Zheng Qiang Yao

STUDY ON TEMPERATURE FIELD INDUCED IN HIGH FREQUENCY INDUCTION HEATING

A mathematical model was established for the temperature field developed during high frequency induction heating (HFIH) by Maxwells equations. It required solving the coupled equations of the electromagnetic and temperature fields. The numerical simulation was performed using FEMLAB. The comparison of the calculations using the proposed model with experimental results showed a very good correlation. The effects of the heating parameters in high frequency induction such as the distance between the plate and the coil, the applied current, the frequency, and the turns of the coil on the temperature profiles developed in the plate were also discussed using the established model.

FEM SIMULATION OF RESIDUAL STRESSES INDUCED BY LASER SHOCK WITH OVERLAPPING LASER SPOTS

The finite element method is presented to attain the numerical simulation of the residual stresses field in the material treated by laser shock processing. The distribution of residual stresses generated by a single laser shock with square and round laser spot is predicted and validated by experimental results. With the Finite Element Method (FEM) model, effects of different overlapping rates and impact sequences on the distribution of residual stresses are simulated. The results indicate that: (1) Overlapping laser shock can increase the compressive residual stresses. However, it is not effective on the growth of plastically affected depth; (2) Overlapping rate should be optimized and selected carefully for the large area treatment. Appropriate overlapping rate is beneficial to obtain a homogeneous residual stress field; (3) The impact sequence has a great effect on the residual stress field. It can greatly attenuate the phenomenon of the “residual stress hole” to obtain a homogeneous residual stress field.

Study on residual stress of laser shock processing based on numerical simulation and orthogonal experimental design

Abstract Laser shock processing (LSP) is a competitive alternative surface enhancement process. Shock pressure with high magnitude and short duration induced by LSP is one key parameter to induce a residual stress field in the material. Finite element method (FEM) simulation based on the orthogonal experimental design is adopted to analyse the interaction of different shock pressure profiles with the material. It can give a relatively accurate description of the effect of shock pressure profile on the residual stress field induced in the material with a representative coverage of all parameters by less calculation cost. The analysis results show that laser shock conditions should be selected carefully to ensure a favourable shock pressure to obtain an optimised residual stress field. The simulation on the overlapping laser shock is also presented and indicates that it is an effective method to settle the residual stress drop on the top surface and can obtain a much more favourable residual compressive stress field to enhance the fatigue resistance of the material.

Cooling Effects in Laser Forming

In the laser forming of metal plates, there is a substantial waiting time required for cooling down the workpiece so that a steep temperature gradient can be reestablished during the next scan. Currently, there are no standard techniques that can be used to reduce this waiting time. This paper discusses the possibility of using non-natural cooling systems to cool down the workpiece. A numerical model of thermo-mechanical analyses with moving boundary conditions to simulate the traveling of laser beam and moving forced water cooling system is presented. Based on the proposed model, cooling effects under different laser powers and scanning velocities with various cooling conditions are investigated. The results show that the forced water cooling can significantly reduce the temperature with no adverse effect on the forming of plates.

Minimum Lubrication Milling of Titanium Alloys

During excessive fluid application processing, fluid ends up on the floor, the workers, and the machine, entail serious techno-environmental and biological problems. Very little fluid enters the tool/part interface. Recently, this excess fluid has become another costly control problem. Chemicals of all types introduced into the atmosphere must also be reduced to an absolute minimum. In this paper, the technique of minimum quantity of lubrication (MQL), which is the pulverization of a minimum volume of oil in a flow of compressed air, has been studied in face mill Ti-6Al-4V titanium alloys as one alternative to the use of abundant cooling to suppress the cutting heat resulted from low thermal conductivity and the density of the workpiece material. The results showed that MQL of 125ml/h flow amount was found to be the optimum, and there is no significant difference in temperature between MQL of this flow and wet cooling when low cutting speeds used.

NUMERICAL INVESTIGATION OF STRAIGHT-LINE LASER FORMING UNDER THE TEMPERATURE GRADIENT MECHANISM

Laser forming is a new flexible and dieless forming technique. To achieve the high accuracy forming, the temperature gradient mechanism (TGM) is studied. In the analysis of TGM, the plate bends about x-axis and about y-axis as well. To understand the deformation trend, the numerical simulation of deformation of plate is conducted by choosing different laser powers, laser spot diameters, scanning speeds, lengths, widths and thicknesses. From the results of simulation, it can be seen that the laser spot diameter, the scanning speed, laser power and thickness of plate play dominant roles in the laser forming process. However, the bending angles α x and α y show different trends with the variation of parameters. In addition, in comparison with above four parameters, the effect of length and width of plate on the bending angle may be neglected, but their effects are significant for the bending radius R.

Investigational Advances in Residual Stresses by Hard Turning

Hard turning has been recognized as a substitute for abrasive-based processes not only due to its flexibility, economic benefit and environmental consciousness, but also its determinate surface integrity (surface roughness, micro hardness and residual stress), which is superior and more consistent than ground surfaces. Residual stress is of considerable industrial importance because they can affect failure by fatigue, creep or cracking. It is believed that compressive residual stresses are more favorable for fatigue life than tensile residual stresses. Hard turning generally generates compressive residual stress, which is the dominant role in determining both the variance and average value of fatigue life. This paper focus on the published data, especially C.R.Liu’s research, which address the residual stresses by hard turning in terms of experimental approaches， theoretical modeling，numerical simulation by Finite Element Analysis (FEA) and the correlation with its fatigue life and performance. The potential trends and key technologies for residual stresses are predicated and discussed so as to capture the most effective approach to investigate residual stress by hard turning.

Application of the Hilbert-Huang Transform to Pick up Surface Roughness

The surface roughness is evaluated by decomposing micro-errors from irregular surface image. The wave of surface is designated as signals including high-frequency, mid-frequency, and low-frequency signal, that denote roughness, waveness and the geometry shape error. Hilbert-Huang transform is a promising revolutionary technique for spectral data analysis, which is used to extract roughness from surface. It overcomes the imprecise result of the traditional surface roughness calculation and avoids the complication of the Wavelet analysis. Theory of Empirical Mode Decomposition (EMD) is given in the paper. This method is initially applied in picking up surface roughness, and it is proved to be of very high efficiency and simplicity.

Effects of Interference Fit and Preload on the Performance of Low-Speed Angular Contact Ball Bearing

Based on static analysis, this paper investigates the effects of interference fit and axial preload on the performance of the low-speed angular contact ball bearing. The results show the bearing with heavy preload and large radial clearance has big contact angle and high axial stiffness. Besides, large interference could result in small contact angle but high axial stiffness. When the bearing has large interference the axial stiffness increases rapidly due to the effect of interference on the axial stiffness stronger than that of contact angle. And the stiffness formula in the paper could provide boundary conditions for the finite element analysis of spindle-bearing system.

Experimental Investigation on Power Consumption in Reactor Coolant Pumps with the Function of the Flywheel

This article mainly discusses the dynamic characteristics of the experimental rotor system under the abrupt power shut circumstances, and to search the distribution of the power consumption during special working processes with an experimental method. On the basis of the experimental results, the simulation analysis is carried out on the Andritz RCP, and therefore, the dynamic characteristics of the real nuclear reactor coolant pump can be forecast, which just meets the need of the safety running in nuclear plant.