Forged vs. Cast

[S4toSTI]

Ok I am a little confused about this so I am going to blather on for a minute and i am probably all wrong but just correct what I am missing here. This is mainly about wheels cast vs. forged wheels.

Ok so in my understanding the process of casting a wheel vs. forging a wheel is this.

Forged: Metal is heated and poured in a die and then pressure is applied to the mold and presses the metal into the mold’s shape. Ok so basically it is making the atoms more tightly packed in. By doing this the wheels are stronger.

Cast: Same idea as forged but the metal is simply poured into the mold and no pressure is applied.

Why I am confused: Ok wheels A is forged Wheel B is cast. A and B are the same volume. A and B are made of the same alloy. Wheel a being forged has more atoms of the alloy in it making to denser. If A is denser then b then shouldn't a weigh more. And if a weights more then b, why do people say forged wheels are lighter????

I could be totally off base and if I am that’s awesome but I would like to be set straight thanks.

Knowledgeable facts only I am confused enough as it is.

[xEJ20x]

From what I've understood.
Anything that is forged, is made from 1 solid piece of metal and stamped into a specific shape from a die.

Here's information on the two.

http://encyclopedia.thefreedictionary.com/Forge

http://encyclopedia.thefreedictionary.com/casting

[TROLL]

(Taken from sportcompactcarweb wheel guide - http://www.sportcompactcarweb.com/tech/0205scc_wheelguide/)

Casting
The quality of cast wheels varies dramatically, depending on process, and sometimes on variables beyond the control of the manufacturer, such as ambient temperature or even humidity. In general, pressure casting, in which the metal is pumped into the mold, is better than just pouring it in. Castings tend to be porous -- some carburetors actually leaked fuel through the metal, with no crack or visible flaw present. Porosity is bad, because it means there are places where the metal isn't in direct contact with more metal on all sides. Voids, which tend to form in the spaces between crystals (a chicken and egg situation), are where cracks begin. Larger, chunky grains may beget larger voids, and cracks along crystal boundaries will have farther to travel. All these points mean that cast wheels must contain more metal to achieve an acceptable strength, and are thus heavier. Still, cast wheels can be made to a high standard with attention to quality processes. The vast majority of alloy wheels are cast, and provide many years of good service.

Forging
Forged wheels take advantage of what happens when metal is cold worked. Cold working doesn't necessarily mean you'd want to touch the materials while they're in process, it means the procedures are done at a temperature below the point where the metal starts to melt and regrow a new crystal structure. Just as the spaces between a metal's crystals may hold flaws, the crystals themselves are full of imperfections called discontinuities. They may take a variety of forms, but discontinuities all share one important quality. By traveling through the crystal lattice of the individual grains, they allow the metal to change shape without fracturing like a diamond. When a load is applied to a metal object, it deforms slightly. When the load is removed, it regains its original shape. This happens because discontinuities move a little, and move back. If the load is high enough, the discontinuities will move until they reach the edge of their crystal, or until they run into another discontinuity.

Generally, discontinuities move one atom at a time, and their movement is guided by the regular structure of the crystal. If a discontinuity in the structure runs into another, the regularity is interrupted, and they may become tangled, and can't return to their starting position. This has two effects. 1) When the load is removed from the metal, it will not return to its original shape. 2) The metal is more resistant to deformation in the future, because there are fewer discontinuities available to move around. This description of the process is a single case of what is actually happening by the billions.

What we can measure is the average of them all. The idea behind forging is to get, on average, the right number of discontinuities tangled around each other, with crystals oriented in the right direction, so that the metal is very strong and resistant to further deformation. This is a delicate balance, because too much cold working makes the metal brittle, so that it fractures instead of absorbing loads. You can see how this works for yourself: Bend a paper clip back and forth many times until it breaks. It begins soft, then gets stiffer, before finally fracturing.

Forging also changes the shape and alignment of the crystal structure. When molten metal solidifies, its grain structure is non-directional, amorphous, grains in the sense of "grains" of sand. As metal is forged, these grains are stretched in the direction of deformation, making them more like the "grain" of wood. The metal is formed so the grain goes in the directions where strength is needed most. Think of particle board versus real wood. One is cheap, heavy, and easily formed into a variety of shapes. The other is strong and light. The forging process, because of the vast pressures involved, also compacts the metal, eliminating porosity and the voids that can be a source of cracks or corrosion. The result is that less metal is required to achieve a given strength, meaning lighter, stronger wheels can be made.

[2point4DSM]

Why I am confused: Ok wheels A is forged Wheel B is cast. A and B are the same volume. A and B are made of the same alloy. Wheel a being forged has more atoms of the alloy in it making to denser. If A is denser then b then shouldn't a weigh more. And if a weights more then b, why do people say forged wheels are lighter????

Bryan put up some good info.

But to sum it up...
Although the forged wheel is more dense the strength achieved by the forging process makes it stronger than a cast wheel that is significantly beefier and therefore heavier.

Example: OEM 1g DSM 16x7 wheel weighs almost twice as much as a comparably strong forged wheel. How? Take into consideration that 1g AEM brakes can hardly fit under some 17" wheels but will fit under Volk TE37 16" wheels.

[TROLL]

i think of it like a comparison between iron and titanium. dont know if thats how i should be thinking about it or not, but density/mass does not always equal strength.
bryan

[Safir]

There does not need to be nearly as much material in a forged wheel to be of teh sane strenght, therefore a forged wheel can weigh less than a cast wheel.

[1988 Olds]

You beat me too it man.

[2point4DSM]

Think of cast as cardboard and forged as balsa wood.

[Safir]

so cast wheels will fall apart if they get wet? ;)

[99SL2_Modder]

Also, forged wheels bend, cast wheels break/shatter/kaboomernate.

[2point4DSM]

Some wheels are called forged but are not entirely forged. I've seen some with forged centers with cast rims. I think that sort of makes sense considering forged rims can not be repaired.

[MuddyREX]

Here's some video of the Rays Wheels forging process.

http://www.jrponline.com/downloads/mm/rays.wmv

[D Money]

Here's some video of the Rays Wheels forging process.

http://www.jrponline.com/downloads/mm/rays.wmv
Rays/volk wheels are the ****. I want a pair.