Papers by Author: Hui Xia Liu

Abstract: Based on the laser-driven flyer micro forming and laser high-speed impact welding, this paper put forward the laser high-speed impact synchronous welding and forming new process, and builds the compound welding experiment platform. The three-dimensional deep field digital microscope of KEYENCE VHX-1000C was used to measure the surface morphology and the maximum deformation depth of the welding and forming samples. By observing the surface morphology of the sample, it was found that strong plastic deformation occurred on the surface of the materials and well reproduced the shape of the mold. When the laser energy was below 4.5J, the maximum deformation depth of the samples increased with the laser energy. However, the maximum deformation depth decreased due to the spring back phenomenon when the laser energy was larger than 4.5J. The Axio CSM 700 confocal microscope was used to measure the morphology of the welding interface. The cross profile of the welding interface showed that most regions had been welded and the welding interface was nearly flat.

Abstract: A variety of micro forming processes has been invented, and the size effects have become a research hotspot at home and abroad. Micro bending molds with different feature sizes were designed. Quasi-static tester loading and dynamic laser shock loading with soft punch for micro bending forming was studied by numerical simulation respectively based on ANSYS implicit analysis and LS-DYNA explicit analysis. The constitutive models of workpiece are bilinear kinematic hardening model and Johnson-cook model respectively. The effects of different loading conditions and feature sizes of the die on the forming depth, equivalent plastic strain and equivalent plastic strain rate were studied. The results of numerical simulation show that, with the increasing of feature size of the mold, the forming depth under two kinds of loading conditions shows a tendency to increase. In dynamic laser shock loading, the equivalent plastic strain and equivalent plastic strain rate of the key position of the bent part would decrease with the increasing of the feature size of the die. While in quasi-static loading, the opposite law is shown. The research shows that, the flexible micro-bending processes with different loading models showed similar size effect. However, compared with quasi-static loading, in dynamic loading, the strain of forming parts is more centralized, and there is a high strain rate and better formability of the workpiece.

Abstract: Laser-driven flyer micro forming process is a promising microforming technology with the advantage of high efficiency, low cost, high flexibility. A series of experiments are conducted to investigate forming ability of aluminum foil with the thickness of 50μm. The effect of forming temperature and laser energy on forming ability characterized by forming depth, forming accuracy and surface quality is quantitatively analyzed. It is found that forming depth observed through three dimensional topography increases with the enhancement of forming temperature and laser energy. By elevating the forming temperature, the preheated workpiece suffers more homogenous deformation, presenting better forming accuracy. However, a certain degree of deterioration of surface integrity at the forming temperature of 200°C can be attributed to the earlier appearance of micro cracks caused by excessive thinning even at low laser energy. Overall, it is concluded that the optimal forming temperature is appropriately 150°C as the forming depth and forming accuracy is improved with no deterioration of the surface integrity.

Abstract: This paper presents a laser transmission joining (LTJ) experiment between thermoplastic Polycarbonate (PC) and glass reinforced nylon (PA66GF) using diode laser equipment. Laser transmission joining experimental design and experiment are carried out according to a single process parameters window. Response surface methodology (RSM) in Design-Expert v7 software is employed to develop mathematical models between LTJ process parameters and joint strength. The interaction effects of joining process parameters (line energy, spot diameter, clamp pressure) on the joint strength are investigated using analysis-of-variance (ANOVA), the result shows that the interaction effect of line energy and spot diameter has maximum influence on the joint quality. Finally, the predicted values from mathematical models developed by RSM are compared with the experimental values and it is found that they are nearly agreed with each other. The purpose of predicting joint strength based on reasonable process parameters is achieved.

Abstract: Due to the change of car-body design, the location of exhaust systems hanger is uncertain and always fluctuates around the initial design position. So the Taguchi method is introduced to conduct exhaust systems optimal design. Firstly, the parameterization of hanger location under the grid environment was realized by combining NastranHypermesh and Isight. Then, the Taguchi robust design of the exhaust system is performed taking the hanger location as noise factors and the stiffness of hanger shock absorber as control factors. As a result, modal property and robustness of the exhaust system are improved. At last, the results of Taguchi robust design and traditional sensitivity optimization design based on the finite element method are compared, which reveals the advantage of Taguchi robust design in improving product quality.

