塑料模具钢镦粗过程内部空洞缺陷的有限元模拟

摘要：利用JmatPro软件模拟计算718类塑料模具钢（3Cr2MnNiMo）热物性参数。应用ABAQUS有限元模拟软件建立模具钢镦粗过程中孔洞模型,模拟不同压下率条件下孔洞的闭合规律。模拟结果表明：孔洞闭合分为开始闭合、闭合加速和闭合减速3个阶段;孔洞闭合的2个主要影响因素为孔洞表面等效应变εe、静水压力与等效应力之比σm/σe;随着孔洞所处位置不同,孔洞闭合度不同,根本原因为孔洞所处位置的等效应变不同。所得结果对于塑料模具钢实际锻造生产过程具有指导意义。     

FEM‐Simulation of Drawing Out in Open Die Forging

Experiments and finite element simulations were performed in order to study how the bite ratio influences the closing of inner flaws such as voids and pipes in the open die forging process. Square rolled blooms of carbon steel with a transversal hole in the centre were forged with a constant height reduction but with different bites in order to study the closing of voids during the process. Corresponding finite element simulations were performed in full 3D with full thermo‐mechanical coupling. Also the influence of the friction and of the temperature gradient in the workpiece were studied. The elimination of an artificial defect by forging was successfully simulated by the finite element method. It is established that the closure of voids is highly dependent on the bite ratio. The closure of voids under the edge of the tool is however not improved by a higher bite ratio. There is a slight tendency that the situation under the tool edge is worse when the bite ratio is increased.     

油泵齿轮轴精锻成形工艺研究及缺陷分析

针对油泵齿轮轴特殊形状设计了齿轮轴精锻模具.通过有限元仿真和精锻实验研究了齿轮轴成形过程和金属流动规律.分析了对油泵齿轮轴精锻工艺中产生齿形角隅填充不满缺陷的原因:角隅填充是成形终了时成形载荷陡增的主要原因之一,由于齿轮轴精锻模具结构的特殊性,其强度无法满足齿形角隅填充所需高成形载荷的需要.基于角隅填充状况,提出了齿形端面斜面分流和环形槽分流,并对传统精锻工艺和两种分流锻造工艺进行了有限元仿真.分析结果表明两种分流方法均能有效减小齿形角隅填充时金属流动阻力,保证齿形良好填充,降低成形载荷,并且斜面分流优于环形槽分流.锻造实验验证了有限元仿真的准确性.      

Void Closure Behavior in Large Diameter Steel Rodduring H-V Rolling Process

In order to reveal the mechanism and condition of void closure in large diameter steel rod during horizontalvertical(H-V)groove rolling process,a three-dimensional thermomechanically coupled finite element model was established for 9-stand H-V groove rolling process aiming at a150mm steel rod production line.A spherical hole with diameter from 2to 10mm was preset into the center of continuous casting billet with a rectangle cross section of300mm×360mm in this model to simulate the void defect,and then finite element analyses were carried out to observe and quantify the void shape evolution in each pass on the three orthogonal coordinate plane sections.The results showed that the void was formed roughly in the reduction and extension directions,and crushed gradually from spherical shape to an approximate ellipsoid,micro-crack and finally to be closed.A quantitative analysis was carried out by using elliptic radii and closure ratio to describe this evolution process;it indicated that the longest axis of the ellipsoid coincided with the rolling line,and the second and third axes were alternatively horizontal and vertical on the exit cross section according to change of the reduction direction in H-V groove.The void closure behavior during HV rolling was more complicated than that of common horizontal rolling,and the influence of groove type and the extension coefficient on the void closure ratio was presented.Finally,apilot rolling experiment was performed on a 5-stand H-V experimental mill to verify the numerical simulation results,and the experimental results are in good agreement with the numerical simulation results.     

GH4169合金热模锻直接时效压气机盘件的组织与性能

用热模锻技术成功锻制出我国目前最大推力的航空发动机压气机用437 mmGH4169合金直接时效盘件。通过光学金相检验、室温和650℃拉伸试验、650℃/700 MPa组合持久及595℃/825 MPa蠕变试验,对比研究了该盘件与普通盘件的组织和性能。结果表明,热模锻技术成功克服了模具的激冷影响,获得了尺寸精化、组织均匀的盘件。该盘件的组织性能全部超过了该发动机的技术要求。与普通模锻工艺相比,热模锻工艺的单件节材35 kg,材料利用率提高30%左右,且工艺的可控性和稳定性更好。     

Rotary forging with double symmetry rolls

Abstract

A novel metal plastic forming technology, namely rotary forging with double symmetry rolls (DSRs) is presented in comparison to more conventional single roll rotary forging. Based on a reliable three-dimensional elastic–plastic dynamic explicit finite element model, the fundamental deformation characteristics of cold rotary forging with DSRs of a cylindrical workpiece are made clear. Meanwhile, the interactive effects of two main processing parameters, feedrate v of the lower die and rotational speed n of the two upper dies on the forming process have been comprehensively revealed. As a specific case, hot rotary forging of a spiral bevel gear was analysed and an experiment was carried out on a developed hot rotary forging press with DSRs. The simulation results are in good agreement with the experimental ones and demonstrate that rotary forging with DSRs has a potential prospect in forming a complex spiral bevel gear. The results of this research help to better understand the advanced metal plastic forming technology of rotary forging with DSRs.     

