本文選題：塑性加工 + 拉伸成形�。� 參考：《吉林大學(xué)》2016年博士論文

【摘要】：拉伸成形工藝具有工件回彈小,成形精度高的優(yōu)點(diǎn),是飛機(jī)蒙皮成形的主要方法。隨著航空工業(yè)的快速發(fā)展,機(jī)型更新?lián)Q代加快,蒙皮零件的需求量日益增加,形狀呈現(xiàn)個(gè)性化、復(fù)雜化的趨勢(shì)。傳統(tǒng)拉伸成形工藝材料利用率低,板料貼模困難,很難成形復(fù)雜的曲面件,難以滿足現(xiàn)代生產(chǎn)的要求。因此,亟需更先進(jìn)的拉伸成形工藝解決這一問(wèn)題。高柔性拉伸成形工藝將離散化的思想應(yīng)用于拉伸成形的模具和加載機(jī)構(gòu),使模具和加載機(jī)構(gòu)同時(shí)具有高柔性。使用數(shù)字化多點(diǎn)模具代替?zhèn)鹘y(tǒng)的整體模具,實(shí)現(xiàn)一套多點(diǎn)模具可以成形多種三維曲面件的目的。使用多夾鉗式柔性拉伸成形設(shè)備代替?zhèn)鹘y(tǒng)的拉伸成形機(jī),使板料貼模更容易,減小拉伸成形過(guò)渡區(qū),降低板料拉裂、起皺傾向,提高材料利用率和成形質(zhì)量,可以成形復(fù)雜曲面件。本文通過(guò)數(shù)值模擬方法對(duì)比分析了復(fù)雜曲面件的傳統(tǒng)拉伸成形和高柔性拉伸成形工藝;探討了工藝條件對(duì)高柔性拉伸成形結(jié)果的影響;研究了基本體球頭半徑、固定單元和擺頭單元、整體彈性墊和離散彈性墊對(duì)高柔性拉伸成形的影響,并應(yīng)用高柔性拉伸成形裝置進(jìn)行了相關(guān)的試驗(yàn)。本文主要內(nèi)容和研究結(jié)論如下:1.闡述了高柔性拉伸成形原理與特點(diǎn)探討了傳統(tǒng)拉伸成形工藝原理,指出其應(yīng)用范圍及成形局限;研究了高柔性拉伸成形裝置的結(jié)構(gòu)及成形原理,對(duì)模具和加載機(jī)構(gòu)的柔性化特征進(jìn)行了探討;研究了高柔性拉伸成形過(guò)程中板料的應(yīng)力應(yīng)變關(guān)系和拉力等問(wèn)題。與傳統(tǒng)拉伸成形工藝相比,高柔性拉伸成形工藝具有一模多用、貼模容易、成形質(zhì)量高、成形范圍廣、材料利用率高等優(yōu)點(diǎn)。2.建立了高柔性拉伸成形過(guò)程有限元模型闡述了數(shù)值模擬板料變形問(wèn)題所涉及的彈塑性有限元理論、動(dòng)力顯式方法中的顯式時(shí)間積分、顯式方法的穩(wěn)定性等問(wèn)題;探討了高柔性拉伸成形有限元模型建立過(guò)程中的單元選擇、材料模型、接觸和摩擦處理等問(wèn)題,建立高柔性拉伸成形有限元模型。3.研究了復(fù)雜曲面件的高柔性拉伸成形以扭曲件、梯形輪廓曲面件和雙曲頂件為研究對(duì)象,進(jìn)行了傳統(tǒng)拉伸成形和高柔性拉伸成形過(guò)程的數(shù)值模擬分析。結(jié)果表明:扭曲件和梯形輪廓曲面件用高柔性拉伸成形工藝成形比用傳統(tǒng)拉伸成形工藝成形時(shí)更容易貼模,成形質(zhì)量更高;在拉伸成形力相同時(shí),用高柔性拉伸成形工藝成形雙曲頂件,板料能夠完全貼模,無(wú)拉斷現(xiàn)象;而使用傳統(tǒng)拉伸成形工藝成形,板料不能完全貼模,甚至出現(xiàn)拉斷現(xiàn)象。數(shù)值模擬結(jié)果說(shuō)明高柔性拉伸成形工藝可以較好地成形復(fù)雜曲面件。用高柔性拉伸成形裝置對(duì)上述三種復(fù)雜曲面件進(jìn)行拉伸成形試驗(yàn),成形效果良好,驗(yàn)證了數(shù)值模擬的正確性。4.探討了不同工藝條件下的高柔性拉伸成形針對(duì)梯形輪廓曲面進(jìn)行了高柔性拉伸成形數(shù)值模擬,研究了夾鉗數(shù)量、夾鉗間隙、夾料塊圓角半徑、垂直液壓缸位置和過(guò)渡區(qū)對(duì)成形結(jié)果的影響。