Hydraulic Press

The hydraulic press continues to be the press of choice for today's modern manufacturers. The advantages of the hydraulic press versus mechanical presses is being realized and utilized by more and more manufacturers. Today's modern hydraulic presses provide; Performance, Reliability, and Unlimited Capability in almost any application. Stamping, Punching, Blanking, Drawing, Bending etc. All standard press designs and circuits can be configured to match even the most non-standard press requirements.

Hydraulic Press Benefits

1. Full Tonnage Throughout The Stroke - The hydraulic press has the ability to deliver full pressing force anywhere in the range of stroke, unlike mechanical presses which can only develop full force at close to bottom of stroke. This significantly adds to the inherent flexibility of hydraulic presses.

2. Dedicated or Multi-Functional - The hydraulic presses can be designed to any level of sophistication. Whether the need be a simple dedicated cell press or a fully integrated multi-purpose system, hydraulics are cost effective and easily modified for the task at hand. Their flexibility is further enhanced by additional stroke capability for simplifying die changes and reducing set-up time. Multiple dies with varying shut heights can be run efficiently in a single press.

3. Lower Up Front Costs / Fast ROI - In regard to presses, hydraulic presses are the most simple in basic design and often utilize standardized, proven hydraulic components that are readily available. The basic components to mechanical presses, such as crankshafts, clutch and brake systems, etc..., are expensive and often custom built components which serve to add machine cost. hydraulic presses are often much less expensive up-front and in long term operation.

4. No Design Limitations - The principles of hydraulic force allow for creative engineering. Presses can be designed for traditional down-acting, up-acting, side-acting and multi-action operation. Power systems can be placed above, below or remote from the press and force actuators. Large bed presses can be designed for low tonnage applications and small bed presses can be designed for high tonnage requirements.

5. Over-Pressure Protection - The incorporation of hydraulic relief valves into hydraulic circuits provide built-in overload protection. A press' force cannot exceed the pressure that it is allowed to build, thereby limiting the maximum pressure attainable controls maximum force.

6. Unlimited Control Options - The hydraulic press can be controlled in a variety of ways ranging from basic relays to more sophisticated PLC or PC control systems. Operator interfaces can be added to press systems to facilitate ease of job set by storing individual job parameters for each die. Presses can be controlled for precise pressure and position; including pressure holding, speed control and dynamic adjustments to realtime operating variances. Ram force and speed can be controlled in any direction with various levels of precision.

7. Condensed Footprint - Hydraulics allow for generation of high pressure over small surface area. This ability reduces the overall structure required for support of the force actuators. When compared to mechanical presses, hydraulic presses consume almost 50% less space for the same tonnage capability. This size advantage results in lower manufacturing costs and a faster return on investment by requiring less long term overhead expense.

Hydraulic Press Industrial Terminology

Stroke
The amount of possible ram travel. Stroke is the total distance that the ram can travel, from full extension to full retraction.

Shut Height
The distance between the bed bolster and the ram bolster when the ram is fully extended. This is also commonly known as the Closed Height. As standard, this dimension is usually within "0.25" due to assembly processes. For precision shut height requirements, consult the factory.

Daylight
The distance between the bed bolster and the ram bolster when the ram is fully retracted. This is also commonly known as the Open Height.

Bolster
The removable plate that serves as the working surface for the bed and ram. The plate is typically bolted to the bed and ram substructures. The bolsters can be machined with a variety of work holding features such as; T-Slots, Drilled and Tapped Holes, Lift Rails for Quick Die Change, etc...

Stroke Control
The ram travel of the press may be controlled in a variety of ways. Most hydraulic presses are standard with Adjustable Retract Limit Switches to limit the retract distance of the ram (also know as the Up Limit Position). This can shorten cycle times by only utilizing the required stroke for part loading and unloading. Other adjustable limits may include: Slow Down Limit for deceleration from Fast Speed to Slow Speed; Bottom Stop Position and/or Bottom Stop Pressure, etc...

Bottom Stop
By Pressure:
- The press may be designed to 'return on pressure'. This method utilizes a pressure sensing device which is adjustable and is set to determine the desired maximum pressure to be achieved by the ram. Once this pressure is achieved, the ram typically completes the cycle by returning to the home position or Up Limit position.
By Position:
- The press may be designed to 'return on position'. This method utilizes either a position sensing device or a limit or proximity switch that can be set to signal that the desired ram extension has been achieved.

Bed Height
Bed Height is the distance from the bottom of the hydraulic press structure to the working height or top of the bed bolster.

Dwell
Hydraulic presses are capable of maintaining force on the work for extended periods of time. This is typically accomplished by using pressure lock valves or variable volume pumps that are remotely controlled for precise and long periods of pressure holding.

