Abstract:
Equipment and method for the rapid and easy extraction of formed metal parts from forming dies while in a press and operating at elevated temperatures. The invention features the controlled supply of streams of air or other inert gas to the interface of the hot surface of the forming die and the formed panel to augment removal so that flaws from removal equipment are minimized for optimized production of high quality parts. High velocity air is discharged through nozzles onto the forming surfaces of hot forming dies to cool the forming die and the part that contract at different rates and pop the part from the surface.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to the art of manufacturing parts from metallic sheet material using hot metal forming dies and more particularly to new and improved constructions and techniques for producing metal parts featuring the rapid and trouble-free extraction of formed parts from hot working surfaces of superplastic and quick plastic forming dies.  
         BACKGROUND OF THE INVENTION  
         [0002]    Prior to the present invention, various types of forming equipment and processes have been developed to form sheets of alloys of aluminum and other suitable metallic materials into a wide range of items such as sturdy and lightweight panels for vehicles. Among such equipment and processes are superplastic and quick plastic forming dies and processes in which a ductile sheet of suitable metallic material is heated and stretched onto the forming surfaces of heated dies to improve production of high quality parts. Examples of such processes and equipment are found in U.S. Pat. No. 5,974,847 issued Nov. 2, 1999 to Saunders et al for “Superplastic Forming Process” and U.S. Pat. No. 5,819,572 issued Oct. 13, 1998 to Krajewski for “Lubricating System for Hot Forming”, both assigned to the assignee of this invention and both hereby incorporated by reference. In the patent to Saunders et al, a sheet of metal alloy is heated to a superplastic forming temperature and is pulled over and around a forming insert prior to using differential gas pressure to further stretch the sheet into conformity with a forming die surface so that thinning of the formed part is minimized. In the patent to Krajewski, dry lubricant is applied to metallic sheets which are subsequently heated to predetermined forming temperatures and formed into a part in superplastic forming die equipment. The lubricant initially provides improved forming of the part and subsequently improved release of the formed part from the forming die.  
           [0003]    While such hot plastic forming processes and equipment generate improved parts, production efficiency has at times been diminished because of rejection of blemished or damaged parts produced by production procedures. Often such damage results from mechanical damage occurring from the physical removal of the formed part from the hot forming surface of the die and subsequently from the handling of the hot part. More particularly, after the part has been initially separated from the hot forming die, the part retains sufficient heat energy causing the surfaces thereof to retain some plasticity so that the tooling and handling marks may be imposed on the part from removal and stacking equipment.  
           [0004]    Moreover, initial removal has heretofore been difficult because the formed part often firmly seats or grips on the die-forming surface. Dislodgment of such parts by extraction forces exerted through release tooling often results in part distortion or part marring by the tools or dies. This damage may be so substantial that parts do not meet specifications and have to be scrapped and recycled. The use of larger quantities of lubricants to improve parting requires more frequent and excessive die cleaning between forming operations and provides only minimized improvement in part removal. Often the lubricant remaining on the dies caused part imperfection on the show surfaces as pointed out in U.S. Ser. No. 09/748,096 filed Dec. 27, 2000 by Morales et al, entitled “Hot Die Cleaning for Superplastic and Quick Plastic Forming” and assigned to the assignee of this invention and hereby incorporated by reference.  
         SUMMARY OF THE INVENTION  
         [0005]    In contrast to the prior art, the present invention is drawn to new and improved methods and mechanisms that provide improved parts and meets higher standards for ejection and removal of formed parts from hot superplastic and quick plastic forming dies while in the press and operating at elevated temperatures. More particularly, the invention is directed to the quick and effective removal of formed parts from hot forming dies without part damage and with optimized usage of parting lubricants.  
