内高压成形技术研究与应用新进展

介绍近年来在内高压成形机理、工艺、设备和应用方面的最新进展。针对大截面差管件,弯曲轴线异型截面构件和枝杈管3类工艺,给出典型零件缺陷形式、形状精度、壁厚分布和工艺参数的影响。详细介绍了皱纹控制与利用,降低整形压力的方法和内压与轴向力耦合作用下管材的塑性失稳起皱分析。最后给出了研制的典型内高压成形件及在汽车、航天、航空中的应用。     

Residual stress and softening in welded high-strength low-alloy steel with a buffering layer

Welding residual stresses, Vickers hardness and microstructure of welded high-strength low-allow steel, known for high strength and low carbon content, were studied under the following conditions: as-received high-strength low-alloy steel, welded high-strength low-alloy steel without a buffering layer, and welded high-strength low-allow steel with various thickness buffering layer. A soft buffering layer with a modest thickness between the parent metal and the weld metal could be incorporated to welded high-strength low-alloy steel to effectively reduce the widths of tensile residual stress zone and welding softening zone, to change the residual stress (in y-direction) nature at the weld root from tensile to compressive, and to refine the grains of the welded high-strength low-alloy steel. The width of the tensile residual stress (in x-direction) zone was approximately equivalently to that of the welding softening zone for those welded high-strength low-alloy steel with and without buffering layers.     

谈钢管的不圆度

针对钢管的不圆度在名称上叫法及计算表达方式上的不规范情况提出相关看法。     

Elastic-plastic analysis of tube bending

The aim of the paper is to present a theoretical analysis of the elastic-plastic bending of tube. Analytical methods are given whereby approximate equations are derived to provide a quantitative method for predicting the spring back behaviour and residual stress distributions. Comparisons between experimental and theoretical results of spring back have shown remarkable agreement. Also, a special technique for the bending of thin-walled tubes using a flexible mandrel of elastomer rod, within the ‘Doubtful Bend Region ρ₀/2R< 1.7' is presented. The elastomer is employed as an internal pressure transmitting medium in the bending process. Theoretical analysis based on the upper-bound approach for predicting the required bending load is also presented. Generally, it is found that the theoretical results for the bending loads are in good agreement with experimental values. Both experiments were performed on materials with different work hardening characteristics. Various parameters associated with these techniques are also examined.     

A simplified method of predicting stresses in surfaced steel rods

In this paper computational methodology of elasto-plastic states for rods subjected to thermal loads is presented. The dependence of stresses on strain was assumed on the basis of tension curves taking into account temperature. The computations of strains and stresses in a rod made of S235 steel, loaded by thermal fields generated by a point welding heat source of different intensities, were investigated. The analysis of development of plastic strains was carried out. Experimental tests were made for surfaced rod, with geometry and welding parameters assumed in numerical simulations, to verify the correctness of modelling. A simplified method was proposed to determine the longitudinal stresses in surfaced rods.     

Optimization of loading conditions for tube hydroforming

Tube hydroforming is a developing technology with advanced features of lightness and unified part. This study investigates the best possible regulation for loading conditions between the internal pressure and the axial feeding by hydroforming of a T-shape metal tube. Using conjugate gradient method with finite element method, a program module is generated to check the hydroformed tube quality about its thickness uniformity and the geometry accuracy. Thereby, a batch mode and a sequential mode to optimize the loading conditions of the tube hydroforming process are created and investigated. Regarding the tube quality from the simulation results, the hydroforming process, which follows the loading curve generated by the sequential mode, is better than by the batch mode. The optimal loading procedure generated by this article can offer another possibility for engineer by determining the internal pressure and the axial feeding in tube hydroforming.     

Influence of shallow and deep cryogenic treatment on the residual state of stress of 4140 steel

The present research work studies the effect of cryogenic treatment on the residual stress state in 4140 steel. Two kinds of cryogenic treatment, namely shallow (SCT, −80 °C × 5 h) and deep cryogenic treatment (DCT, −196 °C × 24 h) were carried out between quenching and tempering in conventional heat treatment process. The results evidenced an increase in the compressive residual stress in steel are subjected to cryogenic treatment before tempering. X-ray diffractometry revealed that residual stresses are relieved during tempering, according to the redistribution of carbon in martensite and the precipitation of transition carbides. While conventional heat treatment (CHT) and shallow cryogenic treatment (SCT) promote a tensile state of residual stress, DCT shows a compressive residual stress.     

