Two-step shear bending of tube with small bending radius for satisfying both space conservation and inner gas/liquid fluidity

This paper presents a new shear bending method of tubes for controlling bending radius, of which the target value at the neutral plane is 0.5 times the tube diameter. The method consists of two steps using a pair of mandrels. The first step makes a space inside the tube, and the second step inserts a new mandrel into the space for transferring the mandrel shape to the bent part. As a result, the bending radius becomes a target radius, which has never been achieved by conventional shear bending, the bending radius of which has always been zero.     

镁合金管材挤压工艺及组织性能研究

对镁合金管材挤压成形进行了工艺实验研究,确定了其成形工艺参数,分析了镁合金管材挤压成形时变形力的变化规律和组织性能变化。研究结果表明,镁合金管材挤压成形时必须严格控制坯料温度、模具预热温度、润滑剂、挤压速度、挤压比等工艺技术参数。以上工艺参数对挤压力均有不同程度的影响。     

Fundamentals of the incremental tube forming process

The manufacture of bent tubes made of high-strength materials requires high bending loads, which lead to large springback and eventually distortion of the cross-section. The incremental tube forming process allows significant reduction of the bending moment. This is achieved by combining the continuous bending process with an incremental tube spinning process. The paper describes an analytical model to predict the bending moment reduction as a function of the superposed spinning process parameters. Experimental results are provided to validate the theoretical results. This model allows the design and optimization of the incremental tube forming process with low springback.     

6061铝合金管材热挤压成形模拟分析

铝合金管材热挤压时,采用空心铸锭无润滑穿孔针工艺,管材内表面质量好,但穿孔力大,断针频繁。以外径460mm,壁厚15mm的铝合金管材为研究对象,利用Forge软件对其采用空心铸锭无润滑穿孔针的热挤压成形过程进行模拟。结果表明,挤压前期,铸锭由镦粗进入挤压状态,铸锭内孔与穿孔针经历了接触、分离和再接触的过程,铸锭外圆与挤压筒先是局部接触,而后向两端延伸,至全长接触前,铸锭整体沿长度方向呈鼓形。挤压力和穿孔力峰值同时出现在铸锭头部进入模具工作带时,穿孔力峰值约为挤压力峰值的1/4。     

增压条件下充液旋压成形内螺旋翅片铜管

对增压条件下充液旋压成形内螺旋翅片铜管机理进行了系统的研究,着重分析了加工过程中形成动压油楔的条件并建立了数学模型。理论分析和实验结果表明：随着旋速、润滑油粘度及供油压力提高,流体楔动压作用逐渐明显,此时,被加工管的拉拔力减小,且加工后管外表面粗糙度值减小。     

Tube/tube joining technology by using rotary swaging forming method

With the development of the manufacturing technology, a challenge has been proposed on the joining of difficult welding materials and the poor connection interface of materials. In this paper, rotary swaging technology is utilized as a joining by plastic deformation forming method to join tube/tube parts with different diameters. Experimental set-up of rotary swaging forming was designed and fabricated, in which the forging energy can be adjusted by changing the rotation speed of AC server motor. The rotary swaging model and tension testing model are established by using FE simulation software Forge 2D. The effects of forming parameters on the tension strength of the joined tubes and the joining mechanism are investigated. The results show that a concave arc joint can be formed at the overlapping parts of the tubes. To obtain the high joining strength, the distance from the end of the inner tube to the center of the hammer die need to exceed a certain value. The maximum strain and stress occur at the concave arc joining region in which the thickness variation of the two joined tubes is small. To exam the joining strength, the tension test was performed. The two tubes tend to slide out during tension process and the maximum stress occurs at the relative sliding region. The ratio on tensile load of the joined tubes to the maximum tensile load of the single tube can reach to 68% for the inner tube and 47% for the outer tube. Therefore, the joining strength of the tube/tube parts, formed by using rotary swaging method, is enough high.     

铜包钢复合线材的挤压成形工艺试验

对采用挤压法制造铜包钢双金属导线的工艺参数作了全面实验研究,并与其它方法进行了对比分析。研究表明变形程度、摩擦条件及挤压后热处理规范对两种金属的焊合强度影响最大。给出了这些参数较合理的配合。     

A new method for production of variable thickness aluminium tubes: Numerical and experimental studies

Tube drawing is one of the mostly used techniques for producing tubes in various sizes. In this method, tube passes through the die and mandrel to produce constant wall thickness tube. In some applications like transportation industry, design necessities cause requirement for these kinds of tubes. Furthermore some manufacturing processes like tube hydroforming dictate have a tube with variable thickness. In this study, with a modification made to the classical tube drawing process, the sinking and fixed-mandrel tube drawing methods were mixed together to produce tubes with variable thickness in the axial direction. An optimization method, namely the leapfrog optimizer for constrained minimization, was coupled with a finite element model to study design specifications i.e. effect of initial tube geometry on this new process. The obtained results from finite element method (tube drawing force, the minimum and maximum final thickness of tube) were compared with the experiments performed in the designed and manufactured machine and acceptable agreement was observed. Based on these results, the maximum and minimum thicknesses in the final produced tube are mostly dependent on the thickness and outer diameter of initial tube respectively.     

