Metal Injection Molding

How common is metal injection molding on average consumer products these days? I realize that it is more expensive than plastic injection molding tools. I guess I’m just wondering HOW MUCH more?

I want to suggest using real metal for a part on one of our products, rather than the crappy fake metal, finished plastics. I just need a little more information on it. Anyone used it before? Any suggestions on where to go to get good information? Thanks.

The technical term for “metal injection molding” is die casting.

See:

http://www.themetalcasting.com/pressure-die-casting.html

MIM is a different process from die casting.

We’ve used it on a product recently to create several complex molded stainless steel parts that had certain undercuts and features that would’ve been difficult to achieve using other processes. The parts were fairly expensive, but so was the product so it worked out OK. Went with a wire brushed finish which came out very nice in the end.

we had a guy from Precision Made Products present to us on their capabilities about 2 years ago, and I took diligent notes. It touches on the kinds of parts that are best to be MIM’d. It also might bring up some questions you hadn’t thought of

Braindump commenecing…

  • Metal Injection Molding (MIM) has many of the same constraints as Injection Molding. The primary difference is instead of a single polymer, a combination of metal and polymer (binder) particles are used.

  • The metal powder is mixed with a binder and formed in the mold. At this point the part is called “green” and can still be reground.

  • The binder is then removed through a combination of water (~50% of binder is water soluble) and heat. Once all of the binder is removed, the only thing left holding the metal particles together are the Van Der Waal forces. At this point the part is called “brown”

  • The brown part is then is then sintered, which shrinks it down to size

Design Guidelines

  • The process is best used for complex geometry. If the geometry is simple, you are probably better off die casting.

  • Tolerances are 0.3% of dimension or 0.02mm, whichever is lower.

  • Relative Density is 99.7%

  • Surface Roughness is 1 micrometer Rt and 0.2 micrometer Ra.

  • Part weight from 0.1g to 1.5kg

  • Since the internal stresses caused by MIM are less than those caused by machining, heat treatment will cause significantly less warpage.

  • The density of MIM is high enough that the porosity does not present sterilization issues in a medical setting. It is autoclavable

  • Mechanical Properties are similar to wrought material

  • There needs to be a flat surface support or “sacrificial leg”. Once broken, leaves “gate marks” on part.


    Materials

  • Stainless Steels: 304L,316L,347,17-4PH,410L,420,430L and 440C

  • Carbon and Low Alloyed Steel: FeNi2 and FeNi8

  • Super Alloys: Invar and Lovar

  • Cobalt-based Low Alloy Steels, Inconel 625, Inconel 718, hastalloy X, F75, Stellite

  • Tungsten Alloy: W-Cu

  • Oxygen-free Copper

  • Titanium 6,4 and Titanium CP


    Gotta love evernote.

That is some good info, thanks guys.

So from what I understand, the tooling costs about as much as plastic injection molding, but it is the high cost of the specialized material that gives the part high cost, right? If so, I think I might be able to swing it since the parts are quite small.

Very good info above.

Didn’t have enough visibility to our tooling cost, but I know for the stainless steel parts we used I believe the most expensive part was about $8 which included post-process brushing/finishing and that part was about 1"x1"x.125" in side. I don’t recall which grade of stainless it was. That was at probably around 25,000 pieces/year. I actually believe MIM came in cheaper than what it would have taken to process the same stainless part in another fashion (casting/machining/finishing).

MIM is a different process from die casting.

Thanks for the clarification.

MIM is a process that I like and think that is very promising. It is not a competitor of Plastic Injection molding though, as it is used when rather high performance metal parts are required. Gear is a common application. Good details, and very small parts are possible, like small medical implants. There are various methods, mostly based on the final density, achieved. Usually density does not effect strength too much (it effects but not much to wory), but it effects toughness greatly. A very small decrease in density means large toughness losses. So advanced methods like Hot isostatic pressing, or forging of the powder compact can be used. However it is no longer called MIM, but they are all powder metallurgy techniques. Advanced ones are used in military, aerospace etc.

Related in technology, not industrial, but perhaps useful to some ID’r, is PMC, precious metal clay. A concept that surprised me when first became aware of it a few years ago in Japan. Cool stuff.

“That`s hot!”

I played with PMC some 4-5 years ago. It is very expensive, as it is made of silver or gold. Can be useful for one-off jewelry etc. It is even possible to mix it with water and paint on something. I saw a silver leaf made like that.

“That`s hot!”

did you really say that? :wink:

8 - 30% shrinkage! :open_mouth:

The shrinkage for MPM parts is kind of crazy, luckily it’s very accurate to calculate (if you’re an engineer at least). :smiley:

It’s fun seeing the pre-baked parts. It’s like a shrinky-dink! :laughing:

Hello, at SRAM we use MIM for some of our internal ratchets for our RED shifter. The part carries a great level of detail and precision. It is roughly the diameter of a quarter and around 10mm thick. Each part costs around $3 USD.

The part carries a great level of detail and precision.

Without giving away the store, can you post an image of it?

Alright, it is actually more the diameter of a penny. Here is a quick shot for you.

I have some questions. What finish to do you want? Annodized, metallic, shiny silver, brushed?

Is this part going to be under loads?

What is the alternative? IM plastic?

Don’t pass over IMD too quickly. I recently saw a mixer at the store that had a SS IMD plastic enclosure. I had to look at it for 2 minutes in my hands before I was convinced it was plastic (still not 100% sure). Before I picked it up, I thought it was SS, but it wasn’t cold to the touch and it was too light.