CUTTING INSERT AND HOLDER FOR METAL CUTTING MACHINING

Abstract: A tool for metal cutting machining comprising a cutting insert (8) in a hard material as well as a holder for the cutting insert, wherein the cutting insert is either clamped directly onto the holder, or onto a cassette or shim (3). This in turn is arranged on the holder, whereby the underside of the cutting insert features partly a recess (13) including at least two support surfaces (15), partly a number of bottom support surfaces (18) which are to be found between said recess and the periphery of the underside. The part of said shim (3) adjacent to the underside of the cutting insert or of said holder includes a raised part (24) including at least two support surfaces (16), whereby the cutting insert can be clamped in such a way that it simultaneously abuts both against the said two support surfaces (16) of the raised area (24) with its support surfaces (15) in the recess (13) and against said shim (3) or said holder with one or more of its bottom support surfaces (18). Thereby excessive static definition of position is avoided.

Description: CUTTING INSERT AND HOLDER FOR METAL CUTTING MACHINING The present invention refers to a cutting insert as well as a holder for metal cutting machining. More exactly the invention concerns a tool which enables the clamping of indexable inserts with different geometrical shapes in one and the same insert pocket. The use of detachable, indexable inserts is nowadays accepted practice within more or less the entire field of metal cutting machining, i.e. within both turning, milling, drilling, etc. They are usually manufactured in coated or uncoated cemented carbide, but also certain ceramic materials occur. These different indexable inserts may have very varying geometrical basic shapes, depending on cutting economy and application. They can, for example, be triangular, rhombic, square, rectangular, round, hexagonal (incl. so called trigon inserts) and octagonal. Common for all the different conceivable insert shapes is that they require an insert pocket in the holder adapted to each specific shape. Consequently a square cutting insert normally requires an insert pocket with two support or abutment surfaces which are at right angles to each other, a triangular cutting insert requires generally two abutment surfaces which are angled 60° to each other, etc. This means that a change of insert shape also craves a change of holder. This is both time consuming and expensive. Further the designer ' s freedom of choice when designing a new cutting insert is limited, since the outer contour of the cutting insert must function at least partially as an operational cutting edge and clearance surface, but also as an abutment surface, when the surface in question is indexed in against the actual insert pocket. Thereby making impossible cutting geometries, which in themselves would be desirable when in the operational cutting position. Should the designer nevertheless wish to use such a cutting geometry, he/she will be forced to resort to an insert design without an operational cutting geometry on the side of the cutting insert turned towards the insert pocket. A first aim with the present invention is consequently to create cutting inserts which can be clamped in one and the same insert pocket despite having different contour lines. Another aim with the invention is to produce a cutting insert which does not need to abut against any abutment surfaces with its side surfaces. Still a further purpose with the present invention is to produce an insert pocket with wider manufacturing tolerances. These and other aims have been successfully achieved by developing a tool with the features indicated in the characterizing part of claim 1. Cutting inserts with a recess in the bottom surface of the cutting insert are in itself known previously through US-A-4 674 924. In this case however the recess has a wholly different purpose: it functions in its entirety (also even its three side surfaces) as pure non-contact surfaces, whereby the cutting insert shall abut on its three corner parts, which furthermore most preferably are to be angled upwards and inwards. In order to illustrate but not limit the invention it will now be described more closely with reference to the enclosed drawings. These are presented briefly hereby: Fig 1 shows an exploded view of a tool according to the invention, in perspective obliquely from above. Fig 2 shows an upside-down cutting insert according to the invention, obliquely from above. Fig 3 shows the cutting insert according to fig 2, straight from below. Fig 4 shows another cutting insert obliquely from below. Fig 5 shows the same cutting insert as in fig 4, obliquely from above. Fig 6 shows yet another cutting insert according to the invention, obliquely from below. Fig 7 shows the same cutting insert as in fig 6, straight from below. Fig 8 shows a cutting insert mounted in accordance with the invention, straight from above. Fig 9 shows the vertical section IX-IX in fig 8. Fig 10 shows an exploded view of a tool according to another embodiment of the invention, in perspective obliquely from above. Fig 11 shows a cutting insert according to the other embodiment of the invention, obliquely from below. Fig 12 shows an exploded view of a third embodiment of the invention, in perspective obliquely from above. Fig 13 shows a cutting insert according to the third embodiment of the invention, obliquely from below. Figs 14 and 15 show a cutting insert mounted in a holder according to the embodiment according to figs 12 and 13. Fig 16 shows a shim in accordance with the third embodiment, obliquely from above. Fig 17 shows a cutting insert obliquely from below according to the third embodiment. Fig 18 shows a cutting insert obliquely from below according to an additional embodiment