Abstract:
An assembly includes a first structural member made from a first material, such as aluminum, a second structural member made from a second material, such as magnesium, and adapted to mate and interlock with the first member, and a third structural member made from the first material to facilitate a permanent affixation between the first and second members. The second member fits within the first member and the third member fits within the second member. The second member includes at least one aperture surrounded by a protrusion, and the third member includes at least one aperture that mates and interlocks with the protrusion. A surface of the third member is exposed through the apertures of the first and second members. The first member is welded to the third member through the apertures in order to permanently affix the first and second members to one another without metallurgical altering or local welding of the second member.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Section 111(a) application relating to commonly owned, co-pending U.S. Provisional Application Ser. No. 61/062,268 entitled “SYSTEM AND METHOD FOR JOINING DISSIMILAR MATERIALS” filed Jan. 24, 2008. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a system and method for joining structural and mechanical parts made from dissimilar materials. 
       BACKGROUND OF THE INVENTION 
       [0003]    Two main issues with joining dissimilar materials are material compatibility and applicability of the joining process. More particularly, there are issues involved with joining aluminum to magnesium, to steel or to composites with known joining processes, such as fusion welding (e.g., gas metal arc welding) and solid-state welding (e.g., friction stir welding). These include metallurgical incompatibility, which results in uncontrolled cracking in welds and/or formation of brittle intermetallics; drastic differences in electromotive potential, which may lead to severe galvanic corrosion in the presence of salts and/or moisture; and incompatibility in the coefficient of thermal expansion, which could cause formation of intense residual stresses at joints and lead to failure under certain loading conditions, such as stress corrosion. What is needed is an appropriate system and method for proper joining of structural and mechanical parts made from dissimilar materials (e.g., metals and metal composites) to allow, among other things, the proper transmission of loads between them. 
       SUMMARY OF THE INVENTION 
       [0004]    A structural assembly that includes a first structural member made from a first material, a second structural member made from a second material and adapted to mate and interlock with the first structural member, and a third structural member made from the first material to facilitate the permanent affixation between the first and second structural members. More particularly, the first structural member includes a post made from a first material, such as aluminum, the second structural member includes a tube made from a second material, such as magnesium, and is sized and shaped to fit within the post, and an insert made from the first material (e.g., aluminum) that is sized and shaped to fit within the tube. The post includes at least one aperture encircled by an inwardly extending protrusion, and the tube includes at least one aperture that is sized and shaped to mate and interlock with the protrusion when the post and tube are mated and interlocked with one another. When the post, tube and insert are mated and interlocked with one another, a snug fit is formed between the post and the tube and between the tube and the insert. In such configuration, an outer surface of the insert is exposed through the aperture of the post and the aperture of the tube. The aperture of the tube is substantially encased or shielded by the protrusion of the post such that there are no exposed surfaces of the tube in the area of the aperture of the post and the outer surface of the insert. Consequently, the aluminum post may be welded to the aluminum insert, thereby permanently affixing, for example, the aluminum post and the magnesium tube to one another without metallurgical altering or local welding of the magnesium tube. 
