Cutting insert and cutting tool for chip removing machining

Abstract: An insert (10) for a milling cutter has a chip face (11) and a bottom face (12) which are interconnected by side surfaces. The intersection of side surfaces (14-17) with the chip face forms four cutting edges (12A-12D). Each side surface is beveled at its intersection with a cutting edge to form a planar clearance face, the width of which increases toward one of the cutting corners. Each cutting edge includes a main edge portion (17′), a corner edge portion (17″′), and a secondary edge portion (17″). Each secondary edge portion (17″) extends inwardly from an associated secondary edge at an angle no greater than four degrees. At each corner, a secondary edge portion of one cutting edge forms an actual angle with a main edge portion of another cutting edge greater than ninety degrees. The insert is mounted at a negative radial rake and a positive axial rake such that such actual angle presents to a workpiece an effective angle of ninety degrees to cut a ninety degree shoulder in the workpiece.

Description: The present invention relates to an indexable cutting insert for chip cutting machining comprising a body of generally polygonal shape having an upper chip face, an opposite planar bottom face and side surfaces therebetween intersecting the upper chip face to define main cutting edges therewith. A prior art insert of the afore-mentioned type to be mounted in milling cutters of radial negative and axially positive cutting angle is disclosed for instance in Swedish Patent Publication No. 419,834, corresponding to U.S. Patent No. 3,955,259. When milling with such inserts is carried out, however, the chip formation has not always been satisfactory under certain conditions. Also, with such milling cutters the desired cutting depth has not been achieved, especially with 90° shoulder mills, due to the fact that the required large positive chip angle could not be used with such inserts having four main cutting edges. It is an object of the present invention to provide an indexable cutting insert that enables 90° shoulder milling operations to be carried out with a positive chip angle. A further object is to provide such an insert which has four indexable cutting edges. It is another object of the invention to provide an insert that reduces the energy needed for its engagement with a workpiece. It is yet another object of the invention to provide an insert whose lifetime can be maximized. These objects are achieved with a cutting insert having the features of claim 1. In EP-A-392 729 representing the closest prior art a cutting insert is disclosed according to the precharacterising part of claim 1 which comprises a clearance face between two adjacent corners and has a width extending in a direction transversely of the adjacent cutting edge, this width being largest adjacent one of the two cutting corners and decreasing toward the other of the two corners. However, this cutting insert has no protruding ribs on its upper chip face. Moreover, it has only two useful cutting edges, instead of four. According to the invention, preferrably the wider end of the clearance face extends around one of the corners and is smoothly rounded at such corner. The bottom face is preferrably polygonal and angularly displaced relative to the polygonal chip face as the insert is viewed in plan. The cutting edges preferably include main edge portions, corner edge portions, and secondary edge portions. Each secondary edge portion interconnects a main edge portion with a corner edge portion. The main edge portion is inclined inwardly relative to a respective secondary edge portion to form an acute angle therewith. That angle is no greater than about 4°. The insert has four corners, each adjoining a secondary edge portion and a main edge portion. A secondary edge portion located on one side of a corner of the insert forms an actual angle with a main edge portion located on an opposite side of the corner, which angle is greater than ninety degrees. The insert is mounted in a cutter body at a negative radial rake angle and a positive axial rake angle such that the main and secondary edge portions located at a respective corner form an effective angle of ninety degrees with one another as seen by a workpiece, in order to cut a ninety degree shoulder in the workpiece. The objects and advantages of the invention will become apparent from the following detailed description of a preferred embodiment thereof in connection with the accompanying drawings in which like numerals designate like elements, and in which: FIG. 1 is a plan view of an insert according to the invention; FIG. 2 is a cross-sectional view taken along the line 2-2 in FIG. 1; FIG. 2A is an enlarged fragmentary view of an insert cutting through a workpiece; FIG. 3 is a perspective view of the insert shown in FIG. 1; FIG. 4 is an end view of a shoulder milling cutter equipped with inserts as shown in FIGS. 1-3; FIG. 5 is a side view of the milling cutter shown in FIG. 4; The insert shown in FIGS. 1-5 is an indexable polygonal insert 10 of square shape. It is to be understood that other polygonal shapes can be used within the scope of this invention. The insert 10 comprises an upper chip face 11, an opposite planar bottom face 12 bordered by edges 12A, 12B, 12C, 12D, and four identical side surfaces S intersecting the upper and bottom surfaces to form cutting edges E. Two of the side surfaces