Patent Publication Number: US-2005126243-A1

Title: Apparatus and method for hydroforming a tubular part

Description:
This application claims the benefit of U.S. Provisional Application Ser. No. 60/241,337, filed on Oct. 19, 2000, the entire contents of which are incorporated herein by reference thereto. 
    
    
     FIELD OF THE INVENTION  
      The invention relates generally to an improved apparatus and method for more efficiently hydroforming a tubular part. More specifically, the invention relates to an apparatus and method that uses a punch to shape each end of the part into the desired configuration and hold the part during hydroforming.  
     BACKGROUND OF THE INVENTION  
      Typically, to form a tubular part by hydroforming, a raw tube is positioned within a hydroforming tool and the tube is secured at its ends. The middle portion of the raw tube is then subjected to hydroforming, leaving a transitional zone between the ends of the raw tube and the hydroformed middle portion. The hydroformed part is then finished by having the two transition zones removed from the tube, leaving only the fully hydroformed middle portion. The ends of the tube can be secured by tip portions being generally wedge-shaped as disclosed in EP 1022073A1. Hydroforming is also disclosed in the U.S. Pat. Nos. 5,987,950 to Horton and U.S. Pat. No. 6,014,950 to Jaekel et al.  
      Removing the ends of the hydroformed part creates inefficiencies. For example, the cut away ends become wasted raw material. Also, cutting away ends requires additional cutting tools, which complicates the apparatus needed to create the finished part. Further, time is wasted performing the added step of cutting off the transitional zones at each end.  
     SUMMARY OF THE INVENTION  
      One object of the present invention is to provide an improved apparatus and method for forming a hollow part.  
      Another object of the present invention is to provide an improved apparatus and method for efficiently and cost effectively shaping a hollow part by mechanically shaping at least one end of the part and by hydroforming a portion of the part.  
      Still another object of the invention is to provide an apparatus and method for forming a part that uses a punch to secure each end of the part while the punch shapes the end so that each end has the same configuration as a hydroformed, middle portion.  
      The forgoing objects are basically attained by providing a hydroforming die assembly for hydroforming a part from a tubular blank, the part having a desired configuration different from a configuration of the blank and including a desired cross section at one end thereof, the die assembly comprising: a die structure having interior surfaces defining a die cavity, the die cavity having a cross sectional configuration conforming to the desired cross section of the part; and a pair of tube-end engaging structures disposed at opposite ends of the die cavity and constructed and arranged to engage opposite ends of the tubular blank, the tube-end engaging structures being constructed and arranged to seal the opposite ends of the tubular blank and to pressurize hydroforming fluid within the tubular blank for expanding the tubular blank into conformity with the interior surfaces of the die cavity, a first of the tube-end engaging structures having an outer cross-sectional configuration corresponding to the desired cross section at one end of the part, the first of the tube-engaging structures being movable into forced engagement with one end of the tubular blank to conform the one end of the tubular blank to the outer cross-sectional configuration of the first of the tube-engaging structures and hence the predetermined cross section at the one end of the part.  
      The forgoing objects are also attained by providing a method of forming a hydroformed part comprising the steps of: providing a hydroforming die assembly for hydroforming a part from a tubular blank, the part having a desired configuration different from a configuration of the blank and including a desired cross section at one end of the part, the die assembly including a die structure having interior surfaces defining a die cavity, the die cavity having a cross sectional configuration conforming to the desired cross section of the part, and a pair of tube-end engaging structures disposed at opposite ends of the die cavity and constructed and arranged to engage opposite ends of the tubular blank, the tube-end engaging structures being constructed and arranged to seal the opposite ends of the tubular blank and to pressurize hydroforming fluid within the tubular blank for expanding the tubular blank into conformity with the interior surfaces of the die cavity, a first of the tube-end engaging structures having an outer cross-sectional configuration corresponding to the desired cross section at one end of the part; moving the first of the tube-engaging structures into forced engagement with one end of the tubular blank to conform the one end of the tubular blank to the outer cross-sectional configuration of the first of the tube-engaging structures and hence the predetermined cross section at the one end of the part; and applying pressure within the tubular blank to form the tubular blank in to the desired configuration of the part.  
