EP0733415B1 - Method of manufacture of a metal container in a form - Google Patents

Description

The subject of the present invention is a method manufacturing a metal can of shape, according to preamble of claim 1, of the type drink box, and more particularly a box metallic shape comprising, on the one hand, a bottom and a peripheral skirt comprising a succession of zones of different diameters and, on the other hand, a cover set on the peripheral skirt.

It is known to make metal boxes shaped consisting of a peripheral skirt comprising a succession of zones of different diameters, a bottom set at one end of the peripheral skirt, and a cover crimped at the other end of said peripheral skirt. This cover is provided for example with a easy opening device by breaking a line of lower resistance or a threaded neck intended to receive a screw cap.

The peripheral skirt of this type of box metallic consists of a welded cylindrical shell longitudinally and expanded to spare the succession zones of different diameters.

Generally, the peripheral skirt is produced from a mild steel metal blank with low carbon and with elastic limit approximately equal to 250 MPa.

Such a steel allows an expansion of the welded shell without great difficulty with an expansion rate calculated according to the formula: D final - D initial D initial x 100 up to 20%, initial D being the initial diameter of the welded shell and final D being the diameter of the welded shell after expansion.

To make this type of box, we realize the welded shell, the said shell is expanded to obtain a peripheral skirt comprising a succession of zones of different diameters, and we crimp a bottom and a cover respectively at each end of the shell.

The expansion of the shell generally takes place using an air or nitrogen forming process under pressure or a fluid forming process incompressible.

It is also known to make a box metallic, of the drink-can type, consisting of part, a bottom and a peripheral skirt from material with the bottom and, on the other hand, a cover crimped on the peripheral skirt (see for example WO-A-94 16842 on which the preamble of claim 1 is founded).

The bottom and the peripheral skirt from material with said bottom are manufactured in particular by stamping-ironing from a cut-out cup in a metal blank or strip.

For this purpose, the cup first undergoes a relatively severe swaging on a press which conventionally comprises, on the one hand, a fixed punch and a support forming a peripheral blank holder sliding around said punch and on which rests the cup and, on the other hand, a matrix intended to be applied to the cup with force vertically transmitted by an upper slide.

The cup with a bottom and an edge formed during stamping, is then either calibrated by a light drawing without the use of a blank holder, either re-stamped with a blank holder, then is subject to an ironing operation which consists of stretch by means of a drawing machine, by reductions successive, the edge to gradually form the skirt device of the box.

Then the bottom is formed on the drawing machine to give it a determined geometry and the neck of the peripheral skirt is formed, either according to a technique shrinking with matrix, either using a shrunk with the wheel.

The shrinking technique with matrix is to force the cervix into a matrix with a conical inlet profile and a cylindrical outlet profile. A cylindrical piece guides the wall formed at the outlet of the matrix.

The force required to allow the deformation metal comes from the thrust applied to the bottom of the box and transmitted axially by its skirt peripheral.

The wheel shrinking technique consists in driving the box in rotation which is held between a pusher and a centering ring. The profile of the cervix is obtained by simultaneous movements knobs, centering ring and pusher.

This type of box is generally made at from a very low carbon steel blank.

After stretching the edges of the peripheral skirt, the metal is strongly hardened so that its limit of elasticity in the walls of the peripheral skirt is around 700 MPa and sometimes even exceeds this value, which gives it an ability to expand practically zero.

The overall possible rate of expansion of the peripheral skirt is less than 1%, even for very thin, less than 0.5%.

However, the advantage of such a box is that it allows very small thicknesses, because the metal constituent is a very stiff metal with high mechanical characteristics, which induces a low weight and low material cost.

In addition, such a box is made in two pieces, the bottom and the peripheral skirt having come from material, which gives it an advantage from the point of view aesthetic.

The object of the invention is to propose a method for manufacturing a metal box of obtained shape for example by stamping-ironing, of the drink-can type, comprising a bottom and a peripheral skirt coming of matter with said bottom, which allows to obtain expansion rate at the peripheral skirt greater than 2%.

• on effectue une opération de rétreint de la partie de la jupe périphérique de l'ébauche située au-dessus de ladite zone de diamètre D de la jupe périphérique de la boíte formée pour l'amener à un diamètre D1, D8 déterminé inférieur au diamètre D,
• et on effectue au moins une opération d'expansion de la partie de la jupe périphérique de l'ébauche située au dessus de ladite zone de diamètre D pour réaliser la succession de zones de différents diamètres de ladite jupe périphérique.

