INDEXING OF CUTTING INSERTS

Abstract: A cutting insert for chip-breaking metal machining comprises an upper chip surface, a lower bottom surface, which is substantially plane parallel with the chip surface, one or several side surfaces that extend between said chip and bottom surfaces, and a through hole (12) for the accommodation of a locking screw (11). Said hole (12) comprises a rotation-asymmetrical portion (16) comprising a plurality of radially bulging portions (17) extending in the direction of the hole, the transitions (18) extending substantially in the direction of the hole between adjacent bulging portions being intended to pairwise abutting against the locking screw (11) and guiding the insert towards the right positioning in an insert seat, before the insert is clamped. In this way, it becomes considerably easier to position the cutting insert, particularly when it has a larger number of cutting edges, e.g. six or eight.

Description: TNDF.XTNG OF CUTTING INSERTS The present invention relates to an indexable cutting insert for cutting metal machining in accordance with claim 1. The vast majority ofthe variety of different indexable cutting inserts, both single-sided and double-sided, existing today on the market, have a central through hole. This hole is intended for the accomodation of a suitable locking screw for clamping the indexable cutting insert or the cutting insert in a holder. If the cutting insert is intended for turning, the holder is normally a boring bar; if the cutting insert is intended for milling, the holder is for instance a milling cutter body, a long edge cutter or an end mill. Further, the insert may be intended for drilling and may then be clamped by a screw in a drill shaft. As known, the fact that the cutting insert is an indexable one means that one and the same cutting insert has two or more cutting edges, a new cutting edge being positioned or indexed into an operative position when the previous one has been worn out, and this is done by loosening the screw and turning the insert a certain fraction of a revolution. Indexable cutting inserts are most commonly made of coated or uncoated cemented carbide, but inserts of different ceramic materials also exist. Usually, they have a square, triangular, rhombic, round, rectangular or hexagonal basic shape, but other basic shapes also occur. However, one thing they all have in common, viz. they are normally provided with a through central hole in the geometrical middle point. These holes may have different hole configurations, but a common feature for the vast majority is that the hole is rotation-symmetrical. This implies that the operator has to turn the indexable cutting insert around the loosened screw to substantially the right insert position before he/she tightens the screw again. Normally, the indexable cutting insert is "self-guiding" towards the support surfaces of the insert seat, but if these are small and/or if the insert has a plurality of sides (for instance six or eight), it may happen that the insert is forced into an erroneous intermediate position, and the insert will not be fastened steadily in the intended way and may be broken and/or the insert seat will be damaged. SE-B-346 074 (& US-A-3 341 921) discloses a triangular cutting insert with a central hole that also has a triangular basic shape, and also a conicity that widens upwards. The basic shape of the hole intends to offer a double contact surface instead of a single one for the screw in the insert hole, in order to avoid that the insert is lifted by the cutting forces. Further is it disclosed that the triangular basic shape ofthe hole gives a precise positioning ofthe insert. However, the shape of the hole is not meant to give a pre-positioning of he insert before it is fastened. Moreover, no possibility is given to deviate from the insert seat position predetermined by the triangular hole shape. According to the Swedish patent application No. 9301400-9, the top opening of the insert hole is shaped with recesses in order to provide a well defmed two point abutment between screw and insert. However, these recesses do not extend farther down in the insert hole, wherefore they in no way serve to enabling a certain prepositioning of the insert before the screw is tightened. Thus, a first object ofthe present invention is to shape an indexable cutting insert in such a way that a certain prepositioning or guiding of the insert into the right position is made possible before the insert is clamped. A second object ofthe present invention is to simplify and easy the clamping of indexable cutting inserts into the right position. These and further objects have been attained in a surprising way by shaping the hole configuration with the features as defined in the characterizing clause of claim 1. For illustrative but non-limiting purposes, some preferred embodiments of the invention will now be described in more detail, with reference to the appended drawings. These are herewith briefly presented: Figure 1 shows an exploded view in perspective obliquely from above, of an insert seat with an insert according to the invention. Figure 2 shows an insert according to the invention in perspective, obliquely from above. Figure 3 shows an insert according to figure 2 straight from below, an inserted screw being sectioned in the plane of the insert's bottom surface. Figure 4 illustrates the hole configuration in the insert according to the