Metal working – Method of mechanical manufacture – Shaping by direct application of fluent pressure
Reexamination Certificate
2001-07-09
2003-05-06
Larson, Lowell A. (Department: 3725)
Metal working
Method of mechanical manufacture
Shaping by direct application of fluent pressure
C072S370220
Reexamination Certificate
active
06557233
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for producing a hollow body from sheet metal, especially from aluminum or alloys thereof. Known as one such method for producing a hollow body is, for example, the internal high-pressure forming method wherein the workpiece to be formed is inserted in a die suitable for forming and subsequently a liquid or gaseous, i.e. fluid, pressure medium introduced into the die such that it causes the workpiece in the die to be formed by the pressure of the fluid medium, whereby the workpiece is able to conform to the inner wall of the die.
Furthermore, the present invention relates to a hollow body produced by one such method as well as to an intermediate product as may be used for producing one such hollow body by the method in accordance with the invention.
PRIOR ART
Methods of producing so-called tubular or channel plates, i.e. plates including tubes or coiled tubing, are known in which two flat sheets of aluminum or alloys thereof located one on the other are fixedly joined to each other and the sheet metal portions located inbetween, and not joined to each other, are bulged in a die by introducing a pressure medium to form the channels between the plates. Also known are methods for forming single-ply plates in a die by subjecting them to the pressure of a pressure fluid at one end and stretching them into the cavity of the die (EP-A-0 581 458 and AST Speciality Handbook, Aluminum and Aluminum Alloys, The Materials Information Society, 1993, page 245). These known methods and not always satisfactory, especially when workpieces need to be subjected to a relatively strong change in shape, for example, in cases in which the tubular bodies or extruded sections need to be strongly dilated, particularly where aluminum or alloys thereof are concerned which do not permit forming as good as steel. However, even in the case of steel, strongly forming workpieces fails to be satisfactory with the methods as known.
To increase the inner cross-sections of a workpiece it is known from DE-A-42 32 161 to produce a hollow body in making use of a basic body produced of blanks, welded to each other at the edges, by the combined application of internal high pressure forming and deep drawing. Due to this making it necessary to combine two methods, producing the hollow body is comparitively complicated for one thing. For another, the production means needed for this purpose is extremely complicated and expensive. Furthermore, it is practically not possible to produce very large tanks of aluminum or alloys thereof, such as tanks for motor vehicles, aircraft or ships, due to the insufficient deformation capacity of the aluminum material.
One method of achieving enhanced forming of workpieces of aluminum or an alloy thereof is described in DE-A-195 31 035 in which several flat sheet metal blanks of aluminum or an alloy thereof are abutted edgewise and joined by spot welding into the workpiece to be formed. In this arrangement, individual flat sheet metal blanks are inserted in the workpiece for increasing the volume of the hollow body to be later produced from the workpiece. Subsequently, the workpiece thus configured for forming is inserted in a die and expanded outwards and deformed by the effect of heated oil introduced therein in achieving the hollow body by internal high pressure forming. In this arrangement the joined sheet metal blanks conform to the inner contour of the die by applied internal pressure. However, there are limits to the degree to which the hollow body volume can be expanded as dictated, for one thing, by the stress limit of the solder joints between the individual sheet metal blanks and, for another, the material already expanded becomes consolidated in the region of sharp-edged cross-section transitions of the die due to the extreme deflection of the material in these areas. The increasing strain on the material associated with the increase in strength harbors the risk of cracks occurring, this being the reason why a minimum critical bending radius must not be violated. This is why no acute forming in the corner portions is achievable. Although it is possible with this method to obtain a strong forming of the workpiece in the die in producing a large volume hollow body, however, there are also limits here too, to the size and shape of the hollow body volume to be produced. More particularly, it is not possible with this known method to produce minute forming radii, near to being sharp-edged, and also large hollow bodies in one piece and without flanges extending over the full contour.
SUMMARY OF THE INVENTION
In view of these drawbacks and the problems remaining in methods known from prior art, the invention is based on the objective of providing a method and an intermediate product for producing a hollow body of sheet metal, more particularly of aluminum or alloys thereof, which permits with minimum complication configuring a large hollow body volume corresponding to the space available in the fitted condition (for example as in tanks for motor vehicles in the rear axle area thereof) whilst simultaneously achieving very small forming radii and very large forming depths.
In accordance therewith, first a substantially flat sheet metal blank, more particularly of aluminum or an alloy thereof, is provided as the workpiece, although in general any metal material having a suitable forming capacity may be employed as the workpiece material, i.e. light metals through non-alloyed and alloyed hardened steels up to tempered and stainless steels. In this providing step of the method it is possible to determine the shape and size of the sheet metal blank, and by suitably selecting the dimensions of the sheet metal blank to already influence the desired final outer contour of the hollow body to be produced. Working the sheet metal blank is done preferably by known ways and means mechanically by cutting or thermally by flame and laser cutting.
The suitably blanked sheet metal is then folded and/or bent in a subsequent forming process in the region of a wall intermediate element configured integrally with the sheet metal blank. In this arrangement the wall intermediate element forms a section or partial area of the sheet metal blank, i.e. the wall intermediate element is integrated in the sheet metal blank. This internal configuration greatly facilitates handling the sheet metal blank as well as folding and/or bending. Furthermore, this enables the productivity and accuracy of the sheet metal blank to be enhanced, since particularly unlike the method as it reads from DE-A-195 31 035 no individual formed parts need to be soldered together. The hollow bodies to be produced by the method in accordance with the invention in the internal high pressure forming method can thus replace joined, e.g. soldered, welded or beaded constructions of individual sheet metal blanks in avoiding the problems associated with leakage or dynamic fracture in the jointing zone and assuring improved strength properties.
Bending may be done in this step of the method, for example, by roll forming, providing greater freedom for configuration as regards shaping the wall intermediate element. In this arrangement it is also possible to achieve a very sharp-edged bending of the sheet metal in the region of the wall intermediate element in thus making folding possible in several plies, located substantially superimposed. Accordingly, the individual sheet metal plies may be folded, for example, two-ply, three-ply or multi-ply one on the other.
In the case of folding and/or bending the wall intermediate element, it is furthermore possible to relate positioning the edge portions of the sheet metal blank to facilitate subsequent joining thereof. For joining, the edge portions of the sheet metal blank are abutted, preferably with a certain overlap, and joined together, for example, by soldering, welding, such as e.g. mash seam welding or laser beam welding, or also by edging, preferably along the longitudinal extension of the edges of the sheet metal blanks. This step in t
Alcan International Limited
Cooper & Dunham LLP
Larson Lowell A.
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