Resistance Welding

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29 Νοε 2013 (πριν από 3 χρόνια και 8 μήνες)

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1

Ábhar staidéir do Inne
altóireacht na hArdeteiste


Ceist 1 Roinn A & B + 4 cheist eile


Ceist 1.

Roinn A: Meascán de ceisteanna







Creimneach
/
Corrosive


Aire
/
Caution

In
-
lasta
/
Flammable

Creimneach
/
Corrosive

No Naked Flames







Trasraitheoir


Dordánaí LDR Déóid Toilleoir


Transistor


Buzzer





Diode

Capacitor








Transistor LED



Solenoid



Friteoir inathraithe


Teirmeastar Friteoir


Trasraitheoir





Variable resistor

Therrmistor

Resistor



3/2 valve Shuttle valve Single acting cylinder Double acting cylinder






BCC

FCC BCC


Close Packed Hexagonal








Ionic bond
Metallic bond


Covalent bond






Throttle


Metallic bond
:

The met
allic bond consists of pos
itive

atoms surrounded by a sea

or cloud of electrons. These free electrons are
easily


excited resulting in the

material being very conductive of heat and electricity.


Other properties
include

ductility, malleability, high melting point and insoluble i
n water.

Ionic bond:

In an
ionic bond
, the atoms of the


material are held together by
an

electrostatic attraction between positively and

negatively charged ions.
(An ion is
an atom that has


either gained or lost electrons).

Covalent bond:

In a
covalent
bond
, atoms bond


together by sharing electrons.
The bonds between the atoms in an ethylene

molecule are covalent bonds.











2






Vacancy Interstitial defect Substitutional defect



Narcotic

effects

of toxic materials
:

Nausea, hallucinations, f
ainting

Irritant

effects

of toxic materials
: Itch, rash, redness, swelling

on skin

Systemic

effects

of toxic materials
:

Lung problems, heart problems, liver etc






Compression Tension Bending Torsion


Shear




Tréithe ábhair


Properties:

Teanntacht


Ductility :

The ability of a material to change shape (deform) usually by stretching along its
length.
i.e to be stretched into a wire

Láidreachas


Strength:

The ability of a material to stand up to f
orces being applied without it bending,
breaking, shattering or deforming in any way

Leaisteachas


Elasticity:

The ability of a material to absorb force and flex in different directions, returning to its
original position

Plaisteachas


Plasticity:

The ab
ility of a material to be change in shape permanently.

Intuargaint


Malleability
: The ability of a material to be reshaped in all directions without cracking

Righneas


Toughness:

A characteristic of a material that does not break or shatter when receivin
g a blow or
under a sudden shock.

Cruas


Hardness:

The ability of a material to resist scratching, wear and tear and indentation.

Seoltacht


Conductivity
: The ability of a material to conduct electricity

Tensile Strength:

An tualach

(load) is mó

atá ábh
ar ábalta
iompar

roimh a briseadh




Creimeadh


Corrosion

Corrosion

Corrosion is affected by pollutants dissolved in rain, atmospheric pollution,

climate, moisture, wind and
proximity to the sea shore

Tionchar ar
ráta
chreim
ithe



Factors affecting corro
sion

rates
: Am (time), taiseach (Moisture) leibhéil
ocsaigine (O2 )
, Dearadh (design),
co
-
dhéanamh (alloying elements etc),
pollution levels, wind,
other metals in
contact,

Coasint íobarthach
-

Sacrificial protection
:

miotal

atá níos
airde

ar an tábla lei
ct
rea
-
ceimiceach

a chuir i
n aice
leis an miotal atá le co
saint


(

a technique for preventing corrosion of a metal item by placing a piece of metal
that is electrochemically more active near to and in electrical contact with the item to be protected

(i.e p
ropellor
bád)
)








Forces






3



Tomhais


Measurement

















Wir
e gauge

Plug gauge Drill gauge


Feeler gauge


Go/No go gauge

Sine bar



Táirgeadh


Man
ufacturing











Casting Drop forging


Vacuum forming

Compression m
oulding












Metal pressing

Compression moulding


Injection/Compression



Factóir Sábha
ilteachta
-

Factor of Safety
:
i.e. 3: Tógfaidh an t
-
ábhar 3 oiread an tualach atá ceadaithe

(The amount of load, above the normal operating rating, that a device can handle without failure.)

Snámhaíocht


Creep
:
Laigeacht thar ama i miotal
.

(S
low plastic d
eformation of metals
)
-

elevator cable

Strustuirse


Fatigue
:
Laigeacht mar gheall ar ualach a chuir & a bhaint d’ábhar thar imeacht ama

(
The
weakening or failure of a material resulting from prolonged stress)


airplane landing gear

Sleamhnú


Slip :








Machining

Generating

produces a machined surface by the combined movement of the machine slideways, e.g. taper turning, facing, and parallel
turning.


Forming

produces a surface which is determined by the tool profile. E.g. parting off tool, or spe
cially formed tool.




Ore dressing:


Bealaigh chun miotal a bhgaint as amh
-
ábhar
.
(
methods of seperating

metals from ores)

Concentration =
Ag baint an miotal as an amhiarann
:
optical, gravity, magnetic, flotation

Maighnéadach (Magnetic

ore dressing
)

=
Chun

iarann a bhaint as amh
-
iarann

(Separate iron from iron ore)



ore dressing
)

=

Chun alúmanam a bhaint as
Beauxite (To separate
Snámhú (Flotation

aluminium from beauxite
(aluminium ore)
. Déantar ‘froth’ tré ceimicí a chuir leis & snámhann an alúmanam go
d
tí an barr agus titeann an
salachar go híochtar


FCC
: Densely packed= = tárlaíonn sleamhnú
go héasca (slips easily) = ductile

BCC
: Loosely packed = less ductile = br
ittle

















4








Hydromettalurgy
:
The treatment of metal or the separation of metal from
ores and ore concentrates by liquid processes, such as leaching, extraction,
and precipitation.



Pyrometallurgy
:
using high tem
peratures, as in roasting, smelting, etc., for
the extraction of metals from their ores



Táthú



Welding

Aceitlín tuaslagtha
-

Dissolv
ed acet
ylene

= Nuair atá an gháis suaite
faoi bhrú mór
isteach in ábhar ar nós
spuinse san umar/tanc
(When the acetylene
is dissolved
under high pressure
in a porous/sponge
-
like material in the tank)

Flashback Arrestor

=

Safety device in the torch to stop flame retreating back up the hose





Amorphous structure
:
Has no definite
atomic

pattern

-

glass


Crystalline structure
:

Has a definite
atomic

pattern



iron


Téarmaíocht

RAM

= Random Access Memory

ROM

=
Read Only Memeory


CPU

= Central Processing Unit

ISP

= Internet Service Provider

LAN

=
Local Area Network


IC

=
Integrated Circuit

LCD

= Liquid Crystal Disply


DOS

= Disk O
peraqting System



Scriúsnáitheanna




Square thread

Acme thread ISO thread


Buttress thread


Hi
-
pressure use leadscrew deil


General thread Quick release vice



Comadóirí & a aireagá
in /
Inventors and their contribution to technology


Gustaf Dahlen:

In 1902 he developed acetylene gas and demonstrated gas welding for the first time.

