Material Forming Processes E-Book

Bouchaib Radi

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 293

Veröffentlichungsjahr: 2016

Beschreibung

Manufacturing industries strive to improve the quality and reliability of their products, while simultaneously reducing production costs. To do this, modernized work tools must be produced; this will enable a reduction in the duration of the product development cycle, optimization of product development procedures, and ultimately improvement in the productivity of design and manufacturing phases.

Numerical simulations of forming processes are used to this end, and in this book various methods and models for forming processes (including stamping, hydroforming and additive manufacturing) are presented.  The theoretical and numerical advances of these processes involving large deformation mechanics on the basis of large transformations are explored, in addition to the various techniques for optimization and calculation of reliability.

The advances and techniques within this book will be of interest to professional engineers in the automotive, aerospace, defence and other industries, as well as graduates and undergraduates in these fields.

Leseprobe

Table of Contents

Cover

Title

Copyright

Preface

1 Forming Processes

1.1. Introduction

1.2. Different processes

1.3. Hot and cold forming

1.4. Experimental characterization

1.5. Forming criteria

2 Contact and Large Deformation Mechanics

2.1. Introduction

2.2. Large transformation kinematics

2.3. Transformation gradient

2.4. Strain measurements

2.5. Constitutive relations

2.6. Incremental behavioral problem

2.7. Definition of the P.V.W. in major transformations

2.8. Contact kinematics

3 Stamping

3.1. Introduction

3.2. Forming limit curve

3.3. Stamping modeling: incremental problem

3.4. Modeling tools

3.5. Stamping numerical processing

3.6. Numerical simulations

4 Hydroforming

4.1. Introduction

4.2. Hydroforming

4.3. Plastic instabilities in hydroforming

4.4. Forming limit curve

4.5. Material characterization for hydroforming

4.6. Analytical modeling of a inflation test

4.7. Numerical simulation

4.8. Mechanical characteristic of tube behavior

5 Additive Manufacturing

5.1. Introduction

5.2. RP and stratoconception

5.3. Additive manufacturing definitions

5.4. Principle

5.5. Additive manufacturing in the IT-based development process

6 Optimization and Reliability in Forming

6.1. Introduction

6.2. Different approaches to optimization process

6.3. Characterization of forming processes by objective functions

6.4. Deterministic and probabilistic optimization of a T-shaped tube

6.5. Deterministic and optimization-based reliability of a tube with two expansion regions

6.6. Optimization-based reliability of circular sheet metal hydroforming

6.7. Deterministic and robust optimization of a square plate

6.8. Optimization of thin sheet metal

7 Application of Metamodels to Hydroforming

7.1. Introduction

7.2. Sources of uncertainty in forming

7.3. Failure criteria

7.4. Evaluation strategy of the probability of failure

7.5. Critical strains probabilistic characterization

7.6. Necking and wrinkling probabilistic study

7.7. Effects of the correlations on the probability of failure

8 Parameters Identification in Metal Forming

8.1. Introduction

8.2. Identification methods

8.3. Welded tube hydroforming

Appendices

Appendix 1: Optimization in Mechanics

A1.1. Introduction

A1.2. Classification of structural optimization problems

Appendix 2: Reliability in Mechanics

A2.1. Introduction

A2.2. Structural reliability

A2.3. Modeling a structural reliability problem

Appendix 3: Metamodels

A3.1. Introduction

A3.2. Definition

A3.3. Main metamodels

Bibliography

Index

End User License Agreement

List of Tables

4 Hydroforming

Table 4.1.

Elastic characteristics and density of the DC04 under study

Table 4.2.

Geometrical characteristics of sheet metal (SM) and die

6 Optimization and Reliability in Forming

Table 6.1.

Hardening model coefficients

Table 6.2.

Probabilistic characteristics of the load parametesr

Table 6.3.

Statistical indicators

Table 6.4.

Influence of the starting point on the reliabilistic optimum

Table 6.5.

Probabilistic characteristics of the load parameters

Table 6.6.

Probabilistic characteristics of the optimization parameters

Table 6.7.

Statistic indicators

Table 6.8.

Deterministic optimal variables

Table 6.9.

Reliability optimal variables

Table 6.10.

Probabilistic characteristics of the optimization variables

Table 6.11.

Probabilistic characteristics of the uncertain parameters

Table 6.12.

Deterministic optimal variables

Table 6.13.

Deterministic optimal variables

Table 6.14.

Characteristic of the convergence

7 Application of Metamodels to Hydroforming

Table 7.1.

Tube and die dimensions

Table 7.2.

Probabilistic characteristics of the hardening parameters

Table 7.3.

Material parameters for DC04 steel

Table 7.4.

