Prediction of forming limits and parameters in the tube hydroforming process

Determination of process limits and parameters for hydroforming was conducted applying widely known plasticity, membrane and thin-thick walled tube theories. Analytical predictions were compared with experimental findings. Simple but useful analytical models to predict buckling, wrinkling and bursting as well as axial force, internal pressure, counter force and thinning in tube hydroforming were verified with experimental results.     

Development of semi-dieless metal bellows forming process

A novel semi-dieless metal bellows forming process with local induction heating and axial compression without using any conventional dies is proposed. Firstly, the thickening of a tube is induced by local heating and axial compressive force. Secondly, the buckling of the tube occurs, producing a convoluted shape. The seamless tubes used are stainless steel SUS304 with an outer diameter of 5 mm and a thickness of 0.5 mm and 0.3 mm. The effects of compression ratio on the profiles of the bellows such as convolution height, pitch and thickness are investigated experimentally. It is found that convolution height can be controlled by compression ratio. Additionally, the mechanism of this process for fabrication of the metal bellows can be clarified by loading curve during processing. Furthermore, the validity of a two-step compression technique for improving convolution height and pitch is verified. The fundamental of the proposed technique can be confirmed as a basic key processing to fabricating metal bellows with various dimensions and small quantities.     

Bulge forming of tubes with axial compressive force proportional to the hydraulic pressure

A device for applying an axial compressive force proportional to the internal hydraulic pressure in tube bulging was designed, constructed and tested. Using this device, copper tubes of diameter 25.4 mm were bulged. By varying the ratio of the axial compressive force to the hydraulic pressure, the largest ratio for maximum bulging was obtained. At lower values of the ratio, fracture occurred at lower circumferential expansions, whereas at higher values buckling of the tube resulted. The hydraulic pressure and the maximum strains at bursting were measured. Bulging in three stages, with interstage annealing, a circumferential expansion to a diameter of 48 mm was obtained. The maximum bulging possible in each stage was determined together with the hydraulic pressures necessary using the optimum ratio of axial load to the internal pressure. Meridional, circumferential, and thickness strains measured in each stage are presented.     

Bending of stainless steel thin sheets by a raster scanned low power CO2 laser

Laser forming of thin metal sheet plates using a low output power CO₂ laser has been successfully performed using a mirror based scanning system. Graphite coated AISI 302 stainless steel plates, 0.3 mm thick, have been bent using a 60 W CO₂ laser with a stepped scanning pattern, varying relevant parameters such as scanning pattern width, scanning step and traverse velocity. Due to the small thickness of the metal plates, the resultant bending mechanism is basically buckling, but with two important differences. Unlike traditional buckling mechanism, it seems possible to predict the direction of the bending, which takes place towards the energy source. Secondly, a thermal gradient mechanism component apparently operates perpendicular to the traversing direction due to the high scanning speed of the laser beam along the scanning direction. Additionally, it has been found that when different scanning pattern widths are used, it is possible to change the turn radius of the bending corners, distributing the bending effect evenly across the scanning width, obtaining very smooth and round corners, more suitable from a mechanical resistance point of view, rather than traditional sharp corners.     

薄壁管材激光弯曲过程热力耦合有限元分析

管材激光弯曲是一种柔性金属塑性加工方法,特别适合薄壁管材弯曲。文章对大径厚比薄壁管材的激光弯曲过程进行热力耦合有限元分析,建立了管材激光弯曲热力耦合有限元分析模型,并进行实验验证。对于薄壁管材激光弯曲,弯曲内侧局部凸起现象较为严重,激光光斑尺寸对凸起程度有一定影响,但不显著。     

Hydrogenography of PdHx thin films: Influence of H-induced stress relaxation processes

Hydrogenography is a new optical thin film combinatorial method that follows hydrogenation and determines its associated thermodynamic properties. Due to clamping to the substrate, stresses generated in thin films are larger than in bulk. This must be taken into account for a comparison between these two types of systems. In this article, we follow the microstructure, surface morphology and in-plane stress changes of thin polycrystalline PdH_x films upon several hydrogen ab/desorption cycles and correlate them to the evolution in shape and hysteresis of pressure–optical transmission isotherms (PTIs) recorded by hydrogenography. The in-plane stress in the first instance is relaxed inhomogeneously by buckling, and a more complete, homogeneous relaxation is only reached after the creation of a buckle-and-crack network that is the two-dimensional analogue of bulk decrepitated grains. This sequence of changes is clearly visible in the PTIs, demonstrating another useful facet of hydrogenography for characterizing metal–hydrogen systems.     

