Unit 4 joining process

Sanjivani Rural Education Society’s
Sanjivani College of Engineering, Kopargaon-423 603
(An Autonomous Institute, Affiliated to Savitribai Phule Pune University, Pune)
NAAC ‘A’ Grade Accredited, ISO 9001:2015 Certified
Department of Mechanical Engineering
Gujrathi Sonam
Assistant Professor
Sanjivani College of Engineering, Kopargaon
E-mail : gujrathisonammech@sanjivani.org.in
Contact No: 8483874906
Subject :- Manufacturing Process I (MP I)
S.Y. B.Tech. Mechanical
Unit 4- Joining Process

2
Contents
Gujrathi S.M. Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
Surface preparation and types of joints. Welding Classification, Defects and Applications.
Gas welding - Oxy acetylene gas welding, Hydrogen gas welding.
Arc welding - Metal arc welding(SMAW ), Gas metal arc welding, (MIG, MAG) Tungsten inert gas
welding, (TIG) Submerged arc welding,(SAW ) Flux cored arc welding(FCAW ), Electrode slag metal
arc welding, etc
Resistance welding - Resistance but welding, seam welding, spot welding, percussion welding.
Thermite welding -
Solid state welding - Forge welding, Friction welding, Pressure welding etc

3
Introduction
Joining processes are used for joining metal parts and in general fabrication work.
• Such requirements are generally occur when large/lengthy sections are required in the structure.
• Also these processes are applied when steam or water-tight joints are needed.
The commonly used joining processes are -
• Welding
• Soldering
• Brazing
• Adhesive bonding

4
Introduction
• It is joining process used for various metals and their alloys.
• In these processes, two or more pieces of metals are joined by application of either
heat or pressure or both.
• In plastic/pressure welding, the metal pieces to be joined are heated to a plastic state
and then forced together by external pressure.
• In fusion/non-pressure welding, the metal pieces to be joined are heated to molten
state and allowed to solidify.

5
Classification of welding process
1.Arc welding
a) Gas tungsten arc welding (TIG) b) Shielded metal arc welding
c) Gas metal arc welding (MIG) d) Submerged arc welding
e)Plasma arc welding f) Stud arc welding
2. Gas welding
a) Oxy-acetylene welding b) Oxy-hydrocarbon welding
c) Air-acetylene welding d) Pressure gas welding
3. Resistance welding
a)Spot welding b) Seam welding
c) Projection welding d) Percussion welding e) Resistance butt welding

6
Classification of welding process
4. Solid state welding
a) Cold welding b) Friction welding
c) Ultrasonic welding d) Diffusion welding
e) Explosion welding f) Roll welding
5. Thermo-chemical welding
a) Thermit welding b) Atomic hydrogen welding

7
Advantages and disadvantages of welding
Advantages
• A large number of metals or alloys, both similar and dissimilar can be joined by
welding.
• It can be mechanized.
• Strength of welded joint is more.
• It provides leak-proof joint.
• Welding equipments are not very costly.

8
Disadvantages -
• It gives harmful radiations, fumes and spatter.
• Welding results in residual stresses and distortion of the workpiece.
• Heat generated in welding process produces metallurgical changes hence, the
structure of welded joint is different than that of parent metal.

9
Applications of welding process
• Aircraft construction (welding of engine parts, turbine frames, ducts, etc.)
• Rail-road equipments (Air receiver, engine, front and rear hoods, etc.)
• Piping's and pipelines (open pipe joints, oil and gas pipelines, etc.)
• Pressure vessels and tanks
• Buildings and bridges (column base plates, erection of structures, etc.)

10
GAS WELDING
• Gas welding is done by burning a combustible gas with air or oxygen
in a concentrated flame of high temperature.
• It can weld most common materials.
• Equipment is versatile, inexpensive and serves adequately in many
job and general repair shop.

11
GAS WELDING
Maximum temperature in this process is
32000C
Oxy-acetylene welding

12
GAS WELDING
Gas flames

13
GAS WELDING
a) Leftward or fore-hand welding
Gas welding techniques

14
GAS WELDING
a) Leftward or fore-hand welding
• Welder holds blowpipe/welding torch in his right hand and filler rod in left hand.
• Welding flame is directed from right to left.
• The welding torch is given a small sideways movement and the filler rod should be
moved steadily without sideways movement.
• This technique is generally used on thin metals i.e. having thickness less than 5 mm.

15
GAS WELDING
b) Rightward (Backward) welding

16
GAS WELDING
• Welding torch is held in the right hand of the welder and the filler rod in the left
hand.
• But, welding flame is directed from left to right.
• In this, the welding torch has no lateral movement.
• In this process, the welding speed is 20-25 % higher and fuel consumption is 15-
25 % lower than the leftward technique.

