Forged, billet or cast....

[newfalguy101]

Am I correct in this:

1) Cast is molten metal poured into a cast, then the raw part is final machined

2) Forged is a block of metal ( presumably heated ) and formed into a raw part under pressure, then final machined

3) Billet is a block of metal with everything that doesn't belong machined away

Billet would be the most time consuming and therefore costly, right?? Which is why billet lowers are more expensive??

 

[Jim Watson]

Yes.
More time under the machines to cut away all the stuff that doesn't look like a gun.
Once you are set up for it, near-net forging and investment casting reduce the man and machine hours.

 

[rcmodel]

On the otherhand, one could argue forging is better or stronger because the grain structure in the metal follows the shape of the part.

They forge hammers & wrenches because they are stronger for that reason.

rc

 

[rockhopper46038]

I'm one that will argue for that point, being another who is in one of those industries where we use forging when we need to, stock removal when we have to, and casting (or even MIM) when volumes and specifications allow.

Knowing full well that forgings are overkill for 1911 frames, I still prefer them over cast.

 

[BBBBill]

I am biased toward forgings over other methods, but sometimes one of the other processes is better for the specific part. Example - Jet engine fan blades are cast in a special process called single crystal casting.

 

[Kp321]

Just a point of interest, the original Springfield Armory 1911's (the government arsenal at Springfield Mass.)were machined from a solid piece of steel plate which would be called billet today. As far as I know, they were the only ones made this way. Most were forged until investment casting made its debut.

 

[Jim K]

When forging was first used for gun manufacture, it was touted as being advanced because it required less machining than the other current methods, which seem to have been mainly stock removal. The strength advantage was not recognized until later.

But stock removal (machining from billets) continued for many years; the pre-64 Winchester Model 70 was machined from bar stock. The post-64 rifle, which many believe to be cast, was actually forged (at least as made by the original Winchester company).

Jim

 

[barnbwt]

Also worth noting; billets are cast. Same thing. The casting is done so less material isn't wasted at the milling stage . A shop with nothing but mills and no foundry is therefore limited to the billet (and fewer and fewer foundries these days, and more and more CNC which makes the material wastage less expensive)

Forging work-hardens the bulk material. Makes it harder, more brittle. Makes it permanently deform (i.e. take damage) at a higher level than annealed/soft material. Frames and large gun components are frequently designed far in excess of expected loads, so the extra brittleness of the forging usually doesn't much affect the fatigue life, while it increases the wear-resistance of the parts substantially. Forging is the most expensive process, because it requires dies (akin to moulds in terms of tooling costs) in addition to casting equipment (in many cases a cast part is forged to shape) and machining capabilities. The extra step raises unavoidable costs greatly, and introduces myriad additional chances to scrap the part during the process as well.

TCB

 

[Jolly Rogers]

Forged parts may be more brittle but they don't have to be. All of my wrenches that I use every day are forged. They aren't brittle. The heat treatment after forging eliminates that. I sure wouldn't bet my knuckles on a cast or machined from plate wrench. BTW there are some companies that offer machined from plate wrenches. They are thin but huge to take the stress of the torque without bending. Won't fit most places so they aren't an option for me.
Forged is my process if I have the choice.
Joe

 

[fletcher]

Billet can refer to either a cast or forged product. You are correct on points 1 and 2.

For more information, I explained the casting/forging differences here a while back.

Forging work-hardens the bulk material. Makes it harder, more brittle.

Forging occurs over the recovery temperature, and therefore does not retain any significant degree of work hardening. It certainly does not make the material more brittle. Forging both increases strength and ductility of a material compared to the initial casting. Three main things happen during forging that result in the improved mechanical properties:

1) Sealing of internal porosity from the casting process.
2) Breaking up of coarse cast grain structure. Finer grains = better mechanical properties.
3) Alignment of grains and second phases in the direction of working.

Cold forging a material will make it stronger and more brittle, but making a part in this way is not typical. Hot forging is the norm. Most die forged products also start from wrought, not cast, material (from the forge shop's view - it all started as cast at one point in time). The step from cast to wrought adds a trivial amount of cost due to the sheer amount of material being processed day to day.

 

[sage5907]

Just a few words about the pre 64 Model 70. The receiver was machined from a 7 1/2 pound billet if 4140 chrome-molybdenum bar stock to less than one-sixth of its original weight: 19.3 ounces. The extraction cam, located behind the receiver bridge was spot hardened with a special high intensity torch, next the receivers were immersed into a red hot salt bath which varied from 1200 to 1300 degrees F. After 24 hours, they were removed to air cool, completing the heat treating operation.

