Cutting insert for chipforming machining

Abstract: A cutting insert (10) for chipforming machining of metal workpieces is provided, which comprises top and bottom surfaces and side walls (11) therebetween. A land area (12) extends around the entire insert whilst a descending surface (14a, 14b) joins the inner margin of said land. An elongated rib (17) is provided at each corner region which is terminated at a certain distance from said descending surface. Two distantly provided chipbreaking projections (22) are provided at the forward nose portion of said elongated rib in order to fascilitate chipbreaking at small depths of cut and moderate feed.

Description: The present invention relates to a cutting insert for chipforming machining of workpieces of metal, and in particular to triangular, square, rhombic, rhomboidic or other forms of indexable cutting inserts used with tool-holders. The basic form of such cutting inserts comprises two opposed top and bottom surfaces and a peripheral wall extending therebetween, the cutting edges being formed by the transition between the top surface and said peripheral wall of the insert. The top surface of the insert is a chip face or such a surface which is in contact with the formed chip at the cutting operation, and said peripheral wall being a clearance face in relation to the workpiece. It is generally desirable that these inserts should have a geometry that will minimize the power required in the metalworking operations by controlling the geometry of the chips produced and that the insert chip control geometry should be capable of controlling chips over a wide range of parameters such as depth of cut or feed rate. Typical prior art inserts known to the applicant are US patents 3 815 192, 3 973 308 and 4 787 784. In the first-mentioned patent a plurality of projections are spaced so as to define chip curling zones therebetween and in the second patent a plurality of notches were so formed that the chip could pass or slide over them without being broken or substantially deformed. The third and last mentioned patent corresponds to the preamble of claim 1. The insert of the invention is defined in claim 1. The insert of the present invention has a chip face that is modified to have a more favourable form so as to enable chips to be broken and controlled over a wider range of cutting depth and feed. The invention will now be more closely described in connection with the appended drawings showing a preferred embodiment of the insert, wherein further features and advantages of the embodiment will be apparent. Fig 1 is a perspective view of an indexable cutting insert embodying the invention, Fig 2 is a sectional view taken along the line A-A in Fig 1, Fig 3 is a sectional view taken along the line B-B in Fig 1, and Fig 4 is a sectional view taken along the line C-C in Fig 1. With reference to Fig 1 the illustrated cutting insert 10 is made of hard wear resistant material such as hard metal, and it is provided with substantially triangular top and bottom chip breaking surfaces joined by side walls 11 with rounded corners, whereby said side walls 11 is in perpendicular relation to planes containing said top and bottom chipbreaking surfaces. The insert 10 further includes a plurality of cutting edges 13 extending along all the edges of the insert at the junction of the side walls and the top and bottom chipbreaking surfaces. Each cutting edge 13 is joined to a cutting edge land area 12 which extends inwardly from the cutting edge. This land area 12 is planar and perpendicular to said side wall 12. This land is located to reinforce the cutting edge in the difficult areas and decrease the contact between chips and cutting face in order to delay the crater wear effect. A sloping or descending surface 14a extends from the top inner margin of each land area 12 and joins a first planar floor portion 15a adjacent the corner region whilst oriented parallel with the bottom surface of said insert. This floor 15 is elongated and extends symmetrical at each side of the bisector of the corner whilst extending substantially parallel with the cutting edge 13. An insert aperture 16 normal to said planar floor portion 15a is provided in the center of the insert 10 for the receipt of a suitable locking pin employed to clamp the insert to a pocket wall of a tool holder. The planar floor 15a joins a sloping surface 16 of a raised rib 17, the upper surface 18 of which is planar and located at a level equal to or above the level of the land area 12. The rib 17 is elongated and confined by said sloping surfaces 16 which converge towards the corner in such a way that the bisector along the line A-A divides said rib 17 in two equal halves. In the intermediate portion of the insert, between the ribs 17 at two adjacent corners, there is a projection 19 with a top planar surface 20 in the form of an equilateral triangle aimed to give assisting chipbreaking at greater depts of cut. In similarity with the rib 17 said projection 19 is joining a planar floor 21 which has a curved form at the nose portion of said projection as a consequence of the orientation of said triangle which is oriented such that the bisector at one of its corners is oriented perpendicularly from the cutting edge 13. At the forward nose portion of each rib 17 two distantly provided projections 22 are disposed in said sloping surface 16 of said rib whilst arranged with a planar floor portion 15b therebetween, said floor portion 15b being co-planar with floor portion 15a. These projections are elongate in shape, they are partially disposed in said sloping surface 16, and mutually parallel as they extend onwards over the entire width of said planar floor portion 15b towards the corner of the insert. The rear portions 23 of said projections 22, however, diverge as they extend inwardly toward the center of the insert. The upper surface of each of said projections 22 is substantially flat and each of them is confined by inclined descending surfaces. The upper surface of said projections 22 is located at a level equal to or below the level of the land area 12 that extends around the insert. Further, the top surface of said distantly provided projections 22 is located at a level equal to or below the level of the top surface 18 of the elongated rib 17. The elongated rib 17 is provided with a length which several times exceed the length of said distantly provided projections 22. By providing two distantly arranged projections 22 at the forward nose end portion of the elongated rib 17 the initial chipbreaking will occur against them during ligth cutting, i.e. at small cutting depths and moderate feeds. When cutting depth and feed is increased the angle of shear for the chip will be changed. These distantly arranged projections 22 will therefore not negatively effect the chipbreaking at increased depth of cut and increased feed since the elongated rib will ensure that appropriate chipbreaking occurs at those conditions. Thanks to this arrangement a wider range of controlled chipbreaking is achieved at varying depths of cut and feeds.