The invention therefore relates to a method of manufacturing a shaped metal box, comprising, on the one hand, a bottom and a peripheral skirt comprising a succession of zones of different diameters and, on the other hand, a crimped cover on the peripheral skirt, in which
a cylindrical blank consisting of a bottom and a peripheral skirt of diameter equal to the diameter D of an area of the peripheral skirt of the box is produced from a metal blank, characterized in that:

• we carry out an operation of constriction of the part of the peripheral skirt of the blank located above said zone of diameter D of the peripheral skirt of the box formed to bring it to a determined diameter D1, D8 less than diameter D ,
• and at least one expansion operation is carried out of the part of the peripheral skirt of the blank located above said zone of diameter D to produce the succession of zones of different diameters of said peripheral skirt.

• après avoir effectué l'opération de rétreint de la partie de la jupe périphérique de l'ébauche située au-dessus de la zone de diamètre D, on effectue une seule opération d'expansion pour réaliser la succession des zones de différents diamètres de ladite jupe périphérique.
• le diamètre D1, D8 de la partie de la jupe périphérique de l'ébauche, située au dessus de la zone de diamètre D est égal au diamètre de la zone de la jupe périphérique de plus faible diamètre de la boíte formée,
• après avoir effectué l'opération de rétreint de la partie de la jupe périphérique de l'ébauche, située au-dessus de la zone de diamètre D, on effectue une succession d'opérations, d'expansion et de rétreint sur toute la partie de la jupe périphérique de l'ébauche située au-dessus de la zone précédemment rétreinte ou expansée,
• l'ébauche est réalisée par emboutissage-repassage d'un flan métallique en acier, ou en aluminium ou en alliage d'aluminium,
• l'ébauche est réalisée par emboutissage - réemboutissage d'un flan métallique en acier ou en aluminium ou en alliage d'aluminium.

According to other preferred characteristics of the invention:

• after having carried out the operation of shrinking the part of the peripheral skirt of the blank situated above the zone of diameter D, a single expansion operation is carried out to carry out the succession of the zones of different diameters of said skirt peripheral.
• the diameter D1, D8 of the part of the peripheral skirt of the blank, located above the zone of diameter D is equal to the diameter of the zone of the peripheral skirt of smaller diameter of the box formed,
• after carrying out the operation of shrinking the part of the peripheral skirt of the blank, situated above the zone of diameter D, a succession of operations is carried out, of expansion and of shrinking over the whole part of the peripheral skirt of the blank located above the previously constricted or expanded area,
• the blank is produced by stamping-ironing a metal blank in steel, or in aluminum or aluminum alloy,
• the roughing is carried out by stamping - re-stamping of a metal blank in steel or aluminum or aluminum alloy.

• la Fig. 1 est une vue en demi-coupe longitudinale d'un premier mode de réalisation d'une boíte de forme obtenue par le procédé selon l'invention,
• les Figs. 2 à 6 sont des vues en demi-coupe longitudinale montrant les diverses étapes du procédé de fabrication de la boíte de forme de la Fig. 1,
• la Fig. 7 est une vue en demi-coupe longitudinale d'un second mode de réalisation d'une boíte de forme obtenue par le procédé selon l'invention.

The characteristics and advantages of the invention will become apparent during the description which follows, given solely by way of example and made with reference to the accompanying drawings, in which:

• Fig. 1 is a view in longitudinal half-section of a first embodiment of a shaped box obtained by the method according to the invention,
• Figs. 2 to 6 are views in longitudinal half-section showing the various stages of the manufacturing process of the form box of FIG. 1,
• Fig. 7 is a view in longitudinal half-section of a second embodiment of a shaped box obtained by the method according to the invention.

Note that in these figures, the profile of the boxes shown is deliberately exaggerated for reasons of clarity.

As seen in Fig. 1, the box of shape of the drink-box type comprises a bottom 1 and a peripheral skirt 2 formed integrally with said bottom 1.

