Estimation of die service life for a die cooling method in a hot forging process

Dies may have to be replaced for a number of reasons, such as changes in dimensions due to wear or plastic deformation, deterioration of the surface finish, breakdown of lubrication, and cracking or breakage. In this paper, die cooling methods are suggested to improve die service life with regards to wear and plastic deformation in a hot forging process. The yield strength of die decreases at higher temperatures and is dependent on hardness. Also, to evaluate die life due to wear, a modified Archard’s wear model has been proposed by considering the thermal softening of die expressed in terms of the main tempering curve. This paper describes the effects of die cooling methods such as cooling hole and direct spray cooling on the life of finisher die during the hot forging of an automobile part. It is shown that the cooling hole method during hot forging is necessary for an effective die service life to be obtained.     

弧齿锥齿轮精锻成形模具磨损特性分析

采用刚塑性有限元法对弧齿锥齿轮精锻成形过程中模具表面磨损进行模拟分析,研究了摩擦因数、坯料温度、模具硬度、锻压速度等对模具磨损的影响.分析结果表明,随着摩擦因数的增大,磨损量增大;随着锻压速度、坯料初始温度及硬度的增大,磨损量减小,并且硬度是影响模具表面磨损量最重要的因素.模拟结果可为弧齿锥齿轮精锻成形工艺方案制定及模...     

大型热模锻压力机机架组件有限元分析

以某热模锻压力机机架组件为研究对象,对组件建立有限元模型.通过对机架加载,对机架进行有限元分析,并研究压力机机架的位移和变形量.该研究对热模锻压力机机架组件的设计和应力分析提供重要的理论数据,具有一定的推广应用价值.     

锻造模具的随机疲劳损伤分析

塑性应变控制的低周疲劳失效是锻造模具的主要失效形式，由于受到多种因素的影响，其损伤过程呈现随机性。应用有限元与BP神经网络，建立了一种基于损伤累积理论的锻造模具的随机疲劳损伤分析模型。首先用有限元对锻造过程中模具内的场变量进行分析，由计算结果找到模具的危险部位，认为危险部位失效时的寿命即为模具寿命，并计算出确定性损伤；再考虑模具材料及实际工况的随机性，应用BP神经网络对模具的损伤进行模拟；根据损伤的累积效应，得出考虑随机因素作用下的模具疲劳寿命。以锻造齿轮模作为分析对象，得到不同工况下模具疲劳寿命的频数分布，其分布规律基本服从Weiubull分布。另外，还分析了打击速度对模具寿命的均值和离差的影响及可靠性随使用次数的变化。该 模型可用来对模具进行寿命预测和可靠性分析。     

Wear analysis of hot forging dies

In hot forging, die wear is the main cause of failure. In this paper, the wear analysis of a closed hot forging die used at the final stage of a component has been realized. The simulation of forging process was carried out by commercially available software based on finite volume method and the depth of wear was evaluated with a constant wear coefficient. By comparing the numerical results with the measurement taken from the worn die, the wear coefficient has been evaluated for different points of the die surface and finally a value of wear coefficient is suggested.     

热锻模具热处理工艺试验研究

通过分析热锻模具工作原理,得出模具产生疲劳裂纹是疲劳寿命降低的主要原因。因锻模的工作温度较高,其模腔易高温氧化,因此可以利用适当的表面处理,提高其表面强度,使其具有良好的高温强韧性。本文对锻模进行离子氮化工艺研究,以提高其工作寿命。     

7075铝合金和QRO90模具钢在热成形工况下的摩擦磨损行为

铝合金在热成形制造过程中存在严重的模具磨损,不但缩短模具使用寿命,还造成工件表面拉毛和成形偏差。为模拟模具钢与7系铝合金在热成形工况下的摩擦过程,搭建单向高温摩擦磨损试验平台,对热成形工况下的摩擦磨损行为展开研究,并通过光学轮廓仪和扫描电镜分析模具钢与铝合金磨损表面形貌。结果发现,热成形过程中黏结磨损和磨粒磨损同时存在,磨损颗粒在粗糙表面上被压实和堆积,对后续的摩擦磨损行为有显著影响。对单向高温摩擦试验的接触副局部进行有限元建模,分析粗糙接触表面上的局部接触条件,探讨其对后续摩擦学行为的作用。分析表明,摩擦过程中存在黏滑现象,局部接触压力受表面形貌影响,显著大于名义载荷,最大等效应力出现在表面之下。这对进一步分析磨损行为、提出合适的表面工程方案提供了基础。     

