电流变液辅助超声抛光用于增材制造件表面抛光的加工机理研究

Powder-based layered Additive Manufacturing (AM) techniques lead to high surface roughness due to balling and the partial melting of powder particles, which cannot satisfy the requirements of design and practical use. Consequently, until there is a significant step-change in the resolution of AM technology, finishing process will be a necessary step in the additive process. Cavitation bubble collapse in ultrasonic polishing can remove the partially melted structures efficiently, and a further roughness improvement could be obtained under the micro-cut and impact of micro-particles in the slurry. However, the polishing process is not stable due to the stochastic cavitation bubble collapse and particle movement, the quality of polished surface would be deteriorated again by unnecessary bubble collapse. Therefore, it is necessary to find ways for controlling the occurrence of the two actions and ensuring effective polishing. In the present research, a new electrorheological fluid-assisted (ER fluid) ultrasonic polishing process is proposed for controlling the movement of bubbles and particles in the slurry and improving the polishing performance. Simulations and experiments will be carried out simultaneously. The influence of process parameters on the bubble collapse, the micro-cut and impact of particles will be investigated before ER fluid is applied. The material removal mechanisms involved in the process will be then concluded. After that, the effect of ER fluid on the movement of bubbles and particles will be investigated and the mechanism for improving polishing performance will be discussed. Finally, an optimized polishing condition will be concluded. The results of this project would provide theoretical and technical basis for the practical use of electrorheological fluid-assisted ultrasonic polishing process.

激光增材制造技术固有的粉末粘附和球化使成型面出现球团聚集现象，导致表面粗糙，难以满足设计和使用要求，需要进一步的抛光处理。超声抛光的空化效应可以高效地去除这些球团，并且在磨料颗粒的微小切削与撞击作用下使粗糙表面得到改善。但是，超声抛光效果不可控，光滑表面有可能再次由于空化冲击而变粗糙，因此掌握控制空化气泡冲击和磨料颗粒有效抛光的方法是提高抛光效率和质量的关键。本项目拟利用电流变液辅助超声抛光来控制空化气泡和磨料颗粒的运动，增强它们的有效抛光作用，拟采用模拟计算和实验验证相结合的方法，揭示空化冲击、磨料颗粒微切削及撞击作用对抛光表面的材料去除机理，建立条件参数与加工效果的相关理论架构和模型；研究电流变效应对空化气泡和磨料颗粒运动的影响规律，总结其对抛光过程的控制机理，得出抛光的可控工艺方案。该项目的研究将为实现电流变液辅助超声抛光的应用提供相关理论和基础技术支撑。

粉末床激光熔融是金属增材制造技术的重要工艺之一，成型金属零件致密度高、强度好，但熔融成形过程中无法避免的粉末粘附、台阶效应、球化效应以及熔道搭接等问题导致成形表面质量差，材料和成形策略不同，表面粗糙度Ra在3~50 μm，Rz在20~150 μm，难以满足零部件在表面粗糙度方面的应用要求，必须进行光整加工后才能使用。本项目针对激光金属增材制造表面形貌特征和实际抛光需要，提出了电流变液辅助超声方法，并对其中涉及的材料去除机理进行了研究。通过有无磨粒的超声抛光实验，研究了单纯空化效应和存在磨粒冲击时的抛光能力和效果，并建立了磨粒的加速冲击模型，结合实验结果，揭示了空化和磨粒的材料去除作用；建立了电流变液辅助超声抛光实验平台，研究了电流变效应施加前后磨粒的运动状态和空化程度的变化，建立了电场分布的有限元模型，阐明了电流变效应对抛光过程的作用机制；在上述研究基础上讨论了主要工艺参数对电流变液辅助超声抛光效果的影响规律，初步掌握了优化的工艺方向。该项目实施为激光金属增材制造表面后处理抛光技术提供了新思路，通过引入电流变效应提高超声抛光的抛光能力，指导实现磨粒和空化的有效协同作用。