What are the differences between forging, stamping and casting?

1. Difference between Forging and Casting

(1) Conceptual Difference

Casting: Turning shapeless molten metal into a shaped solid.

Forging: Transforming one solid shape into another solid shape.

Casting is like working with wax: you melt wax (scrap steel or pig iron), pour it into a mold, and after it solidifies you get a part of a certain shape (solid → liquid → solid).

Forging is like making flatbread: you take a lump of dough, heat and press it into a different shape. It’s basically plastic deformation of a solid at high temperature (solid → solid).

In professional terms, casting is the process of pouring molten metal into a mold to obtain a casting. The emphasis is on melting and pouring process control.
Forging is plastic forming in the solid state (hot or cold), including processes such as extrusion, drawing, upsetting and punching.

(2) Forming Method Difference

Casting: One-step forming by filling a mold cavity with molten metal that then cools. Castings tend to develop internal porosity.

Forging: Usually formed gradually under compressive force at high temperature, which can refine the grain structure.

2. Difference between Open-Die Forging and Die Forging

Open-die forging: Heated metal billet is placed between upper and lower anvils of forging equipment and deformed by impact or pressure. Because shapes are simple and operation is flexible, it suits single pieces, small batches and heavy forgings. It is divided into manual and machine open-die forging. Manual open-die forging has low efficiency and high labor intensity, used only for repair or simple small parts. Today machine open-die forging is the main method, especially important in heavy machinery manufacturing.

Die forging: Heated billet is placed in a die mounted on forging equipment and forged to shape. Die forging can be performed on many kinds of equipment. In industry, hammer die forging usually uses steam-air hammers (5 kN–300 kN / 0.5–30 t). On presses, hot die forging presses of 25 000 kN–63 000 kN are common.
Die structures include single-cavity and multi-cavity dies. For example, a single-cavity finishing die uses dovetails and wedges to fix the die and prevent side movement, and keys/keyways to position front-to-back. Preforms are often made under an air hammer, then final forging is done in the finishing die with several blows, then flash is trimmed off.

3. Differences among Casting, Forging, Stamping and Die-Casting

(1) Process Differences

Casting: Melt raw material and let it solidify naturally in a mold.

Forging: Heat raw material to a certain temperature and hammer/press it to shape.

Stamping: Form a part by pressing sheet or strip stock with appropriate stamping dies (usually at room temperature).

Die-casting: Based on casting but molten metal is injected under pressure into the mold cavity to achieve higher density and more precise shapes.

Casting: molten metal fills the mold cavity and cools; internal porosity is common.
Forging: compressive forming at high temperature, refining the grain structure.
Stamping is suitable for relatively uniform-thickness parts formed from sheet material.
Parts with large thickness differences or complex shapes, especially heat-sensitive, are better produced by die-casting.

(2) Additional Notes

Casting can be high-pressure or low-pressure: the difference lies in injection pressure, metal temperature and equipment used.

Forging is not literally a type of casting; instead it shapes metal at lower temperature, sometimes semi-solid, into finished parts.

Stamping is a room-temperature process using presses to form semi-finished into finished products.

Die-casting is a high-temperature casting method for complex, difficult parts, using a die-casting machine to inject molten metal into a mold, cool it, then open the mold to remove the product.