Bed Cushion
A bed cushion is a commonly required for draw tooling and is a system that applies resistance when pushed upon. This resistance can be dynamic or statically controlled throughout the stroke. Bed cushions have a "pusher pin plate" that is located just beneath the bed bolster. The bed bolster is provided with multiple through holes where "pusher pins" are inserted. These pins are used by the tooling to generate resistive force as the hydraulic press ram pushes down. The cushion can also be configured for multiple control zones for on-the-fly dynamic control.

Remote Power Skid
Some press applications may require that the hydraulics be located remotely from the press itself. Other applications may preclude the power system from being able to be installed at the top around the crown structure of the press. In these cases, the power system and even the controls may be designed into a separate unit capable of being placed adjacent to the press or away from the press.

Heated Platens
These are plates that have heating capabilities. They can be heated using electric rods, steam, oil, water or other medium. These system usually require thermal breaks between the heated plates and the hydraulic press structure. Heating controls can be separate or fully integrated into the press control system.

Hydraulic Press Speeds

What Ram Speeds Do You Need?
Hydraulic presses are normally offered with multiple ram speeds, such as; Fast Approach, Pressing and Fast Retract. Typically, these speeds are expressed in Inches Per Minute. The Fast Approach Speed is designed to lower the ram quickly during the portion of the stroke that does not require any force. The pressing speed is commonly referred to as the working portion of the stroke where force is required and is usually slower. After the working or pressing portion of the stroke is completed, the ram retracts at a Fast Retract Speed which affords little force. This Retract Force is commonly referred to as the "Stripping Force".

Many customers with mechanical press experience refer to press speed in cycles per minute. Hydraulic presses can be designed to provide a certain amount cycles per minute once the cycle profile has been determined. The cycle profile consist of an accurate description of the physical aspects of the cycle. These aspects are:

1. Distance of ram travel under no load (Fast Approach)
2. Distance of actual working stroke (Pressing)
3. Distance of Fast Retract (usually the combination of the previous two distances)
4. Any Dwell Time at the bottom of the stroke or while under pressure

Once these parameters have been established, the appropriate ram speeds can be developed in conjunction with the right power system to provide the necessary cycles per minute.

Variable ram speeds are also available through the use of flow controls and variable volume pump systems. These and many other cycle profile characteristics can be provided.

ANATOMY OF HYDRAULIC PRESS

Bed: The press bed is the flat, stationary, machined surface that supports the lower bolster or dies.

Bed Cushion: Commonly required for deep draw applications, a bed cushion is used to apply resistance force when pushed upon. This resistance force ensures the material is drawn smoothly, without wrinkling or tearing. Bed cushion force can be dynamically controlled throughout the stroke, allowing the resistance force to change based on the position of the bed cushion.

Bed Height: The bed height on a press machine is the distance from the bottom of the press structure to the working height or the top of the bed bolster. If a press requires a pit, the working bed height could be defined as the distance from the floor to the top of the bed bolster.

Bolster: The bolster is the removable plate that serves as the working surface of a press. The plate is typically bolted to the bed and ram weldments. Tooling is attached to the bolster, which can feature a variety of work-holding features such as T-slots, drilled and tapped holes, lift rails to accommodate quick die change systems, and more.

Bushing: Found on 2-post and 4-post hydraulic presses, the bushing is a fixed or removable cylindrical metal lining used to guide the ram and reduce friction. Graphite-impregnated bronze bushings that do not require external lubrication are the longest-lasting type of bushing.

Crown: The crown on a press is the upper structural weldment containing cylinders that drive the motion of the ram.

Cycle: A hydraulic press cycle is the complete movement of the ram, from the initial start position back to the same start position, that may include feeding and removal of the material or workpiece(s).

Cylinder: The cylinder is the main actuator of a press. This mechanical actuator converts pressure into linear movement, creating force.

Daylight: Also commonly known as the open height of a press, daylight is the distance between the bed bolster and the ram bolster when the ram is fully retracted.

Deflection: Deflection is the amount of deviation from a straight line that occurs when force is applied to the structure of a press. In c-frame press designs, this is often referred to as yawning, and expresses the amount a frame flexes under a load.

Dwell: Dwell is the amount of time required for a press to maintain pressure during a cycle. This is typically accomplished by using pressure lock valves or variable volume pumps that are remotely controlled during long periods of precise pressure holding. Hydraulic presses often use pneumatic dwell systems, powered by a pneumatic pump integrated into the hydraulic circuit, to reduce noise output and energy consumption.

