ES2242019T3 - METHOD TO CONFORM FOR PRESSURE AND DISPLACEMENT OF THE PISTON METAL AND SIMILAR CONTAINERS. - Google Patents

Abstract

A method of forming a bottle-shaped or other contoured metal container by subjecting a hollow metal preform having a closed end to internal fluid pressure to cause the preform to expand against the wall of a die cavity defining the desired shape, and advancing a punch into the die cavity to displace and deform the closed end of the preform after expansion begins but before it is complete. The pressure-subjecting step is performed by simultaneously subjecting the preform in the die cavity to independently controllable internal and external positive fluid pressures and varying the difference between them to control strain rate.

Description

Method for conforming by pressure and piston displacement metal containers and the like.

Technical field

This invention relates to methods for form metal containers or the like, which use fluid pressure internal to expand a preform or metal workpiece hollowed out, against a cavity of a mold. In a specific aspect importantly, the invention is directed to methods for shaping aluminum or other metal containers, which have a shape profiled, for example such as a bottle shape with asymmetric characteristics

Prior art

Metal cans for drinks are good known and widely used. The bodies of beverage cans current, whether "stretched and ironed" bodies of a single piece, or open bodies at both ends (with an element of different closure at the bottom, as well as at the top), they usually have vertical cylindrical side walls simple. Sometimes it is desired, for aesthetic reasons, to attract to the consumer and / or identify the product, impart a form different and more complex to the side wall of a metal container of beverage and, in particular, dispose of a metal container with the shape of a bottle instead of a cylindrical can shape normal. Conventional operations to produce cans, without However, they do not achieve such configurations.

For these and other purposes, it would be advantageous provide effective and convenient methods for shaping parts Working in the form of bottles or other complex shapes. Further, it would be useful to have such procedures capable of conforming shapes of profiled packages that are not radially symmetrical, to expand the variety of designs that can be obtained.

In US Patent 3,040,684, describes an apparatus for forming door handles from a preform, using a mold cavity and hydraulic pressure. The preform is placed in a cavity of a mold, filled with hydraulic fluid and closes tightly. The mold closes then, and a lower piston moves upward forcing the wall of the preform in accordance with the shape of the cavity of the mold. In this procedure, the volume of fluid does not change, and the expansion of the preform is caused by the movement of the piston.

Another device for shaping a Door handle is described in US Pat. 4,362,037, in which a split mold is used. The preform comprises a partially shaped door handle, and the circular face External handle is placed on a lower mold. A cast upper has a cavity with portions of side walls that define the final shape of the shooter. This upper mold is pressed down on the preform resting on the lower mold. Then, a fluid is internally forced into the preform, with which the preform is forced into the shape of the cavity of the mold.

U.S. Patent 6,182,487 describes a method for manufacturing a metal vessel, which uses a mold match that includes a fixed mold and a mobile mold. First it it forms a cylinder that has a bottom welded to a cover, and it is placed with the lower end mounted on the mobile mold at time that the open end of the cylinder is attached to the mold permanent. The cylinder is pressurized through the fixed mold, and the mold mobile closes on the fixed mold to form the vessel.

Description of the invention

The present invention broadly contemplates provide a method to form a metal container or similar, of defined shape and dimensions, said method comprising:

(a) arrange a hollowed metal preform, which it has a closed end, in a cavity of a mold that has a mold wall that defines said shape and dimensions, being at minus a portion of the preform initially spaced towards in from the wall of the mold, and

(b) subject the preform to fluid pressure internal, to expand the preform out in contact substantially complete with the mold wall, to impart that way to the preform said shape and defined dimensions,

characterized in that the mold cavity is dimensions to contain a metal preform laterally recessed that has a closed end, with a die located in one end of the cavity and translatable into the cavity, being  located the preform inside the cavity, with the closed end of the preform positioned in a close relationship facing the die an internal fluid pressure is applied to the preform to expand the preform out and exert a force of pressure fluid over the closed end and,

(c) either before or after the preform begins to expand, but before the expansion of the preform, the die is moved to the end of the cavity to couple and move the closed end of the preform in a direction opposite to the direction of the force exerted by the fluid pressure on it, deforming the closed end of the preform while the preform expands out in a substantially complete contact with the mold wall.

The transfer of the die is affected by a piston that is able to apply enough force to the die to displace and deform the preform. This method will be called some times in this document as a procedure (PRF) to form by pressurized hydraulic piston, because the container conforms both for the internal fluid pressure applied and for the translation of the die by the piston.

As an additional feature of the invention, the die has a profiled surface, and the end closed the preform deforms so that it conforms to the profiled surface. For example, the die can have a profile domed, the closed end of the preform being deformed in the vaulted profile.

