Renewable energy is fully challenging the traditional energy output methods. For example, in 2016, both photovoltaic grid-connected prices and wind power prices have been reduced. Despite this trend, statistics from the National Energy Administration in recent years show that 70% of the power generation is still derived from thermal power generation, and new energy sources such as water, wind, nuclear power, and solar power have not had a strong impact on traditional energy sources.

However, the current domestic power market has become increasingly saturated. Under the national policy of supporting new energy, traditional forms of power generation such as thermal power are "large and small", and the use of high-power equipment has become the consensus of the power industry.

Challenges Brought by "Big"

As a major manufacturer of large-scale power equipment in my country, Shanghai Electric Power Plant Equipment Co., Ltd. Generator Plant (SEPC) is a subsidiary of Shanghai Electric Group Co., Ltd. Power Plant Group. It is a joint venture with Germany's Siemens. It is mainly engaged in thermal power, nuclear power, and gas turbines. R&D and manufacturing of complete sets of large generator products in the field.

Since 2004, the production, sales, and number of orders for thermal power generating sets of Shanghai Generator Factory have been ranked first in the world. In recent years, the company's annual orders for 1000MW water-hydrogen-cooled units have basically stabilized in the range of 9000MW to 13000MW, and the domestic market share is about 80%. The annual orders for 600MW-level water-hydrogen-cooled units have stabilized at 6000MW-9000MW, and the domestic market share About 60%, the products are exported to many countries.

my country’s existing 300MW, 600MW, 1000MW water-hydrogen-cooled steam turbine generators have reached international advanced levels in terms of efficiency and annual operating hours. In recent years, the country has stipulated that domestically produced subcritical 600MW and below capacity units are generally no longer imported. This Accelerated the development of my country's power station construction manufacturing industry. The power plant manufacturing industry is one of the country’s important basic industries. The vast majority of units in large nuclear power plants and thermal power plants in France, Germany, Japan, Russia, and the United States are manufactured in the country.

With the implementation of the policy of “upgrading the large and suppressing the small”, SEPC has now formed a complete series of products such as air-cooled 50MW~200MW, dual-internal water-cooled 60MW~340MW, water-hydrogen cooling 200~1000MW, etc., in the ultra-supercritical 1000MW class. Historical breakthroughs have been achieved in major projects such as thermal power, nuclear power and gas turbine generators. The internationally large-capacity 1800MW nuclear power generators, 1200MW thermal power generators and other products are currently being developed to form new core technologies for generators. Continuously improve the core competitiveness of the enterprise. Walking into the SEPC plant, you can see: The main plant is 312 meters long, 36 meters wide, and 34 meters high. The lifting capacity can reach 500 tons. It is equipped with the largest capacity in the world-1800MW quadrupole nuclear power generator. And an annual production capacity of 30 million kilowatts.

With the upgrading of the level, the size of power generation equipment has also increased. Large-scale equipment of hundreds of tons and tens of meters will not only cause inconvenience to processing, but also increase the difficulty of processing.

Due to the characteristics of power generation equipment products, there are strict requirements on the reliability of the equipment. For example, the rotor is the core component of the generator, a large-scale power equipment, and the quality of its processing affects the quality of the generator's operation. In addition, the rotor blanks are large in size, costly, and limited in supply. Although the processing requirements are high, they must also be processed with zero error rate.

In addition, the cutting of some other typical key parts in power generation equipment, such as rotor wheel grooves and rotor dovetail grooves, etc., because the processed materials are heat-resistant high-strength alloy steels, stainless steels and other difficult-to-machine materials, the cutting volume is large and the cutting load is It has high requirements on the cutting performance of CNC tools, such as high temperature red hardness, bending shear strength, abrasion resistance, adhesion resistance, and friction coefficient.

But the difficulty is the key point. Controlling and reducing the cutting deformation of the two-pole rotor wire inserting groove is the key to improving the rotor operation accuracy and ensuring the generator's running quality. Generally speaking, the wire embedding groove is deformed during processing, and the deformation of the groove of the wire embedding groove can reach 0.5mm. To reduce the deformation, the appropriate cutting force must be selected and the residual stress must be reduced. This not only puts forward high demands on process engineers and operators, but also puts forward higher demands on the precision of the CNC tool itself for the cutting of high-precision and complex profiles.

Difficulties

Machining is an important part of the production of generator sets. The amount of cutting of generator rotors, stators, bases and other components is very large, and the requirements for machine tools and cutting tools are very high. The wire embedding groove of the rotating shaft of the steam turbine generator is processed on a CNC rotor groove milling machine using a special indexable rotor groove disk milling cutter. Because the shaft is made of high-strength alloy steel, the cutting groove is deep, the diameter of the milling cutter is large, and the cutting speed is high, which requires high overall performance of the tool.

Taking rotor processing as an example, the forged raw material workpiece must first be turned and then milled. Milling is divided into rough milling and fine milling, and each process is divided into two steps. "Slot milling must be segmented, because it involves the dynamic balance of the rotor." This is familiar to every process operator.

The outer circumference of the rotor body has a ring of embedding grooves in the axial direction, which is also called the rotor longitudinal tree groove in the industry. Sometimes there are more than 30 embedding grooves for each rotor. The overall processing requirements for the generator rotor groove shape are relatively high: the width tolerance of the entire groove is ≤0.2mm, the equal division requirement is ≤0.02°, the roughness requirement is ≤Ra3.2, and the processing efficiency of the process requirements is high, and the processing performance of the machine tool needs to be taken into account. And tool cutting performance.

There are generally two ways to improve the performance of products. One is to increase funds to invest in equipment, or to ask for help from outsiders; the other is to improve the cutting process of the tool-this is a direct means, if the cutting efficiency of the tool can be Doubling it is equivalent to adding a machine tool, and the effect it brings is immediate and double the effort. SEPC uses a large number of disk milling cutters and dovetail milling cutters in the machining process of the rotor slot of SEPC. The tools used are mainly indexable disk milling cutters and indexable dovetail milling cutters provided by the German Walter Company.

The development of domestic generator manufacturing technology has gone through three stages. The manufacturing process has also evolved from manual, mechanical, and digital display processing, and gradually developed to CNC intelligent processing. The processing tool of the dovetail groove in the rotor wire groove has been changed from the previous high-speed steel material. Evolve to indexable insert tool.

The coarse-tooth rough-milling disc milling cutter applied to the 300MW class is the first result of cooperation between Walter and SEPC. Because of the large allowance for rough machining of the rotor groove, a good chip removal function is required. In addition, the key is that the iron ring and wear marks must not appear. Now Walter tools are used more and more in SEPC. As long as there is a new product design, you will see the participation of Walter senior technicians at the first time.

At the same time, cost reduction and efficiency enhancement are also important conditions for SEPC to choose tools. For example, the roughness of the 600MW dovetail groove is increased from the original Ra6.3 to no more than Ra3.2 after the high-speed steel tool is replaced by Walter's tool, and the processing efficiency is increased from 90 minutes for each groove using the high-speed steel tool to It only takes 30 minutes after using cemented carbide tools. Although the blade consumption cost is slightly higher than that of the high-speed steel tool solution, the processing time is reduced, and the processing feed rate is much higher than the original: it can be increased from less than 100mm/min to 240～280mm/min, which can be calculated comprehensively. The reduction in actual processing costs is still considerable.