This review of MRF (magnetorheological fluids or MR fluids) brings out the challenges in methods of preparation, difficulties encountered in storage and use, and possible solutions to overcome the challenges.Magnetorheological fluid in the rheological fluid domain has found use due to its ability to change its shear strength based on the applied magnetic field. Magnetorheological fluids are composed of magnetizable micron-sized iron particles and a non-magnetizable base or carrier fluid along with additives to counter sedimentation and agglomeration.Magnetorheological fluids can respond to external stimuli by undergoing changes in physical properties thus enabling several improved modifications in the existing technology enhancing their application versatility and utility. Thus, magnetorheological fluid, a rheological material whose viscosity undergoes apparent changes on application of magnetic field, is considered as a smart material. Such materials can be used for active and semi-active control of engineering systems.Many studies on the designs of systems incorporating MR fluids, mainly for vibration control and also for other applications including brakes, clutches, dynamometers, aircraft landing gears, and helicopter lag dampers, have emerged over last couple of decades. However, the preparation as well as the maintenance of magnetorheological fluids involves several challenges. Sedimentation is a major challenge, even when stored for moderate periods of time. A comprehensive review is made on the problems confronted in the preparation of magnetorheological fluids as well as sustenance of the properties, for use, over a long period of time. Other problems encountered include agglomeration and in-use thickening (IUT) as well as rusting and crusting. Of interest is the mitigation of these problems so as to prepare fluids with satisfactory properties, and such solutions are reviewed here. The control of magnetorheological fluids and the applications of interest are also reviewed.The review covers additives for overcoming challenges in the preparation and use of magnetorheological fluids that include incrustation, sedimentation, agglomeration, and also oxidation of the particles. The methodology to prepare the fluid along with the process for adding selected additives was reviewed. The results showed an improvement in the reduction of sedimentation and other problems decreasing comparatively. A set of additives for addressing the specific challenges has been summarized. Experiments were carried out to establish the sedimentation rates for compositions with varying fractions of additives.The review also analyzes briefly the gaps in studies on MR fluids and covers present developments and future application areas such as haptic devices.

Factors like cutting force, cutting temperature, acoustic emission signals and vibration signals can be effectively used to predict tool wear. Even though each of these factors can be used individually to predict tool wear, a more accurate prediction will be possible if these factors are considered collectively since each of these factors predicts tool wear in its own characteristic fashion. For example, high cutting temperature is an index of flank wear and crater wear, whereas variation in cutting force indicates the fracture type of tool failure more effectively. Hence a better prediction of tool wear is possible by considering the indices of tool wear collectively rather than individually. In the present work, an attempt was made to fuse cutting force, cutting temperature and displacement of tool vibration, along with cutting velocity, feed and depth of cut, to predict tool wear during turning of AISI 4340 steel having a hardness of 46 HRC using a multicoated hard metal insert with a sculptured rake face. A regression model and an artificial neural network model were developed to fuse the cutting force, cutting temperature and displacement of tool vibration signals to predict tool flank wear. The fusion model based on the artificial neural network was found to be superior to the regression model in its ability to predict tool wear.

Hard turning with minimal fluid application is an emerging machining technique in which cutting fluid is applied in the form of a minimal high velocity narrow pulsed jet so that for all practical purpose it resembles dry and wet turning but at the same time offers better cutting performance. Semi-solid assisted machining is a novel concept to control cutting force, cutting temperature, tool wear and to improve surface finish. In the present investigation, an attempt is made to improve the cutting performance during turning of hardened AISI 4340 steel with minimal fluid through the application of a semi-solid lubricant namely grease in pure form and as a mixture with 10% graphite applied at the tool–chip interface, tool–work interface and at the back side of the chip using a special semi-solid lubricant applicator developed for this purpose. The results indicated that the use of semi-solid lubricants – grease and graphite at the tool–chip interface along with minimal fluid application reduces tool vibration, cutting force, cutting temperature, tool wear and improves surface finish.

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In the machine tools, tool vibration is an undesirable phenomenon which affects tool life, quality of machined surface and produces irritating noise. This tool vibration is due to the interaction between metal cutting process and forces acting on the machine tool. In this investigation, an attempt was made to reduce tool vibration during turning of hardened steel using particle and mass impact dampers. A mass impact damper used in this investigation consists of a concentrated mass made of copper mounted on the bottom of the tool holder and particle damper consists of copper particles of 3.5 mm diameter positioned along the axis of the tool holder. Particle size and its location were designed using computational analysis and impact hammer-based modal testing was performed for both dampers. When these dampers were mounted on the tool holder, particles will collide with each other and subdue the vibration produced in the tool holder. Cutting experiments were conducted to study the influence of mass and particle damping on tool vibration and cutting performance during turning of hardened AISI4340 steel using hard metal insert with sculptured rake face. From the results, it was observed that the use of mass impact and particle dampers enhances the rigidity of the tool holder which, in turn, reduces tool vibration and improves the cutting performance. Among the two dampers, it was found that the presence of mass impact damping provides superior cutting performance when compared to particle damping.