what's the difference between stamped, milled, and forged?


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themic
July 23, 2003, 10:31 AM
what's the difference between stamped, milled, and forged?

how are they made? what are their advantages and disadvantages?

what are some examples of guns that use different methods?

is this the right place to post this?

thanks all

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Tamara
July 23, 2003, 10:51 AM
Stamped and milled are two different ways of shaping a piece of steel into a desired shape (say, a SIG P-series slide). You could start with a chunk of ordnance steel and mill away everything that didn't look like a slide (winding up with a large pile of iron filings and a very expensive slide) or you could place a sheet of thick ordnance steel in a machine that will stamp it into the shape of a slide, and then finish it off.

I'll let someone else do "forged" and "cast". (Just because a slide is "milled" doesn't necessarily mean it's "forged", as you can mill something from a rough casting...)

Kharn
July 23, 2003, 11:39 AM
Going off the top of my head (my materials science textbook and machine shop manuals are at home):
Stamped: Sheet metal pressed and bent into the desired shape. Example: AKM reciever, AR180 reciever

Forged: Big chunk of metal beaten into approximately the desired shape under heat and pressure, and then milled/ground/turned to exact fit. A forging will have all of the grains of the metal aligned, with virtually no voids in the metal. Example: (as-required-by-military specs) forged AR15 upper and lower and many 1911s

Cast: Liquid metal poured into a form and allowed to cool, which produces a rough shape of the object desired. It is then milled/ground/turned to exact fit. Casting produces a final product where the grains of the metal are pointing in all different directions and some voids are possible. Example: Ruger centerfire pistols, cheap cast AR15 uppers and lowers, some lower-end 1911s.

Milled from billet: A solid block of raw metal (the block is called a billet) is milled/ground/turned to the desired shape. This produces exact dimensions when Computer Numeric Controlled (CNC) machines are used, so all the parts will be identical. The grain orientation and voids in the final product depend on the source of billet. Example: Custom firearms that have too few sales to justify the expense of a forge vs CNC, some high-end 1911 slides and frames, AK47 reciever, some AR15 lowers and uppers (the SOCOM ones that look more like an AR10 lower than an AR15 lower are the ones that come to mind, as they're too large to use the conventional AR15 forging).

Stamped cant really be compared to the others, as it requires a totally different construction for the firearm, such as between the AK47's 200+ milling operations and the AKM's simple folding, drilling and spot welding.

Forged is typically stronger than billet, which is stronger than cast. Thats why Ruger autopistols are so blocky, to make up for the possible flaws in the casting.

Billet is more dimensionally correct that forged, which is more dimensionally correct than cast, billet is also the most expensive, followed by forging and then casting.

Kharn

DnPRK
July 23, 2003, 11:45 AM
Forging is what the blacksmiths of old did with a coal-fired furnace, hammer and anvil. In modern times, a gas-fired furnace, drop hammer and forging dies are used. The metal ingot is heated until it glows and placed in the drop hammer which pounds the ingot into the forging die. The result is the ingot takes the shape of the cavity machined into the forging die. The benefit of forging is that the metal grain flows around corners and makes a strong, uniform part. Forgings are near net shape and require little machining.

Casting is where molten metal is poured into a mold. After the metal cools, the cast part is removed from the mold. Proper casting technique produces a part that is every bit as strong as other techniques. Improper casting techniques can leave defects like cold shunts, porosity and inclusions that can effect strength. Near net castings also require minimal finish machining.

4v50 Gary
July 23, 2003, 12:27 PM
Why, savings to you the consumer!

In the days of the olde, everything was forged and then milled until it conformed to a specified standard that was generally measured with jigs or "go-gauges." Advantage of forging is that under all that hammer, you align the molecules giving the metal greater strength. Disadvantage - higher labor costs (both in terms of forging and subsequent machining) and greater waste (a lot of the forging ends up as filing or metal chips).

Casting is actually a very ancient process and was used for jewelry making thousands of years ago. Originally, one took the object they wished to duplicate, placed it into sand (or clay), packed it tightly and then removed it. Hot metal was poured into the clay and when the metal cooled and hardened, the clay removed leaving a rough casting (rough depending on the clay's quality). Another method was to pack the object around sand and after the object was removed, the metal was poured (hence sand casting). Lost wax was a process whereby a wax duplicate of the object you wanted to mold was created and then clay packed around it. The clay would be heated, melting the wax and leaving a "reverse" image in the clay. The molten metal was then poured in and after it cooled, the hardened clay removed to yield the casting. It wasn't until perhaps the late '40s or early '50s when Springfield Armory (yep, the real government armory) experimented with castings. Bill Ruger (Pine Tree Castings) made casting big and the advantages are you can make intricate parts that would be otherwise difficult to machine relatively cheaply. Not that they don't require some machining, but it cost less. This freed the engineers from design constraints limited by machine manufacturing (and costs).

Oh, as to the disadvantages, the porosity of the metal makes it more suspectible to failure. A large part of this though depends on the quality of the foundry doing the casting. Ruger does an excellant job while others, well, make junk. Major advantage of casting is reduced labor expense and reduce metal wastage (sprue is tossed back into the smelting pot).

