Hydraulic punch press with workpiece stripper

A punch press comprising, a press frame having stationary tool means thereon, ram means having movable tool means on the lower end thereof, hydraulic ram actuator means including a cylinder mounted on said frame and a piston in said cylinder and operatively connected to said ram means for moving the latter up and down along a ram axis, the piston dividing the cylinder into a first fluid pressure chamber at one side of the piston operative when fluid pressure is supplied thereto to move the ram means downwardly toward the stationary tool means and a second fluid pressure chamber at the other side of the piston operative when fluid pressure is supplied thereto to move the ram means upwardly away from the stationary tool means, stripper sleeve means coaxial with the ram means and guidably engaging the latter for relative axial movement therebetween and having a lower work engaging end, stripper clamp means including (a) a clamp housing fixed on the press frame and encircling the stripper sleeve means and (b) hydraulically operated clamp means having an outer portion engaging the clamp housing and an annular inner portion engaging the stripper sleeve means, said hydraulically operated clamp means being operable between a release condition in which the annular inner portion guidably engages said stripper sleeve means when fluid pressure is exhausted therefrom to a clamp condition in which the annular inner portion is expanded radially inwardly into clamping engagement with the stripper sleeve means when fluid pressure is supplied thereto, hydraulic fluid pressure supply means including four-way control valve means operable to a first condition supplying fluid pressure to said first chamber of said cylinder while exhausting fluid pressure from said second chamber to move the ram means downwardly, said stripper operating spring means including clamp spring means operatively engaging the ram means and the stripper sleeve means for yieldably urging the stripper sleeve means downwardly relative to the ram means and a return spring means operatively engaging the ram means and the stripper sleeve means for yieldably urging the stripper sleeve upwardly relative to the ram means, said stripper operating spring means being constructed and arranged such that the work engaging end of the stripper sleeve means is disposed below the lower end of the movable tool means when the ram means is moved downwardly so that the work engaging end of the stripper sleeve means engages the workpiece before the movable tool means engages the workpiece to press the workpiece against the die means, means operative when the ram means reaches a preselected lower punch position for operating said control valve means to a second condition, said control valve means being operative in said second condition (a) to supply fluid pressure to said hydraulically operated clamp means to expand the inner portion radially inwardly and clamp the stripper sleeve means against movement relative to the clamp housing and (b) to supply fluid pressure to said second chamber of said cylinder while exhausting fluid pressure from the first chamber to move the ram means upwardly away from the die means, means operative when the ram means is raised to a preselected return position for operating said control valve means to a third condition, said control valve means being operative in said third condition to exhaust fluid pressure from said hydraulically operated clamp means to release the clamp means and allow the stripper sleeve means to move upwardly under the bias of said return spring means.