Cutting insert for turning and grooving tools

Abstract: The invention relates to a turning insert (10) that consists of a polygonally shaped body, confined by oppositely disposed side surfaces (11, 12) interconnecting upper and lower surfaces (13, 14) and front and rear end surfaces (15, 16), with a main cutting edge (18) at the intersection between the front end surface (16) and an upper land area (27). A chipforming device (19) is provided in the forward portion of said top surface (14) shaped in the form of a number of distantly provided recesses (28, 30) and ridges (34, 35) in order to promote improved chip control and obtention of narrower chips in grooving operations.

Description: The present invention relates to a cutting insert for turning and grooving tools, primarily for grooving operations in metal workpieces, that could also be useful for cutting off rods, tubes or other rotationally symmetrical details. Such cutting insert is provided with a cutting edge formed by the transition between the top surface or rake surface of the insert and its forward clearance face. In metal cutting operation, the breaking of the chip and the shape of the chip are often of great importance for an undisturbed production. In modern, high-productive machines and tools there are great demands upon an efficient chip removal and good chip control. This is of special importance in such high-productive machines in which a serie of different tools are performing different operations in a continuous sequence. It is not unusual that in such operations the chips may become tangled and wrap around the workpiece or the tool. This creates problems in subsequent operations, especially if automated workpiece handling equipment is involved. These difficulties are compounded when it comes to camshaft or crankshaft turning where several grooves are generated in one operation. The end result is usually high production costs due to expansive machine downtime to clear chips or repair tools. The prior art disclosure of WO-A-89/01375 (cf the preamble of claim 1) relates to a generally rectangularly shaped cutting insert for turning and recessing operations the front portion of which is provided with a main cutting edge formed by the intersection between the upper surface and the front surface of the insert, and a chipforming device in the shape of a singular recess is provided radially inside of said main cutting edge, the rear wall portion of said recess extending upwardly so as to act as a chipbreaking wall. EP-A-360774 discloses an insert provided with a chipforming device formed by a plurality of recesses centrally located on the upper surface. This insert has polygonal symmetry for being indexed to three or more cutting orientations. In view of difficulties with prior art inserts and tools it is a purpose of the present invention to provide an improved type of turning insert that is formed so as to optimize chip control for the specific demands and conditions of the difficult operations referred to above. According to the invention this purpose is achieved by the features of claim 1. Prefered embodiments are defined in the dependent claims. The dimpled chipbreaker and the confining walls thereof are designed so as to form the chip narrower than the groove such that more, efficiently manageable safe chips can be obtained. Chip disposal should become safer and more efficient and less costly. With such inserts it shall become possible to generate a finished groove in one pass in the workpiece such as a crankshaft. These and other objects have been achieved by shaping the insert as described hereinafter in connection with the appended drawings. Fig 1 shows a perspective view of an insert according to the invention. Fig 2 shows a side view of the insert in Fig 1, Fig 3 shows a top view of the insert in Fig 1. Fig 4 shows a front view of the insert in Fig 1, Fig 5 shows a cross-section along the line A-A in Fig 3, Fig 6 shows a cross-section along the line B-B in Fig 3, Fig 7 shows a cross-section along the line C-C in Fig 3, Fig 8 shows a perspective view of a holder for the insert, Fig 9 shows a partial front view of the insert located in the tip-seat of the holder in Fig 8, and Fig 10 shows a chip obtained from chipforming by the insert in Fig 1-7. An insert 10 according to the invention is shown in the figures. The insert is in the shape of a polygonal body of generally parallepipedic shape. It comprises two mainly plane-parallel side surfaces 11, 12, opposed top and bottom surfaces 14 and 13 respectively, two end surfaces 15, 16, and a shoulder 17. The front portion of the insert is provided with a main cutting edge 18 and a chip forming device 19. The insert is intended to be secured to a holder body provided with an integral clamping arm. The top surface 14 is broken at the vicinity of the shoulder 17 so that surface portion 14a forms an acute angle with the remainder of said surface 14. The insert 10 is intended to be removably held in a holder, which comprises a holder body 20 having an integral clamping arm 21 in the front portion 22 of said holder body 20 and an insert receiving recess 23 in which the insert is to be located. The recess 23 communicates at an inner end thereof with an elongated slit 24 which terminates into a circular recess 25. A clamping screw 26 extends into the holder through the clamping arm 21 and through the slit 24. When the screw 26 is threaded into the holder the clamping arm 21 