• une zone 2A adjacente au fond 1 et de diamètre D,
• une portion intermédiaire 2B située au dessus de la zone 2A par rapport au fond 1 et adjacente à celle-ci, dans laquelle le diamètre de la jupe périphérique 2 décroít,
• une zone 2C située au-dessus de la portion intermédiaire 2B et adjacente à celle-ci, de diamètre D1 inférieur au diamètre D de la zone 2A,
• une portion intermédiaire 2D située au-dessus de la zone 2C et adjacente à celle-ci, dans laquelle le diamètre de la jupe périphérique 2 croít,
• une zone 2E située au-dessus de la portion intermédiaire 2D et adjacente à celle-ci, de diamètre D2 supérieur au diamètre D1 de la zone 2C,
• une portion intermédiaire 2F située au-dessus de la zone 2E et adjacente à celle-ci, dans laquelle le diamètre de la jupe périphérique 2 décroít,
• une zone 2G située au-dessus de la portion intermédiaire 2F et adjacente à celle-ci, de diamètre D3 inférieur au diamètre D2 de la zone 2E,
• une portion intermédiaire 2H située au-dessus de la zone 2G et adjacente à celle-ci, dans laquelle le diamètre de la jupe périphérique 2 croít,
• une zone 2I située au-dessus de la portion intermédiaire 2H et adjacente à celle-ci, de diamètre D4 supérieur au diamètre D3 de la zone 2G,
• une portion intermédiaire 2J située au-dessus de la zone 2I et adjacente à celle-ci, dans laquelle le diamètre de la jupe périphérique 2 décroít, cette zone étant appelée souvent col dans le cas d'une boíte-boisson,
• une zone 2K située au dessus de la portion intermédiaire 2J et adjacente à celle-ci, de diamètre D5 inférieur au diamètre D4 de la zone 2I,
• et enfin, une zone 2L correspondant au bordage servant au sertissage d'un couvercle, non représenté, après remplissage de la boíte.

The peripheral skirt 2 comprises a succession of zones of different diameters:

• a zone 2A adjacent to the bottom 1 and of diameter D,
• an intermediate portion 2B located above the zone 2A relative to the bottom 1 and adjacent to it, in which the diameter of the peripheral skirt 2 decreases,
• a zone 2C situated above and adjacent to the intermediate portion 2B, of diameter D1 less than the diameter D of zone 2A,
• a 2D intermediate portion located above and adjacent to the area 2C, in which the diameter of the peripheral skirt 2 increases,
• a zone 2E situated above and adjacent to the intermediate portion 2D, of diameter D2 greater than the diameter D1 of zone 2C,
• an intermediate portion 2F located above and adjacent to the area 2E, in which the diameter of the peripheral skirt 2 decreases,
• a zone 2G situated above and adjacent to the intermediate portion 2F, of diameter D3 less than the diameter D2 of zone 2E,
• an intermediate portion 2H situated above and adjacent to the area 2G, in which the diameter of the peripheral skirt 2 increases,
• a zone 2I situated above and adjacent to the intermediate portion 2H, of diameter D4 greater than the diameter D3 of the zone 2G,
• an intermediate portion 2J situated above and adjacent to the area 2I, in which the diameter of the peripheral skirt 2 decreases, this area often being called a neck in the case of a drink can,
• a zone 2K situated above and adjacent to the intermediate portion 2J, of diameter D5 less than the diameter D4 of zone 2I,
• and finally, an area 2L corresponding to the planking used for crimping a cover, not shown, after filling the box.

To make such a box shape, the method according to the invention consists, in a first step shown in FIG. 2, to be carried out for example by stamping-ironing from a metal blank, in steel, or aluminum or aluminum alloy, a cylindrical blank 3 of diameter equal to diameter D of zone 2A of the peripheral skirt 2 of the box formed, adjacent to the bottom 1 in this exemplary embodiment.

In this example, we make the rough cylindrical 3 by stamping a metal blank for form a cup and stretch the edges of said cup.

In another example not shown, we can make the cylindrical blank 3 by stamping a metal blank to form a cup, deep-drawing from the bottom of the cup to reduce the diameter of the bottom and stretching the edges of the re-drawn cup.

In this case, the area of diameter D is no longer adjacent to the bottom.

In a second step shown in FIG. 3, a shrinking operation is carried out on the part of the peripheral skirt of the blank 3 located above zone 2A of the peripheral skirt 2 of the box formed to bring it to a determined diameter D1 less than the diameter D of zone 2A.

In this embodiment, the diameter D1 is equal to the diameter of zone 2C of the peripheral skirt 2 of the box formed.

This shrinking operation is carried out in one or several passes using a known type of tool consisting of a matrix with an input profile conical and a cylindrical outlet profile, associated with a cylindrical part which guides the wall formed at the outlet of the matrix.

The force required to allow the deformation metal comes from the thrust applied to the bottom of the box and transmitted axially by its skirt peripheral.

