On the optimal die curvature in deep drawing processes

The paper presents an attempt to increase the limit drawing ratio of deep drawing processes by searching an optimal die curvature, which minimizes the drawing load. The search done here for an optimal die curvature is based on experimental observations and followed by a detailed upper bound analysis. The analysis takes into account the non-steady character of the process (from a 2D circular plane blank into a 3D axisymmetric cup). The plastic flow along the die curvature is expressed in a toroidal coordinate system which seemingly describes more naturally a smooth velocity field along the real toroidal profile of the die. The outcome provides more closely the relationship between the energy dissipation rate and the die curvature so that a preferred die curvature is obtainable by energy minimization.Circular sheet blanks, made from aluminum and copper, were drawn through dies with different radii of curvature (with at least five repetitions at each radius) to capture the features of the optimal dies whenever exists.The main result is that under certain circumstances an optimal die curvature does exist. It depends largely on the drawing ratio and the blank/die interfacial friction, m, but appears quite insensitive to the initial thickness of the blanks. The optimal die curvature is pronounced in the cases where the frictional resistance is relatively low, otherwise it is indistinctable and remains practically undeterminable by designers.     

Development of a hydroforming setup for deep drawing of square cups with variable blank holding force technique

Sheet hydroforming is a process that uses fluid pressure for deformation of a blank into a die cavity of desired shape. This process has high potential to manufacture complex auto body and other sheet metal parts. Successful production of parts using hydroforming mainly depends on design aspects of tooling as well as control of important process parameters such as closing force or blank holding force (BHF) and variation of fluid pressure with time. An experimental setup has been designed and developed for hydroforming of square cups from thin sheet materials. Square cups have been deep drawn using constant and variable BHF techniques. A methodology has been established to determine the variable BHF path for successful hydroforming of the cups with the assistance of programmable logic controller and data acquisition system. Finite element (FE) simulations have also been carried out to predict formability with both of these techniques. It has been found that it is possible to achieve better formability in terms of minimum corner radius and thinning in the case of variable BHF technique than in the case of constant BHF technique (constant force during forming and calibration). The results of FE analysis have been found to be in good agreement with experimental data.     

Die design in the complex shape drawing of cross roller guide to improve the dimensional accuracy

A drawing process allows for a smooth and clean surface, metal savings, low cost tooling, and closely controlled dimensions to be obtained in long products that have constant cross-sections. Recently, rods having irregular sections more complex than a rectangle or ellipse are necessary to produce mechanical parts. A cross roller guide is one of the parts produced by complex cold-shaped drawing. A cross roller guide has a linear bearing system that rolls along a guide way. A cross roller guide is one of the most important components in terms of equipment because the quality of the linear rail influences the precision linear motion. Therefore, the final dimensional accuracy of the linear rail in cold-shaped drawing is very important. The aim of this study is the optimization of the optimal die angles to improve the dimensional accuracy and straightness of the final product using design of experiment, FE-simulation, and the Taguchi method. Based on the analytical results, experiments for real industrial products have also been implemented to verify the results. From the experimental results, it was possible to improve the dimensional accuracy and straightness of final product.     

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.     

Development of an automated progressive design system with multiple processes (piercing, bending, and deep drawing) for manufacturing products

This paper describes the research work involved in developing an automated progressive design system with multiple processes such as piercing, bending, and deep drawing for manufacturing products. This approach to make a progressive, flexible working system is based on knowledge-based rules. The knowledge required for this system is formulated from plasticity theories, experimental results, and the empirical knowledge of field experts. The system consists of three main modules: shape treatment, strip layout, and die layout modules. The system is founded on knowledge-based rules and is designed in consideration of several factors, such as the material and thickness of a product, the piercing, bending and deep drawing sequence, and the complexities of blank geometry and punch profiles. The system then generates the strip layout drawing for an automobile product. The die layout module carries out the die design for each process from the results of the strip layout module. The results obtained using the modules enable the designers of manufacturing products with multiple processes to be more efficient in this field.     

方形坯料拉延筒形件压边力系数优化设计

在综合分析了方形坯料拉延筒形件拉延工艺基本特征及力学特性基础上,分析了采用方形坯料深拉延筒形件时金属流动规律,提出了一种优化压边力系数的方法,优化计算结果与实验结果相吻合,为方形坯料深拉延工艺设计及模具设计提供了重要参数.     

