Blanking machine for blanking holes in sheet of metal

A blanking machine for blanking holes in a sheet of metal, comprising:

• a bolster;
• a pair of rails fixedly secured to said bolster;
• said rails extending in a direction right angles to the feeding direction of the sheet of metal to be blanked;
• a lower die set slidably mounted on said rails;
• a die fixedly secured to said lower die set;
• an upper die set having a punch mounted thereon opposite said die;
• coupling means for coupling said upper die set with said lower die set allowing said upper die set to move on said rails together with said lower die set;
• hydraulic cylinder means having a plurality of pressure chambers formed therein defined by a cylinder barrel and partition walls, the length of said pressure chambers being different from one another, each pressure chamber having mounted therein a piston and a piston rod, and each partition wall and rod-end of said cylinder barrel having holes formed therein allowing the piston rods to slide therein, each piston rod except the last one being adapted to contact with the adjacent piston;
• connecting rod means connected to said lower or upper die set at one end thereof;
• and
• transmission means connected to the other end of said connecting rod means at one end thereof, the other end of which is connected to said last piston rod whereby said lower and upper die sets are moved on said rails by the actuation of said hydraulic cylinder means.