The defined form, in which the container, can have a bottle shape that includes a portion of neck and a body portion, larger in dimensions lateral than the neck portion, having the mold cavity a long axis, the preform having a long axis and being arranged substantially coaxially inside the cavity, and being the transferable die along the long axis of the cavity.

Advantageously and preferably, the wall of the mold comprises a split, detachable mold to remove the formed container. With a split mold, the defined shape can be asymmetric around the long axis of the cavity.

The die is initially positioned so preferably close to or in contact with the closed end of the preform, before the application of fluid pressure, to limit axial elongation of the preform by fluid pressure. He die transfer can be started after the portion bottom that expands from the preform has come into contact with The wall of the mold.

The preform to form a container shaped bottle or similar is preferably an elongated work piece, and initial and generally cylindrical, which has an open end opposite to its closed end. In particular embodiments of the invention, can have a diameter substantially equal to the portion of the bottle-shaped neck, and may have enough conformability to be expandable to the shape defined in a only pressure forming operation. If such is missing conformability, before the PRF method described above, perform the preliminary steps of placing the workpiece in a mold cavity smaller than the mold cavity first mentioned, and to submit the work piece there to internal fluid pressure to expand the workpiece to a intermediate size and a smaller shape than the shape and defined lateral dimensions.

Alternatively, if the elongated work piece and initial and generally cylindrical is longer, in diameter initial, that the neck portion of the bottle shape, the method to form a bottle-shaped container may include a Additional stage of submitting the work piece, adjacent to your open end, to a shaping operation with movement of rotation to form a small diameter neck portion, after the execution of the PRF procedure.

Alternatively, the diameter of the neck area of the preform is reduced using a narrowing procedure of the mold. This procedure of narrowing the mold could be apply before the expansion stage.

The preform can be an aluminum preform (being the term "aluminum" used here to refer to aluminum based alloys, as well as pure aluminum metal), and It can be made of aluminum foil that has a microstructure recrystallized or coated with a gauge in a range of about 0.25 to about 1.5 mm. Can be produced as a closed end cylinder subjecting the sheet to a stretching and re-stretching operation, or backward extrusion.

During the stage of submitting the preform to internal fluid pressure, the fluid pressure inside the preform is produces in successive stages of (i) elevation to a first peak before the preform expansion begins, (ii) fall until a minimum value as the expansion begins, (iii) elevation gradually to an intermediate value as the expansion until the preform extends, although not in contact complete with the mold wall, and (iv) pressure rise intermediate during termination of preform expansion. Indicated with reference to this sequence of pressure stages, the initiation of translation of the die to displace and deform the closed end of the preform, in a preferred embodiment of the invention, occurs substantially at the end of step (iii).

Typically, when fluid pressure is applied internal, the closed end of the preform assumes a configuration generally hemispherical and elongated, as it comes into contact with the wall of the mold; and the initiation of die translation occurs substantially at the moment when the end Closed preform assumes this setting.

Also according to the invention, the step of subject the preform to internal fluid pressure comprises simultaneously apply internal positive fluid pressure and pressure positive fluid external to the preform in the cavity, the internal positive fluid pressure greater than fluid pressure external positive External and internal pressure are provided. respectively by two pressure systems independently controllable The degree of deformation in the preform is controlled independently controlling positive fluid pressures external and internal to which the preform to vary the differential between the positive fluid pressure internal and external positive fluid pressure. In this way, it avoid problems associated with excessive degrees of deformation, and additional beneficial results are achieved, such as the reduced hydrostatic stress, which can cause damage microstructural to the wall of the container.

According to still an additional feature of the invention, it has been found that it is advantageous to apply heat during the expansion of the preform, such as to induce a gradient of preform temperature. Adding heaters to the die, it induces a temperature gradient in the preform from the bottom upwards. Different heaters can be added to the part upper mold, which induce a temperature gradient in the preform from the top down. Can be included additional heaters on the side walls of the cavity of the mold. The addition of the temperature gradient during expansion of the preform serves to define the starting point of the expansion and provides improved conformability.

It has also been found to be advantageous keep the die in contact with the bottom of the preform before of the beginning of the expansion phase, and apply some axial load by the die through the expansion phase. With this procedure, in which the die applies some axial load to the closed end of the preform through the expansion phase, the displacement and deformation of the closed end of the preform no it is preferably performed until the completion of the phase of expansion.

Other features and advantages of the invention they will be evident from the detailed description set forth more Go ahead, along with the accompanying drawings.

