Effect of mandrel on cross section quality of thin-walled tube numerical controlled bending

The effect of mandrel with the structure of ball and socket on the cross section quality of thin-walled tube numerical controlled(NC) bending was studied by numerical simulation method, combined with theoretical (analysis) and experiment. Influencing factors of the mandrel include the count of mandrel heads, the diameter of mandrel and its position. According to the principle of NC tube bending, quality defects possibly produced in thin-walled tube NC bending process were analyzed and two parameters were proposed in order to describe the cross section quality of thin-walled tube NC bending. According to the geometrical dimension of tube and dies, the range of mandrel protrusion was derived. The finite element model of thin-walled tube NC bending was established based on the DYNAFORM platform, and key technological problems were solved. The model was verified by experiment. The effect of the number of mandrel heads, the diameter of mandrel and the protrusion length of mandrel on the cross section quality of thin-walled tube NC bending was revealed and how to choose mandrel parameters was presented.

Effect of geometrical parameters on forming quality of high-strength TA18 titanium alloy tube in numerical control bending

The forming quality of high-strength TA18 titanium alloy tube during numerical control bending in changing bending angle β, relative bending radius R/D and tube sizes such as diameter D and wall thickness t was clarified by finite element simulation. The results show that the distribution of wall thickness change ratio Δt and cross section deformation ratio ΔD are very similar under different β; the Δt and ΔD decrease with the increase of R/D, and to obtain the qualified bent tube, the R/D must be greater than 2.0; the wall thinning ratio Δto slightly increases with larger D and t, while the wall thickening ratio Δti and ΔD increase with the larger D and smaller t; the Δto and ΔD firstly decrease and then increase, while the Δti increases, for the same D/t with the increase of D and t.

Deformation behaviors of 21-6-9 stainless steel tube numerical control bending under different friction conditions

For contact dominated numerical control(NC) bending process of tube, the effect of friction on bending deformation behaviors should be focused on to achieve precision bending forming. A three dimensional(3D) elastic-plastic finite element(FE) model of NC bending process was established under ABAQUS/Explicit platform, and its reliability was validated by the experiment. Then, numerical study on bending deformation behaviors under different frictions between tube and various dies was explored from multiple aspects such as wrinkling, wall thickness change and cross section deformation. The results show that the large friction of wiper die-tube reduces the wrinkling wave ratio η and cross section deformation degree ΔD and increases the wall thinning degree Δt. The large friction of mandrel-tube causes large η, Δt and ΔD, and the onset of wrinkling near clamp die. The large friction of pressure die-tube reduces Δt and ΔD, and the friction on this interface has little effect on η. The large friction of bending die-tube reduces η and ΔD, and the friction on this interface has little effect on Δt. The reasonable friction coefficients on wiper die-tube, mandrel-tube, pressure die-tube and bending die-tube of 21-6-9(0Cr21Ni6Mn9N) stainless steel tube in NC bending are 0.05-0.15, 0.05-0.15, 0.25-0.35 and 0.25-0.35, respectively. The results can provide a guideline for applying the friction conditions to establish the robust bending environment for stable and precise bending deformation of tube bending.

A Numerical-analytic Method for Quickly Predicting Springback of Numerical Control Bending of Thin-walled Tube

Springback is one of important factors influencing the forming quality of numerical control （NC） bending of thin-walled tube. In this paper, a numerical-analytic method for springback angle prediction of the process was put forward. The method is based on springback angle model derived using analytic method and simulation results from three-dimensional （3D） rigid-plastic finite element method （FEM）. The method is validated through comparison with experimental results. The features of the method are as follows： （1） The method is high in efficiency because it combines advantages of rigid-plastic FEM and analytic method. （2） The method is satisfactory in accuracy, since the field variables used in the model is resulting from 3D rigid-plastic FEM solution, and the effects both of axial force and strain neutral axis shift have been included. （3） Research on multi-factor effects can be carried out using the method due to its advantage inheriting from rigid-plastic FEM. The method described here is also of general significance to other bending processes.

Effects of process parameters on numerical control bending process for large diameter thin-walled aluminum alloy tubes

Numerical control(NC) bending experiments with different process parameters were carried out for 5052O aluminum alloy tubes with outer diameter of 70 mm, wall thickness of 1.5 mm, and centerline bending radius of 105 mm. And the effects of process parameters on tube wall thinning and cross section distortion were investigated. Meanwhile, acceptable bending of the 5052O aluminum tubes was accomplished based on the above experiments. The results show that the effects of process parameters on bending process for large diameter thin-walled aluminum alloy tubes are similar to those for small diameter thin-walled tubes, but the forming quality of the large diameter thin-walled aluminum alloy tubes is much more sensitive to the process parameters and thus it is more difficult to form.

