How many samples does travel case production need before a decision?

Answer: Five. Three show consistency and two go to destructive work, one for the drop and one cut open to read wall distribution.

Can a 2.8 mm wall be released?

Answer: Only on non-structural panels, never at the corners or the long-side midpoint. Below 3.2 mm on a load-bearing face, the lid shifts 1 mm after a 1.2 m drop.

Is the water test really necessary?

Answer: Yes. 25 mm of water for 30 minutes is the cheapest sealing verdict available, and it matches a case carried on its side better than a spray test.

What closing force is right?

Answer: 120 to 180 N. Below 120 N the lid opens in transit; above 180 N older users cannot seat it and the teeth wear faster.

Samples Versus Batches: Judging Travel Case Production

Quick answer: The first three sample batches almost always pass; the fourth is where travel case production slips. Measure five numbers on the sample, run one full-case check, and judgement moves from feel to repeatable figures.

Five numbers to measure when samples arrive
Handle wobble and wheel housing torque
Wall thickness and the water test floor
Latch wear and closing force
Three signals before releasing a batch
FAQ

1. Five numbers to measure when samples arrive

Lay the sample flat before loading it. Five readings take twenty minutes and beat ten pages of test reports.

The cavity is quoted at 420 x 300 x 180 mm, so measure each axis in three places and keep the spread within 1.5 mm. A spread of 2.5 mm means uneven cooling in the tool, and every later batch inherits it. Wall thickness, read by ultrasonic gauge at four corners and the long-side midpoint, should hold 3.2 mm; 2.8 mm means rib material was moved into the flat panels.

Criterion	Pass line	Fail signal
Cavity spread	1.5 mm	2.5 mm diagonal gap, lid drags
Wall thickness	3.2 mm	Midpoint reads 2.8 mm
Handle wobble	2 mm	Audible slack at full extension
Closing force	120 to 180 N	Needs two hands to seat
Total weight	4.6 kg	Two samples differ by 300 g

Closing force is read at the long rim midpoint. Press right above a latch instead and the gauge drifts 40 N high.

Weight is waved through most often. A 300 g gap between two samples of one drawing means regrind, and every 10 percent of regrind saves 1.8 yuan while drop height falls from 1.2 m to 0.8 m.

2. Handle wobble and wheel housing torque

Pull the handle to full height and push each way once: 0.6 mm of clearance per side and 2 mm of total wobble is the usable ceiling.

Travel Case Production: close view of a grey case corner, a folding handle set in a moulded recess and two latch levers with grip ribs

Housings need screw count and torque. Six screws beat four under off-centre load, and 1.8 N·m is the ceiling on a plastic boss; at 2.4 N·m the boss cracks, and the crack opens on the first rough handling.

Tip the case 15 degrees. A wheel sitting 5 mm off the floor means a sprung base, one wheel carrying the load and tread gone in three months.

The combination is what hides: a loose handle, a soft housing and a sprung base each sit inside tolerance until two kilometres of pushing on finished goods.

3. Wall thickness and the water test floor

Stiffness comes from wall thickness; sealing comes from a flat closing face.

Hold tolerance at plus or minus 0.2 mm. Outside it, a shell whitens when folded 90 degrees at -18℃, and that white line fails the first drop.

Item	Condition	Pass line
Wall tolerance	4 corners and midpoint	Plus or minus 0.2 mm
Cold fold	-18℃, 90 degrees	No whitening
Water test	25 mm, 30 minutes	No seepage
Heat storage	55℃, 24 hours	Deflection 1.5 mm or less

The water test is blunt: fill to 25 mm, wait 30 minutes, then read the four corners and the latch seats. Seepage at a corner points to the mould radius; seepage at a latch seat points to gasket squeeze.

Depth and time belong together, since 10 mm or 5 minutes hides corner leaks. Nine in ten sealing complaints in travel case production land on the corners, where the shell is a single layer.

4. Latch wear and closing force

Travel Case Production: a navy hard case standing in an aircraft aisle beside grey seats with white headrest covers, scratches on the corner

A new case closes at 180 N. After 200 cycles it reads 155 N; 25 N of loss is normal, while 45 N means rounded teeth and a gasket that no longer seats.

Two latches hold better for about 4 yuan. Under 420 mm one is enough, past 520 mm use two, and parcel sorting gets two at any length.

The 1.2 m drop runs once on eight corners and six faces. Heat matters as much: a case stored at 55℃ for 24 hours softens, and the unit beneath takes a 3 mm dent that stops the lid seating the next morning.

5. Three signals before releasing a batch

A good sample does not promise a good batch.

Signal	Pass line	Usual cause
Colour	Difference 2.0 or less	Separate colour lots
Wheel wear	No side-to-side gap	Axle not parallel
Handle stiction	No catching in 5 cycles	Burrs in the tube

Colour is read with five cases side by side at a window, because a difference above 2.0 shows to the eye. Wheel wear is read after a 20 m push: a warmer side means an axle out of parallel, and one airport trip removes 0.5 mm.

Keep one of the five sampled cases for the drop and use the rest for cycling and water tests. Then write the release date into the contract: first delivery 15 days after approval, five units pulled for the routine, a failed pull sending the batch back. Re-run it whenever the resin grade changes, because travel case production drifts with the material.

Conclusion

The figures are few: a 1.5 mm cavity spread, a 3.2 mm wall floor and a 180 N force ceiling. Hold those three and batch four looks like batch one; write them into the acceptance sheet and travel case production needs no retraining when the supplier changes.

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.