Effects of Anisotropy in Drawing and Extrusion Processes of Bulk Metal Forming

The effects of anisotropy of axisymmetric materials (round bars, tubes) on metal forming processes are discussed. These effects are strongest for thin‐walled hollow materials in metal forming processes when the wall thickness is not predetermined by the die (tube drawing without mandrel, free extrusion of hollow components). Similarly to the normal anisotropy of sheet metal, a high radial anisotropy increases the resistance against a variation of wall thickness in tube drawing. There are also effects in forming solid materials such as forward extrusion of bars whereby the buckling of cross sections is influenced through the variation of radial anisotropy with the distance from the axis. The favourable anisotropy properties depend on the actual priorities. If, for example, for a metal forming process the material anisotropy results in high compressive stresses this may be favourable for increasing the ductility of the material whereas the increase of the load acting on the tool reduces tool life.     

Friction Coefficient Between Rolling Tube and Mandrel of Full Floating Mandrel Mill

 In the process of steel tube production, continuous tube rolling is the foremost forming procedure and the critical step that decides the dimension precision and the surface quality. In the actual production of the 140 mm full floating mandrel mill in Steel Tube Branch in Baosteel, steel T91 was chosen to be the typical sample, self made rolling force transducer and mandrel velocity testing equipment were used, and a series of comprehensive tests on rolling parameters including the rolling force and mandrel velocity were carried out. After the experiment, the friction state between rolling tube and mandrel was analyzed. The friction coefficient was calculated and the values of 0033-0074 in each mill were obtained. The friction coefficient increases obviously along the rolling direction.     

A three-dimensional model of the spray forming method

A three-dimensional model has been formulated to calculate the shape of the general preform, using vector calculus. The shape of a rod, tube, plate, or irregular preform can be calculated at given spray forming conditions. The shape of a spray-formed rod was analyzed at various spray forming conditions using the three-dimensional model. The effects of spray forming parameters, such as spray distribution parameters, angular velocity of rotation, withdrawal velocity, spray angle, and eccentric distance on rod shape, were analyzed. The most important parameters affecting the shape of rods are the spray distribution parameters and the withdrawal velocity. The dynamic evolution of rod shape with a stepwise variation of the withdrawal velocity during spray forming was investigated. The effect of a stepwise change of the withdrawal velocity was the same as that of the scanning atomizer. The calculated surface profiles were compared with those of spray-formed 7075 aluminum alloy rods prepared on a pilot scale. The calculated results for the surface profiles were in agreement with those of the spray-formed rods.     

工业纯锆三通液压胀形优化新工艺

通过对工业纯锆三通一次液压胀形后的成品率、壁厚分布情况和残留变形应力进行分析,提出工业纯锆三通液压胀形优化新工艺,即两次成形,两次热处理,并将三通下模内芯棒端头改为内半球形或内椭圆形。采用新工艺得到的工业纯锆三通内外表面光滑,外形美观,经100%PT探伤检测,符合JB/T 4730.5—2005Ⅰ级标准,外形尺寸均满足GB/T 27684—2011要求,合格率提高到90%以上,能够满足石油化工等领域中耐腐蚀性能要求较高的工况条件。     

无缝钢管回退式芯棒二辊连轧特性分析

利用有限元软件MSC.Superform对回退式芯棒钢管连轧过程进行数值模拟,探究回退式芯棒二辊连轧钢管的金属变形、力能参数及运动学特点。结果表明:与全浮动芯棒相比,回退式芯棒轧制时金属横向流动较小,降低了孔型开口处金属过充倾向;钢管平均壁厚偏薄,促进了钢管减壁,但可能会造成壁厚收缩;轧制力有一定的降低。与限动式芯棒相比,芯棒轴向力较大,钢管易发生抱棒。     

Finite element analysis of the bulge defect forming and eliminating on tube continuous rolled by full floating mandrel mill

