Processing parameters in laser powder bed fusion metal additive manufacturing

The work presented in this paper deals with the laser welding simulation. Due to the rise of laser processing in industry, its simulation takes also more and more place. Nevertheless, the physical phenomena occurring are quite complex and, above all, very coupled. Thus, a state of art is necessary to summarize phenomena that have to be considered. Indeed, the electro-magnetic wave interacts with the material surface, heating the piece until the fusion and the vaporization. The vaporization induces a recoil pressure and deforms the liquid/vapor interface creating a vapor capillary. The heat diffused in the material produces thermal dilatation leading to mechanical stress and strain. As a complete simulation is too large to be computed with one model, the literature is composed by two kinds of models, the thermo-mechanical simulations and the multi-physical simulations. The first aims to find the mechanical stress and strain due to the welding. The model is usually simplified in order to reduce the simulation size. The second, compute the more accurately the thermal and the velocity fields. In that case authors usually search also the size of the weld bead and want to be totally self consistent. In this review, the major part of equations and assumptions needed to simulate laser welding are shown. Their effects on simulation results are illustrated for each simulation type. The paper aims to give sufficient knowledge and tools to allow a simulation of laser welding.

/pdf/invited-an-overview-of-the-state-of-art-in-laser-welding-2mfy2t55j6.pdf

[INVITED] An overview of the state of art in laser welding simulation

Thin plates are extensively used in automotive, shipbuilding, and railway industries. Welding technology is the main assembling method to manufacture thin plate structures because of its high productivity and ease of use. Consequently, residual stress and distortion induced by welding are an inevitable part of the manufacturing process in welding thin plate structures. Relatively low stiffness, and a high amount of heat input are the main reasons for distortion of the welded structures. In order to decrease the heat input, laser-based welding processes that generate highly localized heat with a very high intensity can be a good choice as an alternative to traditional fusion welding. To predict residual stress and distortion in welding thin plate structures, a three dimensional, thermo-metallurgical-mechanical finite element method was developed. The results of three different laser-based welding processes including aspects of Autogenous Laser Welding (ALW), Cold Wire Assisted Laser Welding (CWLAW), and Hybrid Laser-Arc Welding were compared with traditional Submerged Arc Welding (SAW) from both predicted and experimental perspectives. SYSWELD commercial code was used for the simulations in which both large and small deformation theories were employed to predict the residual stress and the final deformation. Experiments were executed to verify the simulation results. A digital high-resolution microscope was used to visualize and measure the weld cross- sectional shape and bead geometry. To measure the residual stress, an X-ray diffractometer was employed. A digital Vernier Caliper and a 3D laser-handheld scanner were used to measure displacement in the z-direction. Moreover, the mechanical properties of welds obtained by different welding processes were also verified by tensile and micro-hardness tests. It was concluded that lower heat input can markedly influence the final distortion of the welded structure. This conclusion can strongly support the idea of replacing traditional arc welding method with a laser-based one. Simulation and experimental results were matched fairly.

Numerical simulation and experimental validation of residual stress and welding distortion induced by laser-based welding processes of thin structural steel plates in butt joint configuration

Residual stress analysis in laser welded NiTi sheets using synchrotron X-ray diffraction

Numerical and experimental investigation on microstructure and residual stress of multi-pass hybrid laser-arc welded 316L steel

Simulation of laser butt welding of AISI 316L stainless steel sheet using various heat sources and experimental validation

The objective of this work is to carry out thermo-elasto-plastic analysis of pulsed Nd-YAG laser-beam butt welding of 304L Stainless Steel sheets using Finite Element Modelling. Thermo-mechanical analysis was done by using commercial Finite Element software SYSWELD. Thermal analysis provided thermal cycles and weld bead geometry. Then using thermo-mechanical analysis, residual stresses and distortion values were estimated. In order to validate the model predictions, a single pass autogenous welding with pulsed laser beam was performed on 304L stainless steel sheets. Thermocouples were used to record temperatures at different places close to the fusion line. Vertical displacements after welding were measured using Vertical height gauge equipment. The longitudinal residual stress after welding was measured using an ultrasonic technique. Metallography was employed to view the cross sections of the weld bead. The Finite Element Analysis results were then compared with experimental results. Thermal cycles, distortion and residual stresses obtained in FEA and experiments were found to be in good agreement.

Jazeel Rahman Chukkan

Papers

Simulation of laser butt welding of AISI 316L stainless steel sheet using various heat sources and experimental validation

Numerical Simulation of Pulsed Nd-YAG Laser Butt Welding of AISI 304L Stainless Steel Sheet and Experimental Validation