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RISS 인기검색어
- 검색키워드
- 저자 : DINH SY TRUONG (검색결과 2 건)
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Micro-texturing technology on cylindrical stainless steel surface for biomedical applications
Truong, Dinh Sy Kangwon National Univ 2013 국내석사
Evaluation of micro-texturing technology on biomedical material has been developing in recent decades. In particular, increase or reduction of friction force on surgical equipment has fascinated a larger number of researchers. In this study, we evaluated the micro-texturing technique that changed the needle surface's structure. The results lead to orientation how to minimize pain and damage during injection process or improve the biocompatibility for implantable devices. Biomedical biopsy needles were made from stainless steel 316L. Stainless steel 316L contains Iron, Molybdenum, Chromium and Nickel as main compositions. In general, Chromium helps to prevent corrosion and scratch, Nickel provides smooth and Molybdenum helps to have a greater hardness and maintains a cutting edge. Furthermore, in order to measure friction force, the material that is identical human tissue called phantom tissue was utilized. After that, the textured biopsy needle will be injected through the tissue for calculating friction force. Also, we designed a surface friction measuring system that includes movement and fix part. The movement part brings tissue and move in vertical direction. The fix part helps to keep needle. In order to texture the surface of biopsy needles, a PDMS mold was design as hexahemispherical shape with the pitch of 30?m. Before rolling needles for fabricating patterns, AZ 4620 (PR-photoresist) was poured upon the PDMS mold and carried out doctoring step. After this, PR patterned needles were dipped into etchant solution for etching process, leading to micro-texturing surface. The solution contains FeCl3: HCl: HNO3 = 10:10:5 in weight ratio. The etching stage implemented at 40℃ and etching time interval ranged from 10 seconds to 60 seconds. In general, the results of experiments will provide the influences of pattern depth, pattern diameter as well as velocity of injection.
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Thermally affected high-speed spindle system with angular contact ball bearings
DINH SY TRUONG University of Science and Technology, Daejeon, Rep 2020 국내박사
Failure and vibration of high-speed spindles in machine tools have been the common issues during the machining process. Investigating the vibration of spindles helps engineers to predict the performance of machining elements before manufacturing. As the rotational velocity increases, the spindle performance is affected by a variety of mechanical determinants of bearings such as stiffness, contact loads, contact angle, axial displacement, bearing configurations, and thermal effects. Stiffness of the bearings directly influences the dynamic properties of a high-speed spindle system and plays a significant function with respect to precision manufacturing quality. In this thesis, a new approach is developed to predict the thermal behavior of a high-speed spindle, estimate the thermal expansion and generate stiffness matrices of the bearings for angular contact ball bearings. The heat convection of the balls in the lubricant, bearing inner ring surfaces, the spindle shaft in quiescent air, and spindle housing in the room temperature was calculated. Heat sources such as the heat generated by the embedded motor, and bearing friction, were simulated and utilized in a steady-state thermal model built in ANSYS. The heat effects were incorporated into a static structural model. Ball thermal expansion was determined based on changes in the coordinates of nodal points on the surface of the ball. Also, radial thermal expansion coefficients of the couplings between the bearing inner ring-shaft, and outer ring-housing are included for generating the front and rear bearing stiffness matrices. By applying the Newton-Raphson technique, the matrices of bearing stiffness under thermal effects were produced in five by five. Declines in the coupling stiffness, axial, radial, and angular stiffness values were determined as rotational spindle speed increased. The coefficients of stiffness were increased significantly due to the thermal effects. The bearing stiffness was compared to the one measured using an earlier thermal network method for validation. Also, the thermally affected stiffness matrices of the bearings are generated without the effects of centrifugal expansions. These stiffness matrices were used as inputs for a finite element model generated in the ANSYS Workbench environment, in which the bearings were simulated as bushing joints with five degrees of freedom, to numerically compute the acceleration spindle frequency responses. The findings showed that the spindle natural frequencies are decreasing with the spindle system rising temperature. This was because of reductions in the coefficients of the bearing stiffness, caused by decreases in the bearing inner ring loads. An experimental system was set up to measure the acceleration frequency response function, and the results showed good agreement with the simulations.
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