Difference between metal casting and metal forging

Metal Casting and Metal Forging are two widely used processes for shaping metals.

Forged products generally have improved mechanical properties and higher ductility as compared to casted products. Forging results in elimination of porosities and cavities in the product as it yields a continuous grain flow and fine grain size and the wear resistance is higher. However, to choose which process can prove to be more effective for specific requirements, few factors are to be considered as discussed below.

1. Size
For Casting, metal is heated to its molten state and then poured into the mold of the desired shape. Due to its liquid state, metal can flow into various shapes and sizes of molds. Whereas, for forging metal, at its room temperature, is pounded by a hammer or die and shaped into the desired form. Thus, forging requires a large amount of force to shape the metal and the force increases considerably with an increase in the size of the workpiece.

2. Design
Metal tolerance, part complexity, grain structure, and structural integrity are some of the design factors that are considered when choosing between forging and casting processes.

For complex objects with minute details and inner specifics, forging has its limitations. On the other hand, casting can be easily molded irrespective of the part complexity since it uses molten form of a metal.

3. Alloy Selection
Alloy selection or their availability is one of the important factors for selection of metal shaping process. Forged products are manufactured using billets. At production sites, only a precise number of grades and a limited variety of alloys are used for production. Whereas, casting processes are carried out at foundries, where selecting a suitable alloy is easier and cost-effective.

Additionally, ferrite content of an alloy is also considered an important factor that makes the product more corrosion resistant than forged parts.

4. Component strength
The internal strength and structure of the component is also a significant factor to be considered. Forging directs the path for the grain flow to be in a specific direction forming a directionally stronger component. Forged products have different property-measurement values in different directions and are called anisotropic.

While casted products have similar property-measurement values in all directions and are called isotropic. Hence casted products are strong uniformly in all directions and forged are characteristically stronger in a particular direction. So, it depends on the application of the products as to which manufacturing process should be opted

5. Cost
There is no deciding formula which claims which process is more cost-effective. Both methods have their efficiency in terms of cost in different dimensions. Production magnitude, cost of selected alloy, shape complexity, product specification, and testing affect the price of the overall manufacturing process.

Castings are cost-effective for all sizes whereas forgings are effective for large and medium sizes. For casting the budget of raw materials is usually lower than forging as the cost of initial processing of billets also adds up in forging. Closed Die Forging (CDF) tools are generally more expensive than Open Die Forging (ODF). So, for production on a large scale, the unit cost is reduced if a dedicated tool is acquired for the process.

Machined castings can prove to be more cost-efficient as the foundries can recycle machining chips by re-melting them. This cannot be done for forging. Rates of machining for forging and casting are almost alike. However, due to presence of finer grains in forging, some stainless steels and alloys of nickel have enhanced machinability.