Extrusion mould process instroduction
The degree of extrusion deformation is expressed by the area reduction rate before and after deformation.The ultimate deformation degree of the blank without crack in the first deformation process is called allowable deformation degree.The allowable deformation degree is higher when the blank is extruded under three-way compressive stress.In cold positive extrusion, the allowable deformation degree of low carbon steel is more than 75%, and hard aluminum, copper, brass and so on can reach more than 90%, slightly lower in reverse extrusion.In the thermal state, the allowable deformation degree can be greatly increased, and the increase increases with the increase of temperature.Large deformation degree, the required extrusion pressure is also large, the mold wear faster, and easy to damage, so generally do not use the allowable deformation limit value, for example, in the cold extrusion of carbon steel with 60% of the deformation limit value as the allowable degree of a deformation.If the total deformation from billet to finished product is large, it is divided into several extrusion passes forming step by step.During cold extrusion, softening and annealing between each step is required.The allowable deformation degree of hot extrusion and warm extrusion is larger, which is beneficial to reduce extrusion pressure and extrusion passage times.
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