【作者】 张晓斌；

【导师】 孙宇；

【作者基本信息】 南京理工大学 ， 机械工程， 2008， 博士

【摘要】 板料冲压成形是一种十分重要的金属板料塑性加工技术,在工业领域有着极为广泛的应用,已成为先进制造代表技术之一。板料成形过程同时又是一个极为复杂的过程,工业界在长期的生产中积累了丰富的工艺认识和参数选择经验,但随着市场竞争的日益激烈,要求企业对市场的需求作出快速的响应,同时对成形件的质量要求越来越高,现有的认知经验已不能适应现代生产所提出的对问题作出快速响应要求。快速并合理确定模具型面参数和加工过程工艺参数,同时如何以最少的成本,准确地得到成形过程的系统特征,并进行成形件的质量控制,已成为板料冲压成形加工企业在市场中取得立足的根本技术之一,越来越受到了各国工业界和研究人员的日益关注。本学位论文综合运用弹塑性力学、数理统计、现代控制及数值模拟技术等基础理论,在数值模拟的基础之上,以较经济的样本数据,开展板料冲压成形过程系统特征的建模方法研究,同时以此为基础进行模具型面参数和工艺参数优化及冲压成形件的质量控制技术研究,并把对成形过程的系统特征进行定性分析的结果用来指导实际冲压件的试模和生产。论文的主要工作包括:(1)深刻剖析板料的成形性能及影响成形性能的主要因素,科学并系统地研究各类因素与冲压件成形质量的关系;建立板料成形质量的评价标准,为后续的优化目标函数的建模及质量控制打下理论基础;同时根据在长期生产中已积累的丰富的工艺认识,就成形过程中出现的缺陷给出其预防措施;(2)阐述了数值模拟仿真在板料成形过程的作用和意义,详细研究了目前使用最广泛的动态显式有限元的关键技术;针对有限元法在对复杂冲压件的数值模拟仿真中出现的问题(如网格畸变,计算精度不高等),对无网格法做了一些研究;(3)根据数理统计学的分析原理和试验设计方法,研究了高效建模样本的特点及其获取方法;针对传统建模方法需要较多样本的问题和为了高效并准确地对板料成形过程规律进行数学建模,提出了基于偏最小二乘法的板料成形过程建模方法,该方法有效地解决了建模效率和模型精度两者相互制约的问题;(4)在对成形过程进行高效建模之后,根据成形质量的要求,提出了一种以冲压成形件厚度变薄均匀度为质量评价标准的优化目标函数,为优化分析提供了评判的理论依据,并用矩阵分析方法对文献中几种不同质量评价目标函数表达式给出了统一表达式,使优化函数形式简单,意义明确;同时根据实际生产中的工序,提出“二步法”优化参数步骤,为板料成形质量控制提供了理论依据;(5)针对板料成形过程的规律,结合本文所研究的高效建模方法和现代控制理论,研究了状态空间法和时序分析理论在板料成形过程中的应用,提出了基于状态空间法和时序理论的板料成形闭环控制系统,把板料吸入量的误差转化为控制系统的变压边力输入,以达到保证成形件的质量。仿真结果表明该方法具有简单易行,控制精度高等特点;(6)以某型汽车的中地板为研究对象,开展了数值模拟仿真和试验研究。数值仿真结果与实际冲压结果相符。根据本学位论文第五章的研究部分结论,进行定性分析,找到产生质量缺陷的可能原因,并用分析结论来指导了试验研究。试验结果表明,仿真分析结果可信,有效地解决了成形中的质量缺陷问题,成品率从50%提高到95%左右。更多还原

【Abstract】 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%.更多还原