A NON－INCREMENTAL TIME－SPACE ALGORITHM FOR NUMERICAL SIMULATION OF FORMING PROCESS

A non-incremental time-space algorithm is proposed for numerical. analysis of forming process with the inclusion of geometrical, material, contact-frictional nonlinearities. Unlike the widely used Newton-Raphson counterpart, the present scheme features an iterative solution procedure on entire time and space domain. Validity and feasibility of foe present scheme are further justiced by the numerical investigation herewith presented.

The Design of a Graphical User Environment for Numerical Simulation of Powder Forming Processes

As computer simulation increasingly supports engine er ing design and manufacture, the requirement for a computer software environment providing an integration platform for computational engineering software increas es. A key component of an integrated environment is the use of computational eng ineering to assist and support solutions for complex design. Computer methods fo r structural, flow and thermal analysis are well developed and have been used in design for many years. Many software packages are now available which provi de an advanced capability. However, they are not designed for modelling of powde r forming processes. This paper describes the powder compaction software (PCS_SU T), which is designed for pre- and post-processing for computational simulatio n of the process compaction of powder. In the PCS_SUT software, the adaptive analysis of transient metal powder forming process is simulated by the finite element method based on deformation theories . The error estimates and adaptive remeshing schemes are applied for updated co -ordinate analysis. A generalized Newmark scheme is used for the time domain di scretization and the final nonlinear equations are solved by a Newton-Raphson p rocedure. An incremental elasto-plastic material model is used to simulate the compaction process. To describe the constitutive model of nonlinear behaviour of powder materials, a combination of Mohr-Coulomb and elliptical yield cap model is applied. This model reflects the yielding, frictional and densification char acteristics of powder along with strain and geometrical hardening which occurs d uring the compaction process. A hardening rule is used to define the dependence of the yield surface on the degree of plastic straining. A plasticity theory for friction is employed in the treatment of the powder-tooling interface. The inv olvement of two different materials, which have contact and relative movement in relation to each other, must be considered. A special formulation for friction modelling is coupled with a material formulation. The interface behaviour betwee n the die and the powder is modelled by using an interface element mesh. In the present paper, we have demonstrated pre- and post-processor finite elem ent software, written in Visual Basic, to generate the graphical model and visua lly display the computed results. The software consist of three main part: · Pre-processor: It is used to create the model, generate an app ropriate finite element grid, apply the appropriate boundary conditions, and vie w the total model. The geometric model can be used to associate the mesh with th e physical attributes such as element properties, material properties, or loads and boundary conditions. · Analysis: It can deal with two-dimensional and axi-symmetric applications for linear and non-linear behaviour of material in static and dyna mic analyses. Both triangular and quadrilateral elements are available in the e lement library, including 3-noded, 6-noded and 7-noded (T6B1) triangles and 4 -noded, 8-noded and 9-noded quadrilaterals. The direct implicit algorithm bas ed on the generalized Newmark scheme is used for the time integration and an aut omatic time step control facility is provided. For non-linear iteration, choice s among fully or modified Newton-Raphson method and quasi-Newton method, using the initial stiffness method, Davidon inverse method or BFGS inverse method, ar e possible. · Post-processor: It provides visualization of the computed resu lts, when the finite element model and analysis have been completed. Post-proce ssing is vital to allow the appropriate interpretation of the completed results of the finite element analysis. It provides the visual means to interpret the va st amounts of computed results generated. Finally, the powder behaviour during the compaction of a multi-level component is numerically simulated by the PCS_SUT software, as shown in Fig.1. The predict ive compaction forces at different displacements are computed and compared with the available experimental

Numerical Simulation of Warm Forming Behavior of High Strength Aluminum Alloy 7075

Numerical analysis is critically important to understanding the complex deformation mechanics that occur during sheet forming processes.It has been widely used in simulation of sheet metal forming processes at room temperature in the automotive industry.However,material at elevated temperature behaves more differently than at room temperature and specific material parameters and models need to be developed for the simulation of warm forming.Based on the experimental investigation of material behavior of high strength aluminum alloy 7075(AA7075),constitutive equations with strain rate sensitivity at 140,180 and 220 ℃ are developed.Anisotropic yield criterion Barlat 89 is used in the simulation.Warm forming of limit dome height tests and limit drawing ratio tests of AA7075 at 140,180 and 220℃are performed.Forming limit diagrams developed from experiment at several elevated temperatures in the previous study are used to predict the failure in the simulation results.Punch force and displacement predicted from simulation are compared with the experimental data.Simulation results agree with experimental results,so the developed material model can be used to accurately predict material behavior during isothermal warm forming of the AA7075-T6 alloy.

