There is no essential difference between the wheels of trains and subways, except that the diameters are different. Forged wheels use forging machinery to plastically deform the metal blank and give it certain mechanical properties and shapes. During the forging process, forging can eliminate defects such as looseness in the cast state produced by the metal during the smelting process, optimize the organizational structure, and maintain complete metal streamlines. Therefore, the mechanical properties of forged wheels are much better than those of cast wheels of the same material.
When forging wheels, as long as the pre-forming die cavity and the die forging die cavity are reasonably designed, the forgings can be filled well during die forging. The pre-forming of the blank is free upsetting on the anvil, which only requires one step and does not require a large hydraulic press. In this way, the forging process in the first half of wheel manufacturing has only two steps, which are respectively formed into a production line on two large and small hydraulic presses, and the productivity can reach 120 per hour. If the quality of billet blanking can be guaranteed, the machining allowance can be reduced and energy consumption can be saved.
Usually, the hot wheel forging drawing is calculated by multiplying the cold wheel forging drawing by the thermal expansion amount. However, when the sizes of the various parts of the fine wheel forging are quite different, the small parts cool quickly, and the final forging temperature will be significantly different from the large parts. At this time, different thermal expansion coefficients can be taken for different parts of the hot wheel forging drawing.
After the qualified forging is cooled, the rough turning can be carried out. The rough turning is the workpiece after the hoisting hole processing and the keyway processing. Then it enters the comprehensive heat treatment, quenching, normalizing, modulation, and other processes. Heat treatment refers to the material in a solid state, through heating, insulation, and cooling means, to obtain the expected organization and performance. After heat treatment, the product is tested for hardness and flaw detection before entering the finishing stage. The finishing process is completed by high-speed speed-controlled lathes to control the dimensions to the drawing requirements, with an accuracy margin of 0.02mm to 0.03mm.
Since forged wheels are much lighter than most cast wheels, it is very convenient to replace forged wheels. Forged wheels have other benefits. They have a higher particle density structure than cast wheels. Cast wheels tend to be more porous than forged wheels, which means that forged wheels will retain their polished luster longer than similar polished cast wheels.