17
GAS WELDING
Comparison of Rightward and leftward technique
SR NO Rightward (Backward) technique Leftward (forward) technique
1 The quality of obtained weld is better. The weld quality is poor than rightward
technique.
2 No bevelling is required for welding up to
8.2 mm plate
Bevelling is required for welding above 3mm
plate thickness.
3 The welding is done from left hand to right
hand.
The welding is done from right hand to left hand.
4 The total volume of deposited metal is
smaller, which reduces the shrinkage and
distortion.
The total volume of deposited metal is more.

18
GAS WELDING
Gas welding equipment
1. Oxygen gas cylinder
• These are black painted and valve outlets are screwed right handed.
• The material used for cylinder is generally steel or alloy steel.
2.Acetylene gas cylinder
• These are painted maroon and the valves are screwed left handed.
• It is made up of steel
3.Oxygen and acetylene pressure regulators
• Used to reduce high pressure of gas in the cylinder to working pressure.
• Produce a steady flow, if gas pressure is varying.

19
GAS WELDING

20
GAS WELDING
4. Oxygen and acetylene gas hoses
• An oxygen hose is coloured blue and has right handed thread connections, whereas an acetylene hose is
red and has left handed thread connections.
• They are made up of rubber.
5. Welding torch or blow-pipe
6. Gas welding filler rods and fluxes
7. Goggles and gloves
8. Spark lighter

21
GAS WELDING

22
GAS WELDING

23
GAS WELDING
Advantages
• Operator has control over the temperature of weld zone.
• The rate of heating and cooling is relatively slow.
• The equipment is versatile, low cost, self-sufficient and generally portable.
• Low equipment and maintenance cost.
Disadvantages
• Refractory and reactive metals cannot be welded.
• More time is required than arc welding.
• More safety problems are associated with the handling and storing of gases.
• Fluxes used in welding produces fumes that are irritating to the eyes, nose, throat and lungs.
• Heavy sections cannot be welded economically.
Applications
• Joining thin materials
• Joining most ferrous and non-ferrous metals
• In automobile and aircraft industries
• In sheet metal fabricating plant

24
Arc welding
• Arc welding is the most expensive employed method of joining metal parts.
• Source of heat is an electric arc.
• The arc column is generated between an anode, which is the positive pole of DC power
supply, and the cathode, the negative pole.
• When these two conductors of an electric circuit are brought together and separated for a
small distance of 2 – 4mm such hat the current continues to flow through a path of ionized
particles, called plasma, an electric arc is formed.

25
Arc welding

26
Arc welding
• It is a fusion welding process in which welding heat is obtained from an electric arc between an
electrode and the workpiece.
• The temperature produced at the centre of an arc is 6000 to 70000C.
• In this, the base metal is melted by the temperature of the arc, forming a pool of molten metal.
• Either A. C. or D. C. supply is used.
• The electrodes used in the process are of two types i.e. bare and coated electrodes.
• The length of electrodes varies from 250 mm to 450 mm.

27
Advantages
• It is most versatile process which can be applied for both thick and thin sections.
• Welding of complicated shapes can also be done.
• Welding can be done in any position with high weld quality.
• Welded parts are neat and smooth.
Arc welding

28
Arc welding
Disadvantages
• As the electrodes are coated, the chances of slag entrapment and their related defects are more.
• Welding control is difficult.
• The process needed filler material.
• It is a slow process.
Applications
• Air receiver, boilers, pressure vessels fabrication
• Automobile, chemical and aircraft industry
• Ship building and bridge construction

29
Arc welding
• A.C. or D.C. machine
• Electrode and holder
Bare electrodes
Coated electrodes
Consumable electrodes
Non consumable electrodes
• Filler rod and fluxes
• Cables and cable connector
• Earthing clamps
• Chipping hammer
• Wire brush
• Helmet, safety goggles, hand glove, aprons, sleeves etc.