Significance-based optimization of processing parameters for thin-walled aluminum alloy tube NC bending with small bending radius

Thin-walled aluminum alloy tube numerical control （NC） bending with small bending radius is a complex process with multi-factor coupling effects and multi-die constraints. A significance-based optimization method of the parameters was proposed based on the finite element （FE） simulation, and the significance analysis of the processing parameters on the forming quality in terms of the maximum wall thinning ratio and the maximum cross section distortion degree was implemented using the fractional factorial design. The optimum value of the significant parameter, the clearance between the tube and the wiper die, was obtained, and the values of the other parameters, including the friction coefficients and the clearances between the tube and the dies, the mandrel extension length and the boost velocity were estimated. The results are applied to aluminum alloy tube NC bending d50 mm×1 mm×75 mm and d70 mm×1.5 mm×105 mm （initial tube outside diameter D0 × initial tube wall thickness t0 × bending radius R）, and qualified tubes are produced.

Numerically controlled bending performance of medium strength TA18 titanium alloy tubes under different die sets

The rapid development of aviation and aerospace technologies has led to increased interest in the application of numerically controlled(NC) technology for bending light-weight titanium alloy tubes.In order to study and develop advanced NC bending technology,it is necessary to understand the bending performance of medium strength TA18(Ti-3Al-2.5V,ASTM Gr.9) titanium alloy tubes during NC bending under different die sets.This paper focuses on the bending performance of medium strength TA18 tubes under different NC bending die sets,including the variations in the stress,strain,wall thickness,cross sectional deformation,and defects.The results show that adding a wiper die to the base die set decreases the radial,hoop,and tangential compressive stress and the tangential compressive strain,and adding a mandrel to the base die set also decreases these stresses,but increases the radial and hoop tensile stress and decreases the hoop compressive strain obviously,and brings about a three-dimensional tensile stress concentration where the mandrel provides support.For the NC bending of medium strength TA18 tubes,the flattening of cross section is more sensitive index than the thinning of wall thickness.Introducing a mandrel can improve the flattening of cross section obviously but it has a little worse effect on the thinning of wall thickness,and adding a wiper die to the base die set can inhibit the occurrence of the inside bulge but worsen the flattening of the cross section remarkably.Considering the above effects of the mandrel and wiper die on bending performance,it is reasonable to apply the die set comprising a bending die,clamp die,and pressure die for tubes with a small diameter and the die set including an appropriate mandrel additionally for tubes with a larger diameter,in order to bend the medium strength TA18 tubes with high quality and at low cost.

Integrated Systemfor Tube Bending Digital Manufacturing

An integrated CAD/CAPP/CAM system of tube manufacturing based on integration frame is presented. In this system, two kinds of data conventions describing tube shape are presented in tube CAD subsystem, the object-oriented concept and the goal-driven inference mechanism have been applied in the development of the knowledge-based CAPP subsystem and simulation of tube processing under tube bending simulation subsystem is performed based on the tube model＇s piecewise representation. A tube product case is considered to give the application of the integrated system, and the advantages of the system in the use of tube bending are revealed.

Wall Thinning Characteristics of Ti-3Al-2.5V Tube in Numerical Control Bending Process

A finite element(FE) model for the numerical control(NC) bending of Ti-3 Al-2.5 V titanium alloy seamless tube is established, considering the variation in the contractile strain ratio(CSR) and elastic modulus(E). The wall thinning characteristics of Ti-3 Al-2.5 V tube under different geometric and process conditions were investigated. The results showed that the CSR-E variation can change the wall thickness, but has no remarkable effect on the change characteristics. The reasonable parameter ranges are as follows: a bending-radius range not less than 1.5 times the outer diameter, a bend angle up to 180?, and a mandrel extension of 0-3 mm. The friction coefficient between the pressure die and the tube should be in the range of 0.20-0.35, and between the bending die and the tube should be in the range of 0.05-0.15. As long as the performance meets the requirements, the relative push-assistant speed should be as small as possible.

Forming Characteristics of Al-alloy Large-diameter Thin-walled Tubes in NC-bending Under Axial Compressive Loads

Tube thinning control without wrinkling occurring is a key problem urgently to be solved for improving the forming qualities in numerical control （NC） bending processes of large-diameter Al-alloy thin-walled tubes （AATTs）. It may be a way solving this problem to exert axial compression loads （ACL） on the tube end in the bending. Thus, this article establishes a three-dimensional （3D） elastic-plastic explicit finite element （FE） model for the bending under ACL and has its reliability verified. Through a multi-index orthogonal experiment design, a combination of process parameters, each expressed by a proper range, for this FE model is derived to overcome the compression instability on tube ends. By combining the FE model with a wrinkling energy prediction model, an in-depth study is conducted on the forming characteristics of large-diameter AATTs with small bending radii and it can be concluded that （1） The larger the tube diameters and the smaller the bending radii, the larger the induced tangent tension stress zones on tube intrados, by which the tube maximum tangent compression stress zones will be partitioned in the bending processes; thus, the smaller the ACL roles in decreasing thinning degrees and the larger the compression instability possibilities on tube ends. （2） The tube wrinkling possibilities under ACL are larger than without ACL acting in the earlier forming periods, and smaller in the later ones. （3） For the tubes with a size factor less than 80, the ACL roles in decreasing thinning degrees are stronger than in increasing wrinkling possibilities.

