PERFORMANCE ANALYSIS OF ULTRASONIC ASSISTED ABRASIVE FLOW MACHINING PROCESS

Abstract

Abrasive Flow Machining (AFM) process is an abrasive-based precision finishing process used for achieving surface finish in micro and nano-level. The process is used to polish surfaces by extruding a visco-elastic media in contact with the workpiece. In the present work Ultrasonic Assisted Abrasive Flow Machining (UAAFM) process is being investigated as variant of traditional abrasive flow machining process. In this process, a relatively high frequency (5 to 20 kHz) vibration is provided to the workpiece externally using a piezo actuator and a specially designed fixture. This additional effect is termed as ultrasonic assistance. Owing to this, the abrasives present in the medium hit the workpiece asperities at an angle and at a higher resultant velocity thereby making them more effective in abrading the asperities. The present work highlights on the mechanism of material removal and performance of the UAAFM process, while finishing both internal (cylindrical bushes) and external surfaces (bevel gear). Modelling and simulation of medium behaviour was carried out during UAAFM processing of both internal and external surfaces. A commercially available simulation tool was used to study the effect of different machining conditions on the medium, also called flexible tool. A 3-D model was constructed for the purpose of simulating the UAAFM process. The responses were evaluated in terms of changes in the fluid pressure, velocity profile of the fluid, temperature distribution in the working fluid and possible wall shear on the work surface. Results show that the abrasive particles tend to hit the target surface at an angle ‘ ’, which significantly enhances the effectiveness of the process. The enhanced interaction of the abrasive media in UAAFM while compared to classical AFM could be explained by the resultant pressure-velocity phenomena. Results show that while changes in the amplitude of applied vibration (10 - 50 μm) significantly affect the wall shear; the media velocity and pressure are marginally sensitive to v this parameter. The study confirms that the rise in temperature during the process does not affect the medium stability. Experiments were conducted on EN8 steels (AISI 1040) and Al alloys (2014 series) to evaluate the process performance of the UAAFM in both axial and radial mode of vibration on a double acting horizontal type setup. Response Surface Methodology (RSM) technique was used for designing the experimental plan with major input parameters such as applied frequency, extrusion pressure, abrasive mesh size and processing time. The results obtained after machining by UAAFM were also compared with traditional AFM process. It was found that significant improvements in surface finish could be recorded in UAAFM. The maximum percentage of surface finish improved while finishing EN8 steels was 81.02% while maximum material removed was 14.5 mg for the given trial conditions. However, during axial mode, the maximum improvement in surface finish achieved while finishing Al 2014 alloys was 85.12% and material removed was 21.93 mg. The machined surfaces were also investigated using scanning electron microscope (SEM) and 3-D optical profilometer. The UAAFM technique was also used to finish bevel gears made of EN8 steel. An analysis of the process has been presented with suitable illustrations. The effectiveness of the process was investigated through experimental trials in terms of enhancements in surface finish and material removed. Trials were carried out according to Taguchi’s L9 orthogonal array for the given inputs (3-levels, 4-parameters). Results confirm that improvements in surface finish and material removal are significantly higher than those obtained with conventional abrasive flow machining. The study further reveals that the applied high frequency (ultrasonic) vibration to the workpiece has the maximum influence on the process responses among the variables considered. The study confirms that the process has the potential to be used in the precision manufacturing industries. The study created ample opportunities for future research including – exploring higher frequency domain, attempting finishing of multiple-phase materials etc.