How to Reduce Porosity in Die Casting

Porosity is usually grouped into gas porosity and shrinkage porosity. Gas porosity comes from air or gas trapped during filling; shrinkage porosity comes from thick sections cooling last without enough feed metal.

The two have different causes and different fixes. Adding pressure does not solve shrinkage in an isolated thick section, and redesigning a wall does not remove gas trapped by poor venting.

• Gas porosity: trapped air or gas
• Shrinkage porosity: thick sections cooling last
• Different causes need different fixes
• Confirm the type before changing the process

Uniform wall thickness is the most effective design tool. Gradual transitions, ribs instead of thick bosses and generous radii all help the part cool at a similar rate.

Where a thick section is unavoidable, it should be reviewed for local cooling, feed paths or a design change. Isolated mass is the most common source of shrinkage in a die casting.

• Keep walls as uniform as practical
• Replace thick bosses with ribbed pads
• Use radii and gradual transitions
• Review isolated mass during DFM

Gate position, runner design, overflows and venting control how metal fills and where gas can escape. Vacuum assistance can further reduce trapped gas on demanding parts.

Cooling layout, shot profile, metal temperature and die temperature all influence solidification. These variables are set during tooling trials and then controlled in production.

• Gate and runner design control fill
• Overflows and vents release trapped gas
• Cooling layout controls solidification
• Process windows are set at T1 and locked in production

Porosity requirements should be defined against the function of the part. A cosmetic cover and a pressure-tight housing cannot share the same acceptance rule.

Inspection can include visual checks, sectioning, X-ray and pressure or leak testing. The agreed method, sampling and acceptance level belong in the inspection plan and the quotation.

• Define acceptance by function
• Use visual, section, X-ray or leak testing as agreed
• Record sampling and acceptance levels
• Confirm the method before production release