UG集成环境下数控机床虚拟样机的实现

数控机床是一种重要的技术装备。为提高数控机床的设计水平和能力,在数控机床的设计开发过程中需要引入新的技术和设计手段。为把虚拟样机技术应用到数控机床设计开发的工程实践中,基于虚拟样机的概念讨论了数控机床虚拟样机的具体实现过程,分析比较了实现该过程的分布式软件平台和UG集成软件平台的特点。以数控铣床新产品开发为例,研究了UG集成环境下数控机床虚拟样机的构建与仿真过程,包括数字模型与装配、运动仿真、结构分析以及在虚拟样机上的加工仿真,给出了相应的示例。研究表明,应用UG的各功能模块可以有效地构建数控机床的虚拟样机并对其进行全面的仿真,使所设计的数控机床得到全面优化,为数控机床的开发设计提供了一种可行的先进方法。     

铝合金汽车转向节精密铸造工艺研究

目的 对某铝合金汽车转向节的精密铸造工艺进行设计与优化研究,以得到合格的铝合金汽车转向节的精密铸造工艺方案。方法 结合铝合金转向节铸件的结构特征、铸件材料特性和铸造经验,在转向节铸件主体部和鹅颈部各开设一个内浇口,设计了铝合金转向节初始浇注方案;通过在初始工艺方案中铸件缺陷较严重的区域设置补缩冒口、在铸件顶部增设排气道等措施给出了铝合金汽车转向节的优化浇注方案,基于ProCAST软件建立了铝合金转向节精密铸造2种浇注方案的有限元模型,对铝合金转向节精密铸造的充型过程、凝固过程及缩孔缩松特性进行了数值模拟与分析。结果 铝合金转向节铸件初始浇注方案的充型过程相对稳定流畅,铸件在凝固过程中有孤立液相区的形成,完全凝固后铸件中间部位存在大面积缩松缩孔缺陷;优化浇注方案能够控制金属液的流动、充型顺序及凝固特性,铸件的整个凝固过程基本呈中间对称分布,最后凝固区域位于补缩冒口内部,最大缩孔缩松率控制在2%以下。结论 优化浇注方案的设计合理且有效,能够有效地消除铝合金转向节铸件的缺陷。     

汽车转向节淬火过程温度场数值模拟、淬硬层深度预测与验证

本文采用ANSYS对某汽车40Cr转向节的淬火冷却过程温度场进行了数值模拟、温度场的求解,并考虑了材料热物性参数随温度的变化,得到瞬态温度场,进而对照40Cr的CCT推导组织转变,利用临界冷却速度预测了某些位置的淬硬层深度,并通过金相组织分析和硬度测试进行了验证。模拟结果和实验结果基本吻合。实测淬硬层与预测淬硬层深度相比,其值偏大;实测硬度值与预测硬度值相比,其值偏小。     

Determination of the Failure Susceptibility of a Flat Die Used in Biomass Pelletizing Machines by Means of FEA-Based Design Exploration

This paper focuses on a design analysis of a flat die used in an agricultural biomass pelletizing machine by considering its high-pressure loading failure susceptibility. The pellet die is one of the key elements in a pelletizing machine, and the strength of the die plate has an important role on the pellet’s quality and producibility. In fact, higher compression ratio (CR—the ratio of effective length and the internal (press channel) diameter of a die orifice/hole) will provide denser pellets which is a desired phenomenon, however, if the compression pressure is too high or CR is not determined to compensate high pressures, the raw material may block the die and the die may experience deformation failure due to overloading. If the desire is to make high-quality pellets with no die failure, optimum flat die hole/orifice design parameters should be used which can provide the best CR for a specific compression pressure. This is the core motivation of this research. In this study, finite element analysis (FEA)-based design exploration has been utilized for a sample single hole flat die with various die geometry parameters against various compression pressure values. Following the FEA design exploration undertaken, a response surface analysis (RSA) was carried out and then estimation models (empirical equations), which could be used to calculate parameters of the die hole/orifice against applied compression pressure and failure susceptibility based on structural stress and deformation, was described. The results gained from the RSA have indicated that the estimation models have high R² values (higher than 98%) which could be used for adequately predicting failure susceptibility indicators. In addition to this, FEM-based simulation printouts have provided useful stress distribution visuals on the die against different compression pressure values. Most especially, the study has highlighted that a detailed structural optimization study may be scheduled in order to obtain die geometry design parameters with a focus on the failure susceptibility.     

