MT-284 MANUFACTURING PROCESSES INSTRUCTOR: SHAMRAIZ AHMAD MS-Design and Manufacturing Engineering Shamraiz_88@yahoo.com ICT , Faculty of Engineering & Technology IIU, Islamabad

Today’s Lecture Introduction to the Course Discussion of Course Objectives Formation of Groups (5-members = Max) Introduction to Manufacturing Importance of Manufacturing Processes Materials in Manufacturing Classification of Manufacturing Processes Introduction to Machining Orthogonal & Oblique cutting Mechanics of chips formation Types of chips produced Chip breakers

What is Manufacturing… Technology can be defined as the application of science to provide society and its members with those things that are needed or desired Technology provides products that help our society and its members live better What do these products have in common? They are all manufactured Manufacturing is the essential factor that makes technology possible

What is Manufacturing… Manufacture is derived from two Latin words manus (hand) and factus (make); the combination means “made by hand” “Made by hand” accurately described the manual methods used when the English word “manufacture” was first coined around 1567 A.D. Most modern manufacturing is accomplished by automated and computer‑controlled machinery that is manually supervised

What is Manufacturing… Manufacturing is the application of physical and chemical processes to alter the geometry, properties, and/or appearance of a given starting material to make parts or products; manufacturing also includes assembly of multiple parts to make products Manufacturing is almost always carried out as a sequence of operations

Importance of Manufacturing Historically, the importance of manufacturing in the development of civilization is usually underestimated Throughout history, human cultures that were better at making things were more successful Making better tools meant better crafts & weapons Better crafts allowed the people to live better Better weapons allowed them to conquer other cultures in times of conflict To a significant degree, the history of civilization is the history of humans' ability to make things Manufacturing is a mean by which a nation creates material wealth In the U.S. manufacturing constitutes ~ 20% of GNP

Materials in Manufacturing Most engineering materials can be classified into one of three basic categories: Metals Ceramics Polymers 4. The mixture of basic three materials is called composite material

Metals Usually alloys, which are composed of two or more elements, at least one of which is metallic Two basic groups: Ferrous metals - based on iron, comprise  75% of metal tonnage in the world: Steel = iron‑carbon alloy with 0.02 to 2.11% C Cast iron = alloy with 2% to 4% C Nonferrous metals - all other metallic elements and their alloys: aluminum, copper, gold, magnesium, nickel, silver, tin, titanium, etc.

Ceramics A compound containing metallic (or semi-metallic) and nonmetallic elements. Typical nonmetallic elements are oxygen, nitrogen, and carbon For processing purposes, ceramics divide into: 1. Crystalline ceramics – includes: Traditional ceramics, such as clay (hydrous aluminum silicates) Modern ceramics, such as alumina (Al2O3) 2. Glasses – mostly based on silica (SiO2)

Polymers A compound formed of repeating structural units called mers, whose atoms share electrons to form very large molecules Three categories: Thermoplastic polymers - can be subjected to multiple heating and cooling cycles without altering their molecular structure Thermosetting polymers - molecules chemically transform (cure) into a rigid structure upon cooling from a heated plastic condition 3. Elastomers - exhibit significant elastic behavior

Composites A material consisting of two or more phases that are processed separately and then bonded together to achieve properties superior to its constituents A phase = a homogeneous mass of material, such as grains of identical unit cell structure in a solid metal Usual structure consists of particles or fibers of one phase mixed in a second phase Properties depend on components, physical shapes of components, and the way they are combined to form the final material

Classification of Manufacturing Processes

Manufacturing Processes Processing operation: These processes transform the work material from one state of completion to more advance and value added state. Assembly Operations: These operations involve joining of two or more components in order to create a new entity called an assembly or subassembly.

Shaping Processes 1. Solidification processes - starting material is a heated liquid or semi-fluid that solidifies to form part geometry 2. Particulate processing - starting material is a powder, and the powders are formed into desired geometry and then sintered to harden 3. Deformation processes - starting material is a ductile solid (commonly metal) that is deformed 4. Material removal processes - starting material is a solid (ductile or brittle), from which material is removed so resulting part has desired geometry

Machining and advance Machining

Machining Process Machining is material removal process which produces semi-finished or finished parts. It is essentially done to impart required accuracy and surface finish to enable the product to • fulfill its basic functional requirements • provide better or improved performance • render long service life. Mostly ductile material are machine along with semi-ductile, semi-brittle and very few brittle material. These processes are divided into various categories. Cutting – involve cutting tool process. Abrasive process. – involve grinding, honing, lapping and ultrasonic machining. Advanced machining process. – involve various energy type for material removal from work piece surface.

ORTHOGONAL CUTTING (2-D) In this model, a tool moves along the work piece at a certain velocity, (cutting speed), V, and depth of cut t . The cutting in model is known as orthogonal cutting. The tool has a rake angle, , and a relief or clearance angle. Sum of rake, relief and included angles of the tool is 90° FIGURE 8.2 Schematic illustration of a two-dimensional cutting process, or orthogonal cutting. (a) Orthogonal cutting with a well-defined shear plane, also known as the Merchant model; (b) Orthogonal cutting without a well-defined shear plane.

