EP0819482B1 - Process for forming a concave container out of a blank - Google Patents

Description

The invention has its origin in the manufacture of metal bottles intended to contain a pressurized fluid, for example a liquefied gas, bottles comprising a body, of generally cylindrical shape, with a concave cover and bottom. These bottles can be made in two parts - two half-shells welded together - or in three parts-two half-shells welded to a ferrule. Half a shell is consisting of a concave part extended by a cylindrical neck of more or less important height.

More generally, the present application relates to a process for forming a concave container from a blank, or from a plate (blank round), sheet metal.

We know how to stamp a sheet, held by blank clamps, by pass of a punch. In such a case, the metal is highly stressed, which causes an increase in its hardness and therefore a decrease in its elasticity, i.e. its ability to undergo a certain elongation elastic, as required in many areas, including for pressure vessels. It is therefore necessary to submit the sheet, after stamping, to a heat treatment to restore some of its initial mechanical characteristics.

The present invention aims to propose a method for forming a concave container from a sheet blank, which forces the sheet to the minimum and which is freed from the subsequent heat treatment.

To this end, the present invention relates to a method defined by claim 1.

Document DE-2 450 624-A describes a process according to the preamble of claim 1.

Thanks to the process of the invention, the sheet thus stamped, without stresses excessive, has elastic limit, elongation and tensile strength within satisfactory ranges.

It will be noted that the invention provides for several punches passes, that is to say at least two.

In the preferred implementation of the method of the invention, during the last pass, the peripheral strip is only held by a blank holder at the very beginning of the pass, before the sheet metal blank comes to marry the associated punch.

Advantageously, the sheet blank is curved during three passes punches.

• la figure 1 est une demi-vue en coupe d'une première forme de bouteille réalisée selon le procédé de l'invention, en deux parties ;
• la figure 2 est une demi-vue en coupe d'une deuxième forme de bouteille réalisée selon le procédé de l'invention, en trois parties et
• les figures 3-5 illustrent respectivement les trois passes successives de l'emboutissage des demi-coquilles des bouteilles des figures 1 et 2.

The invention will be better understood with the aid of the following description of the process of the invention and of several forms of bottle produced according to the process, with reference to the appended drawing, in which

• Figure 1 is a half sectional view of a first form of bottle produced according to the method of the invention, in two parts;
• FIG. 2 is a half-view in section of a second form of bottle produced according to the method of the invention, in three parts and
• FIGS. 3-5 respectively illustrate the three successive passes of the stamping of the half-shells of the bottles of FIGS. 1 and 2.

The bottles which will now be described, both in their structure that in their manufacturing process were made from of a sheet of metal sheet, for example steel or aluminum, here of a thin (a few millimeters or less) and according to a diameter here always a few hundred millimeters.

The bottle of Figure 1 has a body 1, of general shape cylindrical, consisting of two half-shells 2, 3 welded together. Each of the half-shells consists of a concave part 4 and a cylindrical neck 5 extending the periphery of the concave part. Both 3,4 half-shells are joined together by their necks, by through a solder joint 22, preferably made by laser for avoid local tensions.

The bottle is provided with a base 19 forming a base. The foot is here made of thermoplastic material, for recycling purposes. In shape complementary to that of the concave part 4, the foot 19 is glued to it. Likewise, provision is also made here, also of thermoplastic material and glued to the bottle, a gripping neck 20, with an annular part 23 breakthrough of grip openings 21. The foot and the gripping neck could be made of metal or any other material secured to the bottle by shrinking, bonding, welding or other means of attachment.

The bottle of figure 2 is very similar to that of figure 1, the same elements of the two bottles being designated by the same references. Unlike the bottle of figure 1, that of figure 2 is in three parts, the two half-shells 11, 12 being joined together via a ferrule 6. The half-shells 11, 12 have the same concave part 4 but this is extended by a peripheral neck 5 much smaller. The ferrule 6 is produced from a sheet metal blank rectangular whose edges 7, 8 have been welded together after bending here blank. One could also proceed by rolling, knurling a sheet blank or by any other method. The half-shells 11, 12 respectively form a cover and bottom joined to the shell 6 by two solder joints 9,10.

