Turning insert

Abstract: The invention relates to a turning insert. The insert (10) consists of longitudinally extending surfaces (13,14), end surfaces (15,16), side surfaces (11), a shoulder (17) and a portion (18) provided with a cutting edge (19). The cutting edge (19) is circular and has a diameter which exceeds the thickness of the insert which makes a plurality of turning operations possible, including grooving into unlimited depth. The portion (18) is provided with rake face (25) sloping downwardly and inwardly from the cutting edge, which face is provided with a plurality of concave recesses (23) intersecting each other.

Description: The present invention relates to a turning insert comprising a pair of longitudinally extending surfaces enclosing an acute angle and forming a wedge-shaped insert body, a forward end of said insert arranged at the wider portion of the insert body which carries a cutting edge, a rearward end arranged at the narrower portion of the insert body and a shoulder. The cutting edge has a circular shape and a diameter which exceeds the thickness of the insert. The insert has a chip breaking device radially inside the cutting edge which device has a mainly circular shape. The US patent No. 3.705.447 shows a turning insert which comprises a partly circular cutting edge which connects to straight cutting edges for outwards facing. The connection between the circular portion and the straight portions weakens the insert. Furthermore, the rake face of the insert does not have any chip forming means and therefore the insert achieves a negative geometry. Thus, this type of geometry transfers large forces from the work piece to the holder carrying the insert. One object of the present invention is to shape an insert such that it can perform a plurality of turning operations. Another object is to adapt the insert for good chip control, irrespective of feed direction. Still another object is to provide an insert that cuts with a varying setting angle. These and other objects have been achieved by an insert as defined in claim 1. Embodiments of the claimed insert are described hereinafter in connection with the appended drawings. Fig. 1 shows a top view of an insert according to the invention. Fig. 2 shows a side view of the insert. Fig. 3 shows a perspective view of the insert. Fig. 4 shows a cross-section of the insert according to the line IV-IV in Fig. 1. Figs. 5 and 6 show cross-sections of the insert taken along lines V-V and VI-VI, respectively, in Fig. 3. An insert 10 according to the invention is shown in the figures. It comprises two mainly plane-parallel side surfaces 11,12, two edge surfaces 13,14, two end surfaces 15,16, a shoulder 17 and a portion 18 provided with a cutting edge and a chip forming device 20. The insert 10 shall be secured to a holder body provided with an integral clamping arm. The insert is clamped in a working position by the resilient force with which the arm influences on the insert. The clamping of the insert is described in our EP-A-242343 which is hereby incorporated with the description. One edge surface 13 constitutes a first support surface for the insert against the holder body, which is parallel with the neutral plane P of the machine. The neutral plane is the plane defined by the axial feed direction of the machine and the radial feed direction of the machine. The other edge surface 14 constitutes a second support surface for the insert against the holder body. The edge surface 14 forms an acute angle with the edge surface 13 at the narrower portion of the insert. The edge surface 14 is broken in the vicinity of the middle of the insert whereafter it becomes mainly parallel with the edge surface 13. The edge surface 14 connects to a shoulder 17 whose crest defines the largest height h of the insert above the neutral plane P . The cutting edge 19 is circular and it has a diameter D which is 1 to 75 %, preferably 10 to 40 %, larger than the thickness t of the insert. The cutting edge describes a curve defined by an angle of at least 200°, preferably of at least 220°. The setting angle of the insert will then vary during outwards facing which will give the insert less vibrations. The cutting edge 19 is formed along the intersection line of a clearance face 21 and a list 22. The clearance face 21 is arranged outside the rectangular basic shape which, in top view, is formed by the side surfaces 11, 12 and the end surface 16, see the dotted lines in Fig. 1. The clearance face 21 forms an acute angle α , about 0.1 to 15°, preferably 2 to 12°, with the end surface 16 (Fig. 2) or the side surface 11 or 12 in a section taken along the mid-line M of the insert and along a line perpendicular to the mid-line of the insert, respectively. The list 22 is mainly planarly shaped and it coincides with the neutral plane P. The list is bordered radially inwardly by an array of recess 23, which intersect one another along ridges 24, which extend perpendicularly to the cutting edge 19. Each recess 23 has the shape of a toroid, alternatively it is spherically, elliptically or parabolically concave. The recesses, which are about 20 in number, aim to give the insert a positive rake angle γ about 5 to 30° and to plasticaly deform (corrugate) a chip such that it becomes easier to break. The ridges 24 support the list 22. The recesses 23 are arranged at a downwardly and inwardly, towards the center of the radius of the cutting edge, sloping rake face 25. The rake face 25 which is concave, has a bottom area arranged radially inside the radially innermost border lines of the recesses. The rake face then rises towards a planar central portion 26, which has been arranged above or in level with the cutting edge 19. The shoulder has a chip forming fuction when the chips flow at small feed in the direction of the mid-line M. The chips flow during turning mainly perpendicularly to the cutting edge 19 and therefore the chip forming device 20 is identical all along the cutting edge. At small feed the chips will flow over the recesses and will be formed at the shoulder 17. At large feed the chips will follow along most of the rake face and the recess and will then break against the work piece. Thus, the invention relates to a turning insert through which shape a plurality of turning operations can be realized including parting and grooving into unlimited depth. The insert has a chip forming device which minimizes transfer of the cutting forces from the work piece.

