B. Mohan

Influence of Discharge Current Pulse on Machinability in Electrical Discharge Machining

In this study, the machining characteristics of AISI 202 stainless steel have been investigated in thermal erosion process. Taguchi method based experiments have been conducted with conventional and modified pulse generators using electric discharge machining. Material removal rate (MRR) and surface roughness were taken to evaluate performance of process. Gap voltage, discharge current, and duty factor have been chosen as input parameters to access the machinability. The efficacy of pulse generators in thermal erosion process is determined by high material removing property and better surface finish. Since this machining process has stochastic nature, conventional RC relaxation pulse generator and transistor pulse train generator could not satisfy both the two requirements. It is proved that modified ISO current pulse generator could produce better surface finish with high MRR than conventional pulse generators in thermal erosion process.

Multi-objective optimization of friction stir welding parameters using desirability approach to join Al/SiCp metal matrix composites

Silicon carbide particulate (SiCp) reinforced cast aluminium (Al) based metal matrix composites (MMCs) have gained wide acceptance in the fabrication of light weight structures requiring high specific strength, high temperature capability and good wear resistance. Friction stir welding (FSW) process parameters play major role in deciding the performance of welded joints. The ultimate tensile strength, notch tensile strength and weld nugget hardness of friction stir butt welded joints of cast Al/SiCp MMCs (AA6061 with 20% (volume fraction) of SiCp) were investigated. The relationships between the FSW process parameters (rotational speed, welding speed and axial force) and the responses (ultimate tensile strength, notch tensile strength and weld nugget hardness) were established. The optimal welding parameters to maximize the mechanical properties were identified by using desirability approach. From this investigation, it is found that the joints fabricated with the tool rotational speed of 1370 r/min, welding speed of 88.9 mm/min, and axial force of 9.6 kN yield the maximum ultimate tensile strength, notch tensile strength and hardness of 265 MPa, 201 MPa and HV114, respectively.

Effect of Heat Input on Mechanical and Metallurgical Properties of Friction Stir Welded AA6061-10% SiCp MMCs

Metal matrix composites (MMCs) reinforced with SiC particles combine the matrix properties with those of the ceramic reinforcement, leading to higher stiffness and superior thermal stability with respect to the corresponding unreinforced alloys. However, their wide application as structural material needs proper development of a suitable joining process. In this investigation, an attempt was made to study the effect of heat input on the evolution of microstructure in weld region of friction stir welded AA6061-10% SiCp MMCs. The tensile properties of the joints were evaluated and they are related with microstructure and heat input of the process. The microstructure characterization of the weld zone shows evidence of a substantial grain refinement of the aluminum matrix and fracturing of reinforcement particles due to dynamic recrystallization induced by the plastic deformation and frictional heating during welding.

Effect of Tool Electrode Resolidification on Surface Hardness in Electrical Discharge Machining

Since the recast layer affects the surface hardness of the workpiece in electrical discharge machining (EDM), it is very important to investigate the effect of the tool electrode on the machined surface. Owing to its importance in the locomotive structural elements, an attempt has been made to analyze the effect of EDM process on surface hardness of AISI 202 stainless steel with different tool electrodes such as brass and tungsten carbide. The investigation was carried out with various process parameters, and surface hardness values were computed using micro Vickers hardness tester. From the experimental results, it has been observed that the surface hardness of the workpiece increases with tungsten carbide tool electrode whereas it decreases with brass tool electrode due to the layer formation on the machined surface of the workpiece.

Influence of Tool Electrode Properties on Machinability in Spark Erosion Machining

High-strength materials can be easily machined by spark erosion process to obtain complex shapes. The discharge energy can be characterized by the current flowing through the dielectric medium in spark erosion process during the machining. The performance measures such as workpiece erosion, tool electrode erosion, and surface finish can be modified by the properties of tool electrode material. This current is determined by the conductivity of the tool electrode material. The erosion process has been experimentally investigated to analyze the effects of tool electrode on machinability of AISI 202 stainless steel in the present study. Copper, brass, and tungsten carbide have been used as the tool electrode with different combinations of electrical input parameters. From the results, it is observed that tool properties of tool electrode material could have an influence on machining characteristics in spark erosion process. Copper tool could give higher material removal rate, whereas tungsten carbide could produce better surface finish after machining process.

