EP1157762A1 - Dome made of aluminium alloy, especially to form a bottom of a tank and method to produce the same - Google Patents

Abstract

The aluminium alloy dome, made from a curved component with a cap welded over its central hole, is produced from a truncated conical blank (5) cut from a flat metal sheet and shaped inside a hemispherical mould (9). A deformable wall (15) with a series of vanes and a pressure membrane (21) are fitted inside the blank, which is then subjected to a two-stage heat and pressure process to form it to the shape of the mould's inner surface.

Description

The present invention relates to an aluminum alloy dome, especially intended to form a tank bottom, and its manufacturing process.

We know that rockets and space shuttles have tanks large dimensions for storing fuels intended for their propulsion. The bottom of such tanks is made of aluminum alloy and has the shape of a dome several meters in diameter.

To manufacture such a tank bottom, it is customary to carry out individually a plurality of curved sectors, for example the number of eight, said sectors then being joined to each other by radial weld lines to form said tank bottom.

Such a manufacturing method, in particular because of the number high of component parts and significant lengths of the many welding lines, is long and expensive. Also, the main purpose of the present invention is to reduce the cost of manufacturing such backgrounds tanks.

To this end, according to the invention, the dome of an aluminum alloy capable of being welded, in particular intended to form a tank bottom, is remarkable in that it consists of a shaped bowl rounded with an opening at the top and a welded cap on said bowl to close off said opening.

Thus, the dome according to the present invention is formed only of two pieces - the bowl and the cap - along a single line of welding of relatively limited length. This therefore results in a reduction significant manufacturing costs compared to the usual method mentioned above.

Of course, said cap can be easily manufactured by any known forming operation. Regarding the manufacture of the bowl, the applicant has developed a particularly advantageous.

a) on réalise un moule dont la face interne de la cavité correspond à la forme de ladite cuvette, ledit moule étant fermé à son sommet et ouvert du côté opposé audit sommet ;

b) à partir d'au moins une pièce plate en forme de portion de couronne, constituée d'un tel alliage d'aluminium non revenu, on réalise une ébauche en forme de tronc de cône, par cintrage et soudage ;

c) on introduit complètement ladite ébauche tronconique dans ledit moule, de façon qu'elle prenne une position initiale dans laquelle elle est concentrique audit moule, avec :

• sa face tronconique externe en regard de ladite face interne de ladite cavité ;
• sa petite base reposant sur ladite face interne de la cavité au voisinage du sommet dudit moule ; et
• sa grande base proche de ladite face interne de la cavité au voisinage de l'ouverture dudit moule ;

d) on dispose périphériquement une paroi de pression déformable à l'intérieur de ladite ébauche tronconique, contre sa face interne et au voisinage de sa petite base ;

e) on soumet ladite ébauche tronconique et ladite paroi de pression déformable à une première phase d'un traitement thermique avec pression au cours de laquelle ladite ébauche tronconique et ladite paroi de pression déformable au contact de celle-ci se cintrent en direction de la face interne de ladite cavité et progressant vers le sommet dudit moule en étant avalées par ce dernier ;

f) on bloque la progression de ladite ébauche tronconique et de ladite paroi de pression déformable en direction du sommet dudit moule, lorsque ladite ébauche et ladite paroi de pression atteignent une position d'avalement prédéterminée ;

g) dans cette position d'avalement prédéterminée, on poursuit ledit traitement thermique avec pression par une deuxième phase au cours de laquelle la face externe de ladite ébauche est amenée à épouser la face interne de ladite cavité, avec ladite paroi de pression pressée contre la face interne de ladite ébauche ;

h) à la fin dudit traitement thermique avec pression, on extrait du moule ladite ébauche conformée en cuvette, ouverte au sommet.

