FEM analysis of vacuum hot bulge forming of Hastelloy C-276 thin-walled cylindrical workpiece

A stress relaxation test has been carried out for Hastelloy C-276 at temperature of 800 ~C and initial stress level of 250 MPa. Based on the experimental stress relaxation curve, the relationship between creep strain rate and stress has been derived. Then, a set of creep constitutive equations has been built and the values of constants arising in the constitutive equations have been determined by fitting the creep strain rate-stress curve. Close agreement between computed results and experimental ones is obtained for stress relaxation data. The creep constitutive equation set has been integrated with the commercial FE （finite element） solver MSC.Marc via the user defined subroutine, CRPLAW, for the vacuum hot bulge forming process modelling of Hastelloy C-276 thin-walled cylindrical workpiece. The temperature field, the radius-direction displacement field and the stress-strain field are calculated and analyzed. Furthermore, the bulging dimension and the final internal diameter of workpiece are predicted and the test results verify the reliability of the finite element method.

Research on Two-Step Hydro-Bulge Forming of Ellipsoidal Shell with Larger Axis Length Ratio

The two-step hydro-bulge forming technique was proposed to manufacture the ellipsoidal shell with the length ratio of the long axis to the short axis larger than 1.4. A central tube was introduced into the first step of the hydro-bulge forming process to constrain the over growth of the short axis during bulging,and then the central tube was replaced with two polar plates in the second step of the hydro-bulge forming process to manufacture an integral ellipsoidal shell. It is shown that the central tube restricts the growth of the short axis and simultaneously reduces the shrunk tendency of the long axis. The wrinkling occurs due to the latitudinal compressive stress at the equator at the early stage of hydro-bulge forming. However,with the increase of internal pressure,the compressive stress areas gradually decrease and finally the tensile latitudinal stress occupies approximately the whole shell,thus the wrinkles are eliminated. A sound ellipsoidal shell with the axis length ratio of 1.8 is obtained after two-step hydro bulging.

Effect of temperature on vacuum hot bulge forming of BT20 titanium alloy cylindrical workpiece

Temperature is one of the key parameters for BT20 titanium alloy cylindrical workpiece manufactured by vacuum hot bulge forming. A two-dimensional nonlinear thermo-mechanical coupled FE model was established. Numerical simulation of vacuum hot bulge forming process of titanium alloy cylindrical workpiece was carried out using FE analysis software MSC Marc. The effects of temperature on vacuum hot bulge forming of BT20 titanium alloy cylindrical workpiece were analyzed by numerical simulation. The simulated results show that the Y-direction displacement and the equivalent plastic strain of the workpiece increase with increasing bulge temperature. The residual stress decreases with increasing bulge temperature. The optimal temperature range of BT20 titanium alloy during vacuum hot bulge forming is 750-850 ℃. The corresponding experiments were carried out. The simulated results agreed well with the experimental results.

Experimental and Numerical Investigation of Cold Bulge Forming of Titanium Alloy Ti55

In this paper, cold bulge forming of titanium alloy Ti55 was investigated. This process was done successfully and titanium alloy Ti55 was formed completely. Also, in the numerical work, this process has been investigated using Abaqus/ Explicit code. The results show that there is a good agreement between experimental and numerical results. Mechanical properties of Titanium alloy Ti55 have been investigated before and after bulge forming. The results show that mechanical properties of titanium alloy Ti55 have been improved during bulge forming. Also, hardness, and thickness variation tests of sheet metal before and after bulge forming were performed and the same results to mechanical properties were obtained.

Research on Extrude-bulge Forming of Tee Tubes with Plastic Medium

This paper presents an experimental research on extrude-bulge forming of tee tubes with plastic medium,an universal device especially designed for this forming process and some parameters having effects on the forming process.Comparison of results of the theoretical analysis with experimental results shows a very good agreement between them.

Bulging in incremental sheet forming of cold bonded multi-layered Cu clad sheet: Influence of forming conditions and bending

Bulge is a defect that causes geometrical inaccuracy and premature failure in the innovative incremental sheet forming (ISF) process. This study has two-fold objectives:(1) knowing the bulging behavior of a Cu clad tri-layered steel sheet as a function of forming conditions, and (2) analyzing the bending effect on bulging in an attempt to identify the associated mechanism. A series of ISF tests and bending analysis are performed to realize these objectives. From the cause-effect analysis, it is found that bulge formation in the layered sheet is sensitive to forming conditions in a way that bulging can be minimized utilizing annealed material and performing ISF with larger tool diameter and step size. The bending under tension analysis reveals that the formation of bulge is an outgrowth of bending moment that the forming tool applies on the sheet during ISF. Furthermore, the magnitude of bending moment depending upon the forming conditions varies from 0.046 to 10.24 N·m/m and causes a corresponding change in the mean bulge height from 0.07 to 0.91 mm. The bending moment governs bulging in layered sheet through a linear law. These findings lead to a conclusion that the bulge defect can be overcome by controlling the bending moment and the formula proposed can be helpful in this regards.

