Abstract:
A pulsed joining tool includes a tool body that defines a cavity that receives an inner tubular member and an outer tubular member and a pulse joining cartridge. The tubular members are nested together with the cartridge being disposed around the outer tubular member. The cartridge includes a conductor, such as a wire or foil, that extends around the outer tubular member and is insulated to separate a supply segment from a return segment. A source of stored electrical energy is discharged through the conductor to join the tubular members with an electromagnetic force pulse.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0001]    The invention was made with Government support under Contract No. DE-EE0006432 awarded by the Department of Energy. The Government has certain rights to the invention. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates to a conductor disposed in a cartridge for a pulse welding tool or a pulse clinching tool that is used to join two tubular members by welding or clinching when the conductor is discharged. 
       BACKGROUND 
       [0003]    Significant amounts of aluminum and magnesium alloys are being included in vehicle body architecture, especially in the passenger compartment safety cage, or “greenhouse,” as a result of the need to introduce more lightweight alloys with higher specific strengths and stiffness. Lightweight alloys frequently must be joined to high strength ferrous materials to meet design and regulatory requirements. Dissimilar metal joints (such as boron steel to 6xxx series aluminum) are now being specified in structures that are subject to specified safety standards. 
         [0004]    Mechanical joints, such as rivets or flow drill screws may be used to join dissimilar materials but the strength, durability, and corrosion resistance of such joints does not match the properties of similar material welds. 
         [0005]    Extrusions and hydro-formed parts are very attractive for the safety cage and specifically the roof rail Body-In-White (BIW) construction because they can achieve very high stiffness and offer much better material utilization compared to sheet metal parts of similar mild steel configurations with welded flanges. A major roadblock to broad implementation of extrusions and hydro-formed parts is the lack of affordable mass production joining methods to integrate these parts into BIW structures. Joining methods such a resistance welding, MIG welding, TIG welding, and spin stir friction welding generate heat may introduce dimensional distortion and may detrimentally impact the microstructure or material properties of the parts made of special heat treatable alloys. 
         [0006]    Several different types of joining methods are currently available and may be categorized as one-sided or two-sided methods. One-sided joining methods are critical to the implementation of extrusion to extrusion joining because of access problems relating to the closed internal voids in some extrusions. One-sided joining methods such as flow drill screws add cost to the assemblies and are not well suited to high strength steel parts. Two-sided joining methods such as self-piercing rivets and clinch joints require access to the back side of a joint and are difficult to use in some applications where extrusions or tubular parts are joined. 
         [0007]    The above problems and other problems are addressed by this disclosure as summarized below. 
       SUMMARY 
       [0008]    According to one aspect of this disclosure, a pulsed joining tool is disclosed that includes a tool body and a cartridge. The tool body defines a cavity for receiving two nested tubular members. The cartridge is disposed in the cavity and includes a supply conductor and a return conductor extending circumferentially from an entry point to a reversal point. Electrical insulation isolates the extrusions, clamps, supply conductor and return conductor. A source of stored electrical energy is discharged through the supply and return conductors to join the tubular members with an Electro-Magnetic Force (EMF) pulse. 
         [0009]    According to other aspects of this disclosure, the pulsed joining tool may include at least two parts that are separable for loading and unloading the tubular members. A mandrel may be inserted inside the tubular members to support the tubular members when the source of stored electrical energy is discharged through the supply and return conductors. The mandrel supports the tubular members in an expanded position and is radially retracted in a retracted position to remove the mandrel from the tubular members. 
         [0010]    According to other aspects of this disclosure, the insulation material may be a plastic casing that encases the loop of wire. 
         [0011]    The tool may include a first part and a second part that are separable by an actuator that moves the first and second parts between an open position and a closed position. 
         [0012]    According to other aspects of this disclosure, a tool is disclosed for joining tubular parts that includes a body defining a cavity receiving overlapping portions of the tubular parts. A cartridge supports a conductor that extends around the overlapping portions. The conductor includes a supply segment extending around the overlapping portions in a first rotational direction to a reversal point and a return segment extending around the overlapping portion in a second rotational direction away from the reversal point. The supply segment and the return segment are insulated from each other. A source of stored electrical energy is discharged through the supply segment and the return segment in opposite rotational directions to create an electromagnetic pulse for joining the tubular members together. 
