Why does 20 mm of height touch three parts of the tool?

Answer: Height changes cavity depth, slide travel and the circuit distance — 22 mm becomes 30 mm, past the 25 mm limit, so 2 circuits are added.

Do two dividers affect airtightness?

Answer: Not the groove, but the lid loads. The walls take lid support from 2 points to 5, so the 1 m, 30 min immersion test is repeated.

Is a 3.5 mm wall better than six ribs?

Answer: Ribs — 0.09 kg and 2 s of cycle for 30% more stiffness, against 0.31 kg and 17 s for 22%. Above 60 kg the wall wins.

How is an extra 30 kg of rating verified?

Answer: Stack 3 layers at 150 kg for 72 h, hold set under 2 mm, then run 10 drops at 0.9 m. Only then does 150 kg enter the specification.

Which case structure custom changes need a new tool?

Answer: More than 30 mm on one outer side, a moved latch or hinge, over 25 mm of depth change, or a third divider — all four re-arrange slides, so 15% no longer applies.

Case Structure Custom: Structural Customisation

Quick answer: Three cheap case structure custom moves — 20 mm taller, 15 mm wider, two dividers — cost 15% of the original tool and lift the rating to 150 kg.

Where a case structure custom starts
20 mm taller: height, cavity and stacking
15 mm wider and two dividers
3.5 mm walls versus six ribs
Three retests after a structural change
FAQ

1. Where a case structure custom starts

The request was 20 mm taller; the quotation came back with slide travel, cooling circuits and ejection. On a 500 × 365 × 200 mm case with a 450 × 320 × 170 mm cavity, those 20 mm deepen the cavity to 190 mm and lengthen the side core, so the two slides no longer fit.

A case structure custom has three entry points: height, width and internal division. Height moves cavity depth and slide travel, width moves the parting line and circuit pitch, dividers move core inserts.

Change	Outer size	Cavity	Tool work
20 mm taller	200→220 mm	170→190 mm	Cavity +20 mm, slide travel +20 mm
15 mm wider	365→380 mm	320→335 mm	Parting line out 15 mm, 2 circuits moved
Two dividers	Unchanged	3 cells, 103 mm clear	2 core inserts, pins 12→16
Wall 3.0→3.5 mm	Unchanged	1 mm less per side	Cavity relieved, clamp +15%

Height and width each disturb one slide and two circuits; dividers touch only inserts. All three at once are charged at 15% of the original tool; beyond that the tool is rebuilt, as a rework runs 30,000 shots short.

2. 20 mm taller: height, cavity and stacking

Height is the only change that alters the envelope. Outer height goes 200→220 mm and cavity height 170→190 mm while the gasket groove stays put, so sealing looks unaffected — but the lid deflects 0.6 mm at 0.03 MPa instead of 0.4 mm, and gasket compression falls with it.

Case structure custom trial shell in olive green, open on a rusted steel bench, plain lid showing the gasket groove and divided grey foam below

Circuits fail first: the deepest point sits 22 mm from the cavity face, becomes 30 mm, past the usual 25 mm limit, and the base sinks. Two more angled circuits are the only fix.

Slide travel forces a new cylinder: 50 mm becomes 70 mm and the shot moves from 55 s to 57 s. Stacking is worse — three warehouse layers put 66 kg on the bottom case, eight truck layers put 176 kg on it, past the 150 kg rating, so the load stops at 6 layers and 11% of load factor goes.

Half the cost of those 20 mm lands on the load factor, not on the tool.

3. 15 mm wider and two dividers

Width moves the parting line. Outer width goes 365→380 mm and cavity width 320→335 mm, so with the same base the side clearance falls from 18 mm to 10.5 mm — too little for lifting, and the base goes up one size.

Circuits are respaced: 65 mm pitch becomes 72 mm, and the freed 15 mm leaves a 40 mm band with no cooling, so 2 circuits go back at 68 mm pitch. Two dividers leave the outside alone: 450 × 320 mm splits into 3 cells of 103 mm clear width.