Friction coefficient in rubber forming process of Ti-15-3 alloy

The forming limit diagram of Ti-15-3 alloy sheet was constituted at room temperature. The effects of different punch and rubber hardness on the limit principal strain distributions were investigated experimentally. Finite element analysis models of the samples with dimensions of 180 mm×180 mm were established to analyze the friction coefficients of different interfaces. Effects of various friction coefficients on the strain distributions were studied in detail. Finally, the friction coefficients in the cold forming were determined by contrasting the strain results between the experimental data and the simulated ones.

毛囊bulge干细胞培养方法的比较研究

目的通过对限定性角质形成细胞无血清培养基(DK-SFM)和3T3滋养层培养毛囊bulge干细胞的比较,寻求既能方便获得大量毛囊bulge干细胞,又能减少其分化的理想培养条件。方法采用DK-SFM和3T3滋养层分别培养毛囊bulge干细胞,通过倒置显微镜观察毛囊bulge干细胞的形态,免疫荧光染色检测毛囊bulge干细胞的特异性标记细胞角蛋白19(CK19)和分化相关抗体群34(CD34)的表达鉴定毛囊bulge干细胞。通过比较2种方法培养的毛囊bulge干细胞的克隆形成率和CD34阳性率的差异,分别比较毛囊bulge干细胞的增殖能力和干细胞的数量,综合评估2种培养方法的优劣。结果倒置显微镜观察2种培养方法所得毛囊bulge干细胞均为铺路石状。免疫荧光染色检测2种培养方法培养的毛囊bulge干细胞CK19和CD34均呈阳性。DK-SFM和3T3滋养层培养的毛囊bulge干细胞克隆形成率分别为69.4%和62.2%。流式细胞仪检测DK-SFM培养的毛囊bulge干细胞中CD34阳性率为72.3%;3T3滋养层培养的毛囊bulge干细胞中CD34阳性率为34.7%。结论DK-SFM和3T3滋养层培养作为毛囊bulge干细胞的2种培养方法,均可以获得未分化的毛囊bulge干细胞。用3T3滋养层培养毛囊bulge干细胞的方法比较复杂,且所获的细胞混杂有3T3细胞,但用此种方法可获得大量的毛囊bulge干细胞。用DK-SFM培养毛囊bulge干细胞方法简单,但细胞不易贴壁,且数量较少,但能有效分离出较纯的毛囊bulge干细胞,保持较好的细胞活性。

Novel approach for analysis of deformation behavior of thin-walled tube in free hydro-bulging process

Based on the assumption that profile of thin walled tube in free hydro-bulging process is a quadratic curve and any point on the profile moves vertically to the profile, mathematical models were deduced for analyzing the deformation behavior. The critical pressure and the maximum bulge coefficient(height) at bursting can be determined based on the models, in which a shape factor a is introduced to tightly communicate the material property and geometric parameters to plastic deformation. Free hydro-bulging experiments of stainless steel and low carbon steel tubes were conducted to validate the models, and the experimental data indicate that the theoretical predictions are reliable and accurate. The results display that the profile, dependent on the material and geometric parameters, can be hyperbola, parabola, arc and ellipse or alternative among them; moreover, the forming pressure and forming limit are both closely connected with material and geometric parameters.

Theoretical prediction and experimental investigation on formability of tailor-welded blanks

Based on the elastoplastic mechanical properties of the weld and heat affected zone metals obtained by a nanoindentation test, a theoretical calculation model was established for the forming limit diagram（FLD） of tailor-welded blanks（TWBs） on the basis of plastic constitutive relations and Hosford yield criteria. Hemispherical punch bulging tests were performed to verify the FLD theoretical calculation results. The results demonstrated that not only the FLD theoretical calculation of base materials but also that of TWBs had a good agreement with their experiments. Besides, poorer formability of TWBs caused its FLD significantly lower than that of base materials. The theoretical calculation model offers a reliable approach to obtain the specific FLD of TWBs.

Viscous warm pressure bulging process of AZ31B magnesium alloy with different ellipticity dies

Based on the bulging principle of different ellipticity dies, the methyl vinyl silicone rubber with excellent thermal stability and heat transfer performance was chosen as the viscous medium. The finite element analysis and experiments of viscous warm pressure bulging （VWPB） of AZ31B magnesium alloy were conducted to analyze the influence of different ellipticity dies on the formability of AZ31B magnesium alloy. At the same time, based on the grid strain rule, the forming limit diagram （FLD） of VWPB of AZ31B magnesium alloy was obtained through measuring the strain of bulging specimens. The results showed that at the temperature range of viscous medium thermal stability, the viscous medium can fit the geometry variation of sheet and generate non-uniform pressure field, and as the die ellipticity increases, the difference value of non-uniform pressure reduces. Meanwhile, according to the FLD, the relationship between part complexity and ultimate deformation was investigated.

