1. Welding

2. Welding Welding conditions
Parts are joined together by Fusion. Fusion is brought about by a combination of heat and pressure between parts being joined. In normal welding processes very high temperatures and little or no pressure is used.
Welding conditions
Smooth joint surfaces that match each other
Surfaces clean and free from oxides, grease and dirt.
Metals to be joined have same microstructure

3. Welding conditions continued….
The metals should be good quality (no internal impurities)
Welding Preparation
Before starting a weld, the joint edges should be carefully prepared.
Beveling large edges
Cleaning (Chemical/Mechanical)
Weld Joints
Welding Symbols
Weld defects
Welding Techniques

4. Weld Joints - Parts of a Weld Joint
Joint root
Groove face, Root face and Root edge
Root opening and Bevel
Bevel angle, Groove angle and Groove radius
Weld Joints - Types of Weld Joint
Butt Joint
Lap Joint
T Joint
Corner joint
Edge Joint
Splice Member

5. Joint Root
is that portion of a joint to be welded where the members are closest to each other
The joint root may be either a point, line, or an area
The joint roots are shown as shaded areas in (A)-(D) and lines in (E) (F)

6. Groove face, Root face and Root edge
Groove face is “ that surface of a member included in the groove”
Root face (land) is “that portion of the groove face within the joint root”
Root edge is a root face of zero width

7. Root opening and Bevel
Root opening is the separation between the work pieces at the joint root
Bevel (chamfer) is an angular edge preparation

8. Bevel angle, Groove angle and Groove Radius

9. Butt Joint
A joint between two members aligned approximately in the same plane

10. Lap Joint
A joint between two overlapping members

11. T Joint
A joint between two members located approximately at right angles to each other

12. Corner Joint
A joint between two members located at right angles to each other

13. Edge Joint
A joint between the edges of two or more parallel or nearly parallel members

14. Splice member
is “ the work piece that spans the joint in a spliced joint
Single-spliced butt joint
Double-spliced butt joint with joint filler

15. Basic components of a WELDING SYMBOL
Reference Line (Required element)
Arrow
Tail
Reference Line must always be horizontal,
Arrow points to the line or lines on drawing which clearly identify the proposed joint or weld area.

16. OTHER SIDE ARROW SIDE Weld Symbol Terminology Work
Fillet Weld (Arrow Side Only)
Fillet Weld (Both sides)

17. Welding Techniques Types of Welding
There are many different methods of welding. The difference between them is outlined by two important features
The way the metal is heated
The way additional filler metal if any is fed into the weld
Types of Welding
Electric Arc Welding
Gas Welding
Resistance Welding
Friction Welding
Robotic Welding

18. Electric Arc Welding
The heat for fusion is supplied by an electric arc
Arc is formed between electrode and work this melts and fuses the joint edges

19. Types of Electric Arc Welding
Manual Metal Arc (MMA)
Metal Arc Gas Shielded (MAGS) MIG
Tungsten Arc Gas Shielded (TAGS) TIG
Submerged Arc Welding (SAW)

20. Manual Metal Arc (MMA) Applications
Most widely used of all the arc welding processes
Commonly called “stick” welding
Applications
repair work, structural steelwork,

21. Touch electrode against work withdraw electrode to establish arc
Touch electrode against work withdraw electrode to establish arc. Heat of arc melts base metal, the electrode’s metal core, and any metal particles in electrode’s covering.
Heat also melts, vaporises, or breaks down chemically
non-metallic substances in covering for arc shielding. Mixing of molten base metal and filler metal from electrode produces coalescence required to effect joining.

22. Advantages Dis-advantages Used with many electrode types & sizes
Used in all positions
Used on great variety of materials
Flexibility in operator control makes it the most versatile of allwelding processes
Low cost of equipment
Dis-advantages
Rod becomes shorter & periodically needs replacing
Slows production rate (% time welder welding)

23. The Electrode and Coating
Coating is a combination of chemicals
Cellulosic electrodes contain cellulose
Rutile electrodes titanium oxide (rutile)
Basic electrodes contain calcium carbonate (limestone) and calcium fluoride (fluorspar)

24. Function of Electrode Coating
Produce gas to shield weld pool from oxidisising effects of atmosphere
Fluxing elements help weld pool to form
Helps slag to form-removes impurities
Slag slows down cooling preventing Brittleness
Can contain alloying elements or additional filler metal

25. Equipment used in MMA

26. AC power source
Takes power directly from mains power supply. It use a transformer to supply the correct voltage to suit the welding conditions.

