DE60205237T2 - METHOD FOR PUSH-PISTON MOLDING OF METAL CONTAINERS AND THE SAME - 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

Technical field

These The invention relates to methods for molding metal containers or the like using an internal fluid pressure to a hollow metallic preform or workpiece against a press die to expand. In one important special aspect is the invention directed to methods of forming aluminum or other metal containers, which have a contoured shape, for example a bottle shape with asymmetric features.

State of the art

metal cans are well known and widely used for drinks. Show today Beverage can body, whether they are now one piece "drawn and ironed "body or open bodies at both ends (with a separate closure element on the bottom and top) in general simple upright cylindrical side walls on. It sometimes turns off establish the aesthetics, due to consumer wishes and / or re the product identification desired, a modified and more complex shape on the sidewalls to apply a metal beverage container and in particular a metal container to disposal to put, rather the shape of a bottle than a conventional cylindrical Canned form. Achieve conventional canning processes but not such configurations.

For this and other purposes It may be advantageous to have suitable and effective methods of molding of workpieces in bottle shapes or other complex forms available too put. About that would be out it makes sense to provide such methods, which in the Location are contoured container shapes form, which are not radially symmetrical to the variety the available To increase designs.

in the U.S. Patent 3,040,684 is an apparatus for molding door knobs a preform using a press-die and hydraulic Print described. The preform is placed in a press die, with hydraulic fluid filled and sealed. The press is then closed and a bottom piston moves up and presses the wall of the mold in uniformity with the shape of the press die. In this process is changing the volume of the liquid not and the expansion of the preform is due to the movement of the Piston causes.

A another device for forming a doorknob is disclosed in U.S. Patent 4,362,037 described in which a split press is used. The Preform comprises a partially formed door knob and the outer circular surface of the Knaufs is placed on a lower press. An upper press has a die with sidewall sections, the final form define the knob. This upper press will go down over the pressed on the lower press resting preform. Subsequently, will a fluid is internally pressed into the preform, causing the preform in the shape of the press die is pressed.

The US Pat. No. 6,182,487 describes a method for producing a Metal boiler using a split press, which one fixed press and a moving press includes. A cylinder is first formed, which has a bottom, which with a Shell welded is, and is with fixed in the movable press bottom end placed while the open end of the cylinder attached to the fixed press becomes. The cylinder is pressurized by the fixed one Press and the movable press closed on the fixed press to form the kettle.

Disclosure of the invention

• (a) Anordnen einer hohlen metallischen Vorform, die ein geschlossenes Ende aufweist, in einem Pressen-Gesenk, welches eine Pressenwand aufweist, die diese Form und diese Dimensionen definiert, wobei zumindest ein Abschnitt der Vorform anfänglich von der Pressenwand nach innen beabstandet ist, und
• (b) Unterziehen der Vorform einem internen Fluid-Druck, um die Vorform nach außen in im Wesentlichen vollen Kontakt mit der Pressenwand zu expandieren, wodurch diese definierte Form und diese definierten Dimensionen auf die Vorform eingebracht werden, dadurch gekennzeichnet, dass das Pressen-Gesenk so dimensioniert ist, dass es eine hohle metallische Vorform seitlich einschließt, welche ein geschlossenes Ende mit einem Kolben, der an einem Ende des Gesenks platziert ist und in das Gesenk hinein versetzbar ist, aufweist, wobei die Vorform innerhalb des Gesenks mit dem geschlossenen Ende der Vorform in nahe gegenüberstehende Beziehung zu dem Kolben positioniert ist, und ein innerer Fluid-Druck auf die Vorform aufgebracht wird, um die Vorform nach außen zu expandieren und Fluid-Druckkraft auf das geschlossene Ende auszuüben, und wobei
• (c) der Kolben entweder bevor oder nachdem die Vorform beginnt zu expandieren, jedoch bevor die Expansion der Vorform abgeschlossen ist, in das eine Ende des Gesenks versetzt wird, um das geschlossene Ende der Vorform in eine Richtung entgegen der Richtung der durch das Fluid ausgeübten Kraft zu ergreifen und zu verschieben, das geschlossene Ende der Vorform zu deformieren, während die Vorform nach außen in im Wesentlichen vollen Kontakt mit der Pressenwand expandiert.

