Browsing by Author "AYDIN, HAKAN"

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A parametric study on weld zone shape of resistance spot welded 22MnB5 steel
(Taylor, 2023-03-04) Tuncel, Oğuz; Aydın, Hakan; Gönül, Alişan; AYDIN, HAKAN; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Makine Mühendisliği Bölümü; JQD-3823-2023
The resistance spot welding of 22MnB5 with different weld currents, weld times, and quenching conditions is investigated in the current study. A Kriging Response Surface Methodology-based local sensitivity analysis is performed to investigate the effect of weld current, weld time, and quench condition on weld zone morphology and tensile shear load (TSL). When welding current, welding time, and quenching conditions are varied between the minimum and maximum values, the geometry of the weld zone was influenced by 40-60%, 20-40%, and 0-20%, respectively, according to sensitivity studies. It is also found that increasing values of welding current are the most effective welding parameter, increasing TSL by about 45%. In order to better understand the TSL variation at different welding parameters, various hardness measurements are applied for each specimen in the fusion zone and the heat-affected zone (HAZ) regions of the weld zone. Based on the location, the HAZ was divided into three regions: the inner, middle, and outer. The middle HAZ had hardness values 12% higher than the base material, while the outer HAZ had hardness values up to 36% lower than the base material. Also, macro-and microstructure images of the sample produced by combining the quenched and non-quenched materials are obtained to demonstrate how the hardness zones are identified.
Investigation of microstructure and mechanical properties of dissimilar electrical resistance spot welded tbf/dp600 steel sheets
(Gazi Üniversitesi, 2022-01-01) Aydın, Hakan; Yılmaz, İmren Öztürk; Bilici, Abdullah Yasin; AYDIN, HAKAN; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Makine Mühendisliği Bölümü.; 0000-0001-7364-6281; JQB-9181-2023
Effects of welding parameters on microstructure and mechanical properties of spot-welded TBF/DP600 sheets were investigated. TBF was welded with and without electro-galvanizing. Microhardness and tensile tests were carried out, and microstructure characterized by optical microscopy. Nugget size was determined by image processing, indentation was measured by ultrasonic technique. Steels were not completely mixed with each other in FZ. Increasing in welding current and time expanded HAZ and increased mixing-ratio in FZ, nugget size, indentation and load capacity. TBF was more affected by thermal cycle than DP600. LME-based microcracks in HAZ of galvanized TBF at high heat input were observed, while corrosion started rapidly in weld zone of ungalvanized TBF. Highest hardness was observed in HAZ on TBF side. However, significant softening occurred in transition zone between HAZ and base metal on TBF side. The nugget size, indentation and load capacity were higher in galvanized TBF group. In dissimilar spot-welded TBF/DP600 sheets, DP600 has determined weld strength. Fractures are of fusion zone button type with higher weld strength in high heat input, while fractures are of partial fusion zone button type with lower weld strength in low heat input. In galvanized TBF, higher weld strength was obtained in lower heat input.
Mechanical characterization and microstructure of fiber laser welded twip980 steel depending on welding speed and focal distance
(Elsevier Gmbh, 2023-01-12) Çavuşoğlu, Oktay; Yüce, Celalettin; Aydın, Hakan; Çavuşoğlu, Oktay; YÜCE, CELALETTİN; AYDIN, HAKAN; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Makine Mühendisliği Bölümü.; 0000-0003-1387-907X; 0000-0001-7364-6281; JIA-6918-2023; R-3733-2017; JQB-9181-2023
The TWIP steels are preferred in the automotive industry due to excellent strength and ductility. In this study, the effect of fiber laser welding parameters has been investigated on the mechanical properties and microstructural points of view twinning-induced plasticity (TWIP) steel. The variation of the mechanical properties depending on fiber laser welding parameters has been determined. The samples were laser-welded with different speeds and focal distances the laser power constant at 4 kW. The stress and elongation decreased when the welding speed increased. The highest stress was obtained at + 1 focal distance. The best energy absorption was seen in b-3 combination (laser power 4 kW, welding speed 130 mm/s, focal distance +1 mm).
Microstructure and mechanical properties of dissimilar resistance spot welded DP1000-QP1180 steel sheets
(Journal of Central South Univ, 2019-01-01) Öztürk Yılmaz, İmren; Bilici, Abdullah Yasin; Aydın, Hakan; AYDIN, HAKAN; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Makine Mühendisliği Bölümü; 0000-0001-7364-6281; JQB-9181-2023
In this study, the effect of welding parameters on the microstructure and mechanical properties of the dissimilar resistance spot welded DP1000-QP1180 joints was investigated. Heat affected zone (HAZ) width of QP1180 side was smaller than that of DP1000 side. HAZ width and indentation depth increased with increasing welding current and welding time. The nugget size increased with increasing welding current whereas it increased at lower currents and decreased at higher currents with increasing welding time. The lowest hardness was on the DP1000 side. On the QP1180 side, the center of HAZ had the peak hardness. With increasing welding current, hardness values throughout the weld zone decreased and the tensile shear load increased. At lower welding currents, the welding time did not affect the tensile shear load. Tensile elongation decreased with the increase of welding time, whereas there is no relationship between the welding current and elongation. The spot-welded joints having higher strength exhibited a more ductile fracture characteristic.
