Chapter 4 Welding

Question 1

What is the advantages and disadvantages of welding? (2+ve and 4-ve)

Answer 1

+ve: permanent & economical
-ve: high labour costs, energy-intensive, low ease of disassembly, quality defects

Question 2

Purpose of welding (2 pts)

Answer 2

a joining process where >= 2 parts (usually metallic) are coalesced at contacting surfaces through application of heat and/or pressure; may involve filler* materials (encourage coalescence)

Question 3

2 types of welding & their differences (2 pts)

Answer 3

Fusion Welding - melting of base metal, addition of filler for bulk & strength, and autogenous weld (no filler)

Solid State Welding - parts remain solid, heat and pressure used, no melting temperature

Question 4

What is a weld joint?

Answer 4

The junction at which the edges/surfaces of parts of joined (via welding)

Question 5

Types of Joints (8 pts)

Answer 5

• Fillet (curved)
• Groove (within)
• Plug (circular hole)
• Slot (slot hole)
• Spot (localised)
• Seam (continuous spot)
• Flange (filler)
• Surfacing (alter surface)

Question 6

Of the 8 types of weld joints, which is/are also most likely considered solid state welds?

Answer 6

Spot and Seam welds

Question 7

What is the purpose of surfacing weld?

Answer 7

1. Alter surface properties (oxidation or corrosion resistance)
2. Deposition of filler/bulk (new surface)
3. NOT for joining

Question 8

What is Arc Welding? And how does it work?

Answer 8

Arc Welding is a form of fusion welding.
Gap between electrode & base metal causes generation of heat, that melts the base metal into a pool that solidifies after electrode passes through.

Question 9

What are the 7 types of Arc Welding?

Answer 9

SMAW - Shielded Metal Arc Welding
MIG - Metal Inert Gas Welding
Flux-cored Arc Welding
Electrogas (vertical) Welding
Submerged Arc Welding
TIG - Tungsten Inert Gas Welding
Plasma Arc Welding

Question 10

What is resistance welding and what is the process?

Answer 10

Fusion welding that uses BOTH heat & pressure, via oppositely charged electrodes squeezing parts together

Question 11

What are the 3 types of resistance welding?

Answer 11

Spot, Seam and Projection resistance welding.

Question 12

Which welding processes can be used for non-ferrous metals?

Answer 12

Basically every welding process can be used

Question 13

Which welding processes cause weld nuggets to form?

Answer 13

Spot and Projection Welding

Question 14

Which welding processes requires filler material?

Answer 14

Arc Welding - SMAW, MIG, Flux-cored, Electrogas
Fusion Welding - Oxyfuel, Laser Beam

Question 15

What is the weld quality affected by?

Answer 15

• Weldability
• Residual stresses & heat/pressure distortion
• Cracks
• Cavities (porosity)
• Solid inclusions
• Incomplete fusion

Question 16

What are the considerations for weldability?

Answer 16

Types of process
Types of Base Metal
Filler
Surface Conditions

Question 17

Good weldability is characterized by?

Answer 17

Ease of welding + Absence of weld defect + Strength, toughness, ductility in joint

Question 18

How is residual stresses & distortion prevented/controlled?

Answer 18

1. Welding Fixtures
2. Heat Sinks
3. Proper Welding Conditions
4. Stress relief heat treatment
5. Preheating base part
6. Tack Welding at multiple points

Question 19

How does cracks form on welds?

Answer 19

Caused by poor weld process control:
- metals are not compatible
- residual stresses
- oxidation
- change in material properties

Question 20

How does cavities occur in welds?

Answer 20

Cavities occur die to gas entrapment during solidification: (Arc Welding)
1. fusion welding causes vaporisation
2. vapors (gases) within weld pool
3. Spherical cavities forms

Question 21

How does solid inclusion occur in welds?

Answer 21

Caused by entrapment of non-metallic material. (Arc Welding)
Formation of metallic oxides due to reaction with atmospheric O2

Examples: Slag, Metallic Oxides

Question 22

How does Incomplete Fusion Occur?

Answer 22

Results in joints that are not completely filled between the 2 workpiece -> intended properties are not achieved.