圆柱体热锻件内部单空洞闭合的模拟分析

为了在热锻中消除锻件内部的空洞缺陷, 本文采用有限元技术对圆柱体内不同位置的单空洞的闭合进行数值模拟, 同时用内部带有人工生成空洞的聚碳酸酯圆柱体试件, 进行了光塑性物理模拟。通过分析模拟结果得出, 空洞位于圆柱体心部闭合最易, 其位置越接近端面或外表面闭合越难; 数值模拟和物理模拟的结果基本相同,数值模拟得到物理模拟的充分验证, 指出数值模拟的有效性和其与物理模拟相结合的重要性。     

圆柱体内部空洞热锻闭合过程的数值模拟

通过合理制定热锻工艺来消除材料内部缺陷是材料加工领域的重要课题。本文应用商用有限元软件MARC ,模拟了圆柱体热镦粗时内部空洞的闭合过程 ,分析了空洞变形时的应力和应变以及影响空洞闭合和焊合的各种因素。模拟结果表明 ,变形过程中空洞边缘微小区域内会产生双向拉应力 ,直到闭合时拉应力才会变成压应力。压下方向的应变是绝对值最大的应变 ,主导着空洞的闭合过程。高温下的空洞闭合后能够立即完成再结晶过程 ,但空洞焊合需要一定的保温时间     

大锻件内空洞形状对闭合影响的模拟研究

利用有限元分析法研究了大锻件内部不同形状空洞在镦粗过程中的闭合情况,以及空洞周围的应力情况.结果表明,椭球形空洞的横轴与竖轴数值之比越大,空洞的闭合情况越理想;基于对空洞闭合过程中应力、应变的追踪分析,提出了一种判断空洞闭合的量化分析方法.     

大型锻件心部空洞型缺陷控制的数值模拟研究

为在锻造过程中消除大型锻件心部的空洞型缺陷,采用数值模拟和实验研究方法对大型圆柱体锻件内部空洞的闭合规律进行研究。以锻件高径比、压下率和空洞位置为试验因素设计正交试验,运用商业软件Deform-3D对试验方案进行数值模拟,分析各因素对空洞闭合的影响效应。研究结果表明:压下率是影响空洞闭合的主要因素,其次是空洞位置和锻件高径比;锻件高径比为1时空洞最易闭合;空洞的闭合度随着压下率的增加而增加;空洞位置在锻件高度方向距中心越近越易闭合。     

钢锭开坯过程空洞缺陷闭合过程的数值模拟研究

采用数值模拟技术结合实际锻造工艺,研究钢锭开坯过程空洞缺陷的闭合规律。研究结果表明:沿轴线分布的空洞直径为钢锭直径130时,当镦粗压下量为50%时,除难变形区的空洞外,其他位置的空洞都可以闭合;当空洞直径不大于钢锭直径120时,空洞尺寸对空洞闭合表征参数Q的临界值没有影响,其值为0. 3;对于镦粗过程难变形区未闭合的空洞,在后续经过5道次拔长,完全可以闭合。该研究结果对钢锭开坯过程空洞缺陷压实具有一定的指导作用。     

基于有限元的汽车曲轴锻件空洞闭合研究

空洞是大型锻件内部的一种常见缺陷,为了提高锻件的性能,必须将其消除.基于有限元软件分别选取高径比、摩擦系数、空洞尺寸、温度、锻件尺寸等因素对空洞的闭合过程进行了模拟.结果表明:影响空洞闭合的主要因素为高径比、温度及摩擦系数.这在很大程度上深化了对空洞闭合的认识.     

