Mar. 07, 2024
Machinery
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This article will take an in-depth look at power presses.
You will learn about the following topics:
This chapter will discuss the definition and purpose of a power press.
A power press is a cold metal stamping machine designed to shape, cut, form, and punch metal. The different types of power presses are fast and efficient mass production pieces of equipment used for the manufacturing of metal parts and components. The two forms of power presses are hydraulically and mechanically powered.
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.
With all three forms of presses, the shape of the workpiece is determined by the meeting of the upper and lower halves of a die as they are pressed together under the force of the press.
Previously, the job of giving shape to metal sheets was done manually with great force and effort. The invention of power press machinery changed the process with the addition of mechanical force and accuracy.
The definition of a power press is related to how it supplies force. The main component of a mechanical power press is its flywheel that rotates and builds up force to drive the ram. In the case of hydraulic power presses, force is supplied by pressure created by hydraulic fluid while a servo motor power press has a motor that provides rotational motion that is converted into linear motion.
The choice of which type of power press is dependent on several factors. The concept of mechanical power presses is the oldest of the three methods with servo motors being the newest form. Hydraulic power presses, which are very widely used, were developed as replacements for mechanical power presses.
The hydraulic press was introduced over 200 years ago by a British engineer. During the first industrial revolution, it was used for forging as a way to replace steam hammers. Over the years, the tonnage of hydraulic presses has gradually increased into the thousands of tons with the capability of mass producing a wide variety of parts and components.
A hydraulic power press uses a pump, endplates, and a piston that creates pressure in a fluid to form and shape metal parts. The main component of a hydraulic press is its pump that pumps oil under pressure into a cylinder.
The cylinder contains a piston that moves up and down to create the compressive force. The piston of the cylinder acts like a pump in order to produce the force. It is the part of a hydraulic press that produces the power to apply force to the workpiece.
The reservoir contains the hydraulic fluid, collects contaminants from the fluid, removes air and moisture from the fluid, and sends heat into the system. The hydraulic fluid is sent from the reservoir to the cylinder through a tube.
The valve helps to relieve pressure and manages the flow of fluid from the pump to the cylinder. Additionally, the valve regulates the speed of the press and the amount of force it produces. It functions as a pressure limiter. A pressure gauge measures the pressure of the hydraulic fluid to ensure it is performing within its pressure 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 hold the workpiece in place and provide a platform for the press to bend, pierce, stamp, or puncture the workpiece. They are the part of the press that makes contact with the workpiece.
The movement of the hydraulic fluid depends on a set of hoses that move the fluid from the pump to the cylinder and reservoir. The hoses are made of durable and sturdy material that is capable of withstanding the pressure and heat produced during the operation of the press. Common hose materials are thermoplastics, synthetic rubbers, and polytetrafluoroethylene (PTFE), which are materials capable of resisting corrosion and the effects of exposure to chemicals.
The ram slides within the frame and applies pressure to the die. Depending on the design of the hydraulic power press, the ram can move horizontally or vertically with some hydraulic presses having multiple rams used for the forming process.
The bed is a flat supportive surface that supports the die as force is applied by the ram.
A servo press uses precision and a servo motor to control the movement of the ram. They are popular for their accurate positioning of the ram, which is ideal for the production of parts that require precision and optimal repeatability. The servo motor is connected to a form of linear actuator, such as a ball screw, that controls the upward and downward movement of the ram.
With a servo mechanical press, the main motor, flywheel, and clutch have been removed and replaced with a servo motor that makes the ram more controllable. The elimination of the parts of a traditional mechanical press results in a servo press having fewer driving parts and a simplified structure. In a typical mechanical or hydraulic power press, the ram moves down with great force and strikes the workpiece to create the desired shape, after which it returns to its original upward position. With a servo press, the ram can be controlled to the extent that it can strike the workpiece and remain in contact for an extended period.
Servo presses are used for applications that require exceptional precision and control, such as aerospace and electronics manufacturing. They are capable of producing the stamping, punching, and forming applications of mechanical and hydraulic power presses but with greater precision.
The servo motor drives the ram of a servo press and provides power and force to the servo press system. Direct drive and servo motor drive with a reducer are the types of motors used in a servo press.
A direct drive motor is connected directly to the actuator and is a low speed high torque motor with a simple structure, high efficiency, and low noise. It has limited torque, which limits its use to low tonnage servo presses.
