Research On Laser Cladding Forming Process Of Nickel-Based Alloy Thin-walled Parts

Laser cladding forming technology is a kind of augmented material manufacturing technology formed under the trend of intelligent and individualized manufacturing industry.Because of its high flexibility,the ability to process complex parts and near net forming,it is widely used in direct forming manufacturing and repair of complex metal thin-walled parts,and has broad application prospects.Laser cladding process is a process of drastic temperature change,and temperature accumulation effect easily leads to cladding defects.At the same time,the selection of process parameters is particularly important,which can ultimately determine the quality of the cladding layer.In order to solve the above problems,the temperature field simulation of laser cladding based on finite element method is firstly studied,and the temperature field characteristics and the temperature field changes under different process parameters are analyzed.Then the process experiments of laser cladding were studied in the order from single channel to multi-channel and then to single-channel and multi-layer.Finally,the microstructure and properties of laser cladding thin-walled parts were studied and evaluated.The main contents of the thesis are as follows:(1)The finite element model of the laser cladding process based on the finite element method is established.The growth of the cladding layer is simulated by the life and death element method.The distribution characteristics of the temperature field during the laser cladding process are analyzed,and the temperature history curve of the special node is derived.The effects of laser power and scanning speed on the temperature field were analyzed.Finally,the initial temperature of the substrate was changed and the scanning interval was increased,and the change of the temperature field was analyzed.(2)Given the dynamic characteristics of the joint surface cannot be directly verified and tested,a rail slider bench was designed to test the dynamic characteristics of typical mechanical joints.The frequency response function of each substructure was tested by modal tests,and the dynamic parameters of the joint were identified according to the method of equivalent single degree of freedom system.Also,the prediction accuracy of proposed model and the causes of the error were finally analyzed.(3)For the cladding of a single-layer multi-layer cladding layer,the common defects of several cladding layers are first introduced,including the phenomenon of protrusion at both ends of the reciprocating scanning.The thermal stress causes the cladding layer and the collective separation defects,and the improper lifting amount leads to melting.Overwrite the failure,etc.and propose a solution.According to the influence of process parameters on singlelayer multi-layer cladding layer,three factors of laser power,powder feeding rate and lifting amount were selected,and the influence trend on single-layer multi-layer cladding layer was explored.Finally,an attempt was made to weld the outer wall of the hollow blade with curved features.(4)The single-wall multi-layer laser cladding thin wall was cut and polished.After corrosion,the metallographic sample was formed and the metallographic structure was observed.It was found that the thin-walled structure formed by laser cladding was columnar dendrites and its microstructure.It is more fine than the casting,and the growth mode is mainly along the direction of the cladding and at an angle.The direction of dendrites in the molten pool is mainly perpendicular to the bottom of the molten pool and is epitaxially grown along the direction of heat flow.After the tensile test,the average tensile strength along the cladding direction was 741.59 MPa,and the average tensile strength in the vertical cladding direction was 819.98 MPa.