Patent Description:
Various fasteners, apparatus and methods for joining and assembling parts or subunits are known, such as welding, riveting, threaded fasteners, etc. In some instances, there is a need to cost effectively join aluminum parts, subunits, layers, etc., to other parts, subunits, layers, etc. made from other materials, such as steel (bare, coated, low carbon, high strength, ultra high strength, stainless), titanium alloys, copper alloys, magnesium, plastics, etc. Solutions for these fastening problems include mechanical fastener/rivets in combination with an adhesive and/or a barrier layer to maintain adequate joint strength while minimizing corrosion, e.g., due to the galvanic effect present at a junction of dissimilar metals. Direct welding between aluminum and other materials is not commonly employed due to intermetallics generated by the aluminum and the other materials, which negatively affect mechanical strength and corrosion resistance. In cases where direct welding is employed, it is typically some type of solid-state welding (friction, upset, ultrasonic, etc.) or brazing/soldering technology in order to minimize the intermetallics, but the mechanical performance of such joints is sometimes poor or only applicable to unique joint geometries.

In the automotive industry, the incumbent technology for joining steel to steel is resistance spot welding (RSW), due to cost and cycle time considerations (less than <NUM> seconds per individual joint and which may be performed robotically). Known methods for joining aluminum to steel, include: use of conventional through-hole riveting/fasteners, self-pierce riveting (SPR), use of flow drill screws (FDS or by trade name of EJOTS), friction stir spot welding/joining (FSJ), friction bit joining (FBJ), and use of adhesives. Each of these processes is more challenging than steel-to-steel resistance spot welding (RSW). For example, when high strength aluminum (above 240MPa) is coupled to steel using SPR, the aluminum can crack during the riveting process. Further, high strength steels (><NUM> MPa) are difficult to pierce, requiring the application of high magnitude forces by large, heavy riveting guns. FSJ is not widely employed in the automotive industry since joint properties (primarily peel and cross tension) are low compared to SPR. In addition, FSJ requires very precise alignment and fitup. As the thickness of the joint increases, the cycle times for the process can increase dramatically where a <NUM> to <NUM> joint stack-up may require <NUM> to <NUM> seconds of total processing time, which is well above the <NUM> to <NUM> second cycle time of RSW when fabricating steel structures. FBJ employs a bit which is rotated through the aluminum and is then welded to the steel. This process requires very precise alignment and fit-up similar to FSJ and high forging forces are required for welding to steel. FDS involves rotating a screw into the work pieces, plasticizing one of the sheets, which then becomes interlocked with the screw's thread. FDS is typically applied from a single side and requires alignment with a pilot hole in the steel sheet, complicating assembly and adding cost. Alternative fasteners, apparatus and methods for joining and assembling parts or subunits therefore remain desirable.

The document <CIT> relates to an apparatus and method for fastening dissimilar metals like steel and aluminum, wherein a steel rivet and a spot welding machine are utilized. The rivet and metals are stacked and the heat from the welder's electric current softens the lower melting point aluminum allowing the rivet to penetrate the aluminum and weld to the steel layer. The fastener may be used to join stacks with several layers of different materials and may be used to apply a threaded socket or stud made from steel or titanium to an aluminum or magnesium alloy structure.

The document <CIT> relates to a method of joining a first electroconductive plate member made of metal to a second electroconductive plate member made of metal dissimilar to the metal of the first plate member by the use of at least one anchor peg made of the same metal as the second plate member. The first and second plate members are initially overlapped one above the other to provide a plate assembly which is subsequently clamped under pressure between welding electrodes with the anchor peg positioned between one of the welding electrodes and the first plate member. Thereafter, an electric current is supplied to the welding electrodes to initially cause a portion of the first plate member held in contact with the anchor peg to melt by resistance-heating of the anchor peg to thereby allow the anchor peg to be pierced through the first plate member and then to cause the anchor peg extending completely across a thickness of the first plate member to be welded to the second plate member.

The document <CIT> relates to attachment methods and attachment means, and more particularly to a method of forming a welded connection.

The document <CIT> relates to attachment methods for connecting a plate made of aluminum with a component made of steel.

The document <CIT> also relates to attachment methods.

The document <CIT> relates to a specific weld connection between a component made of steel and a component made of aluminum.

The document <CIT> relates to a fastener for projection resistance welding to a panel. The fastener includes a base having a fastening element, such as a threaded stud or a nut integral therewith. Multiple projections formed integral with the base extend therefrom to engage with the panel to be welded to the panel by electric resistance welding. A groove is provided in the base facing the panel and is filled with a heat activated expandable sealer material. Upon heating of the base during the electric resistance welding, or in an oven, the sealer expands to fill and seal any gap between the base and the panel.

The document <CIT> relates to a connecting auxiliary part made of steel for electrical resistance welding of an aluminum sheet to a steel part, which connecting auxiliary part is mushroom-shaped or hat-shaped.

The document <CIT> relates to a further resistance welding method used for joining components comprising a first component made of plastic and a second component made of steel.

The present invention relates to a system comprising a welding electrode tip and a resistance welding fastener according to independent claim <NUM>, wherein further developments of the inventive system are provided in the sub-claims <NUM> to <NUM>.

The present invention further relates to a method for fastening a first electrically conductive material to a second electrically conductive material using electrical resistance welding, as recited by independent claim <NUM>, wherein further developments of the inventive method are provided in the sub-claims <NUM> to <NUM>.

The method for fastening a first electrically conductive material to a second electrically conductive material using electrical resistance welding includes in particular: placing the first and second materials together in physical and electrical contact, the first material having a lower melting point than the second material; placing an electrically conductive fastener that is weldable to the second material and which has a higher melting point than the first material in physical and electrical contact with the first material to form an electrically conductive stack inclusive of the fastener, the first material and the second material; prior to or after the step of placing the fastener to form the stack, applying a sealant between the fastener and the first material; applying an electrical potential across the stack, inducing a current to flow through the stack and causing resistive heating, the resistive heating causing a softening of the first material; urging the fastener through the softened first material toward the second material; after the fastener contacts the second material, welding the fastener to the second material.

In accordance with an embodiment, the fastener has a cap and a stem which extends at right angles from the cap and the sealant is in the form of at least one of a bead, a ring, a disc, a band or a deposit of sealant applied to at least one of the cap proximal the first material or on the surface of the first material where the fastener will be placed during the step of placing.

In accordance with another embodiment, the sealant is at least one of an adhesive, a polymer, a brazing material or a solder.

The method may include the step of rendering the sealant flowable during the step of resistive heating, the sealant conforming to and a covering at least a portion of an interface between the cap and the first material after the step of welding is complete.

The method may include the step of placing the fastener includes holding the fastener in a carrier web and moving the web and the fastener over the first material to a selected position and further comprising the step of disassociating the web from the fastener after the step of welding.

A portion of the web may be captured between the fastener and the first material during the step of urging and prior to the step of disassociating.

The portion of the web captured may be the sealant.

In an embodiment, a fastener for fastening a first electrically conductive material to a second electrically conductive material using electrical resistance welding includes: a cap, a shaft extending from the cap and having an end distal to the cap, the fastener, when placed in a stack including first and second electrically conductive materials positioned in electrical contact and subjected to an electrical potential applied across the stack, capable of conducting an electrical current that passes through the stack, the current causing resistive heating and welding to the second material at the end distal to the cap, the first material being captured between the cap and the second material after the end is welded to the second material, the fastener having a plurality of layers, a first layer having a first composition and a second layer having a second composition different from the first composition.

In accordance with an embodiment, the first layer is steel and the second layer is aluminum.

In accordance with another embodiment, the first material is steel and the second material is aluminum, the second layer contacting and joining to the aluminum second material after it is extended through an aperture in the first material and subjected to electrical resistance welding.

In accordance with another embodiment, the second layer is a lower layer present along the entire lower surface of the fastener, including an underside of the cap, an outside surface of the shaft and an outside surface of the end of the shaft of the fastener.

In accordance with embodiment, the second layer is a lower layer present along a lower surface of the end of the shaft distal to the cap.

In accordance with another embodiment, the second layer is a lower layer present along a lower surface of the cap and an outer side surface of the shaft but not on the end of the shaft distal to the cap.

In accordance with another embodiment, the end of the shaft has a peripheral ledge against which the second layer abuts.

In accordance with another embodiment, the first layer is compatible for welding to the second material and the second layer is compatible for welding to the first material.

In accordance with another embodiment, the first layer is steel, the first material is aluminum, the second material is steel and the second layer is selected from titanium, stainless steel and cold sprayed aluminum.

In accordance with another embodiment, the first layer is compatible for welding to the second material and the second layer is an electrical insulator through which the first layer extends to make electrical contact with the second material.

In accordance with another embodiment, the second layer is selected from a ceramic and a polymer.

In accordance with another embodiment, the plurality of layers includes a diffusion barrier interposed between two of the plurality of layers, the two layers being dissimilar metals, a first being an upper layer and a second being a lower layer relative to the diffusion barrier.

In accordance with another embodiment, the first layer is at least one of steel, titanium and copper, the second layer is aluminum and the diffusion barrier is at least one of high purity aluminum, titanium or zinc.

In accordance with another embodiment, the second layer is coupled to the end of the fastener.

In accordance with another embodiment, a fastener for fastening a first electrically conductive material to a second electrically conductive material using electrical resistance welding, includes: a cap, a shaft extending from the cap and having an end distal to the cap, the fastener, when placed in a stack including first and second electrically conductive materials positioned in electrical contact, the first material having a lower melting point than the second material and subjected to an electrical potential applied across the stack, capable of conducting an electrical current that passes through the stack, the current causing resistive heating and welding to the second material at the end distal to the cap, the first material being captured between the cap and the second material after the end is welded to the second material, the shaft having a solid cross-section between the cap and the end distal to the cap.

In accordance with another embodiment, the cap has a depression therein capable of receiving a projection extending from a surface of a welding electrode, a surface area of contact between the electrode tip and the cap exceeding a contact surface area of the tip with the second material.

In accordance with another embodiment, the cap has a radiused depression therein capable of receiving a radiused surface projecting from a welding electrode tip.

In accordance with another embodiment, the cap has a projection extending from a surface thereof capable of being received in a depression in a surface of a welding electrode tip.

In accordance with another embodiment, a fastener for fastening a first electrically conductive material to a second electrically conductive material using electrical resistance welding, includes: a cap, a shaft extending from the cap and having an end distal to the cap, the fastener, when placed in a stack including first and second electrically conductive materials positioned in electrical contact and subjected to an electrical potential applied across the stack, capable of conducting an electrical current that passes through the stack, the current causing resistive heating and welding to the second material at the end distal to the cap, the first material being captured between the cap and the second material after the end is welded to the second material, the cap curving back toward the end of the shaft, such that the outer periphery thereof is approximately co-extensive with the end and further comprising an electric insulator attached to the outer periphery of the cap, the insulator capable of preventing electric current from flowing through the outer periphery in parallel to electric current flowing through the end, the cap capable of bending to accommodate the passage of the end through the first material and welding to the second material while the insulator abuts against a surface of the first material.

