Analysis Of Assisted Gas Flow In Laser Cutting And Optimization On Parameters Of Nozzle

Laser cutting technology is an important part of laser processing applications.It is one of advanced cutting technology on the current world.With the application expanding,some of key technologies which restrict the application expanding must be resolved.Nozzle and its gas jet field is one of the most important factors.So it is important to improve the capability,efficiency and quality of laser cutting on laser cutting nozzle and its gas jet filed.Firstly,according to aerodynamic theory and mechanism of laser cutting,the geometric models of the conical nozzle,supersonic nozzle and simple supersonic nozzle is set up.And then this dissertation analyses the gas jet from the conical,new designed supersonic nozzle and simple supersonic nozzle on different inlet pressure using standard k-εmodel and unstructured grid finite volume method with compressible axis-symmetry N-S equation.The result of analysis indicates that conical nozzle has a great characteristics of gas jet when inlet pressure is low.It is fit for low speed and low pressure situation.There is shockwave at nozzle exit and great fluctuation with increasing inlet pressure;The gas jet from supersonic nozzle with a tidy boundary,high momentum,good uniformity of velocity and pressure distributing can be obtained working on design work pressure.It is fit for high-pressure and high-velocity laser cutting in thick metal plate;Simple supersonic nozzle has some characteristics of gas jet when inlet pressure is high.It is simple structure and convenience for manufacture,more easily production.In order to study the influence of the surface of the shear force and pressure gradient on the appearance of cut front in laser cutting.The relationship between assist gas and workpiece is described as impinging jet onto a surface at an inclined angle.And impinging jet chooses RNG k-εmodel.The results indicates that the smaller angle of inclined surface and nozzle axes and stand off are,the more pressure gradient and shear force are.The great shear force and variation of the pressure gradient would significantly enhance the material removal rate and the appearance of cut front in laser cutting.Lastly,Taguchi is used to design and analyses the parameters of nozzles,and to establish orthogonal array L18 and L9 respectively to optimize the construction parameters of nozzles which is suited for premixed and after-mixed cutting nozzles.It is the basis of the selection of nozzles' structural parameters in actual laser cutting.