The process of forming the half-shells will now be described. 2, 3, 11, 12, considered as concave containers, from a blank, or more precisely of a plate, of sheet metal 18. They are produced here in three stamping passes by three punches 16, 16A, 16B associated respectively to their dies and their hold-downs 13, 14, 15, in three conforming assemblies.

For the first pass, illustrated in Figure 3, and the shaper being open, the plate 18 is placed on the matrix. We bring down the blank holder 13 to first exert slight pressure on a strip device 24 of the stage. We then lower the blank holder 13 and the punch 16 to exert greater pressure and press the plate 18 against the bottom of the shaping die.

During this first pass, the peripheral strip 24 of the plate 18, held by the blank holder 13, is inclined at a first angle a on the starting plane 25 of the plate 18. The punch 16, as well as its associated matrix, not shown, has a curve 17 adapted for that, at the end of the pass, the surfaces 17 and 26 of the punch 16 and the blank holder 13 extending from one another, in other words, to that there is surface continuity from one to the other of the two parts. During of this first pass, the peripheral strip 24 has therefore been straightened around a central portion 27 of the plate 18 in one direction. Then we opens the conformator to perform the next pass.

The objective of the second pass is to accentuate the straightening of the peripheral strip 24 around the central portion 27, on the one hand, and to accentuate the curve of this central portion 27, on the other hand. Thus, and during this second pass, illustrated in FIG. 4, but still under the die of the punch, the peripheral strip 24 is held, by the blank holder 14 of surface 28, inclined by a second angle β on the starting plane 25 of stage 18, with the relation
β> α

Furthermore, the punch 16A has a surface 29 of convexity accentuated compared to that 17 of the punch 16 and such that, at the end of the pass, surfaces 28 and 29 of the blank holder and the punch are still in the extension of one another.

The third pass, illustrated in Figure 5, is here the last and it is distinguished from the first two by the fact that during this pass the peripheral strip 24 is raised vertically, straightened still beyond angles α and β of the two previous passes by an angle of 90 °, the angles α and β, in the present case being substantially equal respectively at 35 ° and 50 °.

The peripheral strip 24 thus straightened constitutes the cylindrical neck 5 of the half-shell. Here, the blank holder 15 only serves to hold the edge 24 at the start of the pass. Its spacing from the matrix 30 is such that it allows then the sheet, under the action of the punch 16B, to marry the matrix 30, under the blank holder 15.

It will be noted that the curve of the punch 16B and of the matrix 30 is not here practically no more accentuated than that of the punch 16A. We have moreover shown in dashes, in FIGS. 4 and 5, illustrating the second and third pass, the deck at the start of the pass. It is during the second pass that the central portion 27 has practically received its curve definitive, while edge 24 has been gradually straightened on the three passes.

Note that we could form the half-shells in half passes or more than three passes, depending on the circumstances.

As the sheet is very weakly stressed during its forming and therefore it will not need to undergo any heat treatment, we may have previously coated it with a layer of anti-corrosion protection.

Claims (4)

1. Process for forming a concave container (4) out of a sheet metal blank (18), the said process being implemented exclusively at ambient temperature, and wherein the sheet metal blank (18) is shaped,

   by holding a peripheral strip (24) thereof

   using blank holding devices (13-15),

   during the course of a plurality of passes of punches (16, 16A, 16B),

   to raise the peripheral strip (24) around a central portion (27) of the blank,

   characterised in that:

   at the end of the pass, except for the last one, each blank holding device and each associated punch (13, 16; 14, 16A) have a continuity of surface (26, 17; 28, 29) and

   all the passes of punches (16, 16A, 16B) cause relative raisings of the peripheral strip (24) always in the same direction.
2. Process according to claim 1, wherein during the last pass the peripheral strip (24) is held by a blank holding device (15) only at the beginning of the pass, before the sheet metal blank (24, 27) conforms to the shape of the associated punch (16B).
3. Process according to claim 2, wherein the peripheral strip (24) is raised by 90° to form a cylindrical neck (5) of a half-shell.
4. Process according to one of claims 1 to 3, wherein the sheet metal blank (18) is shaped during three passes of punches (16, 16A, 16B).

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