楔横轧模具脱空对轧制力影响规律研究

减小设备在现有工艺下的受力,是提高轧机轴承等关键零部件寿命和产品质量的有效方法之一。为此,采用有限元法对楔横轧模具在不脱空和脱空情况下进行了轧制过程数值模拟,详细分析了模具脱空对轧制力影响的规律,得到了在一定断面收缩率范围内模具脱空有利于减小轧制力的研究结果,并与测试结果进行比较。研究结果为合理设计楔横轧模具、改善轧机受力状况提供了重要的理论依据。     

楔横轧模具脱空对轧制力影响规律研究

减小设备在现有工艺下的受力,是提高轧机轴承等关键零部件寿命和产品质量的有效方法之一。为此,采用有限元法对楔横轧模具在不脱空和脱空情况下进行了轧制过程数值模拟,详细分析了模具脱空对轧制力影响的规律,得到了在一定断面收缩率范围内模具脱空有利于减小轧制力的研究结果,并与测试结果进行比较。研究结果为合理设计楔横轧模具、改善轧机受力状况提供了重要的理论依据。     

基于数值模拟的粉末冶金TiAl合金叶片模锻工艺研究

采用Deform-3D有限元软件对粉末冶金Ti-47Al-2Cr-2Nb-0.2W(摩尔分数,%)合金叶片的模锻工艺进行数值模拟研究,分析预热温度和上模速度对TiAl合金叶片锻件的等效应变场和等效应力场分布以及上模载荷的影响。结果表明,随预热温度升高和上模速度减小,叶片锻件的等效应变场和等效应力场分布更均匀,有利于提高叶片组织的均匀性。随着模锻过程的进行,由于TiAl合金加工硬化以及锻坯与模具间的摩擦增大,导致上模载荷不断增大,而预热温度升高和上模速度减小均使上模载荷显著降低。粉末冶金TiAl合金叶片模锻变形的最佳工艺参数为预热温度1200℃、上模速度0.5 mm/s。     

汽车变速器输入轴塑性成形工艺

输入轴是汽车变速器中重要零件,针对其特殊结构提出一火加热和轧锻结合的塑性复合加工工艺,即采用圆柱坯料只进行一次加热,依次采用楔横轧和锻造工艺加工塑性成形输入轴.本文分别设计楔横轧和锻造模具,并进行相关实验.在锻造工艺中轴部圆角采用挤压方案成形,避免其出现折叠缺陷.阶梯轴作为两步工艺的中间产品,其在复合工艺过程中起到承上启下的作用,分别对阶梯轴锥角和轴长进行实验与分析,确定参数的最佳选取范围,并最终通过复合工艺加工成形输入轴.输入轴齿形填充饱满,各部分无缺陷.     

实现等向锻造的水平V型锥面砧锻造法

针对水平Ⅴ型锥面砧拔长矩形截面坯料建立了力学模型,并进行了定性物理模拟实验与生产性实验.研究结果表明,水平V型锥面砧不仅可以实现变形均匀的无横向拉应力锻造,而且提高了轴类锻件的横向力学性能,实现了大型轴类锻件的等向锻造,同部位力学性能值的横纵向之比均约等于1.00.     

锻造比对H13钢组织和力学性能的影响

 利用金相显微镜及SEM研究了在单向热锻拔长的工艺下,锻造比的不同对H13电炉钢组织和力学性能的影响。结果表明：同一锻造比下H13电炉钢的横向冲击功明显小于纵向,且无论在钢锭的横向、纵向边部到心部的冲击功越来越差;不同的锻造比对横向冲击功影响不大,而随着锻造比的增大纵向冲击功增大。研究表明,单向热锻拔长不能有效地提高钢材横向止裂性能;电炉H13热作模具钢的锻比控制在4~6的范围内较为合适。     

Semi‐Solid Rheoforging of Steel

To produce steel components with complex shapes excessive machining is necessary frequently since high pressure die casting of steel is not industrially applied. Forming steel in the semi‐solid state can in principle produce new components and geometries which cannot be realised by conventional closed die forging. Semi‐solid forging of steel combines the possibility of producing geometries not conventionally forgeable in one forming operation and of adding further functions during the same operation. In previous investigations on thixoforming of steels, the semi‐solid steel was generated by reheating precursor material billets. An alternative approach for generating semi‐solid steel from the liquid state with subsequent forging operation is presented in this paper for the first time. The steel grades X210CrW12 cold work tool steel and 100Cr6 bearing steel are molten and driven into a globular semi‐solid state using a cooling slope and a cup. By cooling the steel into the semi‐solid range instead of heating it, the required process temperatures are lower than in the process route via heating. Therefore, the load on the dies in a semi‐solid forging operation is decreased. Suggestions for the respective layout of the process are made for both steel grades. Future potentials and challenges to be solved are discussed, showing advantages especially in the field of high melting point alloys such as steels. This technique enables to produce pre‐shaped semi‐solid billets to optimise the materials flow and the homogeneity of the mechanical properties.     

