KEVOS® MAKEOS · Mechanics
Punch and Shear Flywheel Sizing
What motor power and flywheel rim does this punch or shear need for its energy per stroke?
Simplified flywheel design for punches and shears: average motor power from energy per stroke and stroking rate, energy the flywheel must give up during the cut, rim mass for the permitted speed reduction, rim section for a depth-to-width ratio, and the rim hoop stress from its speed.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Energy per stroke from | choice | Whether to work out the energy from force and travel, or enter it. |
| Peak force | kN | Peak force during the cut. |
| Working travel (e.g. plate thickness) | mm | Distance over which the force acts. |
| Energy per stroke (entered) | kJ | Energy needed per stroke. |
| Strokes per minute | Strokes per minute. | |
| Time of the actual cut | s | Duration of the working part of the stroke. |
| Mean rim diameter | m | Mean diameter of the flywheel rim. |
| Flywheel speed | rpm | Flywheel speed before the cut. |
| Speed reduction during the cut | % | Permitted fall in speed during the cut. |
| Rim material density | kg/m³ | Density of the rim material (cast iron about 7200 kg/m³). |
| Rim depth ÷ width | Ratio of radial depth to axial width of the rim section. |
Method and formulas
- Energy per stroke E = F × travel; average power = E × strokes per minute ÷ 60.
- Energy from the flywheel E₁ = E (1 − T₁ ÷ T), with T the stroke time.
- Rim mass m = 2 E₁ ÷ (v₁² − v₂²), with v the rim speed at the mean diameter and v₂ = v₁ (1 − reduction) — the physics behind the handbook constants C.
- Rim hoop stress σ = ρ v² (the handbook’s s = V² ÷ 10 for cast iron in ft/s and psi).
- Example: the handbook hot-slab shear (120,000 ft-lb per stroke at 20 strokes per minute, 6 ft 6 in. rim at 200 rpm) needs about 2,984.1 kg of rim (handbook 6,570 lb).
Limitations
- Rim only; arms and hub add some inertia (a margin).
- Hoop stress ignores rim bending between arms, which can be considerably higher.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a flywheel for a mechanical press, punch or shear
- Check motor power for a stroking rate
- Check flywheel rim speed and stress
Who it is for
- Machine designers
- Press maintenance engineers
- Mechanical engineers
What you get
- Average motor power
- Energy from the flywheel and rim mass
- Rim section, rim speed and hoop stress
Interpreting the result
- Allowing a larger speed reduction shrinks the flywheel but slows the stroke and loads the motor harder.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3004–3006. Topic reference; no source tables or recommended settings are reproduced.
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