Abstract:
In order to provide a deep-drawing method, with which a drawn part is arranged in a deep-drawing die between a first deep-drawing die part and a second deep-drawing die part and is formed by way of relative movement of the deep-drawing die parts in relation to one another, which—particularly for carrying out several consecutive drawing processes—is more time and energy saving than the known deep-drawing methods, it is suggested that a pressure variable with time during the drawing process be generated selectively at a limited pressure section of one of the deep-drawing die parts, this pressure pressing a section of the drawn part abutting on the pressure section against the respectively other deep-drawing die part.

Description:
This is a continuation of International Application No. PCT/EP01/02795, with an International filing date of Mar. 13, 2001, published in German under PCT Article 21(2) which is incorporated herein by reference in its entirety and for all purposes. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a deep-drawing method, with which a drawn part is arranged in a deep-drawing die between a first deep-drawing die part and a second deep-drawing die part and is formed by way of relative movement of the deep-drawing die parts in relation to one another. 
     Such deep-drawing methods are known from the state of the art. 
     In particular, deep-drawing methods with rigid deep-drawing die parts are known, with which the drawn part is drawn by a drawing punch into a drawing member (also called a female die), wherein the edge of the drawn part can be held securely by means of a drawing ring. 
     In order to achieve the desired, final configuration of the drawn part, it is often necessary to form the drawn part in several consecutive drawing processes (also called operations). 
     In this respect, there is, however, the problem that the structure of the material of the drawn part will be solidified during the first drawing process such that it no longer has sufficient fluidity for an additional drawing process which can lead to the formation of cracks during the additional drawing process. 
     If the material of the drawn part is steel, martensite is formed, in particular, during the first drawing process and this reduces the formability of the drawn part during an additional deep-drawing process. 
     In the case of the known, multiple operation deep-drawing methods, the required formability of the drawn part is therefore established again following the first deep-drawing process in that the drawn part is annealed at a temperature of approximately 1050° C., wherein the martensite, in particular, which has been formed during the first deep-drawing process, is converted into austenite which can be formed more easily. 
     If more than two deep-drawing processes follow one another, the annealing of the drawn part will possibly have to be repeated after each deep-drawing process. 
     On account of the annealing, cooling and washing processes required prior to each additional drawing process, the known, multiple operation deep-drawing methods require considerable time and energy. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a deep-drawing method of the type described at the outset which—particularly when carrying out several consecutive drawing processes—is more time- and energy-saving than the known deep-drawing methods. 
     The present invention relates, in addition, to a deep-drawing die, comprising a first deep-drawing die part and a second deep-drawing die part, in which a drawn part can be formed by way of relative movement of the deep-drawing die parts in relation to one another. 
     A further object underlying the present invention is to provide such a deep-drawing die, with the aid of which drawn parts—in particular within the scope of a multiple operation deep-drawing method—can be formed in a more time- and energy-saving manner than with known deep-drawing dies. 
     These objects are accomplished in accordance with the invention, in a deep-drawing method using cooperating deep-drawing die parts, in that a pressure variable with time during the drawing process is generated selectively at a limited pressure section of one of the deep-drawing die parts, this pressure pressing a section of the drawn part, which abuts on the pressure section, against the other deep-drawing die part. 
     The idea underlying the inventive solution is to achieve a flow of the material of the drawn part sufficient for its forming by concertedly acting upon a limited area of the drawn part during the drawing process even when the flowability of the material of the drawn part is reduced as such on account of the previous history of the material, for example on account of a preceding, earlier drawing process. 
     The desired formability of the drawn part can be ensured, in particular, with the inventive deep-drawing method even when the drawn part contains martensite on account of a preceding drawing process. 
     An annealing process and the cooling and washing processes associated with the annealing process may be omitted in the case of the inventive deep-drawing method even when the deep-drawing method is carried out in several operations. 
     The inventive deep-drawing method allows a particularly large drawing ratio to be achieved and leads to a high form stability of the drawn parts. 
     In a preferred development of the inventive method it is provided for the pressure at the pressure section to be generated hydraulically or pneumatically by means of a pressure fluid. 
     The hydraulic generation of a pressure at one of the deep-drawing die parts is already known as such from the so-called hydroforming method, with which the drawing member is provided with a membrane which is subjected to water pressure during the forming process. With this method, the drawing punch presses the drawn part against the membrane on the drawing member, wherein the drawn part is formed by the water pressure acting against it. With this method, the entire drawn part is, however, subjected to the same water pressure during the drawing process whereas, in the inventive deep-drawing method, a pressure is generated selectively only at a limited pressure section of one of the deep-drawing die parts and this pressure presses the respective limited section of the drawn part, which abuts on the pressure section, against the respectively other deep-drawing die part. 
