This article will take an in-depth look at power presses.
You will learn about the following topics:
This section will explore what a power press is and why it is used.
A power press is a type of metalworking machine utilized for shaping, cutting, and punching metal through cold stamping. These machines come in various types and are highly effective for large-scale production of metal components. Power presses can be categorized into hydraulic and mechanical variants based on their power source.
The operating principles for power presses are mechanical, hydraulic, and servo motor. A mechanical power press changes circular motion into linear motion using a clutch, flywheel, crankshaft, and fixed and moving plungers. Hydraulic power presses use the built up pressure of hydraulic fluid to create the force to compress and shape metals. Servo power presses are powered by a servo motor that drives the eccentric gear that moves the slider of the press.
In all types of presses, the final shape of the workpiece is achieved by the compression of the upper and lower die halves coming together under the press's applied force.
In the past, shaping metal sheets required significant manual labor and strength. The advent of power press machines revolutionized this process by introducing enhanced mechanical force and precision.
A power press is defined by its method of force application. Mechanical power presses use a flywheel to accumulate and transfer force to the ram. Hydraulic power presses rely on hydraulic fluid pressure to generate force, whereas servo motor power presses utilize a motor to create rotational motion, which is then transformed into linear motion.
Selecting the appropriate type of power press depends on various considerations. Mechanical power presses represent the earliest method, while servo motor presses are the most recent advancement. Hydraulic power presses, which are extensively utilized, were introduced as alternatives to mechanical presses.
More than 200 years ago, a British engineer pioneered the hydraulic press. Initially used during the first industrial revolution to replace steam hammers in forging processes, hydraulic presses have evolved significantly. Today, they can exert thousands of tons of pressure and are capable of mass-producing a diverse range of parts and components.
A hydraulic power press operates using a pump, endplates, and a piston to generate pressure within a fluid for metal shaping and forming. The central element of this press is the pump, which pushes oil into a cylinder under high pressure.
The cylinder houses a piston that moves vertically to generate compressive force. This piston functions similarly to a pump, creating the necessary force for the hydraulic press. It is the key component responsible for applying pressure to the workpiece.
The reservoir holds the hydraulic fluid, filters out impurities, eliminates air and moisture, and dissipates heat within the system. Hydraulic fluid is transferred from the reservoir to the cylinder via a connecting tube.
The valve is responsible for controlling fluid flow between the pump and the cylinder, relieving excess pressure, and adjusting the press's speed and force output. It acts as a pressure regulator, while a pressure gauge monitors the hydraulic fluid’s pressure to confirm it remains within the specified range.
The hydraulic pump is the mechanical part of a hydraulic power press that moves hydraulic fluid to the reservoir and converts mechanical energy into hydraulic energy. It generates a powerful flow against the pressure at the outlet.
The press plates secure the workpiece and offer a stable surface for operations such as bending, piercing, stamping, or punching. They are the components of the press that directly interact with the workpiece.
The hydraulic fluid's movement is facilitated by a network of hoses that transfer the fluid between the pump, cylinder, and reservoir. These hoses are constructed from robust materials designed to endure the pressure and heat generated during press operations. Typical hose materials include thermoplastics, synthetic rubbers, and polytetrafluoroethylene (PTFE), all of which offer resistance to corrosion and chemical exposure.
The ram moves within the press frame to exert force on the die. It can travel either horizontally or vertically based on the hydraulic press's design, and some models feature multiple rams to aid in the forming process.
The bed provides a stable, flat surface that holds the die in place while the ram exerts pressure.
A servo press relies on the accuracy of a servo motor to regulate the ram's movement. These presses are favored for their precise ram positioning, making them well-suited for manufacturing parts that demand high accuracy and consistent repeatability. The servo motor is linked to a linear actuator, like a ball screw, which manages the ram's vertical motion.
In a servo mechanical press, the conventional motor, flywheel, and clutch are replaced by a servo motor, offering enhanced control over the ram's movement. This change leads to a simpler design with fewer moving parts compared to traditional mechanical presses. Unlike typical mechanical or hydraulic presses, which forcefully drive the ram downward to shape the workpiece before returning to its original position, a servo press allows for precise control, enabling the ram to strike and stay in contact with the workpiece for prolonged periods if needed.