invention straight from the side, the screw not being fully threaded in. Figure 5 illustrates the hole configuration in the insert according to the invention, straight from the side, the screw being fully tightened. Figure 6 illustrates the hole configuration in an insert according to the invention, straight from underneath, with a hexagonal basic geometry. Figure 7 illustrates the hole configuration in an insert according to the invention straight from underneath, with an octagonal basic geometry. Figure 8 illustrates the hole configuration in an insert according to the invention, straight from underneath, with a square basic geometry. It should be noted that by the terms "horizontal" and "vertical" in the text underneath are intended the directions when the insert lies with its bottom surface on a wholly horizontal, planar ground. In figure 1 an arbitrary insert holder is generally designated by 1. The end that is intended to come into an operative engagement with a workpiece comprises an insert seat 2. which besides a few free surfaces comprises a bottom support surface 3, a threaded hole 6 and two abutment surfaces 4 and 5, respectively, which are intended to bear against and support cooperating abutment surfaces 8 on the insert 7. The geometry ofthe latter does not constitute any essential feature ofthe present invention, although its advantages stand out as most pronounced at a higher number of cutting edges, such as for inserts with a substantially regular pentagonal, hexagonal, heptagonal and octagonal basic geometry, preferably with a hexagonal or octagonal one. Moreover, also wholly round inserts are comprised by the present invention. In figure 1 , the invention is illustrated by an indexable cutting insert 7. whose other geometry (i.e.. disregarding the hole configuration) agrees with our previous Swedish patent application 9502645-6, which is hereby incoφorated by this reference. Two adjacent abutment surfaces 8 ofthe insert bear against the two support surfaces 4 and 5 ofthe insert seat. The hole configuration ofthe insert according to the present invention is glimpsed in the insert hole 12 in figure 1. In a conventional manner, a shim 9 may be placed under the indexable cutting insert 7, which shim is clamped by means of a shim screw 10, which is screwed into the hole 6. In turn, the locking screw 1 1 for the insert 7 is screwed into the inner thread ofthe shim screw 10. Figure 2 shows in a clearer way how the insert hole 12 is configured. The hole configuration above the portion 16. which portion is essential for the invention, is not per se any essential feature of the present invention; the only essential matter of this portion is that it shall be capable of offering a bearing point or line for the underside 20 ofthe screw head 15. Suitably, the top opening portion of the hole is shaped in a conventional way. such as a rotation-symmetrical convex radius surface 13 and a cylindrical or slightly conical surface 14 above surface 13. Surface 14 is there for making possible a certain countersinking of the screw head 15. The surface portion 13 may also be substantially conical, although this constitutes a less preferred embodiment. Below the radius surface 13, the hole configuration transposes into a non-rotation-symmetrical portion 16. which suitably has a cross-sectional configuration that reminds of a flower, cf. figures 3, 6, 7 and 8. However, in principle it may also have another cross-sectional shape that manages to fulfil the prepositioning effect on the insert according to the invention, for instance a multi-point star. The number of "petals" (or, e.g., "star points") corresponds to the basic shape of the cutting insert. Thus, for instance an insert with a hexagonal basic geometry has six radially bulging portions ("petals") 17. Alternatively, the number of "petals" corresponds to the number of indexation positions for a round insert. According to the figures, the uniformly rotation-asymmetrical portion 16 extends the whole way to the lower opening ofthe insert hole. However, said portion may also terminate before the lower opening. Correspondingly, the portion 16 also does not have to extend to the very radius surface 13. Figure 3 shows the cutting insert straight from below, the cross-section of the not fully tightened (cf. fig 4) screw 11 being shown in the plane of the bottom surface ofthe cutting insert. Hereby it may be seen how the at least partly threaded portion 21 of the screw bears against two vertical abutment lines 18, which constitute break lines between two adjacent bulgings 17. This well defined two line abutment is accomplished by the two bulging portions having smaller radii of curvature than the screw. Through the hole in fig 3. the bottom side of the screw head 15 is observable. The hidden upper opening 19 is dashed. The normal radially outwards, to a vertical middle line of a bulging is substantially so directed that the insert is guided to a correct position in the insert seat by means of the abutment lines 18, while the locking screw is screwed downwards, to eventually clamp the insert in that position. In figure 4 a vertical cross-section is shown through the central axis of an insert hole, the hole configuration in this case having six bulging portions 17. By the special hole configuration according to the invention, the insert is localized and guided to a correct position in the insert seat, i.e. the surfaces intended as abutment surfaces