Technical Background The present invention relates to a tool and a cutting insert for milling according to the preambles of the appended independent claims.

At disc milling cutters, the periphery of the milling body is equipped with a number of cutting inserts, every second one of which protrude in relation to one side of the milling body and every second from the opposite side of the milling body. The relative displacement of the cutting inserts is made in order to obtain clearance and in order to obtain grooves having perpendicular bordering surfaces. The bottom surface of the groove is provided by means of the major cutting edges of the cutting inserts while the side surfaces of the groove is provided by means of the minor cutting edges extending substantially perpendicularly to the major cutting edges. Radii between the bottom surface and the side surfaces are obtained by means of more or less rounded cutting corners at a transition between associated pairs of major and minor cutting edges of the cutting insert. The relative displacement requires that the cutting inserts are formed in particular right hand and left hand embodiments in order to guarantee the requisite clearance between the side wall and the portion of the cutting insert following after the minor cutting edge.

Through EP-A-0 873 808 a single sided cutting insert is previously known, which comprises only two, but different, cutting edges, which should not be possible mix-up by the operator. The known cutting insert means bad utilization of the possibilities of the cutting material. In US-A-5,454, 671, another single sided cutting insert is shown.

Objects of the Invention An object of the present invention is to provide a double sided cutting insert for optimal utilization of the edges of the cutting insert.

Another object of the present invention is to provide an easy-cutting double sided cutting insert.

Another object of the present invention is to provide a double sided cutting insert having a good support near the point of action of the cutting forces.

Another object of the present invention is to provide a milling tool that counteracts movements of the cutting insert.

Another object of the present invention is to provide a milling tool and a cutting insert, which avoid negative effects of defects around holes or irregulari- ties in insert pocket or on cutting insert.

Another object of the present invention is to provide a milling tool, the lat- eral support of which does not damage the cutting edge laterally.

Another object of the present invention is to provide a milling tool, which is simple to manufacture to narrow tolerances.

Another object of the present invention is to provide a milling tool having an insert pocket, the geometry of which permits that it accepts varying corner shapes such as radius, chamfer, wiper or another shape.

Another object of the present invention is to provide a milling tool having an insert pocket, the geometry of which permits that overhang of the cutting insert may be held at a minimum.

Brief Description of the Drawings Fig. 1A shows a cutting insert according to the present invention in planar view. Fig. 1 B shows the cutting insert in side view. Fig. 1 C shows the cutting insert in cross-section according to the line ttt-ttt in Fig. 1A. Fig. 1D shows the cutting insert in cross-section according to the line IV-IV in Fig. 1A. Fig. 1 E and 1 F shows the cutting insert in two perspective views. Fig. 1 G shows the cutting insert in an enlarged cross-section according to the line iii-fit in Fig. 1A. Fig. 1 H shows the cutting insert in an enlarged cross-section according to the line V-V in Fig. 1A. Fig. 2A shows a milling tool according to the present invention in an

axial view from one of the sides, only four cutting parts being shown. Fig. 2B shows the milling tool in top view. Fig. 2C shows a cross-section according to the line VI-VI in Fig. 2B. Fig. 2D shows a part of the milling tool in perspective view.

Fig. 2E shows a part of the milling tool according to Fig. 2D partly in an exploded view. Fig. 2F shows parts of the milling tool in an exploded view. Fig. 2G, 2H and 21 shows a cassette in different views.

Detailed Description of the Invention Reference being made to Figs. 1A-1 H, a cutting insert 11 for disc milling according to the present invention is shown. The cutting insert consists of a plate of sintered, preferably coated, cemented carbide and has a polygonal basic shape, in this case a rectangular basic shape in the view according to Fig. 1A.

The cutting insert 11 comprises two, substantially parallel, side surfaces 12,13 as well as edge surfaces 14A-14D uniting them. The side surface 13 is identical to the side surface 12 if the cutting insert is rotated 180° around the line ttt-ttt in Fig. 1A, and therefore substantially only one of the side surfaces is disclosed hereinafter. The cutting insert 11 has a negative basic shape in that the side surfaces 12 and 13 have equally large areas.

The edge surfaces or the negative sides 14A and 14B are intended to constitute flank surfaces for associated major cutting edge 15A and 15B, respectively. The negative sides 14A and 14B provide negative clearances and are substantially parallel with each other. The major cutting edge 15A, 15B is arranged to cut the majority of the material that should be removed in the form of chips. The edge surfaces 14A and 14B are substantially parallel with each other and form a substantially right angle to an imaginary extension P of someone of the planes for the side surfaces 12 and 13.

