曲面零件连续成形的理论与数值模拟研究及控制软件开发

发布时间：2018-07-28 21:45

【摘要】：曲面零件具有质量轻、流线型好、承载能力强等特点，被广泛应用于工业生产的各个领域。随着经济的发展和社会的进步，对各种曲面件的需求开始从大批量单一产品向小批量或单件多样化的产品转变。模具成形是加工曲面零件的重要方法，但每一种零件都要开发相应的模具，并且模具的设计、调试周期长，尤其加工大型曲面件时，成形设备的体积大、制造成本高。因此，开展新的曲面件成形工艺研究具有重要的理论意义和实用价值。卷板成形是一种传统的连续成形方式，曲面连续成形将传统卷板成形的直辊用可弯曲的柔性辊代替，形成一种快速、高效的板料加工技术，适用于不同形状大型双曲度曲面件的成形。目前，曲面连续成形工艺虽然已有一定的研究工作，但在板料连续成形理论、成形曲面件的精度、数值模拟的有限元模型及成形过程控制等方面还有许多亟待解决的问题，迫切需要进一步深入研究，提高工程应用价值，以融入到现代制造业的行列中。本文通过对连续成形过程中板料双向弯曲变形的理论分析，建立了成形过程横向与纵向形状控制模型，并开发了成形过程控制软件。本文研究的主要内容和结论如下： 1.根据板料连续成形的变形历史，对连续成形过程提出了一种平板横向弯曲与柱面纵向弯曲组合的曲面形成机制。板料连续成形时，在局部变形区先形成横向曲率变为柱面，再由上辊下压使柱面发生纵向弯曲变为双曲度曲面，并通过柔性辊滚动实现板料连续进给完成曲面件的成形。由此可见，曲面连续成形的最终曲率要综合考虑单向弯曲回弹及横向与纵向弯曲的相互影响。基于三种不同的材料模型，给出单向弯曲变形中弯矩与回弹比的计算公式。分析了连续成形过程中横向与纵向弯曲的相互影响，结果表明：纵向成形的曲率越大，对横向弯曲形成的附加弯矩越大，上辊下压前后横向曲率的变化值也就越大；横向弯曲对纵向曲率的影响主要体现在截面形状方面，不同的横向曲率形成不同的横截面形状，纵向压下量不变时在横截面上产生的弯矩和惯性矩不同，使纵向弯曲的相对回弹比随横向曲率的减小呈指数递减。 2.描述了不同曲面件的连续成形原理。根据成形曲面的扫略特性，给出成形曲面的数学描述形式。基于横向回弹及纵向弯曲对横向曲率的影响，对横向目标截面线方程进行补偿，得到上、下柔性辊的轴线方程及每个控制点的调形量，建立了横向弯曲的形状控制模型。分析纵向滚弯成形过程中柔性辊与板料接触点和弯曲角的变化，，考虑纵向回弹和横向曲率对纵向成形的影响，得到上辊下压量与成形目标曲率的关系式，建立了纵向弯曲的形状控制模型。采用本文建立的控制理论与方法进行数值模拟，成形的曲面件精度较高，验证了该方法的有效性。 3.提出了一种连续柔性辊的有限元建模方法。连续柔性辊模型中接触方式为光滑曲线接触，避免压痕产生，提高了成形件的表面质量；应力、应变分布更加均匀；成形曲面件的精度较高。对柔性辊调形过程进行有限元仿真，分析控制点数量对调形形状及成形精度的影响，结果表明：控制点数量越多，调形形状越接近于目标形状，成形曲面件的精度也越高。给出了柔性辊调形误差的补偿方法，补偿后成形曲面件的精度提高，验证了补偿方法的可行性。 4.分析了不同材料和板厚对柔性辊产生的作用力，结果表明：随着弹性模量和屈服强度的增加，板料对柔性辊的作用力提高，随着板厚的增加，对柔性辊的作用力也会增加，而且上辊受到的作用力要大于下辊。分析了材料性能、板厚、上辊下压量、柔性辊形状及下辊中心距对成形误差的影响规律，结果表明：横向与纵向成形误差随弹性模量的增加而减小；随板厚的增加而减小；随上辊压下量的增加而减小；随横向曲率半径的减小而减小；随下辊中心距的增加而增大。给出了横向与纵向弯曲的相互影响曲线，压下量不变时，横向曲率半径增加，纵向曲率半径有减小的趋势；柔性辊形状不变时，上辊压下量增大，横向曲率半径增加。 5.基于给出的连续成形过程横向与纵向的控制理论与方法，在VC++平台开发了曲面连续成形过程的控制软件。该软件主要包括曲面造型模块、工艺参数设置模块、程序计算模块及图形显示模块。曲面造型模块可以实现NURBS曲面重构；工艺参数设置模块的功能是输入设备参数、材料力学性能及板料尺寸；程序计算模块能够根据目标曲面横向与纵向曲率，计算出上辊压下量及柔性辊上每个控制点的调形量；图形显示模块结合OpenGL库函数，用来虚拟显示曲面连续成形过程。 6.开发了连续成形过程的计算机控制系统。应用该系统成形典型曲面件并与数值模拟件进行对比，实验结果与数值模拟结果吻合较好。采用数值模拟方法为部分正高斯曲率和负高斯曲率曲面件建立了控形数据库。通过连续成形过程控制系统实现了不同类型曲面件的成形，以鞍面件和凸面件为目标曲面件，分析成形件表面质量和成形精度，结果证明曲面连续成形工艺加工的曲面件质量和精度都符合要求。
[Abstract]:With the characteristics of light quality, good streamline and strong bearing capacity, curved surface parts are widely used in various fields of industrial production. With the development of the economy and the progress of the society, the demand for various surface parts begins to change from a large quantity single product to a small batch or a single piece of diversified product. The mold forming is the important part of the processing of surface parts. Method, but each part should develop the corresponding mold, and the design of the mold, the long debugging period, especially when the large surface parts are processed, the size of the forming equipment is large and the manufacturing cost is high. Therefore, it is of great theoretical significance and practical value to carry out the research of the new forming process of the curved surface parts.
The roll forming is a traditional continuous forming method. The continuous forming of the curved surface is replaced by a flexible flexible roll formed by the traditional roll forming, forming a fast and efficient sheet metal processing technology, which is suitable for the forming of large hyperbolic surfaces with different shapes. There are still many problems to be solved in the continuous forming theory of sheet metal, the precision of forming surface parts, the finite element model of numerical simulation and the control of forming process. It is urgent to further study in order to improve the application value of the engineering, so as to integrate into the ranks of modern manufacturing. Based on the theoretical analysis of the deformation, a lateral and longitudinal shape control model is established, and the software for forming process control is developed.
The main contents and conclusions of this paper are as follows:
1. according to the deformation history of sheet metal continuous forming, a curved surface forming mechanism is proposed for the continuous forming process. In the continuous forming of the sheet, the transverse curvature is formed into a cylinder in the local deformation zone, and then the vertical bending of the cylinder becomes hyperbolic surface by the pressure of the upper roll, and the flexor is passed through the bending. It can be seen that the ultimate curvature of the continuous forming of the curved surface should take into account the mutual influence of the one-way bending rebound and the transverse and longitudinal bending. Based on three different material models, the calculation formula of the bending moment and the rebound ratio in the unidirectional bending deformation is given. The interaction between transverse and longitudinal bending shows that the greater the curvature of the longitudinal forming, the greater the additional bending moment formed by the transverse bending, the greater the change value of the transverse curvature before and after the pressure of the upper roll; the effect of the transverse curvature on the longitudinal curvature is mainly reflected in the shape of the cross section, and the different transverse curvature forms a different cross section. The bending moment and moment of inertia on the cross section are different when the shape of the plane is fixed and the longitudinal pressure is constant, so the relative rebound ratio of the longitudinal bending decreases exponentially with the decrease of the transverse curvature.