A wall 4 mm thick and 170 mm tall has an aspect ratio of 42 and distorts on ejection: it needs R1.5 at the root, 1° of draft and a 0.02 mm vent groove each side. Pins go from 12 to 16, so the ejector plate is new and the stroke grows from 45 mm to 50 mm.

Two dividers are the cheapest option and the easiest to ruin: a wall that leans 0.3 mm gives cells of 102.4 mm and 103.6 mm.

4. 3.5 mm walls versus six ribs

Reaching 150 kg from 120 kg has two routes. A 3.0→3.5 mm wall raises unit weight from 4.2 kg to 4.51 kg, lengthens cooling by 36% and moves the shot from 55 s to 72 s; the bill arrives in cycle time and weight.

Case structure custom comparison of three open instrument cases on a wood-grain shelf, grey and black shells with moulded recesses holding meters and tools

Six ribs take the other route: 2.0 mm thick, 18 mm tall, 65 mm pitch, R1.5 at the root, across the base and long sides. They add 0.09 kg, raise bending stiffness 30% and cost 2 s of cycle.

Option	Added weight	Stiffness	Cycle	Tool work
Wall 3.0→3.5 mm	+0.31 kg	+22%	55→72 s	Cavity relieved, clamp +15%
Six ribs	+0.09 kg	+30%	55→57 s	6 grooves in the cavity
Both	+0.38 kg	+41%	55→74 s	Relief plus grooves

Ribs have one trap: a 2.0 mm rib on a 3.0 mm wall is a 0.67 ratio, and above 0.6 it leaves a 0.05 mm hollow on the visible face. At 1.8 mm the hollow drops to 0.02 mm.

Three conditions decide it. If the rating needs 30 kg more and the case sits in a stack, ribs are enough — 6 grooves, no change to parting line or circuits, the lightest case structure custom change on offer. Above 60 kg, or below −20 ℃, ribs fail: a rib root is a stress raiser in the cold, the wall must grow first, then the latch boss needs 10 mm of engagement instead of 8 mm. Third, a 3.5 mm wall needs 15% more clamp force, so the 530 t press is rechecked.

5. Three retests after a structural change

Any structural change voids the old report. The minimum is three retests: airtightness, drop and stacking.

Airtightness is immersion: 1 m of water, 30 min, no continuous stream of bubbles. It is repeated although the groove did not move, because compression fell from 30% to 26% as the lid softened.

Drop follows 0.9 m, 6 faces, 3 edges and 1 corner, 10 drops, passing if the case still latches 5 times without a crack. With 20 mm more height the centre of gravity rises 8 mm and impact moves to mid-edge.

Stacking is 3 layers, 150 kg on the bottom case, 72 h, no more than 2 mm of set after 1 h; lid interference at a 190 mm cavity must stay inside 0.5 mm.

A divider-only project can skip the drop test, since size and weight are unchanged. Airtightness and stacking cannot: the walls move the lid supports and stacking pressure rises.

Conclusion

Work the case structure custom decision backwards: fix the load and rating, derive the structure, look at the tool last. Thirty kilograms short, and six ribs settle it for 2 s of cycle. Cavity height short, and 20 mm costs 2 more circuits plus 11% of load factor. Two dividers only when the cells are needed. Do all three and the tool change sits at 15% of the original with 18 days extra, after which airtightness, drop and stacking must all be re-run. If 15% and 18 days buy back the missing rating and cavity, rework the tool; if not, build for the new structure.

Change	Tool work	Lead time	Unit cost	When it pays
Two dividers	Lightest, core inserts only	+6 days	+8%	Cells needed, outside fixed
20 mm taller	Medium, 2 circuits and slide travel	+8 days	+6%	Cavity 20 mm short
15 mm wider	Heaviest, may need a new base	+12 days	+7%	Part wider than the cavity
All three	15% of the original tool	+18 days	+19%	New product, one round of changes

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