Materials and finishes

 

An important part of designing is choosing materials and finishes. A material is generally chosen because its properties make it the most suitable choice. You will have to get samples of the common materials and look at them and make a list of their properties, including their relative cost. In some cases, you are just required to identify a material or finish, such as “Name a suitable hardwood for this product”. Make sure you answer with a hardwood. Beech will cover most questions about furniture and toys with Oak as a backup for quality items like trophy stands. Do not put Balsa or a softwood like pine. You will get no marks for the words “timber” or “wood”, as these words are not specific enough. Wood is a renewable resource

 

Also, you will need to know about manufactured boards like plywood and medium density fibreboard, (MDF). MDF comes in large sheets and has a flat surface. It is made from wood dust and resin. It takes paint well but can be hazardous if the dust is inhaled. Refer to your textbook to revise manufactured boards

 

For metals, you should know what is an element, what is an alloy, what is a ferrous metal, (one containing iron), and what is a non-ferrous metal. You should also know the properties of common metals, including their relative cost and the meanings of words like hardness, malleability, ductility and so on. Do not answer a question with the word “metal” as you will generally get no marks; it is not specific enough

 

For plastics, you should know that acrylic is the generic name for Perspex, (which is a trade name). Perspex is used on the line bender, (strip heater). Polystyrene is used in the vacuum former, (also known as HIPS, or high impact polystyrene). Plastics are made from oil and are a non-renewable resource. Some plastics can be recycled. Do not answer a question with the word “plastic”, as, usually, you will get no marks as it is not specific enough

 

Composite materials are materials which are supplied as a combination of two or more materials, such as tufnol. Tufnol is linen impregnated with resin and can be used to make gears. Cardboard bonded to aluminium foil can be used for food packaging. Glass reinforced plastic, (GRP), is used to make dinghies

 

Smart materials can sense and react to their environment, like some change shape or glow when heated or cooled. An example is Shape Memory Alloy, (SMA), which remembers its shape and goes back to that shape when heated. If you sit on your glasses, and they are made of a smart material, they will bend themselves back to the correct shape

 

Finishes are also chosen for their properties, that it protects and enhances the appearance. Plastic is self-finished, that is it doesn’t need finishing, except to be cleaned and polished. Ferrous metals, could be painted to prevent rusting, (except stainless steel which does not rust). Aluminium could be left unpainted or anodised. Brass is normally left unpainted. Wood can be left unpainted but, for outside use, would need to be protected with preservative. It can also have its appearance improved by painting. Other finishes for wood include varnish, (polyurethane), and woodstain which colours the wood but does not hide the natural grain. With all finishes, it is essential that the surface to be finished be clean and free from grease. This would be stage 1 of any finishing process

 

Examples of Materials questions are 1998 Paper 3 question 5(c)(i) and 1998 Paper 3 question 4(a)

 

Examples of Finishes questions are 1998 Paper 3 question 5(c)(iv), 2002 Paper 1 question 1(e) and 2002 Paper 3 question 1(e)