筒坯直径对黏性介质外压缩径成形的影响

针对筒坯直径对黏性介质外压缩径过程的影响问题,采用试验和有限元方法进行了分析,得到了不同筒坯直径条件下1Cr18Ni9Ti薄壁管件的失稳缩径量和极限缩径量。研究结果表明,在缩径区长度一定条件下,筒坯直径对黏性介质外压缩径成形影响较大,失稳缩径量随筒坯直径的增大而减小,极限缩径量随筒坯直径的增大而增大。     

内高压成形起皱行为的研究

对内高压成形起皱过程进行了理论分析、数值模拟和实验研究．分析了加载路径、成形区长径比等因素对皱纹数量和工件成形效果的影响．结果表明：不是所有的皱纹都是失效形式，在某些情况下，管料起皱后仍然可以成形，关键是获得有益皱而不是死皱，通过起皱在成形区聚料是一种有效的预成形方法，该方法拓宽了内高压成形区间．     

一种新型管材液压胀形装置的设计

开发了一种简单实用、可在单动压力机上使用的管材液压胀形装置,用于薄壁金属管材的自由胀形、轴压胀形和异形截面中空件的液压胀形.该装置不需要复杂的外部供液系统,通过增压活塞挤压缸体中液体的方式来为管材成形提供液压力和轴向力,通过设计增压缸体和控制增压活塞的行程等来实现两个载荷的合理匹配.试验表明,该装置结构简单、操作方便、工作可靠;合理的载荷匹配能显著地提高管材液压胀形的成形性能.     

螺杆式连续油管水力振荡器轴向力及其影响因素分析

随着长水平段油气井的增多，外径小、柔性大的连续油管在井下越来越易发生螺旋屈曲锁死以至无法继续下入。连续油管水力振荡器能够有效降摩减阻，延迟螺旋屈曲锁死，增加连续油管的下入深度，因而得到广泛应用。根据螺杆式连续油管水力振荡器工作过程中的运动和受力分析，得出其轴向力计算公式。采用灰色关联度法分析各影响因素对连续油管水力振荡器轴向力的影响程度，得出流量、流体密度以及转子偏心距对其轴向力影响最大。实例计算表明：连续油管水力振荡器最大轴向力随流量、流体密度以及转子偏心距的增加而变大；连续油管水力振荡器轴向力变化频率与流体密度无关，随流量增加而变大，随转子偏心距增加而减小。     

Laser brazing of a dissimilar joint of austenitic stainless steel and pure copper

In many industries, there are applications that require the joining of stainless steel and copper components; therefore, the welding of dissimilar stainless steel/copper joints is a common process. For this investigation, the optimal brazing conditions and suitable filler metals for laser brazing of stainless steel/copper lap joints were studied. Tensile shear force increases with increases in the laser spot diameter or in the laser irradiation angle, which is associated with increased bonding width; however, as bonding width approaches 2 mm, tensile shear force reaches a saturated value due to fracturing at the HAZ of the Cu base plate. In order to obtain joints with high tensile shear strength, laser brazing was optimized by using Cu–Si-based filler metal under the following conditions: laser power, 4 kW; spot diameter, 3 mm; laser irradiation angle, 80°; irradiation position shift, 0.6 mm; brazing speed, 0.30 m/min; and filler metal feed speed, 0.30 min. Concerning filler metals, it was found that the Ni–Cu type showed relatively large tensile shear force even at high welding speeds in comparison with those of the Cu–Si, Cu, Cu–Ni, Ni–Cu and Ni types, respectively.     

