Rahul S. Mulik

Mechanism of Surface Finishing in Ultrasonic-Assisted Magnetic Abrasive Finishing Process

Ultrasonic-assisted magnetic abrasive finishing (UAMAF) integrates the use of ultrasonic vibrations and magnetic abrasive finishing (MAF) processes to finish surfaces of nanometer order within a minutes time. The present study emphasizes the mechanism of surface finishing in UAMAF. This article reports the study of the microscopic changes in the surface texture resulting from interaction of abrasives with ground workpiece surface. In addition to the surface roughness measurement, scanning electron and atomic force microscopy were used to understand the material removal process and wear behavior during finishing and to provide a fundamental insight of the finishing in UAMAF. The observed surface texture showed that the process is an accumulation of the microscratches resulting from the interaction of abrasive cutting edges with the workpiece surface. The X-ray diffraction (XRD) analysis revealed that the SiC is induced in the workpiece surface, increasing the hardness of the workpiece up to 960 HV.

Experimental Investigations and Modeling of Temperature in the Work-Brush Interface during Ultrasonic Assisted Magnetic Abrasive Finishing Process

Ultrasonic assisted magnetic abrasive finishing (UAMAF) integrates ultrasonic vibrations and magnetic abrasive finishing (MAF) process to finish surfaces to nanometer order. During a finishing operation the order of temperature rise is important to study as cutting mechanism, wear, finishing accuracy, and surface integrity of work materials depend on it. In the present study, temperature measurement at workpiece-magnetic brush interface at various positions during UAMAF has been carried out at different processing conditions. Buckinghams dimensional analysis has been used to model this temperature, and the required coefficients are calculated based on the experimental data to predict temperature. The developed empirical model based on dimensional analysis has been validated and was found to be in good agreement with experimental findings.

Experimental Investigations and Modeling of Finishing Force and Torque in Ultrasonic Assisted Magnetic Abrasive Finishing

An ultrasonic assisted magnetic abrasive finishing (UAMAF) process uses an ultrasonic vibrations and magnetic abrasive finishing (MAF) process. In a finishing process there are two types of forces that act during the finishing of the workpiece by UAMAF, namely, normal force and cutting force. The finishing forces have direct influence on the generation of the finished surface and accuracy of the workpiece. Therefore, in the present work, normal force and finishing torque have been measured at various processing conditions during UAMAF. Supply voltage to the electromagnet and finishing gap have been found to be the significant factors affecting the finishing forces and torque. Mathematical models based on process physics have been developed to predict the finishing force and torque. The developed models predict force and torque as a function of supply voltage, machining gap, and workpiece hardness. The developed mathematical models for normal force and finishing torque have been validated and were found to be in good agreement with experimental results.

Experimental investigations and optimization of ultrasonic assisted magnetic abrasive finishing process

In this work a new process, namely ultrasonic-assisted magnetic abrasive finishing (UAMAF), has been conceived. This technique integrates the use of ultrasonic vibrations and a magnetic abrasive finishing (MAF) process to finish surfaces to nanometre order within a short time span. This paper is focused on the development of the UAMAF setup. The performed experimental studies were planned using response surface methodology and the Taguchi method and change in surface roughness (ΔRa) and material removal rate (MRR) were considered as the responses, respectively. The experimental results showed that the UAMAF process yielded better finishing characteristics compared to those obtained using the MAF process. The surface roughness value obtained by UAMAF were as low as 22 nm within 80 s on a hardened AISI 52100 steel workpiece. Analysis of experimental data showed that the percentage change in surface roughness (ΔRa) was highly influenced by mesh number followed by percentage weight of abrasive, rotation speed of the electromagnet, and voltage. Weight of abrasives was found to be the most significant process parameter affecting the MRR. Optimum process parameters were also obtained to maximize ΔRa at minimum MRR.

Improvement in material removal rate (MRR) using magnetic field in TW-ECSM process

ABSTRACT Electro chemical spark machining (ECSM) has the ability to machine electrically nonconducting materials successfully and economically. It has been seen that electrolyte circulation hindered in the close vicinity of the machining zone during the machining process, which leads to the reduction in material removal rate (MRR). In the present research, a magnetohydrodynamic (MHD) convection approach is discussed, which increases the electrolyte flow used in the travelling wire (TW)-ECSM process. The existence of magnetic field in the electrolysis process induces the Lorentz forces , which are responsible for MHD convection in the process. The experimental results showed that the MHD convection pushes the electrolyte to improve the movement of the electrolyte in the sparking zone to improve MRR in the TW-ECSM process. The experimental results revealed that the MRR increased in the presence of a magnetic field as compared to machining under no magnetic field, with the improvement factor ranging from 9.09% to 200% under different processing conditions. The discharge current was also reduced by the application of magnetic field in the machining process.

