Abstract:
A friction stir welding method includes providing a joining tool including a friction surface, a first workpiece, and a second workpiece, and arranging the first workpiece and second workpiece in position with a first joining surface abutting a second joining surface. A friction surface of a joining tool resists at least one of the first treating surface and the second treating surface, and the first workpiece and the second workpiece cooperatively define a slot. Then positioning, rotating, and moving the joining tool to rub and stir at least one of the first workpiece and the second workpiece, thus plasticizing at least part of the first workpiece and the second workpiece to join the first workpiece and the second workpiece.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is a divisional application of U.S. patent application Ser. No. 12/728,387, filed on Mar. 22, 2010, which claims all benefits accruing under 35 U.S.C. §119 from CN 200910310831.8, filed on Dec. 3, 2009, the contents of which are hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present disclosure generally relates to friction stir welding, and particularly, to a friction stir welding method using a joining tool without a mixing pin. 
         [0004]    2. Description of Related Art 
         [0005]    Friction stir welding is widely used to join aluminum alloy because it is simple to perform. 
         [0006]    A metal structure of the stirred product can be constituently uneven, since the material of the stirred portion of the product plastically flows in the friction stir welding process. After treatment, the different areas, specifically the stirred and unstirred portions of the product, may exhibit different aspects, wherein the joining portion of the workpieces provides an unfavorable appearance. Despite product annealing, the difference of the joined portion persists. Therefore, this can not satisfy a product with the stirred surface presented as an outer surface. 
         [0007]    Achievement of a favorable appearance in products obtained by friction stir welding remains a challenge. 
         [0008]    Therefore, an improved friction stir welding method is desired to overcome the described limitations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout several views. 
           [0010]      FIG. 1  is a schematic view of a joining tool used in an embodiment of a friction stir welding method of the disclosure. 
           [0011]      FIG. 2  is a bottom view of the joining tool of  FIG. 1 . 
           [0012]      FIG. 3  is a bottom view of another joining tool. 
           [0013]      FIG. 4  is a schematic view of a first workpiece and a second workpiece to be joined. 
           [0014]      FIG. 5  is a schematic view showing the joining tool friction stirring the first workpiece and the second workpiece. 
           [0015]      FIG. 6  is a schematic view of a third workpiece and a fourth workpiece to be joined. 
           [0016]      FIG. 7  is a schematic view showing the joining tool friction stirring the third workpiece and the fourth workpiece. 
           [0017]      FIG. 8  is a schematic view of a fifth workpiece and a sixth workpiece to be joined. 
           [0018]      FIG. 9  is a schematic view showing the joining tool friction stirring the fifth workpiece and the sixth workpiece. 
           [0019]      FIG. 10  is a schematic view showing the fifth workpiece and the sixth workpiece joined. 
           [0020]      FIG. 11  is a schematic view of a seventh workpiece and an eighth workpiece to be joined. 
           [0021]      FIG. 12  is a schematic view showing the joining tool friction stirring the seventh workpiece and the eighth workpiece. 
           [0022]      FIG. 13  is a schematic view of the fifth workpiece and a sixth workpiece to be joined and a joining member. 
           [0023]      FIG. 14  is a schematic view showing the fifth workpiece and the sixth workpiece joined. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Referring to  FIG. 1  and  FIG. 4 , a joining tool  10  is used to join a first workpiece  20  and a second workpiece  30 . The joining tool  10  is substantially cylindrical and includes a friction surface  11 . The friction surface  11  is substantially flat. The joining tool  10  defines a slot  13  in the friction surface  11 . The slot  13  may be spiral as shown in  FIG. 2 , and may include a plurality of curved slots starting at a rotation axis of the joining tool  10 , as shown in  FIG. 3 . 
         [0025]    Referring to  FIG. 4 , the first workpiece  20  includes a first treating surface  21  and a first joining surface  23  substantially perpendicular thereto. The second workpiece  30  includes a second treating surface  31  and a second joining surface  33  substantially perpendicular to the second treating surface  31 . 
         [0026]    Referring to  FIG. 4  and  FIG. 5 , the first workpiece  20  and the second workpiece  30  abut against each other, thereby defining a joint line  29 . The first joining surface  23  contacts the second joining surface  33 , and the first treating surface  21  and the second treating surface  31  are on the same plane. The first workpiece  20  and the second workpiece  30  are positioned in place by a clamp (not shown). The friction surface  11  of the joining tool  10  resists the first treating surface  21  and the second treating surface  31  and corresponds to the joint line  29 . The joining tool  10  rotates along an axis thereof relative to the first workpiece  20  and the second workpiece  30  and moves along the joint line  29 . Thus, the joining tool  10  rubs and stirs surface layers of the first workpiece  20  and the second workpiece  30 , such that material of the first treating surface  21  of the first workpiece  20  and second treating surface  31  of the second workpiece  30 , adjacent to the joint line  29 , are rubbed and stirred. Heat generated by friction and stirring is transferred to the unstirred material adjacent to the first joining surface  23  and the second joining surface  33 . The joining tool  10  produces a local region of highly plasticized material such that material of the first workpiece  20  and the second workpiece  30  diffuse among each other. As such, the first workpiece  20  and the second workpiece  30  are joined. 
