Metal parts are made mainly in two ways: casting and forging. The names sound similar in Japanese, but the processes — and the properties of the resulting parts — are very different. This article explains the differences and how to choose between them.
Casting: melting metal and pouring it into a mold
Casting melts metal and pours it into a mold, where it cools and solidifies into shape. Its strengths are complex and hollow geometries, large parts, and low unit cost in volume production — engine blocks and manhole covers are familiar examples.
Because the metal solidifies from a molten state, however, small internal voids (porosity) and uneven microstructure can occur, which calls for care in applications subject to strong impacts or repeated loads.
Forging: heating and hammering the metal
Forging shapes a heated billet of metal by applying great force with dies. Just as Japanese swordsmiths hammered steel to strengthen it, forging compacts the internal structure of the metal, and the "grain flow" runs continuously along the shape of the part.
Thanks to this grain flow, forged parts offer superior strength and toughness compared with cast parts of the same material, and withstand impact and repeated loads well. Hot forging — shaping steel at high temperature with presses and hammers — is the most widely used forging method, and it is what we do.
| Casting | Forging | |
|---|---|---|
| Process | Melt and pour into a mold | Heat and shape with dies under force |
| Strength & toughness | Internal voids can occur | Dense structure with grain flow — superior strength and toughness |
| Design freedom | Good for complex and hollow shapes | Less suited to very complex shapes |
| Typical parts | Complex, large, or general parts in volume | Heavily loaded critical and safety parts |
| Cost tendency | Tooling cost relatively low | Dies required (unit cost falls with volume) |
How to choose: let the part’s job decide
Neither process is universally better — the right choice depends on what the part must do. Casting suits parts where complex geometry and efficiency matter most; forging suits heavily loaded parts whose failure could endanger people or stop machinery.
This is exactly why forged parts are used for critical components such as automotive engine and suspension parts and marine fuel-injection parts.
Converting a cast part to a forged part
We often hear: "This part is currently cast — can we switch it to forging for more strength?" Because forging raises strength, the converted part can sometimes be made smaller and lighter.
Since we handle everything from die design and production to forging and inspection in-house, we can propose a forging-friendly shape based on your casting drawing. Prototype and small-lot runs are welcome — feel free to send us a drawing.