The present invention contemplates, as much as possible, the provision of a method of forming a metal container or the like having a defined shape and dimensions, said method comprising:

• (a) disposing a hollow metallic preform having a closed end in a press die having a press wall defining said shape and dimensions, wherein at least a portion of the preform is initially spaced inwardly from the press wall, and
• (b) subjecting the preform to an internal fluid pressure to expand the preform outwardly in substantially full contact with the press wall, thereby introducing that defined shape and dimensions to the preform, characterized in that the press die is dimensioned to laterally enclose a hollow metal preform having a closed end with a piston placed at one end of the die and displaceable into the die, the preform within the die being connected to the closed end of the die Preform is positioned in close opposing relationship to the piston, and an internal fluid pressure is applied to the preform to expand the preform to the outside and exert fluid pressure force on the closed end, and wherein
• (c) the piston either before or after the The preform begins to expand but before the expansion of the preform is completed, into which one end of the die is displaced to engage and displace the closed end of the preform in a direction opposite to the direction of the force exerted by the fluid, the closed end deforming the preform as the preform expands outwardly in substantially full contact with the press wall.

The Displacement of the piston is effected by means of a punch, which in capable of applying sufficient force to the piston to move and deform the preform. This method is sometimes referred to herein as a pressure-punch-molding (PRF) method referred to as the container both by applied internal fluid pressure and by the Displacement of the piston is formed by the punch.

When Another feature of the invention, the piston has a contoured surface and the closed end of the preform is deformed such that it matches the contoured surface. For example, the piston may have a curved contour, wherein the closed end of the preform as well in a curved contour is deformed.

The defined shape in which the container can be formed, a bottle shape including a neck section and a body section that is larger in its lateral dimensions than the neck portion, wherein the press die is a longitudinal axis has, the preform has a longitudinal axis and disposed substantially coaxially within the die and the piston along the longitudinal axis of the die is displaceable.

advantageously, and preferably the press wall comprises a split press, which is separable to remove the formed container. With a split press can be the defined shape along the longitudinal axis of the socket to be asymmetrical.

Of the Piston is preferably close initially positioned in or in contact with the closed end of the preform, before the application of fluid pressure is effected to the axial Elongation of the Limiting preform by the fluid pressure. The shift of Piston can be initiated after the lower section of the Preform was expanded in contact with the press wall.

The Preform for forming a bottle-shaped container or the like preferably an oblong and originally generally cylindrical workpiece, which faces an open end has its closed end. In particular embodiments The invention may be substantially the same diameter to the neck section the bottle shape and have sufficient moldability to expanded into the defined shape in a single pressing operation to become. If the workpiece does not have such formability, are precursors of Placing the workpiece in a press die which is smaller than the one described first Pressing die is, and subjecting the workpiece herein an internal fluid pressure to the workpiece to an intermediate size and intermediate form to expand, smaller than the defined shape and smaller lateral dimensions, before the described PRF method carried out.

alternative can if the elongated and originally generally cylindrical workpiece in his original Diameter is larger as the neck portion of the bottle shape, the method of molding a bottle-shaped container another step of subjecting the workpiece to a Rotary-mold operation near the open end include to a neck section formed with reduced diameter after performing the PRF process.

alternative The diameter of the neck area of the preform is used reduced by a press-neck procedure. This press-neck procedure could be before the expansion stage are applied.

The Preform may be an aluminum preform (the term "aluminum" is used herein to refer to Both aluminum-based and pure aluminum-metal alloys to designate) and may be made of an aluminum sheet, which is a recrystallized or recovered microstructure with a thickness in the range of about 0.25 to about 1.5 mm. She can as Cylinder with closed end by subjecting the sheet to a pull-pull operation or indirect extrusion.

During the step of subjecting the preform to an internal fluid pressure, the fluid pressure within the preform occurs in successive stages of (i) rising to a first peak before expansion of the preform begins, (ii) falling to a minimum value expansion begins (iii) progressively increasing to an intermediate value as expansion progresses until the mold is expanded but not yet fully in contact with the press wall, and (iv) increasing from the intermediate pressure during completion of the preform expansion , on. With respect to this sequence of pressure stages, the init tion of the displacement of the piston to move and deform the closed end of the preform in a preferred embodiment of the invention substantially at the end of stage (iii).

typically, takes the closed end of the preform an enlarged and generally hemispherical Configuration when the internal fluid pressure is applied, and when the preform comes into contact with the press wall; and the Initiation of the displacement of the piston essentially occurs the time at which the closed end of the preform this Configuration accepts.

As well includes in accordance with the invention, the step of subjecting the preform one internal fluid pressure the simultaneous application of an internal positive fluid pressure and an external positive fluid pressure to the preform in the die, wherein the internal positive fluid pressure is higher than is the external positive fluid pressure. The internal and the external Printing is in each case by two independently controllable printing systems to disposal posed. The strain rate in the preform is controlled by independent control the internal and external positive fluid pressures controlled the preform simultaneously for varying the differential between the internal positive fluid pressure and the external positive fluid pressure is subjected. In this way, problems with excessive strain rates are avoided and additional advantageous results, As well as the reduction of hydrostatic load, which microstructure damage to the container wall can cause reached.

