Abstract:
A method for forming a hollow part ( 18 ) that allows the use of hydroforming in cases where the part interconnects between sections having extreme variations in cross-section. A complete hollow part ( 18 ) is formed by joining a hydroformed hollow section with hollow sections. A method for securing a fastener sleeve ( 102 ) insert in a pre-fabricated hollow part ( 100 ) is also provided. In this method, the hollow part ( 100 ) is deformed slightly to form flanges ( 108 ) that secure the insert ( 102 ) in the part. Once the insert ( 102 ) is secure in the hollow part, fasteners can be applied to the part without collapsing it.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates generally to the field of motor vehicle frames, and more specifically to the hydroforming of hollow parts for use in motor vehicle frames.  
         BACKGROUND OF THE INVENTION  
         [0002]    Hollow parts for auto body construction, such as frame members or reinforcement beams, may ideally require a varying cross-sectional shape and/or perimeter along their length. Conventional hollow parts having varying cross-section may, for example, be stamped from two pieces of sheet metal, each piece forming two longitudinal halves of the completed tube. The two pieces are then welded together with two welded seams, each weld running the length of the part. This requires a relatively large amount of labor and welding to produce the finished hollow member, thus resulting in large processing expense.  
           [0003]    One method for producing hollow parts with varying cross section is hydroforming. The process of hydroforming metal structural components is well known. See, for example, U.S. Pat. Nos. 4,567,743, 5,070,717, 5,107,693, 5,233,854, 5,239,852, 5,333,775, and 5,339,667, the disclosures of which are hereby incorporated by reference. In a conventional hydroforming process, a tubular metal blank member is placed into a die cavity of a hydroforming die. Opposite ends of the tube are sealed, and fluid is injected under pressure internally to the tubular blank so as to expand the blank outwardly into conformance with the interior surfaces defining the die cavity. In more recent improvements to the conventional hydroforming process, opposite ends of the tubular blank are forced longitudinally toward one another during outward expansion of the tube so as to replenish the wall thickness of the metal as it is expanded outwardly. An exemplary process for replenishing material by longitudinally compressing the blank is disclosed in U.S. Pat. Nos. 5,718,048, 5,855,394, 5,899,498, and commonly-assigned 5,979,201 and 6,014,879.  
           [0004]    An advantage to hydroforming hollow parts is that high-strength parts having irregular cross-sectional configurations can be made easily and cost-effectively, in a manner which would be extremely difficult if not impossible to accomplish using stamping or roll-forming techniques.  
           [0005]    For some applications where a hollow part requires extreme variations in cross-section, hydroforming becomes somewhat problematic in conventional hydroforming, the cross-section diameter of the uniform cross-sectioned blank (typically cylindrical in shape) is typically chosen to be somewhat less than the smallest dimension of the part to be formed. The blank is then expanded as determined by the size of the die cavity. Where portions of the tube blank are to be expanded to very large extents (e.g., greater than 30%), the wall thickness of the tube at such locations may become overly thin to the detriment of the part.  
           [0006]    For certain applications wherein extended portions of the part can be provided with a generally constant cross-sectional shape (e.g., as would be produced by extrusion) there is no need to subject the entire part to a hydroforming process. In addition, it may be desirable to provide a hollow part that incorporates two or more uniformed cross section tubular members (e.g., formed by extrusion or roll forming), but of different cross-sectional shapes and/or dimensions from one another. To provide such a part is problematic, however, because of the need to connect tubes having dissimilar shapes and/or dimensions.  
           [0007]    It is therefore an object of the present invention to overcome the difficulties noted above in a novel, cost-effective manner.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention is a method for forming a hollow part. To achieve the forgoing object, a first hollow member is provided which has a first open end and a second open end, the first end having a predetermined structural dimension and shape. A second hollow member is provided which also has a first open end and a second open end, the first end having a predetermined structural dimension and shape. The first end of the first hollow member differs from the first end of the second hollow member in dimension or shape or both. A third hollow member is formed, such that it has a first open end with a structural dimension and shape generally the same as the structural dimension and shape of the first end of the first hollow member and it has a second open end with a structural dimension and shape generally the same as the structural dimension and shape of the first end of the second hollow member. The forming of the third hollow member includes placing it into a die cavity of a hydroforming die assembly and expanding it into conformity with surfaces defining the die cavity so as to provide a portion thereof which is to constitute the first end with generally the same structural dimension and shape as the first end of the first hollow member upon expansion. The die cavity is further shaped such that another portion of the third hollow member, which constitutes the second end, will have substantially the same structural dimension and shape as the first end of the second hollow member. The first end of the third hollow member is welded to the first end of the first hollow member and the second end of the third hollow member is welded to the first end of the second hollow member.  