      Other objects, advantages, and features of the invention will become apparent from the following detailed description, appended drawings, and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an exploded perspective view showing upper and lower die structures and box-shaped punches of a hydroforming die assembly in accordance with the principles of the present invention;  
       FIG. 2  is a longitudinal section view of the hydroforming die assembly along section line  1 - 1  in  FIG. 1 , and including a tubular blank positioned within the lower die structure, the upper die structure shown in the raised or fully open position, and box-shaped punches engaging the ends of the tubular blank;  
       FIG. 3  is a longitudinal sectional view of the hydroforming die assembly, similar to  FIG. 2 , but showing the upper die structure in a fully lowered position, with the tubular blank positioned within the lower die structure, the box-shaped punches inserted into the ends of the tubular blank, and fluid injected into the tubular blank;  
       FIG. 4  is a cross-section taken through section line  4 - 4  in  FIG. 3  and showing an unexpanded oval tubular blank disposed within the hydroforming assembly and filled with hydroforming fluid;  
       FIG. 5  is a cross-section taken through line  5 - 5  in  FIG. 9  showing the tubular blank expanded by fluid under pressure within the expansion region of the cooperating upper and lower hydroforming dies;  
       FIG. 6  is a partial perspective view, partially in cross-section, of a box-shaped punch engaging a tubular blank;  
       FIG. 7  is a longitudinal sectional view taken through line  7 - 7  in  FIG. 6  showing a box-shaped punch;  
       FIG. 8  is a cross-sectional view along section line  8 - 8  in  FIG. 9  showing the end of the tubular blank between upper and lower clamping structures with a box-shaped punch inserted therein;  
       FIG. 9  is a longitudinal section view showing a hydroforming step wherein the upper die structure is in the fully lowered position and a tubular blank has been hydroformed into an expanded configuration by fluid under pressure;  
       FIG. 10  is a longitudinal section view showing the use of hydroforming ram extenders attached to punches to permit a relatively short blank to be hydroformed in a relatively long hydroforming die assembly; and  
       FIG. 11  is a longitudinal section view of a hydroforming die assembly with a box-shaped punch and a round punch engaging opposite ends of a tubular blank. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
      Shown generally in  FIG. 1  is an exploded perspective view of a hydroforming die assembly generally indicated at  10  in accordance with the present invention. The hydroforming die assembly  10  includes a movable upper die structure  12 , a movable lower die structure  14 , a fixed die structure  16 , and a fixed base  18  on which the fixed die structure  16  is mounted. A plurality of pneumatic or nitrogen spring cylinders  20  mount the lower die structure  14  for movement on the fixed base  18 . The upper die structure  12 , lower die structure  14 , and fixed die structure  16  cooperate to define a longitudinal die cavity therebetween, having a substantially boxed-shaped or multifaceted cross section as will be described herein. Preferably, the upper die structure  12 , lower die structure  14 , fixed die structure  16 , and fixed base  18  are each made of an appropriate steel material such as P-20 steel and/or 2714 steel.  
      As shown in  FIG. 1 , the upper die structure  12  defines a pair of cradle areas  22  at opposite longitudinal ends thereof. The cradle areas  22  are shaped and arranged to receive and accommodate upper clamping structures  26 , at opposite longitudinal ends of the upper die structure  12 . Particularly, the clamping structures  26  are each connected to the upper die structure  12  at the respective cradle areas  22 , by a plurality of pneumatic or nitrogen spring cylinders  24  which permit relative vertical movement between the clamping structures  26  and the upper die structure  12 .  
      The lower die structure  14  has similar cradle areas  30  at opposite longitudinal ends thereof which are constructed and arranged to accommodate lower clamping structures  28  in a similar fashion. As shown, the longitudinal ends, indicated at  15 , forming cradle area  30  of the lower die structure  14  have a generally U-shaped configuration.  
      The lower clamping structures  28  each have an upwardly facing surface  34  having a cross-sectional configuration that defines one-half of a multifaceted surface configuration. In the context of the present invention, the term multifaceted means square, rectangular, parallelepiped, polygonal, or any other closed, non-circular or oval configuration. In the illustrated embodiment, surface  34  defines one half of a rectangle.  
      In the embodiment shown, the upper two clamping structures  26  are substantially identical to the lower clamping structures  28  but are inverted with respect thereto. More particularly, each upper clamping structure  26 , has a downwardly facing surface  36  having a cross-sectional configuration that defines a second half of the multifaceted (i.e., rectangular) surface configuration. The surface  36 , of each clamping structure  26 , cooperates with surface  34 , of the respective lower clamping structures  28 , to form a multifaceted clamping surface that captures end portions of a tubular blank  40  when the upper die structure  12  is lowered.  
      As can be appreciated from, for example,  FIGS. 2, 3 , and  4 , the upper die structure  12  defines a longitudinal channel  38  having a substantially inverted U-shaped cross section. The channel  38  is defined by a downwardly facing, generally horizontal longitudinally extending surface  44 , and a pair of spaced, longitudinally extending vertical side surfaces  43 , which extend parallel to one another from opposite sides of surface  44 .  
