| With the continuous improvement in performance of aero-engines increasing,the temperature of engine has reached 1300 degree Celsius which has exceeded the melting point of the metal blade.Therefore,it is necessary to design airfoil cooling holes on the blade to ensure that the blade can work sustainably.There are four conventional processing methods for airfoil cooling holes,such as,electric discharge machining,electro-beam machining,laser processing,and composite processing.These processing methods can meet the manufacturing requirements of the airfoil cooling holes basically,but there are some inherent disadvantages which are difficult to work out in a short time.Water-jet guided laser(WJGL)is actually a new micro-fabrication technology with almost no micro-cracks,no thermal stress,no pollution,no burr,highly accuracy,small thickness of recast layer and heat-affected zone,long effective processing distance,straight cutting seam,smooth edge.General Electric Corporation(GE)of the United States has applied this technology to the processing of aero engine airfoil cooling holes.The mechanism of WJGL processing is intertwined,involving multiple disciplines,such as laser,materials,fluids,heat transfer,etc.However,it runs short of systemic studies on the mechanism of WJGL processes and technology of airfoil cooling hole drilling in national.Based on the situation above,this paper had carried out WJGL processing mechanism and technology on the foundation of the research at national and international.Through the combination of experiments and simulations,this paper explored the removal mechanism of materials and optimized the process parameters.First of all,the fluent simulation software was used to study the generation mechanism of laminar water fiber were researched in this paper.And the simulation verifies that sharp-edged nozzles can produce laminar water jets.What’s more,the laser transmission characteristics and transmission methods in water are studied,and the calculation formula for the critical angle of laser total reflection at the water-air interface is deduced;the factors affecting the laser energy distribution in the multi-mode transmission process are mainly analyzed by the numerical aperture of the beam And nozzle aperture;also studied the energy attenuation and influencing factors when the laser propagates in the water beam.Secondly,in order to understand the heat propagation mechanism of WJGL processing and the principle of material removal,this paper conduct a research from the following four aspects,the jet impacting the target,the absorption of the laser by the metal surface,the plasma shock wave,and the thermal erosion simulation of the water-guided laser drilling.Based on the finite element(FEM)theory and life-death element technology,a thermal erosion model of WJGL drilling of super-alloy was established to study single-pulse drilling and multi-pulse drilling processes.The experiments were done to verify the accuracy of the model eventually.Finally,to study the influence of water-guided laser machining parameters on the quality of material micro-hole forming,this paper takes super-alloy GH4169 as the experimental material and uses water-guided laser machining equipment to conduct rotary cutting holes experiment under different laser power and scanning speed.White light interferometer(WLI),scanning electron microscope(SEM),and energy dispersive spectrometer(EDS)were used to measure the two-dimensional and three-dimensional morphology,microstructure,and element content of the recast layer of the machined hole.By sorting and analyzing the experimental data,this paper explored the influence of processing parameters on the ablation of the inner wall of the hole,the diameter of the entrance and exit,the roundness of the entrance and exit,and the roughness of the wall are summarized,and the change of the microstructure of the material wall.This study can enrich the theory of wjgl and provide theoretical reference and data support for broadening the application field of WJGL. |
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