Method of resistance welding

Claim 1

A method for resistance welding two members made of dissimilar metals that includes the steps of placing a surface of a first member made of one metallic material into electrically conductive contact with a surface of a second member made of another metallic material different from the first material, passing an electrical welding current across the contact area between the two members for a time sufficient to render plastic a portion of the metallic material of one of the members, and pressing the first and second members together with sufficient force to squeeze any surface impurities and intermetallic compounds to the edges of the contact area, wherein the improvement comprises: forming at least one small, integral, tapered, flattopped projection of trapezoidal cross section on the first member, the projection having a predetermined height, divided into a top portion, an intermediate portion and a base portion, and a predetermined width of the flat-topped surface, and opposite sides of the tapered projection each making a predetermined angle with a line perpendicular to the flat-topped surface such that passage of a welding current through the projection will generate a temperature distribution that decreases continuously from the top portion to the base portion, and further, that the projection radially spreads in a plastic flow; pressing the top surface of the at least one projection of the first member against the surface of the second member with a high welding pressure selected to be approximately in the range of 15-100 kg/mm 2 of top surface area of the projection, but which does not exceed a force that will deform the projection prior to the application of welding current, and; passing a predetermined high welding current density approximately in the range of 0.75 to 3.4 KA/mm 2 to top surface area of the projection for a short time period approximately in the range of 0.5 to 10 cycles at 60 Hz, such that the contacting surfaces of the two members are melted, said intermediate portion of the projection flows plastically under said welding pressure and the base portion of the projection does not plastically flow, and due to said plastic flow, obtaining welded surfaces having no intermetallic compound of said dissimilar metals remaining at said welded surfaces.

Claim 2

A method for resistance welding two members made of dissimilar metals that includes the steps of placing a surface of a first member made of one metallic material into electrically conductive contact with a surface of a second member made of another metallic material different from the first material, passing an electrical welding current across the contact area between the two members for a time sufficient to render plastic a portion of the metallic material of one of the members, and pressing the first and second members together with sufficient force to squeeze any surface impurities and intermetallic compounds to the edges of the contact area, wherein the improvement comprises: forming at least one small, integral, tapered, flattopped projection of trapezoidal cross section on the first member, the projection having a predetermined height, divided into a top portion, an intermediate portion and a base portion, and a predetermined width of the flat-topped surface, and opposite sides of the tapered projection each making a predetermined angle with a line perpendicular to the flat-topped surface such that passage of a welding current through the projection will generate a temperature distribution that decreases continuously from the top portion to the base portion, and further, that the projection radially spreads in a plastic flow; pressing the top surface of the at least one projection of the first member against the surface of the second member with a high welding pressure selected to be approximately in the range of 15-100 kg/mm 2 of top surface area of the projection, but which does not exceed a force that will deform the projection prior to the application of welding current, and; passing a predetermined high welding current density approximately in the range of 0.75 to 3.4 KA/mm 2 to top surface area of the projection for a short time period approximately in the range of 0.5 to 10 cycles at 60 Hz, such that the contacting surfaces of the two members are melted, said intermediate portion of the projection flows plastically under said welding pressure and the base portion of the projection does not plastically flow, and due to said plastic flow, obtaining welded surfaces having no intermetallic compound of said dissimilar metals remaining at said welded surfaces.