Patent Publication Number: US-8534107-B2

Title: Method and apparatus for pulsed forming, punching and trimming of tubular members

Description:
TECHNICAL FIELD 
     This disclosure relates to a method and apparatus in which pressurized fluid are used to hydro-form, pierce or trim tubular blanks. 
     BACKGROUND 
     Tubular blanks are formed in production processes with pressure pulses that apply static pressure through a fluid in a hydro-forming process. Hydro-forming operations are generally limited to tubes that have a uniform perimeter and are limited to applications that have no corners with small radii. The use of static pressure through a fluid to pierce tubes is difficult because static pressure inside the tube immediately drops after the first hole (or even some portion of the hole) is pierced. Reduction of the static pressure results in partial separation of the offal being pierced. The use of static pressure through a fluid to trim a tube is not a recognized manufacturing process. 
     Pulsed forming of tubular blanks is known in prior art in the form of:
         1) explosive forming, where the explosive is detonated inside the tubular blank;   2) electromagnetic forming, where a conductive insulated coil is positioned inside the tubular blank;   3) electro-hydraulic forming, where electrodes, for example in U.S. Pat. No. 3,566,648, or a disposable wire, for example in U.S. Pat. No. 3,603,127, are positioned inside the tubular blank.       

     In the majority of pulsed forming operations, the ratio of tube&#39;s diameter to its length is relatively large. In other words, the tube is relatively short. One exception to this is disclosed in Applicant&#39;s patent application entitled “Method and Tool for Expanding Tubular Members by Electro-hydraulic Forming” S. Golovashchenko, J. Bonnen U.S. patent application Ser. No. 12/563,191. 
     Generally, in pulsed forming operations the tube is formed in a single pulsed forming operation. Corner filling, hole piercing and trimming of tubes require different levels of pressure to be applied and cannot be performed in a single pulsed operation. If the level of pressure for piercing or trimming is lower than the level of pressure for corner filling, piercing or trimming, then piercing will occur first, and a corner filling operation will become impossible. 
     SUMMARY 
     A method of forming a tubular part is disclosed that comprises loading a tubular preform having a first and a second open ends into a hydroforming die and filling the tubular preform with a fluid. A first and second source of pulsed pressure are positioned near the first and second open ends of the tubular preform. The first and second sources of pulsed pressure are actuated to modify the tubular preform. 
     According to other aspects of the method, the actuating step may be performed in a first instance to hydro-form the tubular member into tight corners of the hydro-forming die. The actuating step may be performed a second time to punch a hole in the tubular member. The actuating step may then be performed a third time to trim the ends of the tubular member. Alternatively, the actuating step may be performed a second time to trim the ends of the tubular member. 
     The sources of pulsed pressure may be a pair of electro-hydraulic electrodes. Alternatively, the sources of pulsed pressure may be at least one pair of fluid accumulators. The sources of pulsed pressure may be a plurality of pairs of fluid accumulators. 
     According to another aspect of the disclosure, a pulsed pressure forming tool is provided for forming a part. A hydroforming die is provided that includes an upper die and a lower die that receive a tubular preform that has a first end and a second end. At least one pair of pulse generators are also provided with a first one of the pulse generators being disposed adjacent a first end of the tubular member and a second one of the pulse generators being disposed adjacent the second end of the tubular member. An actuator actuates each pair of the pulse generators in a predetermined order. 
     According to other aspects of the disclosure as it relates to the pulsed pressure forming tool, the pair of pulse generators may be actuated simultaneously. The pulsed pressure forming tool may comprise a pair of pulse generators that each comprise an electrode of an electro-hydraulic forming tool. The pulsed pressure forming tool may include electrodes that are discharged repeatedly in a sequence to perform a plurality of operations including forming and cutting the part. 
     Alternatively, the pulsed pressure forming tool may include at least one pair of pulse generators that comprise fluid pressure accumulators of a hydroforming tool. As a further alternative, the pulsed pressure forming tool may include a plurality of pairs of hydraulic accumulators that are sequentially discharged in pairs to perform a plurality of operations including forming and cutting the part. 