      The lower die structure  14  has a central opening  42  extending vertically therethrough, between the U-shaped longitudinal ends  15 . The opening  42  receives fixed die structure  16 . Interior vertical surfaces  41  in the lower die structure  14  define the aforementioned central opening  42 . More particularly, a pair of longitudinally extending side surfaces  41 , define the lateral extremities of the opening  42 . The surfaces are vertically disposed in parallel facing relationship with one another. The U-shaped end portions  15  of the lower die structure  14  define the longitudinal extremities of the opening  42 , and have interior surfaces (not shown) vertically disposed in parallel facing relation to one another.  
      The fixed base  18  is in the form of a substantially rectangular metal slab. The fixed die structure  16  is affixed to an upper surface  46  of the fixed base  18 . The fixed die structure  16  is an elongate structure which extends along a major portion of the length of the upper surface  46  of the fixed base  18 , generally along the center of the fixed base  18 . The fixed die structure  16  projects upwardly from the fixed base  18  and has substantially vertical side surfaces  48  on opposite longitudinal sides thereof. The fixed die structure  16  is constructed and arranged to extend within the opening  42  in the lower die structure  14 , with minimal clearance between the generally vertical side surfaces  48  of the fixed die structure and vertical surfaces  41  of the lower die structure  16 . Similarly, there is minimal clearance between the interior transverse side surfaces (not shown) of end portions  15  of the lower die structure  14  and the vertical end surfaces  49  of the fixed die structure  16 . The fixed die structure  16 , further includes an upwardly facing, generally horizontal and longitudinally extending die surface  50 , which is constructed and arranged to extend in spaced facing relation to the longitudinally extending, downwardly facing die surface  44  of the upper die structure  12 .  
      As can best be seen in  FIGS. 4 and 5 , the aforementioned side surfaces  41 , the upwardly facing surface  50 , the side surfaces  43  and downwardly facing surface  44  cooperate to define a die cavity  52 , having a multifaceted cross sectional configuration substantially throughout its longitudinal extent. The die cavity surfaces define the desired shape of a part to be hydroformed from a circular or oval blank tube.  
       FIG. 2  shows the upper die structure  12  in an opened or raised position. In this position the hydroforming die assembly  10  enables the tubular blank  40  to be placed within the lower die structure  14 .  
      After the blank  40  is placed in the lower die structure  14 , the upper die structure  12  is lowered to form the die cavity  52 . The die cavity may be ultimately smaller than what is illustrated in  FIG. 4  to effect a slight crushing of the tubular blank  40  before the blank  40  is expanded in the hydroforming operation, as disclosed in U.S. Pat. No. 5,987,950 to Horton, which is incorporated herein by reference. With the tubular blank  40  positioned between the closed upper die structure  12  and lower die structure  14 , hydroforming rams  80  having punches  81  attached to mounting structures  90  are advanced from opposite sides of the hydroforming die assembly  10  to engage opposite ends of the tubular blank  40 . As shown most clearly in  FIGS. 6 and 7 , each punch  81  includes an initial beveled portion  82  which transitions into a multifaceted, here rectangular, portion  84 . A base  86  forming a lateral shoulder  88  is formed at one end of the multifaceted portion  84  opposite the initial beveled portion  82 .  
      The punch  81  is secured to the end of the mounting structure  90  by means of mechanical fasteners  92 , such as bolts, extending through counter-bored apertures  94  formed in the punch  81  and into the holder  92 . Base  86  preferably has a size and shape that is complementary to the size and shape of the mounting structure  90  so as to form a smooth, uniform transition between the punch  81  and the mounting structure  90 .  
      In the embodiment shown, the beveled portion  82  is preferably formed at an angle θ (see  FIG. 7 ) of between about 13-17°, and most preferably, about 15° with respect to the sides of the box-shaped portion  84 . The multifaceted portion  84  preferably has straight sides so as to have a perimeter that defines a multifaceted shape, such as a polygon, square rectangle, skewed parallelogram, etc. The perimeter shape of the box-shaped portion  84  corresponds substantially to the shape of the clamping surface formed by the upwardly facing surface  34  of the lower clamping structure  28  and the downwardly facing surface  36  of the upper clamping structure  26 . Also, the size of the multifaceted portion  84  is defined so as to provide a sealing interference fit with the wall of the tubular blank  40 , with the clamping surfaces providing external support for blank  40 .  