on the insert are brought to be pre-adjusted relative to corresponding support surfaces in the insert seat. The relation between on one hand the distance between the threaded hole 6 of the insert seat and the support surfaces 4 and 5, respectively, and on the other hand the size of the hole of the insert and the insert hole, respectively, is chosen so that the insert cannot be turned past a break line 18 when the insert bears against the bottom support surface. It is only possible to turn the insert and indexate a new operative cutting edge if one lifts the insert a bit up from the insert seat, so that the abutment surfaces of the insert become located above the support surfaces of the insert seat. It is true that in first hand the support surfaces of the insert seat will hinder a rotation of the insert when it rests upon the bottom support surface, but for wholly round inserts only the break lines 18 prevent this rotation. When the insert has been rotated to the right position, then it is clamped in this position by tightening the locking screw in accordance with figure 5. In a conventional manner, the conical bottom side 20 of the screw head is brought to bear against the radius surface 13. a one-point abutment, alternatively a one-line abutment in a vertical direction being attained between screw and insert. This bearing provides on one hand a horizontal force component, which forces the insert into the insert seat, and on the other hand a vertical force component, which presses the insert downwards against the bottom support surface ofthe insert seat. By the reaction force against the underside of the screw head from radius surface 13, when the insert presses against the support surfaces of the insert seat, the screw is bent somewhat, whereby it is distanced from the rotation-asymmetrical hole portion, and the bearing against the break lines 18 ceases. Figure 6 shows the hole configuration from the bottom side of a cutting insert; in principle this is a partial amplification of fig 3. It illustrates how a cutting insert is directed towards the correct position by means ofthe guiding bearing against the break lines 18, " either with a cutting insert with a hexagonal basic shape, or a round insert, which is intended to be indexed into six determined positions being equally distributed around the periphery of the insert. Analogously with fig 6, fig 7 shows how the hole configuration is shaped for either an insert with an octagonal basic shape, or for a round insert with eight predetermined indexation positions. Analogously with fig 6 and 7, fig 8 shows the shape of the hole configuration for either an insert with a square basic shape, such as for instance the indexable cutting insert according to fig 9, or for a round cutting insert with four predetermined indexation positions. The advantages of the present invention are evident. The operator attains a determined pre-positioning into the correct insert position in the insert seat already before the insert is clamped. This is of great help, specially when there are many cutting edges, such as for hexagonal and octagonal indexable cutting inserts, where a cutting insert by mistake may be forced into an erroneous position. Furthermore, the present invention makes possible a positioning of round cutting inserts into determined positions.

Claims: CLAIMS 1 . Cutting insert for chip-breaking metal machining comprising an upper chip surface, a lower bottom surface, which is substantially plane parallel with the chip surface, one or several side surfaces extending between said chip and bottom surfaces, and a through hole (12) for the accomodation of a clamping arrangement (11), characterized in that said hole (12) comprises a rotation-asymmetrical portion (16) comprising a plurality of radially bulging portions (17) extending in the direction of the hole, the transitions (18) extending substantially in the direction of the hole, between adjacent bulging portions, being intended to pair- wise abut against the clamping arrangement ( 1 1 ) and guide the insert towards the right positioning in an insert seat, before the insert is fastened. 2. Cutting insert according to claim 1, characterized in that the cross- section of the rotation-asymmetrical hole portion ( 16) has the shape of a number of interconnected circle segments (17) extending radially outwardly, in such a way that the hole cross-section reminds of a flower. 3. Cutting insert according to claim 1 or 2, characterized in that each transition ( 18) extending in the direction of the hole between two adjacent bulging portions (17) forms a break line, each pair of adjacent break lines being intended to function as abutment and guiding lines for the insert. 4. Cutting insert according to any ofthe preceding claims, characterized in that it has a hexagonal, octagonal or round basic shape. 5. Cutting insert according to any of the preceding claims, characterized in that, in connection with the upper or chip surface of the cutting insert, above the rotation- asymmetrical hole portion (16). there is located a rotation-symmetrical hole portion, which is intended to abut against the clamping arrangement ( 1 1 ) by means of a point or line contact, which arrangement consists of a locking screw.

Inventors: HELLSTROEM LARS, HELLSTROEM, LARS
Applicants: HELLSTROEM LARS, SANDVIK AB, HELLSTROEM, LARS, SANDVIK AKTIEBOLAG
Application year: 1997
Main classification: B23B27
IPC codes: B23B27, B23C5