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View Full Version : MIM vs Investment Casting


SIGSHR
April 19, 2012, 11:37 PM
With all the controversy involving MIM and the widespread belief that it produces inferior parts, I wonder why many manufacturers don't stick to investment casting as pioneered by Ruger?

James K
April 19, 2012, 11:51 PM
The main reason is that MIM parts (which are not inferior) are good to go as they come out of the mould. Investment castings still have to be machined, hardened and finished. But Ruger still makes many of its small parts by machining from the solid, so I wouldn't be surprised to see MIM parts in Rugers before long.

Investment casting, however, can be used for parts that undergo major stress, like receivers and bolts. So far, MIM has not been used for such parts.

Jim

mete
April 20, 2012, 12:49 AM
MIM parts 'good to go' as they come from the mold ???:confused:
Metal powder is mixed with a polymer [wax] and that is injection molded .Then it is heated to drive off the polymer then heated [sintered] to bond the powder. It may be then heat treated , carburized machined , etc. Lots of variables especially shrinkage .
Ruger has an investment casting company Pine Tree Castings that makes the parts.
In any case where MIM can be used to copy existing parts , efficient and economical investment casting is done by designing things from scratch.

Good engineering involves engineering of the whole process not just part of it.

TMD
April 20, 2012, 01:00 AM
The main reason is that MIM parts (which are not inferior) are good to go as they come out of the mould. Investment castings still have to be machined, hardened and finished. But Ruger still makes many of its small parts by machining from the solid, so I wouldn't be surprised to see MIM parts in Rugers before long.

Rugers been using MIM parts for the past year or so. Asa for MIM being inferior its only if they are formed incorrectly. MIM parts out of the mold require less machining and have closer tolerances than cast. As for the complaints about MIM, they mostly come from keyboard commandos. I would bet that 99% of gun owners don't even know what MIM is.

foghorn leghorn
April 20, 2012, 05:27 AM
like the computer saying, [garbage in garbage out]. I had a 1911 hammer that looked like it was mushed together from leftovers. The Half cock notch crumbled like a lead sinker.
I used to sell carbide inserts, they are sintered from a powder just like MIM parts. When an insert has been out in the weather and chilled, like in my trunk, it can shatter like a chicklet if you try to run cold. I wonder if that can happen with a MIM part?
https://encrypted-tbn1.google.com/images?q=tbn:ANd9GcQvf5S7cTA1jnujynNdSr13T1v3li_z3IdZyWumhc0R0fBo4ObL

James K
April 21, 2012, 07:53 PM
If the shrinkage of MIM is calculated and taken into account, it doesn't matter. As for machining, I have seen a fair number of MIM parts, and read about the process and the major advantage is that they don't require machining and show no sign of it.

The most intricate parts can be made by MIM without machining, an example being the S&W trigger. Investment casting can produce a solid part (e.g., a rifle bolt), but finish machining is needed to hollow it out, machine the threads, cut the bolt face, and so on. It is cheaper than forging, and less metal needs to be removed, but its main advantage is that investment casting can be done about anywhere (say, a shopping center factory), where forging requires large drop hammers that have to be solidly grounded and would shake a normal building apart.

Jim

mapsjanhere
April 24, 2012, 07:32 AM
I think part of the "investment casting makes better parts" stories is that, as cast pieces need rework, there's an inherent quality control in cast pieces. Any obvious defect will likely be caught during post machining, while in MIM the parts drop into the bin and no one takes a second look at them.

CowTowner
April 24, 2012, 09:01 AM
But then, we have the D&D Bren Ten. Awesome guns but the investment castings and final machining left a lot to be desired.
There are always exceptions to the "rules".

James K
April 24, 2012, 05:04 PM
It is not something Ruger brags about, but they do "fix" castings that have air holes or flaws, using welding as necessary. Of course they choose which parts they repair so there are no safety concerns, and the customer never knows the difference.

As to casting giving a better chance at quality control, the forged and machined parts used on the older guns "dropped into bins" as well, and were only spot checked before being hardened and sent to the assembly area. In factory production, it has been almost two centuries since machinists in greasy bib overalls made parts by machining steel stock a thousandth of an inch at a time and measuring the result with calipers.

Jim

mete
April 24, 2012, 05:09 PM
Most of the Bren Ten was made of farmed out parts not in house manufacture. That creates a big quality problem. The gun was mostly hype with promises of many guns which they couldn't fill even a fraction of ! It was said that only those on "Miami Vice" had the necessary magazines !! :rolleyes:

James K
April 24, 2012, 05:20 PM
So fictional cops shot fictional crooks using fictional guns loaded with fictional magazines.

Jim

ClydeFrog
April 26, 2012, 07:13 PM
A detailed article in Soldier of Fortune in the mid-1980s shed a lot of insight into the weapons & SFX of NBC's hit cop series: Miami Vice.
Det Sgt James "Sonny" Crockett used a 10mm Bren 10 from D&D in the first few episodes but when the company had problems, the show producers moved to the S&W 645 .45acp.
In the TV show pilot(a series first episode), Crockett used a SIG P220 .45acp(imported by Browning in the 1970s-1980s).
The Bren 10 was considered new & experimental by many US police agencies in the early 1980s.
For more details see; www.imfdb.org .

ClydeFrog

Jammer Six
April 26, 2012, 10:43 PM
The only thing I remember about that is that Sonny's weapon (a 1911) was a plot point during some multi-episode fiasco that had him kidnapped.

He was identified by his stance ("military style") and his weapon ("a Colt .45"), neither of which were accurate.

I'd hate to argue with such an august opponent as Soldier of Fortune Magazine, of course... (Are they still around? Really?)

BruceM
April 27, 2012, 02:03 AM
Most of the Bren Ten was made of farmed out parts not in house manufacture. That creates a big quality problem. The gun was mostly hype with promises of many guns which they couldn't fill even a fraction of ! It was said that only those on "Miami Vice" had the necessary magazines !

The statement made regarding the blank firing Bren Tens used on Miami Vice isn't close to true but rather "common knowledge and conventional wisdom". Actually, Dornaus and Dixon had no forging, casting or molding facilities. This, however, is not anywhere unique within the industry. There are very few Smith & Wessons, Colts or Rugers and even they outsource some components.

I guess saying that the gun was mostly "hype" can mean many things to many people. That said, later guns which were assembled correctly were excellent. Quality on early guns, for a variety of reasons, was all over the place. While everything was outsourced, almost all machining, assembly and fitting was done in house. And, keep in mind, that all outsourced components except the original dual caliber magazines were made in the USA. The magazines were from MEC-GAR in Italy.

What killed the original Bren Ten was not a lack of magazines (another piece of common knowledge). It was the fact that the company was grossly under-capitalized from the get go. This gun was one of the first that made extensive use of small parts manufactured using either MIM or investment casting methods and these did in fact work well. It was the slides and original magazines which caused the vast majority of the headaches.

The Bren 10 was considered new & experimental by many US police agencies in the early 1980s.

The gun was new & experimental but I don't think the gun was formally researched by any LE agencies or military organizations.

;)

Bruce

BruceM
April 27, 2012, 02:11 AM
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