BIZOMAT MAKEOS · Manufacturing
Drop Hammer Forging Plan (Force Needed, Set per Blow, Number of Blows)
For upsetting or forging a part under a drop hammer, how far will each blow squeeze it, and how many blows will it take?
Plan of a drop hammer or drop stamp operation: the force needed to deform the part from its area, the flow stress at the forging temperature and a constraint factor, then the set per blow at which the hammer’s energy (falling mass, drop height and efficiency) gives that average force (as the drop hammer blow tool, solved for the set), the impact speed and energy per blow, and the number of blows for the total reduction, against the most blows you will allow per heat.
Open the calculatorRuns in your browser. No account needed.
How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Falling mass (tup and die) | kg | Mass of the tup, die and anything else that falls. |
| Drop height before contact | m | Height the tup falls before it touches the work. |
| Blow efficiency (share into the work) | % | Share of the blow energy that goes into deforming the work (the rest goes into the anvil and foundation). |
| Part | ||
| Area being forged (average over the blow) | mm² | Cross-section area being squeezed, averaged over the blow. |
| Flow stress at forging temperature | MPa | Flow stress of the material at the forging temperature and strain rate. |
| Constraint (shape) factor | Factor for friction and die constraint (about 1.2–2 for open-die upsetting, more for closed dies). | |
| Total height reduction needed | mm | Total reduction in height the forging needs. |
| Most blows allowed per heat | blows | Blows you can strike before the part must be reheated. |
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 (tup and die)
- What it is
- The total mass that falls in each blow: the tup or ram, the top die and anything fixed to them.
- 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
- A heavier falling mass gives more energy per blow and a larger set, so fewer blows.
- Get it right
- Include the top die; the tup alone understates the blow energy.
What this means: Drop height before contact
- What it is
- The height the tup falls from its release point to the moment the die touches the work.
- 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
- A greater drop height raises the set per blow and the impact speed, so fewer blows are needed.
- Get it right
- Enter it in metres, measured to first contact with the work, not to the bottom die face.
What this means: Blow efficiency (share into the work)
- What it is
- The share of the blow energy that goes into deforming the work; the rest is lost into the anvil, foundation and rebound.
- 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 80% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Higher efficiency gives a larger set per blow and fewer blows.
- Get it right
- Type the percentage itself, not a fraction.
Part
What this means: Area being forged (average over the blow)
- What it is
- The cross-section area of the part under the die being squeezed, averaged over the blow because it grows as the part spreads.
- Units and format
- Enter a number in mm²: square millimetres. The form accepts 0.000001 mm² to 100000000 mm². Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2000 mm² as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The force needed rises in direct proportion to the area, which lowers the set per blow.
- Get it right
- Enter it in mm²; an area in cm² must be multiplied by 100.
What this means: Flow stress at forging temperature
- What it is
- The stress at which the material flows at the forging temperature and the speed of the blow, from material test data or a forging reference.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 5000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 150 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The force needed rises in direct proportion to the flow stress.
- Get it right
- Use the flow stress at the actual temperature and strain rate; room-temperature yield strength is far too high.
What this means: Constraint (shape) factor
- What it is
- A multiplier on the flow stress for friction at the die faces and the constraint of the die shape, from a forging reference or your process experience.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 10. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.5 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The force needed rises in direct proportion to the factor.
- Get it right
- Closed dies and thin sections constrain the metal more than open-die upsetting, so they need a larger factor.
What this means: Total height reduction needed
- What it is
- The total amount the part’s height must be reduced across all the blows, from the starting and finished heights.
- 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 30 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The number of blows rises with the reduction needed, rounded up to whole blows.
- Get it right
- Enter the reduction itself, starting height minus finished height, not the finished height.
What this means: Most blows allowed per heat
- What it is
- The most blows you can strike on the part in one heat before it cools too much and must be reheated, from your process experience.
- Units and format
- Enter a number in blows: blows. The form accepts 1 blows to 1000 blows. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 4 blows as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- A whole number; the tool rounds the blows needed up to the next whole blow.
Method and formulas
- Force needed F = A × flow stress × factor.
- Average force of a blow F = η m g (h + d) ÷ d (as the drop hammer blow tool), solved for the set: d = η m g h ÷ (F − η m g).
- Blows = total reduction ÷ set per blow, rounded up; impact speed √(2 g h).
- Example: 450 kN is needed; each blow sets 13.191 mm, so 3 blows.
Limitations
- Constant area and flow stress; as the part spreads and cools the force rises and the set falls.
- Rigid anvil; a light anvil absorbs much of the blow.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Estimate the blows to upset a bar end
- Check whether a hammer is big enough for a forging
- Compare drop heights or tup masses
Who it is for
- Forge masters
- Manufacturing engineers
- Blacksmiths
What you get
- Force needed
- Set, energy and impact speed per blow
- Number of blows
Interpreting the result
- Doubling the drop height roughly doubles the set per blow; a heavier tup does the same with less impact speed.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 183–184. Topic reference; no source tables or recommended settings are reproduced.
BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Drop Hammer Forging Plan (Force Needed, Set per Blow, Number of Blows) calculator