           [0009]    In a second aspect of the present invention, a method for securing a fastener connecting sleeve into a pre-fabricated hollow member is provided. The hollow member has first and second opposing walls that have first and second holes respectively formed therein, and the first and second holes are aligned with first and second ends of the connecting sleeve respectively. The method comprises inserting the connecting sleeve into the interior of the hollow member through one end of the hollow member so that the connecting sleeve has its first and second opposing open ends disposed adjacent to the first and second walls of the hollow member. The first wall is then deformed to form a first flange that surrounds the first hole and projects into the first open end of the connecting sleeve. Similarly, the second wall is deformed to form a second flange that surrounds the second hole and projects into the second open end of the connecting sleeve. The first flange and second flange thus secure the first and second open ends of the connecting sleeve in alignment with the first and second hole to permit a fastener to pass therethrough. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is an exploded, isometric view of a hollow part formed in accordance with the present invention;  
         [0011]    [0011]FIG. 2 is a sectional view of a tubular blank in a hydroforming cavity in accordance with the invention;  
         [0012]    [0012]FIG. 3 is a sectional view of the hollow member having been expanded in the hydroforming cavity in accordance with the invention;  
         [0013]    [0013]FIG. 4 is sectional view of a generally conical tubular blank in a hydroforming cavity in accordance with another embodiment of the invention;  
         [0014]    [0014]FIG. 5 is an isometric view of a reinforcing tube being inserted into a hollow member in accordance with another aspect of the invention; and  
         [0015]    [0015]FIG. 6 is a sectional view of a hollow member and a reinforcing tube with flanging punches in accordance with the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    In a preferred embodiment of the present invention two hollow members  10 ,  12  are provided as shown in FIG. 1. The first of the two hollow members  10  has a first open end  14  with a predetermined structural dimension and shape and a second open end  15 . The second of the two hollow members  12  also has a first open end  16  with a predetermined structural dimension and shape and a second open end  17 . One or both of the dimension and shape of the first end  16  of the second hollow member  12  differ from that of the first end  14  of the first hollow member  10 . The two hollow members  10 ,  12  may be of any metallic material and may be formed in any manner appropriate to the material and desired application, but most preferably extruded, and preferably made from aluminum. The members  10 ,  12  preferably have a multi-sided, non-cylindrical cross-section shape (e.g., triangular, quadrilateral, pentagonal).  
         [0017]    In an alternate embodiment, each of the two hollow members  10 ,  12  may be hydroformed tubes.  
         [0018]    To join the two hollow members  10 ,  12 , a third hollow member  18  which acts as an adapter or transition member is formed which has a first open end  20  with generally the same structural dimension and shape as that of the first end  14  of the first hollow member  10 , and which also has a second open end  22  with generally the same structural dimension and shape as that of the first end  16  of the second hollow member  12 . Shown schematically in FIG. 1 are the weld lines  24  used to connect the third hollow member  18  to the first and second hollow members  10 ,  12 .  
         [0019]    The adapter  18  is formed by hydroforming. More particularly, referring now to FIGS. 2 and 3, a tubular metal blank  30  is hydroformed into a component having differing transverse (cross-sectional) dimensions and/or shapes at the opposite ends  20 ,  22  thereof. As shown in FIG. 2, the blank  30  is placed into a hydroforming die  32  which has an upper portion  34  having an upper die surface  36  and a lower portion  38  having a lower die surface  40 . When the upper and lower die portions  34 ,  38  are placed together, the upper die surface  36  and lower die surface  40  together define a die cavity  42 . The die cavity  42  includes a first expanding portion  44  that is constructed and arranged to expand a first portion of the blank  46  to a first predetermined shape and dimension, and a second expanding portion  48  that is constructed and arranged to expand a second portion of the blank  50  to a second predetermined shape and dimension. At least one of the shape and dimension of the first portion is different from that of the second portion. After the blank  30  is placed between the upper and lower die portions  34 ,  38  and the upper and lower die portions  34  and  38  are placed together to define the die cavity  42 . The ends of the blank are sealed by sealing rams as known in the art, as exemplified by the patents previously incorporated by reference. A high pressure hydroforming fluid  52  is introduced through one of the sealing members into the blank  30 , causing it to expand into conformity with the surfaces  36 ,  40  of the die cavity as shown in FIG. 3.  
