Parametric study for laser hole drilling of Inconel 617 alloy

In laser hole drilling, the end-product quality, the efficiency of the process and the cost of operation are important. In the present study, the laser drilling process is examined by means of statistical analysis. The significance levels of the parameters affecting the hole feature are tested using an F-test. The thermal efficiency of the drilling process is presented. Tantalum is selected as the workpiece material, while four levels of ambient gas pressure (subatmospheric), laser output energy, focus setting of the focusing lens and workpiece thickness are selected as affecting parameters. The drilling experiment is conducted according to the levels of the parameters selected. It is found that all the parameters influence the hole feature and the hole geometry improves for certain combinations of the affecting parameters, provided that overall hole quality is sensitive to the levels of ambient gas pressure and workpiece thickness.

Reflected blast pressure and impulse for bare 226.8 g spherical C-4 charges under various atmospheric pressure conditions were studied both experimentally and numerically. Blast pressure measurements were conducted using an array of high resonant frequency tourmaline-based piezoelectric pressure transducers to record normally reflected blast pressure histories at a 61 cm standoff. The explosive detonation and pressure measurements were conducted inside a pressure vessel which allowed the ambient pressure surrounding the C-4 charge to be varied. The recorded pressure histories were analyzed for blast wave arrival time, peak reflected overpressure, and positive phase impulse. The numerical analysis of blast pressures under varying ambient conditions was conducted using an axi-symmetric Arbitrary Lagrangian Eulerian (ALE) finite element technique with LS-DYNA. Numerical predictions were carried out for a 61 cm standoff that allowed direct comparison to the measured data. Additionally, the ALE simulations considered the effects of ambient pressure on blast impulse for varying standoff distances in the range of 12.7 to 61 cm. At a 61 cm standoff, measured peak reflected pressures showed no significant effect of varying ambient pressure while normally reflected impulses increased with increasing ambient pressure. Predictions by LS-DYNA for standoffs less than 61 cm showed a decreasing effect of ambient pressure on the normally reflected impulse as the standoff distance decreased. For small standoff distances it was predicted that the effects of ambient air pressure on normally reflected impulse were not significant. As the standoff distance between the explosive charge and the reflecting structure increases, higher ambient air pressures did cause a significant increase in reflected impulse.

The effect of ambient gas and pressure on the penetration and plasma behavior for AISI 304 stainless steel in CW CO2 laser welding with 4 kW output power was investigated. The major results are summarized as follows ;(1) The penetration depth significantly increased by reducing the ambient pressure. At the same time, the quantity of the laser-induced plasma also decreased as the ambient pressure decreased.The plasma in He and N2 ambient completely disappeared under the pressure of less than 100 torr, resulting in the significant increase in the penetration depth. The penetration depth reached more than 12 mm under the pressure of less than 100 torr at the traveling speed of 25 cm/min, which was around twice as deep as that under the atmospheric pressure. It was mainly because the formation of plasma which blocked the laser beam entering to the workpiece was greatly suppressed under the low pressure.(2) The plasma generation was dependent upon the physical properties of gas element as well as the ambient pressure. The higher the ionization potential and heat conductivity of the gas element was, the larger the plasma became.

Large eddy simulation investigation of ammonia spray characteristics under flash and non-flash boiling conditions

It is widely accepted that evaporation induced recoil pressure plays critical roles in keyhole and weld pool dynamics during laser welding. Recent experiments by some of the authors have demonstrated that the partial pressure of surrounding gas could also contribute an important role to the dynamics of evaporation surface during laser welding under atmospheric pressure. However, most of mathematical models of keyhole and weld pool behaviours of laser welding did not include the effect of ambient pressure. In this study, we formulate a new mathematical model of recoil pressure which considering the effect of ambient gas pressure and adopt it to theoretically investigate keyhole and weld pool behaviours in laser welding under different ambient pressure, based on HUST’s comprehensive transient keyhole welding simulation code. Preliminary theoretical comparisons of three dimensional transient keyhole and weld pool behaviours during laser welding under variable ambient pressure are discussed. Some interesting phenomena which correspond well to recent experimental results are found. This research provides some theoretical backgrounds for applications of laser welding under different atmospheric pressure.It is widely accepted that evaporation induced recoil pressure plays critical roles in keyhole and weld pool dynamics during laser welding. Recent experiments by some of the authors have demonstrated that the partial pressure of surrounding gas could also contribute an important role to the dynamics of evaporation surface during laser welding under atmospheric pressure. However, most of mathematical models of keyhole and weld pool behaviours of laser welding did not include the effect of ambient pressure. In this study, we formulate a new mathematical model of recoil pressure which considering the effect of ambient gas pressure and adopt it to theoretically investigate keyhole and weld pool behaviours in laser welding under different ambient pressure, based on HUST’s comprehensive transient keyhole welding simulation code. Preliminary theoretical comparisons of three dimensional transient keyhole and weld pool behaviours during laser welding under variable ambient pressure are discussed. Some interesting ...