A servo motor with a reducer allows for rapid acceleration and deceleration. It has a speed reduction ratio that matches the inertia of the motor and gearbox with the inertia of the driven load, which makes the motor run more efficiently.
Servo motors with a reducer take three different transmissions, which are deceleration with a crank connecting rod, with a crank elbow rod, or a screw elbow rod. This type of construction makes it possible for a low torque, high speed servo motor to drive high tonnage presses.
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 receives input from sensors, which it uses to send output signals to the servo motor. Algorithms programmed into the controller regulate the motions of the press to ensure precise operation and accurate repeatability. With hydraulic presses and mechanical presses, it is difficult to control the stroke, the pressure of the stroke, and the motion of the slider. A servo press can be programmed to control the stroke, speed, and pressure with precision allowing the press to reach the desired tonnage at a low speed.
Sensors - For the controller to perform properly, it requires data in regard to the position, force, and speed of the ram. Internal and external sensors send feedback to the controller that converts the data into command signals for the press.
Human Machine Interface (HMI) - The HMI connects operators to the servo press and allows them to monitor, adjust, and change aspects of servo press operations, such as speed, force, and positioning. A necessary component of servo presses is a user friendly interface with graphics that are displayed in real time on the HMI, which can be programmed to the needs of the part being manufactured.
For complex systems of HMIs, a supervisory control and data acquisition (SCADA) system is used to interface HMIs in a factory or facility. Information and commands can be sent to a specific HMI or several HMIs using the SCADA system.
The major components for power transmission on a mechanical power press are the clutch, crankshaft, flywheel, moving ram, and stationary ram. The slide is joined to a crankshaft with connecting rods (“pitmans”).
The crankshaft is coupled with the flywheel, which is constantly rotating while the motor is running. A clutch connects the spinning flywheel with the crankshaft. The crankshaft converts the flywheel’s rotational motion to the upward and downward motions of the press slide.
The ram is the primary operating component of a mechanical power press, which operates directly during the reforming of a workpiece. The ram moves to and fro within its guides, which prescribe a stroke length and power. The transferred stroke length and power can be adjusted according to the requirements of the operation. The lower end of the ram carries the punch to process the workpiece.
A driven pulley or driven gear is made in the shape of a flywheel (which is used to store the energy reserve) in order to maintain a constant ram speed when the punch is pressed onto the workpiece. The flywheel is fixed at the driving shaft’s edge and is attached to it via a clutch.
The energy stores up in the flywheel when it is idle. If the machine has insufficient flywheel energy, it will come to a halt and won’t be able to finish the operation. Essentially, by employing a flywheel, the motor can work with less capacity. At the same time, maximum tonnage is supplied at the required need of the operation.
For a bigger working space (in case of a drawing process) and for quicker processing (in case of an automatic piercing or blanking process), more power and energy must be provided.
In the blanking process, the work is finished in a very short portion of the stroke. So in this, energy is to be taken from the flywheel, which then instantly provides all the energy needed for operation. The same applies to the remaining cycle period. The drawing process takes a significant portion of the cycle. Since time is adequate, excess energy can be tapped from the motor and lacking energy provided by the flywheel.
Its value for discontinuous operation = 20%
For continuous operation = 10%
From operation E = P x K x L
If the energy of the flywheel is lower than P x K x L, the speed N must be increased.
The mechanical clutch is used to connect and disconnect the driving shaft from the flywheel when it is essential to stop or start the movement of the ram. A clutch moves the torque generated by the flywheel and drives to the gear shaft. Two different kinds of clutches are used on power presses: full revolution and part-revolution clutches.
As defined by OSHA, a full revolution clutch is a type of clutch that, when tripped, can’t be disengaged till the crankshaft has nearly done a complete revolution and the press slide a complete stroke. Presses with full revolution clutches are generally older and more dangerous because of their cycling operation.
A part-revolution clutch, also defined by OSHA, is a type of clutch that can be disengaged at any time before the crankshaft has done a complete revolution and the press slide has done a complete stroke. The majority of part revolution power presses are air clutch and brake. When air is trapped and compressed in compartments, the clutch engages and the brake disengages. To stop the pressing, the reverse takes place.
The brakes are utilized to stop the motion of the driving shaft promptly after it disconnects from the flywheel.
Brakes are very crucial in any mobile system. Commonly, two types of brakes are used. The first type is a normal brake that can stop the driven shaft quickly after disengaging from the flywheel. The other is an emergency brake which is offered as a foot brake to any power press machine. These brakes have a power-off switch with normal strong braking to bring all movements to rest quickly.
