FASTENING ARRANGEMENT FOR CUTTING INSERTS AND A CUTTING INSERT INTENDED FOR SUCH AN ARRANGEMENT

Abstract: An arrangement has been provided for the fastening of cutting inserts on an insert holder with or without a shim. The bottom side of the cutting insert and the support surface of the shim or of the insert holder are shaped with inter-fitting ribs and grooves for stabilizing the cutting insert. The bottom side of the insert has grooves (12, 12', 12'') and substantially planar portions (14) between said grooves, and said support surface (15, 15', 15'') has a portion with ribs (13, 13', 13''), which ribs are intended to be accommodated in a corresponding number of grooves of the cutting insert. At least a part of the planar portions (14, 14', 14'') functions as bearing surfaces for the cutting insert against parts of the support surface (15, 15', 15'') which do not have ribs. With this construction, a very strong and stable fastening has been achieved, without any high demands on dimension tolerances.

Description: FASTENING ARRANGEMENT FOR CUTTING INSERTS AND A CUTTING INSERT INTENDED FOR SUCH AN ARRANGEMENT The present invention relates to an arrangement for the fastening of cutting inserts on cutting insert holders for the cutting machining of primarily metals, and cutting inserts intended to be fastened in such an arrangement. Different cutting inserts and indexable cutting inserts are fastened in tool holders in several different, known ways. The most usually occurring is that the cutting insert has a through central hole and the insert seat in the holder has a threaded hole. A locking screw is introduced into the central hole ofthe insert and is tightened in the hole ofthe holder by a suitable torque, and frequently also a shim plate with a central hole is placed between the cutting insert and a bottom support surface. Usually, the insert seat also comprises two mutually substantially perpendicular abutment surfaces, or three abutment points, for bearing against two ofthe edge surfaces ofthe cutting insert. The disadvantage of that construction is that a certain play of the insert may easily arise after a period of use. A further disadvantage is that one may easily happen to tighten the screw too strongly, whereby it may be damaged or even broken. Other known insert holders have a clamp or similar fastening arrangement which presses upon the upper side ofthe insert in order to clamp it in the insert seat. The pressing force of the clamp may be regulated by a screw. Such constructions may for instance be used for clamping cutting inserts without any central hole, as is the case for parting inserts for example. In order to avoid a play and to attain a more stable fastening of a cutting insert in general, constructions have been suggested according to which the bottom side ofthe cutting insert and the bottom support surface ofthe insert seat have been shaped as serrated surfaces intended to mesh into each other. Such a constuction is disclosed in US- A-2 140 941 and in US-A-2 453 464. However, one drawback with these embodiments is that they require a very extensive grinding of the serrrated surface of either the insert or the holder, or both. A further drawback is that, even if the cutting insert has been secured in a direction perpendicular to the serrations, a vertical play may arise just as easily as in the case of two wholly planar bearing abutment surfaces, in particular during machining operations prone to vibrations. In US-A -4437 802 there is disclosed how a cutting insert is fastened in a drill, the cutting insert comprising two grooves and the support surface ofthe drill having two corresponding ribs which shall fit exactly into the grooves and occupy their whole cross-sectional area. Again, the problem is that axial play may easily arise, particulariy if the drill is subjected to vibrations. Moreover, an extensive grinding is required of either the ribs or the grooves, in order to attain the required fitting precision. Further, in DE-A-3 533 125 a milling tool is disclosed, according to which the cutting inserts bear against the holder on serrated surfaces in order to strengthen and stabilize the fastening capability. The disadvantage of this construction, as well as with the embodiments according to the above-mentioned patent publications, is that it is not possible to tum the inserts less than half a revolution when indexing a new cutting edge. Moreover, an extensive precision work is required for the production ofthe serrated surface of the holder. Thus, a primary object ofthe present invention is to provide an arrangement for the fastening of cutting inserts, which arrangement makes possible a very strong and very stable fastening ofthe insert, without the slightest