Abstract:
A metal forming apparatus characterized by rapid cooling includes a forming tool having a first portion defining a forming surface and a second portion defining a cavity for a working gas. A plurality of fins are in conductive heat transfer relationship with the forming tool. The metal forming apparatus enables a high thermal efficiency mode of operation when the effect of the fins is negated for use during metal forming operation, and a rapid cooling mode for use in preparing for tool maintenance. A corresponding method is also provided.

Description:
TECHNICAL FIELD 
     This invention relates to metal forming apparatuses that include a metal forming tool and fins in conductive heat transfer relationship with the tool. 
     BACKGROUND OF THE INVENTION 
     Metal forming tools used in superplastic forming (SPF) and quick plastic forming (QPF) typically include a first portion that defines a gas pressure chamber and a second portion that defines a forming surface. During operation of an SPF or QPF forming tool, a metal blank is placed between the first and second portions of the forming tool such that a first side of the blank is in fluid communication with the chamber and a second side of the blank faces the forming surface. Fluid pressure is introduced into the chamber, which acts on the first side of the metal blank, causing the blank to deform so that the second side contacts, and assumes the shape of, the forming surface. 
     The tool is heated so that the metal blank is maintained at a temperature sufficient for plastic deformation at the forming pressure, typically between 825° F. and 950° F. It is therefore desirable for the tool to be configured for minimal heat transfer to the surrounding environment in order to minimize the amount of energy required to maintain the tool at the desired temperature and the costs associated therewith. Accordingly, the prior art teaches thermally efficient forming tools to reduce heat loss to the environment. 
     Maintenance of prior art tools must often be performed after several hundred forming cycles. Such maintenance may include removing aluminum buildup on critical forming surfaces. However, prior art tools often take a significant amount of time to cool from their elevated operating temperatures of greater than 800° F. to a temperature suitable for maintenance, such as less than 110° F. For example, some prior art tools require approximately eighteen hours to cool to a sufficiently low temperature for maintenance, during which time the tool is unproductive. 
     SUMMARY OF THE INVENTION 
     A metal forming apparatus includes a forming tool having a first portion defining a forming surface and a second portion defining a gas pressure chamber. A plurality of fins are in conductive beat transfer relationship with the forming tool. The metal forming apparatus enables rapid heat loss to the surrounding environment because the fins provide increased surface area for heat transfer to a cooling fluid such as air. Thus, the metal forming apparatus reduces the amount of time required to cool the tool from its operating temperature to a temperature at which tool maintenance can be performed compared to the prior art. Accordingly, the metal forming apparatus enables increased tool productivity compared to the prior art by significantly reducing the amount of time required to perform tool maintenance. 
     The metal forming apparatus may also enable two modes of tool operation, namely a rapid cooling mode for use when preparing the tool for maintenance, and a thermally efficient mode for use during metal forming operation. The rapid cooling mode is achieved when the fins are exposed to the cooling fluid for convective heat transfer to the surrounding environment. 
     The thermally efficient mode is achieved when the effect of the fins is minimized or negated by restricting flow of the cooling fluid currents across the fins. In an exemplary embodiment, a member is mountable with respect to the tool to at least partially enclose the fins, thereby minimizing the effect of the fins by restricting the flow of the cooling fluid to the fins. Accordingly, the member acts to inhibit convective heat transfer and therefore provides a higher thermal efficiency for efficient metal forming operation. Preferably, the member comprises an insulating material to further reduce heat transfer from the fins and from the forming tool, thereby further enhancing the thermal efficiency of the tool. 
     A corresponding method is also provided. The method includes providing a metal forming tool having a plurality of fins operatively connected thereto, providing a restriction to fluid flow to or from the fins, and heating the forming tool. The method further includes, subsequent to heating the forming tool, removing the restriction to fluid flow to or from the fins. 
     The above features and advantages, and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic, cross-sectional side view taken about a vertical plane of a metal forming apparatus including a metal forming tool; 
         FIG. 2  is a schematic, cross sectional view of a portion of the metal forming tool of  FIG. 1  taken about a horizontal plane; 
         FIG. 3  is a schematic side view of a face of the metal forming tool of  FIG. 1 ; 
         FIG. 4  is a schematic, cross-sectional view of an alternative metal forming tool in accordance with the claimed invention; and 
         FIG. 5  is a schematic, cross-sectional side view of an insulating member for use with the metal forming tool of  FIG. 4 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , a metal forming apparatus  8  is schematically depicted. The metal forming apparatus  8  includes a metal forming tool  10  for stretch forming a metal blank  14 . The forming tool  10  includes an upper portion  18 A and a lower portion  18 B. The forming tool  10  depicted is configured to form the blank  14  into a decklid outer panel (not shown); however, a forming tool may be configured to form a blank or other metal piece into any form within the scope of the claimed invention. The blank  14  is depicted with bends or curves; however, those skilled in the art will recognize that other blank configurations may be employed. The blank  14  is formed from a flat, cleaned and lubricated sheet blank that is heated with a preheater (not shown) that heats the blank to a suitable forming temperature. 