         [0027]    In the joining method as disclosed, a rotation direction of the joining tool  10  is the same as an extending direction from a center to a periphery of the joining tool  10 . The joining tool  10  rotates at a high speed and moves at a low speed, and an end of the joining tool  10  extends slightly into the first workpiece  20  and the second workpiece  30 . A rotation speed S, moving speed V, and stirred depth H of the first workpiece  20  and the second workpiece  30  are determined by various factors, such as the material and thickness of the first workpiece  20  and the second workpiece  30 , and the size and material of the joining tool  10 , so long as the first workpiece  20  and the second workpiece  30  can be joined. In the illustrated embodiment, the first workpiece  20  and the second workpiece  30  are aluminum alloy plates; the rotation speed S is about 7000 rpm, the moving speed V is about 500 mm/min, and the stirred depth H is about 0.15 mm. 
         [0028]    Referring to  FIG. 1 ,  FIG. 6  and  FIG. 7 , a third workpiece  40  and a fourth workpiece  50  joined by the joining tool  10  are shown. The third workpiece  40  includes a third treating surface  41  and a third joining surface  43  substantially perpendicular to the third treating surface  41 . The third workpiece  40  further includes an inclined connecting surface  45  joining the third treating surface  41  and the third joining surface  43 . The fourth workpiece  50  includes a fourth treating surface  51  and a fourth joining surface  53  substantially perpendicular to the fourth treating surface  51 . The fourth workpiece  50  further includes an inclined connecting surface  55  joining the fourth treating surface  51  and the fourth joining surface  53 . 
         [0029]    The third workpiece  40  and the fourth workpiece  50  abut against each other, thereby defining a joint line  59 . The connecting surfaces  45 ,  55  define a slot  49 . The third joining surface  43  contacts the fourth joining surface  53 . The third treating surface  41  and the fourth treating surface  51  are on the same plane. The third workpiece  40  and the fourth workpiece  50  are positioned in place by a clamp (not shown). The friction surface  11  of the joining tool  10  resists the third treating surface  41  and the fourth treating surface  51  and corresponds to the slot  49 . The joining tool  10  rotates along the axis thereof relative to the third workpiece  40  and the fourth workpiece  50  and moves along the joint line  59 . Thus, the joining tool  10  produces a local region of highly plasticized material such that the third workpiece  40  and the fourth workpiece  50  diffuse among each other. As such, the third workpiece  40  and the fourth workpiece  50  are joined. Some plasticized material flows in the slot  49  and fills the slot  49 , thus enhancing the joint strength of the third workpiece  40  and the fourth workpiece  50 . 
         [0030]    In the joining method disclosed, a rotation direction of the joining tool  10  is the same as an extending direction from a center to a periphery of the joining tool  10 . The joining tool  10  rotates at a high speed and moves at a low speed, and an end of the joining tool  10  extends slightly into the third workpiece  40  and the fourth workpiece  50 . A rotation speed S, moving speed V, and stirred depth H of the third workpiece  40  and the fourth workpiece  50  are determined by various factors, such as the material and thickness of the third workpiece  40  and the fourth workpiece  50 , and the size and material of the joining tool  10 , so long as the third workpiece  40  and the fourth workpiece  50  can be joined. In the illustrated embodiment, the third workpiece  40  and the fourth workpiece  50  are aluminum alloy plates; the rotation speed S is about 7000 rpm, the moving speed V is about 500 mm/min, and the stirred depth H is about 0.15 mm. 
         [0031]    Referring to  FIG. 1  and  FIG. 8  through  FIG. 10 , a fifth workpiece  60  and a sixth workpiece  70  joined by the joining tool  10  are shown. The fifth workpiece  60  includes a fifth treating surface  61  and a fifth joining surface  63  facing the fifth treating surface  61 . The sixth workpiece  70  includes a sixth treating surface  71  and a sixth joining surface  73  facing the sixth treating surface  71 . However, unlike the previous workpieces, the fifth treating surface  61  and fifth joining surface  63 , and sixth joining surface  73  and sixth treating surface  71  are non-perpendicular, disposed with an angle formed therebetween. 
