船用大直径厚壁管数控弯曲工艺参数对壁厚影响的显著性分析

为实现船舶管件数控弯曲精确成型,更好地研究船用大直径厚壁管壁厚变化率,提高其成型质量,需对其弯曲过程中壁厚减薄进行有效控制。基于有限元分析软件Dynaform建立船用20#管绕弯成型过程有限元模型,对其进行可靠性验证,再通过有限元分析和虚拟正交试验对弯曲段外侧最小壁厚数据进行极差分析和方差分析,研究工艺参数对于壁厚减薄影响的显著性及规律。结果表明:管件数控弯曲成形过程中工艺参数对最大壁厚减薄率影响的显著性顺序依次为:芯棒与管材摩擦系数、芯棒前伸量、芯棒与管材间隙、夹模与管材间隙;壁厚减薄率随着芯棒与管材摩擦系数、芯棒前伸量以及夹模与管件间隙的增大而增大,随着芯棒与管件间隙增大而减小。同时利用多元线性回归方法建立显著性工艺参数与最大壁厚减薄率之间的回归方程,经对比验证,对于规格为Φ140mm×4.5mm(t)×420mm(R)船用20#大直径厚壁管,此回归预测模型结果与正交试验之间的相对误差不超过5%。     

工艺参数对21-6-9高强不锈钢管数控弯曲壁厚减薄影响的显著性分析

为实现21-6-9高强不锈钢管数控弯曲精确成形,提高其成形质量与成形极限,需要对弯曲过程中壁厚减薄进行有效控制。基于ABAQUS/Explicit有限元软件平台,建立了21-6-9高强不锈钢管数控弯曲三维弹塑性有限元模型,并对其可靠性进行了验证。通过有限元模拟和正交试验,研究了工艺参数对21-6-9高强不锈钢管数控弯曲壁厚减薄影响的显著性及规律。结果表明,影响壁厚减薄的显著性工艺参数依次为芯棒伸出量、管材与芯棒间隙、管材与防皱块摩擦因数、管材与芯棒摩擦因数、管材与压块摩擦因数和弯曲速度,其影响规律为：壁厚减薄率随着芯棒伸出量、管材与防皱块摩擦因数、管材与芯棒摩擦因数、管材与压块摩擦因数、弯曲速度的增大或管材与芯棒间隙的减小而增大。采用多元线性回归方法建立了最大壁厚减薄率与显著性工艺参数之间的回归预测模型,经对比验证,回归预测模型结果与正交试验结果之间的相对误差不超过5%。     

薄壁管绕弯工艺参数对壁厚影响分析

为探究薄壁管绕弯加工中各工艺参数对管件壁厚的影响。结合正交试验设计,利用有限元软件DYNAFORM进行了管件绕弯过程仿真,对管件弯曲段外侧和内侧壁厚数据进行了极差分析和方差分析。芯棒伸出量和压模摩擦因素对管件弯曲段外侧减薄率有较大影响,其中芯棒伸出量对减薄率的影响具有显著性;防皱模与管件间隙、压模摩擦因素、压模与管件间隙、芯棒与管件间隙对弯曲段内侧增厚率影响较大,但所有工艺参数对内侧增厚率的影响均不具有显著性。优化参数后的试验表明:减小防皱模、压模、芯棒与管件的间隙及芯棒伸出量,适当增大压模及芯棒与管件的摩擦有助于薄壁管获得更高的壁厚质量。     

管件弯曲工艺参数对截面质量影响有限元模拟

大口径船用管件多采用冷弯成形工艺,为掌握管件弯曲工艺参数对截面质量的影响规律,采用ABAQUS对管件弯曲过程进行模拟。模拟结果显示:随着芯棒与管件单侧间隙的增加,壁厚减薄率相应减小,单侧间隙合适范围为0.5mm~1mm;随着芯棒伸出量增加,弯管截面圆度值增大,芯棒伸出量合适范围为25mm~30mm。     

