What is Injection Blow Moulding? A Step by Step Guide

   Plastic injection blow moulding machine with blow moulded bottles
Plastic injection blow moulding machine with blow moulded bottles
Resource: https://www.plasticsnews.com

Many thin-walled plastic products today are being produced using the injection blow moulding process, with the market share for blow molded products having reached $80.47 billion in 2022. This production method, in addition to being cost effective, is usually fast enough for batch production. This guide simplifies the injection blow moulding steps for you.

What is Injection Blow Moulding?

Injection blow moulding is using to mean a technique where injection moulding is used to produce hollow and thin-walled parts or containers. Just as its name suggests, combines injection and blow molding and involves blowing a blast of air to expand molten plastic. This results in the plastic conforming to the shape of the specific mould.

Different types of plastics may be used when injection blow molding products. These include polyethylene, polypropylene, and polyvinyl chloride. These are plastics which possess properties that allow them to be injection molded.

Blow Mould vs. Injection Mould

It’s worth noting that a blow mould slightly differs from that if an injection mould. As its name suggests, a blow mould requires air to be blow for the final part to be produced: an injection blow mould does not.

Another major difference between a blow mould vs. injection mould is that, whereas, blow moulds are used to manufacture hollow products for packaging and other uses, injection moulds are typically meant for solid parts.

Advantages of Injection Blow Moulding

The advantages of injection moulding range from those that concern dimensional quality to the visual appeal of products that the method produced. Key advantages include the following.

  • Parts with tight clearances and good visual appeal
  • Reduced waste or excess material that would require trimming
  • Excellent product finishes
  • High production volumes compared to other blow molding methods
  • Product design flexibility such as thin walls and thick necks for packaging containers
Injection blow moulding process diagram to illustrate the steps
Injection blow moulding process diagram to illustrate the steps
Resource: https://www.sciencedirect.com

Injection Blow Moulding Process

The injection blow moulding process is a little more complex than the conventional injection moulding process. More steps are required, which include a core to introduce air into the blow mould and a source of pressurized air to expand the preformed resin.

These injection blow moulding steps, from the first to the last, are as follows: resin feeding, resin melting and homogenization, injection the preform, clamping the mould and part ejection and cooling.

1. Resin Feeding

Injection blow moulding steps start with feeding the raw materials (usually a resin in pellet or granule form) into the extruding or feed barrel. This is done either directly into the barrel using vacuum pumps, or by use of an elaborate system. Once the feedstock is inside the barrel, melting and mixing can begin.

2. Resin Melting and Homogenization

The resin is, using controlled heat levels, gradually melted in the injection blow molding machine to a form that can be extruded. This is conveniently done by electric heating bands surrounding the barrel. At the same time, a reciprocating screw rotates to mix and heat the feed. It’s at this time that any required coloring material may also be added.

3. Preform Injection

The melted plastic is extruded, through a manifold on one end of the barrel, into what’s called the injection blow moulding core or pin. The extruded resin is the preform that will be used for the actual injection blow moulding process where it will be blown into the required product.

4. Mould Clamping

The preform mould is caught or clamped between two dies, one of which is movable. Here, it’s cooled just until its temperature is low enough to remain in shape after unclamping, but not too low as to harden before the final part of the process, which is blowing air into it.

5. Blow Moulding

The preform is taken to another mould. This mould has the profile of the required product or part, and will shape it accordingly. Once inside the mould, a blast of pressurized air is pushed into the mould via the core, or the metal rod in the middle of the plastic preform. The air expands the plastic onto the mould to take the required shape.

6. Part Cooling and Ejection

In this last stage of the injection blow moulding processes, the formed part is cooled and then ejected from the mould, usually by opening the mould. It’s then ready to be taken through the final phases of the process, such as trimming and quality control:

  • Parts are trimmed to remove excess material. The trimmed plastic waste may re-used
  • Hollow products such as packaging bottles are taken through a leak test where air is fed into or drawn from the bottle to detect any openings.
  • Ejected containers are taken through the entire blow moulding process as raw materials.
  • Other process may include marking the containers before shipping them to manufacturing companies or end users.
Injection blow molding products
Injection blow molding products
Resource: https://www.bioplasticsmagazine.com

Injection Blow Moulding Products

The injection blow moulding process is known for producing parts that possess an attractive visual appearance or profiles and dimensional accuracy. So it’s one of the most used methods to make products today.

The injection blow moulding applications range from packaging containers, and which form the largest share market for blow moulded products at 49%, to automotive and medical or laboratory products.

This below contains the most common injection blow moulding products today. Note that other blow moulding methods may be used as well, depending on the required product characteristics and other reasons.

  • Soda and water packaging bottles
  • Milk bottles or other containers
  • Shampoo bottles
  • Medical packaging containers
  • Plastic storage tanks
  • Medical containers and other products
  • Industrial containers
  • Parts of kitchen and other appliances
  • Parts of cars


The injection blow moulding process is an important manufacturing technique in the world of plastic products. Using this resin molding method, manufacturers can produce a range of plastic articles, from packaging bottles and jars to parts for industrial or end user purposes. IBM also offers a number of advantages, which include part design flexibility, reduce raw material waste, and others.

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