Abstract: Forming a corrugated corner piece or a plurality of interconnected integral corrugated corner pieces for forming corrugated, rectangular, expansion joints or bellows by placing a metal blank between a pair of specially constructed hinge plate members. Each hinge plate member comprises a plurality of adjacent elongated plates with the adjacent edges of the plates secured together by tubular hinge elements. The plates pivot together at spaced locations along their lengths, around zig-zag orientated hinge elements that are positioned to lay normal to the side edges of the plate members and interconnect separate parts of the plate members. The blank is placed between the two hinge plates, with the hinge plates being aligned. Aligned pairs of the hinge elements are then held together with the blank sandwiched therebetween.