Forging and forming
Closed die forging: what goes wrong and where to inspect
Impression die forging produces strong parts with controlled grain flow in high volumes: flanges, connecting rods, crankshafts, gear blanks and hand tools.
01How the process works
A heated billet is pressed or hammered in one or more die impressions until it fills the cavity, with excess metal escaping as flash, which is then trimmed. Parts are heat treated, shot blasted and inspected.
Typical problems are laps where metal folds over, underfill of corners, mismatch between die halves, decarburisation and cracks. Grain flow, revealed by macro etching, confirms that the forging process gives the intended strength.
- Billet cutting. Bar cut to weight and identified.
- Heating. Induction or furnace heating.
- Forging. Blocker and finisher impressions.
- Trimming. Flash removed; piercing if required.
- Heat treatment and finishing. Normalise or quench and temper, shot blast, inspect.
02What typically goes wrong
| Defect | Typical cause | How it is found |
|---|---|---|
| Laps and folds | Die design, wrong billet volume | MT, visual |
| Underfill | Low temperature, insufficient volume | Visual, dimensional |
| Die mismatch | Die setting, wear | Dimensional check |
| Decarburisation | Heating atmosphere | Hardness, metallography |
| Quench cracks | Quench severity, design | MT |
| Burnt material | Overheating | Metallography |
03Where an inspector should look
Before production
- Die and billet weight approval
- Grain flow requirements
- Heat treatment specification
During production
- Billet temperature
- Die temperature and lubrication
- Heat treatment charts
After production
- MT on critical zones
- Hardness and mechanical tests
- Macro etch for grain flow on samples
04Standards and references
EN 10243 (forging tolerances), EN 10222 (forgings for pressure purposes), ASTM A105 for flanges, EN 10228 (NDT of forgings).
Standards are named for orientation. The applicable edition and acceptance criteria are those in your contract and specification.