Numerical Simulation And Experimental Study On The Hole Extrusion Strengthening Effect Of Laser Texturing Mandrel

As the most common connecting component in aircraft,the hole plays a key role in the stability of aircraft structure.Complex alternating load can easily cause the stress concentration of the hole member and cause the fatigue fracture of the member at the edge of the hole.As an effective hole strengthening method,cold-expansion can effectively improve the fatigue strength of holes.In this paper,a new mandrel extrusion strengthening method was adopted,which is to process regularly distributed microconvex texture on the surface of the mandrel to optimize the stress distribution on the surface of the inner hole and refine the grains on the surface of the inner hole.In this paper,a combination of simulation and experiment was used to explore the influence of the extrusion and strengthening of the textured mandrel on the residual stress,the surface quality of the hole wall and the microstructure of the component with a hole.The main research contents of this paper are as follows:(1)The related theories of laser texturing and hole extrusion strengthening were analyzed.Based on the analysis of hole extrusion stress,the effect of hole extrusion on the gain of fatigue life was pointed out.It was proposed that the laser texturing technology is applied to extrusion mandrel for hole extrusion strengthening,and its strengthening theory and process parameters were analyzed.(2)ABAQUS was used to establish a finite element model of hole extrusion strengthening,and the simulation results showed that the residual stress on the hole edge of the mandrel extrusion strengthening has a certain distribution law,and it can increase the residual compressive stress of the hole wall by appropriately increasing cold expansion degree or reducing friction coefficient.It was found that the microconvex texture on the surface of the mandrel can improve the residual stress on the surface of the hole and increase the fatigue life of the hole by setting the micro-convex texture and the micro-pit texture on the surface of the mandrel.It is also found that there is an optimal texture height on the surface of the mandrel,which can maximize the residual compressive stress on the surface of the hole wall.(3)A systematic laser texturing process experiment was carried out on W6Mo5Cr4V2 high-speed steel samples,and the laser process parameters required to set the texture profile size were obtained.This paper explored the influence of laser power,pulse width and defocus on the texture morphology,and on this basis,the value range of the process parameters is clarified.By testing the microhardness of the texturing point,it is found that the microhardness of the texturing point is about 15%higher than the hardness of the sample matrix,which is beneficial to increase the service life of the mandrel.(4)According to the results of simulation and process test,the laser texture were set up in the surface of extrusion mandrel,and the comparison test of hole extrusion with the textured mandrel and non-textured mandrel was carried out.The measurements of residual stress and microhardness around two different mandrel extrusionstrengthened holes have been taken.The residual compressive stress of the surface layer of the hole wall extruded by the textured mandrel has been significantly increased,which is roughly consistent with the simulation results.The microhardness of the surface of the hole wall strengthened by the textured mandrel is increased by 2%～3%.Through the inspection of the microstructure of the hole wall of the extruded sample,it was found that the grains of the hole wall extruded by the textured mandrel are finer than the hole wall extruded by the untextured mandrel.The experimental results showed that the use of textured mandrel extrusion strengthening can optimize the stress distribution on the surface of the inner hole,and refine the grains on the surface of the inner hole.