Claims: A turning insert for parting and grooving comprising plane-parallel side surfaces (11, 12) an upper and a lower longitudinally extending surface (13, 14) a cutting portion (18), a front end surface (16) in the front end of the insert, a rear end surface (15) in the rear end of the insert, said side surfaces connecting to said longitudinally extending surfaces and said end surfaces, said cutting portion (18) carrying a cutting edge (19) defined by the intersection of a rake face and a clearance face (21) of the insert, the cutting edge (19) being arched and having a diameter (D) which exceeds the perpendicular distance (t) between the side surfaces (11, 12), wherein a stop means (17) is arranged between the cutting portion (18) and the upper longitudinally extending surface (14), said stop means projecting relative to a plane (P) defined by the cutting edge (19), that the cutting edge (19) has identical curvature along its entire length, the ends of said cutting edge connecting to lines of intersection between the side surfaces (11, 12) and the rake face in front of said stop means (17), and in that the rake face is provided with a chip forming device (20) arranged radially inside the cutting edge which device has a mainly circular shape, wherein the diameter (D) of the cutting edge (19) is 1 to 75% larger than the distance (t) between the side surfaces (11, 12), preferably 10 to 40% larger and in that the cutting edge (19) describes a curve defined by an angle of at least 200 degrees, preferably of at least 220°. A turning insert according to claim 1, characterized in that the chip forming device (20) gives the insert (10) a positive rake angle (γ). A turning insert according to claim 1, characterized in that the plane (P) is parallel with the lower longitudinal surface (13). A turning insert according to claim 1, characterized in that the insert has a list (22) which is directly connected to the cutting edge (19), said list (22) extending radially inside the cutting edge and in that the chip forming device (20) forms the radially inner border line of the list and is constituted by a plurality of concave recesses (23) which generally slope downwardly and inwardly towards the center of the radius of the cutting edge, said recesses being arranged adjacent and intersecting each other and forming ridges (24) which extend perpendicularly to the cutting edge (19). A turning insert according to claim 2, characterized in that the rake angle (γ) is about 5 to 30 degrees. A turning insert according to claim 4, characterized in that the chip forming device (20) comprises a concave circular rake face (25) which has a bottom area and in that the radially inner border lines of the recesses (23) are arranged radially outside said area and in that the rake face (25) rises upwardly and inwardly towards a central planar portion (26) arranged on level with or above the plane of the cutting edge (19). A turning insert according to claim 1, characterized in that is has a clearance face (21) which forms an acute ange (α) with the front end surface (16) of the insert body, said angle being about 0,1 to 15 degrees, preferably 2 to 12 degrees.

Inventors: PETTERSSON LARS, PETTERSSON, LARS
Applicants: SANDVIK AB, SANDVIK AKTIEBOLAG
Application year: 1987
Main classification: B23B27
IPC codes: B23B27