Cutting insert with an array of surfaces receiving clamping forces

A cutting insert includes a body that forms top and bottom surfaces, and a center hole intersecting at least the top surface (e.g., a through-hole). A portion of the top surface which extends around the center hole includes an array of projections radiating laterally outwardly around the center hole. A distal end of each projection disposed farthest from the center hole defines a tip of the projection. The projections form at least six tips spaced circumferentially apart. Each tip has a planar top face. A clamp has flat contact surfaces which press downwardly against the planar top faces of respective projections simultaneously as the clamp pulls the insert against an upstanding support surface.

BACKGROUND

The present invention relates to plate-like cutting inserts, intended for chip removing machining of metallic materials, the inserts having a central hole for receiving part of a clamp. Such indexable inserts normally have cutting tip angles below 80° and are usually intended for different types of copying. On the market, there is now a plurality of different types of insert holders, which are especially adapted for such indexable inserts, such as rhombic, rhomboid or isosceles triangular indexable inserts. The material used to make such indexable inserts is normally sintered cemented carbide or ceramics.

A frequently used type of indexable insert is provided with a so-called wiper geometry outside in each active cutting corner. The meaning of this is a radius-modified corner geometry, with the corner radius in the cutting corner being composed of a plurality of small radii adjacent each other, with each radius portion adjoining the next radius portion having another radius size. With this type of geometry, it has become possible to increase the feeding of the cutting insert significantly at the same time as a desired good surface finish of the machined workpiece can be attained. Upon the use of such cutting inserts having a wiper geometry, the cutting insert is not clamped by the usual lever holders, e.g., of the type shown and disclosed in U.S. Pat. No. 3,314,126. Upon use of a wiper insert, it is now desirable to employ a holder system, which upon clamping of the cutting insert, applies not only an inward-drawing force but simultaneously also a downward-pressing force. This represents in itself a certain limitation as for the choice of geometries for the upper chip side of the cutting insert.

OBJECTS AND SUMMARY OF THE INVENTION

Against this background, it is an object of the present invention to provide a new insert design, which on the one hand, is adapted for an efficient locking by means of the above-mentioned type of insert holder having inward-directed as well as downward-directed tensile forces, and which on the other hand leaves a sufficiently large margin on the top side of the cutting insert in order to, e.g., enable desired corner marking or other geometric marking or which enables insertion of more advanced chip breaker geometries directly pressed into the upper chip surface.

The present invention relates to a cutting insert which comprises a body that forms top and bottom surfaces, and a center hole intersecting at least the top surface (e.g., a through-hole). A portion of the top surface which extends around the center hole includes an array of projections radiating laterally outwardly around the center hole. A distal end of each projection disposed farthest from the center hole defines a tip of the projection. The projections form at least six tips spaced circumferentially apart. Each tip has a planar top face.

The invention also relates to a cutting tool employing such a cutting insert in combination with a holder and a screwed-in clamp.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The indexable insert10shown inFIGS. 1–2is shown in cooperation with a holder clamp11. The indexable insert has, in this shown embodiment, a rhombic base shape and cutting tip angles δ below 80°. The planar top and bottom surfaces12and13of the indexable insert, which are mutually parallel, form a right angle to the edge surfaces uniting them. The indexable insert11has a central through hole14, the center axis of which is oriented perpendicularly to the flat surfaces12and13of the cutting insert. The seating in which the indexable insert10is received comprises a bottom support surface15and two side support surfaces16and17upstanding perpendicularly from the surface15. The bottom support surface15may be formed either by an insert holder18, as in the shown embodiment, or by a separate conventional shim plate (not shown) mounted by means of a suitable fastening means (not shown).

So as to enable clamping of the indexable insert10in the seat of the insert holder, the clamp11is maneuverable by means of a tightening screw21extending through an elongate recess19of the clamp and threadedly connected in a threaded boring20in the holder18. The center axis C1of the boring20is oriented parallel to the center axis C2of the insert hole14. The clamp11includes an arm2, the front end of which has a downwardly-inwardly directed projection22extending into the insert's center hole14and having a surface4facing the boring20and oriented at an oblique angle α in relation to the center axis C2of the hole14. The projection22is arranged to be brought to engagement with a rear portion of the wall of the hole14i.e., a portion of that wall that is closest to the screw21. The engagement occurs at a contact point23a distance down in the insert hole. Simultaneously, contact surfaces of the bottom side6of the clamp arm2engage the top surface12of the cutting insert at locations24near the rear side of the center hole14.

