Numerical simulation and analysis on the deep drawing of LPG bottles

Deep drawing is one of the most used sheet metal forming processes in the production of automotive components, LPG bottles and household goods, among others. The formability of a blank depends on the process parameters such as blank holder force, lubrication, punch and die radii, die-punch clearance, in addition to material properties and thickness of the sheet metal. This paper presents a numerical study made on the deep drawing of LPG bottles. In particular, the application of both variable blank holder forces and contact friction conditions at specific location during deep drawing are considered. The numerical simulations were carried out with DD3IMP FE code. A variable blank holder force strategy was applied and the numerical results were compared with results from other blank holder force schemes. It is evident that the proposed variable blank holder force scheme reduces the blank thinning when compared to other schemes; the friction coefficient also has a significant influence on the stress–strain distribution.     

基于Dynaform的方盒形体拉深成形的数值模拟与分析

针对方盒形体在拉深成形过程中易出现起皱、破裂等缺陷,采用显式有限元分析软件Dynaform分析压边力、毛坯形状、材料性能参数等因素对其成形极限的影响,以达到优化工艺过程的目的.研究结果表明:盒形件的的拉深成形受压边力影响较大,增大板料硬化指数n、厚向异性系数r及板料厚度t,有利于板料的成形.     

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.     

Evaluation of stamping lubricants in forming advanced high strength steels (AHSS) using deep drawing and ironing tests

In forming AHSS, the lubricant must reduce the friction between die and sheet as well as the effect of heat generated from deformation and friction, especially in forming at high stroking rates. In this study, the effectiveness of stamping lubricants was evaluated by using the deep drawing and ironing tests. Various stamping lubricants were tested in forming of DP590 GA round cup samples. In these tests, the performance of lubricants was ranked via evaluation criteria that include punch force and the geometry of tested specimens. Deep drawing tests were conducted at two different blank holder forces, BHF (30 and 70 ton) at a constant ram speed (70 mm/s). The ironing tests were conducted to evaluate the performance of lubricants at higher tool–workpiece interface pressure than that is present in deep drawing. Polymer-based thin film lubricants with pressure additives (e.g. Lubricants A and B) were more effective than other lubricants as shown by the force (e.g. maximum punch force and applicable BHF without cup fracture) and geometry indicators (e.g. draw-in length, flange perimeter and sidewall thinning).The pressure and temperature distributions at the die–sheet interface were predicted by FE simulation of deep drawing and ironing tests. As expected, the value of interface pressure and temperature were maximum at the die corner radius.     

Experimental and numerical investigation on micro deep drawing process of stainless steel 304 foil using flexible tools

Flexible forming technology provides significant application potential in various areas of manufacturing, particularly at a miniaturized level. Simplicity, versatility of process and feasibility of prototyping makes forming techniques by using flexible tools suitable for micro sheet metal forming. This paper reports the results of FE simulation and experimental research on micro deep drawing processes of stainless steel 304 sheets utilising a flexible die. The study presents a novel technique in which an initial gap (positive or negative) is adopted between an adjustment ring and a blank holder employed in the developed forming system. The blank holder is moveable part and supported by a particular spring that provides the required holding force. The forming parameters (anisotropy of SS 304 material, initial gap, friction conditions at various contact interfaces and initial sheet thickness) related with the forming process are in details investigated. The FE models are built using the commercial code Abaqus/Standard. The numerical predictions reveal the capability of the proposed technique on producing micro metallic cups with high quality and large aspect ratio. To verify these results, number of micro deep drawing experiments is conducted using a special set up developed for this purpose. As providing a fundamental understanding is required for the commercial development of this novel forming technique, hence the optimization of the initial gap in accordance with each sheet thickness, thickness distribution and punch force/stroke relationship are detected.     

汽车座椅外侧板单动拉延成形工艺分析及优化

以某型号汽车座椅外侧板为例,采用Auto Form软件对座椅外侧板拉延成形过程进行模拟分析,并根据分析结果预测出拉延过程中的拉裂风险。通过调整零件的圆角半径和修改局部结构,消除了开裂风险,降低了最大减薄率。为取得更好的成形效果,选取压边力、摩擦系数、冲压速度、凸凹模间隙4个重要成形工艺参数进行正交试验及参数优化,得出最优工艺方案为:压边力250 k N、摩擦系数0.13、冲压速度1000 mm·s-1和凸凹模间隙2.42 mm,最终零件的最大减薄率为24.33%,最大增厚率为6.54%。采用优化后方案进行实际拉深试模,得出零件的成形性能与有限元模拟结果一致,工件质量完全符合设计要求。     

Adaptive FEM simulation for prediction of variable blank holder force in conical cup drawing

Fracture and wrinkling are two primary failure modes in deep drawing of sheet metal parts. Previous studies showed that properly selected variable blank holder force (BHF) profile, i.e. variation of BHF with punch stroke, can eliminate these failures to draw deeper parts. In this study, an adaptive simulation strategy was developed to adjust the magnitude of the BHF continuously during the simulation process. Thus, a BHF profile is predicted in a single process simulation run and the computation time is reduced. The proposed strategy has been applied successfully to two conical cup drawing operations. The predictions have been compared with experiments and the results indicate that the adaptive simulation strategy can also be used to improve the drawing process for forming non-symmetric parts.     

