SOME STUDIES TO ENHANCE THE CAPABILITIES OF ABRASIVE FLOW MACHINING PROCESS

Abstract

Precision finishing of mechanical parts is a critical functional requirement in many applications. There are number of traditional as well as non-traditional processes available to achieve required surface finish. However, most of these established processes have accessibility restriction and finish machining of parts continues to be challenging. Abrasive Flow Machining (AFM) is an advanced finishing process developed in the early 1960s. A significant advantage of the process is that it can be employed to finish parts having intricate shaped features which are usually inaccessible to other finishing processes economically and productively. However, the material removal rate of the process is low and hence requires higher processing time. On the other hand, researchers worldwide are making efforts to improve the overall performance of the non-traditional manufacturing processes by way of combining the features oftwo or more processes called hybrid manufacturing processes. Performance of AFM process can further be enhanced by addition of one or more effects simultaneously. This has resulted in development of few other variants of the AFM process with superimposed effects, also known as hybrid AFM. Present investigation is directed towards improving the capability of the conventional AFM process by applying additional motions. In the present work, studies have been carried out on machining Inconel 718, which is the workpiece material for AFM process, using Wire Electro Discharge Machining (WEDM) and Electro Discharge Machining (EDM) processes. Drilling of Inconel 718 workpiece was carried out using EDM process. A specially designed tubular section copper electrode was used. In order to optimize the material removal rate (MRR), Taguchi's OA was employed. Results show the pulse current, pulse on-time, pulse off-time and flushing pressure are the significant process parameters. The study was further extended to examine the effect of process parameters on MRR, tool wear rate, surface finish and wear ratio using the Response Surface Methodology (RSM) tools. A multi variant, double acting, horizontal AFM setup was designed and developed. The setup is flexible to be used for more AFM variants. A multi-purpose tooling was designed and developed to hold the workpiece during processing through using Teflon. A new natural polymer based media was developed for AFM process. Performance evaluation of the new media, process optimization and performance evaluation of the new AFM variants (hybrid) were carried out using the Taguchi's Orthogonal Array and RSM. Characterization of the abrasive carrier was performed using IR, TGA, XRD, SEM and NMR techniques. It was concluded that the new media is thermally stable up to 71 C , and shows phase stability upto 260°C. The media is flexible, reusable and has distinct advantages over the commercially available media. Two different hybrids of the basic AFM process were attempted; interaction of selected (significant) process parameters on process performance and the evaluation of the process performance were carried out using the response surface methodology. First hybridization method was in terms of adding an additional centrifugal profile rod to assist the media to flow in a spiral way termed as "Spiral Flow Assisted Abrasive Flow Machining" (SFAAFM) process. The second development was attempted with the basic aim to increase the number of active abrasive particles in the media during processing. This was achieved by providing ultrasonic (vibration) assistance to the work piece with a piezo actuator. This innovativeAFM process has been termed as "Ultrasonic Assisted Abrasive VI Flow Machining" (UAAFM). Process optimization of the new process was carried out using the developed media. The surface finish improvement and material removal were considered as process responses. The interaction effects and process parameters were studied; prediction models were developed for the process responses. Characterizations of the AFM processed surfaces were carried out using SEM micrographs. Maximum improvements in surface finish for the new process were recorded as 44.66% and 78.73% for the SFAAFM and UAAFM respectively, while enhancements in the material removal capabilities of the processes were recorded as 1172.32 % and 875.89 % respectively. It was concluded that new media, and new processes will have significant impact on the material finishing operations in the years to come. Further studies involving the analysis of process mechanisms and process simulation shall be able to throw more light on the understanding of the new processes.