Method and apparatus for forming sheet metal

A method of forming a sheet metal by pushing a forming punch having a desired shape to be formed in a sheet thickness direction of a blank workpiece with edges of the blank workpiece being clamped, and performing shape-forming using a shaping tool disposed in the side of the blank workpiece opposite to the forming punch with the forming punch being pushed, the method comprising

• clamping edges of said blank workpiece in a sheet thickness direction with a plurality of clamp fixtures disposed at predetermined intervals on a bed, said clamp fixtures capable of moving in forward and backward directions and stopping with a variable clamping pressure, wherein said forming punch is disposed inwardly of said clamp fixtures and has a desired shape, and wherein a CNC incremental forming device is equipped so as to move in three axis directions, and further comprising the steps of:
• (a) performing drawing-forming to a predetermined height by pushing said forming punch having a desired shape in the sheet thickness direction with a CNC forming punch elevator with the edges of the blank workpiece being clamped;
• and then
• (b) performing shape-forming with said CNC incremental forming device in the side opposite to said forming punch by increasing the clamping pressure to lock movement of the workpiece with said forming punch being pushed;
• (c) performing drawing-forming again by decreasing the clamping pressure and raising said forming punch again to a desired height;
• and then
• (d) again performing shape-forming with said shaping tool by increasing the clamping pressure to lock movement of the workpiece, and repeating steps (a) to (d) at least once.