           [0006]    This invention provides new and improved equipment and method for unseating the formed part from the heated die. In a preferred embodiment of this invention, a series of orificed air passages or jets extending through the forming surface of the die are employed to direct streams of compressed air between the die surface and the formed part. The pressurized air is effective at the interface between the forming surface and the formed part to provide an outwardly directed force, urging the formed part away from the forming surface of the heated die. The air passing through the jet orifices may accumulate between the formed part and the die surface to effectively reduce the amount of static friction that must be overcome in separating the two components.  
           [0007]    Release air may also flow to the periphery of the formed part to break any sealing or loosen the seating between the part and the forming die to augment part release. Additionally, the air that passes through the orifices effectively cools the formed panel, which contracts at a high rate due to its high coefficient of thermal expansion and high surface area-to-mass ratio as compared to that of the die unit with its lower coefficient of thermal expansion and lower surface area-to-mass ratio. Since the die does not contract the same amount as the formed part, the difference in contraction reduces the area of intimate contact between the panel and the die surface, thereby reducing the amount of static friction that must be overcome in separating these two components from one another.  
           [0008]    The above factors all contribute to the lowering of the force required to separate the formed panel from the die. This reduction in force allows the formed part to be removed from the hot die without damage and with minimum effort and distortion. Moreover, since the panel has been cooled by the air streams, its plasticity is reduced and can be quickly handled with removal and stacking equipment with minimized damage. With improved part extraction, parting lubricant usage can be reduced for improved production efficiency and effective cost reduction.  
           [0009]    These and other features, objects and advantages will become more apparent from the following detailed description and drawings in which: 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a pictorial view of an opened forming press with forming die equipment producing parts from sheet metal blanks;  
         [0011]    [0011]FIG. 2 is a diagrammatic cross-sectional view of the profiled hot dies as operatively mounted in the forming press of FIG. 1;  
         [0012]    [0012]FIG. 3 is a diagrammatic cross-sectional view similar to the view of FIG. 2 but showing the forming die set in a forming position;  
         [0013]    [0013]FIG. 4 is a cross-section view similar to the views of FIGS. 2 and 3 but showing the profiling dies in a part release position;  
         [0014]    [0014]FIG. 4 a  is a portion of the profiling dies just prior to part release; and  
         [0015]    [0015]FIG. 5 is a diagrammatic pictorial view of a portion of a part produced by the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]    Turning now in greater detail to the drawings, FIG. 1 illustrates a forming press  10  comprising a lower bolster plate  12  on which lower steel or forming die  14  is mounted. The press additionally has an upper reciprocating ram plate  16  that carries a chambered upper tool  18 , which corresponds to the upper tool of the above-referenced U.S. Pat. No. 5,819,572. Both of the plates  12  and  16  are electrically heated to establish the required heat energy levels in the die and the sheet metal blanks  20  for superplastic forming or quick plastic forming as is known in this art. The forming die  14  can be mounted on the upper plate instead of the lower plate and the chambered upper tool  18  operatively supported on the lower plate if desired and depending on the characteristics of the part to be made.  
         [0017]    The ram plate  16  is moved by hydraulic cylinders  22  to cycle the ram plate from the open position for blank loading to the closed blank forming position and then back to the open shown in FIG. 1 for formed part removal. The blanks  20  utilized with one preferred embodiment of this invention are flattened sheets  24  of aluminum alloy coated with a dry lubricant  26  such as boron nitride to function as a release agent to prevent the formed panel  30  from sticking to the die and furthermore to enhance the stretching and formation of the part during forming operation.  
         [0018]    As shown best in FIGS.  2 - 4 , the upper tool  18  is operatively connected to the lower face of the ram plate and projects downwardly therefrom. This tool has downwardly extending and rectilinear peripheral wall  34  whose free end  36  provides a continuous face seal  38  which sealingly engages the upper surface of the metal sheet  24  to define an air chamber  40  (see FIG. 3) when the upper tool is brought into engagement therewith during a part-forming operation. The air chamber  40  is supplied with pressurized air through an orifice  44  in an internal upper wall  46  connecting the sidewalls. The orifice is fed with pressurized air from a compressor or other source  48  operatively connected thereto by air line  50  and pneumatic controls  52  provided with conventional air control valves therein to control the feed and exhaust of air from the upper and lower tooling for metal-forming operation.  
