大型锻件锻合内部空洞性缺陷及优化工艺规程的研究

由大钢锭锻成的大型锻件,内部空洞性缺陷在周围基体压应变作用下,变形而闭合,在105℃以上焊合。坯料拔长过程的应变分布和砧宽比及压下量相关,合理选择工艺参数和操作程序,优化工艺规程,使钢锭内部有均匀足够的变形量,可以锻合全部空洞性缺陷,获得密实高质的大型锻件。     

大型钢锭内部空洞性缺陷锻合过程的实验研究

本文采用均匀压缩热钢模拟实验,研究了内部空洞在锻合过程中受应力应变的影响,提出空洞沿最大压应变方向闭合,并经由变形→压合→扩散焊合三个阶段得以消除的机制。对坯料内部三维变形条件下对称面上应变分布的实验测量与计算结果,发现在平砧拔长条件下,应变峰值随砧宽比变化而移动的规律,以及在连续锻造过程中,两砧交界处的坯料中心存在小变形区的现象。     

大型锻件锻造新中心压实法及工艺参数研究

针对现有大锻件中心压实(Japan-Tefeno-Shikano,JTS)法工艺操作复杂且对设备吨位要求过大的缺点,提出一种新的大锻件中心压实方法——NJTS(New-Japan-Tefeno-Shikano)法,设计可用于生产的工装,在锻坯上、下、左、右四个方向同时施压。利用数值模拟与物理模拟方法,以在心部预置空洞的坯料为研究对象,对新中心压实法锻造工艺进行研究。结果表明,新中心压实法能在整个横截面上形成大的静水压力,在心部有最大的变形。对相对压下量、砧宽比和侧压角等主要工艺参数进行优选,在砧宽比为1、侧压角为10°时,NJTS法的锻造效果最好,空洞的体积变化率、周围的等效应变和应力三轴度最佳;单向压实时相对压下量为18%～20%,双向压实时相对压下量为8%～9%,都可锻合内部空洞。试验表明:物理模拟与数值模拟结果基本一致。     

平砧拔长矩形截面毛坯的新理论

在拔长工艺理论方面,论证了只有砧宽比ω/h一个工艺参数的不足,而应增加一个工艺参数料宽比b/h,才能正确描述拔长毛坯中心区域的应力状态与有效控制锻件质量。该论述已被实验验证。同时用料宽比和砧宽比这二个工艺参数控制锻件内部质量的拔长工艺,简称为LZ工艺。     

平砧连续拔长矩形截面毛坯的数值模拟

对平砧锻造法进行了连续拔长过程的数值模拟.以前的研究仅仅给出了单次压下拔长模拟结果,忽略了上一次压下所产生的变形对后续压下的影响,这里采用ANSYS有限元分析软件对该锻造法实现了拔长一趟过程的数值模拟,并分析了锻件横截面上的中心轴线横向应力分布.分析结果表明:在使用普通平砧拔长时,在砧宽比为1.0和料宽比为0.5的条件下,坯料横截面上的其横向应力都是拉应力状态.并且随着拔长的进行,横向拉应力越来越大.这一点吻合了平砧拔长矩形截面毛坯的新理论,也表明了应用普通平砧锻造法时要注意控制横向拉应力.     

大型锻件锻造拔长新工艺

在分析现有镦粗、拔长变形工序中难变形区对大型锻件锻造过程变形分布和应力状态影响的基础上,提出一种新的拔长工艺——凹面砧拔长。借助数值模拟方法和物理模拟方法比较了普通平砧与凹面平砧、普通V砧与凹面V砧拔长过程中大型锻件内部的等效应变、静水应力和空洞缺陷的闭合情况。结果表明,对应力状态而言,在变形量相同的情况下,对于凹面平砧锻造(CFAF)工艺,静水应力提高近30%,对于凹面V砧锻造（CVAF）工艺,静水应力提高近50%。对变形而言,静水应力相同情况下,CFAF工艺减少压下量33.5%;CVAF减少压下量26.5%。对空洞缺陷而言,凹面砧拔长空洞变形后的椭圆度较普通拔长小10%以上。与其他特殊拔长方法比较,凹面砧拔长有操作方便,附具简单的优点。     

