Patent Publication Number: US-6986273-B2

Title: Apparatus and method for opening and closing stacked hydroforming dies

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to hydroforming operations. More particularly the invention relates to coordinated movement of dies used to perform concurrently two or more hydroforming operations in a press. 
     Hydroforming is a well known metal working process that uses pressurized fluid to expand a closed channel or tubular workpiece outwardly into conformance with the surface of a die cavity. A typical hydroforming apparatus includes a frame having two die sections supported for relative movement between opened and closed positions. The die sections have cooperating recesses, which together define a die cavity having a shape corresponding to a desired final shape for the workpiece. When moved to the open position, the die sections are spaced apart from one another to allow a workpiece to be inserted and removed from the die cavity. When moved to the closed position, the die sections are adjacent one another and enclose the workpiece within the die cavity. Although the die cavity is usually somewhat larger than the workpiece to be hydroformed, movement of the two die sections from the opened position to the closed position may, in some instances, cause some mechanical deformation of the workpiece. In any event, the workpiece is then filled with fluid, typically a relatively incompressible liquid such as water. Fluid pressure within the workpiece is increased to such a magnitude that the workpiece is expanded outward into conformance with the surface contour of the die cavity. As a result, the workpiece is deformed into the desired final shape. Hydroforming is an advantageous process for forming vehicle frame components and other structures because it can quickly deform a workpiece into a desired complex shape. 
     In a typical hydroforming apparatus, the two die sections are arranged such that a first die section is supported on a displaceable ram, while a second die section is supported on a immovable base. A mechanical or hydraulic actuator is provided for moving the ram and the first die section to the opened position relative to the base and the lower die section, thereby allowing a previously formed workpiece to be removed from the die cavity and a new workpiece to be inserted therein. The actuator also moves the ram and first die section to the closed position relative to the base and second die section before performing the hydroforming process. 
     Use of a single hydroforming die within a single hydroforming apparatus has been found to be somewhat inefficient from a time consumption standpoint. This is because each operational cycle performed by the hydroforming apparatus involves both a preliminary step of filling the article to be hydroformed with the fluid prior to performing the hydroforming process, and a subsequent step of emptying the hydroforming fluid from the article after performing the hydroforming process. These filling and emptying steps can consume relatively long periods of time, particularly when the articles to be formed are physically large, as is often the case in the manufacture of vehicle frame components. This inefficiency is amplified when the hydroforming apparatus is used to manufacture products in relatively high volumes, as is also the case in the manufacture of vehicle frame components. Thus, it would be desirable to provide an improved structure for a hydroforming apparatus that is capable of performing two or more hydroforming operations concurrently in order to decrease the operation cycle time and to increase overall productivity. 
     If multiple die cavities are arranged side-to-side in a horizontal configuration in a hydroforming press, the required press tonnage increases in proportion to the number of cavities. By positioning the die cavities in a stacked vertical arrangement in the press, the required press tonnage does not increase. The use of stacked dies allows multiple parts to be made using the same press tonnage as required to form a single part. It is desirable to provide an improved structure for a hydroforming apparatus that is capable of performing two or more hydroforming operations concurrently without increasing press tonnage. 
     Furthermore, when multiple dies are used to concurrently form parts n a single hydroforming operation, there is need to open the dies, to remove formed workpieces and to insert in the die cavities workpieces to be formed subsequently. Although a ram can assist an operator to open one die cavity, other die cavities not in direct contact with the ram cannot be opened by the ram. This deficiency increases process time and slows the production rate. It is preferable that each die cavity be opened and closed in a process coordinated with movement of the ram. 
     SUMMARY OF THE INVENTION 
     The invention relates to an improved apparatus and method for opening and closing dies that are used to concurrently performing two or more hydroforming operations. The apparatus includes a platen located between a stationary base and a ram that is linearly displaceable relative to the base. A platen, located between the base and the ram, is engageable with the ram so that they move as a unit at certain times during the operation and move separately at other times. Each of several dies, arranged in stacked relationship, includes a pair of cooperating die sections having respective recesses that define a die cavity. 
     A first die section of the first die is preferably mounted on or otherwise connected to the ram for movement therewith. A second die section of the first die is preferably connected to, or formed integrally with the first die section of the second die, and the combined assembly is preferably supported on the platen for movement therewith. The second die section of the second die is preferably connected to or formed integrally with the stationary base. 
