Press tonnage refers to the highest amount of force that a press exerts during a stamping operation. It is an important metric to understand to ensure that a stamping operation is completed successfully and safely.
In this article, we look at what press tonnage is, why it is important, how it is calculated, and the factors that affect it.
Table of Contents
What Is Press Tonnage?
Press tonnage is the highest amount of force that a press exerts during a stamping operation. It is an important metric for manufacturers to understand, as it is used to determine the tonnage required for an operation and ensure that it is below the maximum tonnage rating of the stamping press.
Two concepts that are closely related to press tonnage are reverse tonnage and snap-through. Snap-through refers to the quick acceleration of the press once it cuts through the material. This results in vibrations which may cause damage to the press. Reverse tonnage refers to the strain limitations of the connections between components in the press.
What Is the Importance of Performing a Press Tonnage Test?
A press tonnage test is performed to verify the tonnage required to perform a certain operation. It is very important, as too much tonnage can cause damage to the press, while too little tonnage can lead to low-quality parts. As part of the press tonnage test, the speed of the stroke can also be adjusted to ensure that snap-through and reverse tonnage are at manageable levels.
How Is Press Tonnage Used in the Stamping Process or for an Alternative Service?
Press tonnage is used in the stamping process in several ways as described below:
Press Capacity: The press tonnage capacity is the maximum press tonnage that a press can handle before being damaged.
Required Press Tonnage: Required press tonnage is the amount of tonnage required to perform a stamping operation.
Press Tonnage Curve: The press tonnage curve shows how the tonnage of a press is applied across the entire stroke of the press. Typically, the tonnage will not be as high as the press tonnage capacity at all points of the curve. For example, with mechanical presses, the tonnage is at its highest at the very top and very bottom of the stroke.
Understanding these press-tonnage-related metrics allows manufacturers to produce high-quality stamped parts safely and effectively.
What Factors Affect the Press Tonnage for the Stamping Process?
The press tonnage for stamping press operations is affected by the following:
Material Thickness: Thicker materials require higher press tonnages to process.
Material Properties: The tensile strength and shear strength of the material play a big role in the press tonnage required for a specific operation.
Geometry of Operation: Complex geometries and geometries with longer perimeters will require higher press tonnages than simpler, shorter geometries.
Type of Operation: Each type of operation (blanking, punching, deep drawing, bending, etc.) has its formula for calculating the required press tonnage.
Is It Important To Determine the Press Tonnage for a Stamping Process?
It is very important to determine the press tonnage of a stamping process. The required tonnage of a specific operation needs to be understood to ensure it does not exceed the tonnage capacity of the press. Doing so can result in damage to the press as well as potential safety hazards.
How To Calculate the Press Tonnage of a Material?
The required press tonnage of a material depends on many factors, including the type of operation, material tensile strength, material thickness, and material shear strength.
For example, for punching a square hole, the following formula is used:
Tonnage = P * T * S9.81
Where:
P = Total length of the hole being cut in mm
T = Thickness of the material in mm
S = Shear strength of the material in kn/mm2
What Are the Different Types of Press Tonnage?
Different types of presses have different press tonnage capacities and ways of calculating press tonnage. Below is a list of some of these presses, and how their press tonnage is calculated:
1. Hydraulic Press Tonnage
Hydraulic presses use hydraulic cylinders to produce force on the material. They can deliver full tonnage over the entire stroke, unlike mechanical presses. They are also very reliable, requiring little maintenance. However, their stroke speed and depth can be limited.
The press tonnage of a hydraulic press can be determined in the same way as for mechanical presses. The required press tonnage for a cutting or blanking operation can be determined using the following equation:
Tonnage = P * T * S9.81
Where P is the total length of the hole being cut in mm, T is the thickness of the material in mm, and S is the material’s shear strength in kn/mm2.
2. Mechanical Press Tonnage
Mechanical presses generate pressing force using a mechanical drive assembly. Different types of mechanical drives include: the flywheel, eccentric-geared, double-geared, and single-geared. Each of these drives offers a unique way of generating the force used to press the die into the material.
Mechanical presses are some of the most common types of presses available. They have fast stroke speeds and are quite reliable and durable. However, they are noisy and have limited automation compared to hydraulic and servo presses.
3. Servo Press Tonnage
Servo presses use servomotors to produce the force required to process a part. By using servomotors, operators can have unparalleled control over the operation. Servomotors can also deliver maximum force at any stroke speed. This allows operators to reduce the snap-through and reverse tonnage of an operation by reducing the stroke speed.
