Browsing by Author "Bilgin, Onur"

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Design and development of a durable series elastic actuator with an optimized spring topology
(Sage, 2021-12) Yıldırım, M. C.; Şendur, Polat; Kansızoğlu, Mehmet Taha; Uras, U.; Bilgin, Onur; Emre, Sinan; Yapıcı, Güney Güven; Arık, Mehmet; Uğurlu, Regaip Barkan; Mechanical Engineering; ŞENDUR, Polat; YAPICI, Güney Güven; ARIK, Mehmet; UĞURLU, Regaip Barkan; Kansızoğlu, Mehmet Taha; Bilgin, Onur; Emre, Sinan
This paper aims to present the integrated design, development, and testing procedures for a state-of-the-art torsion-based series elastic actuator that could be reliably employed for long-term use in force-controlled robot applications. The main objective in designing the actuator was to meet weight and dimensional requirements whilst improving the long-term durability, ensuring high torque output, and containing its total weight. A four-fold design approach was implemented: (i) following recursive design-and-test procedures, an optimal torsional spring topology was unveiled with the help of SIMP (Solid Isotropic Material with Penalization) topology optimization method, (ii) the proposed spring was manufactured and multiple specimens were experimentally tested via a torsional test machine to validate linearity, loading rate response, and mechanical limits, (iii) the actuator’s thermal response was experimentally scrutinized to ensure that the generated heat was dissipated for long-term use, and (iv) the fatigue life of the spring was computed with the help of real-life experiment data. Having concluded the development and verification procedures, two different versions of the actuator were built, and preliminary torque control experiments were conducted. In conclusion, favorable torque tracking with a bandwidth of 19 Hz was achieved while peak-to-peak torque input was 20 Nm.
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Effect of boronizing and WC coating on the high temperature mechanical behavior of AISI 321 stainless steel
(Trans Tech Publications Ltd, 2022) Bilgin, Onur; Yapıcı, Güney Güven; Mechanical Engineering; YAPICI, Güney Güven; Bilgin, Onur
In the current paper, the effect of two different coating techniques of boronizing and tungsten carbide (WC) coating on the room and high temperature tensile behavior of the AISI 321 stainless steel were investigated. Consequently, the fracture morphology observations were conducted via scanning electron microscopy (SEM) to inspect the variation of fracture mechanisms after implementing different coating methods. The results of tensile tests at room temperature revealed that despite boronizing reduced the yield strength of the sample due to the softening and grain growth at high coating temperature, the dispersion of boron particles improved the work hardening and ductility of boronized AISI 321. In contrast, the strain to failure of the WC coated sample was decreased due to the fast fracture of the ceramic WC layer at both room and high tensile tests. Furthermore, results of SEM revealed that particle decomposition occured on the fracture surface of the boronized 321 stainless steel represented by dispersed boron particles on the edges of the dimples after failure at high temperature.
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Effect of different surface treatments on the tensile and wear behavior of Inconel 625 superalloy and aisi 321 stainless steel
Bilgin, Onur; Yapıcı, Güney Güven; Yapıcı, Güney Güven; Başol, Altuğ Melik; İpekoğlu, M.; Department of Mechanical Engineering; Bilgin, Onur
AISI 321 stainless steel and Inconel 625 superalloy are utilized in an extensive range of applications such as aircraft engines, nuclear powerplants and industrial furnaces due to their excellent mechanical properties at high temperatures. The surface treatment of these materials is necessary due to the extreme work ing environments. Boronizing and WC coating is the most important surface hard ening processes. In the current work, the effect of boronizing and WC coating on the wear performance and tensile behavior of AISI 321 and Inconel 625 at room and high temperature were investigated. Furthermore, damage mechanisms and fracture morphologies were observed using Scanning Electron Microscopy (SEM) and optical profilometry. According to room temperature tensile test results, yield strength (YS) and ultimate tensile strength (UTS) of the samples are reduced after the boronizing process. This strength reduction may be attributed to the softening of the material throughout the boronizing process at high temperature of 1100°C. On the other hand, ductility of the Inconel 625 samples has been decreased due to dynamic strain aging at 600°C. The yield strength of the boronized samples was significantly reduced because of the decomposition of boron particles throughout tensile test at elevated temperatures. Consequently, the fracture morphology observations revealed that the main fracture mechanism of both coated and uncoated conditions at high temperature was a ductile fracture represented by deep dimples. However, the boronized sample was drastically affected by grain growth during boronizing process and decomposition of dispersed particles. In contrast, the strain to failure of the WC coated sample was decreased due to the fast fracture of the ceramic WC layer at both room and high temperature tensile tests. Furthermore, results of SEM revealed that particle decomposition occured on the fracture surface of the boronized 321 stainless steel represented by dispersed boron particles on the edges of the dimples after failure at high temperature. Due to the high hardness and heat resistance of WC coated layer, the friction coefficient of the sample was higher than that of boronized and uncoated conditions at room tempearature. It was seen that the wear rates of boronized and WC coated AISI 321 were extremely lower than that of uncoated sample. On the other hand, at 600°C, WC coated wear rate was still lower but uncoated and boronized samples’ values were similar to the room temperature results. Inspection of room temperature the wear test results revealed that the wear rates of Inconel 625 uncoated and coated samples were similar to the results of AISI 321. WC coated samples’ wear rate was tremendously lower than the others. At high temperature, the boronized Inconel 625 had higher friction coefficient than the WC coated sample. A fluctuation was also noticed, which is linked to boron particle aggregation on the surface at high temperatures.
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An integrated design approach for a series elastic actuator: Stiffness formulation, fatigue analysis, thermal management
(IEEE, 2017-12-22) Yıldırım, Mehmet Can; Şendur, Polat; Bilgin, Onur; Gülek, Berk; Yapıcı, Güney Güven; Uğurlu, Regaip Barkan; Mechanical Engineering; YAPICI, Güney Güven; UĞURLU, Regaip Barkan; ŞENDUR, Polat; Yıldırım, Mehmet Can; Bilgin, Onur; Gülek, Berk
This paper presents an integrated mechanical design approach for the long-Term and repetitive use of series elastic actuators (SEAs). Already, computational models for series elastic actuator design have been developed in order to address the challenging weight and volume targets. However, an integrated design method in which the coupling effects between various interacting requirements that are explored at every stage of the design cycle does not exist. In particular, the interactions between the torsional stiffness, strength, fatigue life and thermal performance are not analyzed in-depth. To this end, we propose a comprehensive design approach in which the aforementioned requirements (FEA, stiffness formulation, fatigue analysis, and thermal management) are integrated in a complementary manner. Computer-Aided analyses and experimental results verified the effectiveness of our design approach. The proposed approach is employed to manufacture our SEA module CoEx-SEA.