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 machine is a hydraulic machine used to cut, bend, shape, and press any metal sheet into a required shape. A power press is a multi-faceted machine for shaping metal sheets in order to achieve the required shape of the components. They can be used in electronics and electric appliances, the vehicle industry, and in many other places.
Previously, the job of giving shape to metal sheets was done manually with great force and effort. The invention of power press machinery has changed this process by adding force and accuracy to the pressing process.
The major components for power transmission on a 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.
This is the primary operating component of the 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.
In many presses, 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.
Correctly determine operation method and engineering – 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.
Degree of production – 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,
Material shape and size – This should be known with regards to processing method, usage rate, and material usage rate.
Supplying materials, taking out products, and disposing of waste – These are collectively called material handling. In a production plant, material handling accounts for a huge proportion of the work.
Frequency of die buffer use – 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.
Calculate the processing pressure and stroke curve – 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.
Eccentric load – 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.
Calculate the reduction of effective die buffer capacity – the buffer capacity is generally 1/6 of the minimal punch press capacity. When necessary, it’s better to use a double-acting punch.
Necessary accuracy is determined by using the product and its relationship with the next project. If high operating precision is needed, a high rigidity punch or one with a huge capacity should be selected.
Fully investigate the specifications - catalog specifications specify the main abilities and dimensions of punch presses and are the core for choosing the punch presses.
Selecting attachments for punch – Proper use of accessories will increase productivity, so different accessory devices must also be fully reviewed.
Security – pressing operations have a high disaster risk, hence full consideration must be given to safety measures. One with safety equipment function must be selected.
Noise and vibration – 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).
There are different power press types available in the market, such as the C-frame type and H-frame type for metal sheet machining work used in the manufacturing industry.
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.
Assembly – 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 draw – 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.
Coining – 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.
Forming – 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.
Embossing – 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.
Piercing – 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.
Trimming – 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.
Press fitting – 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.
Pipelines – No leakages on lubrication, air, and hydraulic pipelines
Circuits – Not damaged and well connected.
Air pressure – The air pressure is close to 0.5Mpa
Seeper – No water inside pneumatic dual part, mist catcher, or filter relief valve
Oil – Adequate oil in gear casing, ball coupling between link and ram, hydraulic overload protection, and lubrication pump
Direction of flywheel – Start the primary motor to check if the flywheel runs according to the arrow marked there.
Emergency stop – Press the emergency stop button to ensure the primary motor will immediately stop. Press and hold the emergency stop button while performing other actions; the motion should not be completed.
Guideway – the guideway surface should be completely lubricated five minutes later and with no thermal hazards.
Opto-electronic – Stop immediately to shield the beam in operation. After an opto-electronic emergency stop, the machine can’t be started without first resetting the module.
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 forging press is a process that uses a vertical ram to apply gradual controlled pressure to a die holding a workpiece. The process is similar to drop forging but uses slow pressure instead of a series of blows. The slow movement of the ram penetrates deeper into the workpiece...
A hydraulic press is a mechanical device that uses the static pressure of a liquid, as defined by Pascal‘s principle, to shape, deform, and configure various types of metals, plastics, rubber, and wood. The mechanism of a hydraulic press consists of a mainframe, power system, and controls...
Power supplies are electrical circuits and devices that are designed to convert mains power or electricity from any electric source to specific values of voltage and current for the target device...
An AC power supply is a type of power supply used to supply alternating current (AC) power to a load. The power input may be in an AC or DC form. The power supplied from wall outlets (mains supply) and...
A DC DC power supply (also known as DC DC Converter) is a kind of DC power supply that uses DC voltage as input instead of AC/DC power supplies that rely on AC mains supply voltage as an input...
A DC power supply is a type of power supply that gives direct current (DC) voltage to power a device. Because DC power supply is commonly used on an engineer‘s or technician‘s bench for a ton of power tests...
Die stamping is a cold forming process that takes a sheet of metal, referred to as a blank or tool steel, and cuts and shapes it using a single or series of dies to create a desired shape or profile. The force that is applied to the blank modifies and changes its geometry...
An eyelet is a metal, rubber, or plastic ring with flanges are used to strengthen or reinforce holes punched in thin fabrics. It is a smaller counterpart of a grommet that is bigger in size and used for more heavy duty materials...
By definition a power supply is a device that is designed to supply electric power to an electrical load. An electrical load refers to an electrical device that uses up electric power. Such a device can be anything from...
When examining hydraulics and pneumatics, it is important to understand the mechanical differences between them. Both are essential parts of various industries and are critical to the performance of several types of tasks...
A hydraulic lift is a device for moving objects using force created by pressure on a liquid inside a cylinder that moves a piston upward. Incompressible oil is pumped into the cylinder, which forces the piston upward. When a valve opens to release the oil, the piston lowers by gravitational force...
A lift table is a platform capable of holding materials and raising, lowering, and adjusting them to any height to meet the needs of an application and the user’s requirements. Lift tables are supported by a strong, rigid, and stable base frame placed flat on the floor, in a pit, or equipped with casters or wheels...
A machine guard is a mechanism whose role is to act as a safety barrier between a worker and machines used in manufacturing facilities, factories, plants, and warehouses. Furthermore machine guards keep vehicles out of certain areas...
Metal stamping is a coldworking process that transforms sheets of metal into specific, preset shapes. It uses specialized tooling which involves the stroke of the punch that brings conformational change to the metal sheet...
A metal washer is a small flat piece of metal that has a hole in the center and is used as a spacer, a method for absorbing shock, or distributing the load of a fastener. The hole in the middle of a metal washer allows for a bolt or screw to pass through...
Scissor lifts are a type of manlift that is commonly used in construction and facility maintenance to raise employees and their tools to working heights. A power system and a control system make up the scissor lift...
A hydraulic system is based on Pascal‘s principle of fluid pressure, which hypothesizes that a change in pressure in a fluid is transmitted to all points of the fluid in all directions. With a hydraulic lift, an electrically powered pump pushes fluid into a cylinder at the base of a lifting jack system that lifts the platform up and down...
The metal stamping process began during the industrial revolution as a cold forming means for producing frames and handlebars for bicycles. From its beginnings in Germany, it has grown into an essential part of modern industry for the production of parts and components for a wide variety of industries...