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Kurniawan, Rendi,Thirumalai Kumaran, S.,Arumuga Prabu, V.,Zhen, Yu,Park, Ki Moon,Kwak, Ye In,Mofizul Islam, Md.,Ko, Tae Jo Elsevier 2017 MEASUREMENT -LONDON- Vol.110 No.-
<P><B>Abstract</B></P> <P>An ultrasonic assisted dry electrical discharge machining (US-EDM) process in a gaseous fluid medium was proposed to remove the burrs formed on the exit region of a drilled hole. In preliminary experiment, three different electrode tools (copper, brass, and aluminum) were utilized. In secondary experiment, US-EDM and dry-EDM were compared and performed using the copper tool. US-EDM parameters, such as capacitance (C), pulse-on time (T<SUB>ON</SUB>), and vibration amplitude (A<SUB>p-p</SUB>) were considered as functions of the predicted burr removal rates (BRRs) model. Based on signal to noise (S/N) ratio analysis, machining parameters C=10<SUP>−2</SUP> µF, T<SUB>ON</SUB> =150µs, and A<SUB>p-p</SUB> =4.919µm provided the optimal BRR. The BRR was affected the most by capacitance, followed by pulse-on time and ultrasonic vibration amplitude. The copper tool provided a higher BRR than other tools. US-EDM is considerably effective when T<SUB>ON</SUB> is low and the performance of US-EDM is better than that of Dry-EDM. Scanning electron microscopy (SEM) analysis showed that the US-EDM method created a heat-affected zone surrounding the machined surface of the deburred exit hole in range of 200µm–500µm.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The novelty of a burr removal rate (BRR) model was proposed and validated in this study. </LI> <LI> The influence of the US-EDM process parameters on the BRR value was studied. </LI> <LI> The relationship between the input and output processes was evaluated statistically. </LI> <LI> The optimal machining parameter for the BRR value was validated. </LI> <LI> The comparison between US-EDM and Dry-EDM process was evaluated. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Kumaran, S. Thirumalai,Ko, Tae Jo,Uthayakumar, M.,Islam, Md. Mofizul Elsevier 2017 Journal of Alloys and Compounds Vol.724 No.-
<P><B>Abstract</B></P> <P>In the present work, two different carbon fiber-reinforced plastics (CFRP), namely, unidirectional (UD) and UD with a woven fabric surface, were selected in order to investigate the surface roughness as a result of machining with an abrasive water jet machine (AWJM). The experiments were conducted based on an L27 orthogonal array by varying the process parameters such as jet pressure (JP), traverse speed (TS), and standoff distance (SOD). Regression models were developed to predict the correlation between the input parameters and the surface roughness for each composite. The experimental results showed that increased pressure with lower TS and SOD produced a good surface finish on the composites. Very low roughness was achieved when machining the UD with woven fabric surface CFRP composite. The developed regression models indicated the significance of the design (at a 95% confidence level) with reduced error. The JP followed by the SOD were found to be the major parameters affecting the surface roughness. Finally, the deformation, delamination, and machined surface morphology were studied using a non-contact three-dimensional surface measurement system and scanning electron microscopy (SEM) images.</P>
Rotary ultrasonic machining of woven CFRP composite in a cryogenic environment
Thirumalai Kumaran, S.,Ko, Tae Jo,Li, Changping,Yu, Zhen,Uthayakumar, M. ELSEVIER SCIENCE 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.698 No.-
<P><B>Abstract</B></P> <P>In the present study, rotary ultrasonic machining (RUM) was adopted to perform drilling of carbon fiber reinforced plastics (CFRP) in a cryogenic environment. An L27 orthogonal array was selected to conduct experiments by varying the spindle speed (denoted as N), feed rate (denoted as f), and ultrasonic power (denoted as P). The thrust force (denoted as Fz), exit burr area, and surface roughness (denoted as Ra) were measured to evaluate the machining performance. The influence of process parameters and the regression model were derived for each output quality response. Additionally, multi-objective optimization was performed using desirability analysis, and the predicted levels were used for confirmation. The results indicated that the feed rate (f) contributed more to the thrust force (Fz) by 45.85% and a maximum thrust force was recorded at 0.1 mm/rev. A decrease in spindle speed (N) was associated with an increase in feed rate (f) and ultrasonic power (P), and it resulted in minimum exit burr area. The influence of ultrasonic power (P) was highly significant in reducing burrs with a contribution of 52.45%. Conversely, the surface roughness (Ra) of the drill holes decreased at 3000 rpm, and this was attributed to the brittle fracture of the fibers at a lower temperature. Both N (30.88%) and f (30.83%) had an equal influence on producing a better surface finish in the drill holes. Furthermore, the predicted optimal settings were used to validate the results and were found to be within 95% confidence and prediction interval. Finally, the microscopic images of tool wear, burr formation, and drill hole surface morphology were analyzed and examined.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Prediction of regression model for RUM of CFRP in a cryogenic environment. </LI> <LI> Output responses such as thrust force, burr area and roughness are investigated. </LI> <LI> The adequacy of an ANOVA model is checked for each output response. </LI> <LI> Optimization is performed by desirability analysis and the results are validated. </LI> <LI> Tool wear, burr formation, and drill hole surface morphology are analyzed. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
