RU2296641C2 - Method for plunger molding of metallic containers and similar articles - Google Patents

Abstract

FIELD: plastic working of metals, namely molding of metallic containers and similar articles.

SUBSTANCE: method is realized for three stages. At stage (a) hollow metallic blank with closed end is placed in cavity of die. Sizes of die cavity are sufficient for embracing lateral surface of hollow metallic blank and wall of die cavity defines desired shape in order to provide initial gap between blank portion and wall of die. At stage (b) blank is subjected to action of inner pressure of fluid for expanding blank outwards practically till its complete contact with wall of die and for imparting to it desired size and shape. At stage (c) punch acts upon blank. Said punch is mounted in zone of one end of die cavity with possibility of motion before or after starting blank expansion but before termination of its expansion inside said end of die cavity. Punch acts upon closed end of blank for shifting said end and for providing deformation of closed end of blank at process of blank expansion till its complete contact with wall of die. Blank is arranged in die cavity in such a way that its closed end is directed to punch and is arranged near punch. Fluid pressure for expanding blank outside is fed by supplying excess inner pressure and providing action of fluid pressure upon closed end of blank. At stage (c) simultaneous feed of excess inner pressure of fluid and control of plunger of punch are realized and closed end of blank is shifted in direction opposite to that of fluid pressure action upon end of blank.

EFFECT: enlarged manufacturing possibilities of method.

19 cl, 12 dwg

Description

FIELD OF THE INVENTION

The present invention relates to a method for forming metal containers and similar products, using the internal pressure of the fluid to expand a hollow metal billet or product in the cavity of the matrix. An important aspect of the invention relates to methods for forming aluminum or other metal shaped containers, for example, having the shape of an asymmetric bottle.

State of the art

Metal cans are well known and widely used for drinks. Existing beverage can housings, either solid cans with a thinned down hood when the hood is drawn, or cases open at both ends (with separate “lids” at the top and bottom) usually have simple vertical cylindrical side walls. It is sometimes desirable, for example, for reasons of aesthetics, attractiveness to the consumer and / or product identification, to give the side walls of the metal beverage container a more complex shape and, in particular, to make the metal container in the form of a bottle rather than a simple cylinder. However, this configuration cannot be obtained using the usual operations used to make cans.

For these and other purposes, convenient and effective methods are needed to give the blanks “bottle-shaped” or other complex shapes. In addition, it is desirable to use such technologies that would ensure the formation of shaped containers without radial symmetry, which will increase the diversity of the resulting configurations.

US Pat. No. 3,040,684 describes a device for forming door handles from blanks using a die and hydraulic pressure. The blank is placed in the cavity of the matrix, filled with hydraulic fluid and sealed. Then the matrix is closed, the lower plunger is moved upward, forcing the walls of the workpiece to take the form of a cavity of the matrix. During this operation, the volume of the fluid does not change, and the preform is expanded by moving the plunger.

US Pat. No. 4,362,037 describes another device for molding a door handle that uses a split matrix. The blank is a partially molded doorknob, the round outer end of which is placed in the lower matrix. The upper matrix has a cavity, sections of the side walls of which determine the final shape of the handle. This upper matrix is pressed down onto the workpiece resting on the lower matrix. Then, liquid is injected into the preform, thereby forcing the preform to take the form of a matrix cavity.

US Pat. No. 6,182,487 describes a method for manufacturing a metal vessel using a split matrix that consists of a fixed and a movable matrix. First, a cylinder is formed, the bottom of which is welded to the shell, after which the cylinder is installed with the bottom end in the movable matrix, and the open end of the cylinder is attached to the fixed matrix. Pressure is applied to the cylinder through the stationary matrix, and the movable matrix is closed to the stationary one to form the vessel.

SUMMARY OF THE INVENTION

The present invention provides a method of forming a metal container of a given shape and given transverse dimensions, according to which a hollow metal billet having a closed end is placed in the matrix cavity. The cavity of the matrix is surrounded by a wall of the matrix that defines the specified shape and transverse dimensions. A punch is located at one end of the cavity with the ability to move inside the cavity. The closed end of the preform is placed in the direction and near the punch, with at least a portion of the preform initially having a gap with the walls of the matrix. The workpiece is subjected to internal fluid pressure to expand the workpiece outward until it comes into substantially full contact with the walls of the matrix in order to give the workpiece a given shape and predetermined transverse dimensions. The pressure of the fluid acts on the closed end of the workpiece with a force directed towards the specified end of the cavity. The punch is moved into the cavity either before the expansion of the preform begins, or after the beginning, but before the expansion of the preform is completed, to come into contact with the closed end of the preform and to displace this end in the direction opposite to the direction of the force of the fluid acting on the closed end of the preform. The result is the deformation of the closed end of the workpiece. The movement of the punch is carried out using a plunger capable of applying sufficient force to the punch to displace and deform the workpiece. This method is sometimes called the method of plunger molding under pressure (PRF-molding), because the container is molded due to the applied internal pressure of the fluid, and due to the movement of the punch by the plunger.