         [0005]    Further features and advantages of the invention will appear more clearly on a reading of the detailed description of the embodiments of the invention, which is given below by way of example only with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    For a better understanding of the present invention, reference is made to the following detailed description of the embodiments considered in conjunction with the accompanying drawings, in which: 
           [0007]      FIG. 1  is an exploded top perspective view of a post and tube joint assembly in accordance with an embodiment of the present invention; 
           [0008]      FIG. 2A  is an exploded top plan view of the post and tube joint assembly illustrated in  FIG. 1 ; 
           [0009]      FIG. 2B  is an exploded side elevational view of the post and tube joint assembly illustrated in  FIG. 1 ; 
           [0010]      FIG. 3A  is a top perspective view of the post and tube joint assembly illustrated in  FIG. 1 , showing an intermediate step of the components thereof being interlocked with one another; 
           [0011]      FIG. 3B  is a top perspective, cross-sectional view of the post and tube joint assembly illustrated in  FIG. 3A ; 
           [0012]      FIG. 3C  is a side cross-sectional view of the post and tube joint assembly illustrated in  FIG. 3A ; 
           [0013]      FIG. 4A  is a top perspective cross-sectional view of the post and tube joint assembly illustrated in  FIG. 1 , showing the components thereof interlocked with one another; 
           [0014]      FIG. 4B  is a side cross-sectional view of the post and tube joint assembly illustrated in  FIG. 4A ; 
           [0015]      FIG. 4C  is an enlarged cross-sectional view showing detail  4 B from  FIG. 4B ; 
           [0016]      FIG. 5A  is a top perspective view of the post and tube joint assembly illustrated in  FIG. 4A , showing the components thereof welded to one another; 
           [0017]      FIG. 5B  is a side cross-sectional view of the post and tube joint assembly illustrated in  FIG. 5A ; 
           [0018]      FIG. 5C  is an enlarged cross-sectional view showing detail  5 B from  FIG. 5B ; 
           [0019]      FIG. 6A  is an exploded top perspective view of a post and tube joint assembly in accordance with a another embodiment of the present invention; 
           [0020]      FIG. 6B  is a side cross-sectional view of the post and tube joint assembly illustrated in  FIG. 6A , showing an intermediate step of the components thereof being interlocked with one another; 
           [0021]      FIG. 6C  is a side cross-sectional view of the post and tube joint assembly illustrated in  FIG. 6A , showing the components thereof interlocked with one another; 
           [0022]      FIG. 6D  is a side cross-sectional view of the post and tube joint assembly illustrated in  FIG. 6C , showing the components thereof welded to one another; 
           [0023]      FIG. 7A  is an exploded top perspective view of a post and tube joint assembly in accordance with yet another embodiment of the present invention; 
           [0024]      FIG. 7B  is a side cross-sectional view of the post and tube joint assembly illustrated in  FIG. 7A , showing an intermediate step of the components thereof being interlocked with one another; 
           [0025]      FIG. 7C  is a side cross-sectional view of the post and tube joint assembly illustrated in  FIG. 7A , showing the components thereof interlocked with one another; 
           [0026]      FIG. 7D  is a side cross-sectional view of the post and tube joint assembly illustrated in  FIG. 7C , showing the components thereof welded to one another; 
           [0027]      FIG. 8A  is an exploded top perspective view of a post and tube joint assembly in accordance with another embodiment of the present invention; 
           [0028]      FIG. 8B  is a cross-sectional view of an insert employed by the post and tube joint assembly illustrated in  FIG. 8A ; 
           [0029]      FIG. 8C  is perspective view of another embodiment of an insert employed by the post and tube joint assembly illustrated in  FIG. 8A ; 
           [0030]      FIG. 8D  is an exploded top perspective view of the post and tube joint assembly illustrated in  FIG. 8A , showing an adhesive applied to the components thereof; 
           [0031]      FIG. 8E  is a top perspective view of the post and tube joint assembly illustrated in  FIG. 8A , showing the components thereof interlocked with and welded to one another; and 
           [0032]      FIGS. 9 through 12  show a flat sheet assembly in accordance with another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0033]    Referring to  FIGS. 1 through 2B , a post and tube joint assembly  10  includes a hollow, rectangular-shaped post  12 , a hollow, rectangular-shaped tube  14 , and a hollow, rectangular-shaped insert  16 . While the post  12 , the tube  14  and the insert  16  are each rectangular in shape, they can consist of different shapes and sizes (e.g., cylindrical, triangular, hexagonal, etc.) to suit the purposes of the varied configurations to be appreciated from the teachings herein. In addition, the post  12  and the insert  16  may be manufactured from the same material, while the tube  14  is manufactured from a different material. The post  12  and the insert  16 , as well as the tube  14 , may be made from many types of metals suitable for the characteristics contemplated from the teachings herein. For example, the post  12  and the insert  16  may be made from aluminum, and, more particularly, T6 temper 6061 aluminum alloy, while the tube  14  may be made from steel, an aluminum alloy composite, or magnesium. The tube  14  may also be made from other materials, such as an organic based composite (e.g., carbon fibers bonded together) an inorganic based composite (e.g., metallic fibers braded and adhesively bonded), or similar composites. 
