Milling cutter and insert therefor

Abstract: A fully indexable negative geometry polygonal insert uses an active cutting edge extending in a first direction from each corner of the polygon downwardly from an associated major polygonal surface of the insert along with a wiping or finishing cutting edge lying substantially in the plane of the associated major surface and extending in a second direction from the insert corner. The geometry of the cutting edge enables mounting of the insert to a milling cutter with negative axial rake, such that the cutting edge is substantially parallel to an axis of rotation of the cutting tool.

Description: BACKGROUND OF THE INVENTION The present invention relates to an indexable cutting insert comprising a polygonal body having substantially parallel major surfaces joined by flank surfaces substantially perpendicular to the main surfaces to form corners of the polygon, a main cutting edge extending in a first direction from each corner in a downwardly direction from a major surface associated with the comer to the other major surface, and a wiping edge disposed adjacent each comer and extending in a second direction leading away from the corner and lying substantially in the plane of the associated major surface. Such an indexable cutting insert is known from EP-A-0 577 011. It is an object of the present invention to provide an indexable cutting insert adaptable for mounting in a cutting tool which can be oriented to yield an active cutting edge exhibiting zero axial rake, yet capable of providing protection to a trailing cutting edge of the insert. For solving the above object, the present invention provides an indexable cutting insert as defined in claim 1. Preferred embodiments of the present invention are set out in the dependent claims. The objects and features of the invention will become apparent in view of a detailed description of a preferred embodiment, taken in conjunction with the drawing, in which: FIG. 1 is a perspective view of a fully indexable negative insert arranged in accordance with the principles of the invention; FIG. 2 is a perspective view of a face mill mounting at least one of the inserts of the FIG. 1 thereto; FIG. 3 is a side view of the milling cutter body 200 of FIG. 2; FIG. 4 is an end view of the milling cutter 200 of FIG. 2; FIG. 5a is another end view of milling cutter 200 showing negative radial rake; and FIG. 5b is another side view of milling cutter 200 demonstrating negative axial rake. With reference to FIG. 1, insert 100 has a "negative" form - i.e. active cutting edges around its periphery on both major surfaces, due to the fact that the flank surfaces are substantially perpendicular to both major surfaces. A principal advantage of negative inserts is that they provide twice as many indexable cutting edges as provided by one-sided, or positive form, inserts. Each main cutting edge of insert 100, 102a-d associated with major surface 108 and 102e-h (edges 102f,g, and h not visible in the view of FIG. 1) extend from an associated corner of the insert in a direction which proceeds downwardly from the associated major surface, such as 108. When mounted to a face mill in accordance with the principles of the invention to be discussed below, each active cutting edge such as 102a will provide a depth of cut as shown at 114 in FIG. 1. Each cutting edge 102a-h exhibits a positive form (i.e. the top surface behind each cutting edge forms an acute angle with the associated side or flank surface of the insert) through use of a groove formed by a first surface 110 which extends downwardly from cutting edge 102a to join a bottom-most portion of an upwardly rising ramp surface 112 which terminates substantially in the plane of major surface 108. Additionally associated with each main cutting edge 102a-h is a respective finishing or wiping edge 104a-h (104e, f, g, and h, not shown in FIG. 1). Each wiping edge 104a-h lies substantially in the plane of its associated major surface. For example, wiping edges 104a, b, c and d lie substantially in the plane of their associated major surface 108. Connecting each cutting edge 102 with its associated finishing edge 104 is a transitional cutting edge 103a-h, which basically functions as a chip forming element. The insert additionally comprises a second major surface not shown in the drawing of FIG. 1 but which is substantially parallel to major surface 108. The two major surfaces are joined by four side or flank surfaces 106 (only one of the flank surfaces being visible in the perspective view of FIG. 1.) It will be understood that the flank surfaces 106 are substantially normal or perpendicular to the major surfaces 108 to form a polygon, such as the square insert shown in FIG. 1. It will be understood that the insert of this invention could comprise a polygon of virtually any shape. However, the square shape with the cutting edge and its associated wiping edge extending at substantially 90° angles to each other from a respective corner of the insert is preferred in forming a 90° shoulder in a workpiece. With each main cutting edge 102 extending downwardly from its associated corner as shown in FIG. 1, the insert may be advantageously mounted to a cutting tool such as a rotating face mill 200 of FIG. 2 in a manner such that the cutting edge may be parallel to the axis of rotation of the tool, even though the insert itself is mounted in a pocket to exhibit an overall negative axial rake. The view of FIG. 3 demonstrates the principle of negative axial overall rake, yet neutral rake of the cutting edge 102a with respect to an axis of rotation 301 of a face milling cutter 200. Note from FIG. 3 that cutting edge 102a lies substantially parallel to the axis of rotation 301 of cutter 200, thereby providing effective neutral axial rake cutting action, while the negative axial positioning of the insert body provides necessary clearance between flank surface 106 and the workpiece material being milled. In addition to negative axial rake of the overall insert in a mounting pocket of the face mill 200, the invention utilizes negative radial rake for the overall insert as seen in the end view of FIG. 4 of milling cutter 200 where the insert 100 is mounted to the milling cutter in a manner exhibiting negative radial rake (i.e. where the active cutting edge lies ahead of center) as shown at the angle 401 of FIG. 4. While the overall insert body is thus mounted in a cutter body pocket with negative axial and radial rake angles to provide clearance, it is a feature of this invention that the actual effective cutting edge radial rake angle may be negative, neutral or positive. The choice of cutting edge radial rake geometry depends upon the amount of required cutting edge strength, which, in turn, is a function of the type of material being machined. It will be understood by those skilled in the art that the insert 100 of the invention may also be advantageously mounted in a shallow boring bar as well as in the face mill of FIGs. 2-5. FIG. 5a is another end view of milling cutter 200 demonstrating a negative radial rake angle 501 and the resulting clearance angle 503 which will protect the trailing edge of the insert as the tool rotates through the workpiece material. Finally, FIG. 5b is another side view of milling cutter 200 depicting the negative axial rake 505 and the resulting clearance angle 503 provided by this mounting arrangement. Hence, using the principles of the invention, a negative insert (that having formed cutting edges on both sides thereof to provide maximum indexability) is raked in the cutter body such that a high point on the insert extends beyond the rest of the insert creating clearance or protection for the trailing cutting edge of each insert 100. Additionally, the high point of the insert is formed to create a wiping edge associated with main cutting edge to produce a good part finish and, in the case of a polygonal insert having substantially 90° corners to finish off an ideal 90° shoulder in a workpiece. The design allows for an insert to be double-sided with a built-in wiper edge and will produce a square shoulder on the finished part while protecting the trailing cutting edge of the inserts employed. The invention also enables the insert pockets to be more easily machined into the cutter body relative to compounding angles. The top form of the cutting edges with the associated depressions inwardly of each edge allows the cutting geometry to be neutral to positive. The invention has been described with reference to a preferred embodiment for the sake of example only. The scope of the invention are to be determined from a proper interpretation of the appended claims.

