Metals - 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 metal, and many engineering companies have welcomed this technology as 3D printing is classed as additive manufacture, rather than subtractive. Additive manufacture builds up the metal 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.

A custom-made or bespoke product that is made from metal could be made based on a customer design specification. Products such as rings and jewellery are often made personally for a customer and only one will ever exist.

Batch production

Batch production is where many items of the same product are produced, such as a bike frame or parts for a metal fence. Many metal products are joined by welding, often done by hand rather than by machines, and the metal is held in place with a jig during the manufacturing process. The jig ensures that each part stays in place whilst the welding is completed.

When a product is made in a batch, it is often far cheaper per product than when making just one.

Mass production

Mass-produced products are manufactured in large volumes, and often assembly line workers can be used to fit standard components, such as screws and hinges, to parts. Mass-produced metal products include door handles, barbecues and cooking utensils.

Continuous production

Continuous production takes place 24 hours a day, 7 days a week and, in some cases, 365 days a year. Many cars are made using a continuous production process, and the huge amount of sheet steel that is bought for this brings down the prices.

When cars are made using continuous production methods, most of the work in the factory is automated using robots, with sheet steel being cut and pressed, transported, welded and painted by them. However, people are needed to work alongside the robots to fit parts to the cars, as robots currently lack manual dexterity.

Accuracy

Unlike metal, materials such as timber, paper and board change shape easily depending on temperature or the amount of moisture they are holding. Metal can change shape and expand in the heat, but it is not prone to the same amount of movement as timber is. It is often the case that engineers can work to a fine tolerance when using metal.

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 1 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 metal parts are engineered to a fine tolerance, there are specific quality control tools to ensure that metal 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 = 2.54 mm

2.54 ÷ 1,000 = 0.0254 mm, so:

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

If an engineer was asked to mill a 50-mm slot in a block of aluminium to the tolerance above, it would be possible to check whether the slot was correct by using a ‘go-no-go gauge’:

50 mm - 0.03 mm = 49.97 mm

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

50 mm + 0.03 mm = 50.03 mm

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