In fact, according to the invention, the method for producing a rounded bowl, open at its top, made of an aluminum alloy capable of being welded, in particular for producing a tank bottom, is remarkable in that:

a) a mold is produced whose internal face of the cavity corresponds to the shape of said bowl, said mold being closed at its top and open on the side opposite to said top;

b) starting from at least one flat piece in the form of a portion of a crown, made up of such an unincorporated aluminum alloy, a blank in the form of a truncated cone is produced, by bending and welding;

c) said frustoconical blank is completely introduced into said mold, so that it assumes an initial position in which it is concentric with said mold, with:

• its external frustoconical face opposite said internal face of said cavity;
• its small base resting on said internal face of the cavity in the vicinity of the top of said mold; and
• its large base close to said internal face of the cavity in the vicinity of the opening of said mold;

d) a deformable pressure wall is disposed peripherally inside said frustoconical blank, against its internal face and in the vicinity of its small base;

e) subjecting said frusto-conical blank and said deformable pressure wall to a first phase of a heat treatment with pressure during which said frusto-conical blank and said deformable pressure wall are in contact with the latter bending towards the face internal of said cavity and progressing towards the top of said mold while being swallowed by the latter;

f) the progression of said frustoconical blank and of said deformable pressure wall is blocked in the direction of the top of said mold, when said blank and said pressure wall reach a predetermined swallowing position;

g) in this predetermined swallowing position, said heat treatment with pressure is continued by a second phase during which the external face of said blank is brought to conform to the internal face of said cavity, with said pressure wall pressed against the internal face of said blank;

h) at the end of said heat treatment with pressure, said blank shaped in a bowl, open at the top, is extracted from the mold.

• grâce à l'avalement progressif de l'ébauche tronconique par le moule, à chaud et sous pression, il était possible de limiter, à un niveau acceptable, les contraintes mécaniques subies par ladite ébauche pour la faire passer de la forme tronconique à la forme d'une cuvette arrondie, par exemple sphérique ;
• le blocage de l'avalement de ladite ébauche tronconique à une valeur prédéterminée évitait une accumulation indésirable de la matière de l'ébauche tronconique au voisinage du sommet du moule ; et
• l'action de la paroi de pression au voisinage de la petite base de l'ébauche, en coopération avec le blocage de l'avalement, permettait de donner à ladite cuvette une forme parfaite au voisinage de son ouverture en évitant le flambage de ladite cuvette à cet endroit.

The Applicant has found that:

• thanks to the gradual swallowing of the frustoconical blank by the mold, hot and under pressure, it was possible to limit, to an acceptable level, the mechanical stresses undergone by said blank to make it pass from the frustoconical shape to the shape a rounded, for example spherical, bowl;
• blocking the swallowing of said frustoconical blank at a predetermined value avoided an undesirable accumulation of the material of the frustoconical blank in the vicinity of the top of the mold; and
• the action of the pressure wall in the vicinity of the small base of the blank, in cooperation with the blocking of the swallowing, made it possible to give said bowl a perfect shape in the vicinity of its opening, avoiding buckling of said bowl in this location.

Of course, it is possible to have said bowl has a constant thickness at all points or on the contrary presents a thickness reinforced in some of its zones, by providing in consequently the thickness distribution of said piece (s) flat (s) in the shape of a crown portion, from which is carried out the frustoconical draft.

In an advantageous embodiment of the method according to the invention, after said second phase, said treatment is continued thermal with pressure by a third tempering phase allowing structurally hardening said open bowl at the top.

Said deformable anti-buckling pressure wall can be formed by a set of deformable blades, preferably curved, distributed at the periphery of the internal face of said frustoconical blank. So he is advantageous that said deformable blades are integral with each other others at their ends close to said small base of the frustoconical blank, for example by means of a peripheral strip.

The strain pressure to which they are subjected during heat treatment, said frustoconical blank and said pressure wall, is preferably exerted by a pressure bladder introduced at the interior of said frustoconical blank. The wall of said mold is then advantageously pierced with through holes through which we can make the vacuum between said bladder and the internal face of the mold cavity, in order to pressing said bladder against said frustoconical blank and said wall of pressure to deform them until they are pressed against the face internal of said mold cavity.

