Casting
High pressure die casting: what goes wrong and where to inspect
Thin walled aluminium housings, brackets and covers in high volume. Very productive, very sensitive to process parameters, and prone to porosity that leaks or appears after machining.
01How the process works
Molten aluminium or zinc is shot into a hardened steel die at high velocity and held under intensification pressure while it solidifies. Cycle times are measured in seconds, and parts are trimmed, deburred, sometimes impregnated, and machined.
Because air and die lubricant are trapped during the fast fill, HPDC parts almost always contain some porosity. The question is where. Critical zones (sealing faces, threads, bearing seats) must be defined on the drawing with porosity limits, and process parameters must be monitored shot by shot.
- Die preparation. Die heated and sprayed with release agent.
- Shot. Metal injected at high velocity in milliseconds.
- Intensification. Pressure held during solidification.
- Ejection and trim. Part ejected, gates and overflows trimmed.
- Post processing. Deburring, impregnation, machining, leak test.
02What typically goes wrong
| Defect | Typical cause | How it is found |
|---|---|---|
| Gas and shrinkage porosity | Trapped air, lubricant, hot spots | X-ray, sectioning, leak test |
| Cold flow and laps | Low die or metal temperature | Visual, PT |
| Blisters after heat treatment | Entrapped gas expanding | Visual after T5/T6 |
| Soldering and drag marks | Die damage, poor release | Visual |
| Leakage | Connected porosity in sealing zones | Pressure decay or helium leak test |
| Dimensional distortion | Ejection, trimming, die wear | CMM, fixtures |
03Where an inspector should look
Before production
- Porosity classes for critical zones on the drawing
- Die and trim tool approval
- Alloy grade and degassing practice
During production
- Shot curves: velocity, intensification, cycle
- Die temperature
- Melt hydrogen or density index
After production
- X-ray sampling of critical zones
- Leak test results
- Dimensional and machined surface checks
04Standards and references
EN 1706 (aluminium casting alloys), VDG P 201 and P 202 (porosity in castings), ASTM E505 reference radiographs, customer leak rate specifications.
Standards are named for orientation. The applicable edition and acceptance criteria are those in your contract and specification.