(1. University of Science and Technology Beijing, Beijing 100083, China) (2. Haomei Aluminium Co. Ltd. Guangdong 511540, China)
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DOI:
10.7502/j.issn.1674-3962.2013.05.07
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Abstract:
This paper introduces the research and progress of isothermal extrusion in the world, clarifies the control principle and method of this technology, and develops a new real-time automatic control system of rapid isothermal extrusion composed by the gradient water-cooling system of billets, the liquid nitrogen cooling system of mould and the closed loop control system of extrusion speed and outlet temperature. Studies have found that it can inhibit the temperature elevating of billet during extrusion through the gradient water-cooling device with the pre-produced axial temperature gradient of billet, which is controlled by the finite difference method and discretized heat conduction equation. Exit temperature regression model are adopted to control liquid nitrogen intake to cool the extrusion mold, which stabilizes the mold operating temperature, prolongs the mould life and improves the quality of profile surface. The temperature of the profile can be adjusted accurately by the predictive fuzzy model though adjusting extrusion speed using closed loop method. Consequently, the temperature of the profile at the extrusion exit would maintain constant due to the triple linkage control system. This system is also beneficial to improve the speed of extrusion, and ensure the accuracy of dimension and stability of microstructures and properties along the length direction of the profiles. For rapid extrusion, the fluctuations of profiles temperature at the exit can be limited within ± 10℃, and for slow extrusion speed producing industrial profiles, the temperature accuracy of the exit profile can be contained within ±5℃, also the extrusion speed can increase by more than 30% for the extrusion alloy with good performance