Joining vs Assembly
Joining: Forms a permanent joint between parts.
Assembly: Some methods allow for easy disassembly, while others do not.
What is welding?
Joining process in which two or more parts are coalesced at their contacting surfaces by the application of heat and/or pressure and/or filler material.
What are faying surfaces?
The part surfaces in contact or close proximity that rae to be joined.
What are the two forms of welding?
Fusion (molten material, filler material can be added) and solid-state (atomic diffusion below melting point, no filler material).
What is an autogenous weld?
A fusion weld done without using filler material.
What are the most popular types of fusion welding?
Arc welding, resistance welding, oxyfuel gas welding, electron beam welding, laser beam welding, etc.
What are the most popular types of solid-state welding?
Diffusion welding, friction welding, ultrasonic welding.
What are the types of automated welding?
- Machine welding (operator supervision)
- Automatic welding
- Robotic welding
What are the different weld types?
- Fillet weld (corner, lap, tee)
- Groove weld (mostly butt, but all except lap)
- Plug and slot weld (lap)
- Spot and seam weld (lap, edge)
- Flange and surface weld (edge)
What is the purpose of surface welding?
Increase the thickness or provide a protective coating.
What is a monolithic structure?
A one-piece, continuous piece produced by welding.
Can a welded joint stop crack propagation? If not, what type of joint can?
No. Bolted joints.
What is the heat affected zone?
A zone where the metallurgical properties were change by the exposure to heat.
What are the three zones created by a fusion weld?
- Fusion zone (columnar grains)
- Heat affected zone (coarse grains to finer grains)
- Unaffected base metal zone (original cold worked grains)
Failures often occur in which weld zone?
In the heat affected zone.
The changes in properties are a function of what?
Heat input rate.
When is pre and post heat processes most important?
When welding high thermal conductivity metals.
Are restraints useful during welding?
Yes, to reduce distortion. However, too many can create reaction stresses.
