Simulation And Experimental Analysis Of Laser-oxygen Cutting Of Thick Mild Steel Plate

Laser cutting is a widely used method in plate processing at present,with many remarkable advantages, such as rapid cutting velocity, narrowkerf, large range of cutting materials and so on. But periodic striations arefound on the kerf surface both in inert gas cutting and laser-oxygen cutting,especially in thick plate cutting. Striations cause the changing of surfacegeometry and increase surface roughness, leading to stress concentration,so reducing striation is very important to improve the quality of lasercutting.This paper discusses the current research situation and developmenttrend of flow field, temperature field simulation and striation formationmechanism in laser cutting. A3-D thermal-fluid coupled finite elementmodel of laser-oxygen cutting is established, the distribution of flow field,temperature field and molten metal in kerf is analyzed, the metal meltingprocess and the influencing laws of typical cutting parameters on striationshape are also studied, the detailed research contents are as follows:At first, the physical theories of laser-oxygen cutting are described indetail. Based on physical theories, with10mm carbon steel as the researchobject, considering the coupling effect between laser source, assisted gasand chemical reaction, a3-D finite element model of laser-oxygen cuttingis established. According to the change of maximum velocity values, thewhole cutting process is divided into four stages, the change of flow fieldin each stage is analysed, and the reason for change is also explained. It isfound that the disturbances of sheet metal and molten metal are the twomain factors that lead to changes in the flow field. The distribution of flow field, temperature field and molten metal instable cutting stage is analysed. Two characteristics of metal melting arefound: the melting process is cyclical and melting rate varies with themelting position. Based on the change characteristics of melting rate, thestriation on the cutting surface is divided into three parts: instantaneousremoving part, rapid melting part and slow melting part, then striationshape characteristics and formation mechanism of each part are analyzedin consideration of aided gas and laser heat source. At the same time, theinfluences of different laser powers, cutting speeds, and assisted gaspressures on the striation shape are analyzed.A laser-oxygen cutting experiment is carried out. Using controlvariable method, under different laser powers, different assised gaspressures and different cutting speeds,10mm low carbon steel plates werecut. Then the striations on the kerf surface were observed by stereoscopicmicroscope. The variation of striation shape under different cuttingparameters is analysed. The experiment verified the theoretical analysisand simulation results.Finally, the paper summarizes all the done work and views the studydirection in the future.