Superplastic sheet metal forming of a generalized cup part ii: nonuniform thinning

A computational process model for the super plastic formation of a generalized cup is presented that takes into account the variation in thinning in the unsupported region. The relative pole to edge thinning arises due to the change in the state of stress from balanced biaxial at the pole to plane strain at the edge. Using kinematic conditions and material constitutive equations, a relationship between the instantaneous thickness at the pole and edge is developed. An equation for thickness variation from center to edge in terms of convected coordinates is postulated. Process parameters including thickness profile and pressure-time cycle for the generalized cup are determined using an incremental formulation. The solution developed in Part II depends on process and material parameters, unlike the uniform thinning model. The thickness profile for different shapes like the dome, cup, and cone formed from superplastic aluminum 7475 and aluminum-lithium alloys are compared with experimental results.     

MODELING OF SUPERPLASTIC FORMING PROCESS FOR ALUMINUM ALLOYS WITH STRAIN HARDENING EFFECT

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薄壁杯形件单道次拉深旋压成形质量试验研究

通过试验研究了拉深旋压工艺参数对工件壁厚、工件外径及成形性能的影响。试验结果表明,旋轮进给比f、旋轮与芯模间隙δ等对工件壁厚、名义拉深比K和拉深旋压成形性有很大的影响。在毛坯厚度较小的情况下,较大的进给比和名义拉深比都容易导致工件产生起皱和开裂,给出了使拉深旋压能顺利进行的工艺参数范围。     

Superplastic Forming of Triangular Channels with Sharp Radii

The superplastic forming process is used to form light weight components with complex features in one manufacturing step. However, the non-uniformity of the produced part thickness and the possibility of severe thinning are among its major disadvantages. The goal of this parametric study was to investigate feasible geometries for triangular channels to be manufactured by superplastic forming. The channels considered had sharp radii and served as secondary features extending along a circular path at the base of a shallow cup. An axisymmetric finite element model in ABAQUS? was used to simulate the forming process. Effects of the aspect ratios of both the cup and the triangular channel on the thickness distribution and the pressure profiles were investigated. An experimental setup was used for validating the simulation results for AA5083 at 500 °C.     

Application of flow model in metal cutting to cold forging of tubular products

The flow model in metal cutting is applied to cold forging for forming a H-shaped double cup by moving the bottom of an ironed cup to a predetermined position. In the proposed process, the cutting flow occurs between the internal corners of the upper cup and the lower cup and the tool pressure is lower than half of the plasticity coefficient of the cup material. Products are formed without defects when the ratio of the depth of cut to the bottom thickness of the cup is larger than the critical value related to the corner radius of the ironed cup.     

Influence of variables in deep drawing of AA 6061 sheet

Deep drawing is one of the most important processes for forming sheet metal parts.It is widely used for mass production of cup shapes in automobile,aerospace and packaging industries.Cup drawing,besides its importance as forming process,also serves as a basic test for the sheet metal formability.The effect of equipment and tooling parameters results in complex deformation mechanism.Existence of thickness variation in the formed part may cause stress concentration and may lead to acceleration of damage.Using TAGUCHI's signal-to-noise ratio,it is determined that the die shoulder radius has major influence followed by blank holder force and punch nose radius on the thickness distribution of the deep drawn cup of AA 6061 sheet.The optimum levels of the above three factors,for the most even wall thickness distribution,are found to be punch nose radius of 3 mm,die shoulder radius of 8 mm and blank holder force of 4 kN.     

An investigation of cold extruding hollow flanged parts from sheet metals

Hole flanging with cold extrusion can avoid necking or fracture as encountered in conventional sheet metal-forming operations. Substantial flange height and lip thickness can be achieved with flange extrusion because the forming load is compressive. Using a hydraulic press, flange extrusions of 5 and 10 mm inner diameters were produced in pieces of cup-shaped galvanized steel, as well as aluminum 5052 workpieces with a thickness of 0.8 mm, both of which had a pre-hole on the cup bottom. As the punch load was exerted on the cup rim, a clamping force was applied to suppress dilation on the cup bottom.The experiments showed that with sufficient clamping force, significant flange height could be extruded. The utmost extruded flange of 5 mm i.d. was 6 times larger than that drawn from the conventional method, whereas that of 10 mm i.d. was 3.8 times larger than that drawn from the conventional method. However, no flange was extruded and buckling occurred on the cup bottom when the clamping force was insufficient. The experiments confirmed the results predicted by the FE simulation. For a selected flange inner diameter, the ratio of the extruded flange height to the increase in cup bottom thickness was directly related to the normalized clamping pressure, i.e. the ratio of clamping pressure to workpiece yield strength. Therefore, both the application of a larger clamping force or the use of low-strength workpiece materials facilitated the extrusion of flange while suppressing the dilation of the cup bottom. Flange extrusions with a larger diameter correspond to a smaller extrusion ratio or reduction of area. Experiments showed that a significant flange height could be extruded with a 10 mm inner diameter for both galvanized-steel and aluminum 5052, while results for extrusions with a 5 mm inner diameter were unfavorable when using galvanized-steel. High-strength materials and a high extrusion ratio required greater clamping force for the flange extrusion process, and consequently caused excessive forming load on the forming dies as well as on the hydraulic press, thus rendering the process less effective.     