Monitoring and Fuzzy Control Approach for Efficient Electrical Discharge Machining Process

The intricate shape die for manufacturing industries can be easily produced by the electrical discharge machining (EDM) process. Since the surface roughness of the die directly affects the surface finish of the product, it is very important to enhance the surface quality of machined surface using the EDM process. In the present study, a fuzzy base control algorithm has been developed for monitoring discharge current and spark gap. The discharge current has to be monitored during machining process to reduce the surface roughness, whereas the spark gap has to be monitored to avoid the abhorrent arcing effect. The levels of process such as roughing, semifinishing, and finishing have been taken as the input to fuzzy rule base. The control algorithm has been evaluated with real-time environment. From the experimental results, it has been observed that the developed control approach for the EDM process has considerably improved the surface quality of the EDM product with higher material removal rate.

Experimental Investigation of Iso Energy Pulse Generator on Performance Measures in EDM

It is important to improve the process mechanism of the electrical discharge machining (EDM) to achieve fine surface quality due to its stochastic nature. The conventional transistor pulse generator produces higher surface roughness in electro-erosion process. In the present study, an attempt has been made to investigate the influence of iso (identical) energy pulse generator on machining characteristics of erosion process. The modified pulse generator can produce uniform discharge energy distribution which is characterized by variable pulse width modulation adopted with the current sensor. The proposed pulse generator can control the ionization path diameter of insulator medium by varying the pulse duration. From the experimental results, it has been observed that the modified iso energy pulse generator has improved the surface quality with higher material removal rate (MRR). The iso energy pulse generator has removed 5% more material from the work piece than the conventional transistor pulse generator. It has also viewed that the modified iso energy pulse generator has generator 40% lower surface roughness than the conventional transistor pulse generator. It has also observed that the modified pulse controller could considerably minimize the arcing effect in the machining process.

Influence of Cell Size on the Core Shear Properties of FRP Honeycomb Sandwich Panels

This article deals with the influence of cell size on the core shear modulus and shear strength of fiber-reinforced plastic (FRP) honeycomb core sandwich panels. A relationship between the cell size and core density has been established for the honeycomb core made by matching the mold method. The cell size ranges from 8 to 25 mm, with the cell height kept constant at 8 mm. The sandwich panels are prepared with facings made of Bi-woven glass “E” fabric, using the vacuum bagging technique. The core shear modulus “G” and flexural stiffness “D” of the sandwich panels have been experimentally determined as per the ASTM C393. The shear strength of the sandwich panel has been determined using a short beam bend test. A correlation has been established between the core density and the core shear modulus as well as the core density and the core shear strength. The results have been compared with those of sandwich panels made with polyurethane (PUR) foam as the core material of different densities. It has been found that for the given core density the core shear modulus of the FRP honeycomb core is far higher than that of PUR foam. However, the shear strength of the FRP honeycomb sandwich panels is only marginally higher when compared to that of PUR foam.

Design and fabrication of control system-based ISO pulse generator for electrical discharge machining

Electrical discharge machining (EDM) is good example for mechatronics application, in which, the material is removed by thermal energy. The thermal energy is produced by applying DC pulses between tool electrode and work piece. The characteristics of DC pulses are determined by the pulse generators. Due to its high material removal nature, transistor pulse train generator is commonly employed. Since EDM process has stochastic nature, transistor pulse generator produces high surface roughness. To produce better product quality, a constant discharging current is needed throughout the process. In this research, an ISO duration current pulse generator has been designed and developed for obtaining good surface finish. It is found that modified ISO pulse generator could produce better surface finish.

Nonlinear Mathematical Modelling of Servo Pneumatic Positioning System

Servo pneumatics is a mechatronic approach that enables accurate control of pneumatic drives which are widely used in automated systems. This technology can provide an alternative for less efficient electromechanical and high cost hydraulic systems. The main problem in the servo pneumatics is the fact that the variables associated with the system such as frictional forces, mass flow rate and pressure in the chambers, varies in nonlinear fashion. The paper presents nonlinear mathematical model for motion of cylinder, pressure in the cylinder chambers and mass flow rate from valve to cylinder are derived from basic gas laws and dynamics of the system. The equation for friction force based on LuGre model is also presented in the paper. Further, a nonlinear state space representation for the servo pneumatic positioning system is obtained. The developed model can be used to simulate the system response, which will help in choice of components used and also in the development of precise controller for the system.