forming edges. In the example, the drill tool is assumed to be of a so-called DELTA-type, whereby two edges 6, 6', illustrated schematically in figs 1 and 2, extend at an obtuse angle to a common tip 7 at the centre of the cutting body. In fig 1, numeral 8 designates a screw, the purpose of which will be described closer below. Reference is now made to figs 3-5, which more clearly illustrate the seat in which the cutting body 2 is housed. In these figures, it is seen how the two axially projecting protrusions 4, 5 are spaced apart by a plane bottom surface 9, which extends in a plane perpendicular to the geometrical length or centre axis of the drill shaft 1. Inwards, the protrusions 4, 5 are defined by plane surfaces or inner surfaces 10 and 11, respectively, which to advantage are mutually parallel and extend parallel to the centre axis of the shaft, i.e. perpendicular to the bottom surface 9. The external surfaces 12, 13 of the protrusions are, on the contrary, arched in order to, in the main, fit in with the cylindrical basic shape of the shaft 1. A threaded hole 14 is formed in the first protrusion 4, which to advantage - though not necessarily - may be a through hole, i.e. extend from the inner surface 10 to the outer surface 12. The screw 8 can be fastened in this threaded hole 14. A supporting shoulder 15 is formed on the inner surface11 of the second protrusion 5 which has an abutment surface 16 (below denominated first abutment surface), as well as a support surface 17 (below denominated first support surface) which is parallel to the inner surface 10 of the protrusion 4 (advantageously - though not necessarily - it may also be parallel to the inner surface 11 of the protrusion 5). In the embodiment example which is shown in figs 4 and 5, the shoulder 15 is, in the area of the inner or rear end thereof, formed with a narrowed waist 15', which is delimited by an arched surface 18 which, together with an arched countersunk surface 19 in the plane bottom surface 9, define a curved corner space between the shoulder and the bottom surface 9. Ducts 20 for cooling liquid may port in the two protrusions 4, 5. Reference is now made to figs 6-9, which in detail illustrate the design of the cutting body 2. The cutting body has a bottom side in the form of a plane surface 21 axially opposite the cutting edges 6, 6'. Two plane, external surfaces 22, 23 extend perpendicularly to said surface, of which the one first-mentioned is intended to be turned towards the inner surface 10 of the protrusion 4, while the second is intended to be turned towards the inner surface 11 of the protrusion 5. In the exemplified embodiment, the cutting body 2 has, at the opposite short ends thereof, arched flank surfaces 24, 25, which extend from the bottom side 21 to the area of the cutting edges 6, 6'. In a conventional manner, said flank surfaces have a certain clearance, i.e. extend at a limited angle obliquely inwards rearwards from the outer ends of the edges (the requisite clearance may also be provided in another manner). An arched surface 26 extends between the plane surface 23 and the flank surface 24,having the same basic shape as the chip channel 3. Therefore, when the cutting body is assembled in the appurtenant seat, the surface 26 together with an arched surface 27 of the protrusion 5 (see fig 1) define an extension of the arched surface in the drill shaft defining the chip channel 3. Correspondingly, an arched surface 28 extends between the plane surface 22 of the cutting body and the flank surface 25 in order to form, together with an arched surface 29 (see fig 2) of the protrusion 4, an extension of the chip channel 3' up to the appurtenant cutting edge. A through hole 30 which is not threaded extends through the flank part of the cutting body 2 as illustrated to the left in fig 6, which is defined between the surfaces 26 and 22. The part of the hole 30 that ports into the surface 22 has only a slightly larger diameter than the shaft of the screw 8. At the opposite end thereof, however, the hole widens into a space 30' in which a head of the screw may be housed. In doing so, the head of the screw may be pressed against a ring-shaped surface 31, which forms the bottom of the space 30'. In a manner characteristic of the invention, the holes 14 and 30 are non-centric or eccentric in relation to each other in order to, in manner known per se, apply a certain pre-stressing force to the cutting body 2 in connection with the tightening of the screw. Such an eccentricity between the holes 14, 30 may be effected in various manners. One manner is to tilt either of the two holes in relation to the other one. The threaded hole 14 may, for instance, extend at a certain (extraordinarily moderate) angle in relation to the surface 10, while the non-threaded hole 30 extends perpendicularly to the surface 22. Another manner is to form the holes mutually parallel, although somewhat laterally displaced in relation to each other. In combination with the eccentricity between the holes, the threads of the screw 8 and, of the hole 14, respectively, may be made with a certain play, and the material in the screw having a certain elasticity. Thanks to the eccentricity between the holes, in combination with a certain thread play and a certain elasticity in the screw, the screw may be brought to affect the cutting body with two pre-stressing forces acting in different directions, namely on one hand, a force acting laterally and which is schematically outlined at X in fig 3, and on the other hand an axial force Y which aims to pre-stress the cutting body axially