Casting

Question 1

Sand casting

Answer 1

Principle
- molten metal poured into cavity in sand

Products
- engine block , garden furniture

Advantages
- inexpensive, complex shapes can be produced, Large components can be made

Disadvantage
- moulds can only be used once
- poor surface finish
- labour intensive
- slow production rates

Question 2

sand casting process

Answer 2

1) A pattern (model of the final part) is placed in the drag (the bottom half of the moulding box).

2) Sand is packed tightly around the pattern in the drag.

3) The cope (top half of the box) is placed on top, and more sand is packed around the pattern.

4) The pattern is removed, leaving a cavity in the shape of the part.

5) A runner and riser system is added for pouring and venting the metal.

6) Molten metal is poured into the runner, filling the cavity.

7) Once the metal cools and solidifies, the mould is broken open.

8) The final casting is removed, cleaned, and any extra metal (like from risers) is cut off.

Question 3

Investment casting

Answer 3

Princliple
- ‘Lost wax casting’

Products
- mechanical parts, fan blades

Advantages
- Excellent surface finish
- High dimensional accuracy
- Any metals can be cast

Disadvantages
- Cost of production
- specialised equipment
- usually limited to small casting

Question 4

Investment casting process

Answer 4

1) wax pattern tree is created for investement casting
2) refractory slurry invested over wax pattern
3) Wax melted out of mold for investement casting
4) Mold for investment casting is heated for strength
5) Molten metal is poured into the mould
6) metal cools in mold and solidifies
7) mold is brocken off around the product

Question 5

Die casting

Answer 5

Principle
- forcing molten metal under high pressure into a mould cavity

Products
- Traditional toy cars, engine parts

Advantages
- High dimensional accuracy
- Fast production
- Wide range of possible shapes

Disadvantages
- High initial costs
- A large production volume is needed to make process cost
effective

Question 6

Die casting process

Carl is calm every tuesday.

Answer 6

1. Clamping
   The two halves of the metal mould (called a die) are closed tightly and held together by a clamping unit.
2. Injection
   Molten metal (like aluminium or zinc) is forced into the mould under high pressure.
3. Cooling
   The metal is left to cool and harden into the shape of the mould.
4. Ejection
   Once the metal is solid, the mould opens and pins push the finished part out.
5. Trimming
   Any extra metal (called flash) is trimmed off to clean up the final product.

Question 7

Resin casting

Answer 7

Principle
- A mould is filled with a liquid synthetic resin.

Products
- Industrial prototypes, model making

Advantages
- Cheaper molds than injection molding
- Can be casted or painted in any desired colour

Disadvantages
- Drying time
- Not good for batch / mass production

Question 8

Resin casting process

Answer 8

1. Preparing the mould
   The flexible silicone mould is cleaned and a release spray is added so the resin won’t stick.
2. Mixing
   Liquid resin and its hardener are measured accurately and stirred together.
3. Pouring
   The mixed resin is slowly poured into the mould, filling every detail.
4. Curing
   The mould is left undisturbed while the resin hardens (this can take minutes to hours, depending on the type).
5. Demoulding
   Once fully cured, the mould is peeled back and the solid resin part is taken out.
6. Finishing / Trimming
   Any rough edges or flash are sanded or trimmed, and the piece can be polished or painted if required.

Question 9

Plaster of paris casting

Answer 9

Principle
- similar to sand casting

Products
- lock components
- gears
- tooling
- ornaments

Advantages
- excellent surface finish
- dimensional accuracy
- little scrap material

Disadvantages
- Only used for non ferrous metals
- Metal cools slowly

Question 10

Plaster of paris process

Answer 10

1. Preparing the mould
   A mould (usually made from silicone, rubber, or plastic) is cleaned and a release agent is applied to stop sticking.
2. Mixing
   Plaster of Paris powder is mixed with water to form a smooth paste.
3. Pouring
   The mixture is gently poured into the mould, tapping the sides to remove air bubbles.
4. Setting
   The plaster is left to harden and set — this usually takes around 20–40 minutes.
5. Demoulding
   Once solid, the mould is carefully removed to reveal the cast object.
6. Finishing / Trimming
   Edges can be sanded smooth, and the surface can be painted or decorated if needed.