The Research Of Programmable Pulse Power Supply For Micro-arc Oxidation

Micro-arc oxidation is a new surface treatment technique applied to valve metals and their alloys to form the ceramic membrane on the surface with a high-quality performance. It has a wide application in the aviation, aerospace, mechanical, electronic and biological materials etc. as the resistance to abrasion, corrosion resistance and insulation properties of the metals forming the protective film are greatly improved. At present, the organizational structure of ceramic coating and performance analysis aspects were mainly studied except the power supply of micro-arc oxidation, and the best static, dynamic characteristics of power supply, the structure of output waveform are still not put forward clearly. Based on the research of micro-arc oxidation process and load characteristics, the micro-arc oxidation power supply with multiple output mode was developed. The output cross-flow mode or constant voltage mode can be selected, but also the power-supply can produce three kinds of output mode, which were pulse with discharge circuit, unipolar pulse and bipolar pulse. Besides, the pulse amplitude, frequency and duty cycle had a very wide adjustment range, the process control for micro-arc oxidation was achieved. The main research work is as follows:Study shows that micro-arc oxidation process can be divided into three stages, namely, anodic oxidation stage, the micro-arc oxidation stage and continuous arc stage, which consists of a series of arc discharge in discrete micro arc. Micro arc discharge consists of electrolysis, discharge, oxidation, the process of cooling. The oxidation power was required to have the output pulse with a cooling time to reduce the tendency of large arc. The studies of load on the micro-arc oxidation have found that it is highly capacitive, equivalent to the RC topology. This pulse output model with discharge circuit was proposed to adapt to the load characteristics.The power supply includes main circuit and power control system. The main circuit includes rectifier circuit, filter circuit, chopper circuit, the discharge circuit and protection circuit.Rectifier circuit and filter circuit can control the output pulse amplitude of positive and negative. When discharge circuit was used in the output pulse mode, storage electrical energy of the load capacitance-loading was deposited and loaded temporarily. The output mode, output pulse frequency and duty cycle were controlled through the chopper control. The Protection circuit is mainly used to protect the power devices to be safe and reliable.Power control system consists of two parts:power master control system and human-computer interface system. The 80C196KB MCU(microprogrammed control unit) was serving as the core of control system, which can collect the voltage and current signals and the parameters set in manual mode, the trigger pulse of SCR(silicon controlled rectifier) and drive pulse of IGBT(insulated gate bipolar transistor) were generated to monitor the working status.The AT89C52 MCU was serving as the core of human-computer interface systems.Through the chip use of HD7279A, the preset of power parameters, power output mode and the working methods were realized. During the process of the micro-arc oxidation, power supply parameters, time and work status can be displayed in real-time. The data and command can be exchanged using serial interface communication between the two control systems. The field use and evaluation showed that the power developed showed good stability and reliability in operation.