     The lower portion  18 B defines a complex forming surface  26  that defines the back side of the decklid outer panel. The forming surface  26  includes a forming surface portion  30  that defines a horizontal portion of the decklid. Another portion  34  of the forming surface  26  forms a vertical portion of the decklid. Still another portion  38  of the forming surface  26  forms a license plate recess. Other portions  42 ,  46  of the forming surface  26  form flanges at the forward edge of the horizontal portion of the decklid and the bottom of the vertical portion. The periphery  50  of the lower portion  18 B has a surface for clamping and sealing the peripheral portion of the blank  14 . 
     The upper portion  18 A is complementary in shape to the lower portion  18 B and is provided with a shallow cavity  54  that forms a chamber for the introduction of a high pressure working gas, e.g., air, nitrogen or argon, against the back side of the blank  14 . The periphery  58  of the upper portion  18 A incorporates a sealing bead  62  that is adapted to engage the perimeter of the blank  14  and to seal against working gas pressure loss when the upper portion  18 A is closed against the blank  14  and lower portion  18 B. The upper portion  18 A also includes a working gas inlet  66  to admit fluid pressure to the chamber  54  and against the back side of the blank  14 . 
     The lower portion  18 B defines a plurality of passageways  70  that extend from the forming surface  26  to an exhaust port (not shown) to enable air or other entrapped gas to escape from below the blank  14  so that the blank can subsequently be stretched into strict conformance with the shaping surface  26  of the lower portion  18 B of the forming tool  10 . 
     The upper and lower portions  18 A,  18 B define holes  74  in which heating elements  80  are disposed. In the embodiment depicted, the holes  74  are bores formed through the tool portions  18 A,  18 B. The heating elements  80  are preferably electrical resistance heating elements, and are provided to maintain the tool  10  at the desired operating temperature of about 825° F. to 950° F. The placement of the heating elements is preferably configured to ensure uniformity of the temperature throughout the tool  10  to prevent warping during tool heat-up and at the operating temperature. It should be noted that the heating elements  80  preferably contact the entire circumference of the holes  74  in order to maximize heat transfer from the heating elements  80  to the tool  10 . 
     The forming tool  10  is preferably constructed of a solid material to maximize the heat transfer from the plurality of heating elements  80  through the forming tool  10 . The forming tool  10  may be constructed of a tool grade steel that exhibits durability at the forming temperatures of a superplastic or quick plastic forming operation. Preferably, the forming tool detail is constructed of AISI P20 steel that is readily available in large billets to accommodate a large forming tool. The initial forged steel billet is machined to form a curved detail specific to the part being produced by the heated metal forming tool  10 . AISI P20 steel may be readily weld repaired and refinished, as opposed to higher carbon material compositions, which are more difficult to weld repair and refinish. 
     The upper portion  18 A is attached to an upper mounting plate  84 A with fasteners  88 . The lower portion  18 B is attached to a lower mounting plate  84 B with fasteners  88 . The upper mounting plate  84 A is attached to a press  92  for selectively opening and closing the metal forming tool  10 , i.e., for selectively moving the upper portion  18 A between open and closed positions with respect to the lower portion  18 B of the forming tool  10 . The mounting plates  84 A,  84 B are preferably formed of plate steels, such as ASTM A36 steel, or AISI P20 steel, depending on the load carrying requirements. The fasteners  88  are preferably formed of heat resistant alloys, such as RA330 or other suitable heat resistant and load bearing alloys. 
     The metal forming apparatus  8  includes insulation to minimize heat loss from the tool  10 , and thereby minimize the energy supplied to the heating elements  80  in order to maintain the tool  10  at elevated operating temperatures. Load-face insulation  96 A is positioned between the upper portion  18 A of the tool  10  and the upper mounting plate  84 A. The load-face insulation  96 A includes a combination of load bearing insulation members  104  and non-load bearing insulation  100 . The load bearing insulation members  104  of load-face insulation  96 A are spaced from each other, and each of the members  104  of load-face insulation  96 A contacts the upper mounting plate  84 A and the upper portion  18 A of the tool  10  to transfer loads therebetween. Non-load bearing insulation  100  fills the spaces between the load bearing insulation members  104  of load-face insulation  96 A. 
