Not All Pores Are Created Equal
Where pores come from
Gas porosity forms when air or volatiles are trapped by fast filling; it shows as smooth, rounded voids, often near the surface. Shrinkage porosity forms as metal solidifies and feeds poorly in hot spots; it appears as irregular, internal sponge-like voids.
Location matters as much as size. Pores in a machining stock zone or a non-structural wall rarely matter; the same pores under a sealing face or a load path do.
Choosing an inspection level
X-ray earns its cost on safety-critical or pressure-tight features, where a defined inspection zone and class per drawing zone is the standard approach. For general cosmetic or bracket parts, sampling with section cuts often covers the risk at a fraction of the cost.
Write acceptance as zones plus classes: which areas are critical, which pore class is acceptable there, and what happens on a rejected lot.
FAQ
Can porosity be eliminated completely?
No. Process tuning reduces size and frequency, but die castings always contain some voids. Engineering means locating and limiting them.
Does machining expose porosity problems?
Yes. Machining removes the dense skin and can open internal pores on sealing faces. Plan machining allowances with porosity risk in mind.
Is X-ray required for all castings?
No. It is justified where internal soundness affects safety or pressure integrity; otherwise sampling and leak tests are more economical.
All figures above refer to standard product data sheets; final confirmation is subject to written quotation.