【作者】 张双杰；

【导师】 李强； 李军；

【作者基本信息】 燕山大学 ， 机械设计及理论， 2012， 博士

【摘要】 厚壁管件因其需求量大，应用范围广，是机械制造业中的一种重要零件。实际应用的大部分厚壁管件，均需对所购置的管件进行大量的切削加工才能满足使用要求。因此，存在着低效、高耗等问题。所以，研究高效、低耗的厚壁管件制造方法不仅具有重要的理论意义，而且也有很大的经济效益和社会效益。本文采用理论建模、数值模拟和实验研究相结合的方法，对厚壁管件有芯棒开式冷挤压成形工艺进行了系统的研究。对有芯棒开式冷挤压成形工艺进行了分析，把其分为外缩径内径不变、内扩径外径不变、外缩径内扩径三种变形形式，并确定了影响成形的关键工艺参数为：变形程度ε、模具锥角（凹模锥角2α，芯棒锥角2α′）、摩擦系数μ、坯料原始厚径比t₀/D₀、材料屈服强度σ_s。借助DEFORM软件对有芯棒开式冷挤压工艺进行了模拟分析。通过对应变场的分析，直观地把金属变形过程分为未变形区、变形区和已变形区。形象地模拟出了当参数选择不当发生挤压失效时的变形情况，确定了验证实验中最大镦粗量测量位置。模拟了金属质点的运动轨迹，与理论分析所得流线具有很好的一致性。通过引入流体力学理论建立了厚壁管件有芯棒开式冷挤压成形理论的综合分析方法。依据流体力学的理论，初次引入确定连续变形流动模型的动可容速度场的严格理论方法--流函数法，用速度边界条件和体积不变条件建立运动学许可的连续速度场模型；根据应变速率场与速度场关系求得应变速率场；采用上限法得出了厚壁管件有芯棒开式冷挤压外缩径内径不变、内扩径外径不变、外缩径内扩径三种变形形式统一功率计算公式，建立了力能与各影响参数之间的定量解析式，通过计算得到了一定参数组合下的力能关系。确定了最佳模具半锥角的取值范围：α_opt(α′_opt)=6°¹2°，确定了模具设计的关键参数。根据厚壁管件有芯棒开式冷挤压工艺的失稳判据，得到了厚壁管件有芯棒开式冷挤压外缩径内径不变、内扩径外径不变、外缩径内扩径三种变形形式统一的极限变形程度的理论判据模型；基于极限变形程度的理论模型，研究了各参数组合下的极限变形程度变化规律及成形极限条件，在给定参数范围内，厚径比t₀ / D₀ = 0.15，μ=0.03时，外缩极限变形程度ε_max取值可达41%，相应内扩极限变形程度ε_max最大值为36%，填补了有芯棒开式冷挤压工艺制订时无数据可查的空白。对理论结果进行了实验验证，验证结果表明：理论计算与实验结果最大相对误差小于10%，证明了理论计算的实用性。应用上述研究成果及相关数据，制订了液压支架上典型零件毛坯的节材、高效的挤压工艺，并设计制作了挤压模具。在自行研制的专用挤压机上，成功挤制了液压支架上的典型零件毛坯。为相关零件有芯棒开式冷挤压工艺的制订提供了借鉴和指导。更多还原

【Abstract】 Thick-walled tube is an important manufacturing mechanical parts in a great demandand for a wide range of applications. Most of the required thick-walled pipe in theproduction would meet the using requirements only after a lot of machining, which resultsin low efficiency and material consumption. Therefore, the study on the efficient, low-costmanufacturing method of thick-walled tube has important theoretical significance andgreat economic benefits.In this paper, a lot of the system research on the process parameters related of thethick-walled tube open-die cold extrusion with mandrel technology by a combination ofcombining theoretical modeling, numerical simulation and experimental study.On the basis of preliminary studies, the open-die cold extrusion with mandrel wasanalyzed by dividing into the three kinds of deformation, reducing outer diameter with thesame inner diameter, expanding inner diameter with the same outer diameter and neckingouter diameter with expanded inner diameter. And the critical process parameters weredefined: deformationε, mold cone angle （cone angle of the die 2α, mandrel coneangle2α’） coefficient of frictionμ, billet original thickness to diameter ratiot 0D0, theyield strength of materialσs.The open-die cold extrusion with mandrel was simulated and analyzed. The metaldeformation process was intuitively divided into the unreformed stage, deformation stageand the deformation stage. The failure form of extrusion was simulated when parameterswas not correctly selected, and the measurement of the upsetting value was determined inthe verification experiment. The trajectory of the metal particles which was simulated ingood agreement with the theoretical analysis of flow lines.As the simulation results is discrete, a large of systematic theoretical studies arecarried out in this paper. The comprehensive analysis methods of forming theory is createdfor open-die cold extrusion with mandrel.Based on the theory of fluid mechanics, stream function method was introduced firstlywhich is a rigorous theory of kinematically admissible velocity field to determine thecontinuous deformation flow model. The establishment of a continuous velocity fieldmodel in kinematics was performed by the introduction of stream function and the use ofvelocity boundary conditions and constant volume. strain rate field was obtained based onthe relationship between the strain rate field and velocity field. A unified expanding power calculation formula was deduced using the upper limit method for open-die cold extrusionof the thick-walled tubes with mandrel, including the three kinds of deformation, reducingouter diameter with the same inner diameter, expanding inner diameter with the sameouter diameter and necking outer diameter with expanded inner diameter. The quantitativeanalytic solution was established between the force and energy and the impact forceparameters, the relationship of the force and energy was obtained in the combinations ofcertain parameters. The best mold half cone angle range was detemined:α_opt(α′_opt)=6°¹2°,and the key parameters of the mold design was obtained.According to the instability criterion for thick-wall tube forming by open-die coldextrusion with mandrel, the theoretical criterion model for maximum deformation degreeis obtained for the three kinds of deformation, reducing outer diameter with the same innerdiameter, expanding inner diameter with the same outer diameter and necking outerdiameter with expanded inner diameter. Based on the theoretical maximum deformationdegree model, the variation law of maximum deformation degree in combinations of theparameters is investigated. Whent₀ / D₀ = 0.15，μ=0.03, the max value of the maximumreduction in reducing outer diameter with the same inner is up to 41%. Compounding theis up to 36% in expanding inner diameter with the same outer diameter, which filled theblank of no available data in formulating open die cold extrusion with mandrel.Based on the theoretical and simulated parameters range, targeted, feasibilityexperimental program was designed. A series of typical experiments is conducted and thetheoretical result was verified by experiments. The verification results show that: themaximum relative error of the theoretical calculations and experimental results is less than10%, and the accuracy of theoretical calculations is proved.The extrusion process of the typical part billet with material saving and efficient in ahydraulic cylinder bracket was developed initially by the application of research resultsand related data, and extrusion dies was designed. By the self-developed special extrusionmachine, the successful extrusion of the connecting column billet was realized whichprovides guidance and reference for formulating process of the relevant parts of open diecold extrusion.更多还原