Abstract:
A hydro-forming tool for use in a method of forming a blank into a liquid filled chamber. The chamber is formed by a container ring and a moveable wall that together define a variable volume chamber for containing the liquid. The wall is moveable relative to the container ring to provide a chamber in which the volume of liquid required to back up the blank is minimized. The liquid reduces friction at the chamber entry rim. Liquid may be ported through a counter punch to hydro-form the blank into the detail forming areas.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     The invention was made with Government support under Contract No. DE-FG36-08G018128. The Government has certain rights to the invention. 
    
    
     BACKGROUND 
     1. Technical Field 
     This disclosure relates to hydro-mechanical forming tool having a chamber that is filled with a liquid during a method of reducing the cycle time for a hydro-mechanical forming operation. 
     2. Background Art 
     In one type of hydro-mechanical drawing process, a sheet metal blank is formed by drawing the blank onto a punch with the area below the blank being filled with a liquid. The liquid is compressed and forms the blank against the punch. The liquid eliminates the need for one side of the tooling. 
     The required pressure to completely form a production part is dictated by the tightest local radius of the part to be formed. A large press is required to apply maximum pressure to the entire surface of the blank that is required to form relatively small tight local radii. 
     Hybrid hydro-mechanical drawing followed by conventional forming in two-sided dies is a known process being conducted in a single tool, in which the blank is initially formed by hydro-mechanical drawing. Then, local features that may have tight local radii are formed subsequently in a two-sided die. Hybrid hydro-mechanical drawing enables deeper drawing of the blank compared to forming on a conventional press. However, the maximum elongation of the blank usually remains within the forming limit diagram of the material being formed. 
     One problem with hydro-mechanical drawing is that a relatively long cycle time is required, which can approach one minute for forming large automotive panels. The long cycle time is required because a substantial volume of water (several hundreds of liters) must be delivered to the tool and drained from the tool within each forming cycle. 
     Substantial energy and time is required to generate sufficient pressure for forming operations. Specialized equipment, including a several thousand ton hydraulic tool, may be required to implement the hydro-mechanical drawing process. The size of the press can be significantly reduced, and pre-existing press equipment in manufacturing plants can be used if the volume of liquid required to form a part is substantially reduced. There is a need for a process and tooling that focuses the hydro-mechanical force in limited areas where the application of pressure applied by the liquid is most beneficial. 
     The above problems are addressed by applicant&#39;s developments as summarized below. 
     SUMMARY 
     According to one aspect of this disclosure, a hydro-mechanical tool for forming a metal blank is provided that includes a punch having a die forming surface, a blank holder ring that engages a first side of the blank, and a liquid chamber. The liquid chamber includes a liquid container ring that engages a second side of the blank and a counter punch in the form of a movable wall, or floor, that forms the liquid chamber in combination with the container ring. A volume of liquid is contained within the liquid container ring and on the counter punch. When the forming surface engages the blank while the blank is retained between the blank holder ring and the liquid container ring, the liquid forms the blank to the forming surface. 
     According to another aspect of the disclosure as it relates to the hydro-mechanical tool, the container ring may include a die entry radius. A portion of the liquid is supplied through the container ring to the die entry radius to reduce friction between the blank and the die entry radius of the container ring. 
     According to another aspect of the disclosure as it relates to the hydro-mechanical tool, an actuator may be provided that moves the wall toward and away from the blank. 
     According to another aspect of the disclosure as it relates to the hydro-mechanical tool, the wall of the hydro-mechanical tool may engage the second side of the blank without any liquid being provided between the wall and the blank. Liquid may be provided between the container ring and the blank outboard of the punch, as the blank is formed into the container ring. The liquid flows underneath the flange of the blank, as it is drawn, and lifts the area where the blank enters the die cavity. The liquid under the flange eliminates or reduces friction at the entry into the die cavity. 
     According to another aspect of the disclosure, the hydro-mechanical tool may have a space provided between the container ring and a side portion of the wall that extends from a die entry radius of the container ring to a seal point between the container ring and a side portion of the wall. The liquid flows underneath the flange of the blank as it is drawn and lifts the area where the blank enters the die cavity. The liquid under the flange reduces friction at the entry into the die cavity. 
     According to another aspect of the disclosure as it relates to the hydro-mechanical tool, the wall of the hydro-mechanical forming press may define at least one port that is in fluid flow communication with a source of pressurized liquid and opens into a surface on the wall that faces the blank. The hydro-forming pressure is applied to the blank in localized areas where the port opens into the surface of the wall to form the blank into a detail area of the forming surface. 
     According to another aspect of the disclosure, the hydro-mechanical tool may further comprise a face seal provided on the surface of the wall that faces the blank to form a seal with the blank to limit the area within which the hydro-forming pressure is applied. 
     According to another aspect of the disclosure, the hydro-mechanical tool may further comprise at least one recessed area formed in the forming surface of the punch into which a portion of the blank is drawn by the action of the punch. A protrusion may be provided on the surface on the wall that faces the blank within the seal that extends towards the recessed area in the forming surface of the punch. The protrusion is provided to reduce the volume of liquid required to form the blank in the detail area of the forming surface. 
