MOULDING PROCESSES

Many people are confused by the different moulding processes.  To help you understand and decide the most appropriate method for your application, each process will be explained here.

Please note: Rutland Plastics is an Injection Moulder and does not provide any other moulding services.

Below is a brief description of the processes to be covered together with typical applications.

A simple cost comparison of the different methods can be found here.

Injection Moulding

This is the process offered by Rutland Plastics.  For this reason it will be explained in a bit more detail.

Injection Moulding Process

An overview of how the process works.  Molten thermoplastic material injected under pressure into a mould tool.

Moulding Machine

How the moulding machine works from the taking in of plastic granules to how the molten plastic is injected into the mould and the part extracted.

Mould Tool

An explanation of how a mould tool is constructed.

Thermoplastic Materials

A list of the most widely used thermoplastics along with their properties and typical applications.

Blow Moulding

This covers a range of different processes:

Blown Film – Extrusion of polymer through a circular die.  Then expanded into tube for packaging.  Either bags, sacks or sliced to form sheet.

Extrusion Blow Moulding – Molten polymer is extruded into a pipe shape.  The mould closes around a set length and this tube is then inflated.  This method is used for bottles.
Injection Blow Moulding – This is the most common method for high volume.  Generally used for bottles and jars.  Superior visual and dimensional properties to extrusion blow moulding.

Injection Stretch Blow Moulding – Similar to injection blow moulding but the plastic is stretched as well as blown into shape.  Used for high quality containers.

Extrusion

Plastic granules are melted and fed through a die to form the shape.  Unlike injection moulding which produces individual parts, this is a continuous process.  Used for pipes, curtain tracks, window profiles and plastic sheet.  Can be cut to shorter lengths as required.

Rotational Moulding

Also know as Rotomoulding or Rotamoulding.  Used for hollow plastic products.  The polymer is placed in the mould in its powder form.  The mould is rotated around two axis in an oven spreading molten plastic around the mould.  Typical products include tanks, children’s large toys such as slides and playhouses, canoes and pallets.

Vacuum Forming

Plastic sheet is heated until soft and then draped over a mould.  A vacuum is applied to suck the sheet into the mould to form the shape.  Typical products include baths and shower trays, refrigerator linings and yoghurt pots.

Thermoforming is similar but air pressure and other assistance may be applied to the sheet.  Faster cycle times than for vacuum forming.  The largest application is food packaging.

Reaction Injection Moulding (RIM)

Also known as structural foam moulding.  Two materials are combined and placed into a mould.  The chemical reaction causes the material to expand and fill the mould.  Some finishing to the parts is required, including painting.  Typical applications include business machine housings and decorative wood effects

Dip Moulding

Mandrels are dipped into a bath of plastic paste or fluidised powder to produce a peelable skin.  Typical applications include protective gloves, handle grips and balloons.

Compression Moulding

Moulding of thermosets.  The powder is compressed and heated in a mould to produce a precision part.  Typical applications include fuse boxes, saucepan handles and insulators.

Pultrusion

Extrusion process with materials composed of a polymer and high performance fibre, such as glass.  Used for solid or hollow profiles in demanding environments such as aerospace, building and civil engineering applications.