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Mechanical Engineering 1-2

By Leonard Henry,2014-02-23 17:23
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Mechanical Engineering 1-2

    Chapter 1 Introduction

    1.1 Definition of Manufacturing 1.2 Machining Technology

1.1 Definition of Manufacturing

    ?What is manufacturing?

    Manufacturing is more than transformation of raw materials into value-added outputs meeting

    specifications.

?Definition[1]: Manufacturing is a series of interrelated activities and operations involving design, material

    selection, planning, production, quality assurance, management, and marketing of discrete consumer and

    durable goods.

    ?

    ?Two broad categories of present-day manufacturing activities:

    (1) Continuous-process production ( food industry and oil industry )

    (2) Discrete-product production (motor car industry, aircraft manufacture, production of domestic equipment

    and the machine tool industry)

    In this course, the focus is on discrete-product manufacturing.

    Metal cutting plays a very important role in those discrete-product manufacturing systems.

     According to a survey, about 10% of all the metal produced is turned into chips (切屑).

1.2 Machining Technology

    According to the last section, metal cutting(machining) is a very important operation in modern

    manufacturing. In the coming chapters, the following topics will be introduced:

    ?Understanding the evolution of metal cutting technology

    ?Metal cutting operations and terminology

    ?Machine tools (traditional & nor traditional machining)

    ?Automation of machining operations & systems

    ?Rapid prototyping a new way to make a part

    Chapter 2 Metal Cutting

    2.1 Brief Review Over Metal Cutting History

    2.2 Metal Cutting Related Industries

2.1 Brief Review Over Metal Cutting History

    The first cutting tool used by mankind:

    Broken bone

    Splintered flint(带锐角燧石).

    The search to find better tool materials and more efficient cutting methods started ever since. This

    search is still going on:

Before the middle of the 18th century

    ?WOOD: the main material used in engineering structure ?LATHES: the machine tools mainly used to cut these material

    ?Exceptions: boring of cannon, production of metal screws and small instrument parts.

    thIn the middle of 18 century

Why?Because the steam engine needs:

    ? Large metal cylinders and other parts

    ? Very high dimensional accuracy

    The materials for the first steam engines weregray cast iron (灰铸铁)wrought iron(熟铁)、brass

    (黄铜)、bronze(青铜)

    Those materials were not difficult to machine using hardened carbon steel tools (cutter). Cutting speed

    should be kept very low to avoid rapid failure of the cutting tools.

    It required 27 and half working days to bore and face one of Watt’s large cylinders.

    ?

    Between 1760 and 1860

    Many machine tools enterprises appeared.

    Many great engineers devoted their lives to perfecting the machine tools required for generating many shapes in metallic components.

    ?Cylindrical and flat surfaces

    ?Threads

    ?Grooves

    ?Slots and holes.

    ?

    ?By 1860

     The basic problems of how to produce the necessary shapes in the existing materials had largely been

    solved.

    ?

    ?From 1860 to the present day ?Shifting of development emphases in metal cutting

?Steel rapidly replaced wrought iron as a major construction material

    ?

    ?Towards the end of the 19th century

    Solution: cutting faster and automating the cutting processSolution: cutting faster and automating the

    cutting processSolution: cutting faster and automating the cutting process

    This continues to be the mainspring of the major developments in the metal cutting field.

2.2 Metal Cutting Related Industries

    ?The technology of metal cutting has been improved by contributions from all the branches of industry with

    an interest in machining

    ?Material industry

    ?Machine tool industry

    ?Lubricant industry

Material industry

    ? Development of cutting tool materials

     With the replacement of carbon tool steel by high-speed steel and cemented carbide, cutting speeds has

    been increased by many times. The requirement to machine steel at high speed have led to the development

    of the most advanced tool materials (such as ceramic and ultra-hard tool materials). The producers of those

    metallic materials which have to be machined played a double role.

    They had to develop new alloys to meet the increasingly severe conditions of stress, temperature and

    corrosive atmosphere imposed by the requirement of our industrial civilization. Some of these like aluminum

    and magnesium(镁)are easy to machine, but others, like high-alloy steels and nickel-based alloys, become

    more difficult to cut as their useful properties improve.

    On the other hand, metal producers have responded to the demands of production engineers for metals

    which can be cut faster. New heat treatments have been devised, and the introduction of alloys like the

    free-machining steels (易切钢)and leaded brass(铅黄铜)has made great savings in production costs.

Machine tool industry

    Machine tool manufacturers have developed machines capable of making full use of the new tool

    materials. In the mean time, automatic machines, numerically controlled(NC) machines, often with computer control

    (CNC), and transfer machines greatly increase the output per worker employed.

    Lubricant industry

    Lubricant manufacturers have developed many new coolants and lubricants to improve surface finish and permit increased rates of metal removal.

    ?Today metal-cutting is a very large segment of our industry

    ?Automobile industry

    ?Electrical engineering

    ?Railways

    ?Shipbuilding

    ?Aircraft manufacture

    ?Production of domestic equipment

    ?Machine tool industry itself

    All these industries have large machine shops with many thousands of employees engaged in machining.

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