Experimental Investigations and Multi-response Optimization of Silicon Dioxide (Quartz) Machining in Magnetic Field Assisted TW-ECSM Process

Travelling wire electrochemical spark machining (TW-ECSM) has the potential for the machining of advanced non-conducting materials like glass, quartz, silicon nitride, various composites and ceramics. In the present work, experimental investigations have been conducted on the magnetic field assisted travelling wire electrochemical spark machining (TW-ECSM) process. In this technique, a magnetic field has been introduced in the TW-ECSM process in order to improve the machining performance in terms of improved material removal rate (MRR) and reduced surface roughness (Ra) of non-conducting materials. Material removal rate (MRR) and surface roughness (Ra) were selected as the responses during the experimentation. The experimental results revealed that the magnetic field assisted approach gives reduced values of Ra and increased MRR when compared to the TW-ECSM process. The minimum and maximum values of surface roughness and MRR were found to be 7.42 µm and 0.19 mg/min with magnetic field assisted TW-WCSM process respectively. The optimization function has been developed to minimize Ra and maximize MRR for obtaining the optimum process parameters.

Experimental Investigations Into the Finishing Force and Torque in Magnetic Abrasive Finishing Process

Magnetic abrasive finishing (MAF) is a finishing process in which surface is finished by removing the material in the form of micro-chips by the magnetic and abrasive particles in the presence of a magnetic field. In a finishing process, forces have direct influence on the generation of finished surface and accuracy of the workpiece.The magnitude of force or torque is also of importance as the surface integrity is affected. In the present research work, new design of electromagnet which gave relatively lesser force and torque as compared to conventional annular electromagnet was used to perform MAF. The measurements of normal force and finishing torque were carried out at different processing conditions using Kistler’s dynamometer and were found in the order of 24 N and 8 Nm respectively. The experiments were planned using Taguchi’s L16 orthogonal array and supply voltage to electromagnet, rpm of electromagnet, finishing gap and abrasive weight percentage at four levels were considered as process parameters. Supply voltage to the electromagnet and finishing gap were found to be the significant factors affecting finishing force and torque in this work. The scanning electron microscopy (SEM) study of the finished workpiece showed that there was no surface or subsurface damage due to very low finishing force and torque.© 2013 ASME

Thermal stresses during electro-chemical spark machining

The high temperature distribution generated during electro-chemical spark machining (ECSM) results in large localised thermal stresses in a very small heat affected zone. These thermal stresses can lead to micro-cracks and a decrease in strength and fatigue life of the components. A finite element model is developed to estimate the temperature distribution and thermal stresses due to a single spark (Gaussian distributed heat flux) and within the zone of influence of a single spark. Firstly, the finite element based (FEM) code is developed to estimate temperature distribution in the workpiece due to a single spark and, based on this temperature distribution, thermal stresses are calculated. Thermal stress analysis shows high temperature gradient zones and the regions of large stresses where, sometimes, they exceed the material yield strength.

A New Hot Tearing Assessment by Using Stepped Ring Core Mold and the Effect of Strontium on the Hot-Tearing Resistance of Al–6 wt% Zn Based Alloy

Automobile and aerospace industries use thin wall aluminium alloy castings which provide lighter structures with excellent mechanical properties. Production of thin wall castings is more challenging due to hot tear formation. Lack of fluidity in molten alloy causes hot tears and must be addressed in thin wall castings of Al-alloys. The present study is focused on a new technique known as stepped ring mould casting. It is possible to assess the hot tear susceptibility of Al–6Zn alloys by varying ring thickness to find out the critical thickness for occurrence of hot tears. The alloy was cast using different strontium (Sr) concentrations (0.2, 0.4, 0.6%). Effects of strontium concentrations were studied in terms of fluidity, porosity content, microstructure and tensile properties of Al–6Zn alloy. In the present work, unmodified and Sr modified alloy casts were characterized by SEM, EDS and XRD respectively. Al–6Zn ingots were procured by master alloy route. Repetition of stepped ring test on the critical thickness showed that hot tear were successfully eliminated significantly due to the addition of Sr. On the other hand, 0.6% Sr also exhibited a good amount of porosity and decrease in elongation. Shorter fluidity length was observed in 0.2% Sr modified alloy. Mechanical and metallographic tests revealed that the alloy castings modified with 0.4% Sr offered better results in yield strength, less porosity and an improved hot tear resistance at micro and macro levels.

Experimental Set Up to Improve Machining Performance of Silicon Dioxide (Quartz) in Magnetic Field Assisted TW-ECSM Process

In the present scenario, machining of the pioneering engineering materials such as various ceramics and composites which possess high hardness, brittleness, strength and electrically insulated becomes very difficult. This study focuses on the development of magnetic field assisted traveling wire electrochemical spark machining (MF-TWECSM) process set up and its utilization for the machining of electrically insulated materials. TW-ECSM process is a combination of the Wire-EDM and ECM processes. In this process, effects of the electrochemical reaction and electric spark are responsible for the material removal from the workpiece. Quartz found to be suitable as work material due its high hardness, good chemical stability and piezoelectric properties. Magnetic field has been applied during the machining for better circulation of the electrolyte during experimentation. Enhanced electrolyte circulation improves the efficiency of the process resulting in higher material removal rate (MRR) of the work material and reduction in the discharge current during experimentation. The improvement in MRR with magnetic field was found in the percentage range of 9% to 200% during experimentation. For the very first time, a brass wire with diameter 0.1 mm has been used during TW-ECSM process.