Four-ball assessment of deep drawing oils

A comparative study has been made of four-ball friction and wear test results and the cup-drawing performance of a number of commercial fatty drawing oils and mineral oils. A linear correlation was observed between the maximum punch load required to draw a flat-bottomed cup from a lubricated mild steel blank of fixed diameter and the four-ball friction coefficient μ₁₄₂₅ determined at 1425 r.p.m. within a pre-transition load range. Both quantities showed dependence on lubricant density and viscosity, confirming an (elasto)-hydrodynamic mechanism contributed in both the cupdrawing and the 1425 r.p.m. four-ball tests, under conditions that were insufficient to promote chemical action between the lubricant and the sliding metal surfaces. A theoretical equation between the cup wall stress and μ₁₄₂₅ has been derived, of similar form to the empirical equation expressing the observed correlation. Drawing efficiencies of the oils calculated from values of μ₁₄₂₅ were within 1–2% of those estimated from cup-drawing loads. Information on the extreme pressure properties of the oils was obtained from standard four-ball wear-load tests. It is concluded that, overall, fourball friction and wear test data suffice to rate drawing oils for both simple and severe forming of steel sheet, provided that the test conditions allow similar lubrication mechanisms to operate as in the relevant drawing operation.     

Full film lubrication of deep drawing

An analytical model for full film lubrication of deep drawing is developed, combining the elastic–plastic membrane finite element code of deep drawing together with full film lubrication theory. In full film lubrication, the surfaces are not in contact, and the gap in between includes two types of lubrication: the thick film lubrication regime and the thin film lubrication regime. The film thickness and the strain distribution of full film lubrication are predicted here. The theoretical results show excellent agreement with the experiment data.     

On a novel press system with six links for precision deep drawing

The objective of this paper is to propose a novel press system with six links for precision deep drawing, and verify its feasibility. First, the system is presented and its advantages are discussed. Then, the kinematic analysis of the system is obtained by examining the geometry of the design. Moreover, kinematic dimensions of the variable coupling are found by using optimization method. Furthermore, the proposed approach is illustrated by a design example, its solid model for the proposed design is established, and then kinematic simulation is performed by ADAMS software. Finally, a prototype and an experimental setup are established, and the experiment is conducted. The results show that the proposed new mechanism is feasible and of reasonable accuracy. In addition, it has the advantages of easy manufacture, lower cost, higher precision, and easy adjustability.     

Study on the crushing and hydroforming processes of tubes in a trapezoid-sectional die

A study on the bulging processes of tubes in a trapezoid-sectional die has been carried out through finite-element (FE) analysis. A FE model of the single-step hydroforming process and several FE models of crushing combined with subsequent hydroforming processes in a trapezoid-sectional die with different die closing seams are proposed. The simulations are performed using the FE code LS-DYNA. For the single-step hydroforming process, the effects of loading paths on the formability of the trapezoid-sectional part are investigated. In the case of the crushing combined with subsequent hydroforming processes, the effects of die closing seams, tube diameters, and preforming loading paths on the forming process and the final parts are analyzed. A comparison between the parts formed through single-step hydroforming process and through crushing combined with subsequent hydroforming processes is performed. Finally, an experiment of tube hydroforming in a trapezoid-sectional die is carried out on the hydroforming machine developed by Shanghai Jiaotong University. The simulation results show good agreement with the experimental results.     

影响电位滴定法测定石油产品溴值准确度的原因及提高方法

电位滴定法测定石油产品的溴值,以死停终点法指示反应终点,在实际操作过程中经常会出现重复性差、准确度低的情况,本文主要从空白实验、滴定参数、终点判定、样品量等方面进行了讨论.以期找出影响准确度的原因,并提出解决办法.     

小盖拉深胀形镦压模具设计

小盖拉深胀形镦压模具是用来生产GHT6472盘式制动器轮廓组件上轴承的防尘盖零件．该零件虽然结构不复杂，但尺寸精度要求较高．给成形带来困难，为解决此问题，通过对零件的工艺分析、计算，零件拉深成形的特点分析，成形工艺的确定，胀形镦压的条件验算．进行了合理的模具结构设计。     

Simulation of dissimilar tailor-welded tubular hydroforming processes using EAS-based solid finite elements

Developments in the numerical simulation of the hydroforming process of tubular metallic components, tailor-welded before forming, are presented. Both technologies, tailor-welded joining operations and hydroforming processes, are well known in industry, although most commonly separately used. Tailor-welded joining operations are usually encountered in plain sheets, subsequently formed by stamping. Tube hydroforming processing, on the other hand, is frequently associated with parts consisting of uniform thickness, material properties, and dimensions. The present analysis focuses on the influence of process parameters, such as the position of the weld-line and initial thickness values, in the innovative process of combining tailor-welded tubes (with distinct thickness values) and hydroforming. Particular attention is posed on the relation of imposed axial displacement vs. imposed hydraulic pressure into the tube, forming parameters that are not known a-priori in the manufacturing of a new part. Another point of practical interest is the numerical simulation of the weld-line movement, after forming is complete. The finite element method is directly employed in the numerical simulation by means of innovative solid elements suited for incompressibility applications, and included by the authors into the commercial program ABAQUS as user-elements. The obtained results can then lead to a better understanding, along with design tools, for the process of hydroforming of tailor-welded tubular parts, accounting for dissimilar thickness of the basic components.     

