Hydraulic Press

About Hydraulic Presses and Hydraulic Press Manufacturers Including: C-Frame Presses, Laminating Presses, Pneumatic Presses, Power Presses, Press Brakes, Stamping Presses & Transfer Presses

A hydraulic press is a press machine that uses hydraulic pressure, or fluid pressure, in order to exert force on an object. Also known as Bramah presses, after their inventor Joseph Bramah, hydraulic presses depend on Pascal's principle; mainly, that the pressure throughout a closed system will act with equal force on all areas. As both the most common and most efficient type of industrial press, hydraulic presses apply a large lifting or compressing force that cannot be achieved using pneumatic presses or mechanical presses. There are many different types of hydraulic press; each with its own set of applications, although there is some overlap. For instance, C-frame presses can be used for a variety of industrial operations including forming, straightening, blanking, punching, drawing and riveting. H-frame presses are used similarly for a wide range of industrial applications such as coining, crimping, bending, punching and trimming. Laminating presses, on the other hand, have a few specialized applications such as applying film to a variety of materials as well as encapsulating layers of materials in plastic for electronics industries, credit cards and identity cards. Stamping presses, much like laminating presses, have specialized applications and are used for the two main purposes of shaping or cutting materials by deformation with a die for metalworking or automotive industries. Transfer presses are used for the stamping and molding of plastic, rubber and metal such as in the medical and aerospace industries. Press brakes cold work sheet metal and bend or fold them into different shapes.

A hydraulic press is a type of power press. Power presses can be pneumatic, hydraulic or mechanical. Pneumatic presses serve applications similar to hydraulic presses, including piercing, metal working, crimping, stamping, bending and punching. However, pneumatic presses use compressed air in order to gain movement and are not capable of creating the extremely high pressures of hydraulic presses. The various types of hydraulic presses are typically differentiated not only by application but by design and operation as well. C-frame presses can be operated manually or automatically and take up less floor space than most hydraulic presses due to their narrow but sturdy c-shaped frame, generally made from steel, which provides minimal deflection. H-frame presses differ from C-frame presses as a result of the welded H-shape of their frame as well as being able to handle multiple operations. Laminating presses are manually operated compression presses with two openings that are known as plates. One is used for heating whereas the other is used for cooling, thus making the lamination process faster as a result of the simultaneous cooling of one platen while heating the other. Transfer presses work by feeding flat plastic, rubber or metal blanks automatically into the right end of the press. From there, feed bar fingers take the part and move it from die to die. Most machines are designed to handle extremely heavy loads, reaching 3500 tons but they can also be small machines which can handle about 15 tons.

Hydraulic presses are powered by hydraulics, which provide force through fluid pressure. Consisting of the main components used in a hydraulic system, the basic form of a hydraulic press is comprised of a set of cylinders, pistons, also called punches, hydraulic pipes and a stationary anvil, or die. The piston, which is a mechanical device that provides a plunging or thrusting motion, uses liquid under pressure to exert a compressive force upon the anvil. The liquid is first forced into the cylinder by a pump or lever. The hydraulic system consists of two cylinders; the fluid, usually oil or water, is poured in the smaller of the two cylinders. This cylinder is often referred to as the slave cylinder. The small piston is located in this cylinder and is pushed so that it compresses the fluid that will then flow through a pipe into the larger cylinder, also known as the master cylinder. The pressure of the compressed liquid is then exerted on the larger cylinder and the larger piston in the master cylinder pushes the fluid back to the smaller cylinder. The force applied on the fluids in the smaller cylinder results in a larger force when pushed in the master cylinder. This force brings the punch in contact with the die, and deforms the material into the desired product shape. Typically constructed from stainless steel and other durable materials, hydraulic presses are available in both single and multi-station configurations. Single station presses consist of a single set of press tools, a die and punch, inside of a table. Multi-station presses have multiple sets of press tools, which either perform the same operation on many materials or perform various press operations on single or multiple materials as they move between stages.

Alternatives to hydraulic presses include mechanical presses, electric presses and pneumatic presses. Mechanical presses are driven by a flywheel which stores energy then releases it, thus transferring energy to the main slide by the use of mechanisms such as a crank, eccentric, knuckle joint or toggle. In a mechanical press, the stroke of the slide is adjustable within the limits of daylight. In addition, the strokes are also classified by the number of slides or ram they have, which can be single, double or triple action. All-electric presses are fairly recent developments, offering more efficient drive systems due to the mechanical linkage of the ram with the drive motor. This ensures that the controller is able to give a signal to the motor for a specific speed. If the motor is not overloaded then that speed will be reached. Also, the elimination of hydraulic fluid variations is beneficial because hydraulic fluid changes across time and temperatures, they can even vary within a single day. Pneumatic presses are advantageous because they can have stroke cycles of up to 400 strokes per minute, or SPM. Even at high stroke speeds, pneumatic presses are able to offer a controlled flow rate that makes them ideal for applications in which the material flow rate, or ram velocity, is crucial. Pneumatic presses do not convert rotary motion to linear motion and therefore have fewer moving parts than hydraulic press or machine presses. However, for applications requiring shear force and the ability to reach high pressure, hydraulic presses remain the best solution.

