How Does a Hydraulic Press Work?

 If you work in an industrial environment, you may well have come across a Hydraulic Press before. This piece of equipment is used in a variety of different operations, such as pressing metallic objects into a sheet of metal, thinning glass, crushing cars and making powders. A hydraulic press can be used to suit the needs of most industrial environments.

 


 

So, how does a hydraulic press work? 

A hydraulic press contains two cylinders which are connected to one another. Each cylinder contains hydraulic fluid and one cylinder is larger than the other. The larger cylinder is known as the Ram and the smaller one is known as the Plunger

Liquids do not compress easily, which is why they are used in a hydraulic press. The hydraulic press works by pressing a small amount of force onto the Plunger which presses the fluid below. This pressure is then distributed evenly which in turn raises the Ram. The pressure between the Plunger and the Ram then works to crush the item placed between them. 

This works due to Pascal's Law which dictates that the pressure in the larger cylinder (the Ram) will stay the same as the pressure in the smaller cylinder (the plunger). 

To see a hydraulic press working in action, take a look at the Hydraulic Press Channel which focuses entirely on the crushing power of different hydraulic presses.

 

 

What are the benefits of a hydraulic press? 

Due to the way hydraulic presses work, they also provide a multitude of different benefits when compared to a mechanical press. Here are just a few benefits of a hydraulic press.

Lower cost. A hydraulic press is typically much cheaper than a mechanical press due to their simple nature. The original cost is lower and the maintenance cost is also lower due to a smaller amount of breakdowns and it is easier to replace the moving parts within a hydraulic press.

Overload protection. If you have a 30-ton hydraulic press, this will only ever exert 30 tons of pressure. Or if you set the pressure level for less, it will only release this level of pressure. Once that level is reached, a relief valve is opened which will not allow the hydraulic press to surpass that level. 

Less noise. Because hydraulic presses use less moving pieces, the noise level is reduced. As you have complete control with a hydraulic press, this means you can also control the noise level. 

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Mechanical Press vs. Hydraulic Press

A press is a machine that shapes and forms a variety of materials. It can perform many metalworking tasks, including forging, stamping, and die cutting. There are two main types of presses today –  the mechanical press and the hydraulic press. Although both serve the same purpose, it’s important that we understand their key differences.

Generally, a mechanical press features high production speed, while a hydraulic press offers higher flexibility for more complex forming processes. In this article, we'll discuss how they differ in terms of the mechanism and applications.



The Working Principle of the Mechanical Press

Figure 1. Mechanical Press

As the name implies, a mechanical press generates its power mechanically. Its main motor is connected to a crankshaft that cycles the ram and to a flywheel. In simple mechanical presses, a clutch controls the motor directly. In bigger and more complex press machines, the flywheel activates in motion pinion gear system that rotates the crankshaft.

As the motor powers the main system, the flywheels store this kinetic energy and convey it to the rest of the machine. Flywheels with bigger mass will yield a higher level of energy. This allows mechanical presses to achieve highest production speeds and forces. Especially when working with relatively flat and simple work pieces. 

The simple setup and operation requirements translate to fast and repeatable results. Mechanical presses are also less prone to leakage as they do not require hydraulic fluid to power itself. That being said, they do suffer from the lack of variable stroke lengths, which in turn limits their applications.
 



 

The Working Principle of the Hydraulic Press

A hydraulic press exerts force on a fluid that in turn generates power. It mainly consists of a piston, a hollow cylinder, and a power unit/pump. The pump moves the piston which increases the internal fluid pressure. The cylinder then moves along the axis of the piston. This generates a linear momentum which forces the ram onto the workpiece.


Unlike mechanical presses, how much force a hydraulic machine can generate is subject to the operating pressure and cylinder bore size. The power unit also plays an important role in determining the ram speed. Overall, hydraulic presses are more versatile thanks to the variable stroke lengths. 

Despite the advantages, hydraulic presses are often susceptible to leakage owing to the fluid mechanism. Some types of hydraulic fluids can even catch fire. Also, it has a relatively low operational speed.
 


   Figure 2. A heavy-duty mechanical press for processing automotive parts

Figure 2. A heavy-duty mechanical press for processing automotive parts

Differences in Applications

The major applications of mechanical and hydraulic presses are as follows:

    Mechanical Press Hydraulic Press Function

✓ Sheet metal blanking

✓ Forming

✓ Shaping

✓ Deep Drawing

✓ Piercing

✓ Glassmaking

✓ Sheet metal blanking

✓ Forming

✓ Shaping

✓ Deep Drawing

✓ Punching

✓ Forging

Industry

✓ Automotive

✓ Electronics

✓ Communications

✓ Household Appliances

✓ Furniture

 Automotive

✓ Oil & Gas

✓ Marine Transport

✓ Commercial Transport

✓ Aerospace

Figure 3. Applications and Industries of Mechanical and Hydraulic Press


As you can see, while both machines perform similar functions, hydraulic presses are more versatile. This is because they can create very intricate shapes and are more economical to maintain. The automotive industry uses hydraulic presses especially often to process a wide spectrum of car parts. Mechanical presses, on the other hand, are used in applications where speed and production output are the primary concerns. 

