Striation Formation and Melt Removal in the Laser Cutting Process

Introduction The formatIOn of periodIC patterns (stnatlOn) has drawn much attentIon In contInUOUS wave laser cutt time (s) tp time penod per oxidation cycle (s) U gas velOCIty profile (m/s) Uo streamwlse gas velOCIty (m/s) V Interfacial velOCIty (m/s) u lIqUId velOCIty In x dIrectIOn (m/s) v hqUId velOCIty In y dIrectIOn or cuttIng speed (m1s) v. fnctIon velOCIty (m/s) W actIvatIOn energy (J) W Internal energy (1) x dIrectIOn along mterface y dIrectIOn perpendIcular to mterface a ex = kh, dImensionless wave number {3 defmed In Eq (20) {) InItIal dIsturbance (m) y surface tensIOn (kg/s) A wave length (m) JL VISCOSIty of melt (kg/(ms)) JLg VISCOSIty of gas (kg/(ms)) p densIty of melt (kg/m) Pg densIty of gas (kg/m) uxy tangentIal perturbatIOn stress (Pa) Uyy normal perturbation stress (Pa) T mean shear stress (Pa) v kInematIc VISCOSity of melt (m/s) vg kInematIc VISCOSity of gas (m /s) I/J stream function functIOn in Eq. (3) T1 dIsturbance (m) Abstract The mechanisms of melt ejection and striation formation In continuous wave laser cutting of mild steel are discussed Melt ejection from the cutting front IS shown to be a cyclic phenomenon Striation formation IS strongly affected by the oscillatory characteristic of the thin liqUid film on the cutting front dUring melt eJection, together with the oXidation and heat transfer process Cutting speed determines whether the liquid film will rupture or generate waves on the cutting front Theoretical explanations are given according to the Instability theory of a thin liqUid film In a high-velocity gas Jet and the diffusion-controlled oXidation theory Stnatlon frequency and depth are predicted according to the above theones Expenmental Investigations wer~ carned out and the results are consistent with the calculations The better understanding has shed light on further Investigations and optimal process development