according to the invention. A shaft holder 1 for turning applications is shown in fig 1. The invention is however not limited to turning applications, but also, for example, applications within milling and drilling can be considered. In the forward part of the shaft holder an essentially planar recess 2 is provided, which is intended to accomodate a cassette plate or shim 3. This cassette plate can be stabilized in the recess 2 by a locking screw 4, which is fed through a hole 5 in the shim and is screwed fast in a threaded bore 6 in the shaft holder. Further the cassette plate comprises a raised portion 24, which includes a plateau surface 7 which is raised in relation to the remaining upper surfaces of the shim, which is not intended to come in direct contact with a cutting insert 8. Both the cassette plate 3 and the shaft holder 1 include protruding parts 11 respectively 12 to support the operative cutting corner on a cutting insert 8, which according to fig 1 (as well as even figs. 4 and 5) are intended for grooving and are of the fundamental embodiment which is described in US-A-4 755 085, which is hereby incorporated through this reference. The cutting insert is clamped by a screw 9, which is fed through smooth holes in both the cutting insert and the cassette plate and is screwed firmly into a threaded bore 10 in the recess 2. Alternatively the screw 4 can be dispensed with, whereby both the cutting insert 8 and the cassette plate 3 are clamped only with the clamping screw 9. Further the cassette plate 3 can be wholly dispensed with, whereby geometries on this upper side can instead be transferred to the recess 2. Figs. 4 and 5 show the same cutting insert as fig 1. From fig 4 it is apparant that the cutting insert includes a recess 13 on its under side or bottom surface, which corresponds to the raised plateau surface 7. The depth of the recess 13 can be between 0,8 and 3 mm depending on the size of the insert and the application. The bottom surface 14 of the recess 13 is not intended to abut against said support surface 7, instead a certain gap should exist between these. Further the recess 13 includes three support surfaces 15A, 15B and 15C, which suitably form an angle with the vertical plane of between 0 and 25°, preferably between 3 and 15°. The corresponding support surfaces 16A, 16B and 16C of the support surface 7 are angled to the same degree. In order to make it possible to index the cutting insert the angle between the two surfaces 15 or 16 is substantially 60°. By deliberately displacing the centre hole 17 of the the cutting insert somewhat in the direction away from the side surface 16C, the cutting insert is given a certain pretensioning, whereby two of the cutting insert ' s three support surfaces 15 come to abut against the support surfaces 16A and 16B, whereby a gap arises between the surface 16C and the corresponding support surface on the cutting insert. This double sided contact is intended to avoid excessive static definition of position. Consequently the geometrical figure described by sides 15 is somewhat larger than the figure described by sides 16. When two of the sides 15 are brought into abutment, the gap between the third side 15 and the corresponding side 16 is suitably between 0,2 and 2 mm, preferably between 0,2 and 1 mm. The actual clamping is shown in figs. 8 and 9. It can easily understood from the eccentric position of the screw 9 relative to the insert hole 17 that the cutting insert will be pushed in a direction corresponding to the arrow P. Thereby the cutting insert is brought to abut with two of its sides 15, whilst the side 15 face to face with side 16C does not abut. As can be seen from the section in fig 9, the cutting insert abuts also with the undersides 18 of its three insert corners or of the insert part 19 plane upper side 23 against of the cassette plate, in order to convey the necessary stability to the cutting insert. Owing to that fact that the cutting insert can be displaced until two of its sides 15 lie tight against sides 16A, 16B, this does not imply any excessive static definition of position. Further the gap which arises between the plateau surface 7 and the surface of the recess 14 is shown in fig 9, as well as the gap 20 which arises between the surfaces 15 and 16, which do not abut against each other. In order to avoid a possible fillet, which could occur on the cassette plate in the transition between a support surface 16 and the upper surface of the cassette plate, a shallow edge recess 21 can be provided along the support surfaces 16. Line 22 indicates the border line of the edge recess against the adjacent upper surface of the cassette plate. As mentioned above, one of the substantial advantages of the present invention is that inserts of very differing geometrical basic shape can be clamped in the same insert location. Hence the triangular cutting insert according to fig 2 and 3 can be clamped firmly in the same cutting insert location which is described in connection with fig 1. Thereby also this cutting insert features a recess 13' with a bottom surface 14' and support surfaces 15A\ 15B' and 15C Further the cutting insert includes corner support surfaces 18' for abutment against the upper side 23 of the cassette plate 3. As shown in figs 6 and 7 a cutting insert in accordance with the invention can also have a square basic form. In this case the lower side of the cutting insert includes a recess 13" with a bottom surface 14" as well as four support surfaces 15A", 15B", 15C" respectively 15D", the said support surfaces form substantially a square with cut-away corners, which are twisted in relation to the square of the cutting insert by essentially 45°. When installing the insert two adjacent support surfaces of these four support surfaces are intended to abut against two corresponding support