The forging of helical gears (II): comparisons of the forging processes

In this study, the forging processes of helical gears have been investigated wherein they have been classified into two types: the guiding type and the clamping types. These two types of forgings of helical gears have been analyzed by using the upper-bound method. New kinematically admissible velocity fields of the clamping-type forging of helical gears have been proposed, where an involute curve has been introduced to represent the tooth profile of the gear. The proposed velocity fields of the clamping-type forging of helical gears have been applied to the non-symmetric lateral extrusion forging and the result has been compared with the solution proposed by Plancak et al. [J. Mater. Process. Technol. 1992; 34:465–472]. Numerical calculations have been carried out to investigate the effects of various parameters, such as modules, number of teeth, helix angles and friction factors on the clamping-type forging of helical gears. For the forging of helical gears, the results of the upper-bound analysis of the clamping type have been compared with those of the guiding ones. Some experiments of the clamping-type forging were carried out with commercial aluminum alloy to show the validity of the analysis. Good agreement was found between the predicted values of the forging load and the experimental forging load.     

DESIGN AND MANUFACTURE OF STRAIGHT BEVEL GEAR FOR PRECISION FORGING DIE BY DIRECT MILLING

In the manufacture of straight bevel gears, a precision forging method has been mainly used in recent years and the precision forging die has been usually manufactured using electric discharge machining. However, it is difficult to content the high productivity and low manufacturing cost using electric discharge machining because the gears are produced through a process of several steps. In this article, a design and manufacture of a straight bevel gear for a precision forging die by direct milling is developed in order to improve the productivity and manufacturing cost for the gear production. The tooth profile of a straight bevel gear generated by a quasi-complementary crown gear instead of a usual complementary crown gear is introduced. For this study, first the numerical coordinates on the tooth surface of the straight bevel gear were calculated and the tooth profiles were modeled using a 3D-CAD system. Afterward, the direct milling of the precision forging die of the straight bevel gear in the hardened state was carried out using a CNC milling machine based on a CAM process through the calculated numerical coordinates.     

A study on the forging of spur gears

In this paper, the forging of spur gears have been analysed by using the upper-bound method. The tooth profile of the gear consists of an involute curve and a circular arc shaped fillet. A kinematically admissible velocity field is newly proposed. Numerical calculations have been carried out to investigate the effects of various parameters, such as module, number of teeth, addendum modification coefficient and friction factor on the forging of spur gears. Some forging experiments were carried out with Al-2024 to show the validity of the analysis. Good agreement was found between the predicted values of the forging load and those obtained from the experimental results.     

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.     

Upper bound analysis for forging of trochoidal gears

Forging of trochoidal gears has been investigated by means of upper-bound analysis. A kinematically admissible velocity field for forging of a trochoidal gear was proposed. A neutral surface has been used to represent the inward flow of material during forging operation by using a hollow billet with a flat punch. By using the suggested kinematically admissible velocity fields, the applied forces were successfully calculated and compared with experimental inspections. The experimental set-up was installed in a 200-ton hydraulic press for forging. The billets of A1 2218 aluminum alloys were slightly coated with phosphate. It was found that the theoretical solutions were useful to predict the forging load forforging of trochoidal gears.     

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。     

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.     

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。     

大型座舱骨架整体成形有限元模拟及实验研究

为研究飞机大型座舱骨架的整体成形,在DEFORM一3D软件中对该铝合金锻件的整体锻造过程进行了有限元模拟,并优化了模具结构及坯料。在模拟结果的基础上生产了坯料和模具,并在万吨水压机上对坯料进行了整体锻造,实际生产的锻件质量良好。研究表明,模拟结果与实际生产基本一致,通过大型座舱骨架整体成形的有限元模拟实现了模具结构和坯料的优化,减少了试模次数,提高了锻件的质量。     

纳米Si2N2O-Sialon陶瓷齿轮超塑性锻造研究

采用Deform有限元软件对纳米Si2N2O-Sialon陶瓷超塑性锻造成形过程进行模拟,较直观地预测了齿轮成形过程中齿形充填情况。在1550℃,纳米Si2N2O-Sialon陶瓷显示出良好的超塑性成形性能,通过试验,超塑性锻造成形出了质量良好的齿轮零件。在模拟与试验的基础上,通过与金属齿轮的齿形充填情况进行对比,建立了陶瓷齿轮齿形充填模型,得到了纳米陶瓷齿轮超塑性锻造成形的基本规律:陶瓷齿轮锻造过程中齿形充填过程分为5个基本阶段,与金属齿轮锻造成形充填过程相比,齿形前端的鼓形量和齿形侧面的鼓形量明显较小。     

2A70铝合金转子等温闭塞式锻造工艺研究

2A70铝合金转子是导弹发动机上重要的受力构件,对组织性能的要求很高。采用等温闭塞式锻造的方法生产转子锻件。为了使成形后的锻件顺利出模,采用了组合式凹模的结构。等温成形时,进行了大量的试验研究加热温度对成形过程的影响,最终确定模具和坯料的加热温度均为435 ℃。经检测,采用所设计的工艺方案生产的转子锻件的尺寸精度及组织性能均符合设计要求,成功地解决了切削加工的转子力学性能差、不能满足使用要求的问题。     

