Abstract:
A mechanical mechanism is disclosed for supplementing the action of a pressurized working gas in hot blow forming of a sheet material. Opposing complementary heated forming tools grip the sheet material and form a shaping surface on one side of the sheet and a gas pressure chamber on the other side. An internal complementary mechanical forming device is located inside the pressure chamber. The device is operated by an internal rotatable shaft supported through the chamber defining tool wall. The internal shaft is coupled outside the tool wall to an external shaft for external activation of the mechanical forming device. The external shaft and coupling are enclosed in a housing structure that provide a pressure seal, thrust support and thermal insulation for the external activation mechanism.

Description:
TECHNICAL FIELD 
     This invention pertains to hot blow forming a sheet material workpiece in a heated and gas pressurized chamber having a forming surface for the sheet. More specifically, this invention pertains to a machine having a activation mechanism external to the forming chamber for operating a mechanical sheet stretching device positioned in the chamber to complement the action of the gas pressure in shaping a product from the sheet material. 
     BACKGROUND OF THE INVENTION 
     In the automotive industry the hot blow forming of certain highly formable aluminum alloy sheet materials has been developed by the assignee of this invention for the forming of body panels and other parts of complex shape. In the case of superplastic AA5083 sheets, for example, such forming is often done between opposing heated tools that grip edges of a preheated sheet blank profile. One tool provides a forming surface on one side of the sheet material and the other tool provides a chamber on the other side of the sheet for application of a pressurized working gas to stretch the sheet against the forming surface. The pressurized gas, of course, applies a shaping force on the surface of the sheet. 
     It has been found in forming some product shapes that it would be useful to apply the force of a mechanical device to supplement the pressurized gas in stretching the sheet to shape the part. The mechanical device would be used inside the forming chamber but activated from outside the hot high pressure chamber during a stretch forming operation. In hot blow forming one to two millimeter thick AA5083 sheet material, for example, the temperature of the forming tools and sheet material is typically in the range of about 400° C. to 500° C. and air pressures of 100 to 200 psi and higher are employed. The outside mechanical actuator must be operatively connected with the internal forming device to seal against pressure and manage heat loss. It is an object of this invention to provide a mechanism or machine for such use in combination with heated and pressurized blow forming tools for sheet materials. 
     SUMMARY OF THE INVENTION 
     This invention provides a machine for the hot blow forming of a sheet material in which a pressurized working gas and a complementary mechanical device are used in stretching a heated sheet material into conformance with a forming surface. 
     In a hot blow forming operation, opposing, complementary forming tools are closed to grip edges of a sheet material workpiece. The forming environment is heated to a suitable stretch forming temperature for the sheet material taking into account its composition, thickness and ductility. One of the tools provides a forming surface on one side of the sheet. The opposing tool provides a chamber on the opposite side of the sheet for introduction of a pressurized working gas to stretch the heated sheet into conformance with the forming surface. As the working gas, for example air, is admitted into the pressure chamber, the pressure is gradually increased over a period of seconds or minutes to stretch the sheet against the product shape defining surface of the forming tool(s). The pressure increase at the forming temperature is scheduled and controlled to form the part rapidly but without damaging it. 
     Sometimes, it may be advantageous in the shape evolution of the sheet product to supplement the working gas pressure with a mechanical shaping or marking device. The mechanical device can be activated to push or mark the sheet before gas pressure is applied, during gas pressure application, or after the gas pressure has reached it maximum level. The mechanical device is located in the pressure chamber of the forming machine and brought into contact with the sheet material at an appropriate time in the forming cycle by an activation mechanism located outside the forming machine. Since the forming environment is heated and pressurized, activation of the mechanical device must be accomplished with minimal pressure and heat loss from the forming chamber. 
     In accordance with a preferred embodiment of the invention it is preferred that the forming tools be individually heated and their external walls covered with a suitable insulation material. The mechanical sheet forming device is made of a suitable heat resistant material and located in the pressure chamber defining tool. The forming device is activated by a rotatable shaft extending from within the pressure chamber through the wall of the chamber defining tool member. The internal end of this shaft is suitably connected to the forming device so that rotation of the shaft moves the device into contact with the sheet material for its forming contribution and then removes the device from contact with the sheet so that the sheet can be removed from the opened (separated) tools at the completion of stretch forming operation. The outer portion of the internal shaft is supported in a bushing in the wall of the chamber defining tool member, and its end is coupled with an end of a second rotatable shaft, external to the wall. Suitably the rotational axis of the external shaft is co-axial with the rotational axis of the internal shaft and both shafts are supported in a horizontal attitude. The coupling portion of the shafts and the support and pressure sealing of the external shaft is providing by a suitable housing architecture. 
