the invention refers to a method of forming over the edge of a plastic jacket against a workpiece using vibratory energy . specifically , the workpiece and jacket are disposed on a resiliently mounted anvil . as the jacket forms over and shortens its axial length , the anvil is displaced to provide a decreasing engagement force between the jacket and the horn of the vibratory apparatus . as a result , the jacket is free of scars or distortions in the region of forming .