Difference between Casting & Forging.

You have always heard the terms such as forged pistons & cast alloys and wondered what they actually mean?




Casting is the process where metal is heated until molten. While in the molten or liquid state it is poured into a mold or vessel to create a desired shape.(i.e pistons or wheels)





Forging is the application of thermal and mechanical energy to steel billets or ingots to cause the material to change shape while in a solid state. i.e applying pressure to a solid structure to make it more resistant and strong. In the above picture you can see that the material is first heated and then massive amount of pressure is applied to make it a uniform and closely knitted structure which enables it to withstand more pressure then it normally would with the casting process.


Why use forgings?

Forging offers uniformity of composition and structure. Forging results in metallurgical recrystalisation and grain
refinement as a result of the thermal cycle and deformation process. This strengthens the resulting steel product particularly in terms of impact and shear strength.

Forged steel is generally stronger and more reliable than castings and plate steel due to the fact that the grain flows of the steel are altered, conforming to the shape of the part.

The advantages of forging include:

Generally tougher than alternatives
Will handle impact better than castings
The nature of forging excludes the occurence of porosity, shrinkage, cavities and cold pour issues.
The tight grain structure of forgings making it mechanically strong. There is less need for expensive alloys to attain high strength components.
The tight grain structure offers great wear resistance without the need to make products “superhard”.

Why use castings?

We use castings for a wide range of wearparts and components that are too large, complicated, intricate or otherwise unsuitable for the forging process. We can forge parts up to 50kgs but the sheer energy required to forge larger items make casting a much more viable alternative. The casting process better lends itself to making parts where internal cavities are required.

The advantages of casting include:

No real upper size limit in casting weight
Large range of alloy choices
As forgings remain solid, custom alloys are far more difficult to get into production whereas with casting, alloys including Chrome, Nickel and Moly can be added at the molten stage.
Tooling is often less expensive than forge dies
Smaller production “runs” required
Complicated/complex parts are no problem
For general GET as well as large and complex components - casting is a fantastic method of manufacture.




Here is a picture of a TE-37 Volk rim which is formed by the Forging process. Which is the reason why a staggered set of its costs almost $3500 canadian dollars or 1 lakh 50 thousand Indian rupees. Whereas the replica's or other rims made by the casting process are much cheaper and not as strong.

For more info on wheel construction check out - http://www.tirerack.com/wheels/tech/....jsp?techid=90

good post mate..

excellent info man..as far as engine parts go...
the following are forged:
camshaft
crankshaft
con rods
big end bearing
pistons(performance)
castings:
head
block
pistons

as a thumb rule all machinery that is directly subjected to stress and strains and fluctuating loads are forged, because they have mode load bearing capacity compared to their casting counterparts as they have been tempered when they are forged, these techniques are used for materials that are easy to work with...however you will find after market, titanium pistons(cast and machined), and conrods(machined), although you might experience a bump in power because the engine will be able to rev higher because of the lighter pistons and con-rod, and rev faster too because of the lower inertia of the rotating parts, but its mostly used for racing applications...!

i know this very vell