A power press is a crucial piece of equipment in sheet metal processing, enabling efficient punching, blanking, forming, and stamping.
The correct press is not simply the next nameplate size above a calculated force. A buyer must also confirm where rated tonnage is available in the stroke, whether the press has enough working energy, whether the die fits the shut-height window and whether the frame, bed and slide can carry the intended load distribution.
Start with the available machine families in the power press machine category.
1. Estimate the Required Punching Force
For perimeter punching or blanking, theoretical force can be estimated as F = L × t × τ.
- F = theoretical cutting force in newtons (N).
- L = total cut perimeter in millimetres (mm).
- t = sheet thickness in millimetres (mm).
- τ = material shear strength in newtons per square millimetre (N/mm²).
Convert newtons to metric tonnes-force by dividing by approximately 9,806.65. Use a verified shear-strength value for the actual grade and condition; do not substitute tensile strength without applying the method specified by the press or tooling supplier.
Worked Example: One 20 mm Hole in 6 mm Mild Steel
Hole circumference: L = π × D = 3.1416 × 20 = 62.83 mm.
Using an example shear strength of 300 N/mm², theoretical force is 62.83 × 6 × 300 = 113,094 N. That equals about 11.5 metric tonnes-force. This is the force for the stated example only; it is not yet the final press capacity.
For a broader comparison of punching technologies, read metal punching machine types and selection.
2. Check Rated Tonnage, Energy and Load Position
Mechanical presses may deliver full rated tonnage only within a specified distance above bottom dead centre. A forming operation can also run out of flywheel energy even when its peak load is below the nameplate tonnage. Ask the supplier for the tonnage rating point, energy per stroke at the intended speed, allowable off-centre load and maximum concentrated or distributed die load.
- List every cutting perimeter that contacts at the same time, including multiple holes and blanking edges.
- Add stripping force and any forming, coining or embossing load using the tooling supplier’s method.
- Show the load position on the bed. A large off-centre load can exceed guide or frame limits before total tonnage is reached.
- Confirm strokes per minute, feed pitch and actual production duty. Intermittent hand-fed work and continuous coil production are different applications.
3. Choose Stroke Length from the Die and Part Motion
Stroke length is the total vertical travel of the slide. It must provide enough opening to load and unload the part, clear the strip and scrap, accommodate feeding or transfer motion and complete the forming depth. More stroke is not automatically better: on many mechanical presses it affects speed, energy and the position at which load is applied.
| Stroke question | Evidence to provide | Why it matters |
|---|---|---|
| How far must the tool open? | Die drawing and stripper travel | Prevents part or strip interference |
| How deep is the operation? | Form depth and material flow | Confirms usable working travel |
| How is material fed? | Manual, coil, robot or transfer layout | Sets opening and timing needs |
| What production speed? | Required strokes per minute | Stroke and speed affect available energy |
4. Distinguish Die Height from Shut Height
Die height is the height of the closed die during the working portion of the stroke. Shut height is a press dimension: the distance from the bed or bolster surface to the slide face at the bottom of the stroke with the slide adjustment in the specified reference position. Quotations must state the datum because some specifications are measured from the bed and others from the bolster.
The installed closed die height must fall inside the press adjustment window while leaving practical setup allowance. Also verify bolster thickness, slide adjustment, maximum daylight/open height, die clamping method and any die cushion or knockout requirements.
The APA Series pneumatic punching machine page provides one current BEIGEMA configuration family for comparison.
5. Check Throat Depth, Bed Area and Deflection
Throat depth is the horizontal distance from the ram or slide centreline to the nearest frame obstruction. It determines how far a workpiece can reach into a gap-frame press. Select it from the furthest work location plus clearance for gauging, handling and part rotation. A deeper throat does not guarantee a better press because frame deflection and off-centre-load limits also matter.
For a second mechanical configuration, compare the JB23 Series mechanical power press.
Power Press Selection Worksheet
| Input | Buyer should provide | Supplier should confirm |
|---|---|---|
| Part and material | Drawing, grade, thickness, tolerances | Process route and material assumptions |
| Tool | Die drawing, closed height, weight | Fit, clamping, load distribution |
| Force | All simultaneous cut/form features | Rated position and approved capacity margin |
| Motion | Stroke, feed method, target SPM | Energy, speed range and timing |
| Workspace | Part envelope and handling direction | Throat, bed, daylight and access |
| Utilities/safety | Power, air, layout and local rules | Motor, guarding, controls and documentation |
The practical procurement sequence is also covered in buying sheet metal machinery from China.
Power Press Selection FAQs
Can press tonnage be selected from sheet thickness alone?
No. Cutting perimeter, material shear strength and the number of simultaneous features all change the force. Forming operations require a process-specific calculation.
What is the difference between stroke and shut height?
Stroke is slide travel. Shut height is the closed machine space at a defined slide-adjustment position and datum. Both must match the die and part-handling sequence.
Why is the rated-tonnage position important?
A mechanical press may only deliver full nameplate tonnage close to bottom dead centre. The required load must occur inside the approved part of the capacity curve.
What should be sent for a reliable quotation?
Provide part and die drawings, material grade and thickness, required rate, feed method, load position, closed die height, utility details and the applicable safety standard.
Send the worksheet through the BEIGEMA contact page for a model-specific capacity review.