CHAPTER NO.
TOPIC
PAGE NO.
TABLE OF CONTENTS
CHAPTER NO. TOPIC
Abstract
Acknowledgement
Symbols and glossary
1 Introduction
1.1 Overview
1.2 Objectives of project
1.3 Organization of the report
2 Literature review
3 Sheet metal forming
3.1 Sheet metal forming process
3.1.1 Hammering
3.1.2 Multipoint forming
3.1.3 Shot peen forming
3.1.4 Lase forming
3.1.5 Water jet forming
3.1.6 Spinning process
3.1.7 Incremental sheet forming
3.1.8 Stamping
3.1.9 Roll forming
3.1.10 Hydroforming
3.2 Sheet metal properties
3.2.1 Anisotropy
3.2.2 Strain hardening
3.2.3 Strain rate sensitivity
3.2.4 Young modulus
3.3 Forming limit diagram
3.4 Modes of deformation
4 Die face design and simulation
4.1 Methodology
4.2 Material
4.3 Die faced design
4.4 Inverse simulation
4.5 Forming simulation
4.5.1 Phases in sheet metal forming
4.5.2 Implicit and explicit solver
4.5.3 Setting up simulation
5 Results and discussion
5.1 Results of inverse simulation
CHAPTER NO. TOPIC
5.2 Forming approaches
5.2.1 Develop a SPM
5.2.2 Use forming and restrike operation
5.2.3 Use top and bottom blank holder
5.2.4 Use draw operation
5.2.5 Roll forming
5.2.6 Increase the stroke
5.3 Solution adapted
5.4 Validation of results
6 Conclusions
References
FIGURE NO. FIGURE NAME
1.1 3WH chassis main member
2.1 Springback on stress-strain diagram
2.2 Effect on springback
2.3 Wrinkling in sheet metal forming
2.4 Tearing in sheet forming
3.1 Hammering
3.2 Multipoint forming
3.3 Shot peen forming
3.4 Spinning process
3.5 Incremental sheet forming process
3.6 Stamping process
3.7 Roll forming
3.8 Sheet hydroforming
3.9 Strain rate sensitivity
3.10 Forming limit diagram
3.11 FLD indicating mechanics of sheet metal forming
3.12 Deformation modes in Formed Parts
4.1 Methodology in designing Main Member
4.2 Basic geometry features of die face
4.3 Algorithm of inverse simulation
4.4 Difference in linear and actual strain paths.
4.5 Meshed input to inverse simulation
4.6 Phases in sheet metal forming simulation
4.7 Implicit solution method
5.1 Developed blank contour with inverse simulation
5.2 Thickness distribution in part - inverse simulation
5.3 FLD – inverse simulation
5.4 Stages in forming with SPM
5.5 Tools for forming and restrike operation
5.6 Results of forming and restrike approach
5.7 Use of top and bottom blankholder
5.8 Tooling and results of preliminary simulation
5.9 Defects observed in preliminary simulation
5.10 Springback in preliminary simulation
5.11 Bending defects in component
5.12 Strain in part before and after bottoming
5.13 Optimization of blank contour
FIGURE NO. FIGURE NAME
5.14 Thickness variation in part final simulation
5.15 FLD - final simulation
5.16 Part areas earlier having defects
5.17 Directional springback final simulation
5.18 Part deviation after deviation
5.19 Strain path linearity
5.20 Comparison of scan part with simulation result - I
5.21 Comparison of scan part with simulation result - II
5.22 Comparison of scan part with simulation result - III
5.23 Image of Main Member
TABLE NO. TABLE NAME
4.1 Material parameters
4.2 Meshing parameters for Inverse simulation
4.3 Tool meshing parameters for forming simulation
4.4 Blank meshing parameters for forming simulation
Symbols and Glossary
illustration not visible in this excerpt
Sheet metal forming is one of the most widely used manufacturing processes for the fabrication of a wide range of products in many industries. The reason behind sheet metal forming gaining a lot of attention in modern technology is due to the ease with which metal may be formed into useful shapes by plastic deformation processes in which the volume and mass of the metal are conserved and metal is displaced from one location to another. For mass production, stamping is favoured to form complex parts from sheet metal due to the low cost and short cycle times.
The production of new stamping tools gets more troublesome, as the geometries get more complex and smaller tolerances on the dimensions are requested. The part ‘3WH chassis Main Member’ is very complex and some defects are inheriting due to S-rail shape of part.
