Simulation of media behaviour in vibration assisted abrasive flow machining

• Analysis of a new variant in hybrid abrasive flow machining has been presented.
• Simulation of media flow behaviour in UAAFM is presented using CFD approach.
• Mechanism of workpiece–abrasive interaction in the UAAFM has been explained.
• Enhancement in performance using ultrasonic assistance in AFM is demonstrated.

Abrasive flow machining (AFM) is an abrasive-based precision finishing process used for achieving surface finish in micro and nano-level. The AFM polishes surfaces by extruding a visco-elastic media in contact with the workpiece. The media, also called a ‘flexible tool’, plays a key role in the performance of the process. Ultrasonic assisted abrasive flow machining (UAAFM) is a new variant of the AFM process in which the workpiece is subjected to mechanical vibration orthogonal to the media flow direction. In this process a high frequency, in the range of about 5–20 kHz, is given to the workpiece with the help of a piezo actuator and a specially designed fixture. The present work highlights on the possible behaviour of the tool (media) during UAAFM and its effect on the machining process through a computation based approach. Commercially available simulation tool was used to study the effect of the media in response to different set of machining conditions. The responses were evaluated in terms of changes in the fluid pressure, velocity profile of the fluid, temperature distribution in the working fluid and the possible wall shear on the work surface. A three-dimensional model was constructed for simulating the UAAFM process. The simulation shows that the abrasive particles tend to hit the target surface at an angle ‘θ’ which significantly affects the basic mechanisms involved and enhances the effectiveness of the process. The computed wall shear explains that the process will have higher finishing rate and hence the performance. The enhanced interaction of abrasive media in UAAFM while compared to simple AFM could be explained by the resultant pressure–velocity phenomena. Results show that while changes in the amplitude of applied vibration (10 μm and 50 μm) significantly affect the wall shear, the media velocity and pressure profiles are only marginally sensitive to this parameter. The simulation results also confirm that the rise in temperature during the process will not affect the media stability. Results have been discussed vis-a-vis the basic mechanism of the process through suitable illustrations.