Willhelm Roentgen:

In 1895 he produced X
-
rays in a high voltage discharge tube. The results have signi
ficant importance in engineering and medicine.

Henery Maudslay:

In 1780 he used a revolving cutting tool to mill a slot in a lock. He mounted the tool on an arbor and set it up between cent
ers on a lathe.
This was the beginning of the process now called
milling.

Germain Sommeiller
:


In 1887 he invented the compressed air drill. He was also chief designer for Mont Censis tunnel in the Alps from Italy to Fr
ance.

Jack Kilby
:


In 1958, he co
-
invented the integrated circuit where complete sets

of electronic

components could be embedded, and connected, to create a complex circuit, i.e. The microchip.

Chester Carlson
:


In 1938, he duplicated the first, blurred photocopy image.

Theodore Maiman
:


Laser development.

Charles Parsons:


Steam Turbine.

Eli Whitney:


Mass Production and

Interchangeability



Dendrites

The most important thing to remember when dealing with the solidification of metals is that it is not sudden throughout the e
ntire liquid.
As molten pure metal soidifies, crystals start to form and these
crystals grow by the addition of atoms to form a

dendrite
which as can be
seen be is a crystal skelton with a backbone from which arms grow in other directions, fixed by the regularity of the unit ce
ll.The growth
of a tree , starting from its trunk and gro
wing branches and twigs, is often used as an analogy to describe dendritic growth.


Use:


5

The dendrites grow outwards until contact is made with neighbouring growths and this contact surface becomes the boundary of
the
crystal or grain.


6




Tástáil teanntach
ta



Tensile Test:



















Eolas ón tástáil

-

Information from
test =



Neart teanntachta

Tensile strength



Teorann leaisteach

Elastic limit



Pointe teipe

Yield point



Upper/lower yield point


Strus :
Stress
=

Ualach/ Achar trasghearrtha

Load
/
Cross sectional area


Stra
idhn :
Strain

=

Síneadh/bun
-
fhad

Extension
/
Original Length


Young’s Modulus

= Strus / Straidhn


= Stress /Strain



Saotharphíosa cothrom


Saotharphíoisa ciorclach


Flat specimen


Ro
und specimen

Proof Stress
:

A theoretical vlaue for specimens that have an undefined yield point.

Neart teanntachta

:
Tensile Strength
:
An tualac
h is mó i kN

roimh a briseadh. An pointe is airde ar an graf.
Maximum load in
kN

applied to a load before it beaks.
The highest point on the graph.

Sample:

Find the
0.1%

Proof stress for a sample of gauge length
56
mm.
Note:

graph can be either a
stress/
strain
graph

or
load/extension

graph.




For a load/extension graph

0.1% of 56 = 0.056. Draw a line from 0.056mm parallel to the straight part of the graph until you hit
the curve.


Load read
here

10,000kN

Proof stress

= load (read from graph /
cross

sectional area (csa)

Example: say load is 10,000kN and csa =
100mm
2

thn

Proof stress

= load/csa


=10000/100 =
100N/mm
2



Ceist 2

Tástáil Ábhair


Condition at max load


Cup & Cone
fr
acture

Load for force (kN)

Extension (mm)

Tensile Strength

Lower
Yield
Point

Upper Yield
Point

Elastic
limit

Limit of
Proportional
ity

Gauge Length

Gauge Length

1

2

3

1.

Elastic Extension

2.

Plastic or Ductile
Extension

3.

Necking Range




7

Proof Stress

Some materials do not have a well defined yield point or an indication at what stress, yield occurs. To overcome
this, a value of stress, know as proof stress is used.


Reading
0.1%
Proof Stre
ss from a force
-
extension graph

A distance equal to 0.1% of the gauge length, from the origin, is located. If the gauge length is 56 mm, then the
distance from the origin for 0.1% proof stress is 0.056 mm. A line, parallel to the straight part of the gra
ph, is
drawn from the 0.056 mm mark until it cuts the graph line. The stress at that point is the 0.1% proof stress.




















Reading 0.1%
Proof Stress from a stress
-
strain graph

Proof stress is much easier to find from a stress
-
strain graph.
Proof stress is read almost directly from this type of
graph. If the 0.1% proof stress is required, then a line is drawn from 0.001 strain, parallel to the straight part of
the graph.


















Load or Force
-

kN

Line drawn parallel
to straight part of
graph from 0.1% of
the 56mm gauge
length

Extension (mm)

0.056
mm

Number
of kN read off
here. This gives the total
force acting on the CSA

The stress per mm
2

is
calculated.

E.g. If the
figure read is 26,
000 N,
and the CSA is 100mm
2

then the stress is



260 N/mm
2

Stress


force per mm
2

Line drawn parallel
to straight part
of
graph from 0.1% of
the 56mm gauge
length

Strain

0.001

Proof Stress read here

The proof stress can be read
directly from the stress
-
strain
graph.

0.056 mm is 0.1% of the gauge
length and since strain =
extension/original length


0.1%

= 0.056 / 56



= 0.001 (strain)

0.1% proof stress from 0.001 strain

0.2% proof stress from 0.002 strain



8

Tástáil Cruais

/ Hardness Testing

Brinnell

= sféar

/ sphere indenter

Vickers

= Pirimid bun
-
cearnógach / Square based pyramid

Rockwell

= Sféar nó cón


Brinnell









Meaisín Tástála Cruais

Hardness Testing Machine





pulse

Locht
/flaw

Ultrasonic

Internal Flaw detection





Readout

Echo ar ais

Eddy Current Testing




Tástáil i gcomhair Lochtanna inmheánacha

Detecting internal flaws

Magnetic particle ,Ultrasonic, x
-
ray, eddy current,



Penetrant Test

I gcomhair lochtanna ar dhromchla (
surface
flaws
/cracks)

Flourescent penet
rant spray applied to piece
soaks into the crack and can be easily seen
under a UV light


Píosa

Eddy
currents

Electric current
thru coil

Transducer

Radiography / X
-
ray testing





Vickers


Rockwell




Magnetic Particle Testing





Read Out

Activating Lever

Position of Indenter

Test
Specimen
Placed here

Adjusting Nut

The
Principal of a
Basic
Hardness Testing Machine

Most machi
nes in use
are almost fully
automatic and can
carry out various
hardness tests.


