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Articles by Ahsan Ali Khan
Total Records ( 6 ) for Ahsan Ali Khan
  A.K.M. Asif Iqbal and Ahsan Ali Khan
  Problem statement: Electrical Discharge Machining (EDM) is the most widely used non conventional machining process for removing material from workpiece by means of a series of repeated electric discharges. Electrical Discharge milling (ED-milling) is an emerging technology where a cylindrical tool electrode follows a programmed path in order to obtain the desired shape of a part. During machining of metals by EDM process, a large amount of heat is generated for which the surface characteristics of the metals are affected. This phenomenon is unavoidable but this can be controlled by suitable selection of the process parameters. Though in most of the cases only electrical parameters are chosen but non electrical parameters also play significant role in the area of surface integrity of the machined surface. The present study emphasized to establish a comprehensive analysis of surface integrity, including the micro cracks, recast layer thickness and material migration by combining both electrical and non electrical process parameters under a wide range of machining condition. Approach: In this research, experiment was designed by using design expert software (DOE). Response Surface Methodology (RSM) was used for designing the experiment. The process parameters varied in the present study were the rotational speed of the electrode (N), Voltage (V) and feed rate (f). Stainless steel AISI 304 was chosen as work material while a copper electrode was used for EDM milling operation. The EDM milling operations were performed on EDM machine mikrotools integrated multi process machine tools DT 110. In this research, Scanning Electron Microscope (SEM) was used to investigate the effect of machining parameters on recast layer thickness, micro cracks on the machined surface as well as the percentage of material migration on the workpiece surface. Results: Electrode rotation reduces recast layer thickness of about 16.58% than that of stationary electrode with same voltage and feed rate. Moreover, it was observed that migration of C and Cu on the workpiece surface reduces 8.8 and 60% respectively when using rotary electrode instead of stationary electrode with same parameters setting. Conclusion: These results indicated that voltage and rotary speed of electrode significantly affect various criteria of surface integrity. Electrode rotation helped to reduce micro cracks, recast layer thickness as well as migration of material became less when rotary electrode is used. Besides, the combination of reasonably low voltage and high rpm reduced micro cracks, recast layer thickness and minimized the surface contamination on workpiece surface during EDM milling of stainless steel.
  A.K.M. Asif Iqbal and Ahsan Ali Khan
  Problem statement: Electrical Discharge Machining (EDM) has grown over the last few decades from a novelty to a mainstream manufacturing process. Though, EDM process is very demanding but the mechanism of the process is complex and far from completely understood. It is difficult to establish a model that can accurately predict the performance by correlating the process parameters. The optimum processing parameters are essential to increase the production rate and decrease the machining time, since the materials, which are processed by EDM and even the process is very costly. This research establishes empirical relations regarding machining parameters and the responses in analyzing the machinability of the stainless steel. Approach: The machining factors used are voltage, rotational speed of electrode and feed rate over the responses MRR, EWR and Ra. Response surface methodology was used to investigate the relationships and parametric interactions between the three controllable variables on the MRR, EWR and Ra. Central composite experimental design was used to estimate the model coefficients of the three factors. The responses were modeled using a response surface model based on experimental results. The significant coefficients were obtained by performing Analysis Of Variance (ANOVA) at 95% level of significance. Results: The variation in percentage errors for developed models was found within 5%. Conclusion: The developed models show that voltage and rotary motion of electrode are the most significant machining parameters influencing MRR, EWR and Ra. These models can be used to get the desired responses within the experimental range.
