Open-die forging calculator
Enter the part you want to forge and, if you like, the bar you have. The calculator adds machining allowance and tolerances, scale and crop ends, gives the cut per part and tells you whether the forging is feasible on our hammer.
2Result
Cut per part–
Material to send–
Operation–
Forging ratio–
Reduction of area–
Slenderness (h₀ ÷ d₀)–
Upset ratio–
Forging weight–
Losses–
Difficulty–
Forging (estimated)–
Constant-volume calculation with the tables below. Estimated value for the forging service only, without material, heat treatment, machining, testing and freight; the final price is confirmed in the quote. Values marked * are forge estimates, to be confirmed in the order.
Scale by material
Scale is the oxide that forms and falls off at each heating. The values below are from the Dustre forge for bars forged under a 1,000 kg hammer (parts up to 500 kg). Large forgings made from ingots on a press have different losses, which are the ones most often found in the literature.
| Material | 1st heating | Each reheating |
|---|---|---|
| Carbon and alloy steel (Cr-Mo, Ni-Cr-Mo) | 8 % in total (Dustre forge value) | |
| Maraging and high-alloy steels | 1.5 %* | 1.0 %* |
| Stainless (austenitic, martensitic, PH) | 1.0 %* | 0.5 %* |
| Duplex and super duplex | 1.0 %* | 0.5 %* |
| Nickel alloys | 0.6 %* | 0.3 %* |
| Titanium (alpha case, removed in machining) | 0.5 %* | 0.3 %* |
| Copper and copper alloys | 1.0 %* | 0.5 %* |
| Reduction (forging or upset ratio) | Heatings |
|---|---|
| up to 2:1 | 1 |
| above 2:1 up to 4:1 | 2 |
| above 4:1 up to 8:1 | 3 |
| above 8:1 | 4 |
For the other materials scale is calculated per heating (table below). Nickel alloys, duplex, super duplex and titanium have a narrow temperature window: we add 1 heating when the reduction exceeds 2:1*. For titanium the loss is the alpha case, removed in machining. For comparison, the literature cites 2–3 % in the 1st heating and 1.5–2 % in the following ones for carbon steel in a flame furnace (EKTU, Tecnologia de conformação; Durukan, METU thesis 2007; Gerke, Behrens et al., ESAFORM 2024).
Crop ends and other losses
| Loss | Value |
|---|---|
| Crop ends (cut-off ends), except discs and parts whose diameter is larger than the length, with length up to 200 mm | 5 % (Dustre forge value) |
| Punching slug (rings and sleeves) | Punch diameter equal to 50 % of the forged bore* |
Value for bars forged under the hammer, parts up to 500 kg. For large ingot forgings the literature cites 5 to 10 % (EKTU), because the ingot head and foot are also cut off.
Machining allowance
Round bar, square bar and disc: the calculator uses Dustre's table (INF 002 Rev. 003), by finished size and by length or height. Example: a finished Ø 110 × 800 mm shaft is forged to Ø 117 × 814 mm (7 mm allowance on the diameter, tolerance +6 / −0, and 14 mm on the length, tolerance +14 / −11). Full tables in supply tolerances. Other shapes use GOST 7829-70, below. If you tick "Dimensions already include the forging allowance", nothing is added: the dimensions entered are those of the forging.