extending to a cutting corner 13 are designated as surfaces 14 and 15 in the drawings, and those two surfaces form two cutting edges 16 and 17, respectively (see FIG. 3). The insert has a positive geometry which means that the side surfaces intersect the bottom surface 12 at obtuse angles X while intersecting an upper plane P₂ of the upper face 11 at an acute angle Y (see FIG. 2). A central aperture 18 is provided which extends through both of the upper and bottom faces 11 and 12 and is oriented perpendicularly to the bottom face 12. The central aperture is intended for the receipt of a suitable fastener such as a screw. The bottom face 12 has a polygonal shape, which is angularly displaced relative to the polygonal shape of the upper face 11 about the axis of the hole 18, i.e., as viewed in plan (FIG. 1). Each cutting edge E includes a main edge portion, a corner edge portion, and a secondary edge portion interconnecting the main and corner cutting edge portions. Thus, for example, the cutting edge 17 includes a main cutting edge portion 17′, a secondary edge portion 17″, and a corner edge portion. The cutting edge 16 includes similar portions 16′, 16″. The main edge portion 17′ extends slightly inwardly from the associated secondary edge portion 17″ (i.e., toward the center of the insert) at a very slight angle G (see FIG. 1) which is in the range of 0.5 to 4.0°. Therefore, for example, in the case of an angle G of 4.0°, the actual angle I (see Fig. 1) formed between the secondary edge portion 17″ located on one side of the corner 13 and the main edge portion 1G′ located on the opposite side of the corner 13 is 94°. The secondary edge portion 17″ extends into the smoothly rounded corner cutting edge portion. Instead of being smoothly rounded, the corner edge portion could be constituted by a number of small facets. Each edge 12A-D of the bottom face 12 extends parallel with a respective secondary cutting edge 17″, i.e., edge 12A is parallel to secondary edge portion 17″ (see FIG. 1). Accordingly, the secondary edge portion will generate the surface WS of the workpiece with which the insert is in engagement (see FIG. 2A). The edge 12A forms an acute angle with the main cutting edge 17′ (as viewed in plan (FIG. 1 ). The insert 10 is, along a major portion of its side surface S, provided with a bevel which forms a planar clearance face 20. The clearance face 20 is situated between two respective corners 3 and has a width dimension extending perpendicularly relative to the respective cutting edge. The width increases progressively towards one cutting corner 13 and extends smoothly around such cutting corner. The clearance face 20 is oriented in a plane that extends perpendicularly to the plane P₂, while intersecting with the rest of edge surface S at an obtuse angle L (see FIG. 2). At the corner 13, the clearance face 20 extends into a convexly rounded surface 21 having a radius R which then extends to the adjacent side surface S to form therewith an intersection line. For example, the clearance face 20 of side surface 14 extends into a convexly rounded surface 21 at the corner 13, and then extends to the adjacent side surface 15 to form therewith an intersection line 22. The intersection line 22 is oriented obliquely in relation to the adjacent upper cutting edge 17. The clearance face 20 extends to an upper strengthening land 23. The land 23 has a maximum width at the cutting corner 13. This can be achieved by a land which is of constant width except at the corner where it expands, or by a land of continuously increasing width as shown. The land 23 is located in the same plane as four raised surface portions 24, 25, 26, 27, which are raised from inner portions of the upper surface 11. Each of these raised surface portions 24-27 extends frog an edge towards the upper end of the central aperture 18 and is symmetric relative to the respective corner 13 in that it is located at some distance from a bisector B of the corner. More specifically, each such raised portion 24 forms an angle K with the bisector B (see FIG. 3), the angle preferably being 0-20°. Each raised surface portion 24-27 has a constant width W′ (see FIG. 1) although the width could vary under certain conditions. The surface area 11A located between two adjacent raised surface portions 24 and 27 is a recess which is concave in cross-section. A chip angle γ is thus provided between the surface 11 close to cutting edge 16 and a normal N to the plane P₂ (see FIG. 2), which is preferably in the range of 60-85°. Close to the insert's center the raised surface portions 24-27 extend into concave surface portions 24A-27A which then extend to a cylindrical upper end of the aperture 18. Each recessed surface area 11A extends from cutting edge 16 at an increasing depth which at most amounts to H and then extends inwards at a decreasing depth. The decreasing depth is smallest close to the central aperture 18 as shown in FIG. 2. The maximum depth H of each recessed surface area 11A occurs along a midplane 2-2 of the inserts, and that depth could be of the same size as the width of clearance face 20 taken in the same cross-section. However, the size of depth H could also be different than the width of the face 20. Further, the inner intersection line 28 between the concave surface portions 24A-27A, and the recessed surfaces 11A are in the shape of a wave-shaped line, as best appears from FIG. 1. This wave-shaped line 28 then extends