Byline: Jung-Won Lee (1), Seok-Jae Ha (2), Yong-Kyu Cho (2), Ki-Beom Kim (2), Myeong-Woo Cho (1) Keywords: Flow analysis; Micro magnetorheological (MR) fluid jet polishing; Micro mold material; Surface roughnes Abstract: Abrasive fluid jet polishing processes have been used for the polishing of optical surfaces with complex shapes. However, unstable and unpredictable polishing spots can be generated due to the fundamental property of an abrasive fluid jet that it begins to lose its coherence as the jet exits a nozzle. To solve such problems, MR fluid jet polishing has been suggested using a mixture of abrasives and MR fluid whose flow properties can be readily changed according to imposed magnetic field intensity. The MR fluid jet can be stabilized by imposed magnetic fields, thus it can remain collimated and coherent before it impinges upon the workpiece surface. In this study, Micro MR fluid jet polishing system was developed to investigate the polishing characteristics of micro mold material (Brass and nickel). Preferentially, to evaluate the stability of the developed Micro `MR fluid jet polishing system, polishing spots and cross-section profiles with polishing time were investigated. As a result, the surface roughness of brass was Ra = 1.84 nm, and the nickel was Ra = 2.31 nm by the developed micro MR fluid jet polishing system. Finally, it can be confirmed that the developed Micro MR fluid polishing system can be applied for stable and predictable precise polishing of micro mold materials (Brass and nickel). In present study, as a basic step for modeling the fatigue behavior of an extruded Al alloy cylinder, the fatigue crack growth data of the alloy was collected in two orientations. Microstructural analysis revealed that the material had recrystallized grains and clusters of constituent particles aligned in the direction of extrusion. Fatigue life of the samples revealed a shorter fatigue life representing a higher fatigue crack growth rate in transverse direction. Author Affiliation: (1) Division of Mechanical Engineering, Inha University, Incheon, 402-751, Korea (2) Department of Mechanical Engineering, Inha University, Incheon, 402-751, Korea Article History: Registration Date: 13/05/2015 Received Date: 23/09/2014 Accepted Date: 05/11/2014 Online Date: 16/05/2015 Article note: Recommended by Associate Editor Haedo Jeong Jung-Won Lee received his M.S. and Ph.D. degrees in Mechanical Engineering from Inha University, Incheon, Korea, 2008 and 2013. He is currently a research professor at the division of Mecha nical Engineering at Inha University. His research interest includes MR polishing, Micro MR fluid jet polishing, Micro machining, Maskless lithography process, and CAD/ CAM. Myeong-Woo Cho received his B.S. and M.S. in Mechanical Engineering from Seoul University, Seoul, Korea, 1983 and 1985. He then received his Ph.D. degree from Illinois University at Chicago. Dr. Cho is currently a professor at the division of Mechanical Engineering at Inha University. Dr. Cho's research interests include Micro machining and Micro manufacturing system.