Jian Zhong Zhou

The Mechanism and Experimental Study on Laser Peen Forming of Sheet Metal

Laser peen forming of sheet metal is a new plastic forming technique based on laser shock waves, which derives from the combination of laser shock processing and conventional shot peening technique, it uses high-power pulsed laser replacing the tiny balls to peen the surface of sheet metal, when the laser induced peak pressure of shock waves exceeds the dynamic yield strength of the materials, the sheet metal yields, resulting in an inhomogeneous residual stresses distribution in depth. The sheet metal responds to this residual stress by elongating at the peened surface and effectively bending the overall shape. On the basis of analyzing the mechanism of laser peen forming, the line-track-peening experiments of 45 steel sheets with 2 mm thickness were carried out; a curved sheet metal with deep layer of residual compressive stress was obtained. The preliminary experiment result shows that laser peen forming can offer desirable characteristics in shaped metals and is a valuable technique for producing components for a range of industries.

Prediction on Residual Stress and Fatigue Life of Magnesium Alloy Treated by Laser Shot Peening

Numerical study on fatigue life of ZK60 magnesium alloy plate before and after laser shot peening (LSP) was carried out in this paper. Based on the FEA model, residual stress field induced by LSP was analyzed, the fatigue life and position of weak area were predicted with ABAQUS software and MSC.Fatigue code, respectively, and the processing parameters were optimized. The results show that the fatigue life of ZK60 sheet metal by single LSP with one side and both sides increased by 72.9% and 78.5% compared with the untreated sample respectively. The size and depth of compressive residual stress increase with the increment of peening number, but when the peening number gets to a certain value, the residual stress reaches saturation and the fatigue life increase no longer significantly.

Numerical Analysis on the Process of Laser Continuous Peen Forming of Metal Plate

The principle of laser peen forming (LPF) is introduced, the loading model of laser shock wave is established. This paper focuses on applying finite element analyses, instead of a complicated experimental procedure, to predict the development, magnitude and distribution of residual stresses induced by laser impacts on a metal plate, and dynamic process of laser continuous peen forming is realized with the FEM code ABAQUS. Based on the numerical analysis, the laser processing parameters can be optimized and the deformation contour of metal plate can be analyzed. The results calculated by the finite element method are correlated well with the available experimental results. The simulated results also reveal that adjusting the laser energy appropriately can result in an anticipated shape of plate in LPF process.

Finite Element Analysis for Temperature Field of Laser Remelting Plasma Sprayed Ni-Based Gradient Coating on Ti6Al4V Alloy Surface

In order to acquire evolution law of temperature field of laser remelting plasma sprayed Ni-based gradient coating on Ti6Al4V alloy surface，the effects such as heat conduction, heat radiation, heat convection ,phase change and materials highly non-linearity on coatings and substrate are taken into account comprehensively, and a 3D finite element model(FEM) of multi-tracks laser remelting temperature field is established. The analysis results show that mechanical bonding between coatings and substrate change into metallurgical bonding on present processing parameter，the depth of alloy belt vary in each scanning track and the average depth of alloy belt become deeper gradually with the increment of scanning lines. Temperature changing regular of different points on scanning tracks along scanning direction is similar. Temperature become higher and higher in succeeding scanning tracks due to the heat accumulation effect in laser remelting process. The cooling rate on the mid-points of each scanning track reaches 1200 /s above. The thermal gradient from coatings to substrate along Z direction is absolutely predominant compared with that along X,Y direction, so heat dissipates mainly along the direction normal to substrate which help to crystal grain grown preferentially.