In accordance with another embodiment, a method for fastening a plurality of adjacent layers of a first electrically conductive material to a second electrically conductive material using electrical resistance welding, includes: placing the first and second materials together in physical and electrical contact, the first material having a lower melting point than the second material; placing an electrically conductive fastener that is weldable to the second material and which has a higher melting point than the first material in physical and electrical contact with the first material to form an electrically conductive stack inclusive of the fastener, the first material and the second material; applying an electrical potential across the stack, inducing a current to flow through the stack and causing resistive heating, the resistive heating causing a softening of the first material; urging the fastener through the softened plurality of layers of the first material toward the second material; after the fastener contacts the second material, welding the fastener to the second material, the plurality of layers of the first material welding to one another proximate to where the fastener passes through.

In accordance with another embodiment, the second material is a second fastener and wherein the plurality of layers of the first material weld together proximate at least one of the first fastener and the second fastener.

In accordance with another embodiment, a method for fastening a first electrically conductive material to a second electrically conductive material using electrical resistance welding, includes: bending the first material into a configuration having a J-shaped cross-section; inserting the second material into the curve of the J-shape with the first and second materials in physical and electrical contact, the first material having a lower melting point than the second material; placing an electrically conductive fastener that is weldable to the second material and which has a higher melting point than the first material against the short side of the J shape in physical and electrical contact with the first material to form an electrically conductive stack inclusive of the fastener, the first material and the second material; applying an electrical potential across the stack, inducing a current to flow through the stack and causing resistive heating, the resistive heating causing a softening of the first material on the short side of the J shape; urging the fastener through the softened first material toward the second material; after the fastener contacts the second material welding the fastener to the second material. the fastener is inserted through the short side of the J shape and welds to the second material without disturbing the exterior surface of the first material on the other side of the J.

In accordance with another embodiment, the method is repeated for a plurality of fasteners forming a hem.

The invention comprises a tip for an electrical resistance welding electrode for applying a resistance welding fastener, wherein the tip has a bottlenose shape with a larger diameter portion proximate the welding electrode and a reduced diameter portion distal to the electrode, the reduced diameter portion having a radiused end for contacting the fastener during welding.

In accordance with an embodiment, there is a transition from the reduced diameter portion to the larger diameter portion in the form of a straight wall disposed at an angle relative to an outer wall of the larger diameter portion.

In accordance with another embodiment, there is a transition from the reduced diameter portion to the larger diameter portion in the form of a double curve.

In accordance with another embodiment, there is a transition from the reduced diameter portion to the larger diameter portion in the form of a surface having a radius at least two times that of the radiused end.

A method for fastening a first material to a second electrically conductive material using electrical resistance welding may include in particular: providing an aperture in the first material; placing the first and second materials together in physical contact; providing an electrically conductive fastener having a cap larger that the aperture in the first material and a shaft having a least a portion that can pass through the aperture, the fastener capable of being welded to the second material; placing the shaft of the fastener through the aperture in the first material and in electrical contact with the second material to form a stack inclusive of the fastener, the first material and the second material; applying an electrical potential across the stack, inducing a current to flow through the stack and causing resistive heating, the resistive heating causing a softening of the fastener and the second material; welding the fastener to the second material and capturing the first material between the cap and the second material.

In accordance with an embodiment, the first material is electrically non-conductive.

In accordance with another embodiment, the first material is a plastic.

In accordance with another embodiment, the first material is a ceramic.

For a more complete understanding of the present invention, reference is made to the following detailed description of explanatory examples, not all of them being in conformity with the appended claims, considered in conjunction with the accompanying drawings.

<FIG> show a fastener <NUM> having a peripheral cap <NUM> and a tapered shaft <NUM> that has a bluntly pointed end <NUM> opposite to the cap <NUM>. An internal hollow H extends through the cap <NUM> and into the shaft <NUM>. The fastener <NUM> may be made from a conductive metal, e.g., steel or titanium, that is capable of supporting a resistance spot welding process. The cap <NUM> has an edge-to-top dimension CE, and diameter CD. The stem has diameter SD and length from cap <NUM> to end <NUM> of SL. As described below, these dimensions may be varied depending upon the use to which the fastener <NUM> is put, e.g., the thickness and type of parts that the fastener <NUM> is used to join. In one example, the diameter CD may be in the range of about <NUM> to <NUM>, the length SL in the range of about <NUM> to <NUM>, CE in the range of about <NUM> to <NUM> and SD in the range of about <NUM> to <NUM>. <FIG> shows a fastener <NUM>, like that of <FIG>, but having different dimensions, i.e., having a thinner shaft <NUM> with a more severely pointed end <NUM>.

<FIG> shows the insertion of a fastener 10a through a first layer of metal <NUM>, e.g., an aluminum alloy, and being welded to a second layer of metal <NUM>, e.g., a steel alloy, to form a laminate structure L1. This is shown in sequential stages labeled A-E. As shown at stage A, this process may be conducted at a conventional spot welding station having opposing electrodes, the tips 15a and 17a of which are shown spaced apart from the metal sheets/layers <NUM>, <NUM>, allowing the fastener 10a to be inserted between the tip 15a and the layer <NUM>. The tip 15a may have a surface S1 with a shape that accommodates, supports, shapes and/or retains the fastener 10a through the welding process. At stage B, opposing forces F1, F2 exerted by the conventional welding machine (not shown) to move the tips 15b, 17b towards one another, capture the fastener 10b and the layers <NUM>, <NUM> there between and an electric current I is applied through the conjunction of these elements. The forces F1, F2 and current I are applied throughout the stages B-E and the magnitude and duration of each may be varied depending upon the requirements at each stage. For example, the current I required to heat /plasticize the aluminum in stage B may be less than that required to weld steel to steel as occurs in stages D and E. Similarly, the forces F1 and F2 may be varied to accommodate changing processing requirements.

The current I heats each of the fastener 10b, and the layers <NUM>, <NUM> to a temperature at which the aluminum layer <NUM> plasticizes and can be displaced/pierced by the fastener 10b. The aluminum layer <NUM> is heated resistively by current I and also through conduction from both the fastener 10b and the layer <NUM>. The fastener 10b and the layer <NUM> have lower heat and electrical conductivity than the aluminum layer <NUM>, such that a low current typically achieved with a resistance spot welder suitable for making resistance spot welds in steel can be used to generate the heat required to plasticize the aluminum layer, as well as make the weld to layer <NUM>, as described below. Since aluminum has a lower melting point than the steel layer <NUM> or the fastener 10b, which in this example is also steel, the aluminum layer <NUM> reaches a plastic state permitting displacement by the fastener 10b and allowing the end 16b of the fastener 10b to penetrate the aluminum layer <NUM>. As shown at stage C, the insertion of the fastener 10c into the aluminum layer <NUM> causes an upwelling 11U of displaced plasticized aluminum rising above the original upper surface <NUM> of the layer <NUM>. As shown at stage D, the fastener 10d penetrates the layer <NUM> completely and comes into contact with the steel layer <NUM> whereupon the end 16d of the fastener 10d begins to melt and flatten and a zone Pd of molten metal begins to form at the interface of the layer <NUM> and the end 16d of the fastener. The zone Pd is the weld material or "nugget" where the metal of the fastener 10d and the layer <NUM> liquify and commingle. As shown at stage E, the continued application of converging forces F1, F2 and current I result in a further blunting and melting of the end 16e and a portion of the length of the stem 14e, along with the enlargement of the molten zone Pe. Stage E also shows the cap 12e has descended down to the level of the upper surface <NUM>, covering and sealing the upwelling 11U attributable to the insertion of the fastener 10e fully into the layer <NUM> of aluminum.

After having accomplished stage E, the forces F1, F2 and current I can be removed and the tips 15e and 17e, withdrawn. The foregoing process can be conducted with barrier layers, e.g., an adhesive layer of surface pre-treatment or paint/primer (not shown) applied to the surface <NUM> and/or between the layers <NUM>, <NUM>, so long as the barrier layer does not prevent the current I from flowing to create electrical resistance heating. In this manner, the contact between dissimilar metals of layers <NUM>,<NUM> can be reduced, along with unwanted galvanic interaction and corrosion. The partial melting of the fastener <NUM> during the penetration and welding phases of the process allows the fastener 10a to accommodate a range of thicknesses of layer <NUM>.

The cap 12a of the fastener 10a defines an annular recess that can receive, capture and seal off aluminum and intermetallics generated from the penetration (stages B and C) and welding (stages D and E) as the cap 12a "bottoms out" on the surface <NUM> of the aluminum layer <NUM>. This containment of the aluminum and intermetallics may significantly improve the corrosion performance and joint strength attributable to the fastener 10a. The cap 12a can be formed in the fastener 10a prior to the welding process or can be formed in-situ during welding. As described more fully below in reference to <FIG>, the geometry of the fastener 10a and its interaction with / retention by tip 15a and surface S1 enables single-sided welding (welding from one side without an electrode contacting member <NUM> directly in opposition to the electrode tip 15a to provide a counter force). The tip 15a, may be shaped to be grasped by the fastener 10a via a resilience or spring loading of the fastener 10a which retains the fastener 10a on the tip 15a during welding, but detach once the weld has been completed. For example, the tip <NUM> may have a peripheral ledge or concavity that an upper edge of the fastener 10a resiliently and removable grasps.

The fastener <NUM> may be formed from thin sheet steel, e.g., about <NUM> to <NUM> in thickness, but can be made in any given thickness as determined by the thickness of the layers <NUM>, <NUM>, with greater thickness in the layers requiring greater thickness of the fastener. Alternatively, the shaft <NUM> of the fastener <NUM> may be solid or semi-solid. Regardless of the thickness/hollowness of the fastener (density for a given surface area) the shaft <NUM> may be proportioned to collapse when the end <NUM> is welded to the sheet <NUM>, such that the cap contacts the upper surface <NUM> of sheet <NUM> and/or seals off any intermetallics and upwelled areas 11U when welding is completed (stage E).

The final dimensions of the weld zone Pe will depend upon the starting and final dimensions of the fastener shaft 14e, i.e., diameter, length and the thickness of the shaft walls. The greater the dimensions of the fastener shaft 14e, the greater the dimensions of the weld zone Pe. In one example, attaching sheet <NUM> composed of aluminum of thickness <NUM> to <NUM> to sheet <NUM> composed of steel of <NUM> to <NUM> thickness, a weld diameter in the range from <NUM> to <NUM> would exhibit beneficial shear and peel strength properties.