Another feature of the invention is that the punch has a shaped surface, and the closed end of the workpiece is deformed to fit this shaped surface. For example, the punch may have a dome-shaped profile, so that the closed end of the preform takes on the shape of a dome upon deformation.

The predetermined shape that the container takes may be a bottle shape including a neck portion and a body portion having larger transverse dimensions than the neck portion. The cavity of the matrix and the workpiece have longitudinal axes, the workpiece being placed essentially coaxial with the cavity, and the punch is moved along the longitudinal axis of the cavity.

In a preferred embodiment, the matrix wall comprises a component configured to separate to remove the molded container. In the case of a detachable matrix, the predetermined shape may be asymmetric with respect to the longitudinal axis of the cavity.

To limit the axial elongation of the preform under the influence of the fluid pressure, it is advisable that initially, that is, before the application of the fluid pressure, the punch is located near the closed end of the preform or in contact with it. The movement of the punch may begin after the expanding lower part of the preform has come into contact with the die wall.

Preferably, the preform for molding the container in the form of a bottle or a similar configuration is made in the form of an elongated and initially substantially cylindrical product having an open end opposite the closed end of the product. In specific embodiments of the invention, the diameter of such an article may be substantially equal to the diameter of the neck of the bottle-shaped container, and the article is capable of molding sufficient to expand to a predetermined shape in a single injection molding operation. If this molding ability is insufficient, then before proceeding with the PRF molding described above, the preform is preliminarily placed in a cavity of a matrix smaller than the aforementioned cavity and subjected to internal pressure of the fluid in this cavity to expand the preform to an intermediate size and forms that are smaller than the specified transverse dimensions and the given shape.

Alternatively, if the elongated and initially substantially cylindrical product has a larger initial diameter than the neck of the bottle, the method of forming the container in the form of a bottle may include an additional step of rotationally molding the product at a portion near its open end to form a neck of a reduced diameter. This step follows the implementation of the PRF molding.

You can also reduce the diameter of the neck of the workpiece by narrowing with a lingering ring. This narrowing operation using a lingering ring can be carried out prior to the expansion step.

The billet may be aluminum (the term "aluminum" as used herein refers to aluminum-based alloys as well as pure aluminum) and may be made from an aluminum sheet having a recrystallized or reduced microstructure and a thickness in the range of about 0.25 to 1.5 mm. The blank can be made in the form of a cylinder with a closed end by repeated drawing or pressing by the reverse method.

When the internal pressure of the fluid is applied to the workpiece, the fluid pressure inside the workpiece goes through a series of successive stages: (i) increase to the first maximum before the expansion of the workpiece begins, (ii) drop to the minimum value after the start of expansion, (iii) gradually increase to an intermediate value as the preform expands, but until it comes into incomplete contact with the matrix wall, and (iv) an increase from this intermediate pressure at the completion of the preform expansion. In a preferred embodiment of the present invention, the movement of the punch displacing and deforming the closed end of the preform in this sequence of stages of pressure change begins at the end of stage (iii).

During the application of internal fluid pressure, the closed end of the preform takes on an enlarged and substantially hemispherical configuration when the preform comes into contact with the die wall, and the movement of the punch begins essentially at the moment the closed end of the preform acquires this configuration.

In addition, in accordance with the present invention, the application to the preform of the internal fluid pressure is a simultaneous application to the excess fluid pressure and excess external fluid pressure in the preform cavity, the excess internal pressure being greater than the excess external pressure. Internal and external pressures are provided, respectively, by two pressure systems with independent regulation. The strain rate in the workpiece is controlled by independently controlling the internal and external excess pressure of the fluid applied simultaneously to the workpiece in order to change the difference between these pressures. As a result, the difficulties associated with excessive strain rates are eliminated and additional positive results are achieved, for example, a decrease in hydrostatic stresses that can cause damage to the microstructure of the container walls.

A further feature of the present invention is that during the expansion of the preform, it is advisable to heat it, for example, by creating a temperature gradient in the preform. By adding heaters to the punch, a temperature gradient is created in the workpiece, directed upward. To create a temperature gradient in the workpiece, directed from top to bottom, heaters can be installed in the upper part of the matrix. It is possible to incorporate additional heaters into the side walls of the matrix. The introduction of a temperature gradient during the expansion of the workpiece allows you to determine the start of expansion and improves formability.

It was also established the expediency of the contact of the punch with the workpiece before the start of expansion, as well as the advisability of creating a punch of some axial load during the entire expansion process. In cases where the punch applies some axial load to the closed end of the preform during the entire expansion process, it is preferable not to displace and deform the closed end of the preform until the expansion is complete.

