Abstract: A die for the formation of semi-closed channels or other complex configurations comprises a male die member and a female die member. The male die member includes a generally circular mandrel, and elastic, workpiece-retaining pressure means; while the female die member includes an elastically deformable matrix having an open, generally U-shaped forming groove in the upper surface thereof. In operation, the workpiece is driven by the mandrel into the forming groove, and the matrix elastically deformed by matrix deforming apparatus to substantially close the forming groove and wrap the workpiece around the mandrel to form the desired channel. The pressure device retains the workpiece in place during forming while allowing sliding movement of the workpiece to prevent damage to the latter. Following channel formation, the mandrel is withdrawn from the forming groove and the matrix returns to its un-deformed position to re-open the forming groove and enable the ready removal of the workpiece from the die.