CUTTING INSERT FOR CHIP FORMING MACHINING

Abstract: The invention relates to an insert for chip forming machining. The insert (10) is a body having polygonal basic shape and is provided with a cutting edge at the periphery thereof and a chip former. The chip former is provided in the shape of a plurality of ridges (23) whereby the mutual distance between adjacent ridges diminishes in direction towards the middle of the cutting edge so as to form a conical corrugated chip (30) which is forced away from the workpiece during machining.

Description: The present invention relates to a cutting insert for chip forming machining consisting of a body having polygonal basic shape and having at least one cutting edge created by the transition between an upper face and a side surface of the insert, said upper face constituting a rake face or contact face between the cutting insert and the chip formed during machining, said rake face comprises a chip former located inside or connected directly to the cutting edge. This chip former includes a plurality of ridges. There have been proposed several prior art inserts having chip formers that consist of a plurality of ridges. One of these prior inserts, see DE-A-2 845 211, is provided with a chip former which includes recesses located adjacent each other in the rake face. These recesses intersect with each other and thereby provide ridges along their intersections which extend perpendicularly in relation to the adjacent cutting edge. These ridges are arranged with mutually decreasing distances in the direction from the middle of an adjacent cutting edge towards the corner of said insert. The contact area between the chip and the ridges towards the corner is thereby increased and the chip therefore has a tendency to approach the workpiece during turning such that no risk of damage occurs. It is an object of the present invention to provide a cutting insert which urges the chip away from the workpiece during a working operation. It is another object of the present invention to provide a cutting insert having a plurality of cutting edges. These and other objects of the invention are achieved by virtue of those specific features that are outlined in the accompanying patent claims. The invention is described in more detail in the following with reference to the appending drawings disclosing different embodiments of the invention by way of example. Fig. 1 shows a top view of an embodiment of a cutting insert according to the invention. Fig. 2 shows a side view of the insert of Fig. 1 and an enlarged view of a section of the insert. Figs. 3 to 7 show cross-sections along the lines III-III to VII-VII, respectively. Fig. 8 shows an elarged top view of a section of the insert. Fig. 9 shows the insert in engagement with a workpiece. Fig. 10 shows in top view a section of an alternative embodiment of a cutting insert of the invention. Fig. 11 shows a cross-section along the line XI-XI in Fig. 10. Fig. 12 shows in top view a portion of a further alternative embodiment of a cutting insert of the invention, and Fig. 13 shows a cross-section along the line XIII-XIII in Fig. 12. In Figs. 1 - 9 is shown a cutting insert 10 according to one embodiment of the present invention. The insert is made of hard material such as ceramics, cemented carbide or similar material. When selecting ceramics it is advisable to provide a negative strengthening land. The insert has a polygonal basic shape, in this case rhombic basic shape. The insert comprises an upper face 11 and a lower face 12 which are mainly identical in shape. These faces 11 and 12 are connected by mainly continuous side surfaces 13 to 16 located between them. Cutting edges 17 to 20 are created by the peripheral transitions between the upper face 11 and the side surfaces and between the lower face 12 and the side surfaces, respectively. The side surfaces 13-16 intersect along rounded cutting corners 21. The cutting corner 21 is defined by a bisector B . Each upper and lower face has a lower centrally depressed portion 22 which is inclined downwards and inwards from ridges or chip faces 23 and from their corner areas 24. The portion 22 is, during normal turning conditions, not intended to be a rake face or contact face for the chip during its formation. Each said ridge 23 extends in a direction mainly perpendicularly towards the side surfaces 13-16 and is intended to upset the chips during working. Each corner portion 24 is intended, in a passive situation, to be in abutment with a bottom support and, in an active situation, like the ridges 23 contributes to chip upsetting. The ridges and the corner portions could alternatively be located in the same plane. The ridge 23 and the corner portion 24 are connected to the cutting edges 17 directly or indirectly via a negative bevelled face 25 which extends around the insert. The corner portions 24 are symmetrically arranged in relation to the bisector B of the adjacent cutting corner 21. The extension of the ridges 23, in the length direction of adjacent cutting edge 17-20, is limited by a number of mainly spherically concave depressions 26. The lowest point of each recess in its thickness direction t is located lower than the adjacent cutting edge and ridge. The lowest points of the recesses are arranged along a line L which is located at a substantially constant distance from the adjacent cutting edge. Each recess could alternatively have a concave shape in only