Hole flanging with cold extrusion on sheet metals by FE simulation

Flange height and lip thickness are generally restricted by the formability of sheet metals in the conventional hole flanging operation. In the current work, cold extrusion was applied and a special forming die set was designed with a stripper subjected to counter-pressure with an aim to obtain a more substantial flange. FEM software DEFORM was utilized to simulate this flange extrusion process with two forming conditions: forming with a fixed die cavity and forming with the stripper subjected to counter-pressure. The results showed the cup preform tended to buckle on its bottom with insufficient counter-pressure. The cup preform would start extruding a flange when critical counter-pressure was reached. The magnitude of the critical counter-pressure increased in flange extrusion of smaller inner diameters. The corresponding overall forming load was greatly reduced as compared to flange extrusion with a fixed die cavity.     

盒形件多点成形压痕现象数值模拟研究

以盒形件多点成形过程为例,从拉深形状、板厚、材质等方面进行比较,针对多点成形过程中最主要的缺陷之一—压痕现象的产生原因及其抑制方法进行了数值模拟研究,并进行了实验验证。     

Gas detonation forming process and modeling for efficient spring-back prediction

Aluminum cylindrical cups are formed with gas detonation forming technology and finite element modeling of aluminum cylindrical cup production with the detonation forming technology is performed. The forming process simulation is carried out in two-step analysis. 2D and 3D computational models are constructed with both explicit and implicit dynamic analyses are performed. The effects of detonation pressure and die design parameters also are investigated. The thickness distribution and deformed geometry of the cups are compared with the experimentally determined values. The spring-back predictions based on the explicit and implicit methods are criticized in terms of deformed shape accuracy and elapsed time.     

A developed process for deep drawing of metal foil square cups

Deep drawing of non-axisymmetric cross-section cups from thin sheets or metal foils has become increasingly important, especially for miniaturization of mechanical components. However, with a thin sheet thickness, conventional deep drawing processes are not able to offer reasonable drawing ratios due to early formations of localized wrinkling and fractures at cup corners. In this paper, a friction aided deep drawing process has been developed to increase the deep drawability of thin sheets and metal foils. Productions of square cups have been chosen to verify the current proposed process since the shape provides recognizable non-homogeneous deformation, which can then be compared to conventional processes. In the proposed process, a circular blank holder of a square hole is divided into eight identical segments of 45°. During the deep drawing process, four of the eight segments will move radially inward while the other four segments will move radially outwards cyclically under a pre-determined blank holding pressure. A finite element model of the technique was used to simulate virtual experiments to evaluate and optimize the controlling parameters that influence the cup height and forming process. Taguchi and Pareto ANOVA statistical methods were subsequently used to determine the optimum conditions for best cup height. The results have shown that the new technique is capable of producing deep square cups from soft aluminum sheet (Al-O) of 0.5 mm thickness with a high drawing ratio of 3.3. In addition, it was also observed that the radial displacement was the most significant parameter in influencing the cup height.     

THE SHAPE DISTORTION IN DRAWING PROCESS WITH TC1Mδ0.8 TITANIUM ALLOY SHEETS

采用有限元数值模拟与成形工艺实验相结合的方法,对0.84 mm厚的TC1M钛合金板材杯形件室温拉深成形及回弹过程进行了研究.结果显示,拉深制件不仅出现凸耳和杯口厚度不均等熟知的现象,还揭示出因钛合金各向异性所引发的杯口内壁非圆化,这类形状畸变对制件的几何精度将产生不利影响.600 ℃温热拉深能有效地抑制卸载回弹,杯口内壁非圆化得以消除,但却无法改变钛板的各向异性性质,凸耳和杯口厚度不均等畸变现象依然存在.     

金属丝网的毛坯设计

针对工业用过滤产品——过滤杯的形状及工艺条件,建立网格模型,设置成形参数,使用dy—naform软件模拟其板材拉深成形的过程,通过网格数量、形状的变化,成形极限图和厚度变化图,分析比较了金属丝网与板材的性能差别。结果表明：金属丝网没有塑性变形,只有丝网的弯曲和畸变,实际成形中存在着严格的方向性。设计出了冲压金属丝网的毛坯形状。     

Finite element simulation of three dimensional superplastic blow forming

Superplastic blow forming processes are simulated with a finite element method which adopts the con-vective coordinates system. The code developed is applied to cylindrical cup and the square cup blow forming processes to predict the optimum forming pressure cycle. The numerical result demonstrates the validity and accuracy by comparing with the experimental result and the numerical result by a continuum finite element method The numerical results also provide the pole height, the intermediate and final deformed shapes and the thickness distribution with respect to time.     

