Types of Forging
Manufacturers employ various kinds of forging processes, including:
In the drop forging method, a hammer impacts the workpiece to deform it according to the die shape. There are two basic categories of drop forging: open die and closed die drop forging.
- Open die drop forging: Also known as smith forging, open die forging involves workpiece deformation against a stationary anvil. In this forging method, the die or multiple dies do not enclose the workpiece.
- Closed die drop forging: Also known as impression die forging, closed die drop forging involves the use of a die that encloses the metal material. The hammer die is generally also shaped according to the desired configuration of the final product. During closed die forging operations, the hammered metal material flows into the die cavities and assumes the shape of the enclosure once cooled.
Press forging operations involve the application of steady pressure or force (measured in seconds) against the metal workpiece to shape it according to customer specifications.
Upset forging is one of the most widely used forging methods. The method applies compressive forces along the length of the workpiece, increasing the material’s diameter. It is used to manufacture items such as engine valves, bolts, screws, and fasteners.
Automatic Hot Forging
Automatic hot forging operations feed steel bars or other metal parts into one end of the forging machine. The parts are rapidly superheated and plastically deformed according to customer specifications, and emerge as hot forged products. This method offers a high output rate and is suitable for processing inexpensive materials.
Roll forging increases the length and reduces the thicknesses of bars and other metal workpieces. In roll forging operations, a heated workpiece passes between two grooved rolls. As it rolls through the machinery, the workpiece is progressively flattened and shaped. This method generally imparts a favorable grain structure to the metal material.
Net-Shape and Near-Net-Shape Forging
Also known as precision forging, net-shape and near-net-shape forging processes produce parts that are equivalent to, or very nearly equivalent to, the final desired configuration without requiring extensive finishing operations. This method reduces the amount of material waste and the total cost of production.
Cold forging is a forging method that takes place at room temperature with the workpiece gradually undergoing deformation until it assumes the desired shape and size. Near-net-shape forged parts are generally produced in such operations. A commonly cold forged material is aluminum.
Induction forging is characterized by its use of an induction heater as the primary heat source. Manufacturers use many of the above-mentioned forging processes in combination with induction forging.
Multidirectional forging forms the workpiece in multiple directions in a single stage. In this forging method, wedges distribute and redirect the force of the forging press to create the desired part.
In isothermal forging operations, both the workpiece and the machine die are heated to the same temperature. To prevent oxidation, isothermal forging nearly always process superalloys in a vacuum or another controlled environment.