Resistance welding fasteners, apparatus and methods for joining dissimilar materials and assessing joints made thereby

A method for fastening a first electrically conductive material to a second electrically conductive material using electrical resistance welding, comprising:

• (A) placing the first and second materials together in physical and electrical contact, the first material having a lower melting point than the second material;
• (B) placing an electrically conductive rivet that is weldable to the second material and which has a higher melting point than the first material in electrical contact with the first material to form an electrically conductive stack inclusive of the rivet, the first material and the second material, the rivet having a head and a pin extending from the head, the head having a downwardly directed peripheral lip at least partially defining a cavity under the head and at least one vent formed annularly within the peripheral lip of the head, the pin having a tip distal to the head;
• (C) 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;
• (D) urging the rivet through the softened first material toward the second material and into contact with the second material, further urging the fastener after contacting the second material resulting in expanding the tip of the fastener in a radial direction, the expansion of the tip pushing the first material toward the head;
• and
• (E) after the pin contacts the second material, welding the rivet to the second material;
• (F) capturing an upwelled portion of the first material that is displaced when the rivet is urged through the first material and welded to the second material, the upwelled portion being captured within the cavity in the head;
• and
• (G) venting the upwelled portion of the first material through the at least one vent of the head of the rivet.

A rivet for fastening a first material having a pilot hole therein to a second material that is electrically conductive using electrical resistance welding, comprising:

• a head with a downwardly directed peripheral lip and at least one vent formed annularly within the peripheral lip of the head, a pin extending from the head and having a tip at an end distal to the head, the pin capable of being inserted through the pilot hole when the first and second materials are placed in a stack, the rivet being formed from electrically conductive material and capable when subjected to an electrical potential applied across the rivet and the second material of conducting an electrical current that passes through the second material, the current causing resistive heating of the rivet, the rivet being capable of being welded at the tip to the second material and capturing the first material between the head and the second material after the tip is welded to the second material with the peripheral lip contacting the first material, the head being capable of capturing material extruded from the pilot hole when the rivet is welded, wherein a portion of the pin distal to the head is capable of assuming a cross-sectional area greater than a cross-sectional area of another portion of the pin located proximate to the head, and the head is further capable of inducing flow of the material extruded when the rivet is welded along the surface of the shaft in a direction from the portion of the pin distal to the head to the another portion of the pin proximate to the head toward and along a bottom surface of the peripheral lip.

A joint, comprising:

• (A) an upper sheet having a pilot hole therein;
• (B) a lower sheet of electrically conductive material;
• (C) a rivet with a head, a peripheral lip, at least one vent formed annularly within the peripheral lip, and a pin that is welded to the lower sheet by electrical resistance welding, the pin extending through the pilot hole and welded to the lower sheet, the head pressing against the upper sheet clamping the upper sheet between the head and the lower sheet;
• and
• (D) an adhesive disposed between the rivet and the upper sheet.