Investigation of surface integrity in high speed end milling of a low alloyed steel

Understanding the effects of cutting speed, feed rate and cutting depth on surface integrity is very important for the control of workpiece quality. This paper presents a global experimental study of surface integrity in the case of high speed end milling. In the global term, we include measurements of residual stresses, surface roughness and cutting forces. Our observations and conclusions are mainly concentrated on the effect of depth of cut with a set of constant parameters, such as cutting speed, feed rate, and tool/material couple. This set of constants has been determined using the theory of stability lobes. All experiments have been performed with an electro-spindle equipped with magnetic bearings. The results lead to a good understanding of the influence of cutting conditions on surface integrity in high speed milling of a low alloyed steel. The discussion examines a specific point where the residual stress and residual stress gradient are lowest and also the origin of the residual stress value.     

Development of an improved tube galvanizing process by prior metallic coating

Tube galvanizing is a very old and important process industrially. One of the significant process steps in tube galvanizing is the use of flux materials on cleaned tubes for temporary protection before dipping into the liquid zinc bath. However, the fluxing operation is somewhat hazardous and also causes zinc loss by dross and ash generation. An attempt has been made here for the first time to replace fluxing operation by applying a thin metal flash coating on clean tubes prior to galvanizing. The galvanized tubes are then characterized by SEM and EDS to find out the coating thickness and evolved phases. The galvanized tubes are subjected to corrosion tests and coating adhesion tests. The results are very encouraging confirming the presence of desired phases along with excellent corrosion resistance of these tubes.     

某受力耐磨铸钢件脆性断裂的原因分析及改善措施

对断裂的受力耐磨铸钢件进行了化学成分、断口金相和能谱分析。分析结果表明受力耐磨铸钢件中残留铝含量偏高,当残留铝含量超过0.06%时,在一次奥氏体晶界上析出氮化铝而使晶界脆化,在恶劣工况运行条件下受力耐磨铸钢件产生脆断。     

Effect of high pressure rolling on weld-induced residual stresses

Abstract

The formation of large residual stresses continues to be a problematic side effect of all common welding processes. In this work, localised high pressure rolling of gas metal arc welds to relieve these residual stresses has been investigated using strain gauging and neutron diffraction. Rolling was found to remove undesirable tensile stresses and even induce large compressive ones, though only when applied after rather than during welding. Strain measurements taken during combined welding and rolling operations show that this is because material at the weld line continues to yield as it cools. This erases any beneficial effect on the stress distribution of rolling at high temperature. A method of rolling using an oscillating force is also presented and found to be just as effective as the equivalent static force process.     

Һѹ�����ü��⺸�ܲ�Ʒ����������

对液压胀形用激光焊管产品的质量控制过程进行了研究。通过在线非破坏性检测手段对余高、凹陷、错边及气孔等焊接质量缺陷进行控制,同时通过扩口试验、压扁试验、焊缝金相组织及硬度试验等质量检测方法进行了液压胀形用激光焊管产品的离线质量控制。另外,从生产供货角度出发说明了产品质量管控过程中首件检测方法的关键作用,强调了段焊检测和焊缝金相检测的重要性。试验结果表明,激光焊管的各项性能指标满足液压胀形工艺的使用要求。     

管材数控弯曲中的起皱分析与控制

针对内高压成形过程中,对弯曲件质量的严格要求,研究了低碳钢管材的数控弯管过程。采用数值模拟和实验,分析了不同弯曲半径、芯棒和管坯的间隙、芯棒位置和有无防皱块等参数对起皱的影响。结果表明,随着弯曲半径、芯棒直径、芯棒伸出量的增大及采用防皱块的情况下,管材弯曲起皱的趋势减小;在数值模拟的基础上进行了试验研究,试验结果和数值模拟结果吻合较好。采用二倍管径的弯曲半径,芯棒和管材间隙0.015D的情况下,能够有效地避免了弯曲内侧的起皱和外侧的减薄,成形出合格的副车架弯曲件,满足后续的内高压成形。     

On process parameter estimation for the tube hydroforming process

Tube hydroforming is a forming process where an inner pressure combined with axial feeding deforms the tube to the shape of a die cavity. One of the main concerns when designing such a process is to avoid burst pressure, i.e. the process state where the hardening of the material is unable to resist the increase in inner pressure and wall thickness reduction. The success of a hydroforming process strongly depends on the choice of process parameters, i.e. the combination of material feeding and inner pressure. Especially in hydroforming processes, where the free forming phase is substantial, the process is proved to be very sensitive to the inner pressure. By transforming the problem into a deformation controlled rather than a force controlled process, the results from the process parameter estimation become more reliable but on the other hand less intuitive. In this context, three distinct parameter estimation procedures are suggested. Firstly, a self feeding based procedure is proposed with the intention of being a fast method to be used as a first estimate of suitable process parameters. Secondly, an iterative optimization problem set up is presented. Thirdly, and finally, an adaptive simulation procedure based on process response approximations is proposed, which only requires a limited number of simulation runs.     