         [0034]    With continued reference to  FIGS. 1 through 2B , the post  12  includes a first end  18  and a second end  20  opposite thereof, a first pair of opposed walls  22 ,  24  and a second pair of opposed walls  26 ,  28 , which form a rectangular-shaped cavity  30 . The cavity  30  is sized and shaped to slidably receive the tube  14  and the insert  16 , which shall be described in further detail below. The wall  22  includes a first pair of circular-shaped apertures  32 ,  34 , while the wall  24  includes a second pair of circular-shaped apertures  36 ,  38  (not shown in  FIGS. 1 through 2B , but see  FIGS. 3B and 3C ). Each of the apertures  32 ,  34  includes a circular-shaped “tea-cup” protrusion  40 ,  42 , respectively, that extends into the cavity  30  from the wall  22 , while each of the apertures  36 ,  38  includes a circular-shaped “tea-cup” protrusion  44 ,  46 , respectively, that extends into the cavity  30  from the wall  24  (not shown in  FIGS. 1 through 2B , but see  FIGS. 3B and 3C ). The aperture  32  and the aperture  36  are aligned with one another, but they need not be. Similarly, the aperture  34  and the aperture  38  are aligned with one another, but they need not be. While the post  12  includes the apertures  32 ,  34  and the apertures  36 ,  38  (for a total of four apertures), it may include more or less than four apertures. While each of the apertures  32 ,  34  and the apertures  36 ,  38  are each circular in shape, and each of the protrusions  40 ,  42  and the protrusions  44 ,  46  are circular in shape, they may consist of other shapes and sizes to suit the purposes of the varied configurations to be appreciated from the teachings herein. The apertures  32 ,  34 , the apertures  36 ,  38 , the protrusions  40 ,  42 , and the protrusions  44 ,  46  may be formed from any means known in the art, such as, for example, machining, punch forming into dies (i.e., “tea cupping”), cast or forged. 
         [0035]    Still referring to  FIGS. 1 through 2B , the tube  14  includes a first end  48  and a second end  50  opposite thereof, a pair of opposed walls  52 ,  54  and a pair of opposed walls  56 ,  58 , which form a rectangular-shaped cavity  60 . The cavity  60  is sized and shaped to slidably receive the insert  16 , which shall be described in further detail below. The wall  52  includes a pair of circular-shaped apertures  62 ,  64 , while the wall  54  includes a pair of circular-shaped apertures  66 ,  68  (not shown in  FIGS. 1 through 2B , but see  FIGS. 3B and 3C ). The aperture  62  and the aperture  66  are aligned with one another, but they need not be. The aperture  64  and the aperture  68  are aligned with one another, but they need not be. While the apertures  62 ,  64  and the apertures  66 ,  68  are each circular in shape, they may consist of other shapes and sizes to suit the purposes of the varied configurations to be appreciated from the teachings herein. A slot  70  is formed within the wall  52  proximate to a corner  71  where the wall  52  and the wall  56  intersect, while a slot  72  is formed with the wall  52  proximate to a corner  73  where the wall  52  and the wall  58  intersect. Similarly, a slot  74  is formed within the wall  54  proximate to a corner  75  where the wall  54  and the wall  56  intersect, while a slot  76  is formed with the wall  54  proximate to a corner  77  where the wall  54  and the wall  58  intersect. Each of the slots  70 ,  72  and the slots  74 ,  76  have lengths that extend from the end  48  of the tube  14  to a point P 1  intermediate the ends  48 ,  50  of the tube  14 . The length of the slots  70 ,  72  and the length of the slots  74 ,  76  are the same, but the lengths can be different. The functions of the slots  70 ,  72  and the slots  74 ,  76  shall be described below. 