flexes downwardly about said recess 23 and causes the clamping arm 21 into firm clamping abutment with the upper top surface of the insert. More specifically, the nose portion of the clamping arm 21 is somewhat inclined downwardly so that it matches the inclination of upper surface portion 14a of the insert 10. Bottom surface 13 is intended to be a first support surface for the insert against the holder body which shall be parallel with a neutral plane P defined by the axial feed direction of the machine. More specifically bottom surfaces includes two distantly provided flat surface portions 13a and 13d, and two inclined surfaces 13b and 13c therebetween, whereby said inclined surfaces 13b, 13c provide a V-shaped recess. The surfaces 13b and 13c are intended to be in abutment with correspondingly inclined surfaces in the insert site of the holder as shown in Fig 6 and 7. As appears therefrom the surfaces 13a and 13d are not to be active support surfaces. The top surface 14 constitutes a second support surface for the insert against the holder body. The top surface 14 is oriented parallel with the bottom surface 13. The cutting edge 18 is straight and is formed along the intersection line of clearance face 16 and a primary land 27. The clearance face 16, which is the front end surface of the insert, forms an acute angle α, about 1-15° with a normal N drawn to said primary land 27, whereby said primary land 27 coincides with neutral plane P. The land 27 is bordered radially inwardly by an array of spaced recesses or grooves 28 extending on the rake face of the insert starting from the primary land 27. The width of the land 27 is varying along the edge 18 in such a way that the width is smaller at those portions located next to the front end portions of each recess 28 whereas the width is larger at the inclined rake surface portions 29 located therebetween. The maximum width of each recess 28 is preferably larger than the distance between the depressions. Each recess has a depth initially increasing in a direction away from said primary land and thereafter decreasing in said direction. There are a number of more centrally provided oval-shaped recesses 28 having a longitudinal extension, perpendicularly from the cutting edge 18, that is several times larger than the width of said recess 28. Preferably there is, on each side of said central group of oval-shaped recesses 28 a recess 30 having a larger width and shorter length than each of said central recesses 28. Also formed in the top surface 14 of the insert is a recess 31, which curves inwardly and downwardly from the land surface 27 and then curves upwardly to form a rear wall or chip deflector surface 32. The chip deflector surface 32 terminates in a plateau 33 located approximately at the same level as the neutral plane P. The chipforming device 19 additionally includes a pair of ridges 34, each of which extends from the outer periphery of the recess 30. More specifically, the front ridge portion 34a and 34b are so formed that they converge rearwardly, and they extend rearwardly to the point where they meet with rear ridge portions 35a and 35b which are mutually parallel and extending essentially perpendicularly from the cutting edge 18. Furthermore, the said front ridge portions 34a and 34b are formed with a top surface that is raised rearwardly until the portion where said front ridge 34a, 34b intersect with said rear straight ridge 35a, 35b at which intersection the top surface of said rear ridge has a level that remains constant furtheron rearwardly. This level of the upper surface of said rear ridges is located somewhat above plane P. By arranging the ridges as aforesaid it is ensured that the chip remains in contact with said forward ridge portions 34a, 34b and the central portion of the chip is urged deeper into the recess 31 which means that the total width of the chip is made narrower and becomes more easily manageable so that no harm is made from the chip on to the side walls of the groove which is to be formed by said insert during cutting in a metal workpiece. The forward end of the insert 10 additionally is provided with side cutting edges 36a and 36b, which merge rearwardly to an intermediate position along the insert, whilst intersecting with the land surface 27 which extends along both the main cutting edge 18 and along said side cutting edges 36a, 36b. The clearance faces of said side cutting edges 36a, 36b are designated 11a and 11b whereby each said clearance face 11a, 11b intersect with the land 27 at an acute angle β. By virtue of the particular construction of the chip forming device as aforesaid it will be possible to obtain desirable clock-shaped chips 37 such as shown in Fig 8, obtained at a feed rate of 0,30 mm/revolution. If no proper chip deflection device is provided into the upper rake surface of the insert chips obtained would otherwise be difficult to manage. Also at moderate feed rates the chip forming device of this invention effectively contributes to the control and removal of such chips. When large feeds are used the chip will be pressed against the rear wall 32 of recess 31 which forces the chip to be bent in a favourable manner. The embodiment described above also results in a certain reduction of the cutting forces because these grooves mean reduced contact area and increased positive rake angle. Due to the fact that a reduced contact area is obtained a relatively low heat generation is obtained.