工艺参数和材料性能对板料成形回弹的影响

分析总结了数值模拟中模拟参数（有限无算法、单元类型、材料模型、本构方程、积分点选取、接触和摩擦法则等）对回弹模拟精度的影响。对一细长支腿零件的工艺成形过程进行了数值模拟,研究了工艺参数及材料性能参数（压边力、凸模圆角半径、凸凹模间隙、板料厚度、摩擦系数、材料硬化指数）对工件回弹的影响。回弹角随凸模圆角半径和凸凹模间隙的增大而增大,随压边力、扳料厚度、摩擦系数和材料硬化指数的增大而减小。     

基于响应面模型和遗传算法的汽车发罩外板冲压工艺参数多目标优化

以汽车发罩外板为例,将压边力、冲压速度、凹模与板料间摩擦系数和凸模与板料间摩擦系数作为工艺参数变量,以拉延工序最大减薄率和修边工序后最大回弹量为优化目标,应用中心复合试验设计(CCD)及有限元模拟获取样本数据。由试验数据建立二阶响应面模型,结合非支配排序遗传算法(NSGA-Ⅱ)实现多目标优化,得到优化的工艺参数组合为:压边力为1145kN,冲压速度为3480mm·s~(-1),凹模与板料摩擦系数为0.106,凸模与板料摩擦系数为0.13。基于优化的工艺参数指导模面回弹补偿分析并试模,研究结果表明,发罩外板实际冲压成形质量较好。     

汽车大型铝合金覆盖件的充液成形技术

铝合金覆盖件的应用是汽车轻量化的关键,但其制造难度较大。通过研究铝合金发动机罩外板的充液成形工艺过程,了解先进柔性技术在汽车领域应用的可行性。分析了工艺参数中液室压力与凸模行程匹配及压边力对板料减薄率的影响,从成形极限上判断零件无起皱、破裂现象的范围。获得最优的整形液室压力为12～20 MPa,压边力过小,板料不能充分塑性变形,压边力过大,板料易失稳破裂,最优的恒定压边力范围为1600～2000 k N。研究表明,采用板材充液成形柔性制造工艺,可降低噪音,无冲击线,且由于液室压力的作用,滑移线减小,可提高大型铝合金弱刚度板材的质量。     

基于Autoform的汽车覆盖件拉深成形数值模拟研究

以典型覆盖件(汽车外轮罩)为研究对象,板料三维成形分析软件Autoform为平台,研究了板料与凸模、凹模的摩擦、压边力、拉深筋等因素对成形性能的影响。通过Autoform的成形仿真预测板料成形过程中减薄、拉裂、起皱等缺陷,同时分析缺陷产生的原因,进而优化板料成形工艺参数和改进模具结构。     

Deep drawing of cylindrical cups with friction-actuated blank holding

The draw force and the blank-holder variations that are obtained when drawing with friction-actuated blank holding are determined theoretically for a urethane pad of particular dimensions. A prototype tooling for blanking and drawing of sheet metal of thickness 1 mm and less to cups of diameter 100 mm at draw ratio of 1.85 with such a blank holder has been designed, fabricated and tested. Experimental results from the above tooling are presented, these including the punch and blank-holder force variations with stroke and the thickness strains in the cup wall. The experimentally-measured punch force variations are compared with the theoretical predictions. The theoretical and the experimentally-measured blank-holding force variations are presented, together with the variation of critical blank-holding force that is needed to suppress wrinkling. The differences between the theoretical and the experimental force variations are discussed.     

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.     

前翼子板成形数值分析

根据正交试验法原理,应用板料成形软件PamStamp 2G,在其他成形条件一定的情况下,对前翼子板在不同压边力、板料与模具间摩擦因数、凸模和凹模间隙、虚拟凸模成形速度下的成形进行数值分析。将模拟结果同实际成形件厚度比较,通过极差分析,得出上述因素对前翼子板成形的不同影响,其中压边力、虚拟凸模速度对成形影响较其他因素大。     

