A Textbook of Manufacturing Technology

This document contains the content.

This document contains the preface.

In general, manufacturing is the economic term for making goods and services available to satisfy human wants. In fact, manufacturing involves a series of related activities and operations
such as :
(i) Product design and development;
(ii) Material selection;
(iii) Process planning;
(iv) Inventory control;
(v) Quality assurance;
(vi) Marketing, etc.
In view of the above activities and operations, manufacturing is no longer a simple operation
but has become a system where a number of sub-systems interact in a dynamic manner.

Casting is perhaps the oldest method of manufacturing and invariably the first step in the sequence of manufacturing a product. In this process (casting) the raw material is melted, heated to the desired temperature and poured into the mould cavity where it takes the desired shape. After the molten metal solidifies in the mould cavity the product is taken out to get the casting.
 Casting is preferred because of the following reasons :
(i) It is cheap and direct way of producing a shape with desired mechanical properties.
(ii) Metals and alloys, e.g., highly creep resistant alloys cannot be worked mechanically and can only be cast.
(iii) Casting is best suited when different properties are required in different sections of product. These are made by incorporating pre-fabricated inserts in a casting.
(iv) Cost associated in giving details by casting process is minimum whereas cost in mechanical working would be too high to produce them.
(v) Casting is preferred when components are desired in low quantities

The materials which are covered under the scope of material science are available either from nature or industry. However, these materials cannot be used in raw form (whatever the source may be) for useful purposes. They have to be shaped and formed into articles through difference manufacturing processes. Besides there are some processes which improve material properties. In some processes the materials are changed into their primary forms for some selected parts. In some cases the materials are suitably finished for commercial uses. In other cases, neither surface finish nor the dimensions are satisfactory for the final product, and further work is necessary. However, the selection of the best process for a given product requires a knowledge of all possible production methods.

Powder metallurgy is defined as the art of making objects by the heat treatment of compressed metallic powders. ‘‘Powder metallurgy’’ includes the blending and mixing of powders, pressing or compacting powder into an appropriate shape, sintering the pressed-powder compact, and perhaps final sizing or finishing of the product to meet specified dimensional tolerances. The process is applicable to a single metal powder, to mixtures of metals and non-metals. The operation of pressing may be carried out at ordinary or elevated temperatures depending upon the composition and properties desired in the product.

A plastic, in broadest sense, is defined as any non-metallic material that can be moulded to shape. The most common definition for plastics is that they are natural or synthetic resins, or their compounds, which can be moulded, extended, cast or used as films or coatings. Most of the plastics are of organic nature composed of hydrogen, oxygen, carbon and nitrogen.

Ceramic materials are defined as those containing phases that are compounds of metallic and non-metallic elements. The science of ceramics, nearly as old as mankind, is the processing of earthly materials by heat. The crude cooking utensils of early man were the first application of the materials now used in jet engines and atomic reactors. All the early ceramic products were made from clay because the ware could be easily formed. It was then dried and fired to develop the permanent structure. Because the other ceramic materials lacking plasticity also have desirable properties, other methods of forming and processing have been developed. Other forming methods used for ceramic materials are injection moulding, sintering and hot pressing. In other cases the formed materials are allowed to harden on the job by the addition of water, as in case of cements.

It is method of joining metals by applications of heat, without the use of solder or any other metal or alloy having a lower melting point than the metals being joined.
                                                                        Or
Welding is defined as ‘‘a localised coalescence of metals, wherein coalescence is obtained by heating to suitable temperature, with or without the applications of pressure and with or without the use of filler metal’’. The filler metal has a melting point approximately the same as the base metal.

The metal cutting (machining, a generic term, refers to all material removal processes) refers to only those processes where material removal is affected by the relative motion between tool made of harder material and the workpiece. The tool would be single-point cutting tool as used in operations like turning or shaping, or a multi-point tool as used in milling or drilling operation

Machining is the process of cold working the metals into different shapes by using different types of machine tools. This process is mainly used to bring the metal objects produced by means of different fabrication techniques to final dimensions.

SCREW THREADS
A screw thread is helical ridge formed on uniform section round the curved surface. The shape of the normal section of the thread depends upon the shape of the tool which produces its groove. A screw is a male threaded piece generally cylindrical in form, but sometimes, conical (or tapered), used in most cases as a temporary fastening ; less frequently used as a means of transmitting motion or power.

A gear is a wheel provided with teeth which mesh with the teeth on another wheel, or on to a rack, so as to give a positive transmission of motion from one component to another.Gears constitute the most commonly used device for power transmission or for changing power-speed ratios in a power system. They also afford a convenient way of changing the direction of motion. A number of devices such as differentials, transmission gear boxes, planetary drives etc., used in many construction machines employ gears as basic
components :

Gears are made from both metals as well as non-metals. ‘‘Metals’’ normally used for making gears include cast iron, cast steel, structural steel, gun metal, brass, etc. The ‘‘non-metals’’ commonly used for gear manufacture include synthetic plastic, fibres and laminated wood.

With rapid industrialisation, the gears are called upon to yield noise free operation,ensure high load carrying capacity at a constant velocity ratio. The wear and fatigue strength of the gear tooth are the factors that govern its durability and reliability, and depend to a large extent on the manufacturing technology employed.

In conventional machining processes the ability of the cutting tool is utilised to stress the material beyond the yield point to start the material removal process. This requires that the cutting tool material be harder than the workpiece material. The advent of harder materials for aerospace applications have made the removal process by conventional methods very difficult as well as time consuming since the material removal rate reduces with an increase in hardness of the work material. Hence machining processes which utilise other methods such as electro-chemical processes are termed as Unconventional or Non-traditional machining methods.

