investment cast vs forged


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whalerman
August 9, 2011, 08:05 PM
Alright. Teach me what the difference between investment cast and forged is. I've read postings but people gloss over the process itself. What should I look for? What are the advantages? Is it different for revolvers and semi's? Please talk me through it. Thanks.

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The Lone Haranguer
August 9, 2011, 08:23 PM
Very briefly put, casting is pouring molten metal into a mold the shape of the part, while forging consists of taking a red hot piece of metal and beating it into shape with a die the same shape as the part. If you've ever watched a blacksmith at work, he is doing a crude form of forging. For the actual mechanics of the processes, I suggest looking up their respective Wikipedia entries and going from there. Both have advantages and disadvantages, which I predict will generate considerable debate. :D

Shadow 7D
August 9, 2011, 08:26 PM
http://en.wikipedia.org/wiki/Forging

http://en.wikipedia.org/wiki/Investment_casting

They are ways of making forms out of metal, and they differ, and can do different things, strangely enough, they can both be used to make AR's, so... which it better, thats up to you.

dfariswheel
August 9, 2011, 08:35 PM
Investment casting is also known as "lost wax casting".
It was first used in modern times in the jewelery industry.
Ruger pioneered high grade investment casting in the gun industry.

In short, a hard wax exact copy of the item is made.
Wax "spues" are attached to the model to allow the molten metal to drive out air bubbles and properly fill the mold.
In production work, a number of these models with sprues are attached to a "tree" to form a number of parts.

The models are coated with a coating of very fine grained ceramic.
This is then coated with a much heavier coating of a coarser ceramic.

The tree is put into a furnace under very high heat.
The wax melts and runs out or vaporizes.
While the mold is still extremely hot, molten metal is injected (invested) into the mold.
The mold is allowed to cool, then the ceramic is broken away.
The individual molds are cut off the tree and the sprues are cut off.
Molds that failed to fill out properly are simply re-melted and used again.
What's left are perfect replicas of the wax models that require only some final finishing and threading.

In forging, a lump of metal is heated to a red heat.
The red hot lump is put into a drop forge. This is a giant powered hammer device that beats the red hot lump into a rough mold.
What comes out of the rough mold is a part that looks like a vaguely gun shaped part, sort of like a gun frame made by a child from modeling clay.
If you ever watch TV shows about the 1930's or WWII you'll often see men forging red hot machine and gun parts in forges.
Once the forging cools, metal is machined away to make a finished gun part.

Casting and forging are both strong ways to make parts, each has advantages and disadvantages.
The advantage of investment casting is that it's fast, parts are ready to use with minimal machine work and hardening, and bad parts can be re-melted without loosing a lot of machine time.
The disadvantage is that usually, the part has to be a little thicker to be as strong as a forged part, and the casting is more porous.

The advantage of forging is that the same part can be lighter or thinner due to the forging operation compacting the metal and aligning the structure of the metal.
The disadvantage is that considerable machine work time is needed to finish a part, and if anything goes wrong at any stage, the part is a total loss.

Mike1234567
August 9, 2011, 08:46 PM
I'm not a metallurgist but I do know that cast and forged metals have very different properties. Forged is always stronger. Forged metals aren't necessarily beaten into the final shape. More often than not, they're shaped into rods or rectangular cores that are later machined into the final shapes. Casting is faster and easier so, therefore, cheaper.

4v50 Gary
August 9, 2011, 08:54 PM
Forging is stronger because it aligns the molecules, giving it greater strength. It is also less porous than castings.

While not as strong, castings can be strong enough and has the advantage of making more intricate parts cheaper than forging can attain.

I like forging, but will not pass up a Ruger because it is casted. Pine Tree Casting (a separate but Ruger owned operation) is among the best in the business. Back in the early '90s they were casting 1911 slides and frames for other firms. They also cast slides for a major well respected gun American maker.

Other foundries can be good, but it varies. Springfield Inc. used several different foundries to make their M-1A receiver and not all of them are, IMO, good.

whalerman
August 10, 2011, 12:03 AM
I've carefully read the links provided by Shadow and the posts you guys have provided. There is a lot of information here. I'm going to have to reread everything you've provided. Thanks to you all. I hope to learn from this and use the info to help make decisions on future gun purchases. Again, thank you Gentlemen. This is very interesting.

I live in far upstate NY, near the Thousand Islands. We had a big Alcoa aluminum plant in Massena that used the lost wax method to make auto parts and parts for outboard motors. I never understood what that was about until this lesson of yours. I appreciate it.

MachIVshooter
August 10, 2011, 02:58 AM
Dfariswheel summed it up well.

