Renewable energy is comprehensively challenging traditional energy production methods; for instance, plans to lower feed-in tariffs for both solar photovoltaic and wind power were introduced in 2016. Despite this trend, statistics from the National Energy Administration indicate that thermal power still accounts for 70% of total electricity generation; new energy sources—including hydropower, wind, nuclear, and solar—have not yet posed a significant threat to traditional energy sources.

However, the domestic power market is becoming increasingly saturated. Under state policies supporting new energy, the power industry has reached a consensus on the strategy of "replacing small units with large ones" (shutting down smaller, less efficient plants in favor of larger, more efficient ones) and adopting high-capacity equipment for traditional thermal power generation.

**Challenges Posed by "Scale"**

As a key manufacturer of large-scale power equipment in my country, the Generator Factory of Shanghai Electric Power Generation Equipment Co., Ltd. (SEPC)—a subsidiary of the Power Generation Group of Shanghai Electric Group Co., Ltd. and a joint venture with Siemens AG—specializes in the R&D and manufacturing of complete large-scale generator sets for thermal, nuclear, and gas-fired power applications.

Since 2004, the factory has consistently ranked first globally in the production, sales, and order volume of thermal power generator sets. In recent years, annual orders for its 1,000 MW-class water-hydrogen cooled units have remained stable between 9,000 MW and 13,000 MW, capturing approximately 80% of the domestic market. Meanwhile, annual orders for 600 MW-class water-hydrogen cooled units have held steady between 6,000 MW and 9,000 MW, with a domestic market share of around 60%; these products are exported to numerous countries.

Key performance indicators—such as efficiency and annual operating hours—for my country's existing 300 MW, 600 MW, and 1,000 MW water-hydrogen cooled steam turbine generators have reached advanced international levels. Recent state regulations generally prohibit the import of subcritical units with capacities of 600 MW or less if they can be manufactured domestically; this policy has accelerated the development of my country's power plant manufacturing industry. Power plant manufacturing is a vital national industrial sector; indeed, the vast majority of generator units for large-scale nuclear and thermal power plants in countries such as France, Germany, Japan, Russia, and the United States are manufactured domestically. Driven by the "replace small units with large ones" policy, SEPC has developed a comprehensive product portfolio ranging from 50MW–200MW air-cooled units and 60MW–340MW dual-water-cooled units to 200MW–1000MW water-hydrogen-cooled units. The company has achieved historic breakthroughs in major projects, including ultra-supercritical 1000MW thermal power units, nuclear power units, and gas turbine generators. Currently, it is developing world-leading high-capacity products—such as 1800MW nuclear power generators and 1200MW thermal power generators—to establish core generator technologies and continuously enhance its competitiveness. Inside SEPC’s main workshop—measuring 312 meters in length, 36 meters in width, and 34 meters in height, with a lifting capacity of 500 tons—the facility is equipped to manufacture the world's largest-capacity generators (1800MW four-pole nuclear power generators) and boasts an annual production capacity of 30,000 MW.

As power generation units increase in capacity, their physical dimensions grow accordingly. Large-scale equipment—often weighing hundreds of tons and spanning tens of meters—presents not only logistical challenges but also significantly increased manufacturing complexity.

The nature of power generation equipment demands exceptional reliability. For instance, the rotor is a core component of the generator; its manufacturing quality directly impacts the generator's operational performance. Given the rotor forging's massive size, high cost, and limited supply, the manufacturing process demands absolute precision—allowing for zero errors.

Furthermore, the machining of other critical components—such as rotor winding slots and dovetail slots—involves difficult-to-machine materials like heat-resistant, high-strength alloy steels and stainless steels. These processes entail heavy material removal and high cutting loads, placing stringent demands on the cutting performance of CNC tools—specifically regarding high-temperature red hardness, bending and shear strength, wear resistance, anti-adhesion properties, and friction coefficients.

However, these challenges represent the critical technical focal points. Controlling and minimizing cutting deformation in two-pole rotor winding slots is essential for enhancing rotor operational precision and ensuring the overall quality of generator performance. Generally, deformation occurs during the machining of winding slots, with the slot opening potentially deforming by as much as 0.5 mm. To minimize this deformation, it is essential to select appropriate cutting forces and reduce residual stress. This places high demands not only on process engineers and operators but also on the precision of the CNC cutting tools themselves, given the need to machine complex profiles with high accuracy.