         [0020]    In the case where the desired structural dimensions of the ends of the finished third hollow member are of significantly differing dimensions (one end having a much greater cross-sectional perimeter than the other), a conical tubular blank  60  may be used instead of the conventional cylindrical tubular blank (see FIG. 4). Preferably, the conical tubular blank  60  is formed by rolling sheet metal into a generally conical tubular configuration. Such a conical blank  60  helps to overcome potential problems with excessive thinning of the tube where it must expand to a greater degree to conform to the die cavity surfaces  36 ,  40 . That is, each end of the blank has a perimeter that corresponds more closely with the associated portions of the die into which it is to be expanded.  
         [0021]    The shape and size of opposing portions of the die cavity are constructed to have the dimension required for the hydroformed part to have opposite ends  20 ,  22  thereof align geometrically and dimensionally with the ends  14  and  16  of the extruded tubes to be mated (welded) therewith. In this regard, it should be noted that the present invention appreciates that after the hydroformed adapter is removed from the hydroforming die, it may be necessary to cut off end portions of the hydroformed part that have been deformed in order to mate with the opposing sealing rams. This cutting-off step is known in the hydroforming art, but is not always required. In the case where cutting is required, the portions of the hydroforming die cavity which are constructed to provide the adapter member  18  with the desired shape and dimension at said opposite end portions are spaced inwardly from the end portions of the blank, and are located (aligned with) at the areas at which the part pulled out of the hydroforming die are to be cut. These cut ends  20 ,  22  are then welded to the ends  14 ,  16 , respectively.  
         [0022]    Where the finished hollow part is to be secured to another structural component, it may be desirable to punch a hole in the part and pass a fastener, such as a bolt, therethrough. Where tubes are formed from two longitudinal stamped halves which are subsequently welded longitudinally, it is relatively simple to include additional processing steps to include reinforcing members in the finished tube because access to the interior of the tube is available prior to welding. In the case where the tube is integrally formed as a one-piece member, such as by hydroforming or extrusion, however, the process becomes more difficult.  
         [0023]    It is another object of the invention to provide an internal sleeve within an extruded and/or hydroformed tube to serve as reinforcement to the hollow part at such location. Specifically, to increase strength of the tube, a reinforcement sleeve  102  can be used to accept fasteners therethrough without risk of collapsing the tube. FIG. 6 shows a cross-section of a hollow member  100  with the reinforcing connecting sleeve  102  affixed therein. The connecting sleeve  102  is inserted into the hollow member  100  through an open end  103  thereof as shown in FIG. 5. To affix the sleeve  102 , opposing flanging punches  104  are forced through opposite walls  106  of the hollow member, into open ends of the sleeve  102 .  
         [0024]    In a preferred embodiment, pre-punched holes are provided in the opposite walls  106 , such holes having a smaller diameter than the diameter of the punches  104  and aligned with the open ends of sleeve  102 . Thus, when the punches  104  are forced through such holes in the walls  106 , the edges surrounding these holes are bent to form flanges  108  extending into the open ends of the sleeve  102 . The pre-punched holes may, for example, be formed in a hydropiercing operation, in the instance where the tube  100  is a tube section formed by hydroforming.  
         [0025]    In an alternate embodiment, no pre-punched hole is formed in the opposing tube walls  106 , and the flanging punches  104  themselves form holes in opposite walls  106  of the hollow member. Material from the opposite walls  106  of the hollow member is deformed to form flanges  108 . The flanges  108  are disposed around the circumference of the holes formed in the hollow member and extend into the opposite ends of the sleeve  102 . In either embodiment, the flanges  108  fix the ends of the sleeve relative to the hollow member  100 . Preferably, a computer numeric controlled hydraulic system is used to insert the sleeve  102  into the tube  100 , to ensure that the punches  104  are aligned with the opened ends of the sleeve prior to the punching operation, and to force punches  104  inwardly. Alternately, a fixture can be used and the sleeve  102  inserted by hand. While the ends of the sleeve  102  can then be welded to the opposite tube walls  106  (e.g., by laser welding, projection welding, etc.), it is contemplated that the mechanical interlocking relationship of the flanges  108  within the sleeves  102  can be the sole means for securing the sleeve  102  to the tube  100 .  
         [0026]    It will be appreciated that the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the the scope of the present invention.