Ball
Indenter

D
ownward
Force

Test Specimen

Diameter of
indentation
measured

Brinell Test Procedure





Point Angle 136
o









1. Section of material with a surface
-
breaking crack that is not visible to
the naked eye.

2. Penetrant is applied to the surface.

3. Excess penetrant is removed.

4. Develop
er is applied, rendering
the crack visible.




9

Tástáil
Righnis

/ Toughness Testing



Toughness Testing

Toughness testing can also be called
Impact Tes
ting

or
Notched Bar Testing
. The two common methods of
Impact Testing are



The Izod Test



The Charpy Test


Diagram of Impact Testing Machine



















Procedure:

Notched specimens are held in a vice and are struck by a weighted pendulum. The ene
rgy
absorbed in breaking the test piece is measured and a value for toughness is given. The height that
the pendulum swings to after breaking the specimen indicates how much energy was absorbed.




The Izod Test



Specimen is held vertically



Notch is faci
ng the pendulum



Striking energy of 167 Joules



‘I’

for Izod and the specimen
stands in
the vice like an
‘I’
.








The Charpy Test



Specimen is held horizontally



Notch is facing away from the
pendulum



Striking energy of 300 Joules


greater
than the Izod b
ecause the pendulum
is released
from a higher position

Measín Tástála Righnis

Toughness Testing Machine



Specimen

Notch

Notch

Specimen

Knife Edge Striker


10



A different striker is fitted for this test


a knife edge striker

Ceist 3


Iarann
-
Carbón
(Iron/carbon diagram)

Teas chóireáil
(Heat
-
treatments)




Iron Carbon
Equilibrium Diagrams


Allotropic

Iro
n, when cooling from a high
temperature,
displays two special points known as
arrest points
or critical points. These change points
occur at
1390
o
C and 910
o
C. Above 1390
o
C Iron
exists with a
BCC lattice but between 1390
o
C and
910
o
C it
exists with a FCC l
attice. Iron is said to be
allotropic,
which means that it can exist in two
different
forms depending on temperature.


Eutectic Point



At this special change point, the liquid
steel
changes to the solid austenite + cementite phase without going through th
e pasty stage.



This occurs at 1140
o
C for steel when 4.3% carbon is contained in the alloy.


Eutectoid Point



At this special change point the solid austenite changes into solid pearlite.



This occurs at 723
o
C for steel when 0.83 % carbon is contained in
the alloy.



Eutecto
id



Sol
id


Ferrite



This is almost pure iron but contains about 0.02% carbon.



It has a BCC structure.


Cementite



This is a compound of iron and carbon.



It is called Iron Carbide (Fe
3
C). It is a hard, brittle material.



This is wha
t gives the hardness to high carbon steel.



It has a higher melting point than either of its elements.


Pearlite



At the eutectoid point (0.83% carbon) solid austenite changes into two solid phases
-

ferrite and cementite.



These two solids combine to for
m pearlite.



Pearlite is a layered structure of ferrite and cementite.


Austenite



This is an FCC solid solution structure which can contain up to 2% carbon.



It is a hard non
-
magnetic substance.




Aluminium f.c.c

Chromium b.c.c

Copper f.c.c

Gold


f.c.c

I
ron b.c.c

(is feidir leis a bheith f.c.c =
allotropy
)

Lead f.c.c

Magnesium c.p.h



11








Peritectic
region

Solidus Line

% Carbon

Fe
3
C (Cementite)


+
Liquid

723
o
C

Lower critical change line

1140
o
C

γ

(Austenite)


+
Liquid

Eutectoid

Point


Eutectic Point


1

2

3

4

5

6

2 % Carbon

4.3% Carbon

0.83% Carbon

0.02% Carbon

Liquid

δ +
Liquid

δ +
γ

Solid Solution

γ

(Austenite)

Solid

γ

(
Austenite)
+
Fe
3
C (Cementite)

Pearlite

+
Cementite (Fe
3
C)

α


+
γ

δ

α
(Ferrite)

Liquidus

Ferrite


+

Pearlite

Pearlite

+
Cement
ite (Fe
3
C)

CAST IRON

STEEL

1140

200

400

600

800

1000

1200

1400

1535

1600

723


12





Quenching (rapid cooling) of Carbon Steel from
1000
o
C

If rapid cooling of carbon steel occurs the steel takes a
new and different
form. The carbon in the iron gets trapped and is not
allowed to form
as separate cr
ystals of carbide. This results in
considerable
1

2

3

4

1.

Here the carbon steel exists as Austenite. This is a solid solution of carbon
dissolved in FCC Iron (gamma iron,
γ

)

2.

Once the temp
erature reaches the upper critical temperature (approx.
775
o
C, from the graph) the austenite begins to form with ferrite.

3.

At the lower critical temperature (723
o
C) all of the ferrite has been formed.
Austenite and ferrite exist in this zone containing all

of the dissolved
carbon.

4.

Below the lower critical temperature the austenite is transformed into
pearlite. In this zone ferrite and pearlite exist.

The Slow Cooling of 0.6 % Carbon Steel from a Temperature of 1000
o

C


Microstructure of Steel

Austenite

Austenite

+
Ferrite

Pure

Pearlite .8
3% C

Pearlite +
Cementite


Austenite

+
Cementite

Ferrite

Ferrite +

Pearlite

Austenite

Ferrite

Cementite

Microstructure of Martensite


13

distortion of the structure which in turn makes slip impossible. This is displayed as a hard, brittle material. Its
microscopic structure shows a needle
-
like grain composition. This is called Martensite.

Martensite is a BCT
(Body Centred Tetragonal) Structure. Steels existing as Martensite are useless and need to be put through a heat
treatment process called Tempering.


Defination:


When steel is cooled rapidly a structure known as Martensite is formed.

In steels, Martensite is very hard

and
brittle
.


Rapid cooling (quenching) of 0.6 % Carbon Steel




This can be referred to as ‘the hardening of steel’.



The steel must be heated well above the upper critical temperature (775
o
C for 0.6 % Carbon Steel). U
sually
1000
o
C plus.



During the fast cooling the FCC structure tries to change to BCC but fails to do so.



A different structure is produced called Martensite, which is hard and brittle.


Quenching Media In Heat Treatment



Caustic Soda Solution



Brine (water
& salt solution)



Cold Water



Warm Water



Oil (less severe and helps to prevent distortion and cracking).



