Cutting insert and cutting tool for this insert

Abstract: A cutting insert for use in a cutting tool assembly comprising first and second longitudinally directed insert surfaces directed at an acute angle with respect to each other and defining between them a centrally disposed, wedge-shaped body portion of the insert; a leading end portion of the insert formed integrally with a wider end portion of the wedge-shaped body portion and formed with a cutting edge and with an abutment shoulder located between the cutting edge and an adjacent end of said first insert surface and a trailing end portion of the insert formed integrally with a narrower end portion of the wedge-shaped body portion and defined between a wholly recessed extension of said first insert surface and said second insert surface.

Description: This invention relates to a cutting insert for use in a cutting tool assembly according to the preamble of Claim 1. Furthermore, the invention relates to a cutting tool assembly according to the preamble of Claim 4. Such an assembly can be designed for use in parting and/or grooving operations and the cutting insert is formed of a hard metal (for example, tungsten carbide) and is mechanically and releasably retained within an open-ended slot formed in an appropriate tool holder. Alternatively or additionally the cutting tool assembly can be designed for use both for parting and/or grooving and also for lateral turning operations and all this with the same insert which is hereinafter referred to as a "multi-directional cutting insert". BACKGROUND OF THE INVENTION There is described in our earlier EP-A- 0 059 602 a cutting tool assembly for use in parting and/or grooving wherein the cutting insert is formed with a wedge-shaped body portion which is designed to be inserted into, and frictionally retained within, a corresponding wedge-shaped slot formed in the tool holder. Such a cutting tool assembly will hereinafter be referred to as a cutting tool assembly of the kind specified. Our European Patent Specification proceeds to consider the problem which may arise with cutting tool assemblies of the kind specified, wherein the precise positioning of the cutting edge formed on the cutting insert depends, to a large degree, on the degree of insertion of the cutting insert into the slot. Furthermore, our earlier European Patent Specification considers the problem which may arise where the insert is forced into the slot with extreme force, thereby giving rise to the tendency of the tool holder to fracture. In order to overcome or minimise these problems, our earlier European Patent Specification proposes providing the insert, in a region adjacent to its cutting edge, with an abutment shoulder, which shoulder will abut a corresponding end portion of the tool holder. In this way the degree of insertion of the cutting insert into the tool holder is limited (thus avoiding the dangers of fracture of the tool holder) and also ensuring that the degree of insertion of the insert into the tool holder remains constant, this resulting in a constant positioning of the cutting edge. It has been found in practice that with cutting tool assemblies of the kind specified, provided with such limiting abutment shoulders, the regions of the wedge-shaped body portion of cutting insert which are frictionally held by the tapering surfaces of the wedge-shaped slot in the tool holder, are to a large extent dependent on the relative production tolerances of the cutting insert, on the one hand, and the tool holder, on the other hand and by the combination thereof. Situations arise in practice wherein the insert may be held in the tool holder at one or other localised extremity thereof, thereby giving rise to unstable retention of the insert within the tool holder when the insert is subjected to cutting forces. This is especially the case when multi-directional inserts are employed for lateral turning with the consequent subjection of the inserts to side cutting forces. BRIEF SUMMARY OF THE INVENTION It is an object of the present invention to provide a new and improved cutting tool assembly in which the above-referred-to disadvantages are substantially reduced or overcome. To achieve this object there is provided a cutting insert for use in a cutting tool assembly comprising first and second longitudinally directed insert surfaces directed at an acute angle with respect to each other and defining between them a centrally disposed, wedge-shaped body portion of the insert; and a leading end portion of the insert formed integrally with a wider end portion of the wedge-shaped body portion and formed with a cutting edge and with an abutment shoulder located between the cutting edge and an end of said first insert surface; a trailing end portion of the insert formed integrally with an end portion of the wedge-shaped body portion and defined between a wholly recessed extension of said first insert surface and said second insert surface; said trailing end portion being formed integrally with a narrower end portion of the wedge-shaped body portion. Furthermore, there is provided a cutting tool assembly comprising a tool holder; first and second clamping