Reverse microelectrical discharge machining (R-MEDM) process is a recent variant of microelectrical discharge machining process capable of fabricating high aspect ratio arrayed microfeatures and textured surfaces. Efficient flushing of the debris particles from the interelectrode gap is essential for process stability, but extremely small interelectrode gaps (∼5 µm) make the dispelling of debris difficult, rendering the R-MEDM process infeasible for machining difficult-to-erode materials and creation of engineered/textured surfaces. It has been experimentally observed that the electrode vibrations facilitate the flushing of debris particles and improve the erosion rate, surface morphology, and dimensional accuracy of the machined features. Despite the obvious advantages, the vibration-assisted R-MEDM process, specifically the debris motion and dielectric flow under the effect of vibration, is not very well understood. Consequently, this paper is focused on computational modeling of the debris motion and its interaction with the dielectric fluid under low-amplitude vibrations imparted via a magnetorestrictive actuator. The effects of frequency and amplitude of the electrode vibration on the debris motion have been quantified. The higher local debris velocities and oscillatory motion due to flow reversal potentially reduce the debris agglomeration. As a result, the normal discharge duration, which is responsible for the material erosion, is increased and fabrication of arrayed features on difficult-to-erode materials and creation of surface texture over large areas become feasible.[ 2013-0394]Index Terms-Reverse micro electrical discharge machining (R-EDM), vibration assisted EDM, debris simulation, dielectric flow, textured surfaces, micromachining.

The reverse micro EDM (R-MEDM) has emerged as an important process for machining of high aspect ratio arrayed features and textured surfaces. In R-MEDM process, accumulation of debris particles in the inter-electrode gap drives the process towards instability and also the sticking of debris particles on machined microrod increases its surface roughness. Vibration assisted R-MEDM can help to overcome the issues of debris accumulation, produce debris free surfaces and enabled a creation of textured/engineered surfaces. The objective of this paper is to quantify the debris size distribution, number of debris particles generated per discharge and further simulate the debris and dielectric flow under the influence of electrode vibrations in R-MEDM process. Debris particles of estimated sizes, numbers and ejection velocity are injected into channel and simulated under the influence of electrode vibrations. Simulation results show that the electrode vibrations impart oscillatory motion to dielectric fluid and debris particles. During upward motion of plate electrode, dielectric fluid is pushed out of inter-electrode gap while the flow reversal takes place in the inter-electrode gap when plate electrode starts to move in the downward direction. The debris particles also show similar reciprocating motion whereas such motion of debris is completely absent in a fixed inter-electrode gap (no electrode vibration) condition. It is found that displacement of the plate electrode from bottom to middle position (at 6 kHz frequency and 1 μm amplitude) resulted in 6.4 and 3.4 time increase in maximum dielectric velocity and average velocity of debris particles in particular. The flow reversal and the reciprocating motion improves the overall process stability of R-MEDM process.

Wheelchair design for patient safety and comfort has been one of the most concerned topics for practitioners of mechanical engineering and bio-engineers. In the present scenario of medical institutions, transferring of immobilized patients from bed to wheelchair and vice-versa for numerous chronic and emergency activities is a very labor intensive and tedious job. Various attempts have been made in addressing this problem. These were modeled using simple mechanical devices providing the conversion. But still the issue of easy and controlled transition of adjusting the position of wheelchair’s head and base part according to patient’s needs and its full conversion has not been modeled and devised completely. So arises the need for a suitable, efficient and complete designing and development of such a device. This paper focuses on the design and manufacturing of a safe, reliable and low cost wheelchair which is convertible to a bed and vice-versa using a novel mechanical actuation by the effort of a single person. It models out a process of development and evolution of a reliable and verified design. Key areas focused upon are compact and efficient transmission system, discrete angular control of head and leg space with efficient load distribution while optimizing the size, cost (initial, service and disposal) and weight of the device. Further, the model is analyzed and justified by applying Quality Function Deployment (QFD) and Analytical Hierarchy Process (AHP) methods.