Numerical Simulation Of Additive Manufacturing Based On Laser-Particle Interaction

Additive manufacturing(AM),known as 3D printing,is a manufacturing process in which the powder particles are deposited on a substrate by numerical control.The sizes,mechanical properties and manufacturing parameters of the powder particles can affect the temperature variations in AM.The powders are stacked and melted in high temperature.In this process,the residual stress,residual distortion and microstructure can be influenced by the manufacturing temperature.The tensile residual stress leads to the decrease of fatigue strength and service life.Excessive high tensile residual stress can lead to failure of AM structure.The residual distortion influences the geometrical accuracy of the AM product.Large residual distortion can lead to shaping failure of AM product.As the source of the good mechanical properties of the additive manufactured component,the microstructure greatly influences the service performance of the additive component.It is necessary to investigate the temperature variations with consideration of different powder features.Then,the influences of powder features and process parameters on the residual stresses and distortions can be then studied in detail.This is the key problem for the controlling of the AM product quality with combination of the powder features,which is very important for the improvement of the AM product quality.Electromagnetic wave based laser-particle interaction model was established in current work.The effects of the powder features and the particle feeding parameters were systematically discussed.The scaling effects of building height,building radius and building angle on the thermal stress,residual stress and residual distortion were discussed to study the mechanism on the scaling effects of AM products.The Monte Carlo model considering the temperature gradient and the temperature distribution in the cross-section was built.The temperature histories calculated by the heat transfer model considering the laser-particle interaction was used in the Monte Carlo model.Then,the numerical model,which was consisted with single grain model and multi-grains model,was built to model the phase transition of Ti-6Al-4V.The nucleation of the ? phase grain on the boundary of the ? phase grain and the growth process of the ? phase grains were simulated.The simulation result of the grain morphology of a phase grains agree well with the experience observation.Firstly,the laser-particle interaction model based on electromagnetic wave theory was proposed to investigate the interaction between the powder particles and the laser beam.The temperature of the particle and effective laser power absorbed by deposition layers were calculated.The results of the laser-particle interaction model were applied in the finite element model to modify the double ellipsoid heat source model.The temperature field of manufactured product can be simulated using the modified finite element model.The temperature result was validated experimentally.The effects of powder size,powder velocity and powder flow rate on the temperature field were also be discussed.Secondly,coupled sequential thermos-mechanical method considering the laser-particle interaction was proposed to study the effects of parameters of powder particles on the residual stress and distortion.The simulation results indicated that the increase of powder velocity and decrease of powder flow rate decrease the interaction between laser and powder particle.The effective laser power absorbed by deposition layers was increased.As a result,the thermal expansion was also increased.The increased residual stress and distortion can be found in the manufactured product,when it is cooled down.The transverse bending deformation caused by building at the edge of the substrate and the large vertical bending deformation caused by a thin substrate need to be controlled in laser deposition additive manufacturing.Thirdly,numerical model of circular additive manufactured component was built to study the temperature,thermal stress,residual stress and residual distortion in circular additive manufactured component.The building height scaling effect,building radius scaling effect and the building angle scaling effect were studied to analysis the mainly mechanical controlling factor of residual distortion.The simulation results indicate that residual distortion of circular component was exponentially increased with the increase of building height.Residual distortion of circular component was decreased with the increase of building radius,due to the increased bending stiffness.Large transverse thermal deformation and transverse thermal stress can be found,when materials were deposited with a building angle.Residual distortion was increased with the increase of building angle.The substrate was pulled inward,when the inward-shrinking cone was cooling.The vertical residual distortion was increased.The substrate was pulled outward,when the outward-expanding cone was cooling.The vertical residual distortion was decreased.Finally,Monte Carlo method considering the temperature gradient and time-dependent temperature distribution was built to model the morphology of grains in the vertical section of the laser deposited additive manufactured sample.The heterogeneous grain growth in the vertical section of the laser deposited additive manufactured sample can be studied using the proposed model.Then,the numerical model,which was consisted with single grain model and multi-grains model,was built to model the phase transition of Ti-6Al-4V.The nucleation of the a phase grain on the boundary of the ? phase grain and the growth process of the ? phase grains were simulated.The simulation result of the grain morphology of ? phase grains agree well with the experience observation.