In order to minimize weight in a finished welded product made with the fasteners <NUM> of the present invention, the gauge of the sheet employed for making the fastener <NUM> may be reduced. As a result, the reduced sidewall strength of the fastener shaft <NUM> may cause it to prematurely collapse during the welding process. In order to support the shaft <NUM>, the electrode 15a can be formed to extend into the hollow H to partially or fully engage the inner surface of the shaft <NUM> within the hollow H. <FIG> shows an alternative fastener <NUM> in two phases in the welding process, viz. , phase B5 prior to extruding through the layer <NUM> and phase E5 - after welding. An electrode tip <NUM> having a surface S2 that supports the end <NUM> of the fastener <NUM>, allows the end <NUM> to be pushed through the layer <NUM> without the end <NUM> or shaft (sidewall) <NUM> deforming. The tip <NUM> has a concave annular surface S3 that can receive and form /shape a corresponding area of the fastener periphery <NUM> Op in response to the fastener <NUM> being pressed against the upwelling 11U when the fastener is pressed fully through layer <NUM> to form the weld zone Pg as shown in phase E5.

<FIG> shows a more comprehensive sequence of steps A6-F6 in use of the fastener <NUM> to perform spot welding through an upper layer <NUM><NUM>, e.g., an aluminum sheet, to fasten the upper layer <NUM> to a lower layer <NUM>, e.g., a steel sheet. As can be appreciated, this process could also be called "resistance spot fastening" or "resistance spot riveting," in that the fastener <NUM> could be described as a rivet that is plunged through the layer <NUM>, making a hole in the layer <NUM> and joining to the layer <NUM> by welding, the cap <NUM> of the fastener clamping the layer <NUM> against the layer <NUM>. As the fastener <NUM> penetrates the top layer <NUM> and engages the bottom layer <NUM>, the concave annular surface S3 in the electrode tip <NUM> encapsulates and seals against the layer <NUM>, in particular, the upwelling 11U. In one example, stage B6 and C6 may have an associated force FH of a magnitude of, e.g., from <NUM> to <NUM> (<NUM> to <NUM> pounds) and a current level IH of a magnitude of, e.g., from <NUM>,<NUM> to <NUM>,<NUM> amperes, that is appropriate for plasticizing the first layer <NUM> of aluminum having a thickness of <NUM> and welding to a second layer <NUM> of <NUM> MPa galvanized coated steel with a thickness of <NUM>, by a fastener of low-carbon steel with a <NUM> overall diameter, a total height of <NUM> and average wall thickness of <NUM>. These magnitudes of force and current are just exemplary and are dependent upon the dimensions and compositions of the fastener <NUM> and the layers <NUM> and <NUM>. The duration of time to transition from stage B6 to C6 may be in the order of <NUM> to <NUM> sees. Pursuing this example further and using the same dimensions and properties of the fastener <NUM> and layers <NUM>, <NUM>, stage D6 may utilize an associated force Fw of a magnitude of, e.g., from <NUM> to <NUM> (<NUM> to <NUM> pounds) and a current level Iw of a magnitude of, e.g., from <NUM>,<NUM> to <NUM>,<NUM> amperes, that is appropriate for initiating the melting of the fastener <NUM> and the lower level <NUM> to form a molten weld zone Pd. The magnitude of force Fw may be changed to a force FT of a magnitude of, e.g., from <NUM> to <NUM> (<NUM> to <NUM>,<NUM> pounds) and a current level IT of a magnitude of, e.g., from <NUM>,<NUM> to <NUM>,<NUM> amperes at stage E6 to form an expanded weld zone to temper the weld and to render it with an average cross-sectional diameter of <NUM> to <NUM>. The completion of stage D6 may take, e.g., <NUM> to <NUM> sees. At stage F6, the first and second electrode tips <NUM>, <NUM> may be withdrawn. As can be appreciated, since the upwelling 11U forces the cap <NUM> to conform to the surface S3, establishing a close relative fit, there may be some resistance to withdrawing the first tip <NUM> from the fastener 110f at stage F6. In some applications, it may also be preferred to utilize a pre-formed fastener to reduce withdrawal force, cycle time and to reduce the amount of welding force Fw needed to shape the cap <NUM> to conform to the surface S3 and the upwelling 11U.

<FIG> shows a sequence of steps A7-F7 in use of a fastener <NUM> to perform spot welding through an upper layer <NUM><NUM>, e.g., an aluminum sheet, to fasten the upper layer <NUM> to a lower layer <NUM>, e.g., a steel sheet. The fastener <NUM> is preformed to have a shape similar to the fastener <NUM> after it has been formed by the welding force shown in stages D6 and E6 of <FIG>, such that the upper section can encapsulate and seal the top surface without the need to be formed by the electrode during the welding process. Since the fastener <NUM> is preformed, the electrode tip <NUM> does not require the concave annular surface S3 to shape the cap <NUM> to accommodate and seal against upwelling 11U of the first layer <NUM> proximate where it is penetrated by the fastener <NUM>. As a result, the electrode tip <NUM> can taper (be radiused at surfaces S4, S5 to the surface S2 supporting the end <NUM> of the fastener <NUM>. This allows the concentration of heating, welding, and tempering forces FH, FW, FT as well as the heating, welding, and tempering currents IH, IW, IT over a smaller area, allowing reduced force and current to accomplish the tasks of penetration, welding and tempering.

<FIG> depict direct access welding wherein the resistance welding electrodes, e.g., 15a, 17a, clamp the work pieces/welding stack 10a, <NUM>, <NUM> from opposing sides. As shown in <FIG>, spot welding using a fastener <NUM>, <NUM>, <NUM>, <NUM>, in accordance with the present disclosure can be conducted from one side using indirect welding. A structure S8, such as a steel beam or any other type of structure may be connected to one pole of a source of electrical potential for conducting welding. The other pole provides electrical power to welding tip <NUM> to supply electrical power for heating at stages B8 and C8, welding at D8 and tempering at E8. Indirect welding is commonly done on steel, but is difficult to conduct on aluminum to aluminum joints. Since the present disclosure permits welding with a fastener made from materials other than aluminum, it facilitates the conjunction of an aluminum layer <NUM>, e.g., an aluminum sheet, to a steel structure S8, such as a steel tube.

In series welding, two or more electrodes approach from a single side. Multiple welds are then produced as the welding current flows between multiple guns in a series fashion. <FIG> shows that the welding process and apparatus of the present disclosure can be utilized in conducting series welding fasteners 210a and 210b to join layers/members <NUM>, <NUM> in a single welding operation. Current IH passes through electrode 215a, layers <NUM>, <NUM>, through a conductive backer bar S9, then back through layers <NUM>, <NUM> to electrode 215b. As before, the current IH heats layer <NUM> allowing penetration by fasteners 210a, 210b, the fasteners welding on contact with layer <NUM>. The overall process is similar to that explained above, but only stages B9, D9 and F9 are shown. Series welding is not typically conducted on aluminum but is commonly done using steel materials. Since the present disclosure permits welding with a fastener made from materials other than aluminum, it facilitates the conjunction of an aluminum layer <NUM>, e.g., an aluminum sheet, to a steel layer/sheet <NUM> or structure, such as a steel tube or box structure via series welding.

While the foregoing examples refer to a fastener <NUM>, <NUM>, <NUM>, <NUM> made from steel, the fastener <NUM>, <NUM>, <NUM>, <NUM> may be made from any material and the first layer <NUM> and succeeding (second) layer(s) <NUM> may also be varied in composition and number. In order to penetrate an intervening layer like layer <NUM>, the fastener <NUM>. <NUM> should be made of a material with a higher melting point than the intervening layer(s) <NUM> penetrated during the heating/penetrating phase, e.g., B6, C6 (<FIG>). In order to conduct the welding phase, e.g., D6, the fastener <NUM> material must be compatible with the layer to which it is to be resistance welded, e.g., layer <NUM>. For example, if the layer <NUM> is made from high strength (><NUM> MPa) galvanized steel, then the fastener <NUM> may be made, e.g., from standard, low-carbon steels, high strength steels (><NUM> MPa) or stainless steel grades.

<FIG> shows that a fastener 210c may be used with an opposing fastener 210d to conjoin a pair of layers 11a,11b, e.g., made from aluminum or magnesium, by spot welding to one another, such that the caps 212c, 212d capture the layers 11a, 11b there between. The procedure shown in stages A10 to F10 mimics the above-described procedure, e.g., as described in reference to <FIG>, in that electrical resistance is used in heating, penetration of the layers and welding, but instead of the fasteners 210c, 210d reaching a layer <NUM> to which they are welded, they each penetrate the intervening layers 11a, 11b in opposite directions, meet and weld to each other.

<FIG> shows that various combinations of layers may be joined in accordance with an example. As shown in combination G, the stack-up of materials may be aluminum 11A and steel <NUM> like the stack-up shown and described above in relation to <FIG> at stage B7. As described above, the fastener <NUM> can be pushed through the aluminum layer 11A and welded to the steel layer <NUM>. Combination H shows a stack-up of two layers of aluminum 11A1 and 11A2 with a steel layer <NUM>. As before, the fastener <NUM> can be pushed through the aluminum layers 11A1 and 11A2 and then welded to the steel layer <NUM>. Combination I shows a stack-up of a layer of aluminum 11A and a layer of magnesium <NUM> with a steel layer <NUM>. The fastener <NUM> can be pushed through the aluminum layer 11A and the magnesium layer <NUM> and then welded to the steel layer <NUM>. Combination J shows a stack-up of an outer layer of magnesium <NUM> an intermediate layer of aluminum 11A and a steel layer <NUM>. The fastener <NUM> can be pushed through the magnesium layer <NUM> and the aluminum layer 11A and then welded to the steel layer <NUM>. In each of the stack-ups shown in G, H, I and J, the fastener <NUM> may be used to secure the laminate structure shown. Other combinations of material, thicknesses and numbers of layers are possible to be secured by the fastener <NUM>, <NUM>, <NUM>, <NUM>.

<FIG> shows a welding electrode tip <NUM> with a connector sleeve portion <NUM> and a welding portion 215W with radiused tapered surfaces S4 and S5. A tip like this is available from CMW Contacts Metal Welding www. com and is called a G-cap.

<FIG> shows a cap nut repurposed to function as a fastener <NUM>.

The fastener <NUM> has a cap <NUM>, a shaft <NUM> and an end <NUM>. Lugs <NUM> for interacting with a mating tool <NUM> may be used to retain the fastener <NUM> on an electrode tip like tip <NUM> and may also be used to twist the fastener as it is pushed through an intermediate layer <NUM> and/or when it is welded to a layer <NUM>.

