复杂拉形件高柔性拉伸成形工艺及数值模拟研究

发布时间：2018-07-05 08:06

本文选题：塑性加工 + 拉伸成形　；参考：《吉林大学》2016年博士论文

【摘要】：拉伸成形工艺具有工件回弹小,成形精度高的优点,是飞机蒙皮成形的主要方法。随着航空工业的快速发展,机型更新换代加快,蒙皮零件的需求量日益增加,形状呈现个性化、复杂化的趋势。传统拉伸成形工艺材料利用率低,板料贴模困难,很难成形复杂的曲面件,难以满足现代生产的要求。因此,亟需更先进的拉伸成形工艺解决这一问题。高柔性拉伸成形工艺将离散化的思想应用于拉伸成形的模具和加载机构,使模具和加载机构同时具有高柔性。使用数字化多点模具代替传统的整体模具,实现一套多点模具可以成形多种三维曲面件的目的。使用多夹钳式柔性拉伸成形设备代替传统的拉伸成形机,使板料贴模更容易,减小拉伸成形过渡区,降低板料拉裂、起皱倾向,提高材料利用率和成形质量,可以成形复杂曲面件。本文通过数值模拟方法对比分析了复杂曲面件的传统拉伸成形和高柔性拉伸成形工艺;探讨了工艺条件对高柔性拉伸成形结果的影响;研究了基本体球头半径、固定单元和摆头单元、整体弹性垫和离散弹性垫对高柔性拉伸成形的影响,并应用高柔性拉伸成形装置进行了相关的试验。本文主要内容和研究结论如下:1.阐述了高柔性拉伸成形原理与特点探讨了传统拉伸成形工艺原理,指出其应用范围及成形局限;研究了高柔性拉伸成形装置的结构及成形原理,对模具和加载机构的柔性化特征进行了探讨;研究了高柔性拉伸成形过程中板料的应力应变关系和拉力等问题。与传统拉伸成形工艺相比,高柔性拉伸成形工艺具有一模多用、贴模容易、成形质量高、成形范围广、材料利用率高等优点。2.建立了高柔性拉伸成形过程有限元模型阐述了数值模拟板料变形问题所涉及的弹塑性有限元理论、动力显式方法中的显式时间积分、显式方法的稳定性等问题;探讨了高柔性拉伸成形有限元模型建立过程中的单元选择、材料模型、接触和摩擦处理等问题,建立高柔性拉伸成形有限元模型。3.研究了复杂曲面件的高柔性拉伸成形以扭曲件、梯形轮廓曲面件和双曲顶件为研究对象,进行了传统拉伸成形和高柔性拉伸成形过程的数值模拟分析。结果表明:扭曲件和梯形轮廓曲面件用高柔性拉伸成形工艺成形比用传统拉伸成形工艺成形时更容易贴模,成形质量更高;在拉伸成形力相同时,用高柔性拉伸成形工艺成形双曲顶件,板料能够完全贴模,无拉断现象;而使用传统拉伸成形工艺成形,板料不能完全贴模,甚至出现拉断现象。数值模拟结果说明高柔性拉伸成形工艺可以较好地成形复杂曲面件。用高柔性拉伸成形装置对上述三种复杂曲面件进行拉伸成形试验,成形效果良好,验证了数值模拟的正确性。4.探讨了不同工艺条件下的高柔性拉伸成形针对梯形轮廓曲面进行了高柔性拉伸成形数值模拟,研究了夹钳数量、夹钳间隙、夹料块圆角半径、垂直液压缸位置和过渡区对成形结果的影响。结果表明:夹钳数量越多,夹料块圆角半径越大,成形件有效成形区应力分布越均匀,应变值越小;随着夹钳间隙增加,成形件有效成形区的应力、应变先减小后增大,夹钳间隙为10mm时,应力、应变数值最小;垂直液压缸与夹钳钳口的距离越短,成形件有效成形区的应力分布越均匀,应变值越小,厚度值越大;过渡区越小,板料越容易贴模,所需成形力越小,成形件有效成形区应力分布越均匀,应变值、厚度减薄率越小。用高柔性拉伸成形装置对梯形轮廓曲面件进行拉伸成形试验,验证了数值模拟结果。上述分析说明高柔性拉伸成形工艺能够在很短的过渡区内对非矩形板料拉伸成形。5.研究了基本体单元对高柔性拉伸成形结果的影响分析了板料拉伸成形过程中产生压痕的原因,探讨了摆头单元的结构和成形原理。对球形件、抛物球形件进行高柔性拉伸成形数值模拟,通过数值模拟探讨了基本体球头半径、固定单元和摆头单元对拉伸成形结果的影响。结果表明:基本体球头半径越大,成形件表面压痕越小,应力、应变和厚度分布更均匀,但球头半径过大会影响成形精度;用摆头单元多点模具成形时,成形件表面压痕减小,应力、应变和厚度分布更均匀,成形效果明显优于用固定单元多点模具的成形效果。使用摆头单元可以减少弹性垫的厚度,进一步说明了摆头单元的优越性。使用固定单元和摆头单元多点模具进行了相关的拉伸成形试验,试验结果与数值模拟结果吻合。6.研究了弹性垫对高柔性拉伸成形结果的影响对比分析了不同厚度的整体弹性垫对固定单元和摆头单元多点模具拉伸成形结果的影响,以球形件和抛物球形件为研究对象进行了拉伸成形数值模拟,结果表明:固定单元和摆头单元使用整体弹性垫后,成形效果都得到提高。随着弹性垫厚度的增加,成形件的应力、应变和厚度分布越来越均匀,厚度减薄率和压痕逐渐减小,但回弹量增加。当弹性垫厚度为40mm时,固定单元对应的成形件压痕全部消失,当弹性垫厚度为20mm时,摆头单元对应的成形件压痕完全消失,说明弹性垫厚度相同的情况下,摆头单元的成形效果更好。对比分析了不同厚度的离散弹性垫对固定单元和摆头单元多点模具拉伸成形结果的影响。结果表明:当离散弹性垫厚度小于20mm时,随着弹性垫厚度的增加,成形件的应力、应变、厚度分布趋于均匀,厚度减薄率减小,成形效果有所提高。通过上述研究得出结论:在实际生产中应根据具体情况合理选择整体弹性垫厚度;离散弹性垫只能在一定厚度范围内提高成形效果;使用离散弹性垫可以减少对整体弹性垫的使用,降低搬运强度,提高生产效率;摆头单元与离散弹性垫配合使用能够减少或者不使用整体弹性垫,进一步提高成形效果。
[Abstract]:The tensile forming process has the advantages of small rebound and high forming precision. It is the main method of aircraft skin forming. With the rapid development of the aviation industry, the updating and replacement of the machine model is accelerated, the demand of the skin parts is increasing, the shape is personalized and the trend of complexity. The utilization rate of the material of the traditional drawing process is low and the sheet material is stuck to the mold. It is difficult to form complex curved surface parts, which is difficult to meet the requirements of modern production. Therefore, it is urgent to solve the problem with more advanced drawing process. The idea of high flexible stretching is applied to the mold and loading mechanism of the tensile forming, so that the mold and the loader are flexible at the same time. Instead of the traditional whole mold, a set of multi point die can form a variety of three dimensional surface parts. The multi clamp flexible drawing equipment is used instead of the traditional drawing machine to make the sheet metal die easier, reduce the transition zone of the drawing forming, reduce the cracking of the sheet material, raise the wrinkling tendency, and improve the material utilization and forming quality. In this paper, the traditional drawing and flexible drawing process of complex curved surface parts are compared and analyzed by numerical simulation method. The influence of process conditions on the result of high flexible stretch forming is discussed, and the radius