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.     

A study on precision forging of spur gear forms and spline by the upper bound method

Precision forging is an important manufacturing procedure of spline and spur gear forms. It has advantages of improved strength, good tolerance, saving billet material, dispensing with the cutting, etc. In this paper, a mathematical model using an upper bound method is proposed for forging of spur gear forms and spline to investigate the plastic deformation behavior of billet within the die cavity. The material of solid billet was assumed as rigid–plastic and the shape of the tooth profile was accounted for the mathematical modeling of the kinematically admissible velocity field assumed for the plastic zone. The non-uniform velocity was employed for simulating the inhomogeneous deformation and the effect of barreling during the forging. Using the present model, various effects of forming parameter such as the friction factor, reduction, number of teeth, etc. upon the non-dimensional forging pressure, forging force and barreling of the spur gear forms and spline were analyzed systematically and the results compared with those of other researcher's analytical and experimental work. It is shown that the present modeling of the process improves knowledge of the process design performance for the precision forging of spur gear form and spline.     

Analysis and Optimization on Factors Affecting Forming Quality of Half Axle Gears Warm Precision Forging

Half axle gears is produced by precision forging popularly because of the advantages in minimum machining allowances, lower material consumption and good service properties. But the forming quality of precision forging is difficult to control. Many simulations and analysis of precision forging process were taken by previous researchers. But no concrete method is proposed to evaluate and optimize the forming quality of half axel gears. The primary purpose of this work is improving the forming quality of half axel gears by analyzing and optimizing the affected factors of forming quality. The enclosed-die warm forging process of half axle gears was developed, and a new type of die-set used on double action hydraulic press was brought forward. The main influential factors of precision forming quality were analyzed after the forming process had been simulated by using finite element method(FEM). These factors include die structure, web thickness and web position. A method used to evaluate the forming quality was established, which investigated the maximal forming load, the metal filling rate and the material damage factor. The FEM simulations of half axle gears precision forging were evaluated by this method. The results show that the best forming quality can be achieved when the punches were added with bosses, the web located at the middle plant of the gear, and the web thickness was 30 percent of the inner hole diameter. Verification experiments taking the above optimized parameters were performed on a 7.8 MN double action hydraulic press. The trial products were formed well. And their geometric precision meets the demand. The verification result shows that the optimization of the influential factors, according to the simulations and the evaluation method, can improve the forming quality. The new structure of precision forging die-set and the new evaluation method guarantee a high forming quality of half axel gears.     

Multi-field coupling finite element analysis for determining the influence of temperature field on die service life during precision-forming process of steel synchronizer ring

Failure analysis shows that increased die temperature caused by severe plastic deformation of material and heat conduction between hot billet and cavity significantly affects the distortion of gear cavity in steel synchronizer ring forging process. The forging process of steel synchronizer ring and die temperature distribution under different forging conditions are analyzed through finite element method. Simulation results show that severe plastic deformation occurs in the gear cavity. The improvement of lubrication condition results in decreased die temperature. When the initial billet temperature is high, the die temperature is also high. Increasing forging speed in a certain range facilitates the die temperature decrease. The distribution of die temperature in synthetic forming technology is more reasonable than that of one step forging. The synthetic forming technology is adopted in production to reduce the effects of severe plastic deformation caused by die temperature. The ejection mechanism and control system of the double disc friction press are improved to reduce the contact time between the hot billet and cavity. Experimental results show that synthetic forming technology is reasonable, and that the die service life is prolonged.     

斜齿圆柱齿轮冷精确成形数值模拟研究

为了降低斜齿圆柱齿轮精确成形力,在对闭式墩挤成形齿轮分析和分流锻造原理的基础上,提出了双向可控镦挤成形工艺方案,并用有限元软件Deform-3D对此工艺的成形过程进行了数值模拟分析。模拟结果表明:与传统的闭式模锻相比,可明显降低成形力,是适用于斜齿圆柱齿轮精确成形的有效工艺方案。     

