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Multiple Material Injection Moulding

by Nice Rapid | Sep 02,2019 | Plastic Injection Moulding

As we have discussed preciously, it is sometimes necessary to combine different resin materials in a single moulding job in order to enjoy the benefits of both materials for a particular type of production. Relying on single materials for injection moulding is sufficient for low cost and uncomplicated products, but, especially when dealing with components destined for the electronics or medical markets, it is important that the highest quality and most suitable combinations are used in order to meet technical and international regulatory and legislative requirements. To this end, the use of multiple materials is something that is much more prevalent in contemporary injection moulding and this is what we will discover more about in this blog.

Using a single resin material used to be commonplace when moulding simple items for production, but with the advent of multiple material injection moulding techniques, such as multi component, multi shot and overmoulding, this has all changed. Due to the increasing use and cost reduction of this manufacturing process, even everyday items may now possess some form of mixed materials or complicated feature in their designs – such as toothbrushes with rigid handles and flexible heads, for example. Below, we will look in a little more detail as to how these features and differing materials are incorporated into the production process and how they work in practice.

Multi Component Moulding: In this process, multiple resins are included in the same moulding run in order to provide different material properties to the finished product. The resins are fed into the machine simultaneously and are then allowed to mix together, as opposed to being separate entities in the end product. This technique can also be used to create a single product with different properties along its length, such as the adjustable head and rigid handle of the aforementioned toothbrush.

Multi Shot Moulding (MSM): Adding different resins in this method is undertaken by layering each material during the moulding process, thus providing a strong bond between the two different types of material. If this is undertaken whilst both of the materials are still warm, this bonding effect is magnified, providing a very strong alliance between different areas of the part.

Over Moulding: This is one of the most common methods of layering resins in injection moulding, so as to produce different additions or finishes. Liquid resins are used to add another part to an existing mould by heating both to a high temperature and then letting them fuse together. The completed part is then ejected as a single piece, which not only increases the speed of production and, therefore, reduces tool time, but it also simplifies quality control inspections.

Moving on from the above methods, there are also some newcomers known as Gas Injection Techniques (GIT), Water Injection Techniques (WIT) and Micro Injection Moulding. These work with either a co-injection or mono-injection method. Mono injection allows two resins to be inserted into the cavity via one opening and injection method, as opposed to co-injection, which allows two resins to be injected into the cavity through one opening, one after the other. Below is some more information on GIT and WIT and Micro Injection Moulding.

Gas Injection Techniques (GIT): This techniques generally uses nitrogen to form a hollow space in the injected resin, whilst maintaining the wall thickness and structural integrity of the more original techniques. It allows the finished part to be light and strong and can reduce the manufacturing costs, cycle and cooling times of each part by 50% due to the reduction of less resin material used. It also reduces sink in the finished product and this means that there is less likelihood of distortion occurring throughout the whole process.

Water Injection Technology (WIT): WIT has two possible manufacturing combinations – known as full and short shot processes – with the technique itself being more user friendly and preferred over GIT. Due to the nature of the technology, the tool itself must be transparent and capable of providing high-speed shots to force the water into the cavity for the "short" process. The benefits of the process, such as lower weight, sink, cost and cycle times are the same as the GIT technique, but due to the process using water instead of nitrogen gas, it is much cheaper and easier to undertake with the same underlying results.

Micro Injection Moulding: This technique is able to produce very small parts to a very high degree of accuracy, mainly by using traditional moulding machinery and techniques. Specialised micro injection units are high precision tools which are attached to a standard moulding machine and are capable of applying resin into the mould at very high pressures, thus increasing detail and  accuracy. Due to the "bolt on" nature of this extra machinery, it is able to be either retrofitted to existing machines that are currently unused or can be added when required to machines already in use. This allows a manufacturer to reduce costs and increase tooling production only when required or necessary and making full use of their assets.

Multiple Material Moulding is just another aspect of rapid prototyping and injection moulding that we specialise in here at NICE Rapid. We would love to hear from you when you are planning your next injection moulding project, so please call us today!

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