Servo presses are employed in fields that demand high levels of accuracy and control, including aerospace and electronics production. They can perform stamping, punching, and forming tasks similar to those of mechanical and hydraulic presses but with superior precision.
The ram in a servo press is powered by a servo motor, which supplies the necessary force and energy to the system. Servo presses typically use either direct drive motors or servo motors paired with a reducer.
A direct drive motor is linked straight to the actuator and is characterized by its low speed and high torque. It features a straightforward design, high efficiency, and minimal noise. However, its torque capacity is restricted, making it suitable only for low-tonnage servo presses.
A servo motor equipped with a reducer enables quick acceleration and deceleration. The reducer adjusts the speed reduction ratio to align the motor and gearbox inertia with that of the load, enhancing the overall efficiency of the motor.
Servo motors equipped with a reducer use various transmission methods, including deceleration with a crank connecting rod, a crank elbow rod, or a screw elbow rod. This configuration allows a low-torque, high-speed servo motor to power high-tonnage presses effectively.
The actuator is the part of a servo motor press that changes rotary motion into linear motion. Ball screw actuators are the most commonly used, which consist of a screw and nut assembly with ball bearings to provide smooth, even, and efficient motion. The construction of a ball screw actuator consists of a nut mounted on a grooved shaft. As the screw turns, the nut moves up and down the shaft creating linear motion and precision control.
The controller processes data from sensors to generate output signals for the servo motor. It uses embedded algorithms to manage the press's movements, ensuring exact operation and consistent repeatability. Unlike hydraulic and mechanical presses, which struggle with controlling stroke, pressure, and slider motion, a servo press can be precisely programmed to regulate stroke length, speed, and pressure, enabling the press to achieve the required tonnage even at reduced speeds.
Sensors - To ensure accurate performance, the controller needs information about the ram’s position, force, and speed. Both internal and external sensors provide this feedback, which the controller then translates into command signals for the press.
Human Machine Interface (HMI) - The HMI provides a connection between the operators and the servo press, enabling them to oversee, modify, and control various operational parameters like speed, force, and positioning. An essential feature of servo presses is an intuitive interface with real-time graphical displays on the HMI, which can be customized according to the requirements of the part being produced.
In intricate HMI setups, a supervisory control and data acquisition (SCADA) system is utilized to manage multiple HMIs within a plant or facility. The SCADA system facilitates the transmission of data and commands to individual or multiple HMIs as needed.
Key elements for power transmission in a mechanical power press include the clutch, crankshaft, flywheel, moving ram, and stationary ram. The slide is connected to the crankshaft via connecting rods, also known as “pitmans.”
The crankshaft is linked to the continuously rotating flywheel driven by the motor. A clutch engages the rotating flywheel with the crankshaft. This setup allows the crankshaft to transform the flywheel's rotational movement into the vertical motion of the press slide.
The ram is the central functional element of a mechanical power press, directly engaging in reshaping the workpiece. It oscillates back and forth within its guides, which define its stroke length and force. Both the stroke length and power can be modified based on operational needs. At the ram’s lower end is the punch, which is used to work on the workpiece.
A driven pulley or gear, designed as a flywheel to store energy, helps keep the ram's speed consistent when the punch impacts the workpiece. This flywheel is mounted at the end of the driving shaft and connected to it through a clutch.
The flywheel accumulates energy while the machine is not in use. If the flywheel does not store enough energy, the machine will stop and be unable to complete its task. Using a flywheel allows the motor to operate at lower capacity while still providing the necessary maximum tonnage for the operation as needed.
To accommodate a larger working area for tasks like drawing or to speed up processes such as automatic piercing or blanking, increased power and energy are required.
During the blanking process, the operation is completed within a brief segment of the stroke. Consequently, the energy is drawn from the flywheel, which delivers the necessary power immediately. This approach is also valid for the remaining part of the cycle. In contrast, the drawing process utilizes a larger portion of the cycle time. Given the extended duration, surplus energy can be drawn from the motor, while any shortfall is supplemented by the flywheel.
For intermittent operations, its value is 20%
For ongoing operation, the value is 10%
From operation E = P x K x L
When the flywheel's energy is less than P x K x L, the speed N needs to be increased.
A mechanical clutch is employed to engage or disengage the driving shaft from the flywheel, which is crucial for starting or halting the ram's movement. The clutch transmits the torque produced by the flywheel to the gear shaft. Power presses utilize two types of clutches: full-revolution and partial-revolution clutches.
