INDEXABLE CUTTING INSERT

Abstract: The invention relates to an indexable cutting insert for recessing. The insert (10) has a triangular basic shape and comprises three cutting edges. Each cutting edge is arranged at a projection (16) which at least partly is asymmetrically arranged relative to a line parallel with the working direction (I) of the insert. The insert has a good accessibility at work pieces having narrow spaces.

Description: The present invention relates to an indexable cutting insert according to the precharacterizing portion of claim 1, see DE-B-1 223 230. Hitherto known triangular and indexable cutting inserts for recessing have configurations which require a lot of hard material. Hard material is expensive and therefore it is economically advantageous to reduce the amount thereof in each insert. The configuration of the known inserts demand holders which have a special pocket for each insert size. Furthermore, the accessibility of the known inserts into narrow spaces is very limited. A cutting insert of indexable type intended for recessing operations is described in EP-A-0 144 073. The insert has a projection that at least partly has an assymetric shape. This insert geometry, however, is not able to be used in standard type triangular seatings in a toolholder. Also, this insert consists of a relatively bulky central body portion from which only two projections are extending. This insert geometry will therefore require a lot of expensive hard material and it will also be necessary to use non-standardized types of insert-holders for carrying such insert. Another cutting insert of indexable type is disclosed in EP-A-0 162 029. With this three-cornered insert standard type insert-holders can be used. This insert, however, is only tailored for longitudinal turning and copy-turning operations because of its symmetrical design. With such an insert it would not be possible to perform unobstructed penetration into a workpiece during a recessing operation. An object of the present invention is to provide an indexable insert such that its configuration demands a reduced amount of hard material. Another object is to shape the insert such that it fits into a standard type holder mainly regardless of the dimension of the cutting edge. Another object is to provide an indexable insert with three cutting edges. Further another object is to shape the insert such to get better accessibility during machining of work pieces having flanges. These objects are achieved by providing the known insert with the features defined in the characterizing portion of claim 1. The invention will be more closely described hereinafter in connection with the appended drawings. Fig. 1 shows a cutting insert for recessing according to the invention, in a top view. Fig. 2 shows the cutting insert in a side view. Fig. 3 shows a cutting corner of the insert in a top view. Fig. 4 shows a cross-section of the cutting corner according to the line IV-IV in Fig. 3. Fig. 5 shows a part of a tool, in a top view, for recessing comprising a cutting insert according to the invention. Figs. 1 to 4 show an indexable cutting insert 10 for recessing. The insert 10 has a triangular basic shape and comprises an upper face 11 and a lower face 12 and edge surfaces 13,14,15 connecting them. The faces 11 and 12 are mainly parallel. The edge surfaces 13-15 connect the faces mainly perpendicularly. The insert is provided with a central aperture 29 which extends mainly perpendicularly to the faces 11 and 12. Each edge surface, 13 for example, consists of two mutually convexly broken planar or concave portions 13a, 13b, a portion 13a of which is provided to be a support surface for the insert against a pocket. The portion 13b is provided to avoid contact with the work piece during the recessing operaion. The portion 13a constitutes a leg of an imaginary triangle, defined by a circle C inscribed around the centre of the insert 10. The portion 13b forms a chord within the circle C. The insert has three identical cutting corners and only one corner is described hereinafter. A projection 16 is arranged at the cutting corner which connects the portions 13b and 14a. The projection carries a mainly straight cutting edge 17 which is mainly parallel with the portion 13b. The cutting edge 17 has ends which are connected to edges 18, 19 which converge in a direction inwardly from the cutting edge. The cutting edge 17 is mainly perpendicular to the working direction denoted by I. The edges 18, 19 form an acute angle α with each other within the interval 1 to 10 degrees, preferably 3 to 5 degrees. The edge 18 keeps its direction until it connects to the portion 13b, whereas the edge 19 connects to the portion 14a via a mainly straight edge 20 which forms obtuse internal angles β₁ and β₂ with the edge 19 resp the portion 14a. The angle β₁ is 130 to 150 degrees and the angle β₂ is 210 to 230 degrees. The edge 18 and the edge 20 form an acute angle γ with each other which is 30 to 50 degrees. The surfaces below the edges 18 and 19 have clearance angles about 1 to 11 degrees. The surface 21 below the cutting edge 17 may also have this clearance angle. A rake face 22 slopes inwardly and downwardly from the cutting edge 17 and forms an acute angle with the surface 21. An inwardly and upwardly climbing rear surface 23 connects to the rake face via a curved surface or bottom 24 whose radius is about 0.5 mm. The bottom 24 extends mainly parallel with the cutting edge 17 and extends between the edges 18, 19. The rear surface 23 also connects to the upper face 11 of the insert. Alternatively the edge 20 can be concave or convex. In Fig. 1 is shown a hatched area at the edge surface 15 which area illustrates the amount of hard material which is saved with the insert according to the present invention compared to known recessing inserts. Fig. 5 shows a part of a recessing tool in engagement with a partly sectioned round work piece 25. The tool comprises a holder 26 having a pocket 27, a screw 28 and an insert 10 according to the invention. The insert 10 is secured within the pocket by means of the screw 28, which engages in a threaded hole in the holder. The active cutting edge of the insert 10 has machined four grooves in the work piece. The work piece has an annular flange 30 which would counteract the formation of the axially innermost groove if a conventional insert be used. As the insert according to the invention has the above mentioned shape the innermost groove may be formed without problems. The passive projections are at least partly received by recesses in the holder 26. The working direction or feed direction of the insert is illustrated by the arrow I around which the edges of the projection extend such that the outer part of the projection diverge symmetrically whereas the edges at the inner part of the projection diverge asymmetrically around the working direction in direction from the insert. Thus, the invention relates to an indexable cutting insert for recessing. The shape of the insert gives a good accessibility at narrow spaces and saves hard material. Furthermore, standard type holders can be used for the indexable insert.

