Vacuum Die Casting and Porosity Control
Two kinds of porosity, two different fixes
Porosity in a die casting generally comes from one of two sources, and each is corrected in a different way. Gas porosity is air trapped in the cavity or drawn in behind the metal front during injection, and it appears as rounded pores scattered through the section. Shrinkage porosity comes from metal contracting as it solidifies where the section is thick and feeding is poor, so it appears in the last places to freeze. Confusing the two leads programmes to specify the wrong remedy and then wonder why the expensive fix changed nothing measurable.
Why it matters depends entirely on the part. A bracket with scattered internal pores may be perfectly serviceable for its whole life. A housing that has to hold pressure, or a plate machined across a sealing face, is a different matter altogether: machining opens pores that were closed below the surface, and plating solution trapped in them later blisters the coating. That is why porosity limits belong on the drawing alongside dimensional tolerances, not in a separate specification document that nobody opens at the machine.
What vacuum assistance actually changes
In vacuum die casting the cavity is evacuated before injection, so there is far less air available to compress and entrap ahead of the metal front. We run dedicated vacuum die casting lines alongside conventional high-pressure casting on automated cells, choosing the route during DFM rather than defaulting to either one. The practical gains are fewer gas pores in thicker sections, better fill of long thin ribs, improved weldability, and more consistent mechanical properties from one shot to the next.
Vacuum does not solve everything. It does nothing for shrinkage porosity, which is governed by section design, gating strategy and the thermal balance of the tool - all settled during mold-flow simulation and tooling design before any steel is cut. Where machining will open a sealing face, we also review whether the specified stock removal exposes material better left as-cast. Selecting the right route part by part is usually cheaper than blanket-specifying vacuum across an entire assembly of components with very different requirements.
Specifying and verifying gas tightness
Our connector components are produced with a gas-tightness test, and EV motor controller housings are specified at IP67. Both ratings depend on the assembled system rather than on the bare casting: casting soundness, machined sealing faces, gasket compression and fastener spacing each contribute to the result. Treating an ingress rating as a property of the casting alone is a common source of disagreement during qualification, so we settle which element each party owns during the DFM stage, before tooling is committed.
Verification then runs through our QC laboratory - CMM inspection, salt-spray testing and full batch reports - supported by ISO 9001, IATF 16949, RoHS and REACH documentation, with inspection reports and PPAP documents available for automotive programmes. Send the drawing in STEP, IGES or DXF stating the leakage limit, the intended test method and the test pressure you need the part to survive. We will quote the casting route and the matching inspection plan together, and reply with costing within 24 hours.
FAQ
When is vacuum die casting worth specifying?
It pays off where the geometry traps gas in thick sections or long thin ribs, where machining will open a sealing face, or where the part has to survive a leak test. For simple brackets with generous sections, conventional high-pressure casting usually gives an equivalent result at lower cost.
Can you leak test production parts?
Yes - our connector components are produced with gas-tightness testing, and we can discuss the method appropriate to your part. Please state the required test pressure and acceptance criterion on the drawing so the inspection plan and the quotation both cover it from the start.
Does vacuum eliminate porosity completely?
It substantially reduces gas porosity but does not address shrinkage porosity, which depends on section design and thermal balance. Both are handled during DFM and mold-flow simulation, and where it matters the drawing should carry porosity limits alongside its dimensional tolerances.
All figures above refer to standard product data sheets; final confirmation is subject to written quotation.