Forged, Cast & MIM. What's better and why

[DMW1116]

Once upon a time forged was generally better but that was a time when we had less control over impurities, specifically sulfur and phosphorus in steels. Hot gorging doesn’t strengthen materials by work hardening, though proper cooling from the forging temperatures can, depending on the alloy. Cold forging provides considerable strength increases.

MIM is a sintering process but it’s more than that. For an idea of what can be done, look at all the high strength high wear powder metals used in dies and cutting tools.

Casting is nearly as old as forging and probably developed at the same time. It can be as good as you want. Highly stressed parts are cast for a number of applications.

Be careful when looking at fracture surfaces and making judgments on what happened. Without some history in the part and/or a lot of magnification, the appearance can be very deceiving and won’t tell you much.

 

[halfmoonclip]

Good answers here; much of the engineering is above my pay grade.
There's also a bragging rights factor.
Moon

 

[TinNePa]

I had the slide stop break on my older Kahr K9

View attachment 1203836

Pretty sure it was just cast. Really grainy.

View attachment 1203837

The seams were pronounced.
View attachment 1203838

The replacement looks like MIM. With the number cast into it. It’s just a generally smoother finish.

View attachment 1203840

So, apparently Kahr decided MIM was better for that part than casting.

As an aside, they have another slide stop that’s two piece. They are not interchangeable.

I bought a used PM9 that someone traded in. It had the same broken slide stop in the box. The one in the gun looks just like your replacement.

 

[cfullgraf]

Looking at some of Driftwood Johnson's S&W sideplate off pictures, I note that MIM parts have been redesigned with the minimum of holes and slots, a lot of parts interlock rather than being pinned together. Seems like a mold with internal shapes to form holes would be a lot more complicated and expensive.

I was surprised to read a post that they are making MIM barrels for the Chief's Special, even though it is a small part for a low pressure round.



Hey, I live just across the Tennessee River from Colbert County and agree they could use some refinement.

Our refinery was down river from New Orleans. It is a superfund sight now.

Sometimes I have trouble spelling cobalt

 

[Pat Riot]

The only thing that I know about MIM parts is when S&W started using them they were terrible. They were inferior, but then Colt started making DA revolvers with MIM parts and all was right with the world.

 

[CraigC]

Remember when S&W took a jab at Rugers casting?

View attachment 1203881

The funny thing about those ads is that they birthed a lot of myths, because they're misleading at best, at worst utter BS. It implies that Ruger had to add a ton of material only to match S&W's strength and that is patently false. S&W's frames aren't all that strong, as they're left soft to be slapped back into shape with a lead babbitt hammer. Ruger's investment cast frames only require a very slight increase in bulk to make up the difference. The end result is that the 686 and GP100 are the same size and weight. To get an idea of how much material has to be added, look at the top straps of the Ruger Vaquero or New Vaquero and the forged Colt SAA frame. Nearly identical, yet the Ruger Vaquero has been built in .500Linebaugh and the New Vaquero has been built in .480 Ruger. The difference has more to do with Ruger's lockwork design than the manufacturing methods used to make their various parts.

In fact it's the Ruger DA design that makes them demonstrably stronger. Not so much an issue with mid-frame .357's but with the big bores, it's absolutely an issue. The S&W sideplate design allows too much flex and that's what leads to N-frames and X-frames shooting loose in just a few thousand rounds. The strength of Ruger's design allowed their .44 to accommodate the .454 Casull, which proofs over 90,000psi with only a change in alloy.

The fact remains that the strongest revolvers on the market have frames cast by Ruger. Not only does the Freedom Arms 83 live it's life at 65,000psi but it's less bulky than a Ruger.

 

[Jim Watson]

Oh, no, you're not telling me a FA is Ruger cast iron.
I don't care what the starting point is, they are so "crisply" machined that I find them uncomfortable to handle. I looked at the 97 as a deluxe CAS but it would have taken a good dehorning for fast handling.

 

[halfmoonclip]

I had the slide stop break on my older Kahr K9

View attachment 1203836

Pretty sure it was just cast. Really grainy.

View attachment 1203837

The seams were pronounced.
View attachment 1203838

The replacement looks like MIM. With the number cast into it. It’s just a generally smoother finish.

View attachment 1203840

So, apparently Kahr decided MIM was better for that part than casting.

As an aside, they have another slide stop that’s two piece. They are not interchangeable.