To avoid the phenomenon of crushing the bottom 1 and the peripheral skirt 2, we apply inside of the blank 3, during the shrinking operation, a air pressure between 1 and 6 bars.

To reach the desired diameter, several successive reductions are often necessary, each being a separate forming step.

The geometry of the different matrices used in each forming step depends on the desired profile in the intermediate portion 2B so to obtain the desired profile in said intermediate portion 2B.

After this shrinking operation, the process according to the invention consists in performing at least one expansion operation of the part of the peripheral skirt of blank 3, located above the area of diameter D to carry out the succession of zones of different diameters of the peripheral skirt 2 of the box formed.

To make the shape box such as shown in Fig. 1, after performing the operation shrinking of the peripheral skirt part of the blank 3 located above zone 2A of the box formed, a succession of expansion operations is carried out and shrinking all over the skirt device of the blank 3 located above the zone previously shrunk or expanded.

So, to make the box shown on Fig. 1, the third step consists, as shown in Fig. 4, to carry out an expansion of the part of the peripheral skirt of the blank 3 located above zone 2C previously constricted of the peripheral skirt 2 of the box formed, to bring it to the diameter D2.

This expansion operation can be carried out using different techniques.

The technique of matrix expansion consists in forcing the free edge of the peripheral skirt of the blank 3 in a matrix having a profile cylindrical inlet and a conical outlet profile, associated with a part ensuring the guidance of the wall formed at the outlet of the matrix.

To reach the desired diameter D2, several successive expansions are often necessary, each being a separate forming step.

The geometry of the different matrices used in each type of forming depends on the desired profile in the intermediate 2D portion.

The expansion technique can also be a mechanical expansion forming technique using of a sector tool or an expansion technique to using an incompressible fluid such as air, nitrogen or an oil.

The fourth step, shown in FIG. 5, consists in carrying out a new shrinking operation of the part of the peripheral skirt of the blank 3, located above zone 2E, previously expanded, to bring it to diameter D3 taking care to conform the intermediate portion 2F according to the desired profile.

The fifth step, shown in FIG. 6, consists in carrying out a new expansion operation of the part of the peripheral skirt of the blank 3, located above the 2G zone, previously narrowed, to bring it to diameter D4, taking care to conform the intermediate portion 2H according to the desired profile.

Finally, the sixth step is to perform a final operation to shrink the part of the peripheral skirt of the blank 3, located above the zone 2I, previously expanded, to bring it to the diameter D5, taking care to conform the portion intermediate 2J according to the desired profile, and to achieve the planking used for crimping the cover.

The various necking operations and expansion as described to achieve the operations from third to sixth stage are by example the same techniques as those described for carry out the operations of the first and second stage.

As shown in FIG. 7, the box form according to a second embodiment comprises a bottom 10 and a peripheral skirt 11 formed integrally with the bottom 10.

• une zone 11A adjacente au fond 10 et de diamètre D,
• une portion intermédiaire 11B située au-dessus de la zone 11a et adjacente à celle-ci dans laquelle le diamètre de la jupe périphérique 11 croít,
• une zone 11C située au-dessus de la portion intermédiaire 11b et adjacente à celle-ci, de diamètre D6 supérieur au diamètre D de la zone 11A,
• une portion intermédiaire 11D située au-dessus de la zone 11C et adjacente à celle-ci, dans laquelle le diamètre de la jupe périphérique 11 décroít,
• une zone 11E située au dessus de la portion intermédiaire 11D et adjacente à celle-ci, de diamètre D7 inférieur au diamètre D6 de la zone 11C et supérieur au diamètre D de la zone 11A,
• une portion intermédiaire 11F située au dessus de la zone 11E et adjacente à celle-ci, dans laquelle le diamètre de la jupe périphérique 11 décroít,
• une zone 11G située au-dessus de la portion intermédiaire 11F et adjacente à celle-ci, de diamètre D8, inférieur au diamètre D7 de la zone 11E,
• et enfin une zone 11H correspondant au bordage pour le sertissage d'un couvercle, non représenté, après remplissage de la boíte.

