Machining And Moulding

Question 1

Describe process of milling/routing

Answer 1

Milling enables small holes and channels to be created
Slower than routing
Routing machines make slots and holes in the wood and can be done with a manual plunge router or CNC router

Question 2

Drilling process

Answer 2

Rotating drill bit drills into static materials like wood/metal etc
Drill creates holes

Question 3

Describe turning

Answer 3

Turning uses a lathe and can be used for wood or metal
Material rotated and cutting tool is pressed gain at the surface to remove excess material
Makes products like table legs and chess pieces

Question 4

Describe how stamping works

Answer 4

Sheet material removed using a CNC stamping procedure which stamps shape out
Shearing action upper and lower toll remove material
Usually used for smaller production runs of sheet metals

Question 5

Describe pressing

Answer 5

Sheet metal placed between two dies and pressed into 3D form
Aluminium and medium carbon steel commonly used due to malleability and ductility
Pressed using hydraulic press which could have cutting holes if cutting is necessary

Question 6

What are most dies commonly made from?

Answer 6

Hardened steel

Question 7

Describe the process of blow moulding with sketches

Answer 7

1. Polymer fed into hopper (PET, LDPE, HDPE, PP)
2. Archimedes screw pulls polymer through heated section
3. Melted polymer extruded as a tube called parison
   4.mould closes around parison
4. Air blown in through parison
5. This forces polymer to sides
6. Polymer allowed to cool
7. Parison and other end trimmed off

Question 8

Benefits of blow moulding
Examples of use

Answer 8

Creates hollow components
Create thin walled parts
Water bottles, shampoo bottles etc

Question 9

Disadvantages of blow moulding

Answer 9

High startup costs and so mainly used in continuous production

Question 10

Describe how injection moulding works with sketches

Answer 10

1. Thermoplastic granules poured into hopper and melted
2. Hydraulic ram forces Archimedes screw forwards injecting polymer into mould
3. Mould is water cooled
4. Ejector pins push moulding out
5. Excess polymer trimmed and reused

Question 11

Benefits of injection moulding
Examples of use

Answer 11

Makes complex 3D shapes (including small complex parts like circuit holders, gates etc)
Fast process
Electrical product casings
Complex components

Question 12

Disadvantages of injection moulding

Answer 12

High startup costs and so used in mass production or continuous
Parts need to be made in halves for hollow components

Question 13

Describe how vacuum forming works with sketches

Answer 13

1. Mould placed on machine bed called ‘platen’ which is then lowered
2. Polymer sheet clamped in place
3. Heater pulled over polymer until softened
4. Platen raised and vacuum pump switched on
5. Once cooled and solid switch vacuum off and lower platen
6. Remove mould and trim to size

Question 14

Benefits of vacuum forming
Examples of use

Answer 14

Aluminium mould enables large scale production
Moulds easy to make so commonly used for larger batch production as moulds take time to make and so not really cost effective for one off

Lightweight trays, box inserts, coffee cups, yoghurt pots

Question 15

Disadvantages of vacuum forming

Answer 15

Relatively slow
Only suitable for thickness up to 6mm

Question 16

Describe with sketches the process of extrusion

Answer 16

1. Polymers loaded into hopper
2. Archimedes screw powered by hydraulic motor moves polymer granules past heaters allowing them to melt
3. Hydraulic ram forces polymer through steel die which determines shape of extrusion
4. Extrusion can be supported by rollers upon leaving die and is water or air cooled
5. Extrusion cut to desired length

Question 17

Benefits of extrusion
Examples of uses

Answer 17

Any length can be made

Solid rod, hollow tubing etc
PVC commonly used

Question 18

Disadvantages of extrusion

Answer 18

Tends to make stock material and so only specialist manufacturers use them
Expensive startup costs
Continuous production process

Question 19

Describe how rotational moulding works including sketches

Answer 19

1. Polymer powder loaded into mould (PP, HDPE)
2. Mould clamped and sealed
3. Mould continuously rotated about two axes in an oven of temp 260-370 degrees
4. Once mould is coated it is continuously rotated whilst water cooled
5. Once solidified rotation stopped and mould can be removed as slightly shrunk

Question 20

Benefits of rotational moulding
Examples of use

Answer 20

Seamless products made
Hollow
Large wall thickness

Traffic cones, kayaks, water tanks, play equipment

Question 21

Disadvantages of rotational moulding

Answer 21

High setup costs
Slow process
Mass production