Brief description of the drawings

Fig. 1 is a perspective view simplified and somewhat schematic tools for performing the method of the present invention, in embodiments illustrative;

the figs. 2A and 2B are views similar to fig. 1 sequential stages in the realization of a first embodiment of the method of the invention;

fig. 3 is a graph of the internal pressure and piston displacement as time functions, using air as the fluid medium, which illustrates the time relationship between the stages to subject the preform to the internal fluid pressure and to transfer the die in the method of the invention;

the figs. 4A, 4B, 4C and 4D are views similar to fig. 1 sequential stages in the execution of a second embodiment of the method of the invention;

the figs. 5A and 5B are, respectively, a view similar to fig. 1 and a schematic perspective view, simplified, of a stage of conformation with movement of rotation, which illustrates the sequential stages in the execution of a third embodiment of the invention;

the figs. 6A, 6B, 6C and 6D are elevation views computer generated schematics of successive stages in the method of the invention;

fig. 7 is a graph of the variation of pressure over time (using units of time arbitrary), which illustrates the characteristic of applying simultaneously external and internal positive fluid pressures, independently controllable, to the preform in the cavity of the mold, and that compares the internal pressure variation (as in the fig. 3) in the absence of external positive pressure;

fig. 8 is a graph of the variation of deformation over time, derived from the analysis of finite element, which shows the deformation for a position (element) particular under the two pressure conditions different, compared in fig. 7; Y

fig. 9 is a graph similar to fig. 7 that illustrates a particular control mechanism that can be used in the shaping process when positive fluid pressures external and internal apply simultaneously to the preform in the mold cavity;

fig. 10 is a schematic illustration of a preform that expands using a heated die;

fig. 11 is a graph that shows the loads in the die, internal pressures and displacements of the die during the expansion of a preform; Y

fig. 12 is a perspective view that shows the stages in the production of a preform from a flat disk

Better ways to practice the invention

The invention will be described as performed in the methods of forming aluminum containers that have a profiled shape that does not need to have symmetry on the axes (radially symmetrical around a geometric axis of the container), which uses a combination of hydroconformation (fluid pressure internal) and die forming, that is, a procedure from PRF.

The PRF manufacturing process has two stages different: the manufacture of a preform, and the subsequent shaping of the preform in a final container. There are various options for the complete conformation path, and the appropriate selection is determined by the formability of the aluminum foil that is being used.

The preform is made of aluminum foil that it has a coated or recrystallized microstructure and with a gauge in the range of 0.025 mm to 1.5 mm. The preform is a closed end cylinder, which can be manufactured, for example, by a stretch-re-stretch process (-re-stretch) or by extrusion backwards. The diameter of the preform is in some way between the minimum and maximum product diameters of desired container Threads can be formed over the preform, before subsequent forming operations. Profile The closed end of the preform can be designed to help the conformation of the bottom profile of the final product.

As illustrated in fig. 1, the set of tools for the method of the invention includes a mold 10 split, with a profiled cavity 11 defining a form of axially vertical bottle, a die 12 that has the profile desired for the bottom of the container (for example, in the embodiments illustrated, a domed profile convexly, to impart a domed shape at the bottom of the formed container), and a piston 14 that It is attached to the die. In fig. 1, only one of the two is shown halves of the split die, the other being a mirror image of half of the mold illustrated; as will be evident, the two halves they are in a plane that contains the geometric axis of the bottle shape defined by the wall of the cavity 11 of the mold.

The minimum diameter of the cavity 11 of the mold, in the upper open end 11a thereof (which corresponds to the neck of the bottle shape of the cavity), is equal to the diameter outside of the preform (see fig. 2A) to be placed in the cavity, With free space for slack. The preform is positioned at the beginning slightly above die 12, and has adjustment elements 16 pressure, schematically represented at end 11a open, to allow internal pressurization. Pressurization it can be achieved, for example, by coupling the formed threads at the upper open end of the preform, or by inserting a tube inside the open end of the preform and closing airtight by means of the split mold or by any other means of pressure adjustment

The pressurization stage comprises introducing, inside the hollow preform, a fluid such as water or air at sufficient pressure to cause the preform to expand inside the cavity until the preform wall presses substantially totally against the wall of the mold that defines the cavity, thereby imparting the shape and dimensions sides of the cavity to the expanded preform. Indicated Generally, the fluid used may be compressible or not. compressible, with any mass, flow, volume or pressure controlled to control the pressure to which they are subjected to that mode to the walls of the preform. When selecting the fluid, it is it is necessary to take into account the temperature conditions that are going to be used in the shaping operation; If water is the fluid, for example, the temperature is required to be less than 100 ° C, and, if a higher temperature is required, the fluid should be a gas such as air, or a liquid that does not boil at the temperature of the shaping operation

As a result of the pressurization stage, the detailed relief features formed on the wall of the mold are reproduced in the form of inverse mirror image over the resulting container surface. Even if such features, or the total shape of the package produced is not axisymmetric, the container is removed from the tool without difficulty, due to the use of A broken mold.

