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    Analysis of Surface Roughness and Flank Wear Using the Taguchi Method in Milling of NiTi Shape Memory Alloy with Uncoated Tools
    (Mdpi, 2020) Altas, Emre; Gokkaya, Hasan; Karatas, Meltem Altin; Ozkan, Dervis
    The aim of this study was to optimize machining parameters to obtain the smallest average surface roughness (Ra) and flank wear (Vb) values as a result of the surface milling of a nickel-titanium (NiTi) shape memory alloy (SMA) with uncoated cutting tools with different nose radius (r(epsilon)) under dry cutting conditions. Tungsten carbide cutting tools with different r(epsilon) (0.4 mm and 0.8 mm) were used in milling operations. The milling process was performed as lateral/surface cutting at three different cutting speeds (V-c) (20, 35 and 50 m/min), feed rates (f(z)) (0.03, 0.07 and 0.14 mm/tooth) and a constant axial cutting depth (0.7 mm). The effects of machining parameters in milling experiments were investigated based on the Taguchi L18 (2(1) x 3(2)) orthogonal sequence, and the data obtained were analyzed using the Minitab 17 software. To determine the effects of processing parameters on Ra and Vb, analysis of variance (ANOVA) was used. The analysis results reveal that the dominant factor affecting the Ra is the cutting tool r(epsilon), while the main factor affecting Vb is the f(z). Since the predicted values and measured values are very close to each other, it can be said that optimization is correct according to the validation test results.
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    Finite element simulation and experimental investigation on the effect of temperature on pseudoelastic behavior of perforated Ni-Ti shape memory alloy strips
    (Iop Publishing Ltd, 2022) Altas, Emre; Khosravi, Farshid; Gokkaya, Hasan; Arab Maleki, Vahid; Akinay, Yuksel; Ozdemir, Okan; Bayraktar, Omer
    In the present study, the temperature-dependent pseudoelastic behavior of shape memory alloy (SMA) sheets is studied experimentally and by finite element (FE) modeling. For this purpose, temperature-dependent mechanical properties for Ni-Ti alloy materials are first obtained by using direct tensile and three-point bending experiments at 23 degrees C, 50 degrees C, and 80 degrees C temperatures, respectively. The structure of these materials is examined at different temperatures using SEM images and the XRD test. Furthermore, using the FE model, the pseudoelastic behavior and the effect of temperature on the residual deflection of the prose-shape memory strips with a circular hole under three-point bending loads are studied. After validating the results of the FE model with the results of experimental tests, the effects of various parameters such as the diameter and number of holes on residual deformation and residual strains are investigated. The results show that with increasing temperature, the mechanical properties including the tensile strength, Young's modulus, yield stress, and flexural strength of SMA strips increase significantly. For solid strips, although increasing the temperature increases the maximum flexural force, in contrast, it reduces the flexural stiffness. In solid strips, flexural stiffness decreases by 5.5% with increasing temperature from 23 degrees C to 80 degrees C.
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    Investigation of tribological performance of hydrothermal carbon by pin-on-disc test and warm deep drawing process
    (Iop Publishing Ltd, 2024) Yurt, Ozgur Erdem; Sen, Nuri; Simsir, Hamza; Kucuk, Yilmaz; Altas, Emre; Gok, M. Sabri; Civek, Tolgahan
    In this study, the synthesis of hydrothermal carbon (HTC) lubricant and its usability as a lubricant under hot industrial conditions were investigated. In this context, the characterization of HTC produced from organic sources at low cost and in a short time was performed, and its tribological performance was analysed in detail. HTC produced by the hydrothermal carbonization method was characterized through SEM images and EDS analysis. To determine the effect of HTC on friction at different temperatures, HTC was subjected to a pin-on-disc wear test with AA5754 material. The effect of various lubricants, temperatures, blank holder pressure, and forming speed parameters on the forming force for the analysis of the tribological effect of HTC on deep drawing processes were statistically analysed. The performance of HTC was compared with Teflon, fullerenes, graphene, and carbon nanotube (CNT) materials. According to the results obtained from wear tests, the lowest friction coefficient value was achieved in the presence of fullerenes as the lubricant, and as the temperature increased, the friction coefficient decreased. It was observed that HTC exhibited lower performance in the wear test compared to fullerenes due to oxidation. When the effect of deep drawing parameters on the forming force was analysed, it was concluded that the most effective parameters were temperature (72.32%) and lubricant (20.89%). According to the S/N analysis results, the minimum forming force was obtained under the conditions of solid Teflon lubricant, 250 degrees C temperature, 15-bar blank holder pressure, and 2 mm/s forming speed. The tribological performance difference between HTC and Teflon is at the 1% level. The results demonstrate the potential industrial usability of HTC as a lubricant.