Probabilistic characteristics of the thickness and the friction coefficient

Table 7.5.

Probabilistic characteristics of the loading parameters

Table 7.6.

Variabilities associated with the FLC

Table 7.7.

Weibull distribution parameters

Table 7.8.

Student’s distribution parameters

Table 7.9.

Gamma distribution parameters

Table 7.10.

Gumbel distribution parameters

Table 7.11.

Probabilistic characteristics of the first limit state function

Table 7.12.

Probability of failure and associated reliability index

Table 7.13.

Probability of failure and reliability index

Table 7.14.

Effect of a correlation between the strains on the probability of failure of necking

Table 7.15.

Effect of a correlation between the strains on the probability of failures in wrinkling

8 Parameters Identification in Metal Forming

Table 8.1.

Used material properties

Table 8.2.

Swift parameters of the various evolutions of the hardening

Table 8.3.

Pressure levels for various cavities

Guide

Cover

Table of Contents

Begin Reading

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Mathematical and Mechanical Engineering Set

coordinated by Abdelkhalak El Hami

Volume 1

Material Forming Processes

Simulation, Drawing, Hydroforming and Additive Manufacturing

Bouchaib Radi

Abdelkhalak El Hami

First published 2016 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.

Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:

ISTE Ltd27-37 St George’s RoadLondon SW19 4EUUK

www.iste.co.uk

John Wiley & Sons, Inc.111 River StreetHoboken, NJ 07030USA

www.wiley.com

© ISTE Ltd 2016

The rights of Bouchaib Radi and Abdelkhalak El Hami to be identified as the authors of this work have been asserted by them in accordance with the Copyright, Designs and Patents Act 1988.

Library of Congress Control Number: 2016945874

British Library Cataloguing-in-Publication Data

A CIP record for this book is available from the British Library

ISBN 978-1-84821-947-2

Preface

In the current economical climate, the automotive, aviation, aerospace, defense, etc., industries have established the following priority: improve the quality and the reliability of products while reducing production costs. To achieve this goal, the industry strives to modernize its work tools in order to minimize the duration of design cycles and improve manufacturing processes.

The field of metal forming (stamping, thin sheet metal deep-drawing, tubes and plates hydroforming, forging of solid materials, cutting, composite draping, foundry, etc.) is the subject of much research and of different courses destined to engineers and academics (as part of masters and doctoral schools). This interest is due to the increasing demands from different industrial sectors for graduates with experience in these disciplines.

In different industries (automotive, aeronautics, etc.), metal forming constitutes, in the course of the entire manufacturing processes, a decisive phase in the overall quality and cost of the final product. A vehicle is first judged on its design.

Currently, numerical simulations of forming processes are being used almost systematically in the development of industrial products. The studies, based on the modeling of physical phenomena involved in the manufacturing or the utilization of industrial products or infrastructures, answer the growing need to:

– decrease the duration of the product development cycle;

– optimize product development procedures;

– improve the productivity in design and manufacturing phases;

– improve product quality and process reliability;

– optimize testing and reducing its costs;

– simulate non-reproducible complex phenomena by means of trials.

The use of digital educational tools maintains a strong relationship with the training and research strategy (http://mediamef.insa-rouen.fr/).

This book presents the various methods for forming used in the industry: stamping, hydroforming and additive manufacturing and proposes a modeling of the latter by providing the theoretical and numerical advances for each process involving large deformation mechanics on the basis of large transformations. It presents the various techniques relative to the optimization and calculation of the reliability of different processes.

Acknowledgments

We wish to thank everyone who has directly or indirectly contributed to this book, in particular the engineering students and the PhD students of the INSA Rouen that we worked with in recent years.

Bouchaïb RADIAbdelkhalak EL HAMIJune 2016

1Forming Processes

1.1. Introduction

The field of metal forming comprises a wide range of semifinished and finished products. Each requirement of the acquisition criteria is defined, justifying the use of various forming processes. A number of recurring characteristics can be observed in the desired shapes. The latter should respond with the best dimensional precision possible and the most suitable surface condition for its usage. The final product must meet material health conditions for usage properties with the least possible continuity defects. There is, therefore, an interest in what the most appropriate macro- and microstructures are.

1.2. Different processes

Metallic materials offer a rich range of independent or combined forming methods. Among the large families, the following processes are identified:

– smelting;

– machining;

– powder metallurgy;

– hot or cold plastic strain forming.

Each of these processes present characteristics of optimal quality, variable depending on the material being used, on the dimensions and on the desired accuracy, on the metallurgical quality, on the final cost and on the quantity. The choice is oriented according to specific criteria:

– the abilities of the material in relation to the different processes (particular attention should be given to the difference between a foundry alloy and alloys deemed “wrought”) regarding the form and the dimension of the product;

– the defined metallurgical health (limitation of defects such as cracks, porosities and chemical segregations);

– the usage properties of the product in the mechanical field;

– the desired surface condition (in terms of cleanliness, roughness, of residual stresses, etc.).

