Commercial Manufacture Flashcards
What is injection moulding?
Injection moulding is the process of melting plastic pellets (thermosetting/ thermoplastic polymers) that once malleable enough, are injected at pressure into a mould cavity, which fills and solidifies to produce the final product.
Describe the process of injection moudling
Plastic granules are heated until they become fluid.
They are then forced into a mould the shape of the product being produced.
They are then quickly cooled and released from the mould.
Why is injection moulding used?
- The products produced are extremely accurate
- A large number of products can be produced quickly
- All products made using the same mould will be identical
What are the disadvantages of injection moulding
- The tools and equipment are usually expensive to buy.
- A high volume of products needs to be produced to make this cost effective.
What are common uses of injection moulding?
- Bottle caps
- Golf tees
- Toys
Lego bricks
What are the identifying features of injection moulding?
- Shrinkage mark
- Mould split lines
- Ejection pin marks
- Accurate, complex shapes
- High quality finish
Sprue marks
Describe the process of Vacuum forming
- A mould of the shape required is placed in a vacuum forming machine then a thin sheet of plastic is clamped above it.
- The sheet is then heated and the mould is forced into the heated sheet.
- The air is vacuumed out of the space between the plastic and the mould, allowing the plastic to take the shape of the mould.
Once cooled, a small burst of air is pumped into the space to help release the mould from the plastic.
Why is vacuum forming used?
Products can be produced relatively quickly.
Flexibility of the design possibilities.
Tooling costs are less compared to other plastic processes.
What are the disadvantages of vacuum forming?
Only one product can be made in the machine at a time.
Plastic can warp during the heating process.
What are common uses of vacuum forming?
- Trays
- Dishes
- Containers
- Lighting panels
What are the identifying features of vacuum forming?
- Thin sheet plastic
- Surface pips
- Pronounced tapers (draft angles)
- Patterns or textures imprinted
Thinning at corners.
Describe the process of rotational moulding
Plastic beads are placed into a mould where they are then heated.
While the plastic is being heated, the mould rotates both horizontally and vertically to coat the mould evenly.
The mould is then cooled slowly and the product removed.
Why is rotational moulding used?
It provides a uniform wall thickness around the entire product, except on corners where it is thicker.
Smaller numbers of products can be produced as the tooling cost is lower than other processes.
Products are a single part that can then be fitted to other parts if required.
What are the disadvantages of rotational moulding?
it can be quite a slow process as the mould needs to be coated and dried evenly.
Some shapes and detailed features are difficult to incorporate.
What are common uses of rotational moulding
- Balls
- Hollow plastic toys
Road markers
- Hollow plastic toys
What are the identifying features of rotational moulding?
- Split lines
- Draft angles
- Hollow objects
Uniform wall thickness
Describe the process of sand casting
A mould is put into a box (drag) and then the box is filled with sand.
The mould is removed and another box (cope) is placed on top.
The cope has channels in it to pour the molten metal into, which fills the mould cavity.
It is left to cool and then excess metal is removed.