30
Arc welding
ARC welding Methods -
• Gas tungsten arc welding (TIG)
• metal inert gas welding (MIG)
• Submerged arc welding
• Plasma arc welding
• Flux cored arc welding
• Carbon arc welding
• Metal arc welding
• Electro slag welding
• Atomic hydrogen arc

31
Arc welding - TIG
• Gas tungsten arc welding (TIG)
• Uses intense heat of an electric arc between
non consumable tungsten electrode and the
material to be welded.
• The shielding is obtained from an inert gas such
as helium or argon or a mixture of the two.
• It produces high quality welds in nonferrous
metals.
• No weld cleaning is necessary
• The arc and weld pool are clearly visible
to the welder

32Gujrathi S.M. Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
• Metal inert gas welding (MIG) Uses a high heat of an electric arc between a continuously fed, consumable
electrode wire and the material to be welded.
• In this process the wire is fed continuously from a reel through a gun to constant surface which imparts a
current upon the wire.
• The current ranges from 100 – 400 A depending upon the diameter of the wire
• The welding gun can be either air or cooled depending upon the current being used.
• Advantages – no flux is required, high welding speed, increased corrosion resistance, easily automated welding,
high economy, welds all metals including aluminum and stainless still
Arc welding - MIG

33
Arc welding - MIG

34
Arc welding – Submerged arc
• Sometimes called hidden arc or subarc
welding
• The arc is formed between the end of a
continuous depositing surface, under
the layer of protective mineral powder
flux or melt, which can also be used to
add alloying elements to the joint
ahead of the welding wire and while the
weld is being made the arc is
submerged under the powder and is
invisible

35
Arc welding - Plasma arc welding
• Plasma is high temp ionized gas and occurs in any electric arc between two
electrodes
• The main function of the plasma gas is shielding the body of the torch from
the extreme heat of the cathode.
• In this process the penetration is deep and through, and much work can be
done without filler metal.
• Any known material is melted, even vaporized by the plasma arc process
• Results are clean and 2 – 5 times as fast as TIG welding with same equipment
cost
• It requires automatic control and is not practical for short welds.

36
Arc welding - Plasma arc welding

37
Arc Welding - Flux cored arc welding
• The inner core type welding is an
inside out wire with the flux inside a
tubular electrode.
• The equipment needed is simple : a
constant voltage dc power source, a
wire feeder and a lightweight gun,
which is like the MIG holder without
gas and cooling attachment. So
continuous welding is possible.
• The welds are strong and tough

38
Arc Welding - Carbon arc welding
• In this method, a rod of carbon is used as negative
electrode and the work being welded as positive. The
reason to use carbon rod as negative electrode is that
less heat will be generated at the electrode tip than that
at the workpiece and carbon from the electrode will not
fuse and mix up with the job.
• The process is best to the joints which need to be
melted without the addition of filler.
• The process is used for welding sheet steel, copper
alloys, brass, bronze and aluminium

39
Arc Welding - Metal arc welding
• A melt rod is used as one electrode while the work
being welded is used as another electrode.
• Both AC and DC may be used.
• A welding shows different bead characteristic under
different conditions :
• Welding current too low – excessive pilling of
the metal
• Welding current too high – causing excessive
splatter
• Welding too high – bead too small
• Welding speed too slow – cause excessive pilling
up of weld metal
• Proper current and timing – create smooth,
regular, well formed bead.

40
Arc Welding - Electro slag welding
• It produces coalescence through electrically
melted flux which melts both the filler
metal and the surface of the workpiece to
be melted.
• The consumable wire electrode may be
solid or flux coated but most or all of the
shielding is provide by an argon and co2 gas
mixture injected into the gap.
• It is used particularly for welding thick
(25mm or over) plates and structures for
turbine shafts, boiler parts and heavy
presses

41
Arc Welding - Atomic hydrogen arc
• An AC arc is maintained between the two
non consumable tungsten electrodes
while a stream of hydrogen gas under a
pressure of about 0.5 kgf/cm2 is passed
through the arc and around the electrode.
• It is capable of producing smooth,
uniform, strong and ductile welds.
• For welding of stainless steel, non ferrous
metal, alloy steel

42
Difference
SR NO TIG MIG
1 Non-consumable electrodes are used Consumable wires are used
2 Tungsten or tungsten alloys electrode
are used.
Bare welding wire is made of desired
composition.
3 Electrode generate only arc. Electrodes generates arc and melt also.
4 Easier for thin and small parts Widely used for thick plates.
5 Welding torch is water cooled. Welding torch is air or water cooled.
6 Used for joining dissimilar metals. Used for joining similar metals.
7 It is a slow process. Fast process.

43
Resistance Welding
• In this process, coalescence is produced by the heat
obtained from resistance offered by the workpiece.
Factors involved in resistance welding
• Current
• Pressure
• Time
• Area of electrode tip
• 𝑯=𝑰2Rt
• Copper electrodes are used

44
Resistance Welding
Advantages
• Rate of production is high.
• Filler rod is not required.
• The equipments used are semi-automatic.
• Less-skilled operators are required for the operation.
• Both similar and dissimilar metals can be welded.
• High reliability and reproducibility of welding joints are obtained.
Limitations
• High initial cost.
• Skilled persons are required for maintenance of equipment.
• In some materials, special surface preparation is required.
• Workpieces of higher thickness cannot be welded.
Applications
• Joining of sheets, bars, rods and tubes.
• Making of tubes and furniture.
• Welding of aircraft and automobile parts.
• Making of cutting tools, fuel tanks of cars, tractors, etc.

