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Merging two established technologies for an optimal product

10 May 2021

What do you get when you merge the traditional plastic injection molding with powdered metallurgy? Find out about this technique which Rompa Group offers by combining these two technologies in this week's article!

What is Metal Injection Moulding?

This process was developed in the 1970s in the US by Raymond Wiech, he is also considered the inventor of the Metal Injection Molding method. It was however not until the 1990s for the technology to get worldwide recognition in the manufacturing industry.

MIM, Metal Injection Molding, is one of many technologies Rompa Group offers its clients. This innovative technology is established by merging the techniques of plastic injection molding and powdered metallurgy. The powder mixture consists of metal and a polymer binder. With using a standard injection molding machine, we melt the powder and inject it into the mold. The part then cools down and solidifies into the desired shape. The final product is seen in many industries such as medical, dental, aerospace and automotive.

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MIM vs casting

Both these processes are used throughout all industries worldwide. Metal Injection Molding is suitable for production of small and complex metal parts produced that cannot be made with conventional technology. It does not pose a problem if these parts have complex, thin or fine design details. The metal is not melted in the MIM process like you might know from metal casting processes, this allows a longer tool life.

So why choose MIM instead of casting? The biggest difference between casting and Metal Injection Molding is that casting uses (in most cases) an aluminum alloy or zinc alloy as the raw material. Metal Injection Molding on the other hand uses steel or other types of suitable MIM alloys. The most common ones are stainless steel, titanium, nickel, tungsten, copper and combinations of such. At the end of the die casting process the excess metal must be trimmed either manually or go through a different die. This gives a lot of waste and takes extra time which it does not in the case of the MIM process. Both systems have their advantages and disadvantages. We will always advise our clients the best solutions looking at the design, volume and production run of the products or part.

The process

Feedstock

The process starts with deciding and preparing the feedstock or compound. Fine metal powder is mixed with synthetic binding material to precise amounts. At Rompa Group we can offer our clients up to 20 different alloy types.

Molding

The Metal Injection Molding is identical in technique and equipment as how we do plastic injection molding. The products are placed in an oven and undergo a thermal-chemical process. The process happens at around 200 degrees. The molded part will cool down and then ejected from the mold so the process can repeat.

Remove the synthetic binding material

The next step is to remove the synthetic binding material. This is usually done during thermal-chemical processes where the powder fuses and forms a fully metal product.

Finishing

Post processing is possible depending on the requirements of the client.

Disadvantages

However, the Metal Injection Molding method might not always be the best solution for a project. The parts made using this method are typically small. The bigger the part, the fewer will be able to fit in the furnace. Also, smaller parts are more cost effective to produce. So, the main disadvantage of MIM is the fact that it is generally not suitable for larger part production, but it also depends a lot on the design of the part. Every situation is different and at Rompa Group we always aim for the best solution with the most suitable technology.

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Designing parts for MIM

The designing rules for plastic injection molding also apply for the designing of parts for MIM manufacturing. But there are some differences or exceptions to be considered such as the wall thickness. Just as with plastic injection molding the wall thickness should be minimized and kept the same throughout the whole part. Minimizing wall thickness reduces material volume and production time but also reduces time for debinding which is cost saving, but does not have any negative effects on the quality and strength of the product. Whereas with plastic injection molding draft is required, most parts made with the MIM process do not require any draft. The binder used in the powder releases easier from the mold. Just as with all designs it is important to consider the location of gates, ejector pins, parting lines, etc.

Contact us for more information

Rompa Group offers a wide variety of technologies and MIM is one of such techniques. Would you like to know what other technologies Rompa Group offers? Make sure to check it here. There is a lot more to explain about MIM, and we would like to tell you all about it. Do you need help with tooling issues or design difficulties? Our engineers are more than happy to assist you in this process. You can find our contact details here and our specialists are always ready to answer all your questions.