11
MANUFACTURING PROCESSESAND
AUTOMATION
R.S. ParmarB.A., B.Sc. (Mech. Engg.), M.E. Hons. (Prod. Engg.),Ph.D. (Welding), FIE (India), FIIW, MISME, MISTE,
Ex-Professor and Guest Faculty,Department of Mechnical Engineering,
Indian Institute of TechnologyNew Delhi
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Dedicated to
the student community the world overand
the organisations where I had a chance tointeract with them on this subject more
closely and actively, includingI.I.T., Delhi
N.S.I.T., DelhiN.I.T., Srinagar (Kashmir)
andBrunel University, London (U.K.)
Manufactuirng is a very vast field and it employs a wide variety of Manufacturing
Processes to produce the desired end product. It may not be possible to include, in a book, each
and every process that the industry may use. However, innumerable attempts have been made
the world over to pass on the available knowledge to the practising engineers and engineering
students through books on Workshop Technology, Production Engineering, Manufacturing
Processes and the like. This book is another such attempt wherein efforts have been made to
describe all major manufacturing processes which include the conventional very well established
processes and those which have comparatibly recently appeared on the scene.
It is sincerely wished that the book may prove to be useful to the engineering students
both at degree and diploma levels as also to the practising engineers and the engineering
faculty.
New Delhi,
15-10-2008 R.S. Parmar
PREFACE TO THE FIRST EDITION
CONTENTS
Preface v
1. INTRODUCTION 1—71.0 Fabrication Methods 11.1 Casting 11.2 Metal Working (Forming/Forging) 31.3 Welding 51.4 Machining 61.5 Special Manufacturing Processes 7
2. PHYSICAL PROPERTIES AND FABRICATION CHARACTERISTICS OF ENGINEERING MATERIALS 8—18
2.1 Physical Properties of Engineering Materials 82.2 Fabrication Characteristics of Engineering Materials 16
3. ENGINEERING MATERIALS (PROPERTIES AND USES) 19—423.1 Ferrous Metallic Materials 193.2 Non-ferrous Metallic Materials 303.3 Refractory Metals 403.4 Precious Metals 413.5 Other Metals 413.6 Non-metallic Materials 42
4. HEAT TREATMENT OF METALS 43—624.0 Introduction 434.1 Heat Treatment of Steels 434.2 Heat Treatment Processes 444.3 Heat Treatments of Non-ferrous Metals 59
5. CASTING PROCESSES 63—1155.0 Introduction 635.1 Classification of Casting Processes 635.2 Casting Defects 110
6. METAL WORKING PROCESSES 116—2476.1 Hot and Cold Working Processes 1176.2 Rolling Processes 1216.3 Continuous Rolling Processes 1276.4 Discrete Production Processes (Intermittent Rolling) 1326.5 Forging of Metals 1386.6 Forging Processes 1446.7 Intermittent Production Forging Process 1446.8 Intermittent cum Continuous Production Forging Process 169
7. WELDING AND ALLIED PROCESSES 248—3777.1 Classification 2487.2 Arc Welding Processes 2487.3 Resistance Welding Processes 2847.4 Solid-State Welding Processes 3017.5 Radiant Energy Welding Processes 3197.6 Thermit Welding 3337.7 Gas Welding 3357.8 Allied Processes 3467.9 Weld Defects 360
8. MACHINING PROCESSES 378—5228.1 Classification of Machine Tools 3788.2 Conventional Machine Tools 3798.3 Cutting Tool Materials 4948.4 Unconventional Machining Process 502
9. AUTOMATION IN MANUFACTURING 523—5449.0 General Introduction 5239.1 Automation in Manufacturing Processes 5239.2 Types of Production 5249.3 Types of Automation 5259.4 Fixed Automation 5269.5 Programmable Automation 5289.6 Group Technology 5389.7 Flexible Manufacturing Systems (FMS) 5409.8 CAD, CAM and CIM 5419.9 Automated Factories 544
Annexure—I Hardness Conversion Table 545
Question Bank 547
Bibliography 562
Index 564
1INTRODUCTION
Present day world civilization is based on the use of innumerable components made fromvaried materials using one or more of the hundreds of manufacturing processes. The requiredproducts may include anything from a small needle or a pin, produced at the rate of thousandof pieces per minute, to a propeller shaft for a large ship, which may require many months inits production.
Every component cannot be made from the same material nor a single manufacturingprocess can be used to produce all types of components. For example, an ordinary sewing needleis not made of aluminium nor an aeroplane is made of cast iron. Similarly, all materials cannotbe shaped by the same process, e.g., mild steel is not cast nor cast iron is normally beaten toform a product. Thus, it is evident that the selection of a material and the process to shape itinto the desired component is imperative so that a product of desired quality, to be useful forthe intended service, is produced at a reasonable cost. To achieve that aim an engineer isrequired to have comprehensive knowledge about the Manufacturing Processes and the En-gineering Properties of the Materials so as to make an optimal selection of a process (or a set ofprocesses/fabrication methods) to give the desired shape and properties to the selected materialsat the lowest cost.
1.0 FABRICATION METHODS In industry most of the materials are fabricated into the desired shapes mainly by one of
the four methods, viz., casting, forming or metal working, welding, and machining. However,apart from these four families of fabrication processes there are some special methods also, forexample, powder metallurgy.
