Friction aided deep drawing of sheet metals using polyurethane ring and auxiliary metal punch. Part 1: experimental observations on the deep drawing of aluminium thin sheets and foils

Friction aided deep drawing based on the Maslennikov process is investigated as a method to facilitate the deep drawing of sheet metals with poor drawability. Aluminium foils and thin sheets of 0.1–0.4 mm in thickness are used as a model for the material with poor drawability. An auxiliary metal punch is used together with a polyurethane ring to increase the drawing efficiency and to improve the dimensional accuracy of the drawn cup. The effect of drawing conditions such as thickness, hole diameter and the hardness of the polyurethane ring on the cup height are mainly investigated. Also, the optimum number of drawing operations required to achieve a given drawing ratio is examined by repeating compression and unloading the polyurethane ring. The experimental results show that even for foil and thin sheets, deep cups with drawing ratios of 2.25 and with good shape and dimensional accuracy can be obtained by repeating the drawing operation about ten times. The achievable drawing ratio is appreciably larger when compared with that obtained by the conventional deep drawing process.     

Friction aided deep drawing of sheet metals using polyurethane ring and auxiliary metal punch. Part 2: analysis of the drawing mechanism and process parameters

Friction aided deep drawing using a polyurethane ring as a pressure medium has been analyzed by the slab and the energy methods to understand the main features of the process and to find the optimum conditions to achieve successful drawing. The effect of an auxiliary metal punch on the stress distribution of the deformed blank and the increase in height of the drawn cup is also discussed. From these studies, the reason why the unusual circumferential crack occurs at the flange of the deformed blank has been clarified, based on the radial stress distribution of the deformed blank. A process parameter, which denotes the drawing characteristics of the friction aided deep drawing, has been proposed. In addition, the drawing region diagram has been presented to facilitate the drawing pressure control with the progress of the drawing process. It is shown that the successful drawing region is narrow at the early stage of drawing, although it becomes wide as the drawing proceeds. Therefore, in the early stage of drawing, special care should be paid to the drawing pressure control to avoid the flange crack.     

Finite element simulation of warm deep drawing of aluminium alloy sheet when accounting for heat conduction

The deformation behaviour and the temperature change in cylindrical deep drawing of an aluminium alloy sheet at elevated temperatures are simulated by the combination of the rigid-plastic and the heat conduction finite element methods. The comparison with the experimental results shows that the forming limits and the necking sites are successfully predicted by the simulation. It is clarified that the appropriate distribution of flow stress depending on temperature must exist in the sheet for the higher limiting drawing ratio. The numerical as well as the experimental results show that the limiting drawing ratio in the warm deep drawing increases with the die profile radius.     

薄壁紫铜零件多次拉深成形的数值模拟

通过对薄壁紫铜筒形件在大拉深比时二次拉深成形方法的选择研究，由UG建立参数化模型，应用有限元软件Dynaform对拉深成形过程进行数值模拟，分析模具参数选取对成形性的影响和软件中若干参数的设置，得出紫铜薄壁高筒件的合适的拉深工艺和优化的工艺参数。     

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.     

Experimental verification of a deep drawing tool system for adaptive blank holder pressure distribution

In deep drawing, the strain path in the blank during the forming process can be significantly affected by application of temporal and spatial variation of the blank holder force. In this study, an active tool system capable of controlling the distribution of the blank holder force is presented which can be integrated into existing stacked deep drawing tools without need for modification of the press.     

