Study On New Heating Control Method Of Rail AC Flash Welding

At the end of 2017,China's high-speed rail mileage accounted for 66.3 percent of the world's total,which represents that China's high-speed railway development has entered a milestone stage,with CWR receiving more and more attention.As the preferred welding method of high-speed railway seamless line,flash welding has the advantages of stable performance,simple operation and high degree of automation.However,the existing rail flash welding heating methods have the following two problems.Firstly,continuous flash welding heating efficiency is low,the amount of burning is large,the welding time is long,it is used less and less.Secondly,due to the long short circuit time,large short circuit current,serious oxidation in high temperature zone,poor flatness of end face,and large power supply capacity,the short-circuit preheating method commonly used in DC and AC flash welding not only affects the quality of welding joints,but also puts forward higher requirements for power supply.Therefore,it is of great engineering value to carry out efficient and high quality heating control and process research.A new heating control method of rail AC flash welding based on current feedback is proposed in this paper.The fixture of the moving end of the welding machine head is superimposed with a control mode of variable speed feed on the basis of fixed vibration to realize fast and high quality heating of the rail end face.On UN5-150-ZB flash welding machine,based on PLC and servo valve,by transforming the amplitude-time curve of the vibration waveform into the speed-time curve,and then superimposed with the variable feed speed,and combined with the welding current feedback from the detection,the moving speed and direction of the moving end clamp can be obtained.Then the movement of the moving end clamp can be directly controlled,so as to realize the heating control.Based on the heating control method proposed above,under the premise of only changing the heating control method of the original welding machine in the high voltage stage,the PLC detection control algorithm is designed and the PLC control program is compiled.The relationship between the PLC register value and the moving clamp speed was obtained through the calibration of the moving end speed,and the vibration amplitude and frequency were controlled based on the speed and time.High precision timing is realized based on PLC fixed scanning period,and the interference of timer error is avoided.Based on the statistical analysis of the original heating process displacement curve,the velocity variation trend of the variable speed is obtained.Based on the new heating control program,the R350 HT rail of UIC60 and U75 V rail of Chinese standard grade 60kg/m are used to conduct welding tests.The vibration control parameters with good minimum current raising effect,high heating efficiency and less short circuit are obtained.Taking infrared thermal imager as the core,the heating efficiency analysis system of rail flash welding is built.By analyzing the temperature field at the end of the acquisition flash welding high pressure stage,the results show that,under the same heating time,the width of the high temperature region of the new heating control method is higher than that of the original control method.Therefore,the heating efficiency of the new heating control method is higher than that of the original heating control method,and the high temperature field can be established quickly.Taking the depth camera as the core,a rail flash welding end face flatness analysis system is built.By extracting the object from the collected end face point cloud,the point cloud containing only the end face of the rail is obtained.Then,the eigenvalue method is used to calculate the fitting plane of the point cloud,and the distance between each point of the point cloud and the plane is calculated to evaluate the flatness of the end face.The flatness of the new heating control method is better than that of the original heating control method,and the highest lifting rate is 33.1%.Finally,through the joint evaluation of heating efficiency and end face flatness,two groups of vibration control parameters with better effects were selected.