     The ram is displaced relative to the platen and base a distance in a first direction sufficient to open the first die. Later the ram is displaced relative to the base an additional distance in the first direction sufficient to open the second die. A workpiece is inserted in each of the dies. Then the dies are closed by displacing the ram in a second direction opposite the first direction such that the pairs of cooperating die sections of the first and second dies engage one another. End feed cylinders are then moved laterally into engagement with the ends of the tubular blanks to facilitate filling the dies with a hydroforming fluid. The pressure of the fluid within the workpieces is then increased to such a magnitude that the workpieces expand outward into conformance with the surface of their respective die cavities. 
     In this way, the hydroforming apparatus performs two or more hydroforming operations concurrently to decrease process time and increase productivity without increasing press tonnage. The ram assists an operator to open both the dies that are adjacent the ram and other dies distant from the ram. Guide pins transmit certain portions of ram displacement to dies distant from the ram to assist in opening those dies. Linear actuators are used in coordination with the ram to assist in opening die cavities near the ram, and to move interior dies that cannot be opened directly by the ram. This feature reduces process time and further increases the production rate. 
     Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevation view of a hydroforming apparatus according to this invention; 
         FIG. 2  is another hydroforming apparatus according to this invention, in which a platen is formed integrally with the ram; 
         FIGS. 3A–3C  are side elevational views showing a series of method steps employing the apparatus of  FIGS. 1 and 2 ; 
         FIGS. 4A–4C  are side elevational views showing a series of method steps employing another embodiment of the present invention. 
         FIGS. 5A–5D  are side elevational views showing a series of method steps employing another embodiment of the present invention. 
         FIGS. 6A–6C  are side elevational views showing a series of method steps employing another embodiment of the present invention; 
         FIG. 7  is a side elevation cross sectional view of a portion of the hydroforming apparatus taken along plane  7 — 7  of  FIG. 3A . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, there is illustrated in  FIG. 1  an apparatus, indicated generally at  10 , for performing a hydroforming process in accordance with this invention. The apparatus  10  includes a frame  12  that is sized to support hydroforming dies arranged in a vertically oriented relationship, two of which are indicated generally at  14 ,  16 . Although this invention will be described and illustrated in the context of the two vertically stacked hydroforming dies  14  and  16 , it will be appreciated that this invention can be practiced with a greater number of such hydroforming dies if desired. Furthermore, the hydroforming dies can be arranged within the hydroforming apparatus  10  in any desired direction other than the illustrated vertical direction. For example, the dies may be stacked horizontally, in which case the lateral plane of the dies is vertical, and the direction of their movement is horizontal. 
     The first die  14  includes a first pair of cooperating die sections  18  and  20 , which have respective recesses  18   a  and  20   a  formed therein. When the two die sections  18  and  20  are moved together as shown in  FIG. 3A , the recesses  18   a  and  20   a  cooperate to define a first die cavity  21 . Similarly, the second die  16  includes a second pair of cooperating die sections  22  and  24 , which have respective recesses  22   a  and  24   a  formed therein. When the two die sections  22  and  24  are moved together as shown in  FIG. 3A , the recesses  22   a  and  24   a  cooperate to define a second die cavity  25 . 
     Frame  12  supports a ram or actuating cylinder  30 , whose ram  32  is secured by bolts to a first platen  34 , to which die section  18  is secured. In this way, reciprocating linear displacement of the ram  32  is transmitted directly to die section  18  of the first die  14 . A base  36 , fixed to the frame  12  against displacement, supports a die section  24  of the second die  16  in alignment with the other die sections, which are mutually aligned. 
       FIG. 2  shows an alternative arrangement in which a ram  32 ′ is in the form of a platen, and die section  18  is secured to the ram  32 ′. Reciprocating linear displacement of ram  32 ′ is transmitted directly to die section  18  of the first die  14 . Although this invention is described and illustrated in the context of apparatus including a platen  34  and a ram  32 , it will be appreciated that this invention can be practiced with the arrangement of  FIG. 2 , in which the ram  32  and platen  34  are in the form of an integral, unitary ram  32 ′, if desired. 
