不同硬化模型对铝合金板冲压成形模拟结果的影响

研究不同塑性变形硬化模型对汽车5182-O铝合金板材冲压成形模拟结果的影响。采用材料单向拉伸试验得到应力应变关系曲线,基于Hollomom、Krupskowsky与Power方程对曲线进行拟合,建立材料室温下塑性变形硬化模型,对厚度为1.5 mm和0.85 mm的5182板材进行冲压试验和有限元模拟分析,对比分析冲压试验与模拟结果。试验与模拟结果显示,当板料厚度为1.5 mm时,板料冲压试验的成形力最大为42.95 kN,板料拉深深度为30.58 mm,基于Power方程计算得到的最大成形力为41.5kN与试验结果比较接近,Hollomom方程计算得到的拉深深度为30.546 mm,板材成形厚度分布与试验结果比较接近;当板料厚度为0.85 mm时,板料冲压试验的成形力最大为34.47kN,板料拉深深度为33.792 mm,基于Power方程计算得到的最大成形力为34.27 kN与试验结果比较接近,Hollomom方程计算得到的拉深深度为33.636 mm,板材成形厚度分布与试验结果比较接近。基于三种硬化模型铝合金冲压成形过程的计算模拟分析结果,并通过与试验对比得到不同硬化模型对铝合金板材冲压成形计算模拟的影响,进一步为汽车铝合金覆盖件在成形工艺的研究分析提供理论指导。     

内高压成形矩形断面圆角应力分析

采用力学分析和数值模拟方法对圆角部位在内高压成形过程中的应力分布和变形机理进行分析,揭示出圆角和直边过渡区的减薄以及开裂的力学机理。提出内高压成形中圆角和直边的过渡区材料最易满足塑性屈服条件, 并发生厚度方向的压缩应变,因此在过渡区易发生剧烈的减薄变形;并且当管材壁厚与圆角半径的比值大于0．5 时,直边区和圆角区的屈服条件差别较大,引起变形不均匀性增大,更易导致过渡区的过度减薄和开裂。分析结果有助于指导内高压成形零件设计和工艺设计,改善矩形断面零件内高压成形件产品质量。     

A procedure for designing initial thickness variation for superplastic free inflation

A procedure is proposed for determining the required initial thickness distribution in order to produce a given design specification by the superplastic blow forming method. Analytical solutions are first derived to predict the thickness variation during a free inflation process. The equation is then used to obtain the thickness distribution prior to inflation from a prescribed final thickness as though the deformation is reversed. The commercial finite element program, ABAQUS, is adopted to simulate the superplastic blow forming process of the acquired preform. Although the inflated thickness is compared fairly close to the desired result, errors do exist due to the simplified assumptions made in the analytical method. In order to overcome the difficulty, a model describing the thickness variation of the inflated sheet is first obtained from curve-fitting the solutions of finite element simulation instead of analytical derivation. The initial thickness determined from this model is shown to give the intended final thickness from finite element simulation. Experiments have also been performed to verify the results.     

Thickness improvement in single point incremental forming deduced by sequential limit analysis

Multistage forming is one of the most practical solutions to avoid severe thinning in single point incremental forming (SPIF). A successful implementation of multistage SPIF is strongly dependent on an appropriate deformation path. In this paper, firstly, a simplified modeling technique is proposed using sequential limit analysis. It is shown that sequential limit analysis can predict the thickness distribution faster than an equivalent model in a commercial finite element modeling code like Abaqus can. The reliability of the model is assessed by comparing experimental and simulated results for single-stage and multistage SPIF cones. This model is utilized to study the effect of various deformation paths on the thickness distribution. As a result, a new multistage strategy is designed and implemented to form a 70° wall angle cone in three stages. The thickness distribution of the cone is improved significantly compared to cones formed by a single-stage and a conventional three-stage strategy. Besides this improvement, the new multistage SPIF can be carried out in much less time.     

Analytical model of corner filling with granular media to investigate the friction effect between tube and media

In a tube forming process, granular matter is used as pressure transmission medium instead of liquid to expand a circular tube into one with square section. In this process, the friction at media/tube interface has a significant effect on the final result. In this paper, an analytical model was developed to determine the influence of the friction on the deformation developing process and final thickness distribution along the tube section. Experimental researches were also implemented to evaluate the analytical model in the end. In this model, four friction situations were applied to the numerical analysis process according to the active or negative function of friction on the flow of metal. The analysis result showed that different friction situations could lead to different deformation processes and thickness distributions. The examination on experiments of AA6061 tube indicated that the experimental data of thickness was extremely close to the analysis result with the friction situation in which the metal flow toward the corner of square section die was impeded by the friction force. However, the analytical prediction of thinning trend of thickness had a deviation compared with the experimental data in the corner region. In addition, the breaking and caking of granules in the tube forming process make the friction situation between the tube and media very complex. Therefore, a further research needs to be conducted from the direction of granular matter mechanics and friction mechanism in order to acquire a more explicit result.     