         [0019]    The lower tooling or die steel  14  has a rectilinear peripheral wall  54  extending upwardly from connection with the face of the bolster plate  12  to a continuous peripheral edge  56  that has pneumatic sealing engagement with the bottom surface of the alloy sheet  24 . The steel lower tool further comprises a thick main forming body  60  of a mass considerably greater than that of the thin metal blank sheet  20 . The upper surface of the main body of the forming die is profiled to form the desired shape of the part to be made. The main body is further provided with a plurality of air passages  64  therein that have small diameter orifices  63  formed at strategic locations in the forming surface of the die. As shown, the air passages pneumatically connect to lower fittings  65  of a manifold  66 . The manifold pneumatically connects to the controls  52  by air line  68 .  
         [0020]    In operation, a loading arm  74  of a robot  76  or other suitable loading unit picks up a sheet  24  of aluminum alloy from a stack  78  of the blank sheets and moves and releases the sheet into operative position in the opened forming die unit of the forming press  10 . The heated ram and bolster plate elevates and maintains the temperature of the upper and lower tools at a suitable forming temperature so that the temperature of loaded sheet quickly rises to the desired heat energy level for metal forming. The loading arm is removed and cycled to pick up a new sheet. With the sheet in position, the hydraulic cylinders  22  are operated by pressure controls for the press, not illustrated, to move the chambered upper tool  18  downwardly from the FIGS. 1 and 2 position to the forming position in FIG. 3. The controls  52  are then activated to charge the sealed chamber  40  with pressurized air or other inert forming gas that expands to fully stretch the sheet around the profile of the forming die to effect the forming of the panel or part  30 . During such forming, the lower air passages  64  are open to exhaust so that there is no entrapment of gas pockets below the formed part to possibly distort portions thereof during forming thereof. After the panel is formed, the controls  52  are active to exhaust the upper chamber  40  and to pressurize the interface between the formed panel and the profiling surface of the forming die to augment panel release. Press controls are operated to open the press to move the upper forming chamber to the position of FIGS. 1 and 2. Robot arm  80  then extends and the gripping end  84  thereof grips the formed part  30  and removes it to a completed stack  88  for subsequent handling.  
         [0021]    Part removal is enhanced since just prior to the entry of the removal arm into the open press, the controls direct streams of pressurized air into the body of the lower steel die via the manifold. The injected air under the panel tends to break any sealing between the panel and the forming die as diagrammatically illustrated in FIG. 4 a  and further provides a lifting force that urges the panel from the die as best illustrated in FIG. 4. Moreover, since the aluminum sheet has a much smaller mass and thickness and a larger thermal conductivity as compared to the mass, thickness and the thermal conductivity of the steel forming die, the sheet cools at a rate substantially higher than that of the die. With this differential, the panel quickly shrinks relative to the die so that it is no longer the same size as the die and splits therefrom. This further enhances extraction by the robot arm  80  as illustrated in FIG. 4. With the panel cooled, its rigidity is increased, providing for improved removal by the robot arm, particularly eliminating panel deformations previously experienced with removal of parts in which substantial heat energy remains in the formed part. With this invention, removal time is shortened so that press cycling time is shortened to optimize part production.  
         [0022]    [0022]FIG. 5 illustrates the part  30  with some dimpled configuration  90  induced by air distributed through the orifices  63  that may be formed on the outer surface of the part. In such cases, the air passages are strategically located so that that they are hidden in recesses for molding strips, cutouts or other non-observable areas in finished panels or other plastically-formed parts.  
         [0023]    While some preferred methods and mechanisms have been disclosed to illustrate the invention, other methods and mechanisms embracing the invention can now be adapted by those skilled in the art. Accordingly, the scope of the invention is to be considered limited only by the following claims.