在多向模锻挤压液压机上的型材挤压成形研究

在实验室模拟试验和工厂工业性生产试验的基础上,阐述了在多向模锻挤压液压机上实现挤压的工艺特点,找出了分离压余的理想方法－冲切法,给出了冲切间隙的计算方法。为减小挤压型材的弯扭畸变,建立了局部挤压比、挤压带系数的概念。给出了挤压筒中心与挤压模孔型中心距离的计算方法。     

润滑对冷锻模具寿命的影响

在冷锻过程中,模具受到极高的载荷和磨料磨损,表面粗糙度和残余应力受到影响很大。以经过热处理的高速钢制成的模具作为研究对象,试样经过镦粗过程,得到了不同锻造条件下锻件表面粗糙度、残余应力和试样变形随锻造循环次数的变化,并在"有润滑"和"无润滑"条件下,得出了采用两种不同的锻造载荷进行了冷锻镦粗工艺对冷锻模具的影响。     

Theoretical and Experimental Damage Prediction in Cold and Semi‐Hot Bulk Forming of Ductile Steels

Bulk forging is among the most important manufacturing methods in metal forming, due to its wide applicability from some ounces to several tons of steel in a high diversity of shapes and forming conditions. Economical constraints demand for further optimisation and cost‐effective production. This requires the application of suitable finite elements simulation software, in order to support the already digitalised construction processes. Ductile damage is one of the most severe problems to arise during the production sequences, not only in cold but also in semi‐hot forging operations. Mathematical approaches exist for the modelling and simulation of ductile fracture in steel. In this paper some widespread used damage models are introduced and discussed. Their damage prediction quality has been verified by experiments, the tensile test and the collar specimen upsetting with several different steels under cold and semi‐hot forging conditions. The methods for the experimental fracture detection are introduced as well. In cold forging the passive ultrasonic testing with integrated statistical filtering algorithms is used. As this method is not applicable to semi‐hot forging experiments, optical fracture detection by means of a high‐speed camera is used instead. A very interesting material behaviour of the steels tested has been identified in the semi‐hot upsetting of collar specimen. For every steel a distinct temperature crossover interval exists, in which the forging process abruptly changes from damaged to undamaged state. This interval amounts to some degrees Celsius only for each of the seven materials investigated. Among the damage models proposed, the Model of Effective Stresses by Lemaitre is chosen for the application to a cold and a semi‐hot forging operation. These industrial processes of an axle end (cold) and a journal bearing (semi‐hot) are susceptible to damage for reasons to be discussed in this paper. It will be shown that the internal fracture of the axle end (chevrons) and the surface fissures of the journal bearing can be predicted with high accuracy. Moreover, the application of the damage model in the finite element software MSC.SuperForm 2004 offers a promising approach for process optimisation. Several possibilities could be tested for their suitability of reducing the calculated damage: geometry variation of the forming tools, process annealing, different materials. The use of damage models in finite element simulation can be regarded as a further step towards an optimal process design.     

Simulation of the behaviour of voids in steel plates during hot rolling

The prime objective of the work is to predict the behaviour of voids in the steel slab during hot rolling and to assess the tendency of the void to closure, depending on the process parameters. The rigid-plastic thermal-mechanical finite-element program is used for the purpose. The model which simulates the general case of deformation of a single void in a matrix undergoing plastic deformation is developed. This model allows the investigation of the influence of the stress state on the void's behaviour. Finite element calculations carried out for the industrial hot plate rolling process supply information regarding the stress state during rolling depending on the process technological parameters. These data are used as boundary conditions in the void's closure model and, in consequence, allow the analysis of the influence of rolling technology on the void's behaviour.     

TC4合金锥体模锻过程的数值模拟

采用刚塑性有限元法对钛合金锥体的模锻成形进行有限元数值模拟,分析了锥形件模锻过程中的金属流动规律,应力场、应变场、变形区的压力分布,压力的变化规律等。模拟结果表明,锥体模锻成形分为3个阶段:初期变形过程是圆柱体变形为一个小曲率壳体的阶段,应力主要集中在上模的正下方,应变主要发生在此变形区;变形中期是与下模相接触的部分参与变形的体积逐渐增大,直至最后形成所需要的锥体形状;变形后期由于摩擦作用产生严重的不均匀壁厚减薄现象。