Materials & Processes.

This table below is of ferrous metals. It also includes the same properties

Acrylic

Advantages

• Quality feel
• Wide range of colors, including transparent
• Can be bent accurately
• Can be polished, including cut edges.

Disadvantages

• Fairly brittle
• Does not vacuum form easily (if you need to vacuum form acrylic e.g. for transparent shapes, then use cast acrylic)

Polystyrene

Advantages

• Vacuum forms very well, giving and industrial process advantage (can be repeated)
• Can be fabricated quickly and easily

Disadvantages

• Difficult to bend (tends to stretch when heated)
• Does not polish very well
• Does not machine sand easily (tends to melt)

Processes

Below are ways of which different materials can be processed.

• Forming means shaping a material.
• Deforming means bringing about a change of shape without loss of material.
• Reforming involves a change of state of the material (usually from liquid to solid) as in casting.

Former 

Plastics can be heated and bent around a former. Sometimes you use a strip heater. This heats the plastic along a line so you can get a straight fold.

Moulding

Use a vacuum former to shape plastic around a mould or pattern. Remember you have to get the mould out of the plastic, it must have a draft angle. Vacuum formers are used in industry for making small things like yoghurt pots to large things like caravan windows or cockpit covers. The advantage of vacuum forming is that you only need one mould. The disadvantage is that it is not accurate enough for parts that have to fit closely together.

Blow moulding is used for bottles and containers for liquids. A parison (a small blob of soft plastic or glass) is squeezed into the mould. A puff of air blows it against the cold sides of the mould, where it hardens. The mould then opens into two pieces to get the bottle out.

Injection moulding is the most widely used type of plastics processing. It is used for producing kettles, casing for stereos and computers, telephones - anything that has to be made accurately or which is too deep for a vacuum former.

Plastic granules are fed into a turning screw. As they move along they are melted, and squeezed into a mould. The mould has two parts, called male and female. The moulds are machined very accurately, so that they fit together with just the right space between them. The soft plastic cools and hardens, the moulds are separated, and the product pops out.

Rotational moulding - Some large objects such as water barrels are made through rotational moulding. As with blow moulding, there is only one mould which splits into two parts to get the product out. Soft plastic is placed into the mould which then spins fast on two axes. The soft plastic flies outwards and solidifies when it is cooled by the mould.

Extrusion is used for making tubes, pipes or any long strip of material which has to be a special shape. It is similar to making spaghetti or forcing icing onto a cake. Extrusion is used for both plastics and metals. Impact extrusion is used sometimes to produce aluminum drink cans.

Casting is when liquid metal, plastic or ceramics is poured into a hollow mould, where it is held until it solidifies into the required shape. A pattern is made exactly the size and shape of the required object. This is put into a special type of soft sand and then removed to leave a hollow mould. The molten metal can then be poured carefully into the mould. When it is hard, the mould is split into two and the product removed. Parts of car engines are moulded to start with, and then machined on a lathe, mill or drill to complete them.                                                                 A Product made by casting

Die casting uses steel moulds rather than sand. These moulds are much more expensive to make but can be used again and again. Great accuracy is possible. Die casting is used for toys, camera bodies and components for many domestic appliances.

Calendering is the process for making sheets of plastic. It is similar to the way that paper is made.

Presswork - Many metal products are formed with huge presses - saucepans, baking trays, light fittings, tubular furniture, car bodies and aircraft frames. A press can be used for punching out products or components, punching holes in products, bending or folding sheets of metal, or shaping three-dimensional forms (like a car bonnet).

Laminating - This is building up a shape by joining layers of material. Some furniture is made from laminated timber. Many boats and some car boats are also formed this way, by laying down layers of plastic (resin) and reinforcement (often fibreglass) onto a mould. The material is called GRP (glass-reinforced plastic).