Abstract: In this paper, the process of laser transmission joining (LTJ) of polycarbonate (PC) and polyformaldehyde (POM) which are thermoplastic plastics is investigated through a finite element (FE) simulation. Firstly, a 3D thermal model is developed with a moving Super-Gaussian heat source based on the ANSYS parametric design language APDL and the distribution of the temperature field is obtained. Then the effect of process parameters namely laser power, scanning speed and spot diameter on the joint width is analyzed. At the same time, the calculated joint width is achieved. Finally, the curves of calculated results are compared with the curves of experimental results. The comparison shows a good agreement between them which shows that the FE model is reliable. This lays the foundation for reducing experimental times, designing of experiments based on FE simulation and optimizing process parameters.

Abstract: In this paper,the laser transmission joint strength is studied with semiconductor laser based on the surface pitting of 304 stainless steel and PA66.Unevenly distributed pits are formed on the surface of 304 stainless steel with 10% ferric chloride solution for two hours, which have certain morphology, depth and size. Different laser power, welding speed and welding pressure are used in laser transmission joining 304 stainless steel and PA66,which 304 stainless steel contains pitting corrosion before and after. The tensile strength test of joined samples shows that: the joint strength of pitted 304 stainless steel and PA66 with laser transmission joining is improved at least 135%; the riveted structure formed at the joining interface improve the joint strength.

Abstract: In this paper, cold-rolled T2 copper foils with the thickness of 50 were chosen. The foils were annealed at different temperatures, namely, 250°C, 350°C, 450°C, 550°C, respectively. Micro deep drawing experiments on cold-rolled foils and annealed foils by laser driven flyer were achieved in order to investigate annealing effects on the formability of T2 copper foil. The forming depth and material flow uniformity of the workpiece at different conditions were compared and analyzed. The test results showed that: (1) The workpiece of cold rolled foil indicates poor neutral, non-uniform material flow, smaller forming depth, it is due to that the microstructures of cold-rolled foil are fiber organizations, which leads to poor plastic deformation capacity.(2)Annealing can significantly improve the formability of the foil. In the first stage : 250-350°C, recovery and recrystallization occurred in succession in the organization of the raw material, fibrous tissue transformed into equiaxed grains, the residual stress is greatly reduced, thus, the plastic deformation capacity is recovered. The forming depth is also significantly improved, increasing by about twice. In the second stage: 350-450°C, the enhanced formability is relative to the surface layer effect, which is also a reflection of micro-scale effect. This study provided a theoretical and experimental guidance for the practical application of micro deep drawing process by laser driven flyer.

Abstract: Based on the CFD-FSI fluid-solid coupled method, the equivalent elastohydrodynamic lubrication model of the micro-texturing dimple surface on the condition of the medium velocity and medium load, low velocity and heavy load, high velocity and heavy load, low velocity and light load and high velocity and light load is respectively solved by numerical method in this paper. And obtain the oil film pressure distribution curve and the oil the film thickness distribution curve on the conditions of steady state, and analyze the influence of micro-texturing dimples on the bearing capacity of the equivalent elastohydrodynamic lubrication model. Analysis results show that: compared with the corresponding minimum film thickness on the conditions of smooth surface, the minimum film thickness of micro-texturing dimple surface on the conditions of the medium velocity and medium load, low velocity and light load is increased, which indicates the bearing capacity of the equivalent elastohydrodynamic lubrication model of the micro-texturing dimple surface is increased; while the minimum film thickness of the rest conditions is decreased, which shows that the bearing capacity of the equivalent elastohydrodynamic lubrication model of the micro-texturing dimple surface is decreased. The study in this paper lays the foundation for the design and optimization of the micro-texturing dimple.

Abstract: A FE model is built based on one vehicle door, the thickness of door's main components for absorbing energy is considered as the design variable. Firstly, a screening experiment is implemented by using Plackett-Burman design, and the prominent components for crashworthiness are selected. Then, the Latin hypercube experiment design is performed again. The approximation model of polynomial response surface is built by the Least Squares Regression according to the experimental results. At last, the approximation model, of which the objective function are the maximum internal energyand the minimum mass sum of all variables, and the constrain function is the maximum impact force, is optimized by using multi-objective Genetic Algorithm (MOGA). The results of the optimization show that the mass of all design variables and the max impact force are reduced by 4.12% and 4.43%, respectively, and the maximum internal energy is increased by 2.3%. The crashworthiness of vehicle door is improved, and it provides the technological support for the safety and light weight design of the whole vehicle door.