     Similarly, load-face insulation  96 B is positioned between the lower portion  18 B of the tool  10  and the lower mounting plate  84 B. The load-face insulation  96 B includes a combination of load bearing insulation members  104  and non-load bearing insulation  100 . The load bearing insulation members  104  of load-face insulation  96 B are spaced from each other, and each of the members  104  of load-face insulation  96 B contacts the lower mounting plate  84 B and the lower portion  18 B of the tool  10  to transfer loads therebetween. Non-load bearing insulation  100  fills the spaces between the load bearing insulation members  104  of load-face insulation  96 B. 
     Those skilled in the art will recognize a variety of materials that may be used to form the load bearing insulation members  104 , such as high load bearing ceramics, high load bearing composites, INCONEL alloys, and various austenitic steels. In a preferred embodiment, the load bearing insulation members  104  are austenitic steel posts. The non-load bearing insulation is preferably a blanket insulation that is capable of withstanding the elevated temperature of the forming tool. Those skilled in the art will recognize a variety of materials that may be used to form the non-load bearing insulation  100  within the scope of the claimed invention. An exemplary blanket insulation is Cer-wool RT commercially available from Vesuvius, USA. The load-face insulation  96 A,  96 B isolates the high-temperature forming tool portions  18 A,  18 B from the mounting plates  84 A,  84 B to maintain a high temperature within the forming tool  10 , as well as to maintain a lower ambient temperature on the outside of the forming tool  10 . 
     The metal forming apparatus  8  also includes insulation surrounding its periphery. More specifically, insulating members  108 A-D are attached to the tool  10  to cover a respective vertical peripheral surface  110 A-D of the tool. 
     The apparatus  8  includes a plurality of fins  112  in conductive heat transfer relationship with the metal forming tool  10 . More specifically, each of the upper and lower portions  18 A,  18 B of the forming tool  10  has fins  112  operatively connected thereto and at least partially forming surfaces  110 A-D.  FIG. 2  schematically depicts surface  110 A of the upper portion  18 A of the tool  10 , and insulating member  108 A. It should be noted that the configurations of surface  110 A and member  108 A are representative of the configurations of surfaces  110 B-D and members  108 B-D, although the surfaces  110 B-D and members  108 B-D are differently dimensioned than surface  110 A and member  108 A. 
     Referring to  FIG. 2 , wherein like reference numbers refer to like components from  FIG. 1 , the cooling fins  112  in the embodiment depicted are vertically oriented, parallel with one another, and are spaced apart from one another to form a plurality of vertically oriented channels  116  therebetween. Those skilled in the art will recognize a variety of fin configurations that may be employed within the scope of the claimed invention. For example, although the fins  112  are depicted as having a rectangular cross section, other cross sectional fin shapes may be employed within the scope of the claimed invention, such as triangular, semicircular, sinusoidal, etc. Similarly, fins  112  may be characterized by various lengths, thicknesses, amount of protuberance, etc. Further, vertical orientation of the fins as shown may provide maximum natural convection, but other orientations may be used within the scope of the claimed invention. For example, any fin orientation will be effective, particularly with forced convection. 
     In the embodiment depicted, the fins  112  are formed in the tool portion  118 B as part of a one-piece member. However, within the scope of the claimed invention, the fins may be one or more separate pieces attached to the tool in conductive heat transfer relationship therewith, i.e., such that heat from the tool is conductable, through solid material, from the tool to the fins. It may, for example, be desirable for the fins to be comprised of a high-conductivity metal (e.g., a metal having conductivity higher than the material of the tool  10 ). The fins  112  depicted in  FIG. 2  are in conductive heat transfer relationship with tool portion  18 A. 
     Fastening elements  128 A are mounted with respect to the tool portion  18 A. Corresponding fastening elements  128 B are mounted with respect to the member  108 A. Each of the fastening elements  128 B is engageable with a respective one of fastening elements  128 A to secure the member  108 A to the tool portion  18 A, as shown in  FIGS. 1 and 2 . Those skilled in the art will recognize a variety of fastening elements that may be employed within the scope of the claimed invention, including slot and key arrangements, latches, threaded fasteners and holes, etc. 