Claims: Cutting insert for chipforming machining of metal workpieces in the shape of a polygonal body of wear resistant material, comprising opposed top and bottom surfaces and a plurality of peripheral walls (11) extending therebetween, the cutting edges (13) being formed at the transition between said peripheral walls and at least one of said top and bottom surfaces, a land area (12) joining said cutting edge and extending towards the centre of the insert, a number of spaced projections (17, 19) being provided inside a descending surface (14a, 14b) in a spaced relationship to said cutting edges to define curling zones therebetween, which descending surface on one hand joins the inner margin of said land area (12) and on the other hand a bottom surface area (15a, 15b) which then joins an upwardly sloping area (16) of one of said spaced projections having the shape of an elongated rib (17) extending towards a corner of the insert in the direction of the bisector, characterized in that two separate projections (22) are arranged symmetrically with respect to said elongated rib (17) at the intersection between the upwardly sloping end area of said elongated rib (17) and said bottom surface area (15a, 15b), said projections (22) being partially disposed in said sloping area (16). Cutting insert as defined in claim 1, characterized in that said two separate projections (22) are elongated and substantially straight having such orientation that the rear portions of said projections diverge from each other in a direction towards the centre of the insert. Cutting insert as defined in claim 1, characterized in that said two separate projections (22) each is confined by a flat top surface and inclined descending surfaces on both sides thereof, which joins said bottom surface area (15a, 15b). Cutting insert as defined in any of the claims 1 to 3, characterized in that the top surface (18) of said elongated rib (17) extending towards the corner in the direction of the bisector is planar and located at a level equal to or above the level of the top surface of the two separate projections (22) at the nose portion of said elongated rib. Cutting insert as defined in any of the claims 1 to 4, characterized in that the level of the top surface of said two separate projections (22) at the nose portion of said elongated rib (17) is located at a level equal to or below the level of the land area (12) that extends around the insert. Cutting insert as defined in any of the claims 1 to 5, characterized in that the elongated rib (17) provided along the bisector in each corner region is provided with a length which exceeds the length of said two separate projections (22).

Inventors: LUNDSTROEM JAN, LUNDSTROEM, JAN, Lundström, Jan
Applicants: SANDVIK AB, SANDVIK AKTIEBOLAG
Application year: 1993
Main classification: B23B27
IPC codes: B23B27