Abbildung in dieser Leseprobe nicht enthalten
Fig. 1.1 3WH chassis Main Member
A disadvantage of stamping, however, is the large tooling cost associated with producing a die. If a large production run is made, the tooling cost per part becomes small and parts can be made very economically. If small runs or custom parts are desired, however, the cost of the die becomes large in comparison to the part itself. As a result of the expensive and time-consuming die-making process, stamping is rarely used for small productions and custom parts.
The primary objective of this study is to design a press die for 3W chassis Main Member to manufacture a defect free product. The project work includes study of literature, study of different die components and press operation, creating die faces for the simulation purpose, decide the optimum parameters, optimizing the die face according to the results of the simulation. The actual design of CAD model of the die, drafting for the manufacturing purpose and manufacturing assistance is the work thereafter. Finally, a validation is done for the part manufactured and the simulation results.
The main part of this project lies in simulating the different stages of the stamping process and together with a design engineer decide how the forming tools should be designed. The study aims are
i. To test the blank contour development accuracy and capability of FEA software package.
ii. To study the accuracy of springback prediction of simulation software package PAM-STAMP.
iii. To study the die compensation algorithm of FEA simulation software package PAM-STAMP.
The dissertation report is organized in six chapters. Chapter 1 is introduction. In this chapter scope of project and objectives of project are defined. Chapter 2 is literature review. A brief explanation of literature referred is presented in it. Chapter 3 is sheet metal forming, in this chapter various forming processes are discussed. Various sheet metal properties and concept of FLD are explained in this chapter.
Chapter 4 is die face design and simulation. This chapter deals with simulation methodologies used in this dissertation work. Chapter 5 is results and discussion, in which various approaches evaluated for the problem are discussed and simulation results are presented. The comparison of actual results with simulation result is also presented briefly. Chapter 6 is conclusion in which the major conclusions drawn from the study are presented.
The sheet metal forming (SMF) refers to the forming processes performed on metal sheets, strips and coils. Press forming is the term often applied to this process since the machine used for the process is called press machine. SMF process consist of stamping, forming, bending, stretching and thinning. These terms refer to various process used to convert sheet material to various useful product. [1]
The large forces of the order of few tons are associated with this forming operation. Such large forces produce large amount of stress in the part which of course are required to deform the blank to required shape. Too often, these stress changes create serious problems in maintaining forming shape and dimensional consistency during initial forming.
The use of metal forming simulation has evolved dramatically over the past decade, and industrial requirement are still pushing the boundaries. The springback prediction topic is in the forefront in the field of stamping simulation software today. However strong nonlinear behavior in sheet metal forming process makes it a problem to predict springback accurately. [2]
Springback, sidewall curl and panel twist all have their origins in unbalanced stresses in the formed part. [3] These stresses may be inherent in the product design due to non-symmetrical geometry and cut-outs, rapid changes in cross-section, or unequal flange lengths. They may be equally inherent to the forming operation due to the number of highly interactive process parameters. These include die-process lubrication, die-polishing techniques, blankholder forces, blank positioning, and broken or worn draw beads, just to name a few.
Several failure modes such as necking, rupture, wrinkling and excessive springback may occur in sheet metal forming processes. Changes are often necessary during the try-out of stamping tools. These changes may range from adjustments on die and punch designs to the selection of a new material with better formability characteristics. All these actions, however, require time and money creating the need for better initial sheet metal evaluation. [4] Simulation of the forming process is a good way to restrict the conventional trial and error method to predict and compensate for these defects which depends on the die designer’s experience and also spare the company expensive trial and error time. [5]
Every process of sheet metal forming involves elastic forming followed by permanent plastic deformation. The total forming strain can be theoretically divided into two components as elastic strain and plastic strain of which elastic component is recoverable. Since the presence of elastic properties in the metal, after the unloading phase, the elastic recovery of the part takes place. Springback phenomenon always occurs resulting in off target formed shape in sheet forming process. Although it is impossible to eliminate springback the designer can aim to minimize deviation of part. [6]
Abbildung in dieser Leseprobe nicht enthalten
Fig. 2.1 Springback on stress-strain diagram
Springback-compensation techniques usually fall into one of following three categories [7-10]:
i. Apply an additional process that changes undesirable stresses into less damaging stresses.
ii. Modify the forming process or tooling to reduce the level of stresses imparted to the part during the initial forming operation.
iii. Modify product design to resist the release of the elastic stresses.
Abbildung in dieser Leseprobe nicht enthalten
Fig. 2.2 Effect on springback
In the displacement adjustment method of springback compensation, the results of springback solutions are used. Firstly, the displacement of the blank after springback is measured from target at every positions. The obtained distance is called shape error. The amount of shape error is added to current die shape to obtain a new compensated shape. In next iteration blank is simulated with modified die and if shape error is not in the tolerance limit, the cycle is repeated. [11] This method is claimed to be effective by the authors.
