薄壁管矫直过程中性层位移解析

为进一步揭示薄壁金属管材矫直变形机理,基于薄壁构件弹塑性理论及相关假设建立了薄壁管材矫直变形区的应力应变关系模型,基于此完成了矫直过程应变中性层位移模型的解析,通过对模型变化趋势的分析,证明了位移量随相对反弯半径的增大而减小,并给出了不同金属材料位移模型的应用方法,为深入研究薄壁管材的矫直机理和变形过程提供了理论依据。     

Springback Analysis of Two-Layer Strips in Clad Cold Bimetal Bending

Recently, multi-layer metallic materials are increasingly being employed in a wide variety of industrial applications in order to create materials with combined functions and higher performances. Based on a nonlinear finite element analysis, the present study aims to develop a model for investigating the effects of sheet thickness and position on the springback of a stainless-steel clad aluminum sheet. It addresses three different types of strain hardening models, namely isotropic, cyclic, and Johnson–Cook (JC). A purely empirical approach, JC considers strain, strain rate, and temperature in elastic–plastic deformation. Good agreements are seen between the obtained results and the experimental verification data, therefore it is concluded that the bending behavior of a bi-layer metallic sheet/strip can be accurately predicted by the proposed model.     

CT20钛合金薄壁管材数控冷弯成形行为研究

薄壁管材的小弯曲半径数控弯曲成形十分困难,外侧壁厚减薄是弯管成形中的加工缺陷之一,对于钛合金薄壁管尤为严重。采用模拟与实验相结合的方法,对规格为58 mm×1.5 mm的CT20钛合金管材数控弯曲成形过程中弯曲段的壁厚减薄进行了研究,得到相对弯曲半径对壁厚减薄的影响规律。结果表明,CT20钛合金管材冷弯成形时的极限相对弯曲半径(R/D)为2。     

Setting and realizing process plan for straightening thin- walled tube by multiple cross rolls of equal curvature

Since it was difficult to setting the plan and the unifying curvature- radius precisely when the thin- walled tubes were straightened continuously by the rolls of equal curvature. Therefore, based on the mechanism of unifying- straightening for the multiple cross- rolls straightening machine, the judgment method of the unifying curvature- radius was presented firstly in view of the bending and springback equation of the thin- walled tube, and then the searching method of the minimum unifying curvature- radius was presented subsequently, finally the straightening plans were drawn up for different thin- walled tubes with different initial curvature radii, especially for the thin- walled tube with the large initial deformation which could not be unified by the two cross rolls, the new method was pre- bending, unifying, and straightening, and it was also presented whether a thin- walled tube could be straightened. Some procedures were developed by VB to calculate the example, which is shown that the methods are effective, meanwhile it is found that if the unifying curvature- radius exist for an initial curvature- radius, it will not be sole and will be within a scope, and it is also found that there must be a scope of the initial curvature- radius within which the thin- walled tubes can??t be unified by the two cross rolls.     

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。     

Plastic deformation of asperities during consolidation of plasma sprayed metal matrix composite monotape

The plastic deformation of contacts is a principal densification mechanism during the consolidation of metal matrix composite monotape and alloy powders. Models for predicting their densification rely on the accurate prediction of the stresses required to cause contact deformation. In the past, indentation analysis has been used for this.It gives a simple criterion for yielding; namely, the contact stress must equal 2.97 times the uniaxial yield stress. Here, we analyze the plastic blunting of a hemispherical asperity, and compare it with the indentation result. Using the finite element method we calculate the evolution of contact stress to cause continued deformation using both elastic-perfectly plastic and elastic isotropic hardening constitutive laws and frictionless no slip conditions at the contact interface. The calculations reveal that the yiekd criterion depends on three factors: the evolving asperity shape (elastic constraint), lateral (external constraint), and material hardening. While the onset of fully plastic deformation occurs at roughly the same contact stress for both blunting and indentation (at slightly less than three times the uniaxial yield stress), the stress required to cause continued plastic deformation drops sharply during blunting. The drop in effective flow stress arises from geometric changes which lessen the degree of elastic constraint on the expanding plastic zone. Based on the numerical results, an approximate relation for the normalized contact stress vs asperity deformation has been determined and used to improve existing densification models.     

An exponential hardening model for anisotropic sheet metals

A new exponential hardening rule is brought forward to apply for planar anisotropy strain‐hardening sheet metals. Three exponential hardening relations measured along the rolling direction, 45°‐angle and 90°‐angle direction against rolling direction are just the special cases of this model. Based on this model to solve some plastic deformation problems for anisotropic strain‐hardening materials, some functions and calculating results, such as constitutive relations, forming limit characteristic, springback and other parameters associated with these types of materials, should be more likely to approach real states. So this anisotropic strain‐hardening model is very important for applying sheet metal forming simulation.     