45
Resistance Welding
Types of Resistance welding
• Spot welding –
Applications
• Used in automobile and aircraft
industries
• For joining sheet metal stampings

46
Resistance Welding
• Types of Resistance welding
• Seam welding -
Applications
Welding of low carbon, high carbon and low
alloy steels, Al, Ni, Mg and their alloys
These welds can be done in square, round or
rectangular parts

47
Resistance Welding
Types of Resistance welding
• Projection welding
Applications –
• Mostly used in automobile industries
• Small fasteners, nuts can be welded to large
components
• Welding of Naval brass alloys, stainless steel and
titanium alloys

48
Types of welded joint
Lap or fillet weld
1. Lap joint or fillet joint
2. Butt joint
A – single transverse fillet
B – double transverse filet
C – parallel fillet

49
Welding defects

50
Solid state welding
• Interatomic bonds may be established by
bringing atoms of two surfaces in close enough
proximity to assure adhesion
• Relative movement of the surfaces under
pressure and controlled roughness are helpful
in breaking through surface films.
• While theoretically no pressure would be
required for bonding, in practice pressure is
necessary to assure conformity with the
contacting surface.
• Solid state welding is often applied when other
techniques fail.
• It include : friction, ultrasonic, diffusion

51
Solid state welding
• Diffusion –
• It needs two kinds of surfaces that can come
into intimate contact under pressure. This
pressure is applied for a period of hours.
• This process makes it possible to join metal
to metal, metal to ceramic with
intermediate bonding materials. Temp that
approaches is approximately 900 degree
Celsius

52
Solid state welding
• Ultrasonic welding
• Ultrasonic welding will join similar or dissimilar metals by the
introduction of high frequency vibratory energy into overlapping
metals into the area to be joined.
• No flux, filler metal, electric current and heat
• High frequency vibratory energy is then transmitted into the
weld area for a brief interval
• The maximum thickness by this process may vary from 0.38 –
2.5 mm depending upon metal

53
Solid state welding
• Friction welding
• The frictional energy generated when two
bodies slide on each other is transformed
into heat ; when the rate of movement is
high and the heat is contained in a narrow
zone, welding occurs.
• Dissimilar metals are easily joined

54
Brazing
• A process that uses a metal alloy that melts above 840°F, but less than the melting point of the base metal.
• Brazing relies on capillary action to draw the filler metal into the joint or to keep it in the joint.
• The capillary effect is a function of the ability of the liquid to wet a particular material.
• Requires very small gap between metal surfaces, clean surfaces and flux.
• In case of brazing joining of metal pieces is done with the help of filler metal.
• Filler metal is melted and distributed by capillary action between the faying surfaces of the metallic parts being
joined.

55
Brazing
• The filler metal is drawn through the joint to
create this bond is capillary action. In a brazing
operation, you apply heat broadly to the base
metals. The filler metal is then brought into
contact with the heated parts. It is melted
instantly by the heat in the base metals and
drawn by capillary action completely through
the joint

56
Soldering
• Soldering is very much similar to brazing.
• The major difference lies with the filler metal, the filler metal used in case
of soldering should have the melting temperature lower than 450°C.
• Soldering is normally done by melting the solder with a soldering iron and
applying it to the two metals that are going to be joined together.
• The filler metal used in the process is called solder, which distributes
between the closely fitted surfaces.

57
Advantages of Brazing & Soldering
• Joining dissimilar metals and non-metals.
• Low temperature compared to welding.
• less thermal distortion.
• Less chance of damage
• Speed of joining.
• Less manual skills.

58
Braze Welding
• Also called as bronze welding
• Bronze welding does not mean the welding of bronze but it is welding
using bronze filler rod.
• It is a method of welding where a groove, fillet, plug or slot is made
by using a non ferrous filler material having a melting point below
that of the parent metal but above 427 ° C

59
Comparison points
• Write down comparison points between – soldering and brazing
• Soldering, brazing and welding
• Arc welding, gas welding and resistance welding
• Comparison between all types of arc welding

60
Thank
You

Unit 4 joining process

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Unit 4 joining process

Similar to Unit 4 joining process (20)

More from Gujrathi Sonam

More from Gujrathi Sonam (9)

Recently uploaded

Recently uploaded (20)

Unit 4 joining process