Method and apparatus for forming blanks

Metal deforming – By application of fluent medium – or energy field – With actuated tool engaging work

Reexamination Certificate

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C072S063000, C029S421100

Reexamination Certificate

active

06308545

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a method for forming blanks.
BACKGROUND OF THE INVENTION
If small radii are to be produced in edge and corner regions of workpieces by means of internal high pressure forming, i.e. forming by means of pressurizing the workpieces with a high liquid pressure in suitable forming dies, then for shaping these small radii extremely high pressures of about 4000 bar and higher are necessary. Thus, for keeping closed the die parts and/or a surrounding pressure casing, particularly in the case of large-surface area parts, very high keeping closed forces are necessary, which are difficult to achieve. This more particularly applies in conventional internal high pressure forming, in which the die simultaneously constitutes the pressure enclosure for the liquid bringing about forming. The invention more particularly relates to blanks preformed by means of internal high pressure forming and is in particular part of a corresponding method. However, it can also be used for otherwise preformed blanks.
Thus, the problem of the invention is to provide a method and an apparatus by means of which a postforming of blanks can take place in critical edge and corner regions.
SUMMARY OF THE INVENTION
According to the invention, the set problem is solved in the case of a method of the aforementioned type in that a postforming of preformed blanks exclusively takes place by means of high liquid pressure in the edge and corner regions. An apparatus for forming blanks for solving the set problem is characterized by a forming die with concave expansion spaces in its edge and corner regions.
According to a preferred development of the inventive method, only expansion spaces formed at edge and corner regions of a forming die part are subject to a high liquid pressure and in particular in recessed edge and corner regions of a forming die part (forming insert) closed expansion elements engaging in regions of the blank to be formed are subject to high liquid pressure. The expansion spaces of the corresponding die part, which can be a forming insert, but also an upper or lower part of a die, provided that thereon by convex cavity blocks can be constructed concave areas of the workpiece or blank facing the same, are directly exposed to the high liquid pressure. As a result of the tight engagement of a die part enclosing the workpiece or blank within it and e.g. a forming insert in planar areas or regions with large radii, at least if no small radii have to be formed in marginal areas of the workpiece up to the closing edges of the die parts and particularly if the latter are surrounded by a separate pressure casing, it is possible to produce an adequate pressure drop. However, as stated, preferably there are separate expansion elements which, according to a preferred development, can comprise tubes and whose material is preferably polymer or elastically or plastically deformable metal and in the latter case the expansion elements are permanent elements.
As a result of the apparatus according to the invention, in edge or corner regions of a preformed workpiece or blank, local radii can be postformed under high liquid pressure. As a result of the small projection surface in the case of liquid pressurization solely in edge and corner regions and in which the transverse dimensions of the surfaces exposed thereto are only a few millimetres, it is possible to work with limited forces, particularly limited pressing and closing forces. Due to the fact that the expansion spaces to be filled with liquid under high pressure are very small compared with the spaces normally having to be filled in the case of internal high pressure forming, a rapid filling of said expansion spaces in the corner and edge regions is possible, so that short process times can be achieved for the postforming according to the invention.
The invention is more particularly usable with a die for internal high pressure forming with a spacer provided between the upper and lower part of the die, in which in at least one of said die parts is formed a workpiece and in which the liquid supply line for forming the workpiece takes place through the spacer, as described in the parallel patent application “Method and apparatus for the hydraulic forming of a workpiece” of the present applicant and whose content is made fully into part of the present disclosure. In this case the spacer is removed after preforming the workpiece and a forming insert constructed according to the invention is placed in the die and the die upper and lower parts from the first internal high pressure forming phase can be used without any change for postforming. The forming insert is a complete or partial form or shape memory of the sheet metal blank final geometry, which optionally has said expansion elements in the corner and edge regions to be postformed or calibrated. The expansion of the expansion elements is limited by the positive engagement of the insert, i.e. the walls of the insert bounding the expansion spaces receiving the expansion elements and serving as abutments.


REFERENCES:
patent: 2997093 (1961-08-01), Harris
patent: 3280608 (1966-10-01), Parilla
patent: 3344646 (1967-10-01), Moller
patent: 3827130 (1974-08-01), Baumann
patent: 5524466 (1996-06-01), Coe
patent: 5916317 (1999-06-01), Willoughby et al.

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