基于载荷下降法的双相钢DP590拉深减薄率研究

采用载荷下降法研究了双相钢DP590在不同压边力下拉深成形的减薄率。采用BCS-50AR通用板材成形性试验机进行有无润滑条件的对比拉深试验,获得成形力-凸模位移关系曲线。试验结果发现,拉深件凸缘部位和凹模圆角处的润滑有利于拉深成形,而无润滑条件下的拉深容易破裂。拉深件凸缘部位增厚,凹模圆角处和筒壁部位均有不同程度的减薄。危险断面处的减薄率最大,破裂情况下的最小减薄率为28.6%,无破裂情况下的最大减薄率为19.3%,达到实际生产要求。     

Improvement of deep drawability by radially pressurized fluid

Developments in the automobile and other sheet metal industries demand continuous improvements in the deep drawing processes. The areas of improving deep drawing processes include higher forming limits so that much deeper products can be obtained with less power consumption. In this paper, the idea of applying hydraulic pressure in the radial direction on the periphery of the blank is theoretically analyzed. This radial pressure is generated due to the punch movement within the fluid chamber and is directed through a by-pass to the blank periphery. The problem is solved for a work hardening material using the finite difference method. The stress and strain distributions in the flange of the shell are determined and the limiting drawing ratio is calculated at the instant when the strain in the thickness direction reaches a critical value. This critical value is assumed to be the strain hardening exponent of the drawn material. The results show significant increase in the limiting drawing ratio as the radial pressure increases.     

椭球形制件复合成形规律的研究

采用理论分析、数值模拟与实验验证相结合的方法,对椭球形制件的复合成形规律进行了研究。建立了应力分界圆半径的数学表达式,理论分析表明,应力分界圆半径的大小与板料的初始尺寸、厚度、摩擦系数、压边力大小和凹模圆角半径等因素有关。当压边力、坯料尺寸以及摩擦系数加大,而相对圆角半径减小时,应力分界圆半径变大,复合成形中胀形成分加大;反之,应力分界圆半径减小,拉深成分增加,揭示了复合成形的阶段性特征。数值模拟结果表明,应力分界圆半径是动态变化的,椭球形制件复合成形具有明显的阶段性特征,没有直线段的椭球形制件的成形可分为纯胀形、以胀形为主的胀形-拉深复合成形和以拉深为主的拉深-胀形复合成形3个阶段;在成形的第Ⅰ、Ⅱ阶段初期,坯料尺寸和压边力的大小对应力分界圆半径影响不大;在第Ⅱ阶段后期和第Ⅲ阶段,随毛坯尺寸和压边力的增大,应力分界圆增大。在变形过程中存在两个可能发生失稳起皱时刻,即第Ⅱ阶段初期和第Ⅲ阶段初期。试验验证了理论分析和数值模拟所得的结果。     

Prediction of the limiting drawing ratio and the maximum drawing load in cup-drawing

A new, simple and practically applicable equation, including the normal anisotropy value R and the strain hardening exponent n, for estimating the limiting drawing ratio LDR in cup-drawing of a cylindrical cup with a flat-nosed punch is derived. The normal anisotropy is based on Hill's theory of an anisotropy sheet that is isotropic in its plane. Whiteley's equation for estimating the LDR, and Hill's upper limit value of LDR, are two special cases of the new equation. Compared with the published experimental work, good agreement between the calculation and the experiment is obtained. The new equation shows that the most important parameter for LDR is the normal anisotropy value R, the strain hardening exponent n has also some influence on the LDR, and clearly explains the real interaction between the normal anisotropy value R and the strain hardening exponent n on the LDR. It is different from other equations, which are functions of the normal anisotropy value R only.A new equation, incorporating the value of LDR derived as above and the critical drawing load Pc based on the maximum load principle for localization of plastic flow, for estimating the maximum drawing load Pc at a certain drawing ratio DR in cup-drawing with a flat-nosed punch is developed. This equation is simple and supplies an accurate estimation of the maximum drawing load Pd. A comparison between the calculation and the experiment shows that good agreement is also obtained.It is thereby possible to better understand and control the cup-drawing behavior of sheet metal.     

板成形数值模拟影响因素的正交试验分析

根据正交试验原理，应用板料成形软件对不同压边力、模具与板料间摩擦系数、凸凹模间隙和板料初始尺寸进行数值模拟，将数值模拟的厚度同实际成形件的厚度进行比较，得出上述因素对前翼子板成形结果的影响，并预测了前翼子板较优的理论成形条件。     

方形盒制件圆角处拉深破裂的数值模拟

金属薄板成形的数值模拟技术在冲压件生产和模具设计中起着重要的作用。文章借助Dynaform软件对某方形盒制件拉深破裂现象进行数值模拟,分析其产生原因和影响因素,并利用正交实验找出防止该制件圆角破裂的拉深条件组合。结果表明,在冲压速度、凸模圆角半径、摩擦系数和板料厚度4个因素中,凸模圆角半径对盒形件拉深破裂的影响最大。为降低因圆角处板料剧烈减薄而产生破裂的几率,盒形件拉深时应采用较大的凸模圆角半径。