In the view according to Fig. 1 D, the cutting insert substantially forms an equilateral parallelogram, the angles of which are not right. The edge surfaces or the positive sides or parts 14C and 14D provide positive clearances and are

substantially parallel with each other. The parts 14C and 14D form an acute angle a relative to the associated side surface 12 and 13, respectively, during milling. The angle a is less than 90° and is preferably chosen within the interval of 70-85°.

The major cutting edge 15A, 15B is substantially straight as well as parallel with the plane P of the side surface 12. The two ends 16A, 16B of the major cut- ting edge is terminated in roundings in the cutting corners 17A, 17B. Diametri- cally opposite cutting corners 17B on different sides of the cutting insert 11 are defined by a bisector B, which bisector substantially intersects the centre C of an insert hole 18. The insert hole 18 is through-going and the smallest diameter thereof is at in the midst of the cutting insert in the view according to Fig. 1 C.

The insert hole is intended to receive a clamping element 42. Alternatively, the insert hole may consist of two opposite blind holes. The distance X (Fig. 1 C) between the diametrically opposite cutting corners 17B on different sides of the cutting insert constitutes the longest dimension of the cutting insert. The distance X exists at only two positions. The end 16B, which constitutes a cutting nose radius, has a larger radius of curvature than the end 16A. The end 16A is most often not intended to cut in the workpiece. The major cutting edges 15A, 15B are arranged at the intersection between the side surface 12 and the edge surfaces 14A and 14B. The corresponding major cutting edges 15A, 15B are arranged at the intersection between the side surface 13 and the edge surfaces 14A and 14B. Each major cutting edge 15A, 15B connects via the nose radius 16B to a minor cutting edge 21A, 21 B. Only a major cutting edge and a minor cutting edge should be in engagement simultaneously, and thereby these two edges operate in pair.

Two opposite edge surfaces 14C and 14D comprise first recesses 19A and 19B, respectively. Each bottom 20A, 20B of a recess is substantially perpen- dicular to the plane P. Each recess 19A, 19B intersects only one side surface 13,12 in an area Z between two minor cutting edges 22A, 22B. Each recess has

an increasing depth d in the direction of the side surface that the recess intersects. The recess limits the extension of the minor cutting edges 21 A, 21 B in the direction substantially perpendicularly to the major cutting edges 15A, 15B.

Each side surface 12,13 has an elongate second recess 23, which extends on both sides of the insert hole 18. The recess 23 removes negative effects of defects around holes or irregularities in the insert pocket or on the cutting insert by parting the active support surfaces 12A, 13A. The recess 23 connects to a planar surface 12A, 13A, which should constitute support or contact surface against the base surface 45 of the insert pocket, see Fig. 2H.

The length of the recess 23, parallel with the major cutting edge, is by virtue of the shape of the cutting insert different on both sides of the insert hole 18. Each planar surface 12A, 13A connects to a upwardly and outwardly rising rake face 24, which connects to the associated cutting edges, for instance 15A, 16B and 21A. Thus, the side surface 12,13 of the cutting insert comprises a positive, concave rake face.

In Figs. 2A-2F, a disc milling tool 10 according to the present invention is shown, comprising a milling body 30 intended to be rotated in a milling machine, the milling body comprising a plurality of pockets in order to receive cutting inserts 11 according to the present invention. The cutting inserts in said figures are schematically illustrated. The milling body 30 is plate-shaped and is intended to rotate around the centre axis CL in the direction R. The milling body 30 has a central hub portion 31 and a plurality of peripheral recesses 32, which usually are substantially equidistantly arranged around the periphery of the milling body 30. In each recess 32, an insert-carrying cassette 34 is received, wherein the cassette may comprise the entire width of the milling body or possibly be some- what wider than the same. The rear side surface 35 of the cassette in the direc- tion of rotation is substantially axially grooved and is brought in engagement with a correspondingly grooved surface 36 in the recess 32. The grooved surface 36