         [0036]    Still referring to  FIGS. 1 through 2B , the insert  16  includes a first end  78  and a second end  80  opposite thereof, a first pair of opposed walls  82 ,  84  and a second pair of opposed walls  86 ,  88 , which form a rectangular-shaped cavity  90 . A slot  92  is formed within the wall  82  proximate to a corner  93  where the wall  82  and the wall  86  intersect, while a slot  94  is formed within the wall  82  proximate to a corner  95  where the wall  82  and the wall  88  intersect. Similarly, a slot  96  is formed within the wall  84  proximate to a corner  97  where the wall  84  and the wall  86  intersect, while a slot  98  is formed within the wall  84  proximate to a corner  99  where the wall  84  and the wall  88  intersect. Each of the slots  92 ,  94  and the slots  96 ,  98  has a length that extends from the end  78  of the insert  16  to a point P 2  intermediate the ends  78 ,  80  of the insert  16 . The length of the slots  92 ,  94  and the length of the slots  96 ,  98  are the same, but the lengths can be different. The insert  16  includes a first retainment tab  100  that extends outwardly from the wall  82  at the end  78  of the insert  16 , while a second retainment tab  102  extends outwardly from the wall  84  at the end  78  of the insert  16 . Each of the tabs  100 ,  102  has a length that is substantially the width of the walls  82 ,  84 , respectively. The tab  100  includes a curved outer surface  101 , while the tab  102  includes a curved outer surface  103  (see  FIG. 2B ). The functions of the slots,  92 ,  94 , the slots  96 ,  98 , and the retainment tabs  100 ,  102  shall be described below. 
         [0037]      FIGS. 3A through 3C  show an intermediate step of assembling the post  12 , the tube  14  and the insert  16  with one another. More particularly, the end  80  of the insert  16  is inserted into the cavity  60  of the tube  14  at the end  48  thereof. In such position, the retainment tabs  100 ,  102  of the insert  16  abut against the end  48  of the tube  14 , which inhibit the insert  16  from sliding out the end  50  of the tube  14  during assembly. The cavity  60  of the tube  14  is sized and shaped to accommodate the receipt of the insert  16  and firmly retain the insert  16  therein. 
         [0038]    Next, the tube  14  and the insert  16  assembly as described above are slidably inserted into the cavity  30  of the post  12  at an end  20  thereof. The cavity  30  of the post  12  is sized and shaped such that the tube  14  and the insert  16  elastically deflect inwardly when the tube  14  and the insert  16  are inserted into the post  12  (see  FIGS. 3B and 3C ). More particularly, as the tube  14  and the insert  16  assembly are inserted into the post  12 , the tab  100  of the insert  16  reaches the protrusion  42  of the post  12  and the tab  102  reaches the protrusion  46  of the post  12 . At this point, the curved surfaces  101 ,  103  of the tabs  100 ,  102  and the “tea-cup” shapes of the protrusions  42 ,  46  enable the tabs  100 ,  102  to travel over (i.e., ramp over) the protrusions  42 ,  46 , respectively. As the tabs  100 ,  102  travel over the protrusions  42 ,  46 , resulting forces act against the tabs  100 ,  102  and, in turn, against the first end  48  of the tube  14 . As a result of such forces, the walls  52 ,  54  of the tube  14  deflect inwardly, while the walls  82 ,  84  of the insert  16  deflect inwardly. The slots  70 ,  72  of the tube  14  facilitate the deflection of the wall  52  of the tube  14  inwardly, while the slots  74 ,  76  of the tube  14  facilitate the deflection of the wall  54  of the tube  14  inwardly. Similarly, the slots  92 ,  94  of the insert  16  facilitate the deflection of the wall  82  of the insert  16  inwardly, while the slots  96 ,  98  of the insert  16  facilitate the deflection of the wall  84  of the insert  16  inwardly. As indicated above, the lengths of the slots  70 ,  72  and the slots  74 ,  76  of the tube  14  are equal in order to facilitate uniform deflection of the walls  52 ,  54  of the tube  14 . Similarly, the lengths of the slots  92 ,  94  and the slots  96 ,  98  of the insert  16  are equal in order to facilitate uniform deflection of the walls  82 ,  84  of the insert. However, the aforesaid lengths can be adjusted (e.g., shortened or lengthened) to suit the purposes of the varied configurations to be appreciated from the teachings herein. 
