Near-net-shape forming of alumina powder under hot pressing and hot isostatic pressing

Densification and deformation of alumina powder under hot pressing and hot isostatic pressing were investigated. Finite element calculations were performed by implementing constitutive equations for grain growth, power law creep and diffusional creep in the user defined subroutine CREEP of ABAQUS. An alumina compact of valve head shape was produced under hot pressing and its forming process was predicted by the finite element calculation. Densification behavior of an alumina powder compact encapsulated by a stainless steel container was also investigated under hot isostatic pressing. Inhomogeneous deformations of an alumina powder compact due to the shield effect of a container during hot isostatic pressing were observed experimentally and predicted by the finite element analysis.     

Densification behavior of tungsten-fiber-reinforced copper powder compacts under hot isostatic pressing

Densification behavior of tungsten-fiber-reinforced copper powder compacts under hot isostatic pressing was investigated. Hot isostatic pressing was carried out for a bundle of copper-coated tungsten fibers in copper powder. Due to tungsten-fibers and copper coating layers, the densification rate of a tungsten-fiber-reinforced copper powder compact was slower than that of pure copper powder. The constitutive equations by McMeeking and co-workers and by Abouaf and co-workers were implemented into a finite element program (ABAQUS) to analyze densification behavior of tungsten-fiber-reinforced copper powder compacts under hot isostatic pressing. Finite element calculations were compared with experimental results for the variation of relative density with time for copper powder compacts during hot isostatic pressing. Density distributions in copper powder compacts were also investigated by comparing experimental results with finite element calculations.     

Near-net-shape forming of 316L stainless steel powder under hot isostatic pressing

Near-net-shape forming of 316L stainless steel powder is investigated under hot isostatic pressing (HIPing). A stainless steel powder compact and an insert were encapsulated by a stainless steel container and hot isostatically pressed to produce an axisymmetric near-net-shape part. To simulate densification and deformation of a powder compact in the container during HIPing, the constitutive model of Abouaf et al., and that of McMeeking and co-workers were implemented into a finite element analysis. The thickness effect of the container on densification was also studied for the axisymmetric part during HIPing. Densification of a three-dimensional asymmetric part during HIPing was also investigated by comparing finite element calculations with experimental data by Eisen et al.     

Technological information concerning the integrated design of “net-shape” forged parts

This work concerns knowledge integration from manufacturing activities in design in order to make full use of the advantages provided by “net-shape” forging processes, by setting up tools and using specific competencies. The main objectives are improvements in product quality, together with a time reduction required for the design and manufacturing cycle. The specific aspects of this work are to be found in the identification of the pertinent data, information, and knowledge in a context of redesigning industrial products in relation to evolutions in the manufacturing processes. The approach described here is based on analysis of the stages in the product life cycle. This approach is illustrated by the example of forged pinions used in automotive vehicle differentials, and it shows the improvements obtained mainly through design activities. A feature approach is mentioned in perspective in order to make it easier to formalize and capitalize on pertinent information through its integration in a product data management (PDM) system.     

Modeling of microstructure effects on the mechanical behavior of ultrafine-grained nickels processed by hot isostatic pressing

Bulk ultrafine-grained nickel specimens having grain sizes in the range of 0.25-5 μm were consolidated by hot isostatic pressing technique. The resulting microstructures were characterized by transmission electron microscopy and X-ray diffraction analysis. Compression tests were carried out at room temperature and at strain rate of 1.6×10⁻⁴ s⁻¹. It was found that the measured yield strength does not follow the Hall-Petch law as a consequence of the presence of oxide phase. Therefore, the use of micromechanics based model, which takes into account only the Hall-Petch relationship at grain level for predicting the grain sized effects on mechanical behavior of this kind of materials, is not accurate yet. In this study, a modification made to the generalized self-consistent model was proposed for studying both grain size and oxide phase dependence of ultrafine-grained materials behavior. Because of the novel modification, an optimization procedure with two steps was required to identify the parameters of micromechanical model. An acceptable agreement between experimental and numerical results was achieved. Moreover, the influence of texture on the yield strength and the application of the proposed model to the spark plasma sintering processed materials were also discussed.     

An analysis of the can effect in an isostatic pressing of copper powder

Based on an elastic-plastic analysis of the can deformation, experimental data from Wadley et al. (1991, Acta Metall. Mater.39, 979) are used to evaluate the shielding effect of the can in an isostatic pressing of copper powder. The calculation indicates that the consolidation of the powder compact is preceded by a stage of powder rearrangement. Thereafter, during consolidation, it is found that in this particular case, compressive stresses in the powder are about 20 MPa less than the pressure applied to the exterior of the can. Furthermore, the powder is not in a state of hydrostatic pressure. The axial compressive stress in the powder is less than the transverse compressive stress. This effect is due to the can which supports a larger load in the axial direction compared to the radial direction during plastic deformation. A model for the nonisostatic yielding of metal powder is compared to the data. It is found that strain hardening must be allowed for to get agreement between the model and the experiment for cold pressing.     