In order to allow the controlled swallowing of said frustoconical blank and said pressure wall by the mold during the first phase of said heat treatment, as well as the blocking thereof in said predetermined swallowing position, preferably a connection is provided sliding with limit stop between the edge of the opening of the mold and the large base of said frustoconical blank. To this end, the large base of the frustoconical blank can carry an internal protruding rim participating in said limit stop.

The figures in the accompanying drawing will make it clear how the invention can be realized. In these figures, identical references denote similar elements.

Figures 1 and 2 show, flat, examples of flat parts in the shape of a crown portion, from which the dome, in accordance with the present invention.

Figure 3 schematically illustrates the bending of the parts of the figures 1 and 2.

Figure 4 shows in perspective a frustoconical blank obtained from the parts of Figures 1 and 2.

Figure 5 shows in schematic perspective a mold for the implementation of the invention, during the introduction of the frustoconical blank and the deformable pressure wall.

FIG. 6 shows an alternative embodiment of said wall of deformable pressure.

FIG. 7 illustrates, in schematic section, said frustoconical blank in its initial position in the mold.

FIG. 8 is a top view corresponding to FIG. 7.

Figures 9 and 10 correspond respectively to Figures 7 and 8, after the installation of a pressure bladder.

Figure 11 illustrates, in schematic section, the mold with said frustoconical blank in its predetermined blocked swallowing position.

Figure 12 illustrates, also in schematic section, said blank in its final position in the mold.

Figure 13 is a diagram illustrating the heat treatment with pressure exerted on said frustoconical blank in said mold.

Figure 14 illustrates the rounded bowl as it leaves the mold.

FIG. 15 illustrates control tests carried out on said bowl.

Figure 16 shows, in exploded schematic elevation, the dome according to the present invention.

Figures 1 and 2 show aluminum alloy plates 1 and 2, in which flat pieces are cut in the form of crown portion, 3 and 4 respectively. Plates 1 and 2 are by example consisting of known alloys 2219 or 2195, which are found the non-returned state (T37).

From a piece 3 or two pieces 4, a blank is produced 5 in the form of a truncated cone (see FIG. 4) by bending on a form 6 (see Figure 3) and welding along opposite generators. On the face 4, there is shown a welding line 7 for closing the blank tapered 5.

After these operations, we refer to the frusto-conical blank 5, to the inner periphery of its large base 5B, a tuck-in rim 8, for example by welding (see Figure 5).

Furthermore, as shown in FIG. 5, a mold 9 is produced, delimiting a cavity 10, the internal face 10I of which has the shape of a rounded bowl, for example spherical. The mold 9 is closed at its apex and, on the opposite side thereof, is provided with an opening 11, bordered by a peripheral rim 12 projecting outwards. The wall of the mold 9 is pierced with a plurality of through holes 13. In addition, the mold 9 is carried by feet 14, only shown in FIG. 5.

A deformable pressure wall 15 is also produced, by example of conical shape (figure 5) or barrel shape (figure 6), made up of blades 16, interconnected by a common heel 17. The pressure wall is made for example of an aluminum alloy similar to that constituting the blank 5 and it is shaped to be able to be housed in the frustoconical blank 5, in contact with the internal face 5I thereof, at vicinity of the small base 5b of said blank and all around said internal face 5I.

• la face tronconique externe 5E de ladite ébauche 5 se trouve en regard de la face interne 10I de la cavité 10 du moule 9 ;
• la petite base 5b de l'ébauche 5 repose sur la face interne 10I de la cavité 10, au voisinage du sommet du moule 9 ; et
• la grande base 5B de l'ébauche 5, et donc le rebord 8 qu'elle porte, sont proches de la face interne 10I de la cavité 10, au voisinage de l'ouverture 11 du moule 9.