in the inward or rearward direction. Therefore, in connection with the tightening of the screw 8, the cutting body will not only be pressed with the plane surface 22 thereof against the inner surface 10 of the protrusion 4 but also with the bottom side 21 thereof against the bottom surface 9 of the seat, and the cutting body also being subject to a lateral force in the X direction. In this connection, it should be pointed out that the pressing of the bottom side 21 against the bottom surface 9 is particularly marked in that flank part of the cutting body which is situated closest to the hole 30 and the screw 8. In the area between the plane surface 23 and the flank surface 25, the cutting body has a recess 32 which is delimited by a second abutment surface 33, as well as a second support surface 34. Said surfaces 33, 34 are intended to co-operate with the aforementioned surfaces 16 and 17, respectively, of the supporting shoulder 15. Between the surfaces 33 and 34, there is a cavity 35 which guarantees that the edge portion between the surfaces 16 and 17 of the supporting shoulder 15 cannot touch the bottom in the recess 32 (in order to avoid contact between said edge portion and the corner between the surfaces 33 and 34, the edge portion may also be rounded with a suitable radius). Already now, it should be pointed out that the supporting shoulder 15 has a thickness which is at least somewhat larger than the depth of the recess 32; something that means that the plane surface 23 of the cutting body cannot come in contact with the plane inner surface 11 of the protrusion 5 when the cutting body is assembled in the seat and the support surface 34 is pressed against the analogous support surface 17 of the supporting shoulder 15. In the preferred embodiment which is shown in figs 6-9, the abutment surface 33 is oblique at a certain angle α in the direction axially forwards/inwards from the rear-end thereof. It is to advantage if said angle α is within the range of 5-12° and attains, for instance, 8°. Also other angular values are, however, feasible. Thus, the angle may vary all the way from 1° to approximately 15°. By this inclination of the abutment surface 33, the cutting body will, at the fixing thereof by means of the screw 8, be exerted to a wedge action aiming to press the cutting body in the rearward direction. In other words, in particular the part of the bottom side 21 of the cutting body, which is distanced from the screw, will be pressed against the bottom surface 9 of the seat. Thus, the wedge action which is achieved by co-operation between the abutment surfaces 16 and 33 co-operates with the pre-stressing force in the Y direction which is achieved already by the actual screw, whereby the two opposite flank parts of the cutting body are pressed at the same time with a marked force against the bottom surface 9 of the seat. As furthermore is seen in fig 8, the abutment surface 33 extends at a certain angle to the support surface 34. Generally, this angle may vary within the range of 60-89° implying that the complementary angle β may vary within the range of 30-1°. Advantageously, the angle β is within the range of 5-20°. The angle may, for instance, be approx. 15°. Through the inclination of the abutment surface 33 in relation to the support surface 34, an additional wedge action is achieved which, when the cutting body is subject to a pre-stressing force in the X direction, ensures that the support surface 34 is pressed distinctly against the corresponding support surface 17 of the shoulder 15. As has previously been pointed out, the thickness of the shoulder 15 is somewhat larger than the depth of the recess 32, and therefore the surface 23 will go free from the inner surface 11 of the protrusion 5. In this manner, it is guaranteed that the cutting body 2 does not become over-determined in connection with the fixation in the appurtenant seat. It should be pointed out particularly that the two protrusions 4, 5 have a width that is smaller than the diameter of the shaft 1, whereby the protrusions are laterally displaced in relation to each other (i.e. not located opposite each other). In this manner, location of the screw 8 is made possible in an exposed, accessible state beside the protrusion 5. The width of the recess 32 as well as the same width of the co-operating supporting shoulder 15 may vary very considerably. Thus, this width dimension may be increased considerably in comparison with the embodiment example according to figs 6-9, e.g. so far that the abutment surface 33 is located near the centre of the cutting body, whereby the size of the surface 23 is reduced to the same extent. It should also be mentioned that the depth of the recess 32 may vary very considerably. It should furthermore be pointed out that the chip breaking surface 36 in connection with each cutting edge 6, 6' is comparatively narrow as a result of being spaced from the arched surface 26 and 28, respectively, by a transition surface 37. In other words, the arched surface 26, 28 is somewhat countersunk in relation to the chip surface 36. In an analogous manner, each flank surface 38 behind the appurtenant cutting edge 6, 6' is comparatively narrow by being spaced-apart from a countersunk surface 39 via a transition portion 40. Thanks to the surfaces 36, 38 being comparatively narrow, the need of precision grinding in connection with the manufacture of the cutting body is minimised. In the shaft 1 as well as the cutting body 2, different materials may be used. The actual shaft is suitably made of steel, while the cutting body is made of a harder