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In this paper, the process of joining Ti-3Al-2.5V titanium alloy thin sheets by means of micro-plasma arc welding (MPAW) is reported. An experimental set-up was developed using traditional gas tungsten arc welding apparatus and a home-built torch for butt welding of coupon specimens. The specimens were welded under controlled welding parameters, such as voltage, current, travel speed and shielding gas flow rate. An appropriate set of parameters for MPAW process was examined by mechanical properties tests and microstructure characterization. Mechanical tests including tensile test, bending test and micro-hardness evaluation across the weld line generally show that if suitable welding parameters are used, the tensile strength of the welded specimen is well comparable with that of the base metal while its hardness increased at the fusion zone (FZ). The bending test revealed that using appropriate welding parameters, no crack or notch appeared at the welded joint. Fractography, X-ray diffraction and metallograpghy were also performed to study the microstructure evolution. SEM images of the fracture surface presented characteristics of ductile rupture. Studies on microstructure morphology of the specimens at the FZ and HAZ reveal occurrence of phase transformation from high temperature phase to acicular phase

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Abrasive water jet cutting process can produce tapered edges on cutting kerf. This problem can limit the applications of abrasive water jet cutting process and in some cases it is necessary another edge preparation process. In this paper, an experimental investigation kerf characteristics of Ti-6Al-4V titanium alloy under abrasive water jet cutting is presented. In this regards, it is shown how to use the hybrid approach of Taguchi method and principal component analysis to optimize abrasive water jet cutting are used in this paper. The abrasive water jet cutting process input parameters effect on material removal rate and the characteristics of the surface. A considerable effort was made in understanding the influence of the system operational process parameters such as water jet pressure, traverse speed, abrasive flow rate, and standoff distance. Due to appropriate selecting abrasive water jet cutting process parameters leads to optimizing of kerf characteristics include top kerf width, kerf tapper and kerf deviation, therefore it is important to select appropriate input parameters. The obtained results from this method show that the hybrid approach of Taguchi method and principal component analysis is a suitable solution for optimizing of abrasive water jet cutting process.

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Micromilling is a machining process in manufacturing of the miniature parts. Because of high oxidation and corrosion resistance, high fatigue strength and application of Ti6Al4V in hi-tech industries, in this paper surface roughness and burr formation in micromilling of this alloy have been investigated. Cutting parameters including spindle speed, feed rate and axial depth of cuthave been considered as input parameters of tests. Experiments have been performed for two cases: a) in presence of the minimum quantity lubrication and b) wet conditions. Carbide micro-end mill tool of diameter 0.5 mm and TiAlN coating was used. The Taguchi experimental design method has been used to design and analysis of results. Results showed that the spindle speed and feed rate were the most effective parameters on the surface roughness and burr width of titanium alloy, respectively. Also, by increasing both of these parameters, surface roughness and burr width were decreased. In addition, application of minimum quantity lubrication technique significantly improved the surface quality, and it was more effective in upper levels of spindle speed and axial depth of cut. Finally, the best surface quality was attained in spindle speed of 30000 rpm, feed rate of 0.8 μm/tooth and cutting depth of 60 μm.

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Mathematical modeling is an important step in the design and optimization of process parameters for metal forming. Researchers have been concerned the metal forming limit diagram as an efficient tool to optimize the production of components using forming methods. Due to the low ductility of titanium alloys and wide applications of these alloys in advanced industries such as aerospace, researchers have focused on studying the forming behavior of these alloys. Due to the high cost of experimental methods, especially at high temperatures, numerical methods, has attracted the attention of many researchers. The accuracy of the numerical methods is affected by model of elastic-plastic material behavior. Unusual mechanical behavior of Ti-64 titanium alloys such as high in-plane anisotropy/asymmetry of yield stress and hardening response has been observed. In this paper, the Marciniak model with Cazacu and Hill yield criterions has been used for forming limit prediction. It is observed that the prediction of forming limit using the Cazacu criterion is closer to the experimental results. This is due to the better prediction of the behavior of the titanium alloy, specially Lankford and stress anisotropy coefficients by Cazacu criterion. Cazacu and Hill criterions prediction of Lankford coefficients and yield stresses have been compared.

