Applied Mechanics and Materials Vol. 787

Abstract: Inconel 718, a nickel based alloys, addressed as difficult to cut material because of hard carbide particle, hardness, work hardening and low thermal conductivity. Improving the machinability characteristics of nickel based alloys is a major anxiety in aircraft, space vehicle and other manufacturing fields. This paper presents an experimental investigation in Laser assisted turning of Inconel 718 to determine the effects of laser cutting parameters on cutting temperature and cutting forces. This nickel alloy has a material hardness at 48 HRC and machined with TICN/Al₂O₃/TiN tool. This is employed for the manufacture of helicopter rotor blades and cryogenic storage tanks. The experiments were conducted at One-Factor-at-a-Time.The effects of laser cutting parameters, namely cutting speed, feed rate, laser power and laser to work piece angle, on the cutting temperature and cutting force components, are critically analysed and the results are compared with unassisted machining of this alloy. The experiments are conducted by varying the cutting speed at three levels (50, 75, 100 m/min), feed rate (0.05, 0.075 0.1 mm/rev), laser power (1.25 kW, 1.5 kW, 1.75 kW) and at two level laser to work piece angle (60, 75°). At the optimal parametric combinationof laser power 1.5 kW with cutting speed of 75m/min, feed rate of 0.075 mm/min and laser to work piece angle 60°, the benefit of LAM was shown by 18%, 25% and 24% decrease in feed force (Fx), thrust force (Fy) and cutting force (Fz) as compared to those of the conventional machining. Examination of the machined surface hardness profiles showed no change under LAM and conventional machining.

Abstract: This paper presents the experimental study on machinability of micro alloyed steel. Raw material of chemical composition 38MnSiVS5 of diameter 60 mm and length 250 mm was machined using the medium duty lathe of 2 kW spindle power using K20 PVD single coated (TiN) Carbide insert. The investigation (turning) is carried out with three levels of cutting speed, feed rate and depth of cuts. An average surface roughness(Ra) of machined component and power consumption by the main spindle are measured. The optimum machining parameters have been identified. Results show higher cutting speed influence the good surface finish on this steel. In particular, surface finish is directly proportionate to the cutting speed.

Abstract: Influence of a fusion welding process namely gas tungsten (GTAW) and a solid state friction stir welding (FSW) on the microstructural changes and tensile strength variation of cast magnesium alloy joints were investigated and the results are compared. Of the two joints fabricated, FSW joint showed superior tensile properties compared to GTAW joint due to the difference in microstructural gradient across the weld cross section. Wider partially melted zone and heat affected zone was observed in GTAW joint due to the high heat input nature process compared to narrow heat affected zone in FSW joint. Microhardness measurement indicates that, the weld metal is overmatched compared to the base metal irrespective of welding process used.

Abstract: Present work pertains to welding of ZM21 magnesium alloy using three different welding techniques namely Gas Tungsten Arc Welding, Laser Beam Welding and Friction Stir Welding. After careful trial and error method, the process parameters were identified to produce defect free, full penetration welds successfully. The microstructure and mechanical properties of ZM21 magnesium alloy using GTAW, LBW and FSW processes were analyzed by optical microscopy, tensile testing and Vickers micro hardness measurements. The results show that the tensile properties of Friction stir welds and Laser beam welds are much better than those of gas tungsten arc welds. The formation of very fine grains in the friction stir welded region and absence of HAZ in LBW are found to be main reasons for better tensile properties. It has been concluded that the ZM21 magnesium alloy exhibits good weldability in all the three welding processes and laser beam welding process offers higher joint efficiency when compared with GTAW and FSW.

Abstract: Inconel 718, a Nickel based superalloy is widely used for aerospace applications mainly due to its high temperature resistance and high strength to weight ratio. Its poor machinability is a limiting factor in commercial, cost intensive applications. This paper investigates the machinability of Inconel 718 in high speed drilling. The impact of the material on thrust forces, torque and chip microstructure have been measured at four different cutting speeds – 19, 27,43 and 67 m/min. The high tensile strength coupled with low thermal conductivity compounds the machining process. The thrust forces decrease with cutting speed, but the torque fluctuates at intermediate cutting speeds. Chip formation is continuous across cutting speeds, with thin cross sections and evidence of saw tooth edges. Inconel work hardens more than titanium alloys and shows good ductile to brittle transition at low temperatures creating chips of lesser length as observed using scanning electron microscopy.

Abstract: Recent developments in imaging non destructive evaluation techniques offer possibilities of quantitative measurement of strain localizations associated with plastic instabilities. Digital image correlation is a technique now being widely employed for studying the temporal strain evolution associated during tensile deformation. This work focuses on the application of digital image correlation to visualise the two dimensional strain evolutions in the weld zone, heat affected zone and the base metal during monotonic uniaxial tensile deformation of friction stir weld samples of copper – stainless steel. The results indicated that the Cu- Stainless steel weld interface exhibited a lower tensile strength compared to the other regions. The experimental observations are discussed in relation with the current theoretical understanding. The experiments also reveal the potential of advanced imaging NDE methods for providing better insights of the micro mechanisms of deformation and failure including local deformation characteristics of the material under study.

Abstract: In this research work, the effect of cooling rate on fatigue behaviour of eutectic A413 Al-Si cast alloy is investigated. Castings produced by two different cooling rates, water-cooled and air-cooled are studied. The structural morphology of alloy castings was characterized using Inverted Trinocular Metallurgical Optical Microscopy. A Comprehensive tension–tension fatigue test was carried out with a stress ratio of R=0.5, and a sinusoidal waveform under three different mean stress conditions (25%, 50% & 75% of UTS) at room temperature (32°C). The microstructural evaluations show that the eutectic script size is smaller for water-cooled casting than the air-cooled casting. It is also observed that the fatigue life of the water-cooled cast alloy is greater than that of cast alloy produced with conventional air-cooled method.

Abstract: In this investigation, Commercially Pure (Cp) titanium was diffusion bonded to AA7075-T6 aluminium alloy at various temperatures of 450, 475, 500, 525 and 550⁰ C, bonding pressure of 17, MPa and holding time of 40 minutes was applied during the diffusion bonding. The effects of reaction temperature, Bonding time and atmosphere on the diffusion welding characteristics of titanium and aluminum have been studied. The maximum Lap shear strength was found to be 89 MPa for the specimen bonded at the temperature of 525°C, Bonding Pressure 17 MPa and Holding time for 40 min.

Abstract: The present investigation is aimed to study the effect of pulsed current gas metal arc welding on the tensile strength of AISI 904L super austenitic stainless steel joint 1.2 mm diameter solid wire of same composition. The joints were fabricated using pulsed current gas metal arc welding and by varying five factors such as peak current, pulse on time, pulse on frequency, background current and welding speed at five different levels. Design matrix based on central composite rotatable design was selected to conduct the experiment and an attempt is made to maximize the tensile strength by optimizing the factors using graphical and numerical optimization techniques. Results were correlated with weld metal microstructures.

Abstract: In an era of compact cooling requirements, where air cooling systems seem to be ineffective and consistently, being replaced by liquid cooled systems, with greater watt density heat energy dissipation. Such cooling systems must work with good quality enabling high efficiency. Hence, an attempt is made to fabricate an aluminum alloy based flat plate heat sink with cover and base plate using friction stir welding. The base plate is machined to obtain channels for fluid flow and the cover plate is fitted in the base plate and welded. Two such configurations of these heat sinks were fabricated with varying channel lengths and number of channels. The flow characteristics of the model for these configurations were analyzed numerically using computational fluid dynamics (CFD) software tool, ANSYS fluent 14.