预应力钢丝缠绕技术在锻造/挤压压机上的应用

探讨了预应力钢丝缠绕技术应用于锻造/挤压压机承载结构的关键因素——预应力钢丝的蠕变特性及其影响。基于对65Mn钢丝高应力低温蠕变的测量结果及预紧力损失计算,证明钢丝蠕变的影响主要集中在压机工作初期和立柱的局部区域,并可以通过增大预紧系数加以有效补偿。对世界第一台预应力钢丝缠绕25MN自由锻/快锻液压机的温度进行了分析和实地测量,钢丝实际工作温度只有50℃。     

50MN预应力钢丝缠绕液压缸关键技术参数的确定

采用理论分析与有限元模拟相结合的方法对预应力钢丝缠绕液压缸关键技术参数进行了研究。将钢丝层简化为单层厚壁圆筒,建立1/4双层圆筒的平面应力轴对称有限元模型,钢丝层施加不同预紧力,得到外压随钢丝层厚度变化的曲线,可确定缠绕应力和钢丝层厚度。建立了参数化6层钢丝缠绕缸筒的1/4平面轴对称应力有限元模型,以不同预紧力递减增量进行遍历计算,以最终钢丝层对缸筒外壁压力的设计值为依据选择合适的钢丝层初始缠绕应力和预应力递减增量。最终确定了预应力钢丝缠绕缸筒关键技术参数,根据这些技术参数设计制造了内压为80 MPa的50 MN液压缸。     

大型高压简体钢丝预应力缠绕微应变测量

大型高压筒体钢丝预应力缠绕是超长缓变过程,筒体内壁微应变最小为40με,相邻缠绕层之间的应变差最小为10με,因而要求测量系统必须具有高精度、实时性两个特征。首创互联网环境下的高精度实时在线微应变测量方法,通过对筒体微应变过程进行分析,搭建能够实时监测并通过网络传输的应变测量系统,实现对缠绕过程的远程监控。将此方法应用于我国首台770 MN橡皮囊液压成形机(简称770)筒形机架钢丝预应力缠绕过程控制,通过对应变数据的分析验证了方法的有效性。同时,还提出了生产过程在线监测筒体形变的方法,对100 MPa成形压力下的筒体形变数据进行采集和对比分析,为高压筒体健康诊断提供了保障。     

模具冷却系统对压铸模具温度场的影响分析

运用有限元分析软件ProCAST,对压铸模进行了压铸过程热分析,用对比的方法定量地研究了冷却水的温度、冷却水管的直径及其位置对模具温度场的影响。结果表明,水温为30、50℃时,模具的温度梯度和升温速率基本一样;冷却水管的位置对模具的温度场影响较大,当冷却水管离型腔表面35mm时模具的升温速率高,热量传递快,而温度梯度低,模具的温度场分布较合理;改变冷却水管的直径,模具的温度变化明显,且采用10.5mm的管径,冷却效果最好。     

现代设计理论和方法及其在锻压机械设计中的应用6 第六讲 结构优化设计(二)

五、应用举例 (一)预应力多层筒体(模具)的优化设计近年来由于静液挤压相冷挤压技术的发展,对超高压挤压筒和凹模的承载能力提出了更高的要求,一般结构的筒体已无法承受,而预应力结构则可以极大地提高其承载能力。施加预应力的方法有两种:多层过盈配合年轮式和高强钢丝缠绕式(见图12和图13),前者已     

绕带式液静挤压机

金属液静挤压对模具与机床的设计提出了一些特殊的问题,本文将解决的方法详细介绍如下。一、挤压筒结构自十九世纪中叶以来,液静挤压原理即已为人们所熟知,但直到最近才作为一种工业过程而得到发展。其主要原因是在解决密封问题和制造高压容器时遇到了困难。在液静挤压时,挤压缸,即挤压筒需要承受30千巴(约30000公斤/厘米～2)的径向内压。要克服由此而产生的应力,就必须对挤压筒予先施加一切向的高压应力。为达此目的,提出了两种可能的解决方案:其一,以环形套热压配合,其二,以钢丝缠绕。     

挤压筒加热系统优化设计

介绍了挤压筒加热现状,并对典型结构为4个加热区的挤压筒加热系统进行了优化设计,指出挤压筒加热应满足内部热量均衡,采用两组热电偶设计能精确地计算出温度值,每个加热区安装一组防过热加热管可以防止挤压筒过热,达到性能最优.并提出了控制盘箱的合理设计理念,在实际使用中取得了显著的经济效益,提高挤压筒使用寿命.     