A Study on the Extrusion by a two-step process for manufacturing helical gear

Much research has been carried out in the manufacturing of helical gears by cold forging or by extrusion. Although cold forging is applied to some bevel, spur, and helical gears, problems in connection with the reduction forming load and tool life still make it difficult for these methods to be commercialized. In this study, focusing on reducing a load in forming helical gears, the extrusion of helical gears by two-step process is proposed. This process is composed primarily of extruding a billet to a spur gear and then twisting the previous spur gear extruded to a helical gear. Cylindrical billets of Cr-Mo steel(SCM 415) and aluminium alloy(Al60 series) were used as specimen materials for the experiments. The maximum loads obtained by upper-bound analysis and FEM are compared with the results of experiments. The loads of the analysis have good agreements with those of the experiment. The newly proposed method can be used as an advanced technique that remarkably reduces the forming load and replaces the conventional forming.     

The prediction of maximum forging load and effective stress for different material of bevel gear forging

The manufacture of gears by applying hot or cold bulk forming processes is a quite widespread production method due to its well-known basic advantages such as material and time cost reduction and the increased strength of the teeth. However, the associated process planning and tool design are more complicated. In the precision forging of gears, the workpiece volume, the die design, the power requirement and careful processing are more critical than traditional forging technology. For complete filling up, predicting the power requirement is an important feature of the near net-shape forging process. In this paper, a finite element analysis is utilized to investigate the material properties such as yielding stress, strength coefficient and strain hardening exponent effects on forming load and maximum effective stress. The adductive network was then applied to synthesize the data set obtained from the numerical simulation. The predicted results of the maximum forging load and maximum equivalent stress of bevel gear forging from the prediction model are consistent with the results obtained from FEM simulation quite well. After employing the prediction model one can provide valuable references in prediction of the maximum forging load and maximum equivalent stress of bevel gear forging under a suitable range of material parameters.     

汽车差速器锥齿轮的温锻制坯/冷摆辗成形加工技术研究

为提高差速器锥齿轮的齿部强度和静啮合特性,达到少无切削加工及大批量生产的目的,采用温锻制坯、锻件余热退火与冷摆辗成形相结合的精密成形工艺生产差速器锥齿轮精锻件;对变形程度的分配、成形工艺参数的选择、高精度冷摆辗模具的设计与加工等关键技术问题进行了分析。结果表明,采用该工艺生产的差速器锥齿轮精锻件,较好地解决了差速器锥齿轮制造过程中存在的齿轮精度差、齿部强度低、模具寿命低、设备投资大等问题,为提高差速器锥齿轮的国产化率、减轻差速器的重量进而减轻汽车的自重等奠定了技术基础。     

汽车前轴精密辊锻成形过程的数值模拟

汽车前轴的精辊-模锻工艺是一种用小成形力锻造设备成形较大型前轴锻件的塑性加工技术,其工艺关键在于精密辊锻。前轴的精密辊锻分4个道次,是典型的局部成形工艺。辊锻工艺由于旋转的模具与辊锻件之间的接触区域在不断变化,一直以来成为数值模拟的难点。对4个道次的模具建立了模型,采用三维刚塑性有限元程序DEFORM-3D模拟了前轴精密辊锻工艺,分析了辊锻过程中金属变形的规律,研究了模具参数对成形质量的影响以及辊锻力矩的变化规律。模拟结果对于改进辊锻工艺设计、提高模具设计水平具有指导作用。     

基于渐进优化的锻造预成形优化设计研究

体积成形的预成形设计及优化是金属多工序成形设计领域的难点之一,也是获得高质量产品的关键。借鉴渐进结构优化(Evolutionary structural optimization,ESO)的思想,并考虑体积成形特点,建立一种针对体积成形预成形设计的方法——拓扑优化法,并详细给出该方法的优化策略、单元增删准则、插值处理等关键技术。利用自行开发的优化程序,结合DEFORM-2D有限元模拟软件,以理想充填模膛、改善锻件变形均匀性为目标,以静水压力的大小作为单元的增删准则,对开式模锻下轴对称结构的盘形锻件预成形几何外形进行优化设计。优化结果表明,该方法算法原理清晰明确,实现方便,整个过程集成化以后,从模拟到优化均可实现自动进行,运行效率高,同时也有较高的优化精度,预成形结构比较理想。     