     The pulsed pressure forming tool may further comprise a die insert that defines an opening in the hydro-forming die that receives a filler plug. The filler plug is selectively moved between a flush position in which the filler plug backs up a wall of the preform and a retracted position in which the filler plug exposes a piercing edge about the opening in the die insert. Actuation of the pulse generator when the piercing edge is exposed to cause the wall of the preform to be pierced at the piercing edge. 
     The pulsed pressure forming tool may further comprise a collar that defines a ring around an end of the preform. The collar includes a static ring and a movable split ring that is shifted radially outwardly relative to the static ring to expose the preform to an annular trimming edge of the static ring. The split ring is shifted between a flush position in which the split ring backs up a portion of the wall of the preform and a radially outboard position. Actuation of the pulse generator causes when the annular trimming edge is exposed to cause the wall of the preform to be cut against the trimming edge. 
     According to another aspect of the disclosure, a pulsed pressure forming tool is provided for forming a part. The tool comprises a hydroforming die that includes an upper die and a lower die that receive a tubular preform that has a first end and a second end. A first pair of pulse generators includes a first one of the first pair of pulse generators being disposed adjacent a first end of the tubular member and a second one of the first pair of pulse generators being disposed adjacent the second end of the tubular member. A second pair of pulse generators includes a first one of the second pair of pulse generators being disposed adjacent a first end of the tubular member and a second one of the second pair of pulse generators being disposed adjacent the second end of the tubular member. A third pair of pulse generators includes a first one of the third pair of pulse generators being disposed adjacent a first end of the tubular member and a second one of the third pair of pulse generators being disposed adjacent the second end of the tubular member. The first pair of the pulse generators are actuated to form the tubular member against the hydro-forming die. A die insert defines an opening in the hydro-forming die that receives a filler plug. The filler plug is selectively moved between a flush position in which the filler plug backs up a wall of the preform and a retracted position in which the filler plug exposes a piercing edge about the opening. The actuator actuates the second pair of pulse generators to cause the wall of the preform to be pierced at the piercing edge. A collar defines a ring around an end of the preform, the collar includes a static ring and a movable split ring that is shifted radially outwardly relative to the static ring to expose the preform to an annular trimming edge of the static ring. The split ring is shifted between a flush position in which the split ring backs up a portion of the wall of the preform and a radially outboard position. The actuator actuates the third pair of pulse generators when the annular trimming edge is exposed to cause the wall of the preform to be cut against the trimming edge. The pulse generators are preferably accumulators. 
     Alternatively, a pulsed pressure forming tool for forming a part is disclosed that includes a hydroforming die that includes an upper die and a lower die that receive a tubular preform that has a first end and a second end. A pair of pulse generators are provided with a first one of the pair of pulse generators being disposed adjacent a first end of the tubular member and a second one of the first pair of pulse generators being disposed adjacent the second end of the tubular member. The pair of pulse generators are initially actuated to form the tubular member against the hydro-forming die. A die insert defines an opening in the hydro-forming die that receives a filler plug that is selectively moved between a flush position in which the filler plug backs up a wall of the preform and a retracted position in which the filler plug exposes a piercing edge about the opening. The actuator actuates the pair of pulse generators to cause the wall of the preform to be pierced at the piercing edge. A collar defines a ring around an end of the preform and has a static ring and a movable split ring that is shifted radially outwardly relative to the static ring to expose the preform to an annular trimming edge of the static ring. The split ring is shifted between a flush position in which the split ring backs up a portion of the wall of the preform and a radially outboard position in which actuation of the actuator actuates the pair of pulse generators to cause the wall of the preform to be cut against the trimming edge. The pulse generators are preferably electro-hydraulic chambers with electrodes that are connected to a high voltage power supply. 
     Multiple pulse forming, punching and trimming processes are disclosed in which different sequences of operations are possible with a dynamic hydro-forming tool. For example, piercing of holes or trimming can be postponed by introducing moveable punches which support material in the areas of trimming or hole piercing. A plurality of different sources of pulsed pressure can be used with the hydro-forming tool. The pulses may be created sequentially with electrohydraulic discharges in the chambers that are focused inside the tube. Alternatively, a plurality of pressure accumulators may be provided that provide high pressure liquid pulses to the tube that are pumped into the accumulators when the part is loaded and unload from the tool. 
