Cutting insert

Abstract: An indexable improved force distribution cutting insert (10) having an arcuate concave convex cutting edge (18) and a body portion (16) having an arcuate concave convex configuration corresponding to the cutting edge (18).

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high productivity, high metal removal rate insert which improves force distribution across the rake face and has a cutting surface which is configured in an arcuate concave, convex configuration. The present invention further relates to an indexable cutting insert having force distribution which lowers stress concentration at depth of cut line to minimize notch formation and which is equipped with a raised, central island formed in the upper surface to protect the fastening means from injury by the chips during cutting. The present invention further relates to a high productivity, high metal removal rate insert which descends bi-directionally from the cutting edge toward the center of the insert. The bi-directional descending surfaces form a stabilizer pad where they intersect at each corner or nose area of the insert to impart improved impact resistance to the nose area of the insert. The present invention further relates to a high productivity, high metal removal rate insert having a cutting edge shaped in an arcuate concave convex configuration, and further provided with an upper surface whose arcuate concave, convex surface corresponds to the shape of the cutting edge. 2. Description of the related art Plansee TIZIT GmbH has recently introduced an insert designated as Sr137 TR, which is disclosed in their European sales brochure entitled "TIZIT Starmaster". The insert in question features an arcuate concave, convex upper surface and cutting edge, but the two arcuate surfaces are "out of synch" with each other such that when the cutting edge is concave, the upper surface is convex, and vice versa. Moreover, the Plansee insert does not feature bidirectional descending surfaces from the highest point of the cutting edge, which is located at the nose radius, toward the center of the insert. The insert of the present application features an arcuate concave convex cutting surface and upper surface which correspond to each other. In other words, when the cutting surface of the insert of the present application is concave, the upper surface is concave, and vice versa. This allows the insert of the present application to exhibit improved force distribution across the rake surface of the insert which reduces localized stress concentrations at depth of cut and further improves impact strength during heavy cutting operations. In EP-A-307563, there is disclosed a polygonal indexable cutting insert, comprising upper and lower surfaces and a side wall to form a body wherein said upper surface defines an arcuate concave, convex cutting edge along its periphery. A land is formed along and rearward from said cutting edge. The outermost cutting edge is lower than the inner adjacent surfaces of said conventional insert. It is an object of the present invention to provide an improved insert which is capable of high-depth, moderate to high metal removal rate from workpiece, like steel at high to medium cutting speeds and depth of cut. The above object is achieved by the subject matter of claim 1. Preferred embodiments and further improvements are defined in the depending subclaims. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a top perspective of the insert. Figure 2 is a side view of the insert showing the arcuate concave convex configuration of the cutting edge. Figure 3 is sectional view of the insert along line 3-3 showing the cutting action of the insert. Figure 4 is a sectional view of the insert along line 4-4 Figure 5 is a detailed view of the nose portion of the insert showing the stabilizer pad. Figure 6 is a sectional view of the insert along line 6-6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, where like numerals depict like structures, and particularly to Figure 1, there is shown therein a perspective view of the insert 10. The insert shown is polygonal in shape, but it is contemplated that circular inserts could be made featuring the embodiments described for the polygonal insert shown. The insert has an upper surface 12, which forms the rake face, a lower surface (not shown) and a side wall 14 extending substantially unbroken therebetween to define a body 16. The insert as shown is adapted to be seated in a tool holder pocket at its lower surface, and is indexable within such a tool holder. Upper surface 12 has an arcuate concave convex cutting edge 18 along it periphery 20, and is further equipped with a land 22, which extends substantially around the periphery of the upper surface and rearwardly of the cutting edge. Rearward of the land is a chip strain surface 24, which extends around the upper surface of the insert adjacent to the land. The upper surface of the insert is provided with at least one bi-directional chip breaker surface 25 formed therein having arcuate concave, convex configuration corresponding to the configuration of the cutting edge and descending bi-directionally from the land toward the center of the insert and the depth of cut line 4-4. The insert is provided with a central aperture 26 extending at least partially through the body of the insert. The aperture is surrounded with a centrally raised angular chip reflecting island 28 to aid in chip breaking, and further to protect a fastening means 30 (as seen in Figure 3) from chip flow damage. The cutting edge is further provided with a plurality of stabilizer pads 32 at regular intervals to improve impact strength of the cutting edge. The stabilizer pads are formed by the joining of two different angular surfaces formed in the cutting edge. In the polygonal insert shown in the figures, the stabilizer pad is formed by the intersection of a 4 degree angular surface 27 or 29 and an 8 degree angular surface 31 at the nose portion 33 of the insert. It will be understood by those skilled in the art that when the insert has a polygonal shape, each corner thereof is a nose portion. In inserts having no corners, such as circular inserts, the stabilizer pad is formed by the intersection of the two angles described above. It has been found that this combination exhibits greatest improvement in force distribution across the rake face when the center 46 of the insert is in the range of about 0.508 to 0.813 mm (.02 to .032 inches), and preferably 0.711 mm (.028 inches) lower than the highest point of the insert, normally located at the nose area of the insert. It is contemplated that the arcuate concave, convex cutting edge and upper surface described reduce localized stress concentrations in the insert along the rake face at the depth of cut line during cutting to yield reduced tendency to form notches in the insert. Turning now to Figure 2, a side elevation of the insert is shown depicting the arcuate concave convex configuration of the cutting edge and the manner in which the upper surface rake face configuration 32, shown in phantom, corresponds to the configuration of the cutting edge. The correspondence between the upper surface and the cutting edge provides greater impact strength to the cutting edge, as each arcuate concave, convex surface is supported by a similar configuration along the upper surface of the insert. Figure 3 is a detailed sectional view of the insert of Figure 1 taken along line 3-3. The insert is shown while cutting a workpiece 34, at its nose portion 33. The chips 38 which are generated as the insert moves through the workpiece are subjected to strain as they move along the upper surface of the insert, until they finally break. As the chips move along the upper surface of the insert, they encounter the raised angular island which is protecting the fastening means 30, shown as an "H" pin. It was a long felt problem in the art that as chips moved along the surface of an insert during the cutting operation, they would encounter the fastening means and move across it, thereby eventually damaging the fastening means and contributing to the costs incurred in cutting operation. The present invention solves this problem by providing for the raised angular island 28 which directs the chips away from the fastening means and thereby contributes to improved tool holder life and reduced cost of operation. Figure 4 is a sectional view of the insert of Figure 1 taken along line 4-4, showing the relatively uniform cross sectional profile of the insert along much of its body. Figure 5 is a detailed top sectional view of the nose portion of polygonal insert shown in Figure 1. At the corner of the insert there is formed the stabilizer pad and the land and chip breaker surfaces previously described in connection with Figure 1. Referring to Figure 6, there is shown therein a side sectional view of the nose portion of Figure 5 taken along line 6-6. As seen therein, the cutting edge and land merge with the chip breaker surface. It can be seen that extra strain is induced on the chips by arcuate convex surface 42 which merges into the concave surface 40 at the nose portion. Such configuration serves to induce extra strain in the chips, and further to form the stabilizer pad which imparts improved impact resistant properties to the insert. The insert according to the present invention is capable of high depth, moderate to high metal removal rate from workpiece, like steel, at high to medium cutting speeds and depth of cut. Moreover, it has been observed that the insert of the present invention reduces chatter on long shafts or thin walled parts while efficiently machining those parts at high metal removal rates. The insert transfers a substantial amount of the heat generated during the cutting operation into the chips which results in longer insert life. Another advantage of the present invention is reduced contact between the chip and the insert while inducing maximum deformation forces into the chips generated at the shear zone for efficient chip breaking. It should now be clear that, because of the arcuate concave convex configuration of the insert, the chip is induced to curl and break at a wide range of feed rates and depths of cut on a variety of workpiece materials, as well as to strengthen the cutting edge under variable loads and heat fluctuations produced by variations in the depth of cut. The insert of the present invention is useful at 0.355 to 1.27 mm per revolution (.014-.050 IPR) at 2.54 to 15.24 mm (.10 to .60 inches) of depth of cut, at cutting speed of about 91.44-365.76 m/min (300-1,200 ft/minute). It is contemplated that the insert is particularly useful on long shaft parts where chatter reduction is critical, pipes and thin walled parts, and where high metal removal rates/high productivity through forged or cast steels in turning and facing operations are desired. The insert of the present invention allows full utilization of machining horsepower and improved rigidity on older machines and reduction of energy requirements and associated costs for heavy cuts. It will be evident that there are a wide variety of embodiments of the present invention which are not specifically described above but which are clearly within the scope of the present invention. The above description is therefore intended to be exemplary only and the scope of the invention is limited solely by the appended claims.