Based on the ABAQUS explicit dynamic simulation platform,the finite element model of single stand mill with restrained mandrel was adopted to research the influence of mandrel - roller velocity ratio (MRVR),mandrel friction and tension between stands on rolling force.The analysis results show that when the MRVR is lower than 1,the rolling force increases obviously with the increase of MRVR and reaches the peak value when the MRVR is about 1.The rolling force increase induced by the MRVR increase is the main reason of the formation of the bulge defect on the tube head and tail at the entering and exiting stage during tube continuous rolling process by full floating mandrel mill,which can be intensified by the increase of mandrel friction coefficient.The rolling force decreases with the increase of tension.As the tension is larger, the rolling force decrease amplitude is larger.The influence of backward tension on rolling force is greater than that of forward tension distinctly.Tension control can be used to decrease the rolling force increase induced by the MRVR increase,which is imposing tension at the same time when the MRVR increases,in order to improve even eliminate the bulge defect,and enhance the tube dimension precision.     

芯辊直径对异形环件热轧变形影响的有限元研究

采用Simufact软件建立了大型异形截面环件辗扩过程的三维有限元模型,模拟计算并揭示了芯辊直径对环件热辗扩过程中的等效应变、轧制力、环件尺寸的影响规律。结果表明:随着芯辊直径的增大,在径向孔型中,会导致金属在环件内表面流动阻力增大,从而使环件内表面等效应变减小,而在轴向方向,上下表面等效应变并没有明显变化;芯辊与环件内表面接触面积变大,使更多金属发生塑性变形,使径向轧制力逐渐增大,而轴向轧制力的变化趋势并无明显变化;在环件尺寸方面,芯辊直径的变化对环件尺寸的影响并不明显。     

冷拔小径精密管生产工艺研究与实践

介绍了冷拔小径精密管生产工艺,分析了成品质量的影响因素。针对小径精密管冷拔道次多及空拔出成品时内、外径尺寸及内表面质量难以保证的问题,采用了游动芯棒生产工艺及复合外模生产精密管,结果表明,精密管的尺寸精度及内表面质量完全满足标准及用户要求。     

金属雾化过程中气体流场动力学行为

利用流体动力学软件计算了喷射成形雾化室内气体的流场状态，分析了不同导液管出口长度对气体流动的影响，结果表明：雾化室内气体流速随轴向和轻向的位置变化而发生变化，距导液管出口处距离越远，气体速度越低，对于本文选用雾化器，当导液管出头长度小于1mm时，导液管内气体逆流，会造成金属反喷，导液管出口长度大于1mm时，导液管内气体向下流，产生对液态金属的抽吸作用，有利于喷射。     

自动轧管横向壁厚精度研究

摘要：针对自动轧管机轧制薄壁不锈钢管中出现的严重横向壁厚不均问题,借助于三维有限元分析软件Simufact,对X10CrNiTi18不锈钢管典型规格112mm×4.5mm自动轧管过程进行数值模拟。研究了不同轧辊孔型结构参数、芯棒润滑状态、轧辊孔型磨损及穿孔毛管偏心对自动轧管横向壁厚精度的影响。结果表明：随着芯棒摩擦因数的增大,所轧荒管横向壁厚精度明显恶化;偏心毛管轧制所轧荒管依旧偏心,延伸轧制对穿孔毛管偏心壁厚纠偏能力有限;磨损的孔型修模后,采用负芯补轧制较增大芯棒直径轧制所轧荒管横向壁厚不均度增大;采用三段式圆弧孔型,所轧荒管横向平均壁厚更接近目标壁厚,横向壁厚不均度由原孔型的13.55%下降到9.94%,横向壁厚精度明显改善。     

薄壁无缝钢管顶管过程拉凹缺陷研究

摘要：为了解决CPE顶管机组轧制薄壁无缝管实际生产中出现的管壁拉凹问题，基于某钢管公司114mm CPE顶管机组的装备和工艺条件，借助于有限元分析软件Simufact，对42CrMo4钢管典型规格111mm×435mm顶管过程的辊模力、各机架轧件出口壁厚、应力应变及相对滑动速度进行了分析。结果表明，顶管过程中，减壁量较大的机架之间存在张力作用，机架减壁量越大，轧件在辊缝处壁厚减薄量越大；轧件在辊缝处所受到的轴向应力均为拉应力，在靠近轧件头部一段距离内轧件所受到的轴向拉应力较大，发生壁厚拉凹的倾向性增大。机架过大的减壁量和减壁率引起的轧件沿孔型宽度方向的严重不均匀变形、机架间大的张力及芯棒与轧件间过大的速度差引起的芯棒拽入力是顶管过程管壁拉凹缺陷产生的主要原因。     

