What is closed die forging and open die forging? What are the differences between them?

What is closed die forging and open die forging?

Closed Die Forging (Impression Die Forging):

Closed die forging is a precision forging process that involves the deformation of metal between two shaped dies, typically made of steel, with a pre-designed cavity or impression. The process begins with the heated workpiece, known as a billet, being placed between the upper and lower dies. When the dies are brought together, the metal is shaped and compressed within the cavity, forcing it to conform to the die's shape. The material flow is confined, and the excess material, called flash, is expelled from the sides. Closed die forging enables the production of complex, net-shaped parts with high dimensional accuracy and excellent material properties. This process is commonly used for manufacturing components such as automotive parts, aerospace components, and high-performance machinery parts.

Open Die Forging (Free Forging):

Open die forging, also known as free forging, is a forging process where the metal is shaped by the repeated application of localized compressive forces. In this method, the workpiece is not confined within a closed die cavity, allowing it to deform and flow under the applied force. The material is typically heated to improve its plasticity and reduce the risk of fracture. The forging process involves skilled blacksmiths or forging hammers applying precise blows to the workpiece to shape it gradually. Free forging is characterized by its flexibility and versatility, enabling the production of large and custom-shaped components. It is often used for creating items such as shafts, bars, rings, and hand tools.

What are the differences between Closed Die Forging and Open Die Forging?

Die Confinement: In closed die forging, the workpiece is enclosed within a die cavity, confining the material flow and shaping it precisely according to the die's shape. In contrast, open die forging does not employ a closed die cavity, allowing the material to deform more freely.

Complexity and Dimensional Accuracy: Closed die forging offers a higher degree of complexity and dimensional accuracy due to the precise die cavities, allowing the production of intricate and near-net-shaped parts. Open die forging, on the other hand, is more suited for simpler shapes and larger components where dimensional tolerances are relatively less critical.

Material Flow: Closed die forging controls the material flow by directing it within the die cavity, resulting in optimal grain structure and enhanced mechanical properties. In open die forging, material flow occurs more freely, leading to less control over the grain structure, but allowing for better utilization of the starting material.

Equipment and Tooling: Closed die forging requires specific tooling in the form of complex dies, designed to shape the workpiece precisely. Open die forging can be performed using less intricate equipment such as forging hammers or presses without the need for dedicated die cavities.

In summary, closed die forging involves the precise shaping of the workpiece within closed dies, enabling complex and accurate components, while open die forging allows for more freedom in material flow and is suitable for larger, simpler shapes. Both processes have their distinct advantages and applications within the forging industry.