As you can see, while both machines perform similar functions, hydraulic presses are more versatile. This is because they can create very intricate shapes and are more economical to maintain. The automotive industry uses hydraulic presses especially often to process a wide spectrum of car parts. Mechanical presses, on the other hand, are used in applications where speed and production output are the primary concerns.



 

Mechanical vs Hydraulic - Benefits and Drawbacks

So let us summarize the advantages and disadvantages of the two press types. When should you go for a mechanical and when for a hydraulic press?
 

Mechanical Press Advantages +  

High production efficiency: This is attributed to the higher level of control and operation speed, making mechanical presses suitable for fast and high-volume production.

Simple setup: The simpler setup and operation requirements lead to reduced upfront and operational cost. 

Environmentally-friendly: The use of hydraulic fluid is not required, which prevents adverse environmental impacts due to leakage and spillage. 

 

Mechanical Press Drawbacks −

Limited capacity: The fixed stroke length makes mechanical presses unsuitable for applications that require variable stroke lengths, such as open die forging.

High maintenance cost: Components such as the crankshafts, flywheels, and brake systems are all very expensive to replace and often require custom fabrication.

 

Hydraulic Press Advantages +

Full tonnage through strokes: The most notable advantage of a hydraulic press is that it can generate full pressing force anywhere during a stroke. This gives operators a high level of control over various operation parameters such as pressure, travel distance, etc.

Economical components and maintenance: Although relatively more complex to set up, the standard components of a hydraulic press are relatively cheaper than those of a mechanical press. Repair and replacement are cheaper, too

Flexible design: Hydraulic presses come with different designs and sizes to accommodate various applications. This includes the placement of power systems, tonnage requirements, etc. It also allows a high degree of customization.

 

Hydraulic Press Drawbacks −

Leakage: The hydraulic fluid can enter the environment from spills and leakage. There is even a risk that it contaminates the soil and even the groundwater below a factory.  

Low Speed: Unlike mechanical presses, hydraulic presses are not high-speed machines. The cylinder motion and fluid mechanism are not designed for rapid production.

 

Final Thoughts - Mechanical or Hydraulic?

Despite the differences between a mechanical press and a hydraulic press, both machines have their own advantages. Much like choosing between hydraulic and mechanical brakes, you are going to face a series of trade-offs. Therefore, review your metalworking requirements in terms of flexibility, speed, output, cost, etc. before buying your press machine.

 

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Hydraulic Cylinders: A Brief History

Harnessing the power of fluid in motion is nothing new. It’s been a powerful source of energy for thousands of years, right up to the present day, and an integral part of the advancement of mankind.

Initially, water was used to turn wheels and push levers. Hydraulics have evolved in the last century to what we know as fluid power by today’s terms. But even as hydraulic cylinder technology advances, the basic principles of fluid power still apply today: relying on pressurized fluids to produce powerful forces.

Discovering the Magic of Fluid Power

The use of fluid power goes back thousands of years when ancient Egyptians used hydraulics to irrigate crops. But it wasn’t until much later that the laws of hydrodynamics were discovered and presented to the masses.

1648: French physicist Blaise Pascal realized that pressure on a confined fluid exerted an equal force in all directions, and those forces could be harnessed.

1738: Nearly 100 years later, Daniel Bernoulli put Pascal’s fluid power discovery to use by pressurizing water in pumps and mills using Bernoulli’s principle.

1795: Joseph Bramah patented the first hydraulic press in England, paving the way for the industrial revolution. Hydraulic presses harnessed fluid power to automate all types of manufacturing equipment, ranging from printing presses and cranes to machines for cutting and stamping.

The Evolution of Fluids Used for Hydraulics

Over time, it was discovered that water wasn’t the best material for hydraulic pumps and motors, and oil was deemed a better alternative for hydraulic applications. Unlike water, oil was non-corrosive and lubricated the hydraulic press components. Oil was also denser, could handle higher loads, did not evaporate, and remained cooler under the high pressure of hydraulic forces.

As the use of fluid power evolved, so did the use of hydraulic presses. With each technological development came new materials, applications, mounting configurations, and internal designs.

 

Hydraulic Cylinders Today

Major advancements in the last 75 years have brought the power of hydraulics to every market imaginable. Hydraulic cylinders are used on cranes, aircraft control surfaces and landing gear, ships and large watercraft, offshore drilling and mining equipment, and various types of machinery. Hydraulics is even used in hydroelectric power and energy production applications.

Hydraulics can provide up to 10 times the power of an electric motor, making it ideal for heavy pushing, pulling, and lifting applications. The precise control also makes it safer to work on or around hydraulic equipment.

What started with Blaise Pascal’s initial fluid power discovery and Joseph Bramah designing the first hydraulic press has evolved to technologically advanced “smart” hydraulic cylinders you can control using a computer.

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