1.2.1. Smelting

The metal or the alloy is melted inside a crucible and then it is poured into a specific mold inside which it will solidify when cooled down. Complex forms can be obtained often linked with a minimum of induced thickness. Large variations of the latter involve consequences on the development of the final properties. Casting workpieces are produced from simple and often fairly cheap traditional techniques. This results in obtaining monobloc parts whose quality and mechanical properties are lower than those of wrought products (products having undergone hot hammering in order to obtain the desired properties often in a compulsory direction). There are numerous and very varied molding techniques depending on shape, quantities and on the quality requirements:

– The mold is made up of sand and inside it a cavity can be found that will represent the resulting piece. The first operation consists of building a pattern generating the shape of the desired casting by integrating the machining allowances and the useful drafts. The pattern represents the mold cavity left in the sand when the mold is closed. The mold is opened to extract the pattern therefrom and closed to the molten metal. When solidification is achieved after slow cooling, the mold is broken in order to retrieve the final product. One casting is thus obtained per mold.

– The mold is in metal and thus is reusable. The cooling proves to be much faster than the sand casting process. The pattern is obtained by machining the mass and with respect to the hollow parts, they can be achieved with eventually destructible cores.

– Die-casting integrates a metal mold but the filling of the pattern is ensured by means of a piston that pushes the liquid at high speed in a short period of time (a few 1/10 of a second). A slight overpressure can be maintained in the mold, which has the effect of properly feeding the pattern, while avoiding the design of a hot-top to perform this function. The mechanization of the process is total. On the other hand, the tools undergo very significant repeated efforts, which reduces their life expectancy (20,000–50,000 parts depending on the nature of the cast alloy).

– Centrifugal casting concerns all so-called revolution parts. The fundamental difference lies at the level of the introduction of liquid material, which is carried out along an axis around which the mold revolves. The centrifugal force promotes uniform filling. The structural composition is finer and full.

Figure 1.1.Gravity die casting accompanied by the obtained casting

1.2.2. Machining

Machining is a material removal operation making use of a cutting tool. This process allows for highly accurate complex forms and a controlled surface finishing. Different processes are identified and classified into two large categories. The first involves chip formation, which mainly includes turning, milling, grinding and drilling. The second does not involve chip formation and designates flow-turning, electrical discharge machining, shearing and waterjet cutting. From a structural point of view, machining only alters a superficial layer of the material, which therefore causes a hardening of the surface. As a result, we can observe the creation of a residual sublayer stress field, causing significant heating in the superficial layer. Ease of machining is linked to the physical contact of the tool-workpiece pair during machining. It depends not only on the mechanical behavior of the material (resistance, consolidation and malleability of the machined material) but also on its thermal behavior. A low resistance is recommended, which means a sufficient malleability, however this facilitates chip breaking. It can also be noted that a good thermal conductivity most often facilitates the machining. As a result of adding cold or hot particles, the cutting conditions can be improved (controlled inclusions of low melting point lead or even sulfides, etc.). These latter facilitate the fragmentation of the chip:

– Chip formation:

Machining takes place following optimized cutting conditions, which consider the geometry of the cutting tool, the cutting fluid and the dimension of the non-deformed chip. It is formed following primary shearing of the metal when making contact with the cutting edge of the tool and following a secondary shear when in contact with the external edge of the tool. This effort zone undergoes superficial strain hardening and heating. In addition, the chip is subjected to the same efforts coupled to the tool on its external edge. Futhermore, the cutting speed

V

c

plays a paramount role and is thus expressed:

with Vc expressed in m/min, rotational speed in rpm and tool diameter for milling.

– The machined surface:

It is defined by a heated and hard-tempered underlying superficial area. The microstructure can therefore be modified (constituents or phase change) or even undergo local strain hardening by cold working. Often, there remains a significant local residual stress field. Moreover, microcracks can be observed.

– The chip:

When the material is fragile, it quickly becomes fragmented into lemels (for example some smeltings). In the event that it is ductile and slightly consolidates. However, when this consolidation occurs as a result of the hardening phenomenon, it easily fragments. On the other hand, a few obstacles to chip formation may surge notably due to heating and pressure. A galling phenomenon can be observed between tool and chip forming a build-up edge. It is defined by lemel stuck to the tool. Thus, the maximal temperature is variable according to the cutting speed and the hardness of the tool. The stress and strain field induced by the cutting enforces an increase in the temperature of the metal.