TA1板单点渐进成形壁厚变化规律的数值模拟研究

钛及其合金应用越来越广泛,目前单点渐进成形技术已经开始运用于钛及其合金的成形加工,但仍存在成形件壁厚过度减薄的问题,严重影响了成形件的成形质量。文章以TA1钛合金板材成形方锥形件为研究对象,运用Abaqus有限元仿真软件,依据单一变量原则,分别探究工具头直径、底面边长、板材原始厚度和螺距等工艺参数对成形件平均壁厚减薄率与最大壁厚减薄率的影响规律。结果显示:增大工具头直径,平均壁厚减薄率随之增大,最大壁厚减薄率随之减小;平均壁厚减薄率和最大壁厚减薄率都随着底面边长的增加而增加;板材原始厚度增加,平均壁厚减薄率与最大壁厚减薄率都随之减小;随着螺距的增加,平均壁厚减薄率逐渐减小,最大壁厚减薄率逐渐增大。     

聚乙烯管韧性破坏寿命预测方法研究

聚乙烯管在静液压作用下有3种失效模式：蠕变韧性破坏、慢速裂纹脆性破坏和材料劣化破坏。提出基于粘弹性应力分析模型的聚乙烯管材蠕变韧性破坏寿命预测方法。在内压作用下,聚乙烯管材的蠕变导致其壁厚不断减薄,环向应力逐渐增大。同时,基于粘弹性应力分析模型得到管材蠕变的应变率逐渐减小,由于聚乙烯的屈服应力具有明显的率相关性,屈服应力也随之逐渐减小。当增加后的环向应力值与管材瞬时屈服应力相等时,聚乙烯管材发生韧性失效,从而得到韧性失效寿命与内压载荷之间的关系。     

基于POA-BP的TP2管材自由弯曲成形结果预测

将壁厚减薄率和椭圆率作为管材自由弯曲成形结果的评价指标,选取弯曲模与管材间隙值、弯曲模圆角半径值、管材弯曲变形区长度、导向机构圆角半径值、导向机构与管材间隙值作为影响因子。利用数值模拟方法对管材自由弯曲成形结果的评价指标和影响因子建立样本库,并随机选取6组作为测试样本,其余的作为训练样本,结合BP神经网络和鹈鹕优化算法对预测模型进行训练,构建POA-BP神经网络预测模型对管材自由弯曲成形结果进行预测。结果表明,POA-BP预测模型的壁厚减薄率和椭圆率的最大预测误差不超过2%,故POA-BP预测模型能够有效预测管材成形结果。     

AZ31B镁合金管材液压胀形数值模拟分析

基于管材轴向补料液压胀形技术,采用Dynaform有限元仿真软件对0.75mm厚的AZ31B镁合金管材的胀形过程进行了数值模拟分析。研究了模具圆角半径、液压力、模具间隙等工艺参数对镁合金管件壁厚分布和最大壁厚减薄量Δt的影响规律,并探索了相对合理的工艺参数。研究结果表明,镁合金管件的最小壁厚通常分布在最大胀形直径处,除非模具间隙过小;由于受到轴向作用力,管材两端会随模具间隙的改变而出现不均匀的壁厚增厚现象,并且受轴向压头作用的一端的壁厚增厚量相对较大;胀形过程中,当模具圆角半径为5mm,模具间隙为0.8mm时,获得的镁合金管件壁厚分布较均匀,成形效果较好。     

不同模具组合对0Cr21Ni6Mn9N不锈钢管数控弯曲成形质量的影响

采用有限元法研究了不同模具组合下0Cr21Ni6Mn9N不锈钢管数控弯曲应力应变分布、壁厚变化和截面畸变规律。研究结果表明：在弯曲模、夹块和压块组成的基本模块的基础上,添加防皱块会导致等效应力、切向拉应力和切向拉应变增加,而切向压应力、等效应变和切向压应变减小;添加芯棒会导致切向应力和等效应变减小,而等效应力和切向应变增大;同时添加防皱块和芯棒则会导致等效应力、切向应力和切向应变增大,而等效应变减小。添加防皱块会导致弯管截面畸变率增大,但对壁厚变化率影响不大;添加芯棒能够有效抑制弯管截面畸变,且壁厚减薄率仅为9.0%~9.15%,远小于15%的航空标准。综合考虑0Cr21Ni6Mn9N不锈钢管数控弯曲成形质量和生产成本,可确定出最优的模具组合为弯曲模+压块+夹块+芯棒。     

筒形件充液拉深预胀作用仿真分析研究

利用有限元对不同预胀压力下的筒形件充液拉深过程进行仿真,指导该类筒形零件预胀压力的选取。结果表明:初始预胀形能够提高零件的成形质量,有效降低壁厚减薄;预胀压力过大导致零件壁厚分布不均匀,减薄率增加;最小壁厚随着预胀压力的增大,先增大后减小。     