The peripheral skirt 11 comprises a succession of zones of different diameters:

• a zone 11A adjacent to the bottom 10 and of diameter D,
• an intermediate portion 11B situated above and adjacent to the zone 11a in which the diameter of the peripheral skirt 11 increases,
• a zone 11C situated above and adjacent to the intermediate portion 11b, of diameter D6 greater than the diameter D of the zone 11A,
• an intermediate portion 11D situated above and adjacent to the area 11C, in which the diameter of the peripheral skirt 11 decreases,
• a zone 11E situated above and adjacent to the intermediate portion 11D, of diameter D7 less than the diameter D6 of the zone 11C and greater than the diameter D of the zone 11A,
• an intermediate portion 11F located above and adjacent to the area 11E, in which the diameter of the peripheral skirt 11 decreases,
• a zone 11G situated above and adjacent to the intermediate portion 11F, of diameter D8, less than the diameter D7 of the zone 11E,
• and finally a zone 11H corresponding to the planking for crimping a cover, not shown, after filling the box.

The peculiarity of such a box by compared to the box shown in FIG. 1 is that the zone 11C located above zone 11A adjacent to bottom 10 has a diameter D6 greater than the diameter D of zone 11A of the peripheral skirt 11 of the box formed.

The manufacturing process according to the invention of such a form box consists, in a first step, to be carried out for example by stamping-ironing from a metal blank made of steel, or aluminum or aluminum alloy, a cylindrical blank of diameter equal to the diameter D of the zone 11A of the skirt peripheral 11 adjacent to the bottom 10, then, in a second step, to perform a shrinking operation of the part of the peripheral skirt of the blank for bring it to the determined diameter less than the diameter D from zone 11A.

In such an exemplary embodiment, this diameter can be equal to the diameter of the skirt area device 11 of the lower formed box diameter, i.e. the diameter D8 in FIG. 7.

When the area of the peripheral skirt 11 of the box formed, of smaller diameter is the zone 11A adjacent to the bottom 10 of the box, the diameter D8 will be chosen smaller than this diameter D, because it is absolutely essential to start with a shrinking operation to be able to make a form box with rates expansion greater than 1% from a blank obtained for example by stamping-ironing a blank metallic.

After performing this shrinking step, the third step of the process of the invention consists in perform the expansion, in one or more operations, zones 11C and 11E of the peripheral skirt of the blank to give each of these areas the desired profile.

In this exemplary embodiment, the first step consisted in making by stamping-ironing, a cylindrical blank with a diameter equal to the diameter D.

According to a variant, it is possible to in a first step by stamping or stamping-ironing a cylindrical blank of diameter equal to diameter D6 corresponding to zone 11C in Figure 7, then re-stamp this blank to form the bottom and the area 11a of diameter D less than diameter D6.

The second step of performing the shrinking operation is in this case carried out from of zone 11C of diameter D6.

To make the shape box such as shown in FIG. 1, it would also have been possible to carry out, after the first manufacturing step of the blank of diameter D by stamping-ironing a metal blank in steel, or aluminum or alloy of aluminum, a second step consisting in carrying out a shrinking operation of the peripheral skirt part of blank 3 located above zone 2A of the peripheral skirt 2 of the box formed to bring it to diameter of the zone of said peripheral skirt 2 more small diameter, that is to say the diameter D5 of the zone 2K.

Afterwards, an expansion operation is carried out in several successive expansions, to obtain the zones 2B and 2I.

The choice of one or other of the variants of carrying out the method of the invention to carry out the shaped box as shown in FIG. 1 depends of the expansion process used.

Indeed, if the expansion is carried out at by means of a matrix, that is to say according to the so-called technique buffering, it is better to make the box according to the steps shown in Figs. 2 to 6 is say by performing a succession of expansion operations and shrinking.

On the other hand, if the expansion is carried out at using an incompressible fluid it is best perform a shrinking operation down to the diameter minimal, to form the neck when the box requires the presence of a pass and then realize the expansion of different areas to expand.

When the expansion is carried out using of a sector tool, it is possible to use indefinitely the two variants of the process.

As we could see in these two examples shaped boxes, the important characteristic of method according to the invention lies in the fact of starting forming the blank by stamping and ironing by a shrinking operation.

The Applicant has indeed visited account, that prior shrinking facilitates expansion the peripheral skirt, and allows for example for very low carbon steel hardened, accept rates of expansion relative to diameter of the blank before shrinking greater than 2%, while if we do a direct expansion without shrinking beforehand, the expansion rate remains below 1%.

This increase in expansion capacity of the box after prior shrinking is due to the increase thickness in the walls of the peripheral skirt, due to this prior restriction, as well as to slight metallurgical and / or rheological transformations that the metal undergoes during the shrinking operation.

