Can one case mould cover both equipment and cold-chain cases?

Answer: The frame can be shared when the outline matches, but the cavities cannot. Equipment cases need a hinge boss and latch seats; cold-chain cases need a 12 mm rib channel.

Why does the case mould hinge boss go to φ14 mm?

Answer: It holds the M5 counterbore and the 1.8 N·m torque, with three 1.6 mm ribs carrying that load into the side wall. Below φ12 mm the root cracks within three thousand cycles.

What groove size keeps a case watertight?

Answer: 6 mm wide, 4.5 mm deep, with a φ5 mm O-ring at 25% squeeze and an R0.5 floor. A square floor holds the ring off the bottom, and leaks start at the corners.

What is the minimum wall for a case mould at minus 30?

Answer: 3.2 mm holds a 2 kg drop from 900 mm with a cold-grade resin. At 2.8 mm the rib root becomes the weak point and returns climb.

How long does a changeover take on a shared frame?

Answer: About 90 minutes: pull inserts, purge the circuit, fit the new set, confirm the first part. A shared lid is faster at 40 minutes because the lid stays mounted.

Retooling or reworking, which is cheaper?

Answer: Retooling runs about 12,000 CNY, or 4 CNY per case across 3000 units. Rework at 40 CNY each means 300 rejects cost the same, plus the delay.

Case Mould Applications: Four Duty Cycles, Four Cost Gaps

Quick answer: Run the same case mould into equipment, instrument, medical and cold-chain duty, and the difference is not the outline but the assembly action. Get the hinge boss, sealing groove and rib height wrong and the unit price moves 6 CNY while rework runs past 40 CNY a case.

Start from the Assembly Action, Not the Outline
Equipment Cases: Ribs Behind the Hinge Boss
Instrument and Medical Cases: Sealing Groove and Cut-outs
Cold Chain Cases: Ribs and Wall at Minus 30
Two Moulds Instead of Four: The Cost Ledger
FAQ

1. Start from the Assembly Action, Not the Outline

One case mould gives a 3.2 mm wall and four M5 screws on an equipment case, and a 12 mm rib channel for a 10 mm panel on a cold-chain case. The difference is the assembly action.

Duty	Assembly action	Structure that matters	Frequent mistake	Rework cost
Equipment	Four M5 hinges, two latches	φ14 mm boss, 1.6 mm ribs	Boss without ribs, cracks at 1.8 N·m	6 CNY each
Instrument	Cut-out for a meter head	8 mm land, ±0.15 mm	Cut-out too close to the groove	11 CNY each
Medical	O-ring plus handle	Groove 6 by 4.5 mm, 25% squeeze	Square floor, seal never seats	9 CNY each
Cold chain	10 mm insulation panel	12 mm ribs, 3.2 mm wall	Rib steps, panel will not sit	14 CNY each

Every figure there is a rework price, not a quotation difference.

2. Equipment Cases: Ribs Behind the Hinge Boss

Eight of ten failures start at the hinge boss. After three thousand lid cycles the root cracks, since the screw torque is carried by the plastic around it.

Case Mould: two workers lifting black moulded cases at a timber bench, a blue inspection board above them, film-wrapped stacks and pink crates behind

A φ14 mm boss with three 1.6 mm by 12 mm ribs spreads 1.8 N·m into the side wall and survives thirty thousand cycles. Thicker ribs leave sink marks behind the boss.

Latch seats follow the same logic: their load points diagonally outward, so ribs must run along that line rather than across it.

Retooling costs about 12,000 CNY.

3. Instrument and Medical Cases: Sealing Groove and Cut-outs

Instrument and medical cases differ in cut-out and seal, and both depend on mould precision.

Cut-out tolerance ±0.15 mm, with an 8 mm land for the gasket to press against.
Sealing groove 6 mm wide, 4.5 mm deep, matched to a φ5 mm O-ring at 25% squeeze.
R0.5 at the groove floor; a square corner stops the ring short and leaks start at the corners.
Handle mounts moulded in, wall transitions tapered 1:3 to avoid stress risers.
Draft of 1.5°; below 1° the groove wall scuffs and the sealing face turns rough.

The groove floor is the first thing a toolmaker offers to simplify; saving one electrode buys 9 CNY of rework per case, from stripping the ring to re-inspection.

4. Cold Chain Cases: Ribs and Wall at Minus 30

At minus 30 the impact strength of PP falls to about 40% of its room-temperature value, so a case dropped at a cold-store door cracks at the rib root.

Case Mould: red case bodies stacked with black lids on a pallet, two women working at a bench, tape and label sheets on the table

Moving rib height from 8 mm to 12 mm and adding an R2 root keeps the base intact when a 2 kg ball drops from 900 mm after four hours at -30 °C. A 3.2 mm wall is the floor; at 2.8 mm the resin must change to a cold grade costing 11% more.

Cold-chain cases also need a panel seat: a 12 mm rib takes a 10 mm panel with 2 mm clearance, while a step beyond 0.5 mm lifts one corner.

5. Two Moulds Instead of Four: The Cost Ledger

Four duty cycles do not need four case moulds. Fix the outline at 520×380 mm, share a lid frame, change only cavity inserts.

Route	Moulds	Tooling spend	Per case at 3000	Changeover	Risk
Four dedicated	4	520,000 CNY	173 CNY	none	Idle when a model stops
Three, shared lid	3	390,000 CNY	130 CNY	40 minutes	Latch positions must align
Two, shared frame	2	270,000 CNY	90 CNY	90 minutes	Inserts within ±0.05 mm

The two-mould route saves 250,000 CNY and costs 90 minutes of changeover plus tighter insert work. Below 3000 cases a month that pays; above ten thousand on one model, a dedicated tool wins on cycle time.

Whatever is saved belongs in the tooling, not in the wall.

Conclusion

All four duty cycles come back to three features: the hinge boss, the sealing groove and the rib height. Sizing a case mould from the assembly action keeps the unit price within 6 CNY while saving 40 CNY a case in rework. Fix the outline and share the frame, and four duties fit into two moulds at 270,000 CNY instead of 520,000.

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.