Now stamping was something that saw extensive use during WW II by both the Germans (MG-42, MP-40 smg, Stgw 44), Russians (PPsh submachinegun), Americans (M-3 Grease Gun, Liberator and even an experimental 1911) and the British (Sten gun had stampings I think). As described above, one took sheet metal and placed it into a press that had dies (machined) around which the metal was cut and formed. The advantage of stamping is that parts could be made very cheaply but were not "cheap" in terms of durability. Many modern pistols utilize stamped components including Glock and Sig Sauer. Advantage: inexpensive. Disadvantage - some consider it unsightly. Want to see a major stamping? Look at the Sig P220 or P226 slide. Those are stamped. The P229 or P239 are casted (by Ruger) and then machined (by Sig).

Jim K
July 23, 2003, 02:26 PM
Another method is blanking, or punching a part out of thick steel. The result is often mistaken for milling or forging; for example, until recently, all S&W triggers and hammers were blanked out then cold forged and machined.

The word "machined" is often used with intent to deceive buyers. Castings, forgings, and stock removal from a billet are all "machined" since neither castings or forgings can be used without some degree of machining, so cast receivers are often advertised as "machined" hoping the customer believes they are not cast.

Forging was once considered an advance in production methods since it reduced the material to be machined. An example is the Evans rifle which was one of the first to be forged because stock removal would have been extremely expensive.

A newer method is Metal Injection Molding, which can produce intricate parts (ex: safety of a Model 1911 type pistol) to the exact size and shape required with no need for further work except for cosmetic purposes. Unfortunately, some makers rushed into MIM and many early parts were deficient or weak, giving the process a bad name.

Other ways of making guns can involve machining bar stock (Remington 700), use of thick wall tubing (Ruger Standard Model .22), and slicing frames from lengths of extruded aluminum (S&W .22 pistol).

All materials and manufacturing methods have their advantages and disadvantages; it is up to the designer to choose the best for his purposes.

Jim

4v50 Gary
July 23, 2003, 03:09 PM
Jim, is blanking more akin to extruding than stamping? Empty mine wanna no.

braindead0
July 23, 2003, 03:09 PM
In regards to better or stronger, forged and milled can be done with the same strength, ie: neither is necessarily better. It all depends on the process. Milling is easier for a small run shop to get right, because they can start with a quality billet of known composition and temper.. assuming they do their part during milling (proper cooling, sharp tools) the results are every bit as strong as a forged item. Forging requires more expensive tools and processes, but produces excellent quality items in quantity... There's usually (if not always) some milling that goes on after the forging is complete.

mete
July 23, 2003, 03:34 PM
Blanking is just punching out a blank such as the first step in making a coin, something has to be done after that. Kharn explained the different processes well . But the different types of forming are just that, it tells you nothing about the material or heat treatment. And you also have to look at the whole process, for example investment casting ( the type used in guns) is expensive however if you design the part from scratch to be cast you can minimize other operations , machining grinding etc ,to produce an economical part. What is important is that you design the forming process, material, heat treatment to produce a durable, reliable gun at reasonable price.

themic
July 23, 2003, 04:00 PM
hey wow thanks everyone... this helps alot :D

M1911Owner
July 26, 2003, 07:25 PM
Perhaps one of you who are very familiar with these processes can answer a question that has long bugged me: Why do the unmachined areas of my "Forged" Craftsman wrenches have a rough, sand-like texture that looks for all the world like a cheap sand casting? Does the forging process also leave that sort of texture, or should I have taken the class on caveat emptor?

Kharn
July 26, 2003, 07:58 PM
M1911owner:
I would bet the rough, sandlike finish is cut into the forge's hammers so that the tool is more gripable. A smooth tool would be a much bigger pain in the butt to use, especially if your hands were slick with grease or oil.

Kharn

mete
July 26, 2003, 08:04 PM
Forging is done at high temperature therefore an ox ide scale is formed. This oxide is removed by pickling in acid or sand blasted, leaving a textured surface.

M1911Owner
July 26, 2003, 08:17 PM
Kharn and mete, thanks--I now see how they got that texture.

Dave R
July 26, 2003, 09:28 PM
Ya'll are missing the most important point: weight.

At least in AKs and CETMEs, the stamped receivers are going to be a pound or more lighter than the milled. Its enough to really feel.

4v50 Gary
July 27, 2003, 01:48 AM
Weight? With all due respect, cheapy and speed of production and low cost are the mostest and bestest important factor. Military prefers lighter weapons that won't take long to make (faster to equip the soldier) and not expensive (lowest bidder).

BTW, there is a new method and that's EDM. Electro Discharge Matter (correct me if this is wrong). Electrons are used to bombard and chip away at the metal until the desired shape is achieved. It's actually more precise than milling. I've seen an intricate shape cut out from a block and while the inner part slips out, if you apply oil there'll be so much friction that it would be difficult to separate the two. S&W uses it to make pistol bbls.

mete
July 27, 2003, 09:14 AM
Gary, here are the facts. EDM (electro discharge machining) creates an electric arc which vaporizes the steel. It's been in use about 50 years. The first time I played with it I drilled .005" diameter holes with it.

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