叶轮零件磨粒流抛光机理与数值模拟的研究

Mechanism and Numerical Simulation of Abrasive Flow Polishing for Impeller Parts

目的解决增材制造TC4钛合金(Ti6Al4V)叶轮零件表面粗糙度过大的问题。方法采用磨粒流抛光技术对增材制造TC4钛合金叶轮零件进行抛光,研究磨粒粒径、工作压力与抛光时间等因素对叶轮零件表面粗糙度和形貌的影响规律。同时利用Fluent软件对磨粒流抛光过程进行仿真,建立三维叶轮模型,以实际加工条件为仿真参数,探究磨粒对近壁面静压、动压、湍动能、湍流强度的作用机理。结果当磨粒流抛光的磨粒粒径为0.425 mm、加工压力为9 MPa、抛光时间为20 min时,获得了表面粗糙度Ra<2.5μm的增材制造叶轮零件。磨粒流抛光后表面摩擦系数从0.4281降低为0.3853,磨损机制由粘着磨损和剥落磨损变为磨粒磨损。仿真结果表明,随着磨粒流体自上而下运动,叶片间距逐渐增大,叶轮表面所受动压、湍流强度及湍动能逐渐减弱,因与约束装置的作用,底部的动压、湍流强度和湍动能又增大,因此叶轮叶片上端抛光较好,中间部位抛光效果一般,下端抛光效果也较明显。结论磨粒流抛光过程中,试样表面因塑性变形产生了加工硬化,晶粒得以细化,从而有效提高了其耐磨性能。通过数值模拟与试验分析验证了复杂曲面磨粒流抛光技术的有效性,为磨粒流抛光技术提供理论基础。

Additive manufacturing as a new manufacturing technology has significant advantages in producing complex impeller parts,but the surface roughness limits its wide application.Therefore,the work aims to solve the problem of excessive surface roughness of TC4 titanium alloy(Ti6Al4V)impeller parts produced by additive manufacturing.In order to improve the surface roughness of through-hole or complex outer surface parts caused by powder adhesion and spheroidization defects,abrasive flow polishing technology was applied to polish the surface of TC4 titanium alloy specimens.The effect of abrasive flow polishing on the surface roughness and morphology of TC4 titanium alloy was studied under different abrasive particle size,working pressure and processing time.The polishing process of abrasive was simulated by Fluent software to explore the mechanism of abrasive particles on the static pressure,dynamic pressure,turbulent kinetic energy and turbulence intensity near the wall.A three-dimensional impeller model was built and the actual processing conditions were taken as simulation parameters to verify the effectiveness of abrasive flow polishing method.At the same time,wear resistance of the TC4 titanium alloy before and after abrasive flow polishing were tested and analyzed.The TC4 titanium alloy specimens produced by additive manufacturing were cut into 40 mm×40 mm×5 mm by wire cutting,cleaned and dried.The SMK-600 abrasive flow polishing machine was used to optimize the surface roughness of titanium alloy specimens by cutting the workpiece surface through the reciprocating movement of abrasive media.The solid particles of abrasive medium were SiC abrasive particles,and the mixture of methyl silicone oil and polyacrylamide was used as liquid medium.Experiments verified that titanium alloy parts with surface roughness Ra<2.5μm were obtained when the abrasive grain size was 0.425 mm,the processing pressure was 9 MPa and the polishing time was 20 min,meeting the processing requirements.The friction and wear test results demonstrated that the friction coefficient of TC4 titanium alloy specimen surface decreased from 0.4281 before abrasive flow polishing to 0.3853 after polishing,and the reduction of friction coefficient represented the improvement of wear resistance.The wear mechanism was changed from adhesive wear and spalling wear to abrasive wear.The reciprocating movement of the abrasive in the process of abrasive flow polishing caused plastic deformation of the material surface,which resulted in changes in work-hardened and the grains were refined,thus effectively improving the wear resistance.Numerical simulation results indicated that the blade spacing gradually increased as the abrasive fluid moved from top to bottom,the dynamic pressure,turbulent kinetic energy and turbulence intensity on the surface of the impeller gradually weaken.When the fluid reached the bottom of the impeller,the dynamic pressure,turbulence strength and turbulence kinetic energy increased due to the role of the restraint device.Therefore,the polishing effect of upper and lower ends of the blade were better than those at the middle part.In the process of abrasive flow polishing,the surface of the specimen is work-hardened due to plastic deformation,and the grains are refined,thus effectively improving the wear resistance.The abrasive flow polishing is suitable for improving the surface quality of complex outer surface parts such as impeller.The effectiveness of abrasive flow polishing technology for complex curved surfaces is verified by numerical simulation and experimental analysis,which provides a theoretical basis for abrasive flow polishing technology.