Influence of a multi-step process on the thickness reduction error of sheet metal in a flexible rolling process

Flexible rolling is a forming process based on thickness reduction, and the precision of thickness reduction is the key factor affecting bending deformation. The major purpose of the present work is to solve the problem of bending deformation error caused by insufficient thickness reduction. Under the condition of different rolling reductions with the same sheet thickness and the same thickness reduction with different sheet thicknesses, the thickness reduction error of sheet metal is analyzed. In addition, the bending deformation of sheet metal under the same conditions is discussed and the influence of the multi-step forming process on the thickness reduction error is studied. The results show that, under the condition of the same sheet thickness, the thickness reduction error increases with increasing rolling reduction because of an increase in work hardening. As rolling reduction increases, the longitudinal bending deformation decreases because of the decrease of the maximum thickness difference. Under the condition with the same thickness reduction, the thickness reduction error increases because of the decrease of the rolling force with increasing sheet thickness. As the sheet thickness increases, the longitudinal bending deformation increases because of the increase in the maximum thickness difference. A larger bending deformation is divided into a number of small bending deformations in a multi-step forming process, avoiding a sharp increase in the degree of work hardening; the thickness reduction error is effectively reduced in the multi-step forming process. Numerical simulation results agree with the results of the forming experiments.

Studying Formability Limits By Combining Conventional and Incremental Sheet Forming Process

In this work it is assessed the potential of combining conventional and incremental sheet forming processes in a same sheet of metal.This so-called hybrid forming approach is performed through the manufacture of a pre-forming by conventional forming,followed by incremental sheet forming.The main objective is analyzing strain evolution.The pre-forming induced in the conventional forming stage will determine the strain paths,directly influencing the strains produced by the incremental process.To conduct the study,in the conventional processes,strains were imposed in three different ways with distinct true strains.At the incremental stage,the pyramid strategy was adopted with different wall slopes.From the experiments,the true strains and the final geometries were analyzed.Numerical simulation was also employed for the sake of comparison and correlation with the measured data.It could be observed that single-stretch pre-strain was directly proportional to the maximum incremental strains achieved,whereas samples subjected to biaxial pre-strain influenced the formability according to the degree of pre-strain applied.Pre-strain driven by the prior deep-drawing operation did not result,in this particular geometry,in increased formability.

铸造镁合金凝固过程数值模拟研究进展

镁合金以其轻量化、高比强度和良好的阻尼性能在汽车、航空航天等领域应用广泛。数值模拟通过再现铸造成形过程中的各类宏观和微观物理过程,可以调控组织、减少缺陷、提高力学性能和优化铸造工艺参数。本文综述了铸造镁合金在枝晶和共晶凝固组织模拟,偏析、气孔和热裂等缺陷模拟,以及力学性能预测等方面的研究现状,简要介绍了近两年在铸造镁合金成形工艺模拟方面的研究进展。最后,指出了当前铸造镁合金数值模拟研究存在的问题及发展方向。

异形零件渐进成形数值模拟及参数优化

渐进成形具有工艺灵活,适应性强等优点,受到了广泛的关注。本文以一镁合金花形异形零件为例,对其渐进成形工艺进行模拟研究。首先对其成形轨迹进行设定,之后建立有限元数值模拟模型,模拟研究不同的成形工艺参数对成形质量的影响,分析其影响规律,并给出最优的成形工艺参数,对于实际生产具有一定的指导意义。

融合成矿过程数值模拟信息的三维成矿预测方法研究:以安徽宣城茶亭地区为例

茶亭地区位于长江中下游成矿带南陵-宣城矿集区东北部,近年来陆续发现了多个斑岩型和矽卡岩型矿床,显示深部具有很好的热液矿床成矿潜力。目前传统的矿产勘查方法对区内隐伏矿的勘查效果不佳,制约了进一步的找矿突破。三维成矿预测是近年来隐伏矿找矿的重要手段之一,但三维预测信息的缺乏在一定程度上制约了该方法的预测效果。三维成矿过程数值模拟方法能为三维成矿预测方法提供新的预测信息,但对多元数值模拟信息的联合应用以及对三维成矿预测方法的支持能力等均有待深入研究。本文以安徽宣城茶亭地区为例,在力-热-流多场耦合的条件下对热液成矿过程进行三维数值模拟;通过将体应变增量、剪切应变增量等数值模拟变量信息与其他预测信息进行融合,实现深部找矿靶区的圈定。结果显示,成矿过程数值模拟方法可为三维成矿预测提供有效的预测信息,能显著提高预测能力;圈定的找矿靶区可为进一步的深部找矿勘查提供更为有效和可靠的线索和方向。