<FIG> and <FIG> are side and plan views, respectively, of a fastener <NUM> in accordance with another example. The fastener <NUM> can be made as a stamping using a stamping tool and back-up die as shown in <FIG>. The cap <NUM> transitions into the shaft <NUM> at curve C1 and the shaft <NUM> transitions into the end <NUM> at curve C2. The curve C1, when rotated about the axis of symmetry S of the fastener <NUM> and delimited by edge 412e and its projection on the shaft <NUM>, circumscribes a volume V1 that can contain and seal off upwelling of the penetrated layer, e.g., as shown as 11U in <FIG>.

<FIG> shows a fastener stamping tool <NUM> in accordance with an example. The stamping tool may be used to form fasteners like fastener <NUM> from stock material <NUM>, e.g., a sheet of steel. The fastener stamping tool <NUM> has an upset die <NUM> with a forming surface <NUM> (shown in dotted lines). A shaping tool <NUM> (in dotted lines) driven by a punch <NUM> (shaft shown in dotted lines), which acts in conjunction with the upset die <NUM> to form a fastener <NUM> (<FIG>, <FIG>) from the stock <NUM>. In the example shown, the shaping tool <NUM> both cuts the fastener <NUM> from the stock <NUM> and shapes it as it is driven down through the stock <NUM> by the punch <NUM>. Alternatively, disk-shaped blanks (not shown) having the dimensions required to form a fastener <NUM> may be cut from the stock by a separate punch and loaded into a blank holder <NUM> before the punch <NUM> is driven down against the upset die <NUM> to shape the blank into the fastener <NUM>. A spring <NUM> may be inserted between a retainer cap <NUM> and the blank holder <NUM> to return the punch <NUM> to a neutral position after a fastener <NUM> has been stamped out by the fastener stamping tool <NUM>. The punch <NUM> may be coupled to a punch holder <NUM> that is driven mechanically, hydraulically or pneumatically in a conventional manner for actuating punches and presses.

<FIG> shows welding stack-up <NUM> wherein a fastener <NUM> is positioned against first and second layers <NUM>, <NUM> prior to penetration or welding. The first layer <NUM> may be an aluminum, magnesium or copper sheet and the second layer may be a steel, titanium or inconnel sheet. The layers <NUM>, <NUM> and fastener <NUM> are clamped between first and second tips <NUM>, <NUM> that are in electrical continuity with lower and upper electrodes <NUM>, <NUM> of a commercially available electric spot welding machine, such as a 250kVA welding station available from Centerline Welding, Ltd.

In one example of a welding operation conducted in accordance with the present invention, a commercially available 250kVA AC resistance spot welding pedestal machine was employed to heat and plunge a fastener/rivet through an aluminum sheet and weld to a steel backing sheet. The upper electrode tip <NUM> was a commercially available electrode called a G-cap (similar to the tip <NUM> of <FIG>) and the lower electrode tip <NUM> was a standard, flat faced (<NUM> diameter, RWMA type C-Nose). A standard cap nut <NUM> as shown in <FIG> was used for the rivet. The parts to join were <NUM> <NUM>-T6 aluminum alloy and <NUM> 270MPa galvanized steel. The cap nut <NUM> was placed on the G-cap electrode <NUM> and then against the aluminum sheet <NUM> in the stackup as shown in <FIG>. Current pulses about <NUM> secs. in duration at <NUM>,<NUM> amps were generated to cause the cap nut <NUM> to penetrate the aluminum sheet <NUM>. After penetration, the cap nut <NUM> was welded to the steel with a current impulse around 15kA for <NUM>. A weld button, approximately <NUM> in diameter, between the steel cap nut and the <NUM> 270MPa steel sheet was obtained.

Aspects include low part distortion, since the layers to be fastened, e.g., <NUM>, <NUM>, are held in compression during the weld and the heat affected zone is primarily restricted to the footprint of the cap, e.g., <NUM> of the fastener <NUM>. The fasteners, e.g., <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> form a volume relative to the first layer <NUM> to trap intermetallics or materials displaced by penetration of the fastener through the first layer <NUM>. The fasteners, e.g., <NUM>. <NUM> can be used to fasten a range of layer thicknesses and number of layers of different kinds of materials, viz. , by selecting a fastener of the appropriate dimensions and material composition. In addition, a given fastener <NUM>. <NUM> may be operable over a range of thicknesses due to the elasticity of the materials of which it is formed, as well as the shape of the fastener. For example, the cap <NUM> may elastically bend relative to the shaft <NUM> when the fastener <NUM> is used to accommodate various thicknesses and to resiliently press upon the layer(s), e.g., <NUM> when welded to layer <NUM>. The resilient pressing of the cap <NUM> against a layer, e.g., <NUM> may contribute to establishing and maintaining a seal around the perimeter of the fastener <NUM>. <NUM> when it is in place.

The fastener <NUM>. <NUM> of the present disclosure may be applied through adhesives and/or other coatings applied between layers, e.g., <NUM>, <NUM> and/or through coating applied to the top layer <NUM>. The weld formed by use of the fastener, e.g., Pe in <FIG>, does not penetrate the layer <NUM> nor disturb the surface of <NUM> opposite to the weld, preserving appearance, corrosion resistance and being water-tight. During fastener penetration, e.g., at stage C of <FIG> and the welding phase, stage D, the fastener 10c, 10d, 10e will continually collapse and expand along the weld zone Pd, Pe, pushing out intermetallics from the weld zone. The methodology and apparatus of the present invention is compatible with conventional RSW equipment developed for steel sheet resistance welding and the fastener, <NUM>. <NUM> can be made out of a variety of materials, such as, various steel grades (low carbon, high strength, ultra high strength, stainless), titanium, aluminum, magenesium, and copper. The fastener may optionally be coated (galvanized, galvaneal, hot-dipped, aluminized) to improve corrosion resistance.

As noted above, the fastener <NUM>. <NUM> may be used via single-sided or two-side access welding. The fastener <NUM>. <NUM> does not require a pilot hole, but can be also used with a pilot hole in the aluminum or top sheet. Pilot holes may also be used to allow electrical flow through dielectric layers such as adhesive layers or anti-corrosive coatings/layers. The weld quality resulting from use of the fastener <NUM>. <NUM> can be tested in accordance with quality assurance measurements applied to the cavity left by the weld, i.e., by measuring the dimensions of the cavity. Ultrasonic NDE techniques may also be utilized on the backside, e.g., of layer <NUM> (steel side) to monitor the weld quality.

Compared to FDS (EJOTS), SPR, and SFJ, the apparatus used to apply the fastener <NUM>. <NUM> has a smaller footprint, allowing access to tighter spaces. The apparatus and method of the present invention uses lower insertion forces as compared to SPR since the first layer <NUM> is heated/softened during the fastener insertion phase, e.g., see stage C of <FIG>. The methods and apparatus of the present invention provide the ability to join high strength aluminums (which are sensitive to cracking during SPR operations) and to join to high and ultra high strength steels, since there is no need to pierce the steel metal with the fastener but rather the fastener is welded to it.

The apparatus and method of the present invention does not require rotating parts and is conducive to resolving part fit-up issues since the overall process is similar to conventional resistance spot welding (RSW) with respect to how the component layers/parts are fixtured. In addition, the application of the fastener <NUM>. <NUM> can be conducted quickly providing fast processing speeds similar to conventional RSW. The apparatus and method can be applied to use on both wrought and cast aluminum products and may be used to produce a compatible metal joint rather than a bimetallic weld as when welding aluminum to steel, which may have low joint strength. As noted above, the apparatus and method may be used to conjoin multiple layers of different materials, e.g., two layers of aluminum, one layer of steel; one layer of aluminum, two layers of steel; or one layer of aluminum, one layer of magnesium, and one layer of steel.

<FIG> shows a cross-sectional view of a fastener <NUM> like fastener <NUM> of <FIG>, wherein the thickness of the cap <NUM>, shaft <NUM> and end <NUM> are substantially of constant thickness. The end <NUM> is flat.

<FIG> shows a fastener <NUM> wherein the end <NUM> is flat and has a greater thickness than the shaft <NUM> of cap <NUM>.

<FIG> shows a fastener <NUM> with a radiused end <NUM> having a constant thickness. In one example, the radius R is in the range of <NUM> to <NUM> inches (<NUM> to <NUM>).

<FIG> shows a fastener <NUM> having a radiused end <NUM> and splines <NUM> at the conjunction of the end <NUM> and the shaft <NUM>. The splines <NUM> may be aligned with the axis of symmetry/rotation S or disposed at an angle A relative thereto. The splines may be utilized to either guide the fastener in a particular direction, e.g., straight or in a spiral when the fastener is pressed through the layer <NUM> and/or may be used as an anti-rotation feature that prevent rotation of layer <NUM> relative to installed fastener <NUM>.

<FIG> show a fastener <NUM> having a length L greater than the width W thereof. In one example, the length L may be in the range <NUM> to <NUM> and the width in the range <NUM> to <NUM>.

<FIG> shows a fastener <NUM> that in cross-section has left and right portions 1210a, 1210b that converge at 1212c. Fastener <NUM> is a solid of rotation about line of symmetry/rotation S, such that the ends 1216a, 1216b form a continuous ring surface that may be welded to a substrate as further illustrated below.

<FIG> shows fastener <NUM> inserted through first layer <NUM>, e.g., made from aluminum and welded to layer <NUM>, e.g., made from steel at weld zones Pa, Pb, which would have a continuous ring shape. The ring shaped weld would be distributed over a larger surface area then a disc shaped weld, as would be produced, e.g., by the use of a fastener like <NUM> as shown in <FIG>. Tip <NUM> has a surface <NUM> accommodating and supporting the fastener <NUM> as it is heated and pressed toward tip <NUM>.

<FIG> shows a fastener <NUM> in cross-section inserted through a first layer <NUM> and welded to a second layer <NUM> at weld zones Pa, Pb. As in <FIG>, fastener <NUM> is a solid of rotation about line of symmetry/rotation S, such that weld zones Pa and Pb are part of a continuous ring-shaped weld to layer <NUM>. Fastener <NUM> features a threaded, central socket <NUM> having threads 1342t suitable to receive a mating threaded fastener, such as a bolt (not shown). In this manner, fastener <NUM> can perform two functions, viz. , retain layer <NUM> to <NUM> and provide a threaded socket permitting assembly to another member or structure (not shown) via a mating threaded fastener (not shown). Tip <NUM> has a recess 1315r for accommodating the socket <NUM> while welding.

<FIG> and <FIG> show a fastener <NUM> like fastener <NUM>, but having a socket portion <NUM> with threads 1442t that is open ended, allowing a mating threaded fastener (not shown) to pass through the socket portion <NUM>. As shown in <FIG>, in preparation for installation of the fastener <NUM>, the layers <NUM> and <NUM> are preferably drilled or otherwise provided with mating holes <NUM>, <NUM> through which the socket portion <NUM> can be inserted. The penetration of the layer <NUM> and the welding to layer <NUM> can then be performed by resistance welding, as explained above. Tip <NUM> has a surface <NUM> for supporting the fastener <NUM> as it is pressed through layer <NUM> and welded to layer <NUM>. Tip <NUM> has a recess 1417r accommodating the socket portion <NUM> that extends through the layers <NUM>, <NUM> during the welding process.

