Lesson Objectives The ability to identify Thermoplastics and

Lesson Objectives: • The ability to identify Thermoplastics and their uses. • Develop and understanding of the injection moulding process.

Starter Exercise What material properties would this plug socket require? Think about its function and the health and safety requirements.

Material properties of a plug socket: • • • Scratch resistant Brittle Insulates electricity Hard Can be coloured Good heat resistance A plug socket is made out of a resin, that is called Urea Formaldehyde. This is categorised as a thermosetting plastic. Thermosetting or thermoset plastics, can only be heated and formed once. As the name implies thermosetting plastics (or thermosets) set or solidify, when heated and cannot be returned to their original state by further heating. Once formed these plastics have a very good resistance to heat, meaning it can be used for applications like plug sockets, pan handles and heat producing appliances.

Thermoplastics are another category of plastic. These are plastics that soften when heated and formed many times, they then harden as they cool. They have a poor resistance to heat and some types of thermoplastics can deform at fairly low temperatures. When a thermoplastic has been re-heated it will return to it’s original state unless it has been permanently damaged by excessive heat or deformation. Why wouldn’t this type of plastic be suitable for a plug socket?

Thermoplastics are suitable for use in many different shaping/forming processes. As 3 D printers involve the heating and cooling of plastics, thermoplastics are an obvious choice of material. Filament (Thermoplastic wire) on a reel is fed through an extruder whilst being heated up. The printing head then plots the liquid plastic in thin layers, that cool and harden, before another thin layer can be plotted on top of it. Over time this plotting or printing on top of layers builds a 3 D object. This can make very complex shapes that can be hollow or intertwine

Task On your worksheets define the two different categories of plastic, provide an example of products that are normally made from the two types of plastics.

Injection Moulding Injection moulding is also a process that uses thermoplastic. The process melts thermoplastic and using hydraulic rams to push or injection the liquid plastic into a mould. As the plastic is injected into the mould under huge pressures, the process can make very complex shapes. As well as the plastic the temperature of the moulds used can be controlled, meaning liquid plastics can be cooled and hardened very quickly. This allows the whole process to be repeated very quickly, meaning its great for mass producing objects.

Cross Section of an Injection Moulding machine Heaters Mould Chamber Hopper Archimedes Screw Motor and Hydraulic Ram

Components Hopper Motor and Hydraulic Ram Heaters Archimedes Screw Chamber

Injection Moulding process Plastic granules are feed in to the hopper of the machine and are moved into the heating chamber or barrel by gravity. Once in the chamber the plastic granules are slowly melted into liquid. Once it has reached temperature and melted thermoplastic liquid is then moved forward by the Archimedes Screw which is rotated by a motor located at the back of the machine. This forces the plastic towards the end of the chamber. When the liquid plastic is in position at the end of the chamber, a powerful hydraulic ram forces the plastic into a metal mould filling the entire cavity. The plastic begins to harden as it cools. As the plastic solidifies (hardens as it cools) the mould opens and the component is ejected. The process is then repeated.

Task Using the words provided, select the correct name for each part of the injection moulding machine and place them in the boxes provided. The series of diagrams shows an injection moulding machine. In the boxes next to each diagram describe the stages in the Injection Moulding process. Below is a list of advantages and disadvantages of using Injection Moulding to manufacture products. Next to each statement state whether the point an advantage or a disadvantage. The diagram shows an injection moulding machine. Add the correct name for each part of the injection moulding machine and place them in the boxes provided. In bullet Points fully describe the stages in the Injection Moulding process.

The initial cost of the machines are very expensive. Complex products in different shapes can be produced. After the initial cost of the machine and the mould, products can be made very cheaply. The machine is large and takes up a lot of room. Moulds for products could cost anywhere between £ 5000 to £ 40, 000. Advantage or Disadvantage of the injection moulding process? Waste plastic can be recycled into the process. A low labour cost, as you do not require many staff. Many components can be moulded together. Products or components can be mass produced using the process. Products can be made very accurate. Only thermoplastic can be used.

Task On your worksheet there is a list of advantages and disadvantages of using Injection Moulding to manufacture products. Next to each statement state whether the point an advantage or a disadvantage. Explain the advantages and disadvantages of using injection moulding for the production of products.

Plenary Task: Using your knowledge gained this lesson. As a class, separate these objects into groups. Can you identify the products that are: • Injection moulded • Thermoplastic • 3 D Printed • Thermosetting plastic