jaws formed integrally as one unit in an end portion of the tool holder; first and second longitudinally directed jaw surfaces of said first and second jaws respectively forming an acute angle with respect to each other and defining between them an open-ended, wedge-shaped slot opening out towards said end portion of the holder; a cutting insert comprising first and second longitudinally directed insert surfaces directed at an acute angle with respect to each other and defining between them a centrally disposed, wedge-shaped body portion of the insert; a leading end portion of the insert formed integrally with a wider end portion of the wedge-shaped body portion and formed with a cutting edge and with an abutment shoulder located between the cutting edge and an adjacent end of said first insert surface; a trailing end portion of the insert formed integrally with a narrower end portion of the wedge-shaped body portion and defined between a wholly recessed extension of said first insert surface and said second insert surface; one or both of said second surfaces of said insert and said jaw being formed with a pair of contact regions located respectively at opposite ends of said second insert surface; said insert being insertable into said slot and being frictionally retainable between said jaws so that the resultant clamping force developed between said first surfaces of said insert and said first jaw is directed substantially intermediate between said contact regions; said abutment shoulder abutting an exposed end of said first jaw so as to limit the extent of insertion of said insert into said slot. With such a cutting tool assembly, the provision of the insert with the trailing end portion which, in view of the recessed nature of the extension of the first insert edge, is of smaller height than the wedge-shaped body portion of the insert, contact between the first surface of the insert and the corresponding first surface of the jaw is essentially restricted to the trailing portion of the first surface and the resultant clamping force between these first surfaces is directed intermediate the contact regions between the second surface of the insert and the second surface of the second clamping jaw. In this way, the regions of clamping of the insert by the clamping jaws can be to a very large extent predetermined, irrespective of variations caused by the tolerances inherent in the construction of the insert and clamping jaws. As a result, the insert is always firmly held within the slot defined by the clamping jaws. The cutting insert in accordance with the invention may be a multi-directional cutting insert in which case it will be formed with both front and side cutting edges and, in order to ensure the lateral stability of the cutting insert within a tool holder the latter can be provided with additional mechanical means for ensuring the effective clamping of the insert between the clamping jaws. The cutting insert in accordance with the present invention is clearly distinguished from the cutting insert disclosed in WO/89/10224 (Mihic), falling within the terms of Article 54(3) EPC, in that the wedge-shaped body portion of the insert in accordance with the present invention slopes downwardly towards the base of the insert in the direction of the narrow end thereof, and this in contrast to the situation disclosed by Mihic, where the portion 27 of the insert intermediate the incline surface 16 and the engagement surface 19 slopes downwardly towards the base of the insert in the direction of the cutting end of the insert. BRIEF SUMMARY OF THE DRAWINGS For a better understanding of the present invention and to show how the same may be carried out in practice, reference will now be made to the accompanying drawings, in which: Fig. 1 is a perspective view of a cutting insert embodying the invention for use in a cutting assembly; Fig. 2 is a perspective view of the insert shown in Fig. 1, prior to its insertion in a tool holder forming part of the cutting tool assembly; Fig. 3 is a perspective view of the assembled insert and tool holder; and Fig. 4 is a side elevation of a multi-directional cutting insert embodying the invention shown in an appropriate tool holder. DETAILED DESCRIPTION OF PREFERRED EMBODIMENT As seen in Fig. 1 of the drawings, a replaceable cutting insert 1 is of generally prismatic shape and comprises side faces 2, front and rear faces 3 and 4, an upper surface 5 and a lower base surfaced 6 The upper surface 5 comprises a cutting rake surface 7, a chip deflector surface 8, a sloping clamping surface 9 and a recessed trailing surface 10 forming an extension of the clamping surface 9. Defined between the cutting rake surface 7 and the front face 3 is a cutting edge 11. The cutting rake surface 7 can be formed with a suitable chip former construction (not shown). The clamping surface 9 merges with the chip deflector surface 8 via an abutment shoulder 12. The clamping surface 9 slopes downwardly with respect to the base surface 6 so as to define with the base surface 6 a centrally-disposed, wedge-shaped body portion of the insert 1. The clamping surface 9 is constituted by a longitudinally extending