surfaces on a raised area, which is primarily square instead of triangular, but otherwise wholly analogous with the raised area (see 7, 16) in fig 1. Further in an analogous manner, the square raised areas are somewhat smaller than the square recess 13". the corner portions 18" are arranged to abut against an upper surface of the cassette plate (or in those cases where a cassette plate has been dispensed with, directly onto the corresponding surface in the holder). In figs 10 and 11 an exploded view of another embodiment of the the invention is shown. According to this not one but three raised areas 25 are provided on the shim 3. Similarly according to the embodiment above, the shim 3 can be dispensed with, whereby the three raised areas 25 are provided directly on the bottom support surface in the recess 2. The raised areas 25 are substantially shaped as sectors and show both side faces 26A and 26B. The lower side of the cutting insert 27 is formed such that it matches the raised area 25. Consequently the said under side features three recesses 28, each of which is limited on two sides by two support surfaces 29A and 29B. Raised areas 30 are formed between the recesses 28. When installing the cutting insert however only a total of two support surfaces 29 insert will come to abut against two side faces 26 on the shim. Depending on the relative placement of the raised areas 25, the two active support surfaces can be formed by the two side faces 26A and 26B of the raised areas, which are placed furthest away from the operational cutting edges (that is to say the two which are referred to as 26A and 26B in fig 10). Alternatively, the two active support surfaces can also be formed by the two side faces 26A' and 26B', which are to be found just opposite each other on two adjacent raised areas, preferably nearest the operative cutting edge. Besides abutting against two side faces 26, areas of under side of the insert adjacent to the comers of the cutting insert also abut against the upper side 23 of the shim 3. It is the slightly raised under surfaces 31 at the corners which abut against the contact surface. In itself it is not necessasry to have large areas with a certain spread between the active support- or flank surfaces in the holder respectively the under side of the cutting insert. Consequently the active support surfaces can also exist on ridges 32 respectively grooves 33. On the holder itself ridges 32 are provided, which suitably are two or three in number. Each ridge has two main side surfaces, which according to fig 12 result in altogether six side faces, but only two of these constitute active support surfaces, namely those with reference indices 34 and 35. These are provided on each ridge and the angle between them is suitably between 30 and 150°. The remaining four side faces are contact free surfaces. On the under side of the cutting insert altogether twelve grooves 33 are to be found, of which only two come to be in active engagement with the support surfaces 34, 35. If the angle between the support surfaces 34, 35 is 120° the side faces 36 and 37 in fig 13 ° will for example, abut against them, whilst groove 33' will come to surround the third ridge 32 without direct abutment (at least no intentional abutment; this depends on the manufacturing tolerances ). Two or three under surfaces 38 of the corners abut against the upper side 39 of the holder. This happens either through the under surfaces of the corner having raised areas in a similar way to the raised areas 31 (see. fig 11 ), or by the said under surfaces at the corners sloping somewhat, such that their distance from the upper side is somewhat larger under the corner cutting edge than nearer the centre hole 17. Through this variety of grooves on the under side of the cutting insert, the cutting insert can be indexed to a number of positions in relation to the holder and in relation to the workpiece. Figs 14 and 15 show consequently two possible positionings of the cutting insert, whereby the cutting insert according to fig 15 has been turned by one groove spacing, i.e. 30°, in relation to the installation according to fig 14. Fig 16 shows how a shim can be designed in accordance with the embodiment with ridges and grooves. The shim is formed with two ridges 32, the active support surfaces of which consist of the forward flank surfaces 34 and 35. In accordance with the embodiments described above, abutment between these flank surfaces and corresponding flank surfaces in the grooves (or recess) of the cutting insert is brought about by a certain pretensioning through the clamping screw. Naturally if it was not for the fact that so many different positions are required the cutting insert need not have such a large number of grooves as in fig 13. The cutting insert according to fig 17 is designed with three grooves 33, whereby for example the side faces 36 and 37 abut against the support surfaces 34, 35. The raised under surfaces 31 at the comers abut against the upper side of the shim. Finally fig 18 shows how a cutting insert with the basic shape of an equilateral triangular can be designed with three recesses 28 in order to be clamped in a holder according to fig 10. It either abuts against the two support surfaces 29A, 29B on the same raised area 25 of the shim support surfaces, or the two support surfaces 29A', 29B' abut against the two adjacent raised areas 25. The cutting insert may have minor raised areas on the raised areas 25 (corresponding to 31 in fig 11 ) or the raised areas 25 can be slightly angled, in order to guarantee abutment under at least two corner edges. In a similar way the cutting insert can also have for example a rhombic or round basic shape. In these two cases the cutting inserts can suitably also have recesses with a basically square shape, in a corresponding manner to figs 6 and 7.