The base is the supporting structure of the press and offers arrangements for clamping and tilting the frame in an inclined press. It supports the workpiece holding dies and various controlling tools of the press. The table size limits the size of the workpiece that can be processed on the power press.
Different kinds of driving mechanisms are applied in various types of presses, such as piston and cylinder configuration in a hydraulic press, eccentric and crankshaft configuration in a mechanical press, etc. These mechanisms are utilized to drive the ram by moving power from the motor to the ram.
Controlling mechanisms are utilized to run a press under pre-programmed, controlled conditions. Normally, two parameters are configured by controlling mechanisms: the power of the stroke and the length of stroke of the ram. Transferring of power can be cut off with the help of a clutch offered with driving mechanisms as per requirement. In many power presses, controlling mechanisms are inherent to the driving mechanisms. Nowadays, computer-controlled presses are used where control is guided by a microprocessor. These power presses provide accurate and reliable control with automation.
This is a thick plate fixed onto the base or bed of the press. It is utilized to clamp the die assemblage rigidly to support the workpiece. The die used in press working might have more than one component, which is why the name “die assembly” is being used in place of the die.
Manually fed presses are cycled by either foot or by two hand controls or trips. With foot control, the press is triggered by pressing down on a foot pedal or switch.
It leaves the hands free while cycling the press. This free hand movement puts operators using foot control at a higher risk of getting an injury while operating. About twice as many press injuries come from foot-controlled presses. With two hand controls or trips, when a workpiece is positioned on the press, both hands should be removed from the operation point to depress the buttons.
Power press machines work on the principle of reshaping the metal sheets by applying the necessary force. The main parts used are a ram, bed, flywheel, clutch, and crankshaft. The ram and bed are furnished with a combination of dies that enable a metal sheet to be shaped into a particular form. The rotational motion of a flywheel is powered by an electric motor. The rotating flywheel is joined to the crankshaft by a clutch. Upper and lower dies are joined to the ram, one workpiece on the bed is fed into the machine, and the process is initiated. As a result of the rotational motion of the flywheel, pressing and shaping jobs are done when the upper and lower dies apply a force together. Once the process is done, the formed workpiece is detached and replaced by a new workpiece, and the same process is repeated.
To properly calculate the size of a power press, the tonnage needed, the size of the worktable, and the press opening height must be defined.
When choosing a power press, its purpose must be clearly understood. However, the operating methods and the working of the press are very difficult to understand. The wrong choice of a power press will lead to poor efficiency of the press and can lead to waste of equipment investment. Below are factors to consider.
There are different methods for stamping that are sometimes combined with cutting. When choosing a punch, the desired processing method should be checked. If the processing method is chosen, the punch type required is roughly determined.
If a batch is over 3000-5000 pieces, it is more beneficial to utilize automatic feeding. When there are numerous projects and a huge production amount, it is important to consider using continuous and transfer processing,
This should be known with regards to processing method, usage rate, and material usage rate.
These are collectively called material handling. In a production plant, material handling accounts for a huge proportion of the work.
During the extension operation, extra die buffers must be considered in the single-action punch. Due to the die buffer’s high performance, it is conceivable to do difficult drawing processes without using a double-action punch.
The maximum pressure needed during processing should be calculated. For multi-engineering processing, the pressure stroke curve for each project must be attained, and the combined pressure stroke curve must be attained by overlapping. These must be determined to determine the pressure capacity that should be selected.
When one punch press is utilized with more than two dies or a continuous die is utilized, there is an eccentric load, yet many of the punching operations also have an eccentric load. Therefore, for the processing of eccentric load, punching capacity with adequate margin must be selected.
the buffer capacity is generally 1/6 of the minimal punch press capacity. When necessary, it’s better to use a double-acting punch.
Dimensional accuracy is the measurement of tolerance, which defines the plus or minus limits of acceptable errors. When choosing a power press, accuracy or tolerance can be defined by the type of power press that is selected with mechanical presses, hydraulic presses, and servo presses each having different capabilities. When exceptionally accurate and precision performance is necessary, servo presses are the best choice due to their highly efficient control mechanism.
catalog specifications specify the main abilities and dimensions of punch presses and are the core for choosing the punch presses.
Proper use of accessories will increase productivity, so different accessory devices must also be fully reviewed.
pressing operations have a high disaster risk, hence full consideration must be given to safety measures. One with safety equipment function must be selected.