one direction that is parallel with or perpendicualar to the cutting edge. The extension of the ridges perpendicularly towards the adjacent cutting edge is limited by their intersection lines with bevelled face 25 or cutting edge 17-20 and the portion 22. The depressions 26 are designed such that the distance a between adjacent ridges decreases from the cutting corner 21 towards the middle portion of the cutting edge. This is accomplished by providing a depression 26A at the middle of the cutting edge 17 (Fig. 8) having a smaller width a in the area of the ridge 25 than compared with the adjacent depressions 26B. The width of depressions 26B is smaller than the width of depressions 26C when measured in the length direction of the cutting edge. The corresponding relations apply to the depressions 26D and 26E. The length of said depressions 26, however, when measured in the lateral direction is identical for all. Each of said recesses is surrounded by a mainly curved limitation line 27. This limitation line 27 represents the intersection line between the depression 26 and the bevelled face 25, the ridge 23 and the portion 22. The line 27 could alternatively include only straight portions or be a combination of straight and curved portions. The depressions 26 are arranged at a constant distance x from the edge 17. The distance x is about half the width of bevelled face 25 in plane projection. The width of said bevelled face, in projection, is between 0.05 and 2 mm. Each cutting corner 21 is provided with a depression 28 arranged symmetrically around the bisector B . This depression intersects with bevelled face 25 and has an extension inwards from said face and occupies about half of the length of the corner portion 24 along the bisector. The largest width of said depression in a direction perpendicular to said bisector is larger than the width a of the depression 26E. Fig. 9 illustrates the insert 10 while engaged in longitudinal turning with a workpiece 29 whereas the tool holder carrying the insert is not illustrated. When the chip is formed at the cutting edge some portions thereof will at least partially be forced downwards into the depressions 26 whereas intervening chip portions will be subject of chip upsetting when abutting the ridges 23. Therefore a corrugated chip 30 is obtained which easily can be broken and is easily manageable and non-dangerous for the workpiece and the tool. The chip is then allowed to move deeper into the chip former close to the active cutting corner than in the chip former located at a distance from said corner, and the radius of curvature of the chip therefore becomes smallest at the corner such that the chip obtains a conical shape. Thanks to this conical shape said chip will in the corner leave the generated surface of the workpiece very soon thus avoiding occurrence of scratches on the workpiece. Figs. 10 and 11 illustrate an alternative embodiment of an insert 10′ of this invention. With this embodiment the ridges 23′ are arranged along intersection lines between adjacent depression 26′. Each said ridge 23′ is arranged approximately perpendicularly in relation to the adjacent cutting edge 17′. The ridge 23′ is limited by substantially triangular end portions 31 of which the end portion oriented towards the cutting edge is intended to act as a combined support and chip face. The lowest points of said recesses are arranged along a curve or a line L which is provided at an approximately constant distance from the adjacent cutting edge. In similarity with the insert described above there is provided a decreasing distance between adjacent ridges seen in a direction towards the middle of the insert. Compared with the insert there is a larger number of depressions and same type of depressions. The insert 10′ can be located on a bottom support along its entire periphery or it can be supported only at the corner areas. Preferably said insert 10′ is provided with a bevelled face 25′ that extends all around the insert, said bevelled face extending at least from the adjacent cutting edge to the depressions 26′. The insert 10′ will in usage produce corrugated or conical chips in similarity with insert 10. Another alternative embodiment of the insert 10″ is illustrated in Figs. 12 and 13. This insert is provided with a number of elongated ridges 23″ which extend in a direction mainly perpendicular from the cutting edge 17″ or bevelled face 25″. These ridges are surrounded by a downwards and inwards inclined, plane or concave surface portion 22″. The ridges along the periphery of the insert or only at the cutting corners extend beyond the cutting edge or the bevelled face when seen in the thickness direction of the insert, thus enabling them to act as support surfaces for the insert when located on a bottom support. In the case of providing supporting surfaces only in the cutting corner regions there is provided a single corner portion 24″ which has a relatively large area. The mutual distances between the ridges decrease from the cutting corner and towards the middle of the cutting edge 17″. The inserts described in the foregoing can be provided with a central aperture for the receipt of a clamping device such as a screw. The invention thus provides an insert for chip cutting machining which in usage forces the chips in a direction away from the insert and the workpiece and which corrugates the chips to thereby ensuring cutting with good chip control.