     The first die section  18  of the first die  14  is preferably secured to a portion of the hydroforming apparatus, platen  34 , for linear displacement therewith. The second die section  20  of the first die  14  and the first die section  22  of the second die  16  are secured to a platen  38  for movement therewith. Alternatively, if the second die section  20  of the first die  14  and the first die section  22  of the second die  16  are formed as separate pieces, then each may be supported on individual platens, and those platens are secured mutually for movement as a unit. Lastly, the second die section  24  of the second die  18  is preferably secured to or formed integrally with a second portion of the hydroforming apparatus  10 , the stationary base  36 . 
     Platen  34  supports guide pins  40 ,  42  which are secured at connections  44 ,  46  to the lower surface of platen  34 . The connection of the guide pins to the platen  34  may be accomplished by a weld, by mutual engagement of screw threads formed on pins  40 ,  42  and in platen  34 , by bolting each guide pin to the platen, by pinning the guide pins to the platen, or by similar means. Each guide pin is formed with a shank portion  48 ,  50  that extends from its respective connection  44 ,  46  through a opening  52 ,  54  formed through the thickness of the second platen  38  to a head  56 ,  58 , located on the opposite side of platen  38  from the location of platen  34 . Each head is sized in relation to the size of the corresponding opening  52 ,  54  so that the head contacts and releasably engages platen  38  when displacement of platen  34  relative to platen  38  reaches a predetermined magnitude in one direction. 
     When platen  34  moves toward platen  38  in the opposite direction a sufficient distance, each head  56 ,  58  can enter an opening  60 ,  62  formed in the thickness of base  36 . Preferably the fit of each the shank  48 ,  50  in its corresponding opening  52 ,  54 , and the fit of each head  56 ,  58  in its corresponding opening  60 ,  62  is a guided fit that assures mutual alignment of the platens  34 ,  38 , base  36 , and dies  14 ,  16 . 
     During series production of parts using the hydroforming apparatus  10 , an operational cycle begins with the various components arranged in the die closed position of  FIG. 3A , in which the die cavities  21 ,  25  are occupied with parts formed during the prior cycle. Die cavity  21  is opened when ram  32  moves upward due to actuation by its cylinder  30 . Platen  34  moves upward with the ram, and the heads  56 ,  58  of guide pins  40 ,  42  engage the lower surface of platen  38 , as  FIG. 3B  shows. This upward displacement of ram  32  fully opens die  14  without opening the second die  16 . Then, ram  32  moves upward again due to actuation by its cylinder, platen  32  moves upward with the ram, and platen  38  moves upward with the ram due to contact of the heads  56 ,  58  on the lower surface of platen  38 , thereby opening die cavity  25 , as  FIG. 3C  shows. Preferably the length of the shank portions  48 ,  50  of the guide pins  40 ,  42  is a predetermined length that enables die cavity  21  to be opened sufficiently to remove formed parts from the die and to insert workpieces in the die readily within the available extent of travel of the ram  32 . 
     Next, the formed parts located in the die cavities  21 ,  25  are removed, a workpiece  26  is inserted between the spaced apart die sections  18  and  20  of the first die  16 , and another workpiece  28  is inserted between the spaced apart die sections  22  and  24  of the second die  18 . The illustrated workpieces  26  and  28  are substantially circular in cross-sectional shape. However, it should be understood that the invention is not limited to any specific shape of the workpieces  26  and  28 , and that the invention can be practiced using workpieces of any shape, provided they can be located within their respective die cavities  21  and  25  prior to the hydroforming operation. 
       FIGS. 4A–4C  illustrate another embodiment in which a linear actuator  70  is secured to the first platen  34  and intermediate platen  38 . Actuator  70  is secured to platen  38  by bolts and is also secured to platen  34  so that forces, directed up ward and downward and produced by ram  32  and actuator  70 , are transmitted to platens  34 ,  38 . The actuator  70  may be hydraulically, pneumatically or electrically actuated. A hydraulic linear actuator is generally in the form of a double acting piston movable within a hydraulic cylinder. Pressurized fluid is applied within the cylinder alternately to opposite sides of the piston depending on the direction the piston is to be moved relative to the cylinder. The piston is displaced, and the actuator transmits a force to the components to which the cylinder and piston are secured. 