27. DC power source
Two types
DC generator
Transformer-rectifier

28. DC Generator
An electricity generator is driven by a motor. The motor can be electric, petrol or diesel. The generator provides DC current for the arc

29. Transformer-rectifier
A transformer with an electrical device to change AC to DC, this is known as a rectifier. It has the advantage of being able to supply both DC and AC

30. Basic Transformer-rectifier circuit (AC to DC)
Step Down
On/Off
switch
Transformer
Bridge Rectifier
Smothing
Capacitor
High AC Voltage
230V +
DC output _
Low AC Voltage V A B C D

31. A B C D

32. Transformer
A transformer converts AC current at one voltage to AC at a higher or lower voltage
Step Down
Step Up

33. Metal Arc Gas Shielded (MAGS) MIG
MIG is similar to MMA in that heat for welding is produced by forming an arc between a metal electrode and the workpiece
Applications
Sheet and Heavy plate, production
welding by robots on cars

34. MIG is similar to MMA in that heat for welding is produced by forming an arc between a metal electrode and the workpiece; the electrode melts to form the weld bead. The main difference
is that the metal electrode is a small diameter wire fed from a spool and a sheilding gas is used. As the wire is continuously fed, the process is often referred to as semi-automatic welding.

35. Advantages Large gaps filled or bridged easily
Welding can be done in all positions
No slag removal required
High welding speeds
High weld quality
Less distortion of work piece

36. Equipmnt used in MAGS Shielding Gas Three major elements are :
Welding torch and accessories
Welding control & Wire feed motor
Power Source
Shielding Gas

37. Welding torch and accessories
GAS DIFFUSER
NOZZLE
CONTACT TIP
The welding torch guides the wire and shielding gas to the weld zone.
Brings welding power to the wire also
Major components/parts of the torch are the contact tip, shielding gas nozzle, gas diffuser, and the wire conduit

38. Welding control and wire feed motor
Main function is to pull the wire from the spool and feed it to the arc
Controls wire feed speed and regulates the starting and stopping of wire feed

39. Welding power source Positive (+) lead is connected to the torch
Negative (-) lead is connected to the work piece

40. Sheilding Gas
Purpose of shielding gas is to protect the weld area from the contaminants in the atmosphere
Gas can be Inert, Reactive, or Mixtures of both
Argon, Helium, and Carbon Dioxide are the main three gases used in MAGS

41. Tungsten Arc Gas Shielded (TAGS) TIG
TIG is similar to MMA in that heat for welding is produced by forming an arc between a metal electrode and the workpiece
Applications
Used in joining magnesium and
Aluminium, stainless steels
for high quality welding
Thin sheet material

42. In the TIG process the arc is formed between a pointed tungsten electrode and the work piece in an inert atmosphere of argon or helium. The small intense arc provided by the pointed electrode is ideal for high quality and precision welding.
The electrode is not consumed during welding. When filler metal is required, it must be added separately to the weldpool. There are two currents one for starting the arc the other switched on using a trigger or foot pedal, this is a high frequency current
to maintain the arc, this is generated by a separte unit.

43. Advantages Superior quality welding Can be used in mechanised systems
Used to weld aluminium and stainless steels
Free of spatter
Low distortion

44. Equipment used in TAGS Power source Electrodes
TIG must be operated with a constant current power source - either DC or AC
Electrodes
Electrodes for DC welding are normally pure tungsten. In AC welding, as the electrode will be operating at a much higher temperature, It should be noted that because of the large amount of heat generated at the electrode, it is difficult to maintain a pointed tip and the end of the electrode assumes a spherical or 'ball' profile.

45. Sheilding Gas
Shielding gas is selected according to the material being welded.
 Argon
 Argon + Hydrogen
 Argon/Helium
Helium is generally added to increase heat input (increase welding speed or weld penetration).  Hydrogen will result in cleaner looking welds and also increase heat input, however, Hydrogen may promote porosity or hydrogen cracking.

46. Submerged Arc Welding (SAW)
Similar to MIG welding, SAW involves formation of an arc between a continuously-fed bare wire electrode and the workpiece
Applications
SAW welding taking place in the flat position. Ideal for heavy workpieces
Carbon-manganese steels,low alloy steels and stainless steels

50. Submerged Arc Welding (SAW)
The process uses a flux to generate protective gases and slag, and to add alloying elements to the weld pool. A shielding gas is not required. Prior to welding, a thin layer of flux powder is placed on the work piece surface. The arc moves along the joint line and as it does so, excess flux is recycled via a hopper. Remaining fused slag layers can be easily removed after welding. As the arc is completely covered by the flux layer, heat loss is extremely low. There is no visible arc light, welding is spatter-free and there is no need for fume extraction.

51. Equipmnt used in SAW Wire
SAW is normally operated with a single wire on either AC or DC current. Common variants are:
twin wire
triple wire
single wire with hot wire addition
metal powdered flux addition
All contribute to improved productivity through a marked increase in weld metal deposition rates and/or travel speeds.

52. Flux Fluxes used in SAW are granular fusible minerals
The flux is specially formulated to be compatible with a given electrode wire type so that the combination of flux and wire yields desired mechanical properties. All fluxes react with the weld pool to produce the weld metal chemical composition and mechanical properties

53. Gas Welding (Oxy-acetylene)
A number of welding processes use a flame produced by burning a mixture of fuel gas and oxygen. The gas usually used is Acetylene but other gases are also used.
Separate cylinders and a hose pipe from each cylinder transports the gases to a torch.
Gas and fuel mix in the torch
3100°C.

