16.1 Redistribution Methods

Learning outcomes

By the end of this unit you should have developed a knowledge and understanding of:

the different ways that materials can be shaped into products
how products can be shaped by the deforming and reforming methods
why redistribution processes are used rather than additive or fabrication processes
shaping and forming processes that involve redistribution
how the different processes produce varying amount of waste and their effect on the environment

Redistribution: deforming

The processes can be broken down into 3 main sections

Forming

Wasting/deforming, Cutting, drilling, bending

Redistribution

Casting, moulding, Die casting, injection moulding, extrusion

AdDition

Additive processes, fabrication, Welding, joining, 3D printing

Redistribution

Redistribution refers to the fact that material is moved around in order to shape it into a product or component.

This can be done in one of two ways; 1. deforming and 2. reforming.

Deforming involves changing the shape of the material without changing the state. i.e. the material remains a solid throughout the shaping process even though it may be subjected to heat and/or pressure.

Wood is not a material that lends itself to being deformed as it is mostly used in its natural state and its strength resists bending.

Thermoplastic polymers can become soft at relatively low temperatures at which point they can easily be deformed.

Metals are also relatively easy to deform using a combination of heat and pressure.

Deforming wood

Wood is not typically deformed as it is more easily joined but below is the deformation technique you need to know for your exam.

Steam bending

This process involves bombarding wood with steam until it becomes flexible. It is then bent into shape and held in place while the water content is slowly removed from the wood leaving the wood ‘bent’ into shape. Traditionally used to make Windsor style chairs.

Laminating

This is not a way of deforming solid timber like you can with steam bending. Thin sheets (veneers) of wood are stacked with glue in between then placed in a mould. Once the glue has set the wood is removed and retains the shape of the mould. This is how skateboards are made.

Deforming Metal

Metal lends itself well to being deformed with pressure and heat.

Bending and folding

Metal can be bent cold or hot and sheet metal can be folded in similar way to sheet plastic, although it requires specialist high pressure machinery.

Spinning

Spinning is a process by which a disc of metal is rotated at high speed and formed into a symmetrical part.

Metal spinning does not involve removal of material, as in conventional wood or metal turning, but forming (moulding) of sheet material over an existing shape.

Commercial applications include rocket nose cones, cookware, gas cylinders, brass instrument bells, and public waste receptacles. Virtually any ductile metal may be formed.

Press Forming

Press Forming is a sheet metal process that uses a pair of tools called a ‘die’ mounted inside a press and then the metal is placed inside the die. The press then applies high pressure (3000 tons of force or higher on large presses) and the material is formed to match the shape of the die. In other words, press forming is a forming technology where a pressing force is applied to a material to deform it (by bending, stretching, etc.) to match the size and shape of the die, and the material then maintains that shape forever. It is used to make the cases for white products such as fridges and most car body parts are made by press forming nowadays.

Deforming polymers

Polymers are perhaps the most commonly formed material in the D&T workshop due to the ease with which they can be turned into a liquid (or softened) and back to a solid at relatively low temperatures. The following methods rely on the polymer being heated up until it becomes plastic i.e. flexible enough to form but it never becomes a liquid.

Line Bending

A process which involves heating up a small area of plastic sheet so it can be folded or bent like paper. Usually this is done around a former.

Vacuum Forming

Vacuum Forming is a process which involves heating up a sheet of plastic then raising a former or pattern up through the plastic while removing the air below to create a vacuum. This then causes atmospheric pressure outside the vacuum to ‘force’ the plastic down on to the former.

Vacuum Forming is commonly used to produce hollow ‘shell like’ items such as yoghurt pots and other food containers but they can be used to produce larger items such as baths and hot tubs. They are also useful for making moulds for pouring in plaster and concrete.

How Vacuum Forming works

Vacuum Forming moulds should have the following characteristics:

The sides should slope outwards with no ‘under hang’ so the product can be removed from the mould. This is called a draft angle.
There should be no sharp edges (radius edge) to avoid thinning of the plastic.
There should be air holes to avoid trapped air especially in the corners.
There should be sufficient space between peaks (and peaks should not be too high) toavoid webbing.

Blow Moulding (Injection blow moulding starting with a parison)

Blow Moulding is a manufacturing process by which hollow plastic parts are formed. The blow moulding process begins with melting down the plastic and forming it into a parison or in the case of injection (and injection stretch blow) moulding, a preform. The parison is a tube-like piece of plastic with a hole in one end through which compressed air can pass.

The parison is then clamped into a mould and air is blown into it. The air pressure then pushes the plastic out to match the mould. Once the plastic has cooled and hardened the mould opens up and the part is ejected.

Blow Moulding (blow moulding starting with extruded plastic)

Go to Redistribution Methods 2

Lesson Task:

In your notes and presented on your website, make sketches, diagrams and descriptive notes for each of the forming processes described on this page.