<FIG> shows a fastener <NUM> having an upper part 1510u and a lower part <NUM> which may be welded together to attach the fastener to a layer <NUM>, e.g., of aluminum. The lower portion <NUM> features a threaded socket 1510t. The fastener <NUM> may be made from steel or titanium. The welding process is conducted as before only instead of welding to a second layer <NUM>, the upper part 1510u is welded to the lower part <NUM> after the upper part is pushed through the aluminum layer <NUM>. As before, the weld zones Pa, Pb are a part of a ring shaped weld because the fastener <NUM> is a solid of rotation. The layer <NUM> is captured between flange portion 1510f and cap <NUM>. The fastener <NUM> permits a threaded socket 1510t, made from a first material, e.g., steel or titanium, to be attached to a layer <NUM> of dissimilar metal, e.g., aluminum or magnesium.

<FIG> shows a fastener <NUM> having an upper part 1610u and a lower part <NUM> which may be welded together to attach the fastener to a layer <NUM>, e.g., of aluminum. The lower part <NUM> features a threaded stud <NUM>. The fastener <NUM> may be made from steel or titanium. The welding process is conducted as before only instead of welding to a second layer <NUM>, the upper part 1610u is welded to the lower part <NUM> after the upper part is pushed through the aluminum layer <NUM>. The weld zone Pa is approximately disk-shaped and the fastener <NUM> is a solid of rotation. The layer <NUM> is captured between flange portion 1610f and cap <NUM>. The fastener <NUM> permits a threaded stud <NUM>, made from a first material, e.g., steel or titanium, to be attached to a layer <NUM> of dissimilar metal, e.g., aluminum or magnesium.

<FIG> show a self-sealing fastener <NUM> with a bead of sealant <NUM> applied to the underside proximate the conjunction of the cap <NUM> and shaft <NUM>. The sealant may be an adhesive or polymer and may be applied as a liquid, gel or paste and may cure to a solid or semi-solid or may remain in a soft or liquid state prior to use of the fastener <NUM>. When the fastener <NUM> is used to couple layers <NUM> (aluminum), <NUM> (steel) of material together by the welding of the fastener <NUM> to the base sheet <NUM> or to another fastener <NUM>, e.g., as described above for fasteners <NUM> (<FIG>), the sealant may undergo a change of state, e.g., if solid, it may melt due to the heat generated by insertion of the fastener <NUM> through an intermediate layer <NUM> by melting from electrical resistance or during the welding phase to form weld 1710W. After the fastener <NUM> and the metal to which it has welded cools, the sealant <NUM> may return to a solid after conforming to the surfaces of the top layer <NUM> and to any upwelling therein 11U, thereby providing sealed joint 1710J, with a seal between the top layer <NUM> and the fastener <NUM>. The sealant <NUM> prevents infiltration by elements present in the environment, e.g., oxygen or moisture, which can lead to corrosion of the fastener <NUM>, the sheets <NUM>, <NUM> and/or the weld 1710W. In the alternative, the sealant <NUM> may remain a semi-solid or gel after the weld 1710W is completed. The sealant <NUM> may be applied in several different ways, including: (i) application to the fastener <NUM> as a step in fastener manufacture; (ii) application to the fastener <NUM> just prior to use in forming a welded joint; e.g., by applying: a bead (ejected by a nozzle under pressure), a ring preformed in solid or semi-solid form (and placed on the fastener <NUM>), or a band of sealant (provided in the form of a severable strip or painted on by a contact applicator or sprayed on under pressure) to the fastener <NUM> prior to contacting the outer sheet <NUM>. In the alternative, the sealant <NUM> may be applied to the surface of the sheet <NUM>, e.g., in the form of an adhesive dot placed on the top surface <NUM> where the fastener <NUM> will be inserted or around the periphery of a pilot hole in the sheet <NUM> prior to the joining process. The sealant <NUM> may be applied to the fastener <NUM> through the use of 'compound liner' equipment currently used in the beverage can end lining process. The technology disclosed in <CIT> can be utilized to stop rotation of the fastener <NUM> during sealant <NUM> application, reducing damage to the protective coating of sealant <NUM> applied to the fastener <NUM>. The sealant <NUM> can be utilized with any of the fasteners <NUM>, <NUM>, <NUM>, etc. and layers <NUM>, <NUM>, <NUM>, etc., described above. <FIG> shows the sealant <NUM> after the fastener <NUM> has been welded to layer <NUM>. The sealant <NUM> can partially or fully fill the cavity between the underside 1710U of the fastener <NUM> and upper surface <NUM> of the sheet <NUM>. The sealant <NUM> can provide corrosion protection, increase the joint strength between the fastener <NUM> and the top surface <NUM>, and/or eliminate water/moisture from entering the joint J.

<FIG> show a cross section of a bi-layer fastener <NUM> with a first layer <NUM>, e.g., made of steel, titanium, copper or a first aluminum alloy, e.g. 1xxx, and a second layer 1810A, e.g., made of aluminum or a different type of aluminum alloy, e.g., 6xxx. The fastener <NUM> may be formed, e.g., stamped, from a bi-layer sheet of multi-alloy (1xxx clad on 6xxx, etc.) or multi-material (aluminum clad steel, aluminum clad copper, etc.). <FIG> shows the cross section of a joint 1810J formed with the bi-layer fastener <NUM>, a first sheet <NUM>, e.g., of aluminum or aluminum alloy and a second sheet <NUM> of steel, titanium, copper, magnesium or another alloy distinct form the alloy of layer <NUM>. The bi-layer fastener <NUM> allows welding to the aluminum member <NUM>, viz. , by welding layer 1810A to sheet <NUM>. In this instance, an aperture <NUM> is formed in sheet <NUM>, such that the fastener <NUM> can be inserted through the aperture <NUM> rather than melt through it by resistance heating. One aspect of this approach is that it allows joining a steel sheet or member <NUM> to an aluminum sheet or member <NUM>, e.g., a tube, from a single side. The bi-layer fastener <NUM> allows the welding to occur using low current levels since layer <NUM>, which may be, e.g., steel, in contact with the electrode head <NUM>, provides enhanced heating of layer 1810A and sheet <NUM> during the welding. In a first approach, the layer 1810A may be made from or include a brazing alloy, allowing a braze joint to the opposing sheet <NUM> rather than a resistance weld. This would be beneficial to reduce the amount of weld current required. The joint 1810J could be used to join an aluminum or plastic sheet <NUM> to an aluminum sheet <NUM> where low heat inputs are required to prevent melting of the sheet <NUM>. In another aspect of this embodiment, a fastener <NUM> formed from aluminum clad steel could be used to join a plurality of aluminum sheets. A steel layer <NUM> of the fastener <NUM> would contact the electrode <NUM>, while the aluminum side 1810A would contact the aluminum sheets <NUM> (in this embodiment, sheet <NUM> would also be aluminum). As the weld heat is applied, the steel layer <NUM> would provide enhanced heating, enabling the aluminum portion 1810A of the fastener <NUM> to weld with the aluminum sheets <NUM>, <NUM> at low currents. In another aspect of this embodiment, the layer <NUM> may be formed from copper clad to an aluminum portion 1810A. The copper portion <NUM> would contact the electrode <NUM> and the aluminum portion 1810A would contact and weld to aluminum sheets <NUM>, <NUM>. In this embodiment, the copper portion <NUM> of the fastener <NUM> would exhibit good heat transfer and low electrode wear.

<FIG> shows a tri-metallic fastener <NUM>, with layers <NUM>, <NUM> and 1910A. The middle layer <NUM> may be selected to prevent diffusion between the outer layers <NUM>, 1910A when the fastener <NUM> is exposed to elevated temperatures, providing joint strength. The middle layer <NUM> may be composed of a variety of materials, including but not limited to, high purity aluminum, titanium, or zinc. In one example, the outer layer <NUM> is steel and the root outer layer 1910A is aluminum. The middle layer <NUM> may be selected to be a thin layer of titanium, which would prevent the aluminum layer 1910A and steel layer <NUM> from diffusing at high temperatures (><NUM> degree C).

<FIG> shows a bi-layer fastener <NUM> having a disc 2010A of aluminum joined to a stamped / cold-formed steel portion <NUM>. The aluminum disc 2010A can be joined to the steel portion <NUM> through a number of means not limited to cold welding, ultrasonic, friction welding, upset butt welding, high pressure welding, mechanical, or brazing/soldering. Optionally, the aluminum disc 2010A may be joined to the steel portion <NUM> in wire form (cold welding, pressure welding) prior to the shaping of the steel portion <NUM> into the shape shown. The fastener <NUM> may be used in the same fashion as the fastener <NUM> shown in <FIG> to fasten sheet <NUM> to sheet <NUM>.

<FIG> shows a tri-layer fastener <NUM> like the fastener <NUM> of <FIG>, but having an additional layer 2110T, e.g., made from titanium interposed between layers <NUM>, e.g., made from steel and 2110A, e.g., made from aluminum. The fastener <NUM> may be used in a similar manner as fastener <NUM> of <FIG> and fastener <NUM> of <FIG>, but the additional layer 2110T may be used to prevent diffusion between layers 2110A and <NUM> and therefore may be useful for high temperature applications in a similar manner as the fastener <NUM> with middle layer <NUM> shown in <FIG>.

<FIG> shows a fastener <NUM> having mechanically interlocked portions 2210A, <NUM>. The mechanical interlocking may be accomplished by swaging, forging, upsetting or bending. For example, the portion 2210A may be formed with a peripheral recess 2210AR and the portion <NUM> may be formed having an inwardly extending peripheral lip 2210SL. The portion 2210A may then be forced into portion <NUM> such that the peripheral recess 2210AR and the peripheral lip 2210SL interlock. This may be also be accomplished by a forging die that collapses and compresses portion <NUM> about portion 2210A to create an interlocking relationship. In a first aspect, the materials of <NUM> and 2210A may be different aluminum alloys (1xxx to 6xxx, 4xxx to 6xxx, 4xxx to Al-Li) or different materials (steel and aluminum, aluminum and magnesium, aluminum and titanium, etc.). The fastener <NUM> is shown positioned relative an electrode tip <NUM> and may be used similarly to the fastener <NUM> shown in <FIG>.