risk of moving the insert. Another object ofthe present invention is to provide an arrangement that enables a stable and strong fastening o the insert in at least two. preferably three indexed positions. Still another object ofthe present invention is to provide a strong, pJay-free and stable fastening ofthe insert without any costly and time-consuming grinding. Yet another object ofthe present invention is to provide a cutting insert which may be directly pressed and that allows for a very strong and stable fastening in two or more insert positions. A still further object ofthe present invention is to avoid the necessity of abutment surfaces or abutment points in the insert seat, which require a high dimension accuracy. These and further objects have been achieved by forming the fastening arrangement of the cutting insert in the insert holder in accordance with claim J . For illustrative but non-limiting purposes, some embodiments ofthe invention will now by described in more detail, with reference to the appended drawings. These are herewith presented: Figure 1 shows an insert fastening arrangement according to the invention. in the form of an exploded view in perspective, obliquely from above. Figure 2 shows a bottom plan view ofthe cutting insert of Figure 1. Figure 3 shows an exploded view of another embodiment ofthe invention, in perspective obliquely from above. Figure 4 shows an exploded view of still another embodiment ofthe invention, in perspective obliquely from above. Figure 5 shows an exploded view of still another embodiment ofthe invention, in perspective obliquely from above. Figure 6 shows a cross-section ofa first basic embodiment ofthe invention. Figure 7 shows a cross-section of a second basic embodiment ofthe invention. Fig 1 shows a boring bar or insert holder 1 whose shaft part is not essential for the present invention. The front part of the holder comprises a base surface 2, on which are arranged ribs 3 which are intended to fit into grooves 4 on the bottom side of a shim 5. The ribs 3 and the grooves 4 may suitably be made in accordance with Swedish patent application 9401429-7 (corresponds to WO 95/29026). which makes it possible to dispense with rear abutment surfaces or points in the insert seat. Thus, as may be seen in Fig 1 , this insert seat does not require any abutment surfaces, which considerably simplifies the manufacturing ofthe insert seat. The shim 5 is fastened on the base surface 2 by a shim screw 6 that has an outer thread 6A threaded into the hole 9, whereby the bottom side ofthe head ofthe shim screw presses against the abutment surface 7. Thereby, the flange surfaces ofthe grooves are pressed against the corresponding flange surfaces 8 ofthe ribs 3, whereby a small gap is created between the bottom side of the shim on the one hand, and the surfaces 2 A disposed between the ribs 3, and surfaces 2B disposed outside the ribs 3, on the other hand. However, it should be pointed out that the boundary layer or interface comprising the ribs 3 and the grooves 4 is not the boundary layer related to this invention. In Fig 1, the boundary layer that is essential for the invention is the one between the shim 5 and a cutting insert 10, which boundary layer will now be further described. On top ofthe shim 5 there is fastened a cutting insert 10. in this case a triangular, single-sided insert for threading, by means ofa locking screw 1 1. which is tightened into the inner thread 6B ofthe shim screw 6. Usually, the insert 10 is made of coated or uncoated cemented carbide, although other materials may also occur, e.g., different ceramic materials. The bottom side of the cutting insert 10 has grooves 12 in all three corners, which may be seen more clearly in Fig 2. One set of such, substantially parallel grooves is brought into engagement with a set of corresponding ribs 13 on the top side 15 of the shim. Between the grooves 12 on the bottom side, and outside the outermost groove, ribs are formed having substantially planar surfaces or cams 14, which are intended to bear against the top side 15 of a non-ribbed portion ofthe shim in a way that may be seen more clearly at the left side in Fig 6 and 7. Fig 6 and 7 show the principle ofthe present invention, viz., that the ribs 16 with their planar cams 14 fulfil a double function. On one hand the ribs 16 serve for wedging and fastening between the ribs 13 ofthe shim (or ofthe insert holder, if no shim is used), and on the other hand the planar cams 14 of the ribs 16 function as bearing surfaces which bear against planar non-ribbed portions ofthe top surface 15 ofthe shim (or ofthe insert holder, if no shim is used). As may be further seen in Fig 6 (and also Fig 7), the flange (side) surfaces 13A ofthe ribs 13 bear