Prior art Through UK 951 624 is previously known a tool and a cutting insert substantially of the above-captioned type, wherein the tool is provided such that all cutting edges in the active corner portion of the cutting insert comes into engagement with the work piece during the machining operation. This means that all cutting edges in the corner portion are worn simultaneously and therefore for example a tetragonal cutting insert at most can be indexed to 8 positions with new cutting edges. US-A-4,616,962 discloses a milling insert with four cutting edges.

Objects of the invention One object of the present invention is to provide a tool for face milling, wherein at least 16 new cutting edges can be utilized.

Another object of the present invention is to provide a cutting insert for face milling, with many cutting edges which makes utilization economically advantageous.

Still another object of the present invention is to provide a cutting insert according to an alternative embodiment which is developed for bringing the chip to deflect in a direction which entails little contact surface and subsequently a low coefficient of friction between the chip and the cutting insert.

These and other objects have been achieved by a tool and a cutting insert for face milling according to the subsequent claims with reference to the enclosed drawings.

Short description of the drawings

Fig. 1 shows a tetragonal cutting insert according to the present invention in a plane view. Fig. 2 shows the cutting insert in a side view. Fig. 3A shows the cutting insert in a cross-section according to line Ill-Ill in Fig. 1 and Fig. 3B shows an enlarged cross- section of a cutting corner in Fig. 3A. Fig. 4 shows the cutting insert in a cross-section according to line IV-IV in Fig. 1. Fig. 5 shows an alternative embodiment of a tetragonal cutting insert according to the present invention in a plane view. Fig. 6 shows the alternative cutting insert in a side view. Fig. 7 shows the alternative cutting insert in a cross-section according to line VII-VII in Fig. 5. Fig. 8 shows a tool according to the present invention in a side view. Figs. 9 and 10 show magnifications of the tool's active corner for the two alternatives, as seen towards the plane of the active side faces of the cutting insert. Fig. 11 shows an additional embodiment of a cutting insert according to the present invention in a plane view.

Detailed description of the invention With reference to Figs. 1-4 and 9 is shown a cutting insert 11 for face milling according to the present invention. The cutting insert consists of a matrix of sintered, preferably coated, cemented carbide and has a polygonal basic shape, in this case a tetragonal basic shape. The cutting insert may alternatively be pentagonal or hexagonal. The cutting insert 11 comprises two, essentially parallel, side faces 12, 13 as well as them uniting edge surfaces 14A-14D. The side face 13 is identical to the side face 12, and therefore only one side face is described hereinafter. The cutting insert 11 has a negative geometry, i.e. the edge surfaces perpendicularly connect the side faces. However, it is possible within the scope of the invention that the cutting insert has a double positive geometry, i.e. each edge surface forms an acute angle with the connected side face by providing a central circumferential recess in the edge surfaces 1 4A -1 4D. Cutting edges 15, 16 are formed in the area of the side face 1 2 intersection with the edge surface 14. In the cutting corner 17 between two adjacent edge surfaces, for example 14A and 14B, has been provided substantially planar or somewhat cambered bevel surfaces 18A and 18B. The edges which are arranged in

the area of the side face 12 intersection with the respective bevel surface 1 8 around of the cutting corner 1 7 bisector B are called minor cutting edges 16. Said edges will generate the surface on the work piece 40 during the face milling operation by being arranged parallel to the surface of the work piece which shall be generated or arranged perpendicular to the axis of rotation of the milling tool. The remaining edges which are intended to cut the major part of the material in the form of chips are called major cutting edges 1 5. Only one major cutting edge and one minor cutting edge must be in engagement simultaneously and thereby these two edges work in pair. The minor cutting edge 1 6 forms an acute external angle a with the associated major cutting edge 15. The angle a lies in the interval 38° to 420, preferably around 40".

The major cutting edge 1 5 inwardly connects to a chip-upsetting surface or primary bevel 19, Fig. 3B, which constitutes the most peripheral part of the side face 12. The primary bevel is negatively angled and does not extend along the cutting corner 1 7 since the minor cutting edge 1 6 must be as sharp and as easy cutting as possible, but instead a suitable edge radius on the cutting edge 16 is chosen. A first chip forming surface 20 is situated inside the chip-upsetting surface 1 9. A second chip forming surface 21 is situated inside the minor cutting edge in the cutting corner. The second chip forming surface 21, Fig. 4, is shallower than the first chip forming surface 20, for shaping the chips during the face milling operation. An area 22 is provided in the side face 12, symmetrically about the bisector B to further form favorable chips and for best supporting the cutting corner.

In side view is evident that the minor cutting edges 16 are provided in planes parallel with the side faces but somewhat under the associated side face. The minor cutting edge 1 6 connects to the associated major cutting edge 1 5 via a radius R1.