I'll only add that there are three other ways to make gun parts (or car parts, etc)

Metal Injection Molding-This is not far removed from casting, except the molten metal part. Basically, fine powdered metal is mixed with a binding agent and injected into the mold under very high pressure. Weaker than invesment casting, the primary advantage is lower cost of equipment, lower maintenance cost and basically finished parts as they are spit out of the mold.

Powdered metal-Not frequently used in firearms manufacturing, it is very common in automotive, particularly engine parts. Fine powdered metal is put into a high temperature mold where it is then sintered until it all fuses.

Billet-Part is machined from a solid piece of stock. The strength of a billet part simply depends on the stock used and treating process.

Shadow 7D
August 10, 2011, 03:06 AM
Isn't billet kinda a like raw forged, where instead of working it with dies to get the rough shape, it's just cut from a solid stock (rather wasteful, not as strong*)
*depending on the stock, if the stock is raw (unforged- then worked in the forging dies, it will be stronger than billet)

Greg528iT
August 10, 2011, 03:37 PM
Think of it this way. You've seen people break boards with their hands. What they do, is split the wood along the weakest link, the Grain of the wood. If the holder of the wood was to turn the wood so as to turn the grain, it is MUCH tougher to break.

Casting:
When a piece is cast, a similar grain structure forms as the metal cools and solidifies. These grains are in their natural free shape. Air bubbles can stay in weakening the part, but generally a good casting is pretty free of those. The steel / AL / pot metal is at it's most basic strength.

Billet:
When billet material is formed it is also poured or formed thru a mold. Billet stock is furhter worked into general shapes, squares, rectangles, angles etc. This working while the metal is still very hot works out any air bubbles that may be trapped. Also as the material is formed the grain structure is somewhat compressed and made more uniform, but is still linear. When you machine a part out of billet stock you need to be aware of the direction of it's grain structure. Just like trying to drive a nail thru the end of a wood board, you can get splitting, break out etc. If the grain is in the weaker direction, stresses from pulling on it can split it along the grain, ie, breaking a board with your hand.

Forging:
When the metal is forged, the grain structure get's pushed around. You will get grain flowing thru smaller sections. Since these grains now follow the pattern of the item being forged, those grains flow thru and around necked down areas which would normally be a weakend spot. Breaking a forged wooden board is more like breaking a piece of plywood. (actually more like a burl off a tree, but you get the point)

MachIVshooter
August 10, 2011, 04:27 PM
Isn't billet kinda a like raw forged, where instead of working it with dies to get the rough shape, it's just cut from a solid stock (rather wasteful, not as strong*)

Yes.

The advantage to billet is minimal equipment costs to produce high quality, strong parts. All you need is a couple pieces of CNC equipment.

The down side is high production costs in terms of time and waste material. Those costs are usually passed on to the customer.

In my home shop, everything is "billet", because I was able to get into a non-CNC lathe and mill for a minimal cost that was acceptable for what is more hobby than anything.

Billet parts can be just as strong as the stongest forged parts, if they were cut from the same forged stock. Of course, that'll eat tooling quicker.

The strongest race engine parts are made from forged billets or by normal forging. Crankshafts, connecting rods, etc.

Forging (or casting) has a much higher equipment invesment cost, but allows for less wasteful and faster production. The cost of the equipment has to be amortized, though, so it can be difficult for small scale production to justify the costs.

Shear_stress
August 11, 2011, 03:45 PM
Metal Injection Molding-This is not far removed from casting, except the molten metal part. Basically, fine powdered metal is mixed with a binding agent and injected into the mold under very high pressure.

MIM is nearly the same as sintered powder metallurgy, except the powder is initially suspended in a slurry. The "injection molding" step is just a way to get the slurry into the right shape. But there is a very important next step: the sintering that actually fuses the metal together and removes most of the binder. The metal in the final part is not held together by binder but by metal particles sintered together.

Sintered powder metallurgy is exactly how Colt made the lockwork of its Mk III revolvers starting in 1969 and I've never heard anyone complain about them.

silversport
August 11, 2011, 04:47 PM
...that's because they didn't have the internet...:D
Bill

whalerman
August 12, 2011, 08:07 PM
Good Posts. Greg man, thanks on that board breaking analogy.

Jesse Heywood
August 12, 2011, 11:32 PM
A couple of things to clear up.

Strength of casting versus forging. Forgings are not always stronger. Alloy strength, grain flow and production methods all play a part. Also some part shapes lend themselves to casting over forging, where the cast part is stronger due to the shape. The reverse also applies.

Forgings usually have a strength advantage because of the grain flow of the metal. When properly designed, this can be an advantage.But this advantage is usually over-estimated. Also, castings, when properly designed, have grain flow that can add strength to the part.

