Analysis Of The Formation Mechanism Of The Upper Striation On The Cutting Surface During The Laser Fusion Cutting Process

Laser cutting has been used widely with its advantages of fast cuttingspeed、narrow cutting kerf、good cutting quality and non-contact processing.Striation is main structure on the cutting face which determines the resultantcut quality. In this dissertation the formation mechanism of the upper striationon the cutting surface during the fusion cutting process is analyzed. Thecorresponding suppression measures are given.The main characteristics of the upper striation are absent of re-solidifiedmaterial, distinct solid-liquid interface and nearly perpendicular surface. Withthe increase of cutting speed, the striation wavelength and amplitude decrease.Based on this the instantaneous remove mechanism is proposed in the paper.The degree and extent on which the model can explain the phenomenon areclarified from the viewpoint of space variable magnitude.According to the boundary temperature, Laser cutting process is dividedinto heating phase and melting phase. Corresponding mathematical model are given. The equations are solved with finite difference method. The striationshapes for various cutting parameters and materials are given. Based on thetemperature distribution in the sheet under steady melting state the ideal laserpower modulation method to improve cutting quality is obtained.Through the introduction of three characteristic variables which areboundary temperature、melting boundary position and heat content, theunified expression for approximate temperature distribution in the heatingphase and melting phase is given. With the help of Biot variation principleand heat balance integral method the original partial differentials aretransformed into approximate ordinary differential equations. The abovecharacteristic variables versus time variation curve are obtained. Cyclicnature of the system and striation can be easily verified from the figure.Based on the green equality, the explicit representation for thetemperature distribution during the heating phase is expressed in the form ofthe green function for the semi-infinite domain. With the green function forthe infinite domain the implicit expression for the temperature distributionduring the melting phase is obtained. These results are treated as exactsolutions of the model equations. The correctness are verified throughcomparing with the above results.Theoretical analysis results are verified through the mild steel and stainless steel cutting experiment. The cutting face characteristics arebasically consistent with the description in the thesis. There are somediscrepancies between analytical results and the striation versus cuttingparameters variation law. Against the upper striation on the cutting surfacethe main methods to improve the quality are increasing cutting speed andpower modulation.