This article will take an in-depth look at power presses.
You will learn about the following topics:
This part delves into the concept and usage of power presses in metalworking.
A power press is a machine tool designed to shape, shear, and punch metal using a process called cold stamping. These machines are available in diverse types and are particularly essential for mass production of metal parts. Power presses are primarily classified into hydraulic and mechanical, depending on their power source.
Power presses function through mechanical, hydraulic, and servo motor principles. Mechanical presses convert rotational motion to straight-line movement via a clutch, flywheel, and crankshaft. Hydraulic presses generate force by pressurized hydraulic fluid to mold metals. In contrast, servo power presses use a servo motor to operate the press's slider by powering an eccentric gear.
For all press types, the desired form of the workpiece is achieved as the upper and lower die halves mold the metal under applied pressure.
Historically, metal sheet forming relied heavily on manual labor. The introduction of power press machinery transformed this task by offering amplified precision and mechanical power.
The design of a power press is characterized by its force application technique. Mechanical presses use a flywheel to gather force, transmitting it to the ram. Hydraulic presses depend on hydraulic fluid pressure to drive motion, whereas servo motor presses leverage a motor to convert rotational into linear motion.
Choosing a suitable power press involves various considerations. Mechanical presses are the oldest, while servo motor presses embody the latest advancements. Hydraulic presses became popular as alternatives to mechanical ones.
Hydraulic press technology was invented over 200 years ago by a British engineer during the first industrial revolution to replace steam hammers. Nowadays, hydraulic presses can apply immense pressure, mass-producing a wide array of components.
The functioning of a hydraulic press is based on a pump, endplates, and a piston to induce pressure within a fluid for forming metal. The core of this setup is the pump, driving oil into a cylinder under significant pressure.
The cylinder guides a piston that moves vertically to provide force, acting like a pump and generating the necessary pressure for metal shaping.
A reservoir stores hydraulic fluid, filters out impurities, eliminates air and moisture, dissipates heat, and channels fluid from the reservoir to the cylinder through a tube.
The valve manages fluid flow between the pump and cylinder, regulates pressure, and adjusts the speed and force output of the press. The pressure gauge checks the fluid's pressure, ensuring it stays within specified limits.
The hydraulic pump circulates fluid to the reservoir, changing mechanical energy into hydraulic energy to create an output flow against pressure.
The plates secure the workpiece and offer stability for operations like stamping, piercing, and bending.
Hydraulic fluid moves through a network of hoses connecting the pump, cylinder, and reservoir. Made from durable materials like thermoplastics and rubbers, these hoses withstand high pressure and temperature.
The ram moves along the press frame, applying force on the die. It can travel horizontally or vertically depending on the press's design, with certain models having multiple rams to help the process.
The bed is a stable platform that secures the die while the ram applies pressure.
A servo press operates using a servo motor for precise ram positioning, benefiting industries requiring high precision like aerospace or electronics. The motor connects to a linear actuator, such as a ball screw, converting rotary into linear motion.
In servo mechanical presses, traditional motors and clutches are replaced by servo units, simplifying the structure and enhancing control over ram movement, allowing customized contact with the workpiece.
Servo presses are essential in fields requiring high precision and repeatability similar to stamping and forming tasks, with superior accuracy over conventional presses.
Servo motors power the ram, either via direct drive or with a reducer for efficiency. Direct drives are low-torque and suitable for lightweight presses, while reducer-equipped motors accelerate and decelerate swiftly, powering high-tonnage presses effectively.
The actuator turns rotary into linear motion, most often using ball screw systems offering smooth, efficient, and precise control. A ball screw actuator contains a coordinating screw and nut that refines motion accuracy.
The controller generates outputs from sensor inputs to manage servo motors' nuances, surpassing traditional stroke controls in hydraulic or mechanical presses, allowing intricate programming of stroke length, speed, and pressure.
Sensors - Gather data on position and speed for accurate control.
Human Machine Interface (HMI) - Enables management and real-time monitoring of servo press parameters. Sophisticated setups might include SCADA systems to manage multiple HMIs in a facility.
Core elements of a mechanical power press involve the clutch, crankshaft, flywheel, and moving and stationary rams, connected by "pitmans" or connecting rods.
The crankshaft links to a constantly-moving flywheel powered by a motor. The clutch engages the crankshaft to drive the press’s slide for reshaping tasks.
The ram exerts the reshaping force, characterized by adjustable stroke length and power, critical in processing the workpiece with a punch tool.
The flywheel, a force-accumulating pulley, leads to consistent ram speed, storing energy to allow weaker motors yet deliver peak tonnage where needed.
A mechanical clutch enables engagement or disengagement of the driving shaft from the flywheel. Power presses either employ full-revolution or part-revolution clutches to control press function, per OSHA regulations.
Brakes promptly cease motion after disengagement from the flywheel, essential for power presses, featuring standard and emergency types for secure operation.
The base forms the structure for supporting clamping mechanisms, dies, and work scheduling within an inclined press. The table size dictates the maximum workpiece size a press can handle.
These transform motor power into ram movement, incorporating pistons or eccentric and crankshaft arrangements. Control mechanisms dictate pressing conditions and safety, increasingly advanced with microprocessors today.
A hefty plate clamps the die assembly, securing the workpiece firmly for accurate operations, pivotal in manually or foot-controlled presses ensuring worker safety.
Operating a power press involves components like the ram, bed, flywheel, clutch, and crankshaft. Primarily, the die-equipped ram presses the metal sheet precisely driven by the flywheel's rotary connection to an activated crankshaft, facilitating the shaping and removal of finished components for repetition.
Determining power press size involves tonnage ratings, worktable dimensions, and the height dedication for opening. Tonnage relies on material factors, while worktable size needs to match material dimensions. Calculation facilitates efficiency analysis for operational speed and suitability in serial production.
Selecting a power press involves thoroughly understanding its purpose and methodical operation. The wrong choice can lead to efficiency loss. Here are important factors to contemplate:
Identify suitable stamping techniques to ascertain punch types based on processing needs, verifying each's operational viability.
Evaluate the benefits of automatic feeding for extensive production beyond 3000-5000 units, assessing transfer processing techniques for diverse projects.
Analyze processing conditions, consistency frequency, and material usage for efficacy predictions.
Effective material handling affects the workload in manufacturing, necessitating streamlined processes.
Understand high single-action punch efficiency in buffering demands requiring complex operations without dual-action machinery.
Estimate required processing pressure through pressure stroke curves, synthesizing multi-project pressure needs for capacity accuracy.
Select presses with ample margins for imbalance when dealing with multiple or continuous die operations with potential eccentric loading.
Set buffer capacity appropriately, recommending dual-acting punches for specific uses upwards of one-sixth of machine power.
Consider the required tolerance levels when selecting press types, with servo models offering optimal precision through advanced controls for challenging applications.
Extensively review cataloged punch specifications for informed decision-making regarding capacity capability and accessory adaption.
Pressing requires comprehensive safety considerations, selecting machines equipped with robust preventive measures to mitigate risks.
Addressing legal restrictions pertaining to noise pollution, select machines with inherent vibration and noise suppression to ensure compliance.
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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