Patent ID: 8221670

Claim:
A method for injection molding, comprising: a) energizing a traverse actuator in a first direction to advance a moving platen towards a closed position relative to a stationary platen, the moving and stationary platens carrying respective portions of a mold, and leaving a positioning gap between the portions of the mold; b) after step a), locking a first one of the moving and stationary platens to a tie bar extending from the other, second one, of the moving and stationary platens; c) after step b) pre-positioning a clamp piston within a cylinder housing to a datum position axially intermediate a clamping position and an unclamped position, wherein the clamp piston is prepositioned by energizing the traverse actuator in the first direction and further advancing the moving platen to substantially close the positioning gap, the clamp piston affixed to the tie bar and the cylinder housing affixed to the second one of the moving and stationary platens, the clamp piston and cylinder housing cooperating to provide a clamp chamber and an unclamp chamber in the cylinder housing on axially opposite sides of the piston for urging the clamp piston towards the clamping and unclamped positions, respectively, when pressurized; d) after steps c) and b), pressurizing the clamp chamber so as to exert a clamping force urging the portions of the mold together; e) after step d), injecting melt into the mold portions; f) after step e), relieving pressure in the clamp chamber; g) after step f), pressurizing the unclamp chamber to move the piston toward the unclamped position; h) after step f), unlocking the first one of the moving and stationary platens from the tie bar; and i) after step h), energizing the traverse actuator to retract the moving platen to an open position spaced away from the stationary platen.