Method of fastening a tab to a metallic container wall

Claim 1

IN A METHOD OF FASTENING A TAB TO A CENTRAL PORTION OF A METALLIC CONTAINER WALL WHEREIN THE TAB IS FORMED WITH A HOLE TELESCOPED OVER A CUP-SHAPED RIVET BLANK PROJECTING INTEGRALLY FROM SAID CONTAINER WALL AND THE RIVET BLANK IS FORMED WITH A RIM OVERLYING THE TAB SURFACE AROUND THE HOLE, THE STEPS OF: FORMING IN A SHEET METAL WALL BLANK A PRIMARY BUBBLE WALL PORTION HAVING A SPHERICALLY CURVED SHAPE OF PREDETERMINED HEIGHT AND A CONCAVE OPEN END DIAMETER SUBSTANTIALLY LARGER THAN THE DIAMETER OF SAID TAB HOLE WHILE SLIGHTLY REDUCING THE THICKNESS OF THE BLANK OVER A LIMITED ANNULAR AREA ADJACENT SAID PRIMARY BUBBLE; DRAWING, STRETCHING AND THINNING THE METAL IN SAID PRIMARY BUBBLE WALL PORTION DURING FORMATION THEREOF; THEN WHILE CONFINING THE BLANK METAL AROUND THE PRIMARY BUBBLE WALL OPEN END, DRAWING AND STRETCHING THE METAL IN THE PRIMARY BUBBLE WALL PORTION TO FORM A SECONDARY BUBBLE WALL PORTION HAVING A SPHERICALLY CURVED SHAPED AND AN OPEN END OF SMALLER DIAMETER THAN THAT OF THE BUBBLE WALL PORTION AND HAVING A HEIGHT REDUCED FROM THAT OF THE PRIMARY BUBBLE WALL PORTION WHILE SLIGHTLY THINNING THE METAL IN THE SECONDARY BUBBLE WALL PORTION DURING SAID DRAWING AND STRETCHING; REPOSITIONING AND RESHAPING THE METAL IN THE SECONDARY BUBBLE WALL PORTION TO FORM A CUP-SHAPED RIVET BLANK HAVING A CYLINDRICAL SIDE WALL AND AN END WALL DEFINING A RIVET BLANK HEIGHT SLIGHTLY LESS THAN THE HEIGHT OF THE SECONDARY BUBBLE WALL PORTION AND A CUP SIDE WALL OF SMALLER DIAMETER THAN THE SECONDARY BUBBLE OPEN END DIAMETER WHILE MAINTAINING THE CUP END WALL METAL THICKNESS THE SAME AS THE THICKNESS OF THE SECONDARY BUBBLE WALL PORTION DURING FORMATION OF THE RIVET BLANK; TELESCOPING THE TAB HOLE OVER SAID SUP-SHAPED RIVET BLANK; AND AXIALLY PRESSING THE RIVET BLANK END AND SIDE WALLS AND UPSET FOLDING SAID SIDE WALL OUTWARDLY DOWNWARDLY IN THE REGION WHERE SAID SIDE WALL JOINS THE RIVET BLANK END WALL TO REDUCE THE RIVET BLANK HEIGHT AND TO FORM A RIM OVERLYING THE TAB AROUND THE TAB HOLE WHILE INTERNALLY SUPPORTING THE CYLINDRICAL SIDE WALL OF THE RIVET BLANK AND WHILE MAINTAINING SAID INTERNAL SUPPORTING FREE OF RIVET BLANK END WALL CONTACT TO MAINTAIN THE END WALL THICKNESS OF THE UPSET RIVET BLANK THE SAME AS THE THICKNESS OF THE RIVET BLANK AND WALL BEFORE UPSETTING.