     Moreover, in the case of the hydroforming method the water pressure acting on the drawn part is constant during the drawing process. 
     One variation of the hydroforming method is the so-called hydro-mec method, with which the drawn part is pressed by a descending drawing punch into water subjected to pressure without a membrane being provided on the drawing member. With this method, as well, no selective action on a limited section of the drawn part with a pressure variable with time during the drawing process is provided. 
     A uniform distribution of the hydraulic pressure on the surface of the drawn part is the aim not only of the hydroforming method but also of the hydro-mec method and this is completely contrary to the inventive idea of acting upon a limited section of the drawn part selectively with an increased pressure. 
     In a preferred development of the inventive deep-drawing method it is provided for the pressure at the pressure section to be controlled and/or regulated in accordance with a predetermined temporal pressure course. 
     This pressure course may provide, for example, for the pressure section to be switched to a no-pressure state during a first forming phase and for an increased pressure constant throughout a second forming phase to be generated at the pressure section during the second forming phase. Such a pressure course can be controlled and/or regulated particularly simply. 
     However, any optional, other temporal pressure course can also be controlled and/or regulated depending on the type of drawn part and the desired forming of the drawn part. 
     The formability of the drawn part during the drawing process is particularly increased when the pressure section is aligned essentially parallel to the direction of drawing, along which the deep-drawing die parts are moved relative to one another. In this case, areas of the drawn part which are aligned essentially parallel to the direction of drawing can be pressed concertedly onto areas of the respectively other deep-drawing die part which are aligned essentially parallel to the direction of drawing, and this is not possible in the case of the conventional deep-drawing methods. Side wall areas of the drawn part, which are aligned essentially parallel to the direction of drawing, can, in particular, be formed in a particularly exact manner. 
     The inventive deep-drawing method has proven to be particularly successful when the side wall of the drawn part is exclusively acted upon during the drawing process with the pressure variable with time at the pressure section. Such a deep-drawing method is particularly suitable for the production of Gastronorm food containers which have a great depth and tend to form undesired bulges in the side wall area which can lead to a poor stacking capability of the food containers. Such bulging can be prevented or any bulge generated during a preceding deep-drawing process eliminated as a result of the concerted action on the side wall of the Gastronorm food container during the drawing process with the pressure variable with time at the pressure section. 
     In a preferred development of the inventive deep-drawing method it is provided for the pressure section to be of a ring-shaped design. 
     No further details have so far been given as to how the pressure variable with time is generated at the pressure section. 
     It may be provided for the pressure variable with time to be generated by means of a pressure generating device which comprises a chamber for accommodating a pressure fluid subject to pressure and an elastically deformable chamber wall for transferring the pressure from the pressure fluid to the drawn part. 
     Such a chamber may, in particular, be of a ring-shaped design. 
     Such a chamber is particularly easy to produce when it is limited partially by the elastically deformable chamber wall and partially by a chamber limiting wall consisting of a material different from the material of the elastically deformable chamber wall, preferably consisting of a metallic material, in particular, aluminum. 
     In principle, the pressure section may be arranged on the first deep-drawing die part or on the second deep-drawing die part. Furthermore, it may be provided for not only the first deep-drawing die part but also the second deep-drawing die part to each have one or more pressure sections, at which a respective pressure variable with time is generated during the drawing process. 
     In a preferred development of the inventive deep-drawing method it is provided for the first deep-drawing die part to be designed as a drawing member and the second deep-drawing die part as a drawing punch and for the pressure section to be arranged on the drawing member. 
     In principle, the relative movement between the drawing punch and the drawing member required for forming the drawn part may be generated not only by a movement of the drawing punch but also a movement of the drawing member or also by a movement of both deep-drawing die parts. 
     In a preferred development of the inventive deep-drawing method it is provided for the drawing punch to be stationary during the drawing process and the drawing member to be moved towards the drawing punch. 
     As already explained, the inventive deep-drawing method is particularly advantageous when the drawn part is preformed during a first drawing process and postformed during a second drawing process, during which the pressure variable with time is generated at the pressure section. In this case, the annealing required with the known deep-drawing methods and the cooling and washing processes necessary as a result prior to the second drawing process can be dispensed with, which results in a considerable saving on time and energy. 
