Simulation Of Lase-powder Interaction In Laser Directmetal Deposition

A higher thrust and efficiency and a longer life is the higher requirements to the performance of the aircraft engine to promote the development of aerospace enterprise. Single crystal turbine and guide blade produced by directional solidification are the first choice for nearly all commercial and military advanced engines. However, in the process of processing and service unavoidable injuries happen to leaves, causing loss, so repairing damaged blades is a serious problem that needs to be broken through badly. Unfortunately,the above problem is able to be solved by epitaxial laser metal forming(E-LMF) which combines laser engineered net shaping(LENS) and directional solidification. An epitaxial growth in directional solidification from the substrate can be obtained by controlling some parameters, such as setting rate, etc. E-LMF perfectly repair broken blades, including geometry and dimensional accuracy, and does not affect its performance.During laser direct metal deposition(LDMD), the laser beam has a short-time interaction with the powder, attenuated, with its intensity reduced and distribution modified. So, a three dimensional transient model is built to analyze the laser attenuation by the focused powder near the substrate in the coaxial LDMD. A ray tracing method is employed to calculate the intensity distribution on each boundary of the particle system including incident surface, side and emergent surface after the laser beam was partly absorbed and scattered by the powder cloud. The effect of wavelength of laser, particle size and number of particles on the process of laser attenuation is numerical y analyzed. In the other hand, a new three dimensional transient model is developed to study the temperature distribution of particles near the substrate in the coaxial LDMD. Results show that an absorptivity of 5.47% is obtained by a spatially distributed powder cloud with a concentration of 0.01g/ml and the process of laser attenuation by the powder cloud is weakly influenced by wavelength and the attenuation increases as the number of particles increases. The transmission law of laser at 1.06μm in the powder cloud is similar to that in the particulate suspension. The laserpowder interaction region in laser direct metal deposition is able to be magnified stereoscopically by the suspension and taken out alone to study though the size of the interaction region differs for different nozzles. This provides an approximately direct experimental study of the real interaction between laser and powder in laser direct metal deposition, not only in the analytical way. Regardless of relatively little energy they carry to the substrate, it is necessary to analyze the laser absorption by the powder cloud, considering that a correct calculation of characteristics of the laser-processed part is determined by energy conservation.In the other hand, a new three dimensional transient model is set up to simulate the temperature distribution of particles by the preheating in the process of coaxial LDMD. Temperature rises inside particles because of the energy absorption by powder particles. Different traveling paths of particles may also cause different final temperatures, influencing the temperature distribution of the molten pool and even the accumulation of temperature field inside the part during the processing. Results show that, as particles fal s, the temperature gradually increased. And, under the laser of 900 w, titanium powder particles melt.