       FIG. 4A  shows die cavities  21 ,  25  closed, linear actuator  70  fully retracted, and guide pin  40  in its lowermost position. Next, ram  32  moves upward, raising platen  34  and opening die cavity  21 . Actuator  70  may assist in opening die cavity  21  by applying a force on platens  34 ,  38 . When the die cavity  21  is opened, head  56  of die pin  40  contacts the lower surface of platen  38 . Next, ram  32  again moves upward carrying platens  34 ,  38  upward and opening die cavity  25 . After the formed parts are removed from the dies  14 ,  16  and workpieces to be formed are inserted in the dies, ram  32  lowers platens  34 ,  38 , preferably with the assistance of force produced by actuator  70 , until die section  22  engages and seats on die section  24 , thereby closing die cavity  25 . Ram  32  continues to move downward to the position of  FIG. 4A , where both die cavities  21 ,  25  are closed preparatory to pressurizing the die cavities and the workpieces to be formed within the cavities. 
     Use of the embodiment described with reference to  FIGS. 4A–4C  is described next with reference to  FIGS. 5A–5D , in which a space between die sections is adjusted through operation of the linear actuator  70  to assist in removal of formed parts from the die cavities. From the position of the hydroforming apparatus shown in  FIG. 5A  where die cavities  21 ,  25  are fully closed, ram  32 , alone or in combination with actuator  70 , moves platen  34  upward to the position of  FIG. 5B , where the upper die cavity and the lower die cavity  21 ,  25  are partially open. In this case, the head  56  of guide pin  40  is not in contact with the intermediate platen  38 ; therefore, actuator  70  applies a force that moves platen  38  upward to the position of  FIG. 5B  from the closed position of  FIG. 5A . Next, the position of upper platen  34  is substantially maintained, and platen  38  is raised by actuator  70  to a position sufficient to fully open the lower die cavity  25 , the position shown in  FIG. 5C . This displacement of platen  38  further partially closes the upper die cavity  21 . With the apparatus located as shown in  FIG. 5C , a formed part can be removed from die cavity  25  and a workpiece can be inserted in the lower die cavity. Next, actuator  70  extends its length, lowering platen  38 , fully opening the upper due cavity  21 , and partially closing the lower die cavity  25 . Contact between the head  56  and the lower surface of platen  38  provides a visual indication that actuator  70  has been extended sufficient to fully open the upper die cavity  21 , the position shown in  FIG. 5D . Then the formed part is removed from the upper die cavity  21  and a workpiece to be hydroformed is installed in the upper die cavity. Next, ram  32  is lowered and carries platens  34 ,  38  downward. Actuator  70  retracts until the apparatus returns to the position of  FIG. 5A , where the head  56  enters the opening in base  36 , and die cavities  21  and  25  are fully closed. Thereafter, hydroforming fluid fills the die cavities and the cavities are pressurized to force the workpieces into contact with the inner surface of the die cavities, as is described with reference to  FIG. 7 . 
       FIGS. 6A–6C  show another arrangement of the hydroforming apparatus with the guide pins removed, a first linear actuator  72  secured to platen  38  and base  36 , and a second linear actuator  74  secured to platen  38  and base  36 .  FIG. 6A  shows the apparatus in a closed die position. Ram  32  moves platen  34  upward to the position of  FIG. 6B , where the upper die cavity  21  is fully opened. Actuators  72 ,  74  are fully retracted and the intermediate platen  38  is maintained in the lowermost position with die cavity  25  closed. The hydroformed parts are removed from the upper die cavity  21  and workpieces to be hydroformed are placed in the upper die cavity. Then actuators  72 ,  74  are extended, raising platen  38  to the position shown in  FIG. 6C , where the upper die  14  is closed and the lower die  16  is fully opened. Hydroformed parts are then removed from the lower die cavity  25  and a workpiece to be hydroformed is placed in the lower die cavity. Ram  32  is lowered while maintaining die cavity  21  closed and forcing platen  38  downward, either with the assistance of actuators  72 ,  74  or without that assistance. Ram  32 , platen  34  and platen  38  continue to move downward until die section  22  become fully retracted. 
