Abstract:
A hydroforming apparatus for hydroforming a workpiece. The apparatus includes a die in which a die cavity is located, and an outer ring subassembly. The outer ring subassembly is movable relative to the die, and includes a ring and one or more first cam segments attached thereto. The outer ring subassembly also includes one or more second cam segments and one or more tapered wedges positioned between the first and second cam segments. The tapered wedge is movable between an extended position, in which the second cam segment is pushed to an open position in which the second cam segment is engageable with the outer surfaces when the subassembly is proximal to the die, and a retracted position, in which the second cam segment is moved to a closed position by a biasing means. The second cam segment includes a lower surface shaped to engage outer surfaces.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/715,581, filed Sep. 12, 2005. 

   FIELD OF THE INVENTION 
   This invention is related to a hydroforming apparatus for hydroforming a workpiece. 
   BACKGROUND OF THE INVENTION 
   Many parts such as the ones used in automotive structures are manufactured using a hydroforming process. The hydroforming process requires large presses up to 5,000 tons to hold the hydroforming die close during the hydroforming process. These presses are large, expensive, require large amounts of energy to operate and require special and expensive installations, yet the work is done using the hydroforming pressure not the press forces. In an effort to reduce the automotive vehicle weight, high strength steel is being used, which means larger hydroforming presses are required. 
   Processes such as hydroforming process requires large presses to clamp the die in place while forming is done by other means such as applying internal pressure to form the part. 
   As shown in  FIGS. 2   a  and  2   b , the hydroforming technique according to the prior art includes providing a die  10  having a lower portion  12  and an upper portion  14  which combine to define a die cavity  16 . The upper portion  14  is moved generally downward into a closed position forming a die cavity  16  over a round tube  22 . Side plugs  18  and  20  are then moved sideways to engage the tube  22 , to seal both ends of tube  22 , and a hydraulic pressure source is connected to the interior of tube  22  through an opening  24  inside plugs  18  and  20 , thereby expanding tube  22  until it conforms to the shape of the die cavity  16 . 
   The force F required to keep the die  10  closed varies according to the size of the tube  22  and typically is in the magnitude of thousands of tons. In order to supply the force F a large press is used to keep the die  10  closed. For example, the press typically provides a force F of 5,000 tons or more. With reference to  FIG. 3 , the prior art press is relatively large and expensive. The prior art press often is mounted to a subsurface structure, which is relatively expensive. 
   SUMMARY OF THE INVENTION 
   In its broad aspect, the invention provides a hydroforming apparatus for hydroforming a workpiece. The apparatus includes a die and an outer ring subassembly. The die includes a lower die section mounted in a lower die holder and an upper die section mounted in an upper die holder. One of the upper and lower die holders is movable relative to the other between an open position, in which the workpiece is positionable between the upper and lower die holders, and a closed position, in which the lower and upper die sections combine to define a die cavity therebetween in which the workpiece is hydroformed. In addition, each of the upper and lower die holders has an outer surface respectively. The outer ring subassembly includes a ring and one or more first cam segments attached to an inner surface of the ring. The outer ring subassembly also includes one or more second cam segments and one or more tapered wedges positioned between the first and second cam segments. The second cam segment is movable between an open position, in which the second cam segment is positioned distal to the first cam segment, and a closed position, in which the second cam segment is disposed proximal to the first cam segment. The outer ring subassembly also includes one or more biasing means for biasing the second cam segment to the closed position. The tapered wedge is movable between an extended position, in which the second cam segment is pushed by the tapered wedge to the open position, and a retracted position, in which the second cam segment is moved to the closed position by the biasing means. Also, the second cam segment includes a lower surface shaped to engage the outer surface of the upper and lower die holders. In addition, the outer ring subassembly is movable between a forward position, in which the lower surface of the second cam segment engages the outer surface upon the tapered wedge moving to the extended position, and return position, in which the lower surface is disengaged from the outer surface of the upper and lower die holders. 
   In another aspect, the outer surfaces of the upper and lower die holders cooperate to form a cylindrical shape when the upper and lower die holders are combined. 
   In another of its aspects, the hydroforming apparatus additionally includes one or more hydraulic cylinders for moving the tapered wedge between the retracted position and the extended position. 