Optimization of processing parameters for double-ridged rectangular tube rotary draw bending based on grey relational analysis

The rotary draw bending of double-ridged rectangular tube is a complex nonlinear physical process with multifactors coupling effects. Processing parameters, especially clearances and friction coefficients between tube and various dies, have a significant effect on the forming quality of the double-ridged rectangular tube in rotary draw bending. If the values of these processing parameters are inappropriate, some defects including cross-sectional deformation, wall thinning, and wall thickening easily occur in the bending process of double-ridged rectangular tube. So optimization of these processing parameters is of great importance to control these defects. Based on the grey relational analysis method combined with the orthogonal experimental design and finite element simulation, a grey relational analysis model was established for the rotary draw bending process of double-ridged rectangular H96 brass tube. With the model, optimization of clearances and friction coefficients between tube and various dies was implemented with consideration of interactive effects of the above defects. The results show that (1) the main factors influencing cross-sectional deformation, wall thickening, and wall thinning are tube–mandrel clearance Δc _m, tube-bending die clearance Δc _b, and tube–mandrel clearance Δc _m, respectively. (2) The optimal values of clearances Δc _m, Δc _p, Δc _w, and Δc _b and friction coefficients μ_m, μ_p, μ_w, and μ_b of tube–mandrel, tube–pressure die, tube–wiper die, and tube-bending die are 0.15, 0.2, 0.2, 0.2, 0.02, 0.3, 0.06 and 0.17 mm, respectively. Furthermore, the verification for the optimal values of these processing parameters was carried out, and the double-ridged rectangular H96 bent tube obtained by using the optimal values of these processing parameters has the minimum values of cross-sectional deformation, wall thinning, and wall thickening and can satisfy the national aviation industry standards.     

Forming characteristics analysis of the cross-section of axially inner grooved copper tube

The simulation of the cross-section forming of axially inner grooved copper tube (AIGCT) is conducted using finite element (FE) software MSC.Marc. The stress–strain distribution, metal flow rule, and contact force are analyzed based on the simulation and experimental results. The results show that gaps in the groove walls are caused not only by the diametric clearance between the inner wall of the copper tube and the mandrel but also the bending deformation of the copper tube. The cross-sectional geometry and surface characteristics of grooves are determined by the multi-tooth mandrel. Smooth transition of the mandrel teeth addendum improves the metal flow and makes contact force vary slightly, which is good for preventing mandrel from failure. Improving the mandrel surface finish can also improve the inner surface quality of AIGCT. The results help to optimize the forming process parameters and improve the forming quality.     

差厚拼焊管胀形减薄率不均匀性分析

结合有限元数值模拟和试验,研究差厚拼焊管胀形减薄率分布规律,并从应变状态和应变历史角度分析减薄率不均匀性产生的原因,进而研究厚度比、长度比及硬化指数n对减薄率分布的影响。结果表明差厚拼焊管胀形时薄、厚管不同部位始终处于不同的轴向应变状态,导致在发生相同的环向应变时,厚向应变分布不均。厚管愈靠近焊缝区域减薄率愈小,薄管愈靠近焊缝减薄率愈大。厚度比和硬化指数n对壁厚分布影响明显,厚度比越大、n值越低,胀形后薄、厚管的壁厚差越大;但厚度比影响主要集中在焊缝附近,n值影响整个胀形区的壁厚分布。     

芯棒伸出量对薄壁矩形管弯曲失稳起皱影响的数值模拟

基于动态显式有限元平台ABAQUS/Explicit,建立了3A21铝合金薄壁矩形管绕弯成形过程的三维有限元模型,模拟分析了芯棒伸出量对薄壁矩形管绕弯成形过程中失稳起皱的影响规律。结果表明:随着芯棒伸出量的增大,起皱波纹高度逐渐减小,切向压应力极大值波动的峰值减小,等效应力逐渐减小,并且变化趋于平缓;当芯棒伸出量达到一定值后,随着芯棒伸出量的增大,起皱波纹高度极大值变化不明显。该研究对薄壁矩形管绕弯成形工艺参数的确定具有重要的参考价值。     

Research on cross-sectional deformation of double-ridged rectangular tube during H-typed rotary draw bending process