     The above aspects and other aspects of the disclosure will be apparent 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 plan view of an electrohydraulic forming tool; 
         FIG. 2  is a diagrammatic cross-sectional view of the electrohydraulic forming tool taken along the line  2 - 2  in  FIG. 1 ; 
         FIG. 3  is a diagrammatic cross-sectional plan view of a hydro-forming tool including a pair of hydraulic pressure accumulators disposed adjacent to opposite ends of a tubular pre-form in a hydro-forming die; 
         FIG. 4  is a cross-sectional view taken along the line  4 - 4  in  FIG. 3 ; 
         FIG. 5  is a diagrammatic cross-sectional view of a hydro-forming tool having three pairs of accumulators in fluid flow communication with a tubular pre-form disposed in a hydro-forming die to form, pierce and trim the pre-form; 
         FIG. 6  is a fragmentary cross-sectional view of the trimming and piercing attachments shown in part of a hydro-forming die; and 
         FIG. 7  is a diagrammatic view showing the trimming and punching components adjacent to a tubular pre-form with the other parts of the hydro-forming die not shown. 
     
    
    
     DETAILED DESCRIPTION 
     A detailed description of the illustrated embodiments of the present invention is provided below. The disclosed embodiments are examples of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale. Some features may be exaggerated or minimized to show details of particular components. The specific structural and functional details disclosed in this application are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art how to practice the invention. 
     Referring to  FIG. 1 , a hydro-forming tool  10  is shown with a tubular pre-form  12  disposed in a die cavity  16  defined in the hydro-forming tool  10 . A first electrohydraulic forming (EHF) electrode  18  and a second EHF electrode  20  are disposed at a first end  22  and second end  24  of the tubular pre-form  12 . 
     Referring to  FIG. 2 , the hydro-forming tool  10  is shown to include an upper die  28  and a lower die  30  that are opened and closed to load and unload the tubular pre-form  12 . The first and second EHF electrodes  18  and  20  are also shown to include an energized electrode  32  and a grounded electrode  34 . When a stored charge is provided to the energized electrodes  32  at the desired voltage level, electricity arcs to the grounded electrodes to create pressure pulses within the fluid  36 . The pressure pulses in the fluid are used to form or otherwise act upon the tubular pre-form  12 . 
     Referring to  FIG. 3 , a hydro-forming tool is generally indicated by reference numeral  40 . A tubular pre-form  42  is disposed in the die cavity  44  defined within the hydro-forming tool  40 . A pair of accumulators  46  are provided on opposite ends of the pre-form  42 . A rupturable membrane  48  separates the accumulators  46  from the tubular pre-form  42  until a desired level of pressure is developed within the accumulators  46 . A pump  50  pumps fluid  52  into the accumulators  46  and also may be used to pump fluid  52  into the tubular pre-form  42 . 
     Referring to  FIG. 4 , the hydro-forming tool  40  shown in  FIG. 3  is shown in a side cross-sectional view. The tubular pre-form  42  is shown disposed in the die cavity  44 . An accumulator  46  having a rupturable membrane  48  is disposed at one end of the tubular pre-form  42 . The pump  50  pumps fluid  52  into the accumulators and also into the tubular pre-form  42 . When pressure within the accumulator  46  exceeds a predetermined level, the rupturable membrane  48  breaks to provide a pressure pulse that is applied to the tubular pre-form  42  to form the pre-form into a shape of the die cavity  44  that may include corners having small radii. 