Cutting Terminologies Rake Angle: The angle that the front of the cutting tool is tilted either forward or backward from its perpendicular position. Relief Angle: The angle that is formed by the surface of the work piece and the bottom end of cutting tool. Shear Force; A force that attempts to cause the internal structure of a material to slide against itself. Shear plane: Shear plane is the plane of separation of work material layer in the form of chip from the parent body due to shear along that plane. Shear angle: Angle of inclination of the shear plane from the direction of cutting velocity.

MECHANICS OF OBLIQUE CUTTING (3-D) In oblique cutting, the cutting edge is at an angle I, called the inclination angle. The chip flows up the rake face of the tool at an angle, chip flow angle is measured in the plane of the tool face. The chip movement is in lateral direction.

CHIP FORMATION During Machining the material is removed in form of chip and the type of machined chips depend mainly upon : • Work material • Material and geometry of the cutting tool • Levels of cutting velocity and feed and also to some extent on depth of cut • Cutting fluid that affects temperature and friction at the chip-tool and work-tool interfaces.

CHIP FORMATION Knowledge of chip formation helps to understand the characteristics of chips and to attain favorable chip forms. During continuous machining the uncut layer of the work material just ahead of the cutting tool (edge) is subjected to almost all sided compression. Due to such compression, shear stress develops, within that compressed region.

CHIP FORMATION Whenever and wherever the value of the shear stress reaches or exceeds the shear strength of that work material, shear deformation takes place while that region moves along the tool rake surface. The succeeding portion of the chip starts undergoing compression followed by yielding and shear. . This phenomenon repeats rapidly resulting in formation and removal of chips in thin layer by layer.

CHIP FORMATION The ratio is known as cutting ratio, r. Chips are produced by shearing process. Shearing take place along the shear plane, which makes an angle ᶲ, called the shear angle, with the surface of the work piece. The thickness of the chip tc can be determined using the following formula: The ratio is known as cutting ratio, r. FIGURE 8.3 (a) Schematic illustration of the basic mechanism of chip formation in cutting. (b) Velocity diagram in the cutting zone.

TYPE OF CHIPS Type of chips Continuous chip Build-up-edge chips (BUE) Serrated chips Discontinuous chips

1. CONTINOUS CHIP A chip that does not break apart and instead continues to fold in on itself. Ductile metals tend to create continuous chips.  Formed at high cutting speed and/or high rake angle. Continuous chip produces good surface finish, but are not desirable in Computer controlled machine tools. tend to get tangled around the tool operation has to be stopped to clear away the chips

2. BUILD-UP-EDGE CHIPS (BUE) It form at the tip of tool during cutting. It consists of layers of material from the work piece that are gradually deposited on the tool. As it become larger, BUE become unstable and breaks. The upper portion of BUE is carried away on the tool side of the chip while the lower portion is deposited randomly on the machined surface. continuous chip with built-up edge

Effects of BUE Formation of BUE causes several harmful effects, such as: • It changes the rake angle at the tool tip causing increase in cutting forces and power consumption • Repeated formation and dislodgement of the BUE causes fluctuation in cutting forces and thus induces vibration which is harmful for the tool, job and the machine tool. • Surface finish gets deteriorated • May reduce tool life by accelerating tool-wear at its rake surface

BUILD-UP-EDGE Remedies Usually the BUE decreases or eliminated as (a) cutting speed V, increases (b) Depth of cut t0 decreases (c) Rake angle ∝𝑖𝑛𝑐𝑟𝑒𝑎𝑠𝑒𝑠 (d) Tip radius of tool decreases (c) An effective cutting fluid is applied

3. SERATED CHIPS Also known as segmented or non homogeneous chips Semi-continuous chips with zones of low shear and high shear strain. The chip has the appearance of saw teeth

4. DISCONTINUOUS CHIPS Contains segments that are firmly or loosely attached to each other which are separated easily into pieces. Discontinuous chips occur due to following reasons: Work-piece material is brittle. The work-piece material contain hard inclusions and impurities. The cutting speed is very low or very high The depth of cut is large or the rake angle is low. There is lack of effective cutting fluid.

USE OF CHIP BREAKERS Long continuous chips are undesirable as they tend to become entangled and interfere which machining operations. In order to avoid any such danger, a procedure of breaking the chips intermittently is performed with a chip breaker. FIGURE 8.7 (a) Schematic illustration of the action of a chip breaker. Note that the chip breaker decreases the radius of curvature of the chip. (b) Chip breaker clamped on the rake face of a cutting tool. (c) Grooves on the rake face of cutting tools, acting as chip breakers. Most cutting tools now are inserts with built-in chip-breaker features.