According to one Yet another feature of the invention has been found to be advantageous Heat on the Preform during of the expansion, so as to create a temperature gradient in to induce the preform. By adding heaters to the piston becomes a temperature gradient in the preform from the bottom up induced. Separate heaters can be added at the top of the press which detects a temperature gradient in the preform from above induce below. Further heaters can be found in the side walls of the Die cavity be provided. The addition of the temperature gradient during The expansion of the preform serves to define the point of initiation of the Expansion and provides improved formability.

It was also found to be beneficial in contacting the piston the bottom of the preform before the start of the expansion phase and some axial loading by the piston over the expansion phase applied. With this method, in which the piston has some axial Applying stress to the closed end of the preform through the expansion phase, becomes the displacement and the deformation of the closed end Preferably, the preform is not performed until the expansion phase completed is.

Further Features and advantages of the invention will become apparent from the following detailed description together with the accompanying drawings seen.

Short description of drawings

1 Figure 3 is a simplified and somewhat schematic perspective view of a tool for carrying out the method according to the present invention in illustrative embodiments;

the 2A and 2 B are similar to views 1 successive stages in carrying out a first embodiment of the method according to the invention;

3 FIG. 12 is a graph of internal pressure and plunger displacement versus time using air as the fluid medium, illustrating the time dependence between the steps of subjecting the internal fluid pressure preform and displacing the piston in the method of FIG Invention represents;

the 4A . 4B . 4C and 4D are similar to views 1 successive stages in carrying out a second embodiment of the method according to the invention;

the 5A and 5B are each a view similar to the 1 and a simplified schematic perspective view of a rotary forming step illustrating successive stages in carrying out a third embodiment of the invention;

the 6A . 6B . 6C and 6D computer generated schematic raised views are successive stages in the method according to the invention;

7 FIG. 12 is a graph of pressure variation over time (using any unit of time) illustrating the feature of simultaneously applying independently controlled internal and external positive fluid pressures to the mold in the press die and comparing the internal pressure variation therewith (as in 3 ) in the absence of an external positive pressure;

8th is a graph of strain variation over time, derived from the finite element ana lysis, which compared the elongation for a particular position (element) under two different pressure conditions 7 represents; and

9 is a graph similar to that 7 , which illustrates a particular control mechanism that can be used in the molding process when internal and external positive fluid pressures are applied simultaneously to the preform in the press die.

10 Figure 3 is a schematic representation of an expanding preform using a heated piston;

11 Figure 11 is a graph showing the loads on the pistons, the internal pressures and displacements of the piston during expansion of a preform; and

12 Figure 11 is a perspective view showing stages in the production of a preform from a flat disk.

Ways to execute the invention

The Invention is described as used in the method of molding of aluminum containers is realized, which have a contoured shape, not must be asymmetric (radially symmetric about a geometric Axis of the container) using a combination of hydroforming (internal fluid pressure) and piston formation, i. a PRF procedure.

Of the PRF manufacturing process has two distinct stages, on the one hand, the production of a preform and the subsequent molding the preform into a final one Container. in this connection exist different options for execution the final one Formation and the appropriate choice is made by the formability determined of the aluminum sheet used.

The Preform is produced from an aluminum sheet, which is a recrystallized or recovered microstructure and has a thickness in the range of 0.25 mm to 1.5 mm. The preform is a cylinder with a closed end, for example, by a pull-pull-through (retrain) process or can be produced by indirect extrusion. The diameter The preform is somewhere between the minimum and maximum Diameter of the desired Container-product. Can thread before formed subsequent forming operations on the preform be. The profile of the closed end of the preform may be formed be that it's the shape of the bottle profile of the final product supported.

As in 1 As shown, the tool assembly for the method according to the invention includes a split press 10 with a profiled die 11 , which defines an axial vertical bottle shape, a piston 12 having a contour desired for the bottom of the container (for example, a convex contour for applying a domed shape to the bottom of the molded container as provided in the illustrated embodiments; 14 which is attached to the piston in 1 showing only one of the two halves of the split press, the other half being a mirror image of the illustrated press half; It will be seen that the two halves meet each other in a plane that is the geometric axis of the wall through the press die 11 defined bottle shape contains.

The minimum diameter of the press die 11 is at the top 11a of which (which agrees with the neck of the bottle shape of the die) equal to the outer diameter of the preform (see 2A ) to be placed in the die with the clearance being allowed. The preform will initially be slightly above the piston 12 positioned and has a schematically illustrated pressure fit 16 at the upper end 11a so as to allow internal pressurization. The pressurization may be achieved, for example, by coupling with the threads formed in the upper open end of the preform, or by inserting a tube into the open end of the preform and forming a seal by means of the split press or other pressure fits.