As illustrated in FIGS. 5 and 7, the frustoconical blank 5 is completely introduced into the cavity 10 of the mold 9 through the opening 11 to assume an initial position (shown in FIGS. 7 and 8) in which it is concentric with said mold. In this initial position:

• the external frustoconical face 5E of said blank 5 is located opposite the internal face 10I of the cavity 10 of the mold 9;
• the small base 5b of the blank 5 rests on the internal face 10I of the cavity 10, in the vicinity of the top of the mold 9; and
• the large base 5B of the blank 5, and therefore the rim 8 which it carries, are close to the internal face 10I of the cavity 10, in the vicinity of the opening 11 of the mold 9.

In addition, in this initial position, the deformable pressure wall 15 is arranged inside the frustoconical blank 5, against the face internal 5I thereof, in the vicinity of the small base 5b of said blank.

Furthermore, on the rim 12 of the opening 11 of the mold 9, there are distributed lugs 18, integral with said rim 12 in any known manner and not shown. Each tab 18 has a descending arm 19, inside the rim 8 of the blank 5 and provided at its end with a hook 20, disposed under said rim 8. In said initial position, each hook 20 is at a distance d to below the rim 8 of the blank 5.

In this initial position, as illustrated by the figures 9 and 10, a pressure bladder 21 is arranged inside the blank frustoconical 5 and is tightly fixed, by means of fasteners 22, on the periphery of the inlet 11 of the mold 9.

As shown in Figures 11 and 12, the mold 9 thus equipped of the frustoconical blank 5, of the pressure wall 15, of the legs 18 and the pressure bladder 21 is introduced into a thermal enclosure 23, equipped with means (not shown) capable of creating a vacuum, through the through holes 13, in the space between the internal face 10I and the bladder 21.

FIG. 13 illustrates an example of heat treatment with pressure to which the frusto-conical blank 5 and the pressure wall 15 are subjected. In this FIG. 13, the variations in temperature T are shown as a function of time t thermal enclosure 23 (curve 24), of the pressure P exerted by the pressure bladder 21 (curve 25) and of the swallowing a of the blank 5 by the mold 9 (curve 26). This example of heat treatment essentially comprises four successive phases I to IV.

The first phase I begins at an initial instant to, at which the mold 9, the frustoconical blank 5, the pressure wall 15 and the bladder 21 are in the relative positions shown in FIG. 9. At this time, the swallowing a is zero. The temperature T of the enclosure 23 (for example an autoclave) increases regularly until a forming value TF (for example of the order of 120 ° C.), reached at the end of phase I (instant t2). At an instant t1 of phase I, prior to instant t2, a vacuum is created between the internal face 10I of the mold cavity 9 and the bladder 21 through the through holes 13 (arrows 27), so that the pressure exerted by the latter bladder on the frustoconical blank 5 and on the pressure wall 15 increases progressively (curve 25). As a result, said blank 5 and said pressure wall 15 curve in the direction of the internal face 10I of the mold cavity and are swallowed by the mold 9, the rim 8 progressively approaching the hook 20. At time t2 the flange 8 bears against the hook 20 and swallowing has took the value. We are then in the relative positions illustrated by FIG. 11.

In phase II, starting at time t2, the temperature T is maintained at the forming value TF and the pressure P is increased to a level value p , the swallowing remaining constant and equal to the value d. At time t3, at which phase II ends, the forming of the blank 5 is finished and the corresponding state of the different elements is shown in FIG. 12.

Then, from time t3, begins phase III of income, during which the temperature T is raised and maintained at the value TR income, for example of the order of 170 ° C. Draft 5, now shaped like a rounded bowl, it is therefore structurally hardened.

Between times t4 and t5, we proceed, during a phase IV, to blank cooling 5.

Once the cooling phase IV is finished, the blank 5 shaped like a rounded bowl and provided with an opening 28 at its top came out of the mold 9 and was cut along a line 29 along its large base, to eliminate the projecting internal rim 8 (see FIG. 14). The open bowl 30 is then obtained, shown in FIG. 15.

The accuracy of the rounded shape of the bowl 30 is checked by a set of geometric sensors 31, while non-destructive testing of the quality of the wall of this bowl 30 is carried out by a device 32 (X-ray and / or eddy current control).

