extrusion

Extrusion is a manufacturing process in which material is forced through a shaped opening, or die, to produce objects with a continuous cross-section. It applies to metals, polymers, ceramics, and composites and is used to form long profiles such as rods, tubes, channels, and complex hollow shapes.

Most metal extrusion begins with a billet placed in a container and heated for hot extrusion or kept cool for cold extrusion. A ram or screw then pushes the material through a die, forcing it to flow and fill the die cavities. The extrudate emerges as a continuous length with the die’s cross-section and is cut to size and often subjected to downstream processing such as heat treatment, aging, or drawing.

Direct extrusion uses a ram to push material through the die; indirect extrusion attaches the die to the ram, reducing friction and requiring less force. Hot extrusion is performed above the material’s recrystallization temperature; cold extrusion uses near-room temperature for higher strength and precision. Plastic extrusion usually involves a screw mechanism that pushes molten plastic through dies to make pipes, sheets, films, and profiles; it is also used for foams and some food products.

Materials include aluminum, magnesium, copper, steel, and other metals; polymers such as polyethylene, PVC, and nylon; ceramics and composites can also be extruded in some forms. The extrusion ratio, the ratio of the billet cross-section area to the die opening area, is a key design parameter and influences required force and product properties.

Applications cover structural and architectural profiles (windows, doorframes), pipes and tubing, wires and cables insulation, and continuous films or sheets. Advantages of extrusion include efficient material use, the ability to produce long lengths and complex cross-sections, and good surface finish. Limitations include high tooling costs, die wear, equipment demands, and potential defects from processing conditions.