Other features and advantages of the present invention will be apparent from the following detailed description and the accompanying drawings.

Brief Description of the Drawings

Figure 1 as an example implementation shows a simplified and, to some extent, a schematic representation in perspective of equipment for implementing the method of the present invention.

FIGS. 2A and 2B, similar to FIG. 1, show successive steps for implementing the first embodiment of the method of the present invention.

Figure 3 shows a graph of the internal pressure and the displacement of the plunger as a function of time when using air as a fluid; the graph illustrates the time relationship between the operations of exposing the workpiece to internal fluid pressure and displacement of the punch in the method of this invention.

FIGS. 4A, 4B, 4C, and 4D, similar to FIG. 1, show successive steps for implementing the second embodiment of the method of the present invention.

FIGS. 5A and 5B, similar to FIG. 1, are a simplified schematic perspective view of a rotational molding step illustrating successive steps of a third embodiment of the method of the present invention.

FIGS. 6A, 6B, 6C, and 6D show schematic vertical cross-sectional views obtained by computer processing of successive steps of the method of the present invention.

Figure 7 shows a graph of pressure changes as a function of time (using arbitrary time units), which illustrates the feature of the simultaneous application of independently controlled excessive internal and external pressures of the fluid on the workpiece located in the die cavity, and allows comparison with the case of changes in internal pressure (as in figure 3) in the absence of excessive external pressure.

On Fig shows a graph of changes in deformation as a function of time, obtained using the finite element method, the graph shows the deformation for one specific position (element) under two different pressure modes, which are compared in Fig.7.

Fig. 9 is a graph similar to that of Fig. 7 illustrating a specific control mechanism that can be used in the molding method in the case of simultaneous exposure to internal and external excess pressure of the fluid on the workpiece in the die cavity.

10 schematically illustrates an expandable preform in the case of using a heated punch.

11 is a graph showing punch loads, internal pressures, and punch movements during expansion of a workpiece.

12 illustrates in perspective the steps of manufacturing a blank from a flat disk.

The implementation of the invention

The invention is described by its implementation in methods of forming shaped aluminum containers, the shape of which does not have to be axisymmetric, i.e. radially symmetric about the geometric axis of the container, using a combination of hydraulic pressure, i.e. internal fluid pressure, and molding using a plunger, the so-called technology plunger molding under pressure (PRF-molding).

The PRF molding process has two different stages: the preparation of a preform and the subsequent molding of this preform into a finished container. There are several options for a full molding cycle, and the proper choice is determined by the molding ability of the used aluminum sheet.

The billet is made of an aluminum sheet having a recrystallized or reduced microstructure and a thickness ranging from 0.25 to 1.5 mm. The blank is a cylinder with a closed end and can be made, for example, by repeated drawing or pressing by the reverse method. The diameter of the workpiece is between the minimum and maximum diameters of the resulting finished container. Prior to subsequent molding operations, a thread may be applied to the workpiece. The profile of the closed end of the workpiece can be designed so that it contributes to the formation of the profile of the bottom of the finished product.

As shown in figure 1, the equipment for the proposed method contains a detachable matrix 10 with a shaped cavity 11 that defines the shape of the bottle with a vertical axis, a punch 12, the profile of which is designed to form a specific bottom of the container (in the shown options, for example, the punch has a dome-shaped profile for giving the bottom of the finished container the shape of a dome), and a plunger 14, which is attached to the punch. Figure 1 shows only one of the two halves of the split matrix. The second half is a mirror image of the first half shown. It is clear that both halves are joined in a plane containing the geometric axis of the bottle, defined by the wall of the cavity 11 of the matrix.

The minimum diameter of the cavity of the matrix 11 at its upper open end 11a, which corresponds to the neck of the cavity in the form of a bottle, is equal to the outer diameter of the preform (see FIG. 2A) placed in the cavity with a clearance tolerance. Initially, the preform is located above the punch 12 and has an injection fitting 16 (shown schematically) at the open end 11a to provide internal pressure. The injection can be carried out, for example, by connecting to a thread molded at the upper open end of the workpiece, or by inserting a tube into the open end of the workpiece and creating a seal using a split die or other pressure fitting.

The injection stage involves supplying into the hollow preform a fluid, for example water or air under a pressure sufficient to expand the preform inside the cavity so that the preform wall is substantially completely pressed against the wall defining the die cavity, so that the preform will be shaped and transverse in size . Generally speaking, the fluid used can be compressible or incompressible and can have any mass, flow, volume or pressure, with these parameters adjusted in such a way as to control the pressure to which the walls of the workpiece are subjected. When choosing a fluid, the temperature conditions used in the molding process must be considered. If this medium is, for example, water, then the temperature should be below 100 ° C, and if a higher temperature is required, such a medium should be a gas, such as air, or a liquid that does not boil at the molding temperature.