As a result to the cutting conditions, the tool is subjected to the following observations:

– adhesive wear;

– abrasive wear;

– damage due to atomic diffusion or to oxidation;

– damage due to thermal fatigue;

– irreversible deformation (creeping).

1.2.3. Powder metallurgy

This process consists of obtaining a final piece adapted to special needs by means of compression and sintering. From the agglomeration of very fine powders, a compacted object is produced with a form very close to that desired. Then, we control the cohesion of the powder with a thermal sintering process. Different applications can be identified, used in specific categories of workpieces:

– in cases where the production of controlled fine-porosity metal products with complicated forms is sought after;

– in pieces composed of refractory metals presenting a good resistance to heat;

– in alloys that cannot be obtained by smelting, notably tungsten or some magnetic materials such as soft magnetic metal ferrite composites. As an example, we can therefore cite cermets composed of “coarse” ceramics particles distributed in a metal matrix. In the field of cutting tools, we come accross cobalt matrix-based indexable lathe tools;

– in friction materials of which brake pads or clutch discs are made of;

– in electrical contact materials of which we can cite as an example silver-or copper-based contacts.

This technique is often used when some materials are hardly fusible or seldom deformable by plastic deformation. We then obtain products with improved microstructure, finer and more homogeneous than that observed by smelting as some nickel-based superalloys. It is also popular as an alternative with other forming processes to reduce production costs. As a matter of fact, metal losses and machining operations can be significantly optimized because it allows engineers to manufacture complexly shaped pieces with precise dimensions using a single method. The latter is a very common method in the development of multiple products in mineral materials such as oxides, carbides and refractory products. It mainly enables the control of the porosity of the developed products. Two categories can be contrasted:

– weak microporous parts;

– massive parts with almost no porosity providing good mechanical properties as well as good ductility.

The process is defined as follows:

– Powder production:

The shape and the grain size can vary between 1 and 1,000

µm

and are obtained by means of mechanical techniques involving the grinding of hard metals such as molybdenum (Mo) and chromium (Cr). The production can originate from a liquid phase by atomization of aluminum or copper. In addition, the process of atomization is defined by a drying operation that consists of transforming a liquid pulverized in the form of droplets in reaction with a hot gas into powder. It is operational in all processing industries of the material, particularly in the agrifood and the chemistry sectors. Its design is dependent on the properties of the product to be obtained and the characteristics of the drying gas as well as on the specifications of the powder.

– Powder compaction:

This operation is compulsory to reduce the porosity. The latter is measured by the ratio where

V

a

is the apparent volume of the powder and

V

r

its actual material volume. The compaction is given by the following relation and the expansion is . Powder forming is achieved by cold, hot and isostatic compression.

– Powder sintering:

This step consists of forming while respecting the continuity of the solid. It is a process activated by solid-state atomic diffusion at a temperature ranging from 60 to 80% of that of fusion for a variable period according to the material under study. This energy is activated between the contact surfaces of the grains of powder and the shape of the pores is deformed until it is completely reduced.

As a whole, the process must be highly controlled due to the permanent risk of oxidation.

1.3. Hot and cold forming

Liquid casting, hot open-die forging and cold sheet metal forming have been documented as early as 5,000 B.C. These are often relatively simple methods based on the use of molds, a hammering tool and a base. During the first centuries of the Christian era, wire drawing by means of perforated plates and primitive machining using chisels were discovered. During the Renaissance, rolling dominated the industry because of its high productivity and its great versatility. Over the last century, the sector has been in full expansion, with an acceleration in the development of processes since 1940. As a matter of fact, the Germans invented cold forging (extrusion) of steels for the manufacture of weapons. Since 1945, machining has improved considerably and other processes such as electrical discharge machining or waterjet cutting have been invented. We would like to point out the discovery of hot melt spinning of copper alloys by the Frenchman Séjournet.

Forming ability is intrinsically linked to structural evolution, whether under the effect of thermomechanical processing or not, according to its three-dimensional plastic behavior. The latter is subjected to deformation speeds and imposed temperatures. It can be observed that compression efforts associated with the reduction of gradients of strain rate facilitate deformation without necking nor rupture. The literature discusses three major phenomena that have to be avoided:

– ductility generalized to fracture in mismatch with the targeted deformation amplitude. Deformation involving several steps separated by annealing is thus advocated;

– incompatible necking ductility with respect to localized deformation;

– sensitivity to strain rate inconsistent with the field of practiced speeds. Under optimal forming conditions, it is possible to take action on this field by decreasing the average rate or by lubricating the solicited surfaces with the aim to reduce the rate gradients between the edges and the center of the desired shape. Among these methods, we cite the following:

- forming by plastic deformation: