What’s the difference between blow and injection moulding?
Blow moulding and injection moulding are very different methods. Both produce high-quality, cost-efficient components, but the process you choose depends on what you’re producing.
Think of products you have around the house, such as water bottles or shampoo. The bottle is a hollow, singular container with thin walls, and an example of what blow moulding makes. Blow moulding is also used to make bottles for oil and petroleum products, and medical and technical solutions. Manufacturers also use blow moulding to make automotive parts, stadium seating and chairs, coolers and watering cans.
Injection moulding, on the other hand, is used to produce automotive dashboards and bumpers, electrical switches, electronics, medical devices and so much more, at high volumes.
What is blow moulding?
It’s very similar to glass blowing. A plastic tube is heated and filled with air, at which point, it becomes a balloon of hot plastic called a ‘parison’. The mould is then placed around the parison. The plastic is trapped while air continues to fill the parison, creating the shape of your component.
The advantages of blow moulding are:
- The costs are lower than plastic injection moulding
- Machinery costs are also usually lower
- One-piece construction – no need to connect part halves
What is injection moulding?
Here, creating the perfect precision part is all about the mould, which is crafted from aluminium or stainless steel. Melted resin is then injected into the mould, which form the polymer into your desired shape. The mould us held together under intense pressure and then cooled before the component is released. Where air is needed for blow-moulding, it’s death to the injection moulding process. Air can create air pockets or bubbles, resulting in defective parts.
The advantages of injection moulding are:
- Multi-cavity mould options
- Most cost-efficient option for mass production of thousands or even millions of the same part
- Flexibility – you can change the material or colour of the part you’re producing
- Low scrap rate
Both processes are popular, and each has its own advantages. Essentially, blow moulding is for simple, hollow shapes – usually bottles. For anything else, you’re best bet is injection moulding.
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