Claims: Cutting insert for chip forming machining consisting of a body having polygonal basic shape and having a cutting edge (17-20,17′,17″) created at the transition between an upper rake face and a clearance face of the insert (10,10′,10″), said upper rake face comprising a chip former spaced from or directly connected to the cutting edge, whereby said chip former includes a plurality of ridges (23,23′,23″), characterized in that the distance ( a ) between adjacent ridges (23,23′,23″) decreases in a direction towards the middle of the cutting edge (17-20,17′,17″). Cutting insert as defined in claim 1, characterized in that at least a portion of each ridge (23,23′,23″) is provided to be a supporting surface for the insert (10,10′,10″) when locating it against a bottom support. Cutting insert as defined in claim 1 or 2, characterized in that there are surface portions (26,26′,26″) provided on both sides of each ridge (23,23′,23″) in length direction of each adjacent cutting edge (17-20,17′,17″) whereby the lowest point of each said surface portion in direction of thickness ( t ) of the insert is arranged at a lower position than the adjacent cutting edge and ridge. Cutting insert as defined in claim 3, characterized in that the lowest points of said surface portions (26,26′) are oriented along a line (L) which is at an approximately constant distance from the adjacent cutting edge (17-20,17′). Cutting insert as defined in any of the claims 1 - 4, characterized in that the ridges (23,23′) are separated from each other by means of concave depressions (26,26′) which are linearly oriented along the edge whilst provided at an approximately constant distance inside from the adjacent cutting edge and that each said depression is confined by a limitation line (27) which describes an arcuate curve. Cutting insert as defined in any of the claims 1 - 5, characterized in that each ridge (23,23′) is provided as a plane surface intended to act as a combined support and chip face for the insert (10,10′) whereby said plane surface is located next to two adjacent depressions (26,26′), a bevelled face (25,25′) adjacent the cutting edge (17-20,17′) and a downwardly and inwardly inclined surface (22,22′). Cutting insert as defined in claim 6, characterized in that each depression (26,26′) is located next to the bevelled face (25,25′) and that one recess (26A) at the middle of the cutting edge (17-20,17′) is smaller than a depression (26B,26C,26D,26E) arranged at a distance from said middle portion. Cutting insert as defined in ay of the claims 1 - 5, characterized in that each ridge (23′) is arranged along an intersection line between two adjacent depressions (26′) whereby said ridge is oriented mainly perpendicularly from the adjacent cutting edge (17′) and that said ridge has approximately triangularly shaped end portions (31) intended to act as a combined support and chip face. Cutting insert as defined in any of the claims 1 - 5, characterized in that each ridge (23″) in a direction from its adjacent cutting edge (17″) joins a downwards and inwards inclined surface (22″) and that the ridge is, in the length direction of the adjacent cutting edge, surrounded by downwards and inwards inclined plane or concave portions. Cutting insert as defined in any of the claims 1 - 9, characterized in that the insert (10,10′,10″) includes a plurality of corner portions (21) each of which having a recess (28) that is symmetrical in relation to the bisector ( B ) of that corner whereby the limitation line of said recess facing the adjacent cutting edge (17-20,17′,17″) is arranged at a distance from the cutting edge which is shorter than that between the cutting edge and the ridge (23,23′,23″) and that the insert is made of a ceramic material.

Inventors: PETTERSSON, LARS TURE, WIMAN, JOERGEN VIGGO, Wiman, Jörgen Viggo
Applicants: SANDVIK AKTIEBOLAG
Application year: 1989
Main classification: B23B27
IPC codes: B23B27