Hydraulic presses are operated by large pistons driven by high-pressure hydraulic or hydro-pneumatic systems. They are slow moving compared with mechanical and servo presses, and squeeze rather than impact the workpiece. In operation, hydraulic pressure is applied to the top of the piston, moving the ram downward. When the stroke is complete, pressure is applied to the opposite side of the piston to raise the ram.
Speeds and pressures can be closely controlled. In many presses, circuits provide for a compensation control or sequential control, e.g. rapid advance, followed by sequences with two or more pressing speeds. The press can also be regulated to dwell at the bottom of the stroke for a predetermined time, raised at a slow release speed, and accelerated until it reaches original position. When needed, hydraulic press speed can be increased considerably. In many cases, hydraulic presses used for open and some closed die forging presses use microprocessors or computers to control the press operation, for parameters such as ram speeds and positions.
Hydraulic presses are rated according to the maximum force they develop. Presses in use for impression currently range up to 120,000 tons.
Two Post Presses
Four Post Presses
Deep Draw Presses
Heat Tempering Presses
Hot Platen Presses
Laminating and Multi-Opening Presses
Nick and Break Presses
Pressure Welding Presses
Bending Press – bends or straightens material.
Blanking Press – punches a piece of material sized appropriately for the finished product or follow on processing
Compression Molding Press – applies pressure to a material or combination of materials to bond and/or develop desired characteristics and provide shape
Deep Drawing Press – fairly radical process of forming a metal blank into a cup like shape with a punch pushing the material into a die
Extrusion Press – presses material through a die to form the desired shape
Forging Press – shaping hot or cold metal by compressive forces with an open or closed die configuration
Heat Tempering Press – uses heat and pressure to achieve desired material characteristics
Laminating Press – used pressure with or without binders to adhere two or more layers together
Nick and Break Press – notches the material on one side then applies force from the main cylinder in the opposite direction to snap or break material
Notching Press – removes a portion of material by punching a hole or holes on an outside or inside edge
Punch Press – punches a hole or holes into a part
Stamping Press – a single or multiple step process of forming a blank to its final shape
Stretch Forming – places tension on material past its yield point, and then forms it to the final shape with key properties being minimal stress build-up or spring back
Trim Press - removes excess materials from and outside or inside edge or part