BIZOMAT MAKEOS · Mechanics
Average Force of a Blow (Drop Hammer or Pile Driver)
What average force does this falling weight deliver when it drives the work a given distance?
Average force of a blow from a falling weight — a drop hammer, pile driver or drop-test mass — by equating the work of the fall (including the penetration) with force × penetration, with impact speed, energy and an efficiency for losses.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Falling mass | kg | Mass of the ram, hammer or drop weight. |
| Drop height before contact | m | Height of the drop to first contact. |
| Penetration or set per blow | mm | Distance the work moves (deforms or is driven) during the blow. |
| Efficiency (share of energy into the work) | % | Fraction of the energy that does useful work; the handbook formula neglects losses (100%). |
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: Falling mass
- What it is
- The mass of the part that falls and strikes: the ram, hammer head, pile-driver monkey or drop-test weight, including anything that moves with it.
- Units and format
- Enter a number in kg: kilograms. The form accepts 0.000001 kg to 10000000 kg. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 500 kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The average force is directly proportional to the falling mass.
- Get it right
- Use mass in kilograms, not weight in newtons; the tool applies gravity itself.
What this means: Drop height before contact
- What it is
- The height the mass falls freely before it first touches the work. The tool adds the penetration to this height when it works out the energy.
- Units and format
- Enter a number in m: metres. The form accepts 0.000001 m to 1000 m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.5 m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- More drop height raises the energy and impact speed, and the force with them.
- Get it right
- This is in metres while the penetration is in millimetres.
What this means: Penetration or set per blow
- What it is
- How far the work moves or deforms during one blow: the set of a pile per blow, or the crush of a forging or test piece. The fall’s energy is spread over this distance.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The force is roughly inversely proportional to the penetration: halve it and the force about doubles.
- Get it right
- Measure the permanent set per blow from markings over several blows; a small error in a small set changes the force a lot.
What this means: Efficiency (share of energy into the work)
- What it is
- The share of the fall’s energy that actually does work on the pile or workpiece; the rest is lost to rebound, heat, sound and guide friction.
- 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 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 100% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The average force is directly proportional to the efficiency.
- Get it right
- The handbook formula assumes no losses (100 %). Any lower value should come from measurement or the equipment supplier, not a guess.
Method and formulas
- Work of fall = W S, with S the total height including the penetration d.
- Average force × d = W S, so F = η m g (h + d) ÷ d.
- Impact speed = √(2 g h).
- Example: 500 kg falling 1.5 m with a 10 mm set delivers about 740.4 kN.
Limitations
- Average force only; peak force is higher and depends on stiffness.
- Losses from rebound, heat and elastic strain reduce the useful force.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Estimate the force delivered by a drop hammer or press
- Size a stop or anvil for a drop test
- Check pile driving resistance from set per blow
Who it is for
- Forging supervisors
- Test engineers
- Civil and site engineers
What you get
- Average force of the blow
- Impact speed and energy
- Force in weight terms
Interpreting the result
- Halving the penetration doubles the average force: hard stops see very high forces.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 183–184. Topic reference; no source tables or recommended settings are reproduced.
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