Browsing by Author "Gokkaya, Hasan"

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The Effect of Coating Material and Geometry of Cutting Tool and Cutting Speed on Machinability Properties of Inconel 718 Super Alloys
(Elsevier Sci Ltd, 2007) Nalbant, Muammer; Altin, Abdullah; Gokkaya, Hasan
In this study, the effects of cutting tool coating material and cutting speed on cutting forces and surface roughness are investigated. For this purpose, nickel based super alloy Inconel 718 is machined at dry cutting conditions with three different cemented carbide tools in CNC lathe. Metal removing process is carried out for five different cutting speeds (15, 30, 45, 60, 75 m/min.) while 2 mm depth of cut and 0.20 mm/rev feed rate are to be constant. Main cutting force, F. is considered to be cutting force as a criterion. In the experiments, depending on the tool coating material, lowest main cutting force is found to be 506 N at 75 m/min with multicoated cemented carbide insert whose top layer is coated by Al2O3. Lowest average surface roughness (0.806 mu m) is obtained at the cutting speed of 15 m/min with single coated (TiN) cemented carbide inserts. (c) 2006 Elsevier Ltd. All rights reserved.
The Effect of Cutting Speed and Cutting Tool Geometry on Machinability Properties of Nickel-Base Inconel 718 Super Alloys
(Elsevier Sci Ltd, 2007) Nalbant, Muammer; Altin, Abdullah; Gokkaya, Hasan
The effects of cutting speed and cutting tool geometry on cutting forces are investigated in this study. For this purpose, nickel-base super alloy, Inconel 718, is machined with dry cutting conditions by using digital controlled computer lathe with ceramic cutting tools in two different geometries and three different material qualities. Metal removing process is carried out for four different cutting speeds (150 m/min, 200 m/min, 250 m/min, and 300 m/min), while a cutting depth of 2 mm and a feed rate of 0.20 mm/rev are kept constant. As a result of the experiments, the lowest main cutting force, which depends on tool geometry, is obtained as 672 N with KYON 2100 SNGN 120712 ceramic tool and the maximum cutting force is determined as 1346 N with the ceramic cutting tool having KYON 4300 RNGN 120700 geometry. Depending on the cutting speed, the lowest main cutting force is recorded as 812 N at 250 m/min while the highest main cutting force is recorded as 955 N at 150 m/min. Plastic deformation, flank edge wear, notch and build-up edge are determined in high cutting speeds. (c) 2006 Elsevier Ltd. All rights reserved.
Experimental Investigation of the Effects of Aging and Cryogenic Treatments on the Mechanical Properties of Superelastic Nickel-Titanium Shape-Memory Alloys
(Sage Publications Ltd, 2022) Guven, Sedat; Altin Karatas, Meltem; Gokkaya, Hasan; Akinay, Yuksel
In this study, electropolishing and two different heat treatments were applied to wires made of superelastic nickel-titanium (NiTi) shape-memory alloy (SMA) and their mechanical properties and stress-induced deformations were investigated. In experimental studies, cryogenic and aging heat treatments were applied to NiTi SMA wire samples and tensile test experiments were carried out to determine the effect of the heat treatments on their mechanical properties. Following the tensile test experiments conducted at room temperature (23 degrees C), the study investigated changes in the elemental composition, fracture modes, micro cracks, and phase structures and in the mechanical properties formed in the fracture region. Intermetallic phase structures (Ti2Ni, Ni3Ti, and Ni4Ti3) were observed in the X-ray diffraction (XRD) analyses. It was concluded that the aging heat treatment had directly affected the reduction in hardness. In particular, in samples without the aging heat treatment, a stress-induced decrease in the Ni and Ti ratios and an increase in the carbon (C) ratio were observed in the chemical composition of the fracture surface of the superelastic NiTi SMA wires. It was determined that the changes in the chemical composition caused by stress had affected the mechanical properties negatively. In the fractography of the NiTi SMA wires, the samples exhibited mostly ductile fracture behavior with small dimples.
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; Kandas, Halis
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.
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.