The manufacturing of wind turbine main shafts primarily relies on two mainstream processes: forging and casting. Forged shafts offer superior mechanical properties, while cast shafts align well with the trend toward larger turbine capacities; each has distinct advantages and cannot replace the other.
Forging involves using forging machinery to apply pressure to metal billets, inducing plastic deformation to achieve the desired shape and properties. Forged shafts deliver high performance, effectively meeting the demands of high-speed transmission and heavy-load operating conditions typical of doubly-fed turbine models. A notable example is the "forging technology for extra-large bore, specially shaped hollow main shafts," which effectively reduces machining allowances and raw material costs. In 2022, an industry player successfully produced a 9MW forged wind turbine main shaft. Forged shaft products cover turbine models ranging from 1.5MW to 9.5MW.
Casting is a process that involves melting metal, creating a mold, pouring the molten metal into the mold, and allowing it to solidify into a casting. While meeting mechanical performance requirements, cast shafts offer a simpler manufacturing process and lower raw material consumption compared to forged shafts; they boast higher production efficiency and material utilization rates, resulting in a clear cost advantage. Cast shafts are better suited for large-scale, integrated production and represent the mainstream choice amidst the trend toward larger offshore wind turbines. Casting capabilities extend to large components, such as main shafts for 5MW to 30MW wind turbines.
The core manufacturing process for wind turbine main shafts encompasses the entire industry chain, including metal smelting, forging or casting, heat treatment, machining, and coating. Metal smelting employs purification technologies to ensure the purity of steel ingots. Forging or casting is used to form the rough blank; forging techniques may include "full-fiber near-net-shape hollow forging." Heat treatment processes-such as quenching and tempering or carburizing and quenching-are applied to relieve internal stresses and enhance surface hardness and core toughness. Precision machining utilizes deep-hole drilling and boring machines as well as CNC machine tools to ensure dimensional accuracy. Coating is performed using fully automated, intelligent technology to guarantee high-quality surface protection against corrosion and wear.
As offshore wind power shifts toward higher megawatt capacities, the trends of turbine upscaling and lightweighting are driving the evolution of cast shaft technology; large, thin-walled cast shafts are poised to become the mainstream solution in the future. Meanwhile, manufacturing processes are upgrading toward "near-net-shape" production, digitalization, and intelligent manufacturing to boost efficiency, reduce costs, and enhance product consistency.
The trends toward larger and lighter offshore wind turbines are driving technological advancements in main shafts; large, thin-walled cast main shafts are poised to become the mainstream choice. Concurrently, as turbines grow in size, both the price and weight of individual main shafts are expected to rise.
Given the trend toward larger turbines, forged and cast main shafts are utilized in different scenarios due to their distinct performance characteristics. High-speed drivetrains in doubly-fed turbine models exert greater forces on the main shaft and demand higher performance, making forged main shafts the better fit. Conversely, the trend toward larger semi-direct drive models favors cast main shafts, which meet performance requirements while being better suited for large-scale production. To withstand harsh offshore environments, 26MW-class offshore wind turbine main shaft bearings utilize high-quality alloy carburizing steel subjected to special heat treatment, followed by the application of a nano-scale anti-corrosion and wear-resistant coating for enhanced protection. Process innovations include full-fiber near-net-shape hollow forging, forging technology for extra-large bore profiled hollow main shafts, and a novel heat treatment process involving quenching and high-temperature tempering (refining) followed by carburizing and high-frequency quenching.
Significant breakthroughs have been achieved in localization: the first 18MW offshore wind turbine main shaft bearing prototype, independently developed and manufactured by Wafangdian Bearing Group (ZWZ), passed customer acceptance, while Xinqianglian's 12MW offshore main bearing successfully rolled off the production line. In 2024, Sinomach-Precision successfully developed the world's first 26MW-class wind turbine main shaft bearing, marking another milestone in the development of domestically produced wind power bearings in my country. Driven by these advancements, the localization rate for wind turbine main shaft bearings has risen from less than 10% prior to 2020 to 60%.
Integrated drivetrain designs are driving the replacement of spherical roller bearings with double-row tapered roller bearings. The industry enforces design boundaries through certification systems such as IEC 61400-22 and GB/T 3579-2018, while establishing a progressive verification loop comprising type testing, bench testing, and field testing. Regarding maintenance specifications, the China Electric Power Equipment Management Association issued the 'Technical Specifications for Maintenance and Replacement of Main Bearings and Main Shafts of Wind Turbine Generator Units' (T/CEEMA-0201-2025); this standard stipulates the requirements and acceptance criteria for the maintenance of wind turbine main shaft systems and is applicable to the maintenance and acceptance of the relevant components .
