Metal deforming – By application of fluent medium – or energy field – Using fixed die
Reexamination Certificate
1999-05-28
2001-01-30
Jones, David (Department: 3725)
Metal deforming
By application of fluent medium, or energy field
Using fixed die
C072S055000
Reexamination Certificate
active
06178796
ABSTRACT:
TECHNICAL FIELD
The invention relates to a device and a method for shaping flat articles from sheet metal. More specifically the invention concerns shaping flat articles from sheet metal in the automobile industry.
BACKGROUND ART
In a process for forming large, substantially flat articles in an industry such as the automobile industry it is common to use large conventional presses to stamp or press body panels such as roofs, hoods and trunk lids from sheet metal.
Such a stamping or pressing process usually involves a press with a three piece tool which has two large shaping surfaces, typically two halves of a mould made of highly expensive tool steel. There is also a third device to hold a sheet of metal, which is subsequently shaped by the two mould halves.
Depending on the degree of deformation involved, there may be more than one stamping or pressing stage needed to achieve the required shape and profile. However a conventional press is limited to achieving a maximum of between 1%-2% stretching during the shaping of substantially flat articles.
Membrane presses have been used extensively for the forming of articles from sheet and U.S. Pat. No. 2,344,743 and U.S. Pat. No. 3,614,883 describe membrane presses in which a blank sheet of metal is formed against a single forming surface. It is further described that the edges of a blank may be trimmed during a press cycle by being forced into a recess. However, the degree of deformation available with the devices of U.S. Pat. No. 2,344,743, U.S. Pat. No. 3,614,883 is limited to what may be achieved in localized parts of the forming surface by the fixed contours of the forming surface. U.S. Pat. No. 3,566,650 describes a membrane press in which a tool or plunger may be incorporated in a forming tool to shape or deform a blank in one place during a press cycle. U.S. Pat. No. 3,672,194 describes a membrane press in which the edges of a blank may be trimmed or perforated during a single pressure cycle.
EP 0 288 705 A2 describes a membrane press in which a metal blank may be formed against a one sided forming tool. Additionally the tool comprises moving parts which are moveable during a press cycle that includes increasing pressure through various phases. During a cycle edge cutting may be followed by drawing material into recesses of the mould tool, and intermediate cutting may be then carried out by further deep drawing into undercuts, before a finishing pressure is attained. EP 0 288 705 A2 describes how local shaping may be carried out in a continuous operation.
An article entitled “A Giant among Presses” in a Swedish publication Verkst{umlaut over (a)}derna nr 8 dated Aug. 12, 1991 describes a Swedish membrane press of the Quintus type and a forming tool used by an automobile manufacturer. The use of a membrane press for short run production of articles is discussed in the article and it is stated that an integration of trimming edges in a forming tool is especially advantageous in short run production.
However neither EP 0 288 705 A2 nor any of the above references describe how extensive and uniform plastic deformation of a blank may be achieved, extensive deformation greater for example than 1%-2% stretching during the shaping of substantially flat articles, nor a device for achieving such a deformation, and neither is it described how such extensive plastic deformation may be combined with other processes in a single press operation.
In conventional processes, additional shaping stages may be required to cause sufficient plastic deformation to result in work hardening in the sheet metal and thereby achieve a particular strength in the metal. Additional stages are usually required for trimming surplus material. After pressing and trimming the edges the shaped article is ready for surface treatment as part of a painting process.
The conventional stamping or pressing process needs further improvement. In particular to produce high strength, low weight, substantially flat articles from sheet metal without additional shaping stages. It would also be preferable for a stamping or pressing process to be able to handle ready treated or even ready decorated sheet metal. In addition, it would be beneficial if the cost of the tooling for such a shaping process could be reduced so that substantially flat metal articles may be produced in low volume production runs to supply niche or specialised markets.
SUMMARY OF THE INVENTION
The object of the invention is to provide a device and a method for the shaping of substantially flat articles that achieves a finished shape in one single press operation. It is a further object of the invention to make it possible to achieve a high strength substantially flat article in a single press operation method by causing a controlled and evenly distributed degree of work hardening in the substantially flat article. It is a still further object of the invention to shape substantially flat articles from sheet metal that is pre-treated or pre-painted.
These objects are achieved by the invention as described below. One advantage of the invention is that in one and the same continuous press operation it is possible to stretch, trim and shape-to-final-form a finished, surface-treated metal article as an end product. The invention is more useful than existing processes for shaping articles from sheet metal as it is applicable to a wider range of products. The invention is additionally characterised in that it is economical to produce substantially flat articles made of sheet metal in low volume production runs.
There is a requirement in the automobile industry, for example, to lower the finished weight of automobiles in order to improve fuel economy. Automobile outer body panels made from a material with high strength are required so that the weight of the outer body panel may be reduced, compared to a weaker material, while still producing a panel with sufficient strength for its function.
Examples of substantially flat articles within the automobile industry that are particularly suitable for the method and device according to the present invention are roofs, hoods or bonnets, fenders, wings, trunk lids or boot lids.
The invention comprises a method in which a metal sheet, hereafter described as a blank, is placed in a high pressure press and shaped into a substantially flat article. The blank is held by clamps which stretch the blank to a pre-determined degree which may be significantly greater than 2%. After stretching, pressure is applied to the blank. The high pressure press used in the invention is of the membrane type, for example a Quintus press, and the pressure is applied to the blank via a rubber membrane. The blank is pressed against a forming tool and is shaped into the form of a substantially flat finished article. The method and device requires only a single sided forming tool. The function of another half of a conventional forming tool is effectively carried out by the membrane.
An advantage of this invention compared with other processes currently separately available include that the stretching of the metal sheet along an axis to the desired tension level creates plastic deformation, thereby using the material in an optimum way with respect to the work hardening.
Another advantage of the present invention is the use of a rubber membrane against the outer surface of the metal sheet which makes it possible to shape a pre-painted metal sheet.
A further advantage of the present invention is that the pre-painted metal sheet is trimmed in a time during which the process passes from a stretching phase to a flanging phase without the process being interrupted. What is new about the process is to be able to simultaneously carry out in one continuous process actions some of which were only known previously as separate methods and/or devices.
A further advantage of the present invention is that it may be used to produce a wider range of substantially flat articles formed from sheet metal because the method is economic for more articles and applications, including prototypes and other one-of-a-kind product
Flow Holdings GmbH (SAGL) LLC
Jones David
Seed I. P. Law Group PLLC
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