Manufacturing: Topic 3

Question 1

What do all moulding processes require?

Answer 1

Heat and force

Question 2

Do plastics have good defined regions between viscous liquid and elastic solid?

Answer 2

Plastics have a poorly defined region between viscous liquid and elastic solid.

Question 3

What are thermosets?

Answer 3

Long Chain Molecules
Chains linked together by strong chemical bonds
Process is irreversible

Question 4

What are thermoplastics?

Answer 4

Long Chain Molecules
Chains attracted to one another by weak-intermolecular forces
Process is reversible

Question 5

Two applications of silicon

Answer 5

High temp

High grade electrical properties

Question 6

6 Polymer Processes

Answer 6

Extrusion Moulding
Injection Moulding
Blow Moulding
Compression Moulding
Rotational Moulding
Vacuum Moulding

Question 7

What is Compression Moulding?

Answer 7

Compression moulding is a method of moulding in which the moulding material, generally preheated, is first placed in an open, heated mould cavity.The mould is closed with a top force, pressure is applied to force the material into contact with all mould areas, while heat and pressure are maintained until the moulding material has cured.

Question 8

What is Extrusion?

Answer 8

Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed or pulled through a die of the desired cross-section.

Question 9

What is Injection Moulding?

Answer 9

The shaping of rubber or plastic articles by injecting heated material into a mould.

Question 10

What is Rotational Moulding?

Answer 10

Rotational moulding is a process used for producing hollow plastic products. Eg. Hollow sphere partially filled with hot polymer rotated at and cooled at the same time. Thus producing a hollow ball.

Question 11

What is vacuum forming?

Answer 11

Vacuum forming is the process whereby a sheet of plastic is heated to a forming temperature, stretched onto a single-surface mould, and forced against the mould by a vacuum (suction of air).

Question 12

What is Blow Moulding?

Answer 12

Blow moulding is a manufacturing process by which hollow plastic parts are formed. Heated plastic placed inside mould and then a burt of air expands that plastic to fit the mould shape.

Question 13

Two types of semiconductors

Answer 13

N-type

P-Type

Question 14

What re most semiconductors made from?

Answer 14

Silicone

Question 15

Wafer preparation

Answer 15

Grinding
Slicing
0.5mm
Polish

Question 16

What is Ion Implantation?

Answer 16

Ion implantation is a materials engineering process by which ions of a material are accelerated in an electrical field and impacted into a solid.

Question 17

What are rivets?

Answer 17

A short metal pin or bolt for holding together two plates of metal, its headless end being beaten out or pressed down when in place.

Question 18

What are fasteners?

Answer 18

A fastener is a hardware device that mechanically joins or affixes two or more objects together. Fasteners can also be used to close a container such as a bag, a box, or an envelope; or they may involve keeping together the sides of an opening of flexible material, attaching a lid to a container, etc.

Question 19

Joints with no fasteners

Answer 19

Tend to be cheaper, (no cost of fastener)

May be difficult to separate

Question 20

Joints with fasteners

Answer 20

Tend to be more expensive because of
– Fastener cost
– Preparation time (drill holes, tap threads etc.)
– Labour to assemble parts
Often easy to disassemble for maintenance or repair

Question 21

Adhesive Joining

Answer 21

Joint is usually inseparable
Bond strength depends on chosen adhesive
Adhesives bond to surfaces in 2 ways
-- chemical attraction
-- mechanical interlocking

Question 22

Requirements for Good Joint

Answer 22

Intimate contact between adhesive and substrate

Absence of weak layers or contamination at the interface

Question 23

Adhesion Mechanisms

Answer 23

Chemical bonding
Physical attraction
Mechanical Interlocking

Question 24

Adhesive Bond Requirements

Answer 24

Surfaces of the adhesend must be clean
Adhesive in liquid form must achieve thorough wetting of the adhesend
Surfaces should not be perfectly smooth

Question 25

Adhesive Bonding Advantages

Answer 25

``` Ability to join dissimilar materials Ability to join thin sheet efficiently Excellent for small delicate parts Uniform stress distribution in joint Weight savings over mechanical fastenings Smooth external surfaces are obtained Can absorb shock and some movement ```

Question 26

Adhesive Bonding Limitations

Answer 26

Joints generally not as strong as other joining techniques approximately 30 N/mm2 Adhesive must be compatible with materials being joined Service temperatures are limited Generally 130 to 200 ºC (can be as high as 350 ºC Cleanliness and surface preparation a must Curing times can be very long (sometimes) Inspection of joint is difficult Assembly speed restricted by adhesive setting time

Question 27

Welding

Answer 27

Joining process in which two or more parts are coalesced at their contacting surfaces by a suitable application of heat and/or pressure. Used mainly for metals but can be used for plastics

Question 28

Fusion Welding

Answer 28

Fusion welding is a generic term for welding processes that rely upon melting to join materials of similar compositions and melting points.

Question 29

Solid State Welding

Answer 29

Usually requires heat and pressure If done cold surfaces must be exceptionally clean and smooth Good solid state joint has no interface region Can have long cycle time

Question 30

Welding advantages

Answer 30

Provides a permanent joint Joint can be as strong as parent material Very economical Can be done on site

Question 31

Welding disadvantages

Answer 31

Sometimes manually performed therefore can be expensive High energy usage Permanent bonding cannot be easily disassemble Difficult to detect defects

Question 32

Brazing

Answer 32

``` Usually butt or lap joints Large area required for a good joint Parts must be kept in alignment before and during brazing. Entire interface is bonded Filler metal is used ```

Question 33

Brazing Advantages

Answer 33

Several advantages over welding - - Any metals can be joined - - Brazing is quick and consistent - - Multiple joints can be done in one operation - - Less heat and power required - - HAZ problems greatly reduced - - Can braze joints that cannot be welded

Question 34

Brazing Disadvantages

Answer 34

- - Joint strength less than welded - - Good joint is stronger than filler material but not as strong as base metal - - High service temperatures can weaken joint - - Colour of filler material usually not the same as base material

Question 35

Soldering

Answer 35

Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal (solder) into the joint, the filler metal having a lower melting point than the adjoining metal.

Question 36

Soldering Advantages

Answer 36

Low energy input compared to brazing or welding Variety of heating methods possible Good electrical and thermal conductivity in the joint Airtight and liquid tight joints possible Easy to repair and rework

Question 37

Soldering Disadvantages

Answer 37

Low joint strength unless reinforced by mechanical means | Possible weakening of joint in elevated temperature service