Dynamic Detection And Analysis Of Powders Melting Behavior In Off-axis Laser Cladding Process

The surface of metal parts/components is usually damaged under unfavorable conditions such as the heat accumulation,stress concentration and so on,which not only causes serious economic losses,but also poses greater safety risks.The realization of surface strengthening and repairing of parts/components by remanufacturing technology is of great significance to the development of our country's economic and industrial.Laser cladding,which is one of advanced remanufacturing technologies,is widely used in surface strengthening and repairing of components.In order to further improve quality,property and accuracy of laser cladding process,it is imperative to strictly control the distribution of laser energy between base mental and powders.Nowadays,most of heat regulatory modes are based on human experience and procedure qualification to set laser power or powder feed rates.It is still unable to conduct process guidance or quantitative calculation to the distribution relationship of laser energy between powders and base mental according to effective models,formulas,or criteria.and it is also difficult to obtain the optimal process parameters under continuously changing environment of heat absorption and heat accumulation.In order to establish the effect forms and mathematical model of laser cladding thermal physical process,it is essential to clarify the influence of powder melting mode and laser-powder interaction on the cladding process.In this paper,the experimental setup and process acquisition system of off-axis laser cladding process were established.The infrared thermal imaging and high-speed camera were used to detect and analyze laser-powder interaction.The characteristic behavior of powder melting process was proposed,and the influence of process parameters on different characteristic stages was studied.Meanwhile,the models to analyze thermal physical process of each characteristic stage were established.MATLAB was used to quantitatively calculated temperature evolution law of powder and the temperature of the powder coming to the molten pool.A physical model of the relationship between laser heat sources property and powder melting behavior was set up.The results show that the number of liquid powders in laser-powder interaction space increases with increasing of laser power or decreasing of the average particle size of the powders,and the unevenness of the powder temperature distribution decreases,which increases the probability of liquid powders entering the molten pool,and it is easy to obtain a well-spread cladding layer;the number of liquid powders in the laser-powder interaction space decreases with increasing of laser positive defocusing amount,and the number of high temperature solid powder increases.The solid powders entered the molten pool and reversely absorbed energy to melt them,resulting in the formation of a cladding layer with larger width and deeper penetration.The powder melting process was detected by high-speed camera and divided to three typical stages.Combined with the established analytical model of laser-powder interaction,it is shown that the smaller the laser power or the greater the laser defocusing amount and the average particle size of the powders is,the longer the duration of(1)and(2)is,the more uneven of powder temperature distribution along the vertical direction in laser-powder interaction space is;The larger the incident angle of powder particle is,the longer the duration of(1)and(2)is,and the unevenness of powder temperature distribution along the horizontal direction in laser-powder interaction space becomes larger.The powder temperature first increases nonlinearly with increasing growth rate,then increases linearly,and then increases nonlinearly with decreasing growth rate.The temperature of the powder coming to the molten pool decreases with increasing of laser defocusing amount and average particle size.When the average particle size increases from 37.5 ?m to 150 ?m,the temperature of the powder coming to the molten pool decreases by 41 %.When the laser power is greater than 300 W,the temperature of the powder coming to the molten pool increases linearly with increasing of laser power.The temperature of the powder coming to the molten pool decreases with increasing of incident angle and initial velocity of powder.When the incident velocity of powder increases from 150 mm/ms to 350 mm/ms,the temperature of the powder coming to the molten pool decreases by 37 %.