         [0032]    During joining of the fifth workpiece  60  and the sixth workpiece  70 , the fifth workpiece  60  and the sixth workpiece  70  are arranged together and angled to each other, with the fifth joining surface  63  contacting the sixth joining surface  73 , and the fifth treating surface  61  and the sixth treating surface  71  perpendicular to each other. A joint line  69  is defined at the joining portion of the fifth workpiece  60  and the sixth workpiece  70 . The fifth workpiece  60  and the sixth workpiece  70  are positioned in place by a clamp (not shown). The friction surface  11  of the joining tool  10  resists the fifth treating surface  61 . The joining tool  10  rotates along the axis thereof relative to the fifth workpiece  60  and the sixth workpiece  70  and moves along the joint line  69 . Thus, the joining tool  10  produces a local region of highly plasticized material such that material of the fifth workpiece  60  and the sixth workpiece  70  diffuse among each other. As such, the fifth workpiece  60  and the sixth workpiece  70  are joined to form a product  300 . 
         [0033]    In the joining method disclosed, a rotation direction of the joining tool  10  is the same as the extending direction from a center to a periphery of the joining tool  10 . The joining tool  10  rotates at a high speed and moves at a low speed, and an end of the joining tool  10  extends slightly into the fifth workpiece  60  and the sixth workpiece  70 . A rotation speed S, moving speed V, and stirred depth H of the fifth workpiece  60  and the sixth workpiece  70  are determined by various factors, such as the material and thickness of the fifth workpiece  60  and the sixth workpiece  70 , and the size and material of the joining tool  10 , so long as the fifth workpiece  60  and the sixth workpiece  70  can be joined. In the illustrated embodiment, the fifth workpiece  60  and the sixth workpiece  70  are aluminum alloy plates, the rotation speed S is about 7000 rpm, the moving speed V is about 500 mm/min, and the stirred depth H is about 0.15 mm. 
         [0034]    An angle is defined by the fifth treating surface  61  and the sixth treating surface  71 , such that the joint line  69  is in a corner. That is, the joint line  69  is superposed to an edge line. As such, the joint line  69  is hidden. The angle defined by the fifth treating surface  61  and the sixth treating surface  71  may be any degree other than 0° and 180°. In the illustrated embodiment, the angle is about 90°. 
         [0035]    Further, an assisting member  200  can be provided to resist the sixth workpiece  70 . The assisting member  200  includes a first end surface  201  and a second end surface  203  substantially perpendicular to the first end surface  201 . The first end surface  201  of the assisting member  200  resists the sixth treating surface  71  of the sixth workpiece  70  and the second end surface  203  of the assisting member  200  is on the same plane as the fifth treating surface  61  of the fifth workpiece  60 . 
         [0036]    With the assisting member  200 , the friction and stirred area increases, as does the friction heat. The increased heat is transmitted to the fifth workpiece  60  and the sixth workpiece  70  to enhance connection therebetween. 
         [0037]    In the embodiment, after the first workpiece  20  is joined to the second workpiece  30 , the third workpiece  40  is joined to the fourth workpiece  50 , and the fifth workpiece  60  is joined to the sixth workpiece  70 , surface layers adjacent to the treating surfaces  21 ,  31 ,  41 ,  51 ,  61 ,  71  may be removed. That is, material with a changed metal structure is removed and material with unchanged metal structure is exposed. Therefore, a product formed by the above described friction stir welding method can provide a favorable appearance, even if subsequent treatment, such as an anodic process. 
         [0038]    Referring to  FIG. 11  and  FIG. 12 , a seventh workpiece  80  and an eighth workpiece  90  joined by the joining tool  10  are shown. The seventh workpiece  80  includes a seventh treating surface  81 , a seventh joining surface  83  facing the seventh treating surface  81 , and a connecting surface  85  connecting the seventh treating surface  81  and the seventh joining surface  83 . The connecting surface  85  is substantially perpendicular to the seventh treating surface  81 . The eighth workpiece  90  includes an eighth treating surface  91  and an eighth joining surface  93  facing the eighth treating surface  91 . However, unlike the previous workpieces, the seventh treating surface  81  and seventh joining surface  83 , and the eighth joining surface  93  and eighth treating surface  91  are non-perpendicular, disposed with an angle formed therebetween. 