Optimization of laser cladding process parameters of a martensitic stainless steel coating on ggg70l ductile cast iron
(Old City Publishing Inc, 2023-01-01) Karsı, A.; Altay, M. A.; Bayram, A. B.; Aydın, H.; AYDIN, HAKAN; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Makine Mühendisliği Bölümü.; 0000-0001-7364-6281
Laser cladding is an additive manufacturing (AM) method that is widely implemented in surface modification and repair. In this study GGG70L ductile cast iron base material (BM) was clad with Metco 42C martensitic stainless steel powder using a high power diode laser (HPDL) laser. The effect of process parameters (laser power, scanning speed and powder flow rate) on clad geometry, porosity and crack formation, and microhardness was investigated. Taguchi experimental design was created via the L9 orthogonal array and analysed by signalto-noise (S/N) ratio and analysis of variance (ANOVA) method for clad geometry. Clad geometry was investigated in terms of clad height, clad width, aspect ratio and clad depth using an optical microscope. Pores in the clad were characterized with an optical microscope and a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectroscope (EDS). Hardness testing of the clad layers was performed on a Vickers microhardness testing machine to create microhardness depth profiles. High laser power increased the risk of crack and pore formation, and led to larger pores. The optimum laser process parameters for the lowest pore and crack formations were a laser power of 1.7 kW, a scanning speed of 10 mm/s and a powder flow rate of 12 g/min.
Springback/springforward behaviour of dp steels used in the automotive industry
(Univ Osijek, Tech Fac, 2020-01-01) Umur, Yeliz; UMUR, YELİZ; Aydin, Hakan; AYDIN, HAKAN; Yiğit, Kurtulus; YİĞİT, KURTULUŞ; Bayram, Ali; BAYRAM, ALİ; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Makine Mühendisliği Bölümü.; 0000-0001-7364-6281; AAK-4598-2021
The springback/springforward behaviour in a V-die/punch of DP600 and DP780 steels used in the automotive industry was investigated. For this study, experiments were carried out by using different combinations of parameters, including material thickness, die/punch radius, bending angle and rolling direction and the resulting measurements showed that the DP780 steel consistently exhibited greater springback values than the DP600. Augmentation of the rolling direction at an angle from 0 degrees to 90 degrees and punch radius inhibited springback formation and hastened springforward, particularly for small bending angles. The springback angle decreased with increasing material thickness and curvature radius, and increased with the bending angle, particularly for the punch tip radius of 2 mm. Increasing the ratio of curvature radius to material thickness (rt(-1)) also caused the springback to decline. In addition, a new dimensionless parameter was developed and the critical value for calculating the transition from springback to springforward was determined.
The effect of duplex surface treatment on erosion performance of qro 90 supreme steel
(Springer India, 2019-04-01) Tutar, Mumin; TUTAR, MÜMİN; Aydın, Hakan; Durmus, Ali; DURMUŞ, ALİ; AYDIN, HAKAN; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Makine Mühendisliği Bölümü.; 0000-0002-7286-3433; 0000-0001-7364-6281; 0000-0002-5037-1120; J-2753-2016
In this study, CrN and TiAlN thin films were deposited on plasma-nitrided QRO 90 Supreme hot work tool steel by physical vapor deposition process and analysed with regard to their erosion performance under hydro-abrasive erosion conditions. The as-received specimens were quenched to room temperature from 1050A degrees C and tempered gradually at 605A degrees C for 2 h and at 560A degrees C for 4 h. These specimens were plasma-nitrided for 10 h at 500A degrees C at a pressure of 250 Pa in a gas mixture of 80% N-2 + 20% H-2 and then coated with TiAlN or CrN coatings by cathode arc evaporation. The specimens were characterized by metallographic techniques, SEM, EDS and micro-hardness test. Plasma nitriding and duplex surface treatments significantly increased the hardness of the specimens and thus significantly reduced the erosion of the specimens. The hardnesses on the surface of plasma-nitrided, CrN-deposited and TiAlN-deposited QRO 90 steels were 1092 HV0.025, 2436 HV0.025 and 3578 HV0.025, respectively. TiAlN-coated specimens were about 17-fold harder than the as-received specimens and over 3-fold harder than the plasma-nitrided specimens. The erosion resistance of CrN-coated specimens was increased by a factor of 3.6 and 1.5 compared with that of the as-received and plasma-nitrided specimens, respectively. A brittle fracture phenomenon was observed on the eroded surface of the duplex-treated specimens while a ductile material removal was observed on the as-received and the tempered specimens. The plasma-nitrided specimens showed a mixed behaviour of ductility and brittleness.
The optimisation of welding parameters for electrical resistance spot-welded twip steels using a taguchi method
(Pamukkale Üniversitesi, 2018-01-01) Tutar, Mümin; Aydın, Hakan; Bayram, Ali; TUTAR, MÜMİN; AYDIN, HAKAN; BAYRAM, ALİ; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Makine Mühendisliği Bölümü; 0000-0002-7286-3433; 0000-0001-7364-6281; J-2753-2016; JQB-9181-2023; GZC-1297-2022
The aim of this work is to optimize the welding parameters of electrical resistance spot welded TWIP steel sheets using a Taguchi method. The welding parameters, such as weld current, welding time and electrode force, were determined according to the Taguchi orthogonal array L9 using a randomized approach. The optimum welding parameters for the peak tensile shear load of the joints were predicted, and the individual importance of each parameter on the tensile shear load of the resistance spot weld was evaluated by examining the signal-to-noise (S/N) ratio and analysis of variance (ANOVA). The optimum weld current, welding time and electrode force were found to be 12 kA, 300 ms and 3000 N, respectively. The ANOVA results indicated that the weld current has the highest statistical effect with 78.73% on the tensile shear load, followed by the welding time and electrode force. The tensile shear load of the resistance spot welding joints increased with increasing weld current and electrode force. But, higher welding time led to relatively lower tensile shear load. In addition, the fracture surface characterization of the selected joints was conducted using scanning electron microscopy (SEM) technique. In this examination, it has been found that the joints having higher weld strength exhibited a relatively more ductile fracture characteristic.