During a sheet metal forming process, wrinkling can occur in critical regions of the blank subjected to compressive stresses. This may occur if one principal stress is compressive. Wrinkling may also occur in unsupported regions or regions in contact with only one tool. For both functional and visual reasons, wrinkles are usually not acceptable in a finished part especially in skin panels. [12] The development of metal sheets with higher yield strengths and lower thicknesses favours the occurrence of wrinkling, which explains that this defect becomes a major problem in sheet metal stamping industries with trend to use HSLA materials. [13]
The author investigated the wrinkling process with help of a simple conical geometry. The simulations were carried out and the results were validated with the experimental data. ABAQUS explicit software package was used for the simulation purpose. The author finds that Wrinkling is one of the phenomena which limits the depth and complexity of sheet metal components. The result of simulation is very sensitive to the simulation parameters especially the blank mesh, so the simulation must be carried out very carefully to get the exact wrinkling trend. [14]
Abbildung in dieser Leseprobe nicht enthalten
Fig. 2.3 Wrinkling in sheet metal forming
In the beginning of the forming process the distribution of tensile stresses is homogeneous all over the workpiece. However, after deformation large amount of strains might gather in small area thus reducing cross sectional area. This thinning phenomenon is called as Necking. The reason for necking is due to the fact that all real materials are imperfect, in the sense that they have small local variations in dimensions and composition, which lead to local fluctuations in stresses and strains.
If the deformation continuous after necking the sheet will eventually get tear. Through-thickness necks proceed very rapidly towards fracture. Normal process and material variations inevitably lead to necking and rupture during production runs. [15]
Abbildung in dieser Leseprobe nicht enthalten
Fig. 2.4 Tearing in sheet forming
With context to increasing awareness about ecological and environmental issues a trend is developing for lubrication free forming processes (United Nations Conference on Environment and Development, 1992). [16] This dry metal forming technology has greater risk to material necking.
This section gives a brief introduction to various sheet metal forming processes, there characteristics, general applicability and limitations.
One of the oldest processes in sheet metal forming is Hammering. This process was earlier done manually but with the technological developments it can be done on a modern CNC. Nowadays, Hammering takes advantage of the robotic technology and it uses a robotic arm that controls the movement of the tool and punches round. The metal armours were made for soldiers with hammering technique before industrial revolutions. [17]
Abbildung in dieser Leseprobe nicht enthalten
Fig. 3.1 Hammering
Reconfigurable discrete die forming also known as Multi-point forming (MPF) is a flexible manufacturing technique for the forming of three-dimensional surfaces of sheet metals. Multipoint forming is to divide the curved surface of the die into many discrete pins, using many punches instead of the traditional dies, and each punch can be controlled by individually so that the enveloping surface of punch group can be changed at any time. This way, the multi-point die (MPD), which is approximate to continuous forming surface of dies, can be used to carry out the forming of different curved surfaces in place of using many dies. This technique has a great potential for many applications with an increasing demand of special, personalized products. [18]
Abbildung in dieser Leseprobe nicht enthalten
Fig. 3.2 Multipoint forming
Shot Peen Forming is a die less process performed at room temperature, whereby small round steel shot impacts the surface of the work piece. Every piece of shot acts as a tiny peening hammer, producing elastic stretching of the upper surface and local plastic deformation that manifests itself as a residual compressive stress. The combination of elastic stretching and compressive stress generation causes the material to develop a compound, convex curvature on the peened side. The shot peen forming process is ideal for forming large panel shapes where the bend radii are reasonably large and without abrupt changes in contour so it is widely used in aircraft industry. [19]
Abbildung in dieser Leseprobe nicht enthalten
Fig. 3.3 Shot peen forming
Laser Forming Process is based on thermal stresses that are induced on the blank (clamped in a structure) by laser irradiation on the sheet metal. The thermal stresses induce plastic strains resulting in bending or buckling of the material. This process can also be used to make repairs or modifications in sheet metal components. The costs of the forming stand, the need of qualified personnel, the high energy consumption, the need of personal safety protection equipment and the need of pre-coating of the metal sheet in order to enhance the absorptive coupling are the main disadvantages of this process. Some of these problems were successfully solved by replacing the laser by plasma arc.
