Extrusion speed
Extrusion speed
Extrusion speed is also an important parameter in the extrusion process. It has a significant impact on the production efficiency of the extrusion press and the quality of the extruded products. There are two ways to represent the extrusion speed: one is by the travel speed of the extrusion stem: v (that is, the forward speed of the main ram), with the unit of mm/s; the other is by the speed at which the metal flows out of the die hole: u, with the unit of m/min. Generally, the extrusion speed refers to the speed at which the metal flows out of the die hole.
1) Principles for selecting extrusion speed
Under the condition of ensuring that the extruded product dimensions are qualified, without generating extrusion cracks, twisting, waves and other defects, and with the equipment capacity permitted, it is advisable to choose a higher extrusion speed. Generally, the larger the outer peripheral circle of the extruded product cross-section, the larger the extrusion ratio, the larger the extrusion container diameter, the more complex the product shape, the higher the precision requirement, the lower the extrusion speed should be. For hollow profiles, to ensure the welding quality, the extrusion speed should be lower than that of solid profiles. For multi-hole die extrusion, it should be lower than single-hole die extrusion. For unhomogenized billet, the extrusion speed should be lower than that of homogenized billet. For 6063 alloy solid profiles, the extrusion speed is generally 15 to 50 m/min, with a maximum of 100 m/min. For hollow profiles, it is generally 10 to 30 m/min. To ensure the geometric dimensions, surface quality and mechanical properties of the extruded products, it is best to use constant-speed extrusion.
2) Factors affecting extrusion speed
Extrusion speed is related to the composition and properties of the aluminum alloy. For the same alloy, the higher ratio the alloy components, the slower the extrusion speed should be. The better the plasticity of the material, the faster the extrusion speed. For example, alloys like 1060, 1A30, and 3A21, which have excellent plasticity, can have an extrusion speed of up to 100 m/min. On the other hand, alloys with poor plasticity such as 2A12 and 7A04 have an extrusion speed of no more than 3 m/min.
The extrusion speed is related to the extrusion temperature. Generally, the higher the extrusion temperature, the lower the extrusion speed should be. This is because when the extrusion temperature is high, rapid extrusion can cause an increase in frictional force and deformation energy, leading to a significant increase in the temperature of the metal in the deformation zone and an easy exceedance of its maximum critical temperature, causing the product to enter a hot brittle state and form cracks. Usually, only by reducing the extrusion speed can this situation be avoided.
The extrusion speed is related to the complexity of the cross-section of the profile product. When the cross-section of the profile is complex, an excessively high extrusion speed is difficult to ensure uniform flow velocity at every point of the product cross-section, which can easily cause the product to have twisting, bending, opening or closing phenomena, and thus the extrusion speed needs to be reduced. Generally, for complex cross-sections, products with large openings and wall thickness differences, and hollow profiles, a reduction in extrusion speed is also necessary to ensure good welding. Hollow profiles require a lower extrusion speed than solid profiles.
The state of the billet is also one of the factors affecting the extrusion speed. Homogenized billet can increase the extrusion speed. In addition, the extrusion speed is related to the extrusion ratio, extrusion method, lubrication conditions, die mold temperature, and other factors.