     In accordance with a preferred embodiment, the coupling of the shafts is enclosed within a first housing attached to the tool wall. This first housing extends axially with respect to the coupled shafts through the thickness of the insulation on the tool wall and is suitably formed of a heat resistant, relatively low thermal conductivity metal. A second housing attached to the end of the first housing axially along the external shaft contains and provides thrust support for the external shaft against expulsion of the shaft by the pressurized gas in the forming chamber. A third housing attached to the second housing contains a gas seal to retain the working gas in the forming chamber. This third housing may also be provided with cooling fins for the external shaft. 
     Torque for rotation of the external shaft is suitably applied axially external to the housings. And means for fluid cooling of the external shaft may be provided at its external end. 
     The insulation of the forming tools and the structure of the housing members enable the external shaft to be rotated to operate the internal shaft and its connected mechanical shaping device without pressure loss and excessive thermal loss from the hot blow forming tools. Timely rotation of the external shaft during forming of the sheet material is accomplished using any suitable torque applying mechanism. For example, a hydraulic or pneumatic cylinder and connecting rod may be used to rotate the shaft. As another example, an electric motor can be controlled to rotate the shaft to activate the internal mechanical sheet material shaping device. These items and their controls are located outside of the aggressive high temperatures, high pressure forming environment for the sheet material. 
     Other objects and advantages of the invention will become more apparent from a detailed description of preferred embodiments with follow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front elevation view of heated, thermally insulated, and gas pressurized, upper and lower complementary, sheet metal hot blow forming tools, shown in cross section with both the inside-the-forming-chamber portion and the external activation portion of the mechanical former shown. 
         FIG. 2  is a fragmentary side view of the forming tools and side view of the external activation portion of an embodiment of the mechanical sheet forming mechanism of this invention. 
         FIG. 3  is a fragmentary side view of the forming tools, in cross-section, showing the forming movement of the inside-the-forming-chamber portion of the mechanical sheet forming mechanism. 
         FIG. 4  is a side view of the activation portion of the mechanical sheet forming mechanism. This view is enlarged for illustrating more detail of the mechanism as compared with FIG.  1  and in cross-section. 
         FIGS. 5A-5D  are oblique side views illustrating the functional motion of an alternative embodiment of the sheet metal forming portion of this invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The continued use of hot blow forming processes as applied to suitably formable aluminum sheet metal alloys for automotive vehicle body panels and the like has led to improvements in the functionalities and features of the forming tools. The developments started with relatively slow superplastic forming (SPF) practices with fine grain, magnesium containing, aluminum alloys considered as SPF materials and has led to faster forming practices called quick plastic forming (QPF) by the assignee of this invention. Double-action forming tools for preforming and final shape forming of a sheet metal workpiece on the same tool set have been developed. Also tools with internal heaters and insulated walls have been developed for the stretch forming of aluminum sheet metal alloys. Such self-heating technology has required well insulated tools, which in turn creates cool, ambient zones around the tool that can be utilized for placement of other auxiliary mechanisms. The double-action tool technology, especially in applications where the first-stage operation is of mechanical nature can utilize such auxiliary mechanisms. However, situations arise when the extra pre- or post-QPF operation is of such a minor scale that construction of a full-blown double-action tool is not warranted for technical reasons as well as for economic reasons. 
     In these cases, one may desire an externally actuated mechanism, which will carry out the desired mechanical forming operation. A key requirement of such a mechanism is that it has to be pressure-tight when installed into the QPF or other forming tool. The subject invention provides a mechanical device that enables mechanical forming before, during or after the main QPF operation while maintaining necessary pressure tightness. One example illustrated in this specification is a workpiece stuffing operation often used in combination with the hot blow process using pressurized air or other suitable working gas. In a typical stuffing operation the sheet metal workpiece is stretched into a concave cavity close to the shape forming tool surface with a mechanical roller. Then the pressurized working gas is used to finish the shape development of the sheet material by further stretching it into full conformance with the tool surface. 
