| As the key component of train operation,the axle-mounted brake discs of highspeed trains requires high comprehensive performance,Moreover,due to the complex shape and many casting defects,it relies heavily on imports.Therefore,in this study,while ensuring the casting performance of complex brake disc,laser cladding was carried out on the surface of it,in order to manufacture the brake disc with the mechanical properties and wear properties.Firstly,the axle-mounted brake disc body with radiating ribs was cast.According to the manufacturing requirements of brake disc,the casting model with gating system was build,and the sand mold design with seven cylindrical risers and casting process parameters were determined by Pro CAST software.The sand mold was divided into upper,middle and lower three parting dies,which are printed and assembled by 3Dprinting technology.The pouring results show that the casting has good appearance quality,the hardness is in the range of 320～340 HV,the tensile strength is 1092 MPa,and the fracture mode is ductile fracture.The mechanical properties meet the industry standard of brake discs for rolling stock.Secondly,the optimal parameters of laser cladding was optimized.Based on the analysis of the laser cladding efficiency in the early stage,the way to improve the efficiency of laser cladding was put forward.The process parameters of high efficiency laser cladding were optimized by orthogonal design,and the microstructure and properties of high and low efficiency cladding layers were compared.Based on weld width,weld reinforcement,surface smoothness,spatter and cladding efficiency,the better process parameters of high efficiency were obtained.The laser power is 1200 W,powder feeding speed is 15 r/min,scanning speed is 15 mm/s,shielding gas flow is 15L/min,carrier gas flow rate is 8 L/min,defocusing distance is 0 mm,and overlap ratio is 50%.After calculation,the laser cladding efficiency is increased by 8 times and the hardness is increased by 20 HV.The microstructure is lath martensite with fine grains.Thirdly,laser cladding was carried out on the whole surface of brake disc.The friction surface was divided into 12 blocks along the circumference and 4 blocks along the radius,and the temperature and stress field were simulated by three paths.The results show that the jump path is the best,the deformation is 0.0346 mm,and the Mises stress is 393 MPa.The cladding layers with thickness of 4mm on both sides of casting brake disc were manufactured.The maximum deformation is 0.08 mm,which is far lower than the previous 2.7 mm deformation.Finally,the friction and wear properties of laser cladding brake disc were tested.The results show that the highest friction coefficient of the cladding layer is 0.248,and the average wear loss is 2.445 g.Under the same conditions,the wear loss of the cladding layer is 20% less than that of the substrate.The wear mechanism mainly changes from abrasive wear to adhesive wear,accompanied by oxidation wear. |
