双层管内压弯曲过程轴向应力分析

双层管内压弯曲方法为获得大直径超薄弯管提供了可行的途径,文章对该方法避免内层管起皱的机理进行研究。内压在双层管轴向产生的附加拉应力,可降低弯曲内侧轴向压应力,有助于预防起皱。采用弹性理论,得到双层直管状态下附加轴向拉应力表达式,并对理论模型进行验证。通过数值模拟,分析了弯曲过程中支撑内压、外层管厚度,对内层超薄管起皱和轴向应力的影响规律。理论分析结果表明,双层管极限支撑内压,会随外层壁厚的增加而显著提高,因此对于厚度比较大的双层管,可以通过采用较大的支撑内压,提高附加轴向拉应力的方法避免起皱。模拟结果表明,随着外层管厚度增加,外层管弯曲时不易发生失稳起皱,同时弯管内侧轴向压应力绝对值降低。支撑内压越高,内外层界面贴合越紧密,内层管在承受轴向压应力时,其稳定性越高。     

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.     

细小内沟槽铜管的回转模锻管端缩径(英文)

为制造小型沟槽铜热管,设计和采用了回转模锻工艺进行管端缩径。相比传统的回转模锻,所使用的回转模锻机的轴向进给通过恒定的推力实现。采用实验方法,分析旋转模锻过程中缩径段的沟槽变形,测量和计算管端缩径过程的截面收缩率和伸长率。探讨进给推力对缩径段的直径、表面粗糙度、伸长率和加工时间的影响。结果表明:缩径段的管壁厚度沿着轴向逐渐增长,而外径、表面粗糙度和微观裂纹则沿轴向逐渐减小。此外,推力对伸长率的影响很小,而表面粗糙度则随着推力的增大而减小。因此,采用回转模锻进行管端缩径,在允许范围内,增大进给推力对管端缩径质量有益。     

Loading path optimization of tube hydroforming process

Optimization methods along with finite element simulations were utilized to determine the optimum loading paths for closed-die and T-joint tube hydroforming processes. The objective was to produce a part with minimum thickness variation while keeping the maximum effective stress below the material ultimate stress during the forming process. In the closed-die hydroforming, the intent was also to conform the tube to the die shape whereas in the T-joint design, maximum T-branch height was sought. It is shown that utilization of optimized loading paths yields a better conformance of the part to the die shape or leads to a higher bulge height. Finite element simulations also revealed that, in an optimized loading path, the majority of the axial feed needs to be provided after the tube material yields under the applied internal pressure. These results were validated by conducting experiments on aluminum tubes where a good correlation between the experimental results and simulations were obtained.     

基于轮廓法测试惯性摩擦焊接头内部残余应力

采用轮廓法测试小尺寸镍基高温合金惯性摩擦焊接头的内部环向应力、中等尺寸惯性摩擦焊接头内部环向和轴向应力;分析惯性摩擦焊接头内部环向和轴向残余应力分布特征. 结果表明,轮廓法能测试小尺寸及窄小焊缝试件的内部残余应力,能反映出窄小焊缝内部的大梯度焊接残余应力全貌;惯性摩擦焊接头的环向应力沿轴向变化剧烈,沿环向分布均匀,沿厚度分布不均匀;焊缝中心位置外表层区域环向应力小于内表层区域环向应力;焊缝中心外表面轴向应力为压应力,而内表面轴向应力为拉应力,且轴向应力沿厚度呈线性变化.     

An investigation into the forging of Bi-metal gears

This paper introduces a method for the production of bi-metal gears using the forging technique. To study the process, model materials of copper (tooth ring material) and lead (core material), were used for both experimentation and simulation. Firstly, experimental setup and test procedures are introduced and the bi-metal gears are forged with different thicknesses of the outer ring material. A simplified FE model is established based on the symmetry of a gear forging process, which enables the 3D FE analysis to be carried out in an efficient manner. The material flow and thickness distribution of the experimentally forged bi-metal gears are analysed and compared with FE predictions. The effect of friction on the axial lock caused by the material flow of the forged gears is also studied. Finally, simulations of different combinations of the inner core and outer ring materials, specifically steel (ring material), copper (ring and core material) and lead (core material) are performed. The numerical and experimental data showed that: thin rings can deform excessively, affecting the structure of the gear; and that both tooling friction and flow stress can significantly affect the relative material flow between the core and the ring.     

外螺纹铜管拉深成形过程的有限元模拟

利用非线性有限元仿真软件MARC,研究了外螺旋凸筋管成形过程的三维弹塑性有限元模拟技术.对外螺纹铜管的拉深成形过程进行了模拟,得到了成形过程中工件内部的应力和应变分布规律.结果表明,拉拔过程中,管料发生轴向延伸,但各部分延伸量不均匀,最大延伸变形发生在筋底中心部分.在周向,整体上管料发生压缩变形,但在筋底部分产生一定的延伸,应变为正;径向发生压缩变形.在定径区及铜管离开定径区后,轴向应力均为拉应力,但沿壁厚分布不均匀;同样,拉拔周向应力沿壁厚方向也呈不均匀分布,出定径区后在筋底区的外表面为负,内表面为正.     