      The forward end  83  of the punch  81  at the free end of the beveled portion  82  has dimensions that are smaller than the multifaceted portion  84 , thus permitting the forward end  83  to be inserted into the unexpanded end of the tubular blank  40  as shown in  FIG. 2 . With the forward end  83  of the punch  81  engaged with the end of the blank  40 , the hydroforming ram can be further advanced under the force of hydraulic pressure, thus forcing the punch  81  into the end of the tubular blank  40  after the upper die structure  12  is lowered, as shown in  FIG. 3 . The beveled portion  82  of the punch  81  gradually forms the end of the blank  40  until the multifaceted portion  84  is fully inserted into the end of the blank  40 . During this process, the end portions of blank  40  may be stretched outwardly as they are conformed to the multifaceted portion  84  and hence, the adjacent clamping surfaces  34 ,  36 , as best shown in  FIGS. 3 and 8 . The width of the lateral shoulder  88  is preferably substantially the same as the thickness of the tubular blank  40  so that the outer surface of the tubular blank  40  transitions smoothly with the outer surfaces of the base  86  and the holder  90 .  
      Thus, when the tube is formed over the punch to fit the finished tube shape it will not be necessary to remove the scrap portion of the blank, this eliminates the need for cut-off tooling, which saves money and time.  
      While the above description refers to only one punch, it should be appreciated that this discussion may apply to both punches  81  at opposite ends of the tube  40 .  
      The tubular blank  40  may be round (circular cross section). Punches  81  have a similar height and width dimensions as the blank. The blank may be oval for punches that are rectangular or otherwise elongated along a height or width dimension. Hydroforming processes using oval tubular blanks are disclosed in U.S. Pat. No. 5,987,950, the disclosure of which is hereby incorporated by reference, as stated above. Providing a tubular blank having an oval cross-section is advantageous in comparison with the conventional circular cross-section because it provides a circumference that conforms more closely to the final cross sectional perimeter of the generally box-shaped (not square) cross-sectional shaped die cavity  52 . Thus, less expansion of the blank  40  is required when expanding the blank into conformity with the surfaces forming cavity  52 . In addition, the closer conformity of blank  40  and cavity surfaces allows the blank to be more easily expanded into the corners of the cavity  52 , where expansion becomes most difficult due to the increasing frictional surface contact between the exterior surface of the blank and cavity surfaces during expansion of the blank  40 .  
      As can be seen in  FIG. 3 , when the blank  40  is substantially rigidly held in place between die structures  12  and  14  and the hydroforming cylinders or rams  80  are telescopically and sealingly inserted into both opposite ends of the blank  40 , so that beveled surfaces  82  engage the opposite edges of blank  40 . The rams  80  are forced inwardly to cause the opposing edges of blank  40  to ride down surface  82  until it engages surface  88  and thus converts the end portions of the blank into the exterior shape of portion  84  of punch  81 . The hydroforming cylinders then preferably pre-fill, but do not pressurize to any large extent, the tubular blank  40  with hydroforming fluid (preferably water) as indicated by reference character F. The hydraulic fluid is injected through a channel  87  formed in one or both punches  81  which communicates with a channel  97  formed in the corresponding mounting structure  90 . Although the pre-filling operation is preferred to reduce cycle times, and to achieve a more smoothly contoured part, for some applications the upper die structure  12 , may be fully lowered before any fluid is provided internally to tubular blank  40 .  
      End portions of the sealed die cavity  52  are generally rectangular in shape as defined by surface portions  54  having generally the same size and shape as the clamping surfaces  34 ,  36  of the clamping structures  28 ,  26 , respectively. Thus, the portions  54  define areas of the die cavity which have a cross-sectional area that is the same as or only slightly larger than the area defined by the cross-sectional shape of the end portions of the tubular member  40  after the punches  81  have been forced into the ends of the tubular member as illustrated in  FIG. 6 . Otherwise stated, the portions  54  of the die cavity  52  define areas of the die cavity which are used to expand the tubular blank  40  during the hydroforming process only to the extent required to convert the shape of the blank from a round or oval cross section to a multifaceted (here rectangular) cross sectional configuration. Because the end portions of the blank  40  fitted with punches  81  (as illustrated in  FIG. 6 ) will form the shape desired for the final part to be hydroformed, and will not constitute an unexpanded portion that must be cut off after the hydroforming process so that the remaining uncut portions of the tube correspond to the desired part, substantial scrap material is saved. Each unexpanded surface portion  54  of the die structure defines a shape consistent with the shape of the portions  84  and  86  of the punch  81 .  
