TOOL AND CUTTING HEAD FOR CUTTING MACHINING

Abstract: The present invention relates to a tool (27) and a cutting head (26) for cutting machining, rotatable relative to a work piece. The tool comprises a holder (28), a cutting head (26) and means for fastening (29). The holder has a front surface (30) and the cutting head has a support surface (16) provided to releaseably abut against each other substantially in a radial plane. The cutting head (26) consists of injection molded cemented carbide and comprises at least one cutting edge and a central blind hole (15) provided to cooperate with the means for fastening (29). The blind hole and the cutting edge are integrated with the cutting head (26). The means for fastening (29) is provided to influence the cutting head in direction towards the front surface, via the blind hole. An insert (21) of a material softer than injection molded cemented carbide is attached to the blind hole (15). The insert (21) comprises a thread provided to cooperate with the means for fastening (29).

Description: TOOL AND CUTTING HEAD FOR CUTTING MACHINING Background of the invention The present invention relates to a tool and a cutting head according to the preambles of the independent claims. Prior art Through US-A-5,947,660 is previously known a tool of the above- described type. Tools of small dimensions have shown not to have sufficient strength or stability in couplings between the cutting head and the tool body. Objects of the invention One object of the present invention is to provide a coupling for two tool parts, whereby a great load capacity can be transferred. Another object of the present invention is to provide a tool, which is continuously stable. Still another object of the present invention is to provide a tool having good precision. These and other objects have been achieved by a tool and a cutting head such as defined in the appended claims with reference to the drawings. Description of the drawings Fig. 1 A shows a hard metal portion for a cutting head according to the present invention in a longitudinal cross-section according to I-I in Fig. IB. Fig. IB shows the portion in an end view. Fig. 2 shows an insert to cooperate with the portion. Fig. 3 A shows a cutting head according to the present invention in a perspective view. Fig. 4 shows a forward end surface of a tool according to the present invention, partly in a longitudinal cross- section. Fig. 5 shows the tool in an exploded view. Fig. 6A shows a hard metal portion for an alternative embodiment of a cutting head according to the present invention in a longitudinal cross- section. Fig. 6B shows the portion in an end view. Fig. 7 shows an insert to cooperate with the portion. Fig. 8 shows a cutting head according to the present invention in a longitudinal cross-section. Fig. 9 A shows a hard metal portion for an alternative embodiment of a cutting head according to the present invention in a longitudinal cross- section. Fig. 9B shows the portion in an end view. Fig. 10 shows an insert to cooperate with the portion. Fig. 1 1 shows a cutting head according to the present invention in a longitudinal cross-section. Detailed description of preferred embodiments of the invention Figs. 1 A and IB show a, preferably injection molded, hard metal portion 10 according to the present invention. The hard metal portion 10 has a cylindrical basic shape and comprises a base or support portion 1 1 , which connects to a shank portion or an intermediate part 12, which in turn connects to a cutting edge portion 13 provided at the free end of the portion 10. The base 1 1 has a diameter DI , which is substantial greater than both the diameter D2 of the intermediate part 12 and the diameter D3 of the cutting edge portion 13. The diameter D3 is somewhat greater than the diameter D2 to create space for chips at drilling or milling. The portion 13 has, in this example, the shape of a rotary file with a number of bent cutting edges but may alternatively be of drill geometry with only two edges extending towards the rotational axis CL. In case there is a drill it is an advantage if also the part 12 has chip flutes. The base 1 1 connects to the intermediate part 12 via a softly rounded shoulder portion 14. The axial distance X between the shoulder portion 14 and the cutting edge portion 13 defines the maximum machining depth. A blind hole 15 is provided symmetrically about the rotational axis CL and centrally in the base 11. The hole 15 terminates in a support surface 16 and has an axial depth d. The hole 15 has the cross-section of a dove tail, that is the greatest diameter is greater than diameter of the orifice such that a bottom 17 of hole 15 connects to a wall 18 of hole at an acute angle. The blind hole and the cutting edges are integrated with the hard metal portion. The support surface 16 has a ring like basic shape and comprises two groove parts. Each groove part covers substantially the entire support surface 16 and comprises a number of from each other separate, identical flutes or grooves 19 A, 19B. The grooves in the groove parts have two main directions, which are perpendicular to each other. Substantially each groove 19a, 19b in both groove parts intersects the jacket surface 20 of the bases 11 at two places. Each groove 19 A, 19B is elongated and is substantially V- shaped in cross-section. Each groove has two flanks that connect to a bottom, via a sharp or rounded transition. The flanks form an acute angle with each other. The angle lies within the interval of 40° to 80°, preferably 55° to 60°. The number of grooves in each groove part depends on how the front surface of the holder is shaped and the number is chosen in the interval of 5 to 30 grooves. The design of the groove parts gives a considerably greater specific surface than if these should be planar. The groove parts cover at least 80%>, preferably 90-100%, of the accessible area of the support surface 16. The function of the support surface 16 has been more closely described in PCT/SE98/01 146 which hereby is incorporated in the present description as regards cooperation between the support surface 16 and a front surface of a shank, described below, where the coupling comprises two cooperating surfaces and means for forcing the surfaces together. The surfaces are profiled with grooves in order to allow locking by shape against each other. A bushing or insert 21 of a material softer than injection molded cemented carbide is shown in Fig. 2. The bushing is preferably made of steel and has a cylindrical basic shape and has a certain dimension h in the axial direction. The jacket surface of the bushing comprises a number of circumferentially extending grooves or segments 22. The bushing comprises a first 23 and a second 24 end surface. The end surfaces 23 and 24 are preferably parallel with each other and perpendicular to the rotational axis CL. All segments, except for a cylindrical segment closest to the first end surface 23, consist of