Research On Key Technology Of Shape Control And Performance Control In Laser Cladding Of Complex Curved Surface Parts

Curved surface parts with complex structure with high manufacturing cost and great remanufacturing value are extensively used in high-end equipment,aviation manufacturing,petroleum drilling and other fields.Laser remanufacturing is characterized by low heat input,low dilution ratio and metallurgical combination with the substrate,which has become the mainstream technology for repairing key parts.Preparing high-quality coatings on curved parts is not only the key measure to prolong service life,but also the development direction of laser remanufacturing technology.High quality means high precision and high performance,improving the forming accuracy of laser scanning path can meet the high precision requirements of coating,designing reasonable powder system and process method are the key factors to prepare high performance coating.The current researches focused on the selection of laser process parameters,microstructure and mechanical properties of coatings on planar parts.However,there is a lack of relevant investigations on the forming path and mechanical properties control of cladding layers on curved parts.This paper is committed to studying laser remanufacturing process scheme suitable for complex curved surface parts according to the forming accuracy and forming properties of laser cladding.A laser scanning path planning algorithm is proposed on account of the surface characteristics and process parameters.Immediately,the laser cladding scanning path optimization algorithm is raised for curved surface parts with special structure,so as to realize the high precision cladding forming of curved surface parts.Furthermore,Tungsten carbide ceramic coatings with excellent properties were fabricated by in situ formation to explore the enhancement mechanism of carbon nanotubes on the microstructure and mechanical properties of the composite coatings.On the basis of the above,the integrated remanufacturing of “shape control” and “performance control” of key parts has been achieved.(1)The point cloud data of parts is obtained by reverse engineering,and parts model were reconstructed by bicubic NURBS surface and converted to STL format.Firstly,setting the intersection of the tangent plane and the triangular patch to obtain a single initial scanning path.Then,the equal arc length line spacing algorithm is used to search the path interpolation points,and the coordinates & normal vectors of the path points are calculated linked laser process parameters.Besides,the path point structure was adjusted according to the processing requirements to obtain the laser scanning path.The reliability of the algorithm is verified by cladding experiments on curved parts.(2)The reduce of machining efficiency of the robot because of the surface with irregular curvature changes.Therefore,a segmentation algorithm was brought forward to divide the complex surface into sub regions with different curvature,and carried out path planning in a single region.Contrary to the problem of trajectory connection between multiple regions and a combined path optimization algorithm was proposed to control the machine space path which was transformed by graph theory in consideration of the shortest laser processing path as the goal.In order to improve the forming accuracy and prevent unnecessary contact between the laser and the part when the part structure is complex and cannot be disassembled,and the specific interference detection algorithm is proposed as follows: complete the rough inspection process while setting the collision domain.Moreover,the accurate search is carried out to determine the interference points combined with the quadtree algorithm,and the laser attitude was optimized on the premise of meeting the remanufacturing quality.The effectiveness of the above algorithm was verified by achieving the laser repair of high-pressure steam valve parts.(3)In-situ tungsten carbide coatings were successfully prepared on the Ni substrate.The phase and microstructure of in-situ tungsten carbide coating were characterized by means of SEM and XRD,the relationship between particle characteristics of reinforcing phase and process parameters was analyzed,and the evolution law of microstructure and mechanical properties of in-situ synthesized WC coating was clarified.It was found that the laser energy was too high to get the carbon atoms ablated,and the atomic contact was insufficient when the laser energy was to weaken which seriously affects the spontaneous synthesis of tungsten carbide particles.(4)Ni-based composite coatings were prepared by adding different content of carbon nanotube,and the evolution of carbon nanotube content on the microstructure of the coatings was analyzed.The experiments authenticate that the dispersed carbon nanotubes can not only improve the nucleation rate,but also inhibit the grain growth and strengthen the fine grain.The effects of different carbon nanotube contents on the mechanical properties of the coating were clarified,through microhardness and friction and wear tests.And the enhancement mechanism of carbon nanotubes was explored,which provided controllable indexes for the preparation of high-performance coatings.