The Effect Analysis Of Assistant Gas Flow By Nozzle Structure And Cutting Parameter In Laser Cutting

Laser cutting is one of the most important application technologies in laser machining industry. Compared with the traditional flame cutting and plasma cutting, laser cutting has plenty of remarkable advantages, such as excellent cutting quality, rapid cutting velocity, high automation, large range of cutting materials and so on. The implementation of laser cutting is the result of the interaction of high power laser bean and assist gas. On the one hand, the machining materials is melted down by high power laser bean, on the other hand, melten metal and part of heat are expelled from the kerf. Reasonable nozzle structure and cutting parameter can limit the heat effect area to a very small scope, and can also ensure machining quality and efficiency.Under the support of the two important science and technology projects, the paper discusses the research present status and development, analyses the influence law of gas dynamics performance about jet flow effected by nozzle structure, constructs three-dimensional symmetry model of laser cutting impinging flow and studies the influence to gas dynamics performance by cutting parameter in kerf. The concrete research content is as follows: First for two assemble nozzles of taper and convergence, based on the axial symmetric N-S equation of compressible liquid, the paper establishes the onflow model to simulate convergent nozzles'free jet of different internal parameters by using structural grid and finite volume of quadratic precision. The law is revealed that how contractive angle of taper nozzles and curvature radius of convergence nozzles'convergent section effect jet structure parameters, and evidence is provided for optimization selection and design about laser cutting nozzles.The paper describes simply the cutting parameter and kerf structure of laser cutting, analyses the dynamics effect of assist gas in kerf, constructs three-dimensional symmetry model of laser cutting impinging flow, and has a simple description of adopted control equation and onflow model.The plane symmetry impinging jet process is analysed, the interaction mechanism between gas and workpiece is studied and the relationship between gas assistant machining ability and stand off distance, workpiece thickness, kerf width respectively. According to the evaluation criterion of velocity and mass flow rate, the gas dynamics performance of taper nozzle in kerf excels obviously than that of convergence nozzle. And with the increasing of stand off distance, at least two reasonable cutting scopes exist. With the increasing of workpiece thickness, the position of expansion wave will be bigger relatived to the nether surface and it will result in worse gas dynamics performance close to the nether surface and bad cutting quality and efficiency. Under the same inlet pressure, with the increasing of the cutting kerf, the change grads of pressure and velocity on the axes of convergence nozzles are smaller and smaller.On the base of theory research, a kind of taper nozzles and convergence nozzles with optimized structure are developed. By contrast experiment with the German PRECITEC NOZZLEφ1.25HD nozzles, the developed nozzles have corresponding cutting effect. At the same time, the theory analysis result of the relationship between cutting quality and stand off distance, workpiece thickness, kerf width are validated by experiment respectively, and it can provide theory guidance and experiment data with optimization cutting in future.Finally, the paper summarizes all the done work and views the study direction in future.