BIZOMAT MAKEOS · Manufacturing
Press Flywheel and Motor Check (Stroke Energy, Rim Mass, Rim Stress, Motor Power)
For a mechanical press, does the existing flywheel store enough energy for each stroke, is its rim speed safe, and is the motor big enough to recover it between strokes?
Check of a press flywheel and drive motor: the energy per stroke from peak force and working travel or entered directly, the average power, the energy the flywheel must give up during the cut for the allowed speed drop, the rim mass needed and the rim section, and the rim hoop stress from its speed (as the press flywheel sizing tool), against the rim mass fitted, your allowable rim stress and the motor power with drive efficiency.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Energy per stroke from | choice | Work out the energy from force and travel, or enter it. |
| Peak force | kN | Peak press force during the cut. |
| Working travel (e.g. plate thickness) | mm | Travel over which the force acts (about the stock thickness for shearing). |
| Energy per stroke (entered) | kJ | Energy per stroke when entered directly. |
| Strokes per minute | Strokes per minute. | |
| Time of the actual cut | s | Time the cut itself takes. |
| Flywheel | ||
| Mean rim diameter | m | Mean diameter of the flywheel rim. |
| Flywheel speed | rpm | Flywheel speed. |
| Speed reduction during the cut | % | How far the flywheel may slow during the cut. |
| Rim material density | kg/m³ | Density of the rim material (cast iron about 7200). |
| Rim depth ÷ width | Rim section depth divided by width. | |
| Rim mass fitted | kg | Mass of the rim on the press (0 if none fitted yet). |
| Allowable rim stress | MPa | Allowable hoop stress in the rim for its material and construction. |
| Motor | ||
| Motor power | kW | Rated power of the drive motor. |
| Drive efficiency | % | Efficiency of the belts and gears between motor and flywheel. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Energy per stroke from
- What it is
- Whether the energy per stroke is worked out from the peak force times the working travel, or entered directly. Only the inputs for the chosen option are used.
- Units and format
- Choose one of 2 options from the list: Peak force × working travel; Entered energy.
- Example
- The form opens with “Peak force × working travel” selected as a worked example. Choose the option that matches your case.
- Get it right
- Force times travel treats the peak force as acting over the whole travel, which overstates energy for a cut whose force falls off.
What this means: Peak force
- What it is
- The highest force the press exerts during the working part of the stroke, such as the shearing or blanking force. Used only when the energy comes from force and travel.
- Units and format
- Enter a number in kN: kilonewtons (1 kN = 1000 N). The form accepts 0 kN to 1000000 kN. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1601.4 kN as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Energy per stroke, rim mass and motor power rise in direct proportion to the force.
- Get it right
- Enter it in kN; a force in tonnes-force must be converted.
What this means: Working travel (e.g. plate thickness)
- What it is
- The distance the ram travels while the peak force acts, about the stock thickness for shearing or blanking. Used only when the energy comes from force and travel.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 101.6 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Energy per stroke, rim mass and motor power rise in direct proportion to the travel.
- Get it right
- This is the working travel, not the full press stroke.
What this means: Energy per stroke (entered)
- What it is
- The energy one working stroke uses, entered directly, for example from a measured load-stroke curve or press data. Used only in entered-energy mode.
- Units and format
- Enter a number in kJ: kilojoules. The form accepts 0 kJ to 1000000 kJ. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 kJ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Rim mass and motor power rise in direct proportion to the energy.
- Get it right
- Enter it in kJ (1 kJ = 1000 J = 1 kN·m).
What this means: Strokes per minute
- What it is
- How many working strokes the press makes in a minute in continuous running. It sets the time per stroke and the average power.
- Units and format
- Enter a plain number with no unit. The form accepts 0.000001 to 1000. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- More strokes per minute raise the average power and the motor power needed.
- Get it right
- Use the continuous rate; single-stroke operation with pauses gives the motor more time to recover.
What this means: Time of the actual cut
- What it is
- The time the cut or forming operation itself lasts in each stroke. During it the flywheel supplies the energy the motor cannot.
- Units and format
- Enter a number in s: seconds. The form accepts 0 s to 600 s. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.75 s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A longer cut time means the motor supplies more of the energy, so the flywheel can be lighter.
- Get it right
- It must be shorter than the time of one stroke, or the tool rejects the inputs.