Modelling of the heat exchangers of a small capacity, hot water driven, air-cooled H2O–LiBr absorption cooling machine

General models for the design of the heat exchangers (absorber, generator, condenser and evaporator) of a prototype of an air-cooled absorption chiller of 2 kW for air-conditioning using the pair H₂O–LiBr have been developed. An absorption machine of such characteristics has been constructed to be used as a test facility for validating the results obtained from the mathematical models developed. The discrepancies considering the heat exchanged between numerical results and experimental data are under 15% in most cases for all these components except the condenser, where the discrepancies are higher. The conclusions reported will lead to: (i) future improvements of the mathematical simulation models and (ii) improvements in the experimental infrastructure.     

A knowledge-centric CNC machine tool design and development process management framework

To cope with the increasingly competitive and demanding markets, CNC machine tool company needs a new form of development that focuses on two core competency factors: ‘process’ and ‘knowledge’. This study presents a knowledge-centric process management framework for the CNC machine tool design and development (D&D) with the integration of process and knowledge. Requirements for the framework are generated based primarily on the nature of the machine tool design practice. The proposed framework consists of process integration model, process simulation, process execution and knowledge objects management modules. Each of these modules is elaborated to support the knowledge-centric machine tool development process management. Finally, the prototype development is presented. Results of this study facilitate the knowledge integration in CNC machine tool D&D, and thus increase machine tool development capability, reduce development cycle time and cost, and ultimately speed up the effectiveness and ensure the excellent machine tool development.     

Thixoforming of a novel layered metal matrix composite

Abstract

Thixoforming is a semisolid processing route capable of producing near net shape components with low levels of porosity in a single, rapid operation. It has potential for the processing of aluminium alloy based metal matrix composites (MMCs). In contrast with casting of fully liquid metal, the flow of material into the die in thixoforming is primarily laminar. Thus, a novel layered MMC structure, generated by spray forming, consisting of alternate lamellae of reinforced and unreinforced alloy, might be preserved in thixoforming. The laminated structure is intended to give an increase in toughness, compared to a homogeneously reinforced material. The material was produced by spray forming alternate layers of aluminium matrix alloy 2014 (Al–4Cu–0·8Si–0·8Mn–0·5Mg) and matrix alloy reinforced with ～17 vol.%SiC particles. Following thixoforming, the layered structure was well preserved with good retention of layer integrity and arrangement. Impact measurements for estimating toughness (Charpy and Izod) showed limited improvement with the layered materials, relative to homogeneously reinforced ones. However, in slow crack growth (Tattersall–Tappin tests), toughness was nearly doubled when estimated in terms of an average energy of fracture from the area below the load–crosshead displacement curve. This was attributed to the reduction in the energy of the propagating crack at low strain rates, which led to a greater potential for the structure, and in particular for the unreinforced layer, to stop or slow the crack. Additionally, these layered MMC materials have provided a striking record of the die filling behaviour for metallic materials during thixoforming. The flow pattern is akin to that in conventional hot forging. This may assist in the establishment of design rules for thixoforming dies.     

Evolution of microstructure and mechanical properties for 9Cr18 stainless steel during thixoforming

Hot compression tests were carried out in the semi-solid state of 9Cr18 stainless steel on Gleeble-1500 thermal simulation testing machine to investigate the effects of thixoforming parameters on its microstructure and mechanical properties. In this paper, microstructure was observed by scanning electron microscopy (SEM) and analyzed using energy dispersive spectrometer (EDS), and true stress–stain curves of the specimens with different initial microstructures after thixoforming were obtained to study the deformation mechanism. The results showed that thixoforming parameters such as reheating temperature and the strain rate had a significant influence on microstructure and mechanical properties evolution of 9Cr18 semi-solid billet. With increasing reheating temperature or decreasing strain rate, average size of carbides decreased from 2 μm to 0.5 μm, and the phenomenon of liquid extrusion during thixoforming became more obvious. During thixoforming, carbon atoms diffused to molten metal from austenite in the centre of specimens. When thixoforming temperature reached 1300 °C, martensitic transformation occurred after rapid cooling. Flow stress of semi-solid billet was lower than traditional ingot casting and hot rolled state steel, when reheated to the semi-solid range, due to their different original microstructure.     