In the specific embodiment of the invention illustrated in figs. 2A and 2B, preform 18 is a piece of hollow cylindrical aluminum work, with a lower end 20 closed and an open upper end 22, which has a diameter external equal to the outer diameter of the neck of the shape of the bottle to be shaped, and deformations of conformation of the PRF operation are within the established margins by the formability of the preform (which depends on the temperature and degree of deformation). With a preform that has this conformability property, the shape of the cavity 11 of the Mold is manufactured exactly as required for the product final, and the product can be manufactured in a single operation of PRF. The movement of the piston 14 and the degree of internal pressurization they are such that the deformations of the operation of conformation, and that produce the desired shape of the container. The side wall and neck characteristics result mainly from the expansion of the preform due to the pressure internal, while the shape of the fund is mainly defined by the movement of the piston and the die 12, and by the profile of the surface of the die facing the closed end 20 of the preform

The appropriate synchronization of the application of internal and operating fluid pressure (transfer within the mold cavity) of the piston and the die are important in the practice of the invention. Fig. 3 shows a representation graph of computer generated simulated data (sequence of outputs of finite element analysis), which represents the shaping operation of figs. 2A and 2B with air pressure, flow controlled. Specifically, the graph illustrates the history of pressure and piston time involved. As will be evident from fig. 3, the fluid pressure inside the preform occurs in the successive stages of (i) elevation up to a first peak 24 before preform expansion begins, (ii) fall up to a minimum value of 26 as the expansion begins, (iii) Gradually lift up to a custom intermediate value 28 which continues the expansion until the preform is extensive contact, although not complete, with the mold wall, and (iv) elevation faster (at 30) from the intermediate value during the completion of the expansion of the preform. Marked with reference to this sequence of pressure stages, the initiation of the translation of the die to displace and deform the end closing of the preform, in preferred embodiments of the invention, occurs (in 32) substantially at the end of stage (iii). In the graph indicates the time, pressure and units of piston displacement In figs. 6A, 6B, 6C and 6D shows the effect of the operations represented in fig. 3 on the preform (in a computer generated simulation), for times 0.0, 0.096, 0.134 and 0.21 seconds, represented on the x axis of fig. 3.

At the beginning of the introduction of pressure internal fluid to the hollow preform, the die 12 is arranged more below the closed end of the preform (assuming a axially vertical orientation of the tool, as sample), in close proximity (for example, touching) with it, in order to limit the axial stretching of the preforms under the influence of the internal pressure supplied. When the expansion of the preform reaches a substantial degree although not completely complete, piston 14 is activated to forcefully move the die up, moving towards up the metal of the closed end of the preform, and deforming the closed end in die surface profile, custom that the lateral expansion of the preform by pressure is completed internal The upward movement of the closed end of the preform cannot move the preform up relative to the mold, or cause the side wall of the preform to deform (as could happen due to the premature upward operation of the piston), due to the expansion extent of the preform that already has occurred when the piston starts to drive the die towards above.

In Figs 4A-4D a second embodiment of the method of the invention. In this embodiment, as in Figs 2A and 2B, the cylindrical preform 38 has a initial external diameter equal to the minimum diameter (neck) of the Final product. However, in this embodiment it is assumed that the conformation deformations of the PRF operation exceed conformability limits of the preform. In this case, it require two sequential pressure shaping operations. The first (Figs 4A and 4B) does not require a piston, and simply expand the preform into a single split mold 40 to a Workpiece 38a of larger diameter, by internal pressurization. The second is a PRF procedure (Figs. 4C and 4D): it starts with the workpiece as it initially expands in the mold 40 and, using a split mold 42 with a cavity 44 in bottle shape, and a die 46 driven by a piston 48, is that is, using both internal pressure and movement of the piston, produces the final desired bottle shape, which includes all the characteristics of the side wall profile and the background settings, which are mainly produced by the die action 46.

In Figs. 5A and 5B shows a third realization. In this embodiment, the preform 50 is manufactured with a initial outer diameter that is larger than the outer diameter desired minimum (usually the diameter of the neck) of the container bottle-shaped finish This preform choice can result from considerations of the conformation limits of the previous shaping operation, or you can choose to reduce deformations in the operation of PRF. Therefore, the final product manufacturing should include both the expansion of the diameter as the compression of the preform, and thus not You can achieve with the PRF device alone. An operation of Single PRF (Fig 5A, which uses a split mold 52 and a die 54 piston operated) to form the profiles of the wall and the background (as in the embodiment of Figs. 2A and 2B), and required a conformation with rotational movement or other operation of narrowing to form the neck of the container. As illustrated in Fig. 5B, it is possible to employ a shaping procedure with rotational movement of the type set forth in the application for United States patent, pending along with this, nº Serial 09 / 846,169, filed May 1, 2001, which uses set of plural double discs 56 forming with rotation movement, and a conical mandrel 58 to form the bottle neck 60.