of the ball head, the fixed element and the single element of the pendulum, the whole elastic cushion and the discrete elastic cushion are studied. The main contents and conclusions of this paper are as follows: 1. the principle and characteristics of the high flexible stretch forming are discussed and the principle of the traditional drawing process is discussed, its application range and the forming limitation are pointed out, and the structure and forming of the high flexible stretch forming device are studied. The flexibly characteristics of the mold and the loading mechanism are discussed, and the stress strain relationship and tension of the sheet in the high flexible stretch forming process are studied. Compared with the traditional drawing process, the high flexibility drawing process has a multi-purpose mold, easy to die, high forming quality, wide forming range and high material utilization ratio. Point.2. established the finite element model of the high flexible stretch forming process, and expounded the elastoplastic finite element theory, the explicit time integral and the stability of explicit method in the numerical simulation of the sheet deformation, and discussed the element selection and material model in the establishment of the finite element model of the high flexible stretch forming. The high flexible tensile forming finite element model.3. is established to study the high flexible tensile forming of the complex curved surface parts with the distortion parts, the trapezoid contour surface parts and the hyperbolic top parts as the research objects, and the numerical simulation analysis of the traditional stretching and the high flexible drawing process is carried out. The results show that the twists and trapezium are made. The contour curved surface is more easily moulding than the traditional drawing process. The forming quality is higher than that of the traditional drawing process. At the same time, the double curved top is formed by the high flexible drawing process at the same time. The numerical simulation results show that the high flexible stretch forming process can form the complex curved surface better. The three kinds of complex curved surface parts are formed by the high flexible stretch forming device, and the forming effect is good. The correctness of the numerical simulation.4. is proved to be high under the different process conditions. The flexible stretch forming is used to simulate the high flexible stretch forming of the trapezoidal contour surface. The influence of the number of clamp, the gap of the clamp, the radius of the corner of the clamp block, the position of the vertical hydraulic cylinder and the transition zone on the forming result are studied. The results show that the more the number of the clamp, the greater the radius of the corner of the clamp block, the more the stress distribution in the effective forming area of the forming part is. The smaller the strain value is, as the gap increases, the stress of the forming area is reduced first and then increased. When the clamp gap is 10mm, the stress and strain values are minimum; the shorter the distance between the vertical hydraulic cylinder and the clamp jaw, the more uniform the stress distribution in the forming part is, the smaller the strain value, the greater the thickness, and the smaller the transition zone. The easier the sheet material is to stick to the mold, the smaller the forming force is, the more uniform the stress distribution in the forming area is, the less the strain value and the thinning rate of the thickness. The tensile forming test of the trapezoidal contour surface is carried out with a high flexible stretch forming device, and the numerical simulation results are verified. The above analysis shows that the high flexible drawing process