Influence of cooling condition of tools on central deformation of workpiece and tool wear in cross wedge rolling

In this paper, a thermal–mechanical coupled simulation model for two-roll cross wedge rolling (CWR) was developed to investigate the influence of cooling condition of tools on central deformation of workpiece and tool wear by using three-dimensional rigid-plastic finite element method. Based on the simulation results, the information about central deformation of workpiece and tool wear with and without tool cooling was compared and analyzed. The study results indicate that forging quality and tool life can be improved by means of cooling the tools with cooling water. Subsequently, an industrial example of CWR in blank forming for engine connecting rod was presented to verify the feasibility of study results. In this industrial application, higher forging quality and longer tool life were obtained, which benefits the decrease of production cost. This study provides insights into the mechanisms of central deformation of workpiece and tool wear under different cooling conditions of tools in CWR process as well.     

轿车等速万向节星形套冷挤压成型过程有限元模拟

采用大型有限元软件MSC.Marc对轿车等速万向节星形套冷挤压成型过程进行了有限元数值模拟,详细讨论了有关数值模拟技术问题,得出了挤压力在加载过程中的变化曲线、工件随时间变化的温度场分布云图、工件等效塑性应变云图及模具内圈的应力分布云图,较好地解释了模具疲劳破坏的原因.研究结果有助于对轿车等速万向节星形套成型工艺及模具结构进行优化设计.     

Gear hot forging process robust design based on finite element method

During the hot forging process, the shaping property and forging quality will fluctuate because of die wear, manufacturing tolerance, dimensional variation caused by temperature and the different friction conditions, etc. In order to control this variation in performance and to optimize the process parameters, a robust design method is proposed in this paper, based on the finite element method for the hot forging process. During the robust design process, the Taguchi method is the basic robust theory. The finite element analysis is incorporated in order to simulate the hot forging process. In addition, in order to calculate the objective function value, an orthogonal design method is selected to arrange experiments and collect sample points. The ANOVA method is employed to analyze the relationships of the design parameters and design objectives and to find the best parameters. Finally, a case study for the gear hot forging process is conducted. With the objective to reduce the forging force and its variation, the robust design mathematical model is established. The optimal design parameters obtained from this study indicate that the forging force has been reduced and its variation has been controlled.     

Design of overlay coated region with hardfacing,transition and damage diminution layers for the reduction of damages of hot forging tools

Hot forging dies are damaged by the mixed failure modes including wear, thermal cracks, impact cracks, corrosion cracks, etc.. In order to extend the service life of the hot forging die, the diminution technology of the mixed failure modes should be developed. The aim of this paper is to design an overlay coated region consisting of a Hardfacing layer (HL), a Transition layer (TL) and a Damage diminution layer (DDL) to reduce damage of hot forging tools. The HL and the DDL are contrived to improve the wear resistance and the ductility of the overlay coated region, respectively. The TL is adopted to prevent thermal fatigue induced by the difference in the thermal expansion coefficients between successive layers. In order to estimate design alternatives of the overlay coated region, the effects of the thickness and the assignment of the DDL on stress-strain distributions in the overlay coated region are investigated via Finite element analyses (FEAs). The influence of the assignment of the DDL on thermal behaviors of the overlay coated region is investigated through thermal fatigue experiments. From the results of the FEAs and the thermal fatigue experiments, an appropriate design of the overlay coated region is determined.     