轴对称拉深成形多点压边常压边力拉深模设计

对轴对称拉深成形 ,为提高压边效果 ,提出了在径向多个位置施加压边力的方法 ,且根据常力压边原理 ,用弹簧和橡胶作弹性元件 ,使在不同压边位置所产生的压边力 ,在拉深过程中保持定值。以此设计的模具所提供的压边力 ,更符合拉深工艺对压边力的要求。     

Study on hydromechanical deep drawing with uniform pressure onto the blank

Sheet hydroforming has many virtues and has gained increasing interest in industries recently. In this paper, hydromechanical deep drawing (HDD) with uniform pressure onto the blank is proposed and investigated in detail both primarily in experiments and simulation. Final cups with drawing ratios of 2.46 and 3.11 were, respectively, obtained using Al–Mg–Si alloy (Al6016-T4) and soft aluminum (Al1050-H0) that have the strong anisotropic properties. The influence of process parameters on the sheet deformation was studied and the typical failure types including fracture and wrinkling were discussed. Finally, FEM was used to analyze the forming process, and the results from the FEM simulations were in good agreement with those from the experiments.     

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.     

Finite element modeling and experimental results of brass elliptic cups using a new deep drawing process through conical dies

This paper introduces a new technique for deep drawing of elliptic cups through a conical die without blank holder or draw beads. In this technique an elliptic-cup is produced by pushing a circular blank using a flat-headed elliptic punch through a conical die with an elliptic aperture in a single stroke. A 3D parametric finite element (FE) model was built using the commercial FE-package ANSYS/APDL. Effects of die and punch geometry including, half-cone angle, die fillet radius, die aperture length and punch fillet radius on limiting drawing ratio (LDR), drawing load and thickness strain of the cup have been investigated numerically for optimal process design. A die with half cone angle of 18° has shown the best drawability for the new technique. An experimental set-up has been designed, manufactured, and used for experimental production of elliptical shaped sheet-metal cups. A total of seven punches having aspect ratios ranging from 2 to 2.25 and a die with an aspect ratio of 2 have been manufactured and used. Tensile tests were carried out to obtain the stress–strain behavior for the formed sheet metal. Experiments were conducted on blanks of brass (CuZn33) with initial thicknesses of 1.5, 1.9, 2.4 and 3 mm at different clearance ratios (c/t). Effects of blank thickness and clearance ratio on limiting drawing ratio, drawing load and thickness strain were numerically and experimentally investigated. Finite element model results showed good agreement with experimental results. An elliptic cup with a limiting drawing ratio (LDR) of 2.28 has been successfully achieved using the proposed technique and set-up.     

Investigation into the effect of pre-bulging during hydromechanical deep drawing with uniform pressure onto the blank

Many parameters influence the process of sheet hydroforming, but the key one is the pre-bulging. Pre-bulging includes two parameters: pre-bulging height and pre-bulging pressure, which influence the forming process significantly. In this paper, based on the proposed hydromechanical deep drawing with uniform pressure onto the blank, the effect of pre-bulging on the forming is investigated experimentally and the needed process windows for the pre-bulging pressure and the pre-bulging height are built by using pure aluminum and aluminum alloy. Finally, FEM is used to analyze the forming process to explain some results which were found in the experiment.     

Increasing of the drawing depth using tailor rolled blanks—Numerical and experimental analysis

Deep drawing is a common sheet metal forming process. In most cases, sheets with constant thicknesses are formed. At the end of the previous century, new innovative blank technologies have been established for weight saving purposes. The development of the flexible rolling process is an illustrating example for this progression. By changing the roll gap during rolling, longitudinal thickness transitions are produced. The innovative semi-finished product, which is produced in this manner, is called tailor rolled blank (TRB). Its behaviour and characteristics during further processing, especially in forming, are topics of present research. The main emphasis of this paper is placed on the idea that TRB can be used to increase the maximum deep drawing depth compared to blanks having a constant thickness. This can be realised by “weakening” certain areas of the blank in a way that the load in failure at critical areas is reduced. To ensure weight saving in addition to increasing the maximum deep drawing depth, the maximum sheet thickness of the TRB is equal to the constant thickness of the other blanks. The concept is first analysed with the help of numerical simulations and then verified by experimental work.     