結(jié)果表明:夾鉗數(shù)量越多,夾料塊圓角半徑越大,成形件有效成形區(qū)應(yīng)力分布越均勻,應(yīng)變值越小;隨著夾鉗間隙增加,成形件有效成形區(qū)的應(yīng)力、應(yīng)變先減小后增大,夾鉗間隙為10mm時(shí),應(yīng)力、應(yīng)變數(shù)值最小;垂直液壓缸與夾鉗鉗口的距離越短,成形件有效成形區(qū)的應(yīng)力分布越均勻,應(yīng)變值越小,厚度值越大;過(guò)渡區(qū)越小,板料越容易貼模,所需成形力越小,成形件有效成形區(qū)應(yīng)力分布越均勻,應(yīng)變值、厚度減薄率越小。用高柔性拉伸成形裝置對(duì)梯形輪廓曲面件進(jìn)行拉伸成形試驗(yàn),驗(yàn)證了數(shù)值模擬結(jié)果。上述分析說(shuō)明高柔性拉伸成形工藝能夠在很短的過(guò)渡區(qū)內(nèi)對(duì)非矩形板料拉伸成形。5.研究了基本體單元對(duì)高柔性拉伸成形結(jié)果的影響分析了板料拉伸成形過(guò)程中產(chǎn)生壓痕的原因,探討了擺頭單元的結(jié)構(gòu)和成形原理。對(duì)球形件、拋物球形件進(jìn)行高柔性拉伸成形數(shù)值模擬,通過(guò)數(shù)值模擬探討了基本體球頭半徑、固定單元和擺頭單元對(duì)拉伸成形結(jié)果的影響。結(jié)果表明:基本體球頭半徑越大,成形件表面壓痕越小,應(yīng)力、應(yīng)變和厚度分布更均勻,但球頭半徑過(guò)大會(huì)影響成形精度;用擺頭單元多點(diǎn)模具成形時(shí),成形件表面壓痕減小,應(yīng)力、應(yīng)變和厚度分布更均勻,成形效果明顯優(yōu)于用固定單元多點(diǎn)模具的成形效果。使用擺頭單元可以減少?gòu)椥詨|的厚度,進(jìn)一步說(shuō)明了擺頭單元的優(yōu)越性。使用固定單元和擺頭單元多點(diǎn)模具進(jìn)行了相關(guān)的拉伸成形試驗(yàn),試驗(yàn)結(jié)果與數(shù)值模擬結(jié)果吻合。6.研究了彈性墊對(duì)高柔性拉伸成形結(jié)果的影響對(duì)比分析了不同厚度的整體彈性墊對(duì)固定單元和擺頭單元多點(diǎn)模具拉伸成形結(jié)果的影響,以球形件和拋物球形件為研究對(duì)象進(jìn)行了拉伸成形數(shù)值模擬,結(jié)果表明:固定單元和擺頭單元使用整體彈性墊后,成形效果都得到提高。隨著彈性墊厚度的增加,成形件的應(yīng)力、應(yīng)變和厚度分布越來(lái)越均勻,厚度減薄率和壓痕逐漸減小,但回彈量增加。當(dāng)彈性墊厚度為40mm時(shí),固定單元對(duì)應(yīng)的成形件壓痕全部消失,當(dāng)彈性墊厚度為20mm時(shí),擺頭單元對(duì)應(yīng)的成形件壓痕完全消失,說(shuō)明彈性墊厚度相同的情況下,擺頭單元的成形效果更好。對(duì)比分析了不同厚度的離散彈性墊對(duì)固定單元和擺頭單元多點(diǎn)模具拉伸成形結(jié)果的影響。結(jié)果表明:當(dāng)離散彈性墊厚度小于20mm時(shí),隨著彈性墊厚度的增加,成形件的應(yīng)力、應(yīng)變、厚度分布趨于均勻,厚度減薄率減小,成形效果有所提高。通過(guò)上述研究得出結(jié)論:在實(shí)際生產(chǎn)中應(yīng)根據(jù)具體情況合理選擇整體彈性墊厚度;離散彈性墊只能在一定厚度范圍內(nèi)提高成形效果;使用離散彈性墊可以減少對(duì)整體彈性墊的使用,降低搬運(yùn)強(qiáng)度,提高生產(chǎn)效率;擺頭單元與離散彈性墊配合使用能夠減少或者不使用整體彈性墊,進(jìn)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.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：TG306

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