Investigation On Millisecond Pulsed Laser Drilling Using Co-axial Motion Of Stainless Steel Sheets In Magnetic Field Environment

With the development of industrial technology for high-precision manufacturing,the applications of microholes with high aspect ratio and quality are becoming more and more popular.Traditional machinery manufacturing technology can’t fully meet the needs of industrial development.Laser drilling is widely researched and applied due to its advantages of high efficiency,good flexibility and stable processing quality.In order to analyze the forming characteristics of high aspect ratio micro holes on thicker plates,the theoretical analysis,numerical simulation and experimental investigation of millisecond pulsed laser drilling using co-axial motion were carried out in magnetic field environment.Firstly,the basic characteristics of the laser beam and the process of millisecond pulsed laser drilling with co-axial motion were introduced.The generation of plasma,the interaction between laser beam and plasmas,and the effect of magnetic field on plasmas were explained Using the parametric design language of ANSYS finite element analysis software,a finite element model and a heat source model of laser drilling based on co-axial motion were established.The temperature field distribution and microholes morphology of laser drilling with co-axial motion were simulated using the element birth and death technique,and the simulated results were compared to the experimental results.It was shown that the temperature distribution of the simulation results was consistent with the experimental process,which proved the model is effective.The calculated results of the microholes entrance morphology and exit morphology agreed with the experimental results,but there was a deviation in the morphology of hole wall between calculated results and experimental results.The microholes entrance diameter and exit diameter of the calculated results were larger than the experimental resultsBased on the established magnetic assistance device,the experimental study on magnetic fie ld-assisted laser drilling with co-axial motion was carried out.The effects of laser co-axial motion speed and magnetic field flux density on the quality of microholes were discussed,including the microholes diameter,microholes circularity,microholes taper,recast layer and micro cracks.It was indicated that the entrance diameter and circularity didn’t change significantly with the increase of laser co-axial motion speed,but the exit diameter and circularity decreased,while taper angle and recast layer thickness increased.The laser drilling using co-axial motion increased the reflection of laser beam within the drilling hole and improved the microholes wall quality.The magnetic field reduced the effect of shielding effect and shockwave of the plasmas on laser beam,and the effective laser energy input improved for hole-drilling.The microholes diameter,the thickness of recast layer and inner wall surface roughness were decreased,and the quality of microholes inner wall was improved,but the magnetic field didn’t improve the micro crack defects significantly.Finally,the effect of laser motion speed on the hole-drilling using co-axial motion and laser trepanning was studied.Energy dispersive spectrum analysis was carried out for the microhole entrance edge.It was found that the micro holes entrance circularity and aspect ratio drilled using co-axial motion was better,while the microholes diameter of laser trepanned was larger with the better cylindricity.The recast layer thickness of the microhole middle drilled using co-axial motion was the thickest,while the recast layer thickness of the microhole entrance using laser trepanned was the thickest.Oxidation reaction occurred at the hole entrance edge drilled using laser co-axial motion and laser trepanning,the weight percentage of oxygen increased,while the relative weight percentage of iron,chromium and nickel decreased,without great change for other elements.