Apparatus for hemming a workpiece having an upturned edge

An apparatus for hemming a workpiece having an upturned edge, wherein the workpiece is composed of an outer panel having a peripheral upturned edge turned substantially at a right angle, and an inner panel having a peripheral edge to be superimposed on the outer panel adjacent the upturned edge, the apparatus comprising:

• a hem roller having a peripheral surface for pressing the upturned edge of the outer panel;
• a robot hand rotatably supporting the hem roller and adapted to shift the hem roller between a first position in which the hem roller performs a preliminary bending operation on the upturned edge of the outer panel and a second position in which the hem roller performs a finish bending operation on the upturned edge of the outer panel;
• and
• a lower die for supporting the workpiece thereon, the lower die having a guide surface effective to hold the hem roller in the first position such that when the hem roller is rotated on the guide surface of the lower die, the pressing surface of the hem roller abuts against the outer periphery of the upturned edge of the outer panel at a point at least a distance 2TO+TI apart from the lower end of the upturned edge toward the distal end thereof, wherein TO is thickness of the outer panel and TI is thickness of the inner panel;
• whereby when the hem roller is rotated along the guide surface of the lower die with the hem roller disposed in the first position, the upturned edge is preliminarily bent to a predetermined angle, and when the hem roller is pressingly rotated along the upturned edge with the hem roller shifted to the second position such that the pressing surface of the hem roller is substantially parallel to the superimposed portion of the outer panel and the inner panel, the upturned edge is finishingly bent until the upturned edge is superimposed on the peripheral edge of the inner panel.