In the implementation of the PRF procedure described above, PRF deformations can be considerable. Properly select or adjust the alloy composition to provide a combination of the desired product properties and improved formability. Yes a better conformability is still required, the temperature of conformation can be adjusted as described hereafter, since an increase in temperature produces better conformability; therefore, it may be necessary for the PRF operation or operations are carried out at elevated temperatures, and / or that the preform requires an annealing of recovery, to Increase its conformability.

The present invention differs from the operations known pressure forming, such as the conformation of PET containers by blowing, in particular, adding a external die forming component. A internal die, as sometimes used for shaping PET bottles Currently, there is no known way for it to produce an aluminum container, with a profile that has a shape given, with the range of diameters that can be achieved with the present invention Additionally, there is currently no way known to produce an asymmetric profile (for example, legs on the bottom or spiral reinforcements on the side of the container).

The method of the invention could also be used. to form containers from other materials, such as steel.

The importance of moving the die 12 actuated by piston inside the cavity 11 of the mold, for displace and deform the closed end 20 of the preform 18 (as in fig. 2A and 2B), can also be explained by referring to fig. 3 (mentioned above) as considered in conjunction with the figs. 6A-6D, in which the dotted line represents the vertical profile of the cavity 11 of the mold, and the displacement (in millimeters) of die 12 profiled in vault, to various times after the initiation of internal pressure, it represents by the scale on the right side of that line of points.

The piston offers two essential functions in the conformation of the aluminum bottle. Limit deformations by axial traction, and forms the shape of the bottom of the container. Initially, the piston-driven die 12 is held in close proximity to, or just touching, the bottom of the preform 18 (fig. 6A). This serves to minimize axial stretching of the side wall of the preform, which would otherwise occur as result of internal pressurization. In that way, as internal pressure increases, the side wall of the preform is expand until it comes into contact with the inside of the mold, without important elongation Typically, the central region of the preform will first expand, and this region of expansion will grow to along the length of the preform, both upwards and down. At some point in time, the bottom of the preform it becomes almost hemispherical in shape, with the radius of the hemisphere approximately equal to that of the mold cavity (fig. 6B). Is now at this point, or just before this point in time, that the piston 12 must be driven upwards (fig. 6C). The profile of the piston tip (i.e. die surface profile) completely defines the profile of the bottom of the container. As the internal fluid pressure completes the preform molding against the wall of the mold cavity (compare the neck and protrusion of the bottle in figs. 6B, 6C and 6D), the movement of the piston, combined with internal pressure, forces the bottom of the preform inside the die surface profiles so that produces the desired profile (fig. 6D) without excessive deformation due to traction that could conceivably lead to failure. He upward movement of the piston applies compressive forces to the hemispheric region of the preform, reduces overall deformation caused by the pressurization operation, and help in material feed radially out to fill the die tip profiles.

If the piston movement is applied too much soon, in relation to the speed of internal pressurization, it is the preform is likely to deform and fold due to the axial compressive forces. If applied too late, the material will be subjected to excessive deformation in the axial direction, causing failure. In this way, it is required the coordination of the internal pressurization speed and the piston and die tip movement for one operation of satisfactory conformation. The necessary sequence is achieved better through finite element analysis (FEA) of the process. The fig. 3 is based on the results of the FEA.

Thus, the invention has been described and exemplified so far in fig. 3, as if it did not apply no positive fluid pressure (i.e. superatmospheric) at outside of the preform inside the mold cavity. In that case, the external pressure on the preform in the cavity would be substantially ambient atmospheric pressure. As the preform expands, the air in the cavity would be extracted (by the progressive decrease in volume between the outside of the preform and the mold wall) through an opening or exhaust duct adequate, ready for that purpose and communicating between the cavity of the mold and the exterior of the mold.

Indicated with specific reference to the packaging Aluminum, by way of illustration, has been shown by FEA that, in the absence of any positive external pressure applied, once the preform begins to deform plastically (flow), the degree of deformation in the preform becomes very high and It is essentially uncontrollable, due to the low or zero speed of Work hardening of aluminum alloys in the process temperature (for example, approximately 300 ° C) of the pressurized piston forming operation.

