Welding is a method of joining metals through fusion, applicable in various industries such as construction and manufacturing. There are several welding types, with arc welding being common, and safety guidelines are essential to prevent accidents. Various welding joints and techniques, including soldering and brazing, are also outlined, emphasizing the importance of proper equipment and materials.

1. WELDING
Part Three

2. INTRODUCTION
 Welding is a process of joining two similar or
dissimilar metals by fusion, with or without the
application of pressure and with or without the use
of filler metal.
 The fusion of metal takes place by means of heat
 Used as an alternative method for casting and
forging and as a replacement for bolted and
riveted joints.

3. APPLICATIONS
Construction
Military vehicle and
equipments
Ship building
Off-highway
equipments and
machines
Household furniture
Railroad Construction

4. CON..
Automobile & bus
construction Piping and pipe lines
Towers

5. CON..
Aircraft construction
etc.
Bridges construction
Repair of broken & damaged parts Storage tanks

6. WELDING TYPES
 Arc welding:
 MIG (Metal Inert Gas)
 TIG (Tungsten Inert
Gas)
 SAW (Submerged Arc
Welding)
 SMAW (Shielded Metal
Arc Welding)
 Resistance welding
 Gas welding
 Soldering and brazing

7. ARC WELDING
• Process that uses an electric arc to join the metals
being welded.
• All arc-welding processes have three things in
common: a heat source, filler metal, and shielding.
• The source of heat produced by the arcing of an
electrical current between two contacts.
• The power source is called a welding machine or
simply, a welder.

8. SAFETY
• Mishaps/accident frequently occurs in welding
operations.
• Result in serious injury to the welder or other
personnel working in the immediate area.
• In most cases, mishaps occur because of carelessness,
lack of knowledge, and the misuse of available
equipment.

9. CON…
Safety rules
• Never look at arc with naked eyes
• Always use a shield while welding
• Always wear the safety hand glove, apron and
leather shoes
• Ensure proper insulation and check before opening
• Apply eye drop after welding is over to relieve the
strain on eyes.

10. CON..
Eye protection devices

11. CON..
Welders protective clothing

12. CON..
Welders protective clothing

13. SHIELDED METAL ARC WELDING(SMAW)
• Is performed by striking an arc between a coated-
metal electrode and the base metal.
• The molten metal from the electrode flows together
with the molten metal from the base metal to form a
sound joint. This process is known as fusion.
• The coating from the electrode forms a covering,
shielding it from contamination; therefore the process
is called shielded metal arc welding.

14. PRINCIPLES OF SMAW
 The electrode and the work are part of an electric
circuit.
 This circuit begins with the electric power source
and includes the welding cables, an electrode holder,
a workpiece connection, the workpiece (weldment),
and an arc welding electrode.

15. CON..
Principles of SMAW

16. CON..
SMAW arc

17. SELECTING THE TYPE OF CURRENT
 The welding current used for stick welding may
be either alternating current or direct current
depending on the electrode being used.
 Direct current is the most common current
choice for stick welding.
 The current flows in one direction only and has
many advantages over alternating current for the
stick process.

18. CON..
 These advantages include:
 fewer arc outages,
 less spatter,
 easier arc starting,
 less sticking, and
 better control in out-of-position welds.

19. CON..
DCEP (Direct Current Electrode Positive or Direct
Current Reverse Polarity)or Reverse Polarity
connection.
DCEP connection
Best penetration
and bead profile.
For this reason.
Most electrodes
are made to weld
with DCEP.

20. CON..
 Result in a
narrow bead
with little
penetration.
 works well
when welding
on sheet
metal
DCEN connection
DCEN or Straight Polarity Connection

21. CON..
 Alternating current (AC) is an electrical
current that has both a positive and a negative
half-cycle value (polarities) alternately.
 Is a type of electrical current, in which the
direction of the flow of electrons switches back
and forth at regular intervals or cycles.
 Current flows in a specific direction for one half-
cycle, stops at the "zero" line, then reverses
direction of flow the next half-cycle at regular
intervals.

22. CON..
AC circuit

23. EQUIPMENTS AND ACCESSORIES
Welding generator AC/DC
Exhaust fan
Eye Shield
Hand gloves
Apron
Two cables- one for work
and one for electrode
Electrode holder
Electrode
Wire brush
Chipping hammer

24. WELDING TERMINOLOGY
• Filler metals
 A material used to fill
the space between two
pieces of metals when
welding.
 Two types in common
Welding rods
Welding electrodes
• Welding rod does not
conduct an electric current
during the welding
process. Only supply filler
metal to the joint.
• Electrode conducts the
current from the electrode
holder to the metal being
welded.