         [0039]    It is also noted that the apertures  32 ,  34  of the post  12  are not aligned with one another along axis A-A, as shown in  FIGS. 2A and 3A , and that the apertures  36 ,  38  of the post  12  are not aligned with one another along axis A-A. This configuration prevents the aperture  62  from mating with the protrusion  40  and the aperture  66  from mating with the protrusion  44 . As a result, the tube  14  and the insert  16  assembly are prevented from interlocking with the post  12  prematurely. 
         [0040]    As the tube  14  and the insert  16  assembly continues to be inserted within the post  12 , the protrusions  42 ,  46  act against the wall  52  of the tube  14  to maintain the deflection of the tube  14  and the insert  16  as discussed above. Once again, the curved surfaces  101 ,  103  of the tabs  100 ,  102  and the “tea-cup” shapes of the protrusions  42 ,  46  enable the tabs  100 ,  102  to slide over the protrusions  44 ,  48 , respectively. 
         [0041]      FIGS. 4A through 4C  show the tube  14  and the insert  16  assembly fully inserted within the post  12  and snapped into place. More particularly, the apertures  62 ,  64  of the tube  14  engage and cooperate with the protrusions  40 ,  42  of the post  12 , respectively, while the apertures  66 ,  68  of the tube  14  engage and cooperate with the protrusions  44 ,  46  of the post, respectively. In such manner, the walls  52 ,  54  of the tube  14  and the walls  82 ,  84  of the insert  16  spring back into their substantially same original position (i.e., before deflection) and are locked into place within the post  12 . As a result, the protrusions  40 ,  42 , are aligned and interlocked with the apertures  62 ,  64 , respectively, while the protrusions  44 ,  46  are aligned and interlocked with the apertures  66 ,  68 , respectively. The thickness of the walls  52 ,  54  of the tube  14  is sized appropriately to enable the protrusions  40 ,  42 ,  44 ,  46  to sufficiently mate and interlock with the respective apertures  62 ,  64 ,  66 ,  68 . It is also noted that the tube  14  and the insert  16  are designed and manufactured such that their elastic deformation is within the range of approximately 99-100% (e.g., no plastic deformation at &gt;0.2 yield strengths); and, therefore, such components can carry out the mechanical interlocking process described herein. 
         [0042]      FIGS. 5A through 5C  show the welding of the post  12  to the insert  16 , which are made from the same material (e.g., aluminum). More particularly, welds  104  are placed within each of the apertures  32 ,  34  of the post  12  and the apertures  62 ,  64  of the tube  14 , resulting in welded joints between the protrusions  40 ,  42  and the wall  82  of the insert  16 . Similarly, welds  106  are placed within the apertures  36 ,  38  of the post  12  and the apertures  66 ,  68  of the tube  14 , resulting in welded joints between the protrusions  44 ,  46  and the wall  84  the insert  16 . Since the post  12  and the insert  16 , which are made from the same material (e.g., aluminum), are permanently welded to one another by the welds  104 ,  106 , the tube  14 , which is made from a different material (e.g., magnesium) is permanently retained within the post  12 . Consequently, the mechanical interlock between the post  12  and the tube  14  described above is permanently affixed. 
         [0043]    The welds  102 ,  104  may be made from any welding process known in the art, such as fusion-based (e.g., GMAW, GTAW, LBW, LSBW, etc.) or solid-state based (e.g., FSW, FW Plunge, etc.). Alternatively, the welds  102 ,  104  need not be included, and the welding process described above could be substituted with any other joining and fixation processes known in the art, such as rivets, bolts, screws, etc. that enable the post  12  and tube  14  to be secured together in a manner that ensures the mechanical interlocks between them do not separate. 
         [0044]    The mechanical interlocking features of the post and joint assembly  10  enable load transmission through the post  12  and the tube  14 , while simultaneously keeping the subsequent joining operations localized and confined to joining the post  12  and the insert  16  (which are made of the same material) and separate from the tube  14 . 