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    Optimization of Cutting Conditions, Parameters, and Cryogenic Heat Treatment for Surface Roughness in Milling of NiTi Shape Memory Alloy
    (Springer, 2022) Altas, Emre; Erkan, Omer; Ozkan, Dervis; Gokkaya, Hasan
    This study discusses the milling of Nickel-Titanium (NiTi) alloy, one of the innovative and widely used shape memory alloy (SMA). During the face milling operations, the average surface roughness (R-a) was investigated depending on the change in machining parameters, cutting conditions, and cryogenic heat treatment. Experiments were carried out with uncoated and two different coated (PVD, CVD) cutting tools with untreated, shallow (- 80 degrees C) and deep (- 196 degrees C) cryogenic heat treatment. In addition, experiments were carried out using Ethylene Glycol (EG), and boron added Ethylene Glycol (EG+5%BX) cutting fluids as well as dry cutting condition. In the cutting experiments, three different cutting speeds (20-35-50 m/min), three different feeds (0.03-0.07-0.14 mm/tooth), and 0.7 mm fixed cutting depth was used as machining parameters. In the milling mechanism of NiTi shape memory alloys, how the cutting parameters affect the surface quality is discussed in detail. In this context, the cutting parameters were successfully optimized using Taguchi and ANOVA methods. The study is innovative in terms of evaluating the effect of different cutting fluids and cryogenic heat treatment. The results showed that CVD-coated cutting tool, - 196 degrees C cryogenic heat treatment, EG+5%BX cutting fluid, 50 m/min cutting speed, and 0.03 mm/tooth feed are the optimal parameters for the minor surface roughness. In addition, it has been determined that progress is the most influential parameter. On the other hand, ANOVA results showed that the most significant variable on the R-a was feed rate with 42.99%, and then cutting tool type 20.27%, cutting fluid 20.25%, cutting speed 11.68%, and cryogenic heat treatment 1.95%, respectively.
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    Surface Integrity of NiTi Shape Memory Alloy in Milling with Cryogenic Heat Treated Cutting Tools under Different Cutting Conditions
    (Springer, 2021) Altas, Emre; Altin Karatas, Meltem; Gokkaya, Hasan; Akinay, Yuksel
    In this study, the surface integrity of nickel-titanium (NiTi) shape memory alloys (SMAs) was investigated after face milling processes with cryogenically treated/untreated cemented carbide cutting tools at the conditions of dry cutting and minimum quantity lubrication (MQL) of cutting fluids depending on the changing cutting parameters. The integrity of surface layer of the workpiece material was evaluated according to the mean surface roughness, microstructure and hardness, as well as according to the resultant cutting force and flank wear of inserts. Cutting tests were carried out at three different cutting speeds (20, 35 and 50 m/min), feed rates (0.03, 0.07 and 0.14 mm/tooth) and a constant axial cutting depth (0.7 mm). The influence of these parameters on the surface integrity was extensively investigated. The face milling tests of NiTi SMA at optimal cutting parameters show that the surface integrity enhanced at a cutting speed of 50 m/min and feed rate of 0.03 mm/tooth using boron-added cutting fluid (EG + %5BX) with deep cryogenic heat treated (- 196 degrees C) CVD coated S40T grade cutting tool. Under MQL conditions, the minimum mean surface roughness (0.278 mu m), resultant cutting force (268.2 N) and flank wear (0.18 mm) were obtained due to the high thermal conductivity and lubrication property of EG + %5BX cutting fluid. The highest hardness values (343 HV) were measured at the zone subjected to the highest deformation, while the lowest one (316 HV) was measured at the zone at the least deformation.