Numerical Study on Motions of Rolls in Hot Rolling of Titanium Alloy Large Rings

由于钛合金对应变速率十分敏感,因此轧辊运动对钛合金大环热辗扩成形过程有重要作用。提出了相对速率vr的概念来表征轧辊运动参数的综合作用,涉及的运动参数包括驱动辊旋转速率n1和芯辊进给速率v,并且基于稳定成形条件采用解析方法确定了vr的合理取值范围。其次,运用动力显式有限元程序ABAQUS/Explicit 建立了可靠的钛合金大环热辗扩成形过程的热力耦合三维有限元模型。最后,采用有限云模拟方法,探究了vr对该成形过程的影响效应及其机制。结果表明;尽管通过减小n1来增大vr与通过增大v来增大vr 均使每转进给量△ hi 增大,但它们对成形过程的影响效应并非完全一致,比如对非均匀应变分布的影响;较大的vr有助于提高成形环件的端面质量和应变与温度分布的均匀性,但对成形力有不利影响。     

FE analysis on Deformation and Temperature Nonuniformity in Forming of AISI-5140 Triple Valve by Multi-Way Loading

In triple valve forming process by multi-way loading severely nonuniform deformation and temperature distributions are prone to occur, which may lead to poor forming quality and macro-micro defects. A 3D coupled thermo-mechanical rigid-viscoplastic finite element (FE) model for multi-way loading forming of AISI-5140 steel equal diameter triple valve was developed based on DEFORM-3D. Through comprehensive simulation and analysis, the influences of main process parameters on the forming process and nonuniformity of deformation and temperature were studied. The results showed that: (1) the degree of deformation nonuniformity decreased with the increase of the punch loading speed, initial temperature of billet, or the decrease of the friction factor; (2) the average temperature of forming body increased as the punch loading speed, initial temperature of billet and the friction increased, while the degree of temperature nonuniformity decreased with the increase of punch loading speed or decrease of initial billet temperature.     

驱动辊转速对铸态42CrMo钢环件热辗轧微观组织的影响规律

环形铸柸微观组织的演变规律及合理控制是环类零件铸辗复合成形新技术发展面临的主要瓶颈问题.驱动辊转速是影响铸坯材料再结晶行为及组织状态的关键因素之一.本文基于ABAQUS平台,建立了42CrMo铸坯环件热辗轧的宏微观有限元模型,模拟揭示了环形铸坯材料的动态再结晶行为,阐明了驱动辊转速对再结晶晶粒尺寸及其分布的影响规律与机制.结果表明:铸坯材料动态再结晶百分数在环件内、外层高而使晶粒细化,而在环件中间层低导致粗品;驱动辊转速增大,铸坯材料动态再结晶百分数增加,轧制环件的平均晶粒尺寸减小;驱动辊转速对平均晶粒尺寸分布的均匀性影响不大.     

FE simulation and experimental research on cylindrical ring rolling

During the conventional ring rolling process, the ring mainly produces the incremental deformation of wall-thickness reduction and diameter expansion, which makes it difficult to manufacture the cylindrical ring with small diameter and large height. In this paper, a new method for manufacturing the cylindrical ring using a ring blank with smaller height, i.e. cylindrical ring rolling, is proposed and its feasibility is verified. For evaluating the cylindrical ring rolling process and to better understanding its deformation characteristics, a 3D elastic–plastic FE model of cylindrical ring rolling is first established. Then, the comparison between conventional ring rolling and cylindrical ring rolling is investigated using this 3D FE model. Finally, the effects of the process parameters, such as the feed rate of the idle roll, diameter of the idle roll and friction coefficient between the rolls and ring, on cylindrical ring rolling are numerically revealed. The experiment is carried out on a vertical NC ring rolling machine and the good agreements between the experimental and simulation results verify the validity of the established 3D FE model of the cylindrical ring rolling.     

Slab Analysis of Ring Rolling Assuming Constant Shear Friction

In this article, an analytic solution for ring rolling process based on the slab method theory is presented, in which the non-uniformity of the normal and shear stresses across the section of the deforming material throughout the plastic region is considered. The friction factor multiplied by the shear yield strength (τ = mk) is used to present friction between the main roll and the ring. The influence of the process parameters such as friction factor, feed speed, main roll rotational speed, and radii of the main roll and mandrel on process outputs is investigated. Complete expressions for the ring rolling pressure, force, and torque are obtained, and the position of neutral point is predicted. Comparison of the analytic results of this model with the experimental results of other investigators and FEM analysis show that they are in good agreement.     