can be in a short transition. The influence of the basic body element on the result of the high flexible stretch forming is studied in the area of.5.. The cause of the indentation in the sheet metal forming process is analyzed. The structure and forming principle of the pendulum unit are discussed. The numerical simulation of the high flexible forming of the spherical and parabolic parts is carried out by numerical simulation. The effect of the radius of the ball head, the fixed element and the pendulum unit on the forming result shows that the larger the radius of the ball head is, the smaller the surface indentation of the forming part, the more uniform distribution of stress, strain and thickness, but the radius of the ball has an influence on the forming precision, and the surface indentation of the forming part decreases when the multi point die is formed with the head unit. The distribution of stress, strain and thickness is more uniform, and the forming effect is obviously better than the forming effect of multi point die with fixed element. Using the pendulum head unit can reduce the thickness of the elastic cushion, and further explain the superiority of the pendulum head unit. The related tensile forming tests are carried out with the fixed element and the multi point die of the pendulum head, the test results and the number of the test are carried out. The results of the value simulation coincide with.6.. The effect of the elastic cushion on the result of the high flexible stretch forming is compared and analyzed. The effect of the whole elastic cushion with different thickness on the result of the drawing forming of the multi point die of the fixed element and the pendulum head is analyzed. The numerical simulation of the stretch forming is carried out with the spherical and parabolic parts as the research object. The results show that the fixed sheet is fixed. When the integral elastic cushion is used, the forming effect is improved. With the increase of the thickness of the elastic cushion, the stress, strain and thickness distribution of the forming parts are more and more uniform, the thickness reduction rate and the indentation gradually decrease, but the rebound amount is increased. When the elastic cushion thickness is 40mm, the indentation of the forming parts corresponding to the fixed element is all disappeared, when the projectile is projectile When the thickness of the pad is 20mm, the indentation of the forming parts corresponding to the pendulum unit completely disappears. It shows that the forming effect of the pendulum head unit is better under the same thickness of the elastic cushion. The effect of the discrete elastic cushion with different thickness on the multi point die drawing of the fixed element and the pendulum unit is compared and analyzed. The results show that the thickness of the discrete elastic cushion is the thickness of the cushion. At less than 20mm, with the increase of the thickness of the elastic cushion, the stress, strain, thickness distribution of the forming parts tend to be uniform, the thinning rate of the thickness decreases and the forming effect is improved. The conclusion is drawn that the thickness of the whole elastic cushion should be rationally chosen in actual production according to the specific conditions; the discrete elastic cushion can only be raised in a certain thickness range. The use of discrete elastic cushion can reduce the use of the whole elastic cushion, reduce the handling strength and improve the production efficiency. The use of the pendulum head unit and the discrete elastic cushion can reduce or do not use the whole elastic cushion, and further improve the forming effect.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG306

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