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Friction stir welding (FSW) has many advantages in welding dissimilar joints in comparison with fusion welding methods. In this study, weld ability of butt joint of 5052 aluminum alloy and Ti-6Al-4V titanium alloy by FSW process has been studied and discussed. The welding was successfully performed by using a tool with frustum pin. The influences of both rotational and traverse speed of welding tool on mechanical properties are investigated. The results show that the metallurgical and mechanical properties improve by choosing appropriate parameters. The highest tensile strength of 260 MPa was obtained at rotational speed of 500 rpm and a 40 mm/min traverse speed, which was ~ 94% of the aluminum base metal tensile strength. As a result of increasing the rotational speed from 500 to 1000 rpm, high heat input can forms cracks at joint area. In rotational speed of 1000 rpm, increasing traverse speed from 40 to 56 mm/min leads to a sound joint with 192 MPa of tensile strength. This decreasing in tensile strength can be related to the formation of intermetallic compounds such as TiAl3, along the entire interface between the two alloys

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Residual stresses and distortion are of the main disadvantages of welding process which determining the amount and distribution of them have great importance in the design of structures, especially in the space industry. In this study, a finite element method is used to analyze the thermo- mechanical behavior of a spherical shell due to TIG welding. The spherical shell is made of titanium alloy (Ti-6Al-4V) with 2 mm thickness. The modeling of welding process is based on an uncoupled thermo- mechanical coupling. TIG welding is examined for six cases based on current intensity and welding progress speed setting the voltage on 12 V in all cases. Distribution of temperature and residual stresses caused by TIG welding of the titanium spherical shell have been extracted and compared among the six different cases. The effects of current intensity and welding progress speed on shell distortion and residual stress have been investigated. The results showed that increasing the current intensity and decreasing the welding progress speed have the most effects on longitudinal residual stresses which the amount of this increasing reached to %44 for decreasing the welding progress speed. Welding distortion increases to maximum %132 by increasing current and decreasing welding progress speed.

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Nowadays, emerging more advanced computer systems made it possible to simulate and model complex problems even with higher accuracy. Regarding lower time and cost, the use of simulations instead of physical experiments is increasingly considered as an alternative method in the analysis and optimization of process performance. The importance of such methods becomes more significant when talking about micro-processes, since there are lots of difficulties in experimental measurements as a results of scaling problems by scaling down from macro to micro. In this study, a 3D model is developed using Deform-3D software for prediction of micromilling process behavior. Effects of cutting parameters on such characteristics as cutting forces, temperature distribution and tool wear are investigated. To check the validity of the model, force results of simulation are compared with the measured ones. A high level of correlation exists between the obtained simulation and measured results which shows that the 3D developed model has good capability to predict process behavior.

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Selecting tool materials, tool sizes and determining the cutting parameters presents a great challenge in machining operations especially in high speed machining processes. In this study effect of feed rate which is one of the important machining parameters and tool size on tool life in high speed machining of Ti-6Al-4V alloy were investigated. Fixed cutting speed of 200 m/min, feed rate of 0.03 and 0.06 mm/tooth together with axial cutting depth of cut 5.0 mm, and radial cutting depth of cut 1.5 mm were employed as the cutting parameters. TiAlN + TiN coated tungsten cemented carbide insert in two different size was used during machining operations. Flank wear land measurement was taken by using a toolmakers’ microscope and recorded accordingly throughout machining processes. The results showed during the machining employing both feed rate and using smaller tool size chipping occurred on the tool nose along with gradual tool flank wear. Also by increasing the feed rates utilizing the smaller size of tool highly affected tool life compared to employing the larger one during the high speed machining operations. Reduction the feed rate by 50 percent increased the tool life of smaller tool size by 200 percent.

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Micro end-milling is one of the main manufacturing processes of creating miniaturized parts which are increasingly demanded in many industries. Using tools with diameter less than 1 mm results in rising the so-called “size effect” and problems due to ploughing at low feeds per tooth. It is therefore crucial to estimate value of minimum chip thickness which helps to reduce or eliminate the ploughing. In this study role of scaling down is investigated with regard to milling operation in micro- and macro-scale. A titanium alloy Ti-6Al-4V is used as workpiece. Two-flute endmills with diameters of 0.8 and 2 mm are used representing micro and macro-scale, respectively. Effects of axial depth of cut and feed rate as input parameters were evaluated on such output characteristics as specific cutting energy, microhardness, surface roughness, topography and chip formation. Results show higher values of microhardness and specific cutting energy in micro-scale. Microhardness and specific cutting energy in micro-scale were found to be 6 times and 150% greater than the macro-scale, respectively. The study suggests that minimum chip thickness can be varied approximately between 0.25 and 0.49 of the cutting edge radius.

