深拉成形液氮生物容器残余应力数值模拟研究

深拉成形具有制造工艺简单、制造效率高等优点,在压力容器制造中得到了广泛应用,但是经过该方法成形的不锈钢圆筒件容易产生残余应力,影响液氮生物容器质量。文中为了研究压边力、摩擦系数、凹模圆角半径三个主要深拉成形工艺参数对残余应力的影响,建立了液氮生物容器圆筒件数值模型,通过Box-Benhnken响应面法设计试验方案,采用Abaqus软件进行数值模拟计算。结果表明:试验工况下圆筒件最大残余应力均发生在直筒上端部位和直筒与封头连接处,封头上残余应力分布及大小基本相同;压边力越小时,残余应力越大,也越容易出现褶皱,而凹模圆角半径越大时,残余应力越大,但是越不容易出现褶皱,摩擦系数对残余应力影响不大。

深拉成形和3D打印对柱胞轴向压缩吸能性能的影响

设计了一种薄壁半椭球壳体柱胞单元,采用深拉成形工艺和3D打印技术分别制备了柱胞单元,对比分析了两种加工工艺下柱胞单元轴向压缩吸能性能的差异,基于胞体吸能机理,研究了预应变对柱胞吸能的影响。研究表明:轴向压缩前期,3D打印柱胞与深拉成形柱胞屈服规律相似,但3D打印柱胞压缩荷载要略低于深拉成形柱胞;随着压缩距离增大,3D打印柱胞峰值压缩荷载明显低于深拉成形柱胞,但两种加工工艺制备柱胞的最终变形模式相似。深拉成形工艺加工制备的柱胞虽然精度不如3D打印技术,但是其基体材料存在较大的预应变,增大了材料屈服应力,压缩深拉成形柱胞需要更多的荷载,并能够吸收更多的能量。与3D打印相比,深拉成形柱胞吸能性能更优越。

深拉型搪瓷内胆用热轧钢带开发及应用

热水器搪瓷内胆结构由三段式升级为二段式,内胆毛坯的成形方式由卷圆成形+冲压成形方式转变成深拉成形方式,相应的钢板也必须满足深拉成形要求。由于搪瓷内胆结构的变化,对钢板提出了更高的要求,在保障涂搪性能的基础上还需更好的深拉性能。宝钢运用钢厂工业数据与试验设计(DOE)工具,建立钢种设计优化模型,开发出了深拉型搪瓷内胆专用热轧钢板。经工业大生产验证,深拉件报废比例可以控制在千分之四以内,涂搪性能优良。

Reverse deep drawability of 5A06 aluminum alloy plate at elevated temperatures

In order to avoid the occurrence of fracture at room temperature in reverse deep drawing of aluminum alloy plate, the warm reverse deep drawing method was proposed. The experiments were conducted at room temperature, 280 and 360 ℃ with a 4.5 mm thick 5A06 aluminum alloy plate. The effect of temperature, blank-holding force and gap on the fracture and wrinkle of the reverse deep drawing process was investigated. A fully coupled thermal-mechanical simulation was carried out to obtain the stress distribution through the commercial software of Abaqus/Explicit. The results show that the fracture is avoided at 280 ℃ since the bending-induced stress gradient in the transient area between the inside corner and the straight wall decreases from 505 MPa at RT to 72 MPa at 280 ° C. Although the fracture is avoided as the temperature increases, the wrinkle occurs at the outside die corner at temperature over 280 ° C, where the circumferential compressive stress becomes larger than that at the inside. As the temperature increases to 360 ℃, the fracture occurs due to the excessive softening, the tensile stress in the straight wall reaches rapidly to the tensile strength at the beginning of reverse deep drawing. When 1.5t （t=4.5 mm） blank holding gap is applied at 280 ℃, both the fracture and wrinkle can be avoided, and 420 mm deep cups are drawn successfully.