Investigation of rolls size effects on hot ring rolling process by coupled thermo-mechanical 3D-FEA

Hot ring rolling is a significant branch of ring rolling characterized by high nonlinearity, 3D deformation, continuously progressive forming, unsteady-state, asymmetry, etc. with coupled thermo-mechanical behaviors which have significant effects on the deformation behavior, microstructure and mechanical properties of the ring. Changing the sizes of forming rolls including mandrel and driver rolls will considerably affect the roll gap deformation zone which is in close relation to the feed amount of both forming rolls and thus affects forming quality of the ring as well as power parameters. In this study, a reliable coupled thermo-mechanical and 3D rigid-plastic finite-element (FE) model for hot rolling of large rings is established. Then, based on the stable forming condition of the ring rolling process and comprehensive numerical simulations, the size effects of forming rolls on strain and temperature distributions and their uniformity, stress distribution, side spread and power parameters were investigated by 3D coupled thermo-mechanical FE simulation. The results show that there are optimum sizes of mandrel and driver rolls under which the strain and temperature distributions of ring and thus its microstructure are the most uniform where fishtail coefficient and power parameters have reasonable values. The achievements obtained can not only serve as a guide to the design of rolls sizes, optimization and quality control of the hot ring rolling process, but also clarify the plastic deformation and heat transferring of hot rolling of large rectangular-section rings.     

钛合金大型环件热辗扩成形应力-应变场演变规律的尺寸效应(英文)

基于可靠的钛合金大型环件热辗扩成形过程热力耦合三维有限元模型,研究并对比了不同尺寸环件的应力应变场演变规律。结果表明:对于不同尺寸环件的成形过程,当γ(整个成形过程的当量每转进给量分配比)减小时,成形结束时的Mises应力峰值可能从环件的驱动辊侧咬入点转移至芯辊侧咬入点,而等效塑性应变峰值有从环件外表面向内表面转移的可能性;当L(整个成形过程的当量变形区长度)增大时,成形结束时的Mises应力峰值可能出现在中间层。成形结束时Mises应力峰值和等效塑性应变峰值的位置是以上两方面综合作用的结果。在成形环件的变形区,环件表层金属处于三向压缩应力状态,中间层金属处于一向压缩、两向拉伸或者两向压缩、一向拉伸应力状态;整个环件处于一向压缩、两向拉伸应变状态。     

机械密封摩擦副界面温升分析

以接触式机械密封密封环为研究对象,建立摩擦副密封环整体传热模型,通过热-结构耦合模拟与数值计算,得到摩擦副的温度分布以及不同工况条件下摩擦副的变形情况。研究结果表明:密封环最高温度与最大热流密度都集中在密封环靠近摩擦副的内径处;密封介质压力和弹簧比压增大,摩擦副闭合力增大,微凸体接触增加,使得摩擦副变形量增加;随着转速的增加,摩擦副端面逐渐打开,微凸体对开启力的作用减小,使得摩擦副的变形减小。     

铝合金搅拌摩擦焊接参数对温度场的影响

检测搅拌摩擦焊过程中铝合金薄板上各特征点在不同焊接参数下的温度变化规律，研究搅拌摩擦焊接参数对焊接过程温度场的影响。试验结果表明，在搅拌头旋转速度一定时，各特征点的温度峰值随焊接速度的增加而降低；在焊接速度一定时，特征点的温度峰值随搅拌头旋转速度的增加而升高。     

A Fully Coupled Thermomechanical Model of Friction Stir Welding(FSW) and Numerical Studies on Process Parameters of Lightweight Aluminum Alloy Joints

This paper presents a new thermomechanical model of friction stir welding which is capable of simulating the three major steps of friction stir welding(FSW) process, i.e., plunge, dwell, and travel stages. A rate-dependent Johnson–Cook constitutive model is chosen to capture elasto-plastic work deformations during FSW. Two different weld schedules(i.e., plunge rate, rotational speed, and weld speed) are validated by comparing simulated temperature profiles with experimental results. Based on this model, the influences of various welding parameters on temperatures and energy generation during the welding process are investigated. Numerical results show that maximum temperature in FSW process increases with the decrease in plunge rate, and the frictional energy increases almost linearly with respect to time for different rotational speeds. Furthermore, low rotational speeds cause inadequate temperature distribution due to low frictional and plastic dissipation energy which eventually results in weld defects. When both the weld speed and rotational speed are increased, the contribution of plastic dissipation energy increases significantly and improved weld quality can be expected.     

