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Sasi R.,Indian National Institute of Engineering | Kanmani Subbu S.,Indian National Institute of Engineering | Palani I.A.,IIT IndoreMadhya Pradesh
Surface and Coatings Technology | Year: 2017

Texturing the rake face of the cutting tools has recently emerged as a promising and environment friendly method for reducing friction during machining. Laser surface texturing has been the most commonly used method for fabricating textures on the cutting tool. This paper reports the experimental study of fabricating an array of micro scale dimples on the rake face of high speed steel cutting tool using a pulsed Nd:YAG laser. The effect of the laser parameters like wavelength and fluence on the dimensions and form of individual dimples were studied. Analysis of results show that uniform circular shaped dimples with very little spatter can be obtained using low fluence levels at wavelength of 355 nm. An array of micro scale dimples were then fabricated on the cutting tool using the optimized parameter levels. A very low textured area density was used in order to understand the process of chip flow over the textures and study the effect of machining on individual dimples. This textured cutting tool was then used in orthogonal dry machining of Al7075-T6 aerospace alloy and compared with the performance of conventional tools. Use of textured cutting tools resulted in reduction of both cutting and thrust forces. The tool-chip contact length is also less in the case of textured tool. The results show that textured high speed steel tools can significantly improve the metal cutting process while dry machining ductile workpieces. © 2017 Elsevier B.V.

Gautam P.,IIT IndoreMadhya Pradesh | Misra R.,IIT IndoreMadhya Pradesh | Koukaras E.N.,University of Patras | Koukaras E.N.,Foundation for Research and Technology Hellas | And 2 more authors.
Organic Electronics: physics, materials, applications | Year: 2015

We report on the optical and electrochemical characterization (experimental and theoretical) of two donor substituted benzothiadiazole with different cyano based acceptor π-linkers, tetracyanobutadiene (TCBD) SM1 and dicyanoquinomethane (DCNQ) SM2, and explore them as the donor component for solution processed bulk heterojunction organic solar cells, along with PC71BM as the electron acceptor. The solution bulk heterojunction (BHJ) solar cells based on dichloromethane (DCM) processed active layer with SM1 and SM2 as donor and PC71BM as acceptor achieve power conversion efficiency (PCE) of 2.76% and 3.61%, respectively. The solar cells based on these two small molecules exhibit good Voc, which is attributed to their deep HOMO energy level. The higher PCE of the device based on SM2 compared to SM1 is attributed to the its small bandgap, broader absorption profile and enhanced hole mobility. Additionally, the PCE of the SM2:PC71BM based solar cells processed with 1-chloronaphthalene CN (3 v%)/DCM is further improved reaching upto 4.86%. This increase in PCE has been attributed to the improved nanoscale morphology and more balanced charge transport in the device, due to the solvent additive. © 2015 Elsevier B.V.

Jadhav T.,IIT IndoreMadhya Pradesh | Misra R.,IIT IndoreMadhya Pradesh | Biswas S.,LNMIIT | Sharma G.D.,R and nter for Science and Engineering
Physical Chemistry Chemical Physics | Year: 2015

In this study, we have used three D-A type carbazole substituted BODIPY (carbazole connected to the meso position of BODIPY) small molecules as donors along with PC71BM as an electron acceptor for the fabrication of solution processed bulk heterojunction organic solar cells. The devices based on the as cast active layer showed power conversion efficiency in the range of 2.20-2.70%, with high open circuit voltage (Voc) in the range of 0.94-1.08 V. The high Voc is related to the deeper highest occupied molecular orbital energy level of these small molecules. The power conversion efficiency (PCE) of devices based on thermally annealed and solvent vapor annealed (TSVA) 3a:PC71BM and 3c:PC71BM processed active layers improved up to 5.05% and 4.80%, respectively, attributed to the improved light harvesting ability of active layers, better phase separation for exciton dissociation and balanced charge transport, induced by the TA and TSVA treatment. This journal is © the Owner Societies.

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