Manufacturing Processes & Techniques Designers need to understand a wide range of manufacturing processes and techniques to match their knowledge of materials. This topic will outline the main processes undertaken in manufacturing commercial products. It is important to understand how the different processes link together in the manufacture of a product. During manufacture material is usually first shaped crudely, then more precisely into finished parts or components and then assembled. Some products are made by a single process although most require a mixture of processes.

Manufacturing Process A finished product may be required in any one of an innumerable number of shapes and sizes, and there are many different techniques by which to produce the article. These techniques can be categorised into three major groups – shaping, joining and wasting.

Manufacturing Technique A manufacturing technique is a specific manufacturing term – sometimes relating to one material group only, eg Injection moulding The Manufacturing Processes (Techniques)/Materials Matrix details the techniques suitable for different materials.

Shaping The process by which materials are formed into shape by particular techniques. There are 4 sub-groups within this manufacturing process. These are – bending, moulding, casting and weaving.

Bending Bending is the plastic deformation of materials about a linear axis with little or no change in surface area. When multiple bends are made simultaneously with the use of a die or jig, the process is sometimes called forming. Metals are bent using either a bending machine or folding bars.

In order to bend plastic it is necessary to use heat to soften the area around the bend before applying the force. In the case of straight bends, this can be done by a strip heater or bending machine.

Woods are more difficult to bend as they require heating and softening using steam first and then slow bending around a die.

Moulding Moulding (sometimes called forming) is similar to bending but is used when more complex shapes are required. Pressing sheet metal is one example of this process. Modern bending machines are able to produce very complex shapes out of sheet material but they need a lot of energy as large forces are required to press the metal into shape.

Metals can be moulded or formed by hand by beating using special hammers and mallets over leather sand filled bags or shaped formers.

There are several methods of moulding or forming plastics most of which we will examine later. One of the simplest methods is by vacuum forming.

A simpler method for less complex shapes is plug and yoke forming.

Once again woods are harder to mould than other materials. The most common methods of moulding woods is by lamination. This involves layering thin sheets, or veneers, of material over, or between, a forming mould and holding under pressure while the glue sets. The process can be eased by softening the veneer first by heating with steam but the bending forces must always be within the elastic limits of the material otherwise the veneers will crumple or split. If the veneers are inside a former, the force can be applied using cramps, clamps or a vice. If the veneers are over a former, however, this is not possible as the holding tool can mark and damage the woods. In this case, it is usual to use leather straps passing over the top of the mould with the force being applied by screwing them into the board onto which the mould is fixed.

Laminating is the process of building up a thick layer of material using thin layers of material joined with adhesives. Laminating produces products that need little or no specialist finishing. The process can be used to form complex shapes and surfaces and is very suitable for large surface areas. By careful material choice and preparation, combinations of material can be used to take advantage of specific aesthetic, physical or mechanical properties. The process is very labour intensive and requires the production of an accurate mould. The complexity of the shape can be limited by the glue, the clamping force available and elastic properties of the material which affect the angle of curvature attainable.

Casting Casting is a technique that can be applied to metals or plastics and involves heating the material until it liquifies and then pouring it into a hollow mould, allowing it to cool to the shape required. There are several methods of producing the mould into which the molten material is poured varying from plaster of paris to green sand through to wax. As a general rule, the harder a metal is, the higher the temperature required to melt it.

Some very soft metals (like silver or lead) can be melted by the heat from a normal cooker.

Some plastics come as a resin that can be mixed as a liquid and poured into latex moulds. As the chemical harder in the resin reacts, the material hardens and forms the shape required.

Sand Casting is a very common method of producing relatively small numbers of a component.

Casting is a process that is not only applied to resistant materials, it can be applied to foodstuffs as well!

Textiles cannot be shaped by the processes so far described. The most common method of shaping textile fibres is by weaving.

Knitting is just another form of weaving. The important feature of weaving is that fibres are cross threaded to build up a shape. It could perhaps be considered to be more like joining but is classified as a shaping technique.