Claims: CLAIMS 1. A tool for metal cutting machining comprising a cutting insert (8) in a hard material as well as a holder for the cutting insert, wherein the cutting insert is either clamped directly against the holder, or against a cassette- or shim (3), which in turn is arranged on the holder, whereby the under side of the cutting insert features one or more recesses (13, 28, 33) includung at least two support surfaces (15, 29, 36, 37), partly a number of bottom support surfaces (18, 25, 31 , 38) between said recesses, characterized in, that the part of the said shim adjacent to the underside of the cutting insert or of the said holder includes one or more raised areas (24, 25, 32) including at least two support surfaces (16, 26, 34, 35), whereby the cutting insert can be clamped so that it simultaneously abuts against both the raised parts or the said two support surfaces (16, 26, 34, 35) of the parts with their support surfaces (15, 29, 36, 37) in the recess or recesses (13, 28, 33) and against said shim(3) or said holder with one or more of their bottom support surfaces (18, 25, 31 , 38). 2. A tool according to claim 1 , characterized therein, that the said two support surfaces (15, 29, 36, 37) of the insert respectively the two support surfaces (16, 26, 34, 35) of the raised area or the raised areas (24, 25, 32)) are mutually angled in respect to each other with substantially the same angle, whereby the support surfaces (15, 29, 36, 37) of the cutting insert are brought to abut against the raised area or the raised areas of the corresponding support surfaces (16, 26, 34, 35) by displacing the cutting insert whilst it rests on one or more of its bottom support surfaces (18, 25, 31 , 38). 3. A tool according to claim 2, wherein the cutting insert rests on all of its bottom support surfaces (18, 25, 31 , 38). 4. A tool according to claims 1-3, wherein the respective support surfaces (15, 29, 36, 37; 16, 26, 34, 35) of the raised area or of the raised areas of the insert are angled with respect to the vertical plane with an angle of between 0 and 25°. 5. A tool according to claims 1-4, wherein the cutting insert includes three support surfaces (15) and the raised area corresponding to three support surfaces (16), whereby the cutting insert is brought to abut against two of the three support surfaces by a locking screw (9) and a gap arises between the respective third sides 6. A tool according to anyone of the claims 1-4, whereby the cutting insert includes three recesses (28) and the holder or the shim three corresponding raised parts (25) intended to fit into said recesses. 7. A tool according to anyone of the claims 1 -4, whereby the under side of the cutting insert exhibits a number of grooves (33) and the holder or the shim a number of ridges (32) intended to fit into said grooves.

Inventors: ERICKSSON HAAKAN, HANSSON PER, LARSSON BERNT, SJOEOE STURE, ERICKSSON, HAAKAN, HANSSON, PER, LARSSON, BERNT, SJOEOE, STURE
Applicants: ERICKSSON HAAKAN, HANSSON PER, LARSSON BERNT, SANDVIK AB, SJOEOE STURE, ERICKSSON, HAAKAN, HANSSON, PER, LARSSON, BERNT, SANDVIK AKTIEBOLAG (PUBL), SJOEOE, STURE
Application year: 1997
Main classification: B23B27
IPC codes: B23B27