Can foam cutting be bought on unit price alone?

Answer: No. The rate rarely covers the die, nesting loss or sample charge, and the ranking moves once added.

How far apart are die cutting and CNC?

Answer: Die cutting lands near ±0.8 mm, CNC near ±0.3 mm. Kerf and springback explain the gap, which widens with depth.

Is a tighter pocket safer?

Answer: To a point. Two millimetres holds a part; beyond that operators pry at the wall and damage it.

Can a small batch skip the die?

Answer: Under 50 pieces with a simple outline, yes. CNC costs more per piece but saves the 800 to 1,500 CNY die.

What is needed to quote foam cutting?

Answer: The part or a 3D file, the pocket layout, density and colour. Without it, draw to the outline plus 1.5 mm.

Foam Cutting Selection: Five Criteria That Decide the Quote

Quick answer: Judge foam cutting in a fixed order: cut face, kerf compensation, batch and tooling, material, then sampling. The first two decide whether the pocket accepts the part; the last three decide price and lead time.

The Five Criteria and Why the Order Matters
Criterion One: Cut Face and Pocket Mouth
Criterion Two: Kerf Compensation and Tolerance
Criterion Three: Batch, Tooling and Nesting
Criteria Four and Five: Material and Sampling
FAQ

1. The Five Criteria and Why the Order Matters

Quote the same insert as foam cutting to three suppliers and three documents return: a die price, a CNC time estimate, a promise to follow the drawing. Prices differ by a third and none compares: no shared criterion sits under the number.

The first two criteria are hard: a wrong pocket scraps the whole sheet. The last three are commercial. Reverse the order and you negotiate price, then thin a 30 mm pad by 5 mm because the pocket will not take the part.

Criterion	Ask in writing	Cost if wrong
Cut face	How the wall and mouth are held	Edges collapse after 200 uses
Kerf	Kerf width, pocket opened by how much	Part will not enter, or rattles
Batch	Pieces before a die, utilisation	Material bill eats the saving
Material	Blade for this density, springback	Crushed section, short pocket
Sampling	First articles, days, checks	Whole batch reworked

2. Criterion One: Cut Face and Pocket Mouth

Read the face in three places: the grain of the section, the verticality of the wall, the mouth. EVA at 45 kg/m³ shows a fine grain and a bright compressed line at the mouth; at 60 kg/m³ it springs back less and holds the mouth, but the blade is spent by 10,000 hits, not 20,000.

Foam Cutting: three grey hard cases grouped, the front one open to show convoluted lid foam over a grid-cut base, a tall closed case behind

A 15 by 15 mm pluck grid saves tooling and lets users pick an outline, but the tear is serrated and 200 insertions leave crumbs. A cut pocket has straight walls, and anything deeper than 30 mm needs 0.5 mm of draft, or the part drags the wall up.

Load the part, invert the case ten seconds, watch whether it stays. One to two millimetres of interference is the band: under 1 mm it shifts, over 2 mm extraction takes both hands.

3. Criterion Two: Kerf Compensation and Tolerance

A die is not a zero-width cut. Blade stock is 0.71 mm, the foam springs back, and the opening ends 0.4 to 0.5 mm under the drawing. Pockets need half-kerf compensation: 0.45 mm kerf, 0.22 mm per side.

CNC oscillation carries no kerf and holds ±0.3 mm on a 1.2 by 2.4 m bed. Longer inserts are spliced with an unavoidable 0.2 mm step; on a 2.6 m insert, keep the splice off the centre of mass.

Tolerance follows the part: ±0.5 mm for aluminium housings, ±1.5 mm for pouches and textile gear. 'Per drawing' is the commonest hole.

4. Criterion Three: Batch, Tooling and Nesting

A die costs 800 to 1,500 CNY with about 20,000 hits: 16 to 30 CNY per piece at 50 off, below one yuan at 2,000. The crossover sits near 120 pieces.

Foam Cutting: a cut pocket in black foam, granular wall, rounded corner, a knurled metal knob and two screws at the rim

Two pocket shapes can share one plate if the bridge stays at 8 mm. In foam cutting, nesting is the unquoted line: 78 percent utilisation is ordinary, under 65 percent cancels the tooling saving.

5. Criteria Four and Five: Material and Sampling

EPE at 25 kg/m³ is too soft: a die crushes a 2 mm lip. PU sponge must be chilled to about -20 °C. EVA from 45 to 80 kg/m³ cuts well and holds the lowest rework rate in foam cutting.

Sampling needs three things fixed: pieces, days, checks. Three first articles in 48 hours, one loaded and dropped from 1.2 m, one sectioned for wall verticality, one kept as a colour reference.

Item	Number on the order	Acceptance
Cut face	Wall within 1 mm, no chamfer	Section one, measure three points
Batch	120 pieces minimum, 75 percent utilisation	Check nesting drawing
Sampling	3 pieces in 48 hours	Load, invert ten seconds

Conclusion

The first two decide whether the part goes in; the last three decide cost and timing. Cut face and kerf are the process floor, batch and nesting the cost floor, material and sampling the delivery floor. Agree all five as numbers and quotes compare. Foam cutting selection is five numbers settled before the die is made.

This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.