The Input Weight Formula
Start from the finished forged weight, calculated from the forging drawing volume and the material density, not from the machined part drawing. Machined weight plus machining allowance gives you the forged shape; the forging drawing already includes draft angles, fillets and the added stock that machining will remove. Then add the losses.
Input weight equals forged weight plus flash plus connector plus scale loss plus end loss and cutting loss. Flash is the excess that squeezes out at the parting line and is trimmed off. Scale is oxide that forms in the furnace and falls off during forging.
Cutting loss is the kerf from the saw or the shear cut, and end loss is the unusable bar butt.
- Forged weight from the forging drawing, not the finished machined part
- Flash and connector sized from die design or past dies for similar shapes
- Scale loss as a percentage of heated weight
- Saw kerf and bar end loss spread across the billets per bar
Choosing Realistic Flash and Scale Percentages
There is no universal flash number. Flash depends on die design, part shape, how precisely billet weight is held, and whether the part is a simple upset or a complex rib-and-web shape. Small parts often carry a higher flash percentage than large ones because the flash land cannot shrink below a practical width.
Scale loss depends on furnace type, atmosphere, time at temperature and alloy. Carbon and low-alloy steels in gas furnaces typically lose more to scale than the same parts heated by induction, which is one reason induction is common on high-volume closed-die work. Treat any percentage as a starting point and replace it with measured values from your own jobs as soon as you have them.
- Record billet weight and finished weight on the first articles of every job
- Track flash weight by die set, not only by part number
- Separate scale loss estimates by furnace or induction heater
Billet Sizing, Bar Diameter and Cut-to-Weight
Input weight must become a purchasable billet. Bar comes in standard diameters and lengths, so the estimator chooses a bar size, calculates billet length for the target weight, and checks how many billets come from a mill length after kerf and end loss. A slightly oversized bar can increase flash; an undersized one risks underfill.
Cut-to-weight operations add a weighing step so each billet stays within a tolerance band, and the tolerance you can hold sets how much extra flash you must budget. Mills and service centers often charge extra for short quantities or special cutting, so the real cost per pound is not always the list price.
- Pick bar diameter to balance fill, flash and available mill sizes
- Calculate billets per bar after kerf and butt allowance
- Include mill minimums, cut charges and alloy surcharges in cost per pound
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Forging Part Family Input Weight and Yield Worksheet
Calculate input weight, yield and annual material pounds and cost for a family of forged parts using flash, scale and bar-end loss assumptions per part.
Using Actual Yield Data From Past Jobs
The best estimate for a new forging is the measured yield of a similar one. Your ERP holds the data if material issues and finished receipts are recorded accurately: pounds of bar issued to the job against pounds of good forgings received, with scrap and rework recorded separately. Calculate yield by part family, by die set and by material, then compare it to the original quote.
An AI assistant connected read-only to the ERP can pull these comparisons on demand and show which jobs were quoted at, say, 78 percent yield and actually ran at 72. That kind of gap is how a profitable-looking job loses money.
- Compare lbs issued against lbs received by job
- Separate scrap from flash and scale in the yield bridge
- Group by material and die complexity before averaging
When a Simple Spreadsheet Is Enough
A single calculator sheet with fields for forged weight, flash percentage, scale percentage and kerf is perfectly adequate for a small shop with a handful of part families. Moving to software or AI only makes sense when you cannot trust the percentages because actuals are not captured, or when quote volume outpaces the person who maintains the sheet. Start by capturing real billet-in and forging-out weights at the press.
If that data does not exist, nothing built on top of it will be reliable.
Frequently asked questions
How do you calculate billet weight for a forging?
Take the finished forged weight from the forging drawing, add flash, any connector, and scale loss, then add cutting loss if you are sawing or shearing from bar. The sum is input weight. Divide by the density-based volume to check length and diameter, then round to a purchasable bar size and billet length.
What is a typical forging yield?
It varies widely with part shape and process. Compact upset parts can yield well, while thin ribbed closed-die parts with large flash lose much more. Rather than relying on a rule of thumb, calculate yield from your own past jobs, grouped by material and die complexity.
Is scale loss the same for every alloy?
No. It depends on alloy, time at temperature, furnace atmosphere and whether you use gas or induction heating. Stainless, titanium and nickel alloys behave differently from carbon steel, and titanium also forms an alpha case that must be machined away, which affects machining allowance rather than simple scale loss.
Netray can read your job history and show estimated versus actual forging yield by part family, read-only, on your own hardware.