Numerical simulation and experimental study on the tube sinking of a thin-walled copper tube with axially inner micro grooves by radial forging

The current work presents a simulation and experimental study on the formation characteristics of sinking thin-walled copper tube with axially inner micro grooves (TCTAIG) through radial forging. A finite element (FE) model is established. The deformation of grooves, distribution of equivalent stress and strain, and the effects of process parameters are analyzed using a FE software. Experiments with the same parameter settings are compared with the simulations. The axial elongation and radial shrinkage of TCTAIG can be obtained. The grooves are twisted as helical lines in the sinking zone. The metal flows axially and tangentially. The maximal equivalent stress and strain occur at the bottom of the grooves. The equivalent strain increases as the step increases, and finally stays at a certain value: bottom of grooves, 0.9; outer surface, 0.8; and top of teeth, 0.3. The equivalent strain becomes more uniform, the force of dies reduces, and the elongation ratio decreases with increasing feed speed. The equivalent stress, force of dies, and axial pushing force increases rapidly with increasing shrinkage rate. Apparent collapse occurs and the surface quality of the forged part becomes worse at a low feed speed or a shrinkage rate of 50%.     

Investigation of lubrication effect on the backward extrusion of thin-walled rectangular aluminum case with large aspect ratio

Backward extrusion processes are being increasingly considered for the manufacture of thin-walled rectangular aluminum case with large aspect ratio in lieu of multi-stage deep drawing processes. In order to design an optimized backward extrusion process, it is necessary to determine optimal frictional conditions by studying the effects of lubrication.

In this study, numerical analysis based on the finite volume method is performed for investigating the effects of solid lubricants in aluminum backward extrusion processes. Various shear friction factors are used in the numerical study for investigating the friction effects.

Lubrication is found to have a significant effect on the final shape. Larger friction factors are associated with increased forming heights on the wide side of the rectangular container and decreased forming heights on the narrow side. Lubrication is also found to have a significant effect on earing phenomena and a friction factor of 0.2 is found to be optimal for minimizing it. The analysis results presented herein are further validated by comparing them with experimental results.     

On a new concept of rotary draw bend-die adaptable for bending tubes with multiple outer diameters under non-mandrel condition

A traditional rotary draw bending die on the numerically controlled (NC) tube benders or other benders can bend tubes with only one kind of outer diameter. It is difficult for such a situation to meet the requirement of modern manufacturing with characters of much varieties and small batch. The present study proposed a new concept of rotary draw bending die called MDB-Die (Multiple-diameter Bending Die), on which tubes with different outer diameters within a definite range can be bent using the same die by only adjusting the pads inside the die set. Numerical and experimental approaches were employed to investigate the forming process of tubes with different outer diameters when bent on the MDB-Die, especially on the characters of force and elastic-plastic deformation of tube wall, and the effects of groove shapes and bending parameters on the cross-section distortion and wall thinning in the process. Analytical expressions in simple tube bending based on plastic theories given by Tang (2000) for calculating the magnitude of stresses, together with the wall thickness change, deviation of the neutral axis, and section flattening, were also used for comparison. The result proved that tubes with different outer diameters (from 18 to 25 mm in the study) can be bent successfully on MDB-Die without degrading the bending quality, i.e., the aspect ratios of section distortion of less than 5% and wall thinning of less than 7.8%.     

铜连续挤压的有限体积法数值模拟

对铜母线连续挤压过程的几何模型进行简化,基于MSC.Superforge软件平台,对铜母线连续扩展成形过程进行了数值模拟,确定了压下量为铜杆料直径的25%时为压实轮对铜杆压下量的最佳值,分析了铜连续挤压成形过程中坯料在挤压轮沟槽内的温度分布,指出在铜的连续挤压过程中,坯料的温度上升主要源于坯料的塑性变形.结果显示,铜坯料作用在腔体挡料块上的压力高达528～600 MPa,在坯料镦粗段前偶尔会发生折叠回流,这是造成连续挤压产品表面产生较大气泡和冷拔时断线质量缺陷的重要原因之一.为了避免金属流动造成的产品质量缺陷并提高腔体的使用寿命,应对腔体、挤压轮进行优化设计.     

Simulation of sheet metal extrusion processes with Arbitrary Lagrangian-Eulerian method

An Arbitrary Lagrangian-Eulerian（ALE） method was employed to simulate the sheet metal extrusion process, aiming at avoiding mesh distortion and improving the computational accuracy. The method was implemented based on MSC/MARC by using a fractional step method, i.e. a Lagrangian step followed by an Euler step. The Lagrangian step was a pure updated Lagrangian calculation and the Euler step was performed using mesh smoothing and remapping scheme. Due to the extreme distortion of deformation domain, it was almost impossible to complete the whole simulation with only one mesh topology. Therefore, global remeshing combilaed with the ALE method was used in the simulation work. Based on the numerical model of the process, some deformation features of the sheet metal extrusion process, such as distribution of localized equivalent plastic strain, and shrinkage cavity, were revealed. Furthermore, the differences between conventional extrusion and sheet metal extrusion process were also analyzed.     