     Referring to  FIG. 5 , a multiple discharge hydro-forming tool  56  is schematically illustrated. A single tubular pre-form  58  is provided in the die cavity  60  defined by the hydro-forming tool  56 . Six accumulators  64   a - f  are shown to include a rupturable membrane  66   a - f  The rupturable membranes may be calibrated to rupture at different pressure levels within the accumulators  64   a - f . Six different pumps  50  are schematically illustrated to be in fluid flow communication with the accumulators  64   a - f . A manifold  68  allows for fluid flow communication between each of the accumulators  64   a - f  and the interior of the tubular pre-form  58  within the die cavity  60 . Fluid  70  fills the pre-form and the manifold  68  and is also provided to each of the accumulators  64   a - f  The accumulators are charged by high displacement pumps  50  that are capable of restoring pressure within the accumulators within a stamping cycle. In order to deliver several pulses following one another sequentially, several accumulators, as shown, are provided with liquid that is compressed to a high pressure. The paired accumulators may release liquid simultaneously from both ends to perform designated operations. 
     In the embodiment shown in  FIG. 5  that includes three pairs of accumulators, one pair of accumulators may be used for corner filling in the tubular member, while a second pair of accumulators may be used for piercing, and a third pair of accumulators may be used to trim the tubular pre-form. A desired sequence of pressure pulses can be followed with pressure being applied by calibrating the ruptured membranes  66   a - f  to rupture at a designated pressure level. Check valves  72  may be used if a higher level of pressure is applied before a lower level of pressure. The sequence of forming/piercing/trimming is controlled by selectively exposing cutting edges for piercing and trimming operations in conjunction with the timing of the pressure pulses. 
     Referring to  FIGS. 5-7 , a plurality of die inserts  74  may be provided that operate in conjunction with a filler plug  76  to perform a piercing operation. As shown on the right side of  FIG. 5 , the filler plugs  76  are in a flush position in which they are flush to the surface of the tubular pre-form  58 . On the left side of  FIG. 5 , the filler plugs  76  are retracted to provide an opening  78  defined by the die inserts  74 . A piercing edge is formed about the opening  78 . When a pressure pulse is provided inside the tubular pre-form  58  when the filler plug  76  is retracted as shown on the left side of  FIG. 5 , the pressure applied to the pre-form  58  forces the tubular pre-form into engagement with the piercing edge at the opening  78  defined by the die inserts  74 . A slug  79 , as shown in  FIG. 6 , is removed from the pre-form in the area of the opening  78 . The slug may be pushed into the die insert  74  temporarily and then ejected by returning the filler plug  76  to the flush position. 
     A collar assembly  80  may be provided for trimming the end of the tubular pre-form  58 , as will be described below. The collar assembly  80  includes a static ring  82  that has a cutting edge  74 . A split ring  86  is provided adjacent to the static ring  82 . The split ring is shifted between a flush position in which it is flush to the tubular pre-form and a refracted position in which the split ring  86  is shifted radially outwardly to expose the cutting edge  84  of the static ring  82 . 
     One or more actuators  88  may be provided to move the filler plug  76  between the flush position and the retracted position. Similarly, one or more actuators  90  may be provided for shifting the split ring  86  between its flush position and its retracted position. Retraction of the filler plug  76  is coordinated with actuation of one of the pairs of accumulators  64   a - f  when a hole is pierced in the tubular pre-form  58 . Actuator  90  is used to shift the split ring  86  between its flush position and its retracted position and is coordinated with actuation of one of the pairs of accumulators  64   a - f  by rupturing a pair of the rupturable membranes  66   a - f  when the split ring  86  is in its retracted position. 
     Referring to  FIG. 7 , a tubular pre-form  58  is shown with the die insert  74  and filler plug  76  after a hole is formed in the pre-form  58  by removing a slug  70 . Further, a collar assembly  80  is shown in engagement with the tubular pre-form  58 . As shown, static ring  82  and split ring  86  are shown with the split ring  86  in its flush position in solid lines. The split ring  86  is shown in its retracted position in phantom lines in  FIG. 7 . When the split ring  86  is in its retracted position, a cutting edge  84  defined by the static ring  82  may be used to trim the end of the tubular pre-form  58 . A pair of accumulators  64   a - f  are actuated by rupturing a rupturable membrane  66   a - f  that corresponds to the pair of accumulators that cooperate with the collar assembly  80 . 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.