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Flashcards in Surface Treatments Welding 6 Deck (28)
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1
Q

What are some reasons why manufactured parts must be cleaned?

A

1) prepare for subsequent processing
2) hygiene
3) remove contaminants that could react chemically
4) enhance appearance/performance

2
Q

Mechanical surface treatments are often performed for reasons other than or in addition to cleaning, what are these reasons?

A

1) deburring
2) improving smoothness
3) adding lustre
4) enhancing surface properties

3
Q

Name some chemical cleaning methods:

A

1) alkaline
2) acid/pickling
3) solvent
4) emulsion
5) ultrasonic

4
Q

Why do you shot peen?

A

Improve fatigue strength through strain hardening (from cold working)

5
Q

What’s meant by mass finishing?

A

Parts are mechanically cleaned and deburred in bulk usually in a barrel by mixing abrasive media together

6
Q

Why are metals coated?

A

1) corrosion protection
2) appearance
3) colour
4) increase electrical conductivity
5) increase electrical resistance
6) prepare for subsequent processing
7) rebuild worn or eroded surfaces

7
Q

How does electroless plating differ from electrochemical?

A

Electroless uses only chemical whereas electrochemical uses electrolysis

8
Q

What’s a conversion coating?

A

A thin coating produced by chemical reaction of the metallic surface. E.g oxides phosphates chromates

9
Q

4 major ingredients in organic coatings:

A

1) binder (polymer)
2) dyes/pigments
3) solvents
4) additives like surfactants/plasticisers

10
Q

What’s meant by transfer efficiency in organic coating?

A

How much organic coating liquid ends up on the target surface

11
Q

Describe the principle methods by which organic coatings are applied to a surface

A

Brushing, rolling, spraying, immersion (dip coating), flow coating

12
Q

Difference between drying and curing

A

Drying is evaporation of solvent in organic coating liquid but curing is a chemical change in the resin (polymerisation and/or cross linking) which hardens the coating

13
Q

Advantages and disadvantages of welding compared to other assembly methods?

A

1) permanent
2) joint strength is typically as high as strength of base metals
3) economical in terms of material usage
4) versatile in where it can be applied
BUT
1) usually done manually
2) dangerous process
3) hard to disassemble
4) quality defects hard to detect

14
Q

What’s a faying surface ?

A

The contacting surfaces in a welded joint.

15
Q

What’s a fusion weld?

A

A weld in which the metal surfaces have been melted in order to cause coalescence.

16
Q

Difference between fusion and solid state weld?

A

In fusion the metal is melted but isn’t in solid state welding

17
Q

What’s an autogenous weld?

A

A fusion weld made without a filler metal

18
Q

Reasons why most welding operations are dangerous:

A

1) high temps
2) gas welding, fuel is fire hazard
3) arc/resistance welding, high electrical energy
4) arc welding, electric arc emits UV
5) sparks, fumes, smoke, weld splatter

19
Q

Why is it desirable to use energy sources for welding that have high heat densities?

A

Heat is concentrated in a small region for greatest efficiency and minimum metallurgical damage.

20
Q

What’s the heat affected zone HAZ in a fusion weld?

A

Region of base metal surrounding fusion zone where melting hasn’t occurred but temps were high enough to cause solid state microstructual changes

21
Q

What’s an electrical arc?

A

A discharge across a gap in a circuit. In arc welding the arc is made by a thermally ionised column of gas through which a current flows.

22
Q

Electrodes in arc welding are divided into two categories. What are they?

A

Consumable and non consumable. The consumable type provides filler metal for the welding joint as well as being an electrode. In non consumable, it’s made of tungsten or carbon that resist melting.

23
Q

Two basic methods of arc shielding?

A

1) gas like argon/helium

2) flux, which covers the welding operation and protects the molten pool from the atmosphere

24
Q

Why is heat transfer a greater factor in consumable arc welding than non consumable electrodes?

A

Molten metal from the electrode is transferred across the arc and contributes to the heating of the molten weld pool in arc welding processes that utilise consumable electrodes.

25
Q

Describe shielded metal arc welding SMAW:

A

SMAW uses consumable electrodes consisting of a filler metal rod coated with chemicals that act as flux and shielding

26
Q

Why is the shielded metal arc welding SMAW process hard to automate?

A

Stick electrodes must be changed frequently which would be hard for a machine. Easier to automate the feeding of continuous filler wire.

27
Q

Define resistance welding

A

RW consists of a group of fusion welding processes that utilise a combination of heat and pressure to accomplish the coalescence of faying surfaces. Most prominent is resistance spot welding.

28
Q

What are the desirable properties of a metal that would provide good weldability for resistance welding?

A
  • High resistivity
  • Low electrical/thermal conductivity
  • Low melting point