Metal Injection Molding vs. Die Casting—What’s the Difference
Two practical manufacturing methods with diverse abilities
Metal injection molding and die casting are both prominent ways of creating high-quality metal parts. Despite their similar purpose, they each have their own pros and cons and work better in different situations. How do they work, when would you use them, and are there any alternatives? Let’s see.
What is Metal Injection Molding?
Metal injection molding (MIM) works on a principle similar to plastic injection molding and was invented by Raymond Welch in the 1970s. One of the biggest differences between the two is that MIM uses metal powder that’s mixed with a plastic binder which is later burned out and removed, whereas in plastic injection molding, you can add certain additives like glass or ceramic fibers into the mix, but they stay in to improve the part’s qualities.
In MIM, the metal and binder mix is fed into a barrel, inside which a screw pushes it through a narrowing space and, in turn, compresses it as it moves toward the mold. This compression actually generates heat, and so does the barrel itself, which ultimately melts the plastic binder that helps carry the metal powder into the mold. When the melting is done, the screw will move back and then push the material into a two-part mold that is clamped tightly. When the molded piece has cooled down (it’s known as the green part), it’s ejected.
The next step is to remove the binder, and this will leave some gaps that can be filled by sintering. Then, the green part is exposed to certain solvents or a catalyst along with high heat which will remove the binder. The part that’s left is now referred to as the brown part. This brown part is then placed into a furnace where the metal particles will fuse together—the sintering process. This will make the part strong and dense. During this time, though, the part can shrink by around 15–30%, depending on the material. After the sintering, the part has reached its final mechanical properties. This is an example of parts created using MIM:
MIM is a great way of making parts that are small and rather complex in terms of features. It also doesn’t require a molten metal feedstock like other methods do. That’s because it only really uses high temperatures during the sintering process. That’s also good because you can use materials with really high melting points without having to worry about processing and handling them in their molten form. A few potential drawbacks with MIM include the fact that these machines and their tools tend to be expensive. The molds don’t last too long because of the abrasive nature of the metal powder, and the parts need quite a bit of post-processing, which also bumps up the cost. Also, as mentioned, the parts shrink quite a lot. So you’ll need to take this into account beforehand to make sure parts meet your size requirements.
What is Die Casting?
It sounds quite similar to MIM, in that die casting is a way of manufacturing metal parts by injecting molten metal into a mold. It dates all the way back to 1838 when it was first invented and later patented in 1849. This method was first used for lead and tin, and in 1914, aluminum and zinc were introduced. Today, it’s also fine with magnesium, copper, and silicon, but it’s limited to non-ferrous metals. Having said that, if you really want to, you can try die-casting ferrous metals, but it’s not very common.
With this technique, the molten metal can either be injected under pressure or simply flow in by gravity feed. When the part has finally cooled down—which can take up to a minute, subject to part size and wall thickness—it can be ejected from the mold. You can remove any excess material from the gates, runners, and parting line flash manually or using a press die.
Die casting molds last a long time; in some instances, just one can make up to a million parts (compared to MIM molds which make a couple hundred thousand if you’re lucky). Die-cast parts also don’t shrink. This type of casting does have some potential downsides, though. For example, it’s best used with non-ferrous metals. Ferrous metals tend to have a really high melting point, which can ultimately make the molds deteriorate much faster. Also, if you’re injecting molten metal at high pressures and temperatures, it’s very easy to trap gasses within the material. This can make the part porous and reduce its mechanical strength, whereas MIM parts have the chance to get rid of any entrapped gases during sintering.
Kevin Choate, a Senior Solutions Engineer here at Xometry, says "Metal Injection Molding (MIM) is a process developed to mold high melting temp materials, like steel. There are other factors for MIM which are important when looking at part specific or project specific. High melt temperature metals are not suited for die-casting -- with die casting you melt the metal and use pressure to inject or force the molten material into the cavity, or tool, similar to injection molding. You would use MIM over die-casting if you need stainless steel, or other steels/materials that have a very high melt temp. Die-casting is pretty much just for aluminum, and zinc."
| Attribute | Metal Injection Molding | Die Casting |
|---|---|---|
Attribute Wall thickness | Metal Injection Molding 0.04” to 0.12” | Die Casting 0.04” to 0.2” |
Attribute Multi-step process | Metal Injection Molding Yes | Die Casting No |
Attribute Materials | Metal Injection Molding Anything that can turn into a powder, including tungsten, stainless steel, tool steel, cemented carbides, nickel superalloys, and precious metals | Die Casting Aluminum, zinc, copper, magnesium, lead, pewter, tin |
Attribute Volume | Metal Injection Molding Good for high-volume production of intricate parts | Die Casting Suitable for producing a high volume of larger, simple parts |
Metal Injection Molding vs. Die Casting Attributes
Frequently Asked Questions on MIM and Die Casting
Which of these is faster?
When it comes to the actual casting process, MIM wins. But, it also requires post-molding processing which can ultimately make it slower than die casting overall.
Are there any mutual alternatives to these casting types?
The manufacturing technique that can be considered an alternative to both of these is SLM, which stands for selective laser melting. It’s a form of additive manufacturing (3D printing) that can create complex parts made of metal. It works by using a laser to melt a metal powder in select areas. When each layer is complete, it gets started on the next one until the part is finished.
What’s the difference between MIM and binder jetting?
Binder jetting is a type of 3D printing, and it works by binding metal powder together without the need for a mold. It does everything right there on the print bed. When the parts are done, they can be post-processed and sintered, much like MIM parts. Unlike MIM, though, binder jetting is only really good for low-volume production runs.
What’s the difference between die casting and sand casting?
Sand casting is one of the oldest ways of processing metal parts and is still prominent today. It works using a special kind of sand, which is packed around a core that’s shaped like the final part. Holes are made in the mold for filling and letting air escape. The metal is then cast into the mold, and once it’s cooled down, the mold is broken open to get the part out. Any sprues, feeders, and flash need to be ground off after.
How Xometry Can Help
If you have any questions about molding or anything else manufacturing-related, a Xometry representative would be happy to help you. We also offer an abundance of other related services including CNC machining, 3D printing, and laser cutting. You can get your project off the ground today by requesting a free, no-obligation quote right from our website.
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