Forming techniques – blow moulding The process is similar to injection moulding and extrusion. 1. The plastic is fed in granular form into a 'hopper' that stores it. 2. A large thread is turned by a motor which feeds the granules through a heated section. 3. In this heated section the granules melt and become a liquid and the liquid is fed into a mould. 4. Air is forced into the mould which forces the plastic to the sides, giving the shape of the bottle. 5. The mould is then cooled and is removed.

Forming techniques – injection moulding 1. Granules of plastic powder (note the plastics listed above) are poured or fed into a hopper which stores it until it is needed. 2. A heater heats up the tube and when it reaches a high temperature a screw thread starts turning. 3. A motor turns a thread which pushes the granules along the heater section which melts then into a liquid. The liquid is forced into a mould where it cools into the shape. 4. The mould then opens and the unit is removed.

Forming techniques – Dome blowing Forms domes, spheres and oval shapes, usually out of acrylic. The sheet of acrylic is softened in an oven and transferred to a dome- blowing machine. It is clamped under a circular ring. Air pressure is applied which blows the material upwards and forms a perfect dome. Used to produce signage and point of sale displays. dome blowing example

Quality Control (QC) inspection and testing These thermoforming processes are used for high batch or mass production, so it is important that each product is identical in quality. Imperfect products are scrapped, while many are can be recycled, wastage still costs the company time and money. There are many different types of machines used to inspect batches of products including: Laser Measurement – uses a series of lasers to measure the outside dimensions of of a product as they move down a conveyor belt. This is fast, accurate and repeatable process as lasers are computer controlled and ultrasonic. Ultrasonic testing – is used to check the wall thickness of a hollow product by sending high-frequency sound waves at the product as it moves down the conveyor belt. The waves bounce back differently as they hit different materials and different thicknesses. The computer analyses the time it takes the sound waves to bounce back in order to calculate the wall thickness properly.

Forming techniques – Vacuum forming A thermoplastic sheet is clamped and then heated, blown and stretched. The plastic sheet is clamped to the frame and then heated until it is softened and malleable. The plattern is moved up into the plastic. Air is sucked out of the vacuum forming machine to force the softened sheet over a mould which has been pushed up from below. Once the polymer has cooled, it solidifies and cold air is blown up from below to release the formed product. The sheet is unclamped from the frame and the mould is released.

Forming techniques – Line bending Involves heating a thermoplastic sheet material such as acrylic over a strip heater. The plastic is placed across the rests, above the heating element The strip heater is turned on and the plastic is turned over every 30 seconds - one minute. This stops the heat rising from the element damaging the surface of the plastic. When the plastic becomes flexible it is placed in a ‘jig’. The jig is made to the correct angle, 90 degrees in this case. A square section block is then pressed against the plastic to hold it in position as it cools.

blow moulding Advantages Intricate shapes can be formed Can produce hollow shapes with thin walls to reduce weight and material costs Ideal for mass production – low unit cost per moulding. Disadvantages High initial set up costs as mould is expensive to develop and produce injection moulding Advantages Ideal for mass production – low unit cost for high volume. Precision moulding – high quality surface finish and texture can be added to the mould Disadvantages High initial set up costs as mould is expensive to develop and produce

Vacuum forming Advantages Ideal for batch production – inexpensive Relatively easy to make moulds that can be modified Disadvantages Mould needs to be accurate to prevent webbing Large amounts of waste material produced Line bending Advantages Ideal for one-off or batch Straight bends are produced efficiently Precise temp control over heated area gives a neat, precise bend Set up costs low Computer controlled line bending allows precise components be formed again and again Disadvantages Bends must be accurately marked before folding Acrylic can bubble if over heated Formed bend has to be allowed to cool for some time in the exact position or it springs back slightly