Core Formulas

How to Calculate Casting Yield, Pour Weight, Melt Loss, and Forging Tonnage

The core foundry and forging formulas worked line by line, from casting yield and pour weight to melt loss and press tonnage, with real units and numbers.

Start with casting yield, the ratio that governs everything downstream. Yield equals net casting weight divided by total poured weight, expressed as a percentage. If a gray iron pump housing finishes at 42 kg and the mold consumes 58 kg of poured metal including the runner, riser, and gating, yield is 42 / 58 = 0.724, or 72.4 percent. The 16 kg difference is return metal, not loss, but it still gets melted, handled, and shaken out. Run this through the Casting Yield calculator for a batch and you convert a per-part figure into the melt tonnage you actually need to schedule each shift.

Pour weight is the input yield depends on, so calculate it before anything else. Pour weight equals casting weight divided by expected yield, plus a shrinkage allowance for the alloy. For that same 42 kg casting at 72.4 percent yield, required poured metal is 42 / 0.724 = 58 kg. Gray iron shrinks roughly 1.0 percent volumetrically at solidification, ductile iron 0.5 to 0.9 percent, aluminum A356 near 3.5 to 4.0 percent, so the riser volume in your pour weight scales with alloy. The Pour Weight Calculator ties casting geometry, part count per mold, and gating volume into a single ladle target in kg.

Melt loss captures metal that oxidizes, slags off, or vaporizes in the furnace and never reaches the ladle. Melt loss percent equals (charge weight minus tapped weight) divided by charge weight, times 100. Charge 1,000 kg of steel scrap and tap 965 kg of liquid, and melt loss is (1,000 - 965) / 1,000 = 3.5 percent. Induction melting of clean steel runs 2 to 4 percent, aluminum in a reverberatory furnace 3 to 8 percent depending on turnover and dross handling. Feed your charge mix into the Melt Loss Calculator so the number reflects your actual scrap grades, not a textbook average.

Furnace charge is the reverse calculation: how much raw material to load to hit a target liquid weight after melt loss. Required charge equals target liquid weight divided by (1 minus melt loss fraction). To tap 2,000 kg of ductile iron at 3 percent melt loss, charge 2,000 / 0.97 = 2,062 kg. Then split that charge across pig iron, returns, and steel scrap to hit carbon and silicon aim, plus ferroalloys like FeSi at 75 percent silicon for adjustment. The Furnace Charge Calculator solves the charge mix and the total simultaneously so recarburizer and alloy additions land on spec.

Gating ratio controls how metal enters the mold and directly affects turbulence and inclusions. It is written as sprue area to runner area to gate area, for example 1 : 2 : 2 for a pressurized system or 1 : 4 : 4 for an unpressurized one feeding aluminum. Size the choke area from the pour time using A = W / (rho times v times t), where W is pour weight, rho is metal density near 7,000 kg per cubic meter for iron, v is gate velocity, and t is target fill time. The Gating Ratio Calculator turns your choke area and chosen ratio into runner and gate dimensions in square millimeters.

Forging tonnage tells you the press capacity a part needs so you do not underfill or overload the die. Required force equals projected area of the forging at the parting plane times the flow stress of the heated metal times a shape complexity factor, usually 3 to 8. A steel connecting rod with 12,000 square millimeters projected area, flow stress around 100 MPa at forging temperature, and a factor of 6 needs 12,000 times 100 times 6 = 7,200,000 N, about 720 tonnes force, so you would specify a 1,000 tonne press. The Forging Tonnage calculator applies the material and complexity factor for you.

Sand usage closes the loop on molding capacity. Sand to metal ratio, by weight, typically runs 4 : 1 to 10 : 1 for green sand depending on part size and mold density. For a mold pouring 58 kg of metal at a 6 : 1 ratio, you handle 348 kg of prepared sand per mold, and at 120 molds per hour that is 41.8 tonnes per hour through the muller. New sand addition to replace losses runs 2 to 5 percent of throughput. The Sand Usage Calculator converts molds per hour and ratio into hourly sand demand and new-sand makeup in kg.

Chain the formulas so one output feeds the next: casting weight sets pour weight, pour weight and yield set melt demand, melt demand and melt loss set furnace charge, and mold count sets sand and shakeout load. Sanity-check units at every step, kilograms with kilograms, square millimeters with square millimeters, and never mix volumetric shrinkage percent with weight-based yield percent. A single unit slip on gate area, treating 200 square millimeters as 200 square centimeters, inflates your choke by 100 times and floods the mold. The Shakeout Capacity calculator uses the same mold-per-hour input to confirm your shakeout can clear what you pour.

Published 2026-07-01.