How to Calculate Casting Yield (and Why It Sets Your Cost per Kg)
Casting yield
Ask a foundry owner for their rejection rate and you'll get a number straight away. Ask for their yield and you often get a range, or a figure from last year. Yet yield decides how much metal you melt, and pay to melt, for every tonne you ship.
The casting yield formula
Casting yield is the share of melted metal that leaves the plant as good castings.
Foundries use the word for two different numbers. Keep them apart:
- Mould (design) yield is fixed by the method: casting weight divided by casting plus gating plus feeders. It tells the methods engineer how efficient a pattern's running and feeding system is.
- Plant yield is the overall figure: good castings dispatched divided by total metal melted. It includes everything the mould yield misses: rejections, metal left in the ladle, pigged metal and melt loss.
A worked example
Mould yield for one pattern
| Component | Weight |
|---|---|
| Casting | 18.0 kg |
| Gating system | 3.0 kg |
| Feeders (risers) | 6.0 kg |
| Poured weight | 27.0 kg |
Mould yield = 18.0 ÷ 27.0 × 100 = 66.7%.
Plant yield for a month
A foundry ships 300 tonnes of good castings in a month at 70% plant yield. It therefore had to melt 300 ÷ 0.70 = 428.6 tonnes. The other 128.6 tonnes went round the furnace again as returns, or were lost.
Why yield sets your cost per kg
Every kilogram that doesn't end up in a good casting still had to be melted, held and poured. Its melting cost is carried by the castings you do sell.
An illustration: assume melting and holding cost ₹12 per kg of molten metal.
- At 70% yield, the melting cost per kg of good casting is 12 ÷ 0.70 = ₹17.14.
- At 75% yield, it is 12 ÷ 0.75 = ₹16.00.
That ₹1.14 per kg, across 300 tonnes a month, is about ₹3.4 lakh a month, before counting the extra melt loss, refractory wear and labour that recycled metal also carries. Use your own melting cost; the arithmetic is the same.
Where yield leaks
- Oversized feeders and long runners. Methods that were never revisited after a pattern's first trial.
- Rejections. A rejected casting hurts yield twice: its metal goes back to the furnace, and the good casting has to be made again.
- Excess metal per heat. Melting more than the moulds ready for pouring, then pigging the balance.
- Melt loss. Oxidation and slag, which rise with rusty or oily scrap and long holding times.
How to improve it
- Measure yield per pattern, not just per month. A plant average hides the five patterns that drag it down.
- Review methods on the worst patterns. Feeding and gating simulation, or simply trials with smaller feeders where soundness allows.
- Attack rejection first. It is usually the fastest yield gain. See our guide to defect-wise rejection analysis.
- Plan heats against ready moulds. Melt what you can pour.
Tracking yield heat by heat in ICAST
ICAST records each heat from charge to castings, with heat-wise traceability. Because molten metal, moulds poured, good castings and rejections are all captured on the shop floor, yield is calculated per heat, per pattern and per item, with no separate spreadsheet. The same figures flow into item-wise costing, so a low-yield part shows up as a low-margin part.