According to OSHA standards, a full-revolution clutch is a type of clutch that, once engaged, cannot be disengaged until the crankshaft has completed nearly one full revolution and the press slide has finished its entire stroke. Full-revolution clutches are typically found in older presses and are considered more hazardous due to their continuous cycling operation.
As defined by OSHA, a part-revolution clutch is a type that allows disengagement at any point before the crankshaft completes a full revolution and the press slide finishes its stroke. Most part-revolution presses use air-operated clutches and brakes. In these systems, the clutch engages and the brake disengages when air is compressed in compartments. To halt the press, this process is reversed.
Brakes are employed to quickly halt the driving shaft's movement once it has been disconnected from the flywheel.
Brakes play a vital role in mobile systems. Typically, two kinds of brakes are utilized. The first is a standard brake designed to rapidly halt the driven shaft after it has been disengaged from the flywheel. The second is an emergency brake, often operated by foot, which is provided on power press machines. This type of brake includes a power-off switch and delivers robust braking to swiftly stop all movements.
The base serves as the foundational structure of the press, providing support for clamping and tilting mechanisms in an inclined press. It also supports the dies that hold the workpiece and various control tools. Additionally, the dimensions of the table determine the maximum size of the workpiece that can be accommodated by the power press.
Various driving mechanisms are used in different types of presses. For example, hydraulic presses utilize a piston and cylinder arrangement, while mechanical presses use an eccentric and crankshaft setup. These mechanisms are responsible for transferring power from the motor to the ram, enabling its movement.
Controlling mechanisms are employed to operate a press under predefined and regulated conditions. Typically, these mechanisms adjust two main parameters: the stroke power and the ram's stroke length. Power transfer can be interrupted using a clutch integrated with the driving mechanisms as needed. Many modern power presses incorporate these control mechanisms directly into their driving systems. Today, computer-controlled presses use microprocessors to guide operations, offering precise and dependable control with advanced automation.
This is a heavy plate secured to the base or bed of the press. It is used to firmly clamp the die assembly in place to support the workpiece. Since dies used in press operations often consist of multiple components, the term "die assembly" is used to refer to these multi-part dies.
Presses that are manually operated can be cycled using either foot pedals or two-hand controls. In the case of foot control, the press is activated by pressing a pedal or switch with the foot.
Using foot control allows operators to keep their hands free during press operation. However, this can increase the risk of injury, as foot-operated presses tend to result in approximately twice as many injuries. In contrast, with two-hand controls or trips, both hands must be away from the pressing area to activate the controls, which enhances safety during operation.
Power press machines operate by applying force to reshape metal sheets. Key components include the ram, bed, flywheel, clutch, and crankshaft. The ram and bed are equipped with dies that shape the metal sheet into the desired form. An electric motor drives the flywheel's rotation. The flywheel is connected to the crankshaft through a clutch. With the dies mounted on the ram, a workpiece is placed on the bed and the machine is activated. The flywheel’s rotational motion facilitates the pressing and shaping of the metal as the upper and lower dies exert pressure. After the process is completed, the finished workpiece is removed and replaced with a new one, and the operation is repeated.
Accurately determining the size of a power press involves specifying the required tonnage, the dimensions of the worktable, and the height of the press opening.
Understanding the intended use of a power press is crucial when making a selection. Despite this, comprehending the operational methods and functionality of the press can be challenging. Selecting an unsuitable power press may result in decreased efficiency and could waste investment in equipment. Here are some important factors to take into account.
Various stamping techniques, which may include cutting, can be employed. It is important to verify the intended processing method when selecting a punch. Once the processing method is established, the appropriate type of punch can be generally identified.
For production runs exceeding 3000-5000 pieces, automatic feeding becomes more advantageous. When dealing with multiple projects and high-volume production, it's essential to evaluate the use of continuous and transfer processing methods.
Understanding the processing method, usage frequency, and material consumption rate is essential.
These processes are generally referred to as material handling. In a manufacturing facility, material handling constitutes a significant portion of the operational workload.
In single-action punches, it's important to account for additional die buffers during the extension process. With the high efficiency of these die buffers, challenging drawing operations can be performed effectively without the need for a double-action punch.
