Research On The Technology Of Coaxial Wire Feeding In Three Beam Splitting And The Forming Of Twisted Thin-wall Parts

Laser wire cladding technology has been widely used in recent years duing to its advantages such as high material utilization,low environmental pollution,and high cladding efficiency.The wire material is a rigid continuous material,so when the heat input is unsuitable during the cladding process the "dripping" and "stubbing" forms are likely to occur,causing the cladding to be discontinuous.It is also common to find that the lack of spatiotemporal coordination control of the wire at the start or stop of the cladding scan.Improper initial transient wire feed position causes cladding instability,and when the cladding scan is over,if there is no suitable wire breaking process,the wire will adhere to the substrate,affecting the continuity of the process.These technical difficulties of coaxial wire feeding have resulted in that at present domestic and foreign based on coaxial wire feeding technology can only form simple vertical structures such as straight walls and blocks,and have not yet successfully formed twisted thin-walled parts with inclined and overhanging features.In this paper,the following research is carried out to address the shortcomings of the existing coaxial wire feeding technology.The influence of laser power,scanning speed,wire feeding speed and defocusing amount on the morphology of the cladding layer was analyzed qualitatively by single factor experiment.Based on the defined energy absorbed by the volume of the wire fed into the molten pool per unit length as the analysis index,the optimal process window for three-beam coaxial wire laser cladding is obtained.Using neural network and regression analysis two algorithms,respectively,to establish a quantitative model of the mapping relationship between the process parameters and cladding layer geometry.Based on the two evaluation indexes,root mean square error and the accuracy rate of 85%confidence,it is found that the accuracy of the neural network model in predicting the geometry of the laser wire cladding is better than the quadratic regression model.The research on the initial transient stability of the cladding process shows that the initial wire close to the substrate can effectively avoid the "dripping" transition caused by excessive heat input to the wire.The limiting twist angle constraint condition can effectively avoid the cladding failure caused by the wire impacting the cladding layer due to the initial transient energy input lag.A new"three-step method" laser wire breaking scheme is proposed.This wire breaking scheme achieves stable wire breaking without collapse at the end.Then gives the process window of wire breaking time required for different laser powers.Based on ANSYS simulation software,the heat accumulation effect of 3D forming process of thin-walled wall is simulated and analyzed.The results show that when the equivalent cooling time is given,there is no significant difference between the heat accumulation generated by the reciprocating scanning and the unidirectional scanning.The standard deviation of the maximum temperature during the cladding process of these two schemes is 32.39?.In addition,as the cooling time increases,the heat accumulation effect does not decrease non-linearly,but rather decreases non-linearly with a decreasing slope.Given the design of the twisted thin-walled part,based on the established neural network model,constrained by limit twist angle and process window,search processing parameters.Using reciprocating scanning strategy,combined with cooling in each layer and "three-step method"wire-breaking process,the twisted thin-walled part was successfully formed The average hardness of the shaped part is 209.6HV0.2,the hardness of the remelted zone fluctuates around 200HV0.2,and the hardness value of the non-remelted part fluctuates around 210HV0.2.The upper,middle and bottom morphologies of the formed parts are all equiaxed dendrites,which have good mechanical properties.