Forming method of bushing with outer sliding surface

A bushing forming method in that a crowning shape is provided to an outer peripheral surface of a bushing comprising an outer peripheral layer and an inner backing metal layer so that the outer diameter of the bushing is smaller at its opposite longitudinal ends, and increases progressively toward a longitudinal central portion of the bushing, said outer peripheral surface serving as a sliding surface, wherein the method comprises the steps of:

• a) fitting a cylindrical bushing blank having said outer peripheral layer and said inner backing metal layer on a vertically-movable mandrel, said mandrel being coaxial with a pair of upper and lower dies with said bushing bland being situated between said upper and lower dies;
• b) moving said upper die to relatively approach said lower die, thereby plastically deforming said bushing blank and achieving said crowning shape while maintaining initial dimensions of said inner backing layer and an initial axial length of an entire said bushing blank, an inner diameter of said upper die being larger at its lower end an decreasing progressively away from said lower end, and an inner diameter of said lower die being larger at its upper end and decreasing progressively away from said upper end;
• and
• c) moving upper-and lower dies relative to said mandrel, thereby removing the bushing from said dies.