         [0013]    According to additional aspects of this disclosure as it relates to the tool, the tool may include a first part and a second part that are separable by an actuator that moves the first and second parts between an open position and a closed position. The tool may further comprise a mandrel inserted inside the tubular members to support the tubular members when the source of stored electrical energy is discharged through the supply and return segments. 
         [0014]    The body may define a port through which the conductor enters the cavity. The entry point is spaced and/or insulated from the reversal point to prevent arcing between the entry point and the reversal point. 
         [0015]    According to another aspect of this disclosure, a method of joining an inner tubular member and an outer tubular member together is disclosed that includes the steps of loading the tubular members into a tool that defines a receptacle, inserting a cartridge into the receptacle and discharging electrical energy through the conductor to join the tubular members together. The cartridge includes a conductor having a first run and a second run that are separated by an insulator and partially extend about the tubular members to a reversal point. The conductor defines a circumferential gap between an entry port into the cartridge and the reversal point. Electrical energy from a stored source of electrical energy, such as a bank of capacitors, is discharged through the conductor to create an electro-magnetic pulse to join the tubular members together. 
         [0016]    The source of stored electrical energy is discharged through the supply segment and the return segment in opposite rotational directions to create the electromagnetic pulse joining the tubular members together. The conductor may be a wire or a foil. The cartridge may be formed of a polymeric material. The circumferential gap is sufficient to prevent arcing between the entry port and the reversal point. The method may further comprise the step of nesting the tubular members together with overlapping portions of the tubular members being disposed inside the tool. The tubular parts may be welded together or clinched together depending, in part, upon the force of the discharge. 
         [0017]    The above aspects of this disclosure and other aspects are described below in greater detail with reference to the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a diagrammatic cross-sectional view of a pulse joining tool including a cartridge assembly and tubular members disposed within a chamber defined by the tool according to one embodiment of this disclosure; 
           [0019]      FIG. 2  is a diagrammatic cross-sectional view taken along the line  2 - 2  in  FIG. 1 ; 
           [0020]      FIG. 2A  is a fragmentary cross-sectional view of an alternative embodiment of a cartridge including a wire conductor disposed in the tool; 
           [0021]      FIG. 3  is a cross-sectional view of two tubular members shown welded together by the pulse joining tool shown in  FIG. 1 ; 
           [0022]      FIG. 4  is a diagrammatic cross-sectional view of an alternative embodiment of a pulse joining tool having a square chamber for joining two square tubular members made according to another embodiment of this disclosure; and 
           [0023]      FIG. 5  is a flowchart of the method of joining two tubular members according to this disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    The illustrated embodiments are disclosed with reference to the drawings. However, it is to be understood that the disclosed embodiments are intended to be merely examples that may be embodied in various and alternative forms. The figures are not necessarily to scale and some features may be exaggerated or minimized to show details of particular components. The specific structural and functional details disclosed are not to be interpreted as limiting, but as a representative basis for teaching one skilled in the art how to practice the disclosed concepts. 
         [0025]    Referring to  FIGS. 1 and 2 , a pulse joining tool  10  is shown that defines a cavity  12 . The pulse joining tool  10  includes a first tool part  16  and a second tool part  18 . The first and second tool parts  16  and  18  are opened and closed to receive an outer tubular member  20  and an inner tubular member  22 . The inner tubular member  22  is backed by a mandrel  24  that supports the inner tubular member  22  during the pulse joining operation. The mandrel  24  is a conventional expandable mandrel that is retracted to fit inside the inner tubular member, expanded to support the inner tubular member and retracted to remove the inner tubular member from the mandrel  24 . An actuator  26  is diagrammatically illustrated to be attached to the second tool part  18  for moving the second tool part  18  relative to the first tool part  16 . It should be understood that two actuators could be used or the actuator could be attached to the first tool part  16 . 
         [0026]    A cartridge generally indicated by reference numeral  30  is shown to be received in a receptacle  32 . The receptacle  32  is defined by the pulse joining tool  10  within the cavity  12 , as shown and described with reference to  FIG. 2  below. The cartridge  30  includes a conductor  36  that may be a foil conductor (as shown) or a wire conductor as shown in  FIG. 2A . The conductor  36  includes a supply run  38 , conductor or wire segment, and a return run  40 , conductor or wire segment, that extends circumferentially around the outer tubular member  20 . The supply run  38  and return run  40  meet at a reversal point  42 . DC current flowing through the supply run  38  flows in a first circumferential direction (i.e., clockwise) from an entry point  44  into the receptacle  32  until it reaches the reversal point  42 . After current flows past the reversal point  42 , it flows in the opposite circumferential direction (i.e., counter-clockwise) through the return run  40 . The supply run  38  and return run  40  enter the joining tool  10  through a port  46 . The port  46 , as shown in  FIG. 1 , is defined between the first tool part  16  and second tool part  18 . However, it should be understood that the conductor  36  may also enter the cavity  12  from the side of the tool  10  in which case no port would be required to be formed through the tool  10 . 
