[TankerHC]

Can someone tell me, in laymans terms, what is bad about MIM in guns? Or not bad? What exactly is MIM? I googled it and checked Wiki with no satisfactory answers.

Oh, and what is meant by "Roll Marked"?

 

[Xd357]

Mim is metal injected molding. The roll mark is like on the slide of a 1911.

 

[bubbat]

"Metal Injection Molding or MIM, also called Powder Injection Molding or PIM, is a net-shape process for producing solid metal parts that combines the design freedom of plastic injection molding with material properties near that of wrought metals. With its inherent design flexibility, MIM is capable of producing an almost limitless array of highly complex geometries in many different alloys ranging from stainless steels, alloy steels, and soft magnetic materials, controlled expansion materials (low CTE), and custom alloys. Design and economic limitations of traditional metalworking technologies, such as machining and casting, can be readily overcome by MIM. "

Here a couple of sites that might explain it better.
http://www.kinetics.com/

http://www.gknsintermetals.com/technology/mim.htm

The Roll mark is the name markings on the slide. I assume it's called the because in the manufactoring process it rolled on somehow.

 

[jakeg823]

Some people say that mim is weaker.....which is why they'll spend $1000+ on a Kimber and then go spend another $500 to get rid of all the mim parts by replacing them with Ed brown parts....instead of just buying a $1500 Ed brown to begin with.

Now the mim thumb safety on my Kimber did snap once....not sure how but I don't think it's cuz it was mim so much as it was just gonna snap. Got it replaced(with a Kimber safety) and havent had any problems since

 

[DBChaffin]

Can someone tell me, in laymans terms, what is bad about MIM in guns? Or not bad? What exactly is MIM? I googled it and checked Wiki with no satisfactory answers.

Oh, and what is meant by "Roll Marked"?

The benefit, if done correctly, is a part that is nearly as dense as one made from forged steel yet much cheaper to make. However, if done incorrectly, the process can leave small voids in the metal creating a weak part that can fail.

Many manufacturers use MIM in many small parts to save money. While some parts are perfectly fine made with this process, others are not. I would not want an MIM extractor in a 1911 for example, because it has to flex in order to do its job. They don't last and won't hold tension in my experience. At one time or another, Para, Kimber, RIA, Taurus, and I believe Springfield have all used them. I don't know if any or all of them do now or not. If/when an extraction problem occurs with one, re-tensioning is usually a waste of time as it won't last long at all afterwards. My preference is to chunk them and go with a quality barstock or forged part.

Another area is the hammer/sear. Good MIM parts are usually hard and have a decent surface finish, so they work pretty well in stock configuration but still not as long lasting as better parts. If a trigger job is attempted though, often the imperfections of the injection are uncovered and the trigger jobs don't last any time. Many gunsmiths won't do trigger jobs on guns with MIM hammers and sears without replacing the parts. Again, my preference is better quality tool steel or barstock parts.

A firing pin stop in a 1911 is another part that I wouldn't want to be MIM. It is continually pounded as it pushes the hammer back under recoil. If there are flaws internally, it is more likely to crack or break. There are of course others but these are the first ones that came to mind.

As far as what it is, this was taken from another site:

"MIM: Stands for Metal Injection Molded. This is a relatively new process of making small parts for less cost than machined, while making them denser than cast. There are four primary steps to the metal injection molding process (per www.phillipsplastics.com ):

1. Feedstock Formulation – very fine metal powders are mixed with polymeric binders.
2. Molding – parts are molded in specially-equipped injection molding machines. These as-molded components are known as "green" parts.
3. Debinding – 90% of the binder material is removed from the green part. These parts are then referred to as "brown" parts.
4. Sintering – brown parts are sintered using controlled temperature and atmosphere profiles for final densities between 96-99% of theoretical.

In other words, the end product results in no more than a 1% variation in its final size."

"Roll Marking" is just that, marking a slide or other part by rolling under pressure. Here's a link to some machines that do it: http://www.pannier.com/products/Indenting_Products/Roll__Rotary_Marking/Roll_Marking_Machines.html

Generally it is a fine method for marking a bunch of parts identically, but sometimes there are issues and the mark is lighter at one end or the other or off center.

 

[DBChaffin]

Since Ed Brown and thumb safeties were mentioned above, it is interesting to note Ed Brown's take on MIM parts:

Do Ed Brown handguns have any MIM (metal injection molded) parts?

No, we use no MIM parts in Ed Brown firearms. While the current thinking is that MIM parts are "good enough" for firearm applications, this thinking doesn't fit with our philosophy at all. All Ed Brown parts are made from either forgings, bar stock steel, or quality investment castings.

Although I like and have had a mostly good expereience with Ed Brown parts, one thing to note is the "quality investment castings". An Ed Brown beavertail safety is cast, and I have never seen an issue with one and can't imagine there being an issue with one.

However, I have had an Ed Brown thumb safety, also cast, break. It was on a competition gun that had a lot of rounds on it. I have witnessed several other cast or MIM thumb safeties break also. Left handed folks tend to break them ambi's more often than righties.

I now run an SV Infinity thumb safety which is machined from billet: http://sviguns.com/1101.php?indx=9 They are very expensive, running from $60 single sided to basically $100 depending on the options (roughly 2 to 3 times the price of cast safeties) but I haven't had one fail yet or seen or heard of one breaking, for that matter. Not saying they can't, but they are a pretty nice part.

The only other fully machined safety I am aware of is also $60 and is only available single sided, but it is really heavy duty and probably should be the toughest safety available: http://egw-guns.com/store/index.php?main_page=product_info&cPath=34_48&products_id=302