Air



Soaking (leaving the component in the furnace, switching off the furnace and allowing it to cool naturally)



Heat Treatment Process

The basic steps

in a heat treatment process are:

1.

Heating the component to a particular temperature

2.

Soaking or keeping the component at this temperature for a period of time.

3.

Cooling the component in a particular way.


Heat Treatment Processes



Annealing



Normalising



Stress

Relieving



Hardening



Tempering


Specialised Heat Treatments




Case Hardening



Induction Hardening



Flame Hardening



Age Hardening


Annealing

Full annealing
, which is carried out in order to make the metal as soft as possible, also improves ductility, refines
t
he grain size and removes internal stresses. Internal stresses, or residual stresses, result from cold working (when
the material is bent into shape) or from rapid heating and cooling. Internal stresses or residual stresses may speed
up corrosion or enco
urage fatigue. During cold working of a material or a component the grains of the metal are
deformed. As annealing is carried out, a whole new set of grains appear, which replace the old grains or crystals.
Desce
nding order of
quenching speeds
.

Fast
-

Slow


14

This is known as recrystallisation. Once the
desired temperature is reached during annealing, the steel is
soaked
to ensure uniform heating. Cooling is controlled by reducing the temperature of the furnace gradually; this is
often done by switching off the furnace and allowing it to cool naturally.




















Process annealing

is used when components made from up to .25% carbon steel are going through a
manufacturing process which involves cold working. Process annealing is not as costly as full annealing because
the temperatures required

are not as high. To process anneal carbon steel containing up to .25% carbon it is
heated to a temperature of about 80
o
C to 180
o
C below the lower critical temperature. It is allowed to soak for a
time, and then normally cooled in air. Recrystallisatio
n takes place in a similar manner to that in full annealing
but because the temperature is lower, the new grains are much smaller.


Spheroidising

Higher carbon steels are heated to 30
o
C below the lower critical temperature, and put through a process anneal
ing
procedure. This is known as
spheroidising
. This improves the machinability of the steels because the hard
cementite is gathered into spheres.



Normalising

When a material is formed by cold rolling, hot rolling, forging, etc., stresses are set up in

the material.
Normalising is very similar to full annealing and is a process that removes these internal stresses. For
hypoeutectoid steels the metal is heated to the same temperature as for full annealing and allowed to soak until it
is heated evenly t
hroughout. Hypereutectoid steels are heated to their upper critical temperature, soaked and
allowed to cool in air. The cooling rate is slightly faster than in annealing. This gives a fine grain structure which
is free from internal stresses and has imp
roved machinability. Normalised steel has higher strength and lower
ductility than fully annealed steel.


Stress Relieving

This is a process in which the component is reheated, held at a slightly elevated temperature for a period of time
and then cooled

slowly. The temperature and period of time will vary depending on the component.


Hardening

Heating carbon steel until it is red hot, and then quenching it in water produces a significant change in the steel.
It results in the steel becoming hard and br
ittle. The iron carbon diagram provides information about the various
heat treatments for carbon steels. Martensite is formed during this hardening process. The extent to which steel
can be hardened will depend on its composition. The carbon content is

very influential, as is the rate at which the
hot steel is cooled. The chromium or vanadium in some alloy steels will also affect the hardening process.


Tempering


Hypoeutectoid
steels



below
.83% carbon

Hyper
eutectoid
steels



above
.83% carbon

Annealing
hypereutectoid
steels

Hypoeutectoid
annealing &
normalising band

Normalising
hypereutectoid steels

Spheroidising


15

Tempering involves re
-
heating the steel to a temperature below the lower critical tempera
ture (723
o
C for Carbon
Steel). The tempering temperature can range from 250
o
C to 500
o
C. Tempering relieves some of the internal
stresses caused by rapid cooling and allows some of the Martensite to change into Ferrite + Pearlite (or Cementite
+ Pearlite)
. The tempering temperature depends on the properties required for a component. i.e. The balance
between hardness and toughness.


Case Hardening

Using Carbon

The hardening process that we have already discussed is based on the carbon content being greate
r than 0.3%. If
a component does not contain enough carbon then the heating and rapid cooling process will have little effect. It
is possible to add additional carbon to the outer surface of the steel component. This outer surface can be heat
treated in

the normal manner and is called the
‘case’
. This process is known as case hardening and results in a
component with a hard outer skin and a softer tough core.


The addition of carbon to the outer skin is known as carburising and can be carried out by;



Th
e pack method

(solid carburising)



Salt bath carburising

(liquid carburising)



Gas carburising

(gas carburising)


The Pack Method

This is where the component is packed in a box surrounded by a carbon rich material and placed in a furnace at
920
o
C. This temp
erature is above the upper critical point, which allows the carbon to diffuse into the austenite.
The high carbon case has a coarse crystalline structure which is prone to cracking. After cooling, the component
is immersed in a bath of molten salt and ke
pt at a temperature of 780
o
C.





















Salt Bath Carburising

Case hardening without causing course structures is possible using salt bath carburising. The component is
placed in the salt bath at 900
o
C for one hour. This gives a thin carbon ca
se and not too much grain growth. It is
then quenched in water to harden the surface.


Gas Carburising

This is carried out in a special sealed furnace. The carburising agent is a carbon rich gas circulating in the furnace
chamber. This is a fast method
of carburising and greater control over the process is possible.


Case Hardening Using Nitrogen

Nitriding

Case Hardening By Carburising


The Pack Method

Low carbon steel
heated to fully
austenite which is an
FCC structure

Austenite has
a high
solubility for
carbon

Atoms of Carbon diffuse into
the FCC structure

Carbon


16

This is an expensive method of case hardening but is used where high quality is required. It is used for alloys
which contain elements such as chromi
um, vanadium and aluminium. During heating, these elements form
nitrides

at the surface. A nitride is a binary compound of nitrogen


e.g. aluminium nitride. Nitrides are ultra
-
hard, so the cases formed, although thin, are extremely hard also. Nitridin
g is carried out in a furnace in which
ammonia is circulated. Heating the ammonia produces nitrogen. The temperature of the furnace is 500
o
C and the
process can take up to 100 hours. This process can be used to case harden parts which are finish machine
d.
Because no quenching is necessary, no distortion of the component is likely.


Carbonitriding

This is carried out in a gas atmosphere in a special furnace. The gas is a mixture of ammonia and carbon
monoxide. This atmosphere can produce carbon and ni
trogen, and both of these elements diffuse into the steel.
The iron carbides and iron nitrides produced are very hard at the surface of the component. The component is
quenched during this process once the required case depth is achieved.



