Welding Fundamentals

VERY IMPORTANT FOR FINAL.

What is joining?

Welding, brazing, soldering, and adhesive bonding forming a permanent joint between parts

What is assembly?

Mechanical methods (usually) of fastening parts together; Some allow for easy disassembly

What is welding?

A joining process in which two (or more) parts are coalesced at teir contacting surfaces by applying heat and/or pressure

What are some key characteristics of welding?

Provides a permanent join

Usually most economical way to join parts

Not restricted to a factory environment

What are some limitations of welding?

Performed manually with high labor costs

Utilize high energy and are inherently dangerous

Do not allow for convenient diassembly

Joints can have quality defects that can be difficult to detect

What are the two types of welding?

Fusion & solid state welding

What is fusion welding?

Joining processes that melt the base metals

What is arc welding (AW)?

Melting of the metals by an electric arc (ie. stick welding, TIG, MIG)

What is the difference between TIG and MIG welding?

TIG (Tungsten Inert Gas) uses a non-consumable tungsten rod to make the arc.

MIG (Metal Inert Gas) uses a consumable wire electrode that becomes the filler metal.

What is resistance welding (RW)?

Melting by heat from resistance to an electric current between faying surfaces held together under pressure (ie. spot welding)

What is oxyfuel gas welding (OFW)?

Melting by an oxyfuel gas like acetylene

How does arc welding work?

During the weld, the base metal is melted and filler metal is added to the motel pool, protected by a shielding gas like argon

What is diffusion welding (DFW)?

Solid state diffusion between two surfaces held together under pressure at elevated temperature

What is friction welding (FRW)?

Using heat of friction to join two surfaces together

What is the welder & fitter?

Welder manually controls path & placement of welding gun

Fitter arranges parts prior to welding

What are some safety hazards with welding?

High temperatures of molten metals

Certain processes use fuels (acetylene in OFW) that are fire hazards

High electrical power can cause risk of shock

UV radiation from arc welding can be dangerous to eyes (requires welding helmet)

Sparks, smoke, fumes from metal & flux must be ventilated properly

What kind of joint is this?

Butt joint

What kind of joint is this?

Corner joint

What kind of joint is this?

Lap joint

What kind of joint is this?

Tee joint

What kind of joint is this?

Edge joint

How does fusion work with welding?

Fusion requires high density heat energy to cause localized melting of base metals with the least amount of energy possible

What is power density?

Power transferred to workpiece per unit surface area [W/mm²]

What happens if the power density is too high? Too low?

If it’s too high, localized temperatures vaporize metal in the affected region.

If it’s too low, heat is conducted into workpiece so melting never occurs.

What are the features of a fusion welded joint?

Fusion zone, weld interface, heat affected zone (HAZ), unaffected base metal zone

What is the heat affected zone?

Metal has experienced temps below melting but high enough to change the microstructure

Heat treated region that typically negatively affects the mechanical properties.