A study on the forging of gear-like components

This paper describes kinematically admissible velocity fields for forging of gear-like components such as involute spur gear, trapezoidal spline, square spline, serration and trochoidal gear. Half pitch of each gear-like component was divided into several deformation zones with respect to their tooth profile. A neutral surface has been used to represent the inward flow of material during a forging operation by using a hollow billet with a flat punch. By using the suggested kinematically admissible velocity fields, the power requirements were successfully calculated and they were compared with experimental inspections. As a result, the suggested velocity fields are shown to be useful to predict the forging load. The contour of neutral surface varied with the number of teeth.     

高筋薄板构件多自由度摆动辗压成形规律与工艺研究

高筋薄板构件多自由度摆动辗压成形过程中金属流动十分复杂,导致高筋薄板构件筋高分布十分不均匀。根据双偏心套型摆动辗压机运动原理,探究摆动模做圆轨迹和螺旋线轨迹运动时摆动模与坯料的接触模式演化规律,提出了接触区形状数学计算方法。采用有限元模拟仿真技术揭示摆动模做圆轨迹和螺旋线轨迹运动时高筋薄板构件摆动辗压成形金属流动规律以及高筋生长规律,阐明摆动模运动、接触区变化、金属流动和高筋生长之间的关联关系。在此基础上,开展高筋薄板构件摆动辗压成形工艺试验,实现高筋薄板构件摆动辗压成形。研究结果表明,相比圆轨迹运动,摆动模做螺旋线轨迹运动能够减弱金属径向和切向流动,增强金属轴向流动能力,从而有效提高高筋薄板构件摆动碾压成形过程中金属轴向流动的均匀性,获得筋高分布均匀的高筋薄板构件。     

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。     

直齿圆柱齿轮冷精锻实用化工艺研究

以实用化为目标,对１５＾＃钢、４５＾＃钢、２０ＣｒＭｎＴｉ直齿圆柱齿轮冷精锻工艺进行系统研究,提出了闭式镦挤－约束孔分流两步成形实用化工艺方案和基于变位理论和齿形模修正设计方法。     

内啮合斜齿轮高精度三维有限元自动建模方法

为提高内啮合斜齿轮有限元接触分析的建模速度和模型精度,提出了一种齿轮高精度三维有限元模型的自动建模方法。基于齿轮插刀齿廓方程,利用齿廓法线法,得到包括齿根过渡曲线的内、外斜齿轮端面齿廓,建立了内、外齿轮参数化粗网格有限元模型。开发了表层六面体网格剖分方法,自动识别齿面接触带单元,进行分级剖分细化,保证了有限元模型的建模精度和网格密度。进行了齿面接触分析,得到了内啮合斜齿轮的弯曲应力、接触应力、接触印痕、传动误差、时变啮合刚度和载荷分配率。粗细网格有限元模型计算结果对比分析表明,该方法提高了内啮合斜齿轮有限元建模效率和计算精度,缩短了计算时间,为快速准确的齿轮接触分析奠定了基础。     

预锻模形状设计优化的新方法—微观遗传算法

锻造过程实现净形和近净形制造关键是优化预锻模的设计。引入一种可对预锻模形状进行设计优化的新方法－微观遗传算法，并用此方法对平面就方坯锻造进行了预锻模形状设计优化，目标是消除锻件的同鼓形效应。设计结果表明优化效果显著。     

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.     

Experimental measurement of strain and stress state at the contacting helical gear pairs

Contact stress evaluation in gears has been a complex area of research, due to its non-linear and non-uniform nature of stress distribution. The high contact stress on gears results in pitting and scuffing, which leads to tooth failure. Furthermore the effects of friction on gear contacts make the problem more complicated. Hence, in this paper, attempt has been made to study contact stress in gears. The experimental testing and analysis of the helical gear was carried out using Gear Dynamic Stress Test Rig (GDSTR). GDSTR is a newly designed test rig to compute the contact stresses on the gear pair contact, under real gear conditions. GDSTR uses the strain gauge and carbon slip rings to measure the surface contact stresses at the contacting points of a meshed gears. The experimental analysis showed promising results which have been verified by the finite element frictional contact analysis. The experimental testing was carried out on 5° and 25° helical gear pairs. Helical gear models with the same specifications and for different frictional coefficient conditions were also generated using FE modelling. The frictional contact stress analysis using FEM has been used for comparison with the experimental results.     

TC4合金叶片精锻过程的二维数值模拟

采用刚塑性有限元法对钛合金精锻叶片的锻造过程进行了二维有限元数值模拟。在数值模拟过程中 ,考虑了摩擦边界的作用和畸变网格的局部重划分。根据数值模拟结果 ,研究了不同锻造工艺参数 (变形温度、变形速率、压下量等 )对叶片锻造过程中的变形力、应力和应变变化的影响规律。