   In yet another aspect, the hydraulic cylinder exerts a first force directed in a first direction on the tapered wedge to move the tapered wedge to the extended position. 
   In another aspect, the tapered wedge includes a substantially planar contact surface and the second cam segment includes a substantially planar mating surface. Upon movement of the tapered wedge to the extended position, the contact surface and the mating surface engage each other substantially on a contact plane. The contact plane defines an acute angle between the contact plane and the first direction so that, upon movement of the tapered wedge to the extended position, a second force is transmitted which is directed toward the outer surface, to assist in holding the upper and lower die holders together during hydroforming. 
   In yet another aspect, the outer ring subassembly is movable along guide rods between a forward position and a returned position. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings wherein: 
       FIG. 1  is a sectional view of a hydroforming apparatus according to the invention showing an outer ring over a die holder; 
       FIG. 2   a  is a sectional view of a hydroforming apparatus of the prior art showing a prior art hydroforming die in an open position, drawn at a larger scale; 
       FIG. 2   b  is a sectional view of the prior art hydroforming apparatus of  FIG. 2   a  showing the hydroforming die thereof in a closed position; 
       FIG. 3  is a sectional view of the prior art hydroforming apparatus of  FIGS. 2   a  and  2   b  showing the hydroforming die in a hydroforming press, drawn at a smaller scale; 
       FIG. 4   a  is a sectional view of the hydroforming apparatus according to the invention without the outer ring showing the hydroforming die in the open position, drawn at a larger scale; 
       FIG. 4   b  is another sectional view of the hydroforming apparatus of  FIG. 4   a;    
       FIG. 5   a  is a sectional view of the hydroforming apparatus according to the invention without the outer ring showing the hydroforming die in the closed position; 
       FIG. 5   b  is another sectional view of the hydroforming apparatus of  FIG. 5   a;    
       FIG. 6   a  is a sectional view of an embodiment of the outer ring of the invention with tapered wedges thereof each in a retracted position and lower cam segments each in an open position; 
       FIG. 6   b  is a sectional view showing an upper tapered wedge and cam segment, drawn at a larger scale; 
       FIG. 6   c  is a sectional view of the tapered wedge, drawn at a larger scale; 
       FIG. 6   d  is a sectional view of the lower cam segment, drawn at a smaller scale; 
       FIG. 7   a  is a sectional view of the outer ring of  FIG. 6   a  with tapered wedges thereof each in an extended position and lower cam segments each in a closed position; 
       FIG. 7   b  is a sectional view showing an upper tapered wedge and cam segment, drawn at a larger scale; 
       FIG. 8   a  is a cross sectional view of the outer ring of  FIG. 6   a , drawn at a smaller scale; 
       FIG. 8   b  is a cross-sectional view of a portion of the outer ring of  FIG. 8   a , drawn at a larger scale; 
       FIG. 9   a  is a sectional view of the outer ring of  FIG. 6   a  showing guide rods and bushings; 
       FIG. 9   b  is a sectional view of the outer ring of  FIG. 6   a , drawn at a smaller scale; 
       FIG. 10  is a sectional view of the die and die holder and outer ring of  FIG. 6   a  with the die closed and the outer ring in the returned position, drawn at a smaller scale; 
       FIG. 11  is a sectional view showing the outer ring of  FIG. 6   a  in the forward position; 
       FIG. 12  is a sectional view showing the outer ring in the returned position and the die holder in the open position after hydroforming is complete; 
       FIG. 13   a  is a plan view of two rings which are included in an embodiment of the outer ring of the invention, drawn at a smaller scale; 
       FIG. 13   b  is a plan view of a portion of the rings of  FIG. 13   a , drawn at a larger scale; 
       FIG. 14  is a sectional view of an alternative embodiment of a tapered wedge, drawn at a larger scale; 
       FIG. 15   a  is a sectional view of an alternative embodiment of the outer ring of the invention including two sets of tapered wedges and cylinders and upper and lower cams associated therewith, drawn at a smaller scale; 
       FIG. 15   b  is a sectional view of a set of the tapered wedges and cylinders of  FIG. 15   a , drawn at a larger scale; 
       FIG. 16  is a sectional view of an embodiment of a hydroforming apparatus according to the invention with two outer rings, drawn at a smaller scale; 
       FIG. 17  is a sectional view of an alternative embodiment of a hydroforming apparatus according to the invention in which a diaphragm filled with hydraulic pressure is employed to keep the die closed; 
       FIG. 18   a  shows an alternative embodiment of the invention, including a double tapered wedge and lower cam segment; and 
       FIG. 18   b  is a sectional view of an upper tapered wedge and cam segment of the invention illustrated in  FIG. 18   a.    
