Injection Moulding: Plastic Manufacturing Process

Injection Moulding Plastic Manufacturing Process (1)

Plastic is an essential component, as it’s used across various industries. For instance, it’s used to manufacture medical gadgets, automotive, and home appliances. Because it’s applied across many sectors, it’s needed in large quantities to satisfy demand.

But how is plastic made? There are different ways to make plastic, and injection moulding is one of the best ways.

This plastic manufacturing process allows for large-scale and fast manufacturing of crucial components. While plastic is essential, not many manufacturers understand the process despite injection moulding being a popular method for producing quality plastic components.

Read on to learn more about the plastic manufacturing process.

How To Choose The Right Plastic

Plastics differ depending on additives, chemistries, and derivatives. Each type of plastic boasts unique aesthetic and functional properties.

The following are two classifications of plastic:

1. Thermoplastics

These types of plastics undergo several melt and solidification cycles without losing considerable degradation. They originally came in the form of small sheets or pellets, which after heating, can be moulded to the desired shape using different manufacturing processes.

No chemical bonding happens during this process. It explains why this process is 100% reversible, so we never have to worry about melting, recycling, or reusing thermoplastics. It’s also the reason thermoplastics are the most popular kind of plastic.

The common materials include:

  • Polycarbonate (PC)
  • Acrylic (PMMA)
  • Polyethene (PE)
  • Polyvinyl chloride (PVC)
  • Polypropylene (PP)
  • Polyamide (PA)
  • Acrylonitrile butadiene styrene (ABS)
  • Polyether ether ketone (PEEK)
  • Polylactic acid (PLA)

PC, PE, and PVC are common thermoplastics used in packaging.

2. Thermosetting Plastics

These plastics permanently retain their solidness even after curing and are also known as thermosets. During the curing process induced by light, heat or appropriate radiation, the polymers forming the thermosetting plastics cross-link to each other. This leads to the formation of a permanent chemical bond.

The most popular thermosetting plastics are:

  • Epoxy
  • Vulcanized rubber
  • Silicone
  • Cyanate ester
  • Polyurethane
  • Polyester

All of these thermosetting plastics decompose upon heating instead of melting when heated. This means recycling or returning thermosetting plastics to their original state is impossible. As a result, thermosets aren’t environmentally friendly, which is why most plastic manufacturers avoid this type of plastic today.

Types Of Manufacturing Processes

Plastics vary in terms of durability, shape, colour, and size.

3D Printing

This manufacturing process involves using 3D printers and CAD designs to make three-dimensional parts. It’s done by systematically building material layers one after another until the physical part is created.

The materials used in 3D printing include:

  • Ceramics
  • Resins
  • Metals
  • Powders, such as alumide and polyamide
  • Plastics, such as PVA, ABS, and PLA

3D printing offers greater design freedom, unlike other manufacturing processes. Because of this, it’s the best manufacturing process for making complicated geometries on a budget.

The steps to follow during the 3D printing manufacturing process are:

  • Deciding and preparing the print software
  • Printing, which varies from one 3D printing technology to another, includes selective laser sintering (SLS), fused deposition modelling (FDM), and stereolithography (SLA)
  • Post-processing, which entails taking out the parts from the 3D printer and washing or cleaning them (after that, the support structures are taken out if necessary and post-cured)

3D printing, also known as additive manufacturing, is the go-to manufacturing process when creating intricate designs.

CNC Machining

This manufacturing process is subtractive. It involves removing material with computer-controlled cutting tools, such as drills, lathes, and mills, to make plastic parts through rotation.

CNC machining in plastic manufacturing is classified into two:

  • Lathing, which is the use of a spinning part and fixed tools
  • Milling, which is working on a fixed workpiece and using spinning tools

Because it’s a subtractive process, CNC machining is ideal when working on parts that need tight tolerances and are challenging to mould. Some items made through this manufacturing process include gears and brushing.

CNC machining isn’t perfect, with some downsides. One such issue is that it might be impossible to make certain complicated parts using CNC machining. Another issue is that the cost of CNC machining can rise when designing complicated geometric shapes, for instance, curved interior channels.

Injection Moulding

Injection moulding refers to the manufacturing process of melting thermoplastic or thermosetting polymers and injecting them into a mould cavity under pressure. These heated plastic granules are then cooled to retrieve the size and shape of the desired plastic product. The manufacturing process uses materials, such as glass and metals.

Manufacturers often choose the plastic injection moulding process because it’s suitable for the large-scale manufacture of plastic products. Plastic versatility compared to other materials, such as glass or metal, is another reason the process remains popular. Some of the items made through injection moulding include drinking bottles.

  • Other reasons why manufacturers prefer injection moulding include the following:
  • A low amount of waste is produced during the injection moulding process.
  • The manufacturing cost is much lower, which is why it’s ideal for large-scale manufacturing.
  • Fast production speeds are guaranteed even when making complicated parts, as less human input is needed.
  • There are high flexibility levels since we can create a broad range of materials in the same mould.

However, injection moulding comes with a disadvantage: It can be complicated, depending on the moulding conditions and the part’s shape.

What Is The Injection Moulding Process?

The injection moulding process isn’t complex. It follows the steps below:

  • Mould preparation: The first step entails shaping the product so that we can divide it into two halves.
  • Casting: This is where the moulding machine, either a hydraulic motor or press, attaches the two mould halves without destroying them.
  • Cure: This means leaving the hot plastic to cool and solidify by itself to become a usable item.
  • Demould: It’s also known as mould opening, and it’s done once the mould has cooled down. The demoulding is done with a clamping motor, and opening the two parts is meant to make taking out the last product safe and straightforward.
  • Trimming: It involves pushing out the solidified item and using the fabricator to eliminate all the waste products.

Final Thoughts

There will always be high demand for plastic across many industries. To meet this demand, manufacturers turn to injection moulding since it’s ideal for large-scale production of plastic components.

It’s understandable to think that injection moulding is a complicated process. But with this guide, it’s now easier to paint a vivid picture of the process.

9th March 2023