DETERMINATION OF PRESSURIZING CURVE AND COMPUTER CONTROL OF THICKNESS THINNING FOR SUPERPLASTIC BULGING

This paper proposes the assumption that the flow with viscous friction is the stretch of part of the sheet that lies along the walls of a die during the process of superplastic bulging according to superplastic flow equation and geometrical model of bulging of a sheet into a long trapezoid groove or truncated cone, by introducing the friction-factor P which describes the friction effect on the process. Also, the paper proposes the method of controlling thickness nonuniformity and develops the equipment which for uniform thickness of bulging, is automatically controlled with a computerl it also analyzes the important innuence of lubrication on thickness distribution of bulging materials. By the assumption, the relationship between bulging pressure and time is obtained in bulging of a sheet into the groove and cone, and p-t curve of multi-mould-cavity complicated bulging is discussed based on the analysis of single-mould-cavity bulging characteristics.

Numerical simulation of influence of viscous adhesive stress on viscous pressure bulging process of hemispherical sphere

The mechanical model of viscous pressure bulging process is presented. The viscous pressure bulging process of hemispherical sphere is analyzed by the numerical simulation and experiments. The research results show that the viscosity of viscous medium significantly affected the thickness distribution, strain distribution and shape of hemispherical sphere, which provides analytic basis for selecting reasonably viscous medium and designing process of viscous pressure forming.

基于微分方程曲面求交跟踪法的包容式节点相贯区域建模研究

包容式节点是一种新型管状相贯式节点,其形态是一种典型的薄壁自由曲面结构。在进行曲面造型过程中会涉及曲面求交的问题,而曲面求交是计算机辅助几何设计(CAGD)领域中的关键技术之一。本文构建了包容式节点非均匀有理B样条(NURBS)曲面模型,将求包容式节点中的相贯线问题转化为NURBS曲面的求交问题。基于微分方程的跟踪算法原理,在分割法求得初始交点的基础上,采用微分方程追踪法求出所有交点,最后将所求得交点进行曲线拟合,交线包围区域即为包容式节点与腹杆相贯焊接区域。

TA2/Q235B复合板不同作用面成形极限及界面损伤行为

采用Nakazima实验法对不同尺寸的退火态TA2/Q235B复合板样品进行胀形实验,研究不同作用面对TA2/Q235B复合板的成形极限和界面损伤行为的影响。结果表明,当凹模与碳钢侧接触时,由于接触材料、界面变形协调能力和应变状态的不同,复合板的胀形高度和成形极限增加,其中R140试样的极限拱高达到最大值(46.17 mm),R60和R180试样在3个方向上的厚度减薄量和界面裂纹更大。此外,由于硬度和拉应力不同,两组样品中所有的水平和斜向孔都向纯钛侧延伸。

GLARE层板液压胀形成形极限研究

纤维增强金属层板(FMLs)凭借其卓越的力学性能在众多领域中得到了广泛应用,成为当今研究的焦点。为解决未固化层板成形性及破裂形式不清晰的问题,本研究采用液压胀形试验,探讨了在不同边界条件下GLARE层板的成形极限。首先,借助理论方法建立了胀形顶点区域各组分材料受力表达式,并讨论了层间摩擦对成形极限的影响。其次,通过液压胀形试验分析了流体压力作用下纤维增强金属层板的失效形式,并建立了典型成形极限曲线图。最后,借助有限元仿真对上述试验进行了复现,研究结果表明,层间摩擦的增加显著降低了纤维增强金属层板的成形性,与理论分析及实验数据一致。该成形极限图不仅可以对成形效果进行评估,也为工艺参数优化提供参考依据。

分区域软模调控对Al1060板材胀形过程变形行为的影响

针对传统软模成形中软模性能整体调控与零件不同变形区域差异化需求的矛盾,采用磁流变液作为成形软模材料,在分区域软模调控下对Al1060板材开展了软模胀形试验与模拟研究,重点关注了中心主导磁场和边缘主导磁场对板材变形行为的影响。结果表明,采用分区域软模调控的方法可显著改变板材胀形过程中的变形行为。中心主导磁场下试件椭圆度为0.85,破裂位置位于磁场突变处,应变最大值出现在半径约10 mm位置;边缘主导磁场下试件椭圆度为0.47,破裂位置则位于凹模圆角附近,整体应变分布更为均匀。不同区域的磁流变液力学特性的差异影响了板材的变形和受力状态,最终导致胀形件构型和破裂位置发生改变。

有限长薄壁管胀形研究

本文采用塑性增量理论研究了有限长薄壁管胀形过程中的应力、应变关系，提出了薄壁管胀形的应力、应变数值计算理论，解决了薄壁管胀形工艺的工程计算问题。文中首次提出了内压可行域、轴压可行域的概念，阐述了正确制定胀形加载路径应遵循的原则。理论计算与测试结果吻合较好。为应用管材生产凸形零件奠定了理论基础。

板材零件成对液压成形新技术

板材成对液压成形技术是一种新的板材成形技术 ,具有成形性好、制造工期短、费用低等优点 ,特别适用于批量小、形状复杂板材零件的生产 .介绍了板材成对液压成形技术的成形原理、成形过程、分类及研究现状 .