Research On The Morphology And Cooling Rate Of The Thermal Penetration Layer Processed By Moving Gaussian Laser Heat Source

Laser has the features of excellent beam quality and easy to control.Therefore,it is widely used in fields of laser quenching,welding and additive manufacturing.The essential feature of laser processing is the interaction of the laser with the material.It is related to material parameters,laser parameters,process parameters and environmental parameters.The combination of these parameters determines the cooling rate and the morphology of the heat penetration layer during the processing process,which in turn determines the processing quality.Therefore,in this paper,the thermal conduction analysis of the moving Gaussian laser heat source is calculated.Then,this paper conducts process expe riments such as surface heat treatment,direct energy deposition and welding,and explores the influence of process parameters on heat distribution and heat penetration layer morphology.The specific research content and conclusions are as follows:(1)This paper derives and analyzes the distribution law of heat conduction temperature and cooling rate during the processing of moving Gaussian laser heat source based on the heat conduction equation.Subsequently,this paper carr ied out laser surface heat treatment experiments,and obtained the surface peak temperature and cooling rate through the built temperature monitoring system.The results show that the resolved temperature is basically the same as the measured temperature.It also shows that the main factors affecting the depth and hardness of the hardened zone are the surface peak temperature and cooling rate.When the scanning speed decreases,the peak temperature and the hardened layer become larger,and its cooling rate and hardness become smaller.If the laser scanning speed is too low,the strengthening treatment of the material surface cannot be completed.As the power increases,the surface peak temperature increases and the hardened zone depth increases.The cooling rate and hardness also increase with the increase of power,but when the material is melted,the change trend is completely opposite.(2)Direct energy deposition and laser welding process experiments were carried out using 316 stainless steel,and the influence of process parameters on the geometric dimensions of the heat penetration layer and cooling rate was quantitatively analyzed based on the D-MORPH-HDMR global sensitivity analysis method.The direct energy deposition experiment shows that the power,the laser scanning speed and the powder transport rate affect the solidification cooling rate and the width of the deposition layer as follows: the largest is the laser power,followed by the scanning speed,and the smallest is the powder delivery rate.And when the laser power becomes larger or the laser scanning speed decreases,the width becomes larger.Their contribution rate to the depth is as follows: the largest is the laser power,followed by the powder delivery rate,and the smallest is the scanning speed.And when the laser power becomes larger,the depth becomes larger.Their contribution rate to the height is as follows: the largest is the scanning speed,followed by the powder delivery rate,and the smallest is the laser power.And when the laser power or the powder transport rate becomes larger,the height becomes larger,and when the laser scanning speed becomes larger,the height becomes smaller.(3)Laser welding experiments point out that when the power becomes larger,the weld size becomes larger,and when the scanning speed becomes slower,the width becomes smaller.And the contribution of process parameters and their coupling effects on the welding solidification cooling rate is as follows: the largest is the scanning speed,followed by the laser power,and the smallest is the coupling between the scanning speed and the laser power.And their contribution to the weld width is as follows: the largest is the laser power,followed by the scanning speed,and the smallest is the coupling of scanning speed and power.Their contribution rate to the weld depth is as follows: the largest is the laser power,followed by the coupling of power and scanning speed,and the smallest is the scanning speed.(4)In laser metal material processing process,the scanning speed becomes faster,the cooling rate becomes larger.When the material melting occurs,the power becomes higher and the cooling rate becomes smaller.