内高压成形理论与技术的新进展

介绍哈尔滨工业大学在内高压成形基础理论、关键技术及工业应用等方面取得的重要进展。在基础理论方面,利用平面应力屈服椭圆描述典型内高压成形过程中应力状态及壁厚变化趋势;揭示变径管内高压成形过程中壁厚分布规律以及多边形截面环向的壁厚分布特点;指明整形阶段圆角充填时存在极限圆角半径;发明了用于测量管材环向力学性能的管材环向拉伸实验方法。在工艺关键技术方面,针对航空航天领域对大直径薄壁复杂管件的需求,发明了Y型薄壁三通管两步成形方法、双层管充液弯曲方法,试制出超薄Y型三通管、整体不锈钢进气道及弯管零件。在工业应用方面,研制了合模力最大达55 MN的工业生产用大型内高压成形机,并成功地用于轿车底盘零件大批量生产。     

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.     

Tool design guidelines for the equal channel angular swaging (ECAS) process

A new severe plastic deformation (SPD) process of “equal channel angular swaging” (ECAS) is developed by combining the conventional equal channel angular pressing with the incremental bulk metal forming method rotary swaging. The ECAS tool system contains four forming zones in a single forming pass. In the current study, the effect of the multi-stage forming process on both the strain distribution and the material deformation is investigated by means of finite element (FE) simulations and these simulations are verified with model experiments. The results serve as tool design guidelines for the ECAS process.     

Evaluation of effective parameters in metal bellows forming process

Metal bellows have wide applications in aerospace, micro-electromechanical and industrial systems. Forming process of the metal bellows is very sensitive to increasing the ratio of crown to root diameter. In this state, precise control of the parameters is very important in order to form high-quality metal bellows with good thickness distribution and desirable dimensions and resilience. In this paper, a new method has been proposed for manufacturing of the metal bellows and important parameters such as initial length of tube, internal pressure, axial feeding and velocity, mechanical properties and the type of materials were investigated by finite element (FE) analysis (LS-Dyna) and experimental tests. The explicit time integration method is used for modeling the tube-bulging and folding processes. Meanwhile, the implicit time integration method is used for the spring back stage. Finally, the results of finite element method (FEM) and experiments show a very good agreement. The results of the present work could be used as a basis of designing a new type of the metal bellows.     

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%.     

Wrinkling behavior of magnesium alloy tube in warm hydroforming

In tube hydroforming with axial feeding, under the effect of coupled internal pressure and axial stress, wrinkles often occur and affect the forming results. Wrinkling behavior of an AZ31B magnesium alloy tube was experimentally investigated with different loading paths at different temperatures. Features of wrinkles, including shape, radius and width, were acquired from the experiments, as well as the thickness distribution. Numerical simulations were carried out to reveal the stress state during warm hydroforming, and then the strain history of material at the top and bottom of the wrinkles were analyzed according to the stress tracks and yielding ellipse. Finally, effects of loading paths on expansion ratio limit of warm hydroforming were analyzed. It is verified that at a certain temperature, expansion ratio limit can be increased obviously by applying a proper loading path and realizing enough axial feeding.     

内压对薄壁铝合金管材充液压弯过程的影响

采用实验和数值模拟研究5A02铝合金薄壁管材充液压弯成形过程中内压对缺陷的影响规律,分析内压对弯曲内侧起皱、截面畸变及壁厚分布的影响,获得壁厚变化规律;通过数值模拟给出的应力状态,揭示缺陷形成机制。结果表明:提高内压能降低轴向压应力的绝对值,减小失稳起皱趋势,当内压超过一个临界值时,皱纹完全消除。对于直径为63 mm、壁厚为1 mm的5A02-O铝合金管材,其内压临界值为2.8 MPa。充液有效地减小截面畸变程度,随内压的增大,截面畸变程度逐渐减小。弯曲后,壁厚最大减薄点位于弯曲外侧点,且随内压的增大,轴向和环向拉应力均呈增大趋势,弯曲外侧壁厚度减薄的趋势也增大。     

Prediction of welding pressure in the non-steady state porthole die extrusion of Al7003 tubes

This paper describes a numerical analysis of non-steady state porthole die extrusion, which is useful for manufacturing long tubes with a hollow section. Materials divided through several portholes are gathered within a chamber and are then welded under high pressure. This weldability classifies the quality of tube products and is affected by process variables and die shapes. However, porthole die extrusion has been executed based on the experience of experts, due to the complicated die assembly and the complexity of metal flow. To better assist the design of die and to obtain improvement of productivity, non-steady 3D FE simulation for porthole die extrusion is required. Therefore, the objective of this study is to analyze the behavior of metal flow and to determine the welding pressure of hot extrusion products according to various billet temperatures, bearing length, and tube thickness by FE analysis. The results of FE analysis are compared with those of experiments.     

