Development of Large Turbogenerator Coil Milling Machining Center
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The 300,000 kilowatts and 600,000 kilowatts turbine generators produced by Dongfang Electric Co., Ltd. have special coil processing technology. The coil processing quality is directly related to generator efficiency and safety. The shape and arrangement of the vent holes in the copper coil of the rotor coil of the large turbo-generator directly determine the heat dissipation of the turbine generator, which in turn affects the reliability, stability and efficiency of the turbine generator. Therefore, the company developed a coil milling machining center on its own.

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1 The mechanical structure of the coil milling machining center is shown in Fig. 1. The coil milling machining center consists of 1# to 4# milling heads and a workbench. The four milling heads 1# to 4# can be moved up and down as required. Each milling head consists of A and C two disc cutters and one rod milling cutter B; disc cutter A performs milling through hole processing and disc cutter C performs chamfer processing on both sides of the through hole; The milling cutter B is used for deburring after copper milling. The processed copper bar is fixed on the workbench. The workbench is controlled by the servo motor for horizontal movement and accurate positioning. 2 coil milling machining center control system

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The machining center uses an open CNC system (CNC) for control. Open CNC systems based on PCs, microprocessors and their architectures use sophisticated PC hardware to compose their systems, thereby saving the cost of developing dedicated hardware and reducing costs. At the same time, because the PC bus is an open bus, the hardware architecture of the system is open, modular, and embeddable. In addition, in order for the system to better adapt to different needs and meet the requirements of diversity, it is necessary to make efforts in the system software of the control system so that the system software provides different degrees of openness according to the user level, and the system is configured according to the user's needs. To meet the user's requirements. In addition, because the system is based on the PC, so at the same time as the software design can take full advantage of the PC's rich software resources to form a software platform to develop the control system, to achieve a multiplier effect. The large turbine generator coil milling machining center is a special processing equipment, so we used an open CNC system to control it. Control system structure shown in Figure 2. Considering the poor working conditions of the workshop where the machining center is installed (large power fluctuations, more dust, more power equipment and welding machines), we have emphasized reliability in the development and use of CNC systems. The CNC system is a complex whole set of precision electronic technology, precision detection technology, software technology, control technology, and computer technology. Its development trend is high performance, multi-function, high precision, high speed, high flexibility, and high reliability. Reliability is a decisive factor in achieving high performance, high precision, high efficiency, and good efficiency. CNC system reliability guarantee measures should be considered from the design of the CNC system, hardware, software and use, not only to eliminate interference sources that affect reliability, but also to increase the anti-interference ability of the CNC system itself. In the design, we placed the main part of the CNC system outside the machine processing area. However, the execution components and detection components such as servo motors, limit switches, component switches, gratings, encoders, etc. often cannot be separated from the machining area, coolant and oil. Liquid may cause damage to it completely; Industrial site environment is bad, dust, iron filings, static electricity, vibration, etc. are fatal to electronic devices and printed circuit boards widely used in CNC systems; servo motors on some machine tools move with the mechanical actuators. The cable and the signal cable stretch and friction over a long period of time, which is prone to wear, causing failure or even accidents. Therefore, in the design of CNC machine tools and CNC systems, we carefully considered the overall structure of the machine tool, the position of the servo motor and the position of the limit switch, and the running mode of the wire and cable, and paid enough attention to the packaging of the CNC system. . Electromagnetic interference is one of the main factors affecting the reliability of the CNC system. General power supply fluctuations, on/off of electrical switch and power switch elements, inherent interference of electronic devices, ground wire diameter size, circuit layout, common impedance, signal distortion, signal interference, signal distortion, external interference, etc. can all be attributed to electromagnetic interference. . Generally, shielding and balanced interference signals (such as wire stranding), power supply of various functional modules, filtering, photoelectric coupling, resistance and capacitance absorption, and diode discharge are generally adopted. Due to the large number of welding machines used in the large turbine generator coil milling machining center installation site, we have taken the following measures: The power supply current line of the welding machine is far away from the CNC system; the control signal from the CNC system is amplified and sent to the servo system. Ensure that the signal is not disturbed due to the large transmission distance. All switching signals of the machine tool are isolated by the relay and enter the CNC system; the CNC power supply is filtered; the CNC system uses the watchdog function to prevent the CNC system from being affected by the crash; the photoelectric coupling, resistance and capacitance absorption are adopted. RC suppression. In the AC servo system, the harmonic components of the circuit voltage and current pulse oscillations cause strong electromagnetic interference, affecting the work of other electronic devices and CNC systems through radiation and conduction. On the one hand, the interference signal is conducted away from the input power line feedback. The low fundamental wave and high harmonics cause damage to the power supply network. Not only does the CNC system suffer from interference but also reduces the power supply efficiency; on the other hand, the servo output The steep pulse contains multiple high-frequency harmonics, stray capacitance exists between the connecting cable between the servo and the motor, and the high-frequency pulse signal couples with the stray capacitance to generate a leakage current. Leakage currents and multiple high-frequency harmonic radiation affect the CNC system and its electronic devices, causing harm. In the manufacture of large turbogenerator coil milling machining centers, we have taken the following measures: Use filters to prevent the transmission of interference signals along the power line and impedance transformation so that the interference signals are reflected back to the interference source. Filter at the input and output ends of the servo; Correct grounding - Form a low-resistance path for high-frequency interference signals to suppress interference; Good shielding - Prevent the servo system from radiating external interference signals and prevent external interference signals from entering the servo system When compiling CNC system software, software fault tolerance and error avoidance techniques are used to improve reliability. The method of preparation of processing subroutines is used to improve the anti-jamming capability of CNC systems, such as software redundancy detection, timing monitoring, and input/output data processing. When the detection device of the CNC system is disturbed, we generate pairings of plus and minus pulses to the CNC system. When the CNC receives the pulse, it adds memory to the word. When the pulse is received, the program uses the program interruption to make the memory decrease. Word operations. In this way, even if a disturbance is generated and the pulse is added, the pulse is processed using the time difference between the addition and subtraction pulses without affecting the position control of the CNC. CNC users have an impact on their reliability. As the design and manufacturing level of the CNC system continues to increase, the quality of the CNC system's installation and commissioning personnel, operators, maintenance personnel, etc. has a greater impact on the reliable operation of the CNC system. A strict and standardized system is implemented on them. Training is necessary. Let them be able to correctly install, debug, use, maintain, and repair the CNC system and avoid the factors that may affect the reliability from being generated, accumulated, and expanded. Strong logic logic also affects the reliability of the CNC system. The logic error or non-compliance of the machine tool may cause defects, damages to the CNC system, damage to CNC users, and scrapping of processed products. 3 Innovation and practical use of the coil milling machining center The coil milling machining center developed by Dongfang Electric Co., Ltd. has for the first time integrated the operations of milling, chamfering, and deburring of the coil processing into a single row of copper bars. To ensure the accuracy and efficiency of the coil processing. A large number of reliability assurance measures are adopted in the control system of the machining center, so that the performance of the machining center is stable, and the coil processing needs are fully satisfied. In the evaluation of the reliability of the machining center, conventional MTBF statistics and fuzzy evaluation methods are adopted to improve the accuracy of the reliability evaluation. Due to the good investment-to-income ratio of the coil processing center, Dongfang Electric Co., Ltd. has successively manufactured three such equipment and put it into use.

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