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How is a crankshaft manufactured? Is it still necessary to repair it if it's broken?

Release time:

2021-12-03

Do you know what the most expensive and precise single component of a car engine is? Many people might not imagine it, but it is the crankshaft.

It is a very important component of the engine, as it converts the linear motion of the pistons into rotational motion and transforms the gas pressure from the pistons and connecting rods into torque output, while also driving the car's transmission system, engine valve mechanism, and other auxiliary devices.

What material is the crankshaft made of?

The forces acting on the crankshaft are extremely complex. It works under the combined effects of periodically changing gas pressure, reciprocating inertial forces, and their moments, bearing huge alternating loads of bending and twisting. At the same time, it is a slender high-speed rotating part, so strict dynamic balance is required; bending and twisting must not exceed certain values.

Therefore, crankshafts need to be made from very high-quality materials and undergo strict surface treatment processes. Generally, they are forged from medium carbon steels such as 45, 40Cr, or 35Mn2; in recent years, ductile iron has also been used more frequently.

After forging or casting shaping, in order to improve the fatigue strength of the crankshaft and eliminate stress concentration, shot peening treatment needs to be performed on the journal surface; rounding corners should be rolled; to enhance surface hardness of the journal, high-frequency quenching or nitriding treatment should be done on its surface before final machining.

Crankshafts treated in this way have sufficient fatigue strength and stiffness against bending and twisting while having a sufficiently large load-bearing surface area and wear resistance.

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