The formation of thick Ni-based coating on a steel substrate by coaxial laser cladding using the Nd:YAG 2 kW continuous laser was studied both from a theoretical and experimental point of view. The theoretical analysis concentrated on the transfer of laser irradiation and powder particles using a simple model of heat transfer to the substrate. This approach provides predictions of the laser power required for melting powder particles and substrate, respectively. For an appropriate experimental analysis of the main process parameters involved, a method based on a gradual change of a single processing parameter was examined. Correlations between the main processing parameters and geometrical characteristics of an individual laser track have been found and are discussed.

Analysis of coaxial laser cladding processing conditions

A thermo-mechanical model of directed energy deposition additive manufacturing of Ti–6Al–4V is developed using measurements of the surface convection generated by gasses flowing during the deposition. In directed energy deposition, material is injected into a melt pool that is traversed to fill in a cross-section of a part, building it layer-by-layer. This creates large thermal gradients that generate plastic deformation and residual stresses. Finite element analysis (FEA) is often used to study these phenomena using simple assumptions of the surface convection. This work proposes that a detailed knowledge of the surface heat transfer is required to produce more accurate FEA results. The surface convection generated by the deposition process is measured and implemented in the thermo-mechanical model. Three depositions with different geometries and dwell times are used to validate the model using in situ measurements of the temperature and deflection as well as post-process measurements of the residual stress. An additional model is developed using the assumption of free convection on all surfaces. The results show that a measurement-based convection model is required to produce accurate simulation results.

Thermo-mechanical model development and validation of directed energy deposition additive manufacturing of Ti–6Al–4V

Microstructure and mechanical properties of Al-Mg-Zr alloys processed by selective laser melting

A model which takes into account the main phenomena occurring during the laser-cladding process is proposed. For a given laser power, beam radius, powder jet geometry, and clad height, this model evaluates two other processing parameters, namely, the laser-beam velocity and the powder feed rate. It considers the interactions between the powder particles, the laser beam, and the molten pool. The laser power reaching the surface of the workpiece is estimated and, assuming this power is used to remelt the substrate with the clad having been predeposited, the melt-pool shape is computed using a three-dimensional (3-D) analytical model, which produces mmediate results, even on personal computers. The predictions obtained with this numerical model are in good agreement with experimental results. Processing engineers may therefore use this model to choose the correct processing parameters and to establish cladding maps.

A Simple but Realistic Model for Laser Cladding

Modulating laser intensity profile ellipticity for microstructural control during metal additive manufacturing

A transient three-dimensional (3-D) conduction-based heat-flow model has been developed in order to simulate the experimental processing conditions during laser surface remelting. This study concentrates on the validation of the model by comparison with data obtained from laser remelting experiments made in the eutectic alloy Al-Cu 33 wt pct over a range of traverse speeds between 0.2 and 5.0 m/s. It is shown that the simulation not only requires thermophysical data, but also a good knowledge of the laser beam process parameters. When the steady state is reached, the fusion isotherm which outlines the liquid pool yields the trace cross section and the resulting microstructure. Good agreement with experimental data is found over the range of processing speeds for the maximum melt pool dimensions, the transverse profile of the laser trace, the melt surface shape, and the resolidified microstructural spacings.

M. Zimmermann

Papers

Heat-flow simulation of laser remelting with experimenting validation