  Ahsan Ali Khan , Noraziaty Bt. Munajat and Harnisah Bt. Tajudin
  In this study the effect of some cutting variables on the quality of the surface produced during abrasive water jet machining of aluminum has been investigated. The type of abrasive used was garnet of mesh size 80. The machining was done on the abrasive water jet machine WJ4080. The cutting variables were stand-off distance of the nozzle from the work surface, work feed rate and jet pressure. The evaluating criteria of the surface produced were width of cut, taper of the cut slot and work surface roughness. It was found experimentally that in order to minimize the width of cut; the nozzle should be placed close to the work surface. Increase in jet pressure results in widening of the cut slot both at the top and the at exit of the jet from the work. However, the width of cut at the bottom (exit) was always found to be larger than that at the top (at a stand-off distance of 3 mm and the work feed rate of 15 mm min–1). It was found that the taper of cut gradually reduces with increase in stand-off distance and was close to zero at the stand-off distance of 4 mm (at a jet pressure of 30 ksi and a work feed rate of 15 mm min–1). The feed rate of the work should be kept within 40 mm min–1 (at the jet pressure of 30 ksi and the stand-off distance of 3 mm), because a feed rate beyond 40 mm min–1 results in sharp increase in taper angle. The jet pressure does not show significant influence on the taper angle within the range of work feed and the stand-off distance considered. Both stand-off distance and the work feed rate show strong influence on the roughness of the machined surface. It was concluded that stand-off distance should be kept within 3 mm (at a jet pressure of 30 ksi and a work feed rate of 15 mm min–1) and the work feed rate should be kept within 30 mm min–1 (at a jet pressure of 30 ksi and a stand-off distance of 3 mm) in order to have a good surface finish, since beyond those values of the parameters the roughness of the machined surface rises sharply. Increase in jet pressure shows positive effect in terms of smoothness of the machined surface. With increase in jet pressure, the surface roughness decreases (at a stand-off distance of 3mm and work feed of 15 mm min–1). This is due to fragmentation of the abrasive particles into smaller sizes at a higher pressure and due to the fact that smaller particles produce smoother surface. It was also found that within the jet pressure considered, the work surface is smoother near the top surface and gradually it becomes rougher at higher depths.
  Ahsan Ali Khan and Sami Salama Hajjaj
  Cermets tools have very high hot hardness together with a low coefficient of friction, which facilitates machining at high speeds. In the present work cermet tools coated with titanium nitride were used to turn austenitic stainless steel at speeds between 300 and 700 m min-1. Feed rates were varied between 0.05 to 0.4 mm rev-1. Depth of cuts were between 0.1 and 0.5 mm. After machining, tool flank wear and the cutting edges were observed using Scanning Electron Microscope (SEM). The experimental results showed that when cermet inserts were used for finishing cuts, very fine surfaces were produced. However, when used for roughing cuts, they tended to fracture unpredictably rather than having gradual flank wear. Thus, the cermet tools were found to perform satisfactorily only for finishing operations with feed rates ranging between 0.1 and 0.2 mm rev-1 and at the maximum depth of cut of 0.3 mm. For stable operations, the maximum cutting speed should be below 600 m min-1; exceeding this limit resulted catastrophic failure of the cutting edge.
  Ahsan Ali Khan , Munira Bt. Mohd Ali and Norhashimah Bt. Mohd Shaffiar
  Wire EDM is in use for a long time for cutting punches and dies, shaped pockets and other machine parts. Surface finish of the machined surface mainly depends on current and voltage used during machining. In the present research experimental investigations have been conducted to establish relationships of job surface finish with current and voltage. Brass wires of diameters 0.3, 0.25, 0.20 and 0.15 mm were used. Work materials tested were mild steel, aluminum, cemented carbide, copper and stainless steel. After machining each material with specific current and voltage the hardness and the job surface roughness were measured and their surfaces were observed under an electron-scanning microscope. Results of the experiments show that in general the machined surface becomes rougher with increase in current and voltage. Microstructures of the specimens also show that craters on the finished surface become larger as a result of using higher current and voltage. It was also found that wires of smaller diameters give smoother surface than those cut with larger diameters. It has been established that machining of carbides should be limited to wires with diameter equal to or less than 0.15 mm. Use of wires of greater diameters causes frequent wire breakage. A statistical analysis was done to pick up the most probabilistic data from the bank of data obtained from the experiments. Finally, mathematical relationships have been developed between job surface finish with current and voltage within the specified ranges for a few work materials.
  Akm Asif Iqbal and Ahsan Ali Khan
  This study reports on the experimental investigations of Material Removal Rate (MRR), Electrode Wear Ratio (EWR) and surface Roughness (Ra) in EDM milling of stainless steel AISI 304. This research establishes empirical relations regarding machining parameters and the responses in analyzing the machinability of the stainless steel. The machining factors used are voltage, rotational speed of electrode and feed rate over the responses MRR, EWR and Ra. Response surface methodology was used to investigate the relationships and parametric interactions between the three controllable variables on the MRR, EWR and Ra. Central composite experimental design was used to estimate the model coefficients of the three factors. The responses were modeled using a response surface model based on experimental results. The significant coefficients were obtained by performing Analysis of Variance (ANOVA) at 95% level of significance. The developed models show that voltage and rotary motion of electrode are the most significant machining parameters influencing MRR, EWR and Ra. These models can be used to get the desired responses within the experimental range.
 
 
 
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