Surface Treatments Welding 6

Question 1

What are some reasons why manufactured parts must be cleaned?

Answer 1

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

Question 2

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

Answer 2

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

Question 3

Name some chemical cleaning methods:

Answer 3

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

Question 4

Why do you shot peen?

Answer 4

Improve fatigue strength through strain hardening (from cold working)

Question 5

What’s meant by mass finishing?

Answer 5

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

Question 6

Why are metals coated?

Answer 6

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

Question 7

How does electroless plating differ from electrochemical?

Answer 7

Electroless uses only chemical whereas electrochemical uses electrolysis

Question 8

What’s a conversion coating?

Answer 8

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

Question 9

4 major ingredients in organic coatings:

Answer 9

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

Question 10

What’s meant by transfer efficiency in organic coating?

Answer 10

How much organic coating liquid ends up on the target surface

Question 11

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

Answer 11

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

Question 12

Difference between drying and curing

Answer 12

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

Question 13

Advantages and disadvantages of welding compared to other assembly methods?

Answer 13

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

Question 14

What’s a faying surface ?

Answer 14

The contacting surfaces in a welded joint.

Question 15

What’s a fusion weld?

Answer 15

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

Question 16

Difference between fusion and solid state weld?

Answer 16

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

Question 17

What’s an autogenous weld?

Answer 17

A fusion weld made without a filler metal

Question 18

Reasons why most welding operations are dangerous:

Answer 18

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

Question 19

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

Answer 19

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

Question 20

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

Answer 20

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

Question 21

What’s an electrical arc?

Answer 21

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.

Question 22

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

Answer 22

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.

Question 23

Two basic methods of arc shielding?

Answer 23

1) gas like argon/helium

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

Question 24

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

Answer 24

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.

Question 25

Describe shielded metal arc welding SMAW:

Answer 25

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

Question 26

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

Answer 26

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

Question 27

Define resistance welding

Answer 27

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.

Question 28

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

Answer 28

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