truncated conical parts, whose imaginary tips are directed outwardly towards the end surface 23. Each segments base is of greater diameter than the diameter of the narrowest part of the connected segment, whereby a sharp circumferential flange is formed. The end surface 23 defines the greatest diameter of the bushing that is smaller than the smallest diameter of the hole 15. The bushing has a central through-going, finely threaded boring 25. With " finely threaded" is here meant that the pitch for the thread is smaller than that for coarse or normal according to ISO-standard, that is for example the pitch "normal" for M5 is according to standard 0.8 mm while the pitch "fine" is 0.5 mm. The manufacture of a cutting head 26 according to the present invention from the hard metal portion and the bushing is done as follows. The bushing 21 is inserted into the blind hole such that the end surface 23 abuts against the bottom 17, whereafter melted brazing material is inserted radially outside the bushing. Subsequently, the brazing material is cooled such that the bushing is fixed centrally in the blind hole 15, see Fig. 3A. It should be noted that since the height h of the bushing is smaller than the depth d of the hole a gap will develop between the end surface 24 and the plane of the support surface 16. In Figs. 4 and 5 is shown a tool 27 according to the present invention. The tool 27 for milling comprises a substantially cylindrical holder 28, the multi-edged cutting head 26 and a screw or other clamping means 29. The holder 28 may been made of steel, cemented carbide or high speed steel. One free end of the holder 28 is intended to be fastened in a rotatable spindle (not shown) in a machine while the opposite other free end surface comprises a front surface 30 and a non-threaded hole 31. The front surface 30 has a circular basic shape and comprises two groove parts 32a, 32b. Each groove part covers substantially half the front surface 30 and comprises a number of from each other separate, identical flutes or grooves. The grooves in the groove parts have two main directions that are perpendicular to each other. A second groove part 32A is bordered by a first groove part 32B. Substantially each groove in the first groove part 32B intersects the jacket surface of the holder at two places while substantially each groove in the second groove part 32A intersects the jacket surface of the holder at one place. Each groove is elongated and is substantially V-shaped in cross- section. The finely threaded hole 25 of the bushing is provided to receive the screw 29. The screw is formed as an internal pull rod with a threaded free end. Thereby, a possibility to provide cutting edges towards the rotational axis CL for drilling and milling is obtained. In the shown embodiment the groove parts 19, 32 have been made by direct-pressing and sintering or by grinding. The tool 27 is mounted by pushing the support surface 16 of the cutting head 26 by hand against the front surface 30 of the holder 28 in one of four possible positions. Thereby, the grooves 19, 32 are aligned with each other. The screw 29 is brought against the threaded hole 25. At rotation of the screw 29 via a key which is in engagement with a key grip in an axially rearwards part of the holder, the cutting head will be drawn firmly against the front surface, i.e. the position according to Fig. 4 has been achieved. The cutting head 26 is now anchored against the holder 28 in a satisfactorily manner. The gap between the end surface 24 of the bushing and the front surface 30 does not prevent the elastic movement of the bushing at additional tightening of the screw. Therefore, the bushing is wedged harder in the dove-tail hole. The fine thread 25 in engagement with the fine thread of the screw 29 allows relatively great traction in the joint. The reason for that only one surface should have waffle pattern over its entire area is that the tool obtains a more distinct locking effect than if both the surfaces would be waffle patterned. It is also possible, within the scope of the invention, to utilize planar cooperating surfaces instead of the described profiled surfaces. When the cutting head 26 shall be exchanged the mounting process is inverted, whereafter the cutting head can be removed from the holder 28 and be exchanged. Thereby also the geometry of the cutting head can be exchanged to other embodiments, which all fit in the same holder. For example can be used a chip dividing cylindrical end mill head or thread milling cutter; a cylindrical head without chip dividing for example for end mill cutting or reaming; a head for grooving and a truncated conical head for end mill cutting of dove tail slots. Common for all these tools is that they replace conventional end mills in high speed steel where smaller dimensions (2 to 15 mm in diameter) often are desirable. Figs. 6A-8 show alternative embodiments of a hard metal portion 10' for a cutting head, a bushing 21' to cooperate with the portion as well as a cutting head 26' according to the present invention. The hard metal portion 10' is externally as described above. What differs relative to the earlier example is that the bushing 21' and the blind hole 15' cooperate via an external thread 22' and an internal thread 18', respectively. This means that brazing material is inserted in the threads at the manufacture of the cutting head 10', that the bushing is threaded against the bottom of the blind hole 15', whereafter the brazing material is heated and cooled. Figs. 9A-1 1 show alternative embodiments of an hard metal portion 10" for a cutting head, a bushing 21 " to cooperate with the portion as well as a cutting head 26" according to the present invention. Externally the hard metal portion 10" is the same as described above. What differs relative to the earlier example is that the bushing 21 " is wedged in the blind hole 15". This is done by providing the blind hole with a projecting central, conical projection 17", the tip of which is directed towards the orifice of the hole 15". The projection is brought to cooperate with a corresponding central, conical recess 23" of the bushing. Thereby the bushing is pushed radially outwardly in the hole 15" and is plasticized against the wall 18". In this case it is possible to provide the hole with a dove-tail profile just as described above. The bushing 21-21 " in the above-described embodiments is secured in the blind hole 15-15" such that the insert by the effect of the screw is forced against the bore wall 18-18". This is evident since the threads in the screw and the insert at axial strain will be forcing the bushing apart, which then is pushed even harder against the bore wall. Thus the present invention relates to a coupling for two tool parts such that a large traction can be transferred from the screw to the cutting head, a tool which is continuously rigid during use especially for smaller tool dimensions while maintaining good precision at mounting.