As a result of the injection stage, all shaped parts of the matrix wall are transferred in mirror image to the surface of the finished container. Even if such parts or the general shape of the container being manufactured are not axisymmetric, the container is easily removed from the equipment through the use of a split matrix.

In the specific embodiment of the invention shown in FIGS. 2A and 2B, the preform 18 is a hollow cylindrical aluminum product with a closed lower end 20 and an open upper end 22. The outer diameter of the preform is equal to the outer diameter of the neck of the molded bottle. The molding stress during PRF molding is within the limits determined by the ability of the workpiece to molding, which depends on temperature and strain rate. If the preform has the proper molding ability, the shape of the matrix cavity 11 is exactly the same as that of the finished product, and this product can be manufactured using a single PRF molding operation. The movement of the plunger 14 and the intensity of internal injection are such as to minimize stress during molding and to produce a container of the desired shape. The neck and side walls are formed mainly as a result of the expansion of the workpiece under the influence of internal pressure, while the shape of the bottom is determined mainly by the movement of the plunger and punch 12, with the surface profile of the punch facing the closed end 20 of the workpiece.

In the implementation of this invention, proper synchronization of the internal fluid pressure supply and the control of the plunger and punch, that is, their movement inside the cavity, is of great importance. Figure 3 shows a graph constructed by computer simulation (a sequence of results of the analysis by the finite element method), which shows the molding process shown in figa and 2B, using compressed air and flow control. The graph illustrates the time and pressure dependences of the plunger. As is clear from FIG. 3, inside the preform, the fluid creates a pressure that goes through a series of successive steps: (i) increase to the first maximum 24 before the expansion of the preform begins, (ii) drop to a minimum of 26 when expansion begins, (iii ) a gradual increase to an intermediate value 28 as the preform expands, but before it comes into full contact with the matrix walls, and (iv) a more rapid increase (at point 30) from this intermediate value during completion of the preform expansion. In a preferred embodiment of the invention, the movement of the punch to displace and deform the closed end of the workpiece, in the indicated sequence of steps for changing the pressure, begins (point 32) essentially at the end of step (iii). The graph shows the units of time, pressure and displacement of the plunger. On figa, 6B, 6C and 6D shows the result of operations with the workpiece presented on the graph of figure 3, obtained by computer simulation, for time instants 0,0; 0.096; 0.134 and 0.21 seconds counted along the X axis in FIG. 3.

At the beginning of the injection of fluid into the hollow billet, the punch 12 is located under the closed end of the billet in close proximity to it, for example, by touching to limit the axial tension of the billet under the action of applied internal pressure. Here, the vertical orientation of the equipment axis is assumed, as shown in the drawing. When the workpiece has expanded to a large extent, although expansion has not yet been completed, a plunger 14 is actuated to force the punch upward, which shifts the metal of the closed end of the workpiece upward and deforms the closed end to form the surface of the punch, since the lateral expansion of the workpiece is completed under the influence of internal pressure. The displacement of the closed end of the workpiece up cannot cause the workpiece to move upward relative to the die or the side walls of the workpiece to buckle, as would be the case if the plunger was prematurely raised, since when the plunger began to move the plunger up, the workpiece was already significantly expanded.

4A-4D show a second embodiment of the invention. In this embodiment, as in the case shown in FIGS. 2A and 2B, the cylindrical billet 38 has an initial outer diameter equal to the minimum diameter, that is, the neck diameter of the finished product. In this embodiment, however, it is assumed that the deformation during PRF molding exceeds the moldability limits of the workpiece. In this case, two successive molding operations are required. During the first operation (FIGS. 4A and 4B), a plunger is not required, but the workpiece normally expands inside the conventional split die 40 to a larger diameter of the article 38a due to internal pressure. The second operation is a PRF molding process (FIGS. 4C and 4D). It uses the product obtained by the initial expansion in the detachable matrix 40, as well as the detachable matrix 42 with a cavity 44 in the form of a bottle and a punch 46 moved by the plunger 48. Thus, both the internal pressure and the movement of the plunger are used. During this operation, a finished bottle of a given shape is obtained, along with all the features of the profile of the side walls and the bottom, which is achieved mainly due to the punch 46.

5A and 5B show a third embodiment. In this embodiment, the preform 50 is made in such a way that its initial outer diameter is greater than a predetermined minimum outer diameter, which is usually the diameter of the neck of a finished container in the form of a bottle. The selection of such a workpiece can be made based on the limits of molding at the stage of preliminary molding or in order to reduce stresses during PRF-molding. Therefore, the receipt of the finished product must include both transverse compression and transverse expansion of the workpiece, and therefore can not be carried out by only PRF-molding. For molding the walls and the bottom, one PRF molding operation is used, shown in FIG. 5A using a split die 52 and a punch 54 driven by a plunger, as in the embodiment shown in FIGS. 2A and 2B. To obtain the required configuration of the container neck, rotational molding or other appropriate operation is required. As shown in FIG. 5B, the rotational molding operation proposed, for example, may be used, for example, in U.S. Patent Application 09/846169 of May 1, 2001, which is used to form the neck of a bottle 60 using several pairs of rotational molding discs 56 and a taper mandrel 58.

