| The rapid development of high-end equipment manufacturing industry has put forward higher requirements for surface processing technology.The machining method by repeated impact,represented by shot peening,can achieve the purpose of component forming,surface coarsening and surface strengthening through continuous impact on the target.It is a common processing technology to improve the surface integrity and the comprehensive utilization performance of materials,widely used in high-tech fields such as national defense,military industry,aviation,aerospace,navigation and rail transit.Traditional shot peening technology usually uses solid projectile medium to impact material surface,which has the problems of unstable impact strength and coating coverage rate,high projectile quality requirements and difficult recovery.Peening by pulsed water jet is a new type of processing method by liquid impact in recent years,which aims to replace solid particles with liquid.It has the advantages of strong impact effect,low cost,wide processing range and environmental protection.The interrupted pulsed jet is a new jet technology that converts continuous jet into discrete jet by external modulation.It not only has excellent load characteristics of pulsed jet,but also has unique advantages such as simple structure,wide impact area and strong controllability of parameters,which is consistent with the current background of intelligent manufacturing and green manufacturing.At present,the application research of interrupted pulse jet in machining is still in its infancy,and the response characteristics of plastic target under the jet impact is not clear.The influence of jet parameters on machining performance needs to be explored.Therefore,this paper carried out an experimental study on the machining by interrupted pulsed jet,and explored the jet strong dynamic impact effect in the machining process,and the target coarsening and strengthening mechanism under its action.The main work and research results of this paper are as follows:(1)The formation process of interrupted pulsed jet and the evolution law of deflecting flow field structure are clarified,and the mathematical model of axial size of interrupted pulsed jet is established based on the change of modulation parameters and jet parameters.By testing the axial impact pressure and signal processing,the time domain and frequency domain characteristics of axial impact pressure under the influence of modulation parameters are clarified.Combined with impact experiment,the impact performance of interrupted pulsed jet was evaluated.(2)Based on the qualitative analysis of microstructure in impingement region,the evolution law of peak-valley morphology in erosion zone during the process of jet impact was clarified.The surface microstructure characteristics under jet impact were quantitatively characterized,and the influence of jet parameters on the characteristic parameters of microscopic morphology was revealed.Combined with the characteristics of material failure in erosion zone,the three-dimensional fracture morphology of target and the two-dimensional cross-section pore distribution,the evolution law of the surface structure under the impact of interrupted pulsed jet was revealed.(3)The temporal and spatial evolution law of residual stress and hardness of the target under the impact action of interrupted pulsed jet was clarified by experiments,and the characteristics change of crystal structure under jet impact was obtained.The mechanism of stress strengthening dislocation strengthening and fine grain strengthening during jet impingement strengthening was clarified,and the mechanism of mechanical properties strengthening during jet impingement blocking was revealed.(4)The regression models of response characteristics based on jet parameter regulation were established,and the influence of parameters such as impact time,jet pressure,jet frequency,pulse length and their interaction on residual stress and hardness is clarified.The multi-objective response optimization research is carried out,and the optimization parameter conditions of interrupted pulsed jet are obtained and verified. |
PDF Full Text Request