For 24 cells, should a custom case with compartments be slotted or moulded?

Answer: Follow volume. Under 2000 pieces, 6 mm slotted sheet at 5.2 CNY wins; past 5000, a moulded grid can amortise, though any cell change means a new tool.

Can 4 mm and 6 mm sheet be chosen on load alone?

Answer: No. Past 180 mm of span, 4 mm bows even with a light load, while 6 mm under 12 cells is overpaid material.

Is 40 seconds per unit fast or slow?

Answer: Normal for slotted. Below 32 seconds means loosened tolerance; above 60 means glue or rivets entered the design.

How should 5 kg per cell be stated?

Answer: With conditions: four times static load for eight hours, deflection within 1/200 of span, and a 1.5 m drop on six faces.

Can the partitions be removed for cleaning?

Answer: Dry slots can, glued and riveted builds cannot. For wash-down duty, specify a 0.05 mm slot fit.

What rework rate is normal?

Answer: Under 1% for slotted, around 3% for riveted. Above 5% points to cut allowance or assembly order, not to purchasing.

Custom case with compartments: where the unit cost is locked

Quick answer: The unit cost of a custom case with compartments is set by partition material, assembly seconds and rework. Between 4 and 24 cells, slotted PP hollow sheet is cheapest; only past 16 cells at 5 kg does a moulded grid pay off.

Where the Unit Cost of a Custom Case with Compartments Is Locked
Working Back from Load to Cavity and Cell Count
Partition Material and Gauge, 4 mm Against 6 mm
Assembly Time Between Slot-in and Riveted Partitions
Verifying Load per Compartment
Pulling the Rework Rate Back Under One Percent
FAQ

1. Where the Unit Cost of a Custom Case with Compartments Is Locked

A handheld instrument maker moved a 24-cell custom case with compartments from riveted to slotted partitions. Assembly fell from 68 to 32 seconds a unit across 16,000 units a year, and rework dropped from 3.4% to 0.9%.

Partition scheme	Gauge	Usual cells	Cost per unit	Load per cell
Slotted	4 mm	4 to 12	3.4 CNY	under 2 kg
Slotted	6 mm	12 to 24	5.2 CNY	3 kg
Riveted	6 mm	16 to 24	7.9 CNY	5 kg
Moulded grid	2.5 mm rib	4 to 24	6.8 CNY	4 kg

The last row hides the real number: 6.8 CNY is material only, the tool costs 42,000 CNY at a 2000 piece minimum, so each carries another 21 CNY. That lands at 27.8 CNY, five times the slotted sheet.

2. Working Back from Load to Cavity and Cell Count

Cell count is arithmetic: total load divided by allowable load per cell, rounded to fit parts. One tool kit custom case with compartments holds 18 items at 0.9 kg, so 16.2 kg. At 3 kg per cell that is six cells, but the longest item is 320 mm, so the cavity takes two rows of three.

Custom case with compartments: closed black case on a long bench, a charcoal foam sheet with four pockets beside it, timber behind

The cavity also gives up space: a 4 mm sheet across three columns eats 8 mm, a 6 mm sheet 12 mm, rivet heads more. None of it shows on a drawing until parts will not drop in.

Cost does not scale linearly: 12 to 24 cells doubles material and adds 60% to assembly, so cost per cell falls.

3. Partition Material and Gauge, 4 mm Against 6 mm

A 4 mm sheet weighs 0.6 kg per metre, a 6 mm sheet 0.95 kg; at equal span the 6 mm is nearly twice as stiff.

Under 2 kg per cell and 12 cells or fewer: 4 mm slotted sheet
2 to 5 kg per cell and 16 cells or more: 6 mm slotted sheet
Service from -20 °C to 60 °C: copolymer PP, as homopolymer goes brittle

Most material problems come from regrind ratio. Fully reground sheet is 18% cheaper but holds tolerance to ±0.4 mm, so slots fit loose. In a custom case with compartments, a partition that moves 1 mm takes the parts with it.

4. Assembly Time Between Slot-in and Riveted Partitions

Assembly seconds are the least quoted line. A 16-cell custom case with compartments takes 40 seconds slotted and 68 riveted, which needs drilling and pressing.

Custom case with compartments: open dark grey case on a workbench, a charcoal partition angled with spanners and screwdrivers in its slots, spools behind

Structure	Assembly per unit	Rework rate	Main cause
Slotted, dry	32 s	0.9%	Slots too loose
Slotted, glued	51 s	2.1%	Glue squeeze-out
Riveted	68 s	3.4%	Hole offset
Moulded grid	8 s	0.4%	Flash

Forty seconds is the benchmark. A 0.2 mm slot assembles fastest and loosens first in transit; at 0.05 mm, assembly gains 12 seconds and rework halves. Rivets pay off only where the grid must not open.

5. Verifying Load per Compartment

Load per cell of 2 to 5 kg is the normal band for PP hollow sheet; past 5 kg the structure changes, not the gauge.

Static load runs at four times the rating for eight hours, with mid-span deflection within 1/200 of span. Drop runs at 1.5 m per face, no partition leaving its slot. Pass both and a custom case with compartments holds parts through normal freight. Span is the usual culprit. A 600 mm cavity with one central partition has no support at the middle, and 5 kg bows it. A rib costs 0.8 CNY and beats 6 mm sheet.

6. Pulling the Rework Rate Back Under One Percent

Rework comes from slot fit, cut length and assembly order. Cut length is the expensive one: 1 mm short is scrap, 1 mm long crushes the flutes.

Three habits get under 1%: leave 0.3 mm on the cut; fit the centre partition first and work outward, frame last; check the first article on diagonals, stopping past 1.2 mm.

Dropping from 3.4% to 0.9% removes 400 piece-events a year at 16,000 units.

Conclusion

Partition scheme sets material cost, assembly seconds set rework, cell count spreads both. Split the three and the quote stops being opaque. Settle the structure of a custom case with compartments first; the unit price follows.

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.