Milling cutting insert and milling cutter

A shank of a milling cutter can be somewhat elastic. As a result, during plunging down into a workpiece the milling cutter will not plunge in a true axially downward direction and will form a slanted wall in the workpiece. A milling cutting insert is provided which is capable of “straightening out” the slanted wall. The cutting insert has a rear cutting edge which removes material when the milling cutter is moved axially upwardly.

FIELD OF THE INVENTION

The present invention relates to a milling cutting insert and a milling cutter for use in plunge milling operations.

BACKGROUND OF THE INVENTION

When plunge milling along an edge, or along the walls of a pre-existing pocket or cavity of a workpiece, a milling cutter is subjected to unbalanced radial cutting forces which tend to deflect the milling cutter away from the workpiece. This phenomenon is particularly problematic during deep plunging in which the milling cutter has a long shank, or a long extension shank.

Long shanks tend to be somewhat elastic so that during deep plunging the unbalanced radial cutting forces cause the shank to bend. The deeper the plunging, the greater the bending of the shank. As a consequence, the milling cutter will not plunge in a true axially downward direction, and a resulting milled portion of a surface of the workpiece will be slanted. This is a disadvantage if a true vertical surface is required.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention there is provided a milling cutting insert comprising a pair of opposing end surfaces (12), a pair of opposing minor surfaces (14) and a pair of opposing major surfaces (16). Each end surface (12) and major surface (16) intersect at a major edge (20), at least a portion of which forms a major cutting edge (30), and each end surface (12) and minor surface (14) intersect at a minor edge (32), at least a first portion of which forms a minor cutting edge (36) and at least a second portion of which forms a rear cutting edge (44). Each rear cutting edge (44) merges with and is transverse to an adjacent minor cutting edge (36); each rear cutting edge (44) has a rear relief face (48) that extends towards an opposite end surface (12); each rear cutting edge (44) has a rear rake face (50) that extends along the associated end surface (12); and in a top view of the cutting insert (10), one rear cutting edge (44) of each end surface (12) is not obscured by any part of the cutting insert (10).

Preferably, each end surface has a 180° rotational symmetry about a first axis that passes through the end surfaces. Further preferably, each minor surface has a 180° rotational symmetry about a second axis that is perpendicular to the first axis and passes through the minor surfaces. Yet further preferably, each major surface has a 180° rotational symmetry about a third axis that is perpendicular to both the first and second axes and passes through the major surfaces.

In accordance with another aspect of the present invention there is provided a milling cutting insert comprising a pair of opposing end surfaces (12), a pair of opposing minor surfaces (14) and a pair of opposing major surfaces (16). Each end surface (12) and major surface (16) intersect at a major edge (20), at least a portion of which forms a major cutting edge (30), and each end surface (12) and minor surface (14) intersect at a minor edge (32), at least a portion of which forms a minor cutting edge (36). A first axis (A) passes through the two end surfaces (12), a second axis (B) perpendicular to the first axis (A) passes through the two minor surfaces (14) and a third axis (C) perpendicular to the first and second axes (A, B) passes through the two major surfaces (16), the first and third axes (A, C) define a first plane (P1), and the second and third axes (B, C) define a second plane (P2). An intersection between each end surface (12) and each minor surface (14) also forms a rear edge (34) that extends towards an adjacent major edge (20), at least a portion of the rear edge (34) constitutes a rear cutting edge (44) which merges with the minor cutting edge (36) and extends therefrom towards the first plane (P1) in the general direction of the second axis (B). The rear cutting edge (44) has a rear relief face (48) which extends away from the rear cutting edge (44) towards the second plane (P2); the rear cutting edge (44) has a rear rake face (50) which extends away from the rear cutting edge (44) along a portion of its associated end surface (12); and in a top view of the cutting insert (10), one rear cutting edge (44) of each end surface (12) is not obscured by any part of the cutting insert (10).

Preferably, each end surface has a 180° rotational symmetry about the first axis. Further preferably, each minor surface has a 180° rotational symmetry about the second axis. Yet further preferably, each major surface has a 180° rotational symmetry about the third axis.

There is also provided in accordance with the present invention, a milling cutter comprising a cutter body having a forward end, a rear end, a peripheral surface and an axis of rotation extending between the forward and rear ends and defining a direction of rotation; and

a plurality of insert pockets formed on the forward end and opening out to the peripheral surface of the cutter body, each insert pocket retaining a cutting insert in accordance with the present invention.

The cutting insert is retained so that one of its major surfaces faces generally rearwardly, an operative end surface faces generally in the direction of rotation and an operative rear cutting edge, associated with the operative end surface, projects radially outwardly beyond the peripheral surface.

Typically, the operative rear cutting edge extends radially outwardly beyond any portion of the milling cutter.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Attention is drawn toFIGS. 1 to 3showing a tangential milling cutting insert10which is typically manufactured by form pressing and sintering carbide powders. Tangential cutting inserts also known as on-edge, or lay down, cutting inserts, are oriented in an insert pocket in such a manner that during a cutting operation the cutting forces are directed along a major (thicker) dimension of the cutting insert. It should be noted that directional terms appearing throughout the specification and claims, e.g. “forward”, “rear”, etc., (and derivatives thereof) are for illustrative purposes only, and are not intended to limit the scope of the appended claims.