The above-described operation of PRF-molding in practice may be associated with large deformations. Therefore, the composition of the alloy is selected or adjusted in such a way as to provide a certain compromise between the required properties of the product and better formability. If even better formability is required, it is possible to adjust the molding temperature as described below, since increasing the temperature improves the moldability, and therefore, an operation or PRF molding operations at elevated temperatures and / or re-annealing of the workpiece may be required to increase formability.

The proposed technology differs from known stamping operations, for example, blow molding of containers made of polyethylene terephthalate, in particular, in that an external forming element is added in the form of a punch. An inner punch, sometimes used when blow molding polyethylene terephthalate bottles, is not required. Applicants do not know the existing method of manufacturing a shaped aluminum container, the diameters of which would be in the range that is achieved in the present invention. Also, the applicants do not know the existing method for obtaining an asymmetric profile, for example, with legs on the bottom or spiral bands on the side surface of the container.

The proposed method can also be used to form containers of other materials, such as steel.

The significance of the movement of the punch 12 driven by the plunger into the cavity 11 for displacing and deforming the closed end 20 of the workpiece 18, as shown in FIGS. 2A and 2B, can be further explained with reference to FIG. 3 (see above), considered together with FIG. .6A-6D, where the dashed line represents the vertical profile of the die cavity 11, and the displacement (in millimeters) of the dome-shaped punch 12 at different times after the start of the application of internal pressure is shown on the scale to the right of the dashed line.

When forming an aluminum bottle, the plunger performs two important functions: it limits the tensile strain in the axial direction and forms the bottom of the container. First, the punch 12, driven by the plunger, is held in close proximity to the bottom of the workpiece 18 or in easy contact with it (figa). This reduces the axial tension of the side walls of the preform, which would otherwise occur under the influence of internal pressure. Thus, with an increase in internal pressure, the side walls of the workpiece will expand until they come into contact with the inner surface of the matrix without significant elongation. Typically, the central portion of the preform expands first, and this expansion area will increase along the length of the preform, both up and down. At some point in time, the bottom of the preform will acquire an almost hemispherical shape with a radius approximately equal to the radius of the cavity of the matrix (pigv). It is at this point in time or directly in front of it that the plunger must be actuated to move the punch 12 upward (FIG. 6C). The bottom profile of the container is completely determined by the configuration of the nose of the plunger, i.e. the shape of the surface of the punch. As soon as under the influence of the internal pressure of the fluid, the preform is formed into the shape of the walls of the matrix cavity (compare the shoulders and the neck of the bottle in FIGS. 6B, 6C and 6D), the movement of the plunger in combination with the internal pressure presses the bottom of the preform into the profile surface of the punch, which ensures the necessary shape (fig.6D) without excessive tensile deformations, which could lead to destruction. Due to the movement of the plunger upward, a compressive force is applied to the hemispherical region of the workpiece, thereby reducing the total stress caused by the increase in pressure, and contributing to the radial outward flow of material to fill the embossed portions of the nose of the punch.

If the plunger is moved too early compared to the rate of increase in internal pressure, buckling and the appearance of wrinkles on the workpiece under the action of axial compression forces are possible. If the plunger is moved too late, then the material will be subjected to excessive stress in the axial direction, therefore, will collapse. Thus, for the successful completion of the molding operation, coordination of the rate of increase in internal pressure and the movement of the plunger with the nose of the punch is necessary. Proper synchronization is best achieved using finite element analysis (FEA). The results of such an analysis are shown in FIG.

Until now, the present invention has been described and illustrated by the example shown in FIG. 3, if no excess, for example, superbarometric, fluid pressure would have acted on the outer surface of the preform in the die cavity. In this case, the external pressure on the workpiece located in the cavity of the matrix is mainly external atmospheric pressure. When the preform expands, the air in the cavity will be removed due to the gradual decrease in volume between the outer surface of the preform and the walls of the matrix through a suitable outlet or channel provided for this purpose and connecting the cavity of the matrix with the external environment.

As it was established using finite element analysis on a specific example of aluminum containers, in the absence of any excess external pressure, the plastic deformation (flow) of the workpiece that once started will cause a very large and virtually uncontrolled deformation rate. This is due to the low or zero speed of mechanical hardening of aluminum alloys at an operating temperature of, for example, about 300 ° C of the PRF molding process.