These are prohibited by laws and regulations because of pollution problems. Therefore, it is important to include noise and vibration measures into the pressing equipment.
There are different methods of classifying power presses, such as by mainframe type, drive mechanism type, or job operation (mechanism).
All types of power presses can be defined as C-Frame type or H-Frame type, regardless of the type of power. The type of frame can also define the tonnage of a power press.
The frame is C-shaped and is used for small presses up to 250 tons. Due to the C shape, the press frame has angular and longitudinal deflection bigger than other frame types; hence, this frame has a drawback when high accuracy is needed. C-frame power presses are more frequently used with presses up to 100 Tons.
They are utilized for bulk production in cold-working of ductile metals like mild steel, with spinning flywheels operating as energy storehouses to operate the ram to hit onto the workpiece. It is utilized to operate different functions with plate, bed, bolster and ram. The knockout mechanism is used to remove the finished workpiece from the power press.
Proper cushioning should be provided beneath the bolster if heavy impact is applied to the workpiece. The C-type is designed to provide continuous production with high accuracy. The frames are made from solid steel fabricated with appropriate cross ribbing. The clutch offers continuous stroking for mass production. The crankshaft is made from special steel alloy and furnished with gun metal bushes to smoothen work and provide longer life. Table and ram are seamlessly aligned to each other to achieve highly precise power press execution.
The box-type H-shaped design offers more rigidity and has zero deflection and lasting smooth and precise task operations. This frame has four box-type pillars and can only be operated in front of the press. Job size is according to available windows. H-Frame design will improve tool life and precision in job operation. It is more expensive than the C-Frame Power Press and Ring Frame Press.
Generally, this design is utilized for 100-ton to 800-ton power presses with two-point or single-point suspension. For tonnage capacity higher than 400 tons, it’s hard to handle the power press inside the factory floor since the frame will be too big. Therefore, this type of frame is recommended for 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 their frame bodies are divided into four parts: Pillar 1, Pillar 2, Crown, and Base or Bed. All these four parts are furnished with Hydraulic Tie Rods. These bear all the forces generated during the stroke, and it makes these press frames design very rigid, secure, precise, and non-deflecting. Commonly, these frames may be used for heavy piece sheet metal forming and utilized with progressive tools.
Although all power presses are dependent on slider Crank Mechanisms, the crank may be of 3 types. These are eccentric gear, crankshaft, and eccentric shaft. Additionally, instead of utilizing a simple crank drive, a link drive mechanism can be used, for example, a Knuckle Joint and 6 link Mechanism. Link Mechanisms change the movement on the slide, making the movement slow when falling during the forming process and going back swiftly to save idle time.
Gear and crank parts are combined. It is a robust system that is utilized for power presses over 250 to 400 tons and stoves over 10 in (250 mm).
It is utilized for small power presses of up to 250 tons (at times up to 400 tons). It is not suitable for high stoves.
It is basic and robust for high speeds and very low stroke power presses. It is utilized for tonnage reaching 630 tons and strokes of 4 to 4.7 inches (100-120mm) or less.
The basic job operations of power presses include:
The blanking press is utilized in notching and punching applications. These are found in 4-column types and C-type frame designs with high-speed processing to fit individual production requirements. Different capacities are available up to 100 tons as well as power units matching requirements. They are robust in construction and highly reliable through high-end electronics and hydraulics.
The high-speed stamping press is suitable for economical production of precise pieces with high cutting accuracy. These fast and robust machines guarantee high production rates and low costs per piece and are found in the range of 630 kN to 1,250 kN. They are available in H-frame or C-frame. Capacity is in the range of 35 to 500 tons.
A stamping power press is a piece of metalworking machinery utilized to cut or shape metal using a die. It is simply another form of the modern-day hammer and anvil. The variance is that a stamping power press utilizes precision-made female and male dies to order the shape of the end product.
This chapter will discuss the applications, benefits, and safety measures of power presses.
Power presses are used for various applications like curling, bending, piercing, and deep drawing. Automation makes power pressing much faster, which is currently a major requirement for the production industry. This saves money and time. Research and development are currently being carried out for these heavy machines in order to streamline their efficiency, high production, and low wastage of raw material. Power presses are easily operated, with top-notch protection guards to protect the operator’s life and technical enhancements such as power press speed and width of the material.
Below, the major applications of power presses are explained in more detail.
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.