自动穿孔机构的概念设计

为了解决细小链节串链的自动串连问题,结合虚拟设计及仿真手段对自动串链机的关键部件进行概念设计,通过构思-实验-设计法构建关键部件的功能原理解和确定设计过程,并由此进行跳跃式想象设计,得到能解决冲突的关键部件的创新设计及满足功能要求的整机概念模型,并通过对部件的概念设计和发散性创新设计的探讨,提出基于模拟实验及虚拟样机技术的一个应用实例。     

A multi-agent-based intelligent STEP-NC controller for CNC machine tools

ISO 6983 has now been considered as a bottleneck for developing next generation CNC machine tools. STEP-NC is a new interface standard between CAD/CAM systems and CNC machines, which not only provides an object-oriented data model for CNC with a detailed and structured data interface that incorporates feature-based programming, but also represents a data model for intelligent computer numerical controllers. This paper presents a conceptual framework of holonic compliant data interference for numerical control STEP-NC controller to implement intelligent control for Computer Numerical Control (CNC) machine tools. The architecture is comprised of 14 functional agents, such as interpreter agent, process planning agent, NCK/PLC agent, decision-making agent, etc. These agents can co-operate closely to carry out various functions of the intelligent STEP-NC controller in a desired manner. The process flow for the STEP-NC controller is analysed. Furthermore, the implementation for two functional agents (i.e. interpreter agent and process planning agent) is described in detail. Finally, the preliminary development of a prototype system is discussed. As a result, the framework and implementation methods proposed provide a paradigm for future implementation of an intelligent STEP-NC controller.     

Study on Numerical Simulation of Mold Filling and HeatTransfer in Die Casting Process

1. IntroductionDie casting is a very complicated process which involves the high speed flow of molten metal filling into3-dimensional complex geometry. The molten metalflow pattern and the temperature distribution of thedie casting and the dies, have a critical influence onthe quality of the cast products, the production rateand the die life.The application of CAE (computer aided engineering) analysis in die design gradually becomes possibleand popular. The main idea is to analyze or predict…     

转向盘动力吸振器稳健性设计研究与应用

为解决怠速时转向盘振动大问题,用基于稳健性的设计方法,开发了动力吸振器(dynamic vibration ab-sorber,DVA).采用最小二乘迭代法,识别出动力吸振器安装位置的等效参数,运用基于6sigma多目标稳健性优化方法,进行动力吸振器的参数的优化.在样件制作前用有限元仿真预测其固有频率,用激振台测出其固...     

转向节预锻件坯料的优化

以汽车转向节为研究对象,以转向节终锻件为目标,运用计算截面积的方法对获得终锻件飞边截面积的大小进行修正,从而修改预锻件对应截面的截面积大小以达到优化预锻件的目的.通过反复的修正和修改,最终获得最优的预锻件,提高了材料利用率和模具寿命,对复杂锻件的坯料优化具有借鉴作用.     

REVIEW OF NEW PROCESS TECHNOLOGIES IN THE ALUMINUM DIE-CASTING INDUSTRY

There have been many challenges in aluminum die casting to establish casting processes to produce high-integrity components from aluminum alloys. Advances in new casting technology mainly have been in pressure die casting; in particular, to obtain mold filling at low speed. This can be achieved by using innovative filling processes with aluminum alloys in the liquid or semisolid state. Different techniques such as high-pressure die casting (HPDC), Cosworth process, low-pressure systems, squeeze casting, indirect squeeze casting, metal compression forming (MCF), and semisolid metal (SSM) processing have been developed. Semisolid forming includes thixoforming and rheoforming. During the semisolid casting process, preheating by induction is needed to obtain the same temperature and the same liquid fraction through the billet in a short time. Thixocasting in the semisolid state helps to avoid turbulence during mold filling.     

Effect of friction model in numerical analysis of equal channel angular pressing process

During the last decade or so there has been a tremendous growth in the research and development of equal channel angular pressing (ECAP) process which was originally proposed by Segal et al. Numerical analyses are being used extensively to evaluate the effect of various die design and process parameters in ECAP. Friction is one such important parameter. Coulomb and shear friction models have been used in the numerical analysis of ECAP process and contradicting results have been reported. This study evaluates the effect of coulomb and shear friction models on the deformation pattern, strain distribution and load requirement during ECAP process and suggests which friction model should be used in the numerical analysis of ECAP process.     

