Mathematical model and magnetic-control mechanism of the stability of rotating spray transfer

To realize stable rotating spray transfer in the region of high constant current is the key of realizing high deposition rate MAG welding process without helium in shielding gas and extending the welding current range of traditional MAG welding process. In this paper, the magnetic control mechanism of the rotating spray transfer is stated and mathematical model is given. Theoretic basis is established, which implements high deposition rate MAG welding process with magnetic control instead of helium in shielding gas.

Effect of the size and pressure on the modified viscosity of water in microchannels

The phenomenon that flow resistances are higher in micro scale flow than in normal flow is clarified through the liquid viscosity. Based on the experimental results of deionized water flow in fused silica microtubes with the in- ner radii of 2.5 μm, 5μm, 7.5μm, and 10 μm, respectively, the relationship between water flow velocity and pressure gradient along the axis of tube is analyzed, which gradually becomes nonlinear as the radius of the microtube decreases. From the correlation, a viscosity model of water flow derived from the radius of microtube and the pressure gradient is pro- posed. The flow results modified by the viscosity model are in accordance with those of experiments, which are verified by numerical simulation software and the Hagen-Poiseuille equation. The experimental water flow velocity in a fused silica microtube with diameter of 5.03 μm, which has not been used in the fitting and derivation of the viscosity model, is proved to be comsistent with the viscosity model, showing a rather good match with a relative difference of 5.56%.

Quantitative measurement of local elasticity of SiO_x film by atomic force acoustic microscopy

In this paper the elastic properties of SiOx film are investigated quantitatively for local fixed point and qualitatively for overall area by atomic force acoustic microscopy （AFAM） in which the sample is vibrated at the ultrasonic frequency while the sample surface is touched and scanned with the tip contacting the sample respectively for fixed point and continuous measurements. The SiOx films on the silicon wafers are prepared by the plasma enhanced chemical vapour deposition （PECVD）, The local contact stiffness of the tip-SiOx film is calculated from the contact resonance spectrum measured with the atomic force acoustic microscopy. Using the reference approach, indentation modulus of SiOx film for fixed point is obtained. The images of cantilever amplitude are also visualized and analysed when the SiOx surface is excited at a fixed frequency. The results show that the acoustic amplitude images can reflect the elastic properties of the sample.

ZVS of arc welding inverter in light load

It is very difficult for arc welding inverter to realize Zero-Voltage-Switching （ZVS） because the load of arc welding inverter changes violently. An improved PS-FB-ZVS-PWM （ Phase-Shifted Full-Bridge Zero-Voltage-Switching Pulse-Width-Modulation） topology is proposed in this paper. A saturate resonant inductor is in series with the primary side of the transformer, while an auxiliary inductor is in parallel with the secondary side of the transformer to increase reactive current in light load or unload state, so the zero voltage switching of power devices is realized during switching course in light load or unload state.

Downstream pressure and elastic wall reflection of droplet flow in a T-junction microchannel

This paper discusses pressure variation on a wall during the process of liquid flow and droplet formation in a T-junction microchannel. Relevant pressure in the channel, deformation of the elastic wall, and responses of the droplet generation are analyzed using a numerical method.The pressure difference between the continuous and dispersed phases can indicate the droplet-generation period. The pressure along the channel of the droplet flow is affected by the position of droplets, droplet-generation period, and droplet escape from the outlet. The varying pressures along the channel cause a nonuniform deformation of the wall when they are elastic. The deformation is a vibration and has the same period as the droplet generation arising from the process of droplet formation.

Gas film performance of double-row orifices of aerostatic guideways

In order to analyze the performance of aerostatic guidways,the stiffness calculation equation of the aerostatic guideway with two-row orifice has been derived by gas lubrication theory. For the complex structure of the motion guideway and unloading guideway,the frequency of the whole slides in machining direction with gas thickness has been derived. Wavelet transform as a means to process the measured signal of workpiece surface, the frequency characteristics of gas fluctuation of aerostatic guideways has been extracted out from the measured signal,and the errors of the guideway system have been identified according to the power spectral density (PSD) ,and this provide a basis for the identification of machine tool error.

Inverse Eigenvalue Problems for a Structure with Linear Parameters

The inverse design method of a dynamic system with linear parameters has been studied. For some specified eigenvalues and eigenvectors, the design parameter vector which is often composed of whole or part of coefficients of spring and mass of the system can be obtained and the rigidity and mass matrices of an initially designed structure can be reconstructed through solving linear algebra equations. By using implicit function theorem, the conditions of existence and uniqueness of the solution are also deduced. The theory and method can be used for inverse vibration design of complex structure system.