Of the Step of pressurizing involves the introduction of a Fluids such as water or air under a pressure that is sufficient to expand the preform within the die until the wall of the Preform substantially complete is pressed against the press wall defining the die, to the interior of the hollow preform, reducing the shape and the lateral Dimensions of the die applied to the expanded preform become. Generally speaking, the fluid can be compressible or not be used compressible, where mass, flow, volume or pressure can be controlled, to control the pressure applied to the preform walls. When selecting of the fluid, it is necessary to check the temperature conditions at Forming process occur to consider; if water that Fluid is, for example, the temperature must be lower than 100 ° C, and if a higher one Temperature is required, the fluid should be a gas such as air or a liquid that does not cook at the temperature of the molding operation.

As a result of this step of negative pressure In addition, detailed relief features formed in the press wall are reproduced as an inverse mirror image on the surface of the resulting container. Even if such features or the entire shape of the container produced are not axially symmetric, the container is removed from the tool without difficulty due to the use of a split press.

In the in the 2A and 2 B illustrated specific embodiment of the invention is the preform 18 a hollow cylindrical aluminum workpiece with a closed lower end 20 and an open top 22 which has an outer diameter equal to the outer diameter of the neck of the bottle shape to be formed, and the forming expansions of the PRF method are within the limits set by the preform moldability (which depends on the temperature and deformation Rate depends). With a preform that has this property of formability, the shape of the press die 11 exactly as required for the final product, and the product can be produced in a single PRF operation. The movement of the stamp 14 and the rate of internal pressurization are such that the expansions of the molding operation are minimized and to produce the desired shape of the container. The features of the neck and side wall result mainly from the expansion of the preform due to the internal pressure, while the shape of the bottom is mainly due to the movement of the punch and the piston 12 as well as the contour of the piston surface, which is the closed end 20 facing the preform.

Accurate synchronization of the application of internal fluid pressure and the operation of the punch and piston (displacement in the die die) are important in the practice of the invention. 3 FIG. 12 is a graphical representation of computer-generated simulated data (a sequence of Finite Element Analysis outputs) illustrating the shaping operation in accordance with FIG 2A and 2 B with air pressure, which is controlled by the flow rate. In particular, the graph represents the history of the printing and the stamping time involved 3 As can be seen, the fluid pressure within the preform occurs in successive stages of (i) rising to a peak 24 before the expansion of the preform begins, (ii) decreasing to a minimum value 26 when the expansion begins, (iii) gradually increase to an intermediate value 28 as the expansion progresses until the preform expands, but contact with the press wall is not completed, and (iv) faster increase (at 30 ) from the intermediate value during the completion of the expansion of the preform. With respect to this sequence of pressure stages, it should be noted that the initiation of displacement of the piston to displace and deform the closed end of the preform in the preferred embodiments of the invention 32 ) occurs substantially at the end of step (iii). Time, pressure and stamp shift units are shown on the graph. The effect of in 3 operations on the preform (simulation generated in a computer) are for the times 0.0, 0.096, 0.134 and 0.21 seconds, as is the case on the x-axis 3 is shown in the 6A . 6B . 6C and 6D shown.

At the beginning of introducing the internal fluid pressure to the hollow preform, the piston becomes 12 placed beneath the closed end of the preform (assuming an axially vertical orientation of the tool, as shown) in close proximity (e.g., touching) thereto to prevent axial expansion of the preform under the influence of the internal pressure added thereto. When the expansion of the preform has reached a significant but not yet complete degree, the stamp becomes 14 operated to pushingly push the piston up to move the metal of the closed end of the preform upwards and to deform the closed end in the contour of the piston surface when the lateral expansion of the preform is completed by means of the internal pressure. The upward displacement of the closed end of the preform can not move the preform upwardly relative to the press or cause the sidewall of the preform to distort (which may be caused by premature upward movement of the punch) due to the degree of expansion the preform which has already occurred when the punch starts to drive the piston upwards.

A second embodiment of the method according to the invention is shown in FIGS 4A - 4D shown. In this embodiment, as shown in FIGS 2A and 2 B , the cylindrical preform 38 an original outside diameter equal to the minimum diameter (neck) of the final product. However, in this embodiment, it is believed that the molding loads of the PRF operation exceed the limits of formability of the preform. In this case, two consecutive pressure-molding procedures are required. The first ( 4A and 4B ) does not require a stamp and simply expands the preform within a simple split press 40 on a workpiece with a larger diameter 38a by means of internal pressurisation. The second method is a PRF procedure ( 4C and 4D ), which with the in the press 40 originally expanded workpiece starts and a split press 42 with a bottle-shaped gene Gesenk 44 as well as one by means of a stamp 48 driven piston 46 That is, using both internal pressure and the movement of the punch used, which ultimately produces the desired bottle shape, which has all the characteristics of the sidewall profile as well as the contours of the bottle, mainly due to the action of the piston 46 produced.

