Electronics enclosure in FDM: how far can watertightness go?

Watertight off the machine, not necessarily over time

A printed part can be watertight straight off the machine, with enough walls and enough infill. The problem is that it rarely stays so: the micro-interfaces between layers end up letting through under thermal cycling and pressure.

For a sensor enclosure under a canopy, or a board in a damp room, that is of no consequence: the enclosure protects from splashes and dust, which is what it is asked to do. For a pressurised circuit it is a deal-breaker, and we do not take those orders. We claim no ingress protection rating: an FDM part is not an injection-moulded enclosure, and we would rather say so beforehand.

What makes the difference: walls, orientation, seal

An FDM part is a stack of layers welded together: strong in the plane of the layers, markedly less so perpendicular to them. So we orient the enclosure according to the load it will take, which means you have to tell us which: an enclosure screwed to a wall does not work like one that gets dropped.

The seal between body and lid is handled with the material made for it: TPU, soft as a rubber, which we print in three hardnesses (95A, 90A, 85A). Seals, dampers, impact protection are its territory. And when an enclosure exceeds 350 × 350 × 350 mm, it is split into assembled sub-parts, with the joints placed where they show least.

The material: four cases, four answers

PETG for everyday use: it is the material of most of our functional parts, it takes humidity and steam, and it bends before breaking where PLA snaps. PLA stays indoors, away from any heat source: it deforms from 55 °C, never in a car, never near a radiator.

ASA for whatever lives outdoors: it is the ABS that does not yellow, it takes salt and UV, and holds 90 °C. Outdoor signage, garden accessories, exposed automotive parts: outdoors, there is no debate.

PC-FR for applications under a standard: flame-rated polycarbonate, UL94 V-0, with the manufacturer's datasheet supplied with the order. For the rest we pass on datasheets on request, and we do not issue part certifications: that is not our trade.

PA6-CF for permanent stress: stiff, light, very low creep, the material for parts that stay under load without deforming over time. Three times the price of PETG, only worth it if the load demands it, and black only.

The dimensions that matter

We hold ±0.3 mm as standard, and ±0.15 mm on dimensions identified in advance, negotiated one by one. On an enclosure these are rarely the outer faces: they are the lid fit, the board mounting centres and the cable or connector openings. Tell us which, and we compensate material shrinkage on those.

Shrinkage explains a good part of the deviation: plastic contracts as it cools. That is why, beyond 50 parts, a sample is approved in writing before the run: you mount the board, you close the lid, and production starts after your go-ahead.

What we refuse, and why

Pressurised circuits, as said. Safety parts too: an element that injures when it breaks has a brutal, hard-to-predict failure mode in FDM, and no material fixes that. And we promise no post-processing: no sanding, no primer, no paint — layer lines remain visible, discreet at 0.1 mm, marked at 0.3 mm.

This is not excessive caution: a supplier who says yes to everything will cost you time and money. A well-designed FDM enclosure, in the right material and with the right dimensions identified, is a part that serves for years. An enclosure sold as watertight for life is a return in six months.

How to order an enclosure

You have the file: STL, OBJ or 3MF for direct printing, STEP if rework is needed. The instant quote analyses it in your browser and shows price and lead time. You have no file: a dimensioned 2D drawing, a photo with a ruler or the board itself is enough, we model it, and the CAD files created belong to you once paid.

For a run, allow 5 to 8 working days for 50 to 250 parts, with the sample approved first; 2 to 3 working days for a prototype. The lead time written on the quotation is firm.

On the same subject

• Enclosures, boards and batteries
• PETG datasheet
• PC-FR datasheet
• What a 3D-printed part will never do

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