Cutting insert and milling tool

Details Cutting insert and milling tool Cutting insert and milling tool

1999-07-26

2001-05-08

Tsai, Henry (Department: 3722)

Cutters, for shaping

Including tool having plural alternatively usable cutting edges

C407S114000, C407S115000

Reexamination Certificate

active

06227772

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a cutting insert with a substantially cubical base body which is formed as a turning plate with eight usable cutting edges including two mutually parallel planar and large faces traversed by a fastening hole and four lateral faces bounding each of the larger faces, namely, two mutually parallel smaller end faces and two mutually parallel larger longitudinal faces which, centrally along their longitudinal axis, have a projecting rib serving as an abutment surface upon clamping of the cutting insert in a tool carrier, whereby the larger faces have a rounded edge transition into the smaller end faces so that at the longitudinal sides, approximately one-quarter-circular cutting edges are formed as boundary lines to the end faces in the corner regions, whereby the longitudinal cutting edges are formed as boundary lines between the larger faces and the respective longitudinal face bounding same and are curved arc-like so that a mirror-symmetrical body with respect to the longitudinal median plane and to the transverse median plane results.
BACKGROUND OF THE INVENTION
Such a cutting insert is known for example from DE 295 16 668 U1. This cutting insert has four long cutting edges which have convex ground arc contours. The longitudinal faces are bounded by short rectilinear cutting edges with the respective end faces at the short end sides and which via respective one-quarter-circular cutting edge corners, transition into the longer cutting edges. Thus all of the aforementioned cutting edges have positive leading edge angles which are formed on the longitudinal sides at the longer cutting edges with chip-forming troughs and similar troughs are arranged also in the regions of the one-quarter circular cutting edge corners.
A multiplicity of such cutting inserts can be uniformly distributed on a milling cutter head along the periphery. The cutting inserts on the peripheral surface and those on the end face of the tool carrier are so mounted that all of the cutting inserts in their effective positions have cutting edges which can remove chips in the radial or axial direction. Those cutting edges which in their effective positions are active in the radial direction project slightly beyond the cutting edges inserted into the end face of the tool carrier while the cutting edges effective at the end face of the tool carrier are so inserted that in the axial direction the cutting edges each project beyond the cutting edges of the cutting plates inserted into the periphery of the tool carrier.
In order to enable the function described in the aforementioned reference to be achieved, the insertion positions must be radial and axial so that the eight cutters are usable. It is here a disadvantage that the first plate must be offset from the next by a certain amount so that there will be no damage to the milled contour by projecting plates where there is an adjustable free angle. For the milling of crankshafts, the aforedescribed turning plates are not suitable in any case. The same applies also for the substantially identically shaped cutting plates of U.S. Pat. No. 3,762,005.
OBJECT OF THE INVENTION
It is the object of the present invention to provide a cutting insert for tangential incorporation in a milling tool whereby the milling cut depth can be increased and simultaneously a sufficient chip discharge away from the machined workpiece can be ensured.
SUMMARY OF THE INVENTION
These objects are attained with the cutting insert of claim
1
.
According to the invention, the longer cutting edges here form with their respective ends and the rounded edges between the smaller end faces and the larger faces an angle <90°. Stated otherwise, the longer cutting edges have a concave configuration or, in the middle region of the cutting edge a constriction.
A cutting insert is indeed known from DE 83 17 114.2 U1 which, in a plan view, has a substantially rectangular configuration and whose longer sides of the cutting faces are provided at their centers with a substantial constriction but wherein the associated lateral edges are not configured for chip removal or are not cutting edges.
With the configuration according to the invention, the intermediate part which is set back relative to the cutting edge ends on either side thereof is used in the cutting by one or the other cutting edge and thus is “twice” used. In milling, the main wear which arises is in the regions of the cutting corners. The cutting insert according to the invention, which is fastened on a mill tangentially, enables in crankshaft machining greater over-measure of the flanks arising in the crank region to be so overlapped that a cutting depth greater than (0.5×cutting plate length) is possible since, as has already been noted, both the left and the right cutting edge halves of the cutter can be utilized and the middle region of both left and right cutters, can be used.
For forming the arc-shaped curvature, there are two variants which can be selected: in one, the longer cutting edges are at least partly configured as concave or can be formed with an angle >180° between the adjoining linear portions. It is important that the basically concave configuration imparted to the longer cutting edges retain a constriction, i.e. a set back middle region.
According to a further feature of the invention, the intermediate region of the longer cutting edge is linearly shaped, preferably with a length up to one-half the total length of the cutting edge. According to a further feature of the invention, the lateral chip angle between the longitudinal cutting edge and the rounded edge is between 0° and 20°; the cutting angle between the greater surface and the longitudinal side is positive and preferably lies between 0° and 20°.
The concave configuration of the longer cutting edges enables, in combination with the intermediate rib, the formation of specially configured chip chambers. The rib width should not exceed 1.5 mm which ensures a spacial separation of the cutting edges lying respectively on both sides of the rib from one another, whereby the intermediate rib can protect the cutting edge which is not engaged in the machining operation from the chip which is cut away and can serve as an abutment surface for the plate seat. The projecting of the rib in the intermediate region can be positive or negative relative to the bounding surface region, especially when the cutting insert seat is configured as convex. The length/width ratio of the larger face and thus the respective longer cutting edge to the (shorter) rounded edges is preferably between 1.2 and 2. The shortest spacing of the fastening hole edge from the longer cutting edges lies below 2 mm.
To stabilize the region of the cutting edges in the corner regions as a preventative to cutting edge breakage, the cutting insert alternative of claim
9
is proposed.
This cutting insert has longer cutting edges with respective ends forming with the round edges between the smaller end faces and the larger face, an angle between more than 70° and less than 90°. Additionally at least one of the cutting surfaces between the larger face and smaller end faces is a plane which is oriented at an angle between 90° and 180° to the smaller end face and on the longitudinal side forms an auxiliary cutting edge which is disposed at an angle of attack &kgr; between 0°<&kgr;<90°, preferably &kgr;=20°+10°. By the flattening in the corner region with formation of an auxiliary cutting edge, the maximum chip thickness can be reduced correspondingly to the sine of the angle &kgr; which stabilizes the cutting corner.
A further advantage of this cutting insert is given, for example, in the crank bearing machining of crankshaft since the described cutting insert can be used for roughing machining with the concavely formed long cutting edge and the described auxiliary cutting edge, to roughing being followed by (fine) finish machining.
Further features of the invention are described thus according to a first embodiment, the longer cutting edges are compo

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