Research On Properties And Process Of Special-Shaped Variable Section Parts Formed By Laser Metal Deposition

As a kind of additive manufacturing technology,powder feeding laser cladding technology has the advantages of flexible processing,easy conversion of powder materials and high flexibility.This technology has gradually become one of the research hotspots in the field of additive manufacturing,especially for improving the forming quality and efficiency of complex metal parts with high scientific significance and application value.As a common structure of complex metal parts,variable section parts were defined as different thickness at each position of each cladding layer obtained by slicing the parts along the height direction.Because it has compact structure and more functions when satisfying the machine size.At present,it is widely used in aerospace,automobile,mold and other fields.However,the traditional parallel slicing method has some disadvantages,such as "stepping-effect",poor surface quality and low forming efficiency.In addition,there are inevitably defects such as pores and cracks in the powder feeding laser cladding parts,which lead to low mechanical properties and limit wide application in many fields.In order to solve the above shortcomings,based on the laser coaxial powder feeding additive manufacturing technology,this paper proposes adaptive surface slicing method and laser remelting process.The corresponding forming process and microstructure and properties of the two kinds of forming parts are studied respectively.The research contents are as follows:(1)The relationship between scanning speed and powder defocusing and the geometry of single-pass cladding layer was explored.Firstly,the mathematical model of powder concentration distribution was established.According to the probability distribution model and the mass conservation,the relationship between powder defocusing,scanning speed and the geometric size of cladding layer was deduced,and then the process parameters were optimized.Last,the single factor experiment about scanning speed and powder defocusing was designed,and the changing of cladding width,height,width height ratio and dilution ratio was obtained.In order to make the parts with high quality formed by equal thickness,the scanning speed range was optimized based on the error of the section area of the cladding layer.The selection principle of Z-axis increment in multi-layer forming was put forward,and the validity of the principle was verified by the height error of forming parts.In addition,the grain morphology in different regions of single-pass cladding layer and single-pass and multi-layer thin-walled parts were investigated.(2)The variable thickness cladding forming process of the parts was explored and the properties of the parts were tested.Firstly,based on the optimized scanning speed and powder defocusing,the forming method of single-pass cladding layer with variable thickness was proposed.The unequal height overlapping method with variable center distance was proposed to realize changing of parts in overlapping direction.The high quality forming of slope thin-walled parts and wedge-shaped blocks is realized by unequal height overlapping method and variable thickness cladding layer.Then,based on the above analysis,the adaptive surface slicing method was proposed,and the surface slicing process and the corresponding forming process were studied.The forming accuracy and efficiency of the parts formed by the adaptive surface slicing method are significantly improved.Finally,the grain morphology and hardness at different positions of the parts formed by the slicing model were studied.(3)The influence of different scanning direction on the properties of the forming parts by variable thickness cladding layer deposition was investigated,which mainly include:from low to high scanning and from high to low scanning.The grain growth direction of the forming part under different scanning directions was detected,and the influence of the scanning direction on the anisotropy and hardness of the forming part in different directions was analyzed.HyperMesh and simufactwelding software were used to simulate the temperature field of the variable thickness cladding process and uniform thickness cladding process under different scanning mode.Based on the simulation results,the influence of scanning direction on the microstructure and mechanical properties of variable thickness cladding forming parts was researched.(4)In order to eliminate the defects such as pores and cracks in the laser cladding parts,the "laser cladding+lase remelting" alternating progressive composite process was proposed.The influence of different laser remelting power on the pores of single-pass cladding layer was studied.Then,the single-pass laser remelting process is simulated by software,and the evolution process of microstructure of single-pass cladding layer and single-pass remelting layer was analyzed.Based on the results,the optimal remelting power was obtained,which was equal to the initial cladding power.Under the optimal remelting power,the composite process of laser remelting and laser cladding was used to form thin-walled parts,and microstructure and tensile properties of the part were studied.