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.     

Microstructure Modeling of a Ni-Fe-Based Superalloy During the Rotary Forging Process

The microstructure evolution of Ni-Fe superalloys has a great influence on the mechanical behavior during service conditions. The rotary forging process offers an alternative to conventional bulk forming processes where the parts can be rotary forged with a fraction of the force commonly needed by conventional forging techniques. In this investigation, a numerical modeling of microstructure evolution for design and optimization of the hot forging operations has been used to manufacture a heat-resistant nickel-based superalloy. An Avrami model was implemented into finite element commercial platform DEFORM 3D to evaluate the average grain size and recrystallization during the rotary forging process. The simulations were carried out considering three initial temperatures, 980, 1000, and 1050 °C, to obtain the microstructure behavior after rotary forging. The final average grain size of one case was validated by comparing with results of previous experimental work of disk forging operation. This investigation was aimed to explore the influence of the rotary forging process on microstructure evolution in order to obtain a homogenous and refined grain size in the final component.     

Hot forging design and microstructure evolution of a high Nb containing TiAl alloy

With respect to the wrought processing of γ-TiAl alloys, the hot forging processes for ingot-breakdown is one of the most important steps. To obtain a billet with fine and uniform microstructure and excellent mechanical performances, an understanding of the strictly controlled forging processes and microstructure evolution are necessary. The hot forging processes and microstructure evolution of a high Nb containing TiAl alloy with nominal composition of Ti–43Al–8Nb–0.2W–0.1Y (at.%) were investigated in this paper. Three forging routes, one-step canned forging (OCF), one-step non-canned forging (ONF) and multi-step non-canned forging (MNF), were designed to study their effect on microstructure evolution of as-forged materials. Results showed that OCF and ONF produced nonuniform microstructures due to inhomogeneous deformation, while the specifically designed MNF process yielded fine and uniform grains, indicating that it is an effective and economic approach for ingot break-down of the present alloy. Besides, it is also found that forging at (α + β) phase region can retain large amount of β/B2 phase due to the strain-induced segregation of Nb and W, which is beneficial to the workability, and thus enables the use of near-conventional forging operations for the present alloy. The proposed multi-step forging in the present work may yield important information for the development of hot-deformation techniques and new alloy design strategies of γ-TiAl alloys.     

响应面法在大锻件微观组织质量控制中的应用

以某T型截面大锻件分段多道次成形工艺为研究对象,引入数学统计工具-响应面法(RSM)对该分段、不连续变形下的组织均匀性控制问题进行了研究。将工艺条件-道次进行参数表征,采用有限元方法 (FEM)和响应面法相结合,建立了以改善锻件微观组织质量为评价目标,以坯料温度、压力机速度、上模斜角角度和道次表征量为设计变量的二阶响应模型。研究了设计变量与评价目标之间的作用规律,通过Matlab软件得到了最优锻造工艺和工艺参数组合,即采用3道次成形工艺,坯料温度为440℃,压力机速度为8 mm·s-1,上模斜角角度为160°。采用优化结果进行大锻件的生产试制验证,金像分析显示所成形锻件内部组织均匀,表明了应用RSM和FEM可以有效地对分段多道次成形工艺下的锻件组织均匀性进行控制。     

汽车外星轮亚热精锻成形工艺研究

提出汽车外星轮的亚热精锻成形工艺,与传统热锻工艺比较,具有简化工艺、节约能源的优点。并采用数值模拟方法,对汽车外星轮的亚热控制精锻工艺进行了深入研究。将通过热模拟实验研究确定的流变应力模型引入到有限元数值模拟软件中,对外星轮亚热精锻成形过程进行模拟,确定了外星轮亚热精锻的最佳工艺参数,获得了较好的效果。     

法兰轴热锻过程中的微观组织演变的数值模拟

阐述了金属材料塑性加工中微观组织演变数值模拟的重要性。重点介绍了金属热锻过程中材料微观组织演变的机理和数学模型。完成了金属材料热变形过程中再结晶动力学与晶粒长大模型研究,编制用户子程序并嵌入到DEFORM-TM程序中。通过法兰轴的热锻过程中微观组织演变的实例,有效地验证了程序的可行性,对金属热锻过程微观组织预测有一定的指导作用。     

基于田口法的大型锻件微观组织健壮参数控制方法

为对大型锻件微观组织进行控制,提出了一种基于田口法和数值模拟的健壮参数控制方法。以圆柱体两步镦粗为例,研究坯料高径比、始锻温度、锻模击打速度和各工步压下量对终锻件微观组织均匀细小程度的影响,通过信噪比分析,获得了最优参数水平组合,方差分析表明,始锻温度和坯料高径比对微观组织影响很大,而各工步压下量和锻模击打速度对微观组织影响很小。虚拟试验验证表明,试验值与预测值比较吻合,该方法可以避免大量的仿真次数,减少计算时间,对控制大型锻件的微观组织具有一定指导作用。     