大型组合机架的疲劳寿命分析

针对大型模锻压机机架的疲劳失效形式,在承受拉、压复合作用下,以等效应力作为裂纹寿命估算的依据,并采用有限元进行疲劳寿命数值分析。分别计算不同应力集中系数、过载荷、残余应力、表面粗糙度取值下的疲劳寿命,并进行相应的敏度分析。通过仿真分析,得到影响疲劳寿命的关键因素变化趋势,为改进疲劳寿命提供直接依据。     

气孔缺陷位置对SMT焊点热疲劳寿命影响的数值分析

通过用统一的粘塑性本构方程描述SMT焊点的力学行为，对气孔缺陷在SMT焊点中不同位置的情况建立二维有限元分析模型，并采用有限元方法分析了气孔位置对SMT焊点疲劳寿命的影响。分析发现，与无缺陷焊点相比，气孔使焊点中应力应变分布发生了改变，使焊点疲劳寿命缩短；焊角、焊趾和焊点中部位置的气孔对焊点中的应力应变和焊点的疲劳寿命影响较小，而焊点根部气孔的影响则显著。     

Suitability of CAE neural networks and FEM for prediction of wear on die radii in hot forging

Prediction of tool wear in hot die forging along the entire arbor radius by wear models known so far is a very difficult task. On these parts of tools significant changes of contact pressure and sliding lengths occur along the die curvature during the plastic flow of material formed. A new approach presented in the paper combines the use of a conditional average estimator neural network (CAE NN) with the exploitation of results obtained by the finite element method (FEM) and also data from other sources. Consequently new parameters as well as the results of experimental work can be taken into account. In this paper a brief overview of models for prediction of tool (die) wear are discussed. The theoretical background of CAE NN, as well as its application to the modeling of the tool wear phenomenon, is presented. Some results of FEM analysis of the hot forging process that serve as input parameters in the CAE NN model are also briefly discussed. Two relevant practical applications are shown. In the first example, tool wear was modeled at a higher number of strokes (blows), by knowing wear at a lower number of strokes. In the second example, the number of strokes was the output parameter—the number of strokes causing predetermined wear at any point of the tool engraving curvature (arbor radius) was predicted. A comparison between the measured and predicted values of wear demonstrated good agreement that was assessed by a corresponding coefficient of determination.     

Hot shape forging of gas turbine disk using microstructure prediction and finite element analysis

The Waspaloy, a Ni-based superalloy, has been widely used for forging material of gas turbine disk since it requires the high tensile strength at high temperature and good resistance to low cycle fatigue. The purpose of this study is to develop a forging process of turbine disk that satisfies the hot deformation characteristics of Waspaloy. Generally, the hot forging of superalloy has been subjected to isothermal forging since the available temperature range of forging is narrow. However, the non-isothermal forging was used to make a turbine disk in this study. Therefore, the analyses of temperature variation and deformation behavior of the material were important to obtain the sound forging products. The hot compression test was carried out to know formability at high temperature and microstructure evolution during hot deformation. In order to define the optimum forging conditions including material temperature, strain rate, strain, microstructure evolution and forging load, the commercial finite element analysis code was used to simulate the forging procedure of turbine disk. The hot forged turbine disk was heat-treated for obtaining the high temperature properties. The cut-off tests on the heat-treated forged disks were carried out. Experimental results were compared with the simulation results by FE analysis. Test results were in good agreement with the simulations. This study shows that the superalloy turbine disk can be manufactured by the semi-closed die forging.     

基于焊点形态的工艺参数对底部引线塑料封装器件焊点可靠性影响分析

选取焊盘长度、焊盘宽度、钢网厚度和间隙高度为四个关键因素,采用水平正交表L25(56)设计25种不同参数水平组合的底部引线塑料封装(bottom leaded plastic,BLP)器件焊点,建立25种焊点的形态预测模型和有限元分析模型;对热循环加载条件下BLP焊点进行非线性有限元分析,计算25种不同焊点形态的BLP焊点热疲劳寿命;基于热疲劳寿命计算结果进行极差分析.结果表明,四个因素对BLP焊点热疲劳寿命影响由大到小的顺序依次是焊盘宽度、焊盘长度、间隙高度和钢网厚度;可靠性最高的BLP焊点工艺参数水平组合为焊盘长度1.1 mm、焊盘宽度0.65 mm、钢网厚度0.15 mm和间隙高度0.09 mm.     

