Multi-Physics Process Simulation of Static Magnetic Fields in High Power Laser Beam Welding of Aluminum

Transcription

1 Multi-Physics Process Simulation of Static Magnetic Fields in High Power Laser Beam Welding of Aluminum Marcel Bachmann, Vjaceslav Avilov, Andrey Gumenyuk, Michael Rethmeier COMSOL Conference Milan 2012, October 10 12, 2012 Excerpt from the Proceedings of the 2012 COMSOL Conference in Milan

2 Overview Introduction Physical Principles Numerical Modeling & Results Experimental Observation Conclusions COMSOL Conference Milan 2012 Marcel Bachmann 1

3 Introduction Applications deep-penetration laser beam welding Ship-building industry Reactor vessels & tanks Power plant components Aerospace industry High-Speed Car Ferries Austan Ships Aluminum Reactor Vessels Maulifab Engineers NASA tank dome COMSOL Conference Milan 2012 Marcel Bachmann 2

4 Introduction Characteristics of the laser beam welding of thick metal parts laser beam Related issues: Intensive Marangoni convection Buoyancy forces Recoil pressure Surface stability Melt ejections Non-uniform solidification COMSOL Conference Milan 2012 Marcel Bachmann 3

5 Introduction Possibility to decelerate the melt? apply volumetric forces contact-less all welding positions COMSOL Conference Milan 2012 Marcel Bachmann 4

6 Physical Principles Hartmann Effect Flow Deceleration 1.0 u j F L B Norm alized channel widt h Ha 2 = 0 analytic Ha 2 = 1 analytic Ha 2 = 25 analytic Ha 2 = 100 analytic Ha 2 = 0 sim ulation Ha 2 = 1 sim ulation Ha 2 = 25 sim ulation Ha 2 = 100 sim ulation Norm alized Velocity u/ u mean Liquid metal flow induces electric currents Ratio of magnetic induced to viscous drag Ha 2 = (BL) 2 σ/η Resulting Lorentz force directed against melt movement COMSOL Conference Milan 2012 Marcel Bachmann 5

7 Physical Principles Permanent magnets applied to partial penetration welding Mitigation of weld pool dynamics Avoid turbulent flow pattern Achieve parallel side walls COMSOL Conference Milan 2012 Marcel Bachmann 6

8 Numerical Modelling Thermal Simulation Computational Fluid Dynamics Simulation Electromagnetic Simulation Material Properties 50 mm magnet 20 mm Workpiece width: 40 mm Magnet cross section: 50 mm 50 mm 50 mm workpiece Vertical shift of the air keyhole ~21 mm magnet: 20 mm 900,000 tetrahedral finite elements 8,100,000 DoF COMSOL Conference Milan 2012 Marcel Bachmann 7

9 Numerical Modelling free slip Marangoni free slip free slip adiabatic adiabatic adiabatic inflow free slip outflow adiabatic WORKPIECE symmetry Marangoni Marangoni free slip adiabatic Navier Stokes equations volume source term F = ρg c 1 (1 f L ) 2 (u u weld ) + j B f L 3+ɛ Buoyancy Solidification modelling Lorentz force COMSOL Conference Milan 2012 Marcel Bachmann 8

10 Velocity distribution velocity, m/s B = 0 B = 0.5 T 0 Welding speed 0.5 m/min 3D flow 2D flow Buoyancy suppression Marangoni flow suppression B = 1.0 T B = 2.0 T COMSOL Conference Milan 2012 Marcel Bachmann 9

11 Velocity distribution B=0 B=0.5 T m/s m/s z, mm z, mm x, mm x, mm z, mm m/s x, mm z, mm m/s x, mm B=1 T B=2 T COMSOL Conference Milan 2012 Marcel Bachmann 10

12 Temperature distribution B = 0 B = 0.5 T B = 1 T B = 2 T Te m pe rature T, K Marangoni convection suppressed at free surface Weld bead shortening Curvature in solidification line eliminated COMSOL Conference Milan 2012 Marcel Bachmann 11

13 Macro Section Solidification line z - position, mm Marangoni convection suppressed Weld bead width decrease Curvature in solidification line eliminated 30 B = 0 B = 0.5 T B = 1.0 T B = 2.0 T theoretical case y, mm COMSOL Conference Milan 2012 Marcel Bachmann 12

14 Local Hartmann Number 10 6 Hartmann number Ha laminar Hartmann number turbulent Hartmann number magnetic flux density B, T Position: 5 mm behind keyhole and 5 mm below surface η = η lam + η turb Jump in Ha 2 = (BL) 2 σ/η Once turbulence is damped Ha 2 lam Ha2 turb Critical Ha 2 for effective flow control around B=0.4 T COMSOL Conference Milan 2012 Marcel Bachmann 13

15 Experimental Observation AlMg3 Welding Experiments with 16 kw disc laser system and permanent magnets B max around 0.5 T magnet pole Weld narrowing magnet pole Less surface waviness Laser power: 16 kw Welding velocity: 0.5 m/min Focus position: -4 mm Shielding gas: 30 l Ar Wine-glass shape V shape COMSOL Conference Milan 2012 Marcel Bachmann 14

16 Experimental Observation Reference B = 500 mt Same tendency in experiments and simulations! COMSOL Conference Milan 2012 Marcel Bachmann 15

17 Experimental Observation B = 500 mt Same results with changed orientation of the magnet field Evidence for the occurance of Hartmann effect Laser power: 16 kw Welding velocity: 0.5 m/min Focus position: -4 mm Shielding gas: 20 l Ar COMSOL Conference Milan 2012 Marcel Bachmann 16

18 Conclusions Influence of steady magnetic fields in partial penetration laser beam welding of aluminium is shown Significant changes in the velocity distributions Maximal turbulence damping beginning with Ha Weld pool geometry changes due to Hartmann effect with increasing magnetic field from wine-glass shape to V shape Changes in solidification line can influence mechanical and metallurgical properties COMSOL Conference Milan 2012 Marcel Bachmann 17

19 Thank you for your attention. Grant No. GU 1211/2-1 Grant No N COMSOL Conference Milan 2012, October 10 12, 2012