Study of the Effect of Coatings on Mechanical Properties of TC4 Titanium Alloy during Laser Shock Processing

During the process of laser shock processing (LSP), we use high power Nd:Glass laser systems which result in significantly improve fatigue properties and stress corrosion cracking in titanium components. An ablative coating such as black painting and aluminum foil are used to protect the titanium component from surface melting by laser pulse, which adversely affects sample fatigue life. Three different shock-processing configurations are considered: non-ablative exposure, aluminum foil and confined ablation with black painting. We analyzed effect of the coatings on the shock wave propagation into the titanium specimen and the resulting change in mechanical properties versus depth. Near the surface, yield strength and hardness are found to be increased by laser shock, the titanium surface for all coatings increased in yield strength by 16% to 37%. The result have demonstrated that surface hardness can be improved by 31 percent over a machine worked surface with black paintings and be improved by 25 percent with aluminum foil .The experiment aim is to report the effect of the ablative, sacrificial coatings on the laser pulse generation of shock waves and their propagation into the titanium alloys and the resulting change in mechanical properties below the surface versus depth.

Rapid Fabrication of Micro-Gear via Vacuum Casting Technique of Silicone Rubber Mould

A silicone rubber mould was designed and fabricated to study the forming performance of micro-gear based on vacuum casting technique. The effects of process parameters, such as mould temperature, resin temperature, vacuum deaerating time and curing temperature etc, on vacuum casting quality of micro-gear were investigated. The results indicated that high precision micro-gear can be made in batches by means of vacuum casting of silicone rubber mould, and the vacuum deaerating time has the most important influence on the physical dimension of micro-components.

Theoretical Study on the Bending Deformation of Metal Plate Induced by Repetitive Laser Shot Peening

The laser peen forming (LPF) uses high-power pulsed laser beam replacing the tiny medium balls to peen the surface of plate and generate compressive stress near the surface, the metals respond to this residual stresses by elongating at the peened surface and effectively bend the overall shape. In this paper, the deforming process of metal plate induced by repetitive pulsed laser was discussed from theory firstly, and the bending mechanism of LPF was investigated. Then a mathematical model of bending curvature concerning the depth of residual stress was presented, the influence of residual stresses on the deformation of plate was analyzed. Lastly, the line-track-peening experiment for SUS 304 plate was carried out to evaluate the reasonability of the theoretical analysis model.

Non-Traditional Forming Process of Sheet Metal Based on Laser Shock Waves

Traditional forming process of sheet metal is realized with Die and Mould, this technique lacks flexibility and used in the Volume production. The forming process of sheet metal based on laser shock waves is a novel and developing technique. Laser shock forming (LSF) and Laser peen forming (LPF) are two different forming process of sheet metal, both of them are based on a mechanical effect of shock waves induced by laser. In this paper, after introducing the mechanism of laser shock wave generating, these two forming process and technique feature are analyzed and compared, some research progresses are presented. It is indicated that forming technique based on laser shock waves are of high-flexible and great potential application in the fields of plastic forming of sheet metal.

Study on Technology of Flexible Forming of Sheet Metal Based on Laser Shock Waves

The conventional forming of sheet metal is realized by the Die and Mould, this method usually give rise to high cost, long production periods and little flexibility. In order to adapt to the changing requirements of the market and make small batch production of three-dimensional parts of shallow stretching economically, a flexible forming technique of sheet metal based on laser shock waves is presented in this paper. After the forming mechanism and process are introduced, a finite-element analysis method is applied to simulate the shock forming process to obtain the optimized laser parameters and the shocking tracks. The experimental are carried out for the overlapped shock-forming, and the forming contour is measured and compared with the FEA simulation. The investigation provides the theoretical foundation for the selection of forming locus and processing parameters of flexible forming of sheet metal.

Study on Characteristics of Stress and Parameters Influence in Microscale Laser Shock Peening

Microscale laser shock peening (μLSP) can generate beneficial compressive stress distribution in the targets, as the used beam diameter in μLSP is at the order of micron equivalent with grain size, the treated material must be considered as anisotropic and inhomogeneous, this causes an asymmetrical distribution of residual stress. In this paper, shape factor σSF was introduced and defined to characterize the asymmetrical distribution of stress, optimum conditions of factors and the influence degree were explored based on Taguchi design with the optimal object of stress characterization values. The results show that shape factor is a significant characteristic of residual stress induced by μLSP, crystal orientation is the most important influence factor, but laser energy and peening number have significant influence on stress characterization values.