Polymers - EdexcelProduction in quantity

There are four terms used to describe the scale of production in relation to manufacturing a product:

• prototype and one-off production
• batch production
• mass production
• continuous production

Prototypes and one-off production

There are many ways to produce a prototype - some are rough and look like models and others are well finished and function as intended. It is now possible to 3D print many different polymers. Engineering companies have welcomed this technology as 3D printing is classed as additive manufacture, rather than subtractive. Additive manufacture builds up the polymer form in layers, whereas subtractive manufacture takes material away from a larger piece. There is very little waste when using additive techniques, making it more environmentally friendly.

There are many 3D printer filaments to choose from - some polymer-based filaments contain carbon fibre, different wood fibres and even metals. It is possible to make a functioning prototype with these technical filaments.

A custom-made or bespoke product that is made from a polymer could be made to a customer design specification, eg acrylic signs on shops.

Batch production

Batch production is where many items of the same product are produced, such as an acrylic menu stand for use in a chain of restaurants.

It is likely that the acrylic stand would be laser cut, heated on a line bender and then left to cool in a cooling jig. The jig ensures that each menu stand cools and remains in place at the same angle each time.

When a product is made in a batch, it is often far cheaper per product than when making just one. A sheet of acrylic can be bought in many different sizes - for example, if the sheet is 1000 mm × 600 mm, it can fit inside many larger laser cutters and many parts can be cut from it while it is in the machine.

Mass production

Mass-produced products are manufactured in large volumes, and are often made by automated machinery with assembly line workers used to fit parts together or to add standard components, such as screws and hinges. An example of mass production for polymers is blister packs that contain tablets. In this case the whole process would be automated and workers may only be used to check the product or pack it into shipping boxes.

Continuous production

Continuous production takes place 24 hours a day, 7 days a week and, in some cases, 365 days a year. When products are made from a polymer using continuous production methods, injection moulding is likely to be the method used to form the plastic. Children’s building blocks are injection moulded in factories that utilise automation - not many people are involved in the manufacture as robots and machines do most of the work.

Accuracy

Most polymer products that are injection moulded are made by machines with very little human intervention. This ensures that each product is made to a fine tolerance if the mould has been made correctly - a formed product is only as good as the mould or injection-moulding tool.

If machines are maintained and stocked with the required material, the product will be near perfect as machines follow the same motion every time. On-screen simulation reduces the need to produce trial runs and can eliminate errors before production starts.

Digital micrometers can be used to measure the width of a material and digital vernier calipers can be used to measure the outside width, inside dimensions and depth of holes. Both tools measure to 1/100th of a millimetre (mm) and can be read quickly because of the digital screen.

Quality control

Quality control takes place during the manufacture of any product, but, since polymer parts are engineered to a fine tolerance, there are specific quality control tools to ensure that polymer parts have been made correctly - one such tool is called a ‘go-no-go gauge’. The ‘go-no-go gauge’ has a ‘go’ side and a ‘no-go’ side - when testing the product one side must pass and one side must fail.

Example

It is common to hear engineers say they can work to a tolerance of ‘one thou’, meaning 1/1,000th of an inch.

1 inch = 25.4 mm

25.4 ÷ 1,000 = 0.0254 mm, so:

‘one thou’ = 0.03 mm (to 2 decimal places)

If an engineer was asked to mill a 30-mm slot in a block of acrylic, it would be possible to check whether the slot was correct by using a ‘go-no-go gauge’:

30 mm – 0.03 mm = 29.97 mm

This side of the gauge must be able to slide into the milled slot.

30 mm + 0.03 mm = 30.03 mm

This side of the gauge must not be able to slide into the milled slot.