         [0045]    Another embodiment of the present invention is illustrated in  FIGS. 6A through 6D . The embodiment shown in  FIGS. 6A through 6D  includes the same features and is assembled in the same manner as the embodiment shown in  FIGS. 1 through 5C , with the exception that the post  12  has two pairs of circular-shaped apertures  32 ,  34  on the wall  22  thereof and two pairs of circular-shaped apertures  36 ,  38  on the wall  24  thereof, while the tube  14  has two pairs of circular-shaped apertures  62 ,  64  on the wall  52  thereof and two pairs of circular-shaped apertures  66 ,  68  on the wall  54  thereof. In the same manner as the embodiment shown in  FIGS. 1 through 5C , the insert  16  is slidably inserted into the tube  14 , and the tube  14  and the insert  16  assembly is slidably inserted into the post  16  and locked into place (see  FIGS. 6B and 6C ). Afterwards, the mechanical interlock between the post  12  and the tube  14  are permanently affixed by welding the post  12  to the insert  16  by welds  104  through each of the apertures  32 ,  34  of the post  12  and the apertures  62 ,  64  of the tube  14  and welds  106  through each of the apertures  36 ,  38  of the post  12  and the apertures  62 ,  64  of the tube  14 . 
         [0046]    Another embodiment of the present invention is illustrated in  FIGS. 7A through 7D . The embodiment shown in  FIGS. 7A through 7D  includes the same features and is assembled in the same manner as the embodiment shown in  FIGS. 1 through 5C , with the exception that the post  12  has two pairs of oblong-shaped slots  32 ,  34  on the wall  22  thereof and two pairs of oblong-shaped slots  36 ,  38  on the wall  24  thereof, while the tube  14  has two pairs of oblong-shaped slots  62 ,  64  on the wall  52  thereof and two pairs of oblong-shaped slots  66 ,  68  on the wall  54  thereof. In the same manner as the embodiment shown in  FIGS. 1 through 5C , the insert  16  is slidably inserted into the tube  14 , and the tube  14  and the insert  16  assembly is slidably inserted into the post  16  and locked into place (see  FIGS. 7B and 7C ). Afterwards, the mechanical interlock between the post  12  and the tube  14  are permanently affixed by welding the post  12  to the insert  16  by welds  104  through each of the slots  32 ,  34  of the post  12  and the slots  62 ,  64  of the tube  14  and by welds  106  through each of the slots  36 ,  38  of the post  12  and the slots  66 ,  68  of the tube  14 . 
         [0047]    Another embodiment of the present invention is illustrated in  FIGS. 8A through 8D . Elements illustrated in  FIGS. 8A through 8D  that correspond to the elements described above with reference to  FIGS. 1  though  5 C have been designated by corresponding reference numerals increased by two hundred (200). The embodiment of  FIGS. 8A through 8D  operates in the same manner as the embodiment of  FIGS. 1 through 5C , unless it is otherwise stated. 
         [0048]      FIGS. 8A through 8D  show a post and tube joint assembly  210  that includes a hollow, rectangular-shaped post  212 , a hollow, rectangular-shaped tube  214 , and a hollow, rectangular-shaped insert  216 . These components include the same features as those corresponding to the embodiment shown in  FIGS. 1  though  5 C described above, with the exception that the tube  214  includes rectangular-shaped channels  201  formed within and extending transversely across an outer surface of a wall  252  and an outer surface of a wall  254  (not shown in the Figures), and T-shaped channels  203  formed within an outer surface of a wall  258  and an outer surface of a wall  256  (not shown in the Figures). In addition, the insert  216  includes oblong-shaped channels  205  formed within an outer surface of a wall  288  and an outer surface of a wall  286  (not shown in the Figures).  FIGS. 8B and 8C  show additional embodiments of the insert  216 , which include channels  207  and  209 , respectively, that consist of different shapes and sizes. Accordingly, the channels  201 ,  203 ,  205  can consist of a variety shapes and sizes and in any number other than those shown in the Figures. Each of the channels  201 ,  203  of the tube  214  and the channels  205  of the insert  214  are adapted to receive a sealant and/or an adhesive  211 , which provides additional bonding when the post  212 , the tube  214  and the insert  216  are interlocked with and welded to one another (see  FIG. 8D ). In addition, when the post  212  and the tube  214  are interlocked, a sealant and/or adhesive  211  may be applied between the post  212  and the tube  214  around the perimeter of an end  220  of the post  212 , as shown in  FIG. 8E . The sealant/adhesive  211  is used to improve the overall performance and strength (e.g., mechanical strength, corrosion resistance, etc.) of the assembly  210 , as well as to seal area A between the post  212  and the tube  214  to prevent the intrusion of foreign elements (see  FIG. 8E ). The adhesive/sealant  211  may be applied by injection or manually brushed on. Alternatively, the use of heat-activated or non-heat activated adhesives and/or sealing tapes can be utilized. The adhesive or sealant  211  may be applied prior to or after the mechanical interlocking of the assembly  210 , as appropriate. 