Tests have been carried out on bodies of boxes with a diameter of 66mm, varying the rate from the first operation and by performing then a maximum global expansion.

The table below summarizes these tests. Test No. Diameter D1 after shrinking (in mm) Withdrawal rate 66 - D 66 Diameter D2 after expansion (in mm) Rate of expansion D2 - D1 D1 1 66 0% 66.74 1.12% 2 63.79 3.35% 67.34 5.56% 3 62.55 5.23% 66.64 6.54% 4 61.30 7.12% 66.33 8.20% 5 60.06 9% 66.28 10.36% 6 58.81 10.89% 65.83 11.94%

As seen in this table, the fact of carry out a preliminary shrinkage with a shrinkage rate equal to 3.35% (test 2) allows the diameter to be expanded up to 67.34 mm, diameter greater than the diameter of 66.74mm reached in direct expansion without shrinking prior (test 1).

In addition, if we compare the two diameters D1 and D2, we see that in test n ° 1 the variation maximum possible is limited to 1.12% while in test n ° 2, it goes to 5.56%.

We also notice in this table that if the shrinking rate of the first operation increases, approximately above 5%, it is no longer possible to exceed the diameter D2 obtained with test No. 1, that is to say without prior shrinking operation.

But, carry out a constriction operation prior with a shrinkage rate greater than 5% has the advantage of being able to make boxes of shape with very marked curves.

Indeed if we compare test n ° 2 with test n ° 6, we certainly see that the final diameter after expansion reaches only 65.83mm, less than the 67.34mm from test no.1 and even less than the 66mm from starting box body but the overall expansion rate between the restricted area of diameter D1 and the area foam of diameter D2 reaches 11.94% in test no. 6 versus 5.56% in test # 2.

So we see that the more we increase the initial shrinkage rate, plus differences in diameter between the diameter after shrinking and the diameter after expansion increases.

The manufacturing process for shaped boxes according to the invention allows to form boxes with more marked curves and this process is easy to implement industrially because the tools for carrying out shrinking and expansion operations are known and used by packaging manufacturers metallic.

The process according to the invention is not limited stamped-ironed boxes, but can also be applied for the realization of shaped boxes from a blank obtained by stamping-re-stamping a metal blank made of steel, or aluminum or aluminum alloy.

In this case, the expansion rate goes from 3% at around 6%.

Claims (6)

1. Method of manufacture of a formed metal container, comprising, on the one hand, a base (1, 10) and a peripheral skirt (2, 11) which is composed of a succession of regions (2A, 2C, 2E, 2G, 2I, 2K; 11A, 11C, 11E, 11G) having different diameters and, on the other hand, a cover which is crimped on the peripheral skirt (2, 11), wherein there is produced, starting from a preliminary metal blank, a cylindrical blank composed of a base and a peripheral skirt having a diameter equal to the diameter D of a region (2A, 11A) of the peripheral skirt (2, 11) of the container,
   characterised in that

   a necking operation is carried out at the portion of the peripheral skirt of the blank located above the region (2A, 11A) of diameter D of the peripheral skirt (2) of the formed container in order to bring it to a specific diameter D1, D8 which is less than the diameter D;

   and at least one widening operation is carried out at the portion of the peripheral skirt located above the region (2A, 11A) of diameter D in order to produce the succession of regions of different diameters of the peripheral skirt (2, 11).
2. Method according to claim 1, characterised in that, once the necking operation has been carried out at the portion of the peripheral skirt of the blank located above the region (2A, 11A) of diameter D, a single widening operation is carried out to produce the succession of regions of different diameters of the peripheral skirt (2, 11).
3. Method according to claim 1 or 2, characterised in that the diameter D1, D8 of the portion of the peripheral skirt of the blank located above the region (2A, 11A) of diameter D is equal to the diameter of the region of smaller diameter of the peripheral skirt (2, 11) of the formed container.
4. Method according to claim 1, characterised in that, once the necking operation has been carried out at the portion of the peripheral skirt of the blank located above the region (2A, 11A) of diameter D, a succession of widening and necking operations is carried out over the entire portion of the peripheral skirt of the blank located above the region which previously underwent necking or widening.
5. Method according to claim 1, characterised in that the blank is produced by drawing and wall ironing a preliminary metal blank of steel, aluminium or aluminium alloy.
6. Method according to claim 1, characterised in that the blank is produced by drawing and redrawing a preliminary metal blank of steel, aluminium or aluminium alloy.

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