In other words, at such temperatures, the rate of mechanical hardening of aluminum alloys is virtually zero, and with increasing strain rate, ductility (i.e., the molding limit) decreases. Thus, with an increase in the deformation rate during molding and a decrease in the ductility of aluminum, the possibilities of forming containers of a given final shape are reduced.

Another important feature of the invention is the effect on the outer surface of the workpiece located in the cavity of the matrix, the excess pressure of the fluid at the same time as the effect of excessive pressure of the fluid on the inner surface of the workpiece. These excess external and internal fluid pressures are generated by two independently adjustable pressure systems. Excessive external fluid pressure can be achieved without difficulty by connecting an independently adjustable source of excess fluid pressure to the aforementioned outlet or channel so as to maintain excess pressure in the space between the die and the expandable workpiece.

Figures 7 and 8 compare the graphs of pressure and deformation as a function of time for the process of PRF-molding of the container with and without regulation of excess external pressure. The term "deformation" means elongation per unit length created in the body of the workpiece by external force. Curve 101 in FIG. 7 corresponds to the “Pressure” curve in FIG. 3 for the case where the external pressure of the fluid is not exerted on the workpiece. Curve 103 in Fig. 8 represents the resulting deformation for one particular position (element), determined by the finite element method. It is easy to see that in this case, the deformation increases almost instantly, and the preform expands to come into contact with the walls of the matrix at very high strain rates for very short periods of time. In contrast, curves 105, 107, and 109 in FIG. 7 respectively show the excess internal fluid pressure, the excess external fluid pressure, and the pressure difference when these independently adjustable pressures are simultaneously applied to the workpiece in the die cavity. The internal pressure is greater than the external, therefore, the resulting excess pressure necessary to expand the workpiece takes place. Curve 111 in Fig. 8 represents the circumferential deformation, that is, the deformation created in the horizontal plane around the circumference of the workpiece during its expansion, for the case of independently adjustable internal and external pressures shown by curves 105, 107 and 109. As is easy to see, the circumferential deformation, shown by curve 111, reaches the same final value as curve 103, but for a much longer time and, therefore, with a much lower strain rate. Curve 115 in FIG. 8 represents axial deformation, that is, deformation created in the vertical direction during elongation of the workpiece.

Full control of the molding operation, as well as the prevention of very large and uncontrolled strain rates, are achieved by the simultaneous application of internal and external excess pressures, independently regulated and acting on the workpiece in the die cavity, in addition, by changing the difference of these pressures. The increase in the plasticity of the workpiece, thereby increasing the molding limit, is due to two reasons. Firstly, a decrease in the strain rate during the molding operation increases the intrinsic ductility of the aluminum alloy. Secondly, the introduction of excess external pressure reduces, possibly to negative values, hydrostatic stresses in the walls of the expanding workpiece. This can reduce the detrimental effect of destruction associated with micropores and intermetallic particles in the metal. Here, the term "hydrostatic stress" means the arithmetic mean of three mutually perpendicular stresses directed along the x, y and z axes.

This feature of the invention expands the possibilities of PRF molding for the successful manufacture of aluminum containers in the form of bottles or the like by adjusting the strain rate and reducing the hydrostatic stress in the metal during molding.

The choice of pressure difference is determined by the properties of the metal from which the workpiece is made. In particular, the yield strength and the rate of mechanical hardening of the metal should be taken into account. To provide plastic, i.e. inelastic flow of the workpiece material, the pressure difference should be such that the effective value of the stress in the workpiece exceeds the yield strength. If there is a positive rate of mechanical hardening, then a fixed effective stress provided by pressure and exceeding the yield strength will cause the metal to deform to a stress level equal to the applied effective stress. At this moment, the strain rate approaches zero. In the case of a very low or zero speed of mechanical hardening, the metal will deform at a high speed until it comes into contact with the walls of the mold (matrix) or until it breaks. At the elevated temperatures possible during PRF forming, the rate of mechanical hardening of aluminum alloys is close to zero.

For application of both internal and external pressures, for example, nitrogen, air and argon are suitable, moreover, this list is not exhaustive, as well as any mixtures of these gases.

The rate of plastic deformation at any point on the wall of a workpiece at any time depends only on the instantaneous effective stress, which in turn depends on the pressure difference. The choice of external pressure depends on the internal pressure and is made from the general principle of achieving and regulating the effective stress, therefore, the strain rate, in the workpiece wall.

Figure 9 shows another control mechanism that can be used in the molding process. To optimize the process, the finite element method is simultaneously applied. In Fig. 9, curve 120 represents the internal pressure (Pin) acting on the workpiece, curve 122 represents the external pressure (Pout) acting on the workpiece, and curve 124 is the pressure difference (Pdiff = Pin-Pout). This graph shows the nature of the pressure change in one of the control methods. In this case, the mass of the fluid in the inner cavity remains constant, and the pressure in the outer cavity, that is, outside the workpiece, decreases linearly. The modeling also takes into account the properties of the material, depending on the strain rate. Such a regulatory mechanism is currently preferred because it simplifies the process.