A third embodiment is in 5A and 5B shown. In this embodiment, the preform is 50 generated with an original outer diameter that is greater than the desired minimum outer diameter (usually the diameter of the neck) of the finally bottle-shaped container. The choice of a preform may result from consideration of the design limits of the preform operation or may be selected to reduce the expansions in PRF operation. As a result, the generation of the final product must include both the diameter expansion and the compression of the preform, and thus can not be achieved with the PRF device alone. A single PRF operation ( 5A using a split press 52 and a plunger driven piston 54 ) is used to form the wall and floor profiles (as in the embodiment of FIGS 2A and 2 B ), and a rotary-forming or other neck-forming operation is required to form the neck of the container. As in 5B it is possible to use a spin-forming method of the type shown in co-pending U.S. Patent Application Serial No. 09 / 846,169, filed May 1, 2001, wherein a plurality of tandem sets of rotary forming slices 56 and a tapered spindle 58 be used to the bottleneck 60 to shape.

In In practice of the PRF method described above, the Be large PRF stretches. The alloy composition is selected accordingly or set to a combination of desired product properties and an increased Moldability available to deliver. If still a better formability required is, the molding temperature can be as described below, as a temperature increase allows better formability; thus, there may be a need to include the PRF operation (s) increased To carry out temperatures and / or the preform may require a recovery anneal to improve its formability to increase. The present invention differs in particular from known ones Pressure-forming method as well as the blow-molding of PET containers The addition an external piston-forming component. An internal piston, as he sometimes used for molding PET bottles is not required. At the moment there is no den Applicants known way, an aluminum container with a shaped profile with the range of diameters obtained by means of the present invention can be achieved to produce. About that In addition, there is no way familiar to the applicants, an asymmetric one Profile (for example, feet on the ground or spiral Ribs on the side of the container) to produce.

The Method according to the invention could as well used to container made of other materials such as steel.

The importance of moving the piston driven by a punch 12 in the press die 11 to the closed end 20 the preform 18 (as in the 2A and 2 B ) and to deform, can be described below with reference to the 3 (as mentioned above), when combined with the 6A - 6D in which the dotted line represents the vertical profile of the press die 11 represents, and the displacement (in millimeters) of the domed contoured piston 12 at different times after initiation of internal pressure is represented by the scale on the right side of this dotted line.

The stamp serves two important functions in forming the aluminum bottle. It limits the axial tensile forces and forms the shape of the bottom of the container. Initially, the piston driven by a punch is used 12 in close proximity to or nearly touching the bottom of the preform 18 ( 6A ) held. This serves to minimize the axial expansion of the preform sidewall that would otherwise occur as a result of internal pressurization. Thus, as the internal pressure is increased, the sidewall of the preform is expanded to contact the interior of the press without significant elongation. Typically, the central region of the preform will first expand and this region of expansion will grow along the length of the preform, both up and down. At some point in time, the bottom of the preform becomes nearly semicircular in shape, with the radius of the semicircle nearly equal to that of the press die ( 6B ). At this time, or just before this time, it is necessary that the punch is activated to the piston 12 to drive upwards ( 6C ). The profile or nose of the punch (ie the contour of the piston surface) completely defines the profile of the bottom of the container. When the internal fluid pressure completes the molding of the preform against the wall of the press die (see the shoulder and neck of the bottle in Figs 6B . 6C and 6D ), the movement of the punch combined with the internal pressure pushes the bottom of the preform into the contours the piston surface in a way that the desired contour ( 6D ) is generated without applying excessive tensile forces that would conceivably lead to errors. The upward movement of the punch imposes compressive forces on the semi-circular portion of the preform, reduces the overall load caused by the pressure operation, and assists the delivery of material radially outward to the contours of the piston nose to fill.

If the movement of the punch is applied too early relative to the rate of internal pressurization, the preform tends to warp and fold due to the axial compressive forces. If the movement is applied too late, the material undergoes an excessive load in the axial direction, which causes errors to occur. Thus, the coordination of the rate of internal pressurization and movement of the punch and piston nose is required for a successful forming operation. The necessary timing is best achieved by means of a finite element analysis (FEA) of the method. 3 based on the results of an FEA.

The invention has been described so far and in 3 exemplified as if no positive fluid pressure (ie, a pressure above atmospheric pressure) were applied to the outside of the preform within the die die. In such a case, the external pressure on the preform in the die would be substantially the ambient atmospheric pressure. As the preform expands, air in the die would be expelled (by the progressive reduction in volume between the outside of the preform and the press wall) through a suitable outlet opening or passageway provided for this purpose and providing an operative connection between the press die. Gesenk and the outer of the press provides. In particular, with reference to aluminum containers, it has been shown by way of illustration by the FEA that in the absence of any positive external pressure once the preform has begun to plastically deform (flow), the strain rate in the preform is very high and substantially becomes uncontrollable due to the low or nonexistent strain hardening rate of the aluminum alloys at the process temperature (for example, about 300 ° C) of the pressure-stamp molding process. That is, at such temperatures, the strain hardening rate of the aluminum alloy is substantially zero and the ductility (ie, moldability limit) decreases with increasing strain rate. Thus, the ability to produce container products of desired closure shape is lowered as the expansion rate of the molding operation increases and the ductility of the aluminum decreases.