     The two drawing processes may be carried out in the same deep-drawing die, wherein it is normally necessary to change the deep-drawing die parts between the drawing processes, or the two drawing processes are carried out in different deep-drawing dies, which is recommended for a series production since, in this case, the deep-drawing die parts required for the respective drawing process can remain in the respective deep-drawing die. 
     The further object is accomplished in accordance with the invention in that one of the deep-drawing die parts has a limited pressure section, at which a pressure variable with time can be generated selectively during the drawing process, this pressure pressing a section of the drawn part which abuts on the pressure section against the respectively other deep-drawing die part. 
     The advantages of the inventive deep-drawing die have already been explained above in conjunction with the inventive deep-drawing method. 
    
    
     Additional features and advantages of the invention are the subject matter of the following description and drawings illustrating one embodiment. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a schematic perspective illustration of a deep-drawing die; 
     FIGS. 2-5 show schematic cross-sections through the deep-drawing die from FIG. 1 in four different phases of a conventional deep-drawing process; 
     FIGS. 6-9 show schematic cross-sections through a deep-drawing die which comprises a pressure bubble ring in four different phases of an inventive deep-drawing process; 
     FIG. 10 shows a schematic perspective illustration of a drawn part after two deep-drawing processes; 
     FIG. 11 shows a plan view of a pressure bubble ring; 
     FIG. 12 shows a cross-section through the pressure bubble ring from FIG. 11 along line  12 — 12  in FIG. 11; and 
     FIG. 13 shows a cross-section through the pressure bubble ring from FIG. 11 along line  13 — 13  in FIG.  11 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The same or functionally equivalent elements are designated in all the Figures with the same reference numerals. 
     A deep-drawing die illustrated schematically in FIGS. 1 to  5  and designated as a whole as  100  comprises a base plate  102 , a drawing punch  104  arranged stationarily on the upper side of the base plate  102 , and a sheet-metal holder  106  which surrounds the drawing punch  104  in a ring shape and is arranged on a supporting plate  108  which likewise surrounds the drawing punch  104  in a ring shape and is borne by spindle sleeves  110  which can be moved vertically by means of a hydraulic moving device (not illustrated) so that the supporting plate  108  can be moved with the sheet metal holder  106  arranged thereon along the vertical direction of drawing  112 . 
     Furthermore, the deep-drawing die  100  comprises a drawing member  114  which is arranged above the drawing punch  104  and the sheet metal holder  106  and comprises, for its part, a ring-shaped drawing ring support  116  and a drawing ring  118  held on its underside. 
     The drawing ring support  116  is held at its upper side on a holding plate  120  which can be moved by means of a hydraulic moving device (not illustrated) along the direction of drawing  112  relative to the drawing punch  104  and the sheet metal holder  106 . 
     The drawing member  114  forms the first deep-drawing die part  122  of the deep-drawing die  100 ; the drawing punch  104  forms the second deep-drawing die part  124  of the deep-drawing die  100 . 
     A first deep-drawing process is carried out as follows with the deep-drawing die  100  described above. 
     First of all, the drawing member  114  and the sheet metal holder  106  are displaced into their respective upper starting positions by means of the respective hydraulic moving devices (not illustrated). 
     In the upper starting position of the sheet metal holder  106 , the essentially flat upper side of the sheet metal holder  106  is arranged above the upper side of the drawing punch  104 . 
     In this position, a sheet metal blank or a plate  126 , from which the drawn part is intended to be produced, is inserted into the deep-drawing die  100  such that the edge of the plate  126  rests on the sheet metal holder  106  (cf. FIG.  2 ). 
     Subsequently, the deep-drawing die  100  is closed in that the drawing member is displaced by means of the hydraulic moving device (not illustrated) downwards out of its upper starting position to such an extent along the direction of drawing  112  until the underside of the drawing ring  118  rests on the upper side of the plate  126  and the edge of the plate  126  is clamped between the drawing ring  118  and the sheet metal holder  106  (cf. FIG.  3 ). 
     In the subsequent method step, the plate  126  is formed into a drawn part  128  in that the spindle sleeves  110  with the supporting plate  108  arranged thereon and the sheet metal holder  106  as well as the drawing member  114  are moved downwards by means of the hydraulic moving device (not illustrated) along the direction of drawing  112  relative to the drawing punch  104  by the drawing depth, wherein the plate  126  held securely at its edge between the drawing ring  118  and the sheet metal holder  106  fits closely along the outer contours of the drawing ring  118  and the drawing punch  104  (cf. FIG.  4 ). 