and more wear-resistant material. In practice, the cutting body may be composed of different materials in different parts, whereby the actual chip forming portion in connection with the cutting edges may consist of steel, high speed steel, cemented carbide, cubic boron nitride, polycrystalline diamond or the like. This edge portion may also be composed of different materials, e.g. cemented carbide in combination with polycrystalline diamond. The other part of the cutting body may be manufactured from, for instance, aluminium, steel, high-speed steel, heavy alloy, cemented carbide or the like. In practice, the drill tool may have an active diameter within the range of 10-40 mm, although also coarser alternatives are feasible. The Function and Advantages of the Invention The assembly of the cutting body 2 in the front seat of the shaft 1 is simple. Thus, the cutting body is assembled in the seat with the abutment and support surfaces 33, 34 of the body in connection with the corresponding abutment and support surfaces 16, 17 of the supporting shoulder 15, and then the single screw 8 is fastened in the hole 14. As has been pointed out above, the cutting body will, in this connection, be subject to pre-stressing forces which press the bottom side 21 of the flank part of the body situated closest to the screw 8 distinctly against the bottom surface 9 of the seat as well as pressing distinctly on the one hand, the abutment surface 33 against the abutment surface 16 and on the other hand the support surface 34 against the support surface 17, whereby the wedge action of the supporting shoulder also press the opposite flank part of the body against the bottom surface 9. By the axial tensile action of the screw, the outer surface 22 is, simultaneously, pressed against the inner surface 10 of the protrusion 4, while the opposite outer surface 23 goes free from the inner surface 11 of the protrusion 5. In other words, the cutting body is fixed in the seat without being over-determined. If the cutting body should accidentally be placed initially incorrectly in the seat, the cutting body will still be centred to the desired position as a consequence of the described interaction of forces between the cutting body and the supporting shoulder. A substantial advantage of the invention is that the cutting body may be fixed in the desired, centred state by means of a single, simple screw, which can be tightened and loosened, respectively, by means of a simple, conventional key or screwdriver. In other words, each repetitive change of cutting body may be carried out in a simple and fast manner while maintaining a good working precision of the drill tool. Reference is now made to figs 10-13, which illustrate an alternative embodiment of the cutting body 2. In this case, the recess 32 only extends along a part of the flank surface 25, whereby the recess is delimited by not only the abutment surface 33 and the support surface 34, respectively, but also by a bottom surface 41. The supporting shoulder (not shown) co-operating with the recess 32 on the inside of the seat is correspondingly shortened. More precisely, the supporting shoulder ends in a transverse lower surface at a distance outer surface the bottom surface 9 of the seat. In doing so, said lower surface of the supporting shoulder is located in such a manner that it goes free from the bottom surface 41 of the recess 32 in order to avoid over-determination of the cutting body. In figs 14-17, an additional alternative embodiment of the cutting body is shown. In this case, grooves 42 are formed in each one of the plane outer surfaces 22, 23 of the cutting body, each one of which grooves extends from the bottom side 21 of the cutting body to the area of the countersunk surface 39 behind each flank surface 38. Between the inner ends of the grooves 42, an additional groove 43 extends which connects the two grooves 42 with each other. When the cutting body is assembled in the appurtenant seat, these grooves 42, 43 form, together with the surfaces 9, 10, 11, ducts through which a cooling fluid may be fed up to the edge portion of the cutting body. Thus, in this case a cooling fluid duct may extend centrally through the drill shaft 1 and port in the bottom surface 9 of the seat. In other words, the conventional ducts 20 (see fig 5) can be eliminated. An advantage of the cutting body according to figs 14-17 is that the cooling fluid ducts formed by means of the grooves 42, 43 port considerably closer to the edges of the cutting body than in the cases where cooling fluid ducts are formed so that they port in the shaft, as is shown in fig 5. In other words, the cooling fluid supply to the actual cutting edges is made more efficient. Here, it should be pointed out that each one of the grooves 42 may be formed so that they sub-divide into a plurality of different, fine grooves which port in different positions along the surface 39. Feasible Modifications of the Invention The invention is not solely restricted to the embodiments described above and shown in the drawings. Although it is preferred to form the co-operating abutment surfaces 16, 33 of the supporting shoulder 15 and of the recess 32 inclined in the manner described above, said surfaces may also be formed in another manner. The two abutment surfaces may, for instance, extend axially and be either oblique or oriented perpendicularly to the surface 23. It is also feasible to incline the abutment surfaces in relation to the axial extension of the drilling tool, but orientated the same perpendicularly to the outer surface 23 of the cutting body.