大锻件内部空洞的锻合压下率

采用大变形热力耦合有限元法模拟了圆柱体锻件心部空洞的热锻闭合压下率。基于数值模拟结果 ,分析了影响空洞闭合的主要因素及其影响规律 ,构造了考虑各种影响因素在内的锻合压下率计算公式。应用该公式得到的心部锻合压下率与有限元计算结果的相对误差不超过 6 % ,从而在计算锻合压下率时可代替有限元法 ,便于工程技术人员应用     

大型锻件热处理过程的数值模拟研究

在对大型锻件传热分析的基础上，建立了大型锻件的物理模型，对其温度场的变化规律进行了模拟计算，同时将模拟结果和试验结果进行对比分析，最后对26Cr2Ni4MoV钢电机转子的调质处理进行了模拟计算，从而说明了热处理过程的数值模拟方法的准确性和优越性，为进一步分析此类工件的组织转变和应力应变等奠定了基础。     

45钢内部裂纹愈合过程孔洞闭合的数值模拟

在塑性变形条件下,内裂纹愈合过程一般经历裂纹的闭合及焊合两个阶段.闭合阶段可使裂纹内界面充分接近,为焊合阶段实现界面的金属键结合提供有利条件.本文以带有内部球形孔洞的45钢圆柱体试样为例,利用大型有限元分析软件ANSYS,数值模拟了压缩变形时试样内部球形孔洞的闭合过程.分析了孔洞闭合过程形态演化特点和孔洞附近的应力状态.     

大型锻件热处理过程的数值模拟研究

在对大型锻件传热分析的基础上 ,建立了大型锻件的物理模型 ,对其温度场的变化规律进行了模拟计算 ,同时将模拟结果和实验结果进行对比分析 ,最后利用模拟计算对材料为 2 6Cr2Ni4MoV的某一电机转子的调质处理进行了模拟计算 ,从而说明了热处理过程的数值模拟方法的准确性和优越性。为进一步分析此类工件的组织转变和应力应变等奠定了基础。     

A criterion for void closure in large ingots during hot forging

A quantitative investigation of the mesomechanism of void closure in large ingots during hot forging is undertaken in the present study. The constitutive relation of the void-free matrix is assumed to obey the Norton power law. A cell model which includes matrix and void is employed and a Ritz procedure is developed to study the volumetric strain-rate of the void. On the basis of a large number of numerical computations, a criterion for void closure in large ingots during hot forging is proposed. In addition, the significant effects of the Norton exponent, the remote stress triaxiality and the remote effective strain on void closure are revealed: (1) the volumetric strain-rate of the void increases monotonically as the stress triaxiality level and the Norton exponent of the material increase, (2) the remote effective strain required for void closure decreases as the stress triaxiality level and the Norton exponent increase and (3) the void becomes unstable and the collapse rate decreases at the final stages of void closure. With the criterion for void closure, process design and optimization in terms of elimination of voids in large ingots will be convenient since the criterion can be easily applied in CAE analysis.     

A study of pore closure and welding in hot rolling process

The design of processing conditions to eliminate porosity in steel during hot rolling has become more critical with the advent of continuously cast feed stock. To predict appropriate process parameters, experiments were performed in which holes were drilled in steel slabs, at different depth below the surface perpendicular to the rolling direction. After hot rolling, the state of the deformed holes was examined by optical microscopy. The fracture surfaces of tensile specimens notched in the plane of the closed holes were examined under a scanning electron microscope to investigate the bonding ( welding ) between the surfaces of the closed holes because this bonding is the most important factor indetermining the transverse mechanical properties of the rolled product. The deformation of such holes in the roll gap was modelled as an clastic / plastic plane strain problem using the FE software ABAQUS to investigate the strain and stress around holes and to analyze the conditions required to promote pore closure and welding between the closed surfaces.

Experiment results showed that the rate of pore closure was affected by the parameters of rolling process and the position of holes relative to the rolling contact surfaces. FE simulation of pore closure showed a good agreement with experimental results and showed that a certain level of hydrostatic pressure resulted in the closure of pore and that the holding period of the pressure in the compressive state determined the degree of welding of surface of pores; shear is favourable to this welding.     

