半连续等通道挤压过程的力学分析与模拟

半连续等通道挤压法是一种在等径角挤压法思想上发展出来的用于细化钢铁材料晶粒的大塑性变形方法,其特点在于转变施力对象,通过对模具施加压力来驱动工件完成大塑性变形,从而增大可加工的材料尺寸,降低对模具材质与精度的要求,在获得整体均匀细化的晶粒的同时具备连续生产的能力.通过详细描述该方法的实现过程,并结合滑移线法、有限元模拟以及实际数据验证,阐明了在实施该方法过程中工件受力情况.     

Tube Reversing and Extrusion (TRE) as a Novel Method for Producing UFG Thin Tubes

In the present research, a new severe plastic deformation method has been introduced for producing thin walled tubes with ultrafine grained substructure. The tube reversing and extrusion (TRE) technique was applied to a CP-aluminum and thin walled tubes with ultra-fine grained microstructure were successfully processed. The obtained results from tensile tests at room temperature showed the significant increase in mechanical properties of TRE processed thin walled tubes including yield and ultimate strengths and micro-hardness due to grain refinement. The microstructure evolution and deformation behaviour of commercially pure aluminium under TRE processing was simulated by the constitutive model as a micromechanical approach implemented in the finite element framework. The continuous dynamic recrystallization (the evolution of dislocation density and grain size) of aluminum tubes during TRE was considered as the main grain refinement mechanism in micromechanical constitutive model. Also, the flow stress of material in macroscopic scale was related to microstructure quantities. This was in contrast to the previous approaches in FEM simulations of SPD methods where the microstructure parameters such as grain size were not considered at all. The FEM simulated grain refinement behavior was consistent with the experimentally obtained results.     

FEM Simulation of Large Diameter Pipe Bending Using Local Heating

 With the aid of elastic plastic large deformation finite element method (FEM), an elastic plastic and coupling thermo mechanical model was built to calculate the bending process of the bent pipe, combining with local heating or cooling of the bent pipe. Based on the FEM simulation, the metal deformation during the bending process was analyzed in detail. The thinning and thickening ratio of the pipe wall thickness, the ovality of the cross section of the pipe and the spring back angle, etc, are presented.     

Rapid Finite Element Analysis of Bulk Metal Forming Process Based on Deformation Theory

 The one-step finite element method (FEM), based on plastic deformation theory, has been widely used to simulate sheet metal forming processes, but its application in bulk metal forming simulation has been seldom investigated, because of the complexity involved. In this paper, a bulk metal forming process is analyzed by using a rapid finite element simulation method based on deformation theory. The material is assumed to be rigid-plastic, strain hardening. The constitutive relationship between stress and total strain is adopted, whereas the incompressible condition is enforced by penalty function. The geometrical non-linearity in large plastic deformation is taken into consideration. Furthermore, the force boundary condition is treated by a simplified equivalent approach, considering the contact history. Based on constraint variational principle, the deformation finite element method is proposed. The one-step forward simulation of axisymmetric upsetting process is performed by this method. The results are compared with those obtained by the traditional incremental FEM to verify the feasibility of the proposed method.     

Study on Optimization of Parameters Affecting Simple Shear Extrusion of Pure Copper to Fabricate Fine Grain Structure

During last decades, severe plastic deformation (SPD) techniques have developed and increased their applications in variety of industries such as aerospace, nuclear, automotive, marine etc. One of emerging SPD process is simple shear extrusion (SSE). In the present study, an attempt was made to optimize parameters affecting SSE process of pure copper namely maximum distortion angle, channel length and ram speed on effective plastic strain and maximum punch force. Firstly, the process was numerically simulated by use of ABAQUS software. Then, the developed finite element model was verified by confirmatory experiment taking into account the punch force. 15 series of simulation runs were implemented incorporating three aforementioned factors within three levels. Then, response surface methodology was used here to correlate relationship between process parameters to forming force and effective strains. Sensitivity analysis was also carried out to find which factor had greatest impact on process quality characteristics. In order to find optimal parameter setting for maximum strain and strain rate as well as minimum punch force, desirability approach was utilized. Results revealed that distortion angle was the most significant factors affecting plastic strain and punch force, while the ram speed had greatest impact on strain rate. The specimens at optimum parameters (i.e. 45° distortion angle, 90 mm channel length and 0.3 mm/s ram speed that resulted in maximum plastic strain) were processed by SSE and mechanical properties and microstructure analysis were studied. It was found from the results that microstructure of the samples were significantly refined by performing SSE at optimum level that resulted in improvement of samples strength and hardness.     

