Machining and equipment configuration of locomotive diesel engine crankshaft

In addition to gas pressure, inertial forces, and centrifugal forces, the crankshaft is also subjected to additional loads caused by torsional vibrations. As a critical moving component in the diesel engine, it requires complex manufacturing processes, high precision, and comes with a significant cost. Due to the spatial constraints of locomotives, the diesel engines are typically 4 to 6 meters long and 2.5 to 3 meters wide, which means the crankshaft is generally around 4 meters in length. Depending on the engine's power, the main journal diameter can be φ190mm, φ220mm, φ230mm, or φ250mm, while the crank pin (also known as the connecting rod journal) is relatively smaller. The crankshaft is mounted on the main bearings within the engine block. The crank pin connects to the piston-connecting rod assembly, while the output end drives the traction motor via a coupling. The free end, on the other hand, drives the camshaft and oil pump through a gear system, and uses a cardan shaft to power auxiliary devices. Besides the primary forces, the crankshaft is also affected by torsional vibrations, making it a high-stress component. It is prone to fatigue damage due to its large cross-sectional changes, which can cause stress concentration. Its structural rigidity is poor, leading to potential deformation and vibration. This complexity increases the difficulty of processing, requiring precise machining, careful heat treatment, and strict dimensional control. Additionally, the surface of the journals must be strengthened using methods like induction hardening or nitriding. Other treatments such as roller burnishing and shot peening are also applied to enhance durability. Locomotive diesel engines usually operate at medium to high speeds, so the crankshaft must undergo balancing to ensure smooth operation. Crankshafts for locomotives can be made from either cast ductile iron or fully forged alloy steel, each requiring different processing techniques. This text focuses on the forging process of an alloy steel crankshaft using full-fiber extrusion. The manufacturing process begins with rough machining, followed by heat treatment to achieve desired mechanical properties. Then, semi-finishing and precision machining of the main journals and crank pins are performed. Internal oil passages, including straight and oblique oil holes, as well as weight reduction holes, are processed. Surface strengthening techniques such as nitriding and fine grinding are applied to improve wear resistance. Finally, dynamic balancing and oil testing are conducted before delivery. Early crankshaft production lines relied on conventional machine tools like lathes, grinders, drilling machines, and milling machines. These were often supplemented with custom-built equipment. Over time, specialized production lines were developed, improving workflow and reducing transportation between operations. In modern times, computer numerical control (CNC) technology has transformed crankshaft manufacturing. Three main types of equipment dominate: turning-milling centers, boring-milling centers, and crankshaft grinders. Brands like WFL, NILES-SIMONS, and NAXOS are leaders in this field, offering high-precision solutions. These machines allow for more efficient and accurate machining, reducing the need for multiple setups and improving overall productivity. After introducing advanced equipment, the layout of the workshop became more compact, and environmental conditions improved, requiring fully enclosed, air-conditioned spaces. While imported equipment offers higher accuracy and reliability, domestic alternatives have made significant progress in recent years. They provide a more cost-effective solution, especially for mid-sized production runs. Overall, the evolution of crankshaft manufacturing reflects advancements in both technology and efficiency, ensuring that modern locomotive diesel engines operate reliably and with high performance.

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