That is, at such temperatures the speed of Work hardening of aluminum alloys is essentially zero, and ductility (i.e. limit of conformation) decreases with the increase in the degree of deformation. From In this way, the possibility of manufacturing the packaging product with desired final shape decreases as the degree of deformation increases of the shaping operation and decreases the ductility of the aluminum.

According to an important feature In addition to the invention, positive fluid pressure is applied to the outside of the preform in the mold cavity, simultaneously with the application of positive fluid pressure inside the preform These positive internal and external fluid pressures are provided respectively by two pressure systems independently controlled. External positive fluid pressure can be supplied conveniently by connecting a source controllable regardless of positive fluid pressure at exhaust duct or opening mentioned above, in order to maintain a positive pressure in the volume between the mold and the preform that expands.

Figs. 7 and 8 compare the pressure against time, and deformation versus time histories for the pressurized piston forming of a container with and without control of positive external pressure (the term "deformation" refers to here to the elongation per unit of length produced in a body by an external force). Line 101 of fig. 7 corresponds to the line called "Pressure" in fig. 3, for that matter in the that there is no external positive fluid pressure acting on the preform; line 103 of fig. 8 represents the deformation that results for a particular position (element) as determined through FEA. Clearly, the deformation is almost instantaneous in this case, which implies very high degrees of deformation and times too short to expand the preform in contact with the wall of the mold. On the contrary, lines 105, 107 and 109 of fig. 7, respectively, they represent internal positive fluid pressure, external positive fluid pressure, and the differential between the two, when both external and internal pressures are controlled, that is, when the internal and external positive fluid pressures, independently controlled, apply simultaneously to the preform in the mold cavity; internal pressure is higher than external pressure, so that there is a pressure differential net positive external-internal as needed to effect the expansion of the preform. Line 111 in fig. 8  represents a circumferential deformation (deformation produced in the horizontal plane around the circumference of the preform as it expands) for the pressure condition external-internal independently controlled, represented by lines 105, 107 and 109; it will be noted that the circumferential deformation shown by line 111 reaches the same final value as line 103 although for a while much longer and thus to a much more deformation degree low. Line 115 in fig. 8 represents axial deformation (deformation produced in the vertical direction as it lengthens the preform).

Simultaneously providing fluid pressures positive external and internal controllable independently, which they act on the preform in the mold cavity, and varying the difference between these external and internal pressures, the operation of conformation remains completely controlled, avoiding degrees of very high and uncontrollable deformation. The ductility of the preforms, and thus the limit of conformation of the operation, It increases for two reasons. First, the decrease in the degree of deformation of the forming operation increases ductility inherent in aluminum alloy. Second, the addition of the positive external pressure decreases (and could potentially reach to make negative) the hydrostatic stress on the wall of the preform that expands. This could reduce the detrimental effect. of the damage associated with microlagunas and intermetallic particles in the metal. The term "hydrostatic stress" refers here to the arithmetic average of three normal stresses in the x, y, z directions.

The characteristic of the invention thus described increases the capacity of the piston forming operation to pressure to successfully manufacture aluminum containers in the form of bottle and the like, allowing control of the degree of deformation of the forming operation and decreasing the hydrostatic stress on the metal during shaping.

Pressure differential selection is based in the material properties of the metal from which it manufactures the preform. Specifically, the limit should be considered elastic and the degree of hardening by metal work. For for the preform to flow plastically (i.e. inelastically), the pressure differential should be such that the effective effort (Mises) in the preform exceeds the elastic limit. If there is a degree of hardening by positive work, an effective effort applied fixed (from pressure), in excess of the limit elastic, would cause the deformation of the metal at a level of deformation equal to the effective deformation applied. At that point the degree of deformation would approach zero. In the case of a degree Hardening by zero or very low work, the metal will would deform at a high degree of deformation until it is put into contact with the wall of the mold (mold) or until fracture occurs.  At the high temperatures anticipated for the PRF process, the degree of work hardening of aluminum alloys It is low to zero.

Examples of gases suitable for use in the Supply of both external and internal pressures include, without limitation, nitrogen, air and argon, and any of the combinations of these gases.

The degree of plastic deformation in any point on the wall of the preform, at any point in time, it depends only on the instantaneous effective deformation, which in turn It depends only on the pressure differential. Pressure selection external depends on the internal pressure, with the main objective of achieve and control the effective deformation, and thus the degree deformation, in the wall of the preform.

Fig. 9 shows a control mechanism different that can be used in the conformation process. They have used finite element simulations to optimize the process. In fig. 9, line 120 represents the internal pressure (Pin) that acts on the preform, line 122 represents the external pressure (Pout) acting on the preform, and line 124 represents the pressure differential (Pdiff = Pin - Pout). This figure shows the pressure history from a control method. In this case, the fluid mass in the internal cavity remains constant, and the pressure in the external cavity (outside the preform) decreases linearly The material properties dependent on the degree of deformation are also included in the simulation. The latter control mechanism is currently preferred because it gives as result a simpler process.

