Why can't a Case Production Line be planned from nameplate tonnage?

Tonnage only says how hard the clamp holds. Output depends on cycle, cavities, OEE and changeover; a thicker case costs 40% of the day.

Is a two-cavity mold always better than two single molds?

No. It saves a machine and an operator, but costs more, changes slower, and one bad cavity stops both. Under 12000 pieces a month, two molds stay flexible.

How short can cooling go?

Until ejection distorts. A 3.5 mm wall settles at 45 to 47 s; five seconds less pushes warp from 0.8 mm to 1.5 mm.

Mid-range for case molding, where 80 to 88% is common. Below 78%, read the changeover log; above 90%, trial runs are likely excluded.

Why cost the liner stage separately?

Liner work is paced independently of the press. At 150 s a case, one operator on two shifts makes 360, under molding capacity.

Case Production Line Capacity: Machines, Cavities, Changeover

Quick answer: Capacity on a Case Production Line is set in three steps: clamping force picks the machine, cavity count sets output, changeover and OEE take it down. A 500 × 350 mm case needs 665 t, so an 800 t press; at 90 s, 84.8% OEE and two 90-minute changeovers, it yields 407 cases a day.

The Capacity Formula for a Case Production Line
Matching Tonnage to Projected Area
How Many Cavities per Mold
Breaking the Cycle into Seconds
OEE and Changeover Losses
FAQ

1. The Capacity Formula for a Case Production Line

Capacity is a product of factors. A Case Production Line produces:

Daily output = ((shift seconds − breaks − changeovers × changeover minutes × 60) ÷ cycle) × cavities × OEE

An 800 t machine on two shifts has 57600 seconds; breaks take 3600, two 90-minute changeovers 10800, leaving 43200. That is 480 shots at 90 s, or 407 cases from one cavity at 84.8% OEE — the number to plan with.

2. Matching Tonnage to Projected Area

Clamping force is F = A × P ÷ 1000, A the projected area in cm² and P the cavity pressure. A 500 × 350 mm case projects 1750 cm²; at 380 kg/cm² that is 665 t, so a 15% margin lands on 800 t.

Case (mm)	Area (cm²)	Pressure	Force	Machine
400 × 300	1200	380	456 t	530 t
500 × 350	1750	380	665 t	800 t
600 × 400	2400	350	840 t	1000 t
700 × 500	3500	350	1225 t	1600 t

Pressure runs 420 to 480 for thin long-flow walls and 300 to 340 for thick; fifty kilos of assumption moves the machine up a size. Shot weight matters too: 5.8 kg for two cavities.

3. How Many Cavities per Mold

Doubling cavities doubles clamping force and pushes the machine up a size; hanging slows from 60 minutes to over 90. Under 1.5 times monthly demand, add cavities; above 2.5, add machines, so one stoppage does not idle the Case Production Line.

Option	Machine	Cavities	Cycle	Output	Mold
Large case	800 t	1	90 s	407	24k
Small case	1000 t	2	105 s	697	38k
Small case	530 t	1	78 s	470	18k
Oversize	1600 t	1	130 s	282	52k

Two cavities win per case; two presses win on volume.

4. Breaking the Cycle into Seconds

Four segments: injection 9 s, packing 22 s, cooling 47 s, clamp and ejection 12 s. Cooling scales with the square of wall thickness: 30 s at 2.5 mm, 47 at 3.5, 58 at 4.0, each extra 0.5 mm costing a tenth of the day. Packing ends at gate freeze, near 22 s.

One second off the cycle is 1200 cases over 300 days. Mold temperature is the lever: 50 °C to 40 °C cuts cooling 8%, though below 35 °C weld lines show.

5. OEE and Changeover Losses

OEE multiplies availability 94%, performance 96% and yield 94% into 84.8%; yield on a Case Production Line is lost to sink marks, warp and weld lines.

Changeovers a day	Time each	Lost	Share
1	60 min	3600 s	6.7%
2	90 min	10800 s	20.0%
3	90 min	16200 s	30.0%
4	120 min	28800 s	53.3%

A 90-minute changeover is 25 minutes stripping, 30 hanging, 20 for lines, 15 for approval. Quick couplers, hydraulic clamps and off-machine preheating halve it, recovering 60 cases a day.

The liner is the stage most sums miss: at 150 s a case, one operator on two shifts makes 360 against 407, so the Case Production Line is capped at the bench. At 20000 cases a month, two 800 t presses give 20350, steadier than one double-cavity mold.

Conclusion

Estimate a Case Production Line in five moves: tonnage, cavities, cycle, OEE, changeover. One 800 t press with a single cavity gives 407 cases a day, a 1000 t double-cavity mold 697, two single presses 814. Put the liner bench in the table and take the smallest number, so the Case Production Line shows its bottleneck before the order does.

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.