       FIG. 1  illustrates a combination  10  of hot blow forming tools with an externally activated mechanical roller stuffer device for preforming the sheet material. Combination  10  includes an upper forming tool  12  and a lower forming tool  14 , both made of steel and shown in cross-section. Both forming tools  12 ,  14  are individually heated with internal electrical resistance heating rods, not shown. The operating temperatures of the tools may be separately controlled. In the case of the hot blow forming of AA5083 sheet material, forming tools  12 ,  14  will be heated to a controlled temperature in the range of about 400° C. to 500° C. 
     Upper forming tool  12  is covered on each of its side walls, two visible at  18  and  21  in  FIG. 1 , and top  20  with suitable thicknesses of insulation  16 . Upper forming tool  12  is attached to and supported by upper press platen  22 . Upper tool  12  also has a duct  24  for the admission and venting of a working gas. Duct  24  extends through insulation thickness  16  and upper platen  22 . Bottom edge  26  of side wall  18  and bottom edge  28  of side wall  20  of upper tool  12  press against the edges of sheet metal workpiece  30 , shown in cross-section in  FIG. 1  to secure them for the hot blow forming operation. 
     Lower forming tool  14  also has suitable thicknesses of insulation  16  on side walls  32  and bottom  34 . Lower tool  14  is supported on lower press platen  36 . Upper edges  38  of side walls  32  of lower forming tool  14  press against the edges of sheet metal workpiece  30 . Lower tool has a forming surface  40  that defines a concave cavity below a sheet material workpiece placed over lower tool  14  for forming. 
     Upper tool  12  and lower tool  14  have a spaced part open position for removal of a finished sheet material workpiece and for insertion of a new sheet metal blank. This position of forming tools  12  and  14  is not illustrated in FIG.  1 . In  FIG. 1  the tools are shown in their closed position gripping the edges of a sheet material workpiece  30  for forming into a product shape defined by forming surface  40 . Upper tool  12  defines a chamber  42  above sheet material  30  for a pressurized working gas to be admitted through duct  24 . In the practice of this invention, chamber  42  also contains a mechanical sheet material stuffing device  44 . 
     Stuffing device  44  comprises roller  46  carried on roller axle  48 . Axle  48  is carried on radial arms  50 ,  52  which are attached to internal rotatable shaft  54 . Radial arms are separated by spacer  56  in their connection to internal shaft  54 . 
     The operation of stuffing device  44  is illustrated by reference to  FIGS. 1-3 . In  FIG. 3 , stuffing device  44  is shown in its horizontal position (solid line) for removal of a shaped sheet material part and insertion of a new sheet material blank. When the blank is in place between upper  12  and lower  14  forming tools in their closed position, the stuffing device  44  is rotated by external pneumatic actuator  58  ( FIGS. 1 and 2 ) as will be described in more detail below. Stuffing device  44  is progressively moved from its horizontal position downwardly toward the sheet material blank gripped between the forming tools  12 ,  14 . Roller  46  is brought into rolling contact with the upper surface of sheet material  30  to deform it (i.e., stuff it) into the cavity formed between the sheet material and forming surface  40 . Thereafter, pressurized air is admitted into chamber  42  to complete the stretch forming of sheet material  30  against forming surface  40 . 
       FIG. 4  shows a section view of a preferred embodiment of an external actuating mechanism  60  for coupling with internal shaft  54  and rotating it and stuffing device  44  (not shown in  FIG. 4 ) in the mechanical stuffing portion of the forming operation.  FIG. 1  shows a frontal elevation of the activation mechanism  60  as it is mounted to upper press platen  22  and side wall  18  of upper forming tool  12 . 
     Wall  18  of upper forming tool  12  and chamber  42  is machined with a clearance hole  62  for internal shaft  54  (broken off in  FIG. 4 ) and counter-bored to accept a high temperature bushing  64 . A first, end flanged, cylindrical housing  66 , made of austenitic stainless steel to minimize heat flow, is bolted (bolts  68 ) through flange  70  to forming tool wall  18  and sealed with a high temperature gasket  72 . This first cylindrical housing  66  passes through insulation  16  and is attached (shown bolted) using another high temperature gasket  72  to a second, end flanged, cylindrical stainless steel housing  74 . Within first housing  66  the inner end  76  of external shaft  78  is coupled with a stainless steel tubular coupling  80  to the outer end  82  of inner shaft  54 . Inner shaft  54  is suitably made of high silicon stainless steel to prevent galling with the high temperature bushing. The inner shaft  54  may extend across pressure chamber  42  and be inserted in another bushing in wall  20  of the upper forming tool  12 . 
