What is the minimum order at a custom plastic box factory?

Answer: A steel tool starts at 1,000 to 2,000 pieces, a shared frame at 500, aluminium tooling lower.

The drawing says plus or minus 0.2 mm and the plant refuses. Who is right?

Answer: Both, at different sizes. Under 300 mm precision reaches 0.20 mm; above 500 mm the standard band is 0.80 mm.

How much load does 3.5 mm wall add over 2.5 mm?

Answer: About 30 kg to 45 kg, but shot weight climbs 40 percent and cooling adds 8 seconds. Extra ribs buy the same stiffness for less resin.

The second batch is 0.4 mm off. What changed?

Answer: Resin first, since a new PP lot shifts shrinkage by 0.2 percent, which is 0.8 mm over 400 mm. Then mould temperature: 5 C of water difference moves it again.

How is tooling amortised into the unit price?

Answer: Over expected total volume. A 30,000 RMB tool across 10,000 pieces is 3 RMB each, and 0.6 RMB across 50,000.

Custom Plastic Box Factory: Size, Wall Thickness and Load

Quick answer: A custom plastic box factory order is settled by four numbers fixed before tooling: outer size and cavity, wall and ribs, latch span and load, batch and cavitation.

What a custom plastic box factory locks before tooling
Wall thickness and rib layout
Tolerances a mould can actually hold
Cavities, tonnage and batch size
Three-stage sign-off from T1 to volume
FAQ

1. What a custom plastic box factory locks before tooling

The first job at a custom plastic box factory is a drawing, not a price. Outer size runs across the largest form, latches excluded; cavity runs from the mouth wall to the floor.

Draft angle must be written down: at 1.0 to 1.5 degrees per 100 mm of height, a 150 mm body loses 2.6 mm per side, leaving the floor 5.2 mm narrower than the mouth.

Parameter	Measured	Typical	Drawn
Outer size	Largest form	400 x 300 x 150 mm	Minus tolerance
Cavity	Mouth to floor	372 x 272 x 138 mm	Plus tolerance
Wall	Mid side wall	2.5 mm	Minimum
Latch span	Centre to centre	180 mm	Plus or minus 0.5

Latch span is what gets dropped. At 180 mm a 42 mm latch pulls the lid 0.6 mm onto the gasket; write 190 mm and it cannot load the middle, so the first rain test leaks. Tying span to latch model lets a custom plastic box factory change latches without a new mould.

2. Wall thickness and rib layout

Thicker is not stronger. On PP, 2.5 mm with ring ribs carries 30 kg static, while 4.0 mm reaches 38 kg and adds 60 percent to shot weight, stretching cooling from 18 seconds to 32.

Custom plastic box factory sample: light grey case open, two white latches raised in the lid, a perforated tray of glass vials, moulded front handle

Ribs set stiffness: 60 to 80 mm spacing, 3 mm tall, 1.2 mm at the root, and fillets above 0.8 mm or the part cracks there first.

Load counts through the stack: five layers at 25 kg puts 125 kg on the bottom unit, and a 2.5 mm floor creeps 1.5 mm in three months at 25 C.

3. Tolerances a mould can actually hold

One tolerance for a whole drawing is a promise no press keeps. On a 380 tonne machine, the honest bands are 0.3 mm under 300 mm, 0.5 mm to 500 mm and 0.8 mm above.

Size band	Standard	Precision
0 to 150 mm	0.25 mm	0.15 mm
150 to 300 mm	0.35 mm	0.20 mm
300 to 500 mm	0.50 mm	0.30 mm
500 to 800 mm	0.80 mm	0.50 mm

Shrinkage splits by direction: PP runs 1.4 to 1.6 percent along flow and 1.6 to 1.8 across, which is 0.8 mm over 400 mm, so cavities need zone compensation. Fit sits outside the table: 0.15 mm per side on the spigot, 0.3 mm gap after latching.

4. Cavities, tonnage and batch size

Tonnage follows projected area: at 300 to 400 kg per square centimetre for PP, a 400 x 300 body of 1200 square centimetres needs 360 to 480 tonnes, landing on a 500 tonne press.

Custom plastic box factory detail: black case corner close-up, rim flange over a seal groove, black foam cut-out holding one rounded part, ribs outside

Batch size decides cavitation. Under 5,000 a year, one cavity in 718H at 30,000 to 60,000 RMB; above 20,000, two cavities cut tooling per box from 8 RMB to 4. Lead time is 25 to 35 days over three trials.

5. Three-stage sign-off from T1 to volume

Hold a custom plastic box factory to three gates, with the pass line written into the order before the tool is cut.

Gate	Quantity	Checked	Pass line
T1 trial	5 pcs	Size, wall, latch pull-down	Key sizes in tolerance
T2 pilot	500 pcs	Fit, 1.2 m drop, 48 h salt spray	Rejects under 1 percent
T3 volume	Four hours	Weight, flash, colour	Weight plus or minus 2 percent

Salt spray covers hardware only: plating of 8 microns survives 48 hours, thinner coatings spot within 20 hours.

Conclusion

Size, wall, tolerance and tonnage are fixed before the first cut; every later check measures against them. Put all four on one drawing and a custom plastic box factory can quote and deliver in one pass.

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.