Optimization of the design parameters of modified die in hydro-mechanical deep drawing using LS-DYNA

The use of a modified die enhances the limiting draw ratio compared to that obtainable in a conventional deep drawing operation. Application of these dies, in conventional deep drawing, eliminated the use of blank holder but enhances the tendency of wrinkling in drawn products. In hydro-mechanical deep drawing process, the punch deforms the blank to its final shape by moving against a controlled pressurized fluid. In this paper, a new concept of the application of modified dies in hydro-mechanical deep drawing is presented. The finite element (FE) simulations of a deep-drawing process using modified dies are performed using the 2-D explicit finite element code LS-DYNA, with the aim of optimization of design parameters and the results are compared with the experimental values. The initial design steps in the design of modified die in finite element simulation were taken from the concept of Tractrix die. The use of Tractrix die enhances the draw ratio but simultaneously increases the tendency of wrinkling. In this paper the design parameters of modified Tractrix die for hydro-mechanical deep drawing are optimized for the successful drawing of cups. It is also experimentally verified that by using such modified dies in hydro-mechanical deep drawing, deeper cups are drawn without wrinkling.     

The role of die curvature in the performance of deep drawing (hydro-mechanical) processes

A hydromechanical deep drawing process (which replaces the conventional rigid blank-holder tool with a hydrostatic fluid pressure) is utilized to study the roles played by die curvature, interfacial friction, material hardening, etc. in deep drawing performance. The analytical study is based on limit analysis in plasticity (applying both the upper and the lower bounds simultaneously) with a special emphasis on the geometry of the die profile. The resulting relationships between the various parameters obtained through the bounds are backed by an independent numerical solution using Woo's finite difference scheme. The associated experiments, with which the limit analysis is compared, were conducted with aluminium blanks at various die radii and with various holding fluid pressures.The relatively close proximity of the above solutions, in describing the observed behaviour of the process, enables one to draw a few general conclusions about the strength of the limit analysis in describing realistic deep drawing processes. Also potential improvements concerning the choice of die radius of curvature and the blank holding force are indicated.     

Expanding field of application of cold die forging by inducing active contact friction forces

A highly productive method for the cold die forging of blanks makes it possible to fabricate parts with smooth surfaces and the required mechanical characteristics without subsequent heat treatment and machining. The field of application for this method is restricted to high stresses in dies that deform a blank, which reduces their fatigue resistance. Extrusion with applying active friction forces, during which the mold moves in the direction of a blank material flow with a velocity that exceeds the flow velocity, makes it possible to unload dies and produce parts from medium-carbon and low-alloy steels by cold die forging. This work deals with assessing the increase in the fatigue resistance of dies during the extrusion of steel 45 blanks with applying active friction forces.     

Computer-aided structural design of drawing dies for stamping processes based on functional features

This paper describes a structural design system for 3D drawing dies based on functional features using a minimum set of initial information. In addition, it is also applicable to assign the functional features flexibly before accomplishing the design of a solid model for the main parts of a drawing die, such as upper die, lower die, and blank holder. The initial information includes blank sizes, work strokes, die faces, punch open lines, and press data. The proposed system integrated the design knowledge of drawing die into functions of 3D computer-aided design (CAD) software to automate design and to shorten design time. This design system is constructed on a PC and integrated with a Pro/ENGINEER CAD system including feature selector, shape calculator, model generator, design coordinator, and user interface. The proposed system is demonstrated using the example of designing a drawing die for the roof panel of a vehicle within 1 h. The results reveal that it can dramatically improve the design quality and can save both time and costs with excellent design quality.     

The effect of die/blank holder and punch radiuses on limit drawing ratio in angular deep-drawing dies

Deep-drawing is one of the most important methods used to form sheet metal. The radius of die/blank holder and punch is important for deep-drawing dies because of an effective way to promote deep drawability sheet metal. This paper presents an attempt to determine the effect of various radiuses of die and punch on the limit drawing ratio and was investigated using DIN EN 10130–91 sheet metal. The die/blank holder profile with angles of α?=?0°, α?=?2.5°, α?=?7.5°, α?=?12.5°, α?=?15° and die/punch profile with radiuses for R?=?10, R?=?8, R?=?6, R?=?4 and R?=?0 mm were analyzed to determine the influence of punch force on the limit drawing ratio. The aim of this study is to investigate the effect of radius and angle variables on drawability in the deep-drawing process and to obtain useful data from the industrial field. The experiments show that the limit drawing ratio increased with increasing radius of punch (R), die/blank holder angle (α).     