变能量激光选区熔化IN718镍基超合金的成形工艺及高温机械性能

开展了基于激光选区熔化技术对IN718镍基超合金直接激光熔化成形的研究。将零件分为心部与轮廓区,通过改变激光线输入量进行选区熔化研究。首先,建立熔池内烧结的数值模型,改变激光线输入量,获得了激光线输入量对零件致密度的影响规律并观察了成形体中的组织生长。然后,增加轮廓部位扫描,改变激光线输入量与扫描顺序,获得其对零件表面质量的影响规律。最后,通过优化热处理工艺提高零件高温拉伸强度和高温持久性能。试验结果表明,在激光线输入量为300J/m时,成形体致密度最高,为98.9%,成形体沿层间方向组织为树枝晶加等轴晶,在层内方向组织为等轴晶。采用心部+后轮廓扫描的方式,轮廓激光线输入量为100J/m时表面质量最优,粗糙度为3.1μm。对成形体采用1 065℃固溶+双时效的热处理可以获得最佳高温性能组合,高温拉伸强度为1 356MPa,高温持久时间为34h。结果显示,通过激光选区熔化制作IN718镍基超合金可以满足航空结构件对致密度、表面质量和高温性能要求。     

An iterative complementarity approach for elastoplastic analysis involving frictional contact

We consider the nonholonomic (path-dependent) elastoplastic analysis of suitably discretized structures involving classical frictional contact conditions. A mixed generalized variable finite element approach within a mathematical programming framework is developed. Various models of generalized variables plasticity laws and contact conditions can be accommodated. The numerical solution is carried out in typical stepwise holonomic (path-independent) fashion. In particular, the iterative algorithm proposed involves solving a series of complementarity problems, with appropriate updating being carried out to account for changes in contact and possibly also plasticity conditions. Application is illustrated through several examples.     

Automatic tooling design for rotary draw bending of tubes

Cold rotary draw bending of tubes is a CNC metal forming process widely used in industry. When planning a new process, trial and error is often required in order to calculate the proper overbending and to avoid wrinkling, excessive thinning and flattening. Process design is a critical, difficult, experience-based activity, that requires the selection of several variables. In this paper, a comprehensive, computer-based methodology, called Tube ProDes, is proposed for process design of the rotary draw bending of tubes. The approach can be described as follows. First, numerical calculations are carried out in order to compensate for springback, to evaluate the severity of the bend (i.e. the risk of the occurrence of defects), and to assess the sensitivity of the process to a change in the material properties. Then, the tooling setup is completely designed by fuzzy logic, using the tube material properties, the geometrical data of the bend and the variables previously calculated as input.     

An integrated framework for die and mold cost estimation using design features and tooling parameters

Tooling is an essential element of near net shape manufacturing processes such as injection molding and die casting, where it may account for over 25% of the total product cost and development time, especially when order quantity is small. Development of rapid and low cost tooling, combined with a scientific approach to mold cost estimation and control, has therefore become essential. This paper presents an integrated methodology for die and mold cost estimation, based on the concept of cost drivers and cost modifiers. Cost drivers include the geometric features of cavity and core, handled by analytical cost estimation approach to estimate the basic mold cost. Cost modifiers include tooling parameters such as parting line, presence of side core(s), surface texture, ejector mechanism and die material, contributing to the total mold cost. The methodology has been implemented and tested using 13 industrial examples. The average deviation was 0.40%. The model is flexible and can be easily implemented for estimating the cost of a variety of molds and dies by customizing the cost modifiers using quality function deployment approach, which is also described in this paper.     

The effects of hot isostatic pressing (HIP) and solubilization heat treatment on the density,mechanical properties,and microstructure of austenitic stainless steel parts produced by selective laser melting (SLM)

Despite ongoing optimization, selective laser melting (SLM) technology still cannot guarantee the production of completely defect-free components. This wor     

Experimental analysis of applicability of a picosecond laser for micro-polishing of micromilled Inconel 718 superalloy

An increasing number of recent technological advancement is linked to the widespread adoptions of ultra-short picosecond (ps) pulsed laser in various applications of material processing. The superior capability of this laser is associated with the precise control of laser–material interaction as an outcome of extremely short interaction times resulting in almost-negligible heat affected zones. In this context, the present study explores the applicability of a picosecond laser in laser micro-polishing (LμP) of Ni-based superalloy Inconel 718 (IN718). The specific research goals of the present study constitute determination of melting regime—a mandatory phase for LμP, establishing the concept of polishability of the spatial contents of the initial surface topography and experimental demonstration of the process capability of a ps laser for potential micro-polishing applications. The initial surface topography was prepared by micromilling operation with a step-over of 50 μm and scallop height of 2 μm. The LμP experiments were performed at five different levels of fluence associated with the melting regime by changing the focal offset, a parameter denoting the working distance between workpiece surface and focusing lens focal plane. The LμP performance was evaluated based on the line profiling average surface roughness (R _a) spectrum distributed at different spatial wavelength intervals along the laser path trajectory. Furthermore, additional statistical metrics such as material ratio and power spectral density functions were analyzed in order to establish the process parameters associated with best achievable surface finish. The applicability of ps LμP was demonstrated in two regimes—1D (line) and 2D (area) polishing. During 1D LμP, significant (～52 %) improvement of the surface quality was achieved by reducing an R _a value from 0.50 μm before polishing to an R _a value of 0.24 μm across the laser path trajectory on initially ground surface. In addition, an initially micromilled area of 4.5?×?4.5 mm was LμPed resulting in the reduction of an areal topography surface roughness (S _a) value from 0.435 to 0.127 μm (70.8 % surface quality improvement).     