against the flange (side) surfaces 12A ofthe grooves 12. Contrary thereto, the tops 13B, 14 of the ribs 13 and 16. respectively, are not intended to reach the corresponding groove bottom. In order not to cause a statical over-determination, the cutting insert 10 according to Fig 6 is provided with a central, more deeply recessed middle portion 17, which is not in contact with the shim. Another embodiment principle is shown in Fig 7. According to this, the bottom surface ofthe insert is planar and in the same level as the planar rib cams 14. Instead, the shim 5 has been provided with a deeper middle portion 18, in order to obtain the statically well-defined abutment of three points or regions at the three corners ofthe insert. Fig 3 shows another embodiment according to the present invention. Also this one has a boring bar 1 with a front base surface 2' and ribs 3' which cooperate with grooves 4' on the bottom side of the shim 5'. In the same way as in Fig 1, an indexable cutting insert 10' is fastened on the shim 5'. The indexable insert 10' is double-sided and is on both sides provided with grooves 12' and ribs 16', the latter having planar cams 14". As may be glimpsed into the through insert hole according to Fig 3, also the opposite side ofthe insert is provided with similar serrated portions as the visible top surface. In the same way as in Fig 1, the ribs 16' engage between ribs 13' on the top side 15' of the shim, in order to stay and stabilize the operative cutting corner 19. In order to give a well defined, distinct bearing portion, a portion 20 on the top side ofthe shim may be somewhat raised, in order to bear against the planar rib cams 14' ofthe insert. Thus, also in this case the ribs 16' ofthe insert fulfil the double function that is characteristic ofthe invention. According to Fig 1 and 3, the ribs 13 and 13', respectively, are located underneath the operative cutting corner and that is also the prefeπed embodiment. However, they may also be aπanged at one ofthe non-operative corners. The invention may also be applied to round cutting inserts. As illustrated in Fig 4, the shim 5" bears against the boring bar 1" in the same way as in Fig 1 and 3. Also in this case, the cutting insert 10" is double-sided, wherefore the bottom side ofthe insert is basically identical with the visible top side. A number of radial grooves 12 " are aπanged on the two opposed main sides ofthe insert. For instance between 2 and 5. suitably 3 as shown in Fig 4, of those grooves enclose an equally large number of ribs 13' * on the top side 15" ofthe shim 5' " . whereby abutment is accomplished in the above described way on the flank surfaces ofthe grooves and the ribs, as shown in Fig 6 and 7. Any other abutment between the insert and the shim may per se take place over the whole surface 15", but preferably this surface is provided with two protruding bearing surfaces 21. which are intended to bear against coπesponding sector-shaped, planar surface portions 14" on the round insert. Thereby, also according to this embodiment a statically well-defined three-point or three-region abutment is obtained. Fig 5 shows an embodiment that is analogous to the one in Fig 4. The difference is that it lacks a shim. Thus, the ribs 13" and the protrusions 21 are aπanged directly on the boring bar. As should be evident for the skilled man, a new section ofthe cutting edge 22 may be indexed by untightening the locking screw and turning the round insert according to Fig 4 and 5 at lest by a twelfth ofa revolution, since the grooves 12" divide the main surfaces ofthe insert into twelve sectors. Thereafter, the locking screw is tightened again. By the principle described above a number of advantages has been achieved. A considerably stronger and stabler fastening of different cutting inserts has been obtained in comparison with cutting inserts whose bottom surfaces are planar. Moreover, this has been accomplished in a way that puts considerably smaller demands on the manufacturing accuracy than would be the case if the the whole bottom side ofthe insert were made with grooves and ribs, which would be intended to cooperate with coπesponding grooves and ribs on the top side ofthe shim. Another evident advantage is that the improved strength and stability of the fastening is obtained without having to dispense with the possibilities of indexing new cutting edges ofthe insert. As may be clear from the above description, the invention is applicable on any insert shapes, such as triangular, rhombic, square, rectangular, round, hexagonal and octagonal inserts, and inserts for grooving operations. Eventually, it may be pointed out that the fastening anangement according to the invention is also suitable for milling and drilling.

