Research On Efficiency Improving Technology In Edm Process Of Integral Shrouded Blisk

Blisk components are the most crucial parts of turbomachinery,such as aeroengines,rocket engines and gas turbines.The advanced integral shrouded structure of the blisks could benefit the performance and reliability of turbomachinery,however,it brings great challenges to the manufacture of the blisks.Although the machinability of the integral shrouded blisks has been solved by five-axis or six-axis CNC electrical discharge machining(EDM),there still remain several problems: unsatisfying tool electrode feeding path planning method to cover different blisks structures and low blisks machining efficiency compared with the requirements of mass production.In this dissertation,the above-mentioned problems will be studied.The key points for the EDM process of integral shrouded blisks using shaped tool electrodes are electrode design and electrode feeding path planning.To improve the structural adaptability of electrode feeding planning,a new method named maximum free distance was proposed,in which the position and attitude of the electrode were optimized by maximizing the distance that the electrode is able to move along the predefined reference direction before it interferes with the blisk.This method is applicable to many kinds blisks with very complex structures,such as a pump impeller with splitter blades(whose channel has one inlet and two outlets).The influence of NC codes on EDM process was also discussed in the dissertation.The reason why NC codes with compact nodes would consume much more time was given according to the existence of jump motion.Then a feeding path sparsification method was proposed to decrease the amount of NC codes and to improve the integral shrouded blisks machining efficiency.In the experiment,the sparse NC codes saved the machining time by 23.7% compared with the original NC codes.Also,it could save electrode wear.An electrode feeding method with perturbations was proposed for integral shrouded blisks manufactured from solid workblanks.It added extra periodic perturbations to the original feeding path.Thus,the debris evacuation could be good enough to keep a good discharge condition even if in great machining depth.Those perturbations composed of linear motions perpendicular to the original feeding path and rotary motion around the electrode tip.The experiments showed that the machining efficiency was highest when the interval of perturbations was 2.5mm and the perturbation factor was 30%.Compared with the original feeding path after sparsification,the feeding path with perturbations saved another 20.8% of the machining time.There are three aspects how electrode perturbations influences the EDM process and the improvement of machining efficiency mainly comes from the reduction of flow resistance between electrode and workpiece.To improve the integral shrouded blisks machining efficiency by reducing the volume of workpiece material needed to be removed from the blisk blank,a combined manufacturing method of direct forming by additive manufacturing(AM)and precision machining by EDM was proposed.As the workpiece material is titanium alloy,electron beam melting(EBM)was selected to provide the AM forming blank for blisk.A visual identification method was presented to establish the machining reference on the EBM formed blisk blank for the subsequent EDM process.Through the combination of EBM and EDM method,the machining time of the shrouded blisk could be greatly reduced(57.8% and 65.9% for two turbopump components respectively).