Flywheel
What this means: Mean rim diameter
- What it is
- The diameter of the flywheel rim measured to the middle of the rim section. The rim is treated as all the flywheel’s inertia, acting at this diameter.
- Units and format
- Enter a number in m: metres. The form accepts 0.000001 m to 20 m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.9812 m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger rim diameter raises rim speed, so the rim mass needed falls but hoop stress rises with the square of speed.
- Get it right
- Enter it in metres, not millimetres, and use the mean rim diameter, not the outside diameter.
What this means: Flywheel speed
- What it is
- The running speed of the flywheel before the cut begins. With the mean diameter it gives the rim speed.
- Units and format
- Enter a number in rpm: revolutions per minute. The form accepts 0.000001 rpm to 100000 rpm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 200 rpm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Higher speed sharply lowers the rim mass needed but raises the rim hoop stress with its square.
- Get it right
- Use the flywheel speed, not the motor speed.
What this means: Speed reduction during the cut
- What it is
- How much the flywheel may slow down during the cut, as a share of its starting speed, set by your design or the motor’s slip characteristic.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 1% to 50%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger allowed slowdown lets the flywheel give up more energy, so less rim mass is needed.
- Get it right
- Type the percentage itself, not a fraction.
What this means: Rim material density
- What it is
- The density of the flywheel rim material, from the material data sheet. It sets the rim section for the mass needed and the hoop stress at speed.
- Units and format
- Enter a number in kg/m³: kilograms per cubic metre. The form accepts 0.000001 kg/m³ to 25000 kg/m³. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 7200 kg/m³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Rim hoop stress rises in direct proportion to density.
- Get it right
- Enter it in kg/m³; a value in g/cm³ must be multiplied by 1000.
What this means: Rim depth ÷ width
- What it is
- The proportion of the rim cross-section: its radial depth divided by its axial width. It is used only to turn the rim area into a width and depth.
- Units and format
- Enter a plain number with no unit. The form accepts 0.2 to 5. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.22 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Enter depth divided by width, not the other way round.
What this means: Rim mass fitted
- What it is
- The mass of the rim on the press you are checking, from its drawing or by weighing. It is compared with the rim mass needed.
- Units and format
- Enter a number in kg: kilograms. The form accepts 0 kg to 1000000 kg. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3200 kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use 0 if no flywheel is fitted yet. Count the rim only, not the hub and arms, as the tool treats only the rim as inertia.
What this means: Allowable rim stress
- What it is
- The hoop stress you allow in the rim for its material and construction, from your design code, engineer or material data. The rim stress from speed is compared with it.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 1000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 7 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Cast rims and segmented rims usually have far lower allowables than solid steel; take the value for your construction.
Motor
What this means: Motor power
- What it is
- The rated output power of the motor driving the flywheel, from its nameplate. It is compared with the average power divided by drive efficiency.
- Units and format
- Enter a number in kW: kilowatts. The form accepts 0.000001 kW to 100000 kW. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 75 kW as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use rated output power in kW, not input power or a horsepower figure.
What this means: Drive efficiency
- What it is
- The share of motor power passed to the flywheel through the belts and gears between them.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 10% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 90% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Lower efficiency raises the motor power needed in inverse proportion.
- Get it right
- Type the percentage itself, not a fraction.
Method and formulas
- E = F s or as entered; average power = E × strokes ÷ 60 (as the press flywheel sizing tool).
- Energy from the flywheel E₁ = E (1 − t_cut ÷ t_stroke); rim mass = 2E₁ ÷ (v₁² − v₂²); hoop stress = ρ v₁².
- Motor power needed = average power ÷ drive efficiency.
- Example: 162.7 kJ per stroke needs 2,984.1 kg of rim and 60.26 kW of motor.
Limitations
- Rim mass only; arms and hub add a little inertia, which is on the safe side.
- Average power; the motor must also accelerate the flywheel at start-up.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a press for a thicker or stronger blank
- Check a motor change on an old press
- Size a flywheel rim for a new drive
Who it is for
- Press tool designers
- Maintenance engineers
- Manufacturing engineers
What you get
- Energy per stroke and average power
- Rim mass needed, section and stress
- Rim and motor against the press
Interpreting the result
- Allowing more slowdown cuts the rim mass sharply but puts more slip and heat into the motor.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3004–3006, 182–186. Topic reference; no source tables or recommended settings are reproduced.
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