When it comes to forging, designers are no strangers. Some students say that only large-sized parts (such as when suitable specifications of bars are not available in the market), or complex shaped parts (such as when all machining is too wasteful of material), will they think of forging. In fact, when you have high requirements for the toughness, strength, performance, etc. of parts, forging is always a good choice.
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Why does forging have advantages over parts produced by casting or direct turning? In addition to the previously mentioned ability to obtain large-sized and complex shaped parts through forging; Besides being more material efficient compared to machining, forging has the following two main advantages in improving material properties:
One is that forging can reduce or eliminate possible metallurgical defects in raw materials, such as cracks, hot cracks, hot spots, cold shuts, shrinkage, material shortages, and inclusions, to minimize the porosity of the product, improve the mechanical properties of the product, and enhance the stability of production quality between different batches.
In addition, forging can make the parts have a good grain flow direction. We know that most raw materials (such as round steel) are obtained through rolling, and the grain structure inside the material is forced to flow along the centerline of the rolling process. During forging, this inherent grain flow will bend to follow the contour of the forging shape, strengthen directionally, and produce high-quality components, as shown in the following figure. The forged parts have good impact resistance and fatigue resistance.
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Any machined component, regardless of whether the raw material is made of bars or plates, will cut off some grain flow after machining (because grain flow is unidirectional). The presence of open grain ends makes the material more prone to fatigue and more sensitive to stress corrosion cracking. Casting is a process of pouring molten steel ingots into a mold to form a rough shape of the product to be produced, during which there is no grain flow, and therefore the resulting product does not increase its directional strength. The following diagram is a comparison diagram of three methods, which may be more convenient for everyone to understand.
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Here we also share some research and statistical data for reference: under the same material conditions, the strength to weight ratio of parts obtained by forging can be increased by 20% compared to those obtained by casting or pure machining. The material properties after forging can be improved by 30% in terms of strength and toughness compared to the raw materials before forging. Compared to cast parts, forged parts can increase their tensile strength by 26% and fatigue strength by 37%. Are you tempted?