     Once the desired drawing depth for the first deep-drawing process is reached, the spindle sleeves  110  are moved back into their upper starting position with the supporting plate  108  arranged thereon and the sheet metal holder  106  and the deep-drawing die  100  is opened in that the drawing member  114  is moved further along the direction of drawing  112  upwards into its upper starting position (cf FIG.  5 ). 
     As a result, the drawn part  128  formed during the first deep-drawing process is accessible from outside the deep-drawing die  100  and can be removed from it. 
     Following this first deep-drawing process the deep-drawn part  128  has not yet been given the desired final shape. 
     In the present example, the finished drawn part is intended to have the shape of a Gastronorm food container which is provided with a stacking lip  132  extending around beneath its upper edge  130 . Moreover, the depth of the finished food container is intended to be greater than the depth of the drawn part  128  following the first deep-drawing process whereas the length and the width of the finished food container in the side wall area are intended to be less than in the case of the drawn part  128  resulting from the first drawing process. 
     In order to carry out the required, additional formings of the drawn part  128 , the same is subjected to a second deep-drawing process in a second deep-drawing die  100 ′ (cf. FIG.  6 ). 
     The second deep-drawing die  100 ′ corresponds in its fundamental construction to the first deep-drawing die  100  described above, wherein the drawing punch  104  and the drawing member  114 ′ are shaped accordingly in order to obtain the desired forming of the drawn part  128 . 
     Furthermore, the drawing member  114 ′ of the second deep-drawing die  100 ′ comprises a pressure generating device designated as a whole as  134  for generating a variable pressure. 
     The device  134  comprises, for its part, a pressure bubble ring  136  which is accommodated in an annular recess  138  on the inner side of the drawing ring support  116  and has an annular pressure bubble chamber  140  which is surrounded by a chamber wall  142  consisting of an elastically deformable material, for example polyurethane. 
     Fluid supply lines  144 , via which a fluid subject to pressure, for example a hydraulic oil, can be supplied to the pressure bubble chamber  140  by a fluid pressure pump (not illustrated), are guided through the chamber wall  142  and open into the pressure bubble chamber  140 . 
     A second deep-drawing process is carried out as follows with the second deep-drawing die  100 ′ described above. 
     First of all, the second deep-drawing die  100 ′ is opened in that the drawing member  114 ′ and the sheet metal holder  106  are brought into their upper starting positions (cf. FIG.  6 ). Since the drawn part  128  is already preformed as a result of the first deep-drawing process, the upper side of the sheet metal holder  106  can be arranged, in its upper starting position, beneath the upper side of the drawing punch  104 . 
     Subsequently, the deep-drawn part  128  resulting from the first deep-drawing process is inserted into the deep-drawing die  100 ′ and placed on the sheet metal holder  106 . 
     After that, the second deep-drawing die  100 ′ is closed in that the drawing member  114 ′ is displaced downwards along the direction of drawing  112  until the underside of the drawing ring  118  rests on the underside of the edge  130  of the drawn part  128  and the edge of the drawn part  128  is securely clamped between the drawing ring  118  and the sheet metal holder  106 . 
     Subsequently, a first forming phase is carried out in that the spindle sleeves  110  with the supporting plate  108  arranged thereon and the sheet metal holder  106  are moved downwards along the direction of drawing  112  relative to the drawing punch  104  together with the drawing member  114 ′ until the remaining drawing distance amounts to a distance h (cf. FIG.  7 ). During this first forming phase, the pressure bubble ring  136  is switched to no pressure, i.e., the fluid pressure pump is switched off or the fluid supply lines  144  are separated from the fluid pressure pump by a check valve (not illustrated) so that the fluid located in the pressure bubble chamber  140  is not subject to a higher pressure than the atmospheric pressure. 
     As soon as the remaining drawing distance corresponds to the distance h, the fluid in the pressure bubble chamber  140  is acted upon with an increased pressure p in that the fluid pressure pump is started and/or the check valve between the fluid pressure pump and the fluid supply lines  144  is opened. The elastically deformable chamber wall  142  of the pressure bubble ring  136  transfers the increased pressure of the fluid in the pressure bubble chamber  140  to the section of the side wall  146  of the drawn part  128  which abuts on the pressure bubble ring  136  and is formed by those side walls of the drawn part  128  aligned essentially parallel to the direction of drawing  112  so that this section of the side wall  146  is pressed against the drawing punch  104  under increased pressure. 