Claims: A polygonal indexable cutting insert (10), comprising: an upper surface (12) which is a rake face, a lower surface adapted to be seated in a tool holder pocket, and a side wall (14) extending substantially unbroken therebetween to form a body (16), said upper surface defining an arcuate concave, convex cutting edge (18) along its periphery (20), characterized by said cutting edge having its greatest height at each corner (33), the upper surface (12) sloping downwardly and inwardly from the cutting edge (18) to a land (22) and then through an inboard breaker surface 25 of the body (16) to a centrally located aperture (26), said aperture (26) extending at least partially through the insert to accommodate a fastener means (30), a stabilizer pad (32) at each corner of the inboard breaker surface, said each stabilizer pad being an intermediate zone joining parts (27,29,31) of the upper surface (12) that have different inclination with respect to the lower surface disposed inwardly from each corner (33), and the upper surface (12) having a concave, convex contour corresponding in configuration to the contour of the cutting edge (18). The insert of claim 1, which further comprises a raised angular island (28) surrounding the aperture (26) for protecting the fastener means (30) from chip flow damage during cutting operations. The insert of claim 1, wherein said aperture extends completely through the insert (10). The insert of claim 1, wherein a central portion (46) of the upper surface (12) is about 0.508-0.813 mm. (.02-.032 inch) lower than the corners. The insert of claim 1, wherein said insert is used at 0.355 - 1.27 mm per revolution (.014 - 050 IPR), 2.54 - 15.24 mm (.1 - .6 in.) depth of cut and 91.44 - 365.76 m/min (300 - 1,200 ft/min).

Inventors: BERNADIC THOMAS J, BROCKETT BRENDAN L, KATBI KARL, LOWE TONY M, BERNADIC, THOMAS J., BROCKETT, BRENDAN L., KATBI, KARL, LOWE, TONY M.
Applicants: VALENITE INC, VALENITE INC.
Application year: 1992
Main classification: B23B27
IPC codes: B23B27