All You Need to Know About Thermoplastics and Injection Moulding



21 March 2017
30 - Acrylic Sheets 101 (Option1)

If you’ve been keenly following our Science Lessons, you are perhaps already well acquainted with the term ‘Thermoplastics’. To recap, thermoplastics are polymers that can change their form reversibly, when heated or cooled and thus, can easily be moulded, recycled, reused, and coloured.

‘Injection Moulding’ is, however, a term you probably haven’t heard often. On first thought, you might assume that this is a process involving moulds and casts. Agreeably, Injection Moulding is a manufacturing process where a material is injected into a mould to form a final product of a required shape. Depending on the final product required, Injection Moulding can be done on a plethora of materials including metals, glasses, elastomers, and thermoplastics like Polymethyl Methacrylate as well as thermosetting polymers.

“Trivia Check: Did you know that the first injection moulding machine was patented in 1872 by American inventor John Wesley Hyatt together with his brother Isaiah Hyatt.”

Injection Moulding of Thermoplastics:

Speaking of plastics, Injection Moulding and Extrusion are the predominant processes employed in the production of plastic articles. In specific, thermoplastics have certain characteristics which make them highly suitable for injection moulding. These include ease of recycling, the versatility that finds use in a variety of applications, ability to soften and flow upon heating, and a better safety factor as opposed to thermosetting plastics.

Let us take a quick look at how Injection Moulding is done on a thermoplastic resin like Polymethyl Methacrylate (PMMA Polymer), in specific, SUMIPEX® PMMA manufactured by Sumitomo Chemical Asia:

  • Step 1: In the form of pellets / granules, SUMIPEX® PMMA resin is fed via a hopper into a heated barrel and is melted using heater bands and the friction of a reciprocating screw.
  • Step 2: The molten SUMIPEX® PMMA resin is then injected through a nozzle into a mould cavity where it cools and hardens to take the contour of the cavity.
  • Step 3: The mould tool is mounted on a moveable platen. Once the part to be manufactured has solidified, the platen opens and the part is ejected using ejector pins.

Thermoplastic Injection Moulding is thus a manufacturing process that creates fully functional parts by injecting a thermoplastic resin like SUMIPEX® PMMA into a pre-set mould. Moulding conditions, however, vary based on the type and capacity of moulding machine used, the shape and weight of the final product and the design of the mould.

Advantages of thermoplastic Injection Moulding:

There are many evident advantages of the Injection Moulding process on thermoplastic resins like SUMIPEX® PMMA.

  • Injection moulded thermoplastic parts exhibit pinpoint accuracy.
  • The parts created have clean surface finishes, making this production process viable for creating both prototypes as well as small and large production runs.
  • Varied surface texture and finishing can also be obtained.
  • Thermoplastic injection moulded parts are usually turned around within a few days. This helps developers to make design changes quickly, when the parts are used for prototyping,
  • Ideal for bulk manufacturing.

Applications of thermoplastic Injection Moulding:

It goes without saying that Injection Moulding finds itself crucial for the manufacture of a variety of parts, ranging from the smallest components to body panels of cars. Articles such as wire spools, packaging material, bottle caps, automotive components, hair accessories like combs, parts of musical instruments one-piece chairs and small tables, storage containers etc., are some manufactured from SUMIPEX® Polymethyl Methacrylate subject to Injection Moulding.

High Flow Grade, General Purpose Grade and Heat Resistant Grade of SUMIPEX® PMMA is best suited for Injection Moulding. If you have any enquiries about Injection Moulding of PMMA or thermoplastic resins in general, you can reach out to Sumitomo Chemical Asia here.