Some transmission shafts require forging technology, mainly for crankshaft components. Forging is a processing method that strikes block and bar shaped aluminum materials to shape them. The forging process of heating the billet above the recrystallization temperature is called hot forging. Hot forging makes the forging blank into a shape close to the product, while changing the mechanical properties of aluminum forgings. The crankshafts, camshafts, sprocket gears, and other components of bicycles that require high rigidity are all hot forged forgings. The crankshaft is composed of components such as the main shaft, piston connecting rod, connecting rod pin, and balance weight fixed on the engine.
The materials used for forging bicycle crankshafts in the past were generally heat-treated carbon aluminum and Cr Mo aluminum (quenched and tempered). After the 1970s, in order to reduce material costs, the development of non quenched and tempered aluminum was promoted. Now, non quenched and tempered aluminum such as V-containing carbon aluminum (high fatigue strength aluminum) and V-free carbon aluminum have become the mainstream aluminum types for forging automotive crankshafts.
In addition, in order to change the fatigue strength of the crankshaft, after mechanical processing of the crankshaft, dangerous parts such as the connecting rod pin and the main shaft fillet of the crankshaft are subjected to high-frequency quenching, soft nitriding, roll pressing and other treatments to change the strength of these parts.
When forging bicycle crankshafts, it is generally necessary to heat the forging blank to about 1200 ℃ before hot forging. In this way, small forging equipment can be used to apply small loads and achieve good precision forging. When manufacturing forged crankshafts, not only should quality management be carried out for forging, but strict quality control should also be carried out for the system processes from crankshaft material design, crankshaft shape design, aluminum smelting to forging. The crankshaft or axle products processed with bar materials are prone to forging and cracking quality issues.