To calculate the maximum pressure required during processing, it’s necessary to determine the pressure stroke curve for each project. For multi-engineering processing, combine these curves by overlapping them to create a unified pressure stroke curve. This combined curve will help identify the appropriate pressure capacity needed for selection.
When using a punch press with more than two dies or a continuous die, there is an eccentric load, as many punching operations also involve eccentric loading. Therefore, for processing eccentric loads, it is essential to select a punching capacity with a sufficient margin.
The buffer capacity is typically set at 1/6 of the minimum punch press capacity. If needed, it is advisable to use a double-acting punch.
Dimensional accuracy refers to the tolerance, which specifies the allowable range of errors. When selecting a power press, the choice of press type—mechanical, hydraulic, or servo—affects the level of accuracy or tolerance. For applications requiring exceptional precision and performance, servo presses are the optimal choice due to their advanced control mechanisms.
Catalog specifications outline the key capabilities and dimensions of punch presses and serve as the primary basis for selecting the appropriate press.
Proper use of accessories can enhance productivity, so it is important to thoroughly review the various accessory devices.
Pressing operations carry a high risk of accidents, so it is crucial to consider safety measures thoroughly. Choose a press equipped with safety functions.
Due to pollution concerns, laws and regulations prohibit certain practices. Therefore, it is essential to incorporate noise and vibration control measures into the pressing equipment.
Power presses can be classified in various ways, including by mainframe type, drive mechanism type, or job operation mechanism.
Power presses are generally categorized as either C-Frame or H-Frame types, regardless of their power source. The type of frame can also determine the press's tonnage.
The C-Frame, which is C-shaped, is designed for smaller presses with capacities up to 250 tons. However, due to its shape, the C-Frame exhibits greater angular and longitudinal deflection compared to other frame types, making it less suitable for applications requiring high precision. C-Frame power presses are more commonly used for presses up to 100 tons.
C-Frame presses are used for bulk production in the cold-working of ductile metals, such as mild steel. They feature spinning flywheels that store energy to operate the ram, which strikes the workpiece. These presses handle various functions with components like the plate, bed, bolster, and ram. The knockout mechanism is employed to remove the finished workpiece from the press.
Proper cushioning should be placed beneath the bolster to absorb heavy impacts on the workpiece. The C-type frame is designed for continuous, high-accuracy production and is constructed from solid steel with appropriate cross ribbing. It features a clutch that enables continuous stroking for mass production. The crankshaft is made from a special steel alloy and equipped with gunmetal bushes to ensure smooth operation and extended durability. The table and ram are precisely aligned to ensure highly accurate performance.
The box-type H-shaped design provides enhanced rigidity with zero deflection, ensuring smooth and precise operations over the long term. This frame features four box-type pillars and is operated from the front of the press. The job size is limited to the available windows. The H-Frame design improves tool life and precision in job operations, though it is more costly than the C-Frame Power Press and Ring Frame Press.
This design is typically used for power presses with capacities ranging from 100 tons to 800 tons, featuring either two-point or single-point suspension. For presses with a tonnage capacity over 400 tons, handling the frame on the factory floor becomes challenging due to its size. Therefore, this frame type is generally recommended for presses up to 400 tons.
Ring frames are a hybrid or combination of H-frame and C-type frame designs. In this design, the C-type Frame Press offers support in the front. The open size increases rigidity and makes it resistant to deflection. It is useful for 110-ton to 250-ton power presses. H-Frame designs will improve tool life and job operation precision.
These are also Box Type Pillar Frames, but they consist of four distinct parts: Pillar 1, Pillar 2, Crown, and Base or Bed. Each part is equipped with Hydraulic Tie Rods that absorb all the forces generated during the stroke, making the frame highly rigid, secure, precise, and non-deflecting. These frames are commonly used for heavy sheet metal forming and are well-suited for use with progressive tools.
While all power presses rely on slider crank mechanisms, there are three types of cranks: eccentric gear, crankshaft, and eccentric shaft. Alternatively, a link drive mechanism, such as a Knuckle Joint or a 6-Link Mechanism, can be used instead of a simple crank drive. Link mechanisms alter the slide movement by slowing it down during the forming process and speeding it up during the return stroke, which helps reduce idle time.
Gear and crank components are integrated into a robust system designed for power presses with capacities ranging from 250 to 400 tons and for stoves with a diameter greater than 10 inches (250 mm).