Based on the ABAQUS/Explicit, a three-dimensional elastic–plastic finite element model of the H96 brass double-ridged rectangular tube (DRRT) during H-typed rotary draw bending (RDB) was established and its reliability was validated by an experiment. With the model, distribution characteristic of cross-sectional deformation and effects of clearance and friction coefficient between tube and dies and core number on it were studied. The results show that the maximum cross-sectional height distortion ratio appears at the bending angle 60°. And the maximum cross-sectional width distortion ratio between side walls, as well as side walls of the ridge grooves, appears at the bending angle 80° and 60°, respectively. In addition, retracting mandrel has a great effect on the cross-sectional height distortion, but its influence on the cross-sectional width distortion can be ignored. And the maximum cross-sectional distortion ratio initially increases with increasing of clearance between tube and mandrel c _m and friction coefficient μ _b between tube and bending die, and then decreases with their increase, and initially decreases with the increase of core number N, and then increases with increasing of N. Moreover, the reasonable value of N is taken as 4.     

Upper bound analysis of extrusion of axisymmetric, piecewise homogeneous tubes

A kinematically admissible velocity field for tube extrusion is proposed, which reduces to a kinematically admissible field for solid rods in the limit as the mandrel diameter goes to zero. Although these upper bound calculations of extrusion pressures for solid rods are greater than those obtained by a similar analysis using a different kinematically admissible field, the results are qualitatively similar as regards dead zone formation and the form of the relation between extrusion pressure and extrusion ratio for fixed die cone angle and friction conditions.Analysis of tube extrusion shows that the linear relation between extrusion pressure and the logarithm of the extrusion ratio is preserved to a good approximation for friction-less extrusion in the case where the extrusion ratio is varied by fixing the mandrel size and die cone angle and varying the product diameter. However, the analytical results indicate that the linear relation is not exact. Nonlinearity is more evident as mandrel friction increases. The effective die cone angle for dead zone formation depends on friction conditions on the die and mandrel surfaces. The introduction of a stronger core symmetrically placed in the tube wall results in an increase in the extrusion pressure in approximately direct proportion to the relative strengths of the core and sheath and to the volume fraction of core.     

Fabrication of small size inner spiral ribbed copper tube by fluid mandrel drawing

This paper is concerned with the development of ultra-small inner spiral ribbed copper tubes with high-quality heat transfer. Since the demand for the ultra-small tubes in electrical appliances is currently high and will be greater in the future, the technology employed must enable the production of inner spiral ribbed fine tubes with various features, such as small size, high quality, high functionality, and low processing cost so as to meet the increasing demand. The conventional production method is suitable for large tubes with high drawability but is unsuitable for fabrication of long ultra-small tubes because of the difficulty to manufacture both an ultra-small spiral ribbed mandrel and a floating plug. This research paper has proposed four drawing methods as follows: tube sinking, water, oil, and wax as mandrels and presented the comparison of seven parameters, i.e., drawing stress ratio, wall thickness ratio, ribbed base width ratio, ribbed tip width ratio, ribbed height ratio, ribbed pitch ratio, and ribbed spiral angle ratio. It was found that tube sinking was unfit for making the ultra-small inner spiral ribbed copper tubes due to the resulting high ratio of wall thickness. The results of all the parameters were similar in the cases of oil and wax. Despite less impressive outcomes, water was easily removed from the inner spiral ribbed copper tube compared to oil and wax. Thus, the tube drawing using water as mandrel was most suitable for the production of the inner spiral ribbed copper tube.     

An approach to improve thickness uniformity within tailor-welded tube hydroforming

Both experimental and simulation studies were run to investigate the effects of deformation sequence on stress and strain states and thickness distribution during tailor-welded tube hydroforming. The effects of geometrical boundary condition were also studied. Then, an approach to improve thickness uniformity was put forward. Both stress and strain histories indicate that the deformation states of thinner and thicker tubes were obviously different duo to the difference in thickness during tailor-welded tube hydroforming. These induce tensile strain concentrates to happen near weld seam on thinner tube, but compressive strain on thicker tube, which lead to strain mutation around weld seam on tailor-welded tube components. As result, bigger thinning takes place on thinner tube. The difference in thinning ratio between thinner and thicker tubes reaches about 6.6%. By deformation sequence optimization, thickness distribution uniformity can be improved obviously. When deformation sequence altered from thicker tube to thinner tube, the difference in thinning ratio between two segments can be decreased to 1.5%. At last, the effects of geometrical parameters of preform component were analyzed and the suitable parameters were given.