Research On Optimization In Precision NC Bending Process Of Thin-Walled Tube

The thin-walled tube NC bending is a complex process with multi-factor coupling interactive effects. If the forming parameters are chose inappropriately, some common failures, such as wall thinning, cracking in the outer of tube, wrinkling in the inner of tube and cross-section distortion, spring-back will occur easily. The reasonable selection and optimization of parameters has thus become an important subject urgently to be resolved for the development and application of thin-walled tube NC bending technology. Consequently, according to the characteristics of thin-walled tube NC bending process, the optimization strategy of step-by-step optimization and precision optimization for multiple forming parameters are proposed based on the experiment, theoretical analysis and numerical simulation, as well as the implementing method of the strategy. The main contents and achievements are as follows:Key techniques and the optimization strategies of the forming parameters in thin-walled tube NC bending are systematically studied. The influence laws and the significance of the parameters to the forming quality are analyzed. The method for the selection of designing variable and establishment of objective function in optimization are put forward. By expert knowledge and empirical data, the constraint condition and optimization range are determined. Furthermore, step-by-step parameters optimization is carried out. Then the optimization methods for the precision optimization to the processing parameters are adopted.By the proposed optimization design strategy, based on the FEM model established by ABAQUS/Explicit, with the free wrinkling, the allowed cross-section distortion degree as constraint condition and the minimum thinning rate as the optimization goal, the parameters optimization in the thin-walled tube NC bending processing with 57mm bending radius with the tube of φ 38 × 1 stainless and aluminum are carried out. Firstly, the tool parameters and friction coefficients, the number of the core and the clearance between cores are determined and optimized using the step-by-step method. Then the complex method is adopted to optimize mandrel extension and thrust speed. The optimization results are proved byexperiments.The database of tube NC bending processing is developed by MS SQL Server 2000, then a NC tube processing database management system is set up, using object-oriented program language C# as developing language and Visual Studio.NET as the front developing environment. On the basis of expert knowledge and mature process provided by the management system, the determination of optimization range, parameter selection and optimization of NC thin-walled tube bending can be realized conveniently and quickly.