What is material yield?
Material yield (also called sheet utilisation or nest efficiency) is the share of a sheet or tube that ends up as finished parts, with the rest going to remnant and scrap. It decides how much material each part really consumes, so it sits behind the material cost on every quote.
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What does material yield mean in fabrication?
Material yield = total area of the parts ÷ area of the sheet used, as a percentage.
The rest of the sheet is:
- the web: the gaps between parts and around the edge of the sheet
- the skeleton left once the parts are removed
- any remnant big enough to keep
- the kerf, which on a laser is a small share
Yield depends on the part's shape, how it's nested, the sheet size and how many parts share the sheet. Rectangular parts sit edge to edge with only the web between them. Round, triangular and L-shaped parts leave gaps.
How is material yield used?
Shops use yield to price material and to judge nests. Tempus Tools' guide to job shop profitability works through a triangular part with a 100 mm base and 300 mm height, on a 3000 x 1500 mm sheet with a 10 mm web:
- charging the part's own area: 300 parts per sheet, with no allowance for the web or gaps
- rectangular bounds, charging the rectangle around each part: 131 parts per sheet, a 44% yield
- true-shape nesting of the actual outline: 262 parts per sheet, an 87% yield
Quoted on rectangular bounds, the same part carries twice the material cost it does on true-shape nesting.
Why does material yield matter?
Material is a large share of a laser shop's revenue. In a Tempus Tools survey of 100 customers, it made up about 56% of job shop revenue over two years, so a few points of yield on every job add up to a lot of steel.
Yield also explains why two shops quote the same part so differently. A shop charging rectangular bounds builds the waste into every part price and loses work to shops nesting true shape. A shop charging only the part's own area wins work but pays for the scrap itself.
What improves material yield
- true-shape nesting instead of rectangular bounds
- rotating or mirroring parts so they fit into each other
- mixing parts from several jobs on one sheet, filling the gaps with small parts
- choosing the sheet size that suits the part, such as 3000 x 1500 mm, 2500 x 1250 mm or 4 x 8 ft
- common-line cutting, where neighbouring straight edges share one cut
- nesting small jobs into remnants instead of new sheets
At quote time the shop only knows the parts on that quote, so it can't count on other customers' jobs to fill the gaps.
Material yield and quoting
A quote can't charge for the exact yield the job will get in production, so shops choose a material charging method and apply it on every job. Tempus Tools uses true-shape nesting, fitting parts around corners and into each other instead of using rectangular bounds, to work out how many fit on a sheet. It then charges either the full sheet including the remnant or only the nested area, as the remnant entry explains.
Further reading: How to maximise the profitability of your laser cutting job shop
Price material from a real nest
Tempus Tools nests parts true shape, around corners and into each other, to work out how many fit, then charges material by the full sheet or the nested area, whichever you choose.
FAQs
How do you calculate material yield?
Add up the area of all the parts cut from a sheet, divide it by the area of the sheet, and multiply by 100. A 3000 x 1500 mm sheet is 4.5 m², so parts totalling 3.6 m² give a yield of 80%. Use each part's own area, not the rectangle around it.
What is the difference between material yield and machine utilisation?
Material yield measures how much of the sheet becomes parts. Machine utilisation measures how much of the available time the machine spends cutting. Yield drives the material cost of each part and utilisation drives the hourly rate, and shops overestimate both.
What is true-shape nesting?
True-shape nesting arranges parts by their actual outline instead of the rectangle around them, so irregular parts fit into each other. In Tempus Tools' triangle example, it fits 262 parts on a sheet against 131 with rectangular bounds, halving the material cost of each part.
Does kerf reduce material yield?
Only slightly on a laser. A fibre laser kerf is a few tenths of a millimetre wide, so the metal it removes is a small share of the sheet. The web between parts and the skeleton around them waste far more.