水平V型砧和平砧联合拔长圆形棒料的多工步数值模拟

前人的研究表明,使用水平V型砧锻造法可以有效控制锻件内部金属的流动方向和纤维流向,提高锻件的力学性能,使锻件的金属纤维组织、锻件整体性能、内部应力状态、宏观几何形状相比普通锻造法都得到极大改善。采用deform软件完成了水平V型砧和平砧联合拔长圆形棒料的多工步数值模拟。有限元法分析结果显示,使用水平V型砧锻造法,结合平砧法拔长整形压平,甚至在较小砧宽比为0.4的条件下,按一定顺序多工步拔长,也能使锻件内部变形量分布均匀,等效应力合理,避免了普通锻造法出现的力学异向性能,有利于提高拔长大型轴类锻件的效率,具有更广阔的工艺参数范围。     

锻造操作机末端运动轨迹对300MW发电机转子轴向中心线上等效应变的影响

以300MW发电机转子的锻造拔长过程为例,针对操作过程没有错砧、偶数道次错砧量为名义送进量的1/2和按照锻件变形尽可能均匀原则选择偶数道次错砧量等方案,设计3种不同的锻造操作机末端运动轨迹,综合分析锻造操作机末端运动轨迹对锻件轴向中心线上等效应变分布的影响。结果表明,根据变形均匀性原则设置错砧量的方案明显优于另外两个方案,与没有错砧的方案和错砧量为名义送进量一半的方案相比较,锻件中间段轴向中心线上的最小等效应变值分别增大了15%、22%,中间段等效应变平均值分别增大了5.6%、6.2%,且轴向中心线上的等效应变分布最均匀。因此,在规划锻造操作机末端运动轨迹时,必须考虑拔长操作过程中的错砧工艺,而且错砧量要根据锻件变形尽可能均匀的原则优化选择。     

平砧拔长长方体钛合金锻件的数值模拟研究

在钛合金长方体锻件的锻造中,平砧拔长长方体锻件是非常重要的一个工序,也是整个锻造工艺过程中变形量最大的一个工序。利用Dform软件,研究钛合金长方体锻件的拔长过程,不同的砧宽及平砧压下量对锻件内部应变大小分布、质量及其内部孔洞锻合效果的影响。     

轴类拔长工艺的研究与展望

综述了轴类锻件拔长工艺的研究历程,主要介绍了平砧拔长、JTS锻造法、FM锻造法、WHF锻造法、凹型角度砧拔长以及凸面砧拔长的工艺特点。说明了拔长工艺正朝着研究工件心部等效应变的均匀性与控制内部缺陷的方向发展,阐述了未来锻造行业向绿色锻造与实现自动化的方向发展的必要性与可能性。     

Numerical and experimental study on the three-dimensional extrusion of square section from square billet through a polynomial shaped curved die

The geometry of die profile plays a major role in reducing the extrusion pressure and ensuring the smooth flow of material. In general, the extrusion process is mostly affected by billet geometry, die geometry, and interface frictional force at the die billet geometry. In the present investigation, an analysis using three-dimensional upper bound method using fifth-order die profile function has been carried out for extrusion of square sections from square billet. The extrusion pressure and optimum die length have been computed by multivariable optimization technique. The present die shape profile is found to be superior to many other profiles. The results obtained will help in design of optimum die profile and investigation of its performance.     

The design of blank’s initial shape in the near net-shape deep drawing of square cup

Deep drawing process is very useful in industrial field because of its efficiency. The deep drawing is affected by many process variables, such as blank shapes, profile radii of punch and die, formability of materials and so on. Especially, in order to obtain the optimal products in deep drawing process, blank shape is very important formability factor. In this paper, the finite element method is used to investigate the cup height of the square cup drawing process. In order to verify the prediction of FEM simulation of the product’s height and forming load in the square cup drawing process, the experimental data are compared with the results of the current simulation. A finite element analysis is also utilized to acquire the designed profile of the drawn products, a reverse forming method for obtaining the initial blank’s shape according to the forward square cup drawing simulation is proposed. The design of initial blank’s shape is also certified to obtain the designed profile of drawn cups by experiment. The influences of the blank’s shape on the height of product, the forming load, the maximum effective stress and the maximum effective strain are also examined.     

Photoelastic investigations on initial plastic straining

Photoelasticity has been used for an investigation of the stress distribution in billets forged on flat dies. The flat models of the billet were made of birefringent material which were loaded to a state approaching the elastic limit.The authors' experiments were based on Nadai's hypothesis that in the first stages of plastic straining the stresses and strains are commensurate with the corresponding extremal values in the elastic range.The stresses were analysed for different values of feed ratio, i.e. relation of (actual) width of contact area between the die and the billet to its height. The experiments showed that if the feed ratio is less than 1·3, tensile stresses are present in the central zone of the billet under the die centre.There are no unfavourable tensile stresses in the central zone of the billet if the feed ratio is more than 1·3. However, for all values of feed ratio at points on the billet axis at a distance of 0·2 of the height of the billet from the die edge, tensile stresses are present.These conclusions lead to practical recommendations, concerning the forging of ingots and bars of complex brittle alloys at a maximum feed ratio.     