Claims: Drilling tool, including a shaft (1) having a front end to which a cutting body - provided with cutting edges (2) is detachably connected by means of a screw joint, wherein a seat receiving the cutting body (2) is formed in the front end of the shaft (1), which seat is delimited by two protrusions (4, 5) located on both sides of a bottom surface (9) and made with inner surfaces (10, 11), one of which protrusions a first one (4) has a threaded first hole (14) for a screw (8) serving as the only locking means for the cutting body, that a co-operating, not threaded second hole (30) in the cutting body (2) is arranged in a non-centric manner, known per se, in relation to the first hole (14) so as to, on tightening of the screw (8), apply a cross-directed pre-stressing force to the cutting body characterized in, that , a supporting shoulder (15) having a first abutment surface (16) is formed on the inner surface of the second protrusion(5) against which surface a second abutment surface (33) is pressable in connection with a recess (32) in the cutting body (2), more precisely by lateral displacement of the cutting body by means of the pre-stressing force achieved on tightening of the screw, whereby the thickness of the supporting shoulder (15) is larger than the depth of the recess (32) in order to guarantee that the cutting body (2) rides with a first support surface (34) against a second support surface (17) of the supporting shoulder without a nearby outer surface (23) of the cutting body coming into supporting contact with the inner surface (11) of the second protrusion (5), and that the two protrusions (4, 5) are laterally displaced in relation to each other in order to freely expose said second hole (30) together with the screw (8) adjacent to the second protrusion (5) when the cutting body is assembled in the seat. Drilling tool according to claim 1, characterized in, that the first abutment surface (16) of the supporting shoulder (15) as well as the co-operating second abutment surface (33) of the cutting body are oblique in the direction axially forwards/inwards in order to force the cutting body (2), on the lateral displacement of the cutting body, in connection with the tightening of the screw, to endeavour to move rearwards with the purpose of pressing a bottom side (21) of the cutting body against the bottom surface (9) of the seat. Drilling tool according to claim 2, characterized in, that the angle of the two abutment surfaces (16, 33) in relation to a geometrical centre axis of the shaft is within the range of 1-15°, preferably 5-12°. Drilling tool according to any one of the preceding claims, characterized in, that the first abutment surface (16) of the supporting shoulder (15) is laterally oblique in relation to the inner surface (11) of the second protrusion (5) at the same time as the second abutment surface (33) of the cutting body (2) is oblique in relation to an adjacent outer surface (23) of the cutting body so as to press, on the lateral displacement of the cutting body in connection with tightening of the screw, said support surfaces (17, 37) on the shoulder and the cutting body, respectively, against each other by wedge action. Drilling tool according to claim 4, characterized in, that the angle of the two abutment surfaces (16, 33) in relation to the inside of the second shank and of the outer surface of the cutting body, respectively, is within the range of 60-89°, preferably 70-85°. Drilling tool according to any one of the preceding claims, characterized in, that the second hole (30) is eccentric in relation to the first one (14), not only laterally (in the X direction) but also axially (in the Y direction), more precisely in such a manner that the screw at tightening applies not only a lateral pre-stressing force to the cutting body but also a rearwardly directed pre-stressing force which aims to press the bottom side (21) of the cutting body against the bottom surface (9) of the seat. Drilling tool according to any one of the preceding claims, characterized in, that a widened portion (30') of said second hole (30) intended for a head of the screw, ports in an arched surface (26) formed on the cutting body and located in the extension of a chip channel (3) in the outer surface of the shaft (1). Drilling tool according to any one of the preceding claims, characterized in, that a groove (42) is formed in at least one of the two opposite, plane outer surfaces (22, 23) of the cutting body (6), which groove extends from the bottom side (21) of the cutting body towards the area of the front, edge-provided portion of the cutting body in order to define, together with the inside of a protrusion (4, 5), a duct for feeding cooling fluid towards the edge portion.

Inventors: WIDIN LEIF, WIDIN, LEIF
Applicants: SANDVIK INTELLECTUAL PROPERTY, SANDVIK INTELLECTUAL PROPERTY HB
Application year: 2001
Main classification: B23B51
IPC codes: B23B51, B23C5