Plastic deformation: deformed by external force, unloaded by force, unable to recover to its original state.
Elastic deformation: the part subjected to external force, force unloading and deformation recovery.
2 characteristics of plastic deformation
(1) Organizational change and performance improvement.
The steel cast by steelmaking has loose and porous internal structure, coarse and uneven grains and serious segregation. It must be forged, rolled or extruded to make its structure compact, improve its structure and improve its performance.
The metal streamline distribution is reasonable.
(2) No chips are generated, and the material utilization rate is high.
(3) high production efficiency and suitability for mass production.
(4) The dimensional accuracy is high, and many molding methods have reached the requirements of less cutting.
3 classification
According to the different forming characteristics, plastic processing is generally divided into five categories: calendering, extrusion, forging and stamping.
4 extrusion
① Cold extrusion: During cold extrusion, the metal blank is extruded without heating.
② Hot extrusion: In the process of hot extrusion, the metal blank is heated to the hot forging forming temperature for extrusion.
(Aluminum profile extrusion belongs to hot extrusion)
5 plasticity
As a state attribute of metal, plasticity not only depends on the metal material itself (such as lattice type, chemical composition and microstructure, etc.). ), but also depends on the external conditions of deformation. Metals can obtain high plasticity under suitable temperature, speed and mechanical conditions.
6 shaping theoretical hypothesis
Continuity, uniformity and isotropy (any infinitesimal element represents the whole), the volume is constant, the force is balanced at any moment, and the volume force (gravity, magnetism and inertia force) is ignored.
7 Friction during extrusion
Forward extrusion, friction plays an obstacle role, which is not conducive to metal filling, and the extrusion force is large.