   

   DETAILED DESCRIPTION 
   As shown in  FIGS. 1 ,  4   a ,  4   b ,  5   a , and  5   b , in one embodiment, the hydroforming apparatus  108  according to the current invention includes a die  110  having a lower die section  112  and an upper die section  114 . The lower and upper die sections  112 ,  114  preferably combine to define a die cavity  116 . The lower die section  112  is mounted in a lower die holder  126  and the upper die section  114  is mounted in an upper die holder  128 . The lower die  112  and the lower die holder  126  preferably are fixed and the upper die  114  and the upper die holder  128  are movable up and down between an open position (as shown in  FIGS. 4   a  and  4   b ) and a closed position (as shown in  FIGS. 5   a  and  5   b ). 
   The upper die holder  128  is guided to and from the lower die holder  126  by using guide rods  125  and guide bushings  130  or by any other means that are obvious to those who are skilled in the art. Furthermore, the upper die holder  128  is moved up and down using a hydraulic cylinder  132  mounted to a frame  134  or by any other suitable means as would be known by those skilled in the art. 
   Furthermore an outer surface  127  of the lower die holder  126  is provided with a half-cylindrical shape and an outer surface  129  of the upper die holder  128  is provided with a half-cylindrical shape so that when the upper die holder  128  is moved to the closed position, the outer surface  127  of the lower die holder  126  and the outer surface  129  of the upper die holder  128  combine to form a cylindrical shape ( FIGS. 5   a ,  5   b ). 
   As can be seen in  FIGS. 6   a ,  6   b ,  6   c ,  6   d ,  7   a ,  7   b ,  8   a , and  8   b , the current invention includes an outer ring subassembly  136  including a ring  138 , a first cam segment  140 , a tapered wedge  142 , and a second cam segment  144 . The first cam segment  140  is attached to an inner surface  139  of the ring  138  and the second cam segment  144  is attached to the ring  138  using bolts  58  and springs  60  ( FIG. 8 ). The second cam segment  144  is allowed to travel in the directions of arrows R 1 , R 2  ( FIGS. 6   b ,  7   b ) between an open position ( FIGS. 6   a ,  6   b ) and a closed position ( FIGS. 7   a ,  7   b ). 
   The tapered wedge  142  is placed between the first cam segment  140  and the second cam segment  144  and is moved by a cylinder  148 . The tapered wedge  142  is allowed to move in the directions of arrows X 1 , X 2  ( FIGS. 6   b ,  7   b ) between a retracted position ( FIGS. 6   a ,  6   b ) and an extended position ( FIGS. 7   a ,  7   b ). The cylinder  148  is attached to the ring  138  by a mounting bracket  150 . Each tapered wedge  142  has a substantially planar surface  143 . 
   A contact surface  152  of the tapered wedge  142  is positioned at a small angle  153  relative to a plane (“P” in  FIG. 6   c ) parallel to the planar surface  143  that is less than 45 degrees. Also, the second cam segment  144  has a substantially planar surface  145 . A mating surface  154  of the second cam segment  144  is positioned at a small angle  155  relative to a plane (“Q” in  FIG. 6   d ) parallel to the mating surface  154 . Preferably, the angle  155  is the same as the small angle  153  (as illustrated in  FIG. 6   c ) so that when the tapered wedge  142  is in the retracted position, the second cam segment  140  is moved by the spring  160  ( FIG. 8   b ) to the open position as shown in  FIG. 6   b . Also, as the tapered wedge  142  is moved to the extended position, the second cam segment  140  is moved to the closed position as shown in  FIGS. 7   a , and  7   b.    