Flexible-die forming process with solid granule medium on sheet metal

Certain non-metallic granules （NMG） were selected as the research object. It was proposed to conduct the volume compression experiments as well as those on the NMG physical properties at high stress levels. Then, not only the volume compression ratio curve but also the extended Drucker-Prager linear model were obtained. In addition, through the friction strength tests, parameters of the Mohr-Coulomb model were gained, which proved in basic agreement with those of the extended Drucker-Prager linear model. Additionally, curves of the friction coefficients between the NMG and the sheet metal trader different pressures were also obtained. Based on the material performance experiments, numerical analysis in respect of flexible-die forming process with solid granule medium （SGM） was conducted. The die and device for experiments of solid granule medium forming （SGMF） on sheet metal were designed and manufactured. Typical parabolic parts were successfully trial-produced. The tests and simulation results show that the sheet formability is significantly improved for the extraordinary friction performance during interaction between the SGM and the sheet metal surface. The process control and die structure are simple, and the shaped work-pieces enjoy many advantages, such as satisfactory surface quality and favorable die fitability, which offers a brand-new method and means for processing and preparation of sheet metals.

Effects of stress state on texture and microstructure in cold drawing-bulging of CP-Ti sheet

Three different stress states of the combination of tensile（t） stress and compressive（c） stress,t t,t c and t c c,exist in the deformed commercially pure titanium（CP-Ti） sheet during cold drawing-bulging.The textures and microstructures in the different stress state regions were investigated by means of XRD and TEM analysis.Similar development of texture and microstructure is achieved with less thickness strain under multiaxial stresses in drawing-bulging than in cold rolling.The results show that texture and microstructure are much sensitive to multiaxial stresses.Twinning is more easily activated under compressive stress than tensile stress.Prism a slip is heavily affected by tensile stress,resulting in a remarkable change of the intensity of（0°,35°,0°） texture,while pyramidal c＋a slip,forming（20°,35°,30°） texture,weakens with the increase of thickness strain in spite of stress state.

Prediction of fracture limits of Ni-Cr based alloy under warm forming condition using ductile damage models and numerical method

The stretch forming and the deep-drawing processes were carried out at 300 and 673 K to determine the safe forming and fracture limits of IN625 alloy.The experimentally obtained strain-based fracture forming limit diagram(FFLD)was transformed into a stress-based(σ-FFLD)and effective plastic strain(EPS)vs triaxiality(η)plot to remove the excess dependency of fracture limits over the strains.For the prediction of fracture limits,seven different damage models were calibrated.The Oh model displayed the best ability to predict the fracture locus with the least absolute error.Though the experimentally obtained fracture limits have only been used for the numerical analysis,none of the considered damage models predicted the fracture strains over the entire considered range of stress triaxiality(0.33<η<0.66).The deep drawing process window helped to determine wrinkling,safe and fracture zones while drawing the cylindrical cups under different temperature and lubricating conditions.Further,the highest drawing ratio of 2 was achieved at 673 K under the lubricating condition.All the numerically predicted results of both stretch forming and deep drawing processes using the Hill 1948 anisotropic yielding function were found to be good within the acceptable range of error.

Instability analysis of free deformation zone of cylindrical parts based on hot-granule medium-pressure forming technology

The cylindrical part of sheet metal based on hot-granule medium-pressure forming (HGMF) technology was investigated.The stress functions of the free deformation zone and the fracture instability theory were combined to establish the analytical expression of the critical pressure of punch. The results show that the active friction between the granule medium and the sheet metal, as well as the non-uniform internal pressure presented by the solid granule medium, can obviously improve the forming performance of the sheet metal. The critical pressure of punch increases with the increment of the friction coefficient between the granule medium and sheet metal, as well as the plastic strain ratio, whereas it decreases with the increase of the material-hardening exponent. Furthermore, the impact on the critical pressure from high to low order is the plastic strain ratio, the friction coefficient,and material-hardening exponent. The deep-drawing experiment with HGMF technology on AZ31B magnesium alloy sheet verified the instability theory.Key words: hot-granule