数值模拟在轿车转向节闭塞挤压成形中的应用

轿车转向节是轿车上的关键零件，对尺寸精度和产品质量要求很高。应用常规塑性成形方法，工序多、能耗大。闭塞锻造技术是近年发展起来的精密成形技术。以捷达轿车转向节为研究对象，制定了挤压带式可分凹模闭塞挤压精密预制坯和开式终锻成形相结合的“一火两锻”成形工艺。预锻件的成形质量直接影响到整个工艺流程．因此，以DEFORM软件为工具，重点研究预锻件成形过程中的关键工艺参数，如挤压带的长度、冲头尺寸、合模力和挤压力的关系，对于该工艺的实际应用具有重要参考价值。数值模拟结果表明，该工艺是可行的，而且具有降低能耗及材料利用率高的显著优点。     

高温合金环形件环轧工艺研究进展

高温合金因优良的综合高温性能在航空航天、石油化工等领域有广泛应用,高温合金环锻件主要用于机匣、燃烧室、密封环等部件。随着高性能航空发动机的发展,对高品质高温合金环锻件的需求日益增加。以往高温合金研究重点在于涡轮盘和叶片材料的合金优化设计、制备工艺和变形机理研究等,而对高温合金环锻件研究报道稍显薄弱。为此,本文总结了高温合金环形件环轧技术的发展、数值模拟在高温合金环轧技术探索中的应用、主要高温合金环锻件材料的种类以及高温合金环锻件组织控制的难点,以期为高品质高温合金环锻件的研发和制备提供一定的理论参考。     

Fast models for online-optimization during open die forging

One of the most important target parameters during open die forging is the microstructure, respectively the grain size. To guarantee the mechanical properties within the workpiece it is of high interest to predict the microstructure during the forging process. This paper details different semi-empiric models that ultimately help to predict the microstructure properties of a forged block. The results of the fast models show a good match with the slower FEA reference solution. The vision is, to use the developed models in an assistant system which suggests the optimal forging continuation and thus helps to optimize the forging process online.     

螺旋伞齿轮从动轮毛坯锻造成形数值模拟

“热锻造+机加工”是螺旋伞齿轮制造的一种有效方式,热锻件质量的好坏决定了最终产品的性能.通过运用有限元分析软件Deform-3D对螺旋伞齿轮从动轮毛坯的热锻造过程进行数值模拟,研究了锻造过程中金属流动规律.结果显示,金属在阶梯处流动困难,导致锻件阶梯处的应力应变大,温度高.通过对模具参数进行改进,可以改善金属的流动情况...     

锻钢活塞预成形过程的数值模拟分析

锻造成形过程是一个非常复杂的弹塑性大变形过程,有限元法是用于锻造成形过程模拟中一种有效的数值计算方法。通过数值模拟技术分析锻钢活塞的预成形过程,优化预成形模具型腔,获得了合理的生产工艺,达到减少成形工步、提高原材料利用率并获得合格终锻件的目的。     

7050-T7452高强铝合金的开坯与锻造工艺研究

为了研究7050高强铝合金开坯工艺的变形均匀性及锻件的断裂韧性,采用数值模拟、微观组织分析及紧凑拉伸试样的KIC试验等,分析研究7050高强铝合金铸坯改锻和挤压坯锻造的变形均匀性、显微组织和断裂韧性,得到了两种开坯工艺条件下坯料的平均等效应变、变形均匀系数、晶粒尺寸大小及分布和断裂韧度值。结果表明:铸坯改锻工艺的变形均匀性较好,其平均等效应变约为7.2,变形均匀系数约为0.475;挤压坯锻造工艺的变形均匀性较差,其平均等效应变约为1.9,变形均匀系数约为0.954;铸坯改锻工艺的平均晶粒尺寸与挤压坯锻造工艺基本相当,约为7.5μm,但铸坯改锻工艺的晶粒尺寸比挤压坯锻造更均匀;铸坯改锻工艺下锻件的KIC满足AMS4108F标准要求,而挤压坯锻造工艺不满足,其原因是挤压坯锻造后脆性较大,并残留有挤压织构。     

