Must clamp force for an injection molded protective case use the largest projected area?

Answer: Use the pressurised area on the parting plane, lid flanges included, then add 1.2. Estimating from the outer footprint alone guarantees flash.

Why does a 3 mm wall case run nearly twice the cycle of a 2 mm one?

Answer: Cooling scales with wall squared, so the cooling segment grows from about 10 seconds to 18 and the cycle stretches with it.

Is sink in the case body a pressure problem or a time problem?

Answer: Check the gate. Still open, add pressure; frozen, add time. If neither works, the rib root is too thick.

For an injection molded protective case, how many cavities?

Answer: Follow annual volume. Two cavities double tooling cost and tonnage, so the saving only appears above roughly 8000 pieces.

How much does cooling water temperature move case dimensions?

Answer: About 0.2 to 0.3 percent of shrinkage per 10 °C for PP. On a 600 mm case that is 1.2 to 1.8 mm.

Injection Molded Protective Case: Four Stages Explained

Quick answer: An injection molded protective case is formed in one shot: melt is forced into a steel tool, packed to offset shrinkage, then cooled until it is stiff enough to eject. What decides the result is not press size but how four stages agree — draft, clamp force from projected area, packing at gate freeze, and cooling by wall squared.

How an Injection Molded Protective Case Is Built
Clamp Force: Tonnage from Projected Area
Packing: Pressure and Time
Cooling and Ejection: Wall Sets the Cycle
Reading Defects on the Part
FAQ

1. How an Injection Molded Protective Case Is Built

A cycle starts when the moving half locks against the fixed half. Melt enters at 80 to 140 MPa, then the machine packs, cools and ejects. A case body runs 60 to 120 seconds, cooling included.

Draft is where deep cases fail: 1 to 2 degrees per vertical wall, the upper end for deep cavities, or ejection leaves white marks and torn walls. Vents 0.02 to 0.03 mm deep on the parting line keep the last corner from scorching. PP, ABS and PC/ABS melt at 220 to 260 °C.

Stage	Controlled variable	Typical setting	What you check
Clamp	Clamp force	Area × cavity pressure, plus 1.2	Flash on the parting line
Pack	Packing pressure, time	60%–80% of injection pressure	Sink depth, part weight
Cool	Tool temperature, time	40–80 °C tool, time by wall squared	Warpage, ejection marks

2. Clamp Force: Tonnage from Projected Area

Clamp force holds the halves shut while melt pushes them apart. In kilonewtons it equals projected area in square centimetres times cavity pressure in bar, divided by 100.

A 600 by 400 mm case projects about 2400 cm². At 400 bar that gives 9600 kN, roughly 980 tonnes, and 1.2 for safety pushes the choice to a 1200 tonne press. Count area on the parting plane, so lid flanges count and side walls do not; thin ribbed cases run 450 to 500 bar.

3. Packing: Pressure and Time

Packing answers shrinkage. A 3 mm PP wall shrinks about 1.5 to 2.0 percent, and without make-up melt the core voids while the surface sinks.

Packing pressure sits at 60 to 80 percent of injection pressure. Below it, ribs sink on the reverse face; above it, flash and residual stress climb. Time follows gate freeze: a 3 mm gate freezes in 3 to 6 seconds, so packing slightly longer is enough. Weigh ten parts; a 0.3 percent spread means stability.

4. Cooling and Ejection: Wall Sets the Cycle

Cooling scales with wall squared, so 2 mm to 4 mm nearly quadruples the time rather than doubling it. Shaving 0.5 mm often buys more cycle than a faster machine.

Tool temperature is 40 to 60 °C for PP and up to 80 for PC/ABS. Uneven beats hot or cold: a 10 °C split between halves bows a flat base. Core lines sit 10 to 15 mm from the surface, and ejection force belongs on blocks, not pins.

Wall (mm)	Cooling (s)	Estimated cycle (s)	Where it fits
2.0	9–11	35–45	Small light cases, cycle first
2.5	13–15	45–55	General storage and transfer
3.5	27–30	70–85	Transport cases that survive drops
5.0	56–58	105–125	Heavy loads and stacking

5. Reading Defects on the Part

Read location before shape. Sink behind a rib means short packing or a thick rib root; flash on the parting line means low clamp force or a dirty shut-off; a case that rocks means uneven cooling. Weld lines sit where two fronts meet, usually behind handles, and moving the gate downstream pushes them out of the load path. Silver streaks mean moisture, so ABS and PC/ABS need 2 to 4 hours at 80 to 100 °C.

Conclusion

Taken apart, an injection molded protective case is not mysterious: the tool gives melt a clean path and enough draft, clamp force holds the cavity shut, packing replaces the volume lost before the gate seals, and cooling follows the square of wall thickness. Compress any stage and it returns as sink, flash or warpage. Written as a process card, those stages make batches repeatable for an injection molded protective case.

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.