Effects of forming media on hydrodynamic deep drawing

Apart from the punch and the die, a pressurized fluid (water or oil) is used in hydroforming. The presence of such pressure media is the main difference between hydroforming and conventional deep drawing. No comprehensive study has yet been conducted on the effect of forming media on the formation of cylindrical cups via hydrodynamic deep drawing assisted by radial pressure. This study investigated the formation of such cups through Finite element (FE) simulation and experiments. First, the process was modeled numerically using ABAQUS FE software. After simulation, copper and St14 sheets were formed with water and oil as the forming media. The effect of these forming media on thickness distribution and maximum punch force was investigated. By examining the thickness distribution curve of the hydroformed cup, a close agreement was found between experimental and numerical results. Using oil as the forming media reduced thinning at the corner radius zone of the punch and increased the maximum punch force. Changing the forming media does not significantly influence the maximum thickening at the cup wall region.

     

Analysis of plate drawing processes by the upper bound method using theoretical work-hardening materials

The present paper analyses the plate drawing processes carried out in converging dies using theoretical work-hardening materials. The analysis has been carried out by the upper bound method (UBM), modelling the plastic deformation zone by triangular rigid zones (TRZ) and considering that the processes occur under plane strain and partial friction conditions. Explicit expressions for the calculation of the necessary power and the non-dimensional total energy to carry out the process using theoretical work-hardening materials have been established. The results have been compared with those obtained using rigid-perfectly plastic materials. In spite of the fact that the energy involved in the process using a work-hardening material is higher than when a rigid-perfectly plastic material is used, the number of possible sets of variables (die geometries, cross-sectional area reductions and partial friction coefficients) increases, since the stability limit of the process increases as well.     

ANSYS/LS-DYNA在热镀锌板拉深成形中的应用

根据连续介质力学及有限元理论,运用动力显式算法建立有限元模型,利用ANSYS/LS-DYNA软件模拟镀锌薄板的拉深过程,分别采用不同的界面结合力进行拉深过程模拟,确定板料和镀锌层的界面结合力,并对钢板和镀锌层的应力结果进行比较分析,所得结果可为生产实际提供指导.     

The influence of lubrication in rectangular deep drawing

Rectangular deep drawing is a widely used process in the electrical, automobile, and aeronautical industries, in military engineering, etc. Despite its popularity little information is available about the effect of lubrication on limiting drawing ratio, drawing force, and work done. In view of this, rectangular deep drawing experiments were conducted using mild steel, aluminium, and tin sheets in a 100 t double action hydraulic press. The maximum drawing force, the work done during drawing, and the limiting drawing ratio for a number of commercial lubricants were measured, and are reported in this paper. The effect of anodising has also been studied in the case of aluminium sheets. In the case of mild steel sheets the effect of shot blasting the blank has also been reported.     

Hydrodynamic deep drawing process assisted by radial pressure with inward flowing liquid

A radial pressure can reduce drawing force and increase drawing ratio in hydrodynamic deep drawing. However, conventional hydrodynamic deep drawing cannot attain a radial pressure higher than the pressure in the die cavity. In this research, a modified method, named hydrodynamic deep drawing assisted by radial pressure with inward flowing liquid, was proposed and investigated using both primarily experimental and numerical simulation analysis. A radial pressure higher than the pressure in the die cavity was realized by means of the inward flowing of the liquid during this process. After preliminary experimental validation, FEM was used to explore the forming process. The results from the simulation were compared with those from the experiment. The effects of the radial pressure on the wall thickness distribution, punch force, and compressive stress in the blank flange were studied with assistance of numerical simulation. The process window for radial pressures versus drawing ratios was established in 2Al2O alloy experimentally and cups with drawing ratio of 2.85 were successfully formed.     

The effect of cutting conditions on dimensional accuracy

The effects of speed, feed and depth of cut on the dimensional accuracy of aluminium bars turned on a lathe were studied. The optimum values of the dimensional accuracy with respect to speed, feed and depth of cut were determined.