Closed die forging is distinct from open die forging, in which the die only comes into contact with part of the workpiece at a time. Initial costs for developing the processes and tooling for closed die forging can be quite high, but it is the most cost-effective forging method for high volume production, since recurring costs for each part are very low. In addition, closed die forging is capable of producing both symmetrical and non-symmetrical parts.
Materials that frequently undergo closed die forging processes include high alloy steel, naval brass, carbon steel, aluminum, alloy metals, stainless steel, copper, nickel, tool steel and titanium. Closed die forgings are used particularly often by industries such as electronics, aerospace, automotive, commercial, manufacturing, semiconductor, construction, hardware and food processing.
Closed die forging machines consist of two tooling dies: a stationary die (anvil) and a moving die (hammer). Both dies contain an impression of the desired part shape. The moving die presses down onto the stationary die and the metal workpiece and causes the metal to flow into every part of the die and take its shape.
A small amount of excess metal flows into a thin recess at the edges of the two dies called a flash gutter; the flash cools quickly and then serves as a plug keeping the rest of the metal in the die. Often, closed die forging requires that the workpiece be moved through a series of impression cavities, at first forming the rough shape, then proceeding until a finisher cavity turns out the final product.
The closed die forging process can be done with cold forging, hot forging or warm forging. In cold forging the metal is not directly heated, but formed using high pressure. In hot forging the metal is heated to high temperatures then formed. In warm forging the metal is heated to a range that is typically above room temperature, but below the re-crystallization temperature of the metal.
Closed die forging is the most common method of forging utilized in the industry to produce intricate and difficult geometries, offering countless possibilities for creating high strength components and tools with precision.