 

[WestKentucky]

You left out extruded. Extruded parts are much like forged parts in that they are a hunk of metal (a billet) heated and pushed through a die to make a shape. I personally have been involved with this process for 2 years of my life. Several shapes were pretty obvious, especially when you see customer names as obvious as smith&wesson. I made plenty revolver barrels in raw form from 10 to 30 feet long. The grain structure of extruded parts follows the direction of extrusion and often times the parts have to be heat treated to soften them therefore changing grain structure again. Memory metals have to be heated to straighten them as well. (Same factory extrudes titanium for aircraft industry)

 

[barnbwt]

"2) Breaking up of coarse cast grain structure. Finer grains = better mechanical properties.
3) Alignment of grains and second phases in the direction of working."
That's work-hardening, for ya . The finer, distorted grains make the material more resilient (i.e. harder, stronger, more brittle, stretching the stress/strain curve out further; whatever you call it it's the same result). Most parts tend to carry load along their features (like ribs, for example) so the forging process conveniently stiffens them along that direction, by mashing the slip planes along the same path.

"Forged parts may be more brittle but they don't have to be. All of my wrenches that I use every day are forged. They aren't brittle."
Get one to fail and it would likely crack before bending. "Brittle" is incorrectly connoted with fragility/weakness, when it just means that a material shows less plastic (permanent) deformation before ultimate failure. Carbon fiber is incredibly brittle, but is definitely not weak; which is why components made from the material tend to fail dramatically as all the pent up energy is let loose at once. Forgings would be just as bad, except they are stress relieved by heat treating after the forging process (or during, if hot-forged) which undoes some of the work-hardening and makes the tool impact resistant. This makes the yield strength less than it could be, but makes the tool "tougher" and more tolerant of the whole gambit of loads.

As a further illustration of this; in an aircraft repair engineering seminar I once attended, there was a story of a 737 (I think it was) which broke a landing gear trunnion. Broke it clean off. This part was a very large, super-strong steel forging, which was intentionally left very brittle and hard so it could carry as much load as possible for its weight without deforming. What was theorized was that a worker's tool had been dropped onto part of the trunnion while servicing the landing gear bay interior, and the impact point then grew, over several dozen takeoff/landing cycles, a radial crack inside the part until it ultimately failed. The part was properly made, and sufficiently strong as designed; but these trunnions are hardened so close to a glass-like state that they fail in the form of cracking.

Gun slides and frames sometimes have the same problem, but for no benefit since gun parts are typically overdesigned by a much wider margin than aircraft. If a hard surface is the desired benefit of the forging, modern coatings or penetrating finishes are a better solution than hardening the part through. Basically, what I'm trying to say is that the vast majority of forged gun parts are forgings for the sake of forgings (and the number of posters who blindly prefer them 'just cuz' is evidence that it's a smart move for companies to keep making them this way ). It's just a manufacturing technique; other means can accomplish the same ends, and sometimes for less cost. Sheet metal is arguably a forging, btw, but it is somehow not associated with strong, high quality parts

TCB

 

[fletcher]

I am a metallurgist in the aerospace industry, with forgings and mechanical properties being two of my specialties - some of that information isn't accurate, so I will explain further why this is the case.

Dynamic recrystallization during the forging process prevents work hardening from occurring, and the continuous recovery (reversal) of work hardening is a major reason why hot forging is even possible. Forgings do not work harden during the forging process. If forgings work hardened, increasing flow stress would arrest movement before the part had much of a chance to deform. Work hardening, such as cold rolling copper sheet or plate, is a completely different mechanism from forging, and they have very different results. Hot forging / die forging will under no circumstance work harden a part. As-forged parts are usually pretty soft until they've been heat treated.

Slip planes are based on crystallographic directions, and although crystals may develop a preference during forming operations (known as texture), they do not simply align in the direction of work. Slip planes will always be in a variety of directions.

The landing gear is an example of poor damage tolerance. While this design may have been adequate from a static strength perspective, this style of design is no longer preferred in industry. Aircraft have since shifted to flaw tolerant design to prevent such issues. Thus, the design was not sufficient even though it may have been in line with "best practice" at the time.

I agree that forgings are not always necessary. Other wrought products can be more than adequate for most parts - plate, sheet, bar, etc. are just fine for 99% of parts with size on the order of firearm parts. Although, it would be a stretch to call sheet a forging - it is a wrought product, i.e. worked, but not forged.

 

[Jim K]

As an example, the frame of an S&W revolver starts out as a rectangular length of bar stock. The end is heated white hot and put under the forging hammer which produces a rough forging of the frame and also cuts it off so the bar can be heated for the next one. The forging is then put into a second heavy machine that cuts off the "flash" so the machine work can begin. All of that makes a lot of noise and vibration, and requires a factory built to stand up to the pounding.

Casting, machining, MIM, and even light stamping require lighter machinery and a much less sturdy plant. As one production engineer noted, "You can do investment casting in a shopping center and not bother anyone." He might have exaggerated a bit, but certainly the fact that a heavy industry establishment is not needed is one point in favor of casting for firearms manufacture when it can produce a part with the same strength as a forged part, even if it has to be larger.

Jim

 

[newfalguy101]

Thanks for the replies............it seemed like such a simple question, really