A study on μBGA solder joints reliability using lead-free solder materials

In this study, the numerical prediction of the thermal fatigue life of a μBGA (Micro Ball Grid Array) solder joint was focused. Numerical method was performed using the three-dimensional finite element analysis for various solder alloys such as Sn-37%Pb, Sn-3.5%Ag, Sn-3.5%Ag0.7%Cu and Sn-3.5%Ag-3%In-0.5%Bi during a given thermal cycling. Strain values obtained by the result of mechanical fatigue tests for solder alloys, were used to predict the solder joint fatigue life using the Coffin-Manson equation. The numerical results showed that Sn-3.5%Ag with the 50-degree ball shape geometry had the longest thermal fatigue life in low cycle fatigue. A practical correlation for the prediction of the thermal fatigue life was also suggested by using the dimensionless variable γ. Additionally Sn-3.5Ag-O.75Cu and Sn-2.0Ag-0.5Cu-2.0Bi were applied to 6X8μBGA obtained from the 63Sn-37Pb Solder. This 6X8μBGA were tested at different aging conditions at 130°C, 150°C, 170°C for 300, 600 and 900 hours. Thickness of the intermetallic compound layer was measured for each condition and the activation energy for their growth was computed. The fracture surfaces were analyzed using SEM (Scanning Electron Microscope) with EDS (Energy Dispersive Spectroscopy).     

套管叉热挤压成形凸模结构对锻件终成形的影响研究

采用三维有限元法对套管叉锻件热挤压成形过程进行了数值模拟仿真分析。针对其成形过程中出现的叉部顶端及底端充不满现象进行了深入分析，提出了防止这种缺陷形成的一种特殊的凸模结构。生产实践表明，采用这种特殊的凸模结构后，锻件所用的坯料高度减小，每件可节约材料0．08kg；顶部废料厚度的减小，使后续工序切边模具的实际使用寿命至少提高为原来的2倍；台阶约束避免了过多的废料产生，减少了材料的相对流动，延长了终成形模具的实际使用寿命；与传统的锻造工艺相比，采用热挤压方法能获得较高的形状精度和尺寸精度，较好的纤维流向和机械性能。     

基于联合概率密度的随机声疲劳寿命估算方法

针对燃烧室火焰筒结构随机声疲劳问题,根据有限带宽高斯白噪声载荷作用下结构振动响应功率谱密度得到雨流循环均值-幅值条件概率的计算式,结合雨流循环幅值概率密度Dirlik经验公式推导出雨流循环均值-幅值联合概率密度函数,克服了在疲劳寿命估算中只考虑幅值、忽略雨流循环均值影响的局限性。根据Miner线性累积损伤理论,运用获得的联合概率密度函数建立声疲劳寿命的估算方法。以某型航空发动机燃烧室火焰筒结构为例,利用耦合的有限元和边界元方法进行振动响应计算分析。基于应力响应结果,运用提出的方法对火焰筒结构进行疲劳寿命估算,并分析不同声压级的声载荷对火焰筒结构疲劳寿命的影响。研究表明,该方法对航空薄壁结构声疲劳寿命分析具有适用性。     

Prediction of contact pressure,slip distance and wear in cold rotary forging using finite element methods

This paper aims to utilize finite element (FE) methods to predict the wear of dies and workpiece in cold rotary forging through systematically investigating the contact pressure and the contact slip distance. For this purpose, a 3D elastic-plastic FE model of cold rotary forging is developed using the FE code ABAQUS. Using this reliable 3D FE model, the evolution and the distribution of contact pressure and contact slip distance are investigated in detail. Consequently, a new insight into the wear that occurs at the surfaces of the dies and the workpiece is gained based on Archard's wear law.