This paper presents a systematic numerical investigation of the transient transport phenomenon during the pileup of molten metal droplets on the substrate. The physical mechanisms of the pileup process, including the bulk liquid, capillarity effects at the liquid-solid interface, heat transfer, and solidification, are identified and quantified numerically. The droplet diameter is 100 μm, and the impact velocities are 1–3 m/s. These conditions correspond to Re = O(100), We = O(1). The initial substrate temperature is 350 K. The initial droplet temperature of aluminum alloy molten droplets is 960 K. The numerical models are validated with experiments. The comparison between numerical simulations and experimental findings shows a good agreement. The effects of impacting velocity and relative distances between two successive molten droplets on the end-shapes of impact regime are examined. This investigation is essential to implement effective process control in metal microdroplet deposition manufacture.

A three-dimensional (3D) numerical model with the volume of fluid method is developed for high-speed variable polarity gas tungsten arc welding (VP-GTAW) of aluminum alloys. It predicts the thermal flow field in the weld pool, the weld pool surface deformation, and solidified bead geometry during VP-GTAW in successive welding passes. Verification of the numerical model was performed by comparing the calculated results with metallography of welded cross-sections. The prediction showed reasonable accuracy in predicting weld bead geometry. The prediction average relative errors of the bead width and depth of penetration are less than 7%. The deformed weld pool surface, the fluid flow in the weld pool, and maximum fluid temperature in the workpiece based on the developed model, are discussed in detail. The effects of welding speed and pulse frequency on surface depression are studied. The results show that the maximum fluid temperature is closely correlated to the welding speed and pulse frequency. Further, the upper and lower limit of maximum fluid temperature would provide a clue by which the surface depression and the pitch of humps may be recognized. An increase in welding speed will lead to the increase of the pitch of humps, but the reverse is true in the pulse frequency. These detailed physical insights facilitate the prediction of welding surface defects in the high-speed VP-GTAW of aluminum alloy.

Purpose: This paper aimed to propose a novel fused-coating-based additive manufacturing (FCAM); the study of key process parameters and mechanical tests are performed to determine the proper parameters when building metal components. Design/methodology/approach: Sn63Pb37 alloy is deposited in an induction heating furnace with a fused-coating nozzle to build metal parts on a copper-clad substrate. The process parameters including nozzle pressure, nozzle and substrate temperature and nozzle gap between substrate are analyzed and found to have great influence on parts quality. The mechanical property tests between the fused-coating and casting parts are performed in horizontal and vertical directions. Also, the optical microscopy images are used to ascertain under which conditions good bonding can be achieved. Findings: A FCAM method is proposed, and the exploration study about the manufacturing process is carried out. The critical parameters are analyzed, and microscopy images prove the suitable temperature range that requires to fabricate metal parts. The mechanical tests confirm that tensile strength of printing parts is improved by 20.4 and 11.9 per cent in horizontal and vertical direction than casting parts. The experimental results indicate that there is a close relationship between process parameters and mechanical properties. Originality/value: This paper proves that FCAM provides an alternative way to quickly make functional metal parts with good quality and flexibility compared with other additive manufacturing methods. Moreover, good mechanical property is achieved than conventional casting parts.

In varying polarity gas tungsten arc welding (VP- GTAW) based metal fused-coating additive manufacturing (AM), the surface topographies of deposited layer are more complex than conventional welding, therefore, the distribution of the electromagnetic force in molten pool, arc pressure, plasma shear stress and heat flux on thermocapillary-induced deposited shape are not the same as the conventional welding. A three-dimensional numerical model was developed to investigate the transient thermal-fluid behaviors and the shape evolution of deposited layers in fused-coating AM process of aluminum alloys. Various driving forces of thermocapillary-induced melt flow including arc pressure, Lorentz force, arc plasma drag force and surface tension were taken into account in the model. Numerical prediction regarding the solidified shape and size of a single-track deposited layer is compared with the corresponding experimental data, showing that there is a good qualitative agreement between the two, which indicates that the established numerical model is capable of simulating the complex heat and mass transfer phenomena in the VP-GTAW based additive manufacturing. The thermo-physical process in fused-coating additive manufacturing process is systematically analyzed. Trends in deposition width and height with two major process parameters are captured. It is found that the shape of single-track deposited layers is strongly influenced by substrate moving speed. With an increase in the gap height between the substrate and fused-coating head, there are approximate changing trends in the height and width of deposited layers. The parametric study is prime important to understand and control the metal behavior in a layered deposition format.

Through using a novel micro-coating metal additive manufacturing (MCMAM) process in this study, the forming characteristics of the multilayer single-pass specimens were investigated. The forming defects including the porosity and the bonding quality between layers were analyzed. Moreover, we also attempted to study the effect of process parameters such as flow rate, deposition velocity, and layer thickness on the forming morphology. Based on the results, the optimization of process parameters was conducted for the fabrication of thin-wall MCMAM. Finally, estimation criteria for the integrity of the interfacial bond were established.