comprises in the centre thereof an axially extending, threaded recess 33. The recess 33 is a cylindrical hole having open ends and opens in the direction of rotation R. The side surface 35 comprises a partly cylindrical, non-threaded recess or cavity 44 intended to receive an outer part of the screw 29 after the screw has been screwn into the threaded hole 33 in the milling body, whereby the cassette may be fine-adjusted variably axially. When the position of the cassette has been determined, it is clamped by fastening a wedge 37 by means of, for instance, a differential screw 38, the two threaded end portions of which are threaded in separate directions. The screw is threaded down into a threaded hole 39 in the recess 32. In order to give certain stability during assembly and fine adjusting, a compression spring 40A having an abutment element 40B is arranged in a hole in the cassette 34 in order to press against the wedge 37. An insert pocket 41 is formed in the cassette at the radially outer portion thereof being in front in the direction of rotation, in which pocket a cutting insert 11 is mounted by means of a locking screw 42, which is threaded into a threaded hole 43 in the cassette.

The insert pocket 41 comprises a base surface or a tangential support sur- face 45, a first shoulder or a radial support surface 46 and a second shoulder or an axial support surface 47. Said surfaces are mutually substantially perpen- dicular in order to support the cutting insert 11 as well as comprise clearances in order to avoid contact with the cutting edges 15A, 15B, 21 A, 21 B. The second shoulder 47 is substantially perpendicular to the centre line CL as well as arranged on a projection 48, which is arranged at a distance Y from the first shoulder 46, in order to fit together with the recesses 19A, 19B of the cutting insert. The width of the projection is somewhat smaller than the width for the area Z, Fig. 1 B, in order to ensure that the shoulder 47 abuts against the bottom surface 20A, 20B at assembly but preferably not against the clearance of the minor cutting edge.

The disc milling cutter 10 has two types of cassettes which substantially differ in one regard, viz. by the fact that the projection 48 on every second cassette is arranged to the left of centre plane M of the disc milling cutter, see Fig. 2B, i. e. also to the left of the centre plane of the cassette, while the other cassettes are arranged to the right of the centre plane of the disc milling cutter, i. e. also to the right of the centre plane of the cassette. Each projection 48 is arranged so that it trails a cutting insert leading in the direction of rotation without coming into contact with the workpiece. As is seen foremost in Fig. 2B, the cutting insert should be mounted such that the same generally leans outwardly, corresponding to the angle a, in relation to the centre line M.

The cutting insert is, for instance, mounted in the following way. The cutting insert 11 is pressed against the insert pocket 41 so that, for instance, the side surface 13 abuts against the base surface 45 of the insert pocket and, for instance, the recess 19A receives the projection 48, the screw 42 being inserted through the hole 18 of the cutting insert and into the threaded hole 43. At tight- ening of the screw, the passive flank surface 14A of the cutting insert will be forced additionally against the first shoulder 46 and the bottom surface 19A additionally against the second shoulder 47.

Thus, the cassettes 34 are adjusted in the milling body 30 such that every second cutting insert protrudes in relation to one side of the milling body and every second cutting insert from the opposite side of the milling body. The cas- sette is arranged to be clamped in a known way with clamp after fine adjusting.

Thus, the present invention relates to a tool and a cutting insert for milling, the double sided cutting insert optimally utilizing the edges of the cutting insert, which makes the utilization economically advantageous, the double sided cutting insert being easy-cutting because the same has a concave rake face, the double sided cutting insert having recesses in the centre thereof in order to secure the abutment of the cutting insert near the point of action of the cutting forces, the milling tool having a construction which counteracts that the cutting insert

moves, the milling tool avoiding negative effects of defects around holes or irregularities in insert pocket or on cutting insert, the lateral supports on negative side being entirely independent of the cutting edge, the milling tool being simple to manufacture to narrow tolerances, the geometry of the insert pocket accepting varying corner shapes such as radius, chamfer, wiper or another shape, the geometry of the insert pocket being such that the overhang of the cutting insert may be held at a minimum.

The invention is in no way limited to the above-described embodiments. It is fully feasible to form the insert pocket directly in the milling body and thereby avoid the cassettes and the details belonging therewith. The rake face, e. g., may be formed with projections or recesses. The last-mentioned types of chip- formers transfer relatively little heat to the cutting insert from the chip and thereby the problem is avoided which relates to too high temperatures in the cut- ting edge, such as plastic deformation and/or diffusion wear. This results in small wear of the cutting edge and consequently better service life also at high tem- peratures. The invention is applicable to other machining types, such as, for instance, end milling, face milling, copying milling, ramp milling, etc. Also in other respects, the invention may freely be varied within the scope of the appended claims.