54. During the welding heat from the flame is concentrated on the joint edges until the metal melts and starts to flow. When the molten metal from both sides melts it starts to fuse, when the metal cools down the two parts become Permanently joined
Additional Filler Metal is fed in by hand into the weld pool, at regular intervals where it becomes molten and joins with the parent metal.

55. Secondary Combustion envelope
The Oxy-acetylene welding Flame
Reducing or Carburizing Excess acetylene (0.9:1) (Alloy steels and aluminium alloys)
Inner Cone
Max. Temp. Zone
Oxidizing Excess oxygen (1.5:1) (Brasses, Bronzes, copper)
Secondary Combustion envelope
Neutral Equal acetylene & oxygen (low carbon steel, mild steels).
Acetylene feather

56. The Oxy-acetylene welding Flame
Carburising
Neutral
Oxidising

57. Primary Combustion zone
The Oxy-acetylene welding Flame
The oxy-acetylene flame has two distinct zones.
The inner zone (Primary combustion Zone) is the hottest part of the flame. The welding should be performed so as the point of the inner zone should be just above the joint edges.
C2H O CO + H2
Primary Combustion zone

58. Secondary Combustion zone
The outer zone the secondary combustion envelope performs two functions
Preheats the joint edges
Prevents oxidation by using some of the surrounding oxygen from weld pool for combustion and gives off carbon dioxide and water vapour
CO + H2 + O CO2 + H2O
Secondary Combustion zone

59. Equipment used in O-A welding
The oxygen and acetylene hose pipes
Gases used
Gas pressure Regulators
Flashback arrestor
Welding torch/Welding nozzle
Filler rods and fluxes

60. The oxygen and acetylene hose pipes
Reinforced rubber hoses.
Acetylene hose has left hand thread couplings and colour coded red.
Oxygen hose has right handed thread couplings and colour coded blue

61. Gases used
Oxygen extracted from air and compressed into cylinders at high pressure. Cylinder is black. Oil should never be brought into contact and should not be used on fittings
Acetylene (C2H2) is a fuel gas. Cannot be compressed directly as explodes at high pressures. Cylinders are packed with porous material which is filled with acetone Acetone absorbs acetylene. Cylinder colour coded maroon

62. Gas Pressure Regulators
One gauge indicates the pressure of the cylinder and the other indicates the pressure in the supply pipe to the torch.

63. Welding torch Needle valves Mixer
Oxygen and acetylene are delivered to the torch by separate hoses. Each gas is controlled by a valve on the torch. The two gases mix in the torch and after they are ignited burn at the nozzle.
Needle valves
Mixer

64. Flashback Arrestors
These are positioned on both the fuel gas and oxygen supply between the hose and the regulator. Their purpose is to prevent the return of a flame through the hose into the regulator.

65. Filler Rods and fluxes
Filler rods are used when additional filler metal is required in the weld area they come in different diameters.
Fluxes protect the weld pool from contamination by oxygen and nitrogen, they are normally in paste form placed on a heated filler rod before welding begins

66. Resistance welding
Resistance welding uses the application of electric current and mechanical pressure to create a weld between two pieces of metal.  Weld electrodes conduct the electric current to the two pieces of metal as they are forged together. The welding cycle must first develop sufficient heat to raise a small volume of metal to the molten state.  This metal then cools while under pressure until it has adequate strength to hold the parts together.  The current density and pressure must be sufficient to produce a weld nugget, but not so high as to expel molten metal from the weld zone.  

67. Spot welding
Seam Welding

68. Spot welding
Ideal for joining light sheet metal. The electrodes are made from copper. Pressure is applied to the electrodes and an electric current is passed through the circuit. The high resistance between the joint faces causes rapid heating and fusing of a small globule of metal from both faces.

69. Seam welding
The rollers allow the workpiece to move through the welder continously. A stream of electrical pulses pass through the rollers and welds the joint

70. Resistance Welding Benefits
  High speed welding
  Easily automated
  Suitable for high rate production
  Economical
Resistance Welding Limitations
  Initial equipment costs
  Lower tensile and fatigue strengths
  Lap joints add weight and material

71. Friction welding
One part is held stationary while the other part is rotated
When the parts are hot enough the rotation is stopped and the parts forged together

72. Robotic welding
Robots are driven using actuators which control the robotic arm from an input signal. They can use hydraulic (large robots), pneumatic(small actuators with simple control movements) or electrical principles of operation.
A computer sends instructions in electrical signals or pulses. An interface converts these digital pulses into analogue electricity for the motors. The robot is fitted with sensors which can send feedback on the position of the robot.

73. Advantages of Robotic welding
Faster production rates
Efficent continous operation
Safe working practice
Reliable and consistent welds
Full automation
Cost effective
Examples
Automated welding of motor vehicles skeletel frames and bodies.

74. Robotic welding Terms
Lead through programming Teaching robot movements through guiding it manually through a sequence of operations. These are recorded to memeory
Machine Vision Area of vision robot has, limits which robot sensors can operate
Working enevelope The area within which a robot can operate. Where the work is caried out by robotic arm
Yaw left and right movment of robotic arm
Roll rotation of robot about one of its axis
Degrees of freedom These are the number of independent movements of the arm joints( or actuators) the robot has.