The selection of a particular method for fabricating a given component depends upon manyfactors which may include shape and size of the component, precision required, cost, materialand its availability. Sometimes it is possible to use one specific process to achieve the desiredobjective. However, more often it is possible to have a choice between the processes availablefor making the end product. In the latter case economy plays the decisive role in making thefinal selection. Brief description of these five categories of fabrication processes and their specialfields of applications are given in the following sections.
1.1 CASTING Casting is perhaps the oldest known method of giving shapes to metals and alloys. When
found suitable, it is the shortest route from the ore to the end product and usually the mosteconomical. Other advantages inherent in the metal casting process include its high adaptabilityto the requirements of mass production. Thus, a large number of a given casting may be producedvery rapidly, e.g., the castings used in the automotive industry. Also, extremely large and heavymetal objects may be cast when they would be difficult or economically impossible to produceotherwise, for example, large pump housings, valves, and hydroelectric plant parts weighing up
to 200 tons, etc. Though processes and techniques have been developed to cast almost all metalsand their alloys but still certain specific materials have very superior casting properties, forexample, grey cast iron.
The castability of a material depends upon a number of factors, viz., fluidity, solidificationshrinkage, porosity, stress, and segregation characteristics. The castability index of a materialis high if it has high fluidity, low shrinkage, low affinity for absorbing gases, low stresses, anduniform strength. These characteristics are found to occur mainly in pure metals and eutecticswhich have, at least theoretically, a definite melting point. However, pure metals usually havelow strength, therefore mainly alloys are cast for most of the actual applications. Thus, thechoice obviously falls on eutectics and near eutectic alloys*.
Castings can be grouped into two main categories, viz., ingots and shaped castings; of thetotal tonnage cast nearly 75% are in the form of ingots. However, our main concern in the presentdiscussion is shaped castings.
* Eutectic Alloys : An alloy with a specific composition having a definite but lower melting point than theconstituent metals and which on cooling from the molten state precipitates into two solid phasessimultaneously. In iron-carbon equilibrium diagram grey cast iron with 4.3% carbon is a eutectic alloy,having a m.p. of 1130 °C, as shown in Fig. 1.1.
Fig. 1.1 Iron-carbon equilibrium diagram.
2 MANUFACTURING PROCESSES AND AUTOMATION
Castings may weigh from a few grams to many tons. Perhaps, the heaviest object ever madeby casting was the bronze statue of Colossus of Rhodes (Greece) which is included in the sevenwonders of the world. However, leaving aside the wonder the present day heavy castings ofteninclude the machine structures, flywheels, base plates for turbines, etc.
Castings are, as a rule, good in compression loading but have poor elongation and low tensilestrength. The materials which are considered exceptionally good for casting include, apart fromcast iron, the alloys of copper, aluminium, zinc, nickel and magnesium. Some of the typicalcastings include the following:
Pulleys, flywheels, engine blocks, machine tool beds, gear blanks, cast iron pipes, turbineblades, mill rolls, church bells, automotive pistons, and piston rings, intricate parts for moviecameras, armaments, statues, etc.
1.2 METAL WORKING (Forming/Forging)After casting followed the metal working processes in which the metals and their alloys are
given desired shapes by the application of pressure, either by sudden impact as in the case ofhammer blows or by slow kneading action as in presses. Mechanical working of a metal belowits recrystallization temperature is called "Cold Working" and that accomplished above thistemperature is known as "Hot Working". Both hot and cold working (or forming) are practisedextensively in the industry.
Most of the materials can be formed or forged but, as a rule, the materials which are bestsuited to casting have poor forming qualities. In general the materials best suited for formingare those which have a long mushy range during solidification, for example, solid solutionalloys*.
Many alloy properties are affected by the nature of solid solutions, e.g., strength andhardness increase with the amount of solute present while ductility and electrical conductivityare lowered.
Forming quality of a material is usually referred to as formability for sheet material andforgeability for thicker sections and is associated with ductility of the material. The processeswhich can be included in forming are the sheet forming methods like bending, deep drawing,extrusion, HERF (high energy rate forming), spinning, roll bending, stretch forming; whereasforging may include upsetting, cold heading, rotary swaging, drop forging, etc.
Formability testing is commonly done by Erichsen cupping test in which the sheet materialis stretched till cracking. The forgeability on the other hand is the ability of a metal to bedeformed under forging conditions without cracking. One of the best forgeability tests is theupsetting test, expressed as the ratio of maximum upset diameter obtainable to initial bardiameter. For cold heading this ratio is usually referred to as heading limit.
Forgeability Index, F = Dm
Di
where, Di = initial bar diameter,
Dm = maximum diameter that can be obtained by upsetting without cracking. 1.2.1 Materials for Forging
The materials are usually found to occur in three types of unit cells, viz., BCC (body-centredcubic), FCC (face-centred cubic) and HCP (hexagonal close packed), as shown in Fig. 1.2 alongwith some of the well known metals under these three categories of cell structures.
*Solid Solution Alloy : When metals combine to form alloys by completely disolving in each other andcontinue to remain so even in the solid state they are called solid solution alloys, for example, Monel metalis a solid solution alloy of copper and nickel.
INTRODUCTION 3
Manufacturing Processes andAutomation
Publisher : KHANNAPUBLISHERS ISBN : 9788174092366 Author : Dr. R.S. Parmar
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