Upset Forging Stock Length, Strain and Final Diameter Calculator
In upset forging, a bar is shortened and widened between flat dies or in a heading tool. This calculator uses constant volume to predict final diameter and checks whether the stock is too slender to upset without buckling.
Your numbers
The common free upset rule is about 3 times the diameter. Supported stock in a die cavity can allow more.
Your results
Volume constancy treats the stock as a perfect cylinder before and after. Real parts barrel, and hot work scale and die chilling change results. Use as a screening estimate.
Final diameter vs final height
Sweeps Final upset height from 30 to 150, holding your other inputs fixed.
Turn forging routings into ERP data
Optional: a short review of how stock sizes and stage counts could be modelled in your ERP routings.
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How to use the calculator
Enter the bar diameter, the stock length you plan to heat, and the final height of the upset. The calculator returns final diameter, height reduction, upset ratio, true strain and the amount of stock beyond the L/D limit. If the excess is above zero, split the upset into stages or support the stock in a die.
- Use the limit your plant has validated for the alloy and temperature.
- Check final diameter against the die opening.
- True strain helps compare to material workability data.
The method behind it
Volume stays constant in plastic deformation, so pi/4 x D0 squared x L0 equals pi/4 x D1 squared x H1, giving D1 = D0 x sqrt(L0 / H1). True strain is the natural logarithm of the length ratio. The widely used rule is that unsupported stock longer than about three diameters may buckle or fold, and longer stock is upset in a die cavity that constrains it.
Reading the result and common mistakes
The chart shows the diameter growing fast as height falls. A big upset may need multiple heats or stages to avoid folds and cracking at the equator. Remember that friction with the dies makes the cylinder barrel, so mid-height diameter is larger than the ideal figure.
- Using unsupported stock far beyond the 3D rule.
- Ignoring die opening limits for the final diameter.
- Not allowing for taper or heat gradient across the stock.
- Assuming strain capacity is the same cold and hot.
Frequently Asked Questions
What is the 3D rule in upset forging?
It says unsupported stock longer than about three times its diameter can buckle or bend during upsetting. Longer stock should be upset in stages or supported in a die cavity. Different alloys and temperatures shift the practical limit, so validate in your plant.
How is final diameter calculated?
Volume stays constant, so the final diameter equals the initial diameter times the square root of initial length over final height. The result ignores barreling and flash, so measured values are slightly different at the equator.
What does true strain tell me?
True strain is the natural log of the height ratio and measures the amount of plastic deformation. It can be compared with the workability or fracture strain of the alloy at the forging temperature, which helps decide if the part needs several steps.
Can I use this for cold heading?
The geometry is the same, but cold heading has strict limits on upset ratio per blow, often two to three times the diameter, and depends on die support. Use the machine and wire supplier's rules for cold heading limits.
If your forge manages dies, heat lots and process routings in an ERP, we can discuss how to expose that to planners. This tool does not need any of that.
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