Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Having separate expander means – With hole forming means
Patent
1996-09-06
2000-09-19
Green, Brian K.
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Having separate expander means
With hole forming means
4113872, 4113878, 408244, 408225, P16B 2500, B23B 5100
Patent
active
061202258
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a lamina-shaped borepiece for self-boring fastening elements, e.g. rivets, screws, dowels or similar elements, with two front cutting edges which together enclose an angle of less than 180.degree., and with grooves which are assigned to each of the cutting edges and run at least approximately parallel to them when viewed in the drilling direction.
Specifically in the case of a drilling process in thin material, for example in thin sheet metal, there is always the risk that the bore will not be exactly circular, but rather approximately triangular, like a constant diameter cam. Such a phenomenon occurs both with cylindrical borepieces and with lamina-shaped bore pieces.
A self-boring screw with a lamina-shaped borepiece is known from DE-C 28 01 962. Also, a version has already become known (U.S. Pat. No. 4,480,951), in which a lamina-shaped borepiece is formed like a stepped borer. The front bore section with a small diameter is flanked by a borepiece arranged with an axial offset relative to the first, which can then enlarge the bore which was first produced. Particularly in the case of such lamina-shaped borepieces, however, and at relatively small diameters, there is the problem that because of the thickness of the borepiece, high friction forces occur at the bore wall which is produced.
The present invention has set itself the task of developing a lamina-shaped borepiece in such a way that predrilling can take place with a relatively small diameter, and the production of a precisely circular bore is guaranteed.
According to the invention, this is possible in that an indent with a set-back cutting edge is provided, in each instance, in the region of both front cutting edges, with a first delimitation of these indents being aligned parallel to the center axis of the borepiece, in each instance, and a second delimitation, which forms the set-back cutting edge, running at an acute angle to the center axis, and that the indents are formed in the region of the axial extension of the grooves. With this particular design according to the invention, the result achieved is that the region of the borepiece which directly flanks the two front cutting edges, with the exception of the direct cutting edge region, is thinner than the thickness of the lamina-shaped borepiece, since, after all, this region lies directly in the grooves which cross one another from both sides on the opposite delimitation surfaces.
It is also of particular advantage in the design according to the invention that the set-back cutting edges are also formed in the region of the grooves, so that a corresponding cutting angle can be guaranteed and furthermore there is the possibility of changing the cutting angle, depending on the drilling radius, by varying the angle of these set-back cutting edges.
Such a possibility exists, for example, if the angle enclosed by the set-back cutting edges is greater than the angle enclosed by the front cutting edges. The set-back cutting edges then do not run parallel to the front cutting edges and therefore to the grooves, so that the cutting edges have a different cutting angle over their entire length, and then, at their extreme end, return to the cutting angle determined by the front cutting edges, for example.
It has proven to be advantageous if the angle enclosed by the set-back cutting edges lies in the range between 160.degree. and 180.degree.. As a result, the borepiece set back relative to the center preborepiece can almost act like a milling device, guaranteeing that the larger bore region is already fully in use before the preborepiece formed by the front cutting edges has penetrated the work piece. In addition, this guarantees that proper guidance of the preborepiece exists until the larger bore segment is in full use.
To produce a precisely circular bore hole, it has proven to be sufficient if only a relatively short region functions as the preborepiece. It is therefore proposed that the greatest axial extension of the indents leads approximately to half the width of the g
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patent: 5452970 (1995-09-01), Sundstrom et al.
patent: 5697738 (1997-12-01), Stone et al.
patent: 5700113 (1997-12-01), Stone et al.
Green Brian K.
Santos Robert G.
SFS Industrie Holding AG
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