轴对称曲面件拉深智能化控制技术研究

板材冲压智能化是一项涉及控制科学、计算机科学和板材塑性成形理论等领域的综合性新技术。该技术的研究已有 10几年的历史 ,但主要是集中在V型弯曲的回弹控制方面 ,直到 90年代初才开始对筒形件拉深的智能化控制进行探索性研究。本文研究建立了轴对称壳体零件拉深过程智能化控制系统 ,并以锥形件为例 ,分析了轴对称曲面零件拉深过程中的共同特点 ,建立了完整的力学模型 ,实现了轴对称曲面件拉深的智能化控制     

多道次拉深中间构型对成形影响的研究

钣金件多道次拉深中间构型的确定是塑性成形领域的一个难题.针对中间构型对多道次成形的影响,以轴对称盒形件为成形对象,采用试验方法进行了研究.试验设计了两种不同的中间构型,通过网格法研究在第1道次和第2道次中应变的分布规律;通过成形极限图研究两种中间构型第1道次和第2道次的成形性.试验结果表明,轴对称零件多道次成形在第2道次的成形中,底部成形近似为局部成形,容易在底部产生较大的拉伸应变,造成破裂缺陷,设计中间构型的底部应尽量与零件近似;第1道次和第2道次中沿母线方向的应变均为拉伸应变,自零件口部向零件底部周向的应变由压应变逐渐过渡到拉伸应变,以压应变为主,破裂一般发生在拉伸应变区.     

矩盒形件分区压边拉深工艺

以矩盒形件为研究对象,对凸缘部分按几何特征予以分区,并在eta/DYNAFORM 5.6和MSC.Marc/Mentat软件中对其分区压边拉深成形过程进行有限元仿真,分析各区域压边力对零件成形性能的影响,给出了矩盒形件的确定分区压边力大小的原则;结合矩盒形件拉深时的变形特点和材料流动情况,在相关文献研究的基础上,对分区方式进行优化,提出了结合变形特点的分区方式;在YT32-315C四柱液压机和自主研制的分区拉深装置上,对矩盒形件进行分区压边拉深的实验,实验结果和有限元仿真结果基本相符。矩盒形件的分区方式应按几何特征与变形特点划分。     

Prediction of forming limit in hydro-mechanical deep drawing of steel sheets using ductile fracture criterion

It has been observed that the forming limit curve at fracture (FLCF) of steel sheets, with a relatively higher ductility limit have linear shapes, similar to those of a bulk forming process. In contrast, the FLCF of sheets with a relatively lower ductility limit have rather complex shapes approaching the forming limit curve at neck (FLCN) towards the equi-biaxial strain paths. In this study, the FLCFs of steel sheets were measured and compared with the fracture strains predicted from specific ductile fracture criteria, including a criterion suggested by the authors, which can accurately describe FLCFs with both linear and complex shapes. To predict the forming limit for hydro-mechanical deep drawing of steel sheets, the ductile fracture criteria were integrated into a finite element simulation. The simulation, results based on the criterion suggested by authors accurately predicted the experimetal, fracture limits of steel sheets for the hydro-mechanical deep drawing process.     

半球形凸模拉深过程的动力显式有限元分析

本文基于连续介质力学及有限变形理论 ,建立了用于三维板料成形过程分析的有限元模型 ,开发了动力显式算法的板料成形过程模拟的有限元分析程序DESSFORM3D。采取集中质量矩阵 ,用动力显式积分的方法 ,使位移计算显式化 ,避免了由材料、几何、边界条件等高度非线性因素引起的计算收敛问题。对半球形凸模拉深过程进行模拟计算 ,并把模拟结果与实验结果进行对比 ,验证了软件的计算结果     

变压边力拉深的原理及实验系统

板料拉深过程中,压边力是一种重要的工艺参数。由于其在冲压拉深过程中的重要作用及在生产中易于调节、控制,近年来一些汽车工业较为发达的国家,正在进行着变压边力拉深新工艺方法的研究。本文从板料冲压拉深过程对压边力需求的分析中,提出了变压边力控制方法的原理,建立了变压边力拉深实验系统,并以圆锥形件为研究对象对拉深过程中合理的变压边力控制问题进行了探索性研究,取得了阶段性成果。