[材料绿色成形技术]异形排气管多向局部加载液力成形工艺

针对某乘用车异形排气管整体制造的难题，开展4系列不锈钢管材包括多向局部加载液力成形新方法的全流程液力成形工艺研究。基于Dynaform有限元模拟软件，建立绕弯成形及液力成形的有限元模型，监测管材壁厚分布的演化规律，进而优化成形工艺参数，开展实验验证。研究结果表明：初始管材直径对液力成形管材壁厚分布影响显著，初始管材直径为54 mm时能很好地满足工艺要求；在纵向加载液力成形阶段，可通过在上模具设计凸筋来实现对管材的局部加载成形，而在横向加载液力成形阶段，内压为48 MPa时可避免管材破裂、折叠等缺陷的产生；此外，局部加载液力成形可导致管材的应力应变状态发生明显改变，变形区管材的壁厚呈现增大趋势，最大减薄率由27.43%降至24.65%，最终零件的最大减薄率为28.05%。实验结果与模拟结果基本吻合，最大偏差值仅为2.89%。     

一种用于汽车碰撞模拟的网格变量映射算法及其验证

在汽车碰撞模拟中,需要考虑零件冲压后的板料厚度变化、材料硬化以及残余应力对仿真结果的影响。由于冲压仿真后的零件仿真模型中网格变形大,单元尺寸小,并且总的单元数量多,冲压后的网格模型并不适合碰撞仿真。在有限元仿真结果分析基础上,提出一种把冲压仿真模型网格变量(如应力、应变和厚度分布)映射到碰撞仿真模型网格上的变量映射算法,并开发计算程序。通过比较采用不同网格的汽车B柱冲击仿真模型的计算结果,验证上面的算法。该算法解决了网格重划后其变量的映射问题,可以减少网格重划工作,为在汽车碰撞仿真中考虑冲压效应提供一种有效的方法。     

汽车防撞梁超高强钢热成形工艺研究

采用数值模拟与试验相结合的方法研究了防撞梁热冲压成形工艺。根据BR1500HS材料特性,通过数值模拟优化工艺参数,建立了冲压力与初始成形温度和冲压速度的关系模型,指出了冲压力变化趋势,并通过防撞梁热冲压试验验证了冲压力模型的可靠性。零件性能测试结果显示,热冲压件的厚度和硬度分布较为均匀:平均硬度为47.6HRC,最大减薄率为17%,零件抗拉强度达到1545MPa,最大残余应力只有抗拉强度的20%左右,回弹较小,组织为均匀板条状马氏体。     

Numerical and experimental analysis of wall thickness variation of a hemispherical PMMA sheet in thermoforming process

In thermoforming, a heated plastic sheet is stretched into a mold cavity by applying pressure, eventually assisted by direct mechanical loading. Since upon its contact with the cold surface of the mold the sheet is prevented from undertaking any further deformation, the forming sequence induces a thickness variation in the final part. This fundamental inherent defect of thermoforming technology highly affects the optical characteristics of optical products. Therefore, the more uniform the wall thickness, the less chance optical defects will occur. In this research, the production process of a hemispherical transparent PMMA sheet as an optical product was numerically simulated. The simulated process is a two-step process comprising a combination of free forming and plug-assisted forming. In the simulation, the acrylic sheet is assumed to undergo a nonlinear and large elastic deformation which merits application of hyperelastic models. Mooney–Rivlin hyperelastic model is used as the constitutive equation. The obtained numerical results are validated with those achieved from the experiments. Different combinations of free forming and plug-assisted forming methods are studied based on what percentage of total height of the final part is produced by each method. Finally, an optimum combination of the two-step forming process is proposed. With this optimum combination, satisfactorily uniform wall thickness and minimal mold marks on the product surface will be achieved.     