工艺参数对钛合金叶片精锻中微观组织的影响

以叶片中的一类重要叶片——钛合金单榫头叶片为研究对象，利用自主开发的并经实验验证的叶片精锻三维有限元变形．传热一微观组织演变耦合模拟系统对其精锻过程进行了模拟，研究了不同工艺参数下叶身典型截面锻后微观组织的分布规律。结果表明：随着变形温度的升高，晶粒尺寸和β相体积分数增大；随着变形速度的增大，晶粒尺寸和β相体积分数相应增大；随着模具温度的升高，晶粒尺寸分布的均匀性提高：而摩擦条件对晶粒尺寸和β相体积分数的影响不显著。     

带阻尼台叶片精锻过程温度场分布规律研究

温度场分布的不均匀性,影响到带阻尼台叶片精密锻造过程的成形质量和组织性能。本文以DEFORM3D为平台,采用实体模具,建立了包括锻前和锻造两个过程的刚粘塑性有限元模型,使温度场的分布更加接近实际情况。在此基础之上,研究了摩擦因子、上模压下速度和初始模具温度对温度场分布的影响规律及坯料不同变形区域温度场的分布规律。结果表明:摩擦因子对坯料温度场分布的均匀性影响不明显;随着上模压下速度的增加,坯料温度场分布更加均匀;提高初始模具温度,有利于坯料温度场分布均匀;坯料不同变形区域内温度场变化较大。该研究对带阻尼台叶片精锻工艺的制定具有一定的指导意义。     

42CrMo铸坯环件热辗扩有限元模拟与分析

基于ABAQUS软件平台,建立了42CrMo大型环形铸坯热辗扩三维热力耦合有限元模型,模拟了铸坯热辗扩过程中应变场和温度场,研究了初始辗扩温度对辗扩力的影响规律.模拟结果表明在环形铸坯热辗扩过程中：①铸坯等效应变呈阶梯状上升,内外表面应变大于中间层应变;在稳定成形阶段,沿环件径向方向,由于导向辊与芯辊直径差异,导致环件最大平均等效应变可能出现在环件内表面也可能出现在环件外表面;②初始阶段,变形区与成形辊接触处温度降低较快,非变形区温度变化不是很明显;随着辗扩的进行,芯部温度逐渐上升,边缘温度低,温度分布不均匀;③随着铸坯初始辗扩温度升高,平均辗扩力明显下降,但随时间变化趋势保持一致.     

基于DEFORM和正交试验法的前轴辊锻工艺优化

正交试验主要用于解决科研和生产中多因素、多水平的问题,运用正交试验法可以在减少试验次数的情况下获得最佳的参数组合,可有效节约人力、物力和时间。在DEFORM-3D有限元数值模拟过程中应用正交试验优化设计方法,对前轴制坯辊锻模具弹簧座截面的圆角值、辊锻模具角速度、摩擦因子及坯料初始温度四因素、三水平问题,进行前轴制坯辊锻模具结构及工艺优化研究,分析影响前轴辊锻成形过程中最大成形载荷的因素,研究结果有利于前轴辊锻模具结构及工艺的优化,而且可有效提高辊锻模具的使用寿命。     

鼓形环坯轧制的宏微观变化数值模拟研究

针对鼓形环坯建立了环件径轴向轧制三维有限元模型,通过Simufact软件对鼓形环坯轧制的宏微观变化进行了耦合模拟,模拟揭示了鼓形环坯在轧制过程中的温度、等效应变、晶粒、动态再结晶的分布和演化规律;深入研究了轧制成形过程中径向每圈压入量对环锻件微观组织大小的影响规律。结果表明:基于鼓形环坯获得的环锻件,其内外侧棱边处发生的动态再结晶体积分数最大,晶粒最为细小,其次是内外表面和上下表面,心部动态再结晶体积分数最小,晶粒尺寸最大;适当增大径向每圈压入量,能够扩大动态再结晶区域,获得晶粒尺寸细小的环锻件。     

Effect of different production phases on residual stress field in double-layer cast rolls

