Method for one-sided, one step joining of a metal sheet stack
View Patent ↗A joining operation for a stack of three metal sheets performed using only a single welding step, with access to only one sheet side being required. An inner sheet of the stack has formed therein a pair of bifurcated projections, wherein at least one first apex faces in one direction and at least one second apex faces in the opposite direction. First and second outer metal sheets are assembled with the inner sheet, wherein the first outer sheet abuts the at least one first apex, and the second outer sheet abuts the at least one second apex. A projection welding apparatus welds the sheets, using only access to the first outer sheet superposed the bifurcated projections, wherein a majority of the current flows through the second outer sheet.
1. A method for joining a sheet stack assembly via a single welding step, comprising the steps of:
selecting a first outer sheet structurally having a first electrical conductivity;
selecting an inner sheet structurally having a second electrical conductivity;
selecting a second outer sheet structurally having a third electrical conductivity;
forming a pair of elongated bifurcated projections in the inner sheet, wherein each bifurcated projection comprises:
forming a central apex facing in a first direction; and
forming a pair of outer apices facing in a second direction opposite the first direction, one outer apex respectively disposed at each side of the central apex;
assembling a sheet stack assembly comprising the steps of:
placing the first outer sheet in abutting relation to the central apex of the inner sheet; and
placing the second outer sheet in abutting relation to the outer apices of the inner sheet; and
joining the sheet stack assembly together, comprising the steps of:
applying force toward the first outer sheet, the force being superposed each bifurcated projection;
abutting a pair of electrodes of a source of electrical current to only the first outer sheet during said step of applying force, wherein each electrode of said pair of electrodes is superposed a respective bifurcated projection; and
welding the sheet stack assembly joinably together in a singular welding step by delivering electrical current from the source of electrical current to the pair of electrodes;
wherein the third electrical conductivity is much higher than the first and second electrical conductivities such that if the electrical current through the first outer sheet is i 1 , the electrical current through the inner sheet is i 2 , and the electrical current through the second outer sheet is i 3 , then the total electrical current, i, is given by: i =i 1 +i 2 +i 3 , where i 3 >>(i 1 +i 2 ); and
wherein during said step of welding, the electrical current flows between the pair of the electrodes by conducting through the first outer sheet, through the apices of each bifurcated projection of the inner sheet, and through the second outer sheet, wherein due to the third electrical conductivity in relation to the first and second electrical conductivities in combination with the abutment of the pair of electrodes to only the first outer sheet, most of the electrical current flows through the second outer sheet such that the sheet stack assembly is welded together.
2. The method of claim 1 , wherein in said step of forming, the central apex has a height greater than a height of the outer apices in relation to a plane of the inner sheet.
3. A joined sheet stack joined according to the method of claim 2 .
4. The method of claim 1 , wherein said step of welding further comprises placing the sheet stack assembly into a projection welding apparatus.
5. A joined sheet stack joined according to the method of claim 1 .