采用功平衡法求解管材挤压变形力的对比研究

挤压是制备低塑性难变形金属和合金管材的一种精密成形方法,挤压力是选择挤压设备和校核挤压机部件强度的依据;合理地制定生产工艺规程和设计工模具等需要准确的计算挤压力,因此,求解计算精度高的挤压力计算公式在实际生产中显得尤为重要.本文在球坐标和柱坐标系下,采用功平衡法推导了锥模管材挤压变形力的两种理论计算公式;经生产中反复实验验证,两公式的计算结果都比较接近实测值,平均相对误差分别为6.6%左右、9.6%左右;而相关教材所给主应力法求解的管材挤压变形力公式计算结果的平均相对误差为15%左右.这表明本文推导的理论计算公式具有一定的工程实用性.     

双管带隔筋件隔筋形状对内外管成形的影响

为了获得综合性能良好的某铝合金双管带隔筋挤压件,对提出的整体挤压成形工艺方案进行有限元模拟,模拟结果中存在折叠、挤压力大、局部强度不足等缺陷.针对所产生缺陷进行成形工艺方案改进,并确定优化后的挤压方案为:双筒带隔筋挤压件连皮在中间,隔筋的上端面倒有呈水滴状的圆弧.通过模拟对改进后的工艺进行验证分析,结果表明:过渡圆角的大小对折叠有较大影响,增大圆角可减小材料向筋部流动的阻力,可以改善材料的流动状态,并获得了最优过渡圆角半径.利用设计的模具进行了实验验证,获得了成形质量良好的挤压件.     

Applying the finite-element method to determine the die swell phenomenon during the extrusion of glass rods with non-circular cross-sections

In the case of die-wall adhesion during the extrusion of inorganic glass melts, the emerging rod undergoes an undesired expansion, called the die-swell phenomenon, which impairs the precision of its shape. In order to predict the cross-sectional increase of the rod, a 3-dimensional finite-element model has been developed, which can replace extensive experimental preparatory trials. The results obtained with the aid of computer-based simulated flow show a high level of agreement with corresponding experimental results and confirm the suitability of the procedure presented in this paper. The analysis of the influence that the most important test parameters and some fluid properties have on the die swell, supplies valuable information for extrusion processes currently in use. Furthermore, the suitability of the finite-element method in the case of different die cross-sections as well as in the case of the pull-extrusion process is demonstrated in an exemplary manner.     

用有限元法揭示钣材挤压工艺的成形特点

采用刚塑性有限元法、自编程序对钣材挤压工艺进行了模拟 ,从而获得了钣材挤压成形时的网格畸变图、金属流动图、速度场、等效应力场、等效应变场以及H M无量纲数分布场等结果 ,并进一步揭示了钣材挤压工艺的一些成形特点。此外 ,通过实验获得了钣材挤压成形时的网格畸变照片以及裂纹出现照片 ,其结果与采用有限元法所揭示的结果相一致。     

筒形件强力内旋压工艺的正交试验研究

在筒形件强力内旋压的工艺试验研究中,选取进给率、旋轮前角和变薄率作为试验因子,用正交试验法进行旋压试验。用极差分析法分析了试验结果。结果表明：对旋压力的影响主次顺序为变薄率、进给率、旋轮尺寸;影响旋压力的主要因素是变薄率,变薄率越大旋压力越大;对内表面粗糙度的影响主次顺序为：进给率、旋轮前角、变薄率;影响内表面粗糙度的主要因素是进给率和旋轮前角,进给率和旋轮前角越大,粗糙度越大。     

主应力法和功平衡法求解管材挤压变形力的再探讨

在极坐标系下建立了管材挤压变形力的计算模型,采用主应力法和功平衡法推导了管材挤压变形力的理论计算公式;经生产中反复实验验证,管材挤压变形力的理论计算结果接近实测值,主应力法计算结果的相对误差平均值为11.56%左右,功平衡法计算结果的相对误差平均值为-1.94%左右;而相关文献所给出的主应力法和功平衡法求解的管材挤压变形力公式计算结果的相对误差平均值分别为15%左右和6.6%左右。这表明,本文推导的理论计算公式计算精度高,具有一定的工程实用性。     

1Cr18Ni9Ti薄壁曲面件粘性介质内、外压力成形

薄壁曲面零件的加工常常采用分体成形、组合焊接的方法,所需工序较多。该文提出粘性介质内、外压力成形方法,可以直接整体成形薄壁曲面零件,不需要成形后的组合焊接,并针对直径变化比达35%的1Cr18Ni9Ti薄壁曲面零件进行了内、外压力成形试验和有限元分析,给出了变形过程粘性介质和坯料的流动规律和缺陷的预测分析,研究结果表明,薄壁曲面零件内、外压力成形是可行的。