3.1d casting

product design a level

casting

a liquid material is usually poured into a mould, which contains a hollow cavity of the desired shape then allowed to solidify, solidified part is known as a casting, which is ejected or broken out of the mould to complete the process
casting materials are usually metals or various cold setting materials that cure after mixing two or more components together
most often used for making complex shapes that would be otherwise difficult or uneconomical to make by other methods

sand casting

the process where molten metal is poured into a sand mould that contains a cavity of the desired shape of an object or component, once the metal has solidified, the sand is broken open and the product/component is removed
cheap, complex shapes can be produced, large components can be made
moulds can only be used once, surface finish not always good, labour intensive, slow production rate

sand casting process

1. a split pattern is placed in the moulding box (drag) with powder dusted over the pattern to help release is

2. sand is packed around the pattern and smoothed off

3. the drag is turned over and the cope, the runner and riser are put on top and the mould with the second half of the pattern is powder dusted

4. sand is packed around the pattern, smoothed off and pouring basin created

5. the pattern, runner and riser are removed and channel and vents are put in to allow the metal to flow

6. the metal is poured into the hole left by the runner until it appears in the riser hole, it is then left to cool, the casting is removed and the waste cut off

investment casting

excellent surface finish, high dimensional accuracy, extremely intricate parts are castable, , almost any metal can be cast, no flash or parting lines
can be difficult to cast objects requiring cores, expensive, usually limited to small casting, long production cycle

investment casting process

1. produce a master pattern

2. create a mould

3. produce wax patterns

4. assemble wax patterns

5. apply investment materials

6. dewax

7. burnout preheating

8. pouring

9. divesting

die casting

used for smaller metal products - usually non-ferrous such as small parts in household machinery as the process is repeatable at a high quality in large quantities
a die is a shaped piece of metal, often with a hole in it that uniquely matches the shape of the product to be cast
high production rate, good surface finish, economical for large runs, good control of mould temp, elements such as screw threads can be included in casting
high set up costs, long lead time, limited sizes possible, not all alloys are possible, large numbers needed to be economical

pressure die casting process

1. a die is produced to create the desired shape

2. molten metal is collected in the chamber

3. a plunger forces the molten metal into the cavity in the die and pressure is maintained to allow fir shrinkage

4. the die is opened, the casting removed and allowed to cool, and waste is removed

gravity die casting

using sand cores makes it possible to manufacture items with complicated inner shapes in a cost effective way in small and medium quantities

gravity die casting process

1. the heated mould (die) is coated with a die release agent, this also aids cooling of the mould face after the previous part has been removed

2. molten metal is poured into channels in the tool to allow the material to fill all the extremities of the mould cavity, the metal is either hand poured using steel ladies or dosed using mechanical methods

3. once the part has cooled sufficiently, the die is opened, either manually or utilising mechanical methods

resin casting

a method of plastic casting where a mould is filled with a liquid synthetic resin, which then hardens
primarily used for small-scale production like industrial prototypes and dentistry, used in production of collectables and models
cheap, complex shapes can be produced, good for small runs
soft moulds degrade over time, bubbles can form, surface finish is not always good, labour intensive, slow production rate

resin casting process

1. a mould is produced to create the desired shape - usually from latex

2. epoxy, polyurethane or acrylic resin is mixed - when the two part resin is mixed air bubbles tend to be introduced into the liquid which can be removed in vacuum chamber

3. resin poured into mould
   gravity casting - resin is poured into mould
   pressure casting - plunger used to push the liquid into all details of the mould, mould vibrates to remove bubbles

4. mould is opened and product is removed

5. some finishing may be required to remove flash

plaster mould casting

metalworking casting process for non-ferrous metals, similar to sand casting but Plaster of Paris is used instead
plaster is not pure but has additives to improve strength, permeability and cast-ability
additives used: magnesium oxide - prevent cracking and reduce setting time, lime or cement - limit expansion during baking, glass fibres - increase strength
metal or rubber moulds are used for patterns
surface finish, dimensional accuracy
mould is destroyed as part of process, long cooling time, plaster not as stable as sand

plaster mould casting process

1. prepare casting pattern

2. mix plaster of paris with additives and water

3. pour plaster into pattern and set

4. remove pattern

5. bake mould to remove moisture and ensure it is hard enough to pour the metal

6. assemble two halves of mould

7. cast

8. break apart mould to release casting