Claims: A generally rectangularly shaped metal cutting insert for turning and grooving operations comprising upper and lower front-to-rear extending surfaces (13, 14), two oppositely disposed side surfaces (11, 12) interconnecting said upper and lower front-to-rear extending surfaces, and front and rear end surfaces (15, 16) each intersecting said upper and lower front-to-rear extending surfaces and said side surface, a front portion of said upper surface including a main cutting edge (18) formed by the intersection between said upper surface and said front surface (16), a chipforming device (19) disposed radially inside of said main cutting edge, said chipforming device including a first recess which curves inwardly and downwardly from a flat land area (27) adjacent the cutting edge (18), said first recess curving upwardly to form a chipbreaker wall (32) which is disposed radially inside of said chipforming device and extending upwardly therefrom, characterized in that the chipforming device (19) is formed by a plurality of second recesses (28) centrally located on the upper surface and having a bigger depth than the depth of the first recess, each said second recess being located at a predetermined distance inside the cutting edge and having an elongated extension in a direction parallel with the longitudinal extension of the insert, the lateral extension of the first recess being confined by first ridge portions (34a, 34b) that converge rearwardly and merge at a rearward point with integral second ridge portions (35a, 35b), said second ridge portions extending essentially perpendicularly with respect to said main cutting edge (18). An insert according to claim 1, characterized in that the insert is provided with third recesses (30) shorter in length along the longitudinal extension of the insert, said third recesses being arranged on either side of said centrally provided recesses (28). An insert according to claim 1 or 2, characterized in that the recesses (28, 30) are distantly provided from each other and that there is a flat land area (27) provided between the main cutting edge (18) and said recesses (28, 30), said land (27) being oriented in a plane (P) extending in the longitudinal extension of said insert. An insert according to claim 1, characterized in that said first ridge portions (34a, 34b) extend from the outer periphery of said third recesses (30), and that said second ridge portions (35a, 35b) extend to the forward slope of a shoulder (17) provided rearwardly of said chipbreaking wall (32). An insert according to any of the claims 1-4, characterized in that the forward end of the insert is provided with side cutting edges (36a, 36b), which converge rearwardly to an intermediate position along the insert. An insert according to any of the claims 1-5, characterized in that the rear chip breaking wall (32) terminates in a plateau (33) located approximately at the same level as a neutral plane (P) containing also said primary land (27). An insert according to any of the claims 1-6, characterized in that the width of the land (27) is varying along the edge (18) in such manner that said width is smaller at a portion in front of the forward end of each oval recess (28) whereas said width is larger at portions in front of the intermediate rake surfaces (29) located between adjacent recesses (28). An insert according to any of the claims 1-7, characterized in that said front ridge portions (34a, 34b) are each formed with a top surface inclined upwards until they intersect with a top surface of said rear ridge portions (35a, 35b). An insert according to claim 1-8, characterized in that the level of the top surface of the rear ridge portions (35a, 35b) is located at a level above and generally parallel to the level of said neutral plane (P) containing said flat land.

Inventors: LINDSTEDT LARS, LINDSTEDT, LARS
Applicants: SANDVIK AB, SANDVIK AKTIEBOLAG
Application year: 1993
Main classification: B23B27
IPC codes: B23B27