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Laser percussion drilling is one of the advanced drilling processes that its numerous advantages have extended the applications of this process. This study focuses on experimental investigation of laser percussion drilling using Nd:YAG laser on titanium alloy Ti6Al4V sheets with various thickness which is widely used in industry. In this paper the effects of the input parameters peak power, pulse width, frequency, assist gas type, gas pressure and sheet thickness on the most important process outputs include hole entrance diameter, hole exit diameter, hole taper angle, hole entrance circularity and hole exit circularity were studied. Statistical analysis was employed to analyze the experimental data and significant parameters in each response are presented. For conducting the experiments “Design of Experiments” method and for modelling “Response Surface Methodology” were used. The results obtained show that sheet thickness affects all outputs. After that frequency and pulse width, peak power and assist gas type respectively are the most significant parameters influence process outputs. Gas pressure only affects the hole entrance circularity. For this alloy to achieve a hole with high quality, it is recommended to work at lower peak power and frequency, shorter pulse width and higher assist gas pressure with Nitrogen as assist gas.

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In ultrasonic vibration-assisted turning, an ultrasonic vibration is added to the tool, which leads to the periodical disengagement of the tool and the work-piece. In this research, an experimental study of ultrasonic vibration-assisted turning and conventional turning on Ti6Al4V Titanium alloy is conducted. First, by analyzing different parameters, four parameters are selected as the main affecting input parameters (cutting speed, feed rate, depth of cut, and ultrasonic vibration), and the effects of these four parameters are studied on two output parameters, namely tool wear and surface roughness. After the experimental tests, a statistical analysis is performed on the results and a neural network model is developed to predict the tool wear and surface roughness. The results show that the developed neural network model has a good agreement with the experimental results. In all experiments using ultrasonic vibrations, the tool wear and surface roughness were lower in comparison with the conventional turning. The cause of the tool wear and surface roughness reduction in ultrasonic mode are reducing the average forces applied to the tool, the alternative disengagement between the tool and the workpiece and increased dynamic stability of the process.
 

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 Micro-milling process as one of the most widely used methods of making parts due to the small size and their delicate properties in the process. In this study, micro-milling operations were performed on a titanium piece made of Ti6Al4V alloy using a tool with a diameter of 0.5 mm. The effect of nanoparticles used in lubricants on the surface roughness of the micro-milled workpiece is the most important characteristic studied in this research. In this research, experimental test methods and design and analysis of experiments by Taguchi method have been used to study the surface roughness during the process. Experimental tests to compare the role of lubrication in dry, wet and Minimum Quantity Lubrication (MQL) in different machining environments with lubricants containing nanoparticles and without nanoparticles and the effect of shear parameters on different characteristics of micro-milling of Ti6Al4V alloy is done. The results show that the use of Minimum Quantity Lubrication (MQL), especially with lubricants containing nanoparticles, increased the surface quality and had a more effective role in lubrication during micro-milling of Ti6Al4V alloy. Spindle speed and type of lubrication are the most effective parameters in Ti6Al4V alloy micro-milling.
 

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In This study, in order to evaluation of ductility and consequently the optimum workability region of novel Ti-3Al-8Mo-7V-3Cr titanium alloy (Ti-3873), the hot tensile tests were performed at a constant strain rate of 0.1 s^-1 and the temperature range of 650-850 ℃ . To establish the relationship between microstructural evolution and ductility, the microstructure of the specimen was examined by optical microscopy (OM) and scanning electron microscopy (SEM) after and before hot deformation. The results showed that ductility at the temperatures of 650-750 ℃ , increased from 33% to 54% as a consequence of transformation of α  to β  phases and gradually eliminating the α  phase. The maximum ductility obtained at 850 ℃  with a 71% increase in ductility. Microstructural studies showed the elongated and serrated boundaries confirmed the occurrence of dynamic recovery. Recrystallized grains were also observed at 850 ℃ . Therefore, it can demonstrate that the restoration mechanism of the Ti-3873 alloy during hot tension is dynamic recovery and partial dynamic recrystallization. Finally, according to tension results, the appropriate range of deformation deformation of the Ti-3873 alloy in this study is 800-850 ℃ .