四辊平整机辊系与带材耦合变形有限元分析

 采用大变形弹塑性有限元法将辊系弹性变形与带材弹塑性变形耦合在一起建立四辊平整机三维模型。研究了不同宽度和厚度下工作辊弯辊力对辊系变形、辊缝形状及轧件出口厚度的影响规律。计算结果对平整机设备设计和生产工艺制定具有实际参考价值。所建模型也为轧制过程离线分析提供了一种有力的手段。     

Tube Reversing and Extrusion (TRE) as a Novel Method for Producing UFG Thin Tubes

In the present research, a new severe plastic deformation method has been introduced for producing thin walled tubes with ultrafine grained substructure. The tube reversing and extrusion (TRE) technique was applied to a CP-aluminum and thin walled tubes with ultra-fine grained microstructure were successfully processed. The obtained results from tensile tests at room temperature showed the significant increase in mechanical properties of TRE processed thin walled tubes including yield and ultimate strengths and micro-hardness due to grain refinement. The microstructure evolution and deformation behaviour of commercially pure aluminium under TRE processing was simulated by the constitutive model as a micromechanical approach implemented in the finite element framework. The continuous dynamic recrystallization (the evolution of dislocation density and grain size) of aluminum tubes during TRE was considered as the main grain refinement mechanism in micromechanical constitutive model. Also, the flow stress of material in macroscopic scale was related to microstructure quantities. This was in contrast to the previous approaches in FEM simulations of SPD methods where the microstructure parameters such as grain size were not considered at all. The FEM simulated grain refinement behavior was consistent with the experimentally obtained results.     

一类转向夹送辊主要结构参数的研究

转向夹送辊可分为平送斜出和斜送平出两种类型。从基本工作原理出发建立了斜送平出式转向夹送辊的力学模型，利用弹塑性弯曲变形理论推导出上下夹送辊半径比、偏移距、偏移角以及实际咬入角的定量计算公式，实例计算结果与国外进口设备吻合，为今后该类装置的自主设计提供了有益的参考。     

二十辊轧机支撑辊组变形及板形调控分析

 板带材的产能和质量是一个国家工业水平发展的重要标志,铜板带材的生产能力和地位更加显著。森德威二十辊轧机是冷轧铜板带材轧制生产的关键设备,其最外层A、D支撑辊组的弯曲变形是最重要的板形调整手段之一。支撑辊组鞍座位移变化可以使支撑辊芯轴发生弯曲变形,变形会反映到背衬轴承上并且向下依次传递给中间辊和工作辊,最终影响板厚和板形。传统的假设折线法和超静定梁法将芯轴和背衬轴承考虑为一个整体,而忽略了两者之间的变形对整体支撑辊组变形的影响。因此,基于有限元方法进行仿真拟合各段背衬轴承弯曲变形得到简化后的一次函数表达式,将各段背衬轴承拟合结果汇总进而得到整体的支撑辊组弯曲变形的线性表达式,再结合辊系弹性变形模型和金属塑性变形模型构成的板形预报模型评估支撑辊组变形程度对板形和板厚的影响。研究结果表明,对上辊系中的4个鞍座施加不同的位移组合之后,板厚和板形分布在整个板宽方向上并非局部变化,而是呈现整体的变化趋势,且4个鞍座对板形和板厚的调整效果并不相同;在施加同样的鞍座位移条件下,中部鞍座比边部鞍座对板形和板厚的影响效果更加显著,并且即使在支撑辊组中心两侧施加对称的鞍座位移,其对板厚和板形的影响也是非对称的。     

Effects of Material Properties and Punch Tip Radius on Spring-Forward in 90° V Bending Processes

Bending process is one of the most significant fields of application of sheet metal die. Sheet metals are exposed to some spring-back or spring-forward depending on elastic deformation following bending process. S235JR (1.0038) materials having a thickness of 4 mm were bent with 90° punches having 5 different tip radiuses. The bending process was carried out by making the punch waited on the material for 30 s (30 s wait bending) and by removing the punch without waiting (direct bending). Specimens were prepared in three forms as non-heat-treated, normalized and tempered. At the same time, all experiments were performed at a deformation speed of 25 mm/min. As a result, it was determined that as punch tip radius increased, the amount of spring-forward decreased. Although normalizing process applied to specimens increased the amount of spring-forward, tempering process decreased it. The amount of spring-forward was decreased in 30 s wait bending process.     

