What is the advantages and disadvantages of welding? (2+ve and 4-ve)
+ve: permanent & economical
-ve: high labour costs, energy-intensive, low ease of disassembly, quality defects
Purpose of welding (2 pts)
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)
2 types of welding & their differences (2 pts)
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
What is a weld joint?
The junction at which the edges/surfaces of parts of joined (via welding)
Types of Joints (8 pts)
- Fillet (curved)
- Groove (within)
- Plug (circular hole)
- Slot (slot hole)
- Spot (localised)
- Seam (continuous spot)
- Flange (filler)
- Surfacing (alter surface)
Of the 8 types of weld joints, which is/are also most likely considered solid state welds?
Spot, Seam and Projection Welding
What is the purpose of surfacing weld?
- Alter surface properties (oxidation or corrosion resistance)
- Deposition of filler/bulk (new surface)
- NOT for joining
What is Arc Welding? And how does it work?
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.
What are the 7 types of Arc Welding?
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
What is resistance welding and what is the process?
Fusion welding that uses BOTH heat & pressure, via oppositely charged electrodes squeezing parts together
What are the 3 types of resistance welding?
Spot, Seam and Projection resistance welding.
Which welding processes can be used for non-ferrous metals?
Basically every welding process can be used
Which welding processes cause weld nuggets to form?
Spot and Projection Welding
Which welding processes requires filler material?
Arc Welding - SMAW, MIG, Flux-cored, Electrogas
Fusion Welding - Oxyfuel, Laser Beam
What is the weld quality affected by?
- Weldability
- Residual stresses & heat/pressure distortion
- Cracks
- Cavities (porosity)
- Solid inclusions
- Incomplete fusion
What are the considerations for weldability?
Types of process
Types of Base Metal
Filler
Surface Conditions
Good weldability is characterized by?
Ease of welding + Absence of weld defect + Strength, toughness, ductility in joint
How is residual stresses & distortion prevented/controlled?
- Welding Fixtures
- Heat Sinks
- Proper Welding Conditions
- Stress relief heat treatment
- Preheating base part
- Tack Welding at multiple points
How does cracks form on welds?
Caused by poor weld process control:
- metals are not compatible
- residual stresses
- oxidation
- change in material properties
How does cavities occur in welds?
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
How does solid inclusion occur in welds?
Caused by entrapment of non-metallic material. (Arc Welding)
Formation of metallic oxides due to reaction with atmospheric O2
Examples: Slag, Metallic Oxides
How does Incomplete Fusion Occur?
Results in joints that are not completely filled between the 2 workpiece -> intended properties are not achieved.
