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Press capacity, primarily referred to as Pressure Capacity (加壓能力/圧力能力) or Nominal Pressure (公稱壓力), is the maximum force that a stamping press can safely and repeatedly exert during its stroke,.

According to the sources, it is defined and measured through several critical dimensions:

1. Definition and Units

• Definition: It is the maximum allowable pressure generated during the stamping process that the machine’s frame and drive mechanism can withstand without damage,.
• Measurement Units: Formally, it is expressed in kilonewtons (kN), though in practical industrial environments, tons (tf) are more commonly used (where 1 Ton ≈ 10 kN). For example, a “100-ton press” is rated for a nominal pressure of approximately 1000 kN.

2. The Nominal Pressure Stroke (Rating Point)

In mechanical presses, capacity is not constant throughout the ram’s travel.

• Rating Position: Nominal pressure is defined at a specific distance above the Bottom Dead Center (BDC). This distance is called the Nominal Pressure Stroke.
• Standard Guidelines: For many mechanical presses, this rating occurs when the slide is approximately 0.05 to 0.07 times the total stroke length away from BDC. For specific models like the JC23-40, this might be 7mm above BDC, while for the JA31-400, it is 13mm.

3. The Three Dimensions of Press Capacity

To fully define a press machine’s capability, engineers look at “The Three Capacities”,:

• Pressure Capacity (Nominal Tonnage): The maximum force the machine can exert.
• Torque Capacity (トルク能力): The ability of the crankshaft and gears to transmit force at a specific height above BDC,. If the processing starts too high in the stroke, the torque limits might be exceeded even if the tonnage is within the nominal rating.
• Work/Energy Capacity (仕事能力): The total amount of energy (measured in kgf·m or J) stored in the flywheel that can be used in a single stroke,. If the energy required for deformation exceeds this capacity, the flywheel speed will drop excessively, potentially stalling or damaging the motor,.

4. The Importance of the Tonnage Curve

The available force of a mechanical press decreases significantly the further the ram is from BDC,.

• Force Reduction: At heights of 100mm or 200mm above BDC, a mechanical press’s available tonnage may drop to less than 50% of its nominal capacity.
• Hydraulic Exception: Unlike mechanical presses, hydraulic presses can output their full nominal pressure at any point throughout the entire stroke.

5. Selection and Safety Standards

When selecting a press based on its defined capacity, a safety factor is required:

• General Rule: The press’s nominal capacity should be 1.2 to 1.3 times the calculated total process force,,.
• Deep Drawing: Because deep drawing requires sustained force over a long distance, it is recommended to choose a press with a capacity 1.6 to 2.0 times the calculated force to ensure sufficient energy and torque.