Why does cooling take 35 s?

Answer: The square rule gives 3.9 × 3² = 35.1 s, within 0.1 s of measurement, and ejecting above 78 ℃ leaves pin marks, so only mould temperature, flow or wall thickness help.

What does a second cavity do?

Answer: The shot becomes 66 s and each part 33 s, 47% faster per piece, but clamp demand rises to 860 t and the tool costs 65% more.

How much does 40 ℃ mould temperature save?

Answer: Cooling drops from 35.0 s to 28.5 s, cutting 6.5 s per shot and adding 130 parts a day, though visible surfaces coarsen.

Can packing be cut to 4 s?

Answer: The part then weighs 1842 g instead of 1852 g, sinking the base and loosening wall tolerance from ±0.08 mm to ±0.14 mm, so weigh until the curve flattens.

Does a bigger machine shorten the case moulding cycle?

Answer: No. A 1000 t press on one cavity adds 120 mm of travel and 1.8 s of dry cycle, turning 62 s into 64 s.

Case Moulding Cycle: Moulding Cycle for 3 mm Walls

Quick answer: A 3 mm wall PP case runs a 62 s case moulding cycle: 3.4 s injection, 6.8 s packing and 35.0 s cooling, so cooling alone eats 56.5% of the shot.

Splitting the cycle into stages
Injection and packing seconds
Cooling and the square rule
Mould temperature and tonnage
Cycle time into daily output
FAQ

1. Splitting the cycle into stages

A 420 mm × 320 mm × 180 mm PP case, 3 mm walls, one cavity on a 530 t machine at 60 ℃ mould and 230 ℃ melt, ran 62 s per shot on a stopwatch: 2.6 s clamp close, 3.4 s injection, 6.8 s packing, 35.0 s cooling, 2.2 s open, 3.0 s ejection, 6.0 s robot removal, 3.0 s waiting.

Cycle time is not machine speed: it follows wall thickness, mould temperature and circuits, and a faster press saves 0.4 s of injection while cooling stays frozen.

Stage	s	Share	Headroom
Clamp close	2.6	4.2%	None
Injection	3.4	5.5%	0.4 s, vent limited
Packing	6.8	11.0%	1.5 s, gate limited
Cooling	35.0	56.5%	5–8 s
Open and eject	5.2	8.3%	0.5 s
Robot removal	6.0	9.7%	2.5 s, chute drop
Waiting	3.0	4.8%	1.0 s
Total	62.0	100%	9–12 s

Removal is the stage quotes forget: the 420 mm square case forces the robot to turn the lid 90°, and a chute drop cuts 6.0 s to 3.5 s for 4% more output.

2. Injection and packing seconds

Injection runs 3.4 s for a 2.0 kg shot, 210 mm stroke and 95 MPa peak, and cannot be slow: PP melt held above 5 s at 230 ℃ marks the wall.

Case moulding cycle tooling area with stacked steel mould bases, blue racking, red crane hook on chains and a worker in a red helmet

Speed is profiled in three steps, 60% then 45% then 25%, still 3.4 s but 0.6 s faster than constant speed with 8 MPa less vent pressure.

Packing has one test: weight stops rising. Five shots weighed 1842 g at 4 s, 1852 g at 6 s and 1853 g at 8 s, so the gate froze near 5.5 s and 6.8 s leaves 1.3 s of wear margin; pressure falls from 95 MPa to 55 MPa at 12 mm.

3. Cooling and the square rule

Cooling follows t = 3.9 × s², s in millimetres: 3 mm gives 35.1 s against 35.0 s measured, 2 mm gives 15.6 s and 4 mm gives 62.4 s.

Wall (mm)	Cooling (s)	Cycle (s)	Parts a day
2.0	15.6	43	1826
2.5	24.4	51	1540
3.0	35.1	62	1276
3.5	47.8	75	1056
4.0	62.4	89	880

The coefficient 3.9 moves with melt and mould temperature: 210 ℃ melt pulls it to 3.6, 70 ℃ mould pushes it to 4.3. Ejection waits for 78 ℃ or pins mark the base.

Circuits decide whether it is reachable: supply and return within 3 ℃, 12 L/min per circuit, 18 mm to the cavity.

4. Mould temperature and tonnage

Cooling runs 28.5 s at 40 ℃, 31.6 s at 50 ℃, 35.0 s at 60 ℃ and 41.0 s at 70 ℃, about 12% per 10 ℃, with finer surfaces on slow shots.

Case moulding cycle cooling stage on a large injection moulding machine, white hopper dryer on a steel platform, grey guarding, green drum and polypropylene sacks

Tonnage is projected area times cavity pressure: 134,400 mm² at 32 MPa needs 430 t, so a 530 t press leaves 20% margin.

Two cavities are not double output: 120 mm more travel adds 1.8 s of dry cycle, so the shot is 66 s and each part 33 s.

Oversizing costs too: a 1000 t press on one cavity turns 62 s into 64 s, and below 8000 parts a month one cavity on two shifts beats a tool costing 65% more.

5. Cycle time into daily output

Daily output is 3600 divided by cycle seconds, times hours and availability. At 62 s that is 58 shots an hour, 1276 in 22 h and 1085 parts a day at 85% availability.

Cycle (s)	Shots/h	Day, 22 h	Year, 6000 h	Vs 62 s
48	75	1650	450,000	+29%
55	65	1430	390,000	+12%
62	58	1276	348,000	Baseline
70	51	1122	306,000	−12%
85	42	924	252,000	−28%

From 24 h, deduct 1.2 h for material change, 0.5 h for inspection and 0.3 h for adjustment, leaving 22 h; three mould changes at 40 min each cut output by 9%.

One second saved is 6000 parts a year; quoted shots must carry the same case moulding cycle.

Conclusion

The case moulding cycle lives on the 62 s breakdown, not on the nameplate. Cooling at 35.0 s is 56.5% of the shot: a wall reduction from 3.5 mm to 3 mm saves 12 s, mould temperature from 70 ℃ to 60 ℃ saves 6 s, and circuit spread from 5 ℃ to 3 ℃ brings the coefficient from 4.1 to 3.9 for another 3 s. Those three moves push the cycle toward 45 s and lift output from 1276 to 1760 parts with no capital spend, while packing and removal yield only 4 s. Judge with the table: convert the cycle into shots per hour, multiply by 22 h, 85% availability and margin, and fund circuit or wall changes only when the gain exceeds twice the tool cost.

This article discusses container-side specifications and design implications only, and does not cover any handling, loading or use of the contents.