Induction H
ardening

It is sometimes necessary to heat treat a component in such a way that it has a very hard outer surface and a softer
inner core. An example of this would be the slideways of a lathe. The process of induction hardening involves
the heating of the

component very quickly in small areas using a high frequency electric current. This high
frequency current passing though the coil produces eddy currents in the component. These cause a rapid rise in
temperature in the outer surface. Water is then spra
yed onto the surface by a number of jets, to quench the
component.




Flame Hardening

This process is similar to induction hardening. It uses a flame of hydrocarbon gas with oxygen. The flame is hot
enough to raise the tempe
rature of the outer surface above the upper critical temperature without allowing the
core to become heated. The component is quenched with water jets similar to that used in the induction
hardening process.

Direction of
movement

The Princi
ple Of
Induction Hardening

Moving Induction Coil
Assembly

Water Jets to Cool
Surface

Metal Being
Hardened

Induced Eddy
Currents Heat up
the Surface of the
Steel


17


Age Hardening

Ferr
ous and non
-
ferrous alloys can be age hardened. The age hardening process involves quenching from high
temperatures and allowed to remain at room temperature for a few days. In modern times, components are heated
to a higher temperature than room tempera
ture to speed up the age hardening process.


Measurement Of Furnace Temperature

The measurement and control of the temperature in a heat treatment furnace is of extreme importance. Modern
heat treatment furnaces use pyrometers to measure the temperature
s. Ordinary thermometers are of no use due to
the extremely high temperatures used, up to 1100
o
C.


Two common methods of temperature measurement used in modern times are;



The Thermocouple Pyrometer
(Thermo
-
electric)



The Optical Pyrometer


The Thermocouple

Pyrometer

If one end of a thin wire is heated, heat will flow from the hot end to the cool end. This movement of electrons
will produce a very small voltage in the wire. This is called a
thermo
-
electric effect
. If a couple of different types
of wire
(N
ickel
-
chromium & Nickel
-
aluminium) of
the same length are joined at each end a useful output can be
obtained for measuring temperature. This can be referred to as the
‘Seebeck effect’
. The hot junction, known as
the thermocouple, is placed in the furnace
. The other junction, known as the reference junction, is kept at a set
temperature, this
is commonly
0
o
C. The output
is measured
across the two
wires. This
output can be
measured by a
sensitive meter
(Galvanometer)
or amplified and
interfaced to a
comp
uter.




Cold water
quenching the
component

Hot jets heating
the component

Direction of
Componen
t
Movement

The Principle of Flame Hardening

Nickel
-
chromium
(Chromel) wire

Hot
Junction

Reference Junction

Wall of furnace

Output voltage
converted to
o
C
and read directly
or interfaced to a
computer.

Nickel
-
aluminium
(Alumel) wire

Door


18

The Optical Pyrometer

This pyrometer compares the intensity of the light coming from the furnace with the light coming from the
filament of a lamp. The current flowing in the lamp is varied, until the light coming from the lamp matches that
comi
ng from the furnace. The variable resistance which is used to vary the current flowing in the lamp is
graduated in
o
C. The light from the lamp and the light from the furnace match when the filament of the lamp is
no longer visible. Accuracy is good with

this method but it requires a skilful eye and good judgement from the
operator. The furnace doors must be transparent and clean otherwise they may have to be opened to get a
reading. This will obviously lead to heat loss.


Properties of /
Differences b
etween
,
Gre
y Cast Iron &
White Cast Iron


Gre
y Cast Iron



Most common form
of cast iron




Least expensive of
cast irons



Carbon takes the
form of graphite
flakes



When fractured, the
freshly exposed
surface has a grey
appearance



Alloy of iron, carbon,
silicon
and
manganese



Excellent
compressive strength, machinability and wear resistance



Weak in tension



Self lubricating properties



Outstanding vibration
-
damping characteristics



Good corrosion resistance



Great fluidity
-

desired for casting applications



Formed un
der slow cooling conditions


White Cast Iron



Receives its name from the white surface that appears when it is fractured


this whiteness is caused by the
presence of cementite



Carbon is present in the form of iron carbide



Very hard and brittle



Used where h
igh abrasion resistance
is required



Formed under quick cooling
conditions


Recales
ence

&
Decalesence

When a piece of high carbon steel is
heated to its
critical point (723
o
C), the structure
begins to change
internally. The point at which the critical
cha
nge begins is
called
Decalesence
. When cooling high
carbon steel these
internal changes occur in reverse and the
corresponding
point is called
Recalesence
. At the
points of
decalesence and recalesence there should
not be any
Optical Py
rometer

Temperature Scale

Battery

Light from
Furnace

Eye Lens

Lamp Filament

Lens

Variable Resistor
for lamp

Low Reading

High Reading

Correct Reading

High Reading

Temp

Time

Recalesence

/ Decalesence


19

temperature change but in fac
t there is.




Critical Range

The critical range starts at the point of Decalesence (723
o
C). During this period the material glows less brightly
and contracts. A loss of magnetism is also experienced.


Ceist
4

Co
-
mhiotail
(Alloys)













Miotail feiriúla

Miotail neamh
-
fheiriúla




Iarann



Maighnéadach uaireannta




Maighnéadach


Tréithe breise; éadrom, láidreacht, seoltóir,




Meirg
each


Cos
c in aghaidh chreimeadh, etc

cast iron and steel


Alúmanam

stainless steels



Copar

special steels



Zinc


















Folúntas

(Vacancy
)






Ionadach

Subtitutional





Bearnach
Interstitial




20

















Solid Solution Alloys


As you can see the area in
green
is t
he liquid
state while the area in black is the solid state
while the area in

yellow
is the pasty state
which consists of a solid phase and a liquid
phase. A very important pint to note is that the
line joining all the points where the liquid
begins to soli
dify is known as the

Liquidus
line

while the line joining all the points where
solidification is just complete is known as the
Solidus line.

This is the thermal equilibrium
diagram for the alloy of Copper and
Nickel. In order to find what
temperature 60%

copper solidifies at
we simply draw a vertical line from
60% copper until it hits the solidus
line and at this is the point where 60%
Copper has fully solidified.


What is a solid solution?

A solid solution occurs when we alloy two metals and
they are co
mpletely soluble in each other. If a solid
solution alloy is viewed under a microscope only one
type of crystal can be seen


just like a pure metal.
Solid solution alloys have similar properties to pure
metals but with greater strength but are not as good
as electrical conductors.



Substitutional S
olid Solution

The name of this solid solution tells you exactly
what happens as atoms of the parent metal ( or
solvent metal) are replaced or substituted by atoms
of the alloying metal (solute metal) In this case, the
atoms of the two metals in the alloy,
are of similar
size.


Here we see the brown atoms have been replaced
or substituted by the blue atoms.

