Research On Abrasive Flow Machining Of Pipeline Defects Based On SLM Technology

Electro-Hydrostatic Actuator(EHA)is the dominant airborne actuator system of future aircraft.High power to weight ratio is one of its key technical indexes.Selective Laser Melting technology(SLM)can effectively improve the power to weight ratio of EHA.However,the top of the inner surface of EHA shaped pipe is prone to defects such as sticky powder and slag removal.Therefore,abrasive flow processing technology is adopted to reduce the surface roughness of the pipe and improve the flow characteristics of the pipe by scouring the abrasive material in the pipe.In order to solve the problem of rough surface on the top of inner wall of EHA shaped pipeline after additive forming,the deviation between the forming profile and the designed profile was reduced by using process parameter control method.The effects of powder layer thickness,laser scanning speed and forming power on the forming quality of special-shaped pipe top were studied by 24 groups of different specifications of pipe printing and morphology detection.The forming profile of the inner surface of the pipeline was scanned,the deviation between the forming profile and the designed profile was calculated,and the optimum process parameters were obtained.Considering the characteristics of defects in forming of additive manufacturing,a fluid-structure coupling finite element model was established to study the stress state and damage mechanism of defects with different aspect ratio under given pressure.Based on the erosion wear theory and the simulation of the erosion process,the fracture judgment conditions of the defects with different aspect ratio were established.The influence of different specification defects and different machining parameters is analyzed.The results show that the defect with large aspect ratio is prone to direct fracture,while the defect with small aspect ratio is first erosion and then fracture.The abrasive flow processing experiment was carried out on the pipeline printed with the above optimal process parameters.The material removal rate,pipeline deviation value and surface roughness before and after pipeline processing were analyzed from three dimensions.Through the comparison of the effects before and after abrasive flow processing under different processing parameters,it was found that 54 mesh abrasive particles were first used for rough machining.The best polishing effect was obtained by using 100 mesh and 220 mesh abrasive.The process can not only effectively remove the sticky powder defects,but also not cause damage to the pipe wall.