When should I use Metal Injection Moulding and what can it achieve?

Metal Injection Moulding (MIM) has many capabilities that are not generally recognised. The application of the technology has often been associated with high value parts made from exotic metal, as the technology becomes more readily adopted and the range of alloy powders increases, this is changing. Let’s take a look at what MIM can do…

MIM provides repeatability for high numbers of parts

Plastic injection moulded parts are everywhere, but did you know that MIM enables metal parts to be mass-produced with the same complexity and repeatability as their plastic contemporaries. That means thin walled features (>0.5mm), complex curvature, text, threads, ribs, bosses and holes are all possible.

Naturally this opens up several design for manufacture possibilities including combining an assembly of numerous simpler individual parts into one integrated metal part. An added bonus for anyone designing a part for MIM is that it often needs a lower angle of draft applied than a plastic part, and in some cases none at all!

Almost any standard material that can be turned into a fine powder (0.4-45 micron range) can be used as the basis for a MIM feedstock. Commonly available low alloy and stainless steels can be processed, as well as more exotic materials such as Cobalt Chrome and Zirconium Oxide. This enables engineers to select a part material based on its performance characteristics and not it’s ability to be machined or cast.

Small, lightweight parts are ideal for MIM

The most suitable parts for MIM are small (<100mm) and low weight (<100g) and in production quantities above 1000 parts; making the process competitive with precision casting, die casting and machining. Part tolerances are similar to those found in plastic injection moulding and superior to die-casting.

There are 3 distinct stages to the process

Injection – The metal powder is combined with a suitable plastic binder and then injected into a mould tool. Both the tool and the injection moulding machine used are very similar to those used for plastic injection moulding. After moulding, parts are placed on ceramic trays for inspection. Any scrap at this stage can be fed straight back into the process with negligible material wastage.

Debinding – The plastic binder is removed using a matched solvent. These can be liquids, vaporised acids or water and are chosen based on the metal being processed and the end use application of the part. Thousands of parts are treated at one time reducing the individual cycle time for each part.

Sintering – The particles of the metal part are welded together by heating close to their melting point in a furnace. The process is carried out in a vacuum or protective atmosphere and achieves part densities of >98%. If required, a finishing process can then be applied such as polishing or plating, but in most cases parts are supplied as moulded with a surface finish of Ra1.6.

If you have a requirement that you think would suit MIM or would like more information, then get in touch today.