Claims: Cl ims 1. Anangement for the fastening of cutting inserts on insert holders with or without a shim between the cutting insert and the insert holder, the bottom side ofthe cutting insert and the support surface ofthe shim or the insert holder being shaped with inter-fitting ribs and grooves for stabilizing the cutting insert, characterized in that the bottom side of the cutting insert has grooves (12, 12', 12") and substantially planar portions (14, 14', 14") between said grooves, in that said support surface (15, 15", 15") has a portion with ribs (13, 13', 13"), which ribs are intended to be accomodated in a coπesponding number of grooves in the cutting insert, and that at least a part ofthe planar portions (14, 14', 14") functions as support surfaces for the cutting insert against parts ofthe support surface (15, 15', 15") which do not have any ribs. 2. Anangement according to claim 1, characterized in that the cutting insert has two or more groups of grooves (12, 12'), the grooves in each group being substantially parallel. 3. Anangement according to claim 2, characterized in that between the grooves (12. 12') in each group are provided ribs (16, 16 * ) whose cams constitute the substantially planar portions (14, 14') which function as bearing surfaces against parts of the support surface (15, 15') without any ribs. 4. Anangement according to claims 1 to 3. characterized in that the parts of the support surface that lack ribs have one or several planar, raised portions (20. 21 ). which function as bearing surfaces for the planar portions (14. 14 * . 14") ofthe cutting insert. 5. Anangement according to claims 1 to 4. characterized in that the cutting insert has a deeper middle portion (17) between the groups of grooves (12), which middle portion does not come into contact with the support surface (15). 6. Anangement according to claims 1 to 4, characterized in that the support surface (15) has a deeper middle portion (18) which does not come in contact with the bottom side ofthe insert. 7. Anangement comprising a cutting insert and a support element: the insert including a bottom surface having grooves (12, 12', 12") formed therein, and substantially planar surface portions (14, 14', 14") disposed between the grooves; the support element including a support suface upon which the bottom surface is directly supported; a portion ofthe support surface including ribs (13, 13', 13"), and another portion thereof being rib-free; the ribs fitting into respective ones of the grooves (12. 12 " . 12"); at least some ofthe substantially planar surface portions (14, 14', 14") bearing against the rib-free portion ofthe support surface (15, 15', 15"). 8. Anangement according to claim 7, wherein the bottom surface includes at least two groups of grooves (12, 12'), the grooves of each group extending substantially parallel to one another. 9. Anangement according to claim 8, wherein the substantially planar surface portions (14, 14') are disposed between the grooves of each ofthe groups. 10. Anangement according to claim 9, wherein the rib-free portion ofthe support surface is planar and raised (20, 21) with respect to bottoms ofthe ribs. 1 1. Anangement according to claim 10, wherein a middle portion ( 17) of the bottom surface is deeper than the substantially planar surface portions and is out of contact with the support surface (15). 12. Anangement according to claim 10, wherein a middle portion (18) of the support surface (15) is deeper than the rib-free portion ofthe support surface and is out contact with the bottom surface. 13. Anangement according to claim 7. wherein the support element is a shim (5). 14. Anangement according to claim 7. wherein the support element is an insert holder (1). 15. Cutting insert for cutting metal machining comprising a top side, a bottom side and side surfaces extending between these, characterized in that the cutting insert is round and that at least the bottom side has grooves or depressions (12. 12 " , 12 " ) which are radially placed from the centre to the periphery. 16. Cutting insert for cutting metal machining comprising a top side, a bottom side and side surfaces extending between these, characterized in that the bottom side ofthe cutting insert has two or more groups of grooves (12. 12') and ribs, which within each group are substantially parallel. 17. Cutting insert according to claim 16. characterized in that the ribs (16. 16') between the grooves (12. 12') have substantially planar cams (14, 14'). 18. A round cutting insert for metal cutting machining, comprising round top and bottom surfaces and a side surface extending therebetween, at least the bottom surface having grooves (12") extending generally radially from a center of the insert. 19. A cutting insert for metal cutting machining, comprising top and bottom surfaces and side surfaces extending therebetween, the bottom surface including at least two groups of grooves (12"). the grooves of each group aπanged substantially parallel to one another. 20. The cutting insert according to claim 19. wherein ribs are formed between adjacent grooves of each group, the ribs having substantially planar end surfaces (14").

Inventors: BYSTROEM LENNART, WIMAN JOERGEN, BYSTROEM, LENNART, WIMAN, JOERGEN
Applicants: BYSTROEM LENNART, SANDVIK AB, WIMAN JOERGEN, BYSTROEM, LENNART, SANDVIK AKTIEBOLAG, WIMAN, JOERGEN
Application year: 1996
Main classification: B23B27
IPC codes: B23B27, B23B51, B23C5