<FIG> shows a fastener <NUM> with a protective sleeve 2310T positioned about the portion <NUM> proximate the cap <NUM> and stem <NUM> of the fastener <NUM>. The protective sleeve 2310T may provide corrosion protection between the fastener <NUM> and sheet that is penetrated. For example, where the portion <NUM> is steel and passes through an aluminum sheet <NUM> by resistance heating to weld to a steel sheet <NUM>, as shown in <FIG>, the coating 2310T may be titanium, stainless steel or cold sprayed aluminum. The sleeve 2310T can be mechanically interlocked to the portion <NUM> as shown in <FIG> (showing sleeve 2410A), applied by cold spray coating, plasma spray coating, etc. The protective sleeve 2310T may be made from metal or from materials having low thermal or electrical conductivity, such as ceramics. In this aspect, the low (thermally/electrically) conductive materials will focus the heat and current though the end <NUM> of the fastener <NUM>, enabling lower current demand to accomplish welding to a layer <NUM> than if the protective sleeve 2310T were not present. Once welded to a layer <NUM>, e.g., to fasten a layer <NUM> of aluminum to a layer <NUM> of steel (see <FIG>), the protective sleeve <NUM> may function to isolate the portion <NUM>, which may be made from steel, from the aluminum layer <NUM> through which it passes, preventing corrosion due to contact between dissimilar metals and the galvanic effect.

<FIG> shows a fastener <NUM> having a protective sleeve 2410A disposed on the portion <NUM> in a similar manner to the fastener <NUM> described in <FIG>. The protective sleeve 2410A is retained on the fastener <NUM> by a rim 2416R that captures the sleeve 2410A between the rim 2416R and the cap portion <NUM>. The rim 2416R may be preformed and the sleeve 2410A slipped over the rim 2416R followed by compression by a die, or the sleeve 2410A may be slipped onto the shaft <NUM> followed by formation of the rim 2416R, e.g., by upsetting/forging. As with the fastener <NUM>, the fastener <NUM> may exhibit enhanced resistance to corrosion and heat transfer and may be used in a similar manner to couple a first sheet or member <NUM>, e.g., of aluminum to a second sheet or member <NUM>, e.g., of steel (See <FIG>). Since the rim 2416R is the leading element as the fastener is pushed through an intermediate layer <NUM> (see <FIG>), and may be formed from steel, it will form an aperture through the intermediate layer <NUM> large enough to accommodate the sleeve 2410A, such that the sleeve itself does not need to play a part in forming the aperture in the intermediate layer <NUM> and is therefore preserved from distortion or loosening on the shaft <NUM> when the fastener <NUM> is pressed through the intervening layer <NUM>.

<FIG> shows a "semi-solid" fastener <NUM> having a solid shaft <NUM>. The cap <NUM> has an electrode depression 2512D matingly accommodating an electrode extension 2515E of electrode <NUM>. This arrangement may be used to reduce electrode <NUM> wear. In one example, the electrode depression 2512D and the electrode extension 2515E each approximate <NUM>-<NUM> in diameter and have a depth of <NUM> to <NUM>. Since the shaft <NUM> is solid, it is not as collapsible as a thin wall shaft like shaft <NUM> of fastener <NUM> shown in <FIG>. When penetrating an intermediate layer <NUM> (e.g., made from aluminum) to reach a layer <NUM> (e.g., made from steel) to weld to (See <FIG>), the shaft <NUM> of the fastener <NUM> is shorter and does not have to collapse. As a result, the fastener <NUM> reaches the layer <NUM> quicker. This reduces the amount of time that current flows through the electrode <NUM> and the fastener <NUM>, reducing electrode erosion and improving the productivity of the process. The contact area between the electrode extension 2515E and the electrode depression 2512D increases the electrical contact area over that of smooth mating surfaces, reducing electrical resistance and providing a mechanical coupling that preserves the relative position of the fastener <NUM> and the electrode <NUM> during placement of the fastener <NUM>.

<FIG> shows a "solid" fastener <NUM> with a solid shaft <NUM>. The cap <NUM> has an upper electrode receiving surface <NUM> with a constant radius, of, e.g., <NUM> to <NUM> inches, which allows the use of a conventional, radiused spot welding electrode <NUM> having a similar radius. This relationship reduces the need for special electrode designs and dressing equipment and also reduces electrode wear. The cap <NUM> may be proportioned to allow collapse toward the sheet <NUM> (see <FIG>) through which the shaft <NUM> is pushed during the insertion process, with the cap <NUM> flattening against the sheet <NUM> when fully inserted. A small tip element 2616T can extend from the end <NUM> of the fastener <NUM>, which may be used to concentrate current and heating to help initiate heating/softening of a sheet <NUM> to be pierced and it initiate welding to a sheet <NUM>.

<FIG> shows a solid fastener <NUM> similar to fastener <NUM> but having an electrode alignment projection 2712P extending up from the radiused surface <NUM>. The projection 2712P may be received in a mating recess 2715R of the electrode <NUM>. The mating projection 2712P and recess 2715R may help keep the fastener <NUM> aligned with the electrode <NUM> during the insertion and welding processes (through a sheet <NUM> to weld to a sheet <NUM>, as shown in <FIG>). The radius of the projection 2712P may be, e.g., <NUM>/<NUM>" to <NUM>/<NUM>". While the recess 2715R requires s unique electrode geometry, it is compatible with conventional electrode dressing equipment.

<FIG> shows a joint 2800J wherein a pair of opposing fasteners 2810A, 2810B penetrate through layers 11A, 11B (such as sheets of aluminum), respectively, e.g., by resistance heating and pressure, and weld to a central layer <NUM>, e.g., made from steel. To achieve this configuration, the fasteners 2810A, 2810B may be inserted simultaneously (in a single operation) through the aluminum sheets 11A, 11B and weld to the steel layer <NUM>. Alternatively, the fasteners 2810A, 2810B may be inserted and welded sequentially.

<FIG> shows a cross section of a fastener <NUM> having an extended grip range. The cap <NUM> extends down to an extent comparable to the shaft <NUM>. A ring 2912I, of insulating material is attached to the terminal end of the cap <NUM>, such that the bottom edge of the ring 2912I is approximately co-extensive with the end <NUM>. In use, the fastener <NUM> may be placed on a surface of a sheet <NUM>, e.g., made from aluminum and then heated by electrical resistance by a resistance welder as described above, e.g., in relation to <FIG>, to penetrate the sheet <NUM> and weld to an underlying sheet <NUM>, e.g., made from steel. Because the ring 2912I is an insulator, the electrical current passes only through the end <NUM>. As the end <NUM> presses through the sheet <NUM>, the ring 2912I abuts against the sheet <NUM> as the end <NUM> passes through the sheet <NUM>. As a consequence, the cap <NUM> bends to the degree necessary to allow the end <NUM> to reach and weld to sheet <NUM>, while the ring 2912I abuts against sheet <NUM>. As a result, the shaft <NUM> can penetrate a variety of thicknesses of sheet <NUM> and (the ring 2912I thereof) will still press against the sheet <NUM> urging it into contact with sheet <NUM>.

<FIG> and <FIG> show a first panel <NUM>, e.g., made from an aluminum alloy, positioned against a second panel <NUM>, e.g., made from steel. The first panel <NUM> is bent to form a J-shape 11J, which embraces an edge 13E of the panel <NUM>. The panel <NUM> is staked to the panel <NUM> proximate the J-shape 11J and edge 13E by a fastener <NUM> which passes through one thickness 11T of the panel <NUM> and welds at 3010W to the steel panel <NUM>, forming joint 3000J. As shown, the weld 3010W does not disturb the remainder 11R of the panel <NUM>, such that the joint 3000J is suitable for applications, like an automobile body, requiring a smooth surface appearance on the remainder 11R of the panel. As shown in <FIG>, electrodes <NUM> and <NUM> may approach from the same direction, with <NUM> pressing against the fastener <NUM> and electrode <NUM> contacting the steel panel <NUM>. As resistance heating softens the sheet <NUM>, the fastener <NUM> is pressed through the sheet <NUM> and welds to the sheet <NUM>. As shown in <FIG>, a plurality of fasteners <NUM> may be used to form a "hem" <NUM> along the edge 13E of the sheet <NUM>, with the J-shape 11J wrapped around the edge 13E. The hemmed joint <NUM> may employ an adhesive to aid in holding the sheets <NUM>, <NUM> together.

<FIG> shows a pair of sheets 11A, 11B, e.g., of aluminum, coupled to a layer <NUM>, e.g., of steel, by fastener <NUM>. The fastener <NUM> has penetrated both aluminum sheets 11A, 11B, e.g., by electrical resistance heating, prior to contacting and subsequently welding to the steel sheet <NUM> at 3110W and forming joint 3100J. In joint 3100J, the heat from penetrating and welding, e.g., emitted from the fastener <NUM>, which may be steel, locally melts the aluminum sheets 11A and 11B adjacent to the fastener <NUM>, producing a weld 3110W2 between the sheets 11A and 11B that partially or completely encircles the fastener <NUM>. The weld 3110W2 consolidates the aluminum sheets 11A, 11B, and strengthens the joint 3100J. The aluminum sheets 11A, 11B can be of identical or dissimilar thicknesses. An adhesive may be present between one or all the sheet interfaces.

<FIG> shows a joint 3200J coupling two sheets 11A, 11B, e.g., made from aluminum, by two opposing fasteners 3210A, 3210B, e.g., made from steel. The fasteners 3210A, 3210B may be installed simultaneously from opposite sides via a pair of opposing welding electrodes in a similar manner to the embodiment shown in <FIG>. The fasteners 3210A, 3210B are urged together and by resistance heating, penetrate the aluminum sheets 11A, 11B and then weld to each other, forming weld 3210W. As noted above with respect to the embodiment shown in <FIG>, in passing through the sheets 11A, 11B, the steel fasteners 3210A, 3210B locally heat the aluminum sheets 11A, 11B adjacent thereto and create a weld 3210W2 that partially or completely encompasses the weld 3210W between the fasteners 3210A, 3210B. <FIG> shows sheets 11A, 11B of equal thickness, resulting in a symmetric joint 3200J, but as shown below, the process will work for sheets 11A, 11B of different gauges. In another alternative, two different fasteners 3210A, 3210B, with different operational reaches (shaft lengths) may be employed, the greater length being applied to the sheet with the greater thickness and vice-versa.

<FIG> shows a joint 3300J coupling two sheets 11A, 11B, e.g., made from aluminum, by two opposing fasteners 3310A, 3310B, e.g., made from steel. The fasteners 3310A, 3310B may be installed simultaneously from opposite sides via a pair of opposing welding electrodes in a similar manner to the embodiment shown in <FIG>. The fasteners 3310A, 3310B are urged together and by resistance heating, penetrate the aluminum sheets 11A, 11B and then weld to each other, forming weld 3310W. As noted above with respect to the embodiment shown in <FIG>, in passing through the sheets 11A, 11B, the steel fasteners 3310A, 3310B locally heat the aluminum sheets 11A, 11B adjacent thereto and create a weld 3310W2 that partially or completely encompasses the weld 3310W between the fasteners 3310A, 3310B. <FIG> shows sheets 11A, 11B of unequal thickness, resulting in an asymmetric joint 3300J. As shown the fasteners 3310A, 3310B, have equal operational reaches (shaft lengths) resulting in a weld 3310W that is not at the interface 3311I between the sheets 11A, 11B. An aspect of the joint 3300J is that the load path through the joint 3300J follows several directions (not on the same axis) so it will have enhanced mechanical performance. As noted above, joint 3300J can be employed with or without adhesives, e.g., applied at the interface 3311I. The weld zone 3310W2 between the aluminum sheets 11A, 11B can be selectively made larger or smaller by selecting the weld schedule employed during the welding process. Additional heat cycles can be added to extend the aluminum weld zone 3310W2, and increase the overall performance of the joint 3300J.