   The cylinder  148  exerts force F 1  on the said tapered wedge  142  ( FIG. 7   b ). The contact surface  152  of the tapered wedge  142  is in contact with the mating surface  154  of the second cam segment  144  so that the force F 1  that is exerted on the tapered wedge  142  results in a force F 2  that is exerted on the second cam segment  144  in a direction perpendicular to the said force F 1  ( FIG. 7   b ). Because the angles  153  and  155  are each less than 45 degrees, the force F 2  is greater than the force F 1 . In practice and according to this invention, the angles  153  and  154  provide a slope having a ratio between 5:1 to 20:1 (i.e., relative to the planar surfaces  143 ,  145  respectively) so that the force F 2  is greater than the said force F 1  by a ratio of between about 5 times and about 20 times respectively. 
   With reference to  FIG. 8   b , a lower surface  156  of the second cam segment  144  is curved with the same cylindrical radius as the outer surfaces  127  and  129  of the lower die holder  126  and the upper die holder  128 . 
   With reference to  FIG. 8   b , the first cam segment  140 , the tapered wedge  142 , and the second cam segment  144  preferably are equal in number to each other.  FIG. 8   a  shows 24 first cam segments  140 , the tapered wedges  142 , and second cam segments  144 . 
   With reference to  FIGS. 9   a  and  9   b , the outer ring subassembly  136  is guided by guide rods  162  and guide bushings  164  so that the outer ring subassembly  136  can be moved horizontally between a forward position ( FIGS. 1 ,  11 ) and a returned position ( FIG. 10 ). The movement of the outer ring subsequently  136  can be by a cylinder or a motor and gear and rack or any other suitable means as is known by those who are skilled in the art. The means of guiding the outer ring subassembly  136  can be as described using the guide rods  162  and the guide bushings  164  or by any other suitable means. 
     FIG. 10  shows the upper die holder  128  and the upper die section  114  in the closed position, with the tube  22  in the cavity  116 . The side plugs  18  and  20  are positioned to seal both ends of the tube  22 . The outer ring subassembly  136  is in the returned position and the tapered wedges  142  are in the retracted position ( FIG. 10 ) allowing the second cam segments  144  to move to the open position ( FIG. 10 ). The outer ring subassembly  136  is moved horizontally to the forward position ( FIGS. 1 ,  11 ) so that the lower die holder  126  and the upper die holder  128  are contained inside the second cam segments  144 . Next, the cylinders  148  are extended, moving the tapered wedges  142  to the extended position and the second cam segments  144  to the closed position. The curved lower surfaces  156  of the lower cam segments  144  contact the curved outer surface  127  of the lower die holder  126  and the curved outer surface  129  of the upper die holder  128 . The cylinders  148  exert the force F 1  ( FIG. 7   b ) on the tapered wedges  142  and the tapered wedges  142  consequently exert the force F 2  ( FIG. 7   b ) on the second cam segments  144 . Since the second cam segments  144  are in contact with the lower die holder  126  and the upper die holder  128 , the force F 2  is transmitted to the lower and upper die holders  126  and  128 . The force F 2  keeps the lower and upper die holders  126  and  128  closed and keeps the lower die section  112  and the upper die section  114  closed during the hydroforming operation. 
   Next, a hydraulic pressure source (not shown) is connected to the interior of the tube  22  through the opening  124  inside the plugs  118  and  120  to provide fluid under pressure which expands the tube  22  until the tube  22  conforms to the shape of the die cavity  116 , as is known in the art. Then, the hydraulic pressure source is disconnected and the cylinders  148  are retracted, moving the tapered wedges  142  to the retracted position and the second cam segments  144  to the open position ( FIGS. 6   a ,  6   b ). This allows the outer ring subassembly  136  to move horizontally to the returned position ( FIG. 10 ). After the outer ring subassembly  136  has been moved to the returned position, the upper die holder  128  and the upper die segment  114  are moved to the open position, allowing the removal of the tube  22  as illustrated in  FIG. 12 . 
   Since the force F 2  is greater than the force F 1 , the force require to keep the die  110  closed during the hydroforming operation of the invention is smaller than would be needed in a prior art hydroforming apparatus. 
