Cutters – for shaping – Including tool having plural alternatively usable cutting edges
Reexamination Certificate
1999-04-05
2001-07-10
Tsai, Henry (Department: 3722)
Cutters, for shaping
Including tool having plural alternatively usable cutting edges
C407S114000, C407S115000
Reexamination Certificate
active
06257807
ABSTRACT:
The invention relates a cutting insert for drilling with a substantially rhomboid basic shape, whose four cutting edges forming respectively four cutting corners are broken, whereby two first opposite cutting edges each have cutting edge segments forming an obtuse angle between 140° and <180°.
The invention relates further to a drill for drilling in solid materials, with a shank and at least two exchangeable cutting inserts having several cutting edges, arranged in a recess on the front face of the shank, whose work areas are adjacent to each other and overlap partially, whereby each cutting insert has cutting edges with mutually inclined cutting edge segments, which in the operational state are simultaneously effective, whereby the radial innermost cutting insert borders directly on the drill axis or slightly surpasses the same.
A cutting edge of the aforementioned kind is known for instance from EP 0 088 505 A1, This cutting insert has a rhomboid basic shape with pointed and dull cutting edges arranged opposite to each other in pairs, whereby each cutting edge is broken in a roof-shaped manner, so that the respective cutting edge segments with the approximately identical length of each cutting edge form an angle between 135° and 170°.
In the EP 0 088 505 a drill of the mentioned kind is also described, whose drill front face has a radially inner and a radially outer cutting insert of the mentioned king, whereby the connection line of two cutting corners of the cutting edge of each of the cutting inserts brought into contact with the workpiece is approximately perpendicular (vertical??) to the longitudinal axis of the drill.
The EP 0 181 844 B1 describes a cutting insert with a substantially rectangular contour, which has roof-shaped (convex) cutting edges only on the short sides. The two longer lateral surfaces, which are offset in the middle area with respect to the respective cutting corners, can not be used for machining. The construction of this cutting insert is such that two regular triangles with convexly broken sides are arranged in such an overlapping manner, that two corners of each of the triangles and one side of each of the triangles coincide with one cutting edge of the rectangular cutting insert and parts of the other side of the triangle coincide over a certain distance, in order to form adjoining cutting edges, so that both third corners of the triangles, which are arranged in the cutting insert, overlap over a distance which equals 0.5 to 0.7 times the length of the cutting insert between the breaking or bending points of the cutting edge, and that in the plane of the upper surface the shortest distance between the long lateral surfaces of the cutting insert is shorter than the distance between the ends of the respective cutting edges.
For drilling in solid material primarily hexagonal cutting plates are used, which essentially have a triangular basic shape and wherein each time two cutting edges forming an obtuse angle between 120° and 170° are involved in the chip-removal process. The use of such cutting plates is proposed for instance in DE 27 30 418 C2, whereby the cutting plates are each arranged in a recess of the drill shank, in such a manner that the bisecting line of the angle of the engaged cutting plates of each indexable insert is parallel to the drill axis or arranged at a slight inclination of maximum 2°. The disadvantage of this drill consists in that a force balancing of the drill shank is possible only when the respective two cutting edges in operation of a cutting plate are basically involved over their entire length, respectively when the work areas of two neighboring cutting plates do not overlap.
In the EP 0 054 913 B1 it is proposed to arrange the recesses for receiving the individual indexable inserts in such a way that the radial cutting force components of the cutting edges in operation for each individual indexable insert are balanced, in that the bisecting line of the angle of this cutting edge be inclined with respect to the parallel to the drill axis by an angle which depends on the effective length of the cutting edge in operation along a partial segment.
In order to balance the radial forces it has also been proposed in the DE 27 51 255 C2 that, for balancing the radial forces acting on the drill shank, the radial plane of the inner cutting insert be inclined rearwards, in a direction opposite to the rotation direction of the drill, at a certain angle against the peripherally arranged cutting insert. However by this the forces are merely directed parallelly, but not balanced, since the offset angle can not have any influence on the size of the radial forces and the cutting forces. Therefore the forces are preserved as a function of the cutting conditions and do not depend on the tool geometry.
The cutting inserts for a drill proposed by FR-A-2 387 723 have cutting edges with a notch in the center which should serve for interrupting, respectively limiting the effective cutting edge length. Depending on the position of the cutting insert with respect to the drill axis, only one of the two cutting edge halves is effectively engaged in cutting.
The WO 93/02824 describes a cutting insert with at least three cutting edges bordering the face and with cutting edges lying between two cutting corners, wherein at least one cutting edge has two projecting cutting points. The projecting cutting points can be formed either by the cutting corners of a concavely curved cutting edge itself, respectively one provided with a central constriction, or by projecting points, which extend beyond the roofed connection line of two cutting edges and which lie on one side of two middle cutting edge segments, which are arranged with respect to each other at an angle of >180° forming a constriction. In a corresponding variant the projecting points can also be realized in square or rectangular cutting inserts. From this reference it is also known to develop, in a broken cutting edge to be brought into contact with the workpiece, a prolongation beyond the cutting corner, which serves as a secondary cutter for the smoothing of the cut bore wall.
The EP 0 775 547 A1 (State of the Art according to Article 54 (3) EPU) describes a drill with cutting inserts with a polygonal basic shape with two first opposite cutting edges, each consisting of two cutting edge segments forming an obtuse angle, and two further cutting edges arranged on opposite sides, consisting of individual cutting edge segments, whereby one of this segments protrudes with respect to the adjacent cutting edge segment. The protruding cutting edge segment has a length which corresponds approximately to the half of the entire cutting edge. The cutting inserts are arranged on the drill front face in such a manner that the cutting edge with the protruding cutting edge segment comes to be radially outward and a roof-shaped cutting edge comes to be radially inward during the cutting operation, whereby the cutting edge of the radially inward cutting insert slightly surpasses the longitudinal axis of the drill.
Finally the DE 44 16 040 A1 describes a drill with two indexable inserts which are basically triangular and peripherally staggered at about 180°, with cutting edges whose rectilinear main cutting edges run at an acute setting angle radially outwards and rearwards with respect to the advance direction, and which during drilling both sweep at least approximately the same surface, whereby the cutting edges with inner corner areas or parts of the same extend up to the center of the tool or beyond it. This corner area has a rounding and an adjacent edge which is shorter in relation to respective straight main cutting edge, whereby the corner angle between the respective main cutting edge and the shorter straight edge is 90° or bigger. Due to the respective chamfered corner areas, during the drilling of a workpiece a pointed cone remains in the center.
It is the object of the present invention to create a cutting insert representing an alternative to the cutting insert mentioned in the
Dubno Herbert
Tsai Henry
Widia GmbH
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