GCSE Graphic Products Shaping and Forming Plastics

1. GCSE Graphic ProductsShaping and Forming Plastics Summer Examination 2011

2. Vacuum forming is a manufacturing technique whereby thin plastic such as high density polystyrene is shaped by heat and force. Blister Packaging is manufactured in this way. Stages of Vacuum forming 1. The first stage of vacuum forming is to manufacture a precise mould. This is a skilled job as any imperfections to the mould will show up every time it is used to shape plastic such as high density polystyrene. The mould can be used hundreds and even thousands of times to produce the same plastic part. Each part will be exactly the same. 2. The mould is placed in the vacuum former. It is placed centrally Vacuum forming

3. 3. A sheet of high density polystyrene is paced above the mould and clamped in position. Various thicknesses are available. Usually material 1mm thick is the most suitable for this type of vacuum forming. 4. The heater is turned on. When the machine is being used from ‘cold’ it takes approximately five to ten minutes to warm up to the temperature needed to heat the polystyrene sufficiently.Once warm, polystyrene of this type takes only four or five minutes to heat up before vacuum forming can begin. 5. The plastic (polystyrene) becomes pliable and flexible after a short time. It must be very flexible before it can be formed properly. Vacuum forming

4. 6. When the polystyrene is ready the shelf is then lifted up towards the polystyrene sheet. The air underneath the former is pumped out and the polystyrene takes the form of the mould. The mobile phone seen below has plain packaging. The back is made from card with a lacquered, gloss finish. The front is manufactured from vacuum formed high density polystyrene. The polystyrene is transparent which means that the mobile phone can be seen through it. This type of packaging is called 'blister packaging'. Vacuum forming

5. Materials such as polystyrene, nylon, polypropylene and polythene can be used in a process called injection moulding. These are thermoplastics - this means when they are heated and then pressured in a mould they can be formed into different shapes. The DVD Storage unit seen opposite has been made in one piece using this process 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 (in this case a DVD storage unit).4. The mould then opens and the unit is removed. Injection Moulding

6. Blow moulding follows the same stages of manufacture as injection moulding. HDPE (high density polyethylene) is ideal for this type of manufacturing technology. The HDPE granules / powder is placed into the hopper. It drops down on to a rotating thread and travels along its distance. During this process the granules / powder is heated and becomes fluid.However, when it reaches the mould compressed air is also blown into the mould. This pushes the HDPE around the edges of the mould, forming a hollow shape, in this case the recycling bin. Blow Moulding

7. Plastics such as acrylic can be formed (shaped) in different ways. One of the most popular methods of shaping plastic materials like acrylic is to fold (bend) it on a ‘strip heater.’ The desk organiser seen opposite has a steel wire frame and plastic shelves. The selves have been folder on a strip heater. This heats the plastic along a line so that it becomes soft and flexible. It can then be folded to almost any angle. Thermoplastics such as Acrylic (Perspex) are most suitable for this type of product as they can be shaped when heated. Stages of Line Bending: 1. The position of the fold is marked with a china-graph pencil. With this type of pencil line can be removed easily later. Line Bending

8. 2. The plastic is placed across the rests, above the heating element 3. 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. 4. 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. 5. A second line can be drawn on the plastic with a china-graph pen, heated and folded in the same jig. The shelf is complete. Line Bending

9. An acrylic display stand is made using a strip heater/line bender. Explain in detail, with notes and sketches, how it is formed. Consider accuracy, safety and quality with your answer. ( 7 marks) A model MP3 player is formed from a block modeling Material. • Name a suitable block modeling material, and explain why it is suitable for this task. (4 marks) • The surface of the shaped block is to be covered with a layer of plastic sheet by vacuum forming. • (i) Explain the advantages of vacuum forming over the block. (3 marks) • (ii) Sketch the process of vacuum forming step by step. (6 marks) Practice Question