정상태,S. Thirumalai Kumaran,Changping Li,쿠르니아완렌디,고태조 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.9
Micro-dimple formation improves the tribological behavior of a material. This study investigates dimple formation on a titanium (Ti-6Al-4V) alloy by using electrical discharge drilling. Input parameters, namely capacitance (C), pulse-on-time (Ton), and voltage (V), were varied to measure the output quality responses including dimple depth, burr height, and burr width. The experimental results indicated that the quality of the dimple is determined based on the spark energy and rate of material removal. A regression analysis was performed for each output response. The developed model confirmed the fitness at a 95 % confidence interval. The contribution of each factor and its significance was determined by using analysis of variance (ANOVA). Further, the optimum drilling condition was predicted by using desirability analysis (C = 10000 pF, Ton = 100 µs, and V = 180 V). The microscopic view of the dimple array and the micro-dimple geometry were analyzed by using scanning electron microscopy images.
Rendi Kurniawan,S. Thirumalai Kumaran,Tae Jo Ko 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.22 No.9
This paper compares UEVC (ultrasonic-elliptical-vibration-cutting) and a CC (conventional-cutting) process for microgrooving in AISI 1045 via FEA (finite-element-analysis) in 2D orthogonal technique. The stress, cutting force, temperature, and residual stress have been examined. Average cutting forces in UEVC can be decreased when the velocity ratio is reduced. The average cutting forces in UEVC are declined as the vibration magnitude increases and inclined as the feed velocities and DOC increases. The stress concentration and peak cutting tool temperature in UEVC are higher than those in the CC technique because of the higher relative cutting velocity. Additionally, the peak thrust force in UEVC is larger than that in the CC technique. The main simulated residual stresses for both processes are tensile stresses, which decrease rapidly in UEVC. The compressive stress in UEVC can be more negative than that in the CC technique owing to the compression effect of the vibrated cutting tool.
Mechanism study of micro-electrical discharge drilling method during micro-dimpling
Sang Tae Jung,Rendi Kurniawan,S. Thirumalai Kumaran,In Jun Yoon,Tae Jo Ko 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.6
This paper reports the cutting mechanism in micro-electrical discharge drilling (µEDD) during a micro-dimpling process. A combination of fundamental micro-drilling and micro-electrical discharge machining (µEDM) is considered the main mechanism in the µEDD process. First, the cutting force in micro-drilling was modeled on a chisel and lip section based on a mechanistic model of the oblique cutting. Second, the model of the µEDM was also included based on uniform heat flux. Experiments of a micro-dimple were carried out on a titanium alloy (Ti6Al4V) to confirm the model validity. The validation confirms that the proposed cutting force model can be applied to predict the thrust force during micro-dimpling under µEDD. In addition, a micro-dimple morphology is also discussed.
Farooq Ahmed,Tae Jo Ko,Lee Jongmin,Yein Kwak,In Jun Yoon,S. Thirumalai Kumaran 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.22 No.7
Materials with high hardness are usually difficult to machine, and accomplishing precise and economical machining depends on all the cutting conditions. Appropriate tool geometry is one important aspect for the cutting process that can be optimized based on the machining parameters. In this study, the finite element simulation method was applied to analyze the effects of tool geometry on the cutting forces and tool temperature during the ball end milling of tool steel (AISI H13). Multiobjective optimization of the geometrical parameters was performed using the grey relational method, which gave a set of input parameters to obtain the minimum cutting forces and temperature. The findings of this work could be used as a basis for tool design. Experiments were conducted with mono-objective and multi-objective optimal geometries to validate the finite element analysis. The finite element and experimental results were both congruous with an error limit of 5%.