Alternatively the radius R1 can be replaced by a number of plane facets. By the expression "associated major cutting edge and minor cutting edge" is here meant that only these cutting edges cooperate during milling and that they are physically connected to each other possibly via a radius. Connecting minor cutting edges 1 6

form an obtuse inner angle E, which is of the magnitude of 170" and the minor cutting edges are mirror-imaged about the bisector B. Each minor cutting edge connects to a substantially planar bevel surface on the clearance surface.

Adjacent bevel surfaces connect along a line E, which coincides with the plane of the bisector. The major cutting edge 1 5 is concavely curved with a radius R2 with the intention to form a somewhat positive axial angle although the cutting insert has been mounted negative in the milling body. The radius R2 is bigger than the length of the side L of the cutting insert. The biggest distance between the major cutting edge and the plane of the connected side face is at the mid M of the major cutting edge, said distance being smaller than 1 mm but bigger than 0,4 mm.

To be able to use all 16 cutting edge pairs in the most suitable manner the major cutting edge 1 5 should be used not more than to the half of its longitudinal extension, i.e. to the middle of the cutting insert. This means that the cutting depth A should not exceed the half of the length of the side L of the cutting insert, i.e. the cutting depth should maximum be A=L/2 * sin K, where K is the setting angle.

With reference now to Figs. 5-7 an alternative embodiment of a cutting insert lit is shown according to the present invention for face milling. The same details in the alternative embodiment has been given the same number. The cutting insert 11' is changed from the earlier described cutting insert in that it, except for the corner portions of the cutting insert 11', comprises a number of recesses 23' in the chip forming surface 20', which recesses are separate along the associated major cutting edge 15' and extend essentially laterally relative to the associated major cutting edge 15'. The recesses are provided in groups Of seven pieces or the like about the mid line M of the cutting insert. Crests 24' are situated between the recesses 23' in the chip forming surface 20', said crest 24' bridging the recesses 23' in a direction along the associated major cutting edge 15'. The recesses 23' do not extend perpendicularly to the cutting edge 15' but they form an acute angle with a line perpendicular to the

associated cutting edge 15', such as shown in Fig. 5. The angle is in the interval of 5°-55°, preferably in the interval of 10°-20°. A preferred value for the angle is in the magnitude of 15". An advantage with this type of chip former is that a relatively seen little heat is transferred to the cutting insert from the chip and therefore problems which relate to high temperatures in the cutting edge 15', such as plastic deformation and/or diffusional wear, are avoided. This results in limited wear of the cutting edge and subsequently in better tool life also at high temperatures. Such a type of chip forming is more closely described in US-A-5,074,720, which is hereby incorporated in description regarding chip forming.

In Fig. 8 is shown a face milling cutter according to the present invention, including a milling body 30 intended to be rotated in a milling machine. The milling body comprises a number of seats for receiving tetragonal, pentagonal or hexagonal cutting inserts. An adjustment device 31 is provided in order to facilitate fine adjustment of the cutting insert in the cutting insert pocket. The cutting insert is provided to be clamped in a known manner with a clamp after fine adjustment. As is apparent from the figure, the associated major cutting edge 1 5 and minor cutting edge 1 6 are provided at one and the same side of the bisector B and two minor cutting edges connect to each other in or in close proximity of the bisector B. The active minor cutting edge 16 is arranged substantially perpendicular to the axis of rotation CL of the face milling cutter. One minor cutting edge 16A generates the surface of the workpiece while the other the minor cutting edge 1 6B is provided at a distance from the workpiece surface by forming a clearance angle with said surface. The tool has a setting angle K, which is maximum 42". The major cutting edge 1 5 is provided to cut the major part of the material which shall be machined in the form of chips and should therefore be reinforced by means of the chip-upsetting surface 19 while the minor cutting edge 1 6A constitutes a finish cutting edge and should therefore be sharper than the major cutting edge 1 5.

In Figs. 8 and 10 the cutting inserts 11 and 11', respectively, are shown in engagement with the work piece 40. The tool works with a setting angle K, K' of about 40".

Fig. 11 shows a pentagonal cutting insert 11", wherein the setting angle K" is chosen in the interval of 15° to 300, preferably between 20° and 25". The cutting insert 11" has 20 pairs of cutting edges.

Thus the present invention relates to a tool and a cutting insert for face milling wherein at least 16 new cutting edges can be utilized. The cutting insert has at least 8 pairs of cutting edges to be used in one rotational direction and at least 8 pairs of cutting edges to be used in an opposed rotational direction, which makes utilization economically advantageous.

The invention is in no way limited to the above described embodiments. For example the basic shape of the cutting insert may be pentagonal or hexagonal. In addition the recesses 23' may be replaced by projections of similar shapes. Also in other respects the invention can be freely varied within the limits of the appended claims.