The opposite rear end of the clamp arm2comprises a second projection25which is received in a recess26in the insert holder18, the end surface27of the projection25being convexly formed and arranged to be brought into surface contact with a corresponding planar stop face28of the recess26, which stop face is formed at an oblique angle to the center axis C1of the tightening screw. Alternatively, the end surface27may be flatly formed for surface contact with the planar stop face28. The size of the oblique angle a should be substantially the same as, or somewhat less than, the acute angle of inclination β at which the rear contact surface28in the holder is oriented.

According to the invention, the portion of the upper surface of the cutting insert extending around the central hole14includes an array of projections which radiate laterally outwardly around the center hole and which can be raised or recessed with respect to the adjacent portions of the insert's top surface. For example, inFIGS. 1–5cthere is an array29. of projections40which radiate around the center hole14in a laterally outward direction, i.e., laterally relative to the axis C2of the center hole14. Each projection has a planar (flat) top face42which is spaced from adjacent portions of the insert's top surface, e.g., the projections are recessed with respect to those adjacent surface portions, but they could instead be raised. The distal ends30of the projections, i.e., the ends of the projections spaced farthest from the center hole, could be in the form of one or more tips, which could be sharp, rounded or blunt.

For example, in the embodiment shown inFIGS. 1–5c, there are six projections40a–40fwhich are joined together to create a generally star-shaped projection array as viewed inFIG. 4. Each of the projections40aand40dhas a distal end comprised of two sharp tips30a,30b(e.g., seeFIG. 4a), whereas each of the remaining projections has a distal end comprised of three sharp tips30c,30d,30e(e.g., seeFIG. 4b).

In a polygonally shaped insert having a pair of oppositely disposed corners which are bisected by a common imaginary bisector that passes through the center of the center hole, the projection array is preferably configured symmetrically about that bisector.

For example, in the rhombic-shaped insert shown inFIGS. 1 through 5c, a bisector B bisects two opposing acutely-angled corners G, G′ of the insert10and passes through the center of the hole14. The projections40a,40d(each of whose distal end comprises two tips30a,30b) are arranged symmetrically with respect to the bisector B such that the tips30a,30bare symmetrically disposed on opposite sides of the bisector.

The substantially star-shaped array29is intended to be in surface contact (in contrast to point contact or line contact) with contact surfaces of the clamp arm2at locations situated near the central insert hole14, namely a pair of spaced-apart flat (planar) contact surfaces32aand32b. A laterally inner edge of the array29coincides with the hole14.

The contact surfaces32a,32bare shown as being arc-shaped, having a tapering width. Alternatively, other shapes are possible, such as triangular as shown at33aand33binFIG. 4.

InFIGS. 5a,5band5cis shown how the indexable insert10can enable exposure of the acute-angled cutting corner, designated34inFIG. 5a, as well as the obtuse-angled cutting corner, designated35, for chip forming machining with one and the same type of clamp.

InFIG. 6, an alternative insert10′ having a projection array29′ is shown, having six spaced-apart heart-shaped projections36a,36b,36c,36d,36eand36fradiating laterally outwardly around the center hole. The distal end of each projection comprises two convexly rounded tips50a,50b. Planar top faces of the projections are parallel with the surrounding flat surface portions12as well as being raised relative thereto, i.e., elevated a distance in relation to the surface portions12. The laterally inner limiting edge38of each heart-shaped projection is concavely curved with radius substantially equal to the radius of curvature of the central hole14. Each edge38is spaced laterally (radially) outwards by a small distance from the hole14.

InFIG. 7, another insert embodiment10″ is shown, with the radiating projection array29″ radiating around the insert hole14being in the form of six projections37a–37fspaced-apart from each other in circumferential directions, the distal end of each projection being in the form of two blunt tips60a,60b. The inner limiting edge of each projection is, as in the case ofFIG. 6, concavely circularly curved with a radius of curvature substantially equal to the radius of curvature of the central hole14. Each such surface segment is, furthermore, terminated a small distance from the hole14.

In accordance with the present invention, there is provided a cutting insert whose top surface can be engaged by a clamp to be effectively clamped in two directions, and which leaves sufficient area on the top surface in order to, e.g., enable desired corner marking or other geometric marking or which enable insertion of more advanced chip breaker geometries directly pressed into the upper chip surface.