We are diving into injection moulding once again this week.


| 16-07-2022
Leestijd: 5 min.
We are diving into injection moulding once again this week. Rompa Group has been working with injection moulding and many different techniques ever since the beginning. We are very enthusiastic about the future of injection moulding and what different methods it has to offer and are more than happy to share this with you. This week we take a deep dive into the multi-material injection moulding technique: interval injection moulding. Let us explain further below!

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What is interval injection moulding?

Interval injection moulding is one of the easier and simpler multi-component moulding techniques. We can also refer to interval injection moulding as “marbling moulding”. This procedure involves the injection of two different coloured plastics through the same nozzle into the desired mould. The meaning of interval is a pause or break during an activity and the same goes for interval injection moulding, where the two different coloured plastics are being injected with pauses. This results in a finished product with a unique multi coloured design with no clear colour lines but a more mixed coloured finished look.

How does the interval injection moulding machine work?

Interval injection moulding is one of the newest developments in injection moulding. To achieve this moulding method an additional barrel is added to our traditional plastic injection moulding machine. The barrel together with the machine forms an independent double barrel with a special nozzle. When the machine is fully set up for our client we start the process. Two different types of molten plastic flow through the same nozzle into the mold, this will achieve the double material design. The inner layer is also known as the core material and the outer layer is a mix of molten plastic called the skin material.

What are some advantages of interval injection moulding?
  • Traditional injection moulding needs two steps to create an inner and outer layer of a product, while interval or sandwich injection moulding only needs one step to create a combination of material products.
  • The colour combinations are endless, this gives our clients many options in design and colour usage.
  • We can reduce injection pressure thanks to the use of low viscous products.
  • Recycled plastics can be used with the interval injection moulding manufacturing technique
  • For the skin materials we can offer high-quality and anti-magnetic materials.
  • We want optimal product hardness and as little residual stress as possible, this can be achieved by optimally combining skin and core materials.

What are other multi-material injection moulding techniques?

As mentioned before, interval injection moulding is one of the multi-injection moulding techniques. Multi-injection moulding techniques are also known as twin-show injection moulding. The traditional process remains the same, but with techniques such as interval injection moulding we can offer our clients more creative options for their finished products.

Sandwich injection moulding
This technique is similar to interval injection moulding, it too involves a superficial element. The process also has an interval unit for the necessary pauses in between the injections. So, what’s the difference? This technology uses two injection units. These units are connected to nozzles but it gives the possibility to inject two different materials into the mould. While with interval injection moulding we can ‘only’ inject the same material but in different colours.

Over injection moulding
​​During the overmoulding process, we start by forming the base layer (around an insert, if need be). Next, we inject the extra plastic layer (or layers) over and around the component. Depending on the compatibility of the material, you can use one or more synthetic resins to create a specific texture or a certain look. This is a multi-material manufacturing technique Rompa Group has a lot of experience with. It is a manufacturing process we have dedicated a special blog article to, where we go into detail regarding this process. Make sure to read it here!

Core-back injection moulding
If our clients want simple yet beautiful geometries in their design then the core-back process is very suitable. It might be the simplest multi-material injection moulding process and it is suitable for injection moulding with a single cavity. Note that in addition to the single cavity it also allows the cavity for displacement, this means that it can expand by using a sealing slide for injection of a second component.

Contact Rompa Group

There are still many things to tell you about the different techniques of injection moulding. If you are interested in learning more, make sure to subscribe to our newsletter to be the first to receive news regarding Rompa Group. Don’t hesitate to contact us if you would like to know more about interval injection moulding and if you would like to discuss this with a specialist in this field.




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