利用RBF神经网络预测反挤压连杆衬套过程中的挤压力

采用单因素试验法,利用模拟软件Simufact进行了锡青铜连杆衬套反挤压试验,试验选取了挤压温度、凹模圆角半径和挤压比为试验因素,挤压力为评价指标。基于MATLAB软件,建立了挤压因素与挤压力之间的RBF神经网络模型,得到挤压温度、凹模圆角半径、挤压比和挤压力之间的非线性关系。通过试验数据进行RBF神经网络模型训练,然后再用训练好的RBF神经网络模型预测挤压力,并将预测的挤压力值与模拟的挤压力值做对比。结果表明:该神经网络模型能高精度地预测反挤压连杆衬套过程中的挤压力。     

远场涡流-电感耦合效应的数值仿真

在役预应力钢筒混凝土管道结构内部预应力钢丝断裂会引发爆管,威胁长距离调水工程的长期安全稳定运行。基于"远场涡流-电感耦合效应"的电磁检测法可用于检测和定位预应力钢丝断裂区域。应用轴对称有限元方法模拟极低频电磁场从预应力钢筒混凝土管内到管外的传播情况,分析预应力钢丝环绕形成的电感效应和薄钢筒内涡流场的耦合作用,总结预应力钢丝断裂数量对管内壁附近磁感应强度和相位分布的影响规律,为预应力钢筒混凝土管道断丝检测提供初步的理论依据。     

工艺参数与模具结构对压铸模具温度场的影响

运用有限元分析软件ProCAST对压铸模进行了压铸过程热分析,研究了浇注温度、冷却水的温度、冷却水管的直径、以及冷却水管的位置对模具温度场的影响。结果表明,在压铸过程中模具温度呈周期性的变化。冷却水管的直径(即冷却水的流量)可调节模具内部温度变化,采用φ10.5 mm的管径,冷却效果好。改变水温,模具温度变化基本一致。     

液氮冷却模具——提高型材挤压速度的有效途径

在铝合金挤压生产过程中采用液氮带走挤压过程中产生的热量,同时对挤压工作区进行惰性保护,能有效提高挤压生产率、模具寿命及型材质量。分析了铝挤压过程中缺陷产生的原因,介绍了液氮冷却技术的原理。并基于实践经验介绍了该技术的应用方法及注意事项。     

TiZrNiCuBe块体非晶合金激光焊接行为及温度场数值模拟研究

采用数值模拟研究了Ti40Zr25Ni3Cu12Be20块体非晶合金激光焊接过程中的温度场变化和冷却速度变化规律,分析了Ti基非晶合金在激光焊接过程中保持非晶态结构的机理。以高斯表面热源和圆柱体热源相结合的复合热源模型作为焊接热源,考察了不同焊接参数下Ti Zr Ni Cu Be非晶合金在激光焊接过程中的热历史,结合实验结果分别对接头焊缝区和热影响区显微组织变化进行了分析,分别从加热和冷却两阶段给出非晶合金激光焊接接头非晶相得以保持的理论解释。完全非晶态接头的显微硬度测试表明:热影响区体现出较母材以及焊缝区更高的显微硬度,从玻璃转变温度、冷却速度以及屈服强度三者之间关系的角度对该现象进行理论分析,并通过实验验证分析的准确性。     

液氮冷却模具技术在铝型材挤压生产中的应用研究

简要介绍了液氮冷却模具技术的基本原理以及常用的冷却通道布置方法。通过收集现场生产试验数据,分析了铝型材挤压过程中液氮冷却模具技术对模具温度、挤压速度、出料口型材温度及其表面光洁度的影响。结果表明:采用对模垫的液氮冷却技术是可行的;液氮开度值设定为70%时,模具温度显著下降,挤压速度最高提速可达37.5%,出料口型材降温幅度达到最大4.6%,型材表面光洁度明显提高;采用液氮冷却模具技术,大大提高了铝型材生产效率和表面质量。     

扁挤压筒设计

采用扁挤压筒挤压大型宽幅薄壁型材是一种非常有效的方法，它可以实现用高比压挤压大挤压系数，大宽厚比的薄壁宽幅型材。由于扁挤压筒需要在高温、高压、高摩擦等十分恶劣的条件下工作，应力状态十分复杂，而且局部拉应力很大，因此很容易在危险断面产生破裂。为了改进扁挤压筒设计，提高内套强度，通过在扁挤压筒优化扁孔参数基础上对不同比压、不同过盈量的扁挤压筒进行了分析，获得了各种不同情况下扁挤压筒等效应力数值，并给出优化扁挤压筒几何参数及结构。     

Sensitivity analysis of a finite element model for the simulation of stainless steel tube extrusion

In this work, a sensitivity analysis has been performed on a finite element model of glass-lubricated extrusion of stainless steel tubes. Fifteen model parameters, including ram speed, billet and tool temperatures, friction coefficients and heat transfer coefficients, were considered. The aim of the study was to determine the parameters that are most important for the response of the extrusion force. The relationship between the model parameters and the responses was analyzed by a calculation of two different regression models: one linear polynomial model and one model that includes interaction terms. Additional simulations were then carried out to validate the regression models. The results show that the initial billet temperature is the factor that has the strongest impact on the extrusion force within the parameter ranges studied in this work. The goodness of prediction and goodness of fit are very good for both regression models.     

