Research On Key Technology Of High Speed Milling Of Nickel-based Superalloy Complex Thin-walled Parts

The Nickel-based superalloy,for its working in the High-temperature and oxidized situation and gas corrosive condition, and being subjected to complex stress,is an indispensable one in the component parts of the impeller and blades in the aeroengine and the steam turbine.As the material difficult to machine,the nickel-based superalloy has the features that high stress,big shaping, low thermal conductivity,easy to produce serrated chips in the cutting process, serious hardening machined surface,large cutting force, Severe tool wear,and so on.So above,the machining efficiency of the nickel-based super alloy is very low and the quality and accuracy of the products are very unstable.Except for difficult machining,the nickel-based superalloy thin-walled parts also belong to the difficult machining material and have the thin and severely-changing-curvature wall.So there are some challenges in the process of machining the nickel-based superalloy thin-walled parts,such as the vibration of tools spindle and vertical veins or oversize cutting appeared on the surface of the blades,which caused by the constantly changing of the cutting direction,and so on.The surface topography and the grains of the blades playing a decisive role on the power transmitting efficiency of the blades,the utilized performance of the blades was severely impacted,which would result in the scrap.Above all,in the paper,the NC machining nickel-based superalloy blades-type parts was chose as the studied background.By the theoretical analysis and cutting experiment, the related machining mechanism,of cutting nickel-based super alloy and the related technology, of the milling stability would be revealed,and the commonly basic scientific issues,existing in the cutting the complex and thin-walled parts in the Aerospace fields,would be solved,which would provide strong technical supportfor efficiently machining nickel-based superalloy parts and reducing tool wear,and provide more accurate theoretical basis for machining the parts stablly.For the influence on the cutting process produced by the serrated ships,the experiment of milling nickel-based superalloy was conducted,the serrated chip formation law in different cutting parameters was probed,and the adiabatic shear phenomenon was revealed.By observing the chip organizations with the optical microscope, the evolution of the micro-structure in the adiabatic shear band was obtained, the serrated ships formation was raised:deformation- bands serrated ships---transition-zone serrated ships---series changing serrated ships. Lastly,the influence of cutting parameters on geometrical characteristics of the serrated ships was studied,which provided the theoretical basis for the choice of cutting conditions.For the processing characteristics of the nickel base superalloy blades,using the ceramic tools in the rough and semi finish machining process, would improve the processing efficiency.By milling experiments obtained cutting speed on tool wear will affect larger, with the increase of cutting speed, the rake surface abrasion form for a variety of wear mechanism, flank wear, mainly for the groove wear, and the cutting chip edge on the tool of impact caused by the groove wear is intensified. Combined with the simulation results, the machining surface hardening is also affected by the groove wear of the tool. The above work provides a theoretical basis for the milling of nickel base superalloy materials to reduce tool wear and improve the service life of the tool.According to the path switching in the process of the interpolation algorithm machining nickel-based superalloy blade surface, the four-element method was introduced into the five-axis machining tool attitude optimization, and the four-elements method was set up to optimize the tool attitude. Combining with the surface projection processing method provided by the POWERMILL software,and planning the tool path finely cutting the blades by driving surface method,the over cutting phenomenon of the blade and the machining precision of milling the complex surface were improved.For the cutting vibration in the process of side milling nickel-based super-alloy thin-walled parts,the cutting force prediction and cutting dynamics were studied.During the process of machining the nickel base superalloy thin-walledparts,the dynamic characteristics of which was considered,and the delay dynamic model was established,and the stability criterion of radial angle is proposed.The actual processing results showed that the stable domain of cutting parameters,obtained by this method, has a certain practicality,and good consistency, and is simple and practical,easy to project, compared with the traditional two dimensional lobe stability criterion.By the comprehensive considering of the key challenges appeared in the process of machining the nickel-based superalloy complex thin-walled parts,and the application of the combination with theoretical analysis, cutting simulation and the cutting experiment,such sides were deeply studied as characteristics of cuttin chip formation in the process of machining nickel-based superalloy thinwalled parts and impellers parts, tool wear mechanism,the planning of tools posture and the prediction of machining stability limits.The research would provide the theoretical basis and technical supports for the promotion and application of the technology of machining the nickel-based superalloy complex thin-walled parts and impellers and so on.