Interstitial

Solid Solution


In interstitial solid solutions the atoms of the
parent or solvent metal are bigger than the
atoms of the alloying or solute metal. In this
case, the smaller atoms fit into interstices i.e
spaces be
tween the larger atoms.


The purple atoms are small enough to fit into
the spaces between the larger solvent atoms.




Ratio

of the Phases


If we take the diagram for the Copper
-
Nickel alloy as
above and we take the

composition of 60% copper
and
40% Nickel the lever rule will apply like this.





Weight of solid solution of composition q


=
bm



Weight of liquid of composition m


qb




Ratio = bm/pb



21













The Second type of alloy combination we will look at is
eutectic alloys.


The solid solution equilibr
ium diagram discussed in the last section was formed by two metals being totally soluble in both the liquid
and solid states. A Eutectic equilibrium diagram results when the two metals are soluble in the liquid state but
insoluble in the solid
state
. In th
e liquid state the two metals are soluble in each other but when cooling is complete, the grain of the solid alloy consist of

two
distinguishable metals which can be seen under a microscope to be like a layer of one metal on top of a layer of the other me
t
al. This
situation is completely different where the cooled solid grains look just like one metal when viewed under a microscope. In o
rder to fully
understand this type of alloy combination we will look at the Cadmium/ Bismuth Eutectic thermal eqlibrium di
agram.





Cadmium
-

Bismuth Eutectic thermal equilibrium diagram


Cadmium and Bismuth are completely soluble in the liquid state, but are completely insoluble in solid state



The first and most noticable point on this diagram


is the Eutectic point. The eutectic point as can be seen above is
a point in the diagram where the liquid alloy changes to a solid without going through a pasty state. This is the
lowest melti
ng point of any composition for the alloy.


As you would except everything
above the liquidus line is in the liquid state and in this state the two metals are total
ly soluble in each other.


In the eutectic point


region (represented by the green line) there is only the eutectic composition alloy .


If you look at 100% Cadmium you will see that there is a large amount of solid Cadmium while this decreases in
the allo
ys found nearer to the eutectic. The same applies for Bismuth. Therefore we can say that as the
composition of the alloy moves away from the eutectic composition, grains of either Cadmium or Bismuth appear
in the
eutectic matrix.



Eutectic alloys


22

Partial solubility


The
partial solubility equilibrium diagram is derived from the previous two
diagrams that indicated soluble and
insoluble states. Few alloys exhibit total insolubility or total solubility and many
metals combine to form a partial solubility system. The ends o
f the totally
soluble system are amalgamated with the central portion of the insoluble or
eutectic system to form the partially soluble in the solid state equilibrium
diagram as shown here.







The partial solubility diagram looks very different to what

we have encountered
so
far so we will work on its various components before we move on to seeing its
uses.



Lines "ae" and "eb" (grey) are the

liquidus lines.

Lines "ac" and "bd
" (maroon)
are the

Solidus lines
.


Two new lines exist in this diagram "cf" and "dg"



Lead and Tin

combine to form solder and the equilibrium diagram is shown below. On this diagr
am I have
included drawing of a typical microstructure for six different alloys of Lead and Tin these microstructures are
fairly self explanatory further explanations can be gotten by clicking on the relevant microstructure in the
diagram.









23

Ceist
5

Táthú

(
Welding
)


Táthú gháis


Oxy
-
acetylene


Trealamh

Hose dearg
=gáis

Hose dubh/dubhghorm
=ocsaigin

Regulators

= An méid gáis
a ligtear amach as an


mbaraille
& an méid gáis

a ligtear amach
tríd an hose

Flashback arrestor

= stopann sé an lasair (Flame)

dul siar sa hose

Dissolved acetylene = an gháis suite (dissolved) isteach


in ábhar spuinse (porous material)




3 chineál lasair



1.

A
neutral flame



this has an
inner cone and a secondary
combustion envelope. Most
welding is done with this flame.

2.

An
oxidising flame


this has
excess oxygen and is used in
welding brass.

It can also be
used as a decarburising flame
for steels (the oxygen reacts
with the carbon in the steel)

3.

A
carburising

flame


this has
excess acetylene and is used for
special welding




24

WELDING



Welding refers to the process of
joining parts by fusing them together. Ideally fusion is
brought about by a combination of heat and pressure but normal welding requires no
pressure. Pressure welding can be used to carry out special welding.


Ideal conditions for welding



Smooth joint su
rfaces that match each other



Clean joint surfaces. Surfaces free from oxides, grease and dirt.



The metals to be joined should have the same microstructure



The metals should be good quality


no internal impurities


Before starting a weld the joint faces s
hould be carefully prepared. When joining large plates this may mean
machining the edges to a bevel. Cleaning is very important and is sometimes carried out chemically or by
mechanical means.


When metals are heated to high temperatures their surfaces
are more easily affected by the oxygen in the
atmosphere. This is known as oxidation. Oxidation is a problem with all fusion welding. To prevent this
occurring the surfaces are shielded from the atmosphere during the welding operation.


Welding proces
ses differ in the way that they heat the metal, the manner in which the filler metal is added and the
method of preventing oxidation.


Gas Welding



In gas welding, a flame is used to melt the filler rod and the metal to be joined. This
flame is produ
ced by burning a mixture of fuel gas and oxygen.


Fuel gas + Oxygen = Gas welding


The fuel gas is usually Acetylene but other gases can be used. When Acetylene is used
the process is known as oxy
-
acetylene welding.


Oxy
-
acetylene Welding




A fusion weld
ing process



Oxygen stored in a black cylinder and acetylene stored in a red cylinder



Gasses are transported to the torch in two separate coloured hoses, blue for oxygen
and red for acetylene.



The mixture of gasses can be adjusted at the torch



Gas burns to
a temperature of 3100
o
C, this is capable of melting the metal



As the molten metal on both joint faces meet, it fuses. This forms a permanent joint
when allowed to cool.



A filler metal is sometimes required and is fed by hand into the weld pool where it
is kept at melting point. This is fed in at a regular pace to get a uniform weld



There are many different types of filler rod that can be used to suit various metals to
be joined. The rod is not the same composition as the metals to be joined; elements
s
uch as silicon are often added to improve the quality of the weld.


25


















Oxy
-
acetylene Welding Flame


This has two distinct zones, the inner and outer. The
inner zone is the hottest part of the flame. The
welding should be carried out with

the point of the
inner cone at the joint faces.


The outer zone or the secondary combustion envelope
is not as hot but has two functions

1.

To preheat the joint faces

2.