新型管材冲击液压成形装置的设计

针对常规的管材液压成形技术需要昂贵的专用设备及模具、生产效率低等不足,开发了一种简单实用、可在冲床或压力机上使用的管材冲击液压成形装置,可用于薄壁金属管材的自然胀形、轴压胀形和异形截面中空件的冲击液压成形。该装置无需外部高压供给系统和专用液压成形设备,通过撞击轴压头挤压容腔中液体的方式来为管材提供液压力和轴压力。通过设计轴压头的行程和调节溢流阀的溢流压力值等来实现最大液压力和轴向进给量的合理匹配,并以304不锈钢毛细管和H65黄铜毛细管为试验管材做了相关试验。研究结果表明:该装置结构简单、操作方便;可实现最大液压力与轴向进给量的协调控制;合理的载荷匹配能显著地提高管材冲击液压成形的成形性能;H65黄铜毛细管破裂时所需的液压力小于304不锈钢毛细管破裂时所需的液压力。     

Application of optical sensor for arc welding

Summary

In CO₂ gas-shielded arc welding, spatter is scattered and adheres to the base metal surface. The main factors affecting any difference in the bonding force remain obscure. This paper examines the bonding force of spatter adhering to the surface of SS400 base metal (rolled steel sheets) under different temperature conditions in CO₂ gas-shielded arc welding using 1.2 mm dia. solid wire. The following four types of base metal surface condition were adopted:

Type 1: As-received surface covered with an oxide film;

Type 2: Ground surface machined with a plain grinder (R_max = 0.6 μm);

Type 3: Surface with fume adhering to the ground surface;

Type 4: Free-ground surface machined with a disc grinder (R_max = 7–16 μm).

The base metal was heated by a 14 mm dia. x 600 mm ceramic heater arranged on the back of the base metal. The bonding force was measured as the shearing force of the spatter. Some 400 spatter particles on each surface were examined. The particles mostly have diameters ranging between 0.4–1.4 mm.

At a base metal temperature below around 450 K, the spatter on the scaled surface is insufficiently hot to melt the base metal and cannot adhere by melting the base metal surface. The shear stress is mostly below around 40 MPa. Despite a rising base metal temperature, however, spatter removal is still possible at less than 300 MPa.

Fume on the surface or the surface roughness do not affect the bonding force as directly as scale on the surface. The temperature, however, affects the bonding force. At a base metal temperature below around 450 K, the bonding force is slightly smaller.

When spatter adheres to the surface, heat causes the microstructure to change with corresponding hardening. The spatter and HAZ of the base metal here show a slightly higher Vickers hardness value (some spatter particles having HV470) than the base metal hardness (HV156–165), although this depends on the surface conditions and temperature.     

Oxidation Behavior of Ni–Cr–Fe-Based Alloys: Effect of Alloy Microstructure and Silicon Content

The oxidation behavior of Ni–Cr–Fe-based alloys in a low oxygen partial pressure atmosphere (H₂–H₂O) was investigated in terms of the effect of alloy microstructure and their silicon content. It was found that the formation and growth kinetics of the oxide scale are rather sensitive to the alloy microstructure and their corresponding Si contents. Oxide ridges were found to form in areas with eutectic structure, while a thin and homogeneous oxide scale formed on austenite matrix. The thicknesses of the oxide ridges and the oxide layer on the austenite matrix were dependent of their corresponding Si contents. The austenite/carbide phase boundaries in eutectic structure can offer fast diffusion paths for metal outward diffusion, which leads to the formation of ridge-like oxide features. The continuous SiO₂ sub-layer formed at the oxide scale/metal interface on the austenitic matrix acted as an effective diffusion barrier to metal outward diffusion, resulting in rather thin and uniform oxide scales.     

