Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Deforming the surface only
Reexamination Certificate
2002-01-25
2004-11-23
Chin, Peter (Department: 1731)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Deforming the surface only
C072S379200, C419S066000
Reexamination Certificate
active
06821471
ABSTRACT:
TECHNICAL FIELD
The invention concerns a method for the manufacturing of a plate of metal or of a ceramic material, the plate comprising one or more fields which occupy the major part of the surface of the plate and which on at least one side of the plate is high relief patterned, more specifically patterned such that the plate on said at least one side within the area of said field or fields has reliefs with high projections and deep valleys or recesses alternatingly, and between the sides a thin web, said high relief patterned field or fields being at least partly bordered by broad edge portions which have a thickness larger than the mean thickness of the plate within the region of said high relief patterned field or fields. Plates intended to be included in fuel cells or in heat exchangers are typical examples of plates of the above kind.
BACKGROUND OF THE INVENTION
It is difficult to manufacture metal plates of the above described kind, and it is extremely difficult to manufacture such plates which are thin and pronouncedly high relief patterned, at the same time as they are broad. Conventional methods, such as mechanical machining, spark machining, etching, laser working, etc. are slow and expensive and yet it is difficult to provide a perfect product with such conventional methods. This, to a high degree has impeded the development of fuel cells in which numerous high relief patterned plates are included. Such plates in a system can contribute e.g. to separate different gases, transport rest products, and conduct generated current in the fuel cell system and usually have a circular, square or rectangular shape with a central field, which on both sides have grooves, which are separated from one another by relatively high tongues. These high relief patterned fields are surrounded by a circumferential, comparatively broad edge, which forms a flat frame around the high relief patterned central field, the top planes of the tongues coinciding with the two side planes of the frame. The thickness of such plates may vary quite considerably from case to case but does not normally exceed 3 mm, while the thickness of the web between the grooves may amount e.g. in the order of 1 mm. A method of producing the grooves in the plates according to today's technique is by any kind of machining but that is as mentioned a slow and expensive process. It is not possible to cause the material to flow out completely in the tool mould through conventional moulding technique, because considerable friction forces prevent the transportation of material. If, on the other hand, higher pressures were applied in conventional equipment for the provision of necessary transportation of material in order to cause the material to completely fill the tool mould, the tools may be damaged. Similar problems exist in the manufacturing of plates intended to be included in heat exchangers.
DISCLOSURE OF THE INVENTION
It is the purpose of the invention to provide a considerably more convenient process for the manufacturing of metal plates of the type mentioned in the preamble, particularly metal plates for fuel cells and/or for heat exchangers. More particularly the invention aims at providing a manufacturing technique which is considerably cheaper than conventional technique but which nevertheless provides a product which satisfies the very rigorous demands in terms of dimensional accuracy, density and other features which are raised about fuel cell plates and heat exchanger plates. The method of the invention, however, is not restricted only to manufacturing of fuel cell plates and heat exchanger plates but can also be widely used for other metal plates, in particular plates which are broad in relation to their thickness.
According to the invention a moulding technique is used, employing high kinetic energy for the manufacturing of the plate with the high relief patterned sides. But it is not possible to manufacture plates with that pattern by high kinetic energy forming by a single stroke when starting from powder or from a flat plate. Even if the material is softened by the very high pressure that is generated at the high kinetic forming, the ability of the material will nevertheless be too restricted to flow not only in the labyrinth-like passages in that part of the moulding tool that shall form the high relief pattern, but also to flow out to the thicker edge portions. Nor is it possible in the same tool to form the product through a series of strokes. To the contrary, the problems would be accentuated. This is particularly true when starting from a powder, which certainly can be plasticised in a surface layer at the first impact. But that would instead make the plasticising of the powder further down in the powder bed more difficult, resulting in a very inhomogeneous compacting and increased friction.
The principle of the invention therefore is to first manufacture an intermediate product suitable for a final forming operation based on forming the high relief patterned plate in a single stroke through the supply of very high kinetic energy.
According to the invention an intermediate product is manufactured in at least one preliminary step, the intermediate product comprising a first portion which shall form said high relief patterned field(s), which however is(are) not yet high relief patterned but contain(s) a quantity of material essentially corresponding to the quantity of material existing within said field(s) of the finished plate, and second portions which shall form said edge portions and which contain substantially the quantity of material that shall exist in the edge portions of the finished plate. This intermediate product is placed between at least two engraved moulding tool parts, which are movable relative to one another, at least one of said moulding tool parts being high relief embossed and at least one being a punch, said tool parts, when they are maximally brought together, forming between them and/or together with at least one or more tool parts, a mould cavity corresponding to the final shape of the finished plate within the regions of said high relief patterned field(s) and at least near the final shape of said edge portions. Then the high relief pattern within the region/regions of said field(s) is/are established by striking the engraved tool parts against one another, at least said punch being stricken against said intermediate product wherein the material within the regions of said at least one first portion is caused to flow and fill the mould cavity to establish said high relief pattern essentially without transportation of material between said first and second portions.
In order to strike the engraved tool parts against one another one or two, respectively, rams can be used which preferably are hydraulically powered, which are stricken against the punch, or the punches, respectively, which in turn transmit(s) the kinetic energy to the intermediate product. The punches and impact members in this case thus are separate units, wherein the impact members can consist of e.g. hydraulic impact pistons. It is however possible, that the impact members and the punches are integrated units. This may particularly be true when the stroke is performed from above, wherein the impact member, e.g. a hydraulic piston, is united with the punch which from above is stricken down into a die. The punch in this case is an elongation of the piston rod of the impact piston. The same condition in principle can also be conceived in the case when the impact machine comprises also a lower punch which e.g. via a lower punch holder may be united with a lower impact member, which also may consist of a piston. According to this modification, the acceleration of the punches during the strike preferably takes place within the through-hole in said at least one further tool part, which preferably is a die, containing the cavity in which the moulding work takes place.
By employing a very high impact action in the final forming operation through a single, very powerful strike on the working material from one direc
Bednarek Michael D.
Chin Peter
Lopez Carlos
Morphic Technologies Aktiebolag
Shaw Pittman LLP
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