| Part Ø (mm) | L ≤ 250 | L 250–500 | L 500–800 | L 800–1200 | L 1200–1700 |
|---|---|---|---|---|---|
| 50–70 | 6 ± 2 | 7 ± 2 | 8 ± 2 | 9 ± 3 | 10 ± 3 |
| 70–90 | 7 ± 2 | 8 ± 2 | 9 ± 3 | 10 ± 3 | 11 ± 3 |
| 90–120 | 8 ± 3 | 9 ± 3 | 10 ± 3 | 11 ± 3 | 12 ± 4 |
| 120–160 | 9 ± 3 | 10 ± 3 | 11 ± 3 | 12 ± 3 | 13 ± 4 |
| 160–200 | 11 ± 3 | 11 ± 3 | 12 ± 3 | 13 ± 4 | 14 ± 4 |
| 200–250 | 12 ± 3 | 12 ± 3 | 13 ± 4 | 14 ± 4 | 15 ± 4 |
| 250–300 | 13 ± 4 | 13 ± 4 | 14 ± 4 | 15 ± 4 | 16 ± 5 |
| D up to (mm) | H up to 80 | H up to 125 | H up to 180 |
|---|---|---|---|
| 150 | 8 / 10 | 10 / 11 | 12 / 13 |
| 250 | 9 / 12 | 11 / 13 | 13 / 14 |
| 360 | 10 / 14 | 12 / 15 | 14 / 16 |
| 550 | 12 / 17 | 14 / 18 | 16 / 19 |
Total allowance on diameter (sum of both sides), for hammer forgings in carbon and alloy steel. On length we use the same value as on diameter*. For bores of rings and sleeves we add 4 mm to the outside-diameter allowance*. Outside the table ranges we use the nearest range and confirm in the quote. Source: GOST 7829-70, Carbon and alloy steel hammer forgings: allowances and tolerances.
Hammer capacity
Maximum section per the nominal catalog capacity of 1,000 kg hammers (C41-1000 series). The best productivity range is below this maximum.
Formulas used
| Quantity | How to calculate | Reference |
|---|---|---|
| Forging ratio (drawing out) | A₀ ÷ A₁ (starting cross-section area ÷ final cross-section area) | Starting from cast (ingot): usual minimum 3:1; 4:1 for critical parts*. Starting from rolled or forged bar, the minimum does not apply. |
| Reduction of area | (A₀ − A₁) ÷ A₀ × 100 | 3:1 = 66.7 %; 4:1 = 75 %. |
| Slenderness ratio (upsetting) | h₀ ÷ d₀ (height of the upset section ÷ diameter or smaller side of the bar) | Up to 2.5: safe. 2.5 to 3.5: depends on the operation and the alloy. Above 3.5: in stages or with a larger bar. |
| Upset ratio | h₀ ÷ h₁ (height before ÷ height after) | Equivalent to the forging ratio of the upsetting operation. |
| Material per part | Forged V × (1 + scale + crop ends) + punching slug | V from the forging volume (finished part + allowance). |
| Cut length | Starting volume ÷ A₀ | Plus 3 mm of saw cut per part. |
Frequently asked questions
How much material should I send to forge a part?
Choose the material, enter the bar you have (shape and diameter), the shape and dimensions of the finished part and the quantity. The calculator adds machining allowance, scale and crop ends and shows how much to send in kg and in meters of bar, including the saw cut. If the order requires a test coupon, send a little more.
What is the slenderness ratio?
It is the height of the bar section to be upset divided by its diameter (or smaller side). It tells whether upsetting is possible without buckling: up to 2.5 is safe; 2.5 to 3.5 depends on the operation and the alloy; above 3.5 it cannot be done in one step. The calculator indicates the minimum bar diameter to stay at 2.5.
What are forging ratio and reduction of area?
Forging ratio is the starting cross-section area divided by the final area (e.g. 3:1). Reduction of area is the same thing in percent: (initial area − final area) ÷ initial area. 3:1 corresponds to 66.7 % reduction; 4:1, to 75 %.
When do I need a minimum 3:1 reduction?
When the part starts from cast material (ingot or cast billet): the 3:1 reduction closes porosity and refines the grain to reach the mechanical properties. If the starting stock is already rolled or forged bar, the new forging only changes shape and dimensions, and the minimum reduction does not apply.
How much is lost as scale in forging?
In the Dustre forge, for bars forged under the hammer (parts up to 500 kg), we consider 8 % scale for carbon and alloy steel and 5 % crop ends. Stainless, duplex, nickel alloys and titanium oxidize much less and are calculated per heating. Large ingot forgings have other values, which are the ones most often found in the literature.
What is included in the estimated value?
Only the forging service, per kg of starting stock. Material, cutting, heat treatment, machining, testing and freight are quoted separately. The final value comes with the quote.
