Rolling Strengthening Technology For Concave Arc Surface Of Turbine Disk Slots

The turbine disk slots of aero-engine are prone to fatigue fracture at concave arc,because they are subjected to the combined action of high temperature,centrifugal force and vibration in their work.The surface quality of high-speed grinding part is better.However,the surface after grinding still needs to be further strengthened in order to realize the popularization and application of slots profile grinding technology in turbine disk part.Rolling strengthening can improve the machined surface quality and introduce larger residual compressive stress of the workpiece,and then prolonging the fatigue life.But there is no scholar has used rolling strengthening technology in the surface of slots,which is limited by the dimension and structure characteristics of slots and rolling strengthening equipment.Therefore,it has important significance and process value to study the mechanism and process method of rolling strengthening concave arc surface of slots turbine disk in order to improve the performance and the stability of turbine disk.A rolling strengthening method for concave arc surface of turbine disk slots which can be used in NC machining center is proposed in this thesis.It can finish the grinding of slots and the rolling strengthening of concave arc with one tool setting.The main research contents are following:（1）Design and optimization of rolling tool.The cemented carbide rolling tool and the GH4169 slots equivalent structure specimen are designed and manufactured according to the size and structure of slots.The rolling tool is optimized by rolling strengthening test,and the surface quality of concave arc of the machined specimen is improved greatly.The rolling force F_r shows an upward trend and the radial arc runout of the rolling head surface increases slightly by 4μm at the maximum with the increase of the pre-pressing amount;（2）Influence of fillet dimension of concave arc end face of slots on fatigue performance.The local stress concentration at the sharp corner is eliminated by using the grinding wheel to fillet machining the concave arc end face of slots of the slots equivalent structure specimen.The fatigue life of the specimen is increased by about 1.5 times when the fillet size is R=1.5 mm.The stress ratio of the slots bottom of the specimen should not exceed 1.0305 after the fillet machining then before,and there is less influence of fillet dimension on the fatigue life in this range;（3）Influence of rolling process parameters on surface integrity of specimen.The surface roughness of the specimen decreased with the increase of rolling force F_r and rolling times n_r,and increased slightly with the increase of rolling feed velocity v_f.The thickness of plastic deformation layer,the microhardness of surface layer and the residual compressive stress（absolute value）increased with the increase of rolling force F_r and rolling times n_r,and decreased with the increase of rolling feed velocity v_f.Which is obtained by testing the surface integrity index of the specimens processed with different rolling process parameters.The machined surface integrity is most affected by the rolling force F_r and tends to be saturated with the increase of the rolling force F_r and the rolling times n_r.The specimen has better surface integrity when the rolling force F_r is between 425 N and 675 N,the rolling times n_r is between 2 and 3 times,and the rolling feed velocity v_f is 1 mm·s^-1;（4）Optimization of rolling process parameters and the verification of slots rolling strengthening.The fatigue performance of specimens processed by different rolling process parameters is tested,and the results show that the fatigue life shows an"S"-shaped growth trend with the increase of rolling force F_r,increases with the increase of rolling times n_rrapidly at first and then slowly,and decreases monotonously with the increase of rolling velocity v_f.The fatigue life of the specimen can be increased by about 2 times by optimizing the rolling process parameters of rolling force F_r=425 N,rolling times n_r=3 and rolling feed velocity v_f=1 mm·s^-1 based on the surface integrity test,and by about 3 times by combining with fillet machining.All the surface integrity indexes in the verification test of actual concave arc surface of turbine disk slots with rolling strengthen processing are basically consistent with those of the specimens in the previous test.The feasibility of rolling strengthening technology in the actual slots concave arc surface is verified.