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Master Thesis Çökeltilerek Sertleştirilmiş Martensitik Paslanmaz Çelik Malzemede Ultrasonik Destekli Delik Delme(2023) Enis, Metin Berk; Kılıç, Sadık Engin; Lotfi, Bahram17PH4 Paslanmaz Çelik, önemli korozyon direnci, yüksek yorulma ve çekme mukavemeti, tokluk ve yüksek sertliği sayesinde nükleer sektör, havacılık ve savunma sanayi gibi sektörlerde kullanımı oldukça yaygındır. Bu sektörlerde ve genel talaşlı imalat süreçlerinde ise delik delme en çok kullanılan yöntemlerden birisidir fakat bu malzemenin yüksek aşınma direnci, sertliği ve ısıl iletim kapasitesi nedeniyle delik delme performansını oldukça düşürür. İlk kez, bu çalışmada 17-PH-4 paslanmaz çeliğinde delik delme operasyonunun verimini arttırmak için Ultrasonik Destekli Delik Delme (UDDD) yöntemi kullanılmıştır. UDDD düşük genlikli titreşimler ve yüksek frekans kullanarak talaş kaldırma sürecini kolaylaştıran hibrit bir yöntemdir. Test planı, hem geleneksel delik delme (GDD) yöntemi ve UDDD'yi kıyaslamak hem de UDDD'nin gagalama ve direkt delik delme üzerindeki etkisini görmek üzere hazırlanmıştır. Deney sonuçları, UDDD'nin geleneksel delik delme yöntemine göre kesme kuvvetlerini, delik çıkışındaki çapak oluşumunu ve yığıntı talaş (YT) oluşumunu azalttığını, boyutsal doğruluğu arttırdığını ve yüzey kalitesinin iyileştiğini göstermiştir. Test sonuçları, kesme hızının artmasının; kesme kuvvetleri, YT, yüzey pürüzlülüğü ve sürekli talaş formunun azalmasında bariz bir etkisi olduğunu göstermiştir. Ek olarak yüzey pürüzlülüğü, kesme kuvvetleri ve çapak oluşumu sonuçları incelendiğinde direkt delik delmede UDDD' nin olumlu etkisi, gagalamaya göre daha fazla olmuştur.Article Sustainable Stabilization of Expansive Soils Using Waste Marble Powder and Expanded Polystyrene Beads: Experimental Evaluation and Predictive Modelling(Elsevier, 2026) Akis, Ebru; Citak, Mete; Lotfi, BahramExpansive soils exhibit considerable volume changes with moisture fluctuations leading to serious challenges for civil infrastructure, causing structural instability, pavement distortion, and foundation damage. While lime and cement remain widely used stabilizers, recent research has increasingly focused on waste-derived materials such as marble powder (MP) and expanded polystyrene beads (EPSb) as promising alternatives. These materials provide a practical approach to soil stabilization while contributing to the reuse of industrial by-products. In this study, the engineering behavior of high-plasticity clay was improved through the inclusion of MP and EPSb as additive materials. MP was added at 0%, 5%, 10%, 15%, and 20%, and EPSb at 0%, 0.3%, and 0.9% by dry weight of the high plasticity clay. Both additives were used alone and in combination. Laboratory tests, including Standard Proctor, free swell (FS), and unconfined compressive strength (UCS), were conducted. The results confirmed that the additives effectively reduced the liquid limit (LL) by 20.1% and the plasticity index (PI) by up to 22.4%. Results showed that EPSb effectively reduced FS and UCS, while MP decreased FS and increased UCS up to an optimal content. The most effective mixes achieved a maximum reduction of 54.7% in free swell (FS) (at 20% MP and 0.9% EPSb content) and a maximum increase of 13.1% in unconfined compressive strength (UCS) (at 5% MP content) compared to the untreated soil. The compaction tests further revealed a general decrease in optimum moisture content (OMC) and a slight increase in maximum dry density (MDD) with increasing MP content. Accordingly, the free swell (FS) and unconfined compressive strength (UCS) of the treated soils were predicted using multiple linear regression (MLR) and artificial neural network (ANN) models, developed from both the current experimental dataset and previously published studies. Input variables included untreated FS and UCS values, additive percentages, and one index property. The ANN model demonstrated superior predictive capability, achieving R2 values of 0.955 and 0.874 for FS and UCS, respectively, compared to 0.411 and 0.618 obtained with MLR. These results highlight the robustness of ANN in capturing nonlinear soil behavior and underscore its reliability and accuracy, particularly under limited data conditions.Article Citation - WoS: 41Citation - Scopus: 42Enhancing Machining Efficiency of Ti-6al Through Multi-Axial Ultrasonic Vibration-Assisted Machining and Hybrid Nanofluid Minimum Quantity Lubrication(Elsevier Sci Ltd, 2024) Namlu, Ramazan Hakki; Lotfi, Bahram; Kilic, S. EnginTi-6Al-4V offers a balance of good strength with lightweight properties. Yet, Ti-6Al-4V poses machining challenges, including low thermal conductivity, chemical adhesion to cutting tools, and chip removal difficulties. To