Design & Technology – Production techniques -Part 3

Source:http://www.bbc.co.uk/schools/gcsebitesize/design/resistantmaterials/processtechniquesrev1.shtml

Shaping by fabrication

Fabrication involves joining separate pieces of material. This can be done by:

  • cutting joints
  • using other components, such as screws, nails and adhesives
  • using heat processes such as soldering or welding

Fabrication processes can be either permanent or temporary. Temporary fabrications are designed to be easily taken apart.

Read more about fabrication in the Components, joints and adhesives section.

 

Shaping by deforming: woods and metals

Deforming is a method of shaping materials by either bending in a straight line or by creating a bowl or dish shape.

Bending

Metals can be bent in a vice or in folding bars. The material is marked where it is to be bent, and clamped to the line in the vice or folding bars. To prevent damaging the material as you hit it with the mallet, place a piece of wood next to it and hit that instead.

Bending sheet metal in a vice

Metal in a vice, being bent by hammering it

Thin metal may be bent whilst cold, while thicker metal may need heating or annealing. Larger pieces of metal may also need to be heated first.

Laminating

Wood is usually bent by laminating. This is done by cutting thin strips of wood, putting glue on the strips and clamping them into a mould.

Wood is pressed in between two pieces of a mould and heald using clamps

Three-dimensional deforming

Hollowing and press moulding are both ways of three-dimensional deforming. It is important to remember that wood will not deform in three dimensions.

Hollowing

Hollowing is a way of deforming thin sheet metal to produce a bowl shape. The metal is annealed then cooled in cold water. It is placed on a leather sand bag and shaped using a bossing mallet. Finally it is placed on a hollowed wooden block and shaped with a blocking hammer.

Press moulding

Press moulding can be used to force sheet metal into 3D shapes. The metal is placed between two moulds which are then squeezed together.

Shaping by deforming: plastics

Bending

Thermoplastics cannot be bent when cold. They are bent using a strip heater or line bender which will heat the plastic in a straight line, so it can be bent by hand.

Plastic bends where the heat is applied

Press or compression moulding

A mould is made in two halves. Sheet plastic is placed between the two halves, which are then heated and pressure applied, enabling the plastics to assume the new shape.

Piece of plastic is moulded by being pressed between 2 shaped moulds

Press moulding is used to make electrical fittings, handles, and many other products. It can only be used with thermosetting plastics.

Blow moulding

A tube of softened plastic called a parison is extruded into a mould.

Blow moulding

step 1 - parison is inserted into mould. step 2 - parison based pinched by mould, sealing it. step 3 - air is blown in and plastic expands. step 4 - finished product, a plastic bottle
  1. Parison inserted into mould.
  2. Base of parison squeezed by mould.
  3. Air blown in to parison, parison expands to fill mould.
  4. Finished product.

Blow moulding is used to shape plastics, mainly for making bottles, plastic buckets and similar shapes.

Vacuum forming

This process uses a wooden mould or form. A sheet of thermoplastic is heated, then shaped by creating a vacuum underneath it. Air pressure then forces the plastic over the mould.

Vacuum moulding

Step 1 - plastic is above a mould and below a heater. step 2 - plastic is heated and melts. step 3 - air is removed, sucking the melted plastic into the shape of the mould.
  1. Plastic placed over mould.
  2. Plastic heated.
  3. Air in mould removed.

Vacuum forming is used to for food and confectionary packaging, trays, shop fittings and baths.

Shaping by reforming

Reforming is a method of shaping materials which changes their overall appearance by first melting or softening them into a paste, then hardening them. Reforming methods include casting, extrusion and injection moulding.

Die casting

Die casting uses a metal mould that can be very detailed. The mould is made in two parts to allow the casting to be removed. Die casting is a very important industrial process used for many different types of products.

Molten metal is inserted into shaped mould, and fills the cavity.

Extrusion

Extrusion moulding is used to produce long, but fairly thin products such as pipes or curtain tracks. Both plastics and metal can be extruded. The material is forced through a die, which contains a hole which is the same shape as the required product.

material is forced through shaped die

Injection moulding

A metal mould is used and softened or molten plastic is forced into the mould by pressure from a screw thread or pneumatic plunger. The mould is made in two parts to allow the moulding to be removed. Injection moulding is used extensively in industry.

Molten plastic is injected into cavity

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