An Investigation Of Heat Transfer And Fluid Flow Behaviors In Electron Beam Freeform Fabrication

Electron beam freeform fabrication (EBF3) is a rising rapid manufacturing technology.It could be used for the manufacturing of large metal structural parts of aerospace ormedical treatment. This paper investigates the heat transfer and fluid flow behaviors inEBF3by combining experiments and numerical simulations. The major works and resultsare listed below:(1) By developing the electron beam freeform fabrication experiments with differentprocess parameters of TC4titanium alloy and metallographic experiments, the profiles ofcross section morphology of fused zones under different technologies were obtained.Influences of process parameters on the depth, width and depth to width radio of the fusedzone were studied. The metallographic microstructure after rapid forming was investigated.The results showed:1) the molten pool in EBF3was exhibited the characteristics such asbigger width, smaller depth and depth to width radio. The depth to width radio was usuallyless than1.2) EB elliptical scanning could increase the range of processing and thehomogeneity of energy distribution.3) The microstructure showed the presence of and ’in the fused zone and the near heat affected zone. The fused zone experienced theâ†'βâ†'Lâ†'βâ†'/’phase transformation sequence and the near heat affected zoneexperienced theâ†'βâ†'/phase transformation sequence.(2) By considering the major physical phenomenon, such as the melting,solidification and evaporation of the base materials and feeding wires, and convection heattransfer, conduction heat transfer and radiant heat loss of the molten pool, and recoilpressure, thermal capillary force and surface tension at the free interface, a numericalmodel was developed to simulate the heat transfer and fluid flow in EBF3. The model wasvalidated by comparing the simulating results and experimental fusion zones.(3) Based on the numerical simulations in EBF3of TC4titanium alloy, the changes oftemperature fields and velocity fields of the molten pool with time were obtained. Theevolution of the molten pool and influences of droplets deposition on the molten poolwere studied. The results showed:1) the variations of the temperature field characteristicswere consistent with the analysis of experimental results of solidification behavior.2) Recoil pressure and thermal capillary force were the important influencing factors in thefluid flow of the molten pool. Especially, thermal capillary force was the most importantone.3) The droplets deposition could influence the temperature fields and velocity fieldsof the molten pool, but the time-period of influencing was short. The molten pool couldrecover the state that was before the droplets deposition and then the characteristics of thetemperature fields and velocity fields of the molten pool were similar to the ones of theprocess without wires feeding.