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    Comparison of the Mechanical Properties and Drilling Performance of the AISI 316 Parts Produced with Casting, LPBF and WAAM
    (Springer Heidelberg, 2024) Kocaman, Engin; Köklü, Uğur; Morkavuk, Sezer; Coşkun, Mert; Kocar, Oğuz; Dilibal, Savaş; Gürol, Uğur
    AISI 316 stainless steel parts are widely utilized in many industrial fields with a vast scope of applications. These steel parts, which are used in many fields, can be produced using different production methods, but the mechanical properties of the parts produced with different processes may be different, and the machinability characteristics will also be different. In this study, the drilling machinability characteristics of AISI 316 stainless steel parts manufactured via cast, LPBF and WAAM methods were experimentally investigated and compared considering thrust force generation, burr analysis and chip morphology. In order to clarify the differences in machinability behavior among the tested samples, the corresponding microstructure, microhardness and mechanical strength (yield strength, UTS and elongation) were also examined in detail. The experimental results showed the manufacturing method, and particularly cooling rate, significantly affecting the microstructure, mechanical response and further machinability characteristics; besides, due to higher cutting forces generation, the machinability of the parts produced by additive manufacturing methods (LPBF and WAAM) is more difficult compared to the parts produced by conventional manufacturing methods (cast and cast-HT).
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    Effect of Silicon on Machinability in AlSi6, AlSi12 and AlSi18 Alloys
    (Springer, 2023) Gecgel, Berkay; Altintas, Yusuf; Arslan, Muhammet Yasir; Celen, Okan Ozcan; Kocaman, Engin; Kocar, Oguz
    In this study, Al-Si alloys containing 6%, 12%, and 18% silicon by weight were produced using the permanent mold casting method. The samples were examined microstructurally, hardness and tensile tests were conducted. Furthermore, the machinability characteristics of the samples were investigated. The findings showed that the silicon added to aluminum has a significant impact on microstructure, mechanical properties, and machinability. The addition of silicon to aluminum up to 12% by weight increases the amount of Al-Si eutectic in the microstructure. However, unlike other samples, primary silicon particles were detected in the microstructure of the composition containing 18% Si by weight. Also, both hardness and tensile strength increased with the increasing silicon content. However, with the increasing silicon ratio, the ductility of the material and the thrust force during the drilling process decreased. The highest thrust force (961 N) occurred at 6% Si additive ratio (Al6Si) and at a rotational speed of 2500 rpm. Burr formation was observed at the hole exit in 6% Si additive ratio and 12% Si additive ratio. The surface roughness occurring inside the holes increased with the increasing silicon ratio.
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    The effects of aging process after solution heat treatment on drilling machinability of corrax steel
    (Springer, 2023) Güldibi, Ahmet Serdar; Köklü, Uğur; Koçar, Oğuz; Kocaman, Engin; Morkavuk, Sezer
    As a maraging steel, Corrax, is used in many engineering applications in the manufacturing, aerospace, and medical industries thanks to its properties such as high strength, hardness and corrosion resistance. However, these high specifications can cause some issues for manufacturing operations such as forging, machining, grinding. In addition to that, using heat treatment applications changes materials' mechanical specifications, affecting the material's behavior during machining. Therefore, it is important to characterize the influences of different heat treatment conditions on the material's property and behavior. In this study, the effects of heat treatment process on the mechanical properties, drilling machinability and corrosion resistance of Corrax steel were experimentally investigated with the samples of solution heat treated and aged at 400 °C, 525 °C, 600 °C, and 700 °C. The machinability was evaluated based on thrust force, chip morphology, hole quality, and tool wear. The results showed that the thrust force, torque and hole quality depend on feed rate, cutting speed, and mechanical properties affected by aging treatment. The highest hardness (47.4 HRC), ultimate tensile strength (1720 MPa), maximum elongation (33%), and toughness (198 jm-3) were obtained for the sample which aged at 525 °C for four hours, consequently the highest cutting force and surface roughness results were measured for this sample. Better hole surface quality and less burr formation were observed in the samples aged at 600 °C and 700 °C, and not-aged. On the other hand, while the highest value of corrosion potential were measured in the sample aged at 400 °C, the lowest corrosion potential value were measured in the sample aged at 700 °C. Graphical abstract: [Figure not available: see fulltext.].
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    Machining-induced damage and corrosion behavior of monel-400 alloy under cryogenic cooling conditions: A sustainable initiative
    (Korean Soc Precision Eng, 2024) Demirbaş, Ali; Köklü, Uğur; Morkavuk, Sezer; Giasin, Khaled; Kocaman, Engin; Sarıkaya, Murat
    Monel-400 is a nickel-based heat-resistant superalloy (HRSA) that is primarily used in oil and marine applications. Machining Monel-400 alloy for marine applications usually involves drilling and milling operations for assembly purposes, which should meet the requirements to withstand use in salt-water environments (i.e. lower surface finish to reduce corrosion and lack of burrs for tight sealing between mating parts). However, drilling of Monel-400 alloy can be challenging due to its high strength and density, which induces thermal effects that can influence the surface and geometrical integrity of the holes. Consequently, the use of environmentally friendly cooling technologies, such as cryogenics, is an excellent alternative to mitigate these effects, something which has not been widely investigated in the open literature when drilling Monel-400 alloy. Therefore, the current study aims to investigate the machinability of Monel-400 alloy under dry and cryogenic cooling conditions. The effects of cutting parameters and the use of a cryogenic liquid nitrogen bath on the surface integrity and corrosion resistance of holes were evaluated. Additionally, cutting forces, chip formation, and corrosion performance were analyzed. The results showed that the cutting forces increased by up to 8% under cryogenic cooling. Under cryogenic conditions, reduced elastic deformation resulted in a smaller chip size. Both cutting conditions produced a smooth surface finish with a roughness value of less than 0.2 mu m. Corrosion resistance was reduced under cryogenic conditions at spindle speed of 5000 rpm. The current work showcases that cryogenic cooling is recommended for drilling Monel-400 alloy used in marine applications, but care should be taken in employing optimal cutting parameters to mitigate any effects on corrosion resistance.
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    An overview of deformation path shapes on equal channel angular pressing
    (MDPI, 2022) Baysal, Erhan; Koçar, Oğuz; Kocaman, Engin; Köklü, Uğur
    In recent years, research on ultra-fine grain materials has gained attention. While attempts have been made to improve the properties of the material, it has also become increasingly important to decrease the costs. Studies on improving material properties have revealed new production methods or have required the revision of existing production methods. In this direction, severe plastic deformation methods have come to the fore as a good alternative, and by improving the methods with new variations, materials with grain sizes below 1 mu m have been obtained. In addition, this method positively affects the mechanical properties of the material. In this study, the Equal Channel Angular Pressing (ECAP) method, one of the severe plastic deformation methods, which has attracted great attention among researchers, was examined and the development stages of the method were investigated according to recent studies. The effective parameters in the method were examined and the effects of these parameters on the grain structure and mechanical properties of the material were discussed. Channel shapes, which are open to innovation and increase the efficiency of the ECAP method, were kept in the foreground among the prominent parameters in the ECAP process, and the results of the design changes made with new variations were examined.