IIRC, there was a more expensive, up market version of the Kahr .380, and a less costly, simpler one. One of the differences was the quality of the slide stop on the better gun.
Moon

 

[P5 Guy]

• Forging produces predictable and uniform grain structure and flow characteristics which Increase Directional Strength.
• Forging eliminates internal voids/gas pockets that weaken metal parts, providing superior chemical uniformity and Increased Structural Strength.
• Forging ensures proper orientation of grain flow, thus maximizing fatigue resistance and Increasing Impact Strength.

Steel is more difficult to cast than iron. It has a higher melting point and greater shrinkage rate, which requires consideration during mold design. Risers should be given more capacity to draw from as the metal cools and shrinks. Attention should be paid to the thickness of mold cavities, as thinner areas will cool quicker than thicker areas, which can create internal stress points that can lead to fracture.

Molten steel is also less fluid than molten iron, making it more difficult to pour and fill intricate gaps in a mold cavity. Molten steel is also more likely to react with internal mold surfaces, making for more unpredictable results.
Cast parts often require machining to achieve accurate tolerances and desired surface finishes. Carbon steel is the easiest type of steel to machine. High-carbon steel can be more time consuming to cut or grind and will wear tools faster. Low-carbon steel can get gummy, making it difficult to work with.

Generally, the presence of alloys used to increase mechanical performance often make machining more difficult.

The behavior of MIM feedstock is governed by rheology, the study of sludges, suspensions, and other non-Newtonian fluids.

Due to current equipment limitations,[as of?] products must be molded using quantities of 100 grams or less per "shot" into the mold. This shot can be distributed into multiple cavities, making MIM cost-effective for small, intricate, high-volume products, which would otherwise be expensive to produce. MIM feedstock can be composed of a plethora of metals, but most common are stainless steels, widely used in powder metallurgy. After the initial molding, the feedstock binder is removed, and the metal particles are diffusion bonded and densified to achieve the desired strength properties. The latter operation typically shrinks the product by 15% in each dimension.

They all have certain limitation and advantages.

 

[Y-T71]

• Forging produces predictable and uniform grain structure and flow characteristics which Increase Directional Strength.
• Forging eliminates internal voids/gas pockets that weaken metal parts, providing superior chemical uniformity and Increased Structural Strength.
• Forging ensures proper orientation of grain flow, thus maximizing fatigue resistance and Increasing Impact Strength.

Steel is more difficult to cast than iron. It has a higher melting point and greater shrinkage rate, which requires consideration during mold design. Risers should be given more capacity to draw from as the metal cools and shrinks. Attention should be paid to the thickness of mold cavities, as thinner areas will cool quicker than thicker areas, which can create internal stress points that can lead to fracture.

Molten steel is also less fluid than molten iron, making it more difficult to pour and fill intricate gaps in a mold cavity. Molten steel is also more likely to react with internal mold surfaces, making for more unpredictable results.
Cast parts often require machining to achieve accurate tolerances and desired surface finishes. Carbon steel is the easiest type of steel to machine. High-carbon steel can be more time consuming to cut or grind and will wear tools faster. Low-carbon steel can get gummy, making it difficult to work with.

Generally, the presence of alloys used to increase mechanical performance often make machining more difficult.

The behavior of MIM feedstock is governed by rheology, the study of sludges, suspensions, and other non-Newtonian fluids.

Due to current equipment limitations,[as of?] products must be molded using quantities of 100 grams or less per "shot" into the mold. This shot can be distributed into multiple cavities, making MIM cost-effective for small, intricate, high-volume products, which would otherwise be expensive to produce. MIM feedstock can be composed of a plethora of metals, but most common are stainless steels, widely used in powder metallurgy. After the initial molding, the feedstock binder is removed, and the metal particles are diffusion bonded and densified to achieve the desired strength properties. The latter operation typically shrinks the product by 15% in each dimension.

They all have certain limitation and advantages.

@P5 Guy

Thanks, very interesting.

Do you have a background in this field?

 

[P5 Guy]

@P5 Guy

Thanks, very interesting.

Do you have a background in this field?

Yes, I'm a retired factory mechanic.

 

[Jim Watson]

Due to current equipment limitations, products must be molded using quantities of 100 grams or less per "shot" into the mold.

I recently read that the barrel of a Smith & Wesson Model 36 is being made out of MIM. Seems like a big part for the process.