Study Of Process Of Titanium Alloy Laser Deposition Manufacturing In Magnetic Field

As an effective means of aided manufacturing,electromagnetic stirring technique is a way of non-contact stir,which is through the lorentz force that is generated by the conductive liquid metal cutting of magnetic induction line.It is used for improving shaping quality and solving process problems such as porosity and ill bonding in the field of casting,welding and laser deposition manufacturing that involve the metal melt pool solidification.In the field of laser deposition manufacturing,tiny melt happens complex fluid flow under the radiation of laser heat source.After applying magnetic field,the internal transfer,mass transfer behavior become more complicated in melt pool.In order to study the effect of rotating magnetic field on laser melt pool solidification of TA15 titanium alloy in the process of laser deposition repair.First of all,A MHD mathematical model was established on minimal melt pool under the three-phase six-pole rotating electromagnetic stirrer.This model was used to calculate magnetic induction intensity in the center of magnetic field and the melt circumferential flow velocity in melt pool under different exciting current.Then a three-dimensional magnetic-thermal coupling numerical simulation was conducted on the process of single-pass laser melting TA15 titanium alloy with and without the magnetic field based on the finite volume method.The influence of electromagnetic field on flow field,temperature field,temperature gradient distribution,solidification rate and temperature gradient at the solid-liquid interface were analyzed.The impact of electromagnetic on solidification structure formation combined with the theory of columnar-to-equiaxed transition.At last,the numerical simulations and the results of analysis were verified by experiment method.The results showed that the electromagnetic force drived melt to flow circumferentially.The farer from the magnetic field center,the larger ltorentz force promoting the circumferential flow velocity of melt.Magnetic induction intensity was rising with the exciting current,which caused more faster circumferential flow velocity.The consequences of numerical simulation showed that the melt pool maximum flow velocity increased by 20%,which promoted the function of heat exchange resulting in going down of the highest temperature of melt pool and temperature gradient on solid-liquid interface,and meanwhile solidification rate was increased few,which were good for columnar-to-equiaxed transition at the top of melt pool.The experiment results indicated a circumferential force,which caused more faster circumferential flow velocity and a circumferential flow,was produced by electromagnetic stirrer.In the meantime,some equiaxed crystal were generated at the top of melt layer with the magnetic field.Electromagnetic force was enlarged with an increase of the distance from magnetic field center,which causes equiaxed crystal zone had a tendency to expand.The numerical simulations were in good agreement with the experimental results.