A knowledge-based parametric design system for drawing dies

The design of drawing dies is a very complex and knowledge-intensive process. This paper describes a knowledge-based parametric design system for drawing dies which requires only a minimum set of parameters to be set before it is able to complete the design of the main components of a die, such as upper dies, lower dies, and blank holders. This minimum set of parameters includes blank sizes, die faces, punch open lines, drawing strokes, and press data. This design system implemented on top of the Pro/E CAD software consists of a drawing die knowledge base, a subcomponent inferencer, a dimension calculator, a subcomponent generator, a system coordinator, and a user interface. We use the design of drawing dies for inner wheel house as a concrete example to show that our system can greatly improve the design quality while reducing the development time and cost.     

圆锥形凹模径向分块压边拉深工艺实验研究

采用圆锥形凹模拉深工艺可以提高成形极限,但需要用压边圈将板坯先压成与凹模面吻合的形状,当变形程度较大时,板坯很容易起皱。为了克服这一缺点,提出了将圆锥形凹模与径向分块压边方法结合的工艺,该工艺可有效改善压边圈与板坯的约束状态,从而达到抑制起皱的目的。对圆筒形件的拉深成形,采用了刚柔复合的径向分块压边圈结构,设计了圆锥形凹模径向分块多压边圈拉深模,取不同凹模半锥角的圆锥形凹模进行了圆筒形件的拉深成形实验。实验表明,新的压边方法能有效克服初始成形过程的起皱,可与锥度较小的凹模一起使用。采用凹模半锥角为45°的凹模,得到AA5754、AA6061和08Al三种板材的极限拉深系数分别为0.410、0.431、0.373,显著提高了成形极限。对圆锥形凹模的拉深成形,给出了理论计算成形极限的方法,理论与实验结果非常接近。     

Experimental and mathematical analysis of simulation results for sheet metal parts in deep drawing

In this paper, deep drawing of conical and cylindrical cups without blank holder is investigated using a conical die design. These cups are produced by pushing circular blanks by pushing the flat head punch in a single stroke. ANSYS APDL 14.0 was then used to investigate the effects of die and punch geometry, half-cone angle, die and punch fillet radius, and drawing load. The thickness distribution of the cup was numerically investigated to determine the optimal process design, and mathematical analysis was adopted to determine the thickness distribution and longitudinal stress calculation. An experimental set-up was designed to validate the simulation results for conical and cylindrical shaped sheet-metal cups. Tensile tests were carried out to obtain the flow of the stress-strain curve for the simulation. The drawing characteristics of materials were investigated by performing Erichsen cupping and Vickers hardness tests. Experiments were conducted on blanks of aluminum alloys and stainless steel with initial thicknesses of 1.5 mm. A cylindrical cup of ss304 with LDR of up to 2.2 and conical cup of AA1100 with LDR of up to 2.7 were successfully achieved. Finite element simulation results showed good agreement with the mathematical and experimental results.     

An investigation of an expert system for shearing cut progressive die design

The purpose of this paper is to develop an expert system for shearing cut progressive die, with the aim of enhancing the design of shearing cut progressive dies. This study is different from previous research on shearing cut die design by the author in that the design of one station was extended into a progressive die design. The major research objectives achieved in this study can be summarised as follows:

1. This study presents a pattern recognition method called the new combined structural approach to let the user interpret blanks by a better and more direct method, thereby achieving the goal of communicating with this expert system.
2. The layout of the strip can affect the material cost shared by the press-worked pieces. This study presents the near optimal method for seeing a better layout of the strip in order to save material.
3. Owing to the great variety of blank shapes which cause the variations in pressing procedures, this study proposes a matching combination learning method, which is a learning conscious system for pressing procedures, in order to obtain the optimal number of operation stations in shearing cut progressive die design.
4. The establishment of the knowledge-base system for shearing cut progressive die should improve the efficiency for die design problems.

     

采用可移动凹模的板材液压成形技术

提出一种改进的板材液压成形新工艺,即采用可移动凹模,实现拉深与胀形的复合液压成形。在整个变形过程中,板材初始变形部分始终与可移动凹模接触,从而抑制已变形区进一步变形,使变形更加均匀,实现变形的顺序控制,板材成形极限得到提高。从试验和数值模拟两方面对可移动凹模板材液压成形技术进行了研究,分析各种工艺参数,如摩擦因数等对板材成形性的影响,并且分析了可移动凹模对板材成形极限的影响。     

Study on process parameters and its analytic application for nonaxisymmetric rectangular cup of multistage deep drawing process using low carbon thin steel sheet