improve machining efficiency, Ultrasonic Vibration-Assisted Machining (UVAM) has emerged as a promising approach. UVAM has demonstrated reduced tool wear, cutting forces, and improved surface quality compared to Conventional Machining (CM). Additionally, Minimum Quantity Lubrication (MQL) methods offer sustainable coolant alternatives, with recent research focusing on Nanofluid-MQL (NMQL) and Hybrid Nanofluid-MQL (HNMQL) for enhanced performance. Although there exists a body of literature showcasing the promising effects of UVAM and MQL methods individually, comprehensive investigations into the synergistic effects of these methodologies remain limited. This study addresses these critical research gaps by conducting a systematic examination of combined application of multi-axial UVAM and HNMQL. Specifically, it delves into the comparison of different vibration directions within UVAM, evaluates the effectiveness of UVAM when combined with cutting fluids incorporating Al2O3 and CuO nanoparticles in NMQLs and HNMQLs, and contrasts these novel approaches with conventional machining methods. The study unfolds in three distinct stages. The first stage examines the ultrasonic cutting mechanism and its combined application with the MQL technique. In the second stage, the study investigates the physical properties of the cutting fluids, including contact angle and surface tension. The final stage encompasses slot milling operations, where an array of parameters such as cutting forces, surface roughness, surface topography, surface texture, and the occurrence of burr formations are rigorously analyzed. The results demonstrate that the combination of multi-axial UVAM with HNMQL yields substantial advantages over traditional machining methods. Notably, it leads to a remarkable reduction in cutting forces (up to 37.6 %) and surface roughness (up to 37.4 %). Additionally, this combination engenders the production of highly homogeneous and uniform surface textures, characterized by minimal surface defects and a significantly diminished occurrence of burr formations. These findings underscore the potential of multi-axial UVAM combined with HNMQL as a promising approach in enhancing the machining of Ti-6Al-4V, thus offering a pathway to enhance the efficiency and precision of aerospace component manufacturing processes.Article Citation - WoS: 7Citation - Scopus: 10Combined Use of Ultrasonic-Assisted Drilling and Minimum Quantity Lubrication for Drilling of Niti Shape Memory Alloy(Taylor & Francis inc, 2023) Namlu, Ramazan Hakki; Lotfi, Bahram; Kilic, S. Engin; Yilmaz, Okan Deniz; Akar, SametThe drilling of shape-memory alloys based on nickel-titanium (Nitinol) is challenging due to their unique properties, such as high strength, high hardness and strong work hardening, which results in excessive tool wear and damage to the material. In this study, an attempt has been made to characterize the drillability of Nitinol by investigating the process/cooling interaction. Four different combinations of process/cooling have been studied as conventional drilling with flood cooling (CD-Wet) and with minimum quantity lubrication (CD-MQL), ultrasonic-assisted drilling with flood cooling (UAD-Wet) and with MQL (UAD-MQL). The drill bit wear, drilling forces, chip morphology and drilled hole quality are used as the performance measures. The results show that UAD conditions result in lower feed forces than CD conditions, with a 31.2% reduction in wet and a 15.3% reduction in MQL on average. The lowest feed forces are observed in UAD-Wet conditions due to better coolant penetration in the cutting zone. The UAD-Wet yielded the lowest tool wear, while CD-MQL exhibited the most severe. UAD demonstrated a & SIM;50% lower tool wear in the wet condition than CD and a 38.7% in the MQL condition. UAD is shown to outperform the CD process in terms of drilled-hole accuracy.Article Citation - WoS: 26Citation - Scopus: 27Machining Performance and Sustainability Analysis of Al2o3< Hybrid Nanofluid Mql Application for Milling of Ti-6al(Taylor & Francis inc, 2024) Lotfi, Bahram; Namlu, Ramazan Hakki; Kilic, S. EnginMachining of Ti-6Al-4V presents challenges due to its low thermal conductivity, and conventional cutting fluids (CCF) are inadequate in providing a productive and sustainable solution. This study aims to achieve more sustainable and productive machining of Ti-6Al-4V by utilizing Al2O3 and CuO-added Nanofluid Minimum Quantity Lubrication (NMQL) individually and in hybrid form with different concentrations. A comparison is made with pure-MQL, CCF and dry conditions. The study consists of three stages. In the first stage, the physical properties of the coolants, like contact angle and surface tension, are investigated. The second stage