Casting and moulding processes

what is casting and moulding

• shaping processes

• melted plastic/metal poured into a mould

• most cost effective for complicated shapes, reducing labour time and waste

injection moulding overview

• similar to pressure die casting, but for polymers

• plugs, construction kits, toys, etc

• expensive equipment

• sprue point (where plastic was injected, and then the sprue was cut off)

• parting line (line of serparation where the two halves meet)

• flash (where sides of mould didn’t fit perfectly)

1. polymer granules loaded into feed hopper, which feeds material into the barrel of the machine

2. rotating screw thread pushes polymer as its melted by heaters

3. at the end of the heated area, polymer is compressed into a cone, and barrel diameter reduces, which increases pressure

4. melted polymer is pushed in between mould

5. mould cooled, component ejected

6. mould moved back into position for the next part

sand casting

1. Half of the pattern is put into the moulding board, and the bottom half of the moulding box (the drag) is placed upside down over the pattern

2. pattern sprinkled with releasing agent (parting powder), with sand rammed around pattern

3. top half is levelled off (strickled)

4. two halves are fit together, with sprue pins attatched, and then sprinkled with parting powder, and with sand rammed around

5. top half, wooden pattern, and sprue pins removed

6. sand mould reassembled

7. molten metal poured into sprue, solidifies

8. sprue, riser, runners cut off. Part machined

pressure die casting

• non-ferrous metal parts

• very fast

• die (mould) is made of high-carbon steel, which is hard, but difficult to machine and expensive

1. die brought together, pressure forces metal into cavity through system of sprues/runners

2. die taken apart when metal solidifies, and part removed

3. pressure means castings are more accurate than sand casting (detailed features, good surface finish)