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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.

今天 • 上午11:02

How to determine press speed (SPM)?

Determining the appropriate press speed, measured in Strokes Per Minute (SPM), is a critical step in balancing production efficiency, part quality, and tool life. According to the sources, the determination of SPM involves classifying the operation type and analyzing several technical factors.

1. General Speed Classifications

Press speeds are categorized based on their frequency of operation:

• Standard Speed: ≤ 200 SPM.
• Standard Fast Speed: 200 to 400 SPM.
• Sub-High Speed: 400 to 800 SPM.
• High Speed: Generally exceeds 800 SPM, with some specialized automatic presses reaching between 1,000 to 2,000 SPM.

2. Key Factors Influencing SPM Determination

When selecting a speed for a specific job, engineers must consider the following variables:

• Type of Stamping Operation:
  • Blanking and Piercing: These processes can typically run at high speeds (e.g., 300–1000+ SPM) because the material is sheared quickly.
  • Drawing and Bending: These require much lower speeds. Slower movement is necessary to allow the material to flow into the die without rupturing or creating surface defects like “shock marks”.
• Stroke Length: There is an inverse relationship between stroke length and SPM. Presses with short strokes (e.g., 13mm to 38mm) are designed for high-speed operation, while long-stroke presses used for deep drawing must operate at significantly lower SPM.
• Part Size and Complexity: Smaller, simpler parts generally allow for higher SPM. As the size and complexity of the part increase, the speed must be reduced to ensure stability and accuracy.
• Material Properties: Thinner materials are better suited for high speeds. For thicker materials or those with high tensile strength, lower speeds help manage heat generation and reduce the impact force on the die.
• Feeding and Automation: The speed of the press is often limited by the feeder’s capacity. The “feeding pitch” (the distance the material moves) must be synchronized with the press cycle. High speeds require extremely precise feeders (accuracy within ±0.01 to 0.03mm).

3. Practical SPM Guidelines by Die Type

Standard guidelines for different die structures include:

• Manual Feeding (Single-Stage Die): Generally limited to 120 SPM or less to ensure operator safety and proper part placement.
• Compound Dies: Usually operate between 60 to 240 SPM, depending on the difficulty of part ejection.
• Progressive Dies: Designed for automation, these often run between 200 to 800+ SPM.

4. Technical Constraints to Monitor

• Flywheel Energy: Energy is proportional to the square of the rotation speed. If SPM is too low, the flywheel may not store enough kinetic energy to complete the stroke, potentially stalling the motor.
• Heat and Vibration: High-speed operation generates significant heat in the die and material, which can accelerate tool wear or cause thermal expansion that affects precision.
• Tool Life: While increasing SPM improves productivity, it can also lead to more frequent die maintenance due to increased friction and impact forces.

In summary, to determine SPM, you should start with the process requirements (blanking vs. drawing), factor in the stroke length and feeding pitch, and then adjust for material thickness and equipment limitations.