In accordance with another important feature of the invention is a positive fluid pressure on the outside the preform in the press die simultaneously with the application of a positive Fluid pressure on the inside of the preform applied. These positive external and internal fluid pressures are each using two independently controlled pressure systems to disposal posed. The positive external fluid pressure can be suitably by connecting one independently controllable source for the positive fluid pressure on the aforementioned outlet opening or fed the passage so be that positive pressure in the volume between the press and the expanding preform is maintained.

The 7 and 8th compare the history of the pressure over time and the elongation over time for the pressure-stamp-forming a container with and without control of the positive external pressure (the term "elongation" here denotes the extension per unit length, which by means of an external force in a body is created.) The line 101 out 7 agrees with the line 3 denoted there by the term "pressure" in the case where no external positive fluid pressure acts on the preform; the line 103 out 8th As a matter of fact, in this case, the strain is essentially instantaneous, which implies very high strain rates and very short times to contact the preform to expand the press wall. In contrast, the lines represent 105 . 107 and 109 out 7 each of the positive internal fluid pressure, the positive external fluid pressure and the difference between the two, when both the internal and the external pressure are controlled, that is, when the external and the internal positive fluid pressure are controlled independently and be applied simultaneously to the preform in the press die; the internal pressure is higher than the external pressure, so that there is a positive pressure differential from the inside to the outside, as required for effecting expansion of the preform. line 111 out 8th represents the tangential strain (the strain produced in the horizontal plane around the circumference of the preform as it expands) through the lines 105 . 107 and 109 illustrated condition of independently controlled internal-external pressure; It will be apparent that the tangential strain passing through the line 111 shown is the same final value achieved as the off line 103 , but over a much longer time and thus at a much lower strain rate. The line 115 out 8th represents the axial strain (the strain that is generated in the vertical direction as the preform lengthens).

By Simultaneously deploy independently controllable internal and external positive fluid pressures acting on the preform in act on the press-Gesenk and by varying the difference between This internal and external pressure, the molding operation remains completely under Control and very high and uncontrollable strain rates avoided. The ductility the preform and thus the moldability limit of the method becomes for two reasons raised. First, the decrease in the stretching rate of the forming operation increases the inherent ductility the aluminum alloy. Second, the addition of an external positive lowers Pressure to expand the hydrostatic load in the wall of the Preform (and could potentially reduce this to zero). This could be the harmful Effect of having micro-texture defects and intermetallic Reduce particles in the metal related damage. The term "hydrostatic Load ", like as used herein refers to the arithmetic mean of three normal loads in the X, Y and Z directions.

The thus described feature according to the invention elevated the suitability of pressure-stamp-molding operation, successfully aluminum container in Bottle shape or the like to produce, the control of the Strain rate during forming operation and lowering of hydrostatic load in the metal while of the molding is applied.

The Selection of the pressure differential is based on the material properties of the Metal from which the preform was created.

Especially have to the yield strength and strain hardening rate of the metal are considered become. To ensure, that the preform flows plastically (i.e., inelastic), the pressure differential must be configured be that the effective load (Mises) in the preform exceeds the yield point. If there is a positive work hardening rate, a fixed (from the pressure) applied effective load above The yield strength causes the metal to reach a strain level deformed, which is equal to the applied effective elongation is. At this time would the deformation rate approaches zero. In the case of a very small or non-existing strain hardening rate, the metal would be at a deform it to high strain rate until it either comes into contact with the Wall of the mold (press) would come or a break occurred. At the for increased the PRF process expected Temperatures, the strain hardening rate of aluminum alloys is low to zero.

Examples suitable gases for use with both the feed internal and include external pressures without restriction then nitrogen, air and argon and all combinations of these Gases.

The plastic strain rate at each point in the wall of the preform to each Timing only from the instantaneous effective load, which in turn depends only on the pressure differential. The choice of an external Pressure is dependent on the interval pressure, with the overall principle, to achieve and control the effective load and thus the rate of stretching in the wall the preform.

9 shows another control mechanism that can be used in the molding process. Finite element simulations were used to optimize the process. In 9 represents the line 120 the internal pressure (pin) acting on the preform and the line 122 represents the external pressure (Pout) acting on the preform and the line 124 represents the pressure differential (Pdiff = Pin - Pout). This figure shows the history of the pressure from a controlled process. In this case, the fluid mass in the internal cavity is kept constant and the pressure in the external cavity (outside the preform) decreases linearly. Strain rate dependent material properties are also included in this simulation. This latter control mechanism is currently preferred as it leads to a simpler process.

