基于流线型凹模型腔的直齿圆柱齿轮冷挤压数值模拟分析

齿轮挤压属于体积成形,它是一个三维非稳态塑性成形过程,变形机制十分复杂。基于NURBS曲面构造流线型凹模型腔,用大变形刚塑性有限元数值模拟软件对圆柱直齿轮挤压过程进行了模拟。结果表明,采用流线型凹模型腔的连续性挤压成形,在改善角隅部分金属的充填性、减少变形突变以及提高变形分布均匀性等方面十分有效。这一结论可以作为齿轮挤压工艺设计的参考。     

Optimal tool angles for equal channel angular extrusion of strain hardening materials by finite element analysis

Equal channel angular extrusion (ECAE) is a novel deformation process capable of imparting a large amount of plastic strain to bulk material through the application of uniform simple shear. ECAE die geometry, material properties and process conditions influence the shear deformation behavior during extrusion that in turn governs the microstructure and mechanical properties of the extruded materials. Finite element analysis, the most appropriate technique was used to analyze the deformation behavior of extruded materials without neglecting important and realistic factors like strain hardening behavior of the material, frictional conditions and speed of the process. In this study the deformation behavior of material, dead zone/corner gap formation and strain homogeneity achieved in the samples during ECAE were studied by using commercial finite element code Abaqus/Explicit. The influence of tool angles, strain hardening behavior of material and friction between the billet and die was considered for simulations. Results showed that the optimal strain homogeneity in the sample with lower dead zone formation, without involving any detrimental effects, can be achieved with channel angle of 90° and outer corner angle of 10°.     

新型扭转铅挤压阻尼器设计及其有限元分析

传统铅阻尼器一般利用相对平动位移的变化使得铅发生塑性变形,以此消耗能量.提出一种基于中心轴转动挤压铅耗能的新型铅挤压阻尼器,可直接用于扭转耗能结构体系中(如梁柱间的相对转角等),或通过相关转换结构(如齿轮等)将常规的相对平动位移的耗能机制转换为相对转角位移的耗能模式.基于平面应变假定,以Abaqus平台建立了扭转挤压铅阻尼器的非线性有限元模型,模拟了单轴、双轴扭转铅挤压阻尼器的转动过程,给出了中心转轴的转角-弯矩滞回曲线,其形状接近矩形,具有很好的耗能效果,说明了所构造阻尼器的可行性与有效性;研究了凸缘截面高度对转动弯矩峰值的影响;建立了该类扭转铅挤压阻尼器转动弯矩峰值的抛物线型估算公式.依此构思,亦可构造多轴扭转铅挤压阻尼器.     

ZK60镁合金型材挤压过程有限元数值模拟

本文运用DEFORM-3D平台对ZK60变形镁合金型材挤压过程进行了数值模拟.分析了变形温度(T=300℃/350℃)、变形速度(V=2、5mm/s)对合金等效应变、等效应力、温度场以及变形载荷的影响规律.结果表明:温度对等效应力影响显著,变形温度从300℃升高到350℃,合金最大等效应力从75MPa降低到55MPa;变形速度对温升影响显著,挤压速度由2mm/s升高到5mm/s,合金最大温升由81℃升高到118℃.确定了ZK60合金在挤压比为25时,适宜的挤压温度为350℃,挤压速度应在5mm/s以下.     

Deformation behavior in Simple Shear Extrusion (SSE) as a new severe plastic deformation technique

A new method for severe plastic deformation is proposed herein, entitled as Simple Shear Extrusion (SSE) due to the manner in which specimen's cross-section shape changes. This method is based on pressing material through a specially designed direct extrusion die. The process was investigated experimentally on commercially pure aluminum. Additionally, simulation of the process was also carried out, using the commercial finite element code ABAQUS/Explicit. Moreover, effect of back-pressure on the results was studied. Results show that SSE method is capable of imposing high strain values via strain accumulation during repeating the process, which is of great importance in producing ultrafine-grained or nanostructured materials.     