10 relates to another embodiment of the invention in which the preform is heated to create a temperature gradient. As shown in figure 10, the punch 12 is in contact with the bottom of the workpiece 18 and contains a heating element 19. This element heats the workpiece from the bottom up, causing an increase in the expansion of the workpiece from bottom to top with increasing internal pressure.

11 is a graph illustrating an expansion process. One curve shows the movement of the plunger and punch, and the other shows the change in load acting on the plunger and punch versus time. The third curve characterizes the internal pressure in the workpiece.

At point A, the plunger is pre-loaded with a compressive force of 22.7 kg, and at point B, an internal pressure that is maintained at 1.14 MPa is supplied to the workpiece. In the process shown, the position of the plunger between points B and C changes stepwise to maintain the compression force of 68 kg acting on the plunger. When the load on the plunger stops rapidly decreasing after moving the plunger (from point C to point D), the plunger continues to move to a mark of approximately 25 mm and a load of approximately 454 kg (point E). During this linear movement of the plunger from point D to point E, the formation of the bottom of the container occurs simultaneously with the expansion of the workpiece, so that point E corresponds to the completion of the formation of the container.

11 shows a spasmodic process, but it is also possible to expand and shape the workpiece into a container in one smooth operation, for example, when using computer control of this process. The advantage of such an operation is the creation of a temperature gradient, when when raising the plunger and punch, the workpiece expands gradually from the bottom to the top. It has been shown that such a technology leads to an improvement in formability compared to the previously described methods, in which the expansion took place almost simultaneously along the entire length of the workpiece.

Although only one heating element is shown in FIG. 10 within the punch 12, several heating zones can be provided to facilitate molding. For example, you can place a separate additional heater around the upper part of the workpiece and several additional individual heaters inside the side walls of the cavity of the matrix. By independently selecting the temperature in each of these zones, it is possible to create optimal dynamic expansion conditions for various types of containers.

On Fig shows a typical sequence of manufacturing a workpiece from a flat disk. The standard technology of multiple drawing is used from an aluminum sheet 70. First, a hollow cylinder 71 is formed from the sheet with a closed end, which by repeated drawing is transformed into a second cylinder 72 with a smaller diameter having a longer side wall. Then the cylinder 72 is pulled to form a cylinder 73, which is then pulled into a longer thin-walled cylinder 74.

It is clear that the invention is not limited to the methods and options described above for specific examples, but can be implemented in other ways within its essence.

Claims (31)