     According to another aspect of the disclosure, the hydro-mechanical tool may define a cavity in the surface of the wall that faces the blank. The wall defines a hydro-forming chamber with the blank and limits the area within which hydro-forming pressure is applied. 
     According to another aspect of the disclosure, a process for reducing the cycle time of a hydro-mechanical forming operation is disclosed in which a liquid filler forming chamber has a variable volume. The volume of liquid is minimized to reduce the time required to drain and fill the chamber. Also, by reducing the volume of liquid, less force is required to form a part. 
     According to another aspect of the disclosure, a method of forming a metal blank in a hydro-mechanical tool is provided. The tool has a punch with a die forming surface and a blank holder ring on one side of the blank. A container ring cooperates with a movable wall that moves relative to the container ring to define a chamber on the other side of the blank. The method of forming the blank includes the step of loading a blank onto the container ring. The blank is clamped with the blank holder ring against the container ring. The chamber is filled with a volume of liquid up to the level of the blank. The blank is drawn into the chamber with the punch against the resistance of the liquid in the chamber. The die forming surface engages the blank while the blank is retained between the blank holder ring and the container ring. The wall engages the second side of the blank with liquid being provided between the container ring and the blank outboard of the punch as the blank is formed into the container ring. 
     According to other aspects of the method, the hydro-mechanical tool may include an actuator that moves a counter punch in tandem with the punch through at least a part of the drawing step. 
     Other aspects of the method relate to providing a counter punch that defines at least one liquid supply channel that is ported to a hydroforming chamber that is disposed on the opposite side of the blank from a detail forming area on the punch. The method may further comprise supplying the liquid under pressure to the hydroforming chamber to form the blank into the detail forming area. 
     The hydro-mechanical tool may include an actuator that is used to move the counter punch toward and away from the blank. The hydro-mechanical tool may also include a counter punch and container ring that define a space between the blank and the counter punch. If so, the method may further comprise supplying the liquid to the space to reduce friction between the blank and the container ring. The method may also relate to the concept of providing a tool with a die entry radius which according to the method may further comprise supplying a portion of the liquid through the container ring to the die entry radius to reduce friction between the blank and the die entry radius of the container ring. 
     The above advantages and other features of the disclosure will be more fully understood in view of the attached drawings and the following detailed description of the illustrated embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic cross-sectional view of a hydro-mechanical forming tool that has a moveable bottom wall that is provided on a counter punch that supports a volume of liquid and a channel that provides liquid to the die entry radius; 
         FIG. 2  is a diagrammatic cross-sectional view of a hydro-mechanical forming tool that includes a moveable wall that is provided on a counter punch about which a small gap is provided for receiving liquid that also supplies liquid to the die entry radius; 
         FIG. 3  is a diagrammatic cross-sectional view of a hydro-mechanical forming tool with the forming ram engaging the blank while the blank is supported by the counter punch; and 
         FIG. 4  is a diagrammatic cross-sectional view of a hydro-mechanical forming tool with hydro-mechanical forming fluid being provided in small volumes at the bottom of the die cavity. 
     
    
    
     DETAILED DESCRIPTION 
     Several different embodiments of Applicant&#39;s development are disclosed and described in detail below. For brevity, similar parts of the various embodiments are referred to by the same name and reference numeral in the various embodiments. 
     Referring to  FIG. 1 , a hydro-forming tool  10  is used to form a sheet metal blank  12 . The blank  12  is held by a blank holder ring  14  to a container ring  16 . The wall  18 , as shown in  FIG. 1 , is the top surface of a counter punch  20 . The counter punch  20  is moved relative to the container ring  16  by a hydraulic cylinder  21 , or another actuator such as a pneumatic cylinder, press ram or other mechanical linkage. The container  16  and moveable wall  18  together define a chamber in which a process fluid, such as water, is supplied. 
     A punch  26  is retained in a hydraulic or mechanical press that moves the punch  26  reciprocally relative to the counter punch  20 . The blank  12  is formed against a punch forming surface  28  of the punch  26 . The liquid  22  provides a reaction surface that forms the blank  12  against the forming surface  28 . 
     A primary liquid supply channel  30  is used to supply and drain the liquid  22  from the space  24  defined by the container ring  16  and the wall  18 . The wall  18  moves in tandem with the ram  26  as the ram  26  is lowered. A primary advantage of the wall  18  being movable is that a reduced volume of liquid  22  is required for the forming process. As the wall  18  is raised within the container ring  16 , a reduced volume  18  of liquid is contained in the chamber. The reduced volume of liquid reduces the cycle time because less water must be pumped into and drained out of the chamber. 
     The container ring  16  has a chamber entry rim  32  across which the blank  12  is drawn, as the punch  26  draws the blank  12  against the forming surface  28 . A chamber entry fluid channel  36  provides liquid  22  from the primary liquid supply channel  30  to the chamber entry rim  32 . The fluid  22  provides that the chamber entry rim  32  reduces friction as the blank  12  is drawn into the container ring  16 . 
     Several detail forming areas  38  are provided on the forming surface  28 . The blank  12  is formed into the forming areas  38  by the fluid pressure provided by the liquid  22  in the chamber. 