keying groove of substantially V-shaped cross-section. In a similar manner, the base surface 6 is constituted by a longitudinally extended keying groove of V-shaped cross-section, the grooves of the surface 9 and surface 6 being oppositely directed. The recessed surface 10 defines with the rear end of the base surface 6 a trailing end portion of the insert, the height of this trailing portion being less than the height of the wedge-shaped body portion at its narrowest end. The base surface 6 of the insert is formed with a pair of end base regions 6a and 6b and with a relatively recessed central base region 6c. As seen in Fig. 2 of the drawings, the insert 1 is designed to be retained by a suitable tool holder. This tool holder comprises an elongated holder blade 15 at a leading end of which is formed an open-ended, wedge-shaped slot 16. The slot 16 is bounded by surfaces 17 and 18 respectively of clamping jaws 19 and 20 formed integrally as one piece with the holder blade 15. The surfaces 17 and 18 are formed as V-shaped keying ribs which are designed to mate within the V-shaped grooves formed in the surfaces 9 and 6 of the insert 1. The holder blade 15 is designed to be retained in a holder block 21 which, in its turn, is designed to be held in a machine tool (not shown). As shown in Fig. 3 of the drawings, the insert 1 is pushed into the slot 16 of the holder blade 15, with the V-shaped ribs of the surface 17 and 18 mating within the V-shaped grooves of the surfaces 6 and 9 and with the base regions 6a and 6b of the insert 1 firmly seated on the surface 18 of the jaw 20. At the same time, and with the insert fully inserted into the slot 16, an end portion 22 of the jaw 19 bears against the abutment shoulder 12, thereby limiting the degree of insertion of the insert 1 into the slot 16 and in this way ensuring that the cutting edge 11 of the insert 1 is always in a desired predetermined position. By virtue of the provision of the recessed trailing end portion of the insert 1 contact between the jaw 19 and the insert 1 only takes place on the sloping surface 9, and it is ensured that the clamping force generated between the surface 17 of the jaw 19 and the corresponding sloping surface 9 of the insert 1 is localised in a region close to the trailing end of the sloping surface 9. In consequence, a resulting clamping force F₁ developed between the sloping surface 9 of the insert 1 and the surface 17 of the jaw 19 is directed intermediate to the clamping forces F₂ and F₃ generated between the surface 18 of the jaw 20 and the localised base regions 6a and 6b. In this way, there can be ensured maximum stability of clamping of the insert 1 within the tool holder, irrespective of tolerances of manufacture both of the insert and the tool holder. Whilst in the embodiment described above the surfaces 6 and 9 of the insert 1 are provided with V-shaped grooves whilst the surfaces 17 and 18 of the jaws are provided with V-shaped ribs, the sloping surfaces of the insert may be provided with V-shaped ribs whilst the corresponding surfaces 17 and 18 of the jaws may be provided with V-shaped grooves. Whilst the cutting tool arrangement in accordance with the invention has been described above as applied to a stationary tool holder, the invention is equally applicable where the inserts are to be inserted into appropriate slots formed in the periphery of a rotary tool holder. Fig. 4 illustrates a tool holder 21 provided with a cutting insert 22 in accordance with the invention having, in addition to a front cutting edge 23a also side cutting edges 23b, a suitable chip former construction (not shown) being provided. The insert 22 is therefore multi-directional and can be employed for both parting as well as lateral turning operations. The use of such a multi-directional cutting insert in lateral turning gives rise to transversely directed cutting forces and in order to ensure the stability of the insert 21 vis a vis such forces the tool holder 21 is formed with clamping jaws 24a and 24b which are forced into clamping contact with the insert by suitable tightening of a tool block 25 in which the tool holder is held. In the construction described above, with reference to Figs. 2 and 3, localised base regions 6a and 6b of contact between the lower surface 6 of the insert 1 and the adjacent surface 18 of the jaw 20 are achieved by providing the insert with projecting regions 6a and 6b. Equivalent results can be obtained (as seen in Fig. 5 of the drawings) by forming the surface 18 with localised raised portions 18a, 18b at the ends thereof with a central recessed portion 18c, whilst the lower surface of the insert 6 is rendered substantially flat. Alternatively, and as shown in Fig. 4 of the drawings, both the insert 1 and the surface 18 can be provided with these localised, regions (6a, 6b; 18a, 18b), which seat against each other, thereby ensuring localised contact between the insert and the surface 18 and the generation of clamping forces at these localised regions. Furthermore, by restricting the area of contact between the contiguous surfaces of the insert and the lower jaw 18, frictional wear of the jaw surface is also limited.