Fig. 10 refers to a further embodiment of the invention in which heating is applied to the preform, which induces a temperature gradient to the preform. Is according shown in fig. 10, the die 12 comes into contact with the bottom of preform 18, and die 12 contains an element 19 of heating. This element heats the preform from the bottom. up, causing the expansion of the preform to grow from bottom up when internal pressure is increased.

Fig. 11 shows graphs illustrating the expansion process A line on the graph shows the piston / die displacements while the other shows variations in the load on the piston / die, both as a time function A third line shows the internal pressure in the preform.

At point A the piston is preloaded up to a compressive load of approximately 22.7 kg, and at the point B the preform is pressurized internally and is maintained at a level of 1.14 MPa. In the illustrated procedure, the position of the piston it was staggered between points B and C to maintain a load of the 68 kg compression piston. When the piston load is no longer decreased rapidly after an increase in the position of the piston (point C to D), the rise of the piston continued until a displacement of approximately 25 mm and a load of approximately 454 kg (point E). During the rise of the piston from point D to point E, the bottom profile of the container conformed simultaneously with the expansion of the preform, of way that point E represents the completion of the conformation of the container

While the graph in fig. 11 shows a Multi-stage procedure, it is also possible to expand and shape the preform into a container in a uniform operation, for example using a computer control of the procedure. The advantage of this procedure is that, due to the gradient of induced temperature, the expansion proceeds gradually from the bottom towards the top, as the piston and the die They move up. It has been shown that this technique leads at reduced improved formability when compared to previously described methods in which expansion occurs essentially simultaneously along the length Complete the preform.

While fig. 10 shows an element of heating only inside die 12, it is possible to provide Different heating zones to aid in shaping. For example, there may be an additional different heater around from the top of the preform, as well as elements of additional distinct heating inside the side walls of the mold cavity. Manipulating independently the temperatures in each of these areas, the records of Optimal expansion are developed for various designs of packaging

Fig. 12 shows a typical sequence in the manufacture of a preform from a flat disk. One is used standard stretching / re-stretching technique, stretching first the Aluminum foil 70 in a slightly closed end cylinder 71 deep, which will then be re-embedded in a second cylinder 72 of Smaller diameter and longer side wall. The cylinder 72 is it will then be re-formed to form the cylinder 73, which re-form to conform the cylinder 74. It will be noted that the cylinder 74 has a long thin configuration.

Claims (28)