Temperature-dependent 2-D to 3-D growth transition of ultra-thin Pt films deposited by PLD

During the growth of thin metal films on dielectric substrates at a given deposition temperature T_d, the film’s morphology is conditioned by the magnitude and asymmetry of up- and downhill diffusion. Any severe change of this mechanism leads to a growth instability, which induces an alteration of the thin film morphology. In order to study this mechanism, ultrathin Pt films were deposited via pulsed laser deposition onto yttria-stabilized zirconia single crystals at different deposition temperatures. The morphological evolution of Pt thin films has been investigated by means of scanning electron microscopy, atomic force microscopy and standard image analysis techniques. The experimentally obtained morphologies are compared to simulated thin film structures resulting from a two-dimensional kinetic Monte Carlo approach. Two main observations have been made: (i) thin Pt films deposited onto ZrO₂ undergo a growth transition from two-dimensional to three-dimensional growth at T_d > 573 K. The growth transition and related morphological changes are a function of the deposition temperature; and (ii) a critical cluster size of i¹ = 4 in combination with an asymmetric Ehrlich–Schwoebel barrier favoring the uphill diffusion of atoms allows for a computational reproduction of the experimentally obtained film morphologies.     

薄壁管在内压、轴力作用下的初始屈服

本文就有限长薄壁管在内压、轴力作用下的初始屈服问题进行了研究 ,推导出了初始力计算公式 ,并进行了实验验证     

薄板激光焊时失稳变形及其控制

对薄板激光焊时出现的失稳变形进行了试验研究,利用CCD记录和观察0.8 mm 和1.5 mm两种厚度的不锈钢板焊接过程中典型的动态变形行为,这种变形行为既包括变形量的大小又包括变形的方向;根据两种厚度薄板表现出的不同变形行为,分析了各自发生失稳的机理.采用冷却水为介质的背面动态冷却方法对失稳变形进行控制,通过对冷热源距离d和冷却水流量q两个主要冷却参数的优化,在有无拘束两种条件下分别得到了0.8 mm和1.5 mm薄板良好的变形控制效果.同时讨论了合理拘束对失稳变形的影响.     

Intergranular films at metal–ceramic interfaces: Part II – calculation of Hamaker coefficients

We report here theoretical calculations indicating the stability of equilibrium nanometer-thick films at metal–ceramic interfaces. Hamaker coefficients were calculated for metal–ceramic interfaces in the presence of a SiO₂-based film, which indicated that a stronger attractive force is expected for intergranular films at metal–alumina interfaces, relative to alumina grain boundaries, correlating to the experimentally measured film thickness presented in part I of this report. From the combination of an attractive van der Waals force together with steric repulsion due to ordering induced in the amorphous film, a force balance can be obtained leading to the formation of equilibrated films at metal–ceramic interfaces.     

On laser welding of thin steel sheets

Abstract

This paper presents a process–structure–property relationship study of laser welds as a continuous consolidation method for joining thin monophased steel foils, thereby providing a more effective, less costly method to construct automotive catalytic converters. A body centred cubic (bcc) iron–chromium–aluminium alloy doped with Mischmetal was utilised in this study. Both pulsed and continuous wave modes were used to establish the limit welding diagrams for lap joint configuration. Actual laser welding parameters were selected using several testing conditions. The laser welds behaved substantially different from the base material under creep and high temperature oxidation. The difference was mainly attributed to the changes in grain morphology, precipitation of aluminium nitrides and carbides, and relocalisation of the reactive elements during liquid metal flow upon keyhole formation, solidification and cooling.     

Deformation Characterization of Friction-Stir-Welded Tubes by Hydraulic Bulge Testing

In this article, the large-diameter thin-walled aluminum alloy tubes were produced using a hybrid process combining friction-stir welding (FSW) and spinning. For this novel process, rolled aluminum alloy sheets with a thickness about 2–3 times the wall thickness of target tube, were FSW to form cylinders, and then the cylinders were subjected to spinning to get thin-walled aluminum alloy tubes. Both experimental and simulation study were conducted to investigate the deformation characterization of the FSW tube during hydraulic bulge testing, and the stress and strain states and thickness distribution of the FSW tube were investigated. It was found that the common defects of FSW tube can be significantly improved by specific welding devices. The ductility of the tube is considerably improved with nearly two times higher bulge ratio than as-spun tube after annealing treatment at 300°C. But the annealed tube still shows a high nonuniform wall thickness distribution due to the inhomogeneous deformation characteristics. With increasing deformation of the tube, the gap between the hoop and axial stress for the weld and base metal (BM) decreases. However, the hoop and axial stress of the weld are always greater than those of the BM at the same pressure.