Research On Preform Optimization Design Based On Topology Optimization

Preform design and corresponding preform die design are one of the core contents of forging process and forging die design.Because the shape of the final forging die is designed according to the final forging and its shape is fixed,in order to obtain a qualified final forging that meets the size and quality requirements,preform design has become the key and the most difficult link in process design.With the development and wide application of finite element numerical technology,numerical simulation provides a reliable analysis and verification tool for forging process design.The preform design based on numerical simulation can determine the optimal preform design through forming simulation in multiple preform design schemes.When the product shape is complex or has high requirements for product quality,the traditional empirical preform design is difficult to meet the requirements of forging process design.It is necessary to design the preform shape and the corresponding preform die shape based on scientific methods.Therefore,on the basis of numerical simulation,combined with optimization theory and algorithm,realizing the automation and optimization of preform design is an important research direction of preform design,which has important theoretical significance and application value.The author of this thesis participated in the research of key R&D projects in Shandong Province.As a research content of the project,this thesis carried out the research on the preform design of actual forged products and the theoretical method and program development of preform design based on topology optimization.Firstly,the preform design method based on finite element forward simulation is studied in this thesis.Taking Q4041 high-pressure common rail part actually produced by the cooperative enterprise as an example,the shape of its preform is optimized.According to the large amount of flash in the middle of the final forging in actual production,the shape of dumbbell preform is designed,and the process method of roll forging preform instead of the existing preform is put forward.Four different shapes of preforms were designed,and the forging process of the designed preforms was simulated by finite element software.The preform was prepared by machining,and the actual forging experiment was carried out.Compared with the simulation results,the preform shape which can completely fill the cavity and has the least flash was determined in the four roll forging preform schemes.The experimental results show that using the optimized preform for forging production can reduce the flash by 35%and improve the utilization of materials.In this thesis,the preform optimization design method is studied,and the bidirectional evolutionary topology optimization method is applied to the preform optimization design.Bi directional evolutionary topology optimization method is a novel optimization method,which has been successful in the optimization design of continuum structure.In this thesis,the element addition and deletion criteria suitable for the material plastic forming process are established,and the material on the surface of the preform is gradually added and deleted to change its shape,so as to realize the optimal design of the preform shape.One of the common problems of the existing preform optimization methods is the lack of control over the overall shape of preform.In the process of preform shape optimization,with the optimization iteration,the preform shape may become very complex,and even its shape is more complex than that of the final forging.resulting in the impossibility of preform forming,which loses the significance of preform design.The innovation of this thesis is that the control of preform overall shape is considered in the element addition and deletion criterion,the shape control factor is added to the element addition and deletion criterion,and a multi-objective addition and deletion criterion based on filling,deformation uniformity and shape control is proposed.This thesis describes in detail a series of key technologies and implementation processes in the topology optimization algorithm,including the construction of objective function,the tracking and transmission of element data,the determination of the number of element additions and deletions,the operation process of element additions and deletions,the extraction and fitting smoothing of boundary nodes and so on.Based on the preform topology optimization design method proposed in this thesis,the preform optimization design program PREFORM is developed by using Visual C++programming language on Windows platform.The program has a visual user interface,which can facilitate the establishment of finite element analysis model and topology optimization model,and view the results of preform optimization.The main functions of the program include defining the design domain and generating the background mesh,generating the topological mesh,exchanging data with finite element simulation program,tracking and transmitting the field information of the element,calculating the element addition and deletion criteria,implementing the element addition and deletion operation,extracting the boundary nodes and generating the B-spline curve,calculating the value of the objective function,etc.In this thesis,two typical preform shapes of plane strain H-shaped forging and axisymmetric disk forging are optimized by using the developed preform topology optimization program.Taking the material filling performance and deformation uniformity as the optimization objective function,the optimization process and results are given in detail.Using the optimized preform for final forging,the material can completely fill the cavity,the flash is small,there are no defects such as folding,the strain uniformity is improved,and the maximum forming load is greatly reduced.The optimized preform shape has the shape similar to the final forging,and the shape complexity is moderate,which verifies the reliability of the preform optimization design method based on topology optimization proposed in this thesis.