The deep drawing operation is a metal forming operation that happens under a combination of compressive and tensile conditions utilizing a compression power press. To be considered a deep-drawn part, the case height is usually about two times the diameter. Some examples include oil cans, fire extinguishers fan, aerospace ductwork, and housings.
A squeezing process, usually done cold inside a closed die, where the material is forced to flow in the profile and shape of the dies. Due to the high weight requirements of cold working processes, customized power presses are preferred in this application. Coining may be used for high voltage power lugs and resizing powdered metal pieces.
Using a custom power press to change the shape of a material part without deliberately reducing the material thickness. Examples include electrical housings, journal bearing for trains, medical batteries or device cases, ranges, appliances like dishwashers and refrigerators (and formed and stamped panels for these products), flattening exhausts for mounting, HVAC parts, windshield wiper blades, and jewelry.
An operation using a custom power press that creates imprinted designs on sheet metal by means of female and male dies, theoretically without change in material thickness. Examples include structural stiffening and lettering sheet metal pieces.
Punching or cutting an opening, like a hole in a metal sheet, plate, or different parts, with a power C-frame floor press. Examples include high-power electrical connectors and automotive exhaust systems.
generally, a secondary shearing or cutting process on a previously drawn, formed, or forged part. The aim is to “trim” all surplus metals off of the edges and bring the piece to the required shape and size. Examples include dishwasher baskets, automotive carpets and dashboards, die-cast trimming, plastic parts, and truck body panels.
Joining pieces with an interference fit.
The multi-functionality of power presses has led to different advantages:
Just like all machinery, power presses have their own drawbacks discussed below.
Power press machines fall into the class of heavy machinery; hence, it is very important to follow a few guidelines when utilizing power press machinery at a workshop or factory
Power press maintenance and inspection are very important to keep it safely operating and prolong its working life. Therefore, maintenance and inspection before operation should be carefully carried out.
Workers operating power presses without appropriate safeguards can suffer amputations, crushed bones, and even fatalities. General point of operation safeguards for power presses include the following:
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.
A press machine, also known as a forming press, is a heavy industrial machine that uses pressure to change or adjust the size of the workpiece like the steel, aluminum, or other materials. It is operated by a worker who holds the workpiece in place and engages the press. A press machine can perform a variety of machining processes. However, there are many types of press machine, the usages for each type are slightly different from each other.In this article, we will mention several types of press machines that we mainly used.
The types are as follow:
Punching Press Machine
Hydraulic Press Machine
Servo Press
1. Punching Press Machine
Perhaps the most common type and simple principle of press machine is the punching press machine. Punching press machines usually used to "punching" holes into the workpiece. They typically are C frame press and H frame press. The punch can be operated manually or by CNC. In any case, all punch presses are designed to punch the workpiece by punching with a pressurized tool.
2. Hydraulic Press Machine
This type of industrial machine uses the plant's electricity, hydraulic power unit, and hydraulic cylinders to move the head. This kind of press can be purchased in a variety of pressures and sizes. Once the die tools have been installed into the punch and platens, they can be used.
As with pneumatic press machine, the maximum force is determined by the size of the cylinder hole of the machine and the adjusted working pressure. Unlike air/oil presses, the compression force is consistent throughout the travel range. Plunger speed is limited by hydraulic powertrain and loop flow and oil volume. Operator safety is another serious issue and it is important to ensure that the system is engineered using the appropriate safety level switches and sensing equipment.
Because the hydraulic oil is incompressible, the whole press travel will be smooth, thus improving the resolution of the process monitoring system. This press has many advantages, many of which have been used in factories all over the world. The main disadvantage is that hydraulic power units usually produce leaks, noise, smell, and a lot of heat. In addition to higher initial costs, maintenance costs can be high due to system complexity.
3. Servo press
These industrial processing machines have been around for decades and continue to be popular. As the cost of servo motors and control electronic equipment has been significantly reduced in recent years, they are increasingly replaced by other presses in many factories. The higher initial investment is also offset by lower operating and maintenance costs.
This servo press utilizes factory electricity, servomotor that also called drive units, and integrated ball screw actuators to provide linear movement of the press plunger. These press can also be purchased as a pre-designed complete set and offer a variety of options. Integrating weighing sensors, linear sensors, external part sensors, and other quality monitoring equipment to control processes are common, resulting in lower rejection rates and significantly improved quality.
Now you may already have a basic understanding of those three types of press machines. If you want to know more about the press machine, Cutting Machine, Bending Machine. Please connect us.
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