Materials

Materials

1. Metals

   • Ferrous
     • contain varying levels of iron (Fe) e.g. stainless steel, mild steel; tend to go rusty; almost all are magnetic (can you think why?); properties can be improved by adding carbon, chromium, tungsten and nickel.
   • Non-Ferrous
     • do not contain iron e.g. brass (copper and zinc), duralumin (aluminium and copper) and aluminium itself!; since they do not contain iron, they do not rust; often expensive (think of an expensive metal…..); poor working properties on their own.
   • Machine processes
     • Pillar Drill
       • Where the work piece is small enough the pillar drill is used to make round holes in metal: It is accurate and will drill holes perpendicular to the work piece (it will also drill holes at angles) The leverage used on the rack and pinion reduces effort. Centre holes must be punched to prevent slippage. Work must be held securely. Twist drills are used (made from HSS – High Speed Steel) A lubricant/coolant (cutting fluid) can be used to prevent the bit from overheating
     • Centre lathe
       • A single point cutting tool is held against the rotating work to turn cylindrical objects. The tool can be moved parallel to, or at right angles to the work in any combination (to produce tapers or curves). The cutting tool removes waste (swarf). The correct tool and cutting speed are needed for each operation. Accurate surfaces, holes and threads can be produced. CNC lathes automate this process with even more precision
   • Joining
     • Nuts and Bolts
       • Referred to as a temporary method of joining Huge variety available Important factors: Length Thread size (diameter) Head shape Material
     • Rivets
       • Metal pins used to fasten sheets Cheaper, quicker, often less visible

2. Woods

   • Generally the moisture content of wood needs reducing to match the environment it will eventually be situated in. Wood MOVES! Air humidity is constantly changing therefore the moisture content of wood changes therefore wood expands and contracts.
   • Hardwoods
     • generally deciduous; normally slow growing; usually harder and more visually appealing than softwoods.
     • Beech
     • Ash
     • Oak
     • Mahogany
   • Softwoods
     • Pine
     • Spruce
     • does not relate to density or hardness of woods; generally come from evergreen trees; they are normally softer and faster growing than hardwoods.
   • Manufactured boards
     • these boards are timber sheets produced by bonding particles or layers of wood fibres together; they are much more stable than solid timber as the glue/resin locks the layers or particles together; they can be made in large sheets and can be faced with a decorative veneer.

3. Composites

   • A composite material is produced when two or more materials are combined. This gives a material with more useful properties than either material alone.
   • Carbon fibre reinforced plastic Consists of strands of carbon coated in polyester resin. Used in the manufacture of high performance products such as racing bikes and tennis rackets.

4. Plastics

   • Thermosetting
     • Once formed can not be reformed
   • Thermoplastic
     • Can be reformed under heat
   • Vacuum forming
     • A former is made over which the plastic will mould; The quality of the finished piece depends on the quality of the former; This must have a draw angle which depends on the height of the former but must be a minimum of 2°; The sheet is heated, the former is raised and a vacuum is applied.