Introduction to Hydraulic Workholding

Hydraulic cylinders produce the forces required to do three jobs: positioning, supporting, and clamping a part in place during machining. They are available in a huge variety of styles and sizes to perform these three functions. (Future issues of EU will provide more details on cylinders.)

Positioning cylinders
Used to position the part properly on the fixture and also to hold it in place during machining. The part is simply placed on some basic locators, and the positioning cylinders push or pull it into place each time.
Support cylinders
Automatically conform to the size and shape of the part. They help to maintain dimensional control and to prevent deformation. They also absorb a lot of the vibration generated by cutting operations. These cylinders can be set up so that they are normally retracted out of the way and engage the part only when needed.
Clamping cylinders
Used in the same manner as traditional stud and strap setups to hold the part in place during machining. The most popular and versatile is the swing cylinder. The attached clamp arm on these cylinders begins its cycle at a position 90 degrees offset from the clamping location to allow unobstructed part loading and unloading. When hydraulic pressure is applied, the arm swings over the part and comes down to apply the clamping force. Clamping cylinders can be designed with a linkage to reach into tight spaces on the fixture and retract out of the way when not in use.