**Significant Challenges**

Machining is a critical stage in generator set production; components such as generator rotors, stators, and frames require substantial material removal, placing rigorous demands on both machine tools and cutting tools. Winding slots on steam turbine generator shafts are machined using specialized indexable disc milling cutters on CNC rotor slot milling machines. Because the shafts are made of high-strength alloy steel—and the process involves deep slots, large-diameter milling cutters, and high cutting speeds—the cutting tools must possess exceptional overall performance characteristics.

Taking rotor machining as an example, the forged raw workpiece undergoes turning followed by milling. The milling process is divided into rough milling and finish milling, with each stage consisting of two steps. "Slot milling must be performed in segments due to rotor dynamic balance requirements"—a fact well understood by every process operator.

The outer circumference of the rotor body features a series of axial winding slots—often referred to in the industry as "fir-tree" slots—with a single rotor sometimes containing more than 30 such slots. The overall machining requirements for these generator rotor slots are stringent: slot width tolerance must be ≤0.2 mm, angular spacing accuracy ≤0.02°, and surface roughness ≤Ra3.2. Furthermore, high machining efficiency is required, necessitating a balance between the performance capabilities of the machine tool and the cutting efficiency of the tool.

There are generally two ways to improve product performance: increasing capital investment to purchase new equipment or outsourcing the work. Another approach is to optimize the cutting tool process—a direct and effective method. If cutting efficiency can be doubled, it is equivalent to adding an extra machine tool; the results are immediate, yielding twice the output with half the effort. SEPC’s rotor slot machining process extensively utilizes various disc milling cutters and dovetail milling cutters, primarily indexable models supplied by the German company Walter.

Domestic generator manufacturing technology has evolved through three stages, transitioning from manual, mechanical, and digital-readout machining to intelligent CNC machining. Similarly, the cutting tools used for the dovetail slots within the rotor winding slots have evolved from high-speed steel (HSS) to indexable insert designs.

The coarse-tooth roughing disc milling cutter designed for 300MW-class units marked the first collaborative success between Walter and SEPC. Rough machining of rotor slots involves significant material removal, requiring excellent chip evacuation capabilities; furthermore, it is critical to avoid defects such as metal tearing or scoring marks. Walter tools are now increasingly used at SEPC, with Walter technical personnel involved in virtually every new product design.

Cost reduction and efficiency improvement are also key factors in SEPC’s tool selection. For instance, when machining dovetail slots for 600MW units, switching from HSS tools to Walter tools improved surface roughness from Ra 6.3 to Ra 3.2 or better. Machining efficiency also improved dramatically: the time required to machine each slot dropped from 90 minutes with HSS tools to just 30 minutes with carbide tools. Although the cost of inserts is slightly higher than that of HSS tooling, the reduction in machining time—combined with a significant increase in feed rates (rising from under 100 mm/min to a range of 240–280 mm/min)—results in substantial overall savings in actual machining costs.

SEPC’s flagship products—which currently account for the highest order volumes—include the 1000MW water-hydrogen cooled, 600MW water-hydrogen cooled (Type III), and 300MW water-hydrogen cooled generator models. Annual production ranges from 25 to 35 units, with a stable total manufacturing capacity of 20 to 30 million kilowatts (a 30-million-kilowatt capacity represents an annual power generation potential of 240 billion kWh). In addition, water-cooled generator units represent another proprietary product line that SEPC takes great pride in; to date, the company has manufactured over 650 such units. Currently, SEPC is also engaged in the development of the world's largest water-cooled generator units (660 MW) and the world's largest two-pole generator units (1200 MW class).

As China's equipment manufacturing industry advances, manufacturers are placing increasingly high demands on machine tools and cutting tools. Metal-cutting machine tools and cutting tools serve as the fundamental equipment for machining operations and are often described as "twin brothers," as a machine tool relies on excellent "teeth" to function effectively. It is fair to say that the performance and quality of cutting tools directly influence overall production efficiency, machining quality, technical capabilities, and economic returns—which explains the saying among foreign enterprises that "an enterprise's profits lie in the cutting edge."