Study On Modeling And Quality Control Technology For Sheet Metal Forming Process

Sheet metal forming is a very important plastic working technology, which has been widely used in industrial domains, and is also one of the advanced manufacturing technologies. The deforming process of sheet metal forming is very complicated and the abundant process technologies and experience about parameter selection have been accumulated from the long-time practical operation. Along with the more and more drastic market competition, it is very important for enterprise to respond for the market need and improve the quality of the product quickly. So the experience that we have gotten cannot satisfy the problem we meet in the process of modern production. It is one of the fundamental technologies for the metal forming enterprise to confirm die surface parameters and technology parameters rapidly and reasonably, gain the forming process property and control quality with least cost, and it gets more and more attention by engineers and researchers in world.The modeling method for sheet metal forming process is studied under economic samples and based on the numerical simulation technology, which is combined with the basic theories such as elastic-plastic mechanics, mathematic statistics and modern control in this dissertation. The die surface and technology parameters are optimized, and the quality control technology for sheet metal forming is studied also. According to the rules of sheet metal forming process and its qualitative analysis, the experiments and production of sheet metal forming are done. The main contents were as following:Firstly, sheet forming property and its vital influencing factors are studied, and the relations between the parts quality and all factors are studied too. The standard for evaluating the parts quality is established, and it constructs basic theory for modeling of optimum function and quality control; according to abundant process technologies and experience, the measures, which are used to prevent quality defections, are given synchronously.Secondly, the effect and significance of numerical simulation for sheet metal forming is described, and the key technology of dynamic explicit FEM is studied also; aiming at the problems that the calculating precision is not high or the gridding will be aberrant when numerical simulation for complex parts is done by FEM, the mesh-free method is studied initially.Thirdly, based on the theory of mathematic statistics and experiment design, the characteristic and sampling method of the high performance modeling samples are studied; according to the problem that it need much more samples by using traditional modeling method and for the sake of modeling the rules of sheet metal forming process effectively and truly, the modeling method based on Partial Least-squares Regression (PLS) for sheet metal forming process is put forward, and this method will solve the problem effectively that it restricts each another between the modeling efficiency and model precision.Fourthly, based on the modeling for forming process and according to requirement of forming quality, a new object function for optimizing parts quality, which aimed at the attenuation uniformity of sheet thickness, is put forward and it is also the judgment basis for optimizing analysis; a standard object function expression for all optimum object functions, which has some merits such as simple expression, explicit meaning, is given by using the matrix analysis method; then the conception of "two steps method" for optimizing parameters is brought forward based on the practical working procedure, and it provides theory basis for quality control.Fifthly, according to the rules of sheet metal forming and combining the modeling method which is put forward in paper with modern control theory, the application of state space theory and analyzing method of time series is studied during the forming process; closed loop control system of forming processes base on fore mentioned theory is proposed; the error of sheet draw-in is transformed into variable blank-holder force which is the input of the control system, so the parts quality is ensured. The simulation results indicate that this control system has some strongpoint such as simple, feasible and high control precision.Finally, using an automobile part as an object, numerical simulation and experiment are developed. The simulation results match with the forming experiment results. According to the research conclusion of the fifth chapter in this dissertation, the qualitative analysis is done, and the possible reason of quality defection is found out. The experiment is done under the conclusion of qualitative analysis too. The experiment results indicate that the results of simulation are credible and the quality defection problem of sheet metal forming is solved effectively, and success rate for forming is improved from 50% to 95%.