一种新型陶瓷材料3D打印成型工艺的试验研究

将陶瓷粉末与高分子材料共混制备的陶瓷材料喂入自主研制的粉体喂料3D打印机,打印出的陶瓷坯体经脱脂和干燥后,分别在最高烧结温度为1550,1580,1620,1650℃下烧结,测试烧结陶瓷体的物理性能。结果表明:随着最高烧结温度的升高,陶瓷体的致密性改善,物理性能提高;当最高烧结温度为1650℃时,陶瓷体的维氏硬度达到1202.8 HV,烧结密度达到5.45 Mg·m^(-3),抗弯强度达到902.1 MPa,断裂韧性达到11.69 MPa·m^(1/2)。

精密金属丝网拉伸成形有限元分析及工艺优化

目的针对喇叭防尘网罩在拉伸成形过程中的起皱、折叠和断裂等质量问题,研究工艺参数对拉伸质量的影响特性,探寻较佳工艺参数。方法应用Deform软件模拟喇叭防尘网罩的拉伸成形过程并进行仿真验证。在单一条件下分别研究冲压速度、压边间隙、摩擦因数以及凹凸模圆角半径对喇叭网罩拉伸极限的影响规律。以拉伸极限为评判标准,对丝网直径、压边间隙、摩擦因数和冲压速度4个工艺参数进行正交试验优化,结合极差分析研究以上4个因素对评判标准影响的主次关系及最佳工艺参数。结果各参数按对拉伸极限的影响由大到小的顺序依次是丝网直径、压边间隙、摩擦因数、冲压速度,最佳工艺参数如下:丝网直径为0.065mm、压边间隙为0.2mm、摩擦因数为0.05、冲压速度为30mm/s。结论通过有限元模拟与分析,确定了影响产品质量的主要工艺参数及影响特性,通过试验实现了最佳工艺参数组合,提高了产品质量。

复杂曲率铝合金薄壁构件气胀成形技术研究

为满足复杂曲率轻量化薄壁构件快速高质量成形的需求,对5754铝合金复杂构件的气胀成形性能进行了试验与仿真研究。通过单一变量法确定了型腔气压和压边力的最佳工艺参数。结合数值模拟和成形试验,分析研究了型腔气压和压边力对构件成形性能的影响规律及成形机理。结果表明,最佳的成形气压和压边力分别为1.2 MPa和4.6 MPa。当气压小于1 MPa时,最大成形深度不断增加,最大应力位于主特征中心,壁厚分布由中心向两侧递增;当气压超过1 MPa后,最大成形深度保持不变,最大应力位于型腔中心两侧,壁厚分布由中心向两侧先减后增。当压边力小于4.3 MPa时会导致构件边缘起皱;增大压边力可有效抑制起皱,但压边力超过4.9 MPa时会增加构件局部破裂的风险。因此,采用上述最佳工艺参数能够成形质量良好的复杂曲率铝合金薄壁构件。

复合镦挤工艺批生产质量和效率提升研究

基于航天与国防军工等领域对高强韧镁合金坯料产品的大量需求,以复合镦挤工艺为研究对象,开展了该工艺应用于产业化的批生产适应性研究。针对该工艺产业化过程中镦挤产生的压余过大、处理压余导致的工序不连续和镦挤大高径比坯料时挤出坯料弯曲的问题,提出3种改进方案,通过三维建模、数值模拟和成形工艺试验进行了验证。结果表明:挤压模口下方导引板的设计,将原本弯曲1.90°的坯料矫正为0.01°,有效提高了坯料成形直线度;复合镦挤无压余技术的应用,减少了10%的坯料损耗,避免了不必要的工序;连续生产快换模具结构的设计,使得仅更换模具部分构件就可以生产不同规格的坯料,实现连续镦挤,提高了生产效率和模具使用寿命。

《材料成形过程数值模拟》课程的案例型教学实践与持续改进

结合工程教育专业认证的持续改进要求,针对《材料成形过程数值模拟》课程理论性强、内容范围广、实践操作要求高的特点,推行案例型教学改革,通过导入企业工程案例、学校科研项目不断优化教学内容,通过引入企业工程师参与课程评价、反馈,不断完善评价方法。同时,与企业联合推进校企协同育人,将螺钉紧固件的热镦、热处理工艺等工程实际需求融入课程建设,促使教学内容更贴近材料成形“高精尖”制造业发展前沿,提高了工科专业仿真类课程培养学生解决复杂工程问题的能力。

基于Simufact Forming的半空心铆钉自冲铆接参数对铆接成形的影响研究

以1.5 mm+1.5 mm A6062铝合金为研究对象,结合单一变量设计法进行参数组合,使用Simufact forming有限元软件对铆接过程进行模拟仿真,主要研究了凹模深度、凹模凸台高度、冲头速度3个工艺参数对半空心铆钉自冲铆接成形的影响,及参数对几何特征量的影响趋势,为半空心铆钉自冲铆接工艺参数进一步优化提供有益的借鉴。