钢锭内部孔隙性缺陷锻合过程的数值模拟

通过比较圆柱体试样内部孔洞锻合过程的模拟计算结果和实验结果,确立了钢锭内部孔隙性缺陷锻合过程的模拟法,并对长孔型缺陷和短孔型缺陷的锻合过程进行了计算,得到各类孔洞的闭合规律,且定量给出了不同位置处孔洞闭合时所需的临界压下率。从孔洞闭合的力学本质角度,对钢锭内部的等效应变分布情况进行了研究。结果表明,孔洞的闭合完全是由于应力集中并达到一定程度的变形所引起的。其中,四面体孔最难闭合,为所有孔洞锻合所需临界压下率的上限值。锻合区域的给出,为制订锻造工艺提供了理论依据。     

Internal void closure during the forging of large cast ingots using a simulation approach

Large cast ingots often contain defects or undesirable microstructural features, such as voids and zones related to casting. Some of these features can remain after hot open die forging, which is an important process for converting large cast ingots into wrought components. During the initial cogging and deformation steps prior to the detailed open-die-forging operations, any internal voids should be eliminated. The present work focuses on the closure of internal voids during open die forging so as to produce a sound component. Hot compression tests were conducted to obtain the flow strength of the cast microstructure at different temperatures and strain rates. The measured flow strength data together with other appropriate material properties were used to simulate the forging steps for a large cast ingot. The numerical simulations for the forging deformation and for the internal void behavior were performed using DEFORM-3D™. Actual defects were measured in commercial ingots with an X-ray scanner. The simulation results for the void deformation behavior are compared with voids measured before and after forging. Through the comparison of experimental results and numerical simulation, a criterion for void closure is proposed. The criterion is that a local effective strain value of 0.6 or greater must be achieved for void closure during forging. Such a criterion can be used in conjunction with simulations to insure that a sound component is produced during the hot open die forging of large cast ingots.     

无缝气瓶收口热旋压成形过程的数值模拟及分析

通过MSC.Marc有限元分析软件模拟气瓶收口热旋压的成形过程,分析了在不同温度和进给率下管坯壁厚、等效应变速率、应力及旋压力的变化规律.结果表明:径向旋压力与总旋压力很接近,导致管坯周向受压,壁厚在不同区段出现程度不同的减薄和增大;随着旋压温度和旋轮进给率的增加,管坯起旋点处单元壁厚减薄增加,直壁和口部单元的壁厚增厚...     

The structural evolution of superalloy ingots during hot working

This article provides an overview of structural changes that occur during the hot working of superalloys and provides insight into the use of precipitated particles and other thermomechanical factors to achieve desired structures. Examples will focus primarily on alloys 718 and 720, which are iron-nickel and nickel-based alloys, respectively. The availability of a second phase to control grain size is a characteristic of some iron-nickel-and nickel-based superalloys that is not usually available to cobalt-based superalloys; processing with and without the use of a precipitated phase that influences microstructures will be illustrated by the use of these examples. Editor’s Note: A hypertext-enhanced version of this paper can be found on JOM’s web site at www.tms.org/pubs/journals/JOM/9901/ForbesJones-9901.html. Robin M. Forbes Jones earned his Ph.D. in metallurgy at Imperial College of Science and Technology, London University, in 1967. He is currently manager of long-range product/process R&D for Allvac. Laurence A. Jackman earned his Ph.D. in metallurgy at Rensselaer Polytechnic Institute in 1967. He is currently chief materials scientist at Allvac. Dr. Jackman is also a member of TMS.     

一种预测金属锻造过程失稳变形的模拟方法

提出一种利用失稳变形区热力参数窗口条件和有限元模拟相结合来预测锻造失稳变形的方法,并以Ti-6.5Al-3.5Mo-1.5Zr-0.3Si 合金为例,将该钛合金的失稳变形区热力参数窗口条件集成到商业化的有限元模拟软件平台中。利用二次开发后的有限元模拟软件平台模拟了该钛合金在热压缩过程中失稳变形区的分布及其变化。模拟预测结果与实验结果吻合较好,说明所提出的失稳变形模拟与预测方法是可行和有效的。