Steel products may be manufactured either by casting or forging steel. Steel casting is the process by which a metal is heated until it reaches a liquid state and then poured into a mold that shapes the desired product. Steel forging implies the application of mechanical forces to heated solid blocks of steel (such as ingots and/or billets) that are shaped into desired products permanently.
Both manufacturing processes require the application of high temperatures to steel raw materials (to liquify or make it malleable) and the execution of CNC machining work at the end of the process to obtain the final product.
Final products may also undergo surface finish treatment, such as painting, powder coating, polishing, various types of coating (for example zinc plating) and wear protection/hardening (application of tungsten carbide overlay).
Last but not least, cast and forged parts may be assembled, welded, brazed, hard-faced before being shipped as final products.
The products resulting from casting and forging processes have different properties in terms of surface porosity (generally better for forged vs. cast products), grain structure (finer for forged products), tensile strength (generally superior for forged products) and fatigue resistance.
These alternative manufacturing processes are therefore used (and suited for) different circumstances and applications.
The casting process is preferred for:
The forging process is preferred for:
The evolution of the casting technologies has reduced the gap between the physical properties of cast vs. forged products making modern cast products very competitive in terms of quality, strength, and wear resistance: however, in many fields, steel forging remains, still, the preferred manufacturing option (example: small sized valves, i.e. forged valves, or high-pressure valves).
Read about forging steel on Wikipedia.
The main types of casting processes are:
Sand casting is the most traditional casting method and consists in pouring liquid metal into binders that resist the molten metal (such as clay bonded/green sand hard bonded/resin, thermosetting resin sand, and shell).
This term refers to precision molding executed by injecting the liquid metal into a metal die and a ceramic coating. The mold material can be hard wax, lost wax, lost foam and similar.
These processes are used for different applications in terms of parts dimension (sand casting is used for large parts, investment casting for small parts up to 100 kilograms and 1,5 meters of max. length), allowed tolerances (investment casting create more precise parts) and cost targets (investment castings tend to be more economical than sand casting).
Steel forging appeared in China in the ancient ages to produce various types of metal products.
Whereas the procedures and the tools used to produce forged parts have changed through the centuries (from the use of anvils, hammers, and manpower to automated machines as hydraulic presses) the basic steel forging process is still based on the application of thermal energy to solid blocks of steel and their further processing into finished products by the application of mechanical (hammering) forces.
The basic process of forging consists of a few traditional steps:
At the end of the process, the resulting product features extreme strength, impact toughness and wear resistance thanks to the metallurgical recrystallization and grain refinement resulting from the applied thermal and mechanical treatment.
Depending on the temperature applied to the raw material during the forging process, forging is classified into:
The “Closed Die Forging Steel” is a forging process in which the dies move towards each other and covers the workpiece in whole or in part. The heated raw material, which is approximately the shape or size of the final forged part, is placed in the bottom die.
The “Open die forging steel” is the process of deforming a piece of metal between multiple dies that do not completely encapsulate the material. The metal is shaped by the action of the dies that “hammer” or “stamp” the material through a series of movements until the required shape is achieved.
Steel casting and forging are used to produce parts for the following industries:
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