Pressure-Tight by Design, Proven by Test
Where leaks actually come from
Leak paths in die castings are almost always interconnected porosity: gas or shrinkage porosity that links from one surface to another under the wall. They cluster at thick sections, at the last place to fill, and around boss cores.
That is why leak test results are a casting-process signal, not just a pass/fail stamp - a sudden rise in leak rate usually points at a change in fill, metal quality or die condition.
The test methods, honestly compared
Air-under-water immersion is the shop standard: pressurise the part, watch for bubble chains. It is cheap, visual and locates the leak. Pressure decay measures the rate - better for small leak limits and for automated lines, but it does not say where the leak is.
For very small leak requirements, helium or tracer-gas methods exist but are rarely justified for aluminum housings; most specifications resolve to decay or immersion with a defined pressure, stabilization time and dwell.
Impregnation: a fix with rules
Resin impregnation seals micro-porosity and is a legitimate, widely used step - but it is a sealant, not a repair of the casting process. Impregnated parts should still meet the same leak test, and a part family needing impregnation from day one should trigger a look at the process, not just the resin line.
We treat leak testing as part of the process loop: test, log leak locations, feed them back to die and parameter adjustments, and only then accept impregnation as routine.
FAQ
What test pressure should a die-cast housing use?
The pressure that represents the worst service condition with a stated safety factor - set by the part specification, not by the test rig's convenience. Test pressure and dwell must match the drawing note.
Can impregnated parts fail leak test later?
Rarely if the resin and process are correct; possible if the porosity was too large for the resin, or if subsequent machining opens new paths. That is why machining sequence before impregnation is specified.
Does higher casting pressure always reduce leaks?
It helps compact the structure, but porosity has multiple causes - gas, shrinkage, fill pattern. Chasing leaks with pressure alone often just moves the porosity elsewhere in the part.
All figures above refer to standard product data sheets; final confirmation is subject to written quotation.