<FIG> shows a joint 3400J coupling three sheets 11A, 11B, 11C e.g., made from aluminum, by two opposing fasteners 3410A, 3410B, e.g., made from steel. The fasteners 3410A, 3410B may be installed simultaneously from opposite sides via a pair of opposing welding electrodes in a similar manner to the embodiment shown in <FIG>. The fasteners 3410A, 3410B are urged together and by resistance heating, penetrate the aluminum sheets 11A, 11B, 11C and then weld to each other, forming weld 3410W. As noted above with respect to the embodiments shown in <FIG>, in passing through the sheets 11A, 11B, 11C, the steel fasteners 3410A, 3410B locally heat the aluminum sheets 11A, 11B, 11C adjacent thereto and create a weld 3410W2 that partially or completely encompasses the weld 3410W between the fasteners 341OA, 341OB. <FIG> shows sheets 11A, 11B, 11C of approximately equal thickness, resulting in a symmetric joint <NUM> J. As shown, the fasteners 341OA, 341OB, have equal operational reaches (shaft lengths), such that when they join to form weld 3410W, they are roughly in the middle of sheet 11B, resulting in a weld 3410W that is not at the interfaces <NUM>, <NUM> between the sheets 11A, 11B, 11C and therefore has enhanced mechanical performance. As noted above, this joint 3400J can be employed with or without adhesives, e.g., applied at the interfaces <NUM>, <NUM>. The weld zone 3410W2 between the aluminum sheets 11A, 11B, 11C can be selectively made larger or smaller by selecting the weld schedule employed during the welding process. Additional heat cycles can be added to extend the aluminum weld zone 3410W2, and increase the overall performance of the joint 3400J. The sheets 11A, 11B, 11C can be of the same or varying thicknesses and alloy types. The fasteners 3410A, 3410B can be designed to meet in the center of the aluminum sheet 11A, 11B, 11C stackups or at another location which will maximize joint performance and extend the load path.

<FIG> is a photograph of a joint 3500J cut to show a cross section thereof. The joint 3500J couples two aluminum sheets 11A, 11B of <NUM> C710-T4 aluminum alloy between a fastener <NUM> and a steel sheet <NUM> of <NUM> galvanized steel. The fastener <NUM> is a G1A rivet. The weld zone 3510W2 shows the merging of the sheets 11A, 11B proximate the fastener <NUM>. The welding was conducted on the sheets 11A, 11B without a pilot hole. The joint 3500J was created with a weld input of 8kA @ 400msec preheat plus 16kA @ 100msec weld pulse, <NUM> (800lbs). The sample was distorted somewhat while it was being cut for the cross section.

<FIG> is a photograph of a joint 3600J cut to show a cross section thereof. The joint 3600J couples two aluminum sheets 11A, 11B of <NUM> <NUM>-T6 aluminum alloy between two fasteners 3610A, 3610B. The fasteners 3610A, 3610B are G1A rivets. The weld zone 3610W2 shows the merging of the sheets 11A, 11B proximate the fasteners 361OA, 361OB. The welding was conducted on the sheets 11A, 11B without a pilot hole. The joint 3500J was created with a weld input of 8kA @ 400msec preheat plus 12kA @ 300msec weld pulse, <NUM> (800Ib).

<FIG> shows an electrode <NUM> with a tip 3715T having a standard geometry. The electrode tip 3715T inserts into and is retained in electrode shaft <NUM> via mating tapered surfaces 3715TS1, 3715TS2. The tip 3715T has a riveting surface 3715RS having a radius R of about <NUM>. The electrode <NUM> is shown in contact with a fastener <NUM> with a short, solid shaft <NUM> and a wide cap <NUM> having a concave surface 3712CS, which may have a radius R1 of curvature approximating that of the riveting surface 371RS of the tip 3715T. The fastener <NUM> is in place on stacked sheets <NUM>, e.g., made from aluminum and <NUM>, e.g., made from steel. The "semi-solid" fastener <NUM> accommodates a standard electrode radius. The electrode <NUM> is in common use in industry and provides excellent electrode wear and dressing capability. Deviations of electrode orientation from perpendicular frequently occur, particularly in high volume production. The radiused contact surface 3712CS allows the electrode to have a small amount of angularity relative to the perpendicular and still function for driving and welding the fastener <NUM>. For very thick penetration needs (<NUM> or greater) the shaft <NUM> the fastener <NUM> would be very thick as compared to other fastener designs , e.g., shown in <FIG>, where the electrode, e.g., <NUM>, <NUM>, <NUM> penetrates relatively deeply into the fastener, e.g., <NUM>, <NUM>, <NUM>. The fastener <NUM> may be fed to the welding electrode <NUM> via a carrier web or tape or some other means to hold it in place prior to electrode contact, which presses it against the workpiece(s) to be joined.

<FIG> shows an electrode tip 3815T having a "bottlenose" geometry. As in <FIG>, the electrode tip 3815T would insert into and be retained in an electrode shaft like <NUM>. The tip 3815T has a riveting surface 3815RS having a radius R of about <NUM>. The electrode tip 3815T is shown in contact with a fastener <NUM> with a short, solid shaft <NUM>, e.g., having a length greater then <NUM>. The fastener <NUM> has a wide cap <NUM> having a concave surface 3812CS, which may have a radius of curvature approximating that of the riveting surface 3815RS of the tip 3815T. The height of the fastener is about <NUM> to <NUM> overall. The fastener <NUM> is positioned on sheet <NUM>, e.g., made from aluminum and <NUM>, e.g., made from steel. The "semi-solid" fastener <NUM> accommodates the "bottlenose" tip 3815T. As noted above, deviations of electrode orientation from perpendicular frequently occur and the radiused contact surface 3812CS allows the electrode to have a small amount of angularity relative to the perpendicular and still function for driving and welding the fastener <NUM>. The smaller radius of surface 3815RS provides increased flexibility to function at an angular offset from the welding electrode and greater electrode penetration inside the fastener <NUM>, which more closely resembles sheet-to-sheet spot welding. Additionally this type of tip geometry will work with a wider range of fastener shaft lengths since a very thick base is not required when welding sheets <NUM>, <NUM> having a thickness <NUM> or greater. The smaller radius "nose" of the electrode tip 3815T will have a surface 3815RS that closely matches the radius on the contact surface 3812CS. The transition from surface 3815RS to the outer wall 3815OW of the electrode tip 3815T can be done using a variety of shapes, including: a larger radius, a straight wall at an angle or a double curve, as shown in <FIG> (<FIG> showing a double curve). The electrode tip 3815T retains advantages of the standard electrode shown in <FIG>, such as excellent electrode wear and electrode dressing.

<FIG> illustrates that the bottlenose shape of the tip 3815T can accommodate a variety of fasteners, e.g., <NUM> and stack-up thicknesses, making the electrode tip 3815T capable of processing a wide range of stack-up thicknesses with the same electrode tooling.

<FIG> shows another type of the bottlenose electrode tip 4015T that may reduce electrode wear. The radius R of the riveting surface 4015RS has a smaller radius than that shown in <FIG> and <FIG>, viz. , <NUM> versus <NUM>. In general, the radius of the riveting surface 4015RS should be greater than <NUM> but less than <NUM>, preferably <NUM> to <NUM>. In <FIG>, the fastener contact surface 4010CS has a radius of <NUM>, slightly larger than the riveting surface 4015RS. The riveting surface 4015RS transitions to outer wall 4015OW via a straight wall 4015TW disposed at an angle of e.g., <NUM> degrees relative to the outer wall 4015OW. The electrode tip 4015T exhibits operability despite angular and x, y offsets in orientation and position of the electrode tip 4015T relative to that of the fastener <NUM>. In some applications, it is preferred that the radius of the contact surface 4010CS be slightly larger than that of the riveting surface 4015RS and in one embodiment, the contact surface 4010CS may be from <NUM> to <NUM> or <NUM> to <NUM>.

<FIG> shows an electrode tip 4115T that may reduce electrode wear. The radius R of the riveting surface 4115RS may be from <NUM> to <NUM>. The riveting surface 4115RS transitions to outer wall 4115OW via a curved wall 4115TW with a large radius, e.g., between <NUM> to <NUM>. This geometry provides enhanced heat transfer and cooling.

<FIG> shows the bottlenose electrode tip 4015T described above in relation to <FIG> at an orientation misaligned with the fastener <NUM>, e.g., at an angular offset α of up to <NUM> degrees from an orientation perpendicular to sheets <NUM>, <NUM>. The bottlenose tip 4015T will accommodate angular misalignments up to <NUM> degrees or more and still provide workable electrical and mechanical contact. If the fastener <NUM> has a slightly larger radius R it will enhance the ability of spot welding apparatus with electrode tip 4015T to push the fastener <NUM> through the sheet <NUM> and otherwise accommodate variations from ideal production fit-up. The ability to adjust to angular misalignments is new to projection type welding processes which typically employ large, flat faced electrodes and represents another significant departure of the presently disclosed technology from traditional electrical resistance welding.

<FIG> shows composite fasteners <NUM>, <NUM> and <NUM>, each having a plurality of components 4250A, 4250B, 4260A, 4260B and 4270A, 4270B, respectively. As shown, the components 4250A, 4260A and 4270A may be a fastener like any of the fasteners <NUM>, <NUM>, <NUM>, <NUM>, etc. disclosed above. Components 4250B, 4260B and 4270B may be in the form of a sheet of material that is press fitted or adhered to the fastener component 4250A, 4260A and 4270A. The sheet member 4250B, 4260B and 4270B may be composed of materials including: polymer, resin, adhesive (a and b above) or a metal (a, b, and c). The sheet member 4250B, 4260B and 4270B may be integral with and severable from a larger web that serves as a transport or holding mechanism for positioning fasteners <NUM>, etc. relative to materials to be fastened, e.g., sheets <NUM>, <NUM> of <FIG>, during the process of applying the fasteners <NUM>, <NUM>, etc. via electrical resistance heating and welding as described above. Components 4250B, 4260B, 4270B may be selected to remain captured in the joint formed by the fasteners 4250A, 4260A, 4270A. For example, the sheet members 4250B, 4260B and 4270B may be a plastic/polymer sealant for sealing and protecting a joint formed by the fastener from corrosion.