to a straight line 29 which is the inner intersection of the raised surface portion 27. Thereafter, the line 29 intersects with another adjacent wave-shaped line 30, which provided the inner intersection line of recessed surface area 11B. The insert is intended to be radially oriented in a milling cutter body 19 (see FIGS. 4-5) such that the upper face 11 serves as a chip face and the beveled portion of the side surface S is a clearance face. When the insert cuts through a workpiece in a directicn of feed F during a milling operation, the secondary cutting edge 17″ is oriented parallel to the direction of feed and thus also is parallel to the plane P₁ of the cut being made in the workpiece (see FIG. 2A). The secondary edge portion 17″ thus generated the final surface WS in the workpiece along plane P₁. Furthermore, it is desired that the shoulder being cut by the insert be a ninety-degree shoulder, i.e., that the surface WS′ shown in Fig. 2A be oriented at ninety degrees relative to the surface WS. In order to be able to cut such a ninety-degree shoulder by the insert 10 which has a real angle I greater than ninety degrees, the insert is mounted in the milling cutter in such fashion that the effective angle I′ which is "seen" by the workpiece during a milling operation is ninety degrees. This is achieved by orienting the insert 10 at a negative radial angle α (see FIG. 4) and a positive axial angle β in the cuter body 1. Accordingly, the effective angle I′ seen by the workpiece (see FIG. 2A) can be made to be ninety degrees. Thus, in FIG. 2A, as the insert 10 moves toward the viewer during its rotation, the point Q₁ is located farther from the viewer than is the point Q₂, and the point Q₃ is located farther from the viewer than are both of points Q₁ and Q₂ (see also FIG. 5). The entering angle of the insert is from 90-95 degrees, preferably 90-92°. Since the main edge portion 16' extends at an angle relative to the secondary edge 16'', it is possible to provide the insert with four identical cutting corners capable of cutting a ninety-degree shoulder angle I'.

Claims: A cutting insert for chip removing machining of metal workpieces, comprising a body having a polygonal upper chip face (11), a substantially planar bottom face (12), and side surfaces (14, 15) intersecting one another to form corners of said insert and intersecting said chip face and said bottom face, cutting edges (16, 17) being formed by the intersection of said chip face with respective side surfaces, a lower portion of each side surface extending upwardly and outwardly from said bottom face, an upper portion (20) of each side surface being beveled to form a planar clearance face which intersects a respective cutting edge, each clearance face (20) being disposed between two adjacent corners and having a width extending in a direction transversely of said cutting edge, said width being largest adjacent one of said two corners and decreasing toward the other of said two corners, said insert including a strengthening land (23) extending inwardly from said cutting edge (16, 17), a central portion of said chip face (11) is recessed toward said bottom face (12), said chip face including descending walls extending downwardly from said lands to said recessed central portion, characterized in that said descending walls being separated from one another by raised ribs (24-27), said ribs being situated adjacent respective corners and including upper surfaces lying in a common plane oriented parallel to said bottom face (12), whereby each raised rib (24-27) is located at some distance from the bisector of the corner. A cutting insert according to claim 1, wherein said strengthening land (23) lies in a plane, each of said clearance faces (20) forming a substantially ninety degree angle with said plane. A cutting insert according to claim 1, wherein said bottom face (12) is polygonal and being angularly displaced relative to said polygonal chip face as said insert is viewed in plan. A cutting insert according to claim 1, wherein said cutting edges (16, 17) include main edge portions (16', 17'), corner edge portions, and secondary edge portions (16'', 17''), each secondary edge portion interconnecting a main edge portion with a corner edge portion, said main edge portion being inclined inwardly relative to a respective secondary edge portion by a slight angle as said chip face is viewed in plan. A cutting insert according to claim 4, wherein said angle is no greater than four degrees. A cutting insert according to claim 4, wherein a secondary edge portion (16'', 17'') located on one side of a corner forms an angle greater than ninety degrees with a main edge portion located on the other side of said corner. A cutting insert according to claim 4, wherein each secondary edge portion is oriented parallel to a respective edge of said bottom face. A cutting insert according to claim 4, wherein said insert has four said corners each adjoining a said secondary edge portion and a main edge portion. A cutting insert according to claim 1, wherein said land (23) has a maximum width at said corners. A cutting insert according to claim 1, wherein each of said ribs (24-27) forms an acute angle with a respective corner bisector, said angle being no greater than twenty degrees.

Inventors: PANTZAR GOERAN, PANTZAR, GOERAN, Pantzar, Göran
Applicants: SANDVIK AB, SANDVIK AKTIEBOLAG
Application year: 1991
Main classification: B23C5
IPC codes: B23C5