Metal deforming – With 'coating' of work
Reexamination Certificate
2000-09-29
2001-12-11
Jones, David (Department: 3725)
Metal deforming
With 'coating' of work
C072S379200, C072S389300
Reexamination Certificate
active
06327884
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to press brake tooling, and particularly to press brake dies having workpiece contacting surfaces that are nitrided or nitrocarburized to a depth of not greater than 0.06 inches.
BACKGROUND OF THE INVENTION
Press brake tooling comprises a punch having an elongated edge which is generally “V” shaped in cross section, and a die having an elongated groove which has a complementary V-shaped cross sectional configuration. The upwardly open V-shaped groove of the die terminates upwardly in a pair of spaced edges. When a work piece—a piece of sheet metal, for example, is to be bent in the press brake, it is placed between the punch and the die, and the punch , which is vertically aligned with the die, presses downwardly upon the work piece. As the work piece bends, its bottom edges slide across the spaced edge surfaces of the groove. As this occurs, the edge surfaces of the groove may become scratched, chipped or otherwise worn away. The V-shaped punch, on the other hand, has a downwardly facing edge that contacts the upper surface of the workpiece primarily at a single line of contact, and comparatively little sliding motion between the workpiece and the punch edge occurs.
Depending upon the character of the surface of the work piece, and its stiffness (that is, its resistance to bending), the sliding motion between the bottom surface of the work piece and the surfaces of the spaced edges of the die can cause substantial damage to the spaced edges of the die. Once scratches, pits or wear appear in the die, the rate of wear of the die accelerates, and when the die surface is damaged to the point that the workpiece is affected, of course, the die must be replaced.
For reasons of economy, it is important that a die be capable of being used many times before the die needs to be replaced. To this end, die surfaces have been hardened so as to resist scratching, pitting or wear. The hardening of these surfaces, due to the methods of hardening, has been continued deep into the surfaces.
Two basic methods have been used to harden the surfaces of press brake dies. One of these methods involves making the entire die out of a tempered steel piece, but the resulting die is susceptible to breakage during use. The second method involves a heat hardening method, such as flame hardening or induction hardening, in which the surfaces of the die are hardened generally down to a depth of ⅛″ or more in order to achieve the desired surface hardness. This is a somewhat long and expensive process and produces only fair results.
As mentioned above, the hardening processes commonly used continue the hardening process well into the thickness of the die from its surface. Accordingly, die hardening methods involving only surface hardening, for example, have not been thought adequate.
It would be desirable to provide a die having a edge surfaces that are so resistant to abrasion as to be capable of repeated use without significant scratching, pitting or wear, thus reducing the necessity of purchasing expensive tooling and reducing downtime as dies are replaced.
BRIEF SUMMARY OF THE INVENTION
We have found, that, contrary to popular opinion, the surfaces of the die which are subjected to a rubbing or sliding action by the work piece can be nitrided or nitrocarburized to a small depth, generally not greater than about 0.06 inches, and that the resulting tool is highly resistant to scratching, pitting or wear. This surprising result appears to be due not only to the superior hardness that is provided by the nitriding and nitrocarburizing processes, but particularly to the slipperiness that these processes provide. Although we do not wish to be bound to the following explanation, it appears that the smooth, lubricious surface of the spaced die edge surfaces enable work pieces to slide more easily across these surfaces in a bending operation. As a result of their hardness and lubricity, the surfaces accordingly are highly resistant to scratching, pitting or wear or other deformation, and provide dies having a long life. The frequency of repair or replacement of dies can thereby be significantly reduced.
Thus, the present invention provides press brake tooling comprising a die and a mating punch for bending sheet stock, the punch having an elongated, generally V-shaped punch tip and the die being of steel and having an elongated, generally V-shaped groove in which the punch tip is received during a bending operation. The groove in the die has a floor and side walls extending divergently from the floor and terminating in edges spaced from each other across the width of the groove. The edges have edge surfaces that are configured to slidingly encounter the surface of a work piece as it is bent between the tool and the die. The die edge surfaces are nitrided or nitrocarburized to have a hardness in the range of 52-70 Rockwell C (that is, 86 to 94 on a 15-N microhardness scale), with said hardness extending into the die to a depth not exceeding about 0.06 inches.
At least the edge surfaces of the die are thus nitrided or nitrocarburized, and desirably nitriding or nitrocarburizing is performed, if not on the entire die, at least that portion of the die including the spaced edge surfaces and the floor and walls of the V-shaped groove. As noted, the nitriding and nitrocarburizing processes provide a hardness of 52-70 Rockwell C (86-94 on a 15-N microhardness scale to a depth not exceeding about 0.06 inches and preferably not greater than about 0.03 inches.
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Fredrikson & Byron , P.A.
Jones David
Wilson Tool International Inc.
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