A Study on Multi-defect Constrained Bendability of Thin-walled Tube NC Bending Under Different Clearance

Thin-walled tube numerical control （NC） bending is a tri-nonlinear physical process with multi-defect and multi-die constraints. The clearance on each contact interface is the major factor to indicate the contact conditions. A three-dimensional-finite element （3D-FE） model is established to consider the realistic dynamic boundary conditions of multiple dies under ABAQUS/Explicit platform. Combined with experiment, numerical study on bending behavior and bendability under different clearance between tube and various dies is conducted in terms of wrinkling, wall thinning and cross section deformation. The results show that （1）with smaller clearance of tube-wiper die and tube-mandrel, the wrinkling can be restrained while the wall thinning It and cross-section deformation Id increase; while excessive small clearance blocks tube materials to flow past tangent point and causes piles up, the onset of wrinkling enhances It and Id. （2）Both It and Id decrease with smaller clearance of tube-pressure die; the wrinkling possibility rises with larger clearance on this interface if the mandrel’s freedom along Y-axis is opened; smaller clearance of tube-bend die prevents wrinkling while increases It, and the clearance on this interface has little effect on Id. （3）A modified Yoshida buckling test （YBT） is used to address the wrinkling mechanisms under normal constraints in tube bending： the smaller clearance may restrain wrinkling efficiently; the smaller wall thickness, the less critical clearance needed; the critical clearance for tube bending 38 mm×1 mm×57 mm （tube outer diameter×wall thickness×centerline bending radius） equals about 20% of initial wall thickness.

Deformation Behavior of Medium-strength TA18 High-pressure Tubes During NC Bending with Different Bending Radii

To improve the forming quality and forming limit of the numerical control （NC） bending of high-pressure titanium alloy tubes, in this study, using three-dimensional （3D） finite element method, deformation behavior of medium-strength TA 18 high-pressure tubes during NC bending with different bending radii is investigated. The results show that the cross-sectional deformation and the wall thickness variation during NC bending of TA18 tubes using a small bending radius （less than 2 times of tube outside diameter） are clearly different from that using a normal bending radius （between 2 and 4 times of tube outside diameter）. For bending with a normal bending radius, with or without a mandrel, the distribution of the flattening in the bending area resembles a platform and an asymmetric parabola, respectively. For bending with a small bending radius, with or without a mandrel, the flattening both distributes like a parabola, but the former has a stable peak which deflects toward the initial bending section, and the latter has a more pronounced peak with a bending angle and deflects slightly toward the bending section. The wall thickness variations with a normal bending radius, with and without a mandrel, both resemble a platform when the bending angle exceeds a certain angle. For the bending with a small radius, the distribution of the wall thickness variation without a mandrel follows an approximate parabola which increases in value as the bending angle increases. If a mandrel is used, the thickening ratio increases from the initial bending section to the bending section.

小弯曲半径高强不锈钢管数控绕弯过程应力应变分析

为了揭示小弯曲半径高强不锈钢管数控绕弯成形机理,实现精确成形和有效控制的目的,基于ABAQUS有限元平台建立了小弯曲半径21-6-9高强不锈钢管数控绕弯成形全过程三维弹塑性有限元模型;研究了网格尺寸和质量放大因子对有限元模型计算精度和效率的影响,并从理论和实验方面验证了模型的稳定性和可靠性;分析了小弯曲半径高强不锈钢管数控绕弯全过程应力和应变以及对称平面和典型截面上的应力和应变分布的历史演变规律。获取了合理的网格尺寸和质量放大因子分别为0.6×0.6 mm和3000,以及全过程、对称平面和典型截面上的应力和应变分布规律。

数控弯管中芯棒对管壁厚减薄作用的有限元分析

通过对数控弯管过程的三维有限元模拟 ,获得了芯棒提前量、芯棒与管材间的间隙对管壁厚减薄的影响规律 :( 1)随着芯棒提前量的增大 ,管材壁厚减薄率增大。 ( 2 )当芯棒不提前时 ,随着管材与芯棒间间隙的增大 ,管材壁厚减薄率减小 ;当芯棒提前量在 0 .8E～ 1.2E范围时 ,随着管材与芯棒间间隙的增大 。