Peter Groche

Tube hydroforming (THF) is a relatively new but established technology among metal tube forming processes. It is the technology of forming closed sections, hollow parts with different cross‐sections by applying an internal hydraulic pressure and sometimes additional axial compressive loads to force a tubular blank to conform to the shape of a given die cavity. Material properties have a significant influence on the process stability. Often roll‐formed, non‐heat treated tubular materials made of steel with longitudinally oriented welding lines are used in tube hydroforming. Different production processes involve a change of the material properties from the initial flat sheet to the hydroformable tube. Testing methods such as tensile tests and conventional forming limit diagrams do not accurately reflect the state of stress and strain conditions seen in the tubular blank during the hydroforming process. Thus, inaccuracies in FEA predictions and design failures occur. Test methods were developed to characterize the relevant geometrical and mechanical properties of tubular semi‐finished products.     

基于有限元法的PQF连轧过程宽展规律的仿真

 根据PQF连轧孔型及工艺特点,分析了连轧管宽展规律对产品尺寸精度和钢管横截面积的影响,并建立PQF连轧过程三维非线性有限元模型,预报了荒管的尺寸形状,对比某厂现场数据,两者吻合良好。通过对不同孔型、不同规格产品的系列仿真,研究宽展规律的影响因素,分析了延伸系数和空隙率对周长系数的影响,延伸系数和减径率对壁厚系数的影响;并利用多元线性回归分析法得到PQF连轧宽展模型,为PQF连轧孔型设计及产品尺寸精度控制提供了理论指导。     

一种弯头的成型方法

阐述了一种弯头成型方法。采用该方法不仅能够成倍减少推制弯头成型芯棒的数量,降低制造成本,而且使弯头型位公差更易控制,在保证弯头质量的同时极大地提高模具利用率及生产效率。     

Study on transverse wall thickness accuracy of tube rolled by automatic plug mill

In view of serious uneven transverse wall thickness of thin walled stainless steel tube rolled by automatic plug mill，the automatic tube rolling process of X10CrNiTi18 stainless steel tubes with typical specification of 112mm×4.5mm was numerically simulated by using 3D finite element analysis software Simufact. The influence of different roll pass structure parameters, different mandrel lubrication state, roll pass wear and eccentricity of pierced shell on transverse wall thickness accuracy of automatic rolling tube was analyzed. The results show that as the friction coefficient of the mandrel increases, the accuracy of transverse wall thickness of the rolled tube deteriorates obviously. The hollow tube rolled by eccentric pierced shell is still eccentric, and it shows that the elongation rolling has a limited ability to correct the eccentric wall thickness of the pierced shell. With repaired the worn pass, the unevenness of the transverse wall thickness of the rolled tube increases using the negative mandrel compensation rolling compared with the increase of mandrel diameter. The average transverse wall thickness of the rolled tube is closer to the target wall thickness by using three section arc groove, and the transverse wall thickness unevenness decreases from 13.55% of the original groove to 9.94%, and the transverse wall thickness accuracy is obviously improved.     

芯棒直径对楔横轧5Cr21Mn9Ni4 N空心气门壁厚均匀性的影响规律

楔横轧空心轴类件存在壁厚分布不均问题,特别是在小直径大长径比空心件楔横轧成形中更为突出.本文在Gleeble-1500D热模拟实验机上进行了5Cr21Mn9Ni4N耐热钢的热压缩实验,得到了5Cr21Mn9Ni4N的热变形本构方程.通过改变芯棒直径,采用有限元仿真和实验相结合的方法,研究了楔横轧轧制空心气门过程中的壁厚变化规律.研究结果表明,带芯棒轧制时,芯棒直径存在临界值,在该值下进行轧制,空心气门预制坯壁厚均匀性最优;楔横轧空心件时,金属轴向均匀流动是壁厚均匀的必要条件;轧件轴向拉应变减小,径向压应变变大,周向应变在0附近且为拉应变时,壁厚较为均匀.      