To prevent oxidation by using up some of the
excess surrounding oxygen through combustion


Flame Adjustment

The oxygen and acetylene mixture can exit the torch in three different ways. These can be easily identified by the
appearance of the flame.




1.

A
neutral flame



this has an inner cone and a secondary
combustion envelope. Most welding is

done with this
flame.

2.

An
oxidising flame


this has excess oxygen and is used
in welding brass. It can also be used as a decarburising
flame for steels (the oxygen reacts with the carbon in the
steel)

3.

A
carburising

flame


this has excess acetylene and i
s
used for special welding to ensure that the metal is well
protected from oxidation.

Equipment used in gas welding



Pressurised cylinders of oxygen and acetylene


oxygen is in
gas form but acetylene is stored or dissolved in a porous
material called aceto
ne inside of the cylinder
(dissolved
acetylene).



Gas pressure regulators


two gauges on each tank, one to indicate the pressure in the tank and the other to
indicate the pressure in the supply pipe



Welding torch


gases supplied through separate colour co
ded hoses. Separate controls for each gas on torch


26



Gas Hose pipes


reinforced rubber hoses. Fittings for acetylene are left
-
hand threads. Those for oxygen are
right
-
hand.



Flashback arrestors


these are located on both pipes, close to the torch. They
prevent the flame returning
from the torch to the cylinders



Safety Notes

Never use oxygen as compressed air in the workshop.

Special care is always needed when using pressurised gases and flammable gases.

Instruction is needed in the safe handling and op
eration of gas welding equipment.

Always wear the correct protective clothing when welding.

Welding goggles protect your eyes from harmful light rays that are emitted by the welding process.

When welding in confined spaces, ensure that there is sufficient
ventilation.

Ensure that there are no flammable liquids, gases or other materials in or around the welding area.


Electric Arc Welding




Electric arc welding is a fusion welding process.



An arc is produced when a high current
jumps
from the electrode to th
e work
-
piece in
order
to complete a circuit.



Temperatures up to 7000
o
C are possible.



All arc
-
welding processes require an
electric circuit.



Some arc
-
welding processes use
consumable electrodes (electrode used up
in the
process), others do not (they use non
-
consumable electrodes). The electrodes in
these
processes are used to maintain an arc.


Manual Metal Arc Welding Process
(MMA)


An electric arc is formed and
maintained between the work and the
electrode. The heat from the arc
melts the
metal at the j
oint edges. The molten
metal
forms a pool called the ‘weld pool’,
when
this cools or solidifies the parts
become
permanently joined.


The electrode is a metal wire covered by a coating, often
called a
stick electrode. During welding the coating melts a
nd performs many functions.




To produce a gas which shields the weld pool from oxidisation



Contains flux which helps the weld to form



Produces slag, which combines all of the unwanted impurities. This slag floats to the top and during cooling
it protects
the weld from oxidising or cooling too rapidly (preventing brittleness)



Can contain powdered metals, which melt and are added to the weld pool. This is sometimes used to add
alloying elements in order to strengthen the weld



Helps to maintain the arc, espe
cially in AC welding


Electrical terms used in welding



Direct current


DC



Alternating current


AC


27



Current


I


measured in amps



Voltage


V


measured in volts



Resistance


R


measured in Ohms



Ohms Law


current, voltage and resistance are related to e
ach other

Voltage = Current
X

Resistance



V = IR


The Transformer

This is a device for transforming an alternating current at a particular
voltage to an
alternating current at a higher or lower voltage. A simple transformer
consists of an
iron core on w
hich two coils of wire are wound. When the primary coil
is connected to
the electricity supply, the AC current causes an alternating magnetic
field within the
iron core. This magnetic field in turn produces an alternating current in
the second coil.
If
the secondary coil has a smaller number of coils than the primary
coil, the output
voltage will be lower than the input voltage but the output current will
be higher than
the input current.


Equipment used in MMA welding



Welding power source



Cables



Elect
rode holder



Ground clamp (earth clamp)


AC Power Source



Takes its power directly from the main supply of electricity



It uses a transformer to supply the correct voltage to suit the welding conditions



The current in the secondary coil can be adjusted



The pr
imary coil is connected to the electricity supply and the secondary coil is connected to the electrode
holder and the earth clamp.


DC Power Source

There are two types of DC welding plant in use



DC generator



Transformer


rectifier


DC generator

A motor d
rives an electrical generator. This motor can be electric, diesel or
petrol powered.
It provides DC current for the arc.



Transformer


rectifier

This has a built
-
in device to change
alternating
current into direct current. This built
-
in
device is cal
led
a bridge rectifier. The transformer
-

rectifier
has the
advantage that it can supply AC or DC current
for welding.


The rectifier converts AC current to DC
current using a
single phase bridge converter. It uses four
diodes to
conduct the power supply.

During one half
cycle of the AC
supply diodes D1 and D3 are conducting.
During the next
half cycle diodes D2 and D4 are conducting.
The current is
then passed through a smoothing capacitor to
give a DC
output.



28

The Cables

It is important that the diam
eter of the cables is not too small as this could increase resistance and cause them to
heat up during the welding process. They usually contain many strands of thin copper wire, which allows them to
carry the electric current and still remain flexible.



Metal Arc Gas Shielded Welding (MAGS)














Previously known as MIG welding (metal inert gas)



The electrode is a bare wire that is fed continuously from
a spool
through the welding gun. This wire electrode is
consumed
during the welding process a
nd also acts as the filler
metal.



Shielding of the weld pool is carried out by a continuous
supply of
inert gas.



This gas is also fed through the welding gun. Argon (Ar),
Nitrogen
(N), Carbon dioxide (CO
2
) or Helium (He) can be used.



DC power is used in M
AGS welding and is supplied by a
transformer
-
rectifier.



MAGS welding can be used on light sheet metal as well as heavy plate.



It uses a continuous wire electrode feed; therefore no slag is formed on the weld.



Often used in car manufacture and can be carrie
d out by robots.





Tungsten Arc Gas Shielded Welding

(TAGS)














Previously known as TIG welding (tungsten inert gas)



This welding process does not consume the electrode. The electrode is made of tungsten and is referred to as
a non
-
consumable e
lectrode.



This process also uses an inert gas fed from a cylinder to shield the weld pool.



If filler metal is required a filler wire is fed manually into the weld area, similar to oxy
-
acetylene welding.


29



The arc in this process is started differently than i
n previous welding processes. The operator starts it when
the electrode is held close to the work and a foot pedal pressed. This foot pedal operates a separate electric
circuit, which is high frequency and is specifically for starting and maintaining the

arc.



TAGS’ welding normally uses DC current but can also supply the required AC current to weld Aluminium
and Stainless Steel.


