Research And Application On Predicting And Controlling Welding Distortions Based On Numerical Method

The thin-plate structure and the box-beam structure are two typical welded structures in railway vehicles. Because of their structure complexity, bigger size and multi-seams, welding residual distortion which occur in welding process bring unfavorable effect on the quality of welding products manufacturing and service. As a result, welding distortion forecasting and control become an important and urgent research topic in railway vehicles. Although the numerical simulation studies on welding distortion have been conducted for many years at home and abroad, less research work for welding structures in railway vehicles is done, especially in considering multifactor influences for welding distortion based on numerical model validation. According to thorough investigation of enterprise requirements, three different numerical methods are presented corresponding to three typical types of welded structures of railway vehicles-thin-plate structure, multi-pass welded box structure and large size box structure. After the analysis of welding distortion and the validation of welding simulation model, influences of welding parameters, structure parameters, multi-pass welding and welding sequences on welding distortion are studied. It is helpful for mastering the regularity of welding distortion, so as to provide technical support for the design, making, and optimization of railway vehicle welding process.Research work of this dissertation mainly includes:Firstly, prediction and control methods and numerical simulation technologies of welding distortion are reviewed. Basic theories of welding numerical simulation including heat transfer theory and thermo-elastic-plastic theory are developed. At the same time, relative concepts, classifications, advantages and disadvantages of heat source models involving in welding processes are discussed in detail.Secondly, according to the characteristic of thin-plate welded structure in railway vehicles, an equivalent thermal load method based on inherent strain is put forward. Taking truck side-wall as research object, thin-plate buckling distortion is simulated by transforming inherent strain into equivalent thermal loads on the welded seams and heat affected zones. Compartments between numerical simulation results and experiments data show that both have great consistence. Based on the simulation model, influences of different factors include welding and structural parameters on welding distortion are investigated by using orthogonal design method to regulate the parameters, and the optimal design is concluded which provide reliable theoretical references for controlling thin-plate welding distortion of the truck side-walls.Thirdly, according to the characteristic of multi-pass box welded structure in railway vehicles, a heat treatment method of multi-pass welding based on thermo-elastic-plastic theory is put forward. Taking bogie side beams as research object, multi-pass welding distortion is studied by the use of thermal cycling curves as heat source with SYSWELD simulation software. Meanwhile, the experimental measurements are given and the consistence of simulation results with the measured results proves the correctness of the simulation model. The influence of welding sequences to welding distortion in multi-pass welding process is studied which promotes the application of multi-pass welding technology in railway vehicle product design.Finally, according to the characteristic of large size box welded structure in railway vehicles, a "local-global" project FEM method and mcroelements technology are put forward. Taking the middle beam of container underframe as research object, welding distortion using present welding process is simulated based on macro-elements technology with Pam-Assembly simulation software. Influences of welding sequences and structural parameters to the welding distortion are also studied, which provide a kind of fast and effective method to solve welding distortion of large-scale complex structure for solution problems such as large size, long seams, large scale finite element calculation and much solution time etc.This research is sponsored by the National "863" high-tech research and development project:"Coordinated design of complex product, simulation and optimization----integrated platform research, development and application" (Project Number:2006 AA04Z160).