         [0049]      FIGS. 9 through 14  show a similar system and method with respect to a flat sheet assembly  310 . More particularly,  FIG. 9  shows the assembly  310  prior to lock-joining the components thereof, which include a first rectangular-shaped sheet  312 , a second rectangular-shaped sheet  314 , and a third rectangular-shaped sheet  316  that is sandwiched between the first and second sheets  312 ,  314 . While the sheets  312 ,  314 ,  316  are each rectangular in shape, they can consist of different shapes and sizes (e.g., square, triangular, circular, oblong, etc.) to suit the purposes of the varied configurations to be appreciated from the teachings herein. In addition, the sheets  312 ,  314  are each manufactured from the same material, such as aluminum, while the sheet  316  is manufactured from a different material, such as magnesium. Alternatively, the sheets  312 ,  314 , as well as the sheet  316 , may be made from other types of metals suitable for the characteristics contemplated from the teachings herein. For example, the sheets  312 ,  314  may be made from aluminum, while the sheet  316  may be made from steel or an aluminum based composite. The sheet  316  may also be made from other materials, such as an organic based composite (e.g., carbon fibers bonded together) an inorganic based composite (e.g., metallic fibers braded and adhesively bonded), or similar composites. 
         [0050]    Referring to  FIGS. 9 and 10 , the sheet  312  includes a pair of circular-shaped apertures  318 ,  320  encircled by “tea-cup” shaped protrusions  322 ,  324  that outwardly extend from a surface  326  of the sheet  312 . Referring only to  FIG. 9 , the sheet  316  includes two circular-shaped apertures  328 ,  330  that are sized and shaped to receive the protrusions  322 ,  324  of the sheet  312 . As shown in  FIG. 11 , an adhesive  332  may be applied to a surface  334  of the sheet  312  and a surface  336  of the sheet  314 .  FIG. 12  shows the assembly of the sheets  312 ,  314 ,  316 , whereby the protrusions  322 ,  324  of the sheet  312  are received by the apertures  328 ,  330  of the sheet  316 . In  FIG. 13 , the sheets  312 ,  314 ,  316  are clamped together for preparation of a welding process and facilitating the adhesion between them.  FIG. 14  shows the deposition of a GMA spot weld  338  between the sheets  312 ,  314  which are made from the same material (e.g., aluminum) with the sheet  316  (which is made from magnesium) interlocked between them. As a result the sheet  316  is interlocked with the between the aluminum sheets  312 ,  314 . 
         [0051]    The method includes lock-joining together parts made from dissimilar materials through the use of interlocking means on the parts at the joints betwee n them, and the use of another (i.e., secondary) joining process whose application is separate from and confined to joining two parts made from the same material, which ensures that the mechanical interlocks between the parts of dissimilar materials do not become separated. 
         [0052]    The term “snug fit” is defined as a gap or space (or a lack thereof between each of the protrusions  40 ,  42 ,  44 ,  46  of the post  12  and the outer surface of the insert  16  being in the range of zero up to a dimension that does not expose a surface of the tube  14  to the welding process. The term “mate” is defined as to join, fit, associate, assemble or couple parts or components with one another. The term “interlock” means to lock, fasten or fix parts or components with one another to ensure a stable and desirable coordinately functioning structure or action. 
         [0053]    It should be understood that the embodiments described herein are merely exemplary and that a person skilled in the art may make many variations and modifications without departing from the spirit and scope of the invention. Accordingly, all such variations and modifications are intended to be included within the scope of the embodiments described herein as defined in the appended claims.