Resistance welding fastener, apparatus and methods for joining similar and dissimilar materials
An apparatus and method for fastening layers of non-ferrous alloys, like aluminum, magnesium and copper utilizes a steel fastener and a spot welding machine. The fastener and metals are stacked and the heat from the welder's electric current softens the lower melting point aluminum allowing the fastener to penetrate the aluminum. A weld zone between the fastener and the various layers creates an internal weld. The fastener has a rough shaft that is coated by the molten weld zone and is hard to withdraw on solidification. Layers of non-conductive materials like plastics and ceramics may also be affixed to a conductive layer using a fastener made from a compatible material that extends through a pilot hole and welds to or penetrates a conductive layer. The fastener may have projections that initially reduce contact area with the stack.
1. A fastener for fastening a first sheet material to a second sheet material stacked below the first sheet material using electrical resistance welding, comprising:
a cap comprising:
an electrode receiving surface,
wherein the electrode receiving surface includes a concave portion configured to receive a convex portion of an electrode,
an underside portion opposite the electrode receiving surface, and
a downwardly extending peripheral lip;
a shaft extending from the underside portion of the cap,
wherein the shaft includes:
a first end at the underside portion of the cap,
a second end opposite the first end and distal to the cap,
a conical wall extending from the first end to the second end, and
an annular groove within the conical wall and between the first end and the second end; and
an annular recess between the peripheral lip, the underside portion, and the shaft,
wherein the annular groove is axially disposed within the annular recess of the cap or adjacent a circumferential edge of the downwardly extending peripheral lip,
wherein the underside of the cap curvedly transitions from the peripheral lip to the first end of the shaft at a first curve,
wherein the conical wall of the shaft curvedly transitions to the second end at a second curve,
wherein the fastener is electrically conductive, and wherein the shaft, when placed in a stack including the first sheet material and the second sheet material and subjected to an electrical potential applied across the stack, is configured to conduct an electrical current that passes through the stack to resistively heat the first sheet material and the second sheet material such that the first sheet material is softened to form a weld zone extending between the fastener, the first sheet material, and the second sheet material, and to weld to the second sheet material at the second end of the shaft,
wherein the annular groove is configured to receive molten metal of the weld zone and increase the resistance of the fastener from being withdrawn from the weld zone, and
wherein the annular recess is configured to capture material upwelled from the first sheet material between the cap and the second sheet material after the second end of the shaft is welded to the second sheet material.
2. The fastener of claim 1 , wherein the concave portion of the electrode receiving surface has a radius of curvature configured to be greater than a radius of curvature of the convex portion of the electrode.
3. The fastener of claim 1 , wherein the first sheet material includes at least one non-ferrous material component, and
wherein the second sheet material includes a ferrous metal component having a first side,
wherein the fastener is configured to be welded to the ferrous metal component by electrical resistance welding to form the weld zone,
wherein the shaft is configured to extend through the at least one non-ferrous material component and be welded to the ferrous metal component at a first location on the first side of the ferrous metal component, and
wherein the at least one non-ferrous material component is configured to be captured between the cap and the ferrous metal component.
4. The fastener of claim 3 , wherein the at least one non-ferrous material component is a sheet of an aluminum alloy.
5. The fastener of claim 4 , wherein ferrous metal component is a steel sheet.
6. The fastener of claim 1 , wherein the downwardly extending peripheral lip is configured to provide a mechanical connection between the cap and the first sheet material.
7. The fastener of claim 1 , wherein the first material is softened by electrical resistance heating forming a molten weld zone, the shaft having a surface roughness that inter-digitates with the weld zone to resist removal of the fastener from the weld zone after solidification of the weld zone.