| To achieve both of high efficiency and precision has been the primary requirement of the manufacturing industries of heavy turbine mortises for a long time.Among the various processes,the broaching of mortises of the turbine disks and/or the compressor disks in the heavy gas turbines is the most important for stability of the machining quality,which could determine the ability of the disks to support the dynamically coupled workload of heat and mechanical forces.Due to the strict requirements of dimensional accuracy and machined surface quality,as well as the complexity of the mortise geometries,the self-production of the broaching tools for mortises in our nation is still a big challenge.Currently,the basis to precisely design the mortise broaching tools with shapes of Fir-trees is still insufficient,and the broaching mechanisms are yet unknown.Besides,it is extremely hard to protect the dimensional accuracy and the surface integrity of the mortises during the broaching process.The life and wear resistance of the tools need to be improved.To these problems,this paper investigates the fundamental dynamics of the broaching process and precise design of the broach tools analytically and experimentally.The outlines of this paper are as follows.(1)To better reveal the coupled mechanisms of stress field and temperature field in the cutting zone during the broaching process of mortises of turbine disks,the method of Split Hopkinson Pressure Bar(SHPB)is used to investigate the mechanics of the heat-resistant,high Chromium alloy of turbine disks.Based on that,the effects of strain hardening,strain rate hardening,as well as heat softening on the flow stress of the workpiece material at high temperature and high stress conditions are presented.Results show that significant characteristics of strain hardening,strain rate sensitivity,and temperature sensitivity exist in the investigated material.To solve the problem of the basic model that are necessary for the physical simulation of broaching processes,in this paper,the stress-heat coupled constitutive model of the high Chromium alloy is developed,and the errors are also analyzed.Simulation results including cutting forces,temperatures,and chip morphologies are verified by experiments,the results have confirmed the effectiveness of physical simulation of broaching process on the cutting stress and temperature field based on the proposed constitutive model.(2)The effects and mechanisms of geometrical parameters of the broaching tool cutting edge on surface scale burrs,surface hardening,residual stress,as well as surface roughness during the broaching process for the turbine disk mortises are comprehensively investigated in this paper,based on which,the proper range of geometrical parameters of the broaching tool edge is confirmed considering the surface integrity of the broaching process.The result could provide boundary constraints for the precise design of broaching tools based on broaching performances.(3)To develop the geometrical dependencies of the space distribution of cutting forces during the finish broaching process for the mortises of turbine disks,the analytical mapping method between the edge curve of the finish broaching tools and the mortise contours is proposed in this paper,and the fitting equation of the turbine disk mortise profile with a Fir-tree shape is modelled.Space distributions of cutting forces on the curve edge of the finish broaching tool and the linear edge of the rough broaching tool are studied theoretically,and the reconfiguration model of the cutting forces space distribution of the finish broaching tool with the Fir-tree shape is proposed.Finally,the infinitesimal tooth section work and the instant teeth cutting forces acting on the broaching tools of turbine disk mortises are demonstrated,and the dynamical force model is built successfully.Experimental results show that,the reconfiguration of elemental tool edges in space domain could be used for predicting the cutting forces on the finish broaching tools with the profile of the Fir-tree.This work can provide basic knowledge for controlling the stability of mortise broaching and the allowance allocation for designing the group broaching tools.(4)To reveal the evolution of the broaching tool wear,the reliable process to improve the wear resistance of the tool is studied.The wear chaos characteristics of the friction pair composed of the tool material(T15,high speed steel of powder metallurgy)and the workpiece material(X12CrMoWVNb N-10-1-1,heat-resistant and high Chromium alloy)is further investigated.Combined with the non-linear analysis method for the chaos signals,the evolution of the wear chaos attractor is revealed.It is indicated that the recursive and quantitative assessment model of the wear evolution could identify the transition characteristics of wear.In this paper,the model expressing the dynamical friction between the rake face of the tool and the chip surface is developed,and the feasible domain of the rake face wear stability is mentioned.Under wet cutting and dry cutting,Comparison of the recursive morphologies of the rake wear of the high speed steel tools with AlCrN coating and without coating are experimentally investigated.In order to improve the wear resistance performance of the broaching tools,the wear characteristics of the AlCrN coated and uncoated high speed steel tools are investigated experimentally.Based on the duration experiments,the prediction models of the tool durability and the probability distribution function of failure are successfully developed.The predicted broaching length could provide theoretical guidance for the maintaining period of broaching tools.(5)According to the creation principles for mortise forming process,this paper theoretically analyzes the range of the pitch,the tooth-to-tolerance,the law for rises of teeth,for the cases of layered broaching,progressive lamination broaching,and block grouping broaching.In the conditions of multi-constraints,for the optimization objective of the highest material removal rate in rough broaching and the best machined surface finish in finish broaching,broaching allocation parameters using the block-by-block groove forming method are determined.Based on which,the allowance allocation strategy for rough broaching is made for the Fir-tree mortise of the turbine disk in F-class heavy gas turbines with the profile of the Fir-tree.To comprehensively analyze the optimum selection of finish broaching parameters under the constraints of broaching forces,tool strength and machined surface finish.The Coupling Response Surface Method of Multi Constraints(CRSMMC)was proposed in this paper,for the optimal design of broach cutters under multi constraints conditions.The method could give a set of points of design parameters,and the range of flexible parameter sets for the optimal design parameters is obtained.Through experiments,the errors are validated in the proper range,it can solve the non-unique optimal solution problem faced in the broach design process.(6)The finish broaching tool for the F-class heavy gas turbine mortise with the profile of the Fir-tree is trial-produced,and then the cutting performance is experimentally studied.During the trial-production operation,the residual stresses on the surface and subsurface are compared before and after the shot peening hardening.Results show that the shot peening could improve the compressive residual stress on both the surface and subsurface of the tool significantly,which can also improve the fatigue resistance performance of the tool.The standard blocks cutting test of and F-Class turbine disk tests are studied.After that,the indices such as dimensional accuracy of the broaching process,machined surface roughness and wear resistance of the tool are measured carefully.In comparison with the indices of similar products abroad,the trial-produced broaching tool for Fir-tree profile could meet the requirements of the F-class heavy gas turbine mortises.In addition,the shot peening can improve the wear resistance performance of the tool significantly. |
PDF Full Text Request