     Preferably the available length of travel of the linear actuators  70 ,  72 ,  74  enables die cavities  21 ,  25  to be opened sufficiently to remove and insert workpieces readily within the available extent of travel of the ram  32 . 
     The workpieces  26 ,  28  can be manufactured in any conventional manner, such as by rolling a sheet of metallic material into a completely closed tubular configuration and welding the adjacent edges together. Alternatively, the workpieces  26  and  28  can be manufactured as seamless tubes. If desired, the workpieces  26  and  28  can be mechanically pre-bent prior to insertion within the first and second dies  16  and  18  so as to approximate the desired final shapes. It will be appreciated that the two die cavities  21  and  25  can be configured to form the workpieces  26  and  28  into either the same shape or into two different shapes, as desired. 
     After the workpieces are inserted into their respective die cavities  21  and  25 , the ram  32  and platens  34 ,  38  move downwardly relative to the base  36  to the closed position illustrated in  FIG. 3A , and the guide pin heads  56 ,  58  reenter the openings  60 ,  62  in the base  36 . During such closing movement of the first and second dies  16  and  18 , portions of the workpieces  26  and  28  may be mechanically deformed somewhat, although such is not required. When the ram  30  reaches the lowermost position illustrated in  FIG. 3A , the dies  14  and  16  are disposed in a stacked relationship between the ram  32  and the base  36 . As used herein, the term “stacked relationship” means that the cooperating die sections of each of the dies engage one another, and further that the adjacent die sections of different dies engage one another. Thus, in the illustrated embodiment, the first pair of cooperating die sections  18  and  20  of the first die  14  engage one another, the second pair of cooperating die sections  22  and  24  of the second die  16  engage one another, and the second die section  20  of the first die  14  engages the first die section  22  of the second die  18 . At that time, a conventional clamping mechanism (not shown) can be engaged so as to maintain the die sections  18  and  20  of the first die  14  and the die sections  22  and  24  of the second die  18  in the illustrated stacked relationship. Alternatively, if the hydroforming apparatus  10  is adapted from a conventional mechanical press, the ram  32  can function as the clamping mechanism by moving to its bottom dead center position illustrated in  FIG. 3A , thereby holding or otherwise maintaining the die sections  18  and  20  of the first die  14  and the die sections  22  and  24  of the second die  18  in the illustrated stacked relationship. 
     Referring now to  FIG. 7 , a first pair of end feed cylinders  65  and  66  are then moved laterally into engagement with the ends of the first workpiece  26 , while a second pair of end feed cylinders  67  and  68  are moved into engagement with the ends of the second workpiece  28 . The end feed cylinders  65 – 68  have respective passageways  65   a ,  66   a ,  67   a , and  68   a  formed therethrough to facilitate filling the workpieces  26  and  28  with a hydroforming fluid, typically a relatively incompressible liquid such as water, and emptying that fluid. The illustrated end feed cylinders  65 – 68  are intended to be representative of any mechanism or mechanisms for sealing the ends of the workpieces  26  and  28 , for supplying pressurized hydroforming fluid into the interiors of the workpieces  26  and  28 , and for emptying hydroforming fluid from the interiors of the workpieces  26  and  28  at the conclusion of the hydroforming process. 
     In the next step of the hydroforming method, the pressure of the fluid within the workpieces  26  and  28  is increased to such a magnitude that the workpiece  26  expands outward into engagement with the surface of the recesses  18   a  and  20   a  formed in the first and second die sections  18  and  20  of the first die  16 , and the second workpiece  28  is expanded outwardly into engagement with the surface of the, recesses  22   a  and  24   a  formed in the first and second die sections  22  and  24  of the second die  18 . Such expansion causes the workpieces  26  and  28  to conform to the contour of the surfaces of die cavities  21  and  25 , respectively. 
     Preferably, a single source provides pressurized fluid to each of the workpieces  26  and  28  at the same time so that the respective hydroforming processes can be performed substantially simultaneously at the same pressures. As a result, the hydroforming apparatus  10  is capable of performing two or more hydroforming operations concurrently to decrease the overall amount of operational cycle time and, therefore, increase overall productivity. However, the hydroforming processes are essentially independent of one another and, therefore, can be performed with differing parameters, including times, pressures, and the like, if desired. 
     In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.