| Titanium alloy is the most widely used material for key components in the aviation industry.The combination of alternating mechanical and thermal loads can lead to fatigue crack initiation and growth,which greatly increases the risk of fatigue failure.Micro-forging(MF)is a novel surface modification technology,which can generate smooth surface,stable hardened layer,and uniform residual stress distribution at a high efficiency.Researchers have made significant effort to figure out the mechanism of micro-forging and expand its application in antifatigue manufacturing field.Current research works are mainly concentrated on the effect of process parameters on the surface integrity of cast iron,stainless steel,tool steel and other materials.Nevertheless,the performance of micro-forging device itself has been rarely studied and the treatment of TC4 titanium alloy workpiece has not been reported so far.To fill these gaps,this project not only analyzes the kinetic characteristic of an electromagnetic micro-forging system,but also investigates the influence of process parameters on the surface integrity of TC4 titanium alloy.The project aims to provide a reference for the application of micro-forging in the production of titanium alloy components.The main research contents and conclusions are as follows:(1)Research and development of an electromagnetic micro-forging system.In this project,an electromagnetic micro-forging system is designed,produced and assembled based on the surface strengthening mechanism and the typical structure of the MF equipment.According to the dynamic analysis and experimental results,an optimal input voltage selection method is proposed to ensure that the tool moves uniformly and stably between the workpiece and the upper limit block.Afterward,the effect of micro-forging process is preliminarily demonstrated,and the tool head diameter,normalized indentation diameter,and overlapping ratio are designed as key parameters on which the surface integrity is highly dependent.This part lays a solid foundation for subsequent experiments.(2)Establishment of FEM model of the micro-forging process and prediction of the process effect.Firstly,many methods such as mass scaling and reasonable meshing are used to improve the computing efficiency on the premise that the simulation accuracy is satisfied.The comparison between simulation and experimental results verifies the accuracy of the FEM model.Finally,the influence of the tool head diameter,normalized indentation diameter and overlapping ratio on the residual stress field is predicted using ABAQUS software.And the effect of the impact angle on the surface deformation and residual stress distribution is also studied.Simulation results provide a guidance for optimizing process parameters with the objective of inducing an ideal residual stress field.(3)Experimental results and evaluation of the surface integrity.Firstly,the three-dimensional topographical feature,surface roughness,micro-hardness,and residual stress field are utilized to describe the surface integrity of TC4 samples.Experimental results strongly verifies the potential of micro-forging technology,such as the surface roughness Ra and Sa decrease from 0.07 μm and0.51 μm to 0.04 μm and 0.32 μm,respectively,the micro-hardness rises from354.3 HV to 397.6 HV,the maximum value of residual compressive stress reaches-1003 MPa,and the maximum depth of the compressive stress layer is 832.9 μm.These results indicate that the micro-forging method can realize ideal surface smoothening and strengthening effects simultaneously.Using the range analysis method,the influence of different process parameters on the surface integrity are concluded,and the effect of the overlapping ratio in one direction is also investigated.In addition,the metallographic mechanism of micro-forging process is explained in this project.Finally,the selection of optimal process parameters with the goal of optimizing corresponding surface integrity index is presented. |
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