1. By: Dr.Behzad Heidarshenas
Welding technology
By:
Dr.Behzad Heidarshenas

2. JOINING Soldering Brazing Welding
Produces coalescence of materials by heating to soldering temperature (below solidus of base metal) in presence of filler metal with liquidus < 450°C
Brazing
Same as soldering but coalescence occurs at > 450°C
Welding
Process of achieving complete coalescence of two or more materials through melting & re-solidification of the base metals and filler metal

3. Advantages Soldering & Brazing
Low temperature heat source required
Choice of permanent or temporary joint
Dissimilar materials can be joined
Less chance of damaging parts
Slow rate of heating & cooling
Parts of varying thickness can be joined
Easy realignment
Strength and performance of structural joints need careful evaluation

4. Welding Advantages Most efficient way to join metals
Lowest-cost joining method
Affords lighter weight through better utilization of materials
Joins all commercial metals
Provides design flexibility

5. Common Arc Welding Processes
Weldability
Weldability is the ease of a material or a combination of materials to be welded under fabrication conditions into a specific, suitably designed structure, and to perform satisfactorily in the intended service
Common Arc Welding Processes
Shielded Metal Arc Welding (SMAW)
Gas Tungsten Arc Welding (GTAW) or, TIG
Gas Metal Arc Welding (GMAW) or MIG/MAG
Flux Cored Arc Welding (FCAW)
Submerged Arc Welding (SAW)

6. ARC WELDING
Arc welding is a process used to join two pieces of metal together.
How does it work?
A welder creates an electric arc that melts the metal and filler rod to create a pool of molten metal that hardens to fuse the two pieces of metal together.

7. Why is welding important?
Many of the things you use need to be welded.
Your car
Power line towers
Your school desk
Your bicycle

8. Why Learn to Weld?
Welding can help build a successful career to earn money.
Skilled Welders are in high demand.
Welding is challenging and high tech.

9. Basic Electricity and the Science of Welding
Voltage – The electrical potential or pressure that causes current to flow
Measured in Volts
Current – The movement of charged particles in a specific direction
Measured in Amps
Polarity
DC- (Direct Current Electrode Negative)
DC+ (Direct Current Electrode Positive)
AC (Alternating Current)
DC+
DC - AC

10. Basic Electricity and the Science of Welding
The electricity flows from the power source, through the electrode and across the arc, through the base material to the work lead and back to the power source

11. Basic Electricity and the Science of Welding
The electron flow you just learned about is what creates the arc in arc welding.
This is a form of electrical energy
How do we use that electrical energy to fuse metals together?

12. Basic Electricity and the Science of Welding
Here are some places to look to learn more about energy and energy transfers.
Forms of Energy
Energy Transformations

13. Basic Electricity and the Science of Welding
Changes of State and Chemical Reactions
During the welding process the metal changes states or forms.
What are the states of matter?
Solid
Liquid
Gas
Plasma
Click here to learn more about the changes of state

14. Basic Electricity and the Science of Welding
Changes of State and Chemical Reactions
So what changes of state occur during welding?
Initially the metal is a solid
When the arc starts the solid is converted into a liquid
Some of the liquid is converted into a gas vapor
When the arc stops the liquid cools to form a solid again – this is the newly formed weld joint
Liquid Solid
Solid weld joint
(gas vapor)

15. Basic Electricity and the Science of Welding
Changes of State and Chemical Reactions
Chemical Reactions
During the welding process certain chemical reactions take place.
Hydrogen, Oxygen, and Nitrogen can react in the weld puddle and cause changes in the structure of the weld weakening the weld.