The cutting insert10has a generally cuboid body and comprises two identical opposed end surfaces12, two identical opposed minor surfaces14and two identical opposed major surfaces16. The cutting insert10has a first dimension D1measured between the end surfaces12that is greater than a second dimension D2measured between the major surfaces16. A third dimension D3measured between the minor surfaces14is also greater than the second dimension D2.

The cutting insert10has a first axis A passing through the two end surfaces12, a second axis B perpendicular to the first axis A and passing through the two minor surfaces14and a third axis C perpendicular to the first and second axes A, B and passing through the two major surfaces16. The first and third axes A, C define a first plane P1, and the second and third axes B, C define a second plane P2. A through bore18extending between the major surfaces16has a bore axis that coincides with the third axis C. The cutting insert10has 180° rotational symmetry about each of the first, second and third axes A, B, C.

An intersection between each end surface12and each major surface16constitutes a major edge20which extends between a first22and second24limit. A first portion26of the major edge20extends away from the first limit22in the general direction of the second axis B. A second portion28of the major edge20merges with the first portion26, and extends initially towards the second plane P2and then away from the first plane P1to the second limit24. The first portion26of the major edge20constitutes a major cutting edge30.

An intersection between each end surface12and each minor surface14is divided into a minor edge32and a rear edge34. The minor edge32constitutes a minor cutting edge36, and the rear edge34extends to the second limit24of an adjacent major edge20. Two recesses38, each having a recess face40, are formed in each minor surface14, each recess opening out into an adjacent end surface12. Each recess face40and the adjacent end surface12intersect along a recessed edge42which forms part of the rear edge34. At least a portion of the recessed edge42constitutes a rear cutting edge44. The rear cutting edge44merges with the minor cutting edge36and extends therefrom towards the first plane P1in the general direction of the second axis B. A corner cutting edge46is formed between each major cutting edge30and its adjacent minor cutting edge36. Each rear cutting edge44has a rear relief face48and a rear rake face50. The rear relief face48extends away from the rear cutting edge44towards the second plane P2along a portion of its associated recess face40. The rear rake face50extends away from the rear cutting edge44along a portion of its associated end surface12. It is noted that the second portion28of each major edge20, is closer to the first and second planes P1, P2, than an adjacent rear cutting edge44. As a result, in a top view of the cutting insert10(seeFIG. 2); one rear cutting edge44of each end surface12is not obscured by any part of the cutting insert10.

Attention is now drawn toFIGS. 4 and 5showing a plunge milling cutter52having an axis of rotation E defining a direction of rotation R. The milling cutter52has a cutter body54which is provided with a plurality of insert pockets56on a forward end58thereof. Each insert pocket56opens out to a peripheral surface60of the cutter body54and has a cutting insert10in accordance with the present invention retained therein by means of a clamping screw (not shown). A rear end62of the cutter body54is designed to receive an adaptor having a long shank, or a shank extension, for deep plunging operations.

When mounted in the cutter body54, each cutting insert10has adjacent its operative end surface12, that is the end surface12facing the direction of rotation R, one operative rear cutting edge44. The operative rear cutting edge44is located radially outwardly beyond the periphery60of the cutter body54and beyond any portion of the milling cutter52.

During plunge milling operations in which the milling cutter52does not plunge fully into a workpiece64, for example when plunging along an edge, or along the walls of a pre-existing pocket or cavity of the workpiece64, the cutting forces acting on the milling cutter52are not balanced and as a result the milling cutter52is subjected to radial forces directed away from the workpiece64. Due to these radial forces, the shank, or the shank extension, will develop an elastic deformation and bend away from the workpiece64, and thereby form a slanted wall66on the workpiece64while advancing axially downwardly. The deeper the plunging, the greater the bending of the shank, therefore the slant of the workpiece64is greatest at the bottom of a milled portion of the workpiece64, where the milling cutter52terminates its downstroke. Ideally, the plunged portion of the workpiece64should have a vertical surface. The material in the slanted wall66is superfluous material that deviates from the desired vertical surface. The cutting insert10of the present invention is capable of removing, or at least partially removing, the superfluous material.

On completion of the downstroke, the milling cutter52continues to rotate on the spot at the bottom of the milled portion before the upstroke commences. Whilst rotating on the spot, the elastic deformation that has accumulated in the shank will force the minor and corner cutting edges36,46to penetrate radially into the slanted wall66of the workpiece64and thereby mill a depression68in the superfluous material. The milling cutter52is now moved axially upwardly (upstroke) during which the rear cutting edges44of the cutting inserts10remove superfluous material located axially above the depression68thereby “straightening out” the portion of the workpiece64milled during the downstroke.

Although the present invention has been described to a certain degree of particularity, it should be understood that various alterations and modifications could be made without departing from the scope of the invention as hereinafter claimed.