It is used for small power presses with capacities up to 250 tons, and occasionally up to 400 tons. However, it is not suitable for high stoves.
It is a basic and robust system designed for high-speed, low-stroke power presses. It is suitable for presses with tonnages up to 630 tons and strokes ranging from 4 to 4.7 inches (100-120 mm) or less.
The fundamental job operations of power presses include:
Blanking presses are used for notching and punching applications and come in 4-column and C-frame designs. They offer high-speed processing to meet specific production needs and are available in capacities up to 100 tons, with power units tailored to requirements. Built with robust construction, these presses are highly reliable, featuring advanced electronics and hydraulics.
The high-speed stamping press is ideal for cost-effective production of precise components with excellent cutting accuracy. These fast and durable machines ensure high production rates and low per-piece costs, with capacities ranging from 630 kN to 1,250 kN. They are available in both H-frame and C-frame designs, with capacities ranging from 35 to 500 tons.
A stamping power press is a metalworking machine used to cut or shape metal with a die. It functions similarly to a traditional hammer and anvil but uses precision-engineered male and female dies to achieve the desired shape of the final product.
This chapter will cover the applications, benefits, and safety measures of power presses.
Power presses are utilized for a range of tasks, including curling, bending, piercing, and deep drawing. Automation has significantly accelerated power pressing, addressing the industry's demand for faster production, and resulting in cost and time savings. Ongoing research and development aim to enhance these heavy machines' efficiency, increase production rates, and reduce raw material wastage. Power presses are user-friendly and feature advanced safety guards to protect operators, along with technical upgrades that improve press speed and material width handling.
The major applications of power presses are explained in detail below.
Fastening of two or more pieces together. Examples include shafts, bearings, electrical switches, rear axle assembly, water pumps, munitions assembly, fuel injection sensors, windshield wiper blades, gear assemblies, and medical instrument assembly.
Deep drawing is a metal forming process that involves both compressive and tensile forces using a compression power press. A part is classified as deep-drawn if its height is typically about twice its diameter. Common examples of deep-drawn components include oil cans, fire extinguishers, fans, aerospace ductwork, and housings.
Coining is a squeezing process typically performed cold within a closed die, where material is pressed to conform to the die's profile and shape. Due to the high demands of cold working, customized power presses are often used for this application. Coining is commonly employed for high-voltage power lugs and resizing powdered metal components.
A custom power press can reshape a material part without intentionally thinning the material. This process is used for a variety of applications, including electrical housings, journal bearings for trains, medical batteries and device cases, appliances like dishwashers and refrigerators (including their formed and stamped panels), exhaust flattening for mounting, HVAC components, windshield wiper blades, and jewelry.
An operation using a custom power press that imprints designs onto sheet metal with female and male dies, ideally without altering the material thickness, is known as embossing. Examples of this process include creating structural stiffening and applying lettering to sheet metal components.
Punching or cutting openings, such as holes, in metal sheets, plates, or other components using a C-frame power press is a common process. Examples include high-power electrical connectors and automotive exhaust systems.
Secondary shearing or cutting is performed on parts that have already been drawn, formed, or forged. The goal is to trim excess metal from the edges and achieve the desired shape and size. Examples of this process include dishwasher baskets, automotive carpets and dashboards, die-cast trimming, plastic components, and truck body panels.
Joining pieces using an interference fit.
The versatility of power presses offers several advantages:
Like all machinery, power presses also have their drawbacks, which are discussed below.
As power press machines are classified as heavy machinery, it is crucial to adhere to specific guidelines when operating them in a workshop or factory.
Regular maintenance and inspection of power presses are essential for safe operation and extending their lifespan. Therefore, it is important to conduct thorough maintenance and inspections before use.
Workers operating power presses without proper safeguards risk severe injuries, including amputations, crushed bones, and even fatalities. Essential point-of-operation safeguards for power presses include:
Power press machines are highly advantageous and expedient workshop machines wielded for bending, cutting, pressing, and forming metal sheets into different sizes, shapes, and dimensions along with multitasking tools. Power press machines are majorly applied in manufacturing industries for preparing the casing for appliances. Due to their multi-functional features, they are utilized in all factories and industrial workplaces. There are different power press types available in the market, C-frame type and H-frame type, for metal sheet machining work used in the manufacturing industry. A combination of both types is also available.
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