10 refers to another embodiment of the invention which employs heating of the preform which induces a temperature gradient in the preform. As in 10 shown is the piston 12 in contact with the bottom of the preform 18 and the piston 12 contains a heating element 19 , This heats the preform up from the bottom, which causes the expansion of the preform to grow up from the bottom when the internal pressure is raised.

11 shows graphs illustrating the expansion process. One line of the graph shows the displacements of the punch / piston while the other shows the variations of the loads on the punch / piston, both being given as a function of time. A third line shows the internal pressure in the preform.

At point A, the punch is preloaded to a compression load of about 22.7 kg, and at point B, the preform is internally pressurized and maintained at a level of 1.14 MPa. In the illustrated method, the position of the punch was stepped between points B and C to maintain a compression load of 68 kg of the punch. If the stamp load after an increase in the punch position (Point C to D) was no longer lowered quickly, the start of the stamp was continued to a displacement of about 25 mm and a load of about 454 kg (point E). During the raising of the punch from the point D to the point E, the bottom profile of the container was formed simultaneously with the expansion of the preform such that the point E represents the completion of the molding of the container.

While the graph is off 11 shows a stepwise procedure, it is also possible to expand and form the preform in a smooth operation in a container, for example by using a computerized control of the method. The advantage of this method is that due to the induced temperature gradient, the expansion progressively progresses from the bottom to the top as the punch and piston move upwards. It has been found that this technique results in reduced improved formability when compared to previously described methods in which the expansion occurs substantially simultaneously over the entire length of the preform.

While 10 a heating element only within the piston 12 shows, it is possible to provide different heating zones to help with molding. For example, another separate heating element may be provided around the upper part of the preform and further separate heating elements within the side walls of the press die. By independently manipulating the temperatures in each of these areas, optimal expansion histories can be developed for different container design.

12 shows a typical sequence in the formation of a preform from a flat disc. A standard drawing / retracting technique is used with the aluminum sheet 70 used first in a flat cylinder 71 with the end closed, then into a second cylinder 72 is retracted with smaller diameter and longer side walls. The cylinder 72 is then withdrawn to a cylinder 73 retracted to a cylinder 74 train. It will be apparent that the cylinder 74 has a long, thin structure.

Claims (28)