What it all boils down to is engineering design economics. Precision casting can be made that take a minimum of machining to fit together. Forgings usually require far more machining, which costs more. Having done a considerable amount of design of cast and forged parts in the aircraft industry, I have no problem with cast parts that have been properly engineered. Not all gun parts are created equally. Some are designed to fire tens of thousands of rounds, some only tens or hundreds. Buy what fills your needs and fits your pocketbook.

On the use of the term billet. Advertising departments have fooled many buyers on this. A billet is a hunk of metal. It can be roll-formed, extruded, cast, forged, depending on what the manufacturer specifies when the material is purchased. Saying a part is made from billet aluminum (or whatever) means nothing.

Jim K
August 13, 2011, 12:36 AM
Apparently some confusion on forging. While a blacksmith does forge iron by beating it into shape with a hammer, that is not really how a gun company makes parts.

They make a set of forging dies, each of which has a depression the shape of half the part (say a revolver frame). The dies are mounted in a heavy press so they mate with each other when the press comes down. The end of a bar of steel is heated white hot and held between the dies while the top of the press/hammer with the top die comes down on the bottom die, compressing the steel between the dies. The result is a part of the rough shape of a revolver frame. The process is less precise than casting, and more metal has to be removed, but forging compresses the steel fibers and produces a stronger product than casting, even with the same steel alloy.

It is not hard and fast, but metallurgists I have spoken with say that forged steel is about 1/2 again stronger than cast steel. That is another way of saying that for a given strength, a cast part has to be about 50% thicker than a forged part. That is why Ruger's revolver frames are thicker than those of a forged frame; they are not actually stronger, they have to be thicker to have equal strenth.

Of course, modern steel castings should not be confused with the cheap cast iron of olden days. And old designs, like the Model 1911, had far more strength than needed, so major parts can be cast and still have more than adequate strength. Old time designers, like Browning, did not have the analytic tools available today; they made guns based on "gut feeling" as to the amount of metal needed, and always erred on the side of caution.

We also need to remember that a gun needs more than barely adequate stength. Not only must it handle at least some degree of overload, but it must have durability. And it also must have weight (mass). A slide for a .45 auto pistol could be made that would weigh only a few ounces, but it would not provide the mass needed to keep the pressure in check, and would probably not be very durable. Also, if a .45 pistol were made as light as possible, the recoil would be brutal; endurable maybe for a few shots (like those .410 derringers) but certainly not a gun anyone would care to shoot very much.

Jim

SSN Vet
August 13, 2011, 10:58 PM
Here's one little anecdote about casting....

I worked two summers machining after market oil pumps out of cast steel.

Each line would crank out about 900 complete assemblies per shift.

The last station before the assembly bench was the blow off booth, where the cutting fluid and any residual metal shavings were blown off with HP air and the completed pump body was inspected under a bright light.

When I worked the blow off booth, I typically set aside four or five pumps a shift due to pitting or bubbles in the casting.

These were pretty rough castings, however. Likely cast in sand. Definitely not lost wax process, which can produce beautiful parts.

That was a tough job. 105 deg. In the factory on hot August nights. Completely drenched in sweat after the first 15 min. The foremen were very strict and did NOT like the summer help. I made $7.50/hr with the shift premium, worked my tail off, and got a skin infection..... but was VERY happy to have a job!

MachIVshooter
August 14, 2011, 02:50 AM
These were pretty rough castings, however. Likely cast in sand. Definitely not lost wax process, which can produce beautiful parts.

Yup, the process is just as important as the alloy for casting strong parts. Lots can go wrong, and it has to be tightly controlled.

Forging, OTOH, is pretty hard to screw up. Either the piece of metal is smashed, or it's not. As long as you start with quality stock, you'll finish with a quality part.

Then there's heat treating/hardening. But that's a whole different can-o-worms...........

antiquus
August 14, 2011, 03:48 AM
Making comments like 'forged steel is about 1/2 again stronger than cast steel' is misleading to people trying to understand this. It's simply not true.

A poorly designed and made part of any type will never hold up as well as a correctly made part of any type.

Some of the strongest parts made are powdered metal. Knives made of CPM alloys are superb, CPM means Carpenter Powdered Metal. Castings made under pressure can and do resemble forgings, except they are very close to shape coming out of the mold, and don't require as many grain cutting machining operations to be used. Those machining operations create stress and stress risers in a part, and those operations have to be designed correctly the same as a cast part has to be made correctly.


The state of the art of metal forming has moved on about 50 years from the discussion I see about this subject on gun boards. What you and I can do in our garage bears little resemblance to methods used in modern production, and really, we would hope this is so. Things are done routinely today that John Moses Browning could have only dreamed about.

So question comes down to design and a company's skill and efficiency in doing design. Forget process. If we were stuck doing things the same way JMB did them, there would be no plastic guns with 15000 rounds through them, but I've seen a few.

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