Claims: A three-cornered indexable cutting insert for recessing whose basic shape is triangular comprising an upper face (11), a lower face (12), mainly parallel thereto and edge surfaces (13, 14, 15) joining them, each cutting corner of said cutting insert being provided with a projection (16) extending outwardly away from said edge surfaces which carries a cutting edge (17) extending mainly perpendicular to the working direction (I) of the cutting insert, said projections including main cutting edges, the ends of cutting edge connecting to a first edge (18) and a second edge (19) whereby each projection is arranged at least partly outside a triangle defined by an imaginary circle that touches the edge surfaces of the insert, characterized in that a) the edges of the projection which connect to the cutting edge diverge in said working direction such that the projection at least partly has an asymmetrical shape relative to the working direction, b) said first and second edges (18, 19), seen from the main cutting edge (17), converging symmetrically relative to a line parallel to the working direction, c) the second edge (19) connects to a third edge (20) forming a first obtuse angle (β₁) such that the first edge and the third edge converge asymmetrically relative to said line in a direction towards the insert, and d) the third edge (20) connects to a portion (14a) of the edge surface (14) forming a second obtuse angle (β₂), said second obtuse angle (β₂) being larger than said first obtuse angle (β₁). An indexable cutting insert according to claim 1, characterized in that the edge surfaces (13-15) of the insert (10) are convexly broken, a first portion (13a, 14a, 15a) of each said edge surface touching an imaginary circle (C) inscribed around the centre of the insert whereas a second portion (13b, 14b, 15b) of each said edge surface forming a chord within said circle, said first portion being provided to be an upstanding support surface for the insert. An indexable cutting insert according to claim 1, characterized in that a rake face (22) is connected to the cutting edge (17) and slopes downwardly and inwardly from the edge towards a rounded bottom (24) from which a portion (23) extends upwardly and inwardly, said portion connecting to the upper face (11) of the cutting insert (10). An indexable cutting insert according to anyone of the preceding claims, characterized in that the cutting insert (10) is provided with a central aperture (29) which extends mainly perpendicularly to the faces (11, 12). An indexable cutting insert according to claim 2, characterized in that the angle β₁ is 130 to 150 degrees and in that the angle β₂ is about 210 to 230 degrees. An indexable cutting insert according to claim 1, characterized in that the first edge (18) and the second edge (19) includes an acute angle of about 1 to 11 degrees and in that the first edge (18) and the third edge (20) includes an acute angle of 30 to 50 degrees.

Inventors: BIRGERSSON, LARS, ERIKSSON, HAKAN, GUSTAFSSON, LARS-ERIK, MUREN, STURE, Murén, Sture
Applicants: SANTRADE LTD.
Application year: 1986
Main classification: B23B27
IPC codes: B23B27