The aim of this investigation was to determine the effect of different production operations and parameters on residual stress level in double-layer cast rolls. Using a hole-drilling method, residual stress depth distribution in surface layer was measured around and along the body of the double-layer cast roll after casting, heat treatment, turning and grinding. Furthermore, using different turning and grinding parameters (speed, feed), and heat treatment parameters (temperature, time), influence of these parameters on residual stress level and distribution was determined.Results of the investigation show that the conditions in the casting pit have an influence on the residual stress field generated in double-layer cast rolls, with surfaces exposed to faster cooling rates in general showing higher residual stress values. Very critical phase in rolls production is coarse grinding, which if not carried out properly will generate very high tensile stresses in the roll surface and cause surface cracking or even roll fracture. Heat treatment on the other hand results in uniform compressive residual stress field in the roll's surface. However, reduction in tempering time and especially increase in hardening temperature lead to increased residual stress level in the roll surface. Final machining of the roll surface further influences residual stress level in the roll. Increase in turning speed of up to 40% results in compressive residual stress increase of up to 60%, while less than 30% increase in feeding rate gives almost 100% increase in residual stress level.     

焊接参数对摩擦塞焊焊接区域温度场的影响

为了研究焊接参数对摩擦塞焊焊接区域温度场的影响,建立了摩擦塞焊焊接的产热模型,并进行摩擦塞焊焊接工艺试验。通过理论分析得出焊接过程中的产热量与焊接参数的关系,试验对理论分析结果进行验证,并深入探讨焊接参数对焊接区域温度场的影响。结果表明:焊接进给速度的改变影响焊接过程中的焊接压力大小,从而影响摩擦塞焊焊接初始阶段的产热,进而影响焊接区域温度场;较高的焊接转速提高摩擦界面材料的升温速率,提高材料塑化,避免焊接缺陷;应选择适当的焊接摩擦时间,尽量匹配较高的转速以缩短焊接摩擦时间。     

材料流动对连续驱动摩擦焊飞边形成的影响

在建立了45钢环形结构件连续驱动摩擦焊的二维热力耦合有限元模型的基础上,研究了焊接过程中的温度场与材料流动对飞边形成的影响规律.结果表明,在摩擦阶段,材料主要沿轴向流动,而径向流动基本上为0;在顶锻阶段,在大的轴向顶锻压力的挤压作用下,摩擦面边缘及其附近的材料主要沿径向向摩擦面外流动并形成飞边,且飞边的尺寸与弯曲程度随焊接时间的增加而增加.同时,增加旋转频率以及轴向顶锻压力会导致飞边尺寸与弯曲程度的增加;基于飞边形貌给出了45钢环节结构件连续驱动摩擦焊的合理焊接工艺参数.     

Numerical analysis of thermal process in continuous drive radial friction welding

A heat source model for radial friction welding was proposed, which was determined by friction pressure, friction coefficient, material properties and extrusion speed of material. A 3 D model was established to analyze the continuous drive radial friction welding temperature field of 45 steel pipe. The influences of friction pressure, friction time and rotation speed on the temperature of the friction interface were analyzed. The results showed that the temperature on the friction inter face rapidly rose to a peak temperature in initial friction stage and kept constant in the stable friction stage. Welding parameters of friction pressure, friction time and rotation speed had few influences on the peak temperature, while the increase of friction pressure and rotation speed could shorten the time to reach the peak temperature.     

摩擦对高温合金复杂截面圆环多道次滚压成形不均匀变形作用

在高温合金复杂截面薄壁圆环多道次滚压成形过程中,板料要经历多场多因素偶合作用下复杂的不均匀塑性变形和组织演化历程,特别是不均匀塑性变形通常是导致薄壁件成形起皱、椭圆和开裂等缺陷产生的主要因素。摩擦是描述环件与辊轮接触作用的主要参数,很大程度上决定着该环件多道次滚压成形过程中塑性变形的不均匀性,严重的影响着其滚压成形质量。为此,本文以有限元仿真为主并结合实验和理论方法,对高温合金GH4169薄壁w形圆环多道次滚压成形进行了系统的分析;进而提出了不均匀变形度的表征方法,研究获得了摩擦对高温合金复杂截面薄壁圆环多道次滚压成形不均匀变形的影响规律。结果表明：随着滚压成形的进行等效应力极值逐渐增大,且从动辊进给时环件弯曲部分材料变形量较大;随着驱动、从动辊与环件之间摩擦系数的增加,不均匀变形程度先减小,后逐渐增大;导向辊与环件之间的摩擦对不均匀变形度的影响不大。