Optimum weight design of functionally graded material gears

Traditional gear weight optimization methods consider gear tooth number, module, face width or other dimension parameters of gear as design variables. However, due to the complicated form and geometric features peculiar to the gear, there will be large amounts of design parameters in gear design, and the influences of gear parameters changing on gear trains, transmission system and the whole equipment have to be taken into account, which increases the complexity of optimization problem. This paper puts forward to apply functionally graded materials(FGMs) to gears and then conduct the optimization. According to the force situation of gears, the material distribution form of FGM gears is determined. Then based on the performance parameters analysis of FGMs and the practical working demands for gears, a multi-objective optimization model is formed. Finally by using the goal driven optimization(GDO) method, the optimal material distribution is achieved, which makes gear weight and the maximum deformation be minimum and the maximum bending stress do not exceed the allowable stress. As an example, the applying of FGM to automotive transmission gear is conducted to illustrate the optimization design process and the result shows that under the condition of keeping the normal working performance of gear, the method achieves in greatly reducing the gear weight. This research proposes a FGM gears design method that is able to largely reduce the weight of gears by optimizing the microscopic material parameters instead of changing the macroscopic dimension parameters of gears, which reduces the complexity of gear weight optimization problem.     

双联齿轮精锻成形工艺及数值模拟分析

针对双联齿轮的结构特点,提出了两种双联齿轮成形工艺,设计了坯料的合理形状,建立了三维有限元分析模型。通过工艺分析和不同工艺条件下的材料流动过程三维有限元动态仿真,研究了变形全过程的材料塑性变形行为、流动规律、几何尺寸变化以及成形件几何质量和缺陷等。对比有限元模拟结果发现:闭式模锻工艺齿形填充较差,产生折叠缺陷或充不满现象;挤压成形工艺齿形填充良好,是双联齿轮精锻成形的优选方案。研究结果为双联齿轮成形工艺实用化研究提供了理论指导或技术支持。     

多目标质量的粉末包套等通道挤扭成形致密工艺参数优化

剧烈塑性变形法—挤扭以剪切塑变为主变形方式,成形工艺复杂,影响因素很多,难以精确地建立工艺参数与成形质量之间的关系;选取优化合理的工艺参数匹配是材料尤其是粉末材料成形无破裂、塑性好、致密化程度高等成形质量的关键。以等通道横截面扭转角、螺旋角、摩擦因子、挤压速度、初始相对密度为自变量,正交试验为设计方案,对纯铝粉末烧结材料进行一道次包套等通道扭挤数值模拟,获得以等效塑性应变、静水压力、最大损伤值、相对密度数据,通过层次分析法计算多质量目标的权重,运用追踪点法和灰色系统理论的灰色关联度优化工艺参数,使设计目标值达到等效应变最大、静水压力最大、最大损伤值最小、相对密度最大。模拟和试验结果表明,运用多目标优化组合参数进行等通道挤扭成形能使纯铝粉末体材料迅速地形变累积,静水压力提高,损伤值显著地减小,致密效率高,晶粒明显细化,提高了材料综合质量。     

圆柱斜齿轮浮动凹模冷挤压成形仿真与实验研究

采用浮动凹模冷挤压成形工艺,对螺旋角不同的同一型号圆柱斜齿轮进行了数值模拟与实验研究。分析了成形过程中金属的流动特点、成形载荷,并与传统工艺进行了比较。通过不同螺旋角斜齿轮的对比,探索了影响脱模后锻件精度的因素。结果表明:对圆柱斜齿轮采用浮动凹模冷挤压成形可有效降低成形载荷,且在脱模过程中齿轮锻件沿着齿形螺旋方向做刚性旋转运动,脱模后锻件可保持较高精度。研究成果为圆柱斜齿轮精锻成形工艺的深入研究提供了参考。     