基于机器学习的管材数控弯曲质量预测

在管材数控(NC)弯曲过程中,可能出现起皱、过度减薄的质量缺陷,同时会不可避免地发生回弹,都将严重影响成形质量。为了对数控弯曲成形质量进行预测,提出了使用有限元模拟与机器学习相结合的方法,并建立了快速的成形质量预测方法。首先,建立了有效的管材数控弯曲的参数化有限元模型,在工艺参数取值范围中随机选择进行大量的模拟实验作为样本,完成学习数据的挖掘。随后,基于径向基函数(RBF)神经网络建立壁厚减薄与回弹程度的预测模型并使用支持向量机(SVM)建立管材起皱的预测模型。最后,使用模型对新的实例进行预测,并利用模拟与数控弯曲实验对预测模型进行验证。该方法可以对大直径薄壁管材数控弯曲质量进行有效的预测,提高弯曲管件零件设计效率。

三维数控弯管机的研究与开发

将绕弯工艺与滚弯工艺集成在一台机床上,采用专用的送料和转料装置,并将基于工业PC(个人计算机)的数控系统应用于弯管机的控制,取代传统PLC(可编程控制器)的控制系统,以NC(数字控制)嵌入PC的结构形式(工业PC内嵌入工业运动控制卡和工业I/O卡),在Windows操作系统的基础上,运用visual C++进行数控软件开发,实现了三维复杂管件的加工成型。生产与试验结果表明,基于PC的3D数控弯管机不仅提高了加工效率(连续加工)和加工质量,而且提升了三维管件加工的柔性和数控系统的开放性。

TA18高强钛管数控弯曲变形历史特征

基于ABAQUS平台建立TA18高强钛管数控弯曲成形全过程有限元模型,研究弯曲内、外侧和中性层位置材料经历的应力应变历史过程。结果表明,弯曲过程中,位于弯曲中性层的材料会经历较内侧和外侧材料复杂的切向应力、应变历史;位于弯曲初始端的中性层内壁材料应力较小,且经历由拉到压的变化历史,而其余区域材料经历由压到拉的应力历史,且拉应力较压应力大得多;中性层外壁材料的应力历史与其同位置的内壁材料的相似,但其应力值明显大于内壁的值;位于弯曲中性层前端的材料始终经受拉应变;位于中部和后端的材料则经历由压到拉的应变历史,且中部材料的拉应变值较后端的拉应变值大很多。在卸载回弹过程中,位于弯曲内侧外壁前端的材料切向应力增大;位于弯曲外侧、内侧的内、外壁的材料切向应力都经历了卸载和反向加载的历史;几何中性层的外壁和内壁材料切向应力只经历了不同程度的卸载。

材料力学性能对管材数控绕弯成形时壁厚变化的影响

基于ABAQUS/Explicit有限元平台,建立了规格为ψ15.88 mm×0.84 mm的21-6-9高强不锈钢管数控绕弯成形三维弹塑性有限元模型并验证了模型的可靠性;然后采用该模型通过有限元模拟研究了不锈钢力学性能变化对管材数控绕弯成形时壁厚变化率的影响。结果表明:弯管的壁厚变化率随着不锈钢强度系数、硬化指数的增大或屈服强度的降低而减小,弹性模量和泊松比对壁厚变化率基本没有影响;壁厚变化率对力学性能的敏感性由大到小依次为强度系数、硬化指数、屈服强度、弹性模量、泊松比。

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。

考虑材料参数变化的高强钛管数控弯曲回弹行为研究

目的研究钛管数控弯曲回弹角、回弹半径的变化规律,揭示回弹角和回弹半径变化特征的形成机制。方法基于有限元软件平台,建立考虑收缩应变比-弹性模量变化的Ti-3Al-2.5V钛管数控弯曲成形及回弹全过程的有限元模型。结果回弹角随弯曲角和相对弯曲半径的增加而增加;回弹半径在弯曲角小于30°时,随弯曲角的增加而先变化很小,后显著增加;弯曲角大于30°时,回弹半径随弯曲角的增加而逐渐减小。回弹半径随相对弯曲半径的增加而增加。弯曲角越大,应力分布区域越大,回弹变形越大;相对弯曲半径越大,弯管中处于弹性变形的区域占总变形区域的比例较大,回弹变形越大。结论考虑两参数变化时对回弹角和回弹半径的变化趋势无显著影响,但获得的回弹角和回弹半径均大于忽略两参数变化时的值;考虑收缩应变比-弹性模量变化时,弯曲变形区沿外脊线的拉应力大于忽略两参数变化时的拉应力,卸载回弹时,管材发生大的弹性恢复,表现为回弹角和回弹半径的增加。