     Member  108 A cooperates with the tool portion  18 A to enclose the fins  112  that are on surface  110 A. Referring to  FIG. 3 , wherein like reference numbers refer to like components from  FIGS. 1 and 2 , a seal  124  is mounted to the tool portion  18 A to circumscribe the plurality of fins  112  that are at surface  110 A. Referring again to  FIG. 2 , member  108 A contacts seal  124  so that the seal  124  cooperates with the member  108 A and the tool portion  18 A to enclose the fins  112  that are at surface  110 A. In the embodiment depicted, member  108 A cooperates with the seal  124  and the tool portion  18 A so that the fins  112  on surface  110 A are fully enclosed. 
     Referring to  FIGS. 1 and 2 , members  108 B-D likewise cooperate with respective seals  124  to fully enclose the fins  112  of surfaces  110 B-D, respectively. When the members  108 A-D are secured as shown to the tool portions  18 A,  18 B, the members  108 A-D act as restrictions to air flow across, i.e., to or from, the fins  112 , and a thermally efficient mode of tool operation is thereby achieved. By enclosing the fins  112 , members  108 A-D negate the effect of the fins  112  on the transfer of heat from the tool  10  to the surrounding environment. More specifically, in the thermally efficient mode of tool operation, the members  108 A-D obstruct air flow across, i.e., to or from, the fins  112 , thereby negating any increase in convective heat transfer that the fins  112  would provide if exposed to air currents. Furthermore, the members  108 A-D include an insulating material (shown at  136  in  FIG. 2 ) having a low thermal conductivity, preferably significantly lower than the thermal conductivity of the fins  112 , encased in a cover (shown at  132  in  FIG. 2 ), to reduce conductive heat transfer from the tool  10  to the surrounding environment. 
     After heating the tool  10  by the heating elements  80 , blanks  14  may be formed against surface  26 , as understood by those skilled in the art. After a predetermined operating time, or after a predetermined quantity of blanks being formed, it may be desirable to perform maintenance on the tool  10 . However, the tool  10  must first be cooled from its operating temperature prior to performing maintenance. A rapid tool cooling mode is achievable by detaching members  108 A-D from the tool  10 . 
     Fastening elements  128 A are selectively releasable from corresponding complimentary fastening elements  128 B so that members  108 A-D are detachable from the tool  10  to expose the fins  112 . Referring to  FIG. 3 , wherein like reference numbers refer to like components from  FIGS. 1 and 2 , surface  110 A of the upper portion  18 A of tool  10  is shown with member  108 A removed so that the fins  112  are exposed. Currents of air  140  may be produced naturally by convection when the members  108 A-D are removed: air  140  heated by the fins  112  rises, thereby drawing cooler air  140  to the fins  112 . Currents of air  140  may also be forced such as by a fan  142 . Increasing the surface area provided by the fins  112 , for example, by increasing the distance that the fins extend outward from the tool  10  or by increasing the quantity of fins, will result in shorter cooling times. In exemplary embodiments, the fins  112  provide two or three times the surface area where the fins  112  are present compared to a flat surface. It should be noted that, although the fan  142  is schematically depicted below the tool  10 , it is preferable to orient the fan  142  such that the air travels from the fan  142  to the fins  112  perpendicular to the orientation of the tool surface  110 A. 
       FIG. 4  schematically depicts an alternative tool configuration. Referring to  FIG. 4 , wherein like reference numbers refer to like components from  FIGS. 1-3 , tool  10 A defines a vertical peripheral surface  144  characterized by fins  112 . The fins  112  are spaced apart from one another to form channels  116  therebetween. The channels  116  are machined into the peripheral surface  144  to form the fins  112 . Thus, the fins  112  protrude from the base surface  146  of the channels  116 , but do not protrude from the original peripheral surface. Accordingly, insulating member  148  is not characterized by a cavity to accommodate the fins  112 . 
     Referring to  FIG. 5 , exemplary construction for an insulating member  150  is schematically depicted. The construction of member  150  may be representative of the construction of members  108 A-D of  FIG. 1  and member  148  of  FIG. 4 . Member  150  includes enclosures formed of stainless steel plates surrounding an inner core of non-load bearing insulation  136 . In a preferred embodiment, the enclosures include an inner cover  154 , surrounds  158 , and an outer cover  162 . The surrounds  158  include double flanges for enclosing the insulation  136 . Non-heat conductive separators  166 , such as woven glass tape, separate the surrounds  158  from the inner cover  154 . Again, the surrounds  158  are separated from the outer cover  162  by non-heat conductive separaters  166 . In this manner, the inner and outer covers are thermally isolated from the rest of the enclosure such that heat transfer between the various components is minimized. The covers  154  and  162 , in a preferred embodiment, are attached with machine screws  170  which are passed through slotted holes and attached to a nut  174  such that they allow for relative motion between the various components of the enclosure. 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.