How to choose the tonnage of hydraulic press according to process requirements?

Hydraulic presses, as essential equipment in modern industrial production, are widely used in processes such as metal forming, mold processing, assembly, and stamping. Choosing the right tonnage for a hydraulic press not only affects equipment investment costs but also directly impacts production efficiency, product quality, and process safety. Therefore, properly determining the tonnage of a hydraulic press is a crucial prerequisite for equipment selection. This article will begin with the basic concept of hydraulic press tonnage and systematically explain the methods and techniques for scientifically selecting a hydraulic press tonnage, taking into account various factors such as process requirements, material properties, forming process, and equipment parameters.

Basic Concepts of Hydraulic Press Tonnage
The tonnage of a hydraulic press generally refers to the maximum pressure the equipment can withstand or its maximum pressure capacity. Specifically, it refers to the maximum pressure that the hydraulic press's slide can exert, measured in tons (T) or kilonewtons (kN). Simply put, the tonnage of a hydraulic press determines its maximum pressing force.
Tonnage that is too small: It cannot meet the required pressure, resulting in incomplete forming, product defects, or equipment damage due to overload.
Tonnage that is too large: Equipment costs are high, energy consumption increases, and processing accuracy and equipment life may be affected. Therefore, the selection of hydraulic press tonnage should focus on meeting process requirements, ensuring sufficient pressure while avoiding resource waste.

Key Factors Influencing Hydraulic Press Tonnage Selection
Determining the tonnage of a hydraulic press involves multiple factors that require comprehensive consideration:
1. Process Type and Forming Method
The pressure requirements of different processes vary significantly. For example:
Stamping: This involves shearing and punching, requiring high pressure and large instantaneous peaks.
Forging: This requires continuous, high-intensity pressure to change the metal structure.
Pressing and assembly: This involves lower pressure but requires stable and precise control.
Stretching: This requires high pressure and stroke.
The specific process type determines the pressure intensity and stroke requirements of the hydraulic press and is the primary consideration for tonnage selection.
2. Workpiece Material Properties
The material's strength and plasticity directly affect the required pressure:
High-strength steels and alloys require higher pressure.
Soft metals such as aluminum and copper require lower pressure.
The thicker the material, the greater the required pressure.
Based on the material's yield strength, tensile strength, and thickness, a preliminary estimate of the required tonnage can be provided.

3. Workpiece Size and Shape
Workpiece Area: The larger the pressing area, the higher the pressure required.
Workpiece Shape Complexity: Complex shapes require more precise pressure distribution and may require a higher tonnage to ensure complete forming.
Forming Area Size: This affects local pressure peaks.
4. Forming Speed ​​and Process Cycle
High-speed forming processes place higher demands on the response speed of the hydraulic pump system and the hydraulic press, sometimes requiring additional tonnage to ensure instantaneous pressure peaks.
5. Safety Factor
To account for long-term stable equipment operation and unexpected operating conditions, a safety factor is typically added to the calculated theoretical tonnage, typically ranging from 1.1 to 1.5 times.
6. Hydraulic Press Stroke and Structure
Tonnage is not only related to pressure but also to the hydraulic press's stroke range and mechanical structure, such as whether the hydraulic cylinder is single-acting or double-acting and the slide area.

Calculation Methods for Hydraulic Press Tonnage
The key to determining the tonnage of a hydraulic press is to estimate the maximum pressure required for forming. The commonly used calculation method includes the following steps:
1. Calculate the required pressure
Pressure calculation is generally based on the material's yield strength or ultimate strength and the area under pressure.
Simplified calculation formula:
𝐹=𝐴×𝜎
F=A×σ
Where:
F = required pressure (force)
A = area under pressure (e.g., cutting area for stamping)
σ = material strength index (e.g., tensile strength, yield strength).
Select an appropriate strength index based on the specific process.
2. Area Calculation
Area calculation depends on the workpiece shape:
For stamping, the area is the cutting perimeter multiplied by the material thickness.
For pressing, the area is the contact area.
For stretching, the effective forming area of ​​the sheet is considered.
3. Consider a safety factor
Multiply the theoretical pressure by a safety factor. A value of 1.2 to 1.5 is generally recommended to ensure the hydraulic press has sufficient capacity to handle occasional loads.

4. Convert to Tonnage
Convert the calculated results to tonnage (1 ton is approximately equal to 9.8 kN) to facilitate model selection.

Steps for Selecting the Actual Tonnage Based on Process Requirements
1. Clarify Process Parameters and Workpiece Specifications
Collect process parameters, including workpiece material type, thickness, dimensions, forming process type, and production cycle time.
2. Estimate Forming Pressure
Calculate the forming pressure based on the material's mechanical properties and workpiece shape, focusing on the point of maximum pressure.
3. Estimate Safety Factor
Determine the safety factor, considering equipment durability and safety.
4. Preliminary Selection of a Hydraulic Press Tonnage Range
Based on the hydraulic press manufacturer's equipment parameters and technical specifications, select a model that meets the pressure requirements and is economically reasonable.
5. Evaluate Other Hydraulic Press Parameters
In addition to tonnage, consider stroke, slide area, hydraulic system power, control accuracy, and other factors to ensure overall compatibility.
6. Field Test Verification
If conditions permit, conduct a small-batch trial production to verify that the selected tonnage meets the process requirements.

Typical Process Tonnage Selection Example
Stamping Process
The workpiece is made of carbon steel, 5 mm thick, and has a punching circumference of 500 mm.
The material tensile strength is approximately 400 MPa.
Calculated cutting area:
500 mm × 5 mm = 2500 mm² = 0.0025 m²
500 mm × 5 mm = 2500 mm² = 0.0025 m²
Theoretical pressure:
𝐹 = 0.0025 m² × 400 × 10⁶ Pa = 1,000,000 N = 100 tons
F = 0.0025 m² × 400 × 10⁶ Pa = 1,000,000 N = 100 tons
Adding a safety factor of 1.3, the actual selected tonnage is 130 tons.

Press-Fitting Process
For smaller parts, the required pressure is relatively low; typically, tens of tons are sufficient.
Focus on control accuracy and pressure stability.

Considerations for Selecting Hydraulic Press Tonnage
1. Consider Future Process Upgrades
Process upgrades may result in higher pressure requirements, so allow for margin when selecting.
2. Overall Equipment Matching
Even if the tonnage is appropriate, the hydraulic pump, cylinder, and control system must be properly coordinated to avoid bottlenecks.
3. Economic Considerations
Excessive tonnage increases investment and operating costs, while too small a tonnage impacts production. A balance must be struck between economic and technical performance.
4. Equipment Life and Maintenance
Overloaded operation shortens equipment life. A reasonable tonnage ensures equipment stability and ease of maintenance.
5. Special Process Requirements
For processes such as deep drawing, high-precision forming, and composite material processing, specialized design and control solutions may be required.

Summary
Selecting a hydraulic press tonnage based on process requirements is a comprehensive task. It requires considering the workpiece material properties, process type, dimensions, and production requirements. The required pressure must be scientifically calculated, while also appropriately considering safety factors and overall equipment performance. Reasonable tonnage selection can not only ensure product quality and process stability, but also optimize investment costs and improve equipment operating efficiency and service life.