   Also, since the force F 2  required to keep the die  110  closed is contained within the outer ring subassembly  138  (which has a cylindrical shape, known to be efficient in load carrying), the structure of the apparatus of the invention is smaller and lighter than that of the prior art. 
   Additional embodiments of the invention are shown in  FIGS. 13   a ,  13   b ,  14 ,  15   a ,  15   b ,  16 ,  17 ,  18   a , and  18   b . In  FIGS. 13   a ,  13   b ,  14 ,  15   a ,  15   b ,  16 ,  17 ,  18   a , and  18   b , elements are numbered so as to correspond to like elements shown in  FIGS. 1 ,  4   a ,  4   b ,  5   a ,  5   b ,  6   a ,  6   b ,  6   c ,  6   d ,  7   a ,  7   b ,  8   a ,  8   b ,  9   a ,  9   b ,  10 ,  11 , and  12 . 
   As shown in  FIGS. 18   a  and  18   b , in another embodiment of the invention, the bolts  158  and the springs  160  (i.e., such bolts and springs shown in  FIG. 8   b  being included in the hydroforming apparatus  108 ) are replaced by a double tapered wedge  278  (instead of the tapered wedge  42 ) and double tapered lower cam segment  282  (instead of the lower cam segment  44 ) or any other suitable means so that the second taper  280  is used to move the lower cam segments  282  to the open position. 
   In another embodiment of the invention, an outer ring subassembly  336  includes a ring  338  which is made of two or more rings  368  and  370 , as illustrated in  FIGS. 13   a  and  13   b . Preferably, the outer ring  368  is pressed over the inner ring  370  so that the outer ring  368  is exerting pressure F 3  over the outer surface of the inner ring  370 , and the outer ring  368  is under tension forces F 4  while the inner ring  370  is under compression forces F 5 . The amount of the pressure F 3  is such that the compression force F 5  in the inner ring  370  is greater than the force F 2  required to keep the die  10  closed during the hydroforming operation such that no expansion in the ring  338  occurs as a result of the hydroforming operation. Also, the energy required to keep the die  10  closed during the hydroforming operation is kept to a minimum. 
   As shown in  FIG. 14 , in another embodiment of the invention, a tapered wedge  442  is made of one tapered ring  443  and moved by one cylinder  474 . In this embodiment, the tapered lower surface  452  of the tapered ring  443  is cylindrical in shape and the upper tapered surface  454  of the lower cam segment  444  is also cylindrical to match the tapered and cylindrical surface  452 . Similarly an outer surface  472  of the tapered ring  443  is cylindrical and matches the inner surface  439  of the outer cam segments  440 . 
     FIGS. 15   a  and  15   b  disclose another embodiment of the invention. In this embodiment, the outer ring  538  provides the tapered wedges  542  and the upper cam segments  540  and the lower cam segments  544  and the cylinders  548  and the brackets  550  from both sides of the die, as illustrated. 
   In another alternative embodiment of the invention it is preferred that two of the outer rings  636  (one from either side of the upper and lower die holders  626  and  628  as illustrated in  FIG. 16 ) are provided so that the travel of the outer ring  636  between the forward and return positions is kept to a minimum. 
   In another embodiment of the invention a diaphragm  776  is used instead of the tapered wedges, the cylinders, and the upper and lower cam segments ( FIG. 17 ). The diaphragm  776  is filled with hydraulic fluid and hydraulic pressure is added inside the diaphragm  776  such that the diaphragm  776  will exert force on the upper and lower die holders  726  and  728  so that the die  10  is kept in the closed position during the hydroforming operation. 
   The movement of the outer ring horizontally between the open and closed positions can be vertically between an upper and lower position and the die holders  728  and  726  and the die  10  are mounted vertically. 
   The invention describes a fixed lower die holder  26  and lower die  12  and a movable die upper holder  28  and upper die  14 . Both the upper and lower die holders  26  and  28  and the upper and lower dies  12  and  14  can be movable or the upper die holder  28  and the upper die  14  are fixed while the lower die holder  26  and the lower die  12  are movable. 
   The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of this invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.