基于微观组织优化的锻造工艺预成形及毛坯形状优化设计

以锻件晶粒尺寸细小均匀为目标,以预成形形状设计为对象,提出了锻造成形过程微观组织优化设计方法,构建了晶粒尺寸、锻件形状子目标函数以及无量纲化的总目标函数,确定了预成形形状作为优化过程的设计变量;给出了优化设计的具体步骤,采用微观遗传算法和有限元模拟方法开发了基于预成形设计的锻造过程微观组织优化程序;并对典型的圆柱体镦粗进行了面向微观组织优化的预成形设计,给出了能够获得具有良好微观组织的镦粗成形预成形模具型腔形状。通过分析不同高径比的初始毛坯形状对微观组织优化目标函数值的影响,给出了较为合理的初始毛坯形状高径比取值范围。     

皮带轮温精辗压近净成形工艺模拟分析

为了克服当今皮带轮生产中材料浪费、生产率低、精度低等缺点,提出了皮带轮两步温精辗压近净成形新工艺。通过数值模拟的方法,分析了其成形过程和载荷,以及影响锻件成形质量的几个关键因素。数值模拟结果表明：工艺方案合理可行。锻件外围部分变形量大,变形均匀,质量高,所需成形力小。模具形状和运动参数匹配对成形质量和载荷影响很大,模具运动方式可以自由选择。     

直齿圆锥齿轮精锻成形工艺数值模拟研究

齿轮锻造成形是一个复杂的塑性大变形过程.传统的理论分析方法难以很好地分析其复杂的成形过程及成形规律,而有限元数值模拟可以弥补这一不足.通过基于刚塑性/刚粘塑性有限元方法的计算机模拟对直齿圆锥齿轮的温锻和冷锻过程进行了分析,对两成形方法中的模具载荷、应力和应变分布及温度场分布进行了比较.结果表明,温锻成形具有成形载荷小、应力数值小、温度分布均匀等优点.进行了相应的温锻工艺试验研究,为温锻成形技术在工业生产中的应用提供了理论依据.     

25CrNi1MoV钢发电机转子的热处理工艺研究

小功率发电机转子,材料为25CrNi1MoV钢,要求进行调质处理以获得良好而均匀的力学性能。通过数值模拟确定了最大直径约850mm的25CrNi1MoV钢转子锻件的调质处理工艺,即840℃奥氏体化、水淬和620℃回火,采用这样的工艺对转子锻件进行了调质处理,随后检测了转子锻件不同部位的力学性能和显微组织。结果表明,转子锻件表层和心部力学性能均满足要求。     

钢锭铸锻一体化开坯工艺数值模拟

针对13 t的12Cr2Mo1V钢锭开坯后探伤不合格问题,提出了铸锻一体化开坯数值模拟分析方法。首先在THERCAST软件中完成钢锭的浇铸和凝固过程的仿真分析,然后通过数据共享将铸造数据结果导入到锻造分析软件FORGE中,完成最终的开坯仿真分析。分析表明:通过铸锻一体化开坯数值模拟分析方法,有效地预测了锻件疏松出现的部位。钢锭最初的疏松出现在中心部位,其Niyama值较大,随着锻造过程的进行,中心部位的疏松区域逐渐消失,其Niyama值变小。通过调整开坯过程的重要工艺参数,如锻造比、相对送进量、温度控制等,制定合理的开坯工艺来减轻或消除疏松、缩孔影响,使显微空隙及疏松通过锻压焊合。     

基于改进BP神经网络的TA15钛合金近β锻造组织预测模型

文章以训练结果的误差均方差与误差和降低为目标,通过循环和判断语句改进了MATLAB人工神经网络(ANN)工具箱的BP算法,实现BP网络多结构、多次循环训练,建立了TA15钛合金近β锻造变形参数(变形温度、应变速率和变形量)和变形水冷(WQ)及后续热处理(再结晶退火或高低温强韧化处理)后的组织特征参数(等轴α相的含量、平均晶粒直径和轴比,条状α相的含量和厚度)之间关系的BP人工神经网络模型。结果表明,针对近β锻造组织预报输入参数多,输入-输出参数高度非线性,该模型可以有效避免传统BP模型容易陷入局部极小值点的缺点,可较准确的得到各工艺参数组合下的组织特征参数;模型预测结果可以用于近β锻造不同工艺参数组合下组织特征参数的预报,及其演化规律的分析。     

冠型齿坯锻造过程的数值模拟

应用刚塑性有限元法数值模拟锻造加工过程，并以冠型齿坯为例进行模拟分析，结果表明数值模拟能为选择工艺参数、模具设计提供许多有益的信息，是设计模具的有力手段；同时还表明冠型齿坯的锻造分镦粗、预锻、终锻三工步，其中以预锻模的设计最为灵活、重要，合理的设计各工步是保证最终获得合格产品的保证。