involves slot milling operations, and various outputs including cutting forces, surface roughness, surface topography, surface finish, and subsurface microhardness are analyzed. In the last stage, a sustainability analysis is conducted based on the Pugh Matrix Approach. The results indicate that Al2O3-NMQL exhibits lower contact angles and surface tensions compared to other conditions. Furthermore, HNMQL applications result in lower cutting forces (up to 46.5%), surface roughness (up to 61.2%), and microhardness (up to 6.6%), while yielding better surface finish and topography compared to CCF. The sustainability analysis demonstrates that HNMQL application is the most suitable option for achieving sustainable machining of Ti-6Al-4V.Article Citation - WoS: 14Citation - Scopus: 17An Experimental Study on Ultrasonic-Assisted Drilling of Inconel 718 Under Different Cooling/Lubrication Conditions(Springer London Ltd, 2024) Erturun, Omer Faruk; Tekaut, Hasan; Cicek, Adem; Ucak, Necati; Namlu, Ramazan Hakki; Lotfi, Bahram; Kilic, S. EnginUltrasonic-assisted drilling (UAD) is one of the efficient and innovative methods to improve the drillability of difficult-to-cut materials. In the present study, the UAD of Inconel 718 was investigated under different cooling and/or lubrication conditions. The drilling tests were carried out at a constant cutting speed (15 m/min) and a feed (0.045 mm/rev) using uncoated and TiAlN-coated solid carbide drills under dry, conventional cutting fluid (CCF), and minimum quantity lubrication (MQL) conditions. The applicability of UAD to drilling Inconel 718 was evaluated in terms of thrust force, surface roughness, roundness error, burr formation, subsurface microstructure and microhardness, tool wear, and chip morphology. The test results showed that, when compared to conventional drilling (CD), UAD reduced the thrust force and improved the hole quality, tool life, and surface integrity under all conditions. Good surface finish, lower roundness error, and minimum burr heights were achieved under CCF conditions. MQL drilling provided lower thrust forces, better tool performance, and good subsurface quality characteristics. In addition, the simultaneous application of CCF-UAD and MQD-UAD showed significantly better performance, especially when using the coated tool.Master Thesis Uyarlanabilir Big Bang Big Crunch Algoritmalarıyla Kullanarak Esnek İş Atölyesi Planlamasını Optimize Etme(2024) Al-rajab, Maha Layth; Lotfi, BahramBig Bang Big Crunch yöntemi, özellikle esnek iş atölyeleri ve makine ortamları bağlamında olmak üzere, karmaşık iş atölyesi çizelgeleme sorunlarını ele almak için umut verici bir yaklaşım sunmaktadır. Bu yöntem, üretim sistemlerinde makespan'ı, toplam gecikmeyi en aza indirmede ve iş yükü dengesini sağlamada etkinliğini kanıtlamıştır. Potansiyel çözümleri değerlendirmek için bir uygunluk fonksiyonu kullanarak ve bir dizi aşama boyunca nüfusun uygunluğunu artırarak iyileştirerek, Big Bang Big Crunch yöntemi, imalat işletmeleri için güçlü bir optimizasyon yaklaşımı sunmaktadır. Esnek iş atölyesi çizelgeleme bağlamında, Big Bang Big Crunch algoritmasını geleneksel iş atölyelerine kıyasla eklenen karmaşıklığı etkin bir şekilde ele alacak şekilde uyarlamak çok önemlidir. Bu uyarlama, algoritmanın esnek iş atölyeleri ve makine ortamları tarafından sunulan benzersiz zorluklara uygunluğunu sağlamak için değişiklikler ve geliştirmeler yapılmasını içerir. Ayrıca, pekiştirme öğrenimi, sinir ağları ve meta-sezgiseller gibi gelişmiş tekniklerin dahil edilmesi, çizelgeleme yöntemlerinin zekâsını ve dayanıklılığını önemli ölçüde artırabilir, bunların çeşitli dinamiklere u yum sağlamasını ve bireyselleştirilmiş özelleştirme gereksinimlerini karşılamasını sağlayabilir. Bununla birlikte, Big Bang Big Crunch algoritmasının performansı, problem örneği, problem büyüklüğü ve mevcut hesaplama kaynakları gibi faktörlerden etkilenebilir. Bu nedenle, algoritmanın uygulamasının dikkatli bir şekilde değerlendirilmesi ve kişiselleştirilmesi, optimal sonuçları elde etmek için temel oluşturur. Dahası, uygun kodlama ve kod çözme şemaları geliştirme, etkili çeşitlendirme ve yoğunlaştırma stratejileri ve uygunluk değerlendirme işlevleri ile ilgili zorlukları ele almak, Big Bang Big Crunch yöntemini esnek iş atölyesi çizelgelemesine uygularken istenen sonuçlara ulaşmak için çok önemlidir. Sonuç olarak, Big Bang Big Crunch yöntemi, üretim sistemlerinin verimliliğini artırmak ve imalat işletmelerindeki üretim sistemlerini optimize etmek için değerli bir potansiyel sunmaktadır. Bu çalışmada açıklanan önerilere uyarak, kuruluşlar bu yöntemi, esnek iş atölyesi çizelgelemesinin karmaşıklıklarını ele almak ve üretim sistemleri için zeki ve güçlü çözümler elde etmek için etkili bir şekilde kullanabilir.