Experimental study on tangential vibration assisted abrasive flow finishing of circular tubes

Objectives: When the traditional abrasive flow machining (AFM) technology is used to process workpieces with complex shapes and inner walls of the tunnels, the machining quality of the workpiece surface tends to be uneven in each directions. To address this, the vibration assistance is added to traditional abrasive flow machining, forming a wavy machining track on the workpiece surface. This technique generates interwoven scratch textures, reduces the roughness value of the workpiece surface in all directions, and improves the surface quality and material removal efficiency converging the surface roughness. Methods: By rotating a cam to drive a connecting rod, vibration is induced in a round tube, altering the flow field distribution characteristics of the fluid abrasive and the mode of abrasive phase movement. This enables a new relative movement between the fluid abrasive and the workpiece surface. The principle of vibration-assisted machining and the scratching effect of abrasive particles on the workpiece surface were analyzed. At the same time, different frequencies and amplitudes were achieved by varying the motor speed and adjusting the long and short half-axes of the elliptical cam. A test platform for vibration-assisted abrasive flow machining was built to study the effects of abrasive flow rate, amplitude, and frequency on workpiece surface roughness and topography. Results: (1) After 2, 4, and 6 processing cycles without vibration, the surface roughness of the Cu-1 workpiece was reduced to 0.187, 0.123, and 0.112 μm, respectively. After 2, 4 and 6 processing cycles with vibration, the surface roughness of the Cu-4 workpiece decreased from an initial 0.230 μm to 0.139, 0.114, and 0.106 μm, respectively. The surface roughness of the workpiece polished with vibration was lower than that without vibration. At the same time, under non-vibration conditions, the transverse fringes of the original surface of Cu-1 after machining remained visible, although its surface roughness were significantly reduced. When Cu-4 was processed for 6 times under vibration condition, the transverse stripes on the original Cu-4 surface were almost completely removed, and some fine circular scratches appeared, resulting in a relatively ideal machining surface. (2) The cam speed directly corresponded to vibration frequency, higher cam speeds resulted in higher frequencies. When the Cu-2 workpiece was machined at a cam speed of 150 r/min, its surface roughness decreased slowly and steadily. At the cam speed of 225 r/min, the Cu-3 workpiece was experienced a longer micro-cutting length between abrasive particles and the workpiece, resulting in lower surface roughness compared to those of Cu-2. When Cu-4, polished at a higher cam speed, these appeared a significant reduction in surface roughness, decreasing to 0.166, 0.130. and 0.106 μm in the order of Cu-2 > Cu-3 > Cu-4. Higher cam speeds produced more scratches on the workpiece surface under the same flow rate, leading to longer arc scratches and smaller curvature radii. (3) When Cu-3, Cu-7 and Cu-8 workpieces were processed for the same times with three different cam sizes, the surface roughness of Cu-3 slowly reduced to 0.130 μm with L76 cam. The Cu-7 was machined with L47 cam at lower amplitude and relatively stable vibration, had lower surface roughness of 0.111 μm, which was lower than that of Cu-3. The Cu-8 was machined with L102 cam, the connecting rod swings greatly, the vibration was extremely unstable, and the surface roughness of the workpiece changed little. The L76 cam had the larger and more intense amplitude on Cu-3, and the curvature radius of the scratch formed by the machining was larger, and the direction angle of the scratches formed by the abrasive particles on the Cu-3 surface was closer to the original direction angle of scratches of the workpiece. The vibration amplitude of the L47 cam was small, and the scratch amplitude on the Cu-7 workpiece was smaller, and the cutting condition was more stable and the surface roughness was lower. However, the machining of Cu-8 by L102 cam destroyed the surface morphology of the workpiece. (4) The abrasive flow rates for the Cu-3, Cu-6 and Cu-5 workpieces were 38, 28, and 19 mm/s, respectively. After processing, the surface roughness were 0.130, 0.156, and 0.178μm, respectively. Under the same vibration machining conditions, the higher the abrasive flow rate, the lower the workpiece surface roughness, and the relationship between the surface roughness of each workpiece after machining was Cu-5 > Cu-6 >Cu-3. Moreover, there were scratches on the workpiece surface with a certain angle from the original scratches, and the relationship between the curvature radius of the scratch on the surface of the workpiece was Cu-3 > Cu-6 > Cu-5. Conclusions: Compared with traditional abrasive flow machining, vibration-assisted abrasive flow machining extends the cutting path of abrasive particles on the workpiece surface, forming cross scratches and reducing the surface roughness of the workpiece. The higher the vibration frequency, the longer the micro-cutting length between abrasive particles and the workpiece surface, the lower the surface roughness of the workpiece. With the increase of abrasive flow rate, the cutting effect of the abrasive particles on the workpiece surface is enhanced, leading to greater reductions in surface roughness.