TM — Trusted Machinery

Selecting the appropriate stamping press is critical for ensuring production efficiency and part quality. The selection criteria can be categorized into four primary domains: processing load (pressure and energy), process characteristics, machine structure and precision, and production scale/automation requirements.

1. Tonnage and Rated Tonnage Stroke (Tonnage & Tonnage Curve)

• Total Force Calculation: The press’s nominal capacity must exceed the sum of all forces required for blanking, bending, or drawing, including auxiliary loads like stripping, ejection, and blank holder forces.
• Safety Factor: To protect both the machine and the tooling, it is standard practice to select a press with a tonnage rating 1.2 to 1.3 times the total calculated force.
• Tonnage Curve Awareness: Mechanical presses only deliver 100% of their rated tonnage near Bottom Dead Center (BDC). If the peak load occurs higher up in the stroke (such as in deep drawing or heavy-gauge punching), the available tonnage drops significantly. Engineers must verify the requirements against the machine’s tonnage-stroke diagram.
• Special Case for Deep Drawing: Due to the sustained load and deep stroke, it is recommended to select a press with 1.6 to 2.0 times the total process force to ensure sufficient energy and structural overhead.

2. Working Energy and Stroke (Energy & Stroke)

• Work Capacity: The flywheel must store enough kinetic energy to complete the deformation. Insufficient energy leads to excessive flywheel slowdown and potential motor burnout, which is a major concern in heavy-plate processing or deep drawing.
• Stroke Length: The stroke must be long enough to allow for part clearance and smooth feeding.
• Drawing Ratios: For deep drawing operations, the press stroke should typically be at least 2 to 3 times the finished part depth.

3. Process Technology and Drive Mechanisms

• Mechanical Presses: Ideal for blanking, piercing, bending, and shallow drawing. These are the workhorses of mass production due to their high output rates.
• Hydraulic Presses: These deliver full tonnage at any point in the stroke, making them superior for deep drawing and heavy forming. They offer inherent overload protection, though they operate at lower speeds.
• Knuckle-Joint Presses: These generate massive pressure while slowing the slide velocity near BDC. They are the gold standard for coining, extrusion, and cold forging.
• Servo Presses: These provide programmable slide motion, allowing for flexible adjustment of speed and stroke. They are instrumental in forming advanced materials (like High-Strength Steel) while reducing noise and vibration.

4. Frame Types and Structural Rigidity

• Gap Frame (C-Frame): Offers three-sided access for ease of operation and die changes. While suitable for small-to-medium parts, these frames are prone to “angular deflection” (opening up) under high loads.
• Straight-Side Presses: Features a closed-box frame with superior rigidity to minimize errors caused by off-center loads. This is the preferred choice for high-tonnage, high-precision, or progressive die production.
• Eccentric Load Management: If the die’s center of load is offset from the slide center, a two-point or four-point suspension (double/quad crank) press should be used to prevent slide tilting and premature tool wear.

5. Production Volume, Automation, and Installation Parameters

• Production Scale: High-volume runs require high-speed presses (e.g., 600+ SPM) equipped with automatic feeding systems. Small-batch prototypes are better suited for versatile, single-action presses.
• Installation Footprint: The bolster area must be larger than the die set base, with sufficient clearance for mounting hardware and scrap removal (slug chutes).
• Shut Height: The die’s closed height must fall within the press’s shut height adjustment range.
• Automation Integration: Consideration must be given to interfaces for automatic feeders, straighteners (levelers), die-protection sensors, and scrap conveyors.