Claims: An indexable cutting insert (100) comprising a polygonal body having substantially parallel major surfaces (108) joined by flank surfaces (106) substantially perpendicular to the main surfaces (108) to form comers of the polygon, a main cutting edge (102a-h) extending in a first direction from each corner in a downwardly direction from a major surface (108) associated with the corner to the other major surface (108), and a wiping edge (104a-h) disposed adjacent each corner and extending in a second direction leading away from the corner and lying substantially in the plane of the associated major surface (108), characterized in that each wiping edge (104a-h) is spaced from its respective corner in the second direction and that each corner lies in a plane which is lower in the direction to the other major surface than the plane of the associated major surface (108). The insert of claim 1, wherein each main cutting edge runs along a groove in the major surface thereby providing a positive rake cutting form. The insert of claim 2, wherein the groove is formed by a first surface (110) extending from the active cutting edge downwardly from the major surface and terminating in a second surface (112) which extends upwardly and inwardly to terminate at the major surface. The cutting insert of claim 1, adapted for mounting in a rotatable cutting tool pocket having negative radial and negative axial rake resulting in the main cutting edge running substantially parallel to an axis of rotation of the cutting tool such that a 90° shoulder in a workpiece may be formed by the cutting tool. The cutting insert of claim 1 further including a transitional cutting edge (103a-h) which is inclined from each corner up to the associated wiping edge (104a-h). The cutting insert of claim 1, wherein each of the flank surfaces (106) joining the major surfaces (108) lies entirely in a single plane.

Inventors: NOGGLE KENNETH G, NOGGLE, KENNETH G.
Applicants: VALENITE INC, VALENITE INC.
Application year: 2000
Main classification: B23C5
IPC codes: B23C5