Cutters – for shaping – Including tool having plural alternatively usable cutting edges
Reexamination Certificate
2002-08-08
2004-05-11
Fridie, Jr., Willmon (Department: 3722)
Cutters, for shaping
Including tool having plural alternatively usable cutting edges
C407S040000, C407S042000, C407S103000
Reexamination Certificate
active
06733214
ABSTRACT:
This application claims priority under 35 U.S.C. §§119 and/or 365 to patent application Ser. No. 101 38 896.9 filed in Germany on Aug. 8, 2001, the entire content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The present invention concerns a cutting bit for milling, comprising an upper face which at least partially serves as a rake face and a lower support face which is substantially parallel thereto, wherein the upper face and the lower face are connected together by a peripherally extending edge face. The upper face is of a substantially hexagonal peripheral shape and at its intersection with the edge face defines cutting edges, wherein the edge face at least in its region adjoining the cutting edges defines at least six clearance faces which are respectively angled through about 60° relative to each other.
The present invention also concerns a milling tool having a cutting bit carrier for accommodating corresponding cuffing bits.
Substantially hexagonal cutting bits with a hexagonal basic shape are known in principle, thus for example from U.S. Pat. No. 6,004,081, which besides hexagonal also discloses octagonal cutting bits or quadrangular cutting bits, the corners of which are markedly chamfered by bevels. U.S. Pat. No. 5,827,016 also discloses a polygonal and in particular octagonal cutting bit which is intended in particular for use on milling tools.
In the case of milling tools, in particular in the case of surface or planer milling machines, cutting bits are frequently arranged along the periphery of an end of a rotating cutting bit carrier in such a way that a front cutting edge portion which is radially furthest outward defines the active cutting edge which in the milling operation removes material in the form of chips from the workpiece to be machined (which is generally a metal workpiece). In that situation, while the tool is rotating about an axis of symmetry, the tool is moved perpendicularly to that axis and generally parallel to the surface of the workpiece, in which case the cutting bits penetrate into the material and remove it with a cutting action.
The cutting bits generally comprise hard metal, cermet or hard ceramic, in particular sintered carbides, but also other metallic or ceramic materials, possibly with hard coatings. It is also possible to use polycrystalline diamond (PCD) or cubic boronitride (CBN) as the cutting material.
Corresponding cutting bits are admittedly extremely hard and wear-resistant, but to achieve maximum productivity they are also very heavily loaded so that, in spite of their great hardness and resistance to wear, under intensive use they often exhibit considerable traces of wear after just a few hours. As such cutting bits are relatively complicated and expensive to produce, they are also correspondingly costly so that obviously the attempt is made to handle a given machining volume with a minimum consumption of cutting bits. For that purpose very many cutting bits are in the form of what are known as ‘reversible cutting plates’, that is to say they each have a plurality of cutting edges, only one of which is active in use at any given time, while the others do not in practice come into contact with the workpiece, by virtue of their arrangement. After one of the cutting edges is worn the cutting bit is then suitably turned or ‘indexed’ so that now another cutting edge which has not been used hitherto assumes the position of the active cutting edge and the previous active cutting edge changes into the position of one of the non-active cutting edges. That can continue until all cutting edges on a cutting bit are worn.
There are cutting bits having two, three, four and even more cutting edges, as has already been described above. It will be appreciated that the cutting bits can be used in a correspondingly more economical fashion, the more cutting edges they have. However, limits are set in this respect by virtue of purely geometrical conditions and for example also the reaction forces which occur in the milling procedure. In specific terms, this means that the cutting edge cannot be inclined at just any shallow angle, with respect to the working plane, that is to say the plane which the milling tool produces on the workpiece, if on the one hand a good material removal rate is still to be achieved, but on the other hand the reaction forces should also not become excessive. Severe reaction forces result in vibration of the tool and thus shock-like engagement of the cutting edges and can in that respect considerably speed up the rate of wear of the cutting edges. For that reason the cutting edges are generally set through at least 45° with respect to the workpiece surface produced, which means that a corresponding cutting bit could be at a maximum of an octagonal configuration, if it is admitted that in that case a cutting edge which is most closely adjacent to the active cutting edge already comes into engagement with the workpiece surface which is being produced by the corner of the active cutting edge, being the corner which is axially furthest projecting.
More specifically it is frequently wanted that the surface produced by the axially furthest projecting cutting corner is as flat as possible from the outset and does not have any particular roughness or grooves as can otherwise occur if a for example rectangular or square cutting bit is set at an angle (inclined) with respect to the feed direction or the working face. At the same time, a relatively high feed speed is selected so that the cutting corner of a subsequent cutting bit, with respect to the cutting bit which precedes it on the workpiece, is already displaced a distance in the feed direction, when it comes into engagement with the workpiece. For that reason what are referred to as ‘parallel lands’ are generally provided in the corner regions of corresponding cutting bits, that is to say rectilinear chamfers on an otherwise for example right-angled (possibly also slightly rounded) transition between two adjacent main cutting edges, wherein the cutting bit is so set in its working position that the bevel is disposed in a plane which corresponds precisely to the feed plane while the adjoining cutting edge is correspondingly set, that is to say in the case of a regular quadrangular cutting bit with parallel lands angled through 45°, at about 45°. Such a cutting bit admittedly appears octagonal in plan view, but it is only each second one of its edges that serves as a cutting edge and the interposed chamfers serve as parallel lands. Therefore even such a cutting bit can be turned a maximum of four times in each case through 90° order after a main cutting edge has worn to bring the next, as yet unworn cutting edge into operation. Insofar as that technology is substantially applied to hexagonal cutting bits, as for example in the case of U.S. Pat. No. 6,004,081, that means a very shallow setting angle of the cutting edge relative to the workpiece of less than 45°, which is disadvantageous for the reasons already referred to above, as it results in substantial, irregular reaction forces.
The quality of the surface produced by such a milling tool also heavily depends inter alia on the exact configuration and angular orientation of the parallel land. If the parallel land still has a certain inclination with respect to the plane produced on the workpiece, that results in more severe residual roughness of the surface produced and/or more severe reaction forces and vibration of the tool.
In comparison with that state of the art, the object of the present invention is to provide a cutting bit having the features set forth in the opening part of this specification, which is highly productive insofar as it has a maximum number of cutting edges which are interchangeable by turning and is thus inexpensive, but which nonetheless at the same time gives rise to only low reaction forces and can thus also be operated in less powerful machine tools at a high speed of rotation and in that case produces precise and smooth surface structures on the workpiece.
SUMMARY
Burns Doane , Swecker, Mathis LLP
Fridie Jr. Willmon
Sandvik AB
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