Investigation of thermal behavior on cylinder liner during its boring process

Research was conducted on the effect of cutting conditions on temperature rise of cylinder liner during cylinder-boring process. A finite element method (FEM) model was developed to confirm suitable cutting conditions by predicting the temperature distribution in a cylinder liner and thermal expansion of the cylinder liner. To analyze the temperature distribution in the cylinder liner during machining, the partition of the total heat generated during machining which flows into the cylinder liner has to be investigated. A method combining experiment with analysis, called an “inverse heat transfer method”, was used to estimate the heat percentage flowing to the cylinder liner in this paper. To capture the required data for the inverse heat transfer method, sets of dry and wet boring experiments were conducted to estimate the temperature distribution in the cylinder liner wall and the cutting force during machining. The influence of the cutting conditions (for example: cutting speed, feed rate, depth of cut, cutting fluid) on the cutting force and temperature distribution in a cylinder during machining was investigated, and the heat partition flowing to the workpiece under various cutting conditions (especially, under high-speed cutting, with a maximum cutting speed up to 900 m/min) was then determined. A three-dimensional FEM analysis model was developed to simulate the temperature distribution in the cylinder liner and thermal expansion of the cylinder liner during machining. Then, the suitable cutting conditions in cylinder boring were confirmed by FEM analysis. To investigate the influence of the air cooling on the temperature distribution in the cylinder liner after machining, the change of temperature distribution in the cylinder liner under air cooling was predicted.     

基于数值模拟的铝型材挤压变形规律的研究(I)

采用有限变形弹塑性有限元方法 ,以型材挤压过程的有限元模拟为基础 ,研究了局部挤压比、挤压带面积和模孔距离对金属流动速度的影响 ,获得了型材挤压过程的一般变形规律。     

Numerical Simulation and Experimental Study on Porthole Die Extrusion Process of LZ91 Mg-Li AlloyEI北大核心CSCD

Porthole die extrusion is the dominant process to produce hollow profiles due to its high productivity and capacity in producing complex profiles. In this study, the finite element simulation model of porthole die extrusion of LZ91 Mg-Li alloy was established. The effects of extrusion ratio on strain, temperature and flow velocity were studied, and the welding quality was quantitatively evaluated by means of J criterion. The experiments of porthole die extrusion were carried out by varying extrusion ratios. The microstructures of as-cast, homogenized and extruded LZ91 Mg-Li alloy were examined. The results show that the materials near the bridge surface and at the bottom of the bridge have large deformation, while the materials inside the portholes have small deformation. Moreover, with the increase of extrusion ratio, the effective strain of material is increased. Due to the heat generated by plastic deformation and the heat dissipation caused by profile cooling, the temperature of the material on the top of bridge is increased, while that of the material near the die exit becomes lower. The welding quality in the central area of weld seam is lower than that in the edge area of weld seam. With the increase of extrusion ratio, the welding quality is improved. More nucleation is generated in welding zone due to its large strain, resulting in the formation of fine grains. However, the dynamic recrystallization is not complete in the matrix zone, and some coarse grains still remain. Moreover, the material temperature becomes higher with high extrusion ratio, and the phenomenon of grain growth is observed.     

内燃机用保护螺母温挤压成形模具设计及ANSYS分析

研究了DF7C型内燃机车中的气缸螺栓保护螺母的温挤压成形工艺,确定了其成形毛坯、挤压温度、模具预热温度、模具的冷却与润滑方式等.设计了温挤压成形时阶梯轴型凸模和组合式凹模的模具结构,并利用ANSYS软件对其强度进行了有限元分析.结果表明,所设计的气缸螺栓保护螺母的模具结构是合理的,满足生产要求.经实际生产证明,该零件的下料重量由原来自由锻生产的3.85 kg下降为现在的1.3 kg,材料的利用率由原来的22.7%提高到现在的83.6%,每年可节省钢材4t多.这为生产相似零件提供了有益的依据和成功的经验.     

薄板坯在二冷区内温度场的数值模拟

研究了薄板坯在二冷区冷却的不同计算方法对传热现象的影响。采用两种完全不同计算方法即monotonic cooling approach MCA和fluctuated cooling approach FCA计算换热系数和温度。计算中采用二维传热模型对温度分布进行计算。对不同冷却方式的结果进行了比较和讨论。结果显示,FCA比MCA的计算结果准确,能更好地反映每对辊之间的换热系数。