If the sheet members 4250B, 4260B and 4270B are metallic and are integral with a larger structure, e.g., a tape or web employed as a transport/positioning mechanism, the attachment to the tape or web may be by a perforated or an otherwise frangible connection, permitting the sheet members 4250B, 4260B and 4270B to be disconnected from the greater structure when the associated fastener 4250A, 4260A, 4270A is used. The sheet members 4250B, 4260B and 4270B can be made from a variety of materials, e.g., stainless steel, aluminum brazing alloys, high purity aluminum, etc., in order to reduce the galvanic corrosion potential and/or extend joint bond between the fastener 4250A, 4260A, 4270A and all surfaces, e.g., sheets, <NUM>, <NUM>, it may come into contact with. If a brazing alloy is employed, it may be prefluxed to offer improved wetting along the contact surfaces and improved bonding performance. The sheet members 4250B, 4260B and 4270B may be associated with the corresponding fasteners 4250A, 4260A, 4270A mechanically, e.g., an interference fit, or other means, such as adhesion via surface attraction or use of an adhesive. The composition and function of the sheet members 4250B, 4260B and 4270B may be similar or the same of the sleeves 2310T and or 2410A of <FIG>. The fasteners 4250A, 4260A, 4270A and sheet members 4250B, 4260B and 4270B may be assembled prior to performing a fastening operation and different combinations of fasteners 4250A, 4260A, 4270A and sheet members 4250B, 4260B and 4270B may be selected based upon the requirements and objectives of the fastening task.

<FIG> shows a feeding mechanism <NUM> and media <NUM> for loading fasteners <NUM> between the tip 4315T of a welding electrode and a workpiece, e.g., sheets <NUM>, <NUM> to be fastened together by resistance welding with fasteners <NUM>, in accordance with an embodiment of the present disclosure. The fasteners <NUM> are mounted and carried by the media <NUM>, which may be in the form of a belt or tape that runs between coils on the left L and right R of the feeding mechanism <NUM>. The media may be guided by guide rolls or another form of guide, such as a chute or guide surfaces 4380S1, 4380S2 through frame 4380F, such that the fasteners <NUM> carried by the media are presented periodically between the electrode tip 4315T and the sheet <NUM>. The electrode tip is periodically moved up and down to perform a penetration/welding operation as described above in this disclosure by electrical resistance heating and welding. The feeding mechanism <NUM> may also move up and down relative to the sheet <NUM>. The media <NUM> may be partially or fully consumed when the fastener <NUM> is applied to the sheets <NUM>, <NUM>. In the alternative, a remnant portion 4382R of the media <NUM> may pass beyond the applied fastener <NUM> and be taken up by a wind-up roll or other take-up mechanism, for disposal or reuse. As described above in relation to <FIG>, the media <NUM> may be selected to provide a beneficial attribute to the joint formed by the fastener <NUM>, e.g., the media <NUM> may be a sealant or corrosion reducing film, an adhesive or brazing media. Two forms of media 4382A and 4382B with openings <NUM> for receiving the fastener <NUM>.

Aspects of the fasteners <NUM>, <NUM>, <NUM>, etc. and fastening method include the following. The process for applying the fasteners is associated with low part distortion since the layers of material, e.g., <NUM>, <NUM> and the fastener <NUM>, <NUM>, etc. are held in compression during the weld and the heat affected zone is captured below the cap, e.g., <NUM>. The cap <NUM> may have a pre-formed recess or bend to form a recess to accommodate and trap melted metals, intermetallics etc. displaced by the welding operation. Because a given fastener, e.g., <NUM>, <NUM>, etc., can deform, e.g., melt and collapse during the penetration and welding phases, it can handle a range of thicknesses of sheets, e.g., <NUM>, <NUM> to be fastened. During the fastener penetration and welding, as the fastener <NUM>, <NUM>, etc., collapses and expands along the weld zone, intermetallics are displaced from the weld zone. When the fastener <NUM>, <NUM>, etc. (i.e., the cap <NUM> thereof), compresses against the top sheet, e.g., <NUM>, under the influence of the electrode <NUM>, <NUM>, <NUM>, etc., it will come to a stop with the cap <NUM> sealing against the top sheet <NUM>. The fastener <NUM>, <NUM>, etc., can be applied through adhesives applied between the sheets, <NUM>, <NUM>. Since the fastener <NUM>, <NUM>, <NUM>, etc., is welded or brazed to one side of the second sheet <NUM>, the other side of the sheet <NUM> is not pierced and remains water-tight. The welding process of the present invention is compatible with conventional RSW equipment developed for steel sheet resistance welding, e.g., as used in automobile manufacture.

The fastener <NUM>, <NUM>, <NUM>, etc., may be made from a variety of materials such as different steel grades (low carbon, high strength, ultra high strength, stainless), titanium, aluminum, magnesium, and copper and may be coated (galvanized, galvaneal, hot-dipped, aluminized) to improve corrosion resistance. The fastener <NUM>, <NUM>, <NUM>, etc., may be applied via single-sided or two-side access welding techniques. In one approach, no pilot hole is used and the fastener pierces through a first layer <NUM> softened by resistance heating. In another approach, a pilot hole may be provided in the top sheet <NUM>, which may be aluminum, plastic, or in the instance of a fastener having an aluminum shaft end <NUM>, the first sheet may be steel, titanium, or copper and the second sheet aluminum. In the instance where the fastener is inserted through a pilot hole in the first sheet, the first sheet need not be electrically conductive and need not have a lower melting temperature than the second sheet (since the fastener does not penetrate the first sheet by electric resistance heating. Quality assurance measurements may be conducted on the cavity left from destructive disassembly of the weld securing a fastener to a second sheet, e.g., to inspect the dimensions, e.g., depth, volume, etc. of the weld. Ultrasonic NDE techniques may be utilized on the opposite side of the sheet to which the fastener is welded to monitor the weld quality.

The equipment used to apply the fastener <NUM>, <NUM>, <NUM>, etc., has a much smaller footprint than FDS (EJOTS), SPR, and SFJ, allowing access to tighter spaces. The insertion forces used to drive the fastener of the present invention are lower compared to those used in SPR, since the aluminum sheet <NUM> is either heated or apertured, facilitating fastener insertion, enhancing the ability to join high strength aluminums which are sensitive to cracking during SPR operations. The approaches of the present invention also facilitate joining to high and ultra-high strength steels since there is no need to pierce the steel metal with a fastener, instead, the fastener is welded to the sheet metal. The method does not require rotation of the fastener or the workpiece facilitate parts fit-up, since the process is similar to conventional RSW in terms of how the parts to be joined are fixture. The fasteners <NUM>, <NUM> may be applied at processing speeds approximating those of conventional RSW and the process can be used on both wrought and cast aluminum. Since welding of aluminum to steel is avoided, the low joint strength associated with bimetallic welds is also avoided. The process of the present disclosure permits multiple sheets of aluminum and steel and other metals, e.g., <NUM> layers of aluminum and <NUM> layer of steel; <NUM> layer of aluminum and <NUM> layers of steel; or <NUM> layer of aluminum, <NUM> layer of magnesium and <NUM> layer of steel to be fastened.

During the application of the fastener <NUM>, <NUM>, <NUM>, etc., the first sheet <NUM> or sheets 11A, 11B that are penetrated by the fastener may also be melted and welded together, increasing the weld zone and overall joint strength. The fastener may be fabricated from a variety of materials for welding to compatible sheets <NUM> and may be multi-layered, such that the fastener may have mechanical and galvanic properties that are a combination suitable for welding and for the avoidance of corrosion. For example, a fastener may be fabricated having an end that is aluminum and compatible to weld to an aluminum second sheet <NUM>, but have a layer of steel, titanium or copper to improve its mechanical properties. Multi-layer fasteners may be useful in high temperature applications and may include a layer or layers of material to prevent diffusion across multi-material interfaces.

A film, adhesive, or coating may be applied to the fastener or introduced between the fastener and the first sheet <NUM> to improve the sealing of the cap <NUM> to the sheet <NUM>. The process of the present invention may be used to join a wide range of sheet thicknesses by incorporating a retrograde cap that curls back toward the end of the shaft, which may be coated with an insulator to avoid conducting electricity through the cap/sheet <NUM> interface, the cap bending during the heating penetrating phase to accommodate different thicknesses in stack-ups. The present invention contemplates fasteners made from a variety of materials including aluminum, steels, stainless steel, copper, and titanium. The fastener can be made up of two or more different types of aluminum to enable both resistance welding and lower heat processes such as resistance brazing or soldering. Joints made with the fasteners and methods of the present invention can exhibit improved fatigue performance due to parts being held in compression during the welding process.

Claim 1:
A system comprising:
- a welding electrode tip (3815T, 4015T, 4115T) for an electrical resistance welding electrode; and
- a resistance welding fastener (<NUM>, <NUM>, <NUM>) for fastening a first electrically conductive material (<NUM>) to a second electrically conductive material (<NUM>) using electrical resistance welding;
wherein the welding electrode tip (3815T, 4015T, 4115T) has a bottlenose shape with a larger diameter portion proximate the welding electrode and a reduced diameter portion distal to the electrode, the reduced diameter portion having a radiused end for contacting the fastener (<NUM>, <NUM>, <NUM>) during welding, wherein the radiused end of the reduced diameter portion has convex riveting surface (3815RS, 4015RS, 4115RS); and
wherein the fastener (<NUM>, <NUM>, <NUM>) comprises:
- a cap (<NUM>), a shaft (<NUM>) extending from the cap (<NUM>) and having an end distal to the cap, the fastener (<NUM>, <NUM>, <NUM>), when placed in a stack including first and second electrically conductive materials (<NUM>, <NUM>) and positioned in electrical contact and subjected to an electrical potential applied across the stack, capable of conducting an electrical current, the electrical current causing resistive heating and welding to the second electrically conductive material (<NUM>) at the end distal to the cap, the first electrically conductive material (<NUM>) being captured between the cap (<NUM>) and the second electrically conductive material (<NUM>) after the end is welded to the second electrically conductive material (<NUM>),
wherein the shaft (<NUM>) has a solid cross-section between the cap (<NUM>) and the end distal to the cap, wherein the cap (<NUM>) has a concave depression (3812CS, 4010CS, 4110CS) therein capable of receiving the convex riveting surface (3815RS, 4015RS, 4115RS) of the welding electrode tip (3815T, 4015T, 4115T), wherein the radius of curvature of the concave surface (3812CS, 4010CS, 4110CS) of the cap (<NUM>) approximates that of the riveting surface (3815RS, 4015RS, 4115RS) of the welding electrode tip (3815T, 44015T, 4115T).