Servo presses offer the most finely tuned control and automation of any type of stamping press. However, they are costly, and their tonnage capacity is generally less than that of hydraulic stamping presses.
4. Pneumatic Press Tonnage
Pneumatic stamping presses use pneumatic cylinders to generate force to perform stamping operations. Generally, pneumatic presses have lower tonnage ratings than hydraulic or mechanical stamping presses. Pneumatic presses are relatively inexpensive compared to other types of stamping presses.
How Does the Choice of Stamping Press Type Affect Press Tonnage Requirements?
Each type of press has its own unique properties. In the case of press tonnage, the press tonnage curves will differ drastically between different types of press. An example of this is that hydraulic presses can exert the full press tonnage over the entire stroke, whereas mechanical presses cannot. This is useful for applications such as deep drawing. Another example is that servo valves can deliver maximum force regardless of speed. This allows operators to slow down the stroke speed, which can reduce snap-through and reverse tonnage, increasing the longevity of the press.
These characteristics should be considered when selecting a press to do a specific operation.
To learn more, see our full guide on Stamping Press Types.
What Are the Applications of Press Tonnage?
Press tonnage is important in a range of applications and metal-forming processes, such as:
Automotive: The automotive sector uses components that are stamped, including: deep-drawn, punched, and sheared components. The ability to apply the correct tonnage is important to ensure that these parts are manufactured accurately.
Aerospace Components: Metal aerospace components often go through a stamping process. Knowing the correct press tonnage ensures these components are of high quality and dimensionally accurate.
Medical Devices: Medical device components and enclosures may undergo punching, blanking, and deep drawing. Press tonnage assessment is used to ensure that the delicate components can be properly processed without being damaged or broken.
Consumer Appliances: Consumer appliances are commonly made using stamped components. Press capacity is an important metric to help ensure that any deep-drawing, cutting, or punching operations are successfully applied.
What Are the Factors That Can Affect the Press Tonnage of a Material?
Several factors affect the press tonnage of a material including:
Thickness of the Material: Thicker materials have higher required press tonnages.
Type of Operation: Certain operations, such as cutting, require higher forces.
Tensile Strength of the Material: Higher tensile strengths require higher press tonnages.
Friction Between the Die and the Material: Lower frictions lead to lower required press tonnages. The design of the die, or the presence of lubrication can lower the friction between the die and material.
What Are Different Types of Press Tonnage Failure?
The following list explains several different types of failure due to press tonnage:
1. Safety Hazards
Safety hazards refer to the risk of injuries due to the malfunctioning of the press. This can include components of the press or tooling breaking violently, which can pose a danger to press operators.
2. Overloading
Overloading refers to applying force beyond the press’s capacity. This leads to damage to the press or tooling. An example of the types of failures caused by overloading would be the deformation of the frame of the press.
3. Material Failure
Material failure is when the material being processed fails due to the forces applied. Possible failures include: splitting due to excessive thinning, edge cracks, or bending failures.
4. Underloading
Underloading refers to situations in which the force applied by the press is insufficient for the operation. This can lead to inadequate processing of the material, including inaccurate bends, or incomplete cuts.
5. Imbalanced Loading
Imbalanced loading is when the force exerted on the material is distributed unevenly. This can lead to uneven wear on tooling, damage to press components, or poor quality of the final product.
6. Tooling Failure
Tooling failure refers to the tooling malfunctioning or suffering damage, rather than the press itself. This may be due to poor maintenance, defects, or the tonnage of the operation exceeding the tooling’s rated tonnage.
How Does Material Thickness Impact the Required Press Tonnage in a Stamping Process?
The material thickness has a significant impact on the required press tonnage in a stamping process. Thicker materials require higher force for all press operations, which leads to higher press tonnage requirements.
The press must be capable of applying enough force to process the required thickness of the material. Using a press with insufficient tonnage capacity can lead to press failures including: damage to the press, safety hazards, and inadequate material processing.
What Role Does Die Design Play in Determining the Appropriate Press Tonnage?
Die design plays a substantial role in determining the appropriate press tonnage. The geometry and size of the die, as well as the intended operation, will affect the press tonnage significantly. In general, smaller, simpler geometries will result in lower required press tonnages. This is because the smaller footprint causes less friction between the die and the workpiece.
XTJ is a leading OEM Manufacturer that is dedicated to providing one-stop manufacturing solutions  from prototype to production. We are proud to be an ISO 9001 certified system quality management company and we are determined to create value in every customer relationship. We do that through collaboration, innovation, process improvements, and exceptional workmanship.
