Grinding & Finishing Process

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Department Of Technical Education

Andhra Pradesh

Name : V.Yesu prasada Rao

Designation : Senior LecturerBranch : Mechanical Engg.

Institute : M.B.T.S Govt polytechnic,Guntur.

Year/semister : IV Semister

Subject : Manufacaturing technology-IISubject code : M402

Topic : Grinding & Finishing processes

Duration : 50 Minutes

Subtopic : Principle of metal removal by Grinding

Teaching Aids : Diagrams & ppt

Revised by : K.Chakravarty


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Recap

In the last chapter, Milling ad Gear making topics are

discussed..

Another important machining method is grinding


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On completion of this period, you would be able

to know about

Objectives

Grinding

Principle of Grinding

Purpose of Grinding

Its Advantages and Applications

Abrasives and types


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How knife is sharpened ?

How scissors are sharpened ?

How chisels are sharpened ?

How axe are sharpened ?

Do you know?


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Introduction

Quality working surface cannot be produced by the usual

machining

Good surface finish can be obtained by grinding

The art of grinding goes back many centuries over 5,000

years ago by Egyptians


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Grinding A process of removing metal in small quantities by

using an abrasive wheel

Grinding wheel may be regarded as a multi point cuttingtool

A grinding wheel is composed of abrasive grains


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After some time the grains become dull faced

The dull grain breaks away and exposing new cutting edge

to work piece due to pressure and heat created between

wheel and work piece

Working principle of Grinding


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Abrasive grains

Fig-2


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The cutting action of abrasive grains

Fig-3


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Animation of grinding process

Fig-4


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Purpose of Grinding

To bring the component to close size

To obtain required surface finish

To machine very hard surfaces


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Advantages of grinding

The surface finish obtained is superior

One of the most dimensionally accurate machining

processes Hardened components can be machined

Grinding permits to machine light and delicate parts due

to requiring little pressure


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Advantages of grinding

Surface unevenness can be eliminated

Various kinds of works can be grinded

Designed geometrical configuration can be achieved

It removes little material of order 0.25 to 0.50mm


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Disadvantages of Grinding

Work surface gets over heated

Wheel wear results duplicate parts do not have the same

dimensions

Grinding is not suitable for heavy metal removing


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Disadvantages of Grinding

For some complicated parts grinding needs attention.

Achieving true parallelism requires skill.

Achieving concentricity needs attention.


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Grinding

Fig-5


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Applications of grinding

All cast components require grinding

Welded components require grinding

Crank cases , Forged components


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Summary

So far, we have learnt about

Grinding and its uses

Working principle of grinding

Applications of grinding

Advantages and disadvantages of grinding


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Abrasives

An abrasive is a small non metallic hard material having

sharp edge and an irregular shape

The abrasive must have the following characteristics

Must be harder than material being ground

Must be strong to withstand grinding pressure

Must be heat resistant

Must be capable to break when cutting edge is dull.


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Abrasives

Fig-6


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Natural Abrasives

Sand stone is relatively soft and cannot be used for

grinding hard materials

Emery and corundum are natural Aluminum Oxides,having greater hardness and better abrasive action

Diamond is hardest natural abrasive but limited usage

due to high cost


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Sand stone or solid quartz

Is one of the natural abrasive

stones from which grind stones

are shaped

The Quartz of cutting agent is

relatively soft so that materials

harder than the Quartz can be

abraded , grounded rapidly

Fig-7


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Emery

Is a natural aluminium oxide

It contains 55 to 65 percent

alumina and remaining

consists of iron oxide and

other impurities.

Fig-8


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Corundum

It is also a natural aluminium

oxide

It contains 75to95 percent of

aluminium oxide and

remaining consists of

impurities

Fig-9


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Corundum abrasives

Fig-10


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Diamond

It is the best natural abrasive

Diamonds of less than gem quality are gashed to

produce abrasive skins for making grinding wheels to

grind cemented carbides, glass, marbles and garnets


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Diamond (abrasives)

Fig-11


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Artificial abrasives

Silicon carbide is harder but not tougher (brittle)

Used for grinding materials of low strength such as iron,

brass, bronze.

Aluminum Oxide is tough and not easily fractured.

It is used for grinding high tensile strength materials such

as steel and malleable cast iron


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Silicon carbide

It is manufactured from 56 parts of silica sand, 34

parts of powdered coke, 2 parts of salt and 12 parts

of saw dust.

It is used for cemented carbide, ceramic, grey castiron , brass.

This is manufactured under the trade names of

carborundum, crystolen, carbolon,electrolon etc.


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Silicon carbide crystal

Fig-12


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Aluminium oxide

It is manufactured by heating

mineral bauxite, a hydrated

aluminium oxide clay mixed

with ground coke and iron in

an arc-type electric furnace

Fig-13


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Aluminium oxide

It is better adopted to grinding materials of high tensile

strength, such as high speed steels , tough bronzes etc

This is manufactured under the trade names of aloxide,

aluminium, borolon ,electrite etc


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Aluminium oxide grinding wheel

Fig-14


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Comparison of SIC and AL2O3

Abrasivematerial

Year ofDiscovery

Hardness(knoop)

Properties and uses

Sic 1891 2200-2800 Used for brass, bronze,

aluminium, stainless

steel, and cast iron.

AL2O3 1893 1600-2100 Soft and tough then sic,used on steel,

malleable cast iron,

tough bronzes.


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Summary

In this class ,we have discussed about

Principle of Grinding

Purpose and Applications of Grinding

What is an abrasive

Types of abrasives and their properties


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Quiz

1.Grinding process is mainly used to

a) Finishing

b) Shouldering

c) Knurling

d) Centering


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Quiz

2.The ability of the grains to manufacture and expose newsharp edge is known as

a) Malleability

b) Tough

c) Friability

d) Abrasive buffing


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Quiz

3. Which of the following natural abrasive is harder

a) Sand stone

b) Corundum

c) Diamond

d) Emery


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4. The natural aluminum Oxide is

a) Sand stone

b) Emery

c) Corundum

d) B&C

Quiz


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Quiz

5. What is the correct sentence among the listed below

a) Grinding process cannot be used to machine hard parts

b) Grinding requires high pressure

c) We can produce duplicate parts with this process

d) Grinding is not suitable for high metal removal


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1. Explain working principle of grinding

2. Explain advantages and disadvantages of grinding

Frequently asked questions


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Frequently asked questions

3. What are the characteristics of good abrasives?

4. What are the different types of abrasives? Explainbriefly?

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Grinding & Finishing Process