Forging technology must be used for automobiles and some transmission shafts, especially for crankshaft components. Forging is a processing method for forming block and bar steel by striking them. The forging that heats the billet above the recrystallization temperature is called hot forging. Hot forging makes the forging billet close to the final product shape, and improves the mechanical properties of the forging. Forging has higher quality reliability than casting due to its forging effect. Crankshaft, camshaft and sprocket gears with high strength and rigidity are required in automobile parts. The automobile crankshaft is a kind of axle component in the automobile engine, which makes the linear motion of the driving piston change into rotary motion. The crankshaft is composed of spindle, piston connecting rod, connecting rod pin, balance weight and other parts fixed on the engine. According to the types and requirements of automobiles, automobile crankshaft has many forms, such as in-line 3 cylinders, in-line 4 cylinders, in-line 6 cylinders, V-6 cylinders, V-8 cylinders and so on. The shape of the crankshaft is very complex.
The mass production method of automobile crankshaft is to make the casting or forging which is close to the final shape of crankshaft by casting or forging, and then finish the final processing by mechanical processing to make crankshaft. In recent years, the requirement for high performance of automobile crankshaft has become more and more urgent. Forged crankshaft with excellent mechanical properties has become the mainstream type of automobile crankshaft, and its usage has been increasing. The performance requirements of automobile crankshaft are high strength and rigidity, so as to make the engine efficient, silent and low fuel consumption. At the same time, crankshaft is also required to achieve lightweight.
In the past, the materials used for forging crankshafts of automobiles were generally heat treated materials (quenched and tempered) of carbon steel and Cr-Mo steel. Since the 1970s, in order to reduce material costs and promote the development of non-quenched and tempered steels, non-quenched and tempered steels including V-containing carbon steel (high fatigue strength steel) and V-free carbon steel have become the mainstream steels for Automobile Forging crankshaft.
In addition, in order to improve the fatigue strength of crankshaft, after the crankshaft is machined, high frequency quenching, soft nitriding and roll-pressing are applied to the dangerous parts such as connecting rod pin and spindle fillet of crankshaft to improve the strength of these parts, which also shows the advantages of forging crankshaft.
When automobile crankshaft is forged, the forging blank is usually heated to about 1200 C for hot forging. In this way, small forging equipment can be used to exert small load and forge with good precision. When manufacturing forged crankshaft, not only quality control should be carried out for forging, but also strict quality control should be carried out for material design of crankshaft, shape design of crankshaft, steelmaking and systematic process of forging. Crankshaft or axle products processed with bars are prone to disagree with the quality of forging cracking.