Research On Quality Control Key Technical Of Sheet Metal Incremental Forming

Incremental forming is an innovative and flexible forming process which belongs to rapid prototyping of sheet metal, with the support of simple die or without it,Also the sheet metal part with higher forming limit and more complex shape can be manufactured using NC machine according to the pre-programme. And incremental forming technology is particularly suitable for sheet metal manufacturing during the period of single or small batch production and product trial. Currently, poor forming quality & low forming efficiency, especially the poor quality, are the most two important defects that can be hindered the popularization & application of sheet metal incremental forming process. The target of the present work was to solve the quality problem of sheet metal incremental formed parts, and the principle of defects arising, key processes and improving measures including the forming process & mechanism, material flow law, springback, forming compensation technology and automatic programming technology were studied. The main contributions of the present thesis in details are as follow:Sheet metal incremental forming process & mechanism was studied in details. (The process of incrental forming can be roughly divided into three processing: modeling process, technological preparation process and forming process. Also the forming process can be devided into three divisions: initial forming, stabilize forming and end forming) which was suggested in the present research. Indeed mechanical analysis model was established for the study of material deformation mechanism, and deformation area division method was advanced firstly, also the possible existence of instability forms and dangerous instability point of judgment method were proposed, finally the eventually deformation behaviors of judgment scheme was proposed according to comprehensive deformation styles during each forming stage.Researchs which were based on material flow law during sheet metal incremental forming were carried out. A basic law of material flow, cosine rule also was proposed. Under ideal conditions, due to simple fixture and forming parts own restriction, material flow takes place along the axial direction, and its deformation belongs to slip at plane strain. Based on the plane strain principle, a general thickness distribution calculation formula was suggested, and then thickness calculation software modules for incremental formed parts were also developed independently. It's was be noticecd that material flow would not meet the law of basic flow because of the sheet was in a free state without simple fixture restriction effect, and the edge of material could be flow inside during tensile style incremental forming. Also the thickness distribution estimation using FEM method based on "virtual modeling orientation method" was proposed in the present research.Research based on springback of incremental formed parts was considered. The springback evaluation method based on forming error compensation also was proposed, which it can be defined as the difference between theory and the actual amount of compensation along the measured direction. According to forming error compensation evaluation method, expiments was designed and implemented. And from the results that obtained it can be show, the magnitude of springback average (δE) of formed parts was very small, and the forming precision could be significantly improved by adopting compensation method. Based on double tensile stress state in the main deformation area, the hypothesis and springback could not be occured on the formed parts that have been proposed.In order to study the springback by FEM, loading path automatically generation software module which be used for incremental forming simulation, was developed independently. With the help of the software module, elastic-plastic finite element solution based explicit & implicit algorithm could be used in combination, and it can be noticed that forming process simulated using explicit algorithm and springback simulated using implicit algorithm. The simulation results showed that small springback would be taken place in the main deformation area, and springback would be decreased linerly gradually as the forming angle increased.Research based on incremental forming compensation technology was studied. In order to study the quality of formed parts that influenced by forming precision, the forming precision displacement error evaluation method was proposed, which it can be defined as the deformation displacement error along the measured direction. Also the theoretical calculation & correction calculation model of forming force has been advanced. The forming tool system could be simplified as a cantilever beam system during the forming process, indeed elastic deformation on the forming tool was taken place under the action of the forces, and then the insufficient forming would be occurred, and the forming precision would be declined. Contacting relationship between the forming tool and sheet metal was analysed, theoretical formula of forming force was established with the aid of process simplification using geometric graphic method, and the modified computing formula of forming force was established with the aid of experiment. On theses basises, according to the principle of geometrical compensation, forming compensation plan was established. Studies showed that the forming precision could be improved significantly adopting compensation method.Automatic programming technology that used for incremental forming was studied. The three functions, such as parts formability analysis, forming path generation & optimization and forming simulation, were mainly realized in automatic programming system which was be developed independently. Based on the law of thickness thinning, threshold value was setted to determine whether the sheet metal forming could be carried out. The import data from the CAD model was handled to create tooling path using automatic programming system. Smooth of tooling path, vibration reduction, and optimization algorithms were designed according to the spirals and Bessel criteria. Based on the discretization thoughts, the dynamic simulation of forming process could be carried using triangle mesh said blank model.Various analytical models, analytical solutions, calculating model and software functions, which proposed in the present research, were analysed by abundant theoretical, comparative experiments. Also good results were obtained and it can be used these research results in real manufacturing products.