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Materials 2 > Welding > Flashcards

Welding Flashcards

1
Q

What is joining vs assembly?

A

Joining creates a permanant bond, assembly uses some mechanical fastener

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2
Q

What are the faying surfaces?

A

The two surfaces to be joined.

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3
Q

What needs to be considered when welding different metals?

A

Differing thermal expansion

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4
Q

Define fusion welding

A

When the base metals are melted.
Often uses filler material.
Ex. Arc welding, resistance welding, and oxyfuel gas welding

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5
Q

Define solid state welding

A

Base metals don’t melt: uses temp and pressure, no filler materials

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6
Q

What is diffusion welding?

A

DFW: Solid state fusion between two surfaces held under pressure

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7
Q

What is friction welding?

A

FRW: coalescence by heat of friction between surfaces

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8
Q

What is ultrasonic welding?

A

USW: coalescence by ultrasonic oscillatory motion parallel to contact surfaces held under pressure.

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9
Q

What are the three levels of automation in welding?

A

Machine - controlled by human
Automatic - equipment performs welding without human
Robotic - Welding implemented by robot

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10
Q

What are the 5 types of weld joints?

A 
Butt
Corner
Lap
Tee
Edge
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11
Q

What is a fillet weld?

A

Fills in the edges of a corner, lap or tee joint. Filler metal provides a triangular cross section. Requires minimum edge preparation, common in arc and oxyfuel welding.

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12
Q

What is a groove weld?

A

Used when part edges are shaped into some form of groove. Most commonly butt joints. could be V, U, J, square or double-V grooves.

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13
Q

What is a spot weld? Seam weld?

A

Used for lab joints, to hold two pieces together.

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14
Q

What is power density? What process have high power densities? Low ones?

A

PD = P/A
Power transmitted to work per unit surface area
High power density allows localized melting.
OFW has low PD because the heat is spread over large area.
AW has high PD.

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15
Q

What are the zones of a typical fusion weld?

A

The fusion zone is the columnar zone of melted filler, the weld interphase is the seam of coarse grained melted metal, the heat affected zone (HAZ) is the finer grained zone of heated metal, the unaffected zone has original grain structure.

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16
Q

Describe arc welding.

A

Heat comes from an electric arc between an electrode and the work. Usually adds filler.
The electric arc is sustained by a column of plasma.

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17
Q

What is arc time?

A

(time arc is on)/(time worked)
Manual welding has a 20% arc time
Machine welding has a 50% arc time

18
Q

What are the two forms of consumable electrodes?

A

Rods (must be changed frequently)

Wire (fed in continuously)

19
Q

What are nonconsumable electrodes made of?

A

Tungsten

20
Q

What is arc shielding? How is it done

A

Protection of the weld from O2, H2, and N2. Uses gasses or flux.

21
Q

What is flux?

A

Substance that shields the weld from gasses, and prevents other contaminants from getting into the weld.
It stabilizes the arc and reduces spattering.

22
Q

What are the different methods of flux application?

A

Pouring granular flux onto weld
Stick electrode coated with flux that melts
Flux contained in electrode core and released as electrode is consumed

23
Q

What type of power is better for AW?

A

DC has better control, but is more expensive.

24
Q

Describe Shielded Metal Arc Welding.

A

SMAW: Uses a consumable electrode with a filler rod that provides flux and shielding.
Sometimes called stick welding.
Produces slag.
Used for steels, cast irons, but not for aluminum, copper, or titanium

25
Q

Describe Gas Metal Arc Welding.

A

GMAW: Uses consumable bare wire shielded by gas.
No slag.
Has better arc time than SMAW because of continuous wire feed.

26
Q

Describe Flux-Cored Arc Welding.

A

Self-shielded has a core that produces sheilding gas
Gas-shielded uses externally supplied gas
Has a core with flux included.

27
Q

Describe Electrogas Welding.

A

EGW: Uses molding shoes to contain molten metal

28
Q

Describe Submerged Arc Welding.

A

SAW: Uses granular flux and bare wire. Prevents sparks, spatter, and radiation.

29
Q

Describe Gas Tungsten Arc Welding.

A

GTAW: Non consumable tungsten rod. Used with or without filler added from a separate rod or wire.
Used for aluminum and stainless steel.
Slower and more expensive than consumable processes, but has high quality welds, no spatter, and no post-weld cleaning (because no flux).

30
Q

Describe Plasma Arc Welding.

A

PAW: Special form of GTAW that uses a constricted plasma arc directed at weld area. Extremely high temperatures at weld site, high energy density.

31
Q

Describe Resistance Welding.

A

RW: Heat is generated by electrical resistance to current flow at welding junction. Usually used for spot welding.
Done by two opposing electrodes that apply pressure to the place to be welded.
No filler required, easy and fast, usually used for lap joints.

32
Q

What are the advantages of SSW?

A

No heat affected zone, so metal retains cold work properties
Can bond entire contact surface rather than just seams
Can bond dissimilar metals

33
Q

Describe forge welding.

A

Occurs at hot working temperature, metals are hammered together.

34
Q

Describe cold welding.

A

High pressure causes deformation and therefore bonding. Surface must be clean, and at least one metal should be ductile.
No heat is applied, but deformation raises work temp.

35
Q

What causes distortion of work when welding?

A

Rapid heating and cooling causes expansion and contraction, causing residual stresses. These stresses cause warping.
Problematic because heating is localized, melts base metals, and location of heating is in motion.
Can be reduced by physically restraining work or removing heat.

36
Q

What are welding cracks?

A

Small fractures in weld or adjacent base caused by low ductility of weld or metal. Is bad because reduces strength.

37
Q

What are welding cavities?

A

Porosity : caused by trapped gas

Shrinkage voids : caused by shrinkage during solidification.

38
Q

What are solid inclusions?

A

Slag or metal oxides that get trapped in weld metal.

39
Q

What is incomplete fusion?

A

Welds that don’t fully fill grooves.

40
Q

What is the perfect weld profile? What are bad ones?

A

Profile should fully fill weld but not run over. It should not melt away adjacent base metal, nor under fill groove, nor overlap base metal.

41
Q

What are nondestrucive testing methods?

A 
Ultrasonic testing (sound waves to detect imperfections)
Radiographic testing (x-rays or gamma rays to take picture of weld)
42
Q

What are destructing testing methods?

A 
Mechanical tests (similar to tensile or shear tests)
Metallurgical tests (photomicrographs of weld)

Materials 2 (12 decks)

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