Multistage deep drawing process is widely used to obtain various nonaxisymmetric rectangular cups. This deep drawing scheme including drawing and ironing processes consists of several tool sets to carry out a continuous production within one progressive press. To achieve the successive production, design and fabrication of the necessary tools such as punch, die, and other auxiliary devices are critical, therefore, a series of process parameters play an important role in performing the process design. This study focuses on the tool design and modification for developing the rectangular cup with an aspect ratio of 5.7, using cold-rolled low carbon thin steel sheet with the initial thickness of 0.4 mm. Based on the design results for the process and the tools, finite element analysis for the multistage deep drawing process is performed with thickness control of the side wall in intermediate blanks as the first approach. From the results of the first approach, it is shown that the intermediate blanks could experience failures such as tearing, wrinkling, and earing by excessive thinning and thickening. To solve these failures, the modifications for the deep drawing punches are carried out, and the modified punches are applied to the same process. The simulation results for the multistage rectangular deep drawing process are compared with the thickness distributions before and after the punch shape modifications, and with the deformed shape in each intermediate blank, respectively. The results of finite element reanalysis using the modified punches show significant improvement compared with those by using the original designed punch shapes.     

盘形件增量拉深成形过程的数值模拟

增量拉深成形由于旋转的模具与坯料接触区域的不断变化而一直是数值模拟的难点,为此用Deform-3D有限元软件对为A1100铝合金的盘形件增量拉深过程进行了数值模拟.结果表明:增量拉深成形凸模的受力与传统拉深工艺相比大大降低,据此得到了凸模受力图和板料应变云图,每一步凸模受力峰值和坯料等效应变值与已有的盘形件工艺试验研究结果一致.     

The effect of nanoparticulate loading on the fabrication and characterization of multi-doped Zn-Al2O3-Cr2O3 hybrid coatings on mild steel

In this paper, an improved approach is proposed to determine the optimal profiles of two controllable process parameters (hydraulic pressure and blank holder force), which improve the forming condition and/or make better use of forming limits in hydromechanical deep drawing (HMD) process. A method based on adaptive finite element analysis coupled with fuzzy control algorithm (aFEA-FCA) was developed using LS-DYNA to determine the optimal loading profiles and thus to maximize the limiting drawing ratio (LDR). Maximum thickness reduction, maximum wrinkle height in the flange region of the sheet metal blank, and position of the nodes in the unsupported portion of the sheet metal blank between punch and die were used as criteria in the fuzzy control algorithm. Different rule-based matrices were compared by considering the maximum thinning occurred in the sheet metal blank, and thus, the most accurate matrices were determined for the control algorithm. The optimal loading profiles could be determined in a single FEA, thus reducing the computation time. The proposed approach enables determining the optimal loading profiles and also could be applied to complex parts easily. In addition, effects of initial blank diameter and coefficient of friction between the sheet-blank holder and sheet-die on the optimal loading profiles were investigated. An attainable LDR of 2.75 for AA 5754-O sheet material in hydromechanical deep drawing process was proven experimentally using the optimal loading profiles determined by adaptive FEA.     

A FE technique to improve the accuracy of drawbead models and verification with channel drawing experiments of a high-strength steel

A drawbead modeling technique is presented to improve the accuracy of finite element simulations in terms of part draw-in and thickness predictions and validated with channel drawing experiments of a high-strength low-alloy steel. The drawing characteristics of 1.5-mm thickness blanks are obtained with strip drawing tests with a round drawbead, and drawbead model parameters are computed for three bead settings. The consequences of bending deformation cycles are determined experimentally on strip draw-in and thickness values, and model limitations of equivalent drawbead elements are also assessed for test conditions in which the drawbead restraint force is lower than the sectional yield limit. The influence of omitted drawbead geometry and overestimated drawbead-exit thickness are described using an analytical model, and a closed form expression is obtained to correct draw-in model error under sectional deformation conditions. Blank thickness and equivalent strain at the drawbead exit are additional drawbead model parameters of the proposed technique. Then, drawing simulations of a variable section, open-ended channel part are performed. The drawbead design, bead settings and tool-blank interface conditions are identical to those in strip drawing tests. Computed draw-in and thickness distributions were compared with measurements on produced channels using an experimental channel draw die. It is concluded that simulation models, based on drawbead force parameters only, overestimate blank thickness at the die entry and bring about relatively high draw-in values along part border lines. The thickness distribution predicted with proposed technique shows an enhanced correlation with on-part thickness measurements, and bead penetration effects on channel border lines are also simulated acceptably.     

