Design Of Inner Surface Processing Device For Bent Pipe And Optimization Of Its Base Structure

AP1000 nuclear power main pipe is a typical large-diameter,large length-diameter ratio curved pipe,because it needs long-term operation under conditions of high temperature,high pressure,and strong corrosiveness,so it has a higher quality requirement for the inner surface of the pipeline.However,the inside surface of this elbow is a typical elongate profiled cavity surface,and its arc section bore is difficult to process using conventional processing equipment.So the research group proposed a new inner surface processing device based on the built-in guide rail.However,the solution to the problem of specific functional structure design,device centering,and design of arc-shaped rail bases remains to be solved.The main research work of this article is as follows:For the problem that the previous project failed to design the specific structure of the device,the device was divided into modules according to functions,and the circumferential,longitudinal,and matrix modules were improved,and the Z-feed module of the tool was increased.Select the machining parameters of the extreme milling path and calculate the milling force value,and systematically design the power source,execution system,and motion system of each functional module of the device.For the problem that the built-in guide rails are difficult to precisely locate the center of the pipe,the six-point positioning structure of the device is designed in accordance with the high-precision six-point coaxial theorem.The design results make reasonable use of the limited space inside the pipe and meet the requirements for large milling power.For the design of the circular arc guide base,the force analysis must be performed first,starting from the micro-section of the curved beam,it can be found that the basic differential equations of curved beams have complicated solving process and it is difficult to carry out subsequent structural design.Therefore,the pedestal is simplified as a solid-arc beam by the method of structural mechanics of circular arc beam,and the deformation of the circular-arc guide base is predicted by the theoretical formula,it was found that when the external load was loaded at?_F=33.5°,the base deformation was maximum,and the maximum point?_x was33.5°.In the base module,the arc guide base is the main bearing part of the inner surface processing device of the curved pipe.Its structure and rigidity determine the size and shape accuracy when the inner surface of the pipe is processed by the device.Considering the particularity of the arc guide base structure and the complex spatial force loading system,the stiffness design of the circular guide base is carried out by using the structural mechanics of the curved beam based on the simple torsion theory,designed with the maximum deformation point,the base rectangular section has a width of 160mm and a height of 165mm.Because of the complex spatial force system,the bending,torsion and shear effects of the base,it is difficult to check with the theoretical formula.The static model of the device is simplified and established by the force shifting theorem,and to analyze the static and dynamic characteristics of the circular-arc track base.Through static analysis,the stiffness and strength of the arc guide base designed by the above method are in line with the requirements under the limit condition.The arc guide base is positioned and constrained within the pipeline by means of three-point support devices on both sides.Therefore,excessive mass will affect the stability of both sides of the support and the overall performance of the device.Considering that the complexity of working condition of arc guide base and the traditional single-objective optimization design method cannot simultaneously consider the problems of multiple goals.Using compromise programming method and mean frequency formulation to establish the optimal objective function considering the Multi-Stability base station stiffness and the first 3natural frequencies.A variable density topology optimization with constant cross section was established to solve the problem of the result of traditional topological optimization of the arc guide base poor in readability and difficult to carry out subsequent design and manufacturing.Topological optimization results show that the material removal rules under the constant cross section constraints are obvious and the manufacturability is well.Using response surface optimization method to optimizing the wall thickness of the base cross section.After comprehensive optimization,the result indicate that the mass of the arc guide base is significantly reduced by 186.50kg,with weight reduction of 52.11%,and the first three natural frequencies all have different degrees of improvement while meeting the Stiffness and strength requirements.