差厚拼焊板拉深方盒形件成形极限及焊缝移动

采用Dynaform专业板料成形软件,对差厚异质激光拼焊板拉深方盒形件的成形过程进行了研究.结果表明:母材厚度差对压边力的合理范围以及盒形件的成形极限和焊缝移动量有很大的影响;两种母材所占比例不同(焊缝位置变化)时,比例差别越大,成形极限越小,薄侧材料所占比例越大,焊缝移动量也越大.并根据两种母材在成形过程中的应力状态和应变状态分析了这些现象.     

激光拼焊板方盒件及其板料优化设计分析

成形性能的提高对拼焊板车身覆盖件以及结构件冲压成形有重要意义。通过对激光拼焊板方盒件及其板料对成形过程的影响研究,并采用基于板料厚度比、坯料形状和尺寸等板料参数正交设计的成形优化方法,提高激光拼焊板方盒件冲压成形性能。研究和冲压试验表明：当厚度比较小时,破裂出现在薄侧圆角处,而厚度比较大时,破裂出现在薄侧焊缝处;方形坯料拼焊板的成形性能明显低于圆形坯料形状的拼焊板;板料正交设计方法对拼焊板方盒件冲压成形优化是有效可行的。     

拼焊板盒形件充液拉深的数值模拟

随着汽车行业对能源消耗和汽车尾气排放的要求,应用拼焊板成形技术显得越来越重要.以差厚拼焊板拉深方盒件为研究对象,采用板料成形分析软件DYNAFORM对充液拉深和传统拉深工艺进行分析和对比.研究发现,盒形件不同部位其焊缝有不同的移动趋势,传统拉深最大焊缝移动量发生在盒形件底部中心处,充液拉深件焊缝移动最大量发生在侧壁顶部,增大充液拉深凹模油腔的压力,可以有效地减少焊缝移动量和坯料的减簿量.     

Development of optimum process design system by numerical simulation

Now, the development of optimum forming process design system based on computer simulation to reduce the time consumption is strongly required in the industries. In this study, the optimum process design system is newly developed in conjunction with the nonlinear FEA code and the nonlinear optimization code. In the latter code, “Sweeping Simplex Method” is newly proposed, which can find the global minimum. The accuracy and quickness of this method to find the global minimum of objective function, which have several local minimum points, is confirmed by comparison with the grid method.

This numerical system is applied to the process design of complicate shaped cup deep drawing. In order to form the sheet metal with uniform thickness, “Deviation of thickness from uniform average thickness” is employed as the objective function, and the global minimum point in the design variable space is searched by “Sweeping Simplex Method”. For the design variables, the heights of two punches in first stage forming are employed. The optimum process condition was determined by using this numerical code and also the validity of this code was confirmed by the comparison with the experimental observation results.     

Influence of punch geometries on the divided material flow in a double cup extrusion process

This paper provides an analysis of the deformation patterns in a backward can extrusion combined simultaneously with a forward can extrusion process, which is known as a double cup extrusion process. The main objective of this study is to examine the divided material flow characteristics in DCEP. Analyses were conducted in a numerical manner by employing a rigid-plastic finite element method. Among many process parameters, the major design factors chosen for analysis include the reduction in area (RAB), the wall thickness ratio (TR), the punch nose radius (R), and the friction condition. The simulation results were summarized in terms of relationships between the process parameters and the ratios of extruded length and volume, and between the process parameters and force requirements, respectively. Comparisons between a multi-stage forming process in sequential operations and one-stage combined operation were also made in terms of the forming load and pressure exerted on the tool. The force requirement and self-regulating characteristics were more greatly influenced by the wall thickness ratio among the selected major design factors. And more severe load to form the same shape is expected in sequential operations than in a combined extrusion process.     

不锈钢材的橢圆杯拉伸成形分析

采用Prandtl-Reuss塑流法则和Hill的屈服判据,结合有限变形理论及updated Lagrangian formulation的概念,将四边形四节点退化壳元素偶合到刚性矩阵中,组成三维有限元素的分析模式来处理板材成形问题。以材料拉伸试验所得的样片断裂面厚度为数值分析的破断准则,探讨椭圆杯拉伸成形过程中冲击荷载与冲程的关系、工件厚度分布、变形过程及成形极限等。由数值分析与实验结果得知,冲击荷载随着冲程的增加而增大,当载荷达到最大值后,样片随着冲程的增加而继续变形,直到拉伸完成为止。工件最小厚度集中在工件与压头长轴接触处,因长轴的曲率半径比短轴的小,故料片在长轴处承受了最大拉伸应力。经由椭圆压头周长与初始样片周长所定义的极限拉伸比得知,此椭圆杯成形的极限拉伸比为2.136。