Hydro-rim deep-drawing processes of hardening and rate-sensitive materials

The conventional deep drawing process is limited to a certain limit drawing ratio (LDR) beyond which rupture will ensue. An asymptotic solution of the complete governing equations of this process indicates that this relatively low LDR results from the steep build-up of radial tensile stress with maximum value at the die lip. This tensile stress is significantly enhanced by interfacial friction along the die/flange and by high speed of the operating load and thus holds responsible for premature ruptures. The intention of this work is to examine the possibilities of relaxing the above limitation, aiming towards a process with an ‘unlimited drawing ratio’. The ideas which may lead to this goal are:(a) exerting an external fluid pressure on the outside rim of the blank (“Hydro-rim process”) to reduce radial stress and to decrease, in parallel, the interfacial friction,(b) increasing the blank temperature to a level at which the material is more rate sensitive, and thus less prone to early failure. The benefits of these ideas are examined via parametric analysis of the solution and with experiments in deep drawing processes.A clear outcome from the solution is that if changes in the material properties (strain hardening, strain-rate sensitivity, yield stress, etc.) can be controlled, say, by controlling the temperature and/or the operating speed, the process can reach higher drawing ratios with substantially less assisted fluid pressure.     

基于快速有限元分析的冲压件毛料展开

研究了一步法有限元分析技术,开发了冲压件毛料展开软件系统。建立三维冲压件网格和二维毛料网格之间发生塑性变形的平衡方程,求得毛料网格的修正值,得到的收敛值为冲压件的三维模型展开得到的平面形状。在刚度矩阵中引入阻尼矩阵改善矩阵的病态性,采用Newton下降法扩大算法的收敛范围,提高了非线性方程组的收敛性和算法的网格处理能力。实例表明该方法能较快较准确地求得冲压件的最优毛坯形状,在板料冲压成形领域具有良好的实用性。     

差厚激光拼焊板的拉延切边回弹特性

采用数值模拟和试验的方法,对厚度组合为1.2 mm/0.8 mm的激光拼焊板进行拉延切边工艺分析,重点就压边力大小、摩擦因数、凹模圆角等参数对回弹的影响进行研究,测量各工艺参数下拼焊板拉延切边的凸凹模圆角处的回弹角、总的回弹角和侧壁曲率,还测量出拼焊板成形中的焊缝移动和应力分布情况和分析相互联系,并与拼焊板拉延弯曲回弹进行比较。分析认为,与拉延弯曲回弹相似,压边力、摩擦因数、凹模圆角等工艺参数对拼焊板拉延切边回弹有着明显的影响,而压边力是关键因素;拼焊板拉延切边回弹和拉弯回弹都与焊缝移动有密切的关系,控制焊缝移动将有利于回弹的降低;相比之下,拼焊板拉延切边回弹比拉弯回弹要小。     

基于UG平台的冲裁模CAD系统中的图形输入

通过对DXF文件结构及内容、二维冲裁件图形几何信息及拓扑关系的分析,研究了从DXF文件中获取图形数据的方法和基于UG平台的冲裁模CAD系统的二维图形信息在计算机内的存储结构及其信息识别方法,并根据其数据结构特征,构造出了一种二维图形的数据模型,运用C语言直接对文件进行数据提取,然后按照一定的算法识别提取出的数据,构建起冲裁件的几何模型,为冲裁模工艺可行性分析、工艺设计和优化排样提供了必要的信息。     

基于有限元模拟的铜包铝线拉拔参数优化

为研究拉拔参数对铜包铝线质量的影响,运用有限元方法对金刚石涂层拉拔模具拉拔铜包铝线的过程进行了模拟仿真,研究了拉拔过程中模具的应力分布情况,分析了压缩率对铜包铝线残余应力分布均匀性的影响规律。利用正交实验法研究了拉拔参数(工作锥半角α,定径带长度L,过渡圆弧半径R,压缩率β)对铜包铝线尺寸精度和残余应力分布均匀性的影响,获得了最佳拉拔参数(α=6°,L=4.5 mm,R=3 mm,β=1.82%)和各因素对分析指标的影响规律。并在此基础上对优化方案进行了模拟,结果证明了正交实验对拉拔参数优化的有效性,对金刚石涂层拉拔模具的设计及高质量铜包铝线的拉制有重要的指导意义。     

A Study of the Progressive Working of an Electric Product Using a 3D Shape Recognition Method

This paper describes the development of the computer-aided design of an electric product using bending and piercing operations for progressive working. The system is based on knowledge-based rules. Knowledge for the system is formulated from plasticity theories, experimental results, and the empirical knowledge of field experts. The system has been written in AutoLISP in AutoCAD on a personal computer and is composed of four main modules, which are input and shape treatment, flat pattern layout, strip layout, and die layout modules. Based on knowledge-based rules, the system is designed considering several factors, such as bending radius, bending angle, effect of springback, material and thickness of a product, bending sequence, and the complexities of the blank geometry and punch profiles. It generates the 3D strip layout drawing for an electric product. The die layout module carries out die design for each process from the results of the strip layout module. Results obtained using the modules enable the designer and manufacturer of piercing and bending dies to be more efficient in this field.