     The inner side of the pressure bubble ring  136  facing the drawn part  128  therefore serves as a pressure section  148  of the drawing member  114 ′, by means of which a section of the drawn part  128  abutting on the pressure section  148  can be pressed against the drawing punch  104  selectively under a pressure variable with time during the drawing process. 
     During a second forming phase, the drawn part  128  is completed in that the spindle sleeves  110  with the supporting plate  108  arranged thereon and the sheet metal holder  106  are moved downwards together with the drawing member  114 ′ along the direction of drawing  112  relative to the drawing punch  104  until the desired drawing depth for the second deep-drawing process is reached (cf. FIG.  8 ). 
     In this respect, as a result of the side wall  146  of the drawn part  128  being acted upon with the pressure p by means of the pressure section  148  of the drawing member  114 ′ a sufficient amount of material flows downwards during the forming of the drawn part  128  along the direction of drawing  112  in order to form the stacking lip  132  without cracks occurring in the drawn part  128 . 
     Furthermore, it is ensured as a result of the side wall  146  being acted upon with the increased pressure p that the length and width of the drawn part  128  in the side wall area thereof are reduced to the desired values, and the bulging of the drawn part  128 , which resulted during the first deep-drawing process, disappears. 
     Once the desired drawing depth has been reached at the end of the second forming phase, the pressure bubble ring  136  is again switched to no pressure in that the fluid pressure pump is switched off and/or the check valve between the fluid pressure pump and the fluid supply lines  144  to the pressure bubble ring  136  is closed. 
     Subsequently, the second deep-drawing die  100 ′ is opened in that the spindle sleeves  110  with the supporting plate  108  arranged thereon and the sheet metal holder  106  are displaced into the upper starting position and, subsequently, the drawing member  114 ′ is displaced further along the direction of drawing  112  upwards into its upper starting position so that the completely drawn part  128  is accessible from outside the deep-drawing die  100 ′ and can be removed from the deep-drawing die  100 ′ (cf. FIG.  9 ). 
     The drawn part  128  now has the desired final shape of a Gastronorm food container (cf. FIG.  10 ). 
     FIGS. 11 to  13  show in detail a preferred embodiment of a pressure bubble ring  136  as can be used in the inventive deep-drawing method. 
     As is best apparent from the cross-sections of FIGS. 12 and 13, the pressure bubble ring  136  comprises an outer ring  150  consisting of an elastically deformable material, for example polyurethane, into which a chamber limiting ring  152 , which can consist, for example, of a metallic material, in particular aluminum, is embedded. 
     The outer ring  150  is produced in that the chamber limiting ring  152  is introduced into a casting mold, the inner contours of which correspond to the outer contours of the outer ring  150 , and the space between the casting mold and the chamber limiting ring  152  is cast with polyurethane. 
     In this respect, the inner side of the chamber limiting ring  152  is provided with a separating agent so that the outer ring  150  consisting of polyurethane adheres only to the outer side of the chamber limiting ring  152  whereas the material of the outer ring  150  can be lifted away from the chamber limiting ring  152  at the inner side of the chamber limiting ring  152 . 
     At two locations of the pressure bubble ring  136  diametrically opposite one another, the chamber limiting ring  152  has a respective connection member  154 , for example, consisting of steel passing through it and this leads from the chamber limiting ring  152  as far as the outer side of the outer ring  150  and can be connected at its outer end to a fluid supply line  144 . 
     Fluid supplied through the fluid supply line  144  can pass through the connection member  154  into the space between the outer ring  150  and the chamber limiting ring  152  at the inner side of the chamber limiting ring  152  and lift the material of the outer ring  150  away from the chamber limiting ring  152  so that a pressure bubble chamber  140  is formed between the chamber limiting ring  152  and the outer ring  150 , the volume of this pressure bubble chamber  140  being dependent on the pressure, to which the fluid is subject. If this pressure is low, the pressure bubble chamber  140  has only a slight volume (corresponding to the solid boundary line in FIGS.  12  and  13 ). If the pressure of the fluid is high, the volume of the pressure bubble chamber  140  increases accordingly (cf. the dashed boundary lines in FIGS.  12  and  13 ). 
     If the outer ring  150  of the pressure bubble ring  136  is produced from polyurethane, a hydraulic oil can be used as pressure fluid for filling the pressure bubble chamber  140 . 
     If, alternatively hereto, the outer ring  150  of the pressure bubble ring  136  is produced from natural rubber, castor oil is, for example, to be used instead as pressure fluid since natural rubber is corroded by hydraulic oil.