衔铁连续冷挤压模具失效分析及工艺改进

通过对衔铁连续冷挤压工艺进行试验,对挤压过程中模具失效进行了分析,并提出了合理的工艺改进,对薄壁、非对称零件连续冷挤压工艺设计及试验有参考作用。     

发电机转轴断裂失效分析

发电机转轴在耐久试验中发生断裂。用化学分析、金相检验、扫描电镜等方法对断裂转轴进行了分析。结果表明，由于机加工时留下的切削缺陷，使转轴形成早期疲劳，加之热处理淬火加热未达到奥氏体温度，组织中存在少量块状铁素体，降低了材料强度，最终导致转轴断裂。     

H13钢制铝合金挤压模具失效原因技术分析

铝合金挤压模具的失效形式主要有四种,本文通过对一套H13钢制作的铝合金挤压模具进行失效分析,得出H13钢制铝合金挤压模具的主要失效原因。     

汽车发动机曲轴断裂失效分析

采用断口分析、显微组织检验、低倍组织检验、能谱分析和化学成份分析等方法对某汽车发动机曲轴断裂进行了失效分析,判断断裂失效的主要原因是非金属夹杂和次表面的原始微裂纹,建议改进热处理工艺,保证组织的均匀性,选用非金属夹杂物含量小的钢材。     

摩托车铝轮毂断裂失效分析

摩托车铝轮毂在安装过程中发生断裂。采用化学成分分析、力学性能测定和断口分析方法,对摩托车铝轮毂的断裂原因进行了分析。结果表明,铁含量超标、疏松区的存在以及组织中出现大量的针状含铁相,大大降低了材料的力学性能,是造成断裂的主要原因。摩托车铝轮毂断裂为一典型的脆性解理断裂。     

某油田钻铤断裂失效原因分析

某油田钻井队在空气钻井过程中发生一起钻铤断裂失效事故。采用宏观观察、化学成分分析、力学性能试验、硬度测试、金相检验、微观观察等方法对钻铤断裂失效的原因进行了分析。结果表明:钻铤螺纹接头与钻铤尺寸不匹配,内螺纹接头处为薄弱环节,在空气钻井过程中发生了疲劳断裂。建议采用与钻铤尺寸匹配的螺纹接头,并在钻铤接头部位增加应力分散槽,或者使用双台肩接头钻铤。     

外丝直接头断裂失效原因分析

某新建小区住宅楼给水管道发生断裂.采用宏、微观检验、材质化学成分分析、力学性能比较及扫描电镜、能谱仪测定等方法对断裂件进行分析.结果表明,因用材错误,在水介质作用下,金属发生晶界腐蚀及显微组织变化,最终引起性能恶化而断裂失效.     

铁水包耳轴断裂失效分析

某钢厂铁水包耳轴在34炉包龄时发生早期断裂,采用探伤检验、宏观观察、化学成分分析、力学性能试验、金相检验、扫描电镜以及能谱分析等方法对耳轴断裂的原因进行了分析。结果表明:耳轴中心部位存在裂纹缺陷是耳轴发生早期脆性断裂的主要原因,耳轴中心孔内壁粗糙的加工刀痕是耳轴发生早期断裂的次要原因。耳轴服役期间,在应力作用下裂纹扩展并最终断裂。     

线材拉拔断裂原因分析

归纳了线材拉拔断裂的常见原因,总结了线材失效分析的步骤,并将线材拉拔断裂分为两大类：一是断裂源起源于外表面（包括线纹、折叠、钢坯上裂纹、皮下气泡和非金属夹杂物等）;二是断裂源产生于内部（包括中心夹杂物、中心缩孔、中心马氏体和中心网状碳化物等）,并举例进行了说明。     

Impact of Repeated Nitriding Cycles on Extrusion Die Life—Some Statistical and Metallurgical Observations

This paper presents some observations about die failure patterns in commercial aluminum extrusions. A total of 97 dies were analyzed to observe the nature of scatter in the life of these commonly used dies. Each die in its complete life cycle passes through a number of nitriding treatments. The number of these nitriding treatments generally ranges from 5 to 10 in most cases. Each nitriding event is equivalent to die surface renewal, and a new time between failures is calculated after each renewal. This article analyzes the performance of both solid and hollow dies to first failure and to subsequent failures after nitriding. The Weibull model describes the time to first failure and cumulative time to nth failure of this group of dies and indicates an overall wearout pattern. The median time to failure, scatter in cumulative life, and progress of die death rate are discussed. A die is considered to fail when the surface must be nitrided. The interarrival time between failures (nitriding events) is analyzed for both solid and hollow dies. It is shown that interarrival time is also Weibull distributed. Based on these observations, it is concluded that if die is treated as a repairable system and the die surface nitriding makes the die as good as new, the failure can essentially be modeled as a nonhomogeneous Poisson process with a nonlinear intensity of failure. The results presented are of the first phase of an ongoing project dealing with life improvement of extrusion dies. The analyses presented provide a starting point for subsequent in-depth study of die-life reliability, optimal nitriding interval determination, and optimal cumulative time before die replacement.     

GCr15钢冲模失效原因的分析

冲模在短期使用后表面出现微裂缝,导致产品表面呈现许多"闪光点",影响产品外观质量.采用宏、微观检测方法,对模具失效原因进行了分析.结果表明,镀铬层表面存在网状裂纹是导致模具表面出现微裂缝的主要原因.     