25. CON..
Consumable
Not only provide a path for
the current but they also
supply filler metal to the
joint.
An example is the electrode
used in shielded metal-arc
welding.
Non-consumable.
Only used as a conductor for
the electrical current, such as
in gas tungsten arc welding.
The filler metal for gas
tungsten arc welding is a
hand fed consumable
welding rod.
Electrodes are classified into two groups:

26. WELDING POSITIONS
Flat welding position
The letters associated
with the numbers
listed below
are F and G. As
mentioned, F is fillet,
and G is groove.

27. CON..
Horizontal welding position

28. CON..
Vertical welding position

29. CON..
Overhead welding position

30. TYPES OF WELDS
Is a weld deposit produced by a single pass with
one of the welding processes.
Weld bead (bead)

31. GROOVE WELDS
Welds made in the groove between two members
to be joined.

32. FILLET WELD
Used to join two surfaces that are at approximately
right angles to each other in a lap, tee, or corner joint.

33. SURFACING
Used to apply a hard, wear-resistant layer of metal to
surfaces or edges of worn-out parts.

34. CON..
Made to hold parts of an assembly in
proper alignment temporarily until
the final welds are made.
Tack weld

35. CON..
Are welds made
through holes or slots
in one member of a
lap joint.
Plug and slot welds

36. TYPES OF JOINTS
In this type of joint, the
edges of the metal to be
joint should be so made
that it gives a little shape
of ‘V’ at the place of
joint. Now on welding the
‘V’ or ‘U’ shape structure
is filled up giving rise to a
strong joint.
Butt joint

37. LAP JOINT
• This type of joint is used in joining two overlapping
plates so that the corner of each plate is jointed with
the surface of the plate.
• Common types of lap joints are single lap, double lap
or offset lap joint. Single welded lap joint do not
develop full strength as compare to double welded lap.

38. CON..
 Here metal pieces are
placed perpendicular
to each other at one
corner.
 Now the welding is
done in the corner.
Such joints are made
in frames, steel
boxes, etc.
Corner joint

39. CON..
In this type of joint,
the metal pieces are
placed in such a
manner that they
form the shape of ‘T’.
In other words the
angle between
surfaces is kept 900 as
shown in figure.
T-joint

40. CON..
In this joint two
parallel plates are
welded edge to edge.
Edge joint

41. BRAZING AND SOLDERING
• Is the process of joining
metal by heating the base
metal to a temperature
above 800°F and adding a
nonferrous filler metal that
melts below the base metal.
• Advantages does not
affect the heat treatment of
the original metal.
• Allows you to join
dissimilar metals.
 It needs source of heat, filler
metals, and flux.
 Heating Devices
 Furnace (mass production)
Or Individual torches
(oxyacetylene welding torch)
 Filler Metals
 Are nonferrous metals or
alloys
Brazing

42. CON..
• Silver-base alloys
• Aluminum-silicon alloys
• Copper
• Copper-zinc (brass)
alloys
• Copper-phosphorus
alloys
• Gold alloys
• Nickel alloys
• Magnesium alloys

43. CON..
Soldering
 Soldering is a process in which two or
more metal items are joined together by melting
and flowing a filler metal (solder) into the joint,
the filler metal having a lower melting point than
the workpiece.

44. CON..
 Extensively in
electronics industry
because of heat
sensitive components
 Jewelry components,
machine tools and
some refrigeration
and plumbing
components are often
assembled and
repaired. etc.
Used

45. OXYACETYLENE WELDING
 Acetylene is a carbonaceous
combustible gas.
 When it is burnt in presence
of oxygen gas in a controlled
manner the combustion
produces intense heat which
is sufficient to melt a metal.
 The flame is long, smoky
and yellowish in color.
 However when oxygen is
also supplied, the size of
the flame is reduces and it
is not smoky (bluish in
color)
 Heat is produced due to
following exothermic
chemical reaction
 2C2H2 + 5O2 = 4CO2
+H2O + heat

46. CON..
Oxygen cylinders and
houses
 Painted greenish or blush
most of the time.
Acetylene cylinders and
houses
 Painted reddish in color .
Oxygen cylinder
Acetylene
cylinder

47. Oxy-acetylene welding outfits
Con..

48. TYPES OF FLAMES
• Produced when the gas
mixture has equal
volumes of acetylene and
oxygen.
• Has two distinct zones
 Cone and an outer flame
surrounding the cone.
• Used for the welding of
most of the materials like
low carbon steels, cast
steels, cast iron etc.
Neutral flame

49. CON..
 Produced when the
amount of oxygen is
slightly more than the
acetylene.
 Very short in length and
sharper in shape.
 A hissing sound is
produced at the tip of the
torch.
 Used for welding brasses,
bronzes and cast iron.
Oxidizing flame

50. CON..
 Produced when the
oxygen is kept slightly
less than acetylene.
 Has three distinct zones.
 Advantageous for non-
ferrous metals, silver
soldering and hard facing.
Reducing or carburizing flame

51. ገለቶማ !