基于PDM的三维变型工艺设计系统的研究

针对企业已有产品资源重用和对具体的工序设计支持较弱的现状，从信息集成、产品资源重用和系统应具备的功能出发，对PDM平台数据模型进行了分析；以SolidWorks为设计环境，对系统的体系结构、主要功能和工艺设计的思路、流程进行了分析和论述。     

变径管内高压成形有限元模拟

变径管是航空、汽车工业领域常用零件,用来输送压力油、冷却等。通过建立相应的内高压成形有限元模拟模型,用M SC.M arc有限元分析软件进行模拟分析,研究了变径管成形过程的基本变形特征、成形参数的影响规律。模拟分析得知适当地提高变形速率、减少减薄区变形持续时间有缓解该处过度减薄的作用,轴向进给应在减薄前进行补料,而不应在变形的同时补充所需金属。     

航空铝合金复杂构件充液柔性成形过程及质量控制研究

针对某型号飞机铝合金复杂构件充液成形的失效形式,采用有限元数值模拟和试验的手段,研究了毛坯形状、液室压力等关键工艺参数对成形失效的影响,给出了铝合金复杂构件充液成形质量控制的措施,为此类型航空复杂构件的充液成形提供了技术指导。     

[材料成形中的数字化与智能化产品设计]6016铝合金汽车典型结构件固溶成形工艺研究

以某车型铝合金汽车后风挡下横梁为研究对象，利用PAM-STAMP软件进行了一步固溶成形和分步固溶成形工艺分析。通过优化关键工艺参数如摩擦因数和成形温度，结合相应的工艺实验，建立了工艺仿真模型；通过对测量路径上壁厚分布的实验值与数值模拟值进行误差对比分析，判断成形工艺合理性。结果表明：汽车后风挡下横梁采用一次成形方式容易在中间形变突变处造成开裂或减薄现象，随着摩擦因数增大，最小厚度急剧减小；相比一次成形方式，采用分步成形方式，最小减薄率减小了4.67%，回弹量减小了40.21%，温度与摩擦因数对最小厚度的影响较小；经时效处理后进行力学性能检测，铝合金汽车后风挡下横梁抗拉强度达到308 MPa，表明采用固溶成形工艺是可行的。     

Superplastic-like forming of non-superplastic AA5083 combined with mechanical pre-forming

Superplastic forming has been considered as an attractive process in the automotive and aerospace industries. However, the disadvantages of slow forming rate, high-temperature requirement, poor thickness distribution, and expensive base material have hindered its widespread use for high production volume. In this paper, the non-superplastic grade of 5083 aluminum alloy (AA5083) sheets with thickness of 3?mm was employed in a superplastic-like forming process, which is a combination of drawing (mechanical pre-forming) and superplastic forming (blow forming). Experimental trials were conducted to verify the possibility of improving the forming rate and lowering the process temperature. The blank was firstly pre-formed during the mechanical pre-forming phase. As a result, some part of material along the flange area was introduced inside the deformation cavity in advance of the blow forming phase. Secondly, argon gas was applied on the sheet, which would be deformed to come into contact with the inner die surface at the end of pressure cycle. It took only 8?min for the blow forming phase, and the process achieved an almost fully formed part at 400°C. The minimum thickness occurred at the inward corners, and the maximum thinning of the formed part was 54%. Grain growth and cavitation were found from the microstructure observations.     

薄板件台阶孔冲压冷锻组合工艺的数值模拟

针对构想的一种薄板件台阶孔冲压冷锻组合工艺,应用金属塑性加工有限元模拟的关键技术,包括几何模型、材料断裂破坏、网格划分等,用DEFORM-3D软件对此种薄板件台阶孔的冲压冷锻组合变形进行数值模拟。得到了工件材料的等效应力、应变分布,速度场和力—行程曲线。提出细观变形过程可分为冲头小直径处冲孔、冲头大直径处压凹和闭式模锻三个阶段的认识,分析组合工艺特点和材料成形性能。用料厚为2.35 mm的AL-1100铝板材料进行工艺试验,获得了清晰的台阶孔形状,验证了数值模拟的认识。     

Numerical and experimental investigation of inward tube electromagnetic forming

In this work, experimental and numerical simulation of high-speed inward forming of tubes on a die in electromagnetic forming (EMF) system using a compression coil is presented. A 2D axi-symmetric electromagnetic model is used to calculate magnetic field and magnetic forces. Modified loose-coupled simulations of electromagnetic and structural aspects of EMF process are reported and emphasized in this paper. During the simulation, in each time step, the transient magnetic forces are obtained from the electromagnetic model and used as input load to the mechanical model. Based on the calculated deformation, in each step, the tube geometry in the electromagnetic model is updated to calculate the electromagnetic forces in proceeding step. Tube material, AA 6061-T6, is assumed to obey the Johnson-Cook (J-C) rate-dependent model. Displacement and thickness variations of workpieces along the tube length are presented and discussed experimentally and numerically. The results demonstrate that various workpiece zones could be thickened or thinned based on various process parameters. In addition, it is seen that the increase of discharge voltage decreases the thickness at die radius and reverses the thickening trend at tip of the bead.     