基于数值模拟的20MoCr4钢温成形特征研究

20MoCr4钢是一种优良齿轮、齿圈等汽车关键零部件用到强度低合金钢。研究获得其材料性能参数是设计汽车零部件、制定成形工艺路线的前提条件。基于金属材料性能模拟计算软件JMatPro,获得了宽温度范围(25~1200℃)内详细全面的20MoCr4钢材料力学性能和热物理性能,结果表明:在500~750℃的温度变化范围内应力会出现较为明显跳跃式变化,在700~850℃之间热导率和比热容出现较为明显跳跃式变化,580~780℃为该材料较合适的温成形温度区间。相关材料性能数据和研究结果为20MoCr4钢滚轧等温成形过程热力耦合有限元分析提供基础。

小弯曲半径厚壁热揻弯管成形工艺数值模拟

针对小弯曲半径的大口径厚壁弯管成形问题,基于ABAQUS有限元模拟软件,利用Dflux子程序模拟温度场进行顺序热力耦合,对外径Φ426 mm、壁厚50 mm的钢管进行弯曲半径为2.5D的热揻弯管成形工艺过程模拟,对比了不同加热位置对弯管成形质量的影响,发现加热位置与转轴在同一平面时成形质量更高。同时,在一定参数范围内,以减薄率、增厚率、椭圆度和弯曲半径为指标,通过正交试验,结合综合评分法研究了线圈宽度、加热温度和推进速度对热揻弯管成形质量的影响。结果表明,综合得分指标随温度的升高而降低,随线圈宽度增加和推进速度加快而升高,并获取了最佳工艺参数为:线圈宽度40 mm、加热温度900℃、推进速度25 mm·min^(-1)。

颗粒材料柱体崩塌物质点法数值模拟

为了研究颗粒材料崩塌的运动规律和堆积特性,采用物质点法对颗粒材料柱体崩塌试验进行数值模拟,并将模拟结果与试验结果进行对比验证。对颗粒材料柱体崩塌过程中颗粒的流动特性(滑动距离、堆积高度、速度、能量和动能通量的演化)进行了分析。进一步探究了颗粒材料柱体高宽比对颗粒流动能通量的影响,从而反应颗粒材料柱体崩塌过程中颗粒流的破坏能力。颗粒材料柱体高宽比越大,颗粒材料柱体外侧边缘颗粒速度越大,其溃散的程度更加强烈,并且滑动距离和动能均在增大。对于动能通量的分布,水平方向越靠近初始颗粒材料柱体,动能通量越大。

基于物质点法的远程滑坡碎屑流运动过程模拟及特征分析

目的 研究远程滑坡碎屑流运动过程以及运动过程中速度、滑动距离、动能变化,为滑坡碎屑流灾害的预防和治理提供参考。方法 基于物质点法,以塔合曼和乱石包两个远程滑坡碎屑流工程实例为背景,对两个滑坡碎屑流的运动过程进行数值模拟;并对塔合曼滑坡碎屑流运动过程中水平、垂直方向运动速度分布,内摩擦角对运动过程的影响,以及乱石包滑坡碎屑流铲刮效应对堆积形态、动能变化的影响进行分析。结果 两个滑坡碎屑流最终堆积形态模拟结果与实测结果吻合良好,验证了数值模拟结果的有效性;塔合曼滑坡碎屑流随着内摩擦角从18°增加到33°,动能峰值降低71.4%,最终势能增加54.4%,滑坡碎屑流的能量耗散减小47.8%;在乱石包滑坡碎屑流实例的模拟中,速度云图呈现了滑体速度场的层状分布特征。结论 内摩擦角对滑坡碎屑流的动力过程影响十分显著;乱石包滑坡碎屑流的滑体在高速滑移阶段存在强烈的内部剪切作用,并且铲刮效应对滑坡碎屑流的运动起到了一定的阻碍作用。

热-化学场耦合的复合材料固化工艺仿真方法

纤维增强树脂基复合材料固化工艺常用于制造先进飞机、汽车、船舶等关键零部件。复合材料固化工艺主要就是树脂由液态向固态发生转变并与纤维结合在一起的过程,整个过程中存在热-化学场的多场耦合作用,数值仿真是一种高效、低成本研究固化工艺过程的方法。探究了复合材料固化工艺仿真方法,基于ANSYS FLUENT软件二次开发实现了固化工艺仿真;与现有数据对比验证了仿真方法的有效性;研究发现三维制件的固化工艺过程极易产生温度和固化度分布不均匀现象,影响产品质量。

基于Autoform的汽车左右侧围内板前段成形的数值模拟

利用Autoform软件对汽车左、右侧围内板前段进行模拟分析,在压边力、拉深筋等因素已确定的条件下,对板料成形过程中的各个工序进行数值模拟,通过对所得到的成形极限图、厚度减薄率等性能参数的分析,判定各成形工序的合理性,最终确定最优的成形工艺。