基于刚粘塑性有限元模拟的汽轮机叶轮模锻的预成形优化

针对汽轮机叶轮模锻的预成形设计,本文建立了以打击能耗最低和模具作用载荷最小为目标函数,以完全填充为约束条件,以坯料初始高径比为优化变量的预成形坯料优化方案。利用刚粘塑性有限元方法模拟汽轮机叶轮等温模锻成形过程,具体分析了不同坯料初始高径比对成形载荷、塑性应变能以及分流面的影响。数值模拟结果表明获得的预成形H/D最佳尺寸可明显减少模锻锤击次数和模具磨损。所提出的有限元模拟预成形优化方法十分有效,克服了以往凭经验设计的弊端。     

Effects of extrusion variables on temperature distribution in axisymmetric extrusion process

A numerical method was developed to simulate the non-steady-state temperature distributions during forward extrusion process. The velocity, strain rates, and strain fields within the deformation zones during extrusion were obtained, using upper bound method of analysis to obtain internal heat generations coupled to the necessary heat transfer conduction equations. The computer program written in C++ language essentially simulates the extrusion process and takes into account extrusion variables such as material properties, friction conditions, extrusion velocity, extrusion ratio, die preheat temperature, billet height, percentage reduction in area, and die land length. The effects of billet height and percentage reduction in area on the temperature distributions within the dead metal zone give good agreements with experimental results. It is found that the higher the billet's heights and higher the percentages reduction in areas, the higher the temperature rises during the extrusion process. The die land zone shows increasing temperature rise with increasing friction coefficient, while increasing friction coefficient has no effect on the dead zone temperature. Also, increasing speed of deformation shows an increasing dead zone temperature rise than a more gradual die land temperature rise. It can be stated that the extrusion temperature increases proportionally to the increase of the container temperature.     

基于熵权综合评价法的动力电池壳首道次拉深成形参数优化

针对某动力电池壳首道次拉深成形过程中的起皱、破裂、厚度不均匀和模具接触力大的问题,提出了一种基于熵权的综合评价法对其进行多目标工艺参数优化来提高首道次成形质量。选取压边力、凹模圆角半径、凸模圆角半径、模具间隙、摩擦因数为影响因素,以最大减薄率、最大增厚率、最大凸模接触力、最大厚度差为评价指标,进行正交试验仿真。在此基础上应用熵值法和综合评价法,获得了最优的工艺参数组合,提高了动力电池壳首道次成形质量。     

圆杯无压边锥模拉深皱曲强度与拉深极限预测

采用能量法导出圆杯无压边锥模拉深的皱曲强度,考虑了材料性 能,径向和周向弯曲作用,厚度变化及加工硬化效应。应用该强度预测无皱极限拉深比,与 Sowerby等人使用3种材料3种板厚作的无压边锥模拉深试验结果完全一致,最大相对误差不 超过8%。提出的研究方法同样适用于轴对称非直壁零件拉深凸凹模间悬空区的切向压缩失稳 分析。     

基于流函数法的铝型材挤压导流模合理设计

采用模拟试验法和理论分析法研究了导流模内型材挤压的流动机理;提出了确定导流腔最小深度的理论依据;用基于流函数的上限分析法确定了实心薄壁铝型材挤压变形的流线方程、动可容速度场、应变速率场及上限功率;讨论了变形程度等参数对导流模最小理论深度的影响,得出实心薄壁铝型材导流腔深度的理论最小值为导流腔半宽的0.7～0.8倍。理论结果得到了试验证实,为导流模合理设计提供了可靠的依据。     

A study on the warm deep drawability of sheets in Cr-coated die

Some deep drawing characteristics at elevated temperatures were investigated for the SCP1 steel sheets by using a Cr-coated die. For this investigation, six different temperatures between room temperature and 250°C, and six different drawing ratios ranging from 2.4 to 2.9 were considered. As a result, the limiting drawing ratio, the maximum drawing force and the maximum drawing depth were found to be affected sensitively by temperature, and more stable through-thickness strain distribution was observed at elevated temperatures. Some experimental results compared favorably with theoretical, results obtaine by using the finite element method.