1. A method of forming a metal container or similar, of defined shape and dimensions, said said method: (a) arrange a hollow metal preform (18), having an end (20) closed in a cavity (11) of a mold which has a mold wall that defines said shape and dimensions, at least a portion of the preform initially spaced inward from the wall of the mold, and (b) subject the preform (18) to fluid pressure internal to expand the preform out in contact substantially complete with the mold wall, to impart that way said shape and dimensions defined to the preform, characterized in that the cavity (11) of the mold is sized to contain laterally a preform (18) of hollow metal, which has an end (20) closed with a die (12) located at one end of the cavity and translatable into the cavity , the preform (18) being located inside the cavity (11), with the closed end of the preform positioned close to the die (12), an internal fluid pressure is applied to the preform to expand the preform out and exert fluid pressure force on the closed end and, (c) either before or after conformation previous (18) begins to expand, but before the end of the expansion of the preform, the die (12) moves to one end of the cavity for coupling and moving the closed end (20) of the preform in a direction opposite to the direction of the force exerted by the fluid pressure in it, deforming the end closed the preform while the preform expands towards out in substantially complete contact with the wall of the mold. 2. A method according to claim 1, characterized in that the internal fluid pressure is applied by applying both internal positive fluid pressure and external positive fluid pressure to the preform (18) within the mold cavity, the internal positive fluid pressure being greater than the external positive fluid pressure. 3. A method according to claim 1, characterized in that, before the preform (18) is subjected to internal fluid pressure, heat is applied to the preform within the mold cavity to induce a temperature gradient there. 4. A method according to claim 1, characterized in that the preform (18) is an elongated and initial and generally cylindrical workpiece, having an expandable closed end and an open end opposite its closed end. 5. A method according to any one of claims 1-4, characterized in that the die (12) is moved into the cavity (11) after the preform (18) begins to expand but before the expansion of the preform in step (b). A method according to any one of claims 1-4, characterized in that the die (12) moves in contact with the closed end (20) of the preform (18) before the expansion of the preform begins, and the Contact is maintained throughout the expansion of the preform. A method according to any one of claims 1-6, characterized in that said die (12) has a profiled surface, the closed end (20) of the deformed preform being so as to conform to said profiled surface. A method according to any one of claims 1-7, characterized in that said defined form is a bottle shape that includes a neck portion and a body portion larger in lateral dimensions than the neck portion, said cavity having (11) of the mold a long axis, said preform (18) having a long axis and being substantially coaxially arranged with said cavity (11) in step (a), and said die (12) being transferable along the long shaft of the cavity (11). A method according to claim 8, characterized in that said die (12) has a domed profile, and wherein the step (c) deforms said closed end (20) of said preform (18) into said domed profile. 10. A method according to any one of claims 1-9, characterized in that said mold wall comprises a separable split mold (40) for removing the shaped container after step (c). A method according to claims 8, 9 or 10, characterized in that said defined shape is asymmetric about said long axis of said cavity. A method according to any one of claims 1-11, characterized in that said die (12) is initially positioned, at the beginning of step (b), to limit the axial elongation of the preform (18) by said fluid pressure. 13. A method according to any one of claims 8-12, characterized in that said preform (18) is an elongated and generally cylindrical workpiece that has an open end opposite to said closed end (20), and is substantially the same in diameter to said neck portion of said bottle shape. 14. A method according to any one of claims 8-13, characterized in that said preform (18) has sufficient formability to be expandable up to said defined shape, in a single pressure forming operation. 15. A method according to claim 13, characterized by a preliminary step of placing the workpiece (38) in a mold cavity smaller than the first mold cavity mentioned, and subjecting the workpiece therein to fluid pressure internal to expand the workpiece to an intermediate size (38a) and a smaller shape than said shape and defined lateral dimensions, before performing stages (a), (b) and (c). 16. A method according to claim 1, characterized in that said preform (18) is an elongated and generally cylindrical workpiece that has an open end opposite to said closed end (20) and is larger in diameter than said portion neck of said bottle shape; and which includes an additional stage of holding the workpiece, adjacent to said open end, for a forming operation (56, 58) with rotational movement to form a portion (60) of small diameter neck, after execution of stages (a), (b) and (c). 17. A method according to any one of claims 1-16, characterized in that said preform (18) is an aluminum preform. 18. A method according to claim 17, characterized by the step of manufacturing the preform (18) from aluminum foil (70) having a microstructure coated or recrystallized with a caliber in a range of about 0.25 to about 1.5 mm, before the execution of stage (a). 19. A method according to claim 18, characterized in that said preform (18) is produced as a closed end cylinder (74), subjecting said sheet to a stretch-re-stretch or backward extrusion operation. 20. A method according to any one of claims 1-19, characterized in that, during step (b), the fluid pressure within the preform (18) occurs in successive stages of (i) elevation to a first peak before start the expansion of the preform, (ii) fall to a minimum to medium value that begins the expansion, (iii) gradually rise to an intermediate value as the expansion continues, until the preform extends, although not in full contact, with the wall of the mold, and (iv) elevation from the intermediate value during the completion of the expansion of the preform; and wherein the initiation of translation of the die (11) in step (c), to displace and deform the closed end (20) of the preform (18), occurs substantially at the end of stage (iii). 21. A method according to any one of claims 1-19, characterized in that, during step (b), the closed end (20) of the preform (18) assumes a generally hemispherical and elongated configuration as said portion of the preform comes into initial contact with the wall (11) of the mold in step (b); and wherein the initiation of the translation of the die (12) in step (c), to displace and deform the closed end (20) of the preform (18), occurs substantially in the time in which the end (20 ) closed of the preform assumes said configuration. 22. A method according to claim 2, characterized by independently controlling the external and internal positive fluid pressures to which the preform (18) is simultaneously subjected to vary the differential between said internal positive fluid pressure and said external positive fluid pressure, controlling that way the degree of deformation in the preform (18). 23. A method according to claim 3, characterized in that heat is applied to the preform (18) through heating means in the die (12), to thereby induce a temperature gradient in the preform, which begins in the bottom closed and extends upwards. 24. A method according to claim 3, characterized in that heat is applied to the preform (18) by means of heating means around the upper part of the preform in the mold, to thereby induce a temperature gradient in the preform (18), which starts at the top and extends down. 25. A method according to claim 23 or 24, characterized in that heat is applied to the preform (18) through heating means on the side walls of the mold (10). 26. A method according to any one of the preceding claims, wherein said fluid pressure is provided by a pressurizing fluid in the form of a gas. 27. A method according to claim 26, in the that the pressurization fluid is gas, air, argon or nitrogen. 28. A method according to any one of the preceding claims, wherein the temperature of the shaping operation is greater than 100 ° C.