The Water Jet Forming is similar to the laser forming, replacing the laser by a water jet. As advantages we have: more flexibility, better surface integrity, less tooling requirements, lower equipment costs and less environmental impact. In the other hand, Water Jet Forming is less accurate, consumes more energy and takes more time than the other metal forming processes. [19]
There are two types of spinning process as conventional spinning and shear spinning. Shear spinning is quite similar to conventional spinning and the difference is in the action which is stretching in shear spinning instead of bending. In shear spinning the material flows within workpiece. This fact has a major influence on the variation of thickness along the wall which follows the sine law. [17]
Abbildung in dieser Leseprobe nicht enthalten
Fig. 3.4 Spinning process
In spinning axisymmetric parts are gradually formed over a mandrel using a rounded tool or roller. The equipment needed is similar to a lathe to clamp the blank sheet metal on the centre in a mandrel, and this set is revolved. The tool applies a localized pressure to deform the blank by axial and radial motions over the surface of the part. The tool can be manual or mechanically actuated and the tool production costs are low being suitable for producing small series because usually involves a sequence of steps. Generally, coolant is used in shear spinning and large amount of heat is generated.
[...]
[1] Waluo Adi Siswanto, Agus Dwi Anggono, Badrul Omar, Kamaruzman Jusoff, “An Alternate Method to Springback Compensation for Sheet Metal Forming”, The Scientific World Journal, 2014, Article ID 301271.
[2] P. Morgue, H. Porzner, R. Shridhar, “Best Practices and Methodology for Springback Prediction, Compensation and Assembly”, National Conference on Sheet Metal Forming, Mumbai, 2009.
[3] Peter Ulintz, “Springback in High-Strength Steel Stampings -Compensation is Not Commensurate with Experience”, Metal Forming Magazine, April 2009.
[4] Krunal K. Rathod, Mehul D. Gohil, D. R. Shah, “Stress Based Forming Limit”, International Journal of Scientific Engineering Research, 4 (2013), pp. 734-736.
[5] Filip Lindberg, “Sheet Metal Forming Simulations with FEM”, Masters Thesis, Department of Physics, Umeå University, Sweden, 2012.
[6] Stuart Keeler, “General Techniques to Minimize Springback”, Metal Forming Magazine, June 2008.
[7] Xiang An Yang, Feng Ruan, “A Die Design Method for Springback Compensation Based on Displacement Adjustment”, International Journal of Mechanical Science, 53(2011), pp. 399-406.
[8] Rahul K. Verma, A. Haldar, “Effect of Normal Anisotropy on Springback”, Journal of Materials Processing Technology, 190 (2007), pp. 300–304.
[9] Flores, P. Duchene, L. Bouffioux, C. Lelotte, T. Henrard, C. Pernin, N. Van Bael, A. He, S. Duflou, J. Habraken, A.M., “Model Identification and FE Simulations: Effect of Different Yield Loci and Hardening Laws in Sheet Forming”, International Journal of Plasticity, 23 (2007), pp. 420-449.
[10] David William Adams, “Improvements on Single Point Incremental Forming through Electrically Assisted Forming, Contact Area Prediction and Tool Development”, Ph.D. Thesis, Queen's University Kingston, Canada, November 2013.
[11] R. H. Wagoner, W. Gan, K. Mao, S Prise, E. Rasouli, “Design of Sheet Forming Dies for Springback Compensation”, 6th International ESAFORM Conference, 2003.
[12] Fuh-Kuo Chen, Yeu-Ching Liao, “Analysis of Draw-Wall Wrinkling in the Stamping of a Motorcycle Oil Tank”, Journal of Materials Processing Technology, 192–193 (2007), pp. 200–203.
[13] J.P. De Magalhaes Correia, G. Ferron, “Wrinkling of Anisotropic Metal Sheets Under Deep-Drawing: Analytical and Numerical Study”, Journal of Materials Processing Technology, 155–156 (2004), pp. 1604–1610.
[14] M. Kawka, L. Olejnik, A. Rosochowski, H. Sunaga, A. Makinouchi, “Simulation of Wrinkling in Sheet Metal Forming”, Journal of Materials Processing Technology, 109 (2001), pp. 283-289.
[15] Al Azraq Soliman Mohammed Suliman, “Numerical Simulation of Metal Sheet Plastic Deformation Processes Through Finite Element Method”, Ph.D. Thesis, Department of Materials and Production Engineering, University of Naples Federico, 2006.
[16] Frank Vollertsen, Florian Schmidt, “Dry Metal Forming: Definition, Chances and Challenges”, International Journal of Precision Engineering and Manufacturing-Green Technology, 1(2014), pp. 59-62.
[17] http://www.thelibraryofmanufacturing.com/spinning.html