An enhanced analytical model for residual stress prediction in machining

The predictions of residual stresses are most critical on the machined aerospace components for the safety of the aircraft. In this paper, an enhanced analytic elasto-plastic model is presented using the superposition of thermal and mechanical stresses on the workpiece, followed by a relaxation procedure. Theoretical residual stress predictions are verified experimentally with X-ray diffraction measurements on the high strength engineering material of Waspaloy that is used critical parts such as in aircraft jet engines. With the enhanced analytical model, accurate residual stress results are achieved, while the computational time compared to equivalent FEM models is decreased from days to seconds.     

Experimental and numerical modelling of the residual stresses induced in orthogonal cutting of AISI 316L steel

Residual stresses in the machined surface layers are affected by the cutting tool, work material, cutting regime parameters (cutting speed, feed and depth of cut) and contact conditions at the tool/chip and tool/workpiece interfaces. In this paper, the effects of tool geometry, tool coating and cutting regime parameters on residual stress distribution in the machined surface and subsurface of AISI 316L steel are experimentally and numerically investigated. In the former case, the X-ray diffraction technique is applied, while in the latter an elastic–viscoplastic FEM formulation is implemented. The results show that residual stresses increase with most of the cutting parameters, including cutting speed, uncut chip thickness and tool cutting edge radius. However, from the range of cutting parameters investigated, uncut chip thickness seems to be the parameter that has the strongest influence on residual stresses. The results also show that sequential cuts tend to increase superficial residual stresses.     

管件液压成形中加载路径的优化设计方法研究

确定合理的加载路径是管件液压成形工艺设计的关键。文章较为系统地介绍了管件液压成形中加载路径的优化设计方法,比较分析了各种方法的优缺点与适用对象,讨论了研究过程中存在的主要问题和研究的发展方向。     

On the role of residual internal stresses and dislocations on Barkhausen noise in plastically deformed steel

The dependence of Barkhausen noise on elastic and plastic deformations, achieved in tension and in compression, has been investigated both in Armco iron and a low carbon steel. These materials exhibit quite different behaviours, especially with regard to the effect of plastic deformation: a tensile plastic deformation (>1%) induces a marked increase in Barkhausen noise for Armco iron while it induces a steep decrease in the low carbon steel. The comparison between the tensile and compressive behaviours, as well as between the elastic and plastic regimes of deformation enables us to attribute these effects to two underlying mechanisms, i.e. effect of residual internal stresses through magneto-elastic coupling and dislocation–domain wall interaction. In Armco iron, the latter mechanism seems to have the strongest influence on the Barkhausen noise, while in the low carbon steel the influence of residual internal stresses prevails.     

3D modeling of residual stresses induced in finish turning of an AISI304L stainless steel

This paper addresses the development of a new methodology predicting residual stresses induced in finish turning of a AISI304L stainless steel. A hybrid approach combining experimental results and a numerical model is applied. The model simulates the residual stresses generation by applying equivalent thermo-mechanical loadings onto the machined surface without modeling the chip removal process, which enables rapid calculation. The shape and the intensity of equivalent thermo-mechanical loadings are identified through experimental measurements. Friction tests enable to model the thermal and mechanical loadings along the tool-workmaterial interface. Orthogonal cutting tests provide thermal and mechanical loadings below the primary and third shear zone. This model has already been presented in several papers, but only in a 2D configuration. The objective of this paper is to transfer this hybrid approach into a 3D configuration, which is closer to a concrete longitudinal turning operation. Based on this new model, the paper aims at investigating the interactions between each revolution. It is shown that around five revolutions are necessary to reach a steady state. Finally numerical results are compared with experimental measurements obtained by X-Ray diffraction. It is shown that residual stresses cannot be considered as homogeneous over the surface due to tool's feed. Additionally, the X-Ray beam is much too large to be able to quantify this heterogeneity. Based on average numerical values coherent with average values obtained by X-Ray diffraction, it is shown that the numerical model provides consistent results compared to experimental measurements for a large range of cutting speed and feed.     

钛T型管液压成形的工艺参数研究

采用Dynaform软件对Φ219 mm×Φ219 mm×5 mm钛T型管的液压成形工艺进行数值模拟研究,以有效支管高度、最大减薄率和最大增厚率为优化指标,对内压加载路径、加压持续时间、左右及中间冲头速度等多种工艺参数组合方案进行优选计算,获得最优方案,并根据最优方案中的工艺参数进行实际的液压成形试验。研究表明:模拟试验中,采用方案3成形效果最好,有效支管高度达到68.41 mm,最大减薄率和增厚率分别为27.38%和54.34%,满足T型管尺寸和壁厚分布要求。与模拟值相比,成形试验得到的钛T型管零件在有效支管高度、最大减薄率和最大增厚率上的误差均在5.1%以内。