Finite Element Analysis (FEA): Finite Element Analysis is computerized method for predicting how a press’s structure will react to real-world forces such as vibration, heat, fluid flow, etc. Performed during the press engineering phase, FEA works by breaking down a real object into finite elements and using mathematical equations to predict the behavior of each element.

Gibs: Gibs are adjustable metal bolts on gib-guided (or “straight-sided”) presses that guide the reciprocating motion of the ram to ensure squareness and parallelism. Gibs are usually provided with replaceable liners and are adjustable front-to-back as well as left-to-right to enable the setting of proper clearance and to compensate for wear.

Heated Platens: Heated platens are steel plates to which the press’s tooling is attached that are heated using water (steam), oil, or electricity. These systems usually require thermal breaks (insulation) between the platens and the press structure. Heating controls can be separate or fully integrated into the press control system.

Human-Machine Interface (HMI): A Human Machine Interface (HMI) is a programmable touch screen computer that initiates the press cycle, monitors press health, and logs critical data and cycle parameters. On a hydraulic press, the HMI also acts as a check-engine light for the hydraulic system, notifying operators of oil particulate count, viscosity, temperature, and leaks.

Hydraulic Power Unit (HPU): The Hydraulic Power Unit (HPU) on a hydraulic press is a system comprising the tank, motor, hoses, pumps, and chillers that work in unison to create pressure. It is the mechanism that applies pressure to drive motors, cylinders, and other parts of a hydraulic system. HPUs are typically either skid-mounted or crown-mounted on the press, depending on the footprint requirements.

Motor: The motor on a hydraulic press is the electric machine that transforms hydraulic energy (fluid power) into rotary energy.

Platen: Platens are the steel plates, sometimes heated, that are attached to a moving or stationary press member.

PSI: PSI is an abbreviation for Pounds per Square Inch, a unit for measuring pressure in a hydraulic press.

Pump: A pump is the device that converts mechanical force and motion into hydraulic fluid power on a hydraulic press.

Ram (or Slide): The ram (or slide) is the middle weldment on a press that slides within the frame to create pressure on the tool or die. The ram can move vertically or horizontally depending on the press configuration. Some multi-action hydraulic presses even have multiple rams for complex forming processes.

Ram Knockout: A ram knockout is an ejection device required by many press operations that strips the formed part from the punch or die.

Ram Speed: Ram speed on a hydraulic press is the total time it takes for the ram to move from the open to the closed position, measured in IPM (inches per minute). Speed is also commonly measured at the three distinct stages of the stroke:

Fast Approach Speed lowers the ram quickly during the portion of the stroke that does not require any force.

Pressing Speed, commonly referred to as the “working portion” of the stroke, is when force is required and speed is slower.

Stripping/Retract Speed is after the Pressing portion of the stroke is completed, when the ram retracts at a Fast Retract speed which affords little force.

Return on Pressure: Return on pressure is a programmable hydraulic press cycle parameter that uses an adjustable pressure sensing device (transducer) to determine the desired maximum pressure to be achieved by the ram. Once this pressure is achieved, the ram completes the cycle by returning to the “Home” (or “Up Limit”) position.

Return on Position: Return on position is a programmable cycle parameter on a hydraulic press that uses a position sensing device (transducer) to determine the desired position to be achieved by the ram. Once this position is achieved, the ram completes the cycle by returning to the “Home” (or “Up Limit”) position.

Shut Height: Shut height is the distance between the bed bolster and the ram bolster when the ram is fully extended. This is commonly known as the “Closed Height.”

Stroke: Stroke is the total distance the ram can travel, from full extension to full retraction.

Stroke Control: Most hydraulic presses feature Adjustable Retract Limit Switches to restrict the retract distance of the ram (also known as the “Up Limit” Position). Using only the required stroke for part loading and unloading can shorten cycle times. Other programmable limits may include: Slow Down Limit for deceleration from Fast Speed to Slow Speed; Bottom Stop Position and/or Bottom Stop Pressure.

T-Slot: A t-slot is a notch machined into the platens of a press to hold the die in place. This work-holding feature also facilitates quick die changes.

Throat Clearance: On c-frame (gap-frame) presses, the throat clearance is the distance from the vertical centerline of the bed to the back of the press behind the bed. This measure is required to determine the diameter of parts and tools that can be positioned within the press.

Tie Rod: Tie rods on a 2-post or 4-post press are long rods with threads and nuts on both ends that hold the frame members together. These rods are stretched to place the frame members under compressive load.

Tonnage: Tonnage is the maximum amount of force a press machine can exert, typically called out in U.S. tons.

Transducer: A transducer is a device that measures the linear position or pressure of the ram or cylinder rod.

Weldment: Weldments are structural components formed by welding together steel plates. Most hydraulic presses have three main weldments: crown, bed, and ram.