Hydraulic Presses and Hydraulic Press Manufacturers Image Provided by Wabash MPI	Hydraulic Presses and Hydraulic Press Manufacturers Image Provided by Grimco Presses, Inc.

Hydraulic Press Types

• Arbor presses are used for seating stamping and removing bearings and other high-pressure assembly, repair and production jobs.
  
• Assembly presses use great pressure to secure or assemble parts together.
  
• C-frame presses are streamlined-sized, press-shaped like a "C" and normally consist of a single press application.
  
• Compression molding presses use two plates being pushed together to compress the material into the mold.
  
• H-frame presses, sometimes referred to as 4-column presses, are shaped like an "H" and can often field more than one press application at a time.
  
• Laboratory presses are smaller, single run presses used primarily in research laboratories and other short and test run situations.
  
• Laminating presses are used for the lamination of polymers onto the surface of other materials including lumber, metal and paper.
  
• LIM presses refers to liquid injection molding presses which handle plastics that are created via an injection process.
  
• Mechanical power presses are used to shear, punch, form or assemble materials by using tools or dies attached to slides or rams.
  
• Pneumatic presses use energy transfers in the form of compressed airflow to control their movements. Some typical application are shearing, punching, bending and forming.
  
• Power presses are hydraulic powered machines that use tools and dies to shear, punch, and form metals.
• Press brakes are manual, mechanical or hydraulic pressing machines that cold work sheet metal into different bent or folded shapes.
• Stamping presses are devices that use stamping dies.
• Straightening presses apply pressure to metal in order to straighten it. 
• Tableting presses are used for the pressing of powdered materials into shaped tablets or compacts.
• Transfer presses are hydraulic presses which automatically move parts from one stamping process to another using feed bar fingers.

Hydraulic Press Terms

Actuator - A device that converts fluid power into mechanical movement.
 
Age - The amount of time necessary to wait between the molding and appraisal of molded part properties.

Backrind - A defect at the parting line where the material has shrunk inside the part.

Bed - The flat surface that supports the material being worked.
 
Bolster - Plates attached to the rods that carry the platens or any structure mounted to the bed of a press. It is sometimes removable.
 
Check Valve - Any one of several types of valves that allows flow in only one direction.

Compression Set - The lingering deformation after removal of the force, which compressed the section. An example is when one uses a fingernail to depress a molded sample; the impression that remains after a time is the compression set.

Contact Gauge - A feature of hydraulic systems that turns the system off and on at set pressure points.
 
Cylinder Assembly - The cylinder, piston, ram, seals and packing of a press.
 
Daylight - The largest capacity, vertically, that the press can handle or the vertical clearance from the underside of the ram to the top of the bolster. The ram must be in its maximum up position.
 
Die - The tooling used in a press for shearing, punching, forming, drawing or assembling metal or other materials.
 
Gate - The final opening through which injected material flows in order to enter a part cavity.
 
Heat Exchanger - Circulates air or water to maintain oil at operating temperature.
 
Hydraulic Pressure - Pressure caused by fluid under applied force.
 
Hydraulic Cylinders - Actuation devices that produce linear motion and force through the use of pressurized hydraulic fluid.
 
Hydraulic Pump - Pumps that use mechanical energy to deliver high-pressure fluid flow to the outlet through pressurized fluid.
 
Hydraulic Seal - A device that restricts the escape of fluid or entrance of foreign material.

Hydraulic Valve - A device that contains and transfers the flow and pressure of hydraulic fluid in hydraulic power systems.

Knockout - Removes the part from the punch/die.
 
Low Pressure System - A press function that allows it to operate continuously under 10% of its maximum rated force, as well as to ensure a preheat function at reduced pressure.
 
Platen - The place where the mold attaches. It is a series of flat surfaces where one surface is stationary and the other is moving.
 
Rod or Tie Rod - Long stem or pole that connects two pieces of the press so that they act together.
 
Shut Height - With the ram full down, it is the clearance over the bed.
 
Sprue - The main feed guide that runs from the outer face of an injection or transfer mold gate into a single cavity mold or to runners in a multiple cavity mold.
 
Stroke Control - Feature that controls the length of a stroke and can be adjusted accordingly.
 
Throat Clearance - Distance between the frame member behind the bed to the vertical centerline of the ram. This measurement affects the size of the piece that can be used.