An iterative approach to the analysis of EM autoradiographs

An iterative scheme is described for determining the most appropriate ‘model’ for dividing micrographs of EM autoradiographs into identified items of known relative specific activities in such a way that the dispersion of silver grains over the autoradiographs is fully and satisfactorily explained. A trial model is first set up for which, using a square matrix of estimates of notional cross-fire between the chosen items, a ‘solution’ is obtained. The quality of the model is then tested using extended cross-fire data contained in a rectangular matrix. If the model is shown to be unsatisfactory, an improved model (of tissue subdivision) is postulated and the whole process repeated until the model is deemed to be satisfactory. The computations are such that the data can be processed rapidly on the laboratory bench using a small machine. The logical estimation of errors is facilitated by this approach.     

存在模糊信息时机械零部件的优化设计

为使机械零部件的设计更符合实际,更合理,根据模糊数学及优化设计理论,探讨了机械零部件的存在模糊信息时的优化设计数学模型及求解方法,并结合该理论对V带传动设计进行分析,得到了比普通优化设计更为理想的设计结果.其结果证明了该方法的可行性与实用性.     

车身冲压线中端拾器的仿真设计

介绍车身冲压线中端拾器的总体设计架构、建模、虚拟装配及其程序开发。该系统是基于C/S和B/S相结合的架构,采用VisualBasic.NET对CATIA进行二次开发,通过ADO访问数据库Oracle9i来建立的。而且,为了使计算机模型具有可扩充性和智能性,形成智能化的设计系统,对基于知识工程的计算机建模、参数化的虚拟装配进行了研究。     

面向航空发动机工装快速设计系统的信息模型研究

针对航空发动机工装设计过程及企业开发工装快速设计系统的需求,本文旨在研究并开发一个包含航空发动机一系列工装设计信息的信息模型,其中包括:零部件的几何拓扑信息、零部件间的约束信息以及零件的载荷信息,同时,设计了一套基于信息功能特征的编码方法.该信息模型已应用于自主开发的航空发动机工装快速设计系统中.     

Numerical simulation and experimental investigation on densification,shape deformation,and stress distribution of Ti6Al4V compacts during hot isostatic pressing

Hot isostatic pressing of metal powders involves a complex thermal and mechanical coupling process. A constitutive model based on Perzyna’s elastic-viscoplasticity equation was proposed, and a Lagrangian finite element method was applied to analyze the large deformation, nonlinear friction, powder flow, and densification behavior during hot isostatic pressing. The mechanical behavior of the powders was analyzed in terms of stress distribution. For comparison to the simulation results, the density, shape deformation, and residual stress of the specimens were evaluated using Archimedes’ principle, 3D measuring technology, and Empyrean X-ray diffractometer.     

输送带热硫化修补器施压装置的改造

根据设备运行数据统计,胶带损伤尺寸小于500 mm的胶带修复项目占整个胶带损伤修补项目的比例超过85％.具有体积小、操作便捷、修补质量可靠等优势的硫化修补器成为胶带热硫化修补的首选和必备工具.本文就某修补器使用过程中出现的问题和现象进行分析与探讨,介绍了对施压装置进行改进的经验和方法.     

轧机滚子轴承端面油槽加工方法及工装设计

针对轧机滚子轴承端面油槽加工中存在的困难,设计了相应的夹具和刀具,圆满地完成了加工任务。     

An unconstrained approach to blank localization with allowance assurance for machining complex parts

In machining large complex parts with critical stock allowance, even small deviations in the blank parts or slight inadequacy in the fixturing may result in local shortage of material (i.e., insufficient stock allowance). This paper presents an optimal localization algorithm that aligns the measured points from a blank part with the nominal model to assure the weakest allowance area with as much material to be cut as possible. Instead of exploiting extra constraints to force the allowance at each point larger than a specific value, which is a popular strategy for allowance assurance in the previous localization algorithms, we formulate the blank localization problem as an unconstrained max-min problem. To deal with the unsmoothness exhibiting in the max-min objective function, a method based on the entropy optimization principle is adopted to convert the non-differential objective function to an unconstrained differential one, which can be efficiently solved using the conventional Quasi-Newton algorithms. The unconstrained optimization result finally gives rise to localization with the maximum allowance margin. For the blank parts that the material shortage is inevitable, the method can still efficiently achieve reasonable localization results, which confine the material shortage to a least extent. The proposed method is easy to be implemented and works well for both sparse sample points and dense-scanned points. Case studies included justify the superiority of the proposed scheme over the existing non-linear constrained optimization solutions.