Effects of ambient pressure on characteristics of smoke movement in tunnel fires

Numerical simulations that are based on the volume-of-fluid method are performed to study the atomization of impinging jets under the influence of higher steady and oscillating ambient pressures. Both the simulated flow patterns and the statistical features of the droplet size distribution and sheet wave agree well with experimental data from the literature. Then, the instability mechanism of an impinged sheet is explored. The position at which the breakup of the liquid sheet occurs is determined jointly by the velocity distribution of the sheet and aerodynamic effects. Finally, the effects of ambient pressure on the stability of atomization and spray characteristics are discussed in detail. When the ambient pressure is elevated from 0.05 MPa to 0.5 MPa, the sheet’s instability increases as the gas/air density increases. During the above process, the increasing aerodynamic force that is exerted on the liquid sheet increases the impact amplitude values, thereby increasing the spray angle and decreasing the sheet breakup length. However, the breakup of large droplets during secondary atomization is suppressed under high backpressure conditions because of the deceleration of the film’s movement. Additionally, the backpressure oscillation, with the frequency approximating the fundamental frequency of sheet waves, enhances the wave amplitude and the atomization angle, which accelerates the sheet’s breakup and decreases the mean size of the droplets downstream of the impingement point.

Effects of ambient pressure on fire-induced buoyancy driven plume dispersion and re-entrainment behavior in a street canyon

Layer-to-layer thermal runaway propagation of open-circuit cylindrical li-ion batteries: Effect of ambient pressure

Heat transfer mechanism of concurrent flame spread over rigid polyurethane foam: Effect of ambient pressure and inclined angle

Nanosecond laser-metal ablation at different ambient conditions

Nanoparticles of bismuth ferrite (BiFeO3) were fabricated by high-pressure pulsed laser deposition method (PLD) on Pt-coated Si substrates. Effects of the ambient oxygen pressure during deposition (from 1 Torr to 15 Torr) were studied with respect to the microstructures and magnetic properties of the samples. It was found that as the pressure is higher than 5 Torr isolated nanoparticles are formed and the size of these nanoparticles decreases with the deposition pressure. All the nanoparticles exhibit ferromagnetic behavior and the magnetic coercive filed decreases with the particle size.

Under atmospheric pressure, the tendency of members of unsaturated series to smoke generally decreases with the number of carbon atoms. The effect of ambient pressure on the smoke point has been studied to explore the tendency of alkene fuels to smoke at high pressures. A wick lamp used in this experiment is standardized by JIS. The smoke point was determined for several alkene fuels under various ambient pressures from 0.2 MPa to 1.35 MPa. It has been found that the dependence of ambient pressure on the smoke point of alkene fuels is almost the same as in the case of alkane fuels. That is, as the ambient pressure increases, the smoke point decreases sharply up to the pressure of 0.5 MPa, beyond which it decreases gradually. However the effect of ambient pressure on the smoke point of alkenes is not very strong compared with that of alkanes. In alkenes, the smoke point takes the maximum value with a certain number of carbon atoms at ambient pressures of 0.3 MPa and above. In light of this finding, it can be concluded that there may exist a number of carbon atoms at which the tendency to smoke is minimized in alkenes.

Effect of ambient pressure on the extinction limit for opposed flame spread over an electrical wire in microgravity

95/04166 Flammable refrigerants — practical experience of these substances based on the example of propane