Research On Crack Sensitivity Analysis And Process Optimization Of Electron Beam Welding Of Hydraulic Actuating Cylinders

This paper was focused on a crack troubleshooting event of a certain type of aero-engine hydraulic cylinder,and it was started from the analysis of the causes of cracks,at last the fault tee of crack was established.The failure analysis on actuating cylinder crack such as the position,macro morphology,micro area composition,microstructure and fracture characteristics,was taken with the reference of investigation results from fault tree.The causes of the actuating cylinder cracks were revealed gradually with the development of research on the factual effects of a variety of factors.According to the study,cracks were caused by being reheated locally due to the existence of residual chrome layer and the aging and instability of the electron beam welding equipment.The cracks were caused not only by the hardening structure and welding stress under the action of the quenching embrittlement crack(cold crack),but also by the chrome layer and reheat cracking caused by repeated heating.Studies have shown that preventive and improvement measures were made after analyzing the reasons and factors of cylinder crack.For example cleaning the chrome layer before welding,replacing argon arc welding with the electron beam welding during the positioning welding,reducing turnover of the pars,improving the parameters of the electron beam welding.According to the prevention and improvement measures,some tests were carried out by making the testing film s and the analog parts,metallographic examination,mechanical properties test etc.This paper focuses on the optimizing of the electron beam welding parameters(voltage,current,focus current,frequency etc.),the determination test of positioning welding and modification welding.It is found that actuating cylinder will crack easily in the limit parameters,but the crack will not grow The electron beam welding parameters were that: acceleration voltage 200 KV,welding current 6m A,welding speed 10mm/s,swing 1mm,focusing current 2735 m A,frequency 200 Hz.On the basis,the optimal parameters were that: the current of positioning welding reduced to 3m A,as for modified welding,current reduced to 3.6m A,swing increased to 1.2mm and the focusing current increased to 2930 m A.Through the implementation of prevention and improvement measures,the optimization of the electron beam welding process was realized,which can eliminate the hidden trouble of hydraulic cylinder crack and improve the production quality.