Submerged Arc Welding (SAW)




In this process a bare wire consumable electrode is
used
and fed automatically into the weld pool
.



The flux is in powder form and it too is fed
automatically onto the weld area from a hopper.



The flux completely covers the weld area and the
arc;
hence the name ‘submerged arc welding’.



This process is suitable for long, un
-
interrupted weld
runs.
E.g.
reinforcing beams for construction and
fabrication.



Can use AC or DC current.


Resistance Welding


There are many forms of resistance welding. The resistance to the flow of an electric current causes the heat in
the joint area. The greatest resistance to

the current and hottest area is where the joint faces meet. Once the
melting point of the metal is reached the joint is made through fusion.


Resistance Spot Welding



Used to join light gauge sheet metal



Electrodes are made from brass, copper or some oth
er
low
resistance metal



A combination of pressure and electric current at the
electrodes
causes rapid heating and fusing of a small globule of
metal
from both faces



This process can be carried out on both fixed and
portable
machines



Often carried out by ro
botic control in the car
manufacturing industry


Resistance Seam Welding



Used for continuous seams, two methods in general
use



Stitch welding is one method, which uses a series of
overlapping
spots to create the welded seam



Roller welding is another metho
d, which uses
rollers. These
rollers have electrical pulses passing through them to
create the
weld.



Water jets are often used to cool the work piece on
exiting the
rollers




Projection Welding



Used for resistance welding of relatively
large
objects


30



The

contact area between the two parts needs to be reduced. This is achieved by forming points on one of the
surfaces.



The electric current is concentrated to these new contact areas and the weld is formed.



This allows several spots to be carried out simul
taneously



Often used in mass production


Electroslag Welding



This is a very effective process for welding thick
sections of steel plate, usually 50mm plus.



It is totally automatic



The heat required for welding is achieved from the
passage of electrical cu
rrent through a liquid slag



There is an arc involved but the process is totally
different to submerged arc welding. The arc in
this
process is only used to produce molten slag



The resistance of the metal to be welded plays no
part
in the welding process,
it is the molten slag that
melts the joint faces and the filler metal



The molten slag and the molten metal is contained
between two copper dams which travel upwards as
the
weld metal solidifies



The bare metal electrode is continuously fed into
the
weld poo
l



The weld is assisted to solidify by the water
cooling of the copper plates



This process is ideal for the welding of large plates
ranging from 13mm to 900mm



The edges need to be square and approximately 25


30 mm apart prior to welding



Applications inclu
de building construction, machine manufacture, heavy pressure vessels, and the joining of
large castings.

Multi
-
run Welds


This is when multiple layers of weld are
laid on
the weld joint. This
adds to the
penetration of the weld
thus strengthening the fi
nished joint
.

Each
new run
post
-
heats the previous one resulting in more refinement in the
materials
structure.



31

Ceist 7


Meaisíneáil &
Meaisíneanna


Muilleáil (milling)
,

Meillt (Grinding),



Deileadóireacht (Lathe),










Milling
Cutters



End mill





Gang milling


Straddle milling



Meaisín Muilleála Cothrománach

Horizontal Milling Machine

Measín
Muilleála Ingearach

Vertical Milling Machine



Muilleoireacht
ghearra
dh aníos:

Up
-
cut milling

Muilleoireracht
ghearradh
anuas:

Down
-
cut
milling


32

Ualú (loading) =
píosaí ag dul i bhfostú sa scrabhach (abrasive)

Glónrú (Glazing)

=
an scrabhach (abrasive)

ag éirí maol (blunt)


dresser

Ag gléasadh an roth
meillte (Dressing a
grindin
g wheel)


Measiín meilte dhromchla
(Surface grinding machine)


Meilt sorcóra (Cylindrical Grinding)

3 chineál slise i ingearradh miotail

3 types of chip formed in metal cutting



Sreabhán ghearrtha

Cutting fluids


Cutting fluids are used to:


Wash away cutting chips.


Keep the cutting tool cool.


Reduce

friction between cutting tool
and
workpiece.


Prolong tool life.


Improve surface finish.


Hazards include:


Continual contact with cutting fluids can
cause the skin to swell, crack,

and

bleed.


Contact with mineral oils can cause skin
cancer.


Frequent contact with water based emulsions
could lead to dermatitis.

Safety hazards associated with using cutting
fluids include:


Skin irritation or dermatitis.


Staining the work piece espec
ially for
aluminium.


Some give off hazardous odours (rancidity).


Some create a mist or smoke making the work
environment unsafe for the

operator.


Some leave an oily film on the work piece
and require the use of cleaning

solvents.



Factors influencin
g surface finish:


Use of cutting fluids or coolants.


Workpiece material.


Cutting speed.


Sharp well supported cutting tool.



33


4 jaw independent chuck



Travelli
ng steady



Fixed steady

Ríomhaireacht RUR = CNC


Safety features
incorporated in a
CNC

lathe:


Fuses used to prevent circuit overload.


Machine

will not operate if chuck guard is up.


Emergency stop button.


Simulation of machining operation available.


Clear machine guards.


G
-
codes
control the cutting tool movement. G00 denotes
rapid movement

and G01 denotes cutting in a straight line.


M
-
c
odes
cover a variety of operational functions e.g. M04
starts the spindle

in reverse, M30 end of program, M06 pause program to
change cutting tool.


Canned cycle

enables a series of repetitive operations to be
executed

by a single programme block.



Tool p
ark position

is the place where the tool is set in order
to start a

machining operation.


G00

is a code to inform to move as quickly as possible as the
machine is

not involved in a cutting operation.



Computer numerical control
machining is much more
suit
ed to large batch

repetitive production. It gives higher levels of productivity
with uniformity

of end product .There is much less operator involvement in
the process

which improves quality control and reduces costs. Machining
in two or three

axes can occu
r, which allows for more elaborate contours
and shapes.




34

Ceist 8















Bevel gear system:
used transfer motion at
right angles, applications include hand drill.



Ball thrust bearing system:
allows an axial load on a rotating shaft, used

in robotic control, t
ransmission systems, turntables, rotating stools, etc.


Rack and pinion
converts rotary motion to linear motion. As the pinion

rotates, the gear teeth mesh with those on the rack. This allows the rack
to

be moved in a line. Applications of the rack and
pinion include
raising and

lowering the table of a pillar drill and steering in a car.


Worm and worm
wheel transmit motion at right angles. For every

complete turn of the worm shaft, the worm wheel advances only one tooth

of its gear. Worm and wheels are commonly used to reduce the speed of

electric motors.




Chain & Sprocket


Cam & Follower


Ratchet & Pawl


Gear train

Siombóil Leictreonacha



Go n
-
éirí libh !