Routes Investigation in Equal Channel Multi-angular Pressing Process of UFG Al−3% Mg Alloy Strips

Equal channel angular pressing is one of the most efficient techniques among severe plastic deformation methods that enhances the mechanical properties of polycrystalline metals by refining subjected grains. In this article, equal channel multi-angular pressing was conducted on Al5754 strips. At the first step, finite element analysis was applied to evaluate the possible routes (A and C). The initial analysis showed that the route C was better in strain homogeneity compared with route A. Thus, the route C was considered for further investigations. Then, the effects of the die geometrical parameters on the created equivalent plastic strain (PEEQ) and process force were investigated by FEM. The results showed that the die channel angle (Φ₂) was the most effective parameter on both PEEQ and process force, while the die corner angle (ψ₁) had the least effect on both objectives.     

FEM Analysis of Void Closure Behaviour during Open Die Forging of Rectangular Billets

Finite element analysis of open die forging to make rectangular billets has been performed in this study. Three‐dimensional rigid‐plastic finite element method (FEM) was used to analyse the effects of process variables, forging pass design and die configurations on the void closure phenomena. The major objective was to control the internal deformation for better structural homogeneity and centreline consolidation of the rectangular billet. The effect of die width ratio, die feed rate, die shape, and number of passes on the void closure ratio has been examined. Although it is difficult to optimize process parameters in industrial environments, favourable process conditions are recommended to achieve better product quality.     

有限元法在板材热轧中的应用

采用弹塑性大变形热力耦合有限元法研究板材热轧过程．利用有限元理论建立了板材热轧模型;应用MSC／MARC软件进行计算,重点分析了轧制过程和变形区中轧件的温度场分布和变化、金属的流动、应力应变的变化趋势,以及轧制力的变化情况．计算结果与实际生产情况相吻合,同时表明有限元理论可以实现对板材热轧过程的数值模拟．     

数值模拟在极限规格H型钢工艺优化中的应用

针对HW150mm×150mm极限规格H型钢产品偏心问题,采用有限元方法对粗轧阶段孔型系统进行三维热力耦合数值模拟。基于模拟结果分析金属流动、塑性应变及温度变化,以此为基础,根据变形特点及各孔型轧件尺寸分析偏心产生的原因,优化孔型并进行验证,最后进行现场实践,排除缺陷。结果表明,有限元模拟有助于分析轧制过程中的金属成形,尤其对于型钢轧制过程中的变形规律及缺陷分析具有较高的参考价值和指导意义。     

芯棒直径对楔横轧5Cr21Mn9Ni4 N空心气门壁厚均匀性的影响规律

楔横轧空心轴类件存在壁厚分布不均问题,特别是在小直径大长径比空心件楔横轧成形中更为突出.本文在Gleeble-1500D热模拟实验机上进行了5Cr21Mn9Ni4N耐热钢的热压缩实验,得到了5Cr21Mn9Ni4N的热变形本构方程.通过改变芯棒直径,采用有限元仿真和实验相结合的方法,研究了楔横轧轧制空心气门过程中的壁厚变化规律.研究结果表明,带芯棒轧制时,芯棒直径存在临界值,在该值下进行轧制,空心气门预制坯壁厚均匀性最优;楔横轧空心件时,金属轴向均匀流动是壁厚均匀的必要条件;轧件轴向拉应变减小,径向压应变变大,周向应变在0附近且为拉应变时,壁厚较为均匀.      

Nonlinear Spline Finite Element Method for Ribbing of Cold-Rolled Coils

 The ribbing problem has serious influence on the steel product quality, which produces additional shape waves on the surface of uncoiled steel strip on the process of curl. Nonlinear spline finite element method (n-spline FEM) is adopted to establish the relationship between the ribbing height and deflection of additional shape wave, for example, post-buckling deformation. The proposed spline FEM is more effective and convenient than traditional finite element method in the buckling analysis. Using the spline FEM, the shape wave caused by the ribbing is calculated, and then the ribbing values can be obtained which are difficult to measure in practice. At the same time, the judgment rule is also given for estimating the strip quality according to the ribbing value.     