Influence of twist extrusion process on microstructure and mechanical properties of 6063 aluminum alloy

In this study, aluminum alloy 6063 was severely deformed by twist extrusion (TE) technique and its mechanical properties, before and after TE, was investigated using a die with the twist line slope of β = 30°. It was revealed that large strains imposed on the material by this advanced method of severe plastic deformation (SPD) led to a nano-scale ultra-fine microstructure and to an enhancement of the mechanical properties. The more passes of TE the finer grained microstructure was produced. Also with increasing the number of TE passes, yield strength, ultimate tensile strength and hardness increased, while after relative reduction of uniform elongation and elongation to failure by intermediate passes they remained almost unchanged. Therefore, both the strength and ductility of the material were improved when deformed by twist extrusion.     

Extrusion-on-demand methods for high solids loading ceramic paste in freeform extrusion fabrication

Fabrication of highly dense ceramic parts with complex geometries by paste extrusion-based solid freeform fabrication processes requires a precise control of the extrusion start and stop to dispense material on demand, which is often referred to as extrusion-on-demand (EOD). The EOD process for high solids loading pastes is difficult to control due to the paste’s non-Newtonian behaviour, compressibility, and inhomogeneity. In this study, three EOD methods based on ram extruder, shutter valve, and auger extruder are investigated for extrusion of high solids loading (>50?vol.%) aqueous ceramic pastes. The extrusion performance characteristics of the three methods in terms of start and stop accuracy, as well as flowrate consistency, are compared and analysed. The results indicate that the auger extruder-based extrusion method has superior EOD performance, and the highest flowrate consistency. Test parts were printed by using these methods and compared to further validate this conclusion.     

Development of a novel method for the backward extrusion

In this study, a new method of backward extrusion using small diameter billet is proposed. In this new process, the die setup consists of three main parts of the fix-punch, the moveable punch and the matrix. The fix-punch has been used to decrease the cross section of applied billet and finally reducing the total force of the process. To investigate the capability of this process, experimental and finite element (FE) methods were used. The results showed that the first advantageous of the new process is that the load is reduced to about less than a quarter in comparison with the conventional backward extrusion process. This higher reduction in the required force is due to reduce of the cross section of the initial billet. EF results showed that while needing lower loads, the applied plastic strain through the processed sample is about two times higher than that in the sample processed via conventional backward extrusion. This is the second advantageous of the process. Eventually, the most important advantages of the novel method of backward extrusion are the lower process force, imposing higher effective strain and a better strain homogeneity through the tube length. This new process is also very promising for producing ultra fine grained (UFG) samples because the higher level of shear strains.     

难变形材料热静液挤压复合精密塑性成形工艺

目的 研究热静液挤压及其复合塑性变形工艺在高密度钨合金、钨铜合金、钛基复合材料及镁合金薄壁细管等难变形材料方面的制备。方法 通过对高密度钨合金难变形材料进行热静液挤压及旋转锻造等塑性成形,分析了材料在成形过程中的微观组织及性能变化规律和强化机制,制备出大长径比穿甲弹弹芯材料。在此基础上,将该复合塑性变形技术拓展至两相不互溶材料钨铜合金、钛基复合材料及大长径比镁合金毛细管等难变形材料方面的制备。结果 热静液挤压及其复合塑性变形工艺在粉末冶金难变形材料的致密化方面具有显著优势,获得材料不仅致密度高,而且有效实现了控形控性;对于镁合金薄壁细管成形而言,也可以实现组织与性能的有效调配,同时材料的精度较高。结论 热静液挤压及其复合塑性变形工艺在难变形材料的制备与成形方面具有独特的优势与广阔的应用前景。     

IN690合金管热挤压温升与挤压力的研究

温升和挤压力是影响钢管挤压过程的重要指标,利用热模拟实验获得了IN690合金的热加工本构关系,建立了IN690合金钢管热挤压过程的有限元模型.采用正交实验设计的仿真实验系统分析了坯料温度（T b=1000～1200℃）、挤压速度（v=20～200 mm/s）和模具预热温度（T d=300～500℃）对管材成形过程中温升...     

道次和路径对非致密体挤扭致密效果的影响

运用有限元方法对非致密体材料挤扭(Twist Extrusion,TE)进行分析.通过对纯铜多孔材料挤扭的数值模拟,获得了挤压道次和挤压路径对致密效果的影响.研究结果表明,挤扭工艺可以有效的对非致密体材料进行固结;随着道次增加,所需挤压力也越大,路径a下挤压力大于路径b;挤压道次的增加可以提高试样的有效密度;路径a下致...     

转模挤压成形过程的变形机理研究

针对低塑性合金挤压成形时所需能耗大、材料利用率低等问题,提出了对凹模施加转动的成形新工艺———转模挤压成形技术,并设计了特殊的凹模结构.与芯模转挤压仅适于圆截面制品相比,对凹模施加转动可有效地避免异型截面制品挤出成形时引起的垂直模口部位轴向的＂切断＂等难题.数值模拟及理论分析表明：与普通挤压相比,凹模转挤压成形中塑性区...     

Hydrostatic extrusion of solid polymers

Hydrostatic extrusion of a high density polyethylene rod was carried out. Both the process of plastic deformation during hydrostatic extrusion and the changes of properties of the polyethylene with extrusion were studied. Particular attention was paid to the process of molecular orientation and the destruction of the original lamellae. To obtain a better understanding of the deformation process, the lateral dimension of crystallite and the long period were obtained from the X-ray diffraction data. Furthermore, the influence of extrusion conditions on the structure and properties of the extrudate were investigated. The Vickers hardness number and thermal shrinkage of the extrudates were affected considerably by the extrusion conditions, i.e. extrusion temperature and extrusion ratio. In order to determine the relationship between the properties and extrusion conditions, it is necessary to consider not only the molecular orientation but also the crystallinity, fibrosity and the fine-structure of the extrudates.     

Technological basis of SHS extrusion

The results of the development of the SHS extrusion process, including creation of the equipment, studies of the production conditions and product quality are presented. The concepts of the ability of different composite refractory materials to plastic deformation are formulated. Examples of practical applications of the method developed are given.Institute for Structural Microkinetics, Russian Academy of Sciences, Chernogolovka. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 63, No. 5, pp. 525–537, November, 1992.     

变论域模糊PID控制微流挤出型3D打印机的挤压力研究

为了提高微流挤出型3D打印机的打印精度，针对其挤压力控制在挤出成型过程中存在时变性和非线性等典型特性，基于挤压力模型分析打印材料的挤出成型过程，并提出了一种变论域模糊PID（proportion integration differentiation，比例积分微分）控制策略，以实现挤出成型过程中挤压力不规律变化时的快速调节功能。同时，利用MATLAB软件建立挤压力控制系统仿真模型以开展不同控制策略的仿真分析，并利用自主搭建的实验平台进行实物打印，以验证所提出控制策略的可行性。仿真和实验结果表明，变论域模糊PID控制策略对改善成型坯体表面质量和提高成型精度有显著效果。所提出的变论域模糊PID控制策略可为挤出型3D打印机挤压力的稳定控制提供一定参考，也可为类似时变和非线性控制系统提供一定的借鉴。     

Effect of die design parameters on the deformation behavior in pure shear extrusion

Influences of die design parameters in terms of diameter ratio and length of the deformation zone on the distribution of effective strain, filling fraction of the die exit channel and pressing load in pure shear extrusion (PSE) are studied using finite element method (FEM). Dimensional stability, pressing load and hardness measurements are used to validate the predictions of the simulation. Acceptable agreements between the predictions of simulation and experimental results are observed. It is found that strain is inhomogeneously distributed which increases from the center to the corners. Effective strain, inhomogeneity of strain, filling fraction of the die exit channel and pressing load are increased with increasing diameter ratio. In addition, the work-piece is deformed more homogeneously at lower pressing load by increasing the length of deformation zone. However, filling fraction of the die exit channel initially increases by the length of the deformation zone up to 60 mm after which it reduces. The optimum die design parameters covering a range of acceptable effective strain and strain homogeneity, filling fraction of the die exit channel and pressing load are proposed as being 60 mm and 2 for length of the deformation zone and diameter ratio, respectively.     