The accuracy of machine tools, which cut metal by removing chips or swarfs, is tested by means of the following tests :
1. Geometric tests
2. Practical tests.

Newer machine tools have been built to absorb newer machining technologies to cope with newer and tougher materials. New technologies include Ultrasonic Machining (USM), Electro-Chemical Machining (ECM), Laser Beam Machining (LBM) etc.

Besides this the advancement in electronics and applications of computer in the machine tools have brought in a significant and revolutionary change in the machine tool control concept. This has given birth to an entirely new generation of machine tools. “Numerically Controlled (NC) machine tools” are highly flexible and are economical for producing a single or a large number of parts. Numerical Control, NC can be defined simply as control by numbers.

A machine tool having a dedicated computer to help prepare the program and control some or all of the operations of the machine tool is called Computer Numerical Control (CNC) machine tool.

Automatic machines. “Automatic machines” are those machines in which both the workpiece handling and the metal cutting operations are performed automatically. In these machines, operations right from feeding of the stock to clamping, machining and even inspection of the workpiece are carried out automatically.

Jigs and fixtures are production tools used to accurately manufacture duplicate and interchangeable parts. They are specially designed so that a large number of components can be machined or assembled identically, and to ensure interchangeability of components. They eliminate the necessity of a special set up for each individual part.
— Jigs and fixtures are precision tools.
— They are expensive to produce because they are made to fine limits from materials with good resistance to wear.
— They must be properly stored or isolated to prevent accidental damage, and they must be numbered for identification for future us

Metrology, in literary sense, means the pure science of measurements. But for engineering purposes, it is restricted to measurements of length and angles and other quantities which are expressed in linear or angular terms.

Metrology is mainly concerned with :
(i) Establishing the units of measurements, reproducing these units in the form of standards and ensuring the uniformity of measurements :
(ii) Developing methods of measurement :
(iii) Analysing the accuracy of methods of measurement, researching into the causes of measuring errors and eliminating these.

In the broader sense, metrology is not limited to length measurement but is also concerned with the industrial inspection and its various techniques. Inspection is carried out with gauges and the metrologist is intimately concerned with the design, manufacturing and testing of gauges of all types.

ECONOMICS OF MACHINING
The primary concern of the manufacturing engineer is to produce the objects at the most economical cost. In order to achieve this he should be able to analyse the machining process for all possible costs, so that he would be able to optimise the process to get the minimum possible costs satisfying all the requirements.

Now-a-days the manufacturing is facing a formidable challenge in the national and international market place. The need for manufacturing high quality, low cost products is demanding major changes in the manufacturing function resulting in facility modernisation, high level of automation and reduction in inventory and lead times. The designer must understand and accommodate these changes to ensure that a design can be efficiently produced.

COMPUTER INTEGRATED MANUFACTURING
The Computer Integrated Manufacturing (CIM) is the best context in which industrial controls and sensors can be understood. This concept, in some quarters, was formerly called hierarchical control. This concept is applicable in both ‘‘manufacturing’’ and the ‘‘process’’ industries. The structure is very similar, although different terms are used at certain levels, as discussed below.

PRODUCT ANALYSIS
The product which is to be manufactured is first analysed primarily from a technological point of view to determine the processes required.
Assembly charts :

For visualising the material flow and the relationship of parts, schematic and graphic models are commonly developed.

The “assembly chart” can be useful in making preliminary plans regarding subassemblies, where purchased parts are used in the assembly sequence, and appropriate general methods of manufacture. The assembly chart is often called a “Goznito chart” for the words, “goes into”.
Operation process chart :

Presuming that the product is already engineered, we have complete drawings and specifications of the parts, their dimensions and tolerances, and materials to be used. The engineering drawings specify locations, sizes, and tolerances for holes to be drilled and surfaces to be finished for each part.

INTRODUCTION

The manufacturing activities necessary to accomplish the production of an end product must be processed or arranged in an orderly, worktable sequence. This analysis and planning is the bridge between design engineering and product manufacturing. It encompasses every phase of industrial and manufacturing engineering by establishing a manufacturing plan which is economical and supplies a quality product.

Process analysis and operation planning are required for all manufactured products regardless of their size, material make up, or type of construction.

GENERAL ASPECTS
*GROUP TECHNOLOGY (GT) is an approach in which similar parts are identified and grouped together in order to take advantage of their similarities in design and production. The group technology aims at high productivity at a low cost on short run production

Introduction
Inspection may be defined as the function by which the control of quality is maintained. It is one of the most important functions of production control. Just as design and production form the main stream of any production line, inspection acts as the control valve which regulates the flow of production along the main stream according to design and specifications. In an engineering factory, the design department sets the standards of accuracy which production must comply with and inspection department must enforce. Similarly in a chemical factory the technical department sets the standards for production to comply with and quality control section keeps the check. Not only are the standards of the end products to be maintained but in order to make this possible and easy to detect, inspection exercises quality control at different stages in the process. To do this the inspection must know the critical points at which a stricter quality control is called for. The responsibility for detection of faulty work and returning it for correction
or scrapping lies with the inspection department.

MAINTENANCE MANAGEMENT
Types of maintenance :
It is very difficult to classify the types of maintenance as it is an integral part of smooth functioning of a plant as a whole. Fig. 25.1 shows types of maintenance.

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