1. Introduction Assoc.Prof.Dr. Ahmet Zafer Şenalp Mechanical Engineering Department Gebze Technical University ME 612 Metal Forming and Theory of Plasticity

In general, it is possible to evaluate metal forming operations as part of the manufacturing processes. Manufacturing processes in general can be classified as follows: 1) Primary Shaping, such as Casting (sand and die), melt extrusion, metal powder pressing. No initial shape -----> well defined final shape. 2) Metal Forming: Rolling, Extrusion, Cold and Hot Forging, Bending, Deep Drawing, Rod and Tube Drawing,.... Material is formed by Plastic Deformation. 3) Metal Cutting: Sawing, Turning, Milling, Broaching, where a new shape is made by removing of material. 4) Metal Treatment: Heat Treating, Anodizing, Surface Hardening. No change in shape, but changes in properties or appearance. 5) Joining: a) Metallurgical: Welding, Brazing, Diffusion Bonding. b) Mechanical: Riveting, Shrink fitting, Mechanical Assembly (bolts, screws,...). Dr. Ahmet Zafer Şenalp ME 612 2Mechanical Engineering Department, GTU 1. Introduction

In metal forming operations shape change is obtained by plastic deformation. It is preferred as there is no material removal and improvement of material properties is achieved. Dr. Ahmet Zafer Şenalp ME 612 3Mechanical Engineering Department, GTU 1. Introduction

In Metal Forming a simple geometry is transformed into a complex one. The tools (dies) "store" the desired geometry and impart pressure on the material through tool/material interface. The physical phenomena describing a forming operation are difficult to formulate for large number of process variables, e.g., for design of a forming operation the followings should be considered: 1) The kinematics: metal flow, i.e. shape, velocities, strain, strain rate. 2) The limits of formability, i.e. under what condition the material fails internally or on the surface. 3) The forces and stresses required, so, the capacity and type of presses can be determined, etc. Dr. Ahmet Zafer Şenalp ME 612 4Mechanical Engineering Department, GTU 1. Introduction 1.1. Variables, Classification and Description of Metal Forming Processes

Metal forming operations can be performed cold or hot. Hot forming operations are the ones where the metal is heated above the recrystallization temperature. If classified according to dimensions of the material; Bulk (volume) or sheet metal forming If classified according to forces applied: Compresive forces (Ex: forging, extrusion,... ) Tensile forces (Ex: Wire drawing, deep drawing,strech forming... ) Moment in cross secttinal area (Ex: folding, strech folding,... ) Shear forces (Ex: Piercing,…) Dr. Ahmet Zafer Şenalp ME 612 5Mechanical Engineering Department, GTU 1. Introduction 1.1. Variables, Classification and Description of Metal Forming Processes

A Metal forming system is composed of 1) Work piece {Material, Geometry} 2) Tooling (dies) {Material, Geometry} 3) Interface condition, i.e. frictional characteristics of the two surfaces 4) Mechanics of plastic deformation 5) Equipment used 6) Plant environment 7) Characteristics of the final product {Geometry, Mechanical Properties, Metallurgical Properties)} Dr. Ahmet Zafer Şenalp ME 612 6Mechanical Engineering Department, GTU 1. Introduction 1.2. Metal Forming as a System

Figure 1.1. Factors effecting workpiece in transferring to final product Metal flow determines the characteristics of the final product and formation of defects (e.g. cracks, folds, wrinkles). Dr. Ahmet Zafer Şenalp ME 612 7Mechanical Engineering Department, GTU 1. Introduction 1.2. Metal Forming as a System

1) Almost no scrap material. 2) Obtaining final product in short time. 3) Obtaining better mechanical and metallurgical properties. (strength, toughness, grain size,... ) Dr. Ahmet Zafer Şenalp ME 612 8Mechanical Engineering Department, GTU 1. Introduction 1.3. Advantages of Metal Forming As a Manufacturing Process

1.4.1 Structure of Metals: Metals and alloys are crystalline in solid state. It is not yet possible to relate the behavior of individual atoms in and around its lattice to Macroscopic properties of the metal. Unit Cell: (Lattice) the specific arrangement of atoms in a crystal. The crystal of the metal is formed by the 3-D repetition of unit cells. Crystal (Grain): is the 3D array of Unit Cells. Dr. Ahmet Zafer Şenalp ME 612 9Mechanical Engineering Department, GTU 1. Introduction 1.4. Structure of Metals, Deformation Mechanism of Crystals

Most metal's structure fall within 3 groups. BCC, Body-Centered Cubic, such as: V, Cr, Fe, Fe FCC, Face-Centered Cubic, such as: Cu, Al, Fe HCP, Hexagonal Closed-Packed, such as: Zn, Ti, Mg Figure 1.2. (a) BCC, (b) FCC,(c) HCP. Dr. Ahmet Zafer Şenalp ME Mechanical Engineering Department, GTU 1. Introduction 1.4. Structure of Metals, Deformation Mechanism of Crystals

Crystal structures of some metals: Dr. Ahmet Zafer Şenalp ME Mechanical Engineering Department, GTU 1. Introduction 1.4. Structure of Metals, Deformation Mechanism of Crystals BCCFCCHCP ChromeAluminiumBeryllium IronDemirMagnesium MolybdenumCopperZinc TungstenGoldCobalt VanadiumLeadTitanyum TantalumNickelZirconium TitaniumSilver ZirconiumCobalt

1.4.2 Deformation Mechanism of Crystals: 1) The deformation of metals occurs by sliding of blocks of crystal over one another along definite crystallographic planes, called slip planes. Slip planes are the most populated planes and directions in the crystal. Sliding of blocks of material is produced by shear stresses in the slip plane. If the crystal was perfect, the shearing stress required to initiate plastic deformation would be ~ 100 times greater than realistic values; so ---> dislocations {edge, screw} Dr. Ahmet Zafer Şenalp ME Mechanical Engineering Department, GTU 1. Introduction 1.4. Structure of Metals, Deformation Mechanism of Crystals

Figure 1.3. The deformation of metals by sliding of blocks Dr. Ahmet Zafer Şenalp ME Mechanical Engineering Department, GTU 1. Introduction 1.4. Structure of Metals, Deformation Mechanism of Crystals

2) Deformation by Twinning {Mechanical (Shock Loading (large )) and Thermal} The second mechanism of deformation in metals. It results when a portion of the crystal takes up an orientation which has mirror symmetry to the untwined lattice. Dr. Ahmet Zafer Şenalp ME Mechanical Engineering Department, GTU 1. Introduction 1.4. Structure of Metals, Deformation Mechanism of Crystals