单榫头叶片精锻三维热力耦合有限元模拟

叶片是航空发动机中一类量大面广的重要零件,精锻是叶片锻造的发展趋势。叶片精锻过程属于高温大变 形过程,坯料与模具和环境之间存在着热交换,同时塑性变形功以及坯料和模具间的摩擦功不断转化为热能,其结 果促使坯料内的温度场不断发生变化,进而影响到坯料的变形行为,并进一步影响锻件的微观组织及机械性能。因 此,本文采用三维热力耦合有限元数值模拟技术,利用自行开发的叶片锻造过程三维刚粘塑性热力耦合有限元模拟 系统对单榫头叶片精锻过程进行了模拟分析,研究了叶片精锻成形规律。该研究对制定叶片精锻工艺以及发展叶 片精锻技术具有重要的理论意义和实用价值。     

星形套闭塞模锻光塑性模拟研究

利用光塑性方法以聚碳酸脂为模拟材料研究轿车等速万向节星形套闭塞模锻成形过程，获得星形套闭塞模锻成形过程的三维光塑性应变分布，提出其应变分布特征，并对典型截面应变进行计算分析，研究结果可实际钢质星形套闭塞模锻工艺和模具设计起一定的指导作用。     

汽轮机叶片精锻模具预补偿方法研究

针对汽轮机叶片加工精度要求高、精锻模具误差补偿难度大以及加工效率低等问题,以某型号汽轮机叶片为例,利用DEFORM-3D数值模拟软件分别对叶片精锻模具Z=5 mm叶根截面、Z=35 mm叶身截面以及Z=75 mm叶尖截面在不同锻压步数下的弹性变形进行了模拟分析,得出精锻模具型腔曲面变形规律。基于数值模拟结果,提出利用反向迭代补偿与黄金分割相结合的方法来修正精锻模具型腔。以该汽轮机叶片最大允许误差80μm为迭代目标,采用黄金分割法调整迭代区间,对各迭代点进行仿真,确定最优修正系数为0.94,最后得到满足终锻叶片精度要求的合理模具型腔,大大提高了模具设计质量与效率。     

Influence of process parameters on impact toughness and hardness of dissimilar AISI 4140 and AISI 304 continuous drive friction welds

Dissimilar joints between austenitic stainless steel and low alloy steel are extensively used in many high temperature applications in the energy conversion systems. In the present investigation, emphasis is made on the influence of process parameters on the impact toughness and hardness of the friction welded joints between these two materials. The important process parameters in friction welding such as friction force, forge force, and burn-off lengths are considered for optimization by Taguchi method using L₈ 2⁷ orthogonal array. It is found that under low friction force, forging force, and burn-off conditions, the impact toughness is high due to the observed acicular martensite. Low impact toughness is reported for the welds made at higher levels of the parameters. Carbon depletion is also observed close to interface in low alloy steel side. Microhardness at the weld center is less than the microhardness on either side at the interface of low alloy steel and austenitic stainless steel close to weld center. The contribution of each parameter and significance of interactions of these parameters is determined by Taguchi method. Among these parameters, friction force has significant influence and forging force has negligible influence on microhardness. The burn-off has maximum influence while forge force has minimum effect on toughness of the welds. Statistical analysis of variance is carried out, optimum process parameters are evaluated, and regression equations are obtained.     

量球法测绘窄斜齿轮的研究

把优化方法方法用于斜齿轮的测绘,建立了基于跨球（棒）距为优化目标的函数。通过对待测绘斜齿轮参数的优化分析,表明该方法是可行有效的。该方法不必用仪器测量斜齿轮的螺旋角和公法线长度,测量简单,精度高,可用于各种圆柱齿轮和渐开线花键的测绘。     

齿轮冷精锻工艺预锻模具齿形优化设计

在直齿圆柱齿轮两步成形冷精锻工艺中 ,预锻模具齿形设计对改善材料填充性能 ,降低成形载荷具有重要意义。本文采用正交试验法与数值模拟技术相结合的方法 ,来解决预锻模具型腔优化设计问题。选取了描述预锻模具几何形状的 3个参数作为影响因素 ,以预锻终锻总载荷值为指标 ,通过有限元模拟分析来获得虚拟试验结果 ,最终确定预锻模具型腔几何形状参数的最佳值 ,为提高齿轮精锻成形质量提供有效依据。