Casting vs Forging

sand casting versus forging

Sand Casting Benefits

The process of steel making is essentially the same for both wrought and cast steels. Liquid steel is principally an alloy of iron and carbon. Other metals such as chromium, nickel, manganese, and molybdenum are added as alloying agents to impart particular properties to the steel. The quality of both forgings and castings is dependent upon the quality of the raw materials used in the molten steel that is poured into the mold.

The main advantage of the casting process is its versatility. Castings are well suited to producing a very wide range of part types that may have a broad set of application characteristics. Some of the main considerations and benefits the casting process offers relative to forging include:

Size: The forging process requires a very high level of force to shape a part. This limits the size and potential weight of the part that can be produced physically and economically. Castings on the other hand can be produced in varying sizes that range from extremely small to extremely large.

Shape Intricacy:

The casting process offers a fantastic amount of flexibility with respect to part shape, intricacy, and sizing of part features relative to the overall part size. So secondary machining operations and associated costs can be reduced to a minimum.

Forgings on the other hand have significant limitations on the level of intricacy that can be achieved since the part is produced by a hammering process. Producing small, accurate detail on larger parts is either very difficult or impossible without a significantly higher amount of machining after the initial shape is produced.

Internal Cavities:

Castings offer a high degree of freedom with respect to the shape of internal part cavities. Since molten metal is allowed to flow through the mold, core shapes can be used to define internal cavities is completely flexible.

Creating an internal cavity of any shape in a forging is not really practical. The high impact force required to shape a part, and the impossibility of retrieving a tool from within a part once it has been given a shape make it completely impractical for this type of work.

Run Length:

The tooling type and material required to create a casting can be selected to a large extent, based on the size of a desired run. This makes casting any run size - from a single part or prototype to a very large number of parts - more economical than forging in many instances. Since tool creation and maintenance for casting is easier to adapt to the specific part and run size, it is therefore typically less expensive than producing forging dies.

Large range of alloy choices

Foundries formulate, produce and pour their own metal materials to produce a cast part. They have full control of the metal that is used to produce the casting. This gives a foundry the flexibility to create virtually any alloy grade required to meet part and application requirements. By contrast, forging companies are dependent on the quality of the wrought metals they purchase from a third party supplier.

Mechanical Properties Strength

According to the forging industry, the forging process creates a grain flow that makes forgings superior to castings. However, independent testing has shown that although the mechanical properties of a forging are higher in the longitudinal (working) direction, they are significantly lower in the transverse direction, or perpendicular to the grain flow. In contrast, the mechanical properties of a casting are uniform, regardless of the orientation of the material.

The tensile ductility of cast material is significantly higher than for wrought material in the through thickness orientation, although lower than in the longitudinal direction. However, cast steel is less notch sensitive than wrought steel. Notched fatigue properties are a more accurate representation of actual service conditions because most large parts—whether cast or forged—would be expected to have some type of a notch.

Summary

Casting offers a wide variety of options with respect to materials, shape, production run length and finished part strength. While forging does offer specific benefits for applications that fall within the particular accuracy, shape restrictions and production cost considerations, casting offer much greater design flexibility, performance and production cost benefits to manufactures across a broad swath of industries.