      The cavity  52  may also include an enlarged portion  56  towards the longitudinally central portions thereof. With the upper die structure  12  closed with respect to the lower die structure  14  and with the punches  81  sealingly inserted into the ends of the blank  40 , the fluid F can be pressurized to expand the tubular blank  40  into conformity with the surfaces defining die cavity  52  (see  FIGS. 5 and 9 ). The tubular blank  40  is expanded into the non-round, multifaceted (e.g., rectangular) of the die cavity  52 . If the hydroforming assembly includes a die cavity with an enlarged portion  56 , the blank  40  will be enlarged in that area. Because the portions  54  of die cavity  52  define shapes that are consistent with the shape of the multifaceted portion  84  of the punches  81 , the hydroformed member has a consistent shape out to its ends, and it is not necessary to cut the end portions off. If a portion of the blank is to be significantly enlarged in its cross-sectional perimeter (e.g., greater than 5% relative to the original blank perimeter), it may be preferred that the longitudinal ends of the blank be pushed inwardly toward one another to replenish wall thickness as the blank is expanded. If the blank is not to be enlarged, but is only expanded into conformity with a multifaceted die cavity, longitudinal movement of the ends during expansion of the blank may not be necessary. More particulars on the preferred hydroforming process are disclosed in U.S. Pat. No. 6,014,879 to Jaekel et al., the disclosure of which is hereby incorporated by reference.  
      In accordance with another embodiment, if a significant amount of perimeter expansion is required at one end of the tube part so that substantial wall thickness replenishment is required thereat, it is generally preferred to employ a circular or oval punch, as opposed to a multifaceted punch. This is because material flows more effectively and evenly toward the enlargement area from a rounded end than from a box-shaped end. Such a hydroforming configuration is shown in  FIG. 11 , in which the surrounding die structures are not shown for clarity of the illustration. The arrangement shown includes one hydroforming ram  80  having a beveled, rectangular-shaped punch  81  and a rectangular-shaped mounting structure  90 , as shown and described previously. The arrangement also includes a second hydroforming ram  100  that includes a cylindrical base portion  112  and a smaller cylindrical portion  102  with an insertion bevel  116  formed at the end. A circular, annular sealing shoulder  114  that engages the end of the tubular blank  40 ′ is defined between base portion  112  and cylindrical portion  102 .  
      At the end of the blank  40 ′ engaged by the multifaceted punch  81 , the die structure (not shown) presents a surface configuration that forms the blank  40 ′ such that the cross sectional configuration at portion  110  of the blank is expanded only to the extent that the rounded cross section of the blank is converted to a multifaceted cross section. The portion  110  is joined by a gradually tapered segment  108  which extends to an enlarged rectangular-shaped cross sectional portion  106 . Conversely, at the end of the blank  40 ′ engaged by the cylindrical punch  100 , the die structure presents a surface configuration that forms a relatively short, non-enlarged cylindrical portion  105  of the blank. The blank then transitions from the rounded perimeter shape at  105  to the rectangular cross section at area  106 . The cylindrical punch  100  allows for the relatively large expansion of enlarged area  106  and the abrupt transition region  104  because longitudinal pushing at the end of the tubular member  40 ′ is more effective for replenishing wall thickness if the punch is round. The cylindrical end portion of the formed member shaped by the cylindrical punch  100  would typically be cut off during a subsequent finishing operation.  
      The box-shaped end formed by the rectangular-shaped punch  81 , on the other hand, can be tailored to the desired final member shape so the end need not be cut off.  
      As shown in  FIG. 10 , one or more ram extenders  120  can be installed between the punch  81  and the holder  90 . The extenders  120  have a rectangular-shaped cross sectional configuration that conforms with the rectangular-shaped cross sections of the mounting structure  90  and the base  86  of the punch  81 . Accordingly, the hydroforming rams  80 ′ can extend further into the relatively an enlarged portions  54  of the die cavity  52  to accommodate hydroforming of shorter tubular blanks  40 ′ within the same die cavity  52 . Of course, the extended hydroforming blanks  80 ′ cannot extend to an enlarged area  56  of the hydroforming cavity  52  or the seal between the end of the tubular blank  40 ′ and the shoulder  88  of the punch  81  will be lost as the tubular blank expands into the enlarged area  56 .  
      Thus, the present invention includes a hydroforming die assembly for hydroforming a part from a tubular blank comprising a die structure having interior surfaces defining a die cavity, the die cavity having a cross sectional configuration conforming to the predetermined cross section of the part, the part having a predetermined configuration different from a configuration of the blank and including a predetermined cross section at one end thereof.  
      It should be appreciated that the foregoing detailed description and accompanying drawings of the preferred embodiments are merely illustrative in nature, and that the present invention includes all other embodiments that are within the spirit and scope of the described embodiments and appended claims.