Patent ID: 7429169

Claim:
A clamping apparatus comprising: a base; a fixed die plate fixed on the base, the fixed die plate being configured to hold a fixed die; a movable die plate provided movably in a die opening and closing direction on the base, the movable die plate being configured to hold a movable die; a rack fixed with respect to the base and extending in the die opening and closing direction; a pinion pivotally supported by the movable die plate and meshing with the rack; a driving source provided on the movable die plate, the driving source being configured to drive and rotate the pinion to move the movable die plate in the die opening and closing direction; a plurality of tie bars extending in the die opening and closing direction so as to pass through the movable die plate and the fixed die plate, the plurality of tie bars having a plurality of joint portions; a plurality of joint portions provided on the movable die plate, the plurality of joint portions being configured to engage and disengage the plurality of jointed portions of the plurality of tie bars; a plurality of clamping cylinders provided on the fixed die plate, the plurality of clamping cylinders having a plurality of pistons configured to lock the plurality of tie bars, and a plurality of cylinder chambers housing the plurality of pistons, the plurality of clamping cylinders being configured to generate a clamping force by a pressure oil being fed to the plurality of cylinder chambers in a state where the plurality of joint portions and the plurality of jointed portions are jointed; and a control unit configured to control the driving source; wherein, the plurality of tie bars include a lower tie bar provided in a base side of the fixed die plate and the movable die plate and an upper tie bar provided in an opposite side to the base side of the fixed die plate and the movable die plate, the lower tie bar has an extending portion extending from the jointed portion to an opposite side to a piston of the plurality of clamping cylinders and the lower tie bar is longer than the upper tie bar, the rack is provided on the extending portion so as to move the movable die plate toward a die opening direction past the jointed portion of the lower tie bar, a locked portion is provided at an end portion of the upper tie bar on the fixed die plate side, a lock portion configured to engage and disengage the locked portion and locked by the piston is provided on the fixed die plate, and the control unit controls the driving source so that the movable die plate moves toward the die opening direction past the jointed portion of the lower tie bar and the upper tie bar is pulled out from the fixed die plate, when the jointed portion of the upper tie bar and the joint portion of the movable die plate are jointed and an engagement between the locked portion and the lock portion of the fixed die plate is released.