棒材二辊矫直机辊型曲线与矫直精度分析

 为了改进二辊棒材矫直机矫直质量,从弹塑性弯曲理论出发,用Matlab求解双曲线和三曲率二辊矫直机辊型曲线,并绘制相应的辊型图。分别计算了双曲线和三曲率辊型曲线的矫直精度,结果表明三曲率辊型曲线矫直精度高于双曲线辊型曲线的矫直精度。综合考虑棒材的弹塑性变形,基于有限元MARC平台,根据具体实例建立了棒材二辊矫直弹塑性模型,并对其矫直过程进行模拟,分析了棒材在矫直过程中各种参量的变化。对比分析不同辊型下棒材矫直效果,三曲率辊型矫直效果要好于双曲线辊型,可为实际生产提供理论指导。     

Deformation Uniformity of Cold-Rolled Q235 Steel Rebar by FEM in Bending and Rolling Processes

 An analytic model based on ANSYS/LS-DYNA has been developed on the cold rolling process for Q235 steel rebar with 12 mm in diameter. The elastic-plastic finite element method (FEM) and the cold deformation resistance model of Q235 steel were adopted in this model. Deformation uniformity of the final product has been analyzed using this model. The results indicate that the uniformity of the final product is obtained only as the centerline of the bending rolls is vertical to the centerline of the driven roll and parallel to the centerline of the drive roll in the whole rolling process. Besides, the number of the bending rolls must even realize the continuous bending and reverse bending process. Also, the number of the bending rolls must match the deformation degree of the workpiece in the cold rolling process. The validity of this finite element model was verified by the size and distribution of grains from the billet to the rebar in a practical cold rolling process.     

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。     

H65黄铜管冷轧变形模拟分析与实验研究(续)

图3-b可以看出,孔型脊部区域的管坯内表面温度明显高于外表面,这主要是由于外表面摩擦较小,而内表面的摩擦相对较大,产生的摩擦热远远大于外表面。由此可知,对于减壁量不大的皮尔格冷轧管,引起金属温度变化的主要因素不是塑性功的转化而是由于摩擦所引起的,因此实际生产中应加强对管坯表面的润滑,以免产生过高的温升。H65黄铜在200℃～700℃会发生脆性转变,如果实际冷轧管生产中,管坯变形区的温度出现如图3所示的情况,即使工作应力较小,也可能超过材料此时的强度极限,从而产生如图4所示的周期性横向裂纹。     

四辊平整机辊系与带材耦合变形有限元分析

 采用大变形弹塑性有限元法将辊系弹性变形与带材弹塑性变形耦合在一起建立四辊平整机三维模型。研究了不同宽度和厚度下工作辊弯辊力对辊系变形、辊缝形状及轧件出口厚度的影响规律。计算结果对平整机设备设计和生产工艺制定具有实际参考价值。所建模型也为轧制过程离线分析提供了一种有力的手段。     

辊式矫直过程弯辊量对边浪影响的仿真分析

针对辊式矫直过程建立具有边浪特征的带钢有限元仿真模型,通过对比现场工况实测矫直力与有限元模型计算所得的矫直力,得到二者误差在10%以内,验证了有限元模型的精度。分别采用原始曲率补偿法和塑性变形层增加法确定了4种弯辊量设定方案。采用上述方案对浪高为20 mm的带钢进行矫直,对比矫直后带钢平直度情况,得出按最高浪采用原始曲率补偿法计算得到的弯辊量矫直效果最优。同时随着弯辊量的加大,矫直力也随之增加,为现场边浪矫直过程提供了依据。     

二辊矫直机凹辊辊形设计

 针对某钢厂新引进的棒材二辊矫直机的辊子需要国外进口,成本昂贵的问题,在对矫直过程中残余曲率的变化规律及辊形计算方法研究的基础上,结合有限元计算,通过分析塑性变形以及矫直后的棒材平直度,对弯曲曲率进行修正,得出相应辊形并进行有限元模拟,直到矫直后的棒材平直度达到要求,进而得出合理的凹辊辊形。该辊形与实测的辊形进行对比,基本一致。     

Analysis on Shear Deformation for High Manganese Austenite Steel during Hot Asymmetrical Rolling Process Using Finite Element Method

Based on the rigid-plastic finite element method(FEM), the shear stress field of deformation region for high manganese austenite steel during hot asymmetrical rolling process was analyzed. The influences of rolling parameters, such as the velocity ratio of upper to lower rolls, the initial temperature of workpiece and the reduction rate, on the shear deformation of three nodes in the upper, center and lower layers were discussed. As the rolling parameters change, distinct shear deformation appears in the upper and lower layers, but the shear deformation in the center layer appears only when the velocity ratio is more than 1.00, and the absolute value of the shear stress in this layer is changed with rolling parameters. A mathematical model which reflected the change of the maximal absolute shear stress for the center layer was established, by which the maximal absolute shear stress for the center layer can be easily calculated and the appropriate rolling technology can be designed.