1. A method of forming a metal product such as a container of a given size and shape, comprising the step (a) of placing a matrix in the cavity having dimensions that cover the side surface of the hollow metal billet with a closed end, and a wall defining the indicated dimensions and shape of the hollow a metal workpiece with a closed end, so that at least part of the workpiece initially has a gap with the matrix wall, step (b), where the inner part is exposed to the workpiece the appearance of a fluid for expanding the preform outward until it substantially comes into full contact with the matrix wall and gives it the specified size and shape, and step (c), where the workpiece is exposed to a punch located in the region of one of the ends of the matrix cavity with the ability to move before or after the beginning of the expansion of the workpiece, but before the completion of its expansion, inside the specified end of the cavity of the matrix to come into contact with the closed end of the workpiece and displace this closed end, with the deformation of the the finished end of the workpiece in the process of expanding the workpiece outward until it comes into substantially full contact with the matrix wall, and the workpiece is placed in the cavity of the matrix with a closed end directed towards the punch and located near it, characterized in that the workpiece is exposed to fluid pressure for expanding the workpiece to the outside is carried out by supplying excess internal pressure to ensure that the force exerts pressure on the closed end of the pressure, and in step (c), the supply of excess morning fluid pressure and control of the punch ram, the preform closed end is displaced in a direction opposite to a fluid pressure force on it. 2. The method according to claim 1, characterized in that the expansion of the workpiece outward by the action of the fluid is carried out by applying excessive internal pressure of the fluid and excess external pressure of the fluid, while the excess internal pressure of the fluid exceeds the excess external pressure of the fluid. 3. The method according to claim 1, characterized in that before applying to the workpiece the internal pressure of the fluid, the workpiece located in the cavity of the matrix is heated to create a temperature gradient in it. 4. The method according to claim 1, characterized in that gas is used as a fluid. 5. The method according to claim 4, characterized in that the gas is selected from the group comprising nitrogen, air and argon. 6. The method according to claim 4, characterized in that the molding is carried out at a temperature exceeding 100 ° C. 7. The method according to claim 4, characterized in that the molding is carried out at a temperature of about 300 ° C. 8. The method according to claim 1, characterized in that the workpiece is used in the form of an elongated initially substantially cylindrical product having an expandable closed end and an opposite open end. 9. The method according to claim 1, characterized in that the punch is moved inside the cavity after the beginning of the expansion of the workpiece, but before the completion of the expansion of the workpiece in step (b). 10. The method according to any one of claims 1 to 8, characterized in that the punch is moved to come into contact with the closed end of the preform before the expansion of the preform begins and maintain said contact during the entire process of expansion of the preform. 11. The method according to claim 8, characterized in that a punch with a shaped surface is used, and the closed end of the workpiece is deformed to match the specified shaped surface. 12. The method according to claim 1, characterized in that the desired shape is a bottle shape including a neck part and a body part, the transverse dimensions of which exceed the transverse dimensions of the neck part, using a matrix, the cavity of which and the workpiece have longitudinal axes, and the workpiece in step (a), it is mounted coaxially with the cavity, and the punch is movable along the longitudinal axis of the cavity. 13. The method according to p. 12, characterized in that the use of a punch made with a profile in the form of a dome, and at step (c) the closed end of the workpiece is deformed to give it the said profile in the form of a dome. 14. The method according to claim 1, characterized in that they use a matrix, the wall of which has a component made with the possibility of separation to remove the molded container at the end of step (c). 15. The method according to p. 12, characterized in that they use a given shape, asymmetric with respect to the longitudinal axis of the matrix cavity. 16. The method according to claim 1, characterized in that the punch is initially, that is, at the beginning of step (b), placed with the possibility of limiting the axial elongation of the workpiece under the influence of fluid pressure. 17. The method according to p. 12, characterized in that the use of the workpiece in the form of an elongated cylindrical product with an open end opposite the closed end, and the diameter of the workpiece is essentially equal to the diameter of the neck part of a given shape in the form of a bottle. 18. The method according to any one of paragraphs.12-17, characterized in that the use of a workpiece having the ability to molding, sufficient to ensure expansion to a given shape in one molding operation under pressure. 19. The method according to 17, characterized in that prior to the implementation of steps (a), (b) and (c), the preform is preliminarily placed in a cavity of a matrix of smaller sizes than the initially mentioned cavity, and the product is subjected to internal pressure of the fluid with the aim expanding the product to an intermediate size and shape that is less than the specified transverse dimensions and shape. 20. The method according to p. 12, characterized in that the use of the workpiece in the form of an elongated initially essentially cylindrical product having an open end opposite the closed end, and a diameter greater than the diameter of the specified neck portion of the bottle, while after the steps (a ), (b) and (c) the product is subjected to rotational molding in the area near the open end to form the neck portion of a reduced diameter. 21. The method according to claim 1, characterized in that they use a blank of aluminum. 22. The method according to item 21, characterized in that before the implementation of step (a), the preform is made of aluminum sheet having a recrystallized or reduced microstructure and a thickness in the range of about 0.25 to 1.5 mm. 23. The method according to p. 22, characterized in that the use of the workpiece in the form of a cylinder with a closed end, made by multiple stretching of the sheet or pressing by the reverse method. 24. The method according to claim 1, characterized in that in step (b) the pressure of the fluid inside the preform passes through three successive stages: (i) increase to the first maximum before the expansion of the preform begins, (ii) drop to the minimum value after the expansion of the preform begins , (iii) a gradual increase to an intermediate value as the preform expands, but until it comes into incomplete contact with the matrix wall, and (iv) an increase from the indicated intermediate value upon completion of the preform expansion, while in step (c) the punch begins to move be for the purpose of displacement and deformation of the closed end of the preform substantially at the end of step (iii). 25. The method according to claim 1, characterized in that in step (b) the closed end of the preform is given an enlarged and substantially hemispherical configuration when said part of the preform comes into initial contact with the matrix wall in step (b), while in step (c) the punch begins to be moved to displace and deform the closed end of the preform, essentially at the time of acquisition of the closed end of the specified configuration. 26. The method according to claim 2, characterized in that the internal and external excess pressure of the fluid simultaneously applied to the workpiece, independently regulate with a change in the difference between these pressures to control the strain rate in the workpiece. 27. The method according to claim 3, characterized in that the preform is heated using heating means located in the punch to create a temperature gradient in the preform in the direction from the closed bottom up. 28. The method according to claim 3, characterized in that the preform is heated using heating means located in the matrix around the upper part of the preform, in order to create a temperature gradient in the preform in the direction from the indicated upper part down. 29. The method according to item 27 or 28, characterized in that the preform is heated using heating means located in the side walls of the matrix. Priorities: 05/01/2001 - items 1, 4, 6, 8, 9, 11-25; 11/08/2001 - paragraphs 2, 5, 26; 05/01/2002 - pp. 3, 7, 10, 27-29.

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