The Occurrence of Ideal Plastic State in CP Titanium Processed by Twist Extrusion

This paper deals with the analysis of strength and plastic characteristics of commercially pure (CP) titanium as a function of equivalent plastic strain accumulated during Twist Extrusion (TE) process. It is shown experimentally that multipass TE leads to the saturation of the following characteristics of the material: yield stress, reduction in area, elongation to failure, and uniform elongation. This fact indicates the occurrence of an ideal plastic state in the processed material. The threshold value of accumulated plastic strain for ideal plastic behavior of CP titanium during TE is defined. The strain state and mechanical properties of CP titanium billets processed by TE are studied. An explanation for the hardening on the axis of a billet during TE is offered. The analysis of deformation modes on the billet axis during TE and High Pressure Torsion is carried out. It is shown that the differences in strain state on the axis are caused by the difference in symmetry of these processes.

     

Deformation Behavior Study of Multi-Pass ECAE Process for Fabrication of Ultrafine or Nanostructured Bulk Materials

Severe plastic deformation (SPD) is an efficient approach for producing ultrafine or nanostructured bulk materials. Equal channel angular extrusion (ECAE) is the most effective SPD solution for material nanostructuring, as material billet undergoes severe and large deformation and the grains are efficiently broken up in the process. To improve material nanostructuring, the ECAE die design and process configuration are critical. The deformation behavior study through FE simulation in ECAE process provides basic and useful information for optimizing die design and process determination. In this research, the deformation behavior for three different die design scenarios is studied and the related deformation mechanisms and nanostructuring performance are investigated via FE simulation. Through multi-pass simulation, the optimal design scenario is then identified. The simulation results reveal deformation phenomena, and nanostructuring performance of the designs and the corresponding process can be recommended accordingly for improving die and process performance.     

Study on deformation behavior and strain homogeneity during cyclic extrusion and compression

In this paper, the plastic deformation behavior and strain homogeneity of the ZK60 Mg alloy during the multi-pass cyclic extrusion and compression (CEC) was simulated using the finite-element method (FEM) with a view to provide an insight into the mechanics of the process. Physical modeling (PM) experiment with same alloy was carried out to verify the results of the numerical simulations. The results show that two vortex flow regions with opposite flow direction are formed inside the cylindrical workpiece during CEC deformation. Although the deformation is inhomogeneous in both end regions of workpiece, a uniform region of equivalent strain exists, and the extent of uniform deformation increased with the increase in workpiece length.     

Texture evolution in equal-channel angular extrusion

The focus of this article is texture development in metals of fcc, bcc, and hcp crystal structure processed by a severe plastic deformation (SPD) technique called equal-channel angular extrusion (ECAE) or equal-channel angular pressing (ECAP). The ECAE process involves very large plastic strains and is well known for its ability to refine the grain size of a polycrystalline metal to submicron or even nano-size lengthscales depending on the material. During this process, the texture also changes substantially. While the strength, microstructure and formability of ECAE-deformed metals have received much attention, texture evolution and its connection with these properties have not. In this article, we cover a multitude of factors that can influence texture evolution, such as applied strain path, die geometry, processing conditions, deformation inhomogeneities, accumulated strain, crystal structure, material plastic behavior, initial texture, dynamic recrystallization, substructure, and deformation twinning. We evaluate current constitutive models for texture evolution based on the physics they include and their agreement with measurements. Last, we discuss the influence of texture on post-processed mechanical response, plastic anisotropy, and grain refinement, properties which have made ECAE, as well as other SPD processes, attractive. It is our intent to make SPD researchers aware of the importance of texture development in SPD and provide the background, guidance, and methodologies necessary for incorporating texture analyses in their studies.