高强度钢板U形件热冲压凹模结构拓扑优化

为降低热冲压凹模的生产成本和使用成本,基于板料热冲压数值模拟对凹模结构进行了拓扑优化设计.运用有限元软件ABAQUS建立热力耦合有限元模型,对高强钢板U形件的热冲压成形和淬火过程进行了数值仿真.提取凹模与板料间关键工况下接触应力作为凹模拓扑优化的外在载荷,建立约束凹模结构关键区域节点位移的体积最小化拓扑模型,对热冲压凹模结构进行拓扑优化设计,最终实现结构减重20%,且优化后凹模的变形和应力与优化前的结果相差甚微.研究内容对热冲压过程数值模拟和模具结构拓扑优化研究具有一定参考价值.     

Modelling the semisolid processing of metallic alloys

Semisolid processing of metallic alloys and composites utilises the thixotropic behaviour of materials with non-dendritic microstructure in the semisolid state. The family of innovative manufacturing methods based on this behaviour has been developing over the last 20 years or so and originates from scientific work at MIT in the early 1970s. Here, a summary is given of: routes to spheroidal microstructures; types of semisolid processing; and advantages and disadvantages of these routes. Background rheology and mathematical theories of thixotropy are then covered as precursors to the main focus of the review on transient behaviour of semisolid alloy slurries and computational modelling. Computational fluid dynamics (CFD) can be used to predict die filling. However, some of the reported work has been based on rheological data obtained in steady state experiments, where the semisolid material has been maintained at a particular shear rate for some time. In reality, in thixoforming, the slurry undergoes a sudden increase in shear rate from rest to 100 s⁻¹ or more as it enters the die. This change takes place in less than a second. Hence, measuring the transient rheological response under rapid changes in shear rate is critical to the development of modelling of die filling and successful die design for industrial processing.The modelling can be categorised as one-phase or two-phase and as finite difference or finite element. Recent work by Alexandrou and coworkers and, separately Modigell and coworkers, has led to the production of maps which, respectively summarise regions of stable/unstable flow and regions of laminar/transient/turbulent fill. These maps are of great potential use for the prediction of appropriate process parameters and avoidance of defects. A novel approach to modelling by Rouff and coworkers involves micro-modelling of the `active zone' around spheroidal particles. There is little quantitative data on the discrepancies or otherwise between die fill simulations and experimental results (usually obtained through interrupted filling). There are no direct comparisons of the capabilities of various software packages to model the filling of particular geometries accurately. In addition, the modelling depends on rheological data and this is sparse, particularly for the increasingly complex two-phase models. Direct flow visualisation can provide useful insight and avoid the effects of inertia in interrupted filling experiments.     

Fracture Characteristics of Fatigue Failure of a Vehicle’s Ductile Iron Steering Knuckle

The steering knuckle, being a part of the vehicle’s steering and suspension system, undergoes time-varying loading during its service life. Since it is connected to the steering parts and strut assembly from one side and the wheel hub assembly from the other, it has complex restraint and constraint conditions and tolerates a combination of loads. In addition, parameters such as internal defects, stress concentrations and gradients, surface finish, and residual stresses can have considerable influence while designing for fatigue. A vehicle with a 2.500 cm³ (2.5 L) volume engine was being driven during a rainy day in a congested road at a speed of about 10 km/h, when suddenly the vehicle lost its orientation and crushed over a parked vehicle on the right side of the road without any human injury. The driver insisted that he heard an intense noise of a metal undergoing rupture from the front right side of the vehicle’s suspension system and immediately lost control of the vehicle. The producing company of the vehicle on the other hand, after on-site visual inspection, came to the conclusion that due to the driver’s error the vehicle turned to the right and as a consequence of the crash the steering knuckle was broken into two parts. Failure analysis conducted as presented in this article reveals the mechanism of fracture mainly due to bending fatigue.     

精冲压边与间隙的有限元模拟优化研究

运用DEFORM-2D软件对板料精冲过程中压边与间隙进行了数值模拟分析.将NormalC＆L断裂准则应用于预测精冲韧性断裂,分析了不同压边力、压边方式、反顶力以及冲裁间隙对材料涡流流动特性、冲裁断面圆角和撕裂带的影响;根据模拟结果提出了新的工艺建议.     

FD2815X型农用车转向节臂断裂分析

采用光学显微镜和扫描电镜对断裂转向节臂的宏，微观组织进行了分析。检验结果表明，表面碳层的存在及表面粗糙是导致构件断裂的主要原因。断裂性质属疲劳断裂。