Hong Shen

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.

Study on the mechanical behavior of laser micro-adjustment of two-bridge actuators

Laser micro-adjustment is an application of laser forming for the adjustment of micro-, fiber- and electro-optical systems. Experience has shown that conventional material models cannot properly describe the micro-scale deformation behavior due to size effects. As a result, traditional macro-scale laser forming is not suitable for the micro-scale laser forming process. In this study, the mechanical behavior of two-bridge actuators in laser micro-adjustment is investigated under the condition of geometrically scaled actuators. Numerical simulation is conducted by using a material model that takes into account the size effects. Simulation results obtained for cases with and without consideration of the size effects are compared, showing that size effects have a significant influence on the laser forming of micro-adjustment. The results with consideration of the size effects are found to agree well with the experimental data.

A study on bending direction of sheet metal in laser forming

Concave laser forming and convex forming are all required for the complicated curved surface plate forming. Concave laser forming can be readily obtained by temperature gradient mechanism, while convex forming may be achieved based on buckling mechanism. To achieve precise control of bending direction of plate, buckling critical condition is analyzed when the buckling mechanism plays a dominant role, and a judgment criterion of working conditions of buckling mechanism, Fbuckling value, is derived. To verify the validity of the Fbuckling value, the experiments and numerical simulations are carried out. The results suggest that the bending direction of the plate can be exactly judged according to the Fbuckling value. In addition, the effects of the heating location and starting point on the bending direction are discussed, which provide further insight into the convex forming process and is helpful for the parameter selection of future process planning.

The simulation of temperature field in the laser forming of steel plates

Laser forming of metal plates is a flexible forming process that forms sheet by means of thermal stresses induced by external heat source instead of using external forces. The stresses are generated by temperature gradient induced by laser. In this paper, a finite element analysis model including convective and radiation boundary conditions to predict the three-dimensional temperature field is established for a metal plate under the influence of a moving Gaussian heat source. The effects of various laser forming parameters on temperature distributions are investigated using the established model. By using variable scanning velocities a constant temperature gradient in the plate plane is achieved, which can be used to accurately form differently desired shapes of the plate.

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.

Influence of oxidation on flow structure in laser-oxygen cutting

In this paper, a three-dimensional axial symmetrical model of laser cutting is established by adopting N–S equation and shearing-stress transport k-ω turbulent model. Numerical simulation is carried out to analyze the flow field of shield gas inside a cut kerf; the results include velocity and pressure distribution and mass flow rate. The effects of oxidation on flow field are examined, and the formation of gas flow separation and vortex are predicted. The results show that the gas flow structure in the kerf is directly affected by the reaction between iron and oxygen in the case of laser-oxygen cutting.

Processing Optimization in Multiheating Positions for Laser Thermal Adjustment of Actuators

Laser thermal adjustment as an application of laser forming in microsystems attracts much attention. Previous work on laser thermal adjustment of the two-bridge actuator (TBA) shows that the deformations induced by laser forming are limited. In this paper, an actuator with three cut-outs including six heating positions is designed to enhance the deformation range. A deformation model is developed for such an actuator by introducing the factors of the in-plane and out-of-plane angles to the TBAs formula, which takes energy constraints into account to avoid the melting phenomenon and negative deformations. The deformation range of the three cut-outs actuator (TCA) is determined by using the relation between in-plane and out-of-plane angles of the TBA. The optimization of the processing parameters for the TCA is conducted to reach the designed target position based on the optimization algorithm of adaptive simulated annealing (ASA). The model prediction is validated by the finite-element analysis (FEA) simulation and experiments.

Mixed-dimensional coupling modeling for laser forming process

Efficient laser forming modeling for industrial application is still in the developing stage and many researchers are in the process of modifying it. Conventional three-dimensional finite element models are still expensive on computational time. In this paper, a finite element model adopting a shell-solid coupling technique is developed for the thermomechanical analysis of laser forming process. In the shell-solid coupling method, an additional shell element plane is utilized to transfer heat flux and displacement from the solid elements to the shell elements. The effects of the additional interface shell element thickness on temperature distribution and final distortion are investigated. The presented shell-solid coupling method is evaluated by the results of three-dimensional simulations and experimental data.

Numerical Investigation of Dual Heating in Laser Micro-Adjustment of Actuators

Laser micro-adjustment as application of laser forming is a contact less and easily automated technology able to cause very small changes in shape to achieve high accuracies. In this study, a method using dual heating is introduced to reduce the temperature gradient across the thickness during laser micro-adjustment of actuators. The temperature field and deformation behavior using dual heating method are analyzed using a 3D finite element model. The in-plane angles are compared between using single heating and dual heating and the numerical results show that the in-plane angle using dual heating method can be predicted by the results by single heating.

An analytical model for bending angle in metal/ceramic bilayer system of laser forming

An analytical model based on force and moment balances is developed to predict the bending angle in metal/ceramic bilayer material systems when applying a laser forming process. The formula is derived based on the assumptions that the plastic deformation is generated only during heating, while during cooling the plate undergoes only elastic deformation. Results are obtained for a bilayer plate of an Al 6061 metallic layer and a SiC ceramic layer. Moreover, numerical simulation is carried out using the finite element analysis method to estimate the accuracy of the presented model, which shows that the results of analytical model are in good agreement with the numerical simulation.