Milling insert

Details Milling insert Milling insert

2001-03-02

2004-10-12

Wellington, A. L. (Department: 3722)

Cutters, for shaping

Including tool having plural alternatively usable cutting edges

C407S114000

Reexamination Certificate

active

06802676

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to indexable cutting inserts and associated cutting tools. More specifically, the invention is directed to indexable polygonal cutting inserts, for milling, reaming, boring and the like having a wiper geometry which improves surface finish generated during machining.
BACKGROUND OF THE INVENTION
It is known in the industry, that each pass of a cutting insert over a workpiece creates a new surface that, under conventional cutting conditions, has a curved geometry substantially corresponding to the curve of the cutting edge around the active cutting corner of the insert. As has been discussed in the literature, the curved surfaces generated result in a part finish, with high and low points that appears “scalloped” in cross-section. Surface finish irregularities are recognized in the industry to result from ordinary machining variables such as workpiece deflection, the feed rate, the size of the nose radius of the cutting insert used and the stability of the machining environment. Multiple insert tools create further surface finish irregularities due to manufacturing tolerances that result in variables in insert position.
Wiper inserts have been developed in an attempt to reduce surface finish irregularities and produce a smoother part finish. Wiper inserts refer to cutting inserts having various geometries at or near the active cutting edge or edges such that as the cutting insert travels over the workpiece and cuts an area therefrom, the new surface that is generated by the cutting edge is “wiped” or “rubbed” by a wiper geometry. The wiper geometry is positioned on the insert finish cutting edge.
In the past, conventional wiper inserts have been manufactured by forming curved peripheral flanks having a large radius or a series of radii on the finish cutting edge to remove surface irregularities, for example the feed line.
FIG. 1
shows a top view of an example of a conventional insert
100
having a top surface
110
and curved flanks
120
. The flanks
120
of the insert extend outward in the plane of the top surface, which gives this conventional insert the appearance, in top view, of a polygon with sides bulging outward. A drawback of conventional designs and cutting methods based on this concept is that the curved nature of the flanks causes seating problems. When multiple flanks and edges of a conventional insert carry such wiper geometries, expensive tooling of toolholder pockets to match the periphery of the insert is required or the insert does not seat properly in the cutting tool holder. Due to such seating problems, the radiused flank geometry is not put on all sides of the insert, thus retaining flanks with the flat surfaces for seating in the pocket. However, this solution reduces the number of usable wiper cutting edges per insert.
Another design used for wiping is a negative crown applied to top and/or bottom insert surfaces, see
FIGS. 2
a
and
2
b
. The top surface
210
of the insert
200
has a land
220
that descends from the center
290
of the top surface outward and downward to the flanks
230
of the insert. This land intersecting the flanks creates a cutting edge
240
that is lower, with reference to top surface
210
, at the corners
250
of the insert than at mid-flank position
260
, thereby forming a resulting radius along the insert cutting edges, in this design, the highest point on the finish cutting edge, with reference to the top surface performs the wiping action. Bottom surface
270
also has a land
280
, thereby providing additional cutting edges. The negative crown design results in several drawbacks: This prior art design has the highest point on the finish cutting edge fixed at roughly the mid-flank position between the corners adjacent the cutting edge. Thus, the distance from the active cutting corner to the wiper is dictated by the size of the insert A second drawback is increased horsepower required for cutting due to the obtuse angle between flank
230
and land
220
. A third drawback is increased cutting force generated in the workplace and the tool due to the negative crown geometry, which results in workplace deflection, chatter and accelerated tool wear. Furthermore, when the negative crown geometry is used on a positive insert, little, if any, positive cutting angle to the workpiece can be achieved and fewer cutting edges are available, and when used on a negative insert no positive cutting or neutral cutting angle to the workpiece can be obtained and the insert has a limited range of angular presentation of the cutting edge to the workplace.
Hence there is seen to be a need in the cutting tool art for providing an indexable wiper insert for mounting in a cutting tool, such as a rotary milling, reaming, boring tool or the like, having positive cutting action that uses all available cutting edges and seats properly in the tool body. There is a further need for an indexable insert wherein the position of the wiping portion of the cutting edge can be varied for machining around fixtures and the like.
SUMMARY OF THE INVENTION
An object of the invention is to provide a cutting insert, cutting tool and method of machining that overcomes the limitations of the prior art. It is a further object of the invention to provide an indexable wiper insert having positive cutting action that uses all available cutting edges and seats properly in the tool body. It is a yet further object of the invention to provide a positive geometry wiper wherein the position of the wiping portion of the cutting edge can be varied for machining around fixtures and the like.
One object of the invention is to provide a cutting insert of hard, wear resistant material including a body having substantially polygonal major surfaces, flanks extending therebetween, respective pairs of the flanks intersecting to form corners, at least one pair of cutting edges including a lead cutting edge and a finish cutting edge sharing a common corner and being formed by intersection of a major surface with one of the respective pairs of flanks, wherein the finish cutting edge is a curve in a plane of the flank that forms the finish cutting edge, the curve having an apex proximate the common corner, the curve forming a wiper on the finish cutting edge at or closely proximate to the apex. In another aspect of the invention, the wiper may be positioned a selected distance “d2” from the common corner, which can range from 0.5% to 45% of the length of the flank that forms the finish cutting edge. Alternatively, the distance “d2” is selected to range from approximately two times the common corner radius to less than half a length of the flank that forms the finish cutting edge
In another aspect of the invention each finish cutting edge extends along a wiper form in the major surface adjacent the finish cutting edge, the wiper form has a positive or neutral geometry.
In another aspect of the invention, the curve includes a first portion defined by a first radius and a second portion defined by a second radius. It is an object of the invention to provide the curve with a second radius that decreases along the finish cutting edge from the wiper to the common corner. Alternatively, the curve may include a first portion defined by a first radius and a second portion defined by a plurality of radii.
It is another object of the invention to provide a cutting insert of hard, wear resistant material including a body having substantially polygonal major surfaces, flanks extending therebetween substantially perpendicular to the surfaces, respective pairs of the flanks intersecting to form corners, at least one pair of cutting edges including a lead cutting edge and a finish cutting edge sharing a common corner and being formed by intersection of a major surface with one of the respective pairs of flanks, the finish cutting edge being curved in a plane of the flank forming the finish cutting edge and having a wiper at a selected position on the finish cutting edge, wherein each finish cutting edge extends along a positive or neutra

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