| Turbine blade is the key component of aeroengine.Its manufacturing technology is always the focus and difficulty of research.With the development of aviation industry,the blade with complex structure and difficult to process materials is emerging constantly,which poses a greater challenge to its processing technology.Therfore,electrochemical machining(ECM)has become one of the key manufacturing technologies for engine blades because of its advantages,such as not limited by material properties,no tool wear and good surface quality.In this paper,taking the large-size TiAl low-pressure turbine blade with double platforms as the object,the basic research on methods of improving taper and stray corrosion on platform and the experimental research on blade ECM were carried out.The details are as follows:(1)The electrochemical dissolution behaviors of SS304,GH4169 and Ti-48Al-2Cr-2Nb(TiAl4822)were analyzed.The results showed that under low current density,the removal rate of SS304 is low,but the current efficiencies of GH4169 and TiAl 4822 are still high,which means that the stray corrosion of GH4169 and TiAl 4822 is more serious than SS304 during ECM.And SS304 has some electrochemical passivity,which is helpful to improve the localization in ECM.(2)In view of the stray corrosion of blade platform,the simulations and ECM experiments of three methods to improve the taper of platform were carried out,i.e.setting insulating layer,auxiliary anode and gas-assisted insulation.The simulation results showed that setting insulating layer and the auxiliary anode method can reduce the current density and the taper of the platform,while the compressed air can discharge the electrolyte of the side gap to a certain extent and form an insulation protection on the platform.The experimental results showed that the platform tapers of SS304,GH4169 and TiAl 4822 were 0.197°,0.222° and 0.357° respectively when the insulating layer was set on the cathode side wall(the cathode edge is 1 mm wide),which were 98.3%,97.7% and 97.3%lower than the processing done by a traditional cathode;the minimum platform tapers of the three materials under the action of auxiliary anode were-0.097°,-0.086° and-0.080° respectively,which represented reductions of 50.7%,61.3% and 77.6%,compared to the processing conducted by the cathode with insulating layer;the platform tapers of the three materials under the gas-assisted insulation were-0.124°,-0.171° and-0.259° respectively,which represented reductions of 29.5%,13.6% and 15.9%,compared to the processing conducted by the cathode with insulating layer(without gas-assisted insulation).The above results showed that the three methods can inhibit the stray corrosion in varying degrees,and the auxiliary anode and gas-assisted insulation can further reduce the platform taper on the basis of setting insulating layer,but the stability and uniformity of gas-assisted insulation need to be improved.(3)Setting insulating layer and auxiliary anode were applied to inhibit the stray corrosion of the large-size blade platform.The test results indicated that the platform tapers of TiAl blade under the action of side wall insulation and auxiliary anode were 4.761° and 2.866° respectively,which means that the two methods can effectively restrain stray corrosion of platform,and the auxiliary anode can further improve the platform machining accuracy compared to setting insulating layer.At the same time,a large-size TiAl low-pressure turbine blade with good surface quality was obtained by pulse vibration ECM. |
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