         [0027]    A gap  48  is defined between the entry point  44  and the reversal point  42 . The gap  48  may be an air gap or may be filled with insulation similar to the insulation  50  that encapsulates the supply run  38  and return run  40  of the conductor  36 . The gap  48  is provided to prevent arcing between the entry point  44  and the reversal point  42 . The conductor  36  nearly completely encircles the outer tube  20  to provide a relatively continuous circumferential EMF that is applied to the outer tube  20 . The gap  48  is necessary to prevent arcing between the entry point  44  and the reversal point  42 . The gap  48  may be expanded as needed to prevent arcing by shortening the conductor  36 . 
         [0028]    Insulation  50  is provided on the supply run  38  and return run  40  of the conductor  36 . Insulation  50  may be a polymeric material or other suitable insulator that can prevent arcing between the supply run  38  and return run  40 . 
         [0029]    Terminals  52  are provided on the tool  10 . The terminals  52  are provided to allow electrical connection between the tool  10  and a stored power source  54 . The stored power source  54  may be a capacitor bank (or inductor bank) that is capable of storing power that is discharged to the pulse joining tool  10 . 
         [0030]    Referring specifically to  FIG. 2 , the inner tubular member  22  includes a tapered end. The tapered end facilitates welding the outer tubular member  20  to the inner tubular member  22  as the outer tubular member  20  is compressed by the EMF into engagement with the inner tubular member  22  beginning at the widest portion of the tapered end  58 . 
         [0031]    Referring to  FIG. 3 , an outer tubular member  20  is shown connected to an inner tubular member  22  by a weld  60  that is formed by the pulse joining tool  10 . The weld  60  is formed between the overlapping portions  56  of the outer tubular member  20  and the inner tubular member  22 . 
         [0032]    Referring to  FIG. 4 , an alternative embodiment of a pulse joining tool  70  is shown that includes a cavity  72  that is square in shape. A first tool part  74  and a second tool part  76  are disposed within the cavity  72 . The tool parts  74  and  76  are square tubular members in the embodiment of  FIG. 4 . It should be understood that this disclosure of pulse joining tools and methods is not limited to round or square tubular members, but can also be applied to rectangular tubular members, tubular members having rounded ends and flat sides, and any other conventionally shaped tubular members. Inner tubular member  80  is supported by the mandrel  84 . A cartridge  90  is received within a receptacle  92  defined within the cavity  72  of the tool  70 . The cartridge  90  includes a conductor  96  that is a wire conductor. The conductor  96  includes a supply wire segment  98  and a return wire segment  100  that conduct current between a reversal point  102  and an entry point  104 . When discharged, current flows in one circumferential direction through the supply run  98  and in the opposite circumferential direction through the return wire segment  100 . A gap  108  is defined between the reversal point  102  and entry point  104  and may be insulated to prevent arcing between the reversal point  102  and the entry point  104 . Insulation  110  is provided about the supply run  98  and return run  100  of the conductor  96  to prevent arcing between the supply run  98  and the return run  100 . Terminals  112  are provided on the tool  70  to connect the tool  70  to a stored power source  114 . The stored power source, or pulse generator  114 , may be a capacitor bank, or the like. 
         [0033]    Referring to  FIG. 5 , the pulse joining method is illustrated and generally indicated by reference numeral  120 . The pulse joining method begins by loading a cartridge  30 , as previously described, into a pulse joining tool  10  at  122 . An inner tubular member is fitted onto a mandrel at  124 . An outer tubular member and the inner tubular member are assembled together at  126  within the cartridge in the cartridge  30  in the tool  10 . A stored electric charge is discharged at  128  through the tool to vaporize the conductor  36 , compressing the outer tubular member and thereby pulse joining the inner and outer tubular members together. Pulse joining the inner and outer tubular members together may result in formation of a weld or a clinch joint between the inner and outer tubular members. After discharge, the tool and retractable mandrel may be removed from the now joined tubular members at  130 . 
         [0034]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.