Numerical Simulation Study On Thermo-mechanical Coupling Of 12CrNi2 Alloy Steel By Laser Melting Deposition

Laser Melting Deposition(LMD)technology is a new type of Laser Additive Manufacturing(LAM)technology,which has a very broad application prospects.However,LMD forming is a non-steady process of local rapid heating and cooling.The temperature and stress fields caused by LMD forming are extremely complex,which can easily lead to large residual stress and cracks in components.Based on this,this paper takes 12CrNi2 alloy steel for camshaft of nuclear emergency diesel engine as the research object,and combines numerical simulation with experiment,and uses ANSYS parametric design language(APDL)to compile the moving heat source program,and realizes the synchronous adding process of metal powder by using the technology of unit life and death,and establishes the finite element analysis model of temperature field and stress field in LMD process.The temperature field and stress field distribution of LMD process under different process parameters(printing mode,laser power,printing speed and preheating temperature)are studied in detail.It has important guiding significance for solving the key scientific problem of shape control in laser additive manufacturing of high performance alloy steel components.The main contents and conclusions are as follows:(1)The LMD experiment of 12CrNi2 alloy steel was carried out,and the optimum process parameters were obtained.The macro and micro morphologies of the deposition layer were observed and analyzed.It is found that the suitable process parameters are laser power of 2000 W,printing speed of 5 mm/s and powder feeding rate of 11 g/min.Different process parameters have significant effects on the morphology and heat affected zone of deposition layer.The top of deposits is equiaxed crystal,and the middle and lower parts of deposits are columnar crystals with epitaxy growth characteristics.In order to verify the accuracy of the numerical simulation,a single-layer single-channel LMD numerical simulation was carried out.The results show that the simulated and experimental molten pool width and depth are basically consistent within the error tolerance.(2)The distribution law of temperature field distribution under different process parameters was studied.The results show that the temperature field of the single direction printing method is more uniform than the S-shaped printing temperature field.During the forming process,the temperature of the nodes fluctuates periodically and has the characteristics of rapid heat and cooling.The peak temperature of the node increases with the increase of laser power,the decrease of printing speed and the increase of preheating temperature.The heating rate and cooling rate increase with the increase of laser power,printing speed and preheating temperature.(3)The distribution law of stress field under different process parameters was studied.The results show that the residual stress distribution in single direction printing mode is better.With the increase of laser power and the decrease of printing speed,the maximum Mises stress in each layer increases gradually,and the maximum Mises stress increases after cooling.With the increase of deposition height,the Mises stress increases first and then decreases.With the increase of preheating temperature of the substrate,the maximum Mises residual stress decreases after cooling in LMD forming,and the preheating of the substrate improves the temperature gradient distribution,which makes the stress field more uniform and effectively prevents cracking in the printing process.