| The components of steam turbine, like rotor and blades, work under severe conditions of high temperature, high pressure, and high speed. The components and parts are influenced by not only static pressure, but also thermal and mechanical shock. Therefore, the core components should be made of materials with good physical and mechanical performance, and at the same time, the components should be fabricated with high machining precision, fit precision and good surface quality. The integral-type milling cutter with complex profile is widely used in the machining process of leaf-root and rotor-groove profiles. According to a survey of the cutting tool market, most of the complex profile milling cutters used for the core processing are imported from abroad, especially the cutters applied for finish machining. Trial cutting method is adopted for the design of the complex profile milling cutter, which is time-consuming and costly. As a consequence, new technologies should be induced to help with the design of the complex profile milling cutter. In this thesis, the design method for complex milling cutter is systematically investigated, which has been supported by the National Science and Technology Major Project of the Ministry of Science and Technology of China (No. 2013ZX04009-022).The traditional design method of the integral-type milling cutter with complex profile is analyzed during which the advantages and disadvantages are summarized. The stratification-customized optimization method for conical milling cutter is established based on the failure state of conical milling cutter in real cutting. On this basis, numerical design method based on infinitesimal method is put forward. In the process of simplification based on infinitesimal method, a model used for transforming the 3D milling process to 2D orthogonal cutting is defined based on the calculating of the chip thickness obtained during milling process, of which the cutting depth for 2D orthogonal cutting is taken as the same as the maximum thickness during the milling process. By using the parameter transformation model, the other parameters for 2D orthogonal cutting can be transformed from the parameters of milling process. At the same time, the geometry and kinetic of the complex profile milling cutter are analyzed. And a general equation of conical helix is derived based on the helix theory, and then the conversion model between radial angle and normal angle is established.The structure design of the cutting edge for complex profile milling cutter can be transformed to the structure of the cutting edge for 2D orthogonal cutting based on infinitesimal method. Based on the analysis of the failure mechanism, the main reference index for the structure design of the cutting edges could be defined as the damage resistance ability The design criteria for rough and semi-finishing cutter are minimum stress and cutting temperature, while those for finishing cutter are minimum cutting deformation ratio and minimum stress. In order to transform the multi-index constraint problem to simple mathematical calculation based on the response surface equation, the weighting coefficient λ is introduced. The safety factor K is proposed as the critical strength to access the rationality of the design parameters instead of the flexural strength of the tool material.In order to reduce the design cost and shorten the design cycle, finite element method (FEM) is applied to establish the underlying database. Response surface equations in the design process are used to fully express the results of finite element simulation. The ways to build an accurate finite element model have been fully studied in detail to ensure that does not have negative effect on tool design. Precise models of thermal physical properties, dynamic mechanical properties as well as the friction model are established. The main force and radial force obtained from FEM simulation are compared with those obtained from orthogonal experiment, in order to verify the accuracy of the finite element simulation. Based on the precise finite element simulation model, the simulation results (such as stress S, the temperature, cutting deformation ratio ξ, cutting force Force X and Force Y) over the parameter variables (such as cutting speed v, cutting depth ap, rake angle y, edge radius r) are expressed as response surface function, so as to realize the database management and application of the FEM results during the tool design process.A dynamic contact model has been established through analyzing the geometry and kinetic state of the complex profile milling cutter, during which four time nodes are defined to determine the working status of the cutting edges and infinitesimal cutting edges. Meanwhile, the predictive model of milling force for complex profile milling is proposed, and the two-step decomposition model is established to realize the resolution of unit force for infinitesimal cutting edge. The existence of helix leads to the decomposition of Force X, while the tilt angle causes the decomposition of Force Y. Considering the phase angle between different infinitesimal cutting edges with same working status caused by helix angle, the time domain decomposition and transformation models for unit force are established. In order to verify the accuracy of the model, milling experiments were carried out using a profile milling cutter for finish machining. The results show that the dynamic contact model of the cutting edge and the model of milling force applied for a complex profile milling cutter are quite dependable, which provide a foundation for the complex profile milling cutters performance evaluation.The ultimate goal of tool design is to put the cutter into production and use, hence the manufacturability of the cutters should be studied. In this study, the 3D model and grinding process are investigated. In order to achieve three-dimensional modeling of complex profile milling cutter, the radial truncate mathematical models are established. The precise 3D model of complex profile milling cutter is achieved based on Pro/E. On this basis, the NUMROTO is used to develop the grinding process, which can be used to test the manufacturability.In order to realize the widespread use of the numerical design method, a numerical design platform is developed by Visual C# 3.0 based on the numerical design method stated above, Meanwhile, the supporting database for numerical design platform is built by Mysql workbench 6.0. Subsequently, the platform is used to realize the design of three complex profile milling cutters, which are used in the shape processing of rotor-groove in 600MW steam turbine. The milling cutters designed by this method are used in the actual production process, of which the tool life is longer than the imported ones. The results prove that the numerical design method based on infinitesimal method for complex profile milling cutter is reliable and propagable. |
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