铝型材挤压在线淬火系统喷嘴流速的仿真优化

Simulation optimization of water spray velocities of on-line quenching system for extruded aluminum profiles

为制定最优的在线淬火系统喷嘴流速方案,基于Fluent和Workbench软件平台建立了π字形大断面铝型材挤压在线淬火过程的有限元模型.为了准确确定仿真模型中的热边界条件,采用末端淬火实验和反热传导相结合的方法,获得了不同喷水流量下的界面换热系数.系统分析了3种不同喷嘴流速方案铝型材实际挤压在线淬火冷却过程中的流速场、温度场、应力场和残余变形.结果表明:随着喷水流量的增大,淬火介质与型材的界面换热系数增加且到达峰值的时刻越晚.有限元模拟的特征点温度与试验测量的温度变化趋势一致,相对误差范围为-1.1%～7.8%,验证了所建立的淬火有限元模型是准确的.初始方案一型材挤压在线淬火过程中各部位冷却不均匀,在接头处产生较大的热应力,使型材上端面发生内凹. 3种不同的喷嘴流速方案中,方案三中型材表面和中间截面位置淬火冷却过程能得到更为均匀的温度场,残余应力和变形最小.研究方法和结果可为复杂铝合金型材挤压在线淬火系统喷嘴流速的制定和优化提供理论指导.

To obtain the optimal water spray velocities of on-line quenching system,a finite element model for simulating the on-line quenching process of large sectionπ-shaped aluminum profiles was established based on Fluent and Workbench software platform.To determine the thermal boundary conditions in the simulation,methods in spray quenching experiments combined with inverse heat conduction were used to get the heat transfer coefficients under different spray water fluxes.The velocity,temperature,stress fields and residual deformation of extruded profiles during on-line quenching process under three schemes with different nozzles velocities were analyzed systematically.The results show that the heat transfer coefficient increases with the increase of spray water flux,and the time to reach the peak value is later.The simulated temperatures of feature points present corresponding changes with the measured ones and the relative error range is-0.7~7.8%,which verifies the accuracy of finite element model.For the initial quenching process scheme,a large thermal stress is formed at the joint position due to the non-uniform cooling of profile section,which leads to concave defect at the upper surface of profile.A relatively uniform temperature field can be obtained on the surface and middle section of profile by adopting the scheme 3,and the minimum residual stress and deformation can be achieved.The research methods and results are helpful to the design of nozzles velocities in the on-line quenching system for hollow aluminum profiles extrusion.