Thermo-mechanical finite-element simulation of the tube sinking process

Thermo-mechanical finite-element model of the tube sinking process is presented in this paper. The model combines the rigid-plastic finite element approach, used to determine the velocity field, with the numerical solution of the convective-diffusion equation which accounts for the thermal events in the deformation zone. The condition of zero normal velocity and zero normal stress on the free inner surface of the tube was used to determine the shape of this surface. Typical results of calculations include the distributions of strain rates, strains, stresses and temperatures in the wall of the tube during the sinking process.     

Mathematical models for motile bacterial transport in cylindrical tubes

Mathematical models considering motile bacterial transport within a geometrically restrictive cylindrical tube were developed. Two macroscopic transport parameters, the random motility coefficient as a self-diffusion coefficient of the cell population and the chemotactic velocity as a chemical-induced velocity, were derived. The three-dimensional cell balance equation was reduced to forms similar to Segel's one-dimensional phenomenological cell balance equations with additional modifications for bacteria-wall interactions. Two conceptually different approaches accounting for such interactions were presented. The first approach parallels treatments in the gas kinetic theory by viewing bacterial interactions with walls as collisions and subsequent diffusive/specular reflections, which led to the Bosanquet formula for the bacterial diffusion coefficient. Based on the experimental observation that bacterial swimming motion is guided by a straight tube, the second approach considered modifications in the bacterial swimming orientation as a consequence of various long-range interactions with the tube surface. A phenomenological turning model capable of aligning bacterial motion along a tube axis was proposed. The model predicts that under the geometrical restriction of a small cylindrical tube, the macroscopic bacterial transport resulting from the proposed turning model can exhibit behavior that ranges from dimensionally reduced diffusion to pure wave propagation, depending on the influence of the tube diameter on the reversal probability in the bacterial swimming motion. Our theoretical model provides explicit equations that explain how such a transition can occur. The predicted results were then qualitatively compared with experimental data from the literature. As a preliminary comparison, we concluded that bacterial transport in cylindrical tubes of diameter 10 micrometers remains in the mode of a dimensionally reduced diffusion, and shifts to a wave motion when the tube diameter decreases to 6 micrometers.     

方矩形管端部成型机制

 利用非线性有限元方法,结合实际生产中方矩形管辊压成形过程,建立了有限元仿真模型。基于该模型对7机架实际辊压成型过程进行了模拟运算,得到了成形过程中稳定段处节点位移矢量、应力和应变的分布情况。通过对仿真计算结果的分析,得到管头端面上在角部和边部的过渡区存在着“位移中性面”,在端面上角部和边部的中心处伴有明显的金属“外翻”和“内翻”的情况,仿真结果与现场轧制结果相符。     

Development of a Robot‐Based Sheet Metal Forming Process

This paper describes a new sheet metal forming process for the production of sheet components for prototypes and small lot sizes. The generation of the shape is based on kinematics and is implemented by means of a new forming machine consisting of two industrial robots. Compared to conventional sheet metal forming machines, this newly developed forming process offers a high geometrical form flexibility, and comparatively small deformation forces enable high deformation degrees. The principle of the procedure is based on flexible shaping by means of a freely programmable path‐synchronous movement of the two robots. The final shape is produced by the incremental infeed of the forming tool in depth direction and its movement along the contour in lateral direction at each level of the depth direction. The supporting tool with its simple geometry is used to support the sheet metal and follows the forming tool at the rear side of the sheet metal. The sheet metal components manufactured in first attempts are of simple geometry like frustum and frustum of pyramids as well as spherical cups. Among other things the forming results are improved by an adjustment of the movement strategy, a variation of individual process parameters and geometric modifications of the tools. In addition to a measurement of the form deviations of the sheet with a Coordinate Measurement Machine, screened and deformed sheets are used for deformation analyses. Furthermore, the incremental forming process is analysed with assistance of the finite element method. In total the results show that a robot‐based sheet metal forming with kinematic shape generation is possible and leads to acceptable forming results. In order to be able to use the potential of this process, a goal‐oriented process design is as necessary as specific process knowledge. In order to achieve process stability and safety, the essential process parameters and the process boundaries have to be determined.