钛合金管冷弯回弹及其控制研究现状

钛合金管被广泛应用于航空航天等领域的液压管路系统中。然而,高的屈弹比会导致钛合金管冷弯后产生显著的回弹,而过度回弹会严重影响管路的装配及密封性能。为此,对近年来钛合金管冷弯回弹及其控制问题的研究工作与成果进行了综述,重点介绍了研究钛合金管冷弯回弹问题时通常采用的两种方法及相应的研究成果,主要包括理论解析法和有限元模拟法,并指出应对钛合金管材小角度下的弯曲及回弹进行深入研究,进一步提高管材弯曲理论研究的水平,将有限元模拟法与实验验证充分结合。     

Transverse Bending Characteristics in U-channel Forming of Tailor Rolled Blank

Research on the formability of tailor rolled blank (TRB)is of good practical significance and application value because of the enormous potential of TRB in the aspect of automobile lightweight.However,the forming of TRB is problematic because of the varying properties;especially,springback is a main challenge.The transverse bending (bending axis is perpendicular to the rolling direction)of TRB U-channel was studied through simulation and experiment.The forming characteristics of TRB U-channel during transverse bending were analyzed.The mecha-nisms of forming defects,including bending springback and thickness transition zone (TTZ)movement,were re-vealed.On this basis,effects of blank geometric parameters on springback and TTZ movement were discussed.The results indicate that springback and TTZ movement happen during transverse bending of TRB U-channel.Nonuni-form stress distribution is the most fundamental reason for the occurrence of springback of TRB during transverse bending.Annealing can eliminate nonuniform stress distribution,and thus diminish springback of TRB,especially springback on the thinner side.Therefore,springback of the whole TRB becomes more uniform.However,annealing can increase the TTZ movement.Blank thickness and TTZ position are the main factors affecting the formability of TRB U-channel during transverse bending.     

Effect of Thin Polymer Coatings on the Mechanical Properties of Steel Plates

The influence of powder coatings based on an epoxide polyester mixture on the mechanical properties of the plates made of rolled sheet steel is studied. The influence of 100-μm-thick coatings on the mechanical properties of specimens 0.7–1.5 mm thick is considered. The bending and tensile tests performed at room and elevated temperatures show that the thin coatings weakly affect the mechanical properties of the plates. In particular, the stiffness of the coated plates during tension and bending remains almost the same despite the fact that the elastic modulus of the coated plates is always slightly lower than Young’s modulus of steel because of an increased specimen thickness determined with allowance for the presence of a coating. The influence of the coatings is substantial in compressive stability tests. Under supercritical deformation conditions, the bearing capacity of the coated plates decreases substantially, and their critical stability load on the loss of stability falls by 20–30% (depending on the substrate thickness). This effect can be explained by the influence of the residual thermal stresses that appear in the specimens during coating deposition.     

Material Characterisation for Reliable and Efficient Springback Prediction in Sheet Metal Forming

In this paper, a novel experimental‐numerical methodology for an accurate prediction of springback after sheet forming is presented. An advanced phenomenological material model is implemented in the FE‐code ABAQUS. It includes the Bauschinger effect, the apparent reduction of the elasticity modulus at load reversal after plastic deformation, the strain rate dependence and the elastic‐plastic anisotropy and its evolution during the forming process. The required material parameters are determined from stress‐strain curves measured in tension‐compression tests. These tests are carried out with a special test rig designed to avoid buckling of the specimens during compression. The benefits of this procedure for springback prediction are demonstrated. Additionally, parameters for the phenomenological models are determined from texture simulations.     

非线性组合硬化条件下镁合金板料变形回弹预测

变形回弹作为金属板料成形的主要缺陷之一,如何提高变应变路径条件下的回弹预测精度一直是研究者们面临的难题.本文针对镁合金变形特点,提出了同时考虑同向硬化、动态硬化和屈服圆畸变的本构模型.以0.8 mm厚AZ31B镁合金板料为研究对象,施加不同预拉伸后进行弯曲变形试验,观察了不同预变形对回弹规律的影响.同时结合有限元分析ABAQUS-Explicit (Vumat)和ABAQUS-Implicit (Umat)对板料的变形及回弹过程进行模拟仿真,对比试验与模拟结果,验证动态硬化对于镁合金板料变形回弹的重要影响.      

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。     

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.     

轧制差厚板纵向弯曲回弹规律分析

为了推动轧制差厚板在汽车梁结构件上的应用,以U型件为对象,研究了轧制差厚板的纵向弯曲回弹特性。首先完成了差厚板U型零件纵向弯曲成形数值模拟,分析了差厚板的回弹趋势,讨论了差厚板的应力分布,揭示了差厚板弯曲回弹规律,探讨了差厚板等效应力的影响因素,并通过试验对回弹仿真结果进行验证。结果表明,不均匀的应力分布是纵向弯曲的差厚板U型件沿弯曲轴方向上回弹不一致的根本原因,退火处理能够减小差厚板卸载前后的应力差,从而实现抑制差厚板回弹的作用。差厚板的板料尺寸、厚度、过渡区长度均会对差厚板的等效应力造成较大影响,从而改变差厚板的回弹大小及分布。另外,差厚板零件不同厚度部位的回弹相互牵制,使得各部分的回弹量趋向一致,从而导致差厚板的回弹量均介于薄、厚等厚板之间。