         [0039]    When joining of the seventh workpiece  80  and the eighth workpiece  90 , the seventh workpiece  80  and the eighth workpiece  90  are arranged together and angled to each other. The seventh joining surface  83  contacts the eighth joining surface  93 , and the seventh treating surface  81  and the eighth treating surface  91  are perpendicular to each other. A joint line  89  is defined at the joining portion of the seventh workpiece  80  and the sixth workpiece  90 . The seventh workpiece  80  and the eighth workpiece  90  are positioned in place by a clamp (not shown). The friction surface  11  of the joining tool  10  resists the seventh treating surface  81 . The joining tool  10  rotates along the axis thereof relative to the seventh workpiece  80  and the eighth workpiece  90  and moves along the joint line  89 . Thus, the joining tool  10  produces a local region of highly plasticized material of the seventh workpiece  80  and the eighth workpiece  90  which diffuse among each other. As such, the seventh workpiece  80  and the eighth workpiece  90  are joined. 
         [0040]    After the seventh workpiece  80  is joined to the eighth workpiece  90 , surface layers adjacent to the treating surfaces  81 ,  91  may be removed. Therefore, product formed by the above described friction stir welding method can provide favorable appearance, even if subsequent treatment, such as an anodic process. When a removed layer of the eighth workpiece  90  is thinner than that of the seventh workpiece  80 , the joint line  89  may be at a corner, that is, superposed to an edge line of the joined seventh workpiece  80  and the eighth workpiece  90 , thus hidden. 
         [0041]    The workpieces  20 ,  30 ,  40 ,  50 ,  60 ,  70 ,  80 ,  90  may be a material with low melting point, such as aluminum, aluminum alloy, copper alloy, or rubber, and be of any shape. Material of the joining tool  10  is a critical factor determining material of the workpieces  20 ,  30 ,  40 ,  50 ,  60 ,  70 ,  80 ,  90 . Increased melting point of the joining tool  10  allows a higher melting point of the material of the workpieces  20 ,  30 ,  40 ,  50 ,  60 ,  70 ,  80 ,  90 . The melting point of the joining tool  10  must exceed that of the workpieces  20 ,  30 ,  40 ,  50 ,  60 ,  70 ,  80 ,  90 . Joining portions of the workpieces may be point, line or surface. 
         [0042]    The disclosed joining method provides products with lower requirements for joint strength. If a product with strong joint strength is desired, the workpieces may define a slot at the joining portion in which a joining member with a melting point lower than the workpieces is received. The joining member is disposed away from the rubbed and stirred portion of the workpieces, thus the joining member may transmit heat to material far away from the rubbed and stirred portion. Therefore, a joining strength may be enhanced. A joining member provided to join the fifth workpiece  60  and the sixth workpiece  70  is discussed as follows. 
         [0043]    Referring to  FIG. 13  and  FIG. 14 , the fifth workpiece  60  defines a first slot  67  at the fifth joining surface  63  and the sixth workpiece  70  defines a second slot  77  at the sixth joining surface  73 . When the fifth workpiece  60  and the sixth workpiece  70  are arranged together, the first slot  67  and the second slot  77  cooperatively form a receiving slot (not labeled). To join the fifth workpiece  60  and the sixth workpiece  70 , a joining member  400  is positioned in the receiving slot. When rubbing and stirring the fifth treating surface  61  of the fifth workpiece  60 , heat is transmitted to the receiving slot, and the material of the joining member  400  becomes plasticized before the fifth workpiece  60  and the sixth workpiece  70  because the joining member  400  has a lower melting point. Heat transmitted adjacent to the receiving slot may not raise a temperature adjacent to the receiving slot to that of the fifth workpiece  60  and the sixth workpiece  70 , while raising the temperature to the melting point of the joining member  400 . Thus, material of the joining member  400  flows in the receiving slot to join with the fifth workpiece  60  and the sixth workpiece  70  to enhance the joining strength of the fifth workpiece  60  and the sixth workpiece  70 . 
         [0044]    Alternatively, the receiving slot may be only defined in one of the fifth workpiece  60  and the sixth workpiece  70 . A joining member  400  may be positioned in each of the fifth workpiece  60  and the sixth workpiece  70 . The joining member  400  may be solder. 
         [0045]    In the disclosed friction stir welding methods, only the joining portions of the workpieces need be machined, such that the joining tool  10  is small, with a correspondingly low driving force thereof required. Equipment applying the joining tool  10  to friction stir welding is simple and low cost. 
         [0046]    The joining tool  10  may be applied in ordinary machining centers (not shown), whereby workpieces may be machined and joined at the same machining center. As such, the workpieces need only be clamped once, thus improving machining efficiency and precision. In addition, no special machine is needed. Furthermore, the friction stir welding method can join workpieces with complex joining surfaces. 
         [0047]    Finally, while various embodiments have been described and illustrated, the disclosure is not to be construed as being limited thereto. Various modifications can be made to the embodiments by those skilled in the art without departing from the true spirit and scope of the disclosure as defined by the appended claims.