Why is forging technology currently irreplaceable?

Cars and some transmission shafts must use forging technology, especially for crankshaft components. Forging is a processing method of striking and shaping block and bar-shaped steel materials. The forging process of heating the forging billet above the recrystallization temperature is called hot forging. Hot forging produces forging blanks in a shape close to the final product while improving the mechanical properties of the forgings. Forging, due to its forging effect, has higher quality and reliability than castings. The crankshaft, camshaft, sprocket gear, etc. that require high strength and rigidity in automotive components are all hot forged forgings. The automobile crankshaft is a shaft-type component within the automobile engine that converts the linear motion of the driving piston into rotary motion. The crankshaft is composed of components such as the main shaft, piston connecting rod, connecting rod pin, and balance weight fixed on the engine. According to the type and usage requirements of the car, the crankshaft of the car has various forms such as inline 3 cylinders, inline 4 cylinders, inline 6 cylinders, V-shaped 6 cylinders, V-shaped 8 cylinders, etc., with very complex shapes.

The mass production method of automobile crankshafts is to use casting or forging methods to make castings or forgings that are close to the final shape of the crankshaft, and then use mechanical processing methods for final precision machining to make the crankshaft. In recent years, the demand for high-performance automotive crankshafts has become increasingly urgent, and forged crankshafts with mechanical properties have become the mainstream shaft type for automotive crankshafts, with increasing usage. The performance requirements for automotive crankshafts are high strength and rigidity, to make the engine more efficient, silent, and low fuel consumption. At the same time, it is also required that the crankshaft achieve lightweight.

In the past, the materials used for forging automotive crankshafts were generally heat-treated materials (quenched and tempered) of carbon steel and Cr Mo steel. After the 1970s, to reduce material costs, the development of non-quenched and tempered steel was promoted. Now, non-quenched and tempered steel such as carbon steel containing V (high fatigue strength steel) and carbon steel without V have become the mainstream steel types for automotive forged crankshafts.

In addition, to improve the fatigue strength of the crankshaft, high-frequency quenching, soft nitriding, and rolling processing are carried out on the dangerous parts of the crankshaft, such as the connecting rod pin and the main shaft fillet, after the crankshaft is machined, to improve the strength of these parts, which also demonstrates the superiority of forging the crankshaft.

When forging the crankshaft of a car, it is generally done by heating the forging blank to about 1200 ℃ before hot forging. This can utilize small forging equipment, apply small loads, and achieve good precision forging. When manufacturing forged crankshafts, not only is quality management necessary for forging, but strict quality control is also required for the systematic processes from crankshaft material design, crankshaft shape design, and steelmaking to forging. The crankshaft or axle products processed with bars are prone to quality objections due to forging and cracking.