A crown cap 33 having been manufactured elsewhere, by the implementation of any known technique (for example stamping), it is attached and welded to said bowl 30 to close the opening 28. A dome 34 is thus obtained in accordance with the present invention.

Claims (9)

Dome (34) of an aluminum alloy capable of being welded, in particular intended to form a tank bottom,
characterized in that it consists of a bowl (30) of rounded shape provided with an opening (28) at its top and by a cap (33) welded on said bowl (30) to close the opening (28 ). Method for producing a rounded bowl (30), open at its top, made of an aluminum alloy capable of being welded, in particular for producing a tank bottom,
characterized in that : a) a mold (9) is produced whose internal face (10I) of the cavity (10) corresponds to the shape of said bowl (30), said mold being closed at its top and open on the side opposite to said top; b) starting from at least one flat part (3, 4) in the form of a portion of a crown, made up of such an unalloyed aluminum alloy, a blank (5) is produced in the form of a truncated cone, by bending and welding; c) said frustoconical blank (5) is completely introduced into said mold, so that it assumes an initial position in which it is concentric with said mold, with: its external frustoconical face (5E) facing said internal face (10I) of said cavity (10); its small base (5b) resting on said internal face (10I) of the cavity (10) in the vicinity of the top of said mold (9); and its large base (5B) close to said internal face (10I) of the cavity (10) in the vicinity of the opening (11) of said mold (9); d) a deformable pressure wall (15) is disposed peripherally inside said frustoconical blank (5), against its internal face (5I) and in the vicinity of the small base (5b) of said frustoconical blank (5); e) subjecting said frustoconical blank (5) and said deformable pressure wall (15) to a first phase (I) of a heat treatment with pressure during which said frustoconical blank (5) and said deformable pressure wall ( 15) in contact with the latter are bent towards the internal face of said cavity (10) and progressing towards the top of said mold while being swallowed by the latter; f) the progression of said frustoconical blank (5) and of said deformable pressure wall (15) is blocked in the direction of the top of said mold (9), when said blank and said pressure wall reach a predetermined swallowing position; g) in this predetermined swallowing position, said heat treatment is continued with pressure by a second phase (II) during which the external face (5E) of said blank (5) is brought to marry the internal face (10I) of said cavity (10), with said pressure wall pressed against the internal face (5I) of said blank (5); h) at the end of said heat treatment with pressure, said blank shaped like a rounded bowl, open at the top, is extracted from the mold. Method according to claim 2,
characterized in that , after said second phase (II) and before step h), said heat treatment with pressure is continued by a third tempering phase (III) making it possible to structurally harden, in said mold, said bowl open at the top. Method according to one of claims 2 or 3,
characterized in that said deformable pressure wall (15) is formed by a set of deformable blades (16) distributed around the periphery of the internal face (5I) of said frustoconical blank. Method according to claim 4,
characterized in that said deformable blades (16) are integral with each other at their ends close to said small base (5b) of the frustoconical blank (5). Method according to one of claims 2 to 5,
characterized in that the deformation pressure to which said frusto-conical blank (5) and said pressure wall (15) are subjected during the heat treatment is exerted by a bladder (21) introduced inside said blank frustoconical (5). Method according to claim 6,
characterized in that the wall of said mold is pierced with through holes (13) through which a vacuum can be created between said bladder (21) and the internal face (10I) of said cavity (10), in order to press said bladder against said frustoconical blank and said pressure wall. Method according to one of claims 2 to 7,
characterized in that a sliding connection (8, 18, 19, 20) is provided with end-of-travel stop between the edge (12) of the opening (11) of the mold (9) and the large base (5B) of said frustoconical blank (5), in order to allow the swallowing of said frustoconical blank and of said pressure wall by the mold during said first phase (I) of said heat treatment, as well as the blocking of these in said position d predetermined swallowing. Method according to claim 8,
characterized in that the large base (5B) of said frustoconical blank (5) carries an internal protruding rim (8) participating in said limit stop.

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