Claims: A cutting insert (1) for use in a cutting tool assembly comprising first and second longitudinally directed insert surfaces (9, 6) directed at an acute angle with respect to each other and defining between them a centrally disposed, wedge-shaped body portion of the insert; and a leading end portion of the insert formed integrally with a wider end portion of the wedge-shaped body portion and formed with a cutting edge (11) and with an abutment shoulder (12) located between the cutting edge (11) and an end (4) of said first insert surface (9); characterised in that a trailing end portion of the insert (1) is formed integrally with an end portion of the wedge-shaped body portion and defined between a wholly recessed extension (10) of said first insert surface (9) and said second insert surface (6); said trailing end portion is formed integrally with a narrower end portion of the wedge-shaped body portion. A cutting insert according to Claim 1, characterised in that said second insert surface (6) is formed with a central recessed portion (6c). A cutting insert according to Claim 1 or 2, characterised in that said leading end portion is formed with a front cutting edge (23a) and a pair of side cutting edges (23b). A cutting tool assembly comprising a tool holder (15); first and second clamping jaws (19, 20) forming part of an end portion of the tool holder (15); first and second longitudinally directed jaw surfaces (17, 18) of said first and second jaws (19, 20) respectively forming an acute angle with respect to each other and defining between them an open-ended, wedge-shaped slot (16) opening out towards said end portion of the holder (15); a cutting insert (1) comprising first and second longitudinally directed insert surfaces (9, 6) directed at an acute angle with respect to each other and defining between them a centrally disposed, wedge-shaped body portion of the insert; a leading end portion of the insert formed integrally with a wider end portion of the wedge-shaped body portion and formed with a cutting edge (11) and with an abutment shoulder (12) located between the cutting edge (11) and an end (4) of said first insert surface (9), said abutment shoulder (12) abutting an exposed end of said first jaw (19) so as to limit the extent of insertion of said insert (1) into said slot (16); characterised in that a trailing end portion of the insert (1) is formed integrally with a narrower end portion of the wedge-shaped body portion and is defined between a wholly recessed extension (10) of said first insert surface (9) and said second insert surface (6); one or both of said second surfaces (6, 18) of said insert (1) and said jaw (20) being formed with a pair of contact regions (6a, 6b) located respectively at opposite ends of said second insert surface (6); said insert (1) being insertable into said slot (16) and being frictionally retainable between said jaws (19, 20) so that a resultant clamping force (F₁) developed between said first surfaces (9, 17) of said insert (1) and said first jaw (19) is directed substantially intermediate said contact regions (6a, 6b). A cutting tool assembly according to Claim 4, characterised in that the second surface (6) of said insert (1) is formed with a pair of end base regions (6a, 6b) and with a recessed central base region (6c). A cutting tool assembly according to Claim 4 or 5, characterised in that the second surface (18) of said second jaw (24b) is formed with a pair of end regions (18a, 18b) and with a relatively recessed central region (18c). A cutting tool assembly according to any one of the preceding claims, characterised in that said first and second surfaces (5, 6) of said insert (1) are formed with longitudinally directed, substantially V-shaped keying grooves, whilst the first and second surfaces (17, 18) of said clamping jaws (19, 20) are formed with longitudinally directed substantially V-shaped keying ribs. A cutting tool assembly according to any one of Claims 4 to 6, characterised in that said first and second surfaces (5, 6) of said insert (1) are formed with longitudinally directed, substantially V-shaped keying ribs whilst the first and second surfaces (17, 18) of said clamping jaws (19, 20) are formed with longitudinally directed, substantially V-shaped keying grooves.

Inventors: FRIEDMANN JACOB, FRIEDMANN, JACOB
Applicants: ISCAR LTD, ISCAR LTD.
Application year: 1990
Main classification: B23B27
IPC codes: B23B27