Claims: Claims 1. Tool for cutting machining, rotatable relative to a work piece, comprising a holder (28), a cutting head (26-26") and means for fastening (29), said holder having a front surface (30) and the cutting head having a support surface (16) provided to releaseably abut against each other substantially in a radial plane, said cutting head (26-26") consisting of injection molded cemented carbide and comprising at least one cutting edge and a central blind hole (15-15") to cooperate with the means for fastening (29) and said blind hole and the cutting edge being integrated with the cutting head (26- 26"), said means for fastening (29) being provided to influence the cutting head in direction towards the front surface via the blind hole, c h a r a c t e r i z e d i n that an insert (21-21 ") of a material softer than injection molded cemented carbide is secured in the blind hole (15-15"), said insert (21-21") comprising means (25) for cooperating with the means for fastening (29). 2. The tool according to claim 1, at which the insert (21-21") is secured in the blind hole (15-15") such that the insert at operation of the means for fastening (29) is forced radially against a wall (18-18") of the blind hole. 3. The tool according to claim 1 or 2, at which the cutting head (26-26") has a free end, which has a greatest diameter (D3) and at which the front surface (30) and the support surface (16) defines a greatest diameter (DI), which is much greater than the greatest diameter (D3) of the free end. 4. The tool according to anyone of the claims 1 - 3, at which the blind hole (18-18") has a smallest diameter, which is greater than the greatest diameter (D3) of the free end. 5. The tool according to anyone of the claims 1 - 4, at which the insert (21- 21") is wedged in and/or brazed to the blind hole. 6. The tool according to anyone of the claims 1 - 5, at which the insert (21- 21") has an axial extension (h), which is smaller than the depth (d) of the blind hole (18-18"), such that a gap is provided between the insert and the front surface (30). 7. The tool according to claim 1 or 6, at which the front surface (30) and the support surface (16) comprise cooperating projections and recesses, which are provided to substantially alone transfer cutting forces developing at machining and directed towards the holder. 8. Cutting head forming part of a cutting tool for cutting machining, rotatable relative to a work piece, said cutting head having a support surface (16) provided to releaseably abut against a holder, said cutting head (26-26") consisting of injection molded cemented carbide and comprising at least one cutting edge and a central blind hole (15-15") to cooperate with a means for fastening and said blind hole and the cutting edge being integrated with the cutting head (26-26"), said means for fastening being provided to influence the cutting head in direction towards the front surface via the blind hole, c h a r a c t e r i z e d i n that an insert (21 -21 ") of a material softer than injection molded cemented carbide is secured in the blind hole (15-15"), said insert (21-21 ") comprising means (25) for cooperating with the means for fastening. 9. The cutting head according to claim 8, at which the insert (21-21") is secured in the blind hole (15-15") such that the insert at operation of the means for fastening is forced radially outwardly. 10. The cutting head according to claim 8 or 9, at which the cutting head (26-26") has a free end, which has a greatest diameter (D3) and at which the support surface (16) defines a greatest diameter (DI), which is much greater than the greatest diameter (D3) of the free end. 11. The cutting head according to anyone of the claims 8 - 10, at which the blind hole (18-18") has a smallest diameter, which is greater than the greatest diameter (D3) of the free end. 12. The cutting head according to anyone of the claims 8 - 11, at which the insert (21-21 ") is wedged in and/or brazed to the blind hole. 13. The cutting head according to anyone of the claims 8 - 12, at which the insert (21-21 ") has an axial extension (h), which is smaller than the depth (d) of the blind hole (18-18"). 14. The cutting head according to claim 8 or 13, at which the support surface (16) comprises projections and recesses.

Inventors: KOSKINEN JORMA, RYDBERG CHRISTER, KOSKINEN, JORMA, RYDBERG, CHRISTER
Applicants: SECO TOOLS AB
Application year: 1999
Main classification: B23B51
IPC codes: B23B31, B23C5