A method of forming a metal container or the like of defined shape and dimensions, said method comprising: (a) placing a hollow metallic preform ( 18 ), which has a closed end ( 20 ), in a press die ( 11 ) having a press wall defining said shape and said dimensions, wherein at least a portion of said preform is initially spaced inwardly from said press wall, and (b) subjecting said preform ( 18 ) an internal fluid pressure to expand the preform outwardly in substantially full contact with the press wall, thereby introducing that defined shape and dimensions to the preform, characterized in that the press die ( 11 ) is dimensioned to be a hollow metallic preform ( 18 ) which includes a closed end ( 20 ) with a piston ( 12 ) placed at one end of the die and displaceable into the die, the preform ( 18 ) within the die ( 11 ) with the closed end of the preform in close confronting relation to the piston ( 12 ), and an internal fluid pressure is applied to the preform to expand the preform outwardly and apply fluid pressure force to the closed end, and wherein (c) the piston (14) 12 ) either before or after the preform ( 18 ) begins to expand, but before the expansion of the preform is completed, in which one end of the cavity is displaced to the closed end ( 20 ) to grasp and displace the preform in a direction opposite to the direction of the force exerted by the fluid, to deform the closed end of the preform as the preform expands outwardly in substantially full contact with the press wall. A method according to claim 1, characterized in that the internal fluid pressure by applying both internal positive fluid pressure and external positive fluid pressure to the mold ( 18 ) within the die, wherein the internal positive fluid pressure is higher than the external positive fluid pressure. Method according to claim 1, characterized in that before subjecting the preform ( 18 An internal fluid pressure is applied to the preform within the die to induce a temperature gradient therein. Method according to claim 1, characterized in that the preform ( 18 ) is an elongate and originally substantially cylindrical workpiece having an expandable closed end and an open end opposite the closed end. Method according to one of claims 1 to 4, characterized in that the piston ( 12 ) in the die ( 11 ) is moved after the preform ( 18 ) begins to expand but before the expansion of the preform in step (b) is completed. Method according to one of claims 1 to 4, characterized in that the piston ( 12 ) in contact with the closed end ( 20 ) of the preform ( 18 ) is moved before the expansion of the preform begins and the contact is maintained throughout the expansion of the preform. Method according to one of claims 1 to 6, characterized in that the piston ( 12 ) has a contoured surface, the closed end ( 20 ) of the preform is deformed to match that contoured surface. Method according to one of claims 1 to 7, characterized in that the defined shape includes a bottle shape with a neck portion and a body portion which is larger in its lateral dimensions than the neck portion, wherein the press die ( 11 ) has a longitudinal axis, the preform ( 18 ) has a longitudinal axis and substantially coaxial with the cavity ( 11 ) is arranged in step (a) and the piston ( 12 ) along the longitudinal axis of the die ( 11 ) is transferable. Method according to claims 8, characterized in that the piston ( 12 ) has a curved contour and wherein step (c) of this closed end ( 20 ) of the preform ( 18 ) deformed into the curved contour. Method according to one of claims 1 to 9, characterized in that the press wall is a split press ( 40 ) which is separable to remove the molded container after the step (c). Method according to claim 8, 9 or 10, characterized in that the defined shape asymmetrically over the longitudinal axis the excavation is. Method according to one of claims 1 to 11, characterized in that the piston ( 12 ) is initially positioned at the start of step (b) to provide axial elongation of the preform ( 18 ) by the fluid pressure limit. Method according to one of claims 8 to 12, characterized in that the preform ( 18 ) is an elongate and originally substantially cylindrical workpiece having an open end opposite the closed end (FIG. 20 ) and whose diameter is substantially equal to the diameter of the neck portion of the bottle shape. Method according to one of claims 8 to 13, characterized in that the preform ( 18 ) has sufficient formability to be expandable into the defined shape in a single pressure forming operation. Method according to claim 13, characterized by a preceding step of placing the workpiece ( 38 ) in a press die that is smaller than the first-mentioned press die, and subjecting the work piece to an internal fluid pressure to set the work piece to an intermediate size ( 38a ) and a shape smaller than said defined size and side dimensions, before performing steps (a), (b) and (c). Method according to claim 1, characterized in that the preform ( 18 ) is an elongate and originally substantially cylindrical workpiece having an open end opposite the closed end (FIG. 20 ) and is larger in diameter than the neck portion of the bottle shape; and including a further step of subjecting the workpiece near the open end and after performing steps (a), (b) and (c) a spin forming ( 56 . 58 ) around a neck portion ( 60 ) with reduced diameter. Method according to one of claims 1 to 16, characterized in that the preform ( 18 ) is an aluminum preform. Method according to claim 17, characterized by the step of generating the preform ( 18 ) from an aluminum sheet ( 70 ) having a recrystallized and recovered microstructure having a thickness in the range of about 0.25 to about 1.5 mm prior to performing step (a). Method according to claim 18, characterized in that the preform ( 18 ) as a cylinder ( 74 ) is produced with the end closed by subjecting the sheet to a pull-back operation or re-extrusion. Method according to one of claims 1 to 19, characterized in that during step (b) fluid pressure within the preform ( 18 ) in successive stages of (i) rising to a first peak before expansion of the preform commences, (ii) falling to a minimum value as expansion commences, (iii) incrementally increasing to an intermediate value as the extrusion proceeds until the Preform is in extended but not yet complete contact with the press wall; and (iv) rising from the intermediate value during completion of the preform expansion; and wherein the initiation of the displacement of the piston ( 11 ) in the step (c) for moving and deforming the closed end ( 20 ) of the preform ( 18 ) essentially to End of stage (iii) occurs. Method according to one of claims 1 to 19, characterized in that during step (b) the closed end ( 20 ) of the preform ( 18 ) assumes an enlarged and substantially hemispherical configuration when the portion of the preform is in first contact with the press wall (FIG. 11 ) comes in step (b); and wherein the initiation of the displacement of the piston ( 12 ) in step (c) for shifting and deforming the closed end ( 20 ) of the preform ( 18 ) occurs substantially at the time when the closed end ( 20 ) the preform assumes this configuration. Method according to claim 2, characterized by independent regulation of the internal and external positive fluid pressures to which the preform ( 18 ) to vary the difference between the internal positive fluid pressure and the external positive fluid pressure, thereby increasing the loading rate in the preform 18 ) is regulated. Method according to claim 3, characterized in that the heat is applied to the preform ( 18 ) by means of heating means in the piston ( 12 ), thereby inducing a temperature gradient in the preform that begins at the closed bottom and extends upwardly. Method according to claim 3, characterized in that the heat is applied to the preform ( 18 ) is applied by means of a heating medium around the tip of the preform in the press, thereby causing a temperature gradient in the preform ( 18 ), which starts at the tip and extends downwards. Method according to claim 23 or 24, characterized in that the heat is applied to the preform ( 18 ) by means of heating means in the side walls of the press ( 10 ) is applied. Method according to one of the preceding claims, wherein the fluid pressure by means of a pressurizable fluid in the form of a gas available is provided. Method according to claim 26, wherein the pressurizable fluid is gas, air, argon or nitrogen is. Method according to one of the preceding claims, wherein the temperature of the molding operation is higher than 100 ° C.