     Referring to  FIGS. 2 and 3 , an alternative embodiment is shown at two different points in the process. A hydro-forming tool  10  is shown for forming a blank  12 . Many of the components of the hydro-forming tool  10  are the same as were described with reference to  FIG. 1 . The blank holder ring  14  holds the blank  12  against the container ring  16 . A moveable wall  18  is formed as part of the counter punch  40  that differs from the counter punch  22  of  FIG. 1  in that it includes a plurality of hydro-forming liquid supply channels  42 . The liquid supply channels  42  provide liquid to partial hydro-forming chambers  44  that are located on the opposite side of the blank  12  from detail forming areas  38 . Fluid is supplied to the hydro-forming liquid supply channels  42  under pressure to form the blank  12  into the detail forming areas  38 . Fluid is also supplied through the primary liquid supply channel  30  to a counter punch fluid jacket  46  that extends about the counter punch  40 . The fluid in the counter punch fluid jacket  46  reduces friction as the blank  12  is drawn across the chamber entry rim  32 . 
     Referring to  FIG. 3 , a material flow pocket  48  is shown in phantom lines that show the pocket  48 , as the blank  12  is formed in solid lines that show the shape of the blank after forming. The material flow pocket  48 , as shown, may be somewhat exaggerated, but it should be understood that the material flow pocket  48  is created by liquid pressure below the blank  12  as the blank  12  is drawn into the hydro-forming tool  10 . 
     Referring specifically to  FIG. 2 , the blank  12  is shown retained between the blank holder ring  14  and the container ring  16 . The moveable wall  18  is shown supporting the lower surface of the blank  12  at the point in the cycle where the punch  26  initially engages the top side of the blank  12 . The liquid  22  is supplied through the primary liquid supply channel  30  to the counter punch fluid jacket  46 . The liquid reduces friction at the chamber entry rim  32 . 
     Referring to  FIG. 3 , the hydro-forming tool  10  is shown with the punch  26  fully advanced with the blank  12  being shown in its fully drawn condition. The moveable wall  18  of the counter punch  40  is in engagement with the blank  12 . Movement of the counter punch  40  reduces the volume of liquid  22  which also reduces the amount of time necessary to fill and drain the chamber formed by the container ring  16  and the moveable wall  18 . At this point, the blank  12  is nearly fully formed and a final forming process may be performed by introducing a pressurized liquid  22  through the hydro-forming liquid supply channels  42 . The fluid introduced through the supply channels  42  is provided to the partial hydro-forming chambers  44  below the blank  12 . When the pressurized fluid is introduced into the partial hydro-forming chambers  44 , the blank  12  is formed into the detail forming areas  38  of the forming surface  28 . Seals  50  are provided around the forming chambers  44  that seal against the bottom of the blank  12 . 
     The reduced size of the partial hydro-forming chambers  44  reduces the volume of liquid required to form the blank in the detail forming areas  38 . The detail forming areas  38  have less surface area then the entire forming surface  28 . The reduced volume of liquid reduces the force required to form the blank as compared to the force required to form the blank over the entire forming surface  28 . 
     A hydraulic cylinder  21  or other mechanical actuator is connected to the counter punch  40  to move the counter punch  40  and the wall  18  relative to the container ring  16 . When the hydro-forming liquid supply channel  42  is filled, no fluid is disposed between the blank  12  and the wall  18 . By reducing the amount of liquid applying pressure to the surface of the blank, less force is required to form parts of the blank  12  into the detail forming areas  38 . 
     Referring to  FIG. 4 , another embodiment of the hydro-forming tool  10  is shown that includes a counter punch  40  with EHF liquid channels  42  that provide liquid  22  under pressure to a plurality of mini-hydro-forming chambers  62  on the forming surface  28  of the punch  26 . The mini-hydro-forming chambers  62  are further reduced in volume by providing protrusions  64  on the moveable wall  18  that are received within the mini-hydro-forming chambers  62 . The protrusions  64  may be used to start mechanically forming the panel  12  into detail forming areas  38 . Liquid supplied through the hydro-forming liquid supply channel  42  fills the mini-hydro-forming chambers  62 . A plurality of seals forms a seal between the blank  12  and the wall  18  at the outer periphery of the mini-hydro-forming chambers  62 . 
     The entire forming process used to form the panel, as shown in  FIG. 4 , follows the general steps of the process described with reference to  FIGS. 2 and 3  to the point that the blank  12  is fully formed by the punch  26  with the blank  12  being formed against the wall  18 . At this point, fluid is introduced through the hydro-forming liquid channel  42  that fills the mini-hydro-forming chamber  62 . Part of the volume of the space below the blank  12  in the mini-hydro-forming chamber  62  is filled by the space occupied by the protrusion  64 . In this way, the amount of liquid in the mini-hydro-forming chamber  62  is further reduced, which also reduces the volume of liquid and the amount of force required to form the blank into the detail forming areas  38 . 
     Although several embodiments of the invention have been disclosed, it will be apparent to persons skilled in the art that modifications may be made without departing from the scope of the invention. All such modifications and improvements therein are covered by the following claims.