Numerical and experimental approach to reduce bouncing effect in electromagnetic forming process using cushion plate

Electromagnetic forming (EMF) is a high strain rate forming process that uses Lorentz force. In this study, electromagnetic forming with a rectangular block shape in the center of the forming die was examined to determine the possibility and applicability of EMF. However, the high speed of the process in the absence of a medium between the coil and the workpiece results in bouncing of the workpiece, which may result in poor forming. So, in this study, the use of a cushion plate is proposed as a means of reducing the degree of bounce in an EMF process. A 3D electromagnetic numerical model using a spiral forming coil was considered. An RLC circuit, coupled with the spiral coil, was numerically simulated to determine the deformation behavior and design parameters, such as the input current and the magnetic forces. A cushion plate was used between the forming coil and the sheet to be deformed to reduce the extent of bounce. In the numerical simulation, the sheet was found to be well fitted to the objective die with the cushion plate. The simulation results showed that the extent of bounce was drastically reduced because of the velocity direction of the workpiece and the cushion plate. The experiment was performed using 24 kJ to deform Al 1100 with a thickness of 1.27 mm, based on the simulation results. The deformed sheet was well formed, and closely fitted the objective die with a minimum of wrinkling, relative to the results obtained without a cushion plate. As a result, an EMF process with a middle-block die was successfully established both numerically and experimentally to reduce the bouncing.     

高盒形件多道次变薄拉深工艺机理研究及数值模拟模型确立

盒形件有限元模拟通常采用壳单元进行建模,由于薄壳单元在计算中忽略了厚向应力,因此在多道次拉深成形及变薄拉深成形工况下的适用性存在质疑。以3003H14高盒形件多道次变薄拉深为研究对象,利用Dynaform并结合LS-DYNA有限元软件进行数值模拟,对比壳体单元与实体单元的模拟计算数据,通过分析外观模拟结果和Levy-Mises增量理论中瞬时本构关系系数的模拟数据,得到单元类型对薄板多道次变薄拉深成形模拟计算精度的影响规律。利用实际工程中的毛坯尺寸样本数据对建立的盒形件拉深毛坯尺寸计算程序进行训练,从而实现了盒形件拉深工艺毛坯尺寸预测软件的开发。此外,在明确建模方法后,结合实体单元有限元模拟结果研究板料在变薄拉深过程中材料的减薄与增厚的机理,揭示了材料流动规律。研究表明:实体单元模拟计算结果与实际更接近。若以坯料单元在工序前后的理论变形厚度的百分比差值作为变形程度衡量指标,当变形程度为0~11.1%时,两种单元计算差异为0.5%~27.8%;当变形程度为24.2%~34.9%时,两者计算差异为44.4%~79.3%。经多道次变薄拉深后,金属材料增厚区域多发生在凸缘及长边与短边交界处的圆角上;在模具的限制作用下,减薄区域多发生在底部圆角,长边与短边区域都有一定减薄;除工序1外,其他各个工序长边侧直壁平均厚度比工艺设计的理想值大1.00%~2.02%,短边侧直壁平均厚度比工艺设计的理想值小0.86%~12.90%。     

芯板厚度对超塑成形的影响

根据超塑成形的工艺要求,利用ANSYS/LS-DYNA有限元软件对空心风扇叶片成形过程进行数值模拟分析,以此研究不同的芯板厚度对超塑成形结果的影响.分析的结果表明:选取的三种厚度的芯板里,当厚度为0.8mm时,塑性变形最均匀,成形效果最好.     

盒形件固体颗粒介质板材成形工艺研究

固体颗粒介质板材成形工艺是采用固体颗粒微珠代替刚性凸(凹)模(或弹性体、液体)的作用对板材拉深成形的新工艺。选用非金属固体颗粒介质——GM颗粒作为研究对象,以固体颗粒介质在高应力水平下的体积压缩试验和摩擦强度试验为基础,应用散体力学理论中扩展的Drucker-Prager线性模型构建固体颗粒介质有限元材料模型。以具有非轴对称性的方盒形件为代表,进行固体颗粒介质成形工艺的有限元模拟,研究成形过程中板材的流动特征和壁厚分布规律。工艺试验成功得到方盒形零件,将加载曲线、成形过程变形特征和壁厚分布曲线与数值模拟结果比对较为吻合。分析表明,采用以散体力学为基础建立的固体颗粒介质材料模型进行工艺模拟,能够得到与试验较为接近的变形特征和力能参数,可以应用于制定工艺方案的依据,为该技术在板材成形中的应用起到指导和借鉴作用。