     A portion of external shaft  78  enclosed within second housing  74  has a circumferential flange  82  to prevent the shaft  78  from being pushed out of the housings. Flange  82  rotates with or against a cylindrical thrust bearing  84  that bears on reduced diameter shoulder  86  of fixed second housing  74 . 
     Second housing  74  is attached (shown bolted) using a third high temperature gasket  72  to an end flange on aluminum housing  88  that incorporates cooling fins  90  and contains a high temperature bronze sleeve bearing  92  as well as the pressure seal  94 . In this embodiment, pressure seal  94  comprises a series of Teflon “V” ring seals. But as an alternative embodiment several O-rings could be set in grooves in the circumference of external shaft  78  at this region of its length. A compression sleeve  96  is pushed by the compression nut  98  to affect the seal between external shaft  78  and the third housing, aluminum  88 . Locking mechanism  100  anchored to a cooling fin  90  prevents compression nut  98  from turning. 
     The external rotary shaft  78  is made of austenitic stainless steel and is drilled and tapped to form axial hole  112  at its outer end  102  to accept a stainless steel tube  104  and T fittings system  106 . Water is injected into end  108  of tube  104  through to axial hole  112  of the external shaft  78  and exhausted through the lower tube  110 . 
     External shaft  78  is suspended from upper press platen  22  by flanged hanger  114 . As seen in  FIGS. 1 and 2 , flanged hanger  114  is bolted to platen  22  and is also attached to housing member  74 . 
     In order to operate stuffer  44 , pneumatic actuator  58  is used to rotate external shaft  78 . Pneumatic actuator  58  comprises pneumatic cylinder  116  which is suspended from upper press platen  22  by U-shaped hanger bracket  118 . Pneumatic cylinder  116  contains a piston, not shown, which reciprocates in cylinder  116  in response to air pressure and moves piston rod  120 . Piston rod  120  moves lever arm  122  which is secured to and rotates external shaft  74 . Piston rod  120  and lever arm  122  are shown in a piston rod  120  withdrawn position (solid line) and piston rod  120  extended position (dashed line) in FIG.  2 . 
     The “stuffing” application illustrated in  FIG. 3  inside the pressurized upper tool  12  is used to mechanically assist the hot blow forming of sheet material  30 . Mechanical stuffing can be used to improve panel thinning in a particular area or to reduce a metal fold condition. 
       FIGS. 5A-5D  depict another application of a mechanical assist in a hot blow forming operation. In this embodiment, internal shaft  54  is used to obtain a mechanical action on sheet material  30  shown in fragmentary form. Rotation of internal shaft  54  effects a linear action on straight bar  200  and stamping die  202  attached at lower end  204  of bar  200 . Round upper end  206  of bar  200  is carried in bracket  208  attached to upper tool  12  (not shown). The round upper end  206  of bar  200  slides in a hole in bracket  208 . Cam  210  is fixed to the end of internal shaft  54  and cam  210  acts on cam follower  212  attached to a side of bar  200 . 
     During a rotation of shaft  54  and cam  210 , bar  200  is raised against high temperature coil spring  214 , FIG.  5 A. In this position die  202  is elevated above sheet material  30  as, for example, it is being formed by application of working gas pressure. Upon further rotation of cam  210 ,  FIG. 5B , coil spring is released and it forces rod  200  downwardly with die  202  contacting a previously formed portion of the sheet material  30 . In this example the die coins an emblem on the upper surface of the sheet material  30 . Progressive rotation of shaft  54  and cam  210  elevates rod  200  to reveal the QPF emblem  216  coined on the surface of the sheet material. 
     Thus, a mechanical forming action of this embodiment could be used to “coin” sharp features on the exterior of a part or provide a locating feature for post form operations. 
     The mechanical external activation and internal forming mechanism of this invention provides a complementary action in the hot blow forming of a sheet material. The mechanism is capable of many different mechanical forming applications for assisting the forming action of the working gas in the complementary forming tools. While the invention has been illustrated in terms a few representative embodiments it is apparent that other forms could readily be adapted by one skilled in the art. And the invention is intended to be limited only by the scope of the following claims.