2. the continuous forming principle of different curved surfaces is described. Based on the scanning characteristics of the formed surface, the mathematical description of the forming surface is given. Based on the effect of the transverse springback and longitudinal bending on the transverse curvature, the equation of the cross section line is compensated, and the axis equation of the upper and lower flexible rolls and the adjustment of each control point are established. The shape control model of transverse bending is used to analyze the change of the contact point and bending angle of the flexible roll and the sheet in the process of the longitudinal roll forming, considering the influence of the longitudinal springback and the transverse curvature on the longitudinal forming, and the relationship between the pressure of the upper roll and the shape of the forming target is obtained, and the shape control model of the longitudinal bending is established. The theory and method are used for numerical simulation, and the accuracy of the curved surface parts is relatively high, which verifies the effectiveness of the method.
3. a finite element modeling method for continuous flexible roll is proposed. The contact mode of the continuous flexible roller model is smooth curve contact, avoiding the indentation, improving the surface quality of the forming parts; the stress, the strain distribution is even more uniform; the precision of the forming surface is high. The finite element simulation of the flexible roll profile process is carried out and the number of control points is analyzed. The effect of quantity on shape shape and forming precision shows that the more control points, the closer the shape of the shape to the shape of the target, the higher the precision of the forming surface. The compensation method for the adjustment error of the flexible roll is given. The accuracy of the formed curved surface is improved after the compensation, and the feasibility of the compensation method is verified.
4. the force produced by different material and plate thickness to the flexible roll is analyzed. The results show that with the increase of modulus of elasticity and yield strength, the force of the sheet to the flexible roller is increased. With the increase of the thickness of the plate, the force of the flexible roll will increase, and the action of the top roller is greater than the lower roller. The effect of down pressure, the shape of the flexible roll and the center distance of the lower roll on the forming error, the results show that the lateral and longitudinal forming error decreases with the increase of the modulus of elasticity, decreases with the increase of the thickness of the plate, decreases with the increase of the upper roll down and decreases with the decrease of the transverse curvature radius, and increases with the increase of the center distance of the lower roll. The interaction curve of transverse and longitudinal bending is given. When the pressure is constant, the radius of the transverse curvature increases and the longitudinal curvature radius decreases. When the shape of the flexible roll is constant, the amount of the upper roller is increased and the radius of the transverse curvature increases.
5. based on the lateral and longitudinal control theory and method of continuous forming process, the control software of curved surface forming process is developed on the VC++ platform. The software mainly includes surface modeling module, process parameter setting module, program calculation module and graphic display module. The surface modeling module can realize the reconstruction of NURBS surface; The function of the parameter setting module is the input device parameters, the material mechanics performance and the sheet size. The program calculation module can calculate the amount of upper roll down and the control point on each control point on the flexible roll according to the lateral and longitudinal curvature of the target surface. The graphics display module is used in combination with the OpenGL library function, which is used for the continuous forming of the virtual display surface. Cheng.
6. the computer control system of the continuous forming process is developed. The typical curved surface parts are formed and compared with the numerical simulation parts. The experimental results are in good agreement with the numerical simulation results. The control database is established for the partial positive Gauss curvature and the negative Gauss curvature surface parts by numerical simulation. The forming of different types of curved surface parts is realized. The surface parts of the saddle and convex surfaces are used as the target surface parts. The surface quality and forming precision of the formed parts are analyzed. The results show that the quality and accuracy of curved surface parts are all in accordance with the requirements.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TH164;TG306

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