Author: Site Editor Publish Time: 2024-08-29 Origin: Site
Extrusion is a crucial step in the forging of train wheels. This article provides an in-depth look into the features and applications of the extrusion process, helping you better understand this key stage.
The internal fiber structure of extruded parts is continuous and follows the contour of the forging. During extrusion, the material is subjected to tri-axial compressive stress, enhancing the plasticity of the metal, increasing the degree of deformation, and resulting in dense and high-performance forgings.
Extrusion processes are classified into hot, cold, and warm extrusion based on the temperature of the billet during extrusion. Each type has its unique process characteristics:
① Hot Extrusion
Hot extrusion involves heating the billet above its recrystallization temperature. When hot extrusion is performed on low-speed equipment, the temperature should be near the upper limit of the forging temperature; otherwise, it should be 50-100°C lower. Compared to die forging, hot-extruded train wheels offer higher precision and surface roughness. Tolerances for non-ferrous metals can reach 0.2mm with a surface roughness of Ra 1.6, while ferrous metals can achieve a tolerance of 0.4mm. Hot extrusion usually forms parts in a single step with fewer procedures.
② Cold Extrusion
Cold extrusion refers to extrusion forming at room temperature. Its main advantages are high precision and surface roughness below Ra 1.6, with accuracy generally reaching grade 4-5. However, it has higher deformation resistance, limited part sizes, restricted material choices, and requires annealing and surface lubrication treatments before extrusion.
③ Warm Extrusion
Warm extrusion involves heating the billet to a suitable temperature below the recrystallization point. Compared to cold extrusion, warm extrusion reduces equipment load, increases deformation per step, and broadens the range of extrudable materials. Billets usually do not need prior softening or surface treatments, but the precision, surface roughness, and mechanical properties of warm-extruded parts are slightly lower than those of cold-extruded parts.
④ No Draft Angle
Extruded parts typically do not require a draft angle and must be processed on equipment with an ejector mechanism.
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