Formability Limit in Containerless (Open Die) Extrusion of Commercial Purity Titanium Rods and Tubes

Containerless extrusion requires far less forces compared to conventional direct extrusion of rods and tubes due to the elimination of container wall-billet friction. But the strains that can be imparted are less in the former due to the unsupported billet which gets upset first if the axial stress exceeds yield stress of the billet material. If this stress is equal to yield stress, it corresponds to the limit of the process of pure containerless extrusion. It is found that this limit strain as predicted by theory is far less compared to what is observed experimentally. This discrepancy is explained on the basis of heating that takes place in the deformation zone due to ideal, frictional, and shear work done in carrying out the extrusion process.     

复合材料筒体结构水压试验失效分析

本文针对某型复合材料筒体结构在静水外压试验过程中出现的破裂失效现象,通过有限元仿真计算,从筒体的结构设计,试验叠加因素等方面进行了分析,找出了复合材料筒体破裂的主要原因。     

Defining Shape Complexity of Extrusion Dies—A Reliabilistic View

Complexity of the profile being extruded plays a critical role in die design, die reliability, process aberrations, and product defects. Engineering common sense dictates that a more complex die should require a larger amount of extrusion force or pressure. This has been experimentally substantiated by the authors in a recent study. According to a basic definition, therefore, extrusion shape complexity is the ratio of the pressure required to extrude a complex profile to the pressure required for a solid circular profile of the same area. Most of the complexity definitions reported in published literature are based on this interrelationship between extrusion pressure and profile complexity. From a die reliability viewpoint, a complex profile is more difficult to extrude than a simple one, and it generates more stresses in the die. It should therefore lead to an earlier die failure. Another study by the authors confirms that the working life of hot extrusion dies is definitely affected by profile complexity. Reported complexity definitions provide some sort of index to measure extrudability, and can thus be used for pressure prediction to a certain degree. Unfortunately, none of these definitions addresses the very important issue of die reliability, and they generally yield a counterintuitive trend of increasing die life with increasing complexity. None of these definitions includes all the significant geometrical features of a die profile. This article reports the development of two new definitions of shape complexity (linear and power-law) incorporating all significant geometrical features of an extrusion die profile. Die failure data from a large commercial extrusion facility have been collected and analyzed. Regression-based models have been developed for prediction of die failure on the basis of complexity.     

Expert Network for Die Casing Defect Analysis

Due to the competition and high cost associated with die casting defects, it is urgent to adopt a rapid and effective method for defect analysis. In this research, a novel expert network approach was proposed to avoid some disadvantages of rule-based expert system. The main objective of the system is to assist die casting engineer in identifying defect, determining the probable causes of defect and proposing remedies to eliminate the defect. 14 common die casting defects could be identified quickly by expert system on the basis of their characteristics. BP neural network in combination with expert system was applied to map the complex relationship between causes and defects, and further explained the cause determination process.Cause determination gives due consideration to practical process conditions. Finally, corrective measures were recommended to eliminate the defect and implemented in the sequence of difficulty.     

Analysis of the formation mechanism of coarse-dense structure of silver paste in die bonding

The flow behavior of silver paste during die bonding was analyzed by numerical simulation to clarify the formation mechanism of coarse-dense inhomogeneous distribution of silver particles in a die-attach layer. Depending on the loading speed of a die, silver particles in the paste flow and form a coarse-dense distribution under a die. The microstructure of the paste before sintering was observed by X-ray computer tomography (X-ray CT) and Scanning Electron Microscope (SEM). At a slow loading speed of 1.0 μm/s, the paste is densely packed with silver particles along the diagonal of the die. A coarse structure was observed in the other area of the paste. On the other hand, at a high loading speed of 60.0 μm/s, there was no clear segregation and the paste layer has an almost uniform structure. The SPH method was used to calculate the flow behavior of particles in the paste, and the flow velocity and shear stress of the paste were calculated. The paste velocity and shear stress in the region along the diagonal of the die is smaller than those in other area of the die. A comparison of the shear stress applied to the paste at different loading speeds showed that the smaller the loading speed, the larger the value of summation of shear stress. The difference between the maximum and minimum shear stress in a lateral direction through the center of the die increases with decreasing of loading speed. Thus, a large difference in local shear stress acting on the paste causes the formation of coarse-dense structure of the silver paste. It was found that it is necessary to eliminate local differences in the shear stress acting on the paste in order to achieve uniform joint the silver paste to the substrate without forming a coarse-dense structure.     

压盖落料冲孔成形模设计

介绍了在尺寸公差及形位公差要求较高的落料冲孔成形件的模具设计过程中,不降低劳动效率的情况下,如何使模具简化、降低模具成本,并使冲压件满足其设计要求。     

模具使用寿命与失效分析中一些问题的探讨

针对我国模具制造加工和使用中的现状和早期失效问题,从模具结构的应力集中、模具钢材质及碳化物形态和分布、模具钢的热处理淬火和回火工艺、残余应力、模具硬度与寿命的关系以及模具使用等方面进行了论述。提出一些减少模具早期失效、提高模具使用寿命的途径。