What is forging? What is casting? Here, we are going to discuss the fundamentals of these manufacturing processes and their differences. This will help us decide which manufacturing process is better, casting or forging?
What is Casting
Casting is a manufacturing process that has been around for approximately 7,000 years! It’s a process where a liquid material, generally molten metal, is poured into a mould containing the desired shape and allowed to solidify.
A good visual representation is building a sandcastle. We pack sand into a bucket to get the sand into the desired shape. Casting works from a similar fundamental. The solidified product is known as a casting and is removed from the mould once cooled.
Alternatively, it is possible to break the mould, depending on the mould material, to remove the product. A casting process helps produce parts of a complex geometry that would be unrealistic to make with an alternative method. Also, casting is commonly used to mass-produce components.
Components manufactured from casting can range from less than 1 kg up to 200 tonnes. It is common for cast components to be machined to achieve the desired precise dimensions for the profile.
The casting process has been developed throughout its life, including the use of different mould materials. Wax is a common mould material due to the low cost. Recent developments have resulted in pressure die casting, which forces molten metal into a mould under high pressure. Pressure die casting is a method used to create engine blocks.
Unfortunately, due to uneven cooling rates within the molten metal, the microstructure has a random crystal structure. The random crystal structure does not improve the components of mechanical properties. The most common problem resulting from the casting process is porosity.
Porosity is a measure of space or voids within an area. Porosity occurs in casting because the molten metal can contain dissolved gas, which bubbles when undergoing cooling. A method to overcome porosity in casting is by placing the casting in a pressurised vacuum, preventing gas from dissolving into the molten metal.
What is Forging
Forging is a manufacturing process that shapes components by inducing localised compressive forces. Hammer blows are the frequent method of applying compressive forces. Alternatively, dies (which help form components into the desired shape) is also used.
There are various types of forging but are luckily named in a straight forward manner. The processes names include the temperatures of the process: cold forging, warm forging and hot forging. For hot forging, steel reached temperatures up to 1150°C and cold forging is performed at room temperature.
A great example that everyone knows is a blacksmith. A blacksmith creates small products by shaping them using hammer strikes. In industry, when a large number of components are manufactured, large presses are used, which needs a large sum of money.
Unlike casting and other manufacturing processes, forging refines the metals crystal structure during manufacturing. As the product is shaped, the individual grains are elongated in the direction of the metal flow. Refining the grain structure allows aligning of the grain flow in the direction of the principal stresses.
The mechanical properties improved include those linked to preventing crack propagation, such as fatigue strength, impact toughness and ductility. However, these properties only enhance if the grain flow and crack propagation direction are correctly aligned. As the crystal structure is refined, repairing forged components via welding is not advised because it can disrupt the surrounding materials grain structure.
Forging isn’t always the best process to pursue when manufacturing components. Here are a few disadvantages. Unlike casting, forging a complex geometry is tough and often not achievable. For the creation of specified geometries, a die will generally need to be designed. There are high costs associated with die design.
What’s the Difference Between Casting and Forging
As discussed above, forging provides metal products that are stronger and tougher than those made via casting. The increased strength and toughness stems from the refined grain structure produced in forging, aligning it with principal stresses.
However, forging isn’t always the best process to pursue when manufacturing components. Unlike casting, forging a complex geometry is tough and often not achievable. The reason for this is because the metal remains in a solid state throughout the process.
Casting can create complex geometries because molten metal flows into a cavity. For the creation of specified geometries, a die will generally need to be designed. There are high costs associated with die design. Although, casting is generally cheaper than forging.
Casting and forging both have advantage and differences, but the best method comes down to the component/product being created.
Summary
We have discussed the fundamentals of the manufacturing processes of casting and forging and theirs differences.
So what manufacturing process is better? It depends on the requirements of the product you intend to manufacture. It is a component undergoing large amounts of stress? If so, forging will be favoured. If you want to mass-produce parts with complex geometry, casting is the preferred method.
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