Integrated Modeling of Process–Microstructure–Property Relations in Friction Stir Additive Manufacturing

Friction stir additive manufacturing is a newly developed solid-state additive manufacturing technology. The material in the stirring zone can be re-stirred and reheated, and mechanical properties can be changed along the building direction. An integrated model is developed to investigate the internal relations of process, microstructure and mechanical properties. Moving heat source model is used to simulate the friction stir additive manufacturing process to obtain the temperature histories, which are used in the following microstructural simulations. Monte Carlo method is used for simulation of recrystallization and grain growth. Precipitate evolution model is used for calculation of precipitate size distributions. Mechanical property is then predicted. Experiments are used for validation of the predicted grains and hardness. Results indicate that the average grain sizes on diff erent layers depend on the temperature in stirring and re-stirring processes. With the increase in building height, average grain size is decreased and hardness is increased. The increase in layer thickness can lead to temperature decrease in reheating and re-stirring processes and then lead to the decrease in average grain size and increase of hardness in stir zone.     

Influence of axial feeding on the growth of circumferential thickness deviation in free hydraulic bulging

Loading paths (hereafter referred as LPs) that consist of internal pressure and axial feeding are important manufacturing conditions in tube hydroforming. Among the factors that affect LP design, friction between the forming die and tube causes the most difficulty due to its complicated characteristics. Although there is no friction, a number of issues with LP design remain. In this study, free hydraulic bulging (hereafter FHB) with internal pressure and axial feeding is investigated. In FHB, tubes are freely expended without friction. It has been shown that axial feeding affects the circumferential thickness distribution in the tube periphery. The tubes in this study are straight seamless tubes. Seamless tubes typically have predictable thickness deviations resulting from their manufacturing processes. In general, the degree of thickness deviation will increase as the tube expands. A FEM simulator is used to analyze the mechanism of the growth of thickness deviation.     

等径三通管整体液压成形壁厚分布规律

对铝合金薄壁三通管壁厚分布规律进行研究。将管坯放入模具型腔,通过轴向进给补料、内部增压,沿下模具型腔中间倒圆角处凸出一个较高的等径支管,形成等径三通管。通过数值模拟和实验对等径三通管整体液压成形的过程进行研究,分析了三通管整体液压成形4个不同阶段的管材壁厚分布规律和管材关键部位壁厚的变化规律。研究发现,成形管材底部的壁厚最大,过渡圆角周边处次之,支管顶端周边最薄。数值模拟和实验结果相吻合,为T型三通管零件生产奠定了基础。     

Forming characteristics of tubular product through the rotary swaging process

Experiments for the forming characteristics of a tube by a rotary swaging process have been carried out to obtain a tubular product of desirable quality taking into account the process variables such as the forming feed and reduction of diameter of the product using the developed rotary swaging machine and four-split dies. From these experimental results, it is found that the process variables affect the quality of the tube such as the dimensional precision, hardness, surface roughness and microstructure of the product. It is also found that defects can occur at the forming feed of more than 2.0 mm/rev. The thickness of the product increased about 63% from its initial thickness of 2.3 mm to 3.75 mm. The hardness measured on the surface of the tube depended on the reduction of the diameter and is rarely affected by the variation of the forming feed from 0.5 to 2.0 mm/rev. The surface roughness of the product after swaging is about three times better than that before swaging. Based on these results a tubular rod shift for an automobile steering part was shown to be effectively manufactured by the rotary swaging process.     

基于有限元模拟的内螺纹铜管旋压成型参数确定

内螺纹铜管传热面积大,可以造成紊流效果,提高换热效率,是空调、冰箱的主要换热介质。旋压成型是制造内螺纹铜管的高效成型工序。为研究内螺纹铜管旋压成型过程中的材料流动规律,运用非线性有限元分析软件,对内螺纹旋压成型过程进行了仿真。结果表明,在旋压过程中,铜管经历了类似于行星辊轧的,从圆形到多边形,最后恢复圆形的过程;此外铜管除了发生横截面方向弯曲外,还发生轴向运动,两者叠加产生了羽片扭转;当铜管材料填满螺纹槽后,多余的材料沿旋压方向流动,将耗费过多的能量。减少管坯的直径和壁厚,可以减少截面方向弯曲,并可以减少壁厚过大导致多余材料周向流动的能量损失。文章讨论了旋压速度的选取,认为尽可能选用低的旋压速度,可以减少羽片扭转。