Prediction And Control Of Welding Deformation Of Construction Vehicle Frame

Welding has been widely used in the production of the engineering vehicle frame, where T-joints are employed in the manufacturing processes. Welding residual stress and distortion which occur in welding process due to uneven heating bring unfavorable effect on the manufacturing quality of the engineering vehicle and its operational safety. As a result, welding residual stress and distortion forecasting and control become an important and urgent research topic in the filed of engineering vehicles. Numerical simulation method is presented by using the T-joint and the whole frame of the engineering vehicle. The distribution and variation trend of residual stress and distortion is analyzed with the welding simulation professional software SYSWELD and Pam-assembly. It is helpful to shorten the production cycle, so as to provide further scientific basis for the optimization of the welding process and the understanding of welding principle.Research work of this dissertation mainly includes:Firstly, the state of the art of the present numerical simulation of welding residual stress and distortion is reviewed. The reasons for welding residual and distortion are analyzed. Basic theories of welding numerical simulation including heat transfer theory and thermal-elastic-plastic theory are developed. At the same time, the concept of welding heat source models as well as the classifications, advantages and disadvantages are discussed in detail.Secondly, the thermal-elastic-plastic finite element method is applied to simulate welding processes of T-joint structure in the engineering vehicles. Taking the T-joint of two steel plates of 20mm as example, the double ellipsoid heat source model is implemented to adjust the welding heat source, and to simulate the welding temperature and stress fields and to discuss the dynamic process of welding temperature field and the distribution of residual stress. The influences of welding sequences to the residual stress and distortion of the T-joint are also studied.Finally, according to the structural characteristics of the large-complex weldments in engineering vehicles, the "local-global" mapping FEM method is used to forecast the welding distortion. Taking the engineering vehicle frame as the research object, the welding distortion of the whole frame is obtained by extracting the macro elements from the local models and mapping them to the whole frame with Pam-Assembly simulation software. The consistency of simulation results with the measured results proves the correctness of the simulation model. Welding-sequence influence on the welding distortion is also studied, which provide a kind of fast and effective method to forecast welding distortion of large-scale complex weldments.