Sheet utilisation: how to measure nesting yield and how to raise it

Three ways to count, and a fourth

Part area is the net area: the outline minus its holes, so a flange with a large hole counts only its metal. An example: on a 2,500 × 1,250 mm sheet (3.125 m²) the parts have 2.0 m² of net area and the last one ends 2,000 mm along the sheet. Over the whole sheet that is 64 %. Up to the used length (2.0 m × 1.25 m = 2.5 m²) it is 80 %. If the 500 × 1,250 mm strip goes back on the rack, 2.5 m² is consumed and the figure is 80 %; if it goes to scrap, 64 %. One nest, two answers (example).

What the numbers mean

• About 70 %: what Hypertherm calls a typical industry nest, with 30 % scrap.
• Up to about 90 % on rectangles: Zorocut reached 89.36 % on our 117-rectangle test job and 71.11 % on a mix of L-brackets, plates and flanges, with 3 mm spacing and a 10 mm margin, on the used-length definition (our runs, 3 s).
• 68.60–92.24 %: the best published research method on the ESICUP benchmark sets, with zero spacing and 20 minutes of search. The shapes decide much of the figure.
• Low on a small job: two parts on a big sheet read low on whole sheets however well they are nested. That is an offcut to keep, not a bad nest.

How to raise it

1. Nest jobs together. Hypertherm's example is taking all the quarter-inch mild steel due in the next 10 days and nesting it at once: more parts, more ways to fill the gaps. Zorocut keeps the customer's name on each part, so one nest can carry several orders.
2. Fill the holes. Small parts in the holes of large ones turn slugs into parts; CypNest has a “Nest inside first” option for the same reason, and Zorocut does it on every nest — see part-in-part nesting.
3. Allow rotations. Zorocut lets each part turn in 45° steps by default; limit it to 180° or none only where the grain or a brushed finish needs it — CypNest's manual gives the same reason for its 180° option.
4. Use remnants first. A strip from the last job is metal already paid for; see remnants.
5. Keep the spacing as small as your test cuts allow, and no smaller. A 100 × 50 mm part with 3 mm spacing takes a 103 × 53 mm box (5,459 mm²); with 6 mm, 106 × 56 mm (5,936 mm²) — 8.7 % more metal per part (example). See part spacing.

Utilisation and the price

The figure matters most where it reaches the price. Zorocut bills material three ways: the part rectangle plus spacing, the net part area divided by the nest's utilisation, or the whole sheets used. In the net-area mode a free strip you keep is not counted as consumed, so the customer does not pay for metal that goes back on your rack; set offcuts to scrap and the whole sheets count. CypNest's report offers the same choice between whole plates, the parts' bounding rectangle and their envelope area. See material cost in a quote.