Investigations On High-precision Methods To Measure Welding Deformation

The welding process of metal materials is a nonlinear process with very fast cooling rate.The non-uniform temperature field and the local plastic deformation and specific volume of the whole thermal cycle lead to the inevitable welding deformation.However,it is not possible to accurately predict the welding deformation during the welding process,especially the welding deformation of large and complex metal material welding parts.With the development of computer technology,the finite element analysis method is widely used in the field of welding deformation.At present,there are two kinds of methods to predict welding deformation based on finite element analysis.One is the thermal elastic plastic finite element method,the other is the elastic finite element method based on the inherent strain theory.Due to the large amount of calculation and slow speed of the thermo elastic plastic finite element method,it is only suitable for predicting the welding deformation of medium and small weldment.The inherent strain method does not have the whole process of welding and cooling in mind,but takes the inherent deformation as the initial strain and does the elastic finite element analysis.The inherent strain method has been widely used in predicting welding deformation of large welded joints.In this paper,the BRTApe×710 contact three-dimensional coordinate measuring instrument is used to measure the welding deformation of the metal sheet,and the calculation method of obtaining the three-dimensional coordinate value of the metal welded structure is put forward.The mark position selection in welding machining small sheet,and then in the 3D coordinates of eight points near the measurement of these holes,the measured coordinates after a series of operations to get the 3D coordinates of the center hole.By calculating the three-dimensional coordinate value of the small hole center,the inherent deformation of the sheet metal can be obtained by substituting the developed inverse analysis program.Finally,the intrinsic deformation value of the metal plate is substituted into the analytic program,and the elastic finite element analysis of the natural deformation is carried out.In order to verify the validity of the instrument measurement results and measurement accuracy whether to meet the high precision requirements.In addition,two bead-on plate welded joints with 2 mm and 3 mm thickness are selected as research objectives to demonstrate the effectiveness of the new method in this paper.Thecalculated 3-D coordinates are used as known parameters and inherent deformation components are gained based on inverse analysis method,then deformations of the two thin-plate bead-on joints are predicted by the use of inherent strain method.The comparison shows that there are big differences between the two joints with different thickness.The proposed measurement method and algorithm can accurately obtain the3-D coordinates on the neural plane.Whether it is a large deformation of the 2 mm plate or a relatively small deformation of the 3 mm plate,the inherent deformation components obtained by inverse analysis method are accurate and effective.