INVESTIGATIONS OF HYBRID THERMAL ABRASIVE FLOW MACHINING PROCESS

Abstract

Abrasive Flow Machining (AFM) is a nonconventional finishing technique used for the deburring and polishing of the surface and edges through the abrasive laden media. The sharp cutting edges of the abrasive particles abrade the material from the surface and remove the material in the form of micro chips. For the material removal mechanism in AFM process, abrasive particles impart a large amount of force and a lot of energy is lost due to friction between the surface and abrasive particles. This research discuss a new hybrid form of AFM process named as Thermal additive Centrifugal Abrasive Flow Machining (TACAFM), which utilizes the spark energy to melt the surface material and abrasive particles in the media easily removes the material with lesser amount of force and energy loss also minimizes. TACAFM process is a combination of Centrifugal force assisted Abrasive Flow Machining and Electrical Discharge Machining (EDM) process. This process utilizes the EDM mechanism for producing the spark between the rotating electrode and work piece surface. The electrode tip is designed in such a way that it maintains the gap between the electrode tip and the workpiece surface and also it allows the media to pass from one media cylinder to the other. The present work includes mathematical modelling of the developed Thermal additive Centrifugal Abrasive Flow Machining process for the calculation of force exerted by the abrasive particles on the workpiece surface and its material removal due to thermal effect. The mathematical model results were validated through the experimental observations. While finishing the work piece through TACAFM process, higher temperature is developed over the surface due to spark generation. This is important to analyze the temperature distribution over the surface. A simulation model is presented by using ANSYS® 15 software to analyze the effect of temperature around the workpiece surface on changing the gap between the electrode and workpiece surface with variable rotational speed of electrode. The simulation results describe the amount of gap and rotational speed of electrode to be taken for better surface properties. The present work also involves use of the Response surface methodology (RSM) to plan and conduct the experiments and determine the effect of input process variables such as current intensity, duty cycle, abrasive concentration, rotational speed of the electrode and extrusion pressure on material removal, percentage improvement in surface roughness, residual stress, scatter of surface roughness and micro-hardness of the workpiece surface. The finished surface of the components was characterized for the microstructure study using SEM and XRD analysis. The oxide layers and molten material on workpiece surface was also observed from SEM images. The experimental results of xviii

TACAFM process showed average 44.34% improvement in material removal compared to conventional AFM process. The results also showed 18.78% error in mathematical modeling results in compared to the experimental results of TACAFM process. The optimum value of material removal and percentage improvement in surface finish was found as 36.571 mg and 42.38 % simultaneously at 12 ampere of current, 0.78 duty cycle, 250 rpm of rotational speed, 10 MPa of extrusion pressure and 0.3 abrasive concentration. The optimum value of residual stress, scatter of surface roughness, micro hardness was found as -151.921 MPa, 0.151 µm and 345.951 HV simultaneously. The 95% confidence interval of the predicted mean for the MR was 31.7542 < MR